New-Generation Cement-Based Nanocomposites 9819923050, 9789819923052

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Siqi Ding Xinyue Wang Baoguo Han

New-Generation Cement-Based Nanocomposites

New-Generation Cement-Based Nanocomposites

Siqi Ding · Xinyue Wang · Baoguo Han

New-Generation Cement-Based Nanocomposites

Siqi Ding School of Civil and Environmental Engineering Harbin Institute of Technology Shenzhen, Guangdong, China

Xinyue Wang School of Civil Engineering Dalian University of Technology Dalian, Liaoning, China

Baoguo Han School of Civil Engineering Dalian University of Technology Dalian, Liaoning, China

ISBN 978-981-99-2305-2 ISBN 978-981-99-2306-9 (eBook) https://doi.org/10.1007/978-981-99-2306-9 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

To the families! Siqi Ding, Xinyue Wang, Baoguo Han

Foreword

Earth’s human-made mass has exceeded the overall global biomass. Cement-based composite, being the most used human-made substance, has become one of the most obvious manifestations of humankind’s physical footprint on the Earth. The use of cement-based composites changes the world, promotes the rapid development of human society, and shapes the human civilization. Moreover, cement-based composites are still indispensable in the foreseeable future, and their application room is constantly expanding. However, some inherent weaknesses and the existing performances of cement-based composites make them unable to fully meet the demands of constructing and creating future human living space. Additionally, the massive production and application of cement-based composites have an enormous impact on resources, energy as well as environment on the Earth. Nanoscience and technology can change the “gene” of cement-based composites at a more fundamental level. It provides a transformative approach to solve the above issues and boosts the emergence and rapid development of cement-based nanocomposites with sustainable characteristics (e.g., high mechanical performance, long service life, perfect multifunctionality/smartness, easy fabrication, low environmental footprint, strong resilience, and low life-cycle cost). Particularly, in recent years, the development of nanosynthetic technologies and nanocomposite technologies as well as nanosurface modification technologies has constantly enriched the connotation and extension of cement-based nanocomposites. This has led to the emergence of new-generation cement-based nanocomposites that are easier for scalable manufacturing and feature better performances against conventional cement-based nanocomposites. Dr. Siqi Ding from Harbin Institute of Technology, Dr. Xinyue Wang and Prof. Baoguo Han from Dalian University of Technology, based on their years of research accumulations and achievements in the field of new-generation cement-based nanocomposites, authored this wonderful academic monograph together. The monograph totally consists of ten chapters, including the fundamentals of nanomaterials and new-generation cement-based nanocomposites, eight types of the developed new-generation cement-based nanocomposites, and the future challenges and development roadmap for new-generation cement-based nanocomposites. vii

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The distinguishing features of this monograph are presenting both fundamentals and applications, with emphasis on the design and principles, fabrications, characterizations, performances and mechanisms, and applications of new-generation cement-based nanocomposites, delivering current groundbreaking science advances and technical innovations in the field of new-generation cement-based nanocomposites, and deploying the road map to tackle the future development challenges of new-generation cement-based nanocomposites. I solemnly recommend this monograph to the academic researchers and professional engineers in the field of cement-based materials and structures. I believe this monograph will promote the scientific research and engineering applications of newgeneration cement-based nanocomposites, as well as energize the rapid development of cement-based nanocomposites, thus reinventing and cementing the future of cement-based materials and structures.

Surendra P. Shah Presidential Distinguished Professor University of Texas at Arlington Arlington, USA Emeritus Professor Northwestern University Evanston, USA

Preface

As one of the most obvious manifestations of humankind’s physical footprint on the Earth, cement has been used for millennia as a binder that sets, hardens, and tightly holds other materials together. It is typically inorganic and hydraulic, with common types including Portland cement, calcium aluminate cement, and geopolymer cement. Cement is seldom used solely but is combined with fine aggregates to produce mortar, or with coarse and fine aggregates to make concrete. Therefore, cementbased composites (also called cement matrix composites and cementitious composites) broadly cover all materials made of cement. Alongside their excellent mechanical performances (especially high compressive properties and resistance to cyclic loading), cement-based composites are the staple of infrastructure construction since they are resistant to water (i.e., corrosion resistance) and fire. As a result, the infrastructures fabricated with cement-based composites feature high safety and durability as well as require much less maintenance. Therefore, cement-based composites will be around in the foreseeable future due to their superior performances in combination with the profiles that are relatively cheap and simple to make as well as readily available everywhere. However, due to the huge consumption and extensive construction of cement-based composites, their production and use bring significant impact on the resilience of resources and energy as well as environment. The sustainable development of cement-based composites faces some critical challenges: (1) Colossal production and use of cement. Of particular concern for cement-based composites is their substantial environmental footprint, especially carbon footprint. Cement manufacturing is responsible for more than 90% of the carbon emission from and accounts for at least 8% of global human-driven carbon dioxide emissions. (2) Excessive use of natural resources. For example, some raw materials of cementbased composites such as natural river sand and fresh water are scarce in some countries or regions. (3) High energy consumption as well as dust and noise pollution during the process of production and use of cement-based composites. (4) Low tensile and brittle performances as well as easily cracking of cement-based composites. (5) Thermodynamic metastable characteristics of cement-based composites, and action of harshness, extremity, and multifactor coupling of service environment to cement-based composites. (6) Lack of (multi)functionality and smart performances ix

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(e.g., electrical, thermal, electromagnetic, self-sensing, self-healing). In order to address these issues, technical approaches of sustainable development of cementbased composites may include: (1) Modifying cement performances. (2) Developing new types of cement and binders as well as mineral and chemical admixtures (e.g., less energy intensive and less carbon dioxide emission). (3) Utilizing supplementary cement-based materials. (4) Using industrial wastes, recycle materials, and regional natural materials. (5) Adopting advanced manufacturing technology of cement-based composites and their raw materials. (6) Tailoring structures and enhancing performances (e.g., stronger, tougher, more durable, easier to make) of cement-based composites. (7) Developing versatile performances of cement-based composites. Nanoscience and technology infiltrating in the field of civil engineering provides new impetus for addressing the above critical challenges, thus implementing the above technical approaches. Nanoscience and technology refers to the understanding and manipulating structures and phenomena at nanoscale dimensions. Scientists have adopted the Greek word nano as a prefix to mean one billionth of a unit of measure. The characteristics of materials at nanoscale (i.e., 0–100 × 10–9 m) are significantly different from that of bulk materials as the ratio of surface atoms to the total number of atoms remarkably increase with the decrease of particle size. For example, when the size of the object is reduced to 10 nm (around 4000 atoms), this proportion of surface atoms is about 40%, while at 1 nm (around 30 atoms) it stands at 99%. Therefore, nanoscience and technology can make a huge change in the structures and properties of composites by virtues of “small” (i.e., intrinsic merits at nanoscale) and “few” (i.e., low content level). Cement-based composites are multicomponent, multiphase, and multiscale materials. Generally, the normal aggregate in cementbased composites has a particle size ranging from millimeters to centimeters, and the particle size of ordinary cement itself is usually 7–200 µm. However, cement hydration phases are primarily nanostructured materials condensed by C-S-H gel tens of nanometers in size. Therefore, due to their natural attributes, cement-based composites feature the properties of nanomaterials. In addition, the scientific community and industry are always spontaneous to manipulate the nanoscale behavior inside cement-based composites using nanoscience and technology to enhance or modify cement-based composites’ performance in the process of cement-based composites’ development, such as nanocrystals, mineral admixtures and chemical admixtures used for cement-based composites’ preparation. Especially in the past two decades, the rapid development of nanoscience and technology promotes understanding of the nanoscale behavior inside cement-based composites and enriches the methods for cement-based composites’ reinforcement and modification using nanotechnology. In this manner, research on nanoscience and technology in cement-based composites reaches a very active period. In 2001, zero-dimensional nanomaterial, nano-SiO2 , was firstly incorporated into cement-based composites for reinforcement purposes. This pioneering work started the first generation of cement-based nanocomposites, known as Version 1.0 cement-based nanocomposites. After that, nano-ZrO2 , nanoTiO2 , and nanocarbon materials were applied one after another for the enhancement and modification of cement-based composites. Much work indicated that the big gains in mechanical, durable, and functional properties of cement-based composites were

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achieved by nano-nonmetallic oxide and metallic oxide modification. The enhancement/modification mechanisms of the first-generation cement-based nanocomposites nanofillers on cement-based composites can be attributed to nanocore effect including intrinsically excellent mechanical, electrical, thermal, and electromagnetic properties and morphology features (high aspect ratio); and promoting cement hydration, optimizing C-S-H gel structure and forming ultrafine and compact crystals, improving interfacial transition zone and pore structure, controlling nanoscale cracks, autogenous curing, improving early strength and decreasing autogenous shrinkage through nucleating effect. The addition of nano-SiO2 increased the 3d/28d compressive and flexural strengths by 48.1%/48.7% and 45.6%/16.0%, respectively. Meanwhile, the addition of nano-SiO2 can increase the freeze–thaw resistance, chloride penetration and permeability, abrasion resistance and fire resistance of cement-based composites. The fracture toughness of concrete can be enhanced by 400% when nano-ZrO2 is used as fillers. The flexural and compressive strengths of concrete with nano-TiO2 at age of 28 d achieve increases of 87%/6.69 MPa and 12.26%/12.2 MPa with respect to concrete without nano-TiO2 , respectively. Nano-TiO2 can also endow concrete with the photocatalytic effect to decompose both organic pollutants and oxides such as NO, NO2 , and SO2 . Moreover, extensive research endeavors demonstrated the potential of various nanocarbon materials including carbon nanotubes (CNTs), carbon nanofibers (CNFs), and graphene for enhancing/modifying cement-based composites. The observed performance enhancement of cement-based composites with CNTs or CNFs includes a relative/absolute enhancements of 79%/74 MPa and 64.4%/5.6 MPa in compressive and flexural strength, a 34.28% increase in tensile strength, a 270% increase in fracture toughness, a 14% increase in fracture energy, an over 600% improvement in Vickers hardness at the early ages of hydration, a 2200% increase in deflection, a 130% increase in ductility, an over 430% improvement in resilience and a 227% increase in Young’s modulus. Graphene can improve the tensile, flexural, and compressive strength of concrete by 78.6, 60.7, and 38.9%, respectively. The presence of CNTs obviously enhances the transport property and durability of cement-based composites. Graphene significantly improves the moisture transport performance, the acid resistance, and the chloride ion penetration resistance of cement-based composites. In addition to the enhancement of nanofillers on mechanical properties and durability of cement-based composites, the cement-based composites with nanocarbon black show the electrically conductive characteristics. The thermal conductivity of CNTs cement-based composites is 85% greater than that of cement-based composites without CNTs. The damping capacity of cementbased composites with CNTs is 1.6 times than that of cement-based composites without CNTs. The addition of CNTs into cement-based composites can lead to a 27% decrease in electromagnetic wave reflectivity at a frequency of 2.9 GHz. Additionally, the cement-based composites with CNTs, CNFs, or graphene feature smart self-sensing (e.g., sensing stress, strain, crack, damage, temperature and smoke), self-heating, and steel cathodic protection performances. Incorporating nanofillers not only can enhance/modify the above-mentioned performances of cement-based composites in hardened state, but also have strong impact on the rheology and

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workability of fresh cement-based composites. The main characteristic of the firstgeneration cement-based nanocomposites is that single-component, single-phase, and single-scale nanomaterials are directly incorporated into cement-based composites during mixing to improve their mechanical performance and durability as well as impart novel functional properties. However, due to the small size, high surface energy, agglomeration, and difficult dispersion of nanomaterials, the development of Version 1.0 cement-based nanocomposites has several problems such as complex preparation process, low effectiveness and efficiency, and high cost. Recent advances in nanosynthetic technologies and nanocomposite technologies as well as nanosurface modification technologies are driving the progressive exploitation of advanced nanomaterials with multicomponent and multiscale features. In view of their unique structures and mutual synergy, these advanced nanomaterials are expected to allow for the direct manipulation of the fundamental structure of cement-based composites, alleviate the dispersion issue of traditional nanomaterials in cement-based composites, improve their nanocomposite effectiveness and efficiency as well as impart new properties not currently available for Version 1.0 cement-based nanocomposites to cement-based composites, thus boosting the development of new-generation cement-based nanocomposites, i.e., Version 2.0 cement-based nanocomposites. Based on the authors’ latest research accumulations and achievements in the field of new-generation cement-based nanocomposites, this book focuses on both fundamentals and applications, with emphasis on the design, fabrications, characterizations, performances, and applications of new-generation cement-based nanocomposites, thus presenting basic knowledges across the breadth of new-generation cement-based nanocomposites, delivering current groundbreaking science advances and technical innovations in the field of nanoengineered cement-based composites, energizing the sustainable development (e.g., high safety, long service life, strong resilience, low environmental footprint, perfect smartness, easy fabrication, and low life-cycle cost) of cement-based composites for shaping and cementing human civilization. This book is dedicated to students, researchers, scientists, and engineers in the field of civil engineering materials and nanotechnology. The readers can find information on progress of civil engineering materials and nanotechnologies, cuttingedge research ideas and findings, and practical guidance for developing sustainable and multifunctional cement-based nanocomposites. More specifically, this book is organized as shown in Fig. 1. The first part provides the fundamentals of new-generation cement-based nanocomposites (Chap. 1). The second part presents the authors’ research results in this area involving new-generation cement-based nanocomposites with helical CNT (Chap. 2), new-generation cement-based nanocomposites with nickel-coated CNT (Chap. 3), new-generation cement-based nanocomposites with nano-SiO2 -coated TiO2 (Chap. 4), new-generation cement-based nanocomposites with electrostatic self-assembly NCB/CNT (Chap. 5), new-generation cement-based nanocomposites with electrostatic self-assembly TiO2 /CNT (Chap. 6), new-generation cementbased nanocomposites with electrostatic self-assembly NCB/GNP (Chap. 7), newgeneration cement-based nanocomposites with in-situ grown CNT on cement

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Fig. 1 Book framework

(CNT@Cem) (Chap. 8), and new-generation cement-based nanocomposites with in-situ grown CNT on CF (CNT@CF) (Chap. 9). Finally, the third part discusses the future development and challenges of new-generation cement-based nanocomposites (Chap. 10).

Shenzhen, China Dalian, China Dalian, China

Siqi Ding Xinyue Wang Baoguo Han

Acknowledgements

The authors are much indebted to Prof. Jinping Ou (an academician of the Chinese Academy of Engineering) at Harbin Institute of Technology and Dalian University of Technology for giving us overall planning, detailed guidance, and great help in cement-based nanocomposites. The authors are also deeply grateful to Prof. Surendra P. Shah (a member of the US National Academy of Engineering, and a foreign member of the Chinese Academy of Engineering and the Indian Academy of Engineering) at Northwestern University and University of Texas at Arlington for contributing the foreword to this book. Many professional colleagues and friends also have contributed directly or indirectly to this book: Xun Yu (New York Institute of Technology), Ashour Ashraf (University of Bradford), Yi-Qing Ni (The Hong Kong Polytechnic University), Surendra P. Shah (Northwestern University and University of Texas at Arlington), Yanbin Cui (Chinese Academy of Sciences), Xufeng Dong (Dalian University of Technology), Filippo Ubertini (University of Perugia), Simon Laflamme (Iowa State University), Mustafa Sahmaran (Hacettepe University), Sze Dai Pang (National University of Singapore), Yanlei Wang (Dalian University of Technology), Hongjian Du (National University of Singapore), Vijay Kumar Thakur (Scotland’s Rural College), Kenneth Loh (UC San Diego), Monica Craciun (University of Exeter), Yu Xiang (The Hong Kong Polytechnic University), Liqing Zhang (East China Jiaotong University), Zhen Li (Harbin Engineering University), Jialiang Wang (Dalian University of Technology), Sufen Dong (Dalian University of Technology), Hongyan Li (Dalian University of Technology), Linwei Li (Dalian University of Technology), Danna Wang (Dalian University of Technology), Qiaofeng Zheng (University of Cambridge), Yanfeng Ruan (Dalian University of Technology), Liangsheng Qiu (Dalian University of Technology), Xia Cui (Dalian University of Technology), Shan Jiang (Dalian University of Technology), Chenyu Zhang (Dalian University of Technology) and Linyang Han (Dalian University of Technology). The authors are grateful to all of them most sincerely. The authors also thank Springer for his enthusiastic and hard work to make this book published.

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Acknowledgements

This book is financially supported by the National Science Foundation of China (grant Nos. 51978127, 52178188, 51578110, 51428801, 51178148, 50808055, and 51908103), China Postdoctoral Science Foundation (grant Nos. 2022M710973 and 2022M720648), the Ministry of Science and Technology of China (grant Nos. 2011BAK02B01, 2018YFC0705601, and 2017YFC0703410), and the Fundamental Research Funds for the Central Universities in China (grant No. DUT21RC(3)039).

Contents

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Fundamentals of New-Generation Cement-Based Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Fundamentals of Nanomaterials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Definition and Classification of Nanomaterials . . . . . . . . . 1.2.2 Nano-Effect of Nanomaterials . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 Properties of Nanomaterials . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.4 Synthesis of Nanomaterials . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.5 Characterization of Nanomaterials . . . . . . . . . . . . . . . . . . . . 1.3 Brief Introduction of New-Generation Cement-Based Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New-Generation Cement-Based Nanocomposites with Helical CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Preparation of Cement-Based Nanocomposites with Helical CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Mechanical Properties of Cement-Based Nanocomposites with Helical CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Impact Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Functional/Smart Properties of Cement-Based Nanocomposites with Helical CNT . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Electromagnetic Shielding and Absorption Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 4 4 6 9 18 38 62 66 68 73 73 73 77 77 77 78 81 85 85 88 90 92 xvii

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New-Generation Cement-Based Nanocomposites with Nickel-Coated CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Preparation of Cement-Based Nanocomposites with Nickel-Coated CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Mechanical Properties of Cement-Based Nanocomposites with Nickel-Coated CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Elastic Modulus and Poisson’s Ratio . . . . . . . . . . . . . . . . . . 3.3.4 Fatigue Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.5 Impact Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.6 Bond Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.7 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Functional/Smart Properties of Cement-Based Nanocomposites with Nickel-Coated CNT . . . . . . . . . . . . . . . . . . . 3.4.1 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Electromagnetic Shielding and Absorption Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New-Generation Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Preparation of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Rheology of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Mechanical Properties/Performances of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 . . . . . . . . . . . . . . . 4.4.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Fatigue Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.4 Impact Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.5 Bond Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.6 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Functional/Smart Properties of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 . . . . . . . . . . . . . . . 4.5.1 Self-Healing Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Electromagnetic Shielding and Absorption Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.3 Anti-Sewage-Corrosion Properties . . . . . . . . . . . . . . . . . . . 4.5.4 Anti-Seawater-Corrosion Properties . . . . . . . . . . . . . . . . . . 4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

93 93 94 95 95 98 100 101 103 106 107 110 110 113 115 117 119 119 120 121 124 124 124 125 127 130 132 138 138 140 143 151 159

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 5

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New-Generation Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Preparation of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT . . . . . . . . . . . . . . . . . 5.3 Mechanical Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT . . . . . . . . . . . . . . . . . 5.3.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Functional/Smart Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Self-Sensing Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Electromagnetic Shielding and Absorption Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Application of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT . . . . . . . . . . . . . . . . . 5.5.1 Application for Structural Health Monitoring . . . . . . . . . . 5.5.2 Application for Oil Well Infrastructure . . . . . . . . . . . . . . . . 5.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New-Generation Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Preparation of Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT . . . . . . . . . . . . . . . . . 6.3 Mechanical Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT . . . . . . . . . . . . . . . . . 6.3.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Functional/Smart Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Self-Sensing Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Electromagnetic Shielding and Absorption Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

163 163 163 165 165 166 166

168 168 172 192 193 193 198 201 203 205 205 205 207 207 208 208

209 209 211 217 220 224

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Contents

New-Generation Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/GNP . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Preparation of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/GNP . . . . . . . . . . . . . . . . . 7.3 Mechanical Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/GNP . . . . . . . . . . . . . . . . . 7.3.1 Compressive Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Functional/Smart Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/GNP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Self-Sensing Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Electromagnetic Shielding and Absorption Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New-Generation Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Preparation of Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Hydration of Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Mechanical Properties of Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Electrical Properties of Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Self-Sensing Properties of Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Application of Cement-Based Nanocomposites with In-Situ Grown CNT on Cement . . . . . . . . . . . . . . . . . . . . . . . . 8.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New-Generation Cement-Based Nanocomposites with In-Situ Grown CNT on CF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Preparation of Cement-Based Nanocomposites with In-Situ Grown CNT on CF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Mechanical Properties of Cement-Based Nanocomposites with In-Situ Grown CNT on CF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Electrical Properties of Cement-Based Nanocomposites with In-Situ Grown CNT on CF . . . . . . . . . . . . . . . . . . . . . . . . . . . .

227 227 227 229 229 230

231 231 234 236 237 239 241 241 242 242 248 249 252 257 259 260 263 263 264 266 270

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Self-Sensing Properties of Cement-Based Nanocomposites with In-Situ Grown CNT on CF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.6 Application of Cement-Based Nanocomposites with In-Situ Grown CNT on CF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10 Future Development and Challenges of New-Generation Cement-Based Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Nanotoxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Cost and Scalable Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Bridging Nanomaterials to Macroscale Cement-Based Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

274 275 279 280 283 283 284 285 287 292 293

About the Authors

Siqi Ding obtained his Ph.D. degree from the Hong Kong Polytechnic University in 2021. He is now a postdoctoral fellow at School of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzhen, China. His main research interests include smart materials and structures, structural health monitoring, and nanotechnology in building materials. He has published 1 book, 5 book chapters, and more than 30 SCI journal papers. His publications receive an H-index of 15 and over 1500 citations in Web of Science Core Collection, and an H-index of 17 and over 2000 citations in Google Scholar. e-mail: [email protected]; s.q.ding@ connect.polyu.hk Xinyue Wang obtained his Ph.D. degree from Dalian University of Technology in 2021. He is now a postdoctoral fellow at School of Civil Engineering, Dalian University of Technology, Dalian, China. His main research interests include nanoengineered cementitious composites and interfaces in concrete materials and structures. He has published 1 book chapter and 27 papers in reputable journals, as well as hold 2 authorized national invention patents. He was honored Young Scientist Medal by International Association of Advanced Materials in 2022. e-mail: xinyuewang@ dlut.edu.cn Baoguo Han is a professor of civil engineering at Dalian University of Technology since 2012, holds a B.S. and M.S. in Material Science and Engineering (Harbin Institute of Technology 1999, 2001) and Ph.D. in Engineering Mechanics (Harbin Institute of Technology 2005). He was invited to the University of Minnesota and has worked as a visiting research scholar there for 3 years. His main research interests include cement and concrete materials, nanoengineered cementitious composites, smart materials and structures, multifunctional concrete, fiber reinforced concrete, and ultra-high-performance concrete. He has published 5 books (authored), 2 books (edited), 15 book chapters, and more than 200 technical papers. The citations and H-index/i10-index in Google are more than 10000 and 53/145, respectively. The research outcomes have been reported as research highlights for more than 20 times. He has held more than 20 authorized national invention patents and was awarded xxiii

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About the Authors

the first prize of Natural Science by the Ministry of Education of China. Prof. Han is a Fellow of the International Association of Advanced Materials and has served as a member in more than 30 scientific professional societies (including academic organization, journal chief-editor and editorial board member, and review panel for scientific research project and award) and as a reviewer for more than 150 books and journals. He was awarded Top Peer Reviewer in the Global Peer Review Awards powered by Publons in both Materials Science and Cross-Field, Highly Cited Chinese Researchers by Elsevier, and World’s top 2% scientists by Stanford University. e-mail: [email protected]

Chapter 1

Fundamentals of New-Generation Cement-Based Nanocomposites

1.1 Introduction Cement-based composite including cement paste (mainly composed of cement, such as silicate cement, aluminate cement, sulfate cement, and geopolymer cement), cement mortar (cement and fine aggregates), and concrete (cement, fine aggregates and coarse aggregates) is one of the most visible manifestations of man’s physical footprint on the planet. It has become the largest man-made engineering materials (accounting for 40% of man-made objects, the annual amount of about 1.4 billion cubic meters, equivalent to more than 30 billion tons) in the world. Cement-based composites are multi-component, multi-phase, and multi-scale materials in nature. Their main components include cement, water, aggregates, chemical additives, and mineral additives as shown in Fig. 1.1. Due to its excellent mechanical properties (mainly high compressive strength and high modulus of elasticity), good water resistance, easily formed into a variety of shapes and sizes, excellent durability, and cheap availability, cement-based composite is a reliable choice for the sustainable development of human society [1–3]. At the same time, in order to meet the development trend of modern infrastructures in terms of scale, complexity, functionality and intelligence, new-generation cementbased composite not only have excellent mechanical, durability and processing properties necessary as structural materials, but also have functional properties such as electrical, thermal, acoustical, optical, electromagnetic and photocatalytic properties as well as intelligent properties such as self-sensing, self-healing and self-regulating properties. Nanomaterials usually are defined as materials composed of a set of substances where at least one dimension is less than approximately 100 nm, providing unique physical and chemical properties that exist at the nanoscale. Because of the unique nanoscale (1–100 nm) size, nanomaterials are different from microscopic atoms molecules and macro-objects in terms of their physical, chemical, electrical, and magnetic properties. Over the past century, the use of nanomaterials with these exceptional properties has taken huge leaps in chemistry, physics, biology as well

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_1

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

Fig. 1.1 Main components of cement-based nanocomposites

as in civil engineering. In 2000, Colston et al. firstly proposed the use of nanomaterials to fabricate cement-based nanocomposite and showed that the addition of nanomaterials would significantly improve the microstructure of cement-based composite. Then, many innovative achievements have found that nanomaterials can not only improve the mechanical properties and durability of cement-based composites, but also impart functional/smart properties to cement-based composites. Nanoengineering and nanotechnology provides a new impetus for the development of high performance and multifunctionality of cement-based composites. The use of nanomaterials helps to deepen the understanding of the behavior of cement-based composites, enables manipulation of the structure at the nanometer scale, reduces production and ecological costs cement-based composites, and extends the service life of concrete infrastructures, which has significant and profound implications for guiding the development and application trends of concrete structures [1, 4]. As illustrated in Fig. 1.2, the general design principles of cement-based nanocomposites are

1.1 Introduction

3

based on the inherent characteristics and specific application demands of cementbased materials/structures/infrastructures, by tailoring their compositions (e.g., raw materials and mix proportion), fabrication (e.g., processes, tools, and techniques), and structures (e.g., formation, intrinsic characteristics, and microstructures), with full considerations of effectivity, simplicity, economy, and sustainability. In other words, the design of cement-based nanocomposites mainly involves bottom-up approaches. Therefore, it is of first importance to understand what the nanomaterials are and how to use them to develop new-generation cement-based nanocomposites. This chapter will firstly give an overall introduction to the fundamentals of nanomaterials. Then, introduction to new-generation cement-based nanocomposites will be briefly provided.

Fig. 1.2 Design principles of cement-based nanocomposites

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

1.2 Fundamentals of Nanomaterials 1.2.1 Definition and Classification of Nanomaterials Nanomaterials as a subject of nanotechnology are low dimensional materials comprising of building units of a submicron or nanoscale size (i.e., 1–100 nm) at least in one direction and exhibiting size effects. In bulk materials, physical properties are independent of size, whereas in the case of nanomaterials, different physical properties can be dependent on the nanomaterials’ size and shape, as compared in Fig. 1.3. Nanomaterials can be classified into different groups based on different criteria, as listed in Table 1.1. In general, nanomaterials are classified according to their spatial dimension, morphology, state and chemical composition [5]. Based on their dimensions and the overall shapes, nanomaterials can be further classified into four categories: zero-dimensional nanomaterials (0D), one-dimensional nanomaterials (1D), two-dimensional nanomaterials (2D), and three-dimensional (3D) materials. 0D nanomaterials have all dimensions at the nanoscale, i.e., dimensions below 100 nm,

Fig. 1.3 General properties of nanomaterials and bulk materials

1.2 Fundamentals of Nanomaterials

5

including nanorods, nano-polygons, hollow nanospheres, metallic nanomaterials, and quantum dots (QDs). 1D nanomaterials are materials with one dimension not at the nanoscale while the other two dimensions are at the nanoscale, including metallic, polymeric, and ceramic nanotubes, nanorod filament, nanowire, and nanofibers. 2D nanomaterials contain only one nanoscale dimension, including mono-layered and multi-layered, crystalline or amorphous nano thinfilms, nanoplates, and nanocoatings. 3D nanomaterials have all dimensions beyond 100 nm, which are composed of multiple nanomaterials in different directions, such as nanofoams, graphene fibers, nanotube fibers, fullerenes, nanocrystals, honeycombs, and layered skeletons. However, as 3D nanomaterials cannot be used as elementary units (blocks) to build low dimensional nanostructures except 3D matrix, the 3D nanomaterials are often excluded in the classification of nanomaterials. When used in cement-based nanocomposites, nanomaterials are often classified based on their chemical compositions, which can be categorized into four types such as: (1) inorganic-based nanomaterials; (2) carbon-based nanomaterials; (3) organicbased nanomaterials; and (4) composite-based nanomaterials. The first two types of nanomaterials are mostly used for the fabrication of cement-based nanocomposites. Table 1.1 Classification of nanomaterials based on different criteria Criteria

Classification

Examples

Dimensionality

0D

Solid nanoparticles, hollow nanoparticles, clusters, quantum dots, etc

1D

Nanorods, nanowires, nanotubes, nanofibers, etc

2D

Sheets, films, patterned surfaces, coatings, etc

3D

Pillars, nano MEMS device, polycrystals, etc

Morphology

State

Flatness

Graphene, MXene, etc

Sphericity

Metallic nanoparticles, QDs, etc

Aspect ratio

Nanotubes, nanobelts, nanowires, etc

Isometric

–

Inhomogeneous Dispersed or suspensions Agglomerate Chemical composition Inorganic-based

Ag, Au, Al, Cu, Fe, and Zn nanomaterials, ZnO, CuO, Al2 O3 , TiO2 , Fe2 O3 , Fe3 O4 , and SiO2 , etc

Carbon-based

Fullerene, carbon black, carbon nanotube, graphene, etc

Organic-based

Dendrimers, cyclodextrin, liposome, and micelle, etc

Composite-based

Metal–organic framework, covalent-organic framework, etc

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

Inorganic-based nanomaterials include metal nanomaterials, metal oxide nanomaterials, bimetallic nanomaterials, zeolite and silica-based nanomaterials. Many kinds of inorganic-based nanomaterials, such as TiO2 , Fe2 O3 , Al2 O3 , ZnO, and SiO2 , have been studied due to their favorable structure and surface chemistry that can promote cement hydration, densify the microstructure and the ITZ, and leads to a reduced porosity. Carbon-based nanomaterials have unique properties and play a key role in cement and concrete materials. The carbon-based nanomaterials consist of hybridized sp2 carbon atoms that have been developed in various dimensions. Based on the forms, carbon-based nanomaterials can be classified as follows: (1) fullerene (0D), which is an allotrope of carbon (C) with 60 C atoms arranged in the buckyball structure. Derivates of fullerene have unique properties that can neutralize reactive species such as nitrogen and oxygen; (2) CNT (1D), which is a material that has a hollow structure composed of linked carbon atoms in hexagonal structures. CNT can be directly synthesized by chemical vapor deposition (CVD) and the preparation steps allow controlling the homogeneity and size of carbon-based structure, which will be discussed next; (3) graphene (2D) which are sp2 -bonded carbon structures with a hexagonal or honeycomb lattice. Graphene forms a thin layer with one carbon atom bonding covalently to three other carbon atoms. This material has several unique properties, such as large surface area, high electrical conductivity, good stability, and chemical reactivity; and (4) nanodiamonds (3D). Different from graphene, nanodiamonds have a layered sphere-like shape. Nanodiamonds have unique characteristics, such as optical and magnetic properties. Carbon nanomaterials are regarded as one of the most promising admixtures for the cement and concrete industry due to their additional functionalities, good mechanical property, chemical robustness, and abundance [6].

1.2.2 Nano-Effect of Nanomaterials It is well known that classical mechanics provides an accurate description for the behavior of macroscopic objects while quantum mechanics describe the physics of microscopic systems involving electrons, atoms, and molecules. For nanomaterials, the system that falls into the crossover region between macroscopic regime and the microscopic regime is called mesoscopic system and its behavior reveals quantum–mechanical effects. Several new effects have been observed in the nanoscaled systems so that the physical and chemical properties of nanomaterials, such as mechanical, thermal, optical, and electrical properties are remarkably different from that of bulk materials and that of their atomic counterparts. (1) Small size effect. When the size of nanoparticle is comparable to or even less than the wavelength of light, de Broglie wavelength, or the free path length of electrons, periodic boundary conditions and the translation symmetry of crystal nanoparticles would be broken down, and atomic density near the surface

1.2 Fundamentals of Nanomaterials

7

of noncrystal nanoparticles would be decreased under the conditions. Subsequently, the acoustic, magnetic, electrical, thermal, and mechanical characteristics are simultaneously changed so as to cause appearance of some novel phenomena, which is referred to as small size effect. The most obvious effect of reducing the particle size is the increase in specific surface area. The atoms lying at the surfaces or interfaces have different environments both in terms of coordination and chemical properties since the structure of grain boundaries is significantly different from that of bulk materials. Obviously, the restriction of the surface atoms would be less so that they will be fluctuate more easily in their thermal motions, as a result of lowering melting temperature. (2) Quantum size effect. As the particle size is reduced to, or approach the exciton’s Bohr radius, the electron energy level near the Fermi energy level of metal nanoparticles changes from a quasi-continuous state to a discrete energy level, while the energy level between the highest occupied molecular orbital and the lowest unoccupied molecular orbital in semiconductor nanoparticles becomes sharply wider, which is so-called quantum size effect. This is because the energy gap is related to particle size. In bulk materials the energy bands overlap each other, while in nanomaterials the energy bands are separated by energy gaps. Depending on the number and shape of nanoparticles, the conductive metal nanoparticles may become semiconductors or insulators. Figure 1.4 illustrates quantum size effect-induced metal–insulator transition. In the presence of a small non-zero Kubo gap (δ), there is a continuous transition from an insulator at low temperature (δ >> KT ) into a semiconductor at medium temperature (δ = KT ), and to a conductor at high temperature (δ 30 eV). This plasm is accelerated by the electric field and crosses the chamber to bombard target materials, so that the atoms of the target materials eject from the surface to sputter on the substrate (anode). The cooling and condensation of these atoms in

1.2 Fundamentals of Nanomaterials

(b)

(c)

(d)

(3)

23

inert gases result in the formation of nanoparticles, or thin films on the substrate. However, only a very small fraction of the gas atoms are ionized (~0.01%). The ion flux bombarding the target is therefore rather small with deposition rates at the substrate likewise (~0.1 um/h). This technique has several advantages, such as no crucible needed, being able to produce metal nanoparticles with highmelting points, well-controlled size distribution, nanocomposites formed with different target materials. Magnetron sputtering. Magnetron sputtering involves the creation of plasma by applying a large DC potential between two parallel plates. A static magnetic field is applied near a sputtering target for ionization inert gas to produce positive plasma. This plasma is accelerated by the magnetic field to bombard target materials so that the neutral atoms are sputtered from the target to deposit on the surface of a substrate. A further benefit of the magnetic field is that it prevents secondary electrons produced by the target from impinging on the substrate, causing heating or damage. The deposition rates via magnetic sputtering are high enough for industrial application. Multiple targets can be rotated so as to produce versatile nanomaterials. Vacuum arc deposition. Vacuum arc deposition involves a cathode constructed from the target material and an anode attached to an igniter. An arc which is self-sustaining with low-voltage and high-current was generated by contacting a cathode with igniter. The arc ejects predominantly ions and micrometer-sized droplets from a small area on the cathode. The ions in the arc are accelerated towards a substrate and deflected using a magnetic field if desired. Any large particles are filtered out before deposition. A vacuum cathodic arc can operate without a background gas under high-vacuum conditions. However, the deposition can be achieved by introducing a background gas such as nitrogen. The high ion energy produces dense films even at low substrate temperatures and consequently arc technology is commonly used for the deposition of hard coatings. As well as DC sources, plasmas can also be produced using radio frequency and microwave power. The method has the advantages of being able to provide higher current densities and higher deposition rates. Plasma sputtering. In the plasma sputtering process, a metal target material is bombarded with high-energy ions of an inert gas such as argon or krypton ionized. The source of high-energy ions is plasma, which can be generated by DC or plasma gun. The high-energy ions created in the plasma are accelerated to the target and bombard it causing the ejection of predominantly neutral atoms and a small fraction of ions from the target surface. Plasma is ionized gases consisting of positive ions, negative ions, electrons and neutral species produces by DC discharges of plasma gun. The ejected materials are also of high energy and can be collected on a cooled substrate where their energy is no sufficient to form a thin film. The ejected particles can also be swept away by the inert gas atmosphere from the sputter source and are then condensed. Laser ablation

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

The principle of laser ablation method is that a pulsed laser beam with very high energy is focused via an external lens onto a rotating target located within a vacuum chamber causing the target material to be vaporized. The chamber keeps at a constant pressure in the atmosphere of helium gas. The nanoparticles of vaporized material are allowed to cool and condense before being collected on an appropriate substrate. The laser ablation is a zero-contamination process.

Chemical Vapor Deposition (CVD) Method CVD method is a widely used materials processing technology in which thin films are formed on a heated substrate via a chemical reaction of gas-phase precursors. In contrast to the PVD methods, such as evaporation and sputtering, CVD offers a clear advantage by relying on chemical reactions that enable tunable deposition rates as well as high-quality products with excellent conformality. Usually, CVD does not require high-vacuum working environments, making it a popular technology for electronics, optoelectronics, surface modification and biomedical applications. Nanomaterials with high purity and fine structure, such as CNTs, graphene and 2D transition metal dichalcogenides (TMDs) have been successfully produced via CVD method. Figure 1.11 shows a typical CVD system consisting of a gas delivery system, a reaction chamber, a vacuum system, an energy system, an exhaust gas treatment system and an automatic control system. A CVD system must meet the following basic requirements: delivery of the gas-phase reactants in a controllable manner; provision of a sealed reaction chamber; evacuation of the gases and control of the reaction pressure; supply of the energy source for the chemical reactions; treatment of the exhaust gases to obtain safe and harmless levels; and automatic process control to improve the stability of the deposition process. Various advanced CVD systems and their variants have been developed. To obtain different nanomaterials by CVD, suitable equipment is needed, and custom-built systems provide the flexibility of operation often desired by CVD researchers. Table 1.3 provides a summary of typical CVD methods for growing nanomaterials. (a) Horizontal chemical vapor deposition and vertical CVD are based on the reactor configurations or the directions of gas flow. The horizontal tube reactor is the most common configuration, where the substrates are mounted horizontally, vertically or with a tilt angle to adjust the gas flow. The vertical reactor is usually equipped with a showerhead mixer, which is beneficial for material uniformity and growth rate. (b) Low-pressure CVD (LPCVD) and atmospheric pressure CVD (APCVD) are based on the working pressure. In LPCVD, a vacuum pump drives the gas flow. By contrast, APCVD usually does not require a pump and results in a slow flow rate for the reactive gas. (c) Hot-wall CVD (HWCVD) and cold-wall CVD (LWCVD) refer to the heating methods of thermal CVD. In HWCVD, the entire reaction chamber is heated by

1.2 Fundamentals of Nanomaterials

25

Fig. 1.11 Schematic diagram of a typical horizontal CVD system, which includes a gas delivery system, a quartz reaction chamber, a vacuum system, an energy system and an auto-control system Table 1.3 Typical CVD methods for growing nanomaterials [26–29] Material

Substrate

Precursor

Key parameters

Graphene

Copper

CH4

OPCVD with H2 /argon flow, at 1000–1200 °C

Glass

CH4

APCVD with H2 /argon flow, at 1000–1200 °C

SWCNT

SiO2

CH4

APCVD with H2 /argon flow, at 900–1200 °C, Ni/Co/Fe as catalyst

MWCNT

SiO2

C2 H2

APCVD with H2 /argon flow, at 600–900 °C, Ni/Co/Fe as catalyst

Hexagonal boron nitride

Copper, nickel, platinum, SiO2 , sapphire

NH3 –BH3 (heating at 60–100 °C)

LPCVD with H2 /argon flow, at ~1000 °C

Single-crystal substrate SiO2 , mica with steps can induce the mono-orientation of h-BN

Sulfur powder (heating APCVD or LPCVD, at 100–200 °C) with H2 /argon flow at 600–900 °C

MSe2 (M = SiO2 , mica molybdenum, tungsten, etc.)

Selenium powder (heating at 200–300 °C)

APCVD or LPCVD, with H2 /argon flow, at 750–850 °C

Mo2 C, TaC

Molybdenum, tantalum

CH4 , C2 H2

APCVD, at ~1100 °C

Bi2 O2 Se

Mica, SrTiO3

Bi2 Se3 (heating at 650–700 °C)

LPCVD, with argon/O2 flow at 500–600 °C

26

(d)

(e)

(f)

(g)

(h)

(i)

1 Fundamentals of New-Generation Cement-Based Nanocomposites

an external furnace with a uniform temperature. In LWCVD, only the substrate and its vicinity are heated, and the reactor wall is cold, allowing for rapid heating and cooling. Resistance heating, hot plates and induction heating methods are common for LWCVD. Plasma-enhanced CVD (PECVD), photo-assisted CVD (PACVD), and laserassisted CVD (LACVD) are variants of thermal CVD involving additional components and the introduction of other types of energy to promote the CVD reaction. In PECVD, a partially ionized high-energy gas, is generated by direct current, radio-frequency voltage or microwave sources and coupled to the reactor, resulting in a major drop of the reaction temperature. In LACVD/PACVD, light from a high-intensity lamp or laser is used to promote the deposition. Metal–organic CVD (MOCVD) utilizes metal–organic precursors (usually volatile toxic liquids) that are vaporized to form thin films. MOCVD is widely used to synthesize III–V compound semiconductors (made of elements from groups III and V in the periodic table) for optoelectronics. Hot filament/wire CVD utilizes resistively heated filaments (wires) suspended above a substrate held at a lower temperature. The filaments cause thermal decomposition, leading to precursors that then adsorb onto the cooler substrates. A refractory metal such as tungsten, tantalum or molybdenum is commonly used as the filament material. Typically, inorganic films such as amorphous silicon or silicon nitride are deposited. Initiated CVD (ICVD) is a form of hot filament/wire CVD for growing electrically insulating polymer thin films. The ICVD method utilizes an initiator and monomers as vapor-phase reactants, which absorb and undergo chain-growth polymerization on the cooled substrate. The use of the initiator enables much lower filament temperatures, which preserves the organic functional groups of the monomer. Incorporating the functional groups allows control over the wettability and surface reactivity. Oxidative CVD (OCVD) utilizes oxidant and monomer vapors, which undergo spontaneous reaction upon adsorption to the substrate. The OCVD produces step-growth polymerization and, typically, results in conducting and semiconducting polymer films. Atomic layer deposition and molecular layer deposition are two similar variants of CVD for depositing inorganic and organic thin films, respectively. For atomic and molecular layer deposition processes, precursors are introduced sequentially. Self-limiting absorption and surface reactions of the precursors results in layer-by-layer growth of high-quality thin films. Between layers, the remaining precursor is purged out by the carrier gas.

Irrespective of the variations in CVD types, as shown in Fig. 1.12, the fundamental process is similar and consists of the following common elementary steps: First, the reactant gases (blue circles) are transported into the reactor (step a). These reactant gases then either diffuse directly through the boundary layer to the substrate (step b) or undergo gas-phase reactions to form intermediate reactants (green circles) and

1.2 Fundamentals of Nanomaterials

27

Fig. 1.12 Schematic of general elementary steps of a typical CVD process

gaseous by-products (red circles) via homogeneous reactions (step c). In both cases, the reactant gases and the intermediate reactants adsorb onto the heated substrate surface and diffuse on the surface. The subsequent heterogeneous reactions at the gas–solid interface lead to continuous thin film formation via nucleation, growth and coalescence as well as formation of reaction by-products (step e). Finally, any gaseous products and unreacted species desorb from the surface and are carried away from the reaction zone as exhausts (step f). The gas-phase reactions occur when the temperature is sufficiently high or additional energy is introduced, for example, in the form of plasma. In addition, the heterogeneous reaction is essential if the deposition reaction relies on the surface catalysis of the underlying substrate, such as in the case of the catalytic growth of graphene on a metal surface. Table 1.4 lists the carbon solubility and thermal expansion of typical substrates for CVD grown graphene. To obtain high-quality nanomaterials by CVD, a series of designs that satisfy the requirements of nanomaterials synthesis, including the heating methods, gas-flow control, the loading of substrate and the growth parameters, including substrate, temperature, atmosphere, pressure and so on, are essential for controlling the quality of as-grown materials as well as the reaction rate (growth rate).

Liquid Phase Synthesis Method The solution-phase synthesis of nanoparticles was first reported by Michael Faraday in the 1850s, where he developed gold colloids by the reduction of gold salt in the presence of phosphorus in aqueous solution. However, those early experiments on the synthesis of gold colloids yielded nanoparticles of polydisperse sizes, poorly defined shapes, and limited morphologies. Due to the facile synthesis of gold nanoparticles in solution, they have become one of the most studied materials to develop well-defined nanoparticles of controlled sizes and shapes. In solution state, the bottom-up synthesis

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

Table 1.4 Carbon solubility and thermal expansion properties of CVD substrates Substrate

Carbon solubility at 1000 °C (at.%)

Coefficient of thermal expansion (10−6 K−1 )

Graphene

–

−7

Copper

0.04

16.7

Nickel

1.3

12.8

Platinum

1.76

8.9

Cobalt

3.41

13.7

Ruthenium

1.56

6.7

Palladium

5.98

11.6

Iridium

1.35

6.5

SiC

–

3.5

Silicon

–

2.5

SiO2

–

0.4

Al2 O3

–

5.0–5.6

route for the preparation of nanoparticles can occur by precipitation method, solvethermal method, freeze-drying method, sol–gel method, microemulsion, microwaveassisted method, and ultrasonic wave-assisted method. (1) Precipitation method The precipitation method is a convenient and powerful technique for synthesizing metal nanoparticles and nanocapsules. Most solution phase methods for the synthesis of nanoparticles involve the use of metal salts, which act as a source of metal ions for the precursor formation. The monomeric precursor is formed by the complexation of metal ions with ligands, solvents, or surfactants in solution, which is further reduced by chemical photochemical or thermal methods to yield nanoparticles of desired shapes and sizes. The first synthesis of many nanoparticles was achieved by the coprecipitation of soluble products from aqueous solutions, followed by thermal decomposition to produce nano oxides. Coprecipitation reactions involve the simultaneous occurrence of nucleation, growth, coarsening, and/or agglomeration processes. Due to the difficulties in isolating each process for independent study, the fundamental mechanisms of precipitation method are still not thoroughly understood [30]. The synthesis of nanomaterials via precipitation method can be achieved from aqueous solutions and nonaqueous solvents. The precipitation of metals nanoparticles from aqueous solutions or organic solvents usually requires the chemical reduction of a metal cation. Reducing agents take many forms, such as H2 , solvated ABH4 (A is alkali metal), hydrazine hydrate (N2 H2 · H2 O), and hydrazine dihydrochloride (N2 H4 · 2HCl). For example, Au, Pt, Pd, and Ag nanoparticles can be synthesized by the reaction with potassium bitartrate, all of the products can form stable colloids with the addition of a suitable stabilizing agent. Similarly, silver nanoparticles have been prepared by reduction of AgNO3 or AgClO4 by N,N-dimethylformamide (DMF),

1.2 Fundamentals of Nanomaterials

29

where 3-(aminopropyl) trimethoxysilane served as the stabilizing agent and DMF was oxidized to carboxylic acid [31]. (2) Solve-thermal method The term “solvethermal” means reactions in liquid or supercritical media at temperatures higher than the boiling point of the medium. Hydrothermal reaction is of solvethermal reactions. To take reactions at temperatures higher than the boiling point of the reaction medium, pressure vessels (autoclaves) are usually required. Figure 1.13 shows schematic of autoclave. It should be noted that the liquid structure of the solvent is essentially unchanged at above or below the boiling point because the compressibility of the liquid is quite small, but as it is near the critical point, the structure of the solvent is dramatically altered by changes in the solvent density. Most of the solvethermal products are nanoparticles with well-defined morphologies. The distribution of the particle size of the products is usually quite narrow, forming monodispersed particles. However, if the solvent molecules or additives are preferentially adsorbed on (or have a specific interaction with) a certain surface of the products, the growth of this surface would be blocked and therefore nanomaterials with unique morphologies may be formed during the solvethermal reactions. Therefore, temperature, solvent pressure and reaction time are the three principal parameters in the solvethermal process [32]. Table 1.5 lists the critical temperatures and pressures of several commonly used solvents for the solvethermal process. Various nanomaterials have been prepared by the solvethermal method: metals, metal oxides, chalcogenides, nitrides, phosphides, oxometallate clusters, organic–inorganic hybrid materials, and even carbon nanotubes [33]. (1) Freeze-drying method Freeze-drying method, also called cryochemical synthesis method, is a lowtemperature processing method, mainly involving the following steps [34]:

Fig. 1.13 Schematic of autoclave

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

Table 1.5 Critical temperatures and pressure of some common solvents

Solvent

Critical temperature (°C)

Critical pressure (bar)

H2 O

374.1

221

NH3

132.4

112.9

CH4 O

240

79.5

C2 H6 O

243.1

63.9

C3 H8 O

235.6

53.7

C3 H6 O

235

47.6

(a) Freezing process. Freezing of aqueous solutions in cryochemical synthesis is performed via fast cooling. The process is usually realized by spraying the solution into liquid nitrogen via a nozzle or ultrasonic nebulizer under intense mechanical stirring. The product of freezing consists of soft agglomerated spherical granules 0.01–0.5 mm in size, and it is separated from the refrigerant by evaporation. The easy evaporation of liquid nitrogen reduces the cooling rate of freezing droplets so that the use of cold hexane instead of nitrogen is often suggested. In the freezing process, the cryocrystallization product of the salt solution may consist of a fine mechanical mixture of crystalline hexagonal ice and crystalline salt or its higher hydrates; a mixture of crystalline ice and solid amorphous solution; or an amorphous, chemically homogeneous solid. (b) Drying process. The main technique of solvent elimination from the frozen products is freeze-drying based on the direct transformation of solid ice into vapor, avoiding liquid phase formation, i.e., sublimation. The formation of liquid usually degrades the morphological homogeneity of the cryocrystallization products achieved during fast freezing. The sublimation is an endothermic process. The selection of low temperature and low pressure can shorten the drying time. Meanwhile, it can prevent the formation of liquid phase in the macroscale by melting the ice-salt eutectics. The processing conditions can be evaluated using pressure–temperature phase diagrams. According to Gibbs’ rule, the triple point (coexistence of three states: ice, liquid and vapor) in the phase diagram of water can be achieved at T = 273.15 K and P = 610.5 Pa. As a result, the coexistence of ice and water vapor is necessary in the ice sublimation process. The ice can be evaporated (sublimed) without melting under an external heat supply if the pressure in the system doesn’t exceed 610.5 Pa. The usual temperature of freeze-drying is 253–273 K, corresponding to equilibrium water vapor pressure values of 100–610 Pa. A considerable advantage of this process over other processes is the availability of a wide range of industrially produced freeze-drying machines. (c) Thermal decomposition. In most cases, freeze-drying is not the final stage of the synthesis process. The products need further processing in order to be converted to the final nanomaterials. The subsequent thermal decomposition and powder processing techniques are the same or similar to other chemical methods of powder synthesis. The temperature of decomposition of the individual components of salt mixtures are usually shifted to lower temperatures compared to

1.2 Fundamentals of Nanomaterials

31

pure individual salts due to the formation of solid solutions. Formation of the complex oxides usually occurs at the last stage in the thermal decomposition of salt precursors, although the range of possible formation temperature is rather wide from 200 to 900. The crocrystallization product consists of a highly dispersed mechanical mixture of the individual compounds, so that chemically homogeneous complex oxide is formed only at the last stage. (2) Sol–gel method The sol–gel method is a process consisting of solution, sol, gel, solidification, and heat treatment of metal organic or inorganic compounds. Traditionally, sol–gel process involves hydrolysis and condensation of metal alkoxides. Metal alkoxides have the general formula M(OR)x and the alkoxyl group (OR) depends on an alcohol. The general synthesis of metal alkoxides involves the reaction of metal species (a metal, metal hydroxide, metal oxide, or metal halide) with alcohol. For example, Si(OR)4 is easily prepared from SiCl4 and the appropriate alcohol, where R can be CH3 , C2 H5 , or C3 H7 . In the absence of water, a stable sol of Si(OR)4 would be formed. After the introduction of water into the system, the hydrolysis initiates, that is, a hydroxide group from water substitutes for an alkoxide group and a free alcohol is formed. Subsequently, the condensation reactions take place, resulting in the formation of nanomaterial gel [35]. The degree of hydrolysis of the alkoxide strongly influences the structure of the Si–O–Si network. Because OH– is a marginally better leaving group than –OR, the condensation process can be tailored to favor the formation of dimers, chains, or 3D agglomerates described in Fig. 1.14. As a result, Si–O–Si chains tend to preferentially form in the early stages of the polymerization process, followed by subsequent branching and cross-linking of the chains during aging. These gels are made of small polymeric entities (0.5–5 nm), which are more or less aggregated and densely packed according to the process (hydrolysis-polycondensation rate, initial alkoxide-to-solvent and alkoxide-to-water ratios). Sol–gel routes can be used to prepare pure, stoichiometric, dense, equiaxed, and monodispersed particles. For example, amorphous TiO2 nanoparticles with average particles size of 70–300 nm were prepared by controlled hydrolysis of titanium Fig. 1.14 Representation of Sol–gel synthesis process

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

tetraisopropoxide. Monodispersed amorphous powders were synthesized using titanium teraethoxide, where only homogeneous nucleation occurred without flocculation. Depending on the reaction kinetics and subsequent aging of particles, nanoscale oxide particles synthesized can be amorphous or crystalline. These nanostructured oxide particles can be carburized or nitride to form non-oxide powders at reduced temperatures and shorter reaction time due to the significant amount of highly active surfaces. Factors that need to be considered in a sol–gel process are solvent, temperature, precursors, catalysts, pH, additives, and mechanical agitation. These factors can influence the kinetics, growth reactions, hydrolysis, and condensation reactions. The solvent influences the kinetics and conformation of the precursors, and the pH affects the hydrolysis and condensation reactions. Acidic conditions favor hydrolysis, which means that fully hydrolyzed species are formed before condensation begins, so the low crosslink density. By varying influence factors of the reaction rates of hydrolysis and condensation, the structures and properties of the nanomaterials can be tailored [36]. (3) Microemulsion method The combination of water, oil, surfactant, and alcohol or amine-based cosurfactant produces clear, seemingly homogeneous dispersion system which is called as microemulsions. In this case, the oil phases are simple long-chain hydrocarbons. The surfactants are long-chain organic molecules with a hydrophilic head (usually an ionic sulfate or quaternary amine) and a lipophilic tail. For example, cetyltrimethyl ammonium bromide (CTAB) is an amphiphilic surfactant, being miscible in both water and hydrocarbons. By ion–dipole interactions with the polar cosurfactant, the CTAB forms spherical aggregates in which the polar (ionic) ends of the CTAB molecules orient toward the center. The cosurfactant acts as an electronegative “spacer” that minimizes repulsions between the positively charged surfactant heads. The surfactant molecules tend to spontaneously position themselves at the interface of two immiscible media to form different aggregates, producing nanoreactors in the form of droplets. The special composition of these molecules induces a reduction in the surface tension between the two immiscible media. When a critical concentration (termed as the critical micelle concentration, CMC) is reached, the monomers, micelle and reverse micelle can be formed in different conditions, for the growth of well-defined crystallized nanoparticles. The Brownian motion of the two mixed droplets brings them collision and coalescence so that they can react with each other. The concentration of surfactant in water–oil mixture determines the final size of nanoparticles (typical range 1–50 nm in diameter). However, continuous collision and coalescence of these droplets in solution is a major factor in high polydispersity of resultant nanoparticles [37]. The microemulsion method can be used to synthesize many nanomaterials, such as nano semiconductors, nanometals, nanooxides, and nanoalloys (CdS, CdTe, CdMnS, or ZnS, with a size range of 2–4 nm; Ag or Cu, with a size range of 2–10 nm) [38]. (4) Microwave-assisted method

1.2 Fundamentals of Nanomaterials

33

Microwave lies in the electromagnetic spectrum between infrared waves and radio waves, with wavelengths between 1 mm and 1 m and frequency between 300 MHz and 30 GHz. The microwave can heat polar solvent quickly so that it has been used as an auxiliary to the above methods to decrease the reaction time. For example, the use of solvothermal synthesis assisted by microwave radiation to grow metal oxide nanostructures has been of growing interest. This method presents some advantages when compared with conventional solvothermal synthesis. It allows the complete reaction in a very short period of time (for some nanostructures only a few minutes are needed). This is possible because microwave radiation transfers energy directly into the reactive species that are present in the solution, favoring transformations that are not possible to obtain with conventional solvothermal heating. Microwave radiation couples directly with molecule dipoles and will promote a rapid increase in temperature due to localized superheating of molecules (Fig. 1.15). Two distinct mechanisms contribute to microwave heating: dipole rotation (dipoles try to align with the changing electromagnetic field, creating a transfer of energy between molecules and ionic conduction) and ionic conduction (which results from movement and collision between ionic species present in the solution-the friction will increase the solution temperature). Therefore, the solution heating by conventional solvothermal method depends on the thermal conductivity of the reactants and solvents used, and also by energy transfer through convection and radiation between the vessel’s external materials and the solution. In microwave-assisted synthesis, the polarity of the solution is of great importance, thus the choice of the solvent must be carefully planned. The microwave heating is more efficient with a more polar solvent—increasing the solution polarity will increase the ability of a molecule to couple with microwave energy. This interaction can be estimated by the loss tangent, tan δ (an equation that estimates the ability of a solvent to absorb microwave radiation and convert the electric energy into heat). Table 1.6 are some solvents that can be used in microwave-assisted solvothermal synthesis. These solvents can be classified as high (tan δ > 0.5), medium (0.1 < tan δ < 0.5), and low (tan δ < 0.1) absorbers. The higher the tan δ value, the higher the amount of microwave energy that is absorbed and converted into heat [39, 40].

Fig. 1.15 Schematic of heating effect by a conventional solvothermal method and b microwaveassisted solvothermal method

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

Table 1.6 Loss tangents, tan δ, of different type of solvents at 2.45 GHz and 20 °C High (tan δ > 0.5)

Medium (0.1 < tan δ < 0.5)

Low (tan δ < 0.1)

Solvent

tan δ

Solvent

tan δ

Solvent

tan δ

Ethylene glycol

1.17

2-Butanol

0.45

Chloroform

0.091

Ethanol

0.94

2-Methoxiethanol

0.41

Ethyl acetate

0.059

2-Propanol

0.80

1-Hexanol

0.34

Acetone

0.054

1-Propanol

0.76

Dichlorobenzene

0.28

Dichloromethane

0.042

Formic acid

0.72

Acetic acid

0.17

Toluene

0.040

Benzyl alcohol

0.67

DMF

0.16

2-Ethoxyethanol

0.039

Methanol

0.66

Dichloroethane

0.13

Hexane

0.020

Nitrobenzene

0.59

Water

0.12

o-Xylene

0.018

1-Butanol

0.57

Chlorobenzene

0.10

Isobutanol

0.52

(5) Ultrasonic wave-assisted method Different from the microwave-assisted method, ultrasonic wave cannot be adsorbed by the reaction medium. It can transmit through any substances. The energy of ultrasonic wave is insufficient to cause chemical reactions, but when it travels through the reaction medium, a series of compressions and rarefactions are generated. The compression cycles exert a positive pressure on the liquid by pushing the molecules together and the rarefaction cycles exert a negative pressure by pulling the molecules from one another. Because of the excessively large negative pressure, cavitation bubbles are formed in the rarefaction regions. These microbubbles grow in the successive cycles and reach to an unstable diameter so as to collapse violently with shock waves. Therefore, ultrasonic wave-assisted method has been largely used to prepare nanoparticles containing hydrophobic characteristics, such as magnetic Fe3 O4 nanoparticles [41].

Template-Assisted Synthesis Method (1) Hard templates Hard templates are generally used to prepare nanowires, nanotubes and nanorods of inorganic materials by the top-down approach. In this method, porous templates are filled with desired material to fabricate monodisperse nanoparticles. The two most studied templates for synthesis of nanoparticles are porous anodized aluminum oxide (AAO) and track-etched polymer membranes. AAO is created by electrochemical oxidation of aluminum in an acid electrolyte and has a uniform density of parallel pores of 5 nm diameter, which are arranged in hexagonal lattice. The track-etched polymer membranes, on the other hand, are formed by the bombardment of polycarbonate films to create damage tracks, which are then chemically etched into randomly

1.2 Fundamentals of Nanomaterials

35

distributed uniform diameter pores of 10 nm. The drawback of track-etched polymer template is that pores are not parallel in their orientation and may intersect to create larger diameters nanoparticles. The templates (AAO or track-etched membranes) produced are typically coated with a sacrificial metal layer (gold or silver layer), on one side to attain electrical conductivity. The materials of interest are electrochemically deposited into the pores of the template, to gain nanoparticles of desired shape and size. The materials synthesized are then harvested in the form of free nanoparticles by the dissolution of both template and sacrificial metal layer in appropriate solvents. The basic mechanism of nanoparticle synthesis by hard template method is depicted in Fig. 1.16. The surface treatment of templates with organic molecules provides another method to tune of shape of nanoparticles by template mediated approach. For example, the AAO template dissolves in acidic or basic solution, yielding ensemble of homogenous metallic nanoparticles, connected at the base of substrate metal. For electronic applications, these connected nanoparticles are useful, but in order to get monodisperse colloidal carriers, further dissolution of substrate metal is needed. The surface treatment of templates with organic molecules provides another method to tune of shape of nanoparticles by template-mediated approach. For example, galvanostatic deposition of gold on the AAO template leads to the synthesis of gold nanowires, however, the pretreatment of AAO with (2-cyano ethyl) triethoxy silane, facilitates preferential deposition of gold on the walls of template pores, thus forming nanotubes. The nonelectrochemical methods, such as sol–gel approach, and layer-by-layer method have also been used to fabricate semiconductor nanoparticles (quantum dots, graphite-based nanoparticles) by hard template approach. The major advantage of this technique is the synthesis of monodisperse particles of high aspect ratios and multiple chemistries. This is one of the most widely used techniques to prepare metallic nanoparticles by top-down approach. The major concern with this technique is the limited compatibility of nanoparticles with the solvents used to dissolve the template and sacrificial metal layer. Another drawback is the availability of limited choices for defining the shape of nanoparticles and most nanoparticles produced by this method are in cylindrical geometric shapes. Moreover,

Fig. 1.16 The schematics depicting the synthesis of nanoparticles by hard template method

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

the issue of scalability is questionable as this will require large area of high-density templates, which is possible theoretically but has not yet been developed in reality. (2) Microbial biotemplates Biotemplating is a facile, cost-effective, and versatile method to synthesize shapeand size-specific nanostructures. In general, the template approach of nanoparticle synthesis employs support or template to grow the nanoparticles of certain size and shape from their respective materials. In biotemplating, natural, ecofriendly, inexpensive, living systems with preferential metal ion binding capacity yields high concentrations of desired nanoparticles. Some examples of microorganisms-based biotemplates are given as follows: (a) Bacterial biotemplates: Different gram-positive and gram-negative bacteria have been used as a template for the micro/nanostructure formation. The surface layer of proteins on the bacterial cell wall, known as S-layer, is one example of a biotemplate that has been used for the growth of nanoparticle. For example, silicon nanopillar arrays of 60–90 nm tall were synthesized using gold etched Slayer proteins. The efflux system in the bacterial cell wall is another example of biological materials, which has been used as a template to synthesize nanoparticles. These efflux systems oxidize or reduce the metals and help to detoxify the bacteria from metal containments, present in the surrounding media. Nickel nanostructures were synthesized by exploiting the redox reactions of Bacillus subtilis Another source of biotemplating from bacterial species is bacterial flagella. The bacterial flagella and Pilli are used as source of locomotion and communication between bacterial species. The flagella shaped inorganic nanoparticles are generally prepared by the deposition of a thin film of metal ions, followed by its annealing on the surface of flagella to obtain nanotubes ranging from 200 to 300 nm in diameter. (b) Fungal biotemplates: Fungi are eukaryotic organisms, typically known for their filamentous structures and for their excellent bioaccumulation and tolerance to metal species. The fungal hyphae have been used as a template to grow nanostructures. For example, the self-assembly property of gold ions on the surface of hyphae was used as a tool to prepare gold nanowires using Aspergillus nidulans as a template and monosodium glutamate as a reducing agent. The gold nanoparticles produced grew along the length of hyphae and were converted into free-standing gold microwires after the supercritical CO2 extraction process. (c) Algal biotemplates: Algae are aquatic photosynthetic organism, which exist in different morphological shapes, such as unicellular form, filamentous form, and in the form of colonies. Diatoms are a type of algae, which are well characterized by the presence of siliceous rigid cell wall structure, of varying shapes such as rods, and flakes. These diatoms can participate in mineralization processes and are especially interesting for the production of nanostructures of controlled the shapes. Coscinodiscuc lineatus, is a type of diatom that has uniformly shaped hexagonal lattice of frustules of 1 μm in diameter and 700 nm in thickness. This natural 3D assembly of ordered silica is being used as a template to prepare Zinc Sulfide nanostructures by a sono-chemical method.

1.2 Fundamentals of Nanomaterials

37

(d) Viral templates: Viruses are infectious agents, composed of protein-based shells, surrounding their genetic materials. The proteinaceous shell of viral particles facilitates mineralization and metallization with the help of amino acids present on their surface and provides a template for the synthesis of nanomaterials. The frequently studied viruses for biotemplating are M13 phage, tobacco mosaic virus, cowpea mosaic virus, and cowpea chlorotic mottle virus, due to the specific shapes and sizes of their protein coats. Self-Assembly Method The use of self-assembly method for the synthesis of nanoparticles has grown in recent years, with the deep understanding of nanoscience and nanotechnology. Self-assembly is a process in which an organized structure or pattern is assembled as a consequence of specific, local interactions among the components themselves from a disordered system of preexisting components. When the constitutive components are molecules, the process is termed molecular self-assembly. Molecular self-assembly involves noncovalent or weak covalent interactions (van der Waals, electrostatic, and hydrophobic interactions, hydrogen and coordination bonds). Figure 1.17 illustrates the self-assembly process of polar molecules. The self-assembly process can be classified as either a static or dynamic one. In static self-assembly, formation of the ordered structure may require energy, but once it is formed, it is stable. In dynamic self-assembly, there is competition between reaction and diffusion in oscillating chemical reactions for the interactions in the formation of structures or patterns. In templated self-assembly, the structures are formed by interactions between the components and regular features in their environment, e.g., crystallization on surfaces. Biological self-assembly exhibits functional variety and complexity. Self-assembly can be further expanded by a natural process: thermodynamic or kinetic. As listed in Table 1.7, the former includes atomic, molecular, and interfacial self-assemblies, while the latter includes colloidal and some interfacial self-assemblies. Some self-assembly processes are random, e.g., molecular, colloidal, interfacial self-assemblies. Others are directional to some degree, e.g., atomic and biological self-assemblies. Self-assembly associated with large building units, i.e., colloidal self-assembly, is sensitive to external stimuli, e.g., electric field, magnetic field, gravity, flow, and so on. The view of spontaneous association covers a broad range-of-length scale from angström to centimeter, different dimensions, and different sources of origins. Table introduces self-assemblies in dimensions. The typical attractive forces in self-assembly processes include van der Waals force, solvation, depletion, bridging, π-π stacking, hydrophobic, hydrogen bond, and coordination bond, and repulsive forces in self-assembly processes include electric double layer, solvation, hydration, and steric. It is noted that repulsive forces can appear in interactions between dissimilar colloidal objects. The attractive force can sometimes be in interaction between molecules or colloids with different charges, or with the same charge but at very small separation, or between zwitterionic molecules and

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

Fig. 1.17 Schematic of the self-assembly of polar molecules

colloids. The coordination bond is a strong chemical bond compared with the rest of the forces but serves as a unique attractive force for some of the supramolecular self-assembly systems. Self-assembly methods can be used to fabricate nanocrystals, nanowires, and nanorods, as well as monolayer and multilayered films, nanotubes, 3D nanostructures, supermolecular polymers, and biological materials. The components involved can be metals, alloys, oxides, semiconductors, polar molecules, supermolecules, etc.

1.2.5 Characterization of Nanomaterials Surface and Morphology Characterization (1) Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) is a surface-imaging technique, which generates high-resolution and high magnification images of a sample by scanning its

1.2 Fundamentals of Nanomaterials

39

Table 1.7 Self-assemblies in dimensions Dimension

Building units

Self-assembled systems

Atomic

Metal

Epitaxial film, quantum dot Directional, one-step, nonhierarchical

Characteristics

Molecular

Surfactant, polymer

Micelle, bilayer microemulsion, emulsion

Micelle, bilayer microemulsion, emulsion

Colloidal

Nanoparticle, nanotube, fullerene

Suspension, dispersion, sol, colloidal crystal

Random, one-step, nonhierarchical

Biological

Amino acid, lipid biopolymer

DNA, RNA, protein, enzyme, membrane

Directional, stepwise, hierarchical

Interfacial

Surfactant, polymer, lipid

Surface micelle, Langmuir Directional, one-step, monolayer, nonhierarchical Langmuir–Blodgett film, self-assembled monolayer

surface with a focused electron beam. SEM can resolve up to 1 nm and can magnify up to 400,000×. The incident electron beam, with a negative charge, interacts with the material that has a specific arrangement and electron clouds and produces various signals reflecting the topographic detail and the atomic composition of the scanned specimen surface. The incident electron beam causes the emission of X-rays from the atoms on the surface of the sample, of elastically backscattered (or primary) electrons, secondary inelastic electrons, and Auger electrons. Secondary electrons are the most valuable for obtaining the sample morphology/topography. From the secondary electrons, high-resolution images can be produced revealing details of around 1–5 nm, while characteristic X-rays are used by a technique known as energy dispersive Xray spectroscopy (EDX) to identify the elemental composition and Auger electrons are used in surface analytical techniques. In SEM, the surface of the sample must be electrically conductive and grounded to prevent the accumulation of electrostatic charge at the surface, which leads to electrostatically distorted images and artifacts. For this, the surface of nonconductive samples is coated with an ultrathin layer of an electrically conducting material, such as Au, Au/Pd alloys, and Pt. Furthermore, in conventional SEM it is also important to remove the water from the sample since water molecules will evaporate under vacuum and destroy the clarity of the image. The recently developed environmental scanning electron microscope (ESEM) is designed to operate under a lower vacuum and lower voltage. ESEM is useful to visualize specimens under their “natural” form, with minimum sample preparation. This includes the ability to examine moist samples. SEM is often combined with the EDX technique, which is used to analyze the elements present near the surface in the micrometer scale and to determine the elemental composition at different positions. SEM–EDX is a very useful technique because at relatively short time information regarding the size, shape, surface texture and elemental analysis can be obtained. By EDX analysis nanoparticles such as silver, gold, and palladium can be easily identified on the surface of a sample. However, elements of a low atomic number are harder to detect by EDX. SEM can provide information about the shape, the size, and

40

1 Fundamentals of New-Generation Cement-Based Nanocomposites

the size distribution of nanomaterials. However, there is some limitation in the SEM measurements. During sample preparation, the process of drying and contrasting may cause the shrinkage of the nanomaterials which changes their features in terms of size and shape. Besides, due to the small number of particles present in the scanning region, biased statistics of the size-distribution of heterogeneous samples are inevitable. (2) Transmission electron microscopy (TEM) Transmission electron microscopy (TEM) is another electron microscopy technique frequently used for the characterization of the nanomaterials. TEM can provide direct high-resolution images and detailed qualitative/quantitative chemical information for the nanomaterials at a spatial resolution down to atomic dimensions (1100 times). Although cement-based composite can achieve high compressive strengths, its tensile strength is only about one-tenth of its compressive strength. The failure of cement-based composite shows typical brittle failure characteristics. In order improve the ductility of cement-based composite, short-fiber reinforced cementbased composite was developed. The combination of non-metal and metal, inorganic and organic can be realized through fiber composite, so as to reduce the proportion of covalent bonds in microstructure, increase the proportion of ionic bonds, secondary bonds, and even van der Waals forces. At the end of the 20th century, some new theories, new processes, and new materials in the field of concrete continued to emerge, not only new types of cementbased composite (such as reactive powder concrete (RPC), engineered cement-based

64

1 Fundamentals of New-Generation Cement-Based Nanocomposites

composite (ECC), ultra-high performance concrete (UHPC), etc.), and there is a new development direction to make cement-based composite intelligence (self-sensing, self-healing, self-regulating, self-cleaning, etc.) and multifunctional (electricity, heat, sound, light, hydrophobicity, etc.). As introduced in Sect. 1.2, because of their unique nano effects and distinct physical, chemical, electrical, thermal, optical, and magnetic properties, the use of nanomaterials with these exceptional properties has taken huge leaps in cement-based composites. Consequently, with the explosive growth of nanoscience and nanotechnology at the end of the 20th century, using nanotechnology to manipulate the nanoscale behaviors inside cement-based composites to fabricate cement-based nanocomposites is becoming aware among the public and academic community. It has been long recognized that cement-hydrated phases are primary nanostructured materials mainly condensed by calcium silicate hydrate (i.e., C–S–H) gels. The C–S–H gel has been regarded as a layered structure containing some 30,000– 50,000 molecules, with tens of nanometers in size. It means that cement-based composites have the properties of nanomaterials in nature. The conscious application of nanoscience and nanotechnology can be traced back to 1989. Nano-ZrO2 synthesized via coprecipitation method was used to reinforce mechanical properties of cement-based composites [63]. Since then, researchers started to investigate the nanostructure inside C–S–H gels in the early 1990. Since 2001, the studies in the application of nano science technology in cement-based composites step into a very active period. For example, the addition of nano-SiO2 to concrete was first used for cement-based composite reinforcement. After that, nano-TiO2 , nano-ZrO2 , and nano-carbon materials were applied one after another for the enhancement and modification of cement-based composites. Much work indicated that big gains in mechanical, durable, and functional properties of cement-based composites were achieved by nano-nonmetallic oxide and metallic oxide modifications. Traditionally cement-based nanocomposite is a composite system in which nanomaterials as dispersing phase are uniformly distributed in cement-based materials as continuous phase via appropriate preparation methods. With the addition of nanomaterials, cement-based nanocomposite always exhibits unprecedented improvement in the physical and chemical properties, and novel behaviors that are absent in the unfilled cement-based composite. Nano-engineering of cement-based composite at the nanoscale can take place in one or more of three locations: in the solid phases, in the liquid phase, and at interfaces, including liquid–solid and solid–solid interfaces. To date, the research aeras of cement-based nanocomposite mainly include: (a) directly incorporation of nano-oxide (e.g., nano-SiO2 , TiO2 , Al2 O3 , Fe2 O3 , ZrO2 , etc.), nanocarbon materials (e.g., nanocarbon black, CNT, CNT, graphene, etc.), nano-carbide, nano-nitride, nano-salt, nano-clay, nano C–S–H seed, etc. into cementbased materials during mixing to improve mechanical performance as well as impart novel properties, (b) application of nanomaterials on aggregate surfaces before concrete mixing in order to improve interfacial transition zone (ITZ) in cementbased composites, (c) nano-engineering of pore solution and controlled release of chemical admixtures in cement-based composites, (d) improve the workability in special cement-based composites, such as self-consolidated concrete (SCC), (e)

1.3 Brief Introduction of New-Generation Cement-Based Nanocomposites

65

multifunctional applications, such as self-sensing, self-cleaning, self-heating, selfhealing, and antimicrobial functions. The nano-engineered cement-based nanocomposite technology represents an emerging research field that is finding many applications in sustainable infrastructures. The potential benefits of this technology include improved infrastructure reliability and longevity, enhanced structural performance and durability, improved safety against natural hazards and vibrations, a reduction in life-cycle costs in operating and managing infrastructures, and reduced impact on resources, energy, and environment [2, 64]. Over the past decade, the advances in nano-synthetic technologies, nanocomposite technologies and nano-surface modification technologies are driving the progressive exploitation of advanced multiscale nanomaterials. These techniques can be used effectively in a bottom-up approach and hierarchical design to control properties, performance, and degradation processes of cement-based composite and to provide the material with new functions and smart properties not currently available. In view of their unique structures and mutual synergy, these advanced multiscale nanomaterials are expected to allow for the direct manipulation of the fundamental structure of cement phases, alleviate the dispersion issue of traditional nanomaterials in cementbased composites, improve their nanocomposite effectiveness and efficiency and impart new properties and functionalities to cement-based composites, thus boosting the development of new-generation cement-based nanocomposites. Therefore, the pursuit of new-generation cement-based nanocomposites has expanded far beyond the random mixing of functionalized nanoparticles with cement-based matrix to encompass hierarchically structured nanomaterials generated by self-assembly, insitu CVD, electroless deposition, 3D printing, and microwave irradiation, etc. [65– 67]. The key enabling concept is the deterministic, multiscale design and control of advanced nanomaterials/nanoscale building blocks for new-generation cement-based nanocomposite. This includes both synthesis of nanoparticles with tightly controlled size, shape, activity, and crystallinity and self-assembly of the nanoparticles into ordered superlattices over much larger length scales or onto the components of traditional cement-based composite. The following four principles can be used to guide the designing of advanced nanomaterials/nanoscale building blocks for new-generation cement-based nanocomposite: (1) Hierarchical design is an effective strategy to deliver the extraordinary properties of nanoscale building blocks to cement-based nanocomposite, moreover, it significantly expands the design domain to mitigate the trade-off among various properties and functions. (2) At each level of a structural hierarchy, the microstructure needs to be designed rationally to synergize the merits of the constituents. (3) The nanoscale building block should have good compatibility with cementbased materials. (4) The raw components for the fabrication of traditional cement-based composite can be utilized as substrates or raw materials to achieve synergy effects and spatially morphological effects.

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

(5) To generate a high-performance cement-based nanocomposite, the structure– size–property relationships of the nano-scaled constituents must be preserved in the matrix, and not be screened by either the matrix material or deleterious interactions at the plentiful interfaces between the matrix and the nanomaterials. As such, these properties emerge as a universally critical requirement due to the demands of numerous thermal, chemical, and mechanical stimuli, in addition to the functionality driving the composition and structure of new-generation cement-based nanocomposite. Compared to traditional cement-based nanocomposites, new-generation cementbased nanocomposites should have much more features, which include but are not limited to: (1) (2) (3) (4) (5)

Direct manipulation of the fundamental structures at nanoscale; Excellent mechanical properties, durability and sustainability; Versatile and tunable functionality; Multi-scale synergistic modulation; Scalable production via traditional concrete processing technology or additive manufacturing techniques; (6) Smaller environmental footprint for industrial applications. In the past decade, much effort has been made towards the advancement of newgeneration cement-based nanocomposite, and many innovative achievements have been gained in both development and application of new-generation cement-based nanocomposite. To date, more than 10 types of advanced nanomaterials/nanoscale building blocks have been utilized for the fabrication of new-generation cementbased nanocomposite, as listed in Table 1.8. The exploration and research of newgeneration cement-based nanocomposite is still ongoing, and it can be predicted that as the research further develops, more new-generation cement-based nanocomposites will be proposed and their new nano-behaviors will be described, predicted, and controlled, which will constantly enrich the field of nanoscience and cement science. The following chapters will systematically introduce the fabrication, properties, mechanisms and applications of the present new-generation cement-based nanocomposites.

1.4 Summary This chapter first gives a glimpse of the numerous unique and interesting, mainly universal properties, and elaborates on the synthesis and characterizations of nanomaterials. The concept of new-generation cement-based nanocomposite is also extended. The conclusions are summarized as below. (1) Several new effects including small size effect, quantum size effect, surface effect, and quantum tunnel effect are contributed to the unique physical and

1.4 Summary

67

Table 1.8 Classification of advanced nanomaterials/nanoscale building blocks used in newgeneration cement-based nanocomposites Criteria

Classification

Synthesis method

Metamaterials

Helical CNT

CVD

Surface modifications

NCB/CNT

Electrostatic self-assembly

Nano-TiO2 /CNT

Electrostatic self-assembly

Template method

Sol–gel method Ball milling Hydrothermal NCB/Graphene

CVD Electrostatic self-assembly Ball milling

Nano-SiO2 -coated Nano-TiO2

Chemical grafting Electrostatic self-assembly Sol–gel method

In-situ grown on cement components

Nickel-coated CNT

Electrodeposition

CNT on cement

In-situ CVD growth Spray coating

CNT on silica fume

In-situ CVD growth Spray coating

CNT on fly ash

In-situ CVD growth Spray coating

CNT on aggregate

Spray coating

Graphene on aggregate

In-situ annealing and microwave treatment

chemical properties of nanomaterials, such as chemical structure and composition, catalytic reactivity mechanical, thermal, optical, electrical, and magnetic properties are remarkably different from that of bulk materials and that of their atomic counterparts. (2) The synthesis of nanomaterials, in general, can be broadly divided into bottomup approach and top-down approach. The top-down approach is opposite to the bottom-up approach. Based on the two approaches, various methods have been used for the synthesis of nanomaterials, mainly including mechanically milling, physical vapor deposition method (PVD), chemical vapor deposition method (CVD), liquid phase synthesis method, consolidation, template-assisted synthesis and self-assembly method.

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1 Fundamentals of New-Generation Cement-Based Nanocomposites

(3) The precise determination of the properties of the nanomaterials is a very important area in nanotechnology and demands reliable and advanced techniques that are sensitive down to nanoscale dimensions. Nanomaterial characterization tools employed for the characterization of chemical structure and composition, catalytic reactivity mechanical, thermal, optical, electrical, and magnetic properties of nanomaterials have been well developed. (4) The advances in nano-synthetic technologies, nanocomposite technologies and nano-surface modification technologies are driving the progressive exploitation of advanced multiscale nanomaterials., which are expected to allow for the direct manipulation of the fundamental structure of cement phases, alleviate the dispersion issue of traditional nanomaterials in cement-based composites, improve their nanocomposite effectiveness and efficiency and impart new properties and functionalities to cement-based composites, thus boosting the development of new-generation cement-based nanocomposites.

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Chapter 2

New-Generation Cement-Based Nanocomposites with Helical CNT

2.1 Introduction Carbon nanotube (CNT), also known as buckytube or nanoscale hollow tube composed of carbon atoms, possesses large aspect ratio, high elastic modulus, and ultra-high tensile strength, as well as excellent thermal and electrical conductivity [1–5]. Thanks to these merits, CNT shows great potential to not only improve the mechanical properties and durability of cement-based composites, but also endow the materials with functional/smart performance. In addition, the chiral structures of CNT have been widely proven to influence its characteristics. Helical CNT, owing to its unique dielectric properties brought by its chiral and helical structure, can induce cross-polarization under continuous microwave irradiation that leads to resonance losses, which also contributes to electromagnetic shielding and absorption performance [6, 7]. This chapter introduces a new-generation cement-based nanocomposite fabricated by incorporating helical CNT into cement-based composites. The static and dynamic mechanical properties of the cement-based nanocomposites as well as the helical CNT modification mechanisms are presented. Finally, the functional/smart properties including electrical and electromagnetic shielding and absorption properties of the cement-based nanocomposites are demonstrated.

2.2 Preparation of Cement-Based Nanocomposites with Helical CNT The raw materials used to fabricate cement-based nanocomposites with helical CNT include P·O 42.5 R Portland cement, grade II fly ash, silica fume with a particle size range of 0.1–0.3 μm, quartz sand with a size range of 0.12–0.83 mm, water, polycarboxylic superplastizer (SP), and helical CNT. The properties and morphology of helical CNT are shown in Table 2.1 and Fig. 2.1, respectively. The mix proportion © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_2

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2 New-Generation Cement-Based Nanocomposites with Helical CNT

Table 2.1 Properties of helical CNT

Outer diameter Length (μm) Specific surface Morphology (nm) area (m2 /g) 100–200

1–10

≥ 30

Helical

and fabrication process of cement-based nanocomposites in this chapter are shown in Tables 2.2, 2.3, and 2.4, respectively. Fig. 2.1 Morphology of helical CNT

Table 2.2 Mix proportions of cement-based nanocomposites without/with helical CNT Type

Mix proportion (mass ratio) Cement

Fly ash

Silica fume

Sand

Water

SP

Helical CNT

Cement paste

1

–

–

–

0.2

0.0075

0

0.999

–

–

–

0.2

0.0075

0.001

0.995

–

–

–

0.2

0.0075

0.005

0.992

–

–

–

0.2

0.0075

0.008

1

0.25

0.313

1.375

0.375

0.015

0

0.9975

0.25

0.313

1.375

0.375

0.015

0.0025

0.995

0.25

0.313

1.375

0.375

0.015

0.005

Cement mortar

Ultrasonication+non-covalent surface modification by SP

Dispersion method

– 60

Shear mixing (1000 r/min) Shear mixing (2000 r/min)

Cement

300

Vibration

Method

Time (s)

Method Ultrasonication (20 kHz)

Molding

Technology

Nano helical CNT+Water+SP

Feeding order

Fabrication process

Table 2.3 Fabrication process of cement pastes without/with helical CNT

Method

Standing curing

W (20 °C)

40 × 40 × 160 Standard condition

Size (mm)

Curing

180

28

1

Time (d)

2.2 Preparation of Cement-Based Nanocomposites with Helical CNT 75

Ultrasonication+non-covalent surface modification by SP

Dispersion method

60 240

Shear mixing (140 r/min) Shear mixing (140 r/min) Shear mixing (285 r/min) Shear mixing (140 r/min) Shear mixing (285 r/min)

Cement+fly ash

Silica fume

–

Quartz sand

120

120

60

Ultrasonication (20 kHz)

300

Vibration

Molding Method

Time (s)

Technology Method

Nano helical CNT+Water+SP

Feeding order

Fabrication process

Table 2.4 Fabrication process of cement mortars without/with helical CNT Curing Method

W (20 °C)

40 × 40 × 160 Standard condition

Size (mm)

28

1

Time (d)

76 2 New-Generation Cement-Based Nanocomposites with Helical CNT

2.3 Mechanical Properties of Cement-Based Nanocomposites with Helical …

77

Fig. 2.2 Compressive strength of cement-based nanocomposites without/with helical CNT. a Cement pastes. b Cement mortars

2.3 Mechanical Properties of Cement-Based Nanocomposites with Helical CNT 2.3.1 Compressive Strength Figure 2.2 presents the compressive strength of cement-based nanocomposites without/with helical CNT. As shown in Fig. 2.2a, the compressive strength of cement pastes firstly increases and then decreases with the helical CNT content. The addition of 0.1, 0.5, and 0.8 wt% of helical CNT increases the compressive strength of cement pastes by 5.7%, 65.3%, and 50.0%, respectively. However, the presence of helical CNT shows less effect on the compressive strength of cement mortars, as shown in Fig. 2.2b.

2.3.2 Flexural Strength The flexural strength of cement-based nanocomposites without/with helical CNT is shown in Fig. 2.3. The flexural strength of cement paste increases with the helical CNT content. The flexural strengths increase by 21.8, 28.7, and 56.3% when 0.1, 0.5 and 0.8 wt% of helical CNT are incorporated into cement pastes, respectively. Meanwhile, the addition of 0.25 wt% of helical CNT increases the flexural strength of cement mortar by 16.5%.

78

2 New-Generation Cement-Based Nanocomposites with Helical CNT

Fig. 2.3 Flexural strength of cement-based nanocomposites without/with helical CNT. a Cement pastes. b Cement mortars

2.3.3 Impact Properties Hopkinson pressure bar (SHPB) test was employed for characterize the impact performance of cement-based nanocomposites with helical CNT. Figure 2.4 shows the dynamic compressive strength of cement mortars without/with helical CNT. As shown in Fig. 2.4, the dynamic compressive strength increases with the strain rate, indicating the presence of strain rate effect of cement mortar. After adding helical CNT, the dynamic compressive strength significantly increases. The dynamic compressive strengths of cement mortars with 0.25 and 0.50 wt% of helical CNT at the strain rate of 200/500/800 s−1 increase by 78.1%/54.7%/24.3% and 52.%8/89.8%/18.6%, respectively. Fig. 2.4 Dynamic compressive strength of cement-based nanocomposites without/with helical CNT

2.3 Mechanical Properties of Cement-Based Nanocomposites with Helical …

79

Based on the experimental results, the average stress σs , average strain rate ε˙ s , and average strain εs can be calculated through three-wave method, as shown in Formulas (2.1)–(2.3). σs (t) =

EA [εi (t) + εr (t) + εt (t)] 2 As

(2.1)

c [εi (t) − εr (t) − εt (t)] ls

(2.2)

ε˙ s (ε) =

t εs (t) =

ε˙ s (τ )dτ

(2.3)

0

where εi , εr , and εt represent incident strain, reflection strain, and transmission strain in SHPB, respectively. E represents elastic modulus of the rod of SHPB. A and As represent the cross section of SHPB bar and specimens, respectively. In addition, specific energy absorption (SEA), which is a key parameter indicating energy absorption by unit volume of cement mortar, can be calculated from Formula (2.4). AEc SEA = As ls

t [εi (t) − εr (t) − εt (t)]dt

(2.4)

0

where c is the wave speed in SHPB bar. Combining the experimental results and Eqs. (2.1)–(2.3), the dynamic stress– strain curves of cement-based nanocomposites without/with helical CNT are obtained as shown in Fig. 2.5. The dynamic stress–strain curves in Fig. 2.5 can be generally divided into three stages: the approximately linear ascent stage, the nonlinear ascent stage, and the non-linear descent stage, corresponding to the elastic deformation, plastic deformation, and damage softening of cement-based nanocomposites. This three-stage characteristic is observed in stress–strain curves of cementbased nanocomposites without/with helical CNT at different strain rate, indicating the presence of helical CNT and different strain rate do not change the failure process of cement-based nanocomposites. Compared with blank cement mortar, the incorporation of helical CNT increases the slope of the dynamic stress–strain curve during the linear ascent stage and decreases the slope during non-linear descent stage. These phenomena indicate the presence of helical CNT not only increases the elastic modulus of cement mortar, but also modifies the cement mortar energy absorption capacity during the non-linear descent stage, or damage softening stage. In particular, a fluctuating upward trend is observed in the non-linear ascent stage of dynamic stress–strain curve of the cement-based nanocomposites with helical CNT. The dynamic peak strains of cement-based nanocomposites without/with helical CNT are summarized in Fig. 2.6. As shown in Fig. 2.6, the addition of helical CNT

80

2 New-Generation Cement-Based Nanocomposites with Helical CNT

Fig. 2.5 Dynamic stress–strain curves of cement-based nanocomposites without/with helical CNT. a At strain rate of 200 s−1 . b At strain rate of 500 s−1 . c At strain rate of 800 s−1

decreases the dynamic peak strain at a loading rate of 200/500 s−1 . However, the dynamic peak strain of cement-based nanocomposites with helical CNT increases by 49.5–93.8% compared with that of blank cement mortar. This indicates the presence of helical CNT increase the brittleness of cement-based nanocomposites, meanwhile, endows higher ductility of cement-based nanocomposites at high strain rates. Figure 2.7 shows the impact toughness and impact dissipation energy of cementbased nanocomposites without/with helical CNT. As depicted in Fig. 2.7, the impact toughness and impact dissipation energy respectively increase by 49.5–93.8% and 8.7–82.6% after adding helical CNT. In summary, the presence of helical CNT increases the dissipate energy due to the stress enhancement, and simultaneously, modifies the impact properties/performance through its effect on stress redistribution. Fig. 2.6 Dynamic peak strain of cement-based nanocomposites without/with helical CNT

2.3 Mechanical Properties of Cement-Based Nanocomposites with Helical …

81

Fig. 2.7 Impact toughness and impact dissipation energy of cement-based nanocomposites without/with helical CNT. a Impact toughness. b Impact dissipation energy

2.3.4 Modification Mechanisms The results in Sects. 2.3.1–2.3.3 demonstrate the presence of helical CNT can improve the mechanical properties/performance of cement-based nanocomposites, including compressive strength, flexural strength, and impact properties/performance. Such improvements are achieved from the modification of helical CNT on the microstructures of cement-based nanocomposites. Therefore, SEM, XRD, specific gravity (SG) method, mercury intrusion porosimetry (MIP) method, and low field-nuclear magnetic resonance (LF-NMR) were employed to reveal the modification mechanisms of helical CNT on cement-based nanocomposites. Figure 2.8 shows the TG and DTG curves of cement-based nanocomposites without/with helical CNT. Three peaks can be observed in DTG curves in Fig. 2.8b. These three peaks successively indicate the evaporation of water, decomposition of CH, and decomposition of CaCO3 . Based on TG and DTG curves, the hydration degree of cement-based nanocomposites can be calculated from Eqs. (2.5) and (2.6). 

Mwater = M105 − M1000 − MCaC O3 

βt = Mwater /(MW ater −Full × r ) 

(2.5) (2.6)

where Mwater , M105 , M1000 , MCaC O3 , and MW ater −Full represent the mass of nonevaporable water, the mass loss in 105°C, the mass loss in 1000°C, the mass loss of decomposition of CaCO3 , and the mass of water required for full hydration of 1 unit cement. βt is the hydration degree of cement and r is the cement to binder ratio. The calculated hydration degree of cement-based nanocomposites without and with helical CNT is 69.5% and 64.8%, respectively. Therefore, the addition of helical CNT slightly inhibits the hydration of cement-based nanocomposites. The XRD patterns of cement-based nanocomposites without/with helical CNT are shown in Fig. 2.9. It can be seen that the intensities of main diffraction peaks

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2 New-Generation Cement-Based Nanocomposites with Helical CNT

Fig. 2.8 TG and DTG curves of cement-based nanocomposites without/with helical CNT. a TG. b DTG

indicating CH crystals of cement paste with helical CNT are higher than that of blank cement paste. In addition, the CH orientation R can be calculated from (0 0 1) and (1 0 1) crystal face peak intensity through Formula (2.7). R = 1.35I001 /I101

(2.7)

where I001 and I101 represent (0 0 1) and (1 0 1) crystal face peak diffraction intensity, respectively. The CH diffraction intensity and orientation are listed in Table 2.5. The presence of helical CNT reduces CH orientation in cement-based nanocomposites. The CH orientation index of cement-based nanocomposites decreases from 2.70 to 2.63 after 0.5 wt% of helical CNT is incorporated. Fig. 2.9 XRD patterns of cement-based nanocomposites without/with helical CNT

Table 2.5 Cement hydration degree of cement-based nanocomposites without/with helical CNT

Helical CNT content (wt% of cement)

(0 0 1) CH

(1 0 1) CH

CH orientation

0

1794

898

2.70

0.5

2147

1102

2.63

2.3 Mechanical Properties of Cement-Based Nanocomposites with Helical …

83

Fig. 2.10 29 Si NMR spectra of cement-based nanocomposites without/with helical CNT. a Without helical CNT. b With 0.50 wt% of helical CNT

Table 2.6 Deconvolution results of helical CNT Helical CNT content (wt% of cement)

29 Si

NMR of cement-based nanocomposites without/with

Type and content of silicon oxide tetrahedron

Cement

Q0 (%)

Hydration degree (%)

Q1 (%)

Q2 (%)

0

49.8

29.7

20.5

50.2

0.5

47.8

31.5

20.6

52.1

The 29 Si NMR spectrum and corresponding deconvoluted spectrum of cementbased nanocomposites without/with helical CNT are shown in Fig. 2.10 and Table 2.6. As shown in Fig. 2.10, three peaks, namely Q0 , Q1 , and Q2 , were identified in the cement-based nanocomposites. After adding helical CNT, the proportion of Q0 reduces; while the proportion of Q1 and Q2 increases, indicating the incorporation of helical CNT induces more silicon oxide tetrahedron participating hydration. These findings demonstrate the presence of helical CNT increases the hydration degree. Figure 2.11 exhibits the porosity of cement-based nanocomposites without/with helical CNT. As demonstrate in Fig. 2.11, the addition of helical CNT notably decreases the porosity of cement-based nanocomposites. The porosity of cementbased nanocomposites decreases by 21.7, 26.5, and 18.5% after adding 0.5 wt% of helical CNT, measured through SG, MIP, and LF-NMR methods, respectively. Table 2.7 lists the characteristic pore radius of cement-based nanocomposites without/with helical CNT measured through MIP and LF-NMR methods. It can be seen from Table 2.7 the presence of helical CNT reduces the specific surface area median pore radius, average pore radius, and threshold pore radius from 6.5 nm, 17.5 nm, and 42.9 nm to 4.7 nm, 15.3 nm, and 24.6 nm, respectively. Meanwhile, the most probable pore radius and volume median pore radius of cement-based nanocomposites increase by 35.6% and 21.4%, respectively, when 0.5 wt% of helical CNT was incorporated.

84

2 New-Generation Cement-Based Nanocomposites with Helical CNT

Fig. 2.11 Porosity of cement-based nanocomposites without/with helical CNT

Table 2.7 Characteristic pore radius of cement mortars without/with helical CNT Helical CNT content (wt% of cement)

MIP method Most probable pore radius (nm)

LF-NMR method Specific surface area median pore radius (nm)

Volume Average median pore pore radius radius (nm) (nm)

Most probable pore radius (nm)

Threshold pore radius (nm)

0

4.5

6.5

63.2

17.5

2.3

42.9

0.5

6.1

4.7

76.7

15.3

2.3

24.6

Figure 2.12 and Table 2.8 show the pore size distribution of cement-based nanocomposites without/with helical CNT. The presence of helical CNT significant decreases pore content of all sizes. The proportion of pore with size range of 0.1–50 nm increases after adding helical CNT, while that of pore with size greater than 50 nm decreases. These phenomena indicate that the addition of helical CNT optimizes the pore size distribution in cement-based nanocomposites. Figure 2.13 shows the morphology of cement-based nanocomposites with helical CNT. As depicted in Fig. 2.13, the helical CNT embeds into cement-based nanocomposites, thus inhibiting the generation and growth of cracks.

2.4 Functional/Smart Properties of Cement-Based Nanocomposites …

85

Fig. 2.12 Pore size distribution curve of cement-based nanocomposites without/with helical CNT. a MIP method. b LF-NMR method

2.4 Functional/Smart Properties of Cement-Based Nanocomposites with Helical CNT 2.4.1 Electrical Properties Figure 2.14 shows the resistivity of cement-based nanocomposites without/with helical CNT. It can be seen from Fig. 2.14 that the presence of helical CNT reduces the resistivity of cement-based nanocomposites. In addition, the resistivity reduces with the helical CNT content. The resistivity of cement-based nanocomposites reduces by 18.2, 28.1, and 34.1% when 0.1, 0.5 and 0.8 wt% of helical CNT is incorporated, respectively. As cement-based nanocomposites can be modeled by Randles model, the conductive elements of blank cement paste include pore solution (electrolyte solution, Rs ), bulk cement paste (Faraday resistor, Z F2 , and capacitor element, Q2 ), and test electrode (Faraday resistor, Z F1 , and capacitor element, Q1 ). The equivalent circuit model of blank cement paste is shown in Fig. 2.15a. As for cement-based nanocomposites with helical CNT, part of electric current can pass through helical CNT, as shown in Fig. 2.15b. Figure 2.16 shows the AC impedance spectra of cement-based nanocomposites without/with helical CNT. It can be seen from Fig. 2.16 that the impedance value of the cement-based nanocomposites with helical CNT is significantly reduced, and the straight line in the low frequency band of the AC impedance spectrum disappears. Moreover, the AC impedance spectra is composed of double arcs. These phenomena indicate that the conduction of helical CNT plays a leading role in the conduction path of cement-based nanocomposites with helical CNT.

0.12

0.10

0.5 0.05

0.02

6.41

7.42

0.19

0.15

0

0.04

0.1–5 nm (10−2 mL/g)

0.11

LF-NMR method > 1000 nm (mL/g)

1–5 nm (mL/g)

50–1000 nm (mL/g)

5–50 nm (mL/g)

MIP method

Helical CNT content (wt% of cement)

Table 2.8 Pore size distribution of cement-based nanocomposites without/with helical CNT

1.30

2.01

5–50 nm (10−2 mL/g)

0.29

0.15

50–1000 nm (10−2 mL/g)

0.02

0.04

> 1000 nm (10−2 mL/g)

86 2 New-Generation Cement-Based Nanocomposites with Helical CNT

2.4 Functional/Smart Properties of Cement-Based Nanocomposites …

87

Fig. 2.13 Morphology of cement-based nanocomposites with helical CNT Fig. 2.14 Resistivity of cement-based nanocomposites without/with helical CNT

Fig. 2.15 The equivalent circuits model of cement-based nanocomposites without/with helical CNT. a Without helical CNT. b With helical CNT

88

2 New-Generation Cement-Based Nanocomposites with Helical CNT

Fig. 2.16 AC impedance spectra of cement-based nanocomposites without/with helical CNT. a Without helical CNT. b With 0.1 wt% of helical CNT. c With 0.5 wt% of helical CNT. d With 0.8 wt% of helical CNT

2.4.2 Electromagnetic Shielding and Absorption Properties Figure 2.17 shows the electromagnetic shielding properties of cement-based nanocomposites without/with helical CNT. As depicted in Fig. 2.17, the presence of helical CNT increases the electromagnetic shielding effectiveness of cementbased nanocomposites. The electromagnetic shielding effectiveness of cement-based nanocomposites with helical CNT reaches 2.85 dB, increased by 8.4% compared with blank cement paste. Figure 2.18 shows the proportion of reflection loss (R), transmission coefficients loss (T ), absorption loss (A) of cement-based nanocomposites without/with helical CNT. It can be seen from Fig. 2.18 that as the frequency increases, the proportion of reflection loss increases, the proportion of transmission loss decreases, and the absorption loss is little changed. With the increase of helical CNT content, the reflection loss of the cement-based nanocomposites increases, thus achieving shielding effectiveness improvement. Figure 2.19 exhibits the reflectivity of cement-based nanocomposites without/with helical CNT in the frequency range of 2–18 GHz. As shown in Fig. 2.19, the reflectivity of cement-based nanocomposites decreases with the content of helical CNT. When the thickness of the specimen is 20 mm, the incorporation of 0.8 wt% of helical

2.4 Functional/Smart Properties of Cement-Based Nanocomposites …

89

Fig. 2.17 Electromagnetic shielding properties of cement-based nanocomposites without/with helical CNT

Fig. 2.18 Proportion of reflection loss (R), transmission coefficients loss (T ), absorption loss (A) of cement-based nanocomposites without/with helical CNT. a Without helical CNT. b With 0.5 wt% of helical CNT. c With 0.8 wt% of helical CNT

CNT can achieve a reflectivity of 15.12 dB at 15.12 GHz, approximately 1.5 times of that of blank cement paste.

Fig. 2.19 Reflectivity of cement-based nanocomposites without/with helical CNT in the frequency of 2–18 GHz. a 10 mm thick specimen. b 20 mm thick specimen

90

2 New-Generation Cement-Based Nanocomposites with Helical CNT

Figure 2.20 shows the electromagnetic parameters of cement-based nanocomposites without/with helical CNT. It can be seen from Fig. 2.20 that the real part of the dielectric constant of cement-based nanocomposites increases with as the content of helical CNT, which indicates that the degree of dielectric polarization of electromagnetic wave on the cement-based nanocomposites increases. Meanwhile, the imaginary part of the dielectric constant and the electrical loss tangent of cementbased nanocomposites also increase with helical CNT content, leading to the increase of the dielectric loss of the paste to electromagnetic waves. However, the imaginary part of magnetic permeability and magnetic loss tangent of cement-based nanocomposites with helical CNT are basically zero, which indicates that helical CNT have no magnetic loss ability to electromagnetic waves.

2.5 Summary In this chapter, a new-generation cement-based nanocomposite with a nanoscale metamaterial, helical CNT, is introduced. The as-fabricated nanocomposites’ static/dynamic mechanical, electrical, and electromagnetic shielding and absorption properties as well as the modification mechanisms of helical CNT are presented. The conclusions can be summarized as below. (1) The presence of helical significantly increases the mechanical properties of cement-based nanocomposites. The compressive and flexural strength can maximumly increase by 65.3 and 56.3% when 0.5 and 0.8 wt% of helical CNT are incorporated, respectively. Moreover, the dynamic compressive strengths of cement-based nanocomposites with 0.25 and 0.50 wt% of helical CNT at the strain rate of 200/500/800 s−1 increase by 78.1%/54.7%/24.3% and 52.8%/89.8%/18.6%, respectively. The impact toughness and impact dissipation energy of cement-based nanocomposites increase by 49.5–93.8% and 8.7–82.6% after adding helical CNT, respectively. (2) Thanks to the chiral and helical structures of helical CNT and its nano effect, the presence of helical CNT can modify the hydration products and pore structures of cement-based nanocomposites. Moreover, helical CNT inhibits the generation and growth of cracks in cement-based nanocomposites through its bridging effect. (3) Helical CNT can endow cement-based nanocomposites with excellent electrical properties and electromagnetic shielding absorption properties. After adding helical CNT, the conduction of helical CNT plays a leading role in the conduction path of cement-based nanocomposites. The resistivity of cement-based nanocomposites reduces by 18.2, 28.1, and 34.1% when 0.1, 0.5 and 0.8 wt% of helical CNT is incorporated, respectively. In addition, the electromagnetic shielding effectiveness and reflectivity of cement-based nanocomposites with helical CNT reach 2.85 and 15.12 dB, increased by 8.4 and 50% compared with that of blank cement-based composites.

2.5 Summary

91

Fig. 2.20 Electromagnetic parameters of cement-based nanocomposites without/with helical CNT. a Real part of the dielectric constant. b Imaginary part of the dielectric constant. c Real part of the magnetic permeability. d Imaginary part of the magnetic permeability. e Dielectric loss angle of tangent. f Electromagnetic loss angle of tangent

In summary, the cement-based nanocomposites with helical CNT have enhanced static and dynamic mechanical properties as well as excellent electromagnetic shielding and absorption properties, thus presenting excellent application prospects in electromagnetic protection and control of military, nuclear power plant and extraterrestrial infrastructures.

92

2 New-Generation Cement-Based Nanocomposites with Helical CNT

References 1. B. Han, S. Ding, J. Wang, J. Ou, Nano-Engineered Cementitious Composites: Principles and Practices (Springer, Singapore, 2019) 2. B. Han, S. Sun, S. Ding, L. Zhang, X. Yu, J. Ou, Review of nanocarbon-engineered multifunctional cementitious composites. Compos. A Appl. Sci. Manuf. 70, 69–81 (2015) 3. S. Ding, Y. Xiang, Y.Q. Ni, V.K. Thakur, X. Wang, B. Han, J. Ou, In-situ synthesizing carbon nanotubes on cement to develop self-sensing cementitious composites for smart high-speed rail infrastructures. Nano Today 43, 101438 (2022) 4. X. Wang, S. Dong, A. Ashour, W. Zhang, B. Han, Effect and mechanisms of nanomaterials on interface between aggregates and cement mortars. Constr. Build. Mater. 240, 117942 (2020) 5. X. Wang, S. Dong, Z. Li, B. Han, J. Ou, Nanomechanical characteristics of interfacial transition zone in nano-engineered concrete. Engineering 17, 99–109 (2021) 6. F. Wu, K. Yang, Q. Li, T. Shah, M. Ahmad, Q. Zhang, B. Zhang, Biomass-derived 3D magnetic porous carbon fibers with a helical/chiral structure toward superior microwave absorption. Carbon 173, 918–931 (2021) 7. Y. Li, Z. Xu, A. Jia, X. Yang, W. Feng, P. Wang, K. Li, W. Lei, H. He, Y. Tian, Z. Zhou, Controllable modification of helical carbon nanotubes for high-performance microwave absorption. Nanotechnol. Rev. 10, 671–679 (2021)

Chapter 3

New-Generation Cement-Based Nanocomposites with Nickel-Coated CNT

3.1 Introduction Due to its high surface energy, CNT is highly susceptible to entanglement and agglomeration, which makes it difficult to disperse in cement-based composites [1, 2]. Hence, additional physical/chemical dispersion methods, such as high-speed shear, ultrasonic, surface covalent modification, non-covalent modification dispersion methods, have been used to increase the dispersibility of CNT [3–7]. These dispersion methods are detrimental to the wide application of CNT in cement-based nanocomposites due to their high energy consumption and cumbersome process. Nickel coating of CNT can not only improve CNT’s dispersion, but also realize the bonding between CNT and matrix of cement-based nanocomposites [8–10]. In addition, since nickel has high hardness, good toughness, good electrical conductivity, good thermal conductivity, corrosion resistance, and ferromagnetism, its coating on the surface of CNT can endow nickel-coated CNT with unique mechanical, electrical, thermal, and ferromagnetic properties/performances [11–13]. In this chapter, a new-generation cement-based nanocomposite with nickelcoated CNT is introduced. The static/dynamic mechanical properties including compressive strength, flexural strength, elastic modulus, Poisson’s ratio, fatigue performance, impact performance are presented. Then the modification effect of nickel-coated CNT on cement-based nanocomposites is described. Finally, the functional/smart properties including electrical properties and electromagnetic shielding and absorption properties of cement-based nanocomposites with nickel-coated CNT, are demonstrated.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_3

93

94

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

3.2 Preparation of Cement-Based Nanocomposites with Nickel-Coated CNT The raw materials used to fabricate cement-based nanocomposites with nickel-coated CNT included P·O 42.5 R and P·I 42.5 Portland cement, fly ash, silica fume, quartz sand, SP, and 5 different types of nickel-coated CNT. The properties and morphology of nickel-coated CNT are shown in Table 3.1 and Fig. 3.1, respectively. The properties of other raw materials refer to Sect. 2.2. The mix proportion and fabrication process of cement-based nanocomposites are shown in Tables 3.2, 3.4 respectively. Table 3.1 Properties of nickel-coated CNT Code

Outer diameter (nm)

Inner diameter (nm)

Length (μm)

Aspect ratio

Specific surface area (m2 /g)

Nickel content(wt%)

Surface treatment

Nickel-coated

M15

8–15

3–5

50

3333

60

62

M20

10–20

5–10

10–30

1500

60

62

M30

20–30

5–10

10–30

1000

70

62

M50

30–50

5–12

10

200

50

62

M80

30–80

5–15

10

125

40

62

Fig. 3.1 Morphology of nickel-coated CNT. a M15. b M20. c M30. d M50. e M80

3.3 Mechanical Properties of Cement-Based Nanocomposites …

95

Table 3.2 Mix proportions of cement-based nanocomposites without/with nickel-coated CNT Type

Mix proportion (mass ratio) Cement

Paste using P·O 42.5 R cement

Mortar using P·O 42.5 R cement

Mortar using P·I 42.5 cement

Fly ash

Silica fume

Sand

Water

SP

Nickel-coated CNT

1

–

–

–

0.2

0.0075

0

0.999

–

–

–

0.2

0.0075

0.001

0.995

–

–

–

0.2

0.0075

0.005

0.992

–

–

–

0.2

0.0075

0.008

1

0.25

0.313

1.375

0.375

0.015

0

0.9975

0.25

0.313

1.375

0.375

0.015

0.0025

0.995

0.25

0.313

1.375

0.375

0.015

0.005

1

0.25

0.313

1.375

0.3

0.015

0

0.9975

0.25

0.313

1.375

0.3

0.015

0.0025

0.995

0.25

0.313

1.375

0.3

0.015

0.005

1

0.25

0.313

1.375

0.375

0.015

0

0.9975

0.25

0.313

1.375

0.375

0.015

0.0025

0.995

0.25

0.313

1.375

0.375

0.015

0.005

1

0.25

0.313

1.375

0.3

0.015

0

0.9975

0.25

0.313

1.375

0.3

0.015

0.0025

0.995

0.25

0.313

1.375

0.3

0.015

0.005

3.3 Mechanical Properties of Cement-Based Nanocomposites with Nickel-Coated CNT 3.3.1 Compressive Strength Figure 3.2 shows the compressive strength of cement pastes without/with M30 nickelcoated CNT. The presence of M30 nickel-coated CNT can significantly increase the compressive strength of cement pastes. As shown in Fig. 3.2, the addition of 0.1, 0.5 and 0.8 wt% of M30 nickel-coated CNT increases the compressive strength by 64.7%, 65.3%, and 54.0%, respectively. Figure 3.3 presents the compressive strength of cement mortars without/with different types and nickel-coated CNT. It can be seen from Fig. 3.3 that all types of nickel-coated CNT can increase the compressive strength of cement mortar. Meanwhile, the aspect ratio of CNT, cement type, and water to binder ratio show different influence on the compressive strength of cement pastes. For the cement mortar using P·O 42.5 R cement, the addition of 0.25 wt% of M50 nickel-coated CNT can achieve the highest compressive strength when the water to cement ratio equals to 0.3, as shown in Fig. 3.3a. Differently, the compressive strength of cement mortar with 0.5 wt% of M80 reaches 107.7 MPa, increased by 25.2% compared with blank cement mortar using P·I 42.5 cement and a water to cement ratio of 0.375. These findings

Ultrasonication+non-covalent surface modification by SP

Dispersion method

– 60

Shear mixing (1000 r/min) Shear mixing (2000 r/min)

Cement

300

Vibration

Method

Time (s)

Method Ultrasonication (20 kHz)

Molding

Technology

Nano nickel-coated CNT+Water+SP

Feeding order

Fabrication process

Table 3.3 Fabrication process of cement pastes without/with nickel-coated CNT

Method

Standing curing

W (20 °C)

40 × 40 × 160 Standard condition

Size (mm)

Curing

180

28

1

Time (d)

96 3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Ultrasonication+non-covalent surface modification by SP

Dispersion method

120

Shear mixing (140 r/min) Shear mixing (285 r/min)

Silica fume

Quartz sand

120

Shear mixing (140 r/min)

Cement+fly ash

60 240

Shear mixing (140 r/min) Shear mixing (285 r/min)

60

Ultrasonication (20 kHz)

300

Vibration

Molding Method

Time (s)

Technology Method

Nano nickel-coated CNT+Wate+SP

Feeding order

Fabrication process

Table 3.4 Fabrication process of cement mortars without/with nickel-coated CNT Curing Method

W (20 °C)

40 × 40 × 160 Standard condition

Size (mm)

28

1

Time (d)

3.3 Mechanical Properties of Cement-Based Nanocomposites … 97

98

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.2 Compressive strength of cement pastes without/with M30 nickel-coated CNT

indicate the favorable content and type of nickel-coated CNT are related to the cement type as well as the water to cement ratio.

3.3.2 Flexural Strength Figure 3.4 shows the flexural strength of cement pastes without/with M30 nickelcoated CNT. As shown in Fig. 3.3, the addition of M30 nickel-coated CNT can notably increase the flexural strength of cement pastes. The flexural strengths reach 13.5, 14.3, and 11.7 MPa after adding 0.1, 0.5 and 0.8 wt% of M30 nickel-coated CNT, respectively, increased by 57.1, 64.4, and 34.5% compared with that of blank cement pastes. Figure 3.5 shows the factors, including cement type and water to cement ratio, influence the modifying effect of nickel-coated CNT on the flexural strength of cement mortars. It can be seen from Fig. 3.5 the modifying effect nickel-coated CNT on the cement mortar flexural strength is greatly influenced by cement type. For the cement mortar using P·O 42.5 R cement, the compressive strength increases by 19.65% and 12.78% when 0.5 wt% of M50 nickel-coated CNT and M80 nickelcoated CNT are incorporated into cement mortars with a water to cement ratio of 0.375 and 0.3, respectively. Meanwhile, the cement mortar using P·I 42.5 cement with a water to cement ratio of 0.375 shows good compatibility with nickel-coated CNT. The flexural strengths of the cement mortars with M15, M20, M30, M50, and M80 nickel-coated CNT reach 7.14 MPa, 7.37 MPa, 7.51 MPa, 7.41 MPa and 7.65 MPa, respectively, increased by 25.0, 29.1, 31.5, 29.8, and 34.0% compared with blank cement mortar.

3.3 Mechanical Properties of Cement-Based Nanocomposites …

99

Fig. 3.3 The factors influence the compressive strength of cement mortars without/with nickelcoated CNT. a Cement mortar using P·O 42.5 R cement and a water-to-cement ratio of 0.375. b Cement mortar using P·O 42.5 R cement and a water-to-cement ratio of 0.3. c Cement mortar using P·I 42.5 cement and a water-to-cement ratio of 0.375. d Cement mortar using P·I 42.5 cement and a water-to-cement ratio of 0.3 Fig. 3.4 The flexural strength of cement pastes without/with M30 nickel-coated CNT

100

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.5 The factors influence the flexural strength of cement mortars without/with nickel-coated CNT. a Cement mortar using P·O 42.5 R cement and a water-to-cement ratio of 0.375. b Cement mortar using P·O 42.5 R cement and a water-to-cement ratio of 0.3. c Cement mortar using P·I 42.5 cement and a water-to-cement ratio of 0.375. d Cement mortar using P·I 42.5 cement and a water-to-cement ratio of 0.3

3.3.3 Elastic Modulus and Poisson’s Ratio Table 3.5 lists the effect of nickel-coated CNT on the elastic modulus and Poisson’s ratio of cement-based nanocomposites using P·I 42.5 cement with a water to cement ratio of 0.375. As listed in Table 3.5, the presence of nickel-coated CNT can increase the elastic modulus and Poisson’s ratio of cement-based nanocomposites. The elastic modulus and Poisson’s ratio reach 38.83 MPa and 0.236 when 0.25 wt% of M30 nickel-coated CNT is incorporated. 5As the elastic modulus and Poisson’s ratio are related to the compactness of cement-based nanocomposites, it can be deduced that the nickel-coated CNT contributes to modifying the microstructural compactness.

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Table 3.5 Elastic modulus and Poisson’s ratio of cement-based nanocomposites using P·I 42.5 cement with a water to cement ratio of 0.375 Type

– M15 M20

Nanofiller

Elastic modulus

Poisson’s ratio

Content (wt% of cement)

Value (MPa)

Value

–

32.97

Relative increase (%) –

Relative increase (%)

0.166

–

0.25

36.10

9.50

0.201

20.84

0.50

35.95

9.05

0.234

40.68

0.25

35.30

7.8

0.226

36.07

0.50

32.90

−0.20

0.231

38.58

M30

0.25

38.83

17.80

0.236

41.68

0.50

35.27

6.98

0.184

10.32

M50

0.25

38.70

17.39

0.194

16.43

0.50

38.30

16.18

0.175

5.01

0.25

38.45

16.63

0.194

16.63

0.50

35.53

7.79

0.171

2.51

M80

3.3.4 Fatigue Properties The compressive fatigue behaviors of cement-based nanocomposites without/with M30 nickel-coated CNT were characterized by the loading with a continuous sine wave at 5 Hz. The loading scheme is listed in Table 3.6. The minimum stress in fatigue tests was selected as 0.1 times of monotonic ultimate compressive stress. The monotonic ultimate compressive strengths of cement-based nanocomposites with 0, 0.25 and 0.5 wt% of M30 nickel-coated CNT are 137 MPa, 133 MPa and 143 MPa, respectively. Considering the large discrete in fatigue behavior characterization, the twoparameters Weibull distribution [14–16] was introduced to analyze the fatigue life at different failure probabilities. The S–N curves of cement mortar with M30 nickelcoated CNT at 0.1 and 0.5 failure probabilities are shown in Fig. 3.6. It can be seen Table 3.6 Compressive fatigue loading scheme at different stress levels Nickel-coated CNT content (wt% of cement) 0

Stress level 0.9

0.8

0.7

Maximum stress

Minimum stress

Maximum stress

Minimum stress

123.6

13.7

109.8

13.7

Maximum stress 96.1

Minimum stress 13.7

0.25

119.7

13.3

106.4

13.3

93.1

13.3

0.50

128.7

14.3

114.4

14.3

100.1

14.3

102

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.6 The S–N curves of cement-based nanocomposites without/with nickel-coated CNT at different failure probabilities. a 0.1. b 0.5

Table 3.7 Fatigue strength of cement-based nanocomposites without/with nickel-coated CNT Nickel-coated CNT content (wt% of cement)

Fatigue strength Absolute value (Mpa)

The ratio of fatigue strength to compressive strength Relative increase (%)

Absolute value

Relative increase (%)

0

74.3

–

0.54

–

0.25

81.8

9.9

0.62

13.5

0.50

77.1

3.7

0.54

−0.8

from Fig. 3.6 that the fatigue life of cement mortar can maximumly increase one order of magnitude after adding nickel-coated CNT. Table 3.7 lists the fatigue strengths of cement-based nanocomposites without/with nickel-coated CNT. The fatigue strengths of cement mortars increase by 9.9 and 3.7% when 0.25 and 0.50 wt% of M30 nickel-coated CNT are incorporated, respectively. Noteworthily, the ratio of fatigue strength to compressive strength increases by 13.5% after adding 0.25 wt% of M30 nickel-coated CNT to cement mortar. Figure 3.7 shows the strain-fatigue life (in normalized form) curve of cementbased nanocomposites without/with nickel-coated CNT. As shown in Fig. 3.7, whether nickel-coated CNT was incorporated, the strain-fatigue life curve can be divided into three stages: cyclic creep stage, creep-fatigue coupling stage, and fatigue stage, indicating the presence of M30 nickel-coated CNT does not change the fatigue deformation pattern of cement-based nanocomposites. However, the strain-fatigue life curve of the cement-based nanocomposite with M30 nickel-coated CNT lies above that of blank cement mortar, implying that the nickel-coated CNT improves the fatigue deformability of cement-based nanocomposites. In the creep-fatigue coupling stage, the slope of the curve for cement-based nanocomposites with M30 nickel-coated CNT is higher than that of blank cement mortar, which indicates more micro/nano cracks appeared before the fatigue stage. In particular, the incorporation of M30 nickel-coated CNT induces smoother curves in the transition zone between the creep-fatigue coupling and the fatigue stage compared to the blank cement mortar.

3.3 Mechanical Properties of Cement-Based Nanocomposites …

103

Fig. 3.7 Fatigue deformation curves of cement-based nanocomposites without/with nickel-coated CNT. a Without nickel-coated CNT. b With 0.25 wt% of M30 nickel-coated CNT. c With 0.50 wt% of M30 nickel-coated CNT

Table 3.8 Fatigue failure strain of cement-based nanocomposites without/with nickel-coated CNT

Nickel-coated CNT content (wt% of cement)

Fatigue failure strain Absolute value (με)

Relative increase (%)

0

4134

–

0.25

4028

−2.5

0.50

4299

3.9

The smooth transition zone indicates that fatigue fracture is not an abrupt process after adding M30 nickel-coated CNT. Additionally, the presence of nickel-coated CNT shows less effect on the failure strain of cement-based nanocomposites, as listed in Table 3.8.

3.3.5 Impact Properties Figure 3.8 shows the dynamic compressive strengths of cement-based nanocomposites without/with nickel-coated CNT. As shown in Fig. 3.8, the strain rate effect, i.e. the dynamic compressive strength increasing with the strain rate, was observed. After adding nickel-coated CNT, the dynamic compressive strength significantly increases. The dynamic compressive strengths of cement-based nanocomposites with 0.25 and 0.50 wt% of M30 nickel-coated CNT at the strain rate of 200/500/800 s−1 increase by 43.0%/39.5%/−1.7% and 26.1%/23.2%/21.0%, respectively. Combining the experimental results and Eqs. (2.1)–(2.3), the dynamic stress– strain curves of cement mortars without/with nickel-coated CNT are obtained as shown in Fig. 3.9. The dynamic stress–strain curves in Fig. 3.9 can be generally divided into three stages: the approximately linear ascent stage, the non-linear ascent stage, and the non-linear descent stage, corresponding to the elastic deformation,

104

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.8 Dynamic compressive strength of cement-based nanocomposites without/with nickel-coated CNT

plastic deformation, and damage softening of cement mortar, respectively. This threestage characteristic is observed in stress–strain curves of cement-based nanocomposites without/with nickel-coated CNT at different strain rate, indicating the presence of nickel-coated CNT and different strain rate do not change the failure process of cement-based nanocomposites. Compared with blank cement mortar, the incorporation of nickel-coated CNT increases the slope of the dynamic stress–strain curve during the linear ascent stage and decreases the slope during non-linear descent stage. These phenomena indicate the presence of nickel-coated CNT not only increases the elastic modulus of cement-based nanocomposites, but also modifies the cementbased nanocomposites energy absorption capacity during the non-linear descent stage, or damage softening stage. In particular, a fluctuating upward trend is observed in the non-linear ascent stage of dynamic stress–strain curves of the cement-based nanocomposites with nickel-coated CNT. The dynamic peak strains of cement-based nanocomposites without/with nickelcoated CNT are summarized in Fig. 3.10. As shown in Fig. 3.10, the addition of

Fig. 3.9 Dynamic stress–strain curves of cement-based nanocomposites without/with nickelcoated CNT. a At strain rate of 200 s−1 . b At strain rate of 500 s−1 . c At strain rate of 800 s−1

3.3 Mechanical Properties of Cement-Based Nanocomposites …

105

Fig. 3.10 Dynamic peak strain of cement-based nanocomposites without/with nickel-coated CNT

M30 nickel-coated CNT decreases the dynamic peak strain at a loading rate of 200/500 s−1 . However, the dynamic peak strains of cement-based nanocomposites with M30 nickel-coated CNT increase by 49.5–93.8% at a loading rate of 800 s−1 compared with that of blank cement mortar. This indicates the presence of nickelcoated CNT increase the brittleness of cement-based nanocomposites, meanwhile, endows higher ductility of cement-based nanocomposites at high strain rates. Figure 3.11 shows the impact toughness and impact dissipation energy of cementbased nanocomposites without/with nickel-coated CNT. As depicted in Fig. 3.10, the impact toughness and impact dissipation energy respectively increase by 8.8– 39.8% and 5.8–25.7% after adding nickel-coated CNT. In summary, the presence of nickel-coated CNT increases the dissipate energy due to the stress enhancement, and simultaneously, modifies the impact properties/performance through its effect on stress redistribution.

Fig. 3.11 Impact toughness and impact dissipation energy of cement-based nanocomposites without/with nickel-coated CNT. a Impact toughness. b Impact dissipation energy

106

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

3.3.6 Bond Properties Figure 3.12 shows the bond properties of cement-based nanocomposites without/with nickel-coated CNT. In general, the presence of nickel-coated CNT can improve the bond properties of cement-based nanocomposites. As shown in Fig. 3.12a, the bond strengths between cement mortars and aggregates, obtained by three-pointbend test, increase by 23.6, 38.8 and 30.8% when 0.1, 0.3 and 0.5 wt% of M30 nickel-coated CNT are incorporated, respectively. The bond strengths between new and old cement mortars, obtained by splitting tensile test, increase by 15.6, 26.3 and 34.6% after adding 0.1, 0.3 and 0.5 wt% of M30 nickel-coated CNT, respectively, as depicted in Fig. 3.12b. Moreover, the presence of nickel-coated CNT can notably modify the bond behavior between cement-based nanocomposites and steel bar. As shown in Fig. 3.12c, a 1.03 MPa/9.8% increase in cracking bond strength, a 0.97 MPa/8.0% increase in ultimate bond strength, a 1.71 MPa/16.3% increase in residual bond strength, a 0.296 mm/28.2% reduction in ultimate bond slip, and a 0.925 mm/27.1% reduction in residual bond slip are the best achieved due to the addition of nickel-coated CNT.

Fig. 3.12 Bond properties of cement-based nanocomposites without/with nickel-coated CNT. a Bond strength between cement mortar and aggregate. b Bond strength between new-to-old cement mortar. c Bond behavior between cement mortar and steel bar

3.3 Mechanical Properties of Cement-Based Nanocomposites …

107

3.3.7 Modification Mechanisms The results in Sects. 3.3.1–3.3.5 demonstrate the presence of nickel-coated CNT can improve the mechanical properties/performance of cement-based nanocomposites, including compressive strength, flexural strength, elastic modulus, Poisson’s ratio, fatigue performance, and impact performance. Such improvements are achieved from the modification of nickel-coated CNT on the microstructures of cementbased nanocomposites. Therefore, SEM, EDS, XRD, TG, NMR, MIP, and LF-NMR were employed to reveal the modification mechanisms of nickel-coated CNT on cement-based nanocomposites. Figure 3.13 shows the TG and DTG curves of cement-based nanocomposites without/with nickel-coated CNT. Three peaks, indicating the evaporation of water, decomposition of CH, and decomposition of CaCO3 , can be observed in DTG curves in Fig. 3.13b. Based on TG and DTG curves, the hydration degree of cement can be calculated from Eqs. (2.5) and (2.6). The calculated hydration degree of cement-based nanocomposites without and with nickel-coated CNT is 69.5% and 61.5%, respectively. Therefore, the addition of nickel-coated CNT slightly inhibits the hydration of cement. The XRD patterns of cement-based nanocomposites without/with nickel-coated CNT are shown in Fig. 3.14. It can be seen that the intensities of main diffraction peaks indicating CH crystals of cement-based nanocomposites with nickel-coated CNT are higher than that of blank cement paste. In addition, the CH orientation R can be calculated from (0 0 1) and (1 0 1) crystal face peak intensity through Eq. (2.7). The CH diffraction intensity and orientation are listed in Table 3.9. The presence of nickel-coated CNT reduces CH orientation from 2.70 to 2.08 after 0.5 wt% of M30 nickel-coated CNT is incorporated. The 29 Si NMR spectrum and corresponding deconvoluted spectrum of cementbased nanocomposites without/with nickel-coated CNT are shown in Fig. 3.15 and Table 3.10. As shown in Fig. 3.15, three peaks, namely Q0 , Q1 , and Q2 , were identified

Fig. 3.13 TG and DTG curves of cement-based nanocomposites without/with nickel-coated CNT

108

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.14 XRD patterns of cement-based nanocomposites without/with nickel-coated CNT

Table 3.9 Cement hydration degree of cement-based nanocomposites without/with nickel-coated CNT

Nickel-coated CNT content (wt% of cement)

(0 0 1) CH

(1 0 1) CH

CH orientation

0

1794

898

2.70

0.5

1512

980

2.08

in the cement-based nanocomposites. After adding nickel-coated CNT, the proportion of Q0 reduces; while the proportion of Q1 and Q2 increases, indicating the incorporation of nickel-coated CNT induces more silicon oxide tetrahedron participating hydration. The hydration degree of cement-based nanocomposites from 50.2 to 55.8% after adding 0.5 wt% of M30 nickel-coated CNT. Figure 3.16 exhibits the porosity of cement-based nanocomposites without/with nickel-coated CNT. As demonstrate in Fig. 3.16, the addition of nickel-coated CNT notably decreases the porosity of cement-based nanocomposites. The porosity of cement mortar decreases by 20.3, 17.4 and 18.3% after adding 0.5 wt% of M30 nickel-coated CNT, measured through SG, MIP, LF-NMR methods, respectively. Table 3.11 lists the characteristic pore radius of cement-based nanocomposites without/with nickel-coated CNT measured through MIP and LF-NMR methods. It

Fig. 3.15 29 Si NMR spectra of cement-based nanocomposites without/with nickel-coated CNT. a Without nickel-coated CNT. b With 0.5 wt% of M30 nickel-coated CNT

3.3 Mechanical Properties of Cement-Based Nanocomposites … Table 3.10 Deconvolution results of nickel-coated CNT Nickel-coated CNT content (wt% of cement)

29 Si

109

NMR of cement-based nanocomposites without/with

Type and content of silicon oxide tetrahedron

Cement

Q0 (%)

Q1 (%)

Q2 (%)

Hydration degree (%)

0

49.8

29.7

20.5

50.2

0.5

44.2

32.8

23.0

55.8

Fig. 3.16 Porosity of cement-based nanocomposites without/with nickel-coated CNT

can be seen from Table 3.11 the presence of nickel-coated CNT reduces the specific surface area median pore radius, volume median pore radius, average pore radius, and average pore radius from 6.5 nm, 63.2 nm, and 17.5 nm to 5.8 nm, 34.0 nm, and 16.0 nm, respectively. Meanwhile, the most probable pore radius and threshold pore radius of cement-based nanocomposites increase by 35.6% and 51.5%, respectively, when 0.5 wt% of M30 nickel-coated CNT was incorporated. Figure 3.17 and Table 3.12 show the pore size distribution of cement-based nanocomposites without/with nickel-coated CNT. The presence of nickel-coated Table 3.11 Characteristic pore radius of cement-based nanocomposites without/with nickel-coated CNT Nickel-coated CNT content (wt% of cement)

MIP method

LF-NMR method

Most probable pore radius (nm)

Specific surface area median pore radius (nm)

Volume median pore radius (nm)

Average pore radius (nm)

Most probable pore radius (nm)

Threshold pore radius (nm)

0

4.5

6.5

63.2

17.5

2.3

42.9

0.5

6.1

5.8

34.0

16.0

2.3

65.0

110

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.17 Pore size distribution curve of cement-based nanocomposites without/with nickel-coated CNT. a MIP method. b LF-NMR method

CNT significant decreases pore content of all sizes. The proportion of pore with size range of 0.1–50 nm increases after adding nickel-coated CNT, while that of pore with size greater than 50 nm decreases. These phenomena indicate that the addition of nickel-coated CNT optimizes the pore size distribution in cement-based nanocomposites. Figure 3.18 shows the morphology of cement-based nanocomposites without/with nickel-coated CNT. As depicted in Fig. 3.18, the nickel-coated CNT embeds into cement-based nanocomposites and exert bridging and pulling-out effect during fracture, thus inhibiting the generation and growth of cracks and further modifying the mechanical properties of cement-based nanocomposites.

3.4 Functional/Smart Properties of Cement-Based Nanocomposites with Nickel-Coated CNT 3.4.1 Electrical Properties Figure 3.19 shows the resistivity of cement-based nanocomposites without/with nickel-coated CNT. It can be seen from Fig. 3.19 that the presence of nickel-coated CNT reduces the resistivity of cement-based nanocomposites. In addition, the resistivity reduces with the nickel-coated CNT content. The resistivities of cement-based nanocomposites reduce by 29.9, 34.2 and 31.8% when 0.1, 0.5 and 0.8 wt% of M30 nickel-coated CNT are incorporated, respectively. As cement-based nanocomposites can be modeled by Randles model, the conductive elements of blank cement pastes include pore solution (electrolyte solution, Rs ), bulk cement paste (Faraday resistor, Z F2 , and capacitor element, Q2 ), and test electrode (Faraday resistor, Z F1 , and capacitor element, Q1 ). The equivalent circuit model of blank cement paste is shown in Fig. 3.20a. As for cement-based nanocomposites

0.15

0.12

0

0.5

MIP method Nickel-coated CNT content 1–5 nm (mL/g) (wt% of cement)

0.17

0.19

5–50 nm (mL/g) 0.08

0.11

50–1000 nm (mL/g) 0.01

0.04

> 1000 nm (mL/g) 5.62

7.42

0.1–5 nm (10−2 mL/g)

LF-NMR method

Table 3.12 Pore size distribution of cement-based nanocomposites without/with nickel-coated CNT

1.31

2.01

5–50 nm (10−2 mL/g)

0.14

0.15

50–1000 nm (10−2 mL/g)

0.01

0.04

> 1000 nm (10−2 mL/g)

3.4 Functional/Smart Properties of Cement-Based Nanocomposites … 111

112

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.18 SEM images of cement-based nanocomposites with nickel-coated CNT. a Bridging effect. b Pulling-out effect

Fig. 3.19 Resistivity of cement-based nanocomposites without/with nickel-coated CNT

with nickel-coated CNT, part of electric current can pass through the CNT and the nickel coating, as shown in Fig. 3.20b. Figure 3.21 shows the AC impedance spectra of cement-based nanocomposites without/with nickel-coated CNT. It can be seen from Fig. 3.21 that the impedance value of the cement-based nanocomposites with nickel-coated CNT is significantly reduced, and the straight line in the low frequency band of the AC impedance spectra disappears. Moreover, the AC impedance spectra is composed of double arcs. These phenomena indicate that the conduction of CNT and its nickel coating plays a leading role in the conduction path of cement-based nanocomposites with nickel-coated CNT.

3.4 Functional/Smart Properties of Cement-Based Nanocomposites …

113

Fig. 3.20 The equivalent circuits model of cement-based nanocomposites without/with nickelcoated CNT. a Without nickel-coated CNT. b With nickel-coated CNT

Fig. 3.21 AC impedance spectra of cement-based nanocomposites without/with M30 nickel-coated CNT. a Without nickel-coated CNT. b With 0.1 wt% of M30 nickel-coated CNT. c With 0.5 wt% of M30 nickel-coated CNT. d With 0.8 wt% of M30 nickel-coated CNT

3.4.2 Electromagnetic Shielding and Absorption Properties Figure 3.22 shows the electromagnetic shielding properties of cement-based nanocomposites without/with nickel-coated CNT. As depicted in Fig. 3.22, the presence of nickel-coated CNT increases the electromagnetic shielding effectiveness of cement-based nanocomposites. The electromagnetic shielding effectiveness of

114

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.22 Electromagnetic shielding properties of cement-based nanocomposites without/with nickel-coated CNT

cement-based nanocomposites with nickel-coated CNT reaches 2.82 dB, increased by 8.3% compared with blank cement paste. Figure 3.23 shows the proportion of reflection loss (R), transmission coefficients loss (T ), absorption loss (A) of cement pastes without/with nickel-coated CNT. It can be seen from Fig. 3.23 that as the frequency increases, the proportion of reflection loss increases, the proportion of transmission loss decreases, and the absorption loss is little changed. With the increase of nickel-coated CNT content, the reflection loss of the cement-based nanocomposites increases, thus achieving shielding effectiveness improvement. Figure 3.24 exhibits the reflectivity of cement-based nanocomposites without/with nickel-coated CNT in the frequency range of 2–18 GHz. As shown in Fig. 3.24, the reflectivity of cement-based nanocomposites decreases with the content of nickelcoated CNT. When the thickness of the specimen is 20 mm, the incorporation of 0.8 wt% of nickel-coated CNT can achieve a 68.2% increase in reflectivity of cementbased nanocomposites.

Fig. 3.23 Proportion of reflection loss (R), transmission coefficients loss (T ), absorption loss (A) of cement-based nanocomposites without/with nickel-coated CNT. a Without nickel-coated CNT. b With 0.5 wt% of nickel-coated CNT. c With 0.8 wt% of nickel-coated CNT

3.5 Summary

115

Fig. 3.24 Reflectivity of cement-based nanocomposites without/with nickel-coated CNT in the frequency of 2–18 GHz. a 10 mm thick specimen. b 20 mm thick specimen

Figure 3.25 shows the electromagnetic parameters of cement-based nanocomposites without/with nickel-coated CNT. It can be seen from Fig. 3.25 that the real part of the dielectric constant of cement-based nanocomposites increases with as the content of nickel-coated CNT, which indicates that the degree of dielectric polarization of electromagnetic wave on cement-based nanocomposites increases. Meanwhile, the imaginary part of the dielectric constant and the electrical loss tangent of cementbased nanocomposites also increase with nickel-coated CNT content, leading to the increase of the dielectric loss of the cement-based nanocomposites to electromagnetic waves. However, the imaginary part of magnetic permeability and magnetic loss tangent of cement-based nanocomposites with nickel-coated CNT are basically zero, which indicates that nickel-coated CNT have no magnetic loss ability to electromagnetic waves.

3.5 Summary This chapter introduces a new-generation cement-based nanocomposite with nickelcoated CNT, focusing on its static and dynamic mechanical properties and modification mechanisms as well as electrical and electromagnetic shielding and absorption properties. The conclusions can be summarized as below. (1) The presence of nickel-coated significantly increases the mechanical properties of cement-based composites. The compressive and flexural strength can maximumly increase by 64.7 and 64.4% when nickel-coated CNT is incorporated. The elastic modulus and Poisson’s ratio reach of cement-based nanocomposites reach 38.83 MPa and 0.236, increased by 17.8 and 42.2% compared with that of blank cement-based composites. Moreover, the fatigue life of cement-based nanocomposites can maximumly increase one order of magnitude when nickelcoated CNT is incorporated. The ratio of fatigue strength to compressive strength

116

3 New-Generation Cement-Based Nanocomposites with Nickel-Coated …

Fig. 3.25 Electromagnetic parameters of cement-based nanocomposites without/with nickelcoated CNT. a Real part of the dielectric constant. b Imaginary part of the dielectric constant. c Real part of the magnetic permeability. d Imaginary part of the magnetic permeability. e Dielectric loss angle of tangent. f Electromagnetic loss angle of tangent

increases by 13.5% after adding nickel-coated CNT. The dynamic compressive strengths of cement-based nanocomposites with nickel-coated CNT at the strain rate of 200/500/800 s−1 increase by 43.0%/39.5%/21.0%, respectively. The impact toughness and impact dissipation energy of cement-based nanocomposites increase by 8.8–39.8% and 5.8–25.7% after adding nickel-coated CNT, respectively. Besides, the bond strengths between cement mortars and aggregates, new and old cement mortar, as well as cement mortar and steel bar can

References

117

maximumly increase by 38.8%, 34.6%, and 8.0%, respectively, after adding nickel-coated CNT. (2) Thanks to the good dispersion and unique electrical, thermal, and ferromagnetic properties of nickel-coated CNT and its nano-core effect, the presence of nickel-coated CNT can modify the hydration products and pore structures of cement-based nanocomposites. Moreover, nickel-coated CNT exerts bridging and pulling-out effects in cement-based nanocomposites during failure. (3) Nickel-coated CNT can endow cement-based nanocomposites with excellent electrical properties and electromagnetic shielding absorption properties. After adding nickel-coated CNT, the conduction of nickel-coated CNT plays a leading role in the conduction path of cement-based nanocomposites. The resistivities of cement-based nanocomposites reduce by 29.9, 34.2 and 31.8% when 0.1, 0.5 and 0.8 wt% of nickel-coated CNT are incorporated, respectively. In addition, the electromagnetic shielding effectiveness and reflectivity of cement-based nanocomposites with nickel-coated CNT increase by 8.3 and 68.2% compared with that of blank cement-based composites. To sum up, the nickel-coated CNT combining CNT merits with unique wetting and ferromagnetic properties of nanoscale nickel particles endows cement-based nanocomposites with excellent static and dynamic mechanical properties as well as electrical and electromagnetic properties, showing broad application prospects in large-scale infrastructures and military, nuclear power plant and extraterrestrial infrastructures.

References 1. D. Tasis, N. Tagmatarchis, A. Bianco, M. Prato, Chemistry of carbon nanotubes. Chem. Rev. 106, 1105–1136 (2006) 2. J. Hilding, E.A. Grulke, Z.G. Zhang, F. Lockwood, Dispersion of carbon nanotubes in liquids. J. Dispersion Sci. Technol. 24, 1–41 (2003) 3. B. Han, S. Ding, J. Wang, J. Ou, Nano-Engineered Cementitious Composites: Principles and Practices (Springer, Singapore, 2019) 4. B. Han, S. Sun, S. Ding, L. Zhang, X. Yu, J. Ou, Review of nanocarbon-engineered multifunctional cementitious composites. Compos. A Appl. Sci. Manuf. 70, 69–81 (2015) 5. P. Alafogianni, K. Dassios, C.D. Tsakiroglou, T.E. Matikas, N.M. Barkoula, Effect of CNT addition and dispersive agents on the transport properties and microstructure of cement mortars. Constr. Build. Mater. 197, 251–261 (2019) 6. P. Feng, H.L. Chang, X. Liu, S.X. Ye, Q.P. Ran, The significance of dispersion of nano-SiO2 on early age hydration of cement pastes. Mater. Des. 186, 108320 (2020) 7. A. Folli, I. Poschard, A. Nonat, U.H. Jakobsen, A.M. Shepherd, D.E. Macphee, Engineering photocatalytic cements: understanding TiO2 surface chemistry to control and modulate photocatalytic performances. J. Am. Ceram. Soc. 93, 3360–3369 (2010) 8. H.Y. Song, X.W. Zha, Influence of nickel coating on the interfacial bonding characteristics of carbon nanotube-aluminum composites. Comput. Mater. Sci. 49, 899–903 (2010) 9. C. Kim, B. Lim, B. Kim, U. Shim, S. Oh, B. Sung, J. Choi, J. Ki, S. Baik, Strengthening of copper matrix composites by nickel-coated single-walled carbon nanotube reinforcements. Synth. Met. 159, 424–429 (2009)

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10. V. Koti, R. George, P.G. Koppad, K.V.S. Murthy, A. Shakiba, Friction and wear characteristics of copper nanocomposites reinforced with uncoated and nickel coated carbon nanotubes. Mater. Res Exp. 5, 095607 (2018) 11. H.H. Kim, W. Han, K.H. An, B.J. Kim, Preparation of nickel coated-carbon nanotube/zinc oxide nanocomposites and their antimicrobial and mechanical properties. J. Ind. Eng. Chem. 27, 502–507 (2016) 12. S. Arai, M. Kobayashi, T. Yamamoto, M. Endo, Pure-nickel-coated multiwalled carbon nanotubes prepared by electroless deposition. Electrochem. Solid-State Lett. 13, 94–96 (2010) 13. B.S. Sindu, S. Sasmal, Properties of carbon nanotube reinforced cement composite synthesized using different types of surfactants. Constr. Build. Mater. 155, 389–399 (2017) 14. G. Kaur, S.P. Singh, S.K. Kaushik, Influence of mineral additions on flexural fatigue performance of steel fibre reinforced concrete. Mater. Struct. 49, 4101–4111 (2016) 15. K.S. Yeon, Y.S. Choi, K.K. Kim, J.H. Yeon, Flexural fatigue life analysis of unsaturated polyester-methyl methacrylate polymer concrete. Constr. Build. Mater. 140, 336–343 (2017) 16. F. Liu, L. Meng, G. Ning, L. Li, Fatigue performance of rubber-modified recycled aggregate concrete (RRAC) for pavement. Constr. Build. Mater. 95, 207–217 (2015)

Chapter 4

New-Generation Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2

4.1 Introduction Nano TiO2 , also known as nano titanium dioxide, nano titanium oxide or nano titania, has the characteristics of high hardness, high dielectric constant, and excellent functionality e.g., ultraviolet shielding, weather resistance, antibacterial, self-cleaning, and photocatalytic abilities [1–5]. Former studies have demonstrated that the presence of nano TiO2 can achieve increases of 45.0% in compressive strength [6], 43.5% in tensile strength [7], and 61.9% in flexural strength [8], but decreases of 27.0% in shrinkage [9], 43.9% in gas permeability [8], 59.1% in water absorption [10], and 60.9% in chloride ion penetration resistance [11]. In addition, nano TiO2 can endow cement-based nanocomposites with functional/smart properties such as photocatalysis and electromagnetic shielding performance. The cement-based nanocomposites with nano TiO2 can remove 45% of NOx in air [12] and degrade 78% of organic matters [4]. In 2–28 GHz band, the minimum reflectivity of the cement-based nanocomposites reaches −16.26 dB [13]. However, nano TiO2 tends to agglomerate in cement-based nanocomposites due to its large surface energy. The formation of agglomerations weakens the modification effect of nano TiO2 on cement-based nanocomposites, and may even act as defects in the materials [14, 15]. Nano SiO2 -coated TiO2 , a kind of core–shell nanomaterial formed by coating the surface of nano TiO2 with SiO2 , shows synergistic effect on cement-based nanocomposites. On the one hand, the surface of nano SiO2 -coated TiO2 is negative charged due to the formation of Ti–O–Si bond during the coating [16, 17]. The surface electronegativity makes nano SiO2 -coated TiO2 particles repel each other, thus reducing the agglomeration [18, 19]. On the other hand, the coated SiO2 with pozzolanic activity can react with calcium hydroxide, a hydration product considered to possess negative effect on the performance of cement-based nanocomposites [20, 21]. Therefore, nano SiO2 -coated TiO2 shows stronger modification potential on cement-based nanocomposites than nano TiO2 . In this chapter, cement-based nanocomposites, fabricated by incorporating nano SiO2 -coated TiO2 , are introduced, including their rheology, compressive/flexural © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_4

119

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strengths, fatigue performance, and impact performance as well as the modification mechanisms of nano SiO2 -coated TiO2 . Moreover, the functional/smart properties of the cement-based nanocomposites, including self-healing, electromagnetic shielding and absorption, and anti-corrosion properties, are presented.

4.2 Preparation of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 The raw materials used to fabricate cement-based nanocomposites with nano SiO2 coated TiO2 included P·O 42.5 R Portland cement, grade II fly ash, silica fume with a particle size range of 0.1–0.3 μm, quartz sand with a size range of 0.12–0.83 mm, water, SP, and nano SiO2 -coated TiO2 . The SEM image of nano SiO2 -coated TiO2 is shown in Fig. 4.1. The properties of nano SiO2 -coated TiO2 refer to Table 4.1. The fabrication process of cement-based nanocomposites with nano SiO2 -coated TiO2 are listed in Tables 4.2, 4.3 and 4.4. Table 4.1 Properties of nano SiO2 -coated TiO2 SiO2 /TiO2 ratio

Diameter (nm)

Purity (%)

Specific surface area (m2 /g)

Crystal form

0.04

20

≥ 96

≥ 40

Rutile

Table 4.2 Mix proportions of fresh cement pastes without/with nano SiO2 -coated TiO2 Code

Cement

Water

Superplastizer

Nano SiO2 -coated TiO2 content (vol.%)

Control

1

0.24

0.01

0

NT-0.1

1

0.24

0.01

0.1

NT-0.3

1

0.24

0.01

0.3

NT-0.5

1

0.24

0.01

0.5

NT-0.7

1

0.24

0.01

0.7

NT-1.4

1

0.24

0.01

1.4

Table 4.3 Fabrication process of fresh cement pastes without/with nano SiO2 -coated TiO2 Dispersion method

Fabrication process Feeding order

Technology

Time (s)

Shear mixing + non-covalent surface modification by SP

Nano SiO2 -coated TiO2 + Water + SP

Shear mixing (60 r/min)

60

Cement

Shear mixing (60 r/min)

90

–

Shear mixing (500 r/min)

120

–

Shear mixing (60 r/min)

60

4.3 Rheology of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2

121

Table 4.4 Fabrication process of cement mortars without/with nano SiO2 -coated TiO2 Dispersion method

Shear mixing + non-covalent surface modification by SP

Fabrication process Feeding order Technology

Molding

Curing

Method

Time (s)

Method

Size (mm)

Method

Time (d)

Shear mixing (140 r/min)

20

Vibration

40 × 40 × 160

Standard condition

1

Cement + fly Shear ash mixing (140 r/min)

60

Silica fume

Shear mixing (140 r/min)

120

–

Shear mixing (285 r/min)

120

Quartz sand

Shear mixing (140 r/min)

60

Shear mixing (285 r/min)

240

Nano SiO2 -coated TiO2 + Water + SP

W (20 °C) 28

4.3 Rheology of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 To quantitatively analyze the rheology of cement pastes without/with nano SiO2 coated TiO2 , Herschel-Bulkley model (H-B model) was introduced because the H-B model shows highest accuracy in describing the rheology of cement-based composites [22]. The rheological formula of H-B model is shown in Eq. (4.1) [23]. τ = τ0 + K γ˙n

(4.1)

where τ and τ0 are the apparent and true yield stresses (Pa) that are obtained by fitting the rheological model and experiment, respectively. γ˙ represents shear rate (s−1 ). n is flow index that indicates the fluid is shear-thickening (n > 1) or shear-thinning (n < 1). K represent viscosity coefficient that is related to n. Then, the viscosity η can be calculated from Formula (4.2).

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Fig. 4.1 Morphology of nano SiO2 -coated TiO2

η = τ/γ

(4.2)

The effect of nano SiO2 -coated TiO2 on the yield stress, minimum viscosity, flow index, and critical shear rate of fresh cement pastes is shown in Fig. 4.2. As shown in Fig. 4.2a, the yield stress of cement paste increases with the content of nano SiO2 coated TiO2 . The addition of 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1.4 wt% of nano SiO2 -coated TiO2 increases the yield stress of cement paste by 27.7%, 28.6%, 32.7%, 44.5%, and 151.2%, respectively. For the minimum viscosity, it decreases first and then increases with the content of nano SiO2 -coated TiO2 , as depicted in Fig. 4.2b. The minimum viscosity of cement pastes with 0.1–0.7 wt% of nano SiO2 -coated TiO2 is similar with that without nano SiO2 -coated TiO2 , in contrast, the minimum viscosity reaches 0.417 Pa s after incorporating 1.4 wt% of nano SiO2 -coated TiO2 (Fig. 4.2b). As demonstrated in Fig. 4.2c, the cement paste with nano SiO2 -coated TiO2 is a shear-thickening fluid, indicating the presence of nano SiO2 -coated TiO2 does not change the shear-thickening characteristics of cement paste. Besides, the presence of nano SiO2 -coated TiO2 increases the critical shear rate of cement paste from 7 s−1 to 10 s−1 . However, the critical shear rate changes little with the content of nano SiO2 -coated TiO2 . The influence mechanisms of nano SiO2 -coated TiO2 on the rheology of cement paste can be summarized as dilution effect, as shown in Fig. 4.3. The nano SiO2 coated TiO2 particles appear among anhydrous grains, reducing the fracture between adjacent anhydrous grains due to the spherical characteristics of nano SiO2 -coated TiO2 [24, 25]. On the other hand, the Ti–O–Si bond increases the dispersion of nano SiO2 -coated TiO2 due to charge repulsion, which enhances the dilution effect.

4.3 Rheology of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2

123

Fig. 4.2 Effect of nano SiO2 -Coated TiO2 on rheological parameters of cement paste: a Yield stress; b Minimum viscosity; c Flow index; d Critical shear rate

Fig. 4.3 The influence mechanisms of nano SiO2 -coated TiO2 on the rheology of cement paste: a Dilution effect; b Dispersion effect

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Fig. 4.4 Compressive strength of cement mortars without/with nano SiO2 -coated TiO2 at 3 d and 28 d

4.4 Mechanical Properties/Performances of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 4.4.1 Compressive Strength The compressive strengths of cement mortars without/with nano SiO2 -coated TiO2 at 3 d and 28 d are shown in Fig. 4.4. As depicted in Fig. 4.4, the presence of nano SiO2 -coated TiO2 shows no obvious effect on the compressive strength of cement mortar at 3 d. However, the compressive strengths of cement mortars at 28 d increases by 5.97%, 12.26%, and 10.32% when 1 wt%, 3 wt%, and 5 wt% of nano SiO2 -coated TiO2 are incorporated, respectively.

4.4.2 Flexural Strength The flexural strengths of cement-based nanocomposites without/with nano SiO2 coated TiO2 at 3 d and 28 d are shown in Fig. 4.5. Figure 4.5 demonstrated that the presence of nano SiO2 -coated TiO2 significantly increases the flexural strength of cement-based nanocomposites. The flexural strength can maximumly increase by 83.30% after adding 3 wt% of nano SiO2 -coated TiO2 . Meanwhile, the 28-d compressive strength of cement-based nanocomposites increases by 43.43%, 74.90% and 87.00% after incorporating 1 wt%, 3 wt%, and 5 wt% of nano SiO2 -coated TiO2 , respectively.

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125

Fig. 4.5 Flexural strength of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at 3 d and 28 d

4.4.3 Fatigue Properties The compressive fatigue behaviors of cement-based nanocomposites without/with nano SiO2 -coated TiO2 were characterized by the loading with a continuous sine wave at 5 Hz. The loading scheme is listed in Table 4.5. The minimum stress in fatigue tests was selected as 0.1 times of monotonic ultimate compressive stress. The monotonic ultimate compressive strengths of cement-based nanocomposites with 0 wt%, 1 wt%, and 3 wt% of nano SiO2 -coated TiO2 are 137 MPa, 135 MPa, and 141 MPa, respectively. Considering the large discrete in fatigue behavior characterization, the twoparameters Weibull distribution [26–28] was introduced to analyze the fatigue life at different failure probabilities. The fatigue life of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at different stress level are listed in Table 4.6. It can be seen in Table 4.6 the fatigue life of cement-based nanocomposites can maximumly increase 41.3% after adding nano SiO2 -coated TiO2 . Table 4.5 Compressive fatigue loading scheme at different stress levels Nano SiO2 -coated TiO2 content (wt% of cement)

Stress level 0.9 Maximum stress

0.8 Minimum stress

Maximum stress

0.7 Minimum stress

Maximum stress

Minimum stress

0

123.6

13.7

109.8

13.7

96.1

13.7

1

121.6

13.5

108.1

13.5

95.5

13.5

3

127.0

14.1

112.8

14.1

98.7

14.1

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4 New-Generation Cement-Based Nanocomposites with Nano …

Table 4.6 The fatigue life of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at different stress levels Stress level Fatigue life at different failure probabilities Nano SiO2 -coated 0.1 0.2 0.3 0.4 0.5 TiO2 content (wt% of cement) 0

1

3

Fatigue life (in logarithm form) increase (%)

0.9

10

22

36

53

73

–

0.8

101

283

537

879

1335

–

0.7

2894

6454

10,654

15,641

21,673

–

0.9

26

74

141

229

347

21.5–41.3

0.8

199

619

1254

2155

3413

26.5–39.6

0.7

200,228 294,079 373,937 449,476 525,538 28.9–41.3

0.9

10

28

55

94

146

16.0–19.8

0.8

675

1534

2562

3798

5299

17.0–25.2

0.7

18,195

36,814

57,187

80,130

106,728 16.8–27.2

Figure 4.6 demonstrates the S–N curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at 0.1 and 0.5 failure probabilities. It can be seen from Fig. 4.6 the slopes of S–N curves of cement-based nanocomposites with nano SiO2 -coated TiO2 is less steep compared with that without nanofillers, indicating the fatigue life is more sensitive to stress level. Considering fatigue life is 2 × 106 , the fatigue limits calculated from S–N curve of cement-based nanocomposites with 1 wt% and 3 wt% of nano SiO2 -coated TiO2 reach 88.9 MPa and 86.8 MPa, respectively, increasing by 19.4% and 16.6% compared with that of blank cement mortar. Figure 4.7 shows the fatigue deformation curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As shown in Figs. 4.7a–c, the strain-fatigue life curve can be divided into three stages: cyclic creep stage, creep-fatigue coupling stage, and fatigue stage, which approximately occupies 10%, 80%, and 10% of

Fig. 4.6 The S–N curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at different failure probabilities. a 0.1. b 0.5

4.4 Mechanical Properties/Performances of Cement-Based …

127

the total fatigue life, respectively. After adding nano SiO2 -coated TiO2 , the strainfatigue life curve becomes smoother in fatigue stage compared with blank cement mortar, implying the presence of nanofillers refines the microcracks and inhibits their connection in fatigue stage [29]. Noteworthily, the presence of nano SiO2 -coated TiO2 increases the ultimate compressive strain of cement-based nanocomposites. The ultimate compressive strain increases from 4125 με to 4432 με and 4529 με, increased by 7.4% and 9.8% after 1 wt% and 3 wt% of nano SiO2 -coated TiO2 are incorporated, respectively. Figures 4.7d–l show the stress–strain curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 , in which the grey arrows denote the strain amplitude from initial circle to failure and the pink arrows denote the strain amplitude from micro-cracking to macro-cracking at the fatigue stage. It can be seen from Figs. 4.7d–l that the amplitude of cement-based nanocomposites with nano SiO2 coated TiO2 is higher than that without nanofillers, indicating the presence of nano SiO2 -coated TiO2 increase the fatigue toughness of cement-based nanocomposites. In other word, adding nano SiO2 -coated TiO2 leads to a decrease in strain rate, demonstrating a slower microcracking process at creep-fatigue coupling stage.

4.4.4 Impact Properties Hopkinson pressure bar (SHPB) test was employed for characterize the impact performance of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . Figure 4.8 shows the dynamic compressive strengths of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As shown in Fig. 4.8, the dynamic compressive strength increases with the strain rate, indicating the presence of strain rate effect of cement-based nanocomposites. After adding nano SiO2 -coated TiO2 , the dynamic compressive strength significantly increases. The dynamic compressive strength of cement-based nanocomposites with 1 wt% and 3 wt% of nano SiO2 coated TiO2 at the strain rate of 200/500/800 s−1 increases by 46.9%/40.3%/6.9% and 55.3%/58.9%/12.1%, respectively. Combining the experimental results and Eqs. (2.1)–(2.4), the dynamic stress– strain curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 are obtained as shown in Fig. 4.9. The stress–strain curves in Fig. 4.9 can be generally divided into three stages: the approximately linear ascent stage, the non-linear ascent stage, and the non-linear descent stage, corresponding to the elastic deformation, plastic deformation, and damage softening of cement mortar. This three-stage characteristic is observed in stress–strain curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at different strain rate, indicating the presence of nano SiO2 -coated TiO2 and different strain rate do not change the failure process of cement-based nanocomposites. However, after adding nano SiO2 -coated TiO2 , two or multiple peaks appears in the stress–strain curves. The multiple peaks indicate the cement mortar with nano SiO2 -coated TiO2 can continue absorb energy after reaching the peak loading, which contributes to delay the occurrence of brittle

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4 New-Generation Cement-Based Nanocomposites with Nano …

Fig. 4.7 Fatigue deformation curves of cement-based nanocomposites without/with nano SiO2 coated TiO2 . Strain-fatigue life curve of cement-based nanocomposites a without nano SiO2 -coated TiO2 , b with 1 wt% of nano SiO2 -coated TiO2 , and c with 3 wt% of nano SiO2 -coated TiO2 . Stress– strain curves of cement-based nanocomposites without nano SiO2 -coated TiO2 at the stress level of d 0.7, e 0.8, and f 0.9. Stress–strain curves of cement-based nanocomposites with 1 wt% of nano SiO2 -coated TiO2 at the stress level of d 0.7, e 0.8, and f 0.9. Stress–strain curves of cement-based nanocomposites with 3 wt% of nano SiO2 -coated TiO2 at the stress level of d 0.7, e 0.8, and f 0.9

failure [30, 31]. It can be deduced from this phenomenon that the presence of nano SiO2 -coated TiO2 optimizes the stress distribution in cement mortar and increases the energy required for crack growth, thus improving the impact resistance of cement mortar. The dynamic peak strains of cement-based nanocomposites without/with nano SiO2 -coated TiO2 are summarized in Fig. 4.10. As shown in Fig. 4.10, the addition of nano SiO2 -coated TiO2 maximumly increases the dynamic peak strain by 63.5%. The increase is influenced by the content of nano SiO2 -coated TiO2 . When 1 wt%

4.4 Mechanical Properties/Performances of Cement-Based …

129

Fig. 4.8 Dynamic compressive strength of cement-based nanocomposites without/with nano SiO2 -coated TiO2

Fig. 4.9 Dynamic stress–strain curves of cement-based nanocomposites without/with nano SiO2 coated TiO2 . a Without nano SiO2 -coated TiO2 . b with nano SiO2 -coated TiO2 , in which T1 and T2 represent cement mortar with 1 wt% of and 3 wt% of nano SiO2 -coated TiO2 , respectively

of nano SiO2 -coated TiO2 is incorporated, the dynamic peak strains of cementbased nanocomposites increase at all chosen strain rates; While the increase is only identified at the strain rate of 800 s−1 . Such phenomena indicate the presence of nano SiO2 -coated TiO2 endows cement-based nanocomposites with good deformation resistance. The deformation resistance of cement-based nanocomposites is tightly related the compactness of microstructures [31]. Therefore, nano SiO2 -coated TiO2 densifies the microstructure of cement-based nanocomposites, thus increasing the deformation resistance of the cement-based nanocomposites. Figure 4.11 shows the impact toughness and impact dissipation energy of cementbased nanocomposites without/with nano SiO2 -coated TiO2 . As depicted in Fig. 4.11, the impact toughness and impact dissipation energy respectively increase by 60.7– 105.3% and 8.6–55.6% after adding nano SiO2 -coated TiO2 . Noteworthily, the effect

130

4 New-Generation Cement-Based Nanocomposites with Nano …

Fig. 4.10 Dynamic peak strain of cement-based nanocomposites without/with nano SiO2 -coated TiO2

Fig. 4.11 Impact toughness and impact dissipation energy of cement-based nanocomposites without/with nano SiO2 -coated TiO2

of nano SiO2 -coated TiO2 on impact toughness is greater than that on impact dissipation energy. This phenomenon, on the one hand, derives from the compact microstructures of cement-based nanocomposites with nano SiO2 -coated TiO2 , which increases the energy required for cracking. On the other hand, the compact microstructures reduce the conversion of wave energy to other types of energy, thereby reducing the impact dissipation energy.

4.4.5 Bond Properties Figure 4.12 shows the bond properties of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . In general, the presence of nano SiO2 -coated TiO2

4.4 Mechanical Properties/Performances of Cement-Based …

131

can improve the bond properties of cement-based nanocomposites. As shown in Fig. 4.12a, the bond strengths between cement-based nanocomposites and aggregates, obtained by three-point-bend test, are less influenced by adding nano SiO2 coated TiO2 . The bond strengths between new and old cement mortars, obtained by splitting tensile test, increase by 15.6%, 17.1%, and 27.8% after adding 1 wt%, 2 wt%, and 3 wt% of nano SiO2 -coated TiO2 , respectively, as depicted in Fig. 4.12b. Moreover, the presence of nano SiO2 -coated TiO2 can notably modify the bond behavior between cement-based nanocomposites and steel bar. As shown in Fig. 4.12c, a 2.15 MPa/20.5% increase in cracking bond strength, a 1.04 MPa/8.6% increase in ultimate bond strength, a 1.68 MPa/16.0% increase in residual bond strength, a 0.592 mm/56.5% reduction in ultimate bond slip, and a 1.525 mm/44.7% reduction in residual bond slip are the best achieved due to the addition of nano SiO2 -coated TiO2 . Similar to cement mortar-steel bar bond, the ultimate bond strength increases by 4.58 MPa/14.0% and the corresponding slip reduces by 1.122 mm/19.7% after adding nano SiO2 -coated TiO2 .

Fig. 4.12 Bond properties of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Bond strength between cement-based nanocomposites and aggregate. b Bond strength between new and old concrete. c Bond behavior between cement-based nanocomposites and steel bar. d Bond behavior between cement-based nanocomposites and FRP bar

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4 New-Generation Cement-Based Nanocomposites with Nano …

4.4.6 Modification Mechanisms The results in Sects. 4.4.1–4.4.5 demonstrate the presence of nano SiO2 -coated TiO2 can significantly improve the mechanical properties/performance of cementbased nanocomposites, including compressive/flexural strength, fatigue properties/performance, and impact properties/performance. Such improvements are achieved from the modification of nano SiO2 -coated TiO2 on the microstructures of cement-based nanocomposites. Therefore, SEM, EDX, XRD, NMR, MIP and LFNMR were employed to reveal the modification mechanisms of nano SiO2 -coated TiO2 on cement-based nanocomposites. Figure 4.13 shows the TG and DTG curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . Three peaks can be observed in DTG curves in Fig. 4.13c and d. These three peaks successively indicate the evaporation of water, decomposition of CH, and decomposition of CaCO3 . Based on TG and DTG curves, the hydration degree of cement can be calculated from Eqs. (2.5) and (2.6). The calculated hydration degrees of cement-based nanocomposites without/with nano SiO2 -coated TiO2 are listed in Table 4.7. As shown in Table 4.5, the presence of nano SiO2 -coated TiO2 increases the hydration degree of cement, especially at 3 d. the cement hydration is enhanced by 5.2 after adding 5 wt% of nano SiO2 -coated TiO2 . However, nano SiO2 -coated TiO2 shows less effect on the hydration at 28 d. The XRD patterns of cement-based nanocomposites without/with nano SiO2 coated TiO2 at 3 and 28 d are shown in Fig. 4.14. It can be seen that the intensities of main diffraction peaks indicating CH crystals of cement-based nanocomposites with nano SiO2 -coated TiO2 are lower than that of blank cement paste at 3 and 28 d, which indicates the CH content reduces after adding nano SiO2 -coated TiO2 . This can be attributed to the SiO2 coating consumes some CH during curing due to its pozzolanic effect. In addition, the CH orientation R can be calculated from (0 0 1) and (1 0 1) crystal face peak intensity through Formula (2.7). The CH diffraction intensity and orientation are listed in Table 4.8. The presence of nano SiO2 -coated TiO2 reduces CH orientation in cement-based nanocomposites. The CH orientation index of cement pates at the curing age of 3/28 d decreases from 2.62/1.77 to 2.46/1.55, 2.11/1.57, and 1.44/1.47 after 1 wt%, 3wt%, and 5 wt% of nano SiO2 -coated TiO2 is incorporated, respectively. Figure 4.15 illustrates the EDS mapping results indicating the element Ti distribution in cement-based nanocomposites, also indicating the distribution of nano SiO2 coated TiO2 . The EDS mapping results show the nano SiO2 -coated TiO2 particles are uniformly distributed in cement-based nanocomposites, even at a high content. This confirms well dispersibility of nano SiO2 -coated TiO2 due to the Ti–O–Si bond forming from SiO2 coating. The 29 Si NMR spectrum and corresponding deconvoluted spectra of cementbased nanocomposites without/with nano SiO2 -coated TiO2 are shown in Fig. 4.16 and Table 4.9. As shown in Fig. 4.16, a sharp resonance peak Q2 and four weak peaks Q0 , Q1 , Q3 , and Q4 appear in all specimens. After adding nano SiO2 -coated TiO2 , the proportion of Q0 and Q1 reduces, while the proportion of Q2 significantly increases,

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133

Fig. 4.13 TG and DTG curves of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a TG curves at 3 d. b DTG curves at 3 d. c TG curves at 28 d. d DTG curves at 28 d

Table 4.7 Hydration degree of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at 3 and 28 d Age (d)

Nano SiO2 -coated TiO2 content (wt% of cement) 0

1

3

5

3

51.36

53.57

55.60

56.56

28

63.82

64.48

65.74

65.50

as listed in Table 4.9. These phenomena mean the presence of nano SiO2 -coated TiO2 promote the hydration of cement and the polymerization of silicon oxide tetrahedron. Figure 4.17 exhibits the porosity of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As demonstrate in Fig. 4.17, the addition of nano SiO2 -coated TiO2 notably decreases the porosity of cement-based nanocomposites. The porosity of cement-based nanocomposites decreases by 22.4%, 18.8%, and 19.5% after adding 3.0 wt% of nano SiO2 -coated TiO2 , measured through SG, MIP, LF-NMR methods, respectively. Table 4.10 lists the characteristic pore radius of cement-based nanocomposites without/with nano SiO2 -coated TiO2 measured through MIP and LF-NMR methods. It can be seen from Table 4.10 the presence of nano SiO2 -coated TiO2 reduces the

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Fig. 4.14 XRD patterns of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at 3 and 28 d

Table 4.8 Cement hydration degree of cement-based nanocomposites without/with nano SiO2 coated TiO2 at 3 and 28 d Nano SiO2 -coated TiO2 content (wt% of cement)

3d (0 0 1) CH

28 d (1 0 1) CH

CH orientation

(0 0 1) CH

(1 0 1) CH

CH orientation

0

794

409

2.62

463

354

1.77

1

717

394

2.46

432

376

1.55

3

637

407

2.11

444

381

1.57

5

479

448

1.44

345

316

1.47

most probable pore radius, volume median pore radius, average pore radius, and threshold pore radius from 6.1 nm, 96.3 nm, 17.4 nm, 75.0 nm to 5.5 nm, 32.7 nm, 14.5 nm, and 49.3 nm, respectively. Figure 4.18 and Table 4.11 show the pore size distribution of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . The presence of nano SiO2 coated TiO2 significant decreases pore content of all sizes. The proportion of pore with size range of 0.1–50 nm increases after adding nano SiO2 -coated TiO2 , while that of pore with size greater than 50 nm decreases. These phenomena indicate that the addition of nano SiO2 -coated TiO2 optimizes the pore size distribution in cement-based nanocomposites.

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Fig. 4.15 Nano SiO2 -coated TiO2 distribution in cement-based nanocomposites. a With 1 wt% of nano SiO2 -coated TiO2 . b With 3 wt% of nano SiO2 -coated TiO2 . c With 5 wt% of nano SiO2 -coated TiO2

Fig. 4.16 29 Si NMR spectra of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Without nano SiO2 -coated TiO2 . b With 3 wt% of nano SiO2 -coated TiO2 Table 4.9 Deconvolution results of 29 Si NMR of cement-based nanocomposites without/with nano SiO2 -coated TiO2 Nano SiO2 -coated TiO2 content (wt% of cement)

Q0 (%)

Q1 (%)

Q2 (%)

Q3 (%)

0

17.7

15.9

41.0

3

12.1

9.9

45.5

Type and content of silicon oxide tetrahedron

Cement

Supplementary cementitious materials

Q4 (%)

Hydration degree (%)

Residual proportion (%)

13.7

11.7

76.3

25.4

12.6

19.9

82.1

32.5

Figure 4.19 shows the morphology of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As depicted in Fig. 4.19, The CH crystal size decreases with the content of nano SiO2 -coated TiO2 . This confirms the SiO2 coating can react with CH due to its pozzolanic activity, thus compacting the microstructures of cement-based nanocomposites.

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Fig. 4.17 Porosity of cement-based nanocomposites without/with nano SiO2 -coated TiO2

Table 4.10 Characteristic pore radius of cement-based nanocomposites without/with nano SiO2 coated TiO2 Nano SiO2 -coated TiO2 content (wt% of cement)

MIP method Most probable pore radius (nm)

LF-NMR method Specific surface area median pore radius (nm)

Volume median pore radius (nm)

Average pore radius (nm)

Most probable pore radius (nm)

Threshold pore radius (nm)

0

6.1

5.5

96.3

17.4

2.3

75.0

3

5.5

5.5

32.7

14.5

2.0

49.3

Fig. 4.18 Pore size distribution curve of cement-based nanocomposites without/with nano SiO2 coated TiO2 . a MIP method. b LF-NMR method

0.07

0.02

0.04 6.07

7.42

3

0.11

0.19

0.15

0.13

0

0.13

LF-NMR method > 1000 nm (mL/g)

0.1–5 nm (10−2 mL/g)

50–1000 nm (mL/g)

5–50 nm (mL/g)

MIP method

1–5 nm (mL/g)

Nano SiO2 -coated TiO2 content (wt% of cement)

Table 4.11 Pore size distribution of cement mortars without/with nano SiO2 -coated TiO2

1.34

2.01

5–50 nm (10−2 mL/g)

0.29

0.14

50–1000 nm (10−2 mL/g)

0.04

0.04

> 1000 nm (10−2 mL/g)

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Fig. 4.19 Morphology of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Without nano SiO2 -coated TiO2 . b With 2 wt% of nano SiO2 -coated TiO2 . c With 3 wt% of nano SiO2 -coated TiO2

Figure 4.20 shows the distribution of nano SiO2 -coated TiO2 in the interface and bulk cement matrix of cement-based nanocomposites. As shown in Fig. 4.20, nano SiO2 -coated TiO2 particles enrich in all interfaces, including cement mortaraggregate, new and old cement mortars, cement mortar-steel bar, and cement mortarFRP bar interfaces. Moreover, the enrichment degree of nano SiO2 -coated TiO2 in the interface near the upside of reinforcing bars is lower than that in the interface near the underside of reinforcing bars, as shown in Fig. 4.20c and d. The enriched nano SiO2 -coated TiO2 can notably modify the hydration products and pore structures in the interface, similar to the effect of nano SiO2 -coated TiO2 on the matrix of cement-based nanocomposites.

4.5 Functional/Smart Properties of Cement-Based Nanocomposites with Nano SiO2 -Coated TiO2 4.5.1 Self-Healing Properties The self-healing properties were characterized by the following steps: (1) Prepare cement mortars without/with nano SiO2 -coated TiO2 referring to Sect. 4.3.1. (2) Preloading cement mortar specimens to 60% of the 28-d compressive/flexural strength. (3) Curing the pre-loaded specimens in water and air. (4) The specimens were loaded to failure after curing 90 d in water and air. The self-healing ability was quantitively analyzed through self-healing coefficient, as shown in Formulas 4.3 and 4.4. Cs = C1 /C2

(4.3)

Fs = F1 /F2

(4.4)

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Fig. 4.20 Distribution of nano SiO2 -coated TiO2 in the interface and bulk cement matrix of cementbased nanocomposites. a Cement mortar-aggregate interface. b New-to-old concrete interface. c Cement mortar-steel bar interface. d Cement mortar-FRP bar interface

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Fig. 4.21 Compressive and flexural self-healing coefficient of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Compressive self-healing coefficient. b Flexural self-healing coefficient

where Cs and Fs represent the compressive and flexural self-healing coefficient, respectively. C1 , C2 , F1 , and F2 are compressive strength after self-curing, compressive strength without pre-loading, flexural strength after self-curing, and flexural strength without pre-loading, respectively. Figure 4.21 shows the compressive and flexural self-healing coefficient of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As shown in Fig. 4.21, the cement-based nanocomposite possesses obvious self-healing abilities after adding nano SiO2 -coated TiO2 . Apart from nano SiO2 -coated TiO2 , water is also an indispensable factor influencing the self-healing abilities. The compressive and flexural self-healing coefficient of cement-based nanocomposites with nano SiO2 -coated TiO2 cured in water reach 1.26 and 1.02, respectively. The AE instrument was used to characterize the cracks in cement-based nanocomposites without/with nano SiO2 -coated TiO2 before/after self-healing. Table 4.12 shows the accumulative energy of cement-based nanocomposites without/with nano SiO2 -coated TiO2 before/after compressive and flexural pre-loading, respectively. It can be seen from Table 4.12 the presence of nano SiO2 -coated TiO2 decrease the accumulative energy before compressive and flexural pre-loading by 25.2% and 41.9%, respectively, indicating nano SiO2 -coated TiO2 reduces initial cracks in cement-based nanocomposites. At the secondary compressive loading, the accumulative energy reduces by 17.9% and 50.9% after the cement-based nanocomposites curing in air and water, respectively. In contrast, the addition of nano SiO2 -coated TiO2 shows no obvious effect on the flexural self-curing properties.

4.5.2 Electromagnetic Shielding and Absorption Properties Figure 4.22 shows the electromagnetic shielding properties of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As depicted in Fig. 4.22,

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Table 4.12 Accumulative energy of cement-based nanocomposites without/with nano SiO2 -coated TiO2 before/after loading Nano SiO2 -coated TiO2 content

Accumulative energy under compressive Accumulative energy under flexural loading loading Pre-loading

Secondary loading Curing in air

Curing in water

Pre-loading

Secondary loading Curing in air

Curing in water

0

17,734

2,167,974

3,869,802

2072

83,025

75,854

0.5

13,271

1,779,321

1,900,768

1202

78,075

75,510

the presence of nano SiO2 -coated TiO2 significantly increase the electromagnetic shielding effectiveness of cement-based nanocomposites. At the frequency of 18 GHz, the electromagnetic shielding effectiveness of cement-based nanocomposites with nano SiO2 -coated TiO2 reaches 2.45 dB, increased by 25% compared with blank cement mortar. Figure 4.23 shows the proportion of reflection loss (R), transmission coefficients loss (T ), absorption loss (A) of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . At the frequency of 18 GHz, the reflection loss of cement-based nanocomposites r with nano SiO2 -coated TiO2 occupies 36.90% of electromagnetic shielding effectiveness, increased by 16% compared with blank cement mortar. This shows that the reflection loss greatly affects the electromagnetic shielding effectiveness of cement-based nanocomposites. Figure 4.24 and Table 4.13 exhibit the effect of nano SiO2 -coated TiO2 on reflectivity in the frequency range of 2–18 GHz. The results indicate the presence of nano SiO2 -coated TiO2 increase the minimum reflectivity and bandwidth of cementbased nanocomposites. When 3 wt% of nano SiO2 -coated TiO2 is incorporated, the minimum reflectivity of cement-based nanocomposites reaches 15.89 dB, increased by 86.07% compared with blank cement mortar. Fig. 4.22 Electromagnetic shielding properties of cement-based nanocomposites without/with nano SiO2 -coated TiO2

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Fig. 4.23 Proportion of reflection loss (R), transmission coefficients loss (T ), absorption loss (A) of cement-based nanocomposites with nano SiO2 -coated TiO2

Fig. 4.24 Reflectivity of special structure and surface treatment of cement-based nanocomposites without/with nano SiO2 -coated TiO2 and their 3D projection plots with the thickness of 10 mm (a, c) and 20 mm (b, d) in the frequency of 2–18 GHz Table 4.13 Minimum reflectivity and bandwidth of cement-based nanocomposites without/with nano SiO2 -coated TiO2 in the frequency of 2–18 GHz Nano SiO2 -coated TiO2 content (wt% of cement)

Minimum reflectivity (frequency)

Bandwidth (reflectivity ≤ − 10 dB)

0

−8.54 dB (18.00 GHz)

–

3

−15.89 dB (16.16 GHz)

12.56–12.64 GHz and 15.92–16.48 GHz

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143

Fig. 4.25 Electromagnetic shielding and absorption mechanisms of cement-based nanocomposites without/with nano SiO2 -coated TiO2

The experimental results demonstrated cement-based nanocomposites with nano SiO2 -coated TiO2 possess good electromagnetic shielding and absorption properties. The properties, firstly, derives from the quantum size effect of nano SiO2 -coated TiO2 . Nano SiO2 -coated TiO2 can generate new wave absorption channel in cement-based nanocomposites, thus improving the electromagnetic wave absorption performance [13]. Secondly, nano SiO2 -coated TiO2 can convert electromagnetic energy into heat energy through its high transmissivity and large surface that contributes to the polarization and conduction of atoms and electrons. Finally, the nano SiO2 coated TiO2 promote the polarization of cement-based nanocomposites under electric field. Owing to the above merits, nano SiO2 -coated TiO2 can endow cement-based nanocomposites with electromagnetic shielding and absorption properties, as shown in Fig. 4.25.

4.5.3 Anti-Sewage-Corrosion Properties Figure 4.26 shows the strength deterioration of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . The compressive and flexural strength of cement-based nanocomposites in sewage is degraded due to sewage corrosion. The presence of nano SiO2 -coated TiO2 can inhibit the deterioration of cement-based nanocomposites. Figure 4.27 shows the visual morphology and three-dimensional morphology of the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after 14 months of sewage corrosion. As shown in Fig. 4.27, some of quartz sand were exposed in the surface of cement-based nanocomposites. After adding nano SiO2 coated TiO2 , the exposed area of the sand significantly reduces. In addition, the surface of cement-based nanocomposites becomes uneven with obvious undulating peaks and gullies after 14 months sewage corrosion. The addition of nano SiO2 -coated TiO2 reduces the undulations on the surface of cement-based nanocomposites. Based on Fig. 4.25, the average surface roughness reduces by 9.27% and 39.88% when 3 wt% and 5 wt% of nano SiO2 -coated TiO2 are incorporated, respectively.

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Fig. 4.26 Strength deterioration of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Compressive strength. b Flexural strength

Fig. 4.27 The morphology and three-dimension morphology of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after sewage corrosion. a Without nano SiO2 -coated TiO2 . b With nano SiO2 -coated TiO2

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Fig. 4.28 Mass loss of cement-based nanocomposites without/with nano SiO2 -coated TiO2 under sewage corrosion

Figure 4.28 shows the mass loss of cement-based nanocomposites without/with nano SiO2 -coated TiO2 under sewage corrosion. As can be seen in Fig. 4.28, after 3 months of sewage corrosion, the hindering effect of nano SiO2 -coated TiO2 on the mass loss of cement-based nanocomposites in the effluent gradually becomes apparent. The mass loss rate of cement-based nanocomposites was greatest when the age of sewage corrosion was between 3 and 9 months. After 9 months of sewage corrosion, the mass loss rate of cement-based nanocomposites gradually decreases, where the mass losses of cement-based nanocomposites with 3 wt% and 5 wt% of nano SiO2 -coated TiO2 are 56.01 g and 59.68 g, respectively, reduced by 7.10% and 1.01% compared to that of blank cement mortar (60.29 g). When sewage corrosion time reaches 14 months, the mass losses are reduced from 71.11 g to 63.58 g and 69.93 g when 3 wt% and 5 wt% of nano SiO2 -coated TiO2 are incorporated, respectively. Image analysis was used to investigate the effect of nano SiO2 -coated TiO2 on the number and distribution of microorganisms on the surface of cement-based nanocomposites [32]. Figure 4.29 shows the alive/dead microorganisms distribution on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As seen in Fig. 4.29, the addition of nano SiO2 -coated TiO2 significantly reduced the number of live microorganisms on the surface of cement-based nanocomposites, indicating that nano SiO2 -coated TiO2 had a significant inhibitory effect on microorganisms. The microorganism distribution on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 is presented in Table 4.14. From Table 4.14, it can be seen that the nano SiO2 -coated TiO2 can effectively inhibit the attachment of alive microorganisms on the surface of cement-based nanocomposites. The alive microorganisms on the surface of cement-based nanocomposites with 3 wt% and 5 wt% of nano SiO2 -coated TiO2 are 0.35% and 0.18%, respectively, which is 61.59% and 80.93% lower than that of blank cement mortar. In addition, the elimination rates

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Fig. 4.29 Alive/dead microorganism distribution on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Alive and b Dead microorganism distribution on the surface of cement mortar without nano SiO2 -coated TiO2 . c Alive and d Dead microorganism distribution on the surface of cement-based nanocomposites with nano SiO2 -coated TiO2

of cement-based nanocomposites with 3 wt% and 5 wt% of nano SiO2 -coated TiO2 reach 37.35% and 35.07%, respectively. The number of alive microorganisms attached to the surface of cement-based nanocomposites with nano SiO2 -coated TiO2 is only 0.18%, which is much smaller Table 4.14 Microorganism distribution on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 Nano SiO2 -coated TiO2 content (wt% of cement)

Proportion of alive microorganisms (%)

Proportion of Death rate of dead microorganisms microorganisms (%) (%)

Inhibition rate of microorganism (%)

Elimination rate of microorganism (%)

0

0.49 ± 0.05

0.92 ± 0.40

38.25

–

–

3

1.09 ± 0.25

0.35 ± 0.09

75.61

61.59

37.35

5

0.52 ± 0.21

0.18 ± 0.02

73.32

80.93

35.07

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than the alive microorganisms attached to the surface of cement-based nanocomposites with dodecyl dimethyl benzyl ammonium chloride (1.33%), sodium bromide (0.45%), sodium tungstate (0.73%), sodium tungstate (0.81%), and copper phthalocyanine (0.21%) [33]. In addition, compounding nano SiO2 -coated TiO2 into cementbased nanocomposites could result in 37.35% microorganism elimination, which exceeds the elimination effect of other biocides, such as dodecyl dimethyl benzyl ammonium chloride (11.36%), sodium tungstate (12.21%) and copper phthalocyanine (25.88%) [33]. Meanwhile, the presence of nano SiO2 -coated TiO2 could result in 80.93% microorganism inhibition on the surface of cement-based nanocomposites, exceeding the effect of dodecyl dimethyl benzyl ammonium chloride (42.42%), sodium bromide (80.52%), zinc oxide (68.40%) and sodium tungstate (64.94%) on microorganism inhibition [33]. The inhibition and elimination effects of cement-based nanocomposites with nano SiO2 -coated TiO2 on microorganisms are mainly due to the following mechanisms. On the one hand, the cell membrane and cell wall of microorganisms are mainly composed of proteins, enzymes, lipids, peptidoglycans, etc., which have a large number of amino acids, peptide bonds, acylamides and unsaturated double bonds. The hydroxyl radicals generated by nano SiO2 -coated TiO2 can attack the peptide bonds and amino acids (as shown in Fig. 4.30). This in turn causes chain decomposition of proteins, peptidoglycans and phospholipids in microbial cell membranes and cell walls, which affects the permeability of microbial cell membranes and cell walls and causes leakage of important substances such as salts, proteins and nucleic acids from microorganisms leading to their death [34]. On the other hand, nano SiO2 -coated TiO2 can generate reactive oxygen species in the absence of photocatalytic reactions [35]. The reactive oxygen species cause microorganisms to undergo lipid peroxidation, producing substances such as malondialdehyde (MDA) and 4-hydroxynonenal (HNE) [36], leading to derangement of microbial metabolism and decreased immune function [37], causing cytopathy, fibrosis, and other damage. In addition, On the other hand, nano SiO2 -coated TiO2 can cause microorganisms to undergo envelope deformation and envelope penetration, reducing the replication ability of microorganisms [34], thus acting as an inhibitor of surface microbial attachment. Finally, nano SiO2 coated TiO2 induces oxidative stress in microorganisms, increasing the content of oxidative stress proteins and H2 O2 in microorganisms, and the cumulative effects of oxidative stress proteins and H2 O2 can impair microbial growth, prevent the transport of film-forming substances, and block the respiratory and electron transport systems of microorganisms [35]. Figure 4.31 shows the image of sewage corrosion of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . The discolored area on the surface of cement-based nanocomposites in Fig. 4.30 presents the corrosion area. Figure 4.32 shows the sewage corrosion depth of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . As depicted in Fig. 4.32, the addition of 3 wt% and 5 wt% of nano SiO2 -coated TiO2 can both reduce the sewage corrosion depth by 14.7%. This phenomenon indicates the nano SiO2 -coated TiO2 can increase the compactness of cement-based nanocomposites and reduce the porosity.

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Fig. 4.30 The reaction formula of hydroxyl radical attack. a peptide bond. b amino acid

Fig. 4.31 Image of sewage corrosion of cement-based nanocomposites without/with nano SiO2 coated TiO2

Figure 4.33 shows pH values at different sewage corrosion depth of cementbased nanocomposites without/with nano SiO2 -coated TiO2 . From Fig. 4.33, it can be found that the pH value in the depth range of 0–3, 3–6, 6–9 mm is 6.64–7.29, 7.07– 8.74, and 10.54–11.20, respectively. The pH value of cement-based nanocomposites under standard curing is 11.39. Therefore, it can be inferred that the cement-based nanocomposites was subjected to severe biological acid corrosion in the depth range of 0–6 mm and less biological acid corrosion in the depth range of 6–9 mm. In the 0–6 mm depth range subjected to severe bioacid corrosion, the nano SiO2 -coated TiO2 can effectively hinder the reduction of pH of cement-based nanocomposites in the corrosion depth range. In the 0–3 mm depth range, nano SiO2 -coated TiO2 can increase the pH of cement-based nanocomposites by 0.65/9.79%. In the depth

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Fig. 4.32 Sewage corrosion depth of cement-based nanocomposites without/with nano SiO2 -coated TiO2

range of 3–6 mm, nano SiO2 -coated TiO2 can increase the pH of cement-based nanocomposites by 0.88/12.46%. Figure 4.34 shows the morphology of cement-based nanocomposites without nano SiO2 -coated TiO2 after sewage corrosion. The organic and inorganic acids generated by the metabolism of microorganisms performing aerobic metabolism can react with the hydration products of cement-based nanocomposites, thus causing dissolved corrosion in the cement-based nanocomposites and making the materials thin internally [38]. In addition, organic and inorganic acids and alcohols generated by microbial metabolism can hinder the hydration reaction of cement and corrode C–S–H gels, resulting in the formation of a large number of C–S–H gels with holes inside cement-based nanocomposites [39], as shown in Fig. 4.34a. Microorganisms that carry out anaerobic metabolism such as sulfate-reducing bacteria can reduce Fig. 4.33 pH values at different sewage corrosion depth of cement-based nanocomposites without/with nano SiO2 -coated TiO2

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Fig. 4.34 Morphology of cement-based nanocomposites without nano SiO2 -coated TiO2 after sewage corrosion. a C–S–H gel. b Aft and gypsum. c Micro cracks. d Cement paste and aggregate

sulfate to sulfuric acid through biochemical reactions, and sulfuric acid will react with cement components to produce hydration products such as calcium alumina and gypsum, as shown in Fig. 4.34b. When the SO2− 4 concentration in cement is < 1000 mg/L, the deterioration of cement-based nanocomposites is mainly due to the generation of calcium alumina with swelling properties, which produces a large number of microscopic cracks in the cement-based nanocomposites [40], as shown in Fig. 4.34c. In addition, because aerobic microbial metabolism produces carbon dioxide and provides CO2− 3 ions when dissolved in water, sulfate also corrodes and decomposes the most important hydration product of cement, C–S–H gels, generating silica-cement gypsum (Thaumasite, CaO–SiO2 –CaCO3 –CaSO4 –15H2 O) [41]. Silica-ash gypsum is also expansive, and its growth causes expansion pressure on the cement stone, impairing the bond between the cement paste and the aggregate, leading to mutual peeling of the paste aggregate, as shown in Fig. 4.34d. Owing to its nucleation, filling, self-curing and core effects, nano SiO2 -coated TiO2 can improve the compactness of cement-based nanocomposites, reduce the microscopic cracks inside the materials, and decrease the corrosion effect of harmful substances in materials. In addition, nano SiO2 -coated TiO2 has

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151

inhibiting/elimination properties for microorganisms, which can reduce the corrosion of cement-based nanocomposites by bioacids and other metabolites produced by microorganism metabolism at the source, and thus improve the resistance of the materials to sewage corrosion.

4.5.4 Anti-Seawater-Corrosion Properties Figure 4.35 shows the compressive and flexural strength of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after 21 months of seawater attack. It can be seen from Fig. 4.35 that nano SiO2 -coated TiO2 has positive effect on the compressive and flexural strength of cement-based nanocomposites after 21 months of seawater corrosion. The compressive strength increases by 15.6% and 6.7% after adding 3 wt% and 5 wt% of nano SiO2 -coated TiO2 , respectively. The flexural strengths of cement-based nanocomposites with 3 wt% and 5 wt% of nano SiO2 coated TiO2 increase by 14.36% and 10.75%, respectively, compared with that of blank cement mortar. This indicates that nano SiO2 -coated TiO2 can improve or even eliminate the corrosion effect of seawater on cement-based nanocomposites. The shrinkage coefficients of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater immersion are listed in Table 4.15. It can be found from Table 4.15 that the shrinkage coefficient of cement-based nanocomposites in the seawater is small. On the one hand, Na+ and K+ ions in seawater enter the interior of cement-based nanocomposites through pores or cracks and react with alkaline substances and SiO2 to generate alkali silica gels. After absorbing water, the volume of alkali silicate gel can expand to more than 3 times, and a large number of expansive gels will gather inside the cement-based nanocomposites, which will cause the cement-based nanocomposites to expand. On the other hand, SIO2− 4 ions in seawater may enter the interior of cement-based nanocomposites through pores or Fig. 4.35 Compressive and flexural strength of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater corrosion

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Table 4.15 Shrinkage coefficients of cement-based nanocomposites without/with nano SiO2 coated TiO2 after seawater immersion Dimension (mm) Nano SiO2 -coated TiO2 content (wt% of cement)

Average Shrinkage (mm) coefficient

0

40.51

41.08 40.78 42.65 40.68 40.73 40.51 40.71 40.956

−0.001

3

40.36

40.40 40.82 41.23 40.66 40.54 41.10 41.58 40.836

−0.000

5

40.60

40.47 41.42 40.96 40.83 41.12 40.23 40.68 40.789

0.001

cracks and react with CH crystals in the cement-based nanocomposites to generate expansive substance, which may continue to react with the interior of the cement specimen to generate expansive ettringite. Therefore, the shrinkage coefficient of cement-based nanocomposites without/with nano SiO2 -coated TiO2 is quite low. Table 4.16 lists the apparent density of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater immersion. In general, the apparent density of cement-based nanocomposites decreases after seawater erosion. On the one hand, the flowing seawater will impact and scour cement-based nanocomposites, resulting in the loss of paste sand and gravel on the cement-based nanocomposites surface. On the other hand, when sulfate ions in seawater enter cement-based nanocomposites, they will react with cement hydration products. The expansive reaction products, such as ettringite and gypsum, are formed and lead to microcracks caused by expansion stress in cement-based nanocomposites. The hydration products may gradually flow outward with the microcracks, leading to the decrease of apparent density. After adding nano SiO2 -coated TiO2 , it can increase the compactness of cement-based nanocomposites, as well as hinder the occurrence and development of internal microcracks. Thanks to these effects, the presence of nano SiO2 coated TiO2 can increase the apparent density of cement-based nanocomposites after seawater immersion. The biofilm morphology within 50 μm depth was tested using a laser confocal scanning microscope, and a three-dimensional structure map of the biofilm was generated. Figures 4.36, 4.37 and 4.38 and Table 4.17 shows the relationship between biofilm thickness and porosity of the biofilm surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . It can be seen from Figures 4.36, 4.37 and Table 4.16 Apparent density of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater immersion Nano SiO2 -coated TiO2 content (wt% of cement)

Average mass (g)

Average volume (cm3 )

Apparent density (g/cm3 )

0

560.37

274.80

2.04

3

565.70

272.39

2.08

5

561.20

271.45

2.08

4.5 Functional/Smart Properties of Cement-Based Nanocomposites …

153

4.38; Table 4.17, the addition of nano SiO2 -coated TiO2 greatly reduce the thickness of biofilm. The biofilm thickness of cement-based nanocomposites reduces by 13.51 μm/22.38% and 29.66 μm/49.13% when 3 wt% and 5wt% of nano SiO2 coated TiO2 are incorporated, respectively. This phenomenon confirms the nano SiO2 -coated TiO2 can exert inhibition/elimination effects on microorganisms, thus reducing the generation of biofilm. To verify inhibition/elimination effect of nano SiO2 -coated TiO2 on microorganisms, the microorganisms in the biofilm on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 were tested, as shown in Fig. 4.39. It can be seen from Fig. 4.39 that the addition of nano SiO2 -coated TiO2 causes a significant decrease in the number of live microorganisms on the surface of cementbased nanocomposites and a significant increase in the number of dead microorganisms. The distribution of microorganisms in the biofilm on the surface of cementbased nanocomposites after seawater corrosion is presented in Table 4.18. It can be seen from Table 4.18 that nano SiO2 -coated TiO2 can significantly improve the inactivation performance of the specimens against microorganisms in seawater. The inhibition/elimination rate of microorganisms reaches 70.69%/84.31% and

Fig. 4.36 Thickness of biofilm on the surface of blank cement mortar

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4 New-Generation Cement-Based Nanocomposites with Nano …

Fig. 4.37 Thickness of biofilm on the surface of cement-based nanocomposites with 3 wt% of nano SiO2 -coated TiO2

76.98%/96.81% when 3 wt% and 5 wt% of nano SiO2 -coated TiO2 is incorporated, respectively. Figure 4.40 shows the pH values of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at different depths after seawater corrosion. As seen in Fig. 4.40, the pH value of cement-based nanocomposites soaked in seawater is smaller than that of cement-based nanocomposites as the sulfate in seawater penetrates into the interior of cement-based nanocomposites and neutralize some of alkaline substance, resulting in a lower pH value. The bio-acid produced by the metabolism of microorganisms may enter into cement-based nanocomposites, thus corroding the cement-based nanocomposites and lowering the pH value. In addition, the presence of nano SiO2 -coated TiO2 increases the pH of cement-based nanocomposites in the range of 0–3 mm by 0.81/7.83%. Figure 4.41 shows the molar ratio of Si/Ca and Al/Ca of cement-based nanocomposites without/with nano SiO2 -coated TiO2 , in which AV indicates the average value of the data points representing the most likely location of the data points. It can be seen from Fig. 4.34 that C–S–H, CH, and AFm phases are observed in both cementbased nanocomposites without/with nano SiO2 -coated TiO2 . The presence of nano SiO2 -coated TiO2 increases the molar ratio of Si/Ca of C–S–H phases, leading to

4.5 Functional/Smart Properties of Cement-Based Nanocomposites …

155

Fig. 4.38 Thickness of biofilm on the surface of cement-based nanocomposites with 5 wt% of nano SiO2 -coated TiO2

Table 4.17 The thickness of biofilm on the surface of cement-based nanocomposites

Nano SiO2 -coated TiO2 content (wt% of cement)

Thickness of biofilm (μm)

0

60.37

3

46.86

5

30.71

C–S–H gels with greater polymerization and longer chain length in cement-based nanocomposites [42]. Table 4.19 lists the elemental distribution at the edges of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater corrosion. It can be seen from Table 4.19 that the atomic percentages of element Ca decrease and the atomic percentages of element Si increase after adding nano SiO2 -coated TiO2 , indicating that the presence of nano SiO2 -coated TiO2 can promote the decalcification of C–S–

156

4 New-Generation Cement-Based Nanocomposites with Nano …

Fig. 4.39 Microorganisms distribution in the biofilm on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 . a Alive and b Dead microorganism distribution on the surface of cement mortar without nano SiO2 -coated TiO2 . c Alive and d Dead microorganism distribution on the surface of cement-based nanocomposites with nano SiO2 -coated TiO2 Table 4.18 The distribution of microorganisms on the surface of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater corrosion Nano SiO2 -coated TiO2 content (wt% of cement)

Proportion of alive microorganisms (%)

Proportion of Death rate of dead microorganisms microorganisms (%) (%)

Inhibition rate of microorganism (%)

Elimination rate of microorganism (%)

0

1.28 ± 0.30

5.60 ± 1.94

18.61

–

–

3

7.33 ± 1.58

0.88 ± 0.34

89.30

70.69

84.31

5

3.87 ± 4.07

0.18 ± 0.19

95.59

76.98

96.81

4.5 Functional/Smart Properties of Cement-Based Nanocomposites …

157

Fig. 4.40 pH value of cement-based nanocomposites without/with nano SiO2 -coated TiO2 at different depths after seawater corrosion

Fig. 4.41 Molar ratio of Al/Ca and Si/Ca of phases in cement-based nanocomposites without/with nano SiO2 -coated TiO2 : a Without nano SiO2 -coated TiO2 ; b With nano SiO2 -coated TiO2

H gels in cement-based nanocomposites under seawater corrosion as well as increase the polymerization and chain length of C–S–H gels. In addition, the atomic percentages of elemental Cl, S, K, Na, and Fe reduces from 1.00%, 1.94%, 1.37%, 1.02%, and 2.57% to 0.63%, 1.28%, 0.80%, 0.90%, and 1.01%, respectively, after adding 5 wt% of nano SiO2 -coated TiO2 . This phenomenon, on the one hand, derives from the higher density of cement mortar with nano SiO2 -coated TiO2 , which can hinder the penetration and diffusion of ions from seawater into the interior of cement-based nanocomposites. On the other hand, nano SiO2 -coated TiO2 particles can reduce the formation of calcium sulfate, magnesium chloride, hydrated calcium aluminate, and calcium alumina by the adsorption of Mg2+ , Al3+ , K+ , Na+ and Fe2+ ions due to their negative charge.

47.50

36.27 16.49

0

5 71.82

Si 0.63

1.00

Cl

Percentage of element (%) Ca

Nano SiO2 -coated TiO2 content (wt% of cement)

1.28

1.94

S 1.78

1.36

Mg 3.49

6.97

Al

0.80

1.37

K

0.90

1.02

Na

1.01

2.57

Fe

0.50

–

P

Table 4.19 Elemental distribution at the edges of cement-based nanocomposites without/with nano SiO2 -coated TiO2 after seawater corrosion

1.30

–

Ti

158 4 New-Generation Cement-Based Nanocomposites with Nano …

4.6 Summary

159

4.6 Summary This chapter introduces a new-generation cement-based nanocomposites with nano SiO2 -coated TiO2 . The rheology, static/dynamic mechanical properties as well as functional/smart properties of the developed nanocomposites are presented. The conclusions can be summarized as below. (1) The presence of nano SiO2 -coated TiO2 notably influences the rheology of cement-based nanocomposites. The yield stress of cement-based nanocomposites increases with the content of nano SiO2 -coated TiO2 . The addition of 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1.4 wt% of nano SiO2 -coated TiO2 increases the yield stress of cement-based nanocomposites by 27.7%, 28.6%, 32.7%, 44.5%, and 151.2%, respectively. The minimum viscosity of cementbased nanocomposites with 0.1–0.7 wt% of nano SiO2 -coated TiO2 is similar with the composites without nano SiO2 -coated TiO2 , in contrast, the minimum viscosity reaches 0.417 Pa·s after incorporating 1.4 wt% of nano SiO2 -coated TiO2 . Besides, the cement-based nanocomposites with nano SiO2 -coated TiO2 is still a shear-thickening fluid, indicating the presence of nano SiO2 -coated TiO2 does not change the shear-thickening characteristics of cement-based nanocomposites. (2) The presence of nano SiO2 -coated TiO2 significantly increases the mechanical properties of cement-based nanocomposites. The compressive and flexural strength can maximumly increase by 12.26% and 87.00% after adding nano SiO2 -coated TiO2 . Moreover, the fatigue life of cement-based nanocomposites can maximumly increase by 41.3% when nano SiO2 -coated TiO2 is incorporated. The fatigue limit of cement-based nanocomposites with nano SiO2 -coated TiO2 increases by 19.4%. The dynamic compressive strength of cement-based nanocomposites with nano SiO2 -coated TiO2 at the strain rate of 200/500/800 s−1 increases by 55.3%/58.9%/12.1%, respectively. The impact toughness and impact dissipation energy respectively increase by 60.7–105.3% and 8.6–55.6% after adding nano SiO2 -coated TiO2 . Besides, the bond strengths between new and old cement mortars, cement mortar and steel bar as well as cement mortar and FRP bar can maximumly increase by 27.8%, 16.0%, and 14.0%, respectively, after adding nano SiO2 -coated TiO2 . (3) Thanks to its core–shell structures, nano SiO2 -coated TiO2 shows good dispersibility due to the Ti–O–Si bond forming from SiO2 coating. Moreover, nano SiO2 -coated TiO2 tends to move toward the interfaces in cementbased nanocomposites, forming enrichment layer in the interfaces. The welldispersed nano SiO2 -coated TiO2 notably modifies the hydration products by increasing the hydration degree of cement, reducing the size of CH in cementbased nanocomposites, and the polymerization of silicon oxide tetrahedron of C–S–H in the nanocomposites. In addition, the presence of nano SiO2 -coated TiO2 optimizes the pore structures of cement-based nanocomposites. (4) Cement-based nanocomposites with nano SiO2 -coated TiO2 possess excellent functional/smart properties. The cement-based nanocomposites show obvious

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4 New-Generation Cement-Based Nanocomposites with Nano …

self-healing properties. After curing in water, the nanocomposites can be restored to its strength before pre-loading. At the frequency of 18 GHz, the electromagnetic shielding effectiveness and minimum reflectivity of cement-based nanocomposites with nano SiO2 -coated TiO2 reaches 2.45 dB and 15.89 dB, respectively increased by 25% and 86.07% compared with blank cement-based composites. Moreover, the addition of nano SiO2 -coated TiO2 endows cementbased nanocomposites with good anti-corrosion properties. On the one hand, the cement-based nanocomposites with dense microstructures can inhibit the harmful substance into the nanocomposites. The presence of nano SiO2 -coated TiO2 , on the other hand, can inhibit and eliminate microorganisms on the surface of the nanocomposites due to photocatalytic effect of nano TiO2 . In summary, nano SiO2 -coated TiO2 filled cement-based nanocomposites shows both excellent mechanical properties and outstanding anti-corrosion performances. These merits allow the developed nanocomposites to be widely used not only in large-scale infrastructures requiring high-performance cement-based materials but also in sewage, marine, health care, and education infrastructures calling for corrosion inhibition or sterilization/virus killing.

References 1. Z. Li, S. Ding, X. Yu, B. Han, J. Ou, Multifunctional cementitious composites modified with nano titanium dioxide: A review. Compos. A Appl. Sci. Manuf. 111, 115–137 (2018) 2. B. Han, XYu.J. Ou, Self-Sensing Concrete in Smart Structures (Elsevier, Netherlands, 2014) 3. X. Wang, S. Dong, A. Ashour, B. Han, Energy-harvesting concrete for smart and sustainable infrastructures. J. Mater. Sci. 56, 1–35 (2021) 4. K. Demeestere, J. Dewulf, B.D. Witte, A. Beeldens, H.V. Langenhove, Heterogeneous photocatalytic removal of toluene from air on building materials enriched with TiO2 . Build. Environ. 43, 406–414 (2008) 5. E. Mohseni, B.M. Miyandehi, J. Yang, M.A. Yazdi, Single and combined effects of nanoSiO2 , nano-Al2 O3 and nano-TiO2 on the mechanical, rheological and durability properties of self-compacting mortar containing fly ash. Constr. Build. Mater. 84, 331–340 (2015) 6. A. Rahim, S.R. Nair, Influence of nano-materials in high strength concrete. J. Chem. Pharm. Sci. 974, 15–21 (2016) 7. A. Nazari, S. Riahi, The effect of TiO2 nanoparticles on water permeability and thermal and mechanical properties of high strength self-compacting concrete. Mater. Sci. Eng., A 528, 756–763 (2010) 8. B. Ma, H. Li, J. Mei, X. Li, F. Chen, Effects of nano-TiO2 on the toughness and durability of cement-based material. Adv. Mater. Sci. Eng. 65, 583106 (2015) 9. L.Y. Yang, Z.J. Jia, Y.M. Zhang, J.G. Dai, Effects of nano-TiO2 on strength, shrinkage and microstructure of alkali activated slag pastes. Cement Concr. Compos. 57, 1–7 (2015) 10. F. Soleymani, Assessments of the effects of limewater on water permeability of TiO2 nanoparticles binary blended palm oil clinker aggregate-based concrete, Journal of American. Science 8, 698–702 (2012) 11. M. Jalal, M. Fathi, M. Farzad, Effects of fly ash and TiO2 nanoparticles on rheological, mechanical, microstructural and thermal properties of high strength self compacting concrete. Mech. Mater. 61, 11–27 (2013)

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12. G.L. Guerrini, E. Peccati, Photocatalytic cementitious Roads for Depollution (Newsletter, 2016) 13. G. Xiong, Cement-based Composite Material for Microwave Absorbing (Nanjing University of Technology) 14. X. Wang, Q. Zheng, S. Dong, A. Ashour, B. Han, Interfacial characteristics of nano-engineered concrete composites. Constr. Build. Mater. 259, 119803 (2020) 15. X. Wang, S. Dong, A. Ashour, W. Zhang, B. Han, Effect and mechanisms of nanomaterials on interface between aggregates and cement mortars. Constr. Build. Mater. 240, 117942 (2020) 16. A. Jaroenworaluck, W. Sunsaneeyametha, N. Kosachan, R. Stevens, Characteristics of silicacoated TiO2 and its UV absorption for sunscreen cosmetic applications, Surface and Interface. Analysis 38, 473–477 (2010) 17. C. Chen, W. Wu, W.Z. Xu, P.A. Charpentier, The effect of silica thickness on nano TiO2 particles for functional polyurethane nanocomposites. Nanotechnology 28, 115709 (2017) 18. O.K. Park, Y.S. Kang, B.G. Jo, Synthesis of TiO2 nanoparticles coated with SiO2 for suppression of photocatalytic activity and increased dispersion stability. J. Ind. Eng. Chem. 10, 733–738 (2004) 19. Y.L. Liu, C.C. Cao, J. Chen, Preparation of photocatalyst of nano-TiO2 coating on SiO2 carrier and its photocatalytic activity. Adv. Mater. Res. 777, 77–81 (2013) 20. A.N. Givi, S.A. Rashid, F.N.A. Aziz, M.A.M. Salleh, Experimental investigation of the size effects of SiO2 nano-particles on the mechanical properties of binary blended concrete. Compos. B Eng. 41, 673–677 (2020) 21. E. Ghafari, H. Costa, E. Júlio, A. Portugal, L. Durães, The effect of nanosilica addition on flowability, strength and transport properties of ultra high performance concrete. Mater. Des. 59, 1–9 (2014) 22. H. Li, S. Ding, L. Zhang, J. Ouyang, B. Han, Effects of particle size, crystal phase and surface treatment of nano-TiO2 on the rheological parameters of cement paste. Constr. Build. Mater. 239, 117897 (2020) 23. F.D. Larrard, C.F. Ferraris, T. Sedran, Fresh concrete: a Herschel-Bulkley material. Mater. Struct. 31, 494–498 (1998) 24. P.V.R.K. Reddy, D.R. Prasad, A study on workability, strength and microstructure characteristics of graphene oxide and fly ash based concrete. Materials Today: Proceedings. 62, 2919–2925 (2022) 25. B. Han, S. Ding, J. Wang, J. Ou, Nano-Engineered Cementitious Composites: Principles and Practices (Springer, Singapore, 2019) 26. G. Kaur, S.P. Singh, S.K. Kaushik, Influence of mineral additions on flexural fatigue performance of steel fibre reinforced concrete. Mater. Struct. 49, 4101–4111 (2016) 27. K.S. Yeon, Y.S. Choi, K.K. Kim, J.H. Yeon, Flexural fatigue life analysis of unsaturated polyester-methyl methacrylate polymer concrete. Constr. Build. Mater. 140, 336–343 (2017) 28. F. Liu, L. Meng, G. Ning, L. Li, Fatigue performance of rubber-modified recycled aggregate concrete (RRAC) for pavement. Constr. Build. Mater. 95, 207–217 (2015) 29. B. Han, Z. Li, L. Zhang, S. Zeng, X. Yu, B. Han, J. Ou, Reactive powder concrete reinforced with nano SiO2 -coated TiO2 . Constr. Build. Mater. 148, 104–112 (2017) 30. Z. Wang, Y. Liu, R.F. Shen, Stress-strain relationship of steel fiber-reinforced concrete under dynamic compression. Constr. Build. Mater. 22, 811–819 (2008) 31. J.P. Fu, J.L. Yang, L.K. Yin, Z. Chen, Dynamic properties of zirconia ceramic bullets under high-speed impact. J. Chinese Ceram. Soc. 44, 346–352 (2016) 32. L. Kong, J. Fang, Z. Wu, B. Zhang, Evaluation of the effect of surface coatings on protection of concrete against sewage-induced degradation based on gray correlation analysis. J. Coat. Technol. Res. 15, 1311–1323 (2018) 33. L. Kong, B. Zhang, J. Fang, Effect of bactericide on the deterioration of concrete against sewage. J. Mater. Civ. Eng. 30, 04018160 (2018) 34. F. Meng, Z. Li, Pharmaceutical Chemistry (China Pharmaceutical Science and Technology Press, 2016)

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35. J. Jenkins, J. Mantell, C. Neal, A. Gholinia, P. Verkade, A.H. Nobbs, B. Su, Antibacterial effects of nanopillar surfaces are mediated by cell impedance, penetration and induction of oxidative stress. Nat. Commun. 11, 1626 (2020) 36. P. Maness, S. Smolinski, D.M. Blake, Z. Huang, E. Wolfrum, W.A. Jacoby, Bactericidal activity of photocatalytic TiO2 reaction: Toward an understanding of its killing mechanism. Appl. Environ. Microbiol. 65, 4094–4098 (1999) 37. W. Duan, Investigation on the Sterilization Properties of TiO2 Nanoparticles and Nanocomposites (Wuhan University of Technology, 2011) 38. P. Zhang, Application and Optimization of Bactericide in Concrete Under Sewage Environment (Shijiazhuang Tiedao University. 2018) 39. X. Zhang, X. Zhang, Mechanism and research approach of microbial corrosion of concrete. J. Build. Mater. 01, 52–58 (2006) 40. M.D. Cohen, Mather B, Sulfate attack on concrete: research needs. ACI Mater. J. 88, 62–69 (1991) 41. Z. Wu, H. Lian, High Performance Concrete (China Railway Press, 1999) 42. H.K. Kim, I.W. Nam, H.K. Lee, Enhanced effect of carbon nanotube on mechanical and electrical properties of cement composites by incorporation of silica fume. Compos. Struct. 107, 60–69 (2014)

Chapter 5

New-Generation Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT

5.1 Introduction CNT is easy to aggregation and entanglement owing to its high surface energy, which undermines the modification effect and wide application of CNT in cementbased composites [1–3]. Compounding nano carbon black (NCB) with CNT is a promising approach for improving CNT dispersion difficulties. The NCB with bigger particle size can separate CNT and prevent CNT from aggregation and entanglement [4, 5]. Moreover, NCB possesses excellent conductivity. The unique grape string structure of NCB/CNT can exert synergistic conductive effect, which is beneficial to the functional/smart properties/performance of cement-based nanocomposites with NCB/CNT [6, 7]. In this chapter, a new-generation cement-based nanocomposite with NCB/CNT is introduced. The self-sensing properties together with mechanical, electrical and electromagnetic shielding and absorption properties are presented. Finally, the feasibility of using dynamic responses deriving from the cement-based nanocomposite sensors for modal-based damage detection is verified and the potential application of cement-based nanocomposites with NCB/CNT for oil well infrastructures is demonstrated.

5.2 Preparation of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT The raw materials used to fabricate cement-based nanocomposites with NCB/CNT include Portland cement, silica fume, standard quartz sand, SP, and 2 types of NCB/CNT. The CNT with different aspect ratio were used to prepare NCB/CNT. The properties and morphology of NCB/CNT are shown in Table 5.1 and Fig. 5.1, respectively. The properties of other raw materials refer to Sect. 2.2. The mix proportion and fabrication process of cement-based nanocomposites in this chapter are © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_5

163

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5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Table 5.1 Properties of NCB/CNT Code

NCB:CNT (mass ratio)

Conductivity (Ω cm)

S-NCB/CNT

60:40

~ 10–3

65–75

> 50

L-NCB/CNT

60:40

< 0.01

540–560

10–30

Specific surface Outer area of CNT diameter of (m2 /g) CNT (nm)

Specific surface area of NCB (m2 /g) 23 934

shown in Tables 5.2 and 5.3, respectively. It is noted that the content of water and SP was adjusted with the NCB/CNT content to obtain good workability of fresh cement-based nanocomposites.

Fig. 5.1 Morphology of NCB/CNT. a S-NCB/CNT. b L-NCB/CNT

Table 5.2 Mix proportions of cement-based nanocomposites without/with NCB/CNT (mass ratio) Cement

Silica fume

Water

Sand

SP

S-NCB/CNT (vol.%)

L-NCB/CNT (vol.%)

0.9

0.1

0.42

1.5

0

0

–

0.9

0.1

0.42

1.5

0

0.39

–

0.9

0.1

0.42

1.5

0.01

0.77

–

0.9

0.1

0.42

1.5

0.02

1.52

–

0.9

0.1

0.56

1.5

0.025

2.40

–

0.9

0.1

0.70

1.5

0.025

3.12

–

0.9

0.1

0.42

1.5

0

–

0.39

0.9

0.1

0.42

1.5

0.014

–

0.77

0.9

0.1

0.48

1.5

0.037

–

1.41

0.9

0.1

0.72

1.5

0.054

–

2.14

5.3 Mechanical Properties of Cement-Based Nanocomposites …

165

Table 5.3 Fabrication process of cement-based nanocomposites without/with NCB/CNT Dispersion method

Shear mixing + non-covalent surface modification by SP

Fabrication process Feeding order

Technology

Molding

Method

Time (s)

Method

Size (mm)

Method

Time (d)

NCB/CNT + Silica fume

Shear mixing (140 r/min)

30

Vibration

40 × 40 × 160

Standard condition

1

Water + SP

Shear mixing (140 r/min)

30

W (20 °C)

~ 80

Half of cement

Shear mixing (140 r/min)

60

Shear mixing (285 r/min)

30

Shear mixing (140 r/min)

60

Shear mixing (285 r/min)

30

Half of cement

Curing

5.3 Mechanical Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT 5.3.1 Compressive Strength Figure 5.2 shows the compressive strength of cement-based nanocomposites without/with NCB/CNT. As shown in Fig. 5.2, the presence of NCB/CNT undermines the compressive strength of cement-based nanocomposites. The compressive strength of cement-based nanocomposites reduced by 11.1, 13.7, 7.7, 17.5, and 18.4% when 0.39 vol.% of S-NCB/CNT, 0.77 vol.% of S-NCB/CNT, 1.52 vol.% of S-NCB/CNT, 0.39 vol.% of L-NCB/CNT, and 0.77 vol.% of L-NCB/CNT were incorporated, respectively. However, the reduced compressive strength can still reach

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5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.2 Compressive strength of cement-based nanocomposites without/with NCB-CNT. a Without/with (a) S-NCB/CNT. b Without/with (a) L-NCB/CNT

approximate 60 MPa. Such reduction may stem from the NCB that adsorbs on the surface of binder grains and inhibits the hydration of binders.

5.3.2 Flexural Strength Figure 5.3 shows the flexural strength of cement-based nanocomposites without/with NCB/CNT. For the cement-based nanocomposites with S-NCB/CNT, the flexural strength of cement-based nanocomposites firstly decreases and then increases with the S-NCB/CNT content. The flexural strength of cement-based nanocomposites with 1.52 vol.% of S-NCB/CNT reaches 7.1 MPa, increased by 18.3% compared with blank cement-based composites. Meanwhile, the addition of L-NCB/CNT slightly increases the flexural strength at a low content, but decrease the flexural strength at a high content, as shown in Fig. 5.3b.

5.3.3 Modification Mechanisms Figure 5.4 shows the SEM images that indicate the modification mechanisms of NCB/CNT on cement-based nanocomposites. It can be seen from Fig. 5.4 that the NCB/CNT can exert bridging effect during fracture process. This may also explain the addition of NCB/CNT shows stronger modifying effect on flexural strength than on compressive strength of cement-based nanocomposites.

5.3 Mechanical Properties of Cement-Based Nanocomposites …

167

Fig. 5.3 Flexural strength of cement-based nanocomposites without/with NCB-CNT. a With SNCB/CNT. b With L-NCB/CNT

Fig. 5.4 SEM images of cement-based nanocomposites with NCB/CNT. a Cracking bridging of S-NCB/CNT. b S-NCB/CNT pull out. c Cracking bridging of L-NCB/CNT. d L-NCB/CNT pull out

168

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

5.4 Functional/Smart Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT 5.4.1 Electrical Properties Figure 5.5 shows the DC resistivity of cement-based nanocomposites without/with NCB/CNT at different curing ages. The DC resistivity decreases with the NCB/CNT content. At the content between 0.39 and 1.52 vol.%, the DC resistivity of cementbased nanocomposites decreases sharply with increasing NCB/CNT content; While the DC resistivity changed little when the NCB/CNT content was smaller than 0.39 vol.% or larger than 1.52 vol.%. Therefore, the percolation interval of cementbased nanocomposites with NCB/CNT is 0.39–1.52 vol.%. When 1.52 vol.% of S-NCB/CNT/L-NCB/CNT was incorporated, the DC resistivity of cement-based nanocomposites decreases by 95.1%/99.8%, 96.2%/99.8%, and 95.3%/99.8% at 3, 7, and 28 d, respectively. In addition, the DC resistivity does not change significantly with the curing age. Figure 5.6 shows the AC resistivity of cement-based nanocomposites without/with NCB/CNT. The AC resistivity shows similar trend with DC resistivity. The percolation interval of cement-based nanocomposites with S-NCB/CNT and L-NCB/CNT is 0.39 vol.%–1.52 vol.% and 0.39 vol.%–1.41 vol.%, respectively. The AC resistivity of cement-based nanocomposites slightly decreases with the increase of the test frequency, especially the doping levels of NCB/CNT being less than 0.39 vol.% of NCB/CNT. This is mainly due to the fact that the polarization phenomenon is more pronounced in cement-based nanocomposites with low content of NCB/CNT. AC impedance spectra and equivalent circuits were used to analyze the conductivity mechanism of cement-based nanocomposites with NCB/CNT. In the blank cement-based composites, the bulk cement matrix, pore solution and electrode affect

Fig. 5.5 DC electrical resistivity of cement-based nanocomposites without/with NCB/CNT. a With S-NCB/CNT. b With L-NCB/CNT

5.4 Functional/Smart Properties of Cement-Based Nanocomposites …

169

Fig. 5.6 AC electrical resistivity of cement-based nanocomposites without/with NCB/CNT. a With S-NCB/CNT. b With L-NCB/CNT

the AC impedance spectrum. Hence the equivalent circuit can be viewed as a series connection of three parts: pore solution Rs , bulk cement matrix (capacitor original Q1 and resistor R1 ) and electrode (capacitor original Q2 and resistor R2 ), denoted as Rs (Q1 R1 )(Q2 R2 ), as shown in Fig. 5.7a. In cement-based nanocomposites with NCB/CNT, the bulk cement matrix, the pore solution, the electrodes and the conductive NCB/CNT affect the AC impedance spectrum. The equivalent resistance at this point can be considered as a four-part series connection of the pore solution Rs , the bulk cement matrix (capacitor original Q1 and resistance R1 ), the electrode (capacitor original Q2 and resistance R2 ) and the conductive NCB/CNT (capacitor original Q3 and resistance R3 ), denoted as Rs (Q1 R1 )(Q2 R2 ) (Q3 R3 ), as shown in Fig. 5.7b. As in the analysis above, the measured AC impedance spectra are fitted to the equivalent circuits of Rs (Q1 R1 )(Q2 R2 ) for the blank cement-based composites and Rs (Q1 R1 )(Q2 R2 ) (Q3 R3 ) for the cement-based nanocomposites with NCB/CNT. The measured and fitted values of the AC impedance spectrum are represented by Nyquist plots, as shown in Figs. 5.8 and 5.9. As shown in Figs. 5.8 and 5.9, all the Chi-squared values are less than or equal to 8.94 × 10–4 . This indicates that the iterative error

Fig. 5.7 The equivalent circuits of cement-based nanocomposites without/with NCB/CNT. a Without NCB/CNT. b With NCB/CNT

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between the measured and fitted AC impedance values is small, showing the selected equivalent circuit can accurately describe the composite AC impedance spectra. It can be seen from Figs. 5.8 and 5.9, the topology of AC impedance spectra of cement-based nanocomposites with S-NCB/CNT and L-NCB/CNT remains stable when the S-NCB/CNT and L-NCB/CNT content exceed 1.52 vol.% and 1.41 vol.%, respectively. This indicates that the conductive network has formed in cement-based nanocomposites. The AC impedance spectrum of the blank cement-based composites consists of two parts: a circular arc in the high frequency band and a straight line

Fig. 5.8 AC impedance spectra of cement-based nanocomposites without/with S-NCB/CNT. a Without S-NCB/CNT. b With 0.39 vol.% of S-NCB/CNT. c With 0.77 vol.% of S-NCB/CNT. d With 1.52 vol.% of S-NCB/CNT. e With 2.40 vol.% of S-NCB/CNT. f With 3.12 vol.% of S-NCB/CNT

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Fig. 5.9 AC impedance spectra of cement-based nanocomposites without/with L-NCB/CNT. a Without L-NCB/CNT. b With 0.39 vol.% of L-NCB/CNT. c With 0.77 vol.% of L-NCB/CNT. d With 1.41 vol.% of L-NCB/CNT. e With 2.14 vol.% of L-NCB/CNT

in the low frequency band. With the increase of NCB/CNT content, the arc in the high-frequency band gradually decreases until it disappears, while the linear part in the low-frequency band gradually becomes a circular arc. These changes indicate the change of the conductive network in cement-based nanocomposites. When the content of NCB/CNT exceeds 0.77 vol.%, the linear part of the low frequency band disappears and becomes a circular arc, implying the AC impedance is controlled by

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charge diffusion to electron conductivity and the NCB/CNT has played a major role in the conductivity.

5.4.2 Self-Sensing Properties Figures 5.10 and 5.11 show the relationship between the resistivity rate of change and stress/strain for cement-based nanocomposites without/with NCB/CNT under seven cyclic loads with a maximum loading amplitude of 8 MPa. It can be seen from Fig. 5.10a–d that the resistivity rate of change and stress/strain do not show a regular change with stress/strain, but fluctuate up and down around 0%. This indicates the blank cement-based composites and cement-based nanocomposites with 0.39 vol.% of S-NCB/CNT shows no significantly self-sensing properties. As can be seen from Fig. 5.10e–l, the resistivity variation of cement-based nanocomposites increases with increasing stress/strain and decreases with decreasing stress/strain with no polarization, showing good synchronization and repeatability. As shown in Fig. 5.10l, the maximum resistivity change of cement-based nanocomposites reaches −22.18% after adding 2.40 vol.% of S-NCB/CNT. As for cement-based nanocomposites with L-NCB/CNT, the resistivity rate of change and stress/strain changes little with stress/strain when the L-NCB/CNT content is less than 0.77 vol.%. After the content of L-NCB/CNT exceeds 1.41 vol.%, the synchronization and repeatability of self-sensing properties of cement-based nanocomposites are greatly improved. The maximum resistivity change of cement-based nanocomposites with 1.41 vol.% of L-NCB/CNT reaches −13.38%, as shown in Fig. 5.11k. Figures 5.12 and 5.13 show the stress/strain sensitivity of cement-based nanocomposites without/with S-NCB/CNT and L-NCB/CNT, respectively. The stress and strain sensitivity of cement-based nanocomposites with NCB/CNT both tend to increase and then decrease with increasing NCB/CNT content. The stress/strain sensitivity of cement-based nanocomposites can reach 2.69%/MPa/704 and 3.21%/MPa/521 when 2.40 vol.% of S-NCB/CNT and 2.40 vol.% of LNCB/CNT are incorporated, respectively. Table 5.4 compares the sensitivity of different self-sensing cement-based nanocomposites with CNT or/and NCB. As shown in Table 5.4, the cement-based nanocomposites with NCB/CNT possesses the highest stress and strain sensitivity compared to that with CNT or NCB alone. This shows the great potential of NCB/CNT for self-sensing cement-based nanocomposites. Figure 5.14 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT under 7 times of cyclic loading with stress amplitudes of 6, 8 and 10 MPa. It can be seen from Fig. 5.14a–f that the resistivity rate of change exhibits good synchronization and repeatability with the cyclic changes of stress/strain. When the loading amplitude is 6 MPa or the strain is 246 με, the maximum value of the resistance rate of change is 16.06%. When the loading amplitude is 8 MPa or the strain is 314 με, the maximum value of resistance change can reach 22.18%. When the loading amplitude is 10 MPa

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Fig. 5.10 Compressive stress/strain and FCR of cement-based nanocomposites without/with SNCB/CNT under repeated compressive loading with stress amplitude of 8 MPa. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.39 vol.%, c 0.77 vol.%, d 1.52 vol.%, e 2.40 vol.%, f 3.12 vol.% of S-NCB/CNT. Strain-FCR of cement-based nanocomposites with g 0 vol.%, h 0.39 vol.%, i 0.77 vol.%, j 1.52 vol.%, k 2.40 vol.%, l 3.12 vol.% of S-NCB/CNT. m The maximum FCR of cement-based composites without/with S-NCB/CNT

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Fig. 5.11 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 8 MPa. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.77 vol.%, and c 2.14 vol.% of L-NCB/CNT. Strain-FCR of cement-based nanocomposites with d 0 vol.%, e 0.77 vol.%, and f 2.14 vol.% of L-NCB/CNT. g The maximum FCR of cement-based composites without/with L-NCB/CNT

Fig. 5.12 Sensitivity of cement-based nanocomposites without/with S-NCB/CNT under cyclic compressive loading. a Stress sensitivity. b Strain sensitivity

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Fig. 5.13 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under cyclic compressive loading. a Stress sensitivity. b Strain sensitivity

Table 5.4 Comparison about sensitivity of different self-sensing cement-based nanocomposites with CNT or/and NCB Filler type

Content

Stress sensitivity (%/MPa)

Strain sensitivity

Reference

S-NCB/CNT

2.40 vol.%

2.69

704

This study

L-NCB/CNT

1.41 vol.%

3.12

521

This study

CNT

0.10 vol.%

1.35

–

2.00 wt%

–

220

[9]

NCB

–

1.2

200

[10]

8.79 vol.%

0.6

60

[11]

[8]

or the strain is 403 με, the maximum value of the resistivity change can reach 25.48%. In conclusion, the resistivity change rate of cement-based nanocomposites with 2.40 vol.% of NCB/CNT increases with increasing stress/strain. The larger the stress/strain, the smaller the average distance between the packings and the greater the chance of tunneling effect between the packings in cement-based nanocomposites. Therefore, the resistivity change of cement-based nanocomposites with S-NCB/CNT increases with the stress/strain level. Figure 5.15 shows the stress and strain sensitivities of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT at loading amplitudes of 6, 8, and 10 MPa. The stress and strain sensitivities of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT both increase and then decrease with increasing stress/strain. The stress sensitivity is 2.57%/MPa, 2.69%/MPa, and 2.48%/MPa for loading amplitudes of 6 MPa, 8 MPa and 10 MPa, respectively. The strain sensitivity is 652, 704, and 631 for strain values of 246 με, 314 με and 403 με, respectively. The stress and strain sensitivities of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT were less affected by the loading amplitude. The increase or decrease of the sensitivity are within 7.9%.

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Fig. 5.14 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT. Stress-FCR of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT at a 6 MPa, b 8 MPa, and c 10 MPa. Strain-FCR of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT at d 6 MPa, e 8 MPa, and f 10 MPa. g The maximum FCR of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT

Fig. 5.15 Sensitivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT under 7 times of cyclic loading with stress amplitudes of 6, 8 and 10 MPa. a Stress sensitivity. b Strain sensitivity

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Figure 5.16 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under cyclic compressive loading with stress amplitude of 2 and 4 MPa after 28d water curing. As shown in Fig. 5.16, the resistivity rates of change of cement-based nanocomposites without/with L-NCB/CNT at different amplitude conditions varied synchronously with the stress/strain. the maximum resistivity rates of change of cement-based nanocomposites without/with L-NCB/CNT increase with the loading amplitude. When the loading amplitude was 2 MPa, the maximum resistivity change rates of cement-based nanocomposites with 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT are 0.74%, 1.01%, 0.55%, 7.19%, and 7.84%, respectively. The maximum resistivity changes of cement-based nanocomposites with 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT are 1.09%, 1.87%, 1.51%, 12.67%, and 11.89%, respectively, when the loading amplitude is 4 MPa. These findings indicate that the larger the loading amplitude, the better the conductive network in cement-based nanocomposites with L-NCB/CNT, the lower the resistivity and the greater resistivity change. Figure 5.17 shows the sensitivity of cement-based nanocomposites without/with L-NCB/CNT under stress amplitude of 2 and 4 MPa. The stress and strain sensitivities of cement-based nanocomposites without/with L-NCB/CNT are similar when the LNCB/CNT content is less than 1.14 vol.%. With the increase of L-NCB/CNT content, the stress/strain sensitivities of cement-based nanocomposites reach 3.43%/MPa/554 and 3.06%/MPa/493 at loading amplitudes of 2 MPa and 4 MPa, respectively. Figure 5.18 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT under 7 times of cyclic loading at loading rate of 0.2, 0.4, and 0.6 mm/min. From Fig. 5.18a– f, it can be seen that the resistivity rate of change of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT with stress/strain at loading rates of 0.2, 0.4, and 0.6 mm/min exhibit good synchronization and repeatability. The maximum resistivity changes of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT were 21.65, 22.19, and 20.91% when the loading rate was 0.2 mm/min, 0.4 mm/min, and 0.6 mm/min, respectively. Moreover, the maximum resistivity change is changed little with the change of loading rate. Figure 5.19 shows stress and strain sensitivities of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT under 7 times of cyclic compressive loading at loading rate of 0.2, 0.4, and 0.6 mm/min. The stress sensitivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT firstly increases and then decreases with the loading rate. When the loading rate is 0.2, 0.4, and 0.6 mm/min, the stress sensitivity is 2.66%/MPa, 2.69%/MPa, and 2.49%/MPa, respectively. Meanwhile, the strain sensitivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT decreases with the loading rate. The strain sensitivity is 727, 704, and 688 when the loading rate is 0.2 mm/min, 0.4 mm/min, and 0.6 mm/min, respectively. Overall, the loading rate shows less effect on the stress and strain sensitivities. Figure 5.20 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT at loading

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Fig. 5.16 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under cyclic compressive loading with stress amplitude of 2 and 4 MPa after 28d water curing. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.77 vol.%, and c 2.14 vol.% of L-NCB/CNT. Strain-FCR of cement-based nanocomposites with d 0 vol.%, e 0.77 vol.%, and f 2.14 vol.% of L-NCB/CNT. g The maximum FCR of cement-based composites without/with L-NCB/CNT

Fig. 5.17 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under stress amplitude of 2 and 4 MPa. a Stress sensitivity. b Strain sensitivity

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Fig. 5.18 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT under 7 times of cyclic loading. a Strain- and b Stress-fractional change at 0.2 mm/min. c Strain- and d Stress-fractional change at 0.4 mm/min. e Strain- and f Stress-fractional change at 0.6 mm/min. g The maximum fractional change in resistivity

rate of 0.2, 0.4, and 0.8 mm/min. The resistivity change rate of blank cementbased composites shows an increasing trend due to the polarization effect. The resistivity change rate of cement-based nanocomposites with L-NCB/CNT exhibited synchronization, repeatability and stability with the stress/strain at different loading rates. When the loading rate is 0.2/0.4/0.8 mm/min, the maximum resistivity change rate is 1.25%/1.03%/0.83%, 1.81%/1.58%/1.37%, 1.08%/1.18%/1.18%, 12.90%/12.45%/11.98%, and 11.46%/11.39%/11.13% when 0 vol.%, 0.39 vol.%, 0.77 vol.%, 1.41 vol.%, and 2.14 vol.% of L-NCB/CNT are incorporated, respectively. Figure 5.21 shows the sensitivity of cement-based nanocomposites without/with L-NCB/CNT at loading rate of 0.2, 0.4, and 0.8 mm/min. As shown in Fig. 5.21, the stress and strain sensitivities of cement-based nanocomposites without/with LNCB/CNT decrease with the loading rate. At the loading rates of 0.2, 0.4, and

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Fig. 5.19 Sensitivity of cement-based nanocomposites with 2.40 vol.% of S-NCB/CNT under 7 times of cyclic compressive loading at loading rate of 0.2, 0.4, and 0.6 mm/min. a Stress sensitivity. b Strain sensitivity

Fig. 5.20 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT at loading rate of 0.2, 0.4, and 0.8 mm/min. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.77 vol.%, and c 2.14 vol.% of L-NCB/CNT. Strain-FCR of cement-based nanocomposites with d 0 vol.%, e 0.77 vol.%, and f 2.14 vol.% of L-NCB/CNT. g The maximum FCR of cement-based composites without/with L-NCB/CNT

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Fig. 5.21 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT at loading rate of 0.2, 0.4, and 0.8 mm/min. a Stress sensitivity. b Strain sensitivity

0.8 mm/min, the stress sensitivity of cement-based nanocomposites with 1.41 vol.% of L-NCB/CNT is 3.16%/MPa, 2.99%/MPa and 2.78%/MPa, respectively; The strain sensitivity is 510, 482 and 450, respectively. The stress and strain sensitivities maximumly decrease by 0.38%/MPa and 60 when the loading rate increases from 0.2 to 0.8 mm/min. Figure 5.22 shows the thermal sensitivity of cement-based nanocomposites without/with S-NCB/CNT. In general, the change trends of blank cement-based composites and cement-based nanocomposites with 0.39 vol.% of S-NCB/CNT are similar. This indicates that the addition of 0.39 vol.% S-NCB/CNT does not form a conductive network in cement-based nanocomposites. The results of DC and AC resistivity of blank cement-based composites and cement-based nanocomposites with 0.39 vol.% of S-NCB/CNT in Figs. 5.5 and 5.6 also confirm the unformed conductive network. Therefore, the blank cement-based composites and cementbased nanocomposites with 0.39 vol.% of S-NCB/CNT is mainly ionic conductive, which is very sensitive to temperature. When the content of S-NCB/CNT exceeds 0.77 vol.%, the thermal sensitivity of the cement-based nanocomposites notably decreases. As can be seen from Figs. 5.5 and 5.6, 0.77 vol.% is in the percolation zone of cement-based nanocomposites with S-NCB/CNT, i.e., a conductive network has formed in the nanocomposites. The conductivity changes from ionic to electronic conductivity. The thermal sensitivity of cement-based nanocomposites with S-NCB/CNT decreases. When the temperature increases from −30 to 60 °C, the resistivities of blank cement-based composites and cement-based nanocomposites with 0.39 vol.% of S-NCB/CNT firstly increase and then decrease with temperature. For cement-based nanocomposites with 0.77–3.12 vol.% of S-NCB/CNT, the resistivity of the mortar decreases with the temperature. The resistivity changes of cement-based nanocomposites with 0, 0.39, 0.77, 1.52, 2.40, and 3.12 vol.% of SNCB/CNT are −81.38%, −81.50%, −23.66%, −9.78%, −11.73%, and −6.32%, respectively, when the temperature increases from 0 to 60 °C. Overall, the resistivity change of cement-based nanocomposites with S-NCB/CNT decreases with the

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content of S-NCB/CNT, i.e., the thermal sensitivity decreases with the increase of the S-NCB/CNT content. Figure 5.23 shows the relative water content of cement-based nanocomposites without/with L-NCB/CNT under different drying conditions. As shown in Fig. 5.23, the relative water content of cement-based nanocomposites without/with L-NCB/CNT decreases with the drying time. Under the same drying condition, the

Fig. 5.22 Thermal sensitivity of cement-based nanocomposites without/with S-NCB/CNT. a Without S-NCB/CNT. b With 0.39 vol.% of S-NCB/CNT. c With 0.77 vol.% of S-NCB/CNT. d With 1.52 vol.% of S-NCB/CNT. e With 2.40 vol.% of S-NCB/CNT. f With 3.12 vol.% of S-NCB/CNT

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Fig. 5.23 Relative water content of cement-based nanocomposites without/with L-NCB/CNT under different drying conditions

relative water content of cement-based nanocomposites decreases with the increase of L-NCB/CNT content. Taking the water content of cement-based nanocomposites after 28 d of water curing and wiping off the surface water as 100%, the relative water content of cement-based nanocomposites with 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT decreases to 97.57%, 97.27%, 97.20%, 95.41%, and 90.94%, respectively, after 16 d of air drying and 108 h of drying at 45 °C. Figure 5.24 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 3d air drying. Under this condition, the resistivity change rate of cement-based nanocomposites with 0.39–2.14 vol.% of L-NCB/CNT shows good synchronization and repeatability with the cyclic change of stress/strain. As shown in Fig. 5.24, the maximum resistivity changes of cement-based nanocomposites are −0.98%, −1.41%, −8.73% and −7.47%, respectively, when 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT are incorporated. Figure 5.25 shows the sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 3d air drying. As shown in Fig. 5.25, the stress and strain sensitivities of cement-based nanocomposites firstly increase and then decrease with the LNCB/CNT content. The cement-based nanocomposites with 1.41 vol.% of LNCB/CNT possesses the highest stress and strain sensitivities of 2.18%/MPa and 382, respectively. Figure 5.26 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 16d air drying. As shown in Fig. 5.26, the resistivity change rate of cement-based nanocomposites with 0.39–2.14 vol.% of L-NCB/CNT after drying in air for 16 d varies synchronously with the stress/strain and shows good repeatability under cyclic loading. The maximum resistivity changes of cement-based nanocomposites are

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Fig. 5.24 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 3d air drying. Stress-FRC cement-based nanocomposites with a 0 vol.%, b 0.77 vol.%, and c 2.14 vol.% of L-NCB/CNT. Strain-FRC cement-based nanocomposites with d 0 vol.%, e 0.77 vol.%, and f 2.14 vol.% of L-NCB/CNT. g The maximum FCR of cement-based composites without/with L-NCB/CNT

−0.69, −0.64, −3.63 and −6.02%, when 0.39 vol.%, 0.77 vol.%, 1.41 vol.%, and 2.14 vol.% of L-NCB/CNT are incorporated, respectively. Figure 5.27 shows the stress and strain sensitivities of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 16 d air drying. The stress and strain sensitivities of cement-based nanocomposites increase with the L-NCB/CNT content. The stress and strain sensitivities reach 1.51%/MPa and 192, respectively, when 2.14 vol.% of L-NCB/CNT is incorporated. Figure 5.28 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 16 d air drying and 36 h oven drying at 45 °C. The cement-based nanocomposites with L-NCB/CNT shows good sensitivity after d of air drying and 36 h of oven drying at 45 °C.

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Fig. 5.25 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 3d air drying. a Stress sensitivity. b Strain sensitivity

The maximum resistivity change of cement-based composites increases with the L-NCB/CNT content. The maximum resistivity changes of cement-based nanocomposites with 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT are −0.77%, −0.73%, −3.97% and −6.80%, respectively. Figure 5.29 shows the sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 16 d air drying and 36 h oven drying at 45 °C. The stress and strain sensitivities of cement-based nanocomposites increases with the L-NCB/CNT content. The stress and strain sensitivities respectively reach 1.70%/MPa and 202 when 2.14 vol.% of L-NCB/CNT is incorporated. Figure 5.30 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 16d air drying and 108 h oven drying at 45 °C. After the drying treatment, cement-based nanocomposites with L-NCB/CNT still exhibits good sensitivity. As shown in Fig. 5.30k, the maximum resistivity changes of cement-based composites with 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT are −0.07%, −0.80%, −0.81%, −3.53% and −6.84%, respectively. Figure 5.31 shows the sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 16 d air drying and 108 h oven drying at 45 °C. The stress and strain sensitivities of cement-based nanocomposites increase with the L-NCB/CNT content. The stress and strain sensitivities respectively reach 1.65%/MPa and 200 when 2.14 vol.% of L-NCB/CNT is incorporated. Figure 5.32 shows the water adsorption of L-NCB/CNT, CNT and NCB along with pressure at room temperature. The adsorbed water volumes of L-NCB/CNT, CNT, and NCB all increase with increasing pressure at room temperature. This indicates that L-NCB/CNT, CNT, and NCB have the characteristics of adsorbing and desorbing

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Fig. 5.26 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 16d air drying. Stress-FRC cement-based nanocomposites with a 0 vol.%, b 0.77 vol.%, and c 2.14 vol.% of L-NCB/CNT. Strain-FRC cement-based nanocomposites with d 0 vol.%, e 0.77 vol.%, and f 2.14 vol.% of L-NCB/CNT. g The maximum FCR of cement-based composites without/with L-NCB/CNT

water. At a pressure of 2.1 kPa, 1 g of L-NCB/CNT, CNT and NCB adsorbs up to 138.762, 93.000 and 157.307 mg of water. Figure 5.33 shows the DC electrical resistivity of L-NCB/CNT, CNT and NCB in curing box with a RH of 95% for 20 min. The resistivity change rates of LNCB/CNT, CNT and NCB show a trend of increasing and then stabilizing with time. The resistivity of L-NCB/CNT, CNT, and NCB increases by 6.51, 24.72 and 3.50% after saturation of adsorbed water, respectively, compared with the resistivity in the dry state. It should be noted that since the mass and density of L-NCB/CNT, CNT and NCB used in this chapter are different, the magnitude of the resistivity change after water adsorption of the three fillers is not comparable. However, it can be seen that the resistivity of these three nanofillers tends to increase with the increase of

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Fig. 5.27 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 16 d air drying. a Stress sensitivity. b Strain sensitivity

adsorbed water. This indicates that the increase of drying/wetting process would decrease/increase the contact resistance between NCB/CNT (as shown in Fig. 5.34) due to shrinkage/extrusion of cement-based nanocomposites [12]. Figure 5.35 shows the electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT at different relative water content. It should be noted that the hydration degree of cement-based nanocomposites grows slowly after 28-d hydration. Therefore, the relative moisture content is the main factor affecting the resistivity of cement-based nanocomposites. As the relative moisture content decreases, the resistivity of blank cement-based composites increases, with an increase of 62.6%. The main conductivity mode of blank cement-based composites is ionic conductivity. As for the cement-based nanocomposites with L-NCB/CNT, the DC resistivity increases with relative water content. The maximum resistivity reduction fractions for cement-based nanocomposites are 34.2%, 48.0%, 42.7%, and 25.5%, respectively, when 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT are incorporated. The distribution of L-NCB/CNT, i.e. the contact resistance, plays a key role in conductivity [13]. The DC resistivity of cement-based nanocomposites with L-NCB/CNT is lower at low relative moisture content. This indicates that the decrease in contact resistance increases the conductive pathway of cement-based nanocomposites with L-NCB/CNT in the unloaded state. Overall, the DC resistivity increases as the relative water content decreases. In addition to contact resistance, other factors also influence the maximum resistivity variability, stress sensitivity, and strain sensitivity with relative water content. The decrease in water content leads to dry shrinkage of hydration products, especially C–S–H gels, in cement-based composites [14]. This leads to a reduction in the distance among NCB/CNT in cement-based nanocomposites and the formation of conductive pathways. The formation of conductive pathways reduces the change in conductive pathways, thus decreasing the sensitivity of cement-based nanocomposites with NCB/CNT. Moreover, the chance of forming conductive pathways due to

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Fig. 5.28 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with a stress amplitude of 4 MPa after 16 d air drying and 36 h oven drying at 45 °C. a Stress- and d Strain-fractional change in resistivity of cement-based composites without L-NCB/CNT. b Stress- and e Strainfractional change in resistivity of cement-based nanocomposites with 0.77 vol.% of L-NCB/CNT. c Stress- and f Strain-fractional change in resistivity of cement-based nanocomposites with 2.14 vol.% of L-NCB/CNT. g The maximum fraction change in electrical resistivity

tunneling effect during loading is reduced [14]. This also leads to a decrease in the sensitivity of cement-based nanocomposites with NCB/CNT at low water content. It also indicates that the tunneling effect also has a significant effect on the sensitivity of cement-based nanocomposites with NCB/CNT. Figure 5.36 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under ultimate load. As shown in Fig. 5.36a, b, the resistivity change rate of cementbased nanocomposites without/with L-NCB/CNT increases with the stress/strain. The maximum resistivity change of cement-based nanocomposites firstly increases and then decreases with the L-NCB/CNT content. The maximum resistivity change

5.4 Functional/Smart Properties of Cement-Based Nanocomposites …

189

Fig. 5.29 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 16 d air drying and 36 h oven drying at 45 °C. a Stress sensitivity. b Strain sensitivity

corresponding to the ultimate stress/ultimate strain of cement-based nanocomposites with 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT is −11.91%, −33.05%, −44.56%, −35.98% and −27.63%, respectively. The maximum resistivity change rate is correlated with the ultimate load/limit strain and the variation of the internal conductive network of L-NCB/CNT in cement-based nanocomposites. Figure 5.37 shows the sensitivity of cement-based nanocomposites without/with L-NCB/CNT under ultimate load. The stress and strain sensitivities at ultimate load firstly increase and then decrease with L-NCB/CNT content. The stress sensitivity of cement-based nanocomposites with 0, 0.39, 0.77, 1.41, and 2.14 vol.% of LNCB/CNT is 0.15%/MPa, 0.50%/MPa, 0.68%/MPa, 1.29%/MPa, and 1.29%/MPa, respectively. The strain sensitivity of cement-based nanocomposites at ultimate load is 54, 150, 164, 208, and 141, respectively, when 0, 0.39, 0.77, 1.41, and 2.14 vol.% of L-NCB/CNT is incorporated. The change of resistivity under compressive loading is caused by three main factors. First, the resistance of the NCB/CNT itself changes when subjected to compressive loading. Second, the change of the distances between adjacent NCB/CNT, including the distance change between CNT and CNT, CNT and NCB, as well as NCB and NCB. These distances become smaller when subjected to compressive loading, which may form a connection or enhance tunneling effect. Due to the special structure of NCB/CNT, there are multiple distance changes when subjected to compressive loading. This makes the cement-based nanocomposites with NCB/CNT high sensitivity. Third, the contact resistance between S-NCB/CNT and the cement matrix becomes smaller when subjected to compressive loading. It should be noted that the change of the distance is the main factor that causes the excellent sensitivity of cement-based nanocomposites. When the content of NCB/CNT is less than 0.77 vol.%, NCB/CNT does not form a conductive network in the cement-based composites and the distance between adjacent NCB/CNT is too far to produce a tunneling effect even under compressive loading. Therefore, the cement-based nanocomposites

190

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.30 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 16d air drying and 108 h oven drying at 45 °C. a Stress- and d Strain-fractional change in resistivity of cement-based composites without L-NCB/CNT. b Stress- and e Strainfractional change in resistivity of cement-based nanocomposites with 0.77 vol.% of L-NCB/CNT. c Stress- and f Strain-fractional change in resistivity of cement-based nanocomposites with 2.14 vol.% of L-NCB/CNT. g The maximum fraction change in electrical resistivity

with 0.39 vol.% of NCB/CNT still has a high resistivity and no sensitivity. When the NCB/CNT content exceeds 2.40 vol.%, the NCB/CNT is uniformly distributed in the cement-based nanocomposites. The resistivity of cement-based nanocomposites with NCB/CNT decreases sharply to 117.55 Ω cm. The distance between adjacent NCB/CNT is reduced when subjected to compressive loading, thus forming more conductive pathways due to the tunneling effect.

5.4 Functional/Smart Properties of Cement-Based Nanocomposites …

191

Fig. 5.31 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under repeated compressive loading with stress amplitude of 4 MPa after 16 d air drying and 108 h oven drying at 45 °C. a Stress sensitivity. b Strain sensitivity

Fig. 5.32 Water adsorption of L-NCB/CNT, CNT and NCB along with pressure at room temperature. a L-NCB/CNT. b CNT. c NCB Fig. 5.33 DC electrical resistivity of L-NCB/CNT, CNT and NCB in curing box with a RH of 95% for 20 min

192

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.34 Variation of contact electrical resistance of NCB/CNT after water adsorption/desorption

5.4.3 Electromagnetic Shielding and Absorption Properties Figure 5.38 shows the electromagnetic shielding properties of cement-based nanocomposites without/with NCB/CNT. As depicted in Fig. 5.38, the presence of NCB/CNT increases the electromagnetic shielding effectiveness of cementbased nanocomposites. The electromagnetic shielding effectiveness of cement-based nanocomposites with S-NCB/CNT and L-NCB/CNT reaches 5.0 dB and 7.5 dB, respectively increased by 94.6 and 230.7% compared with blank cement-based composites. Figure 5.39 exhibits the reflectivity of cement-based nanocomposites without/with NCB/CNT in the frequency range of 2–18 GHz. As shown in Fig. 5.39, the reflectivity of cement-based nanocomposites decreases with the content of NCB/CNT. When the thickness of the specimen is 20 mm, the incorporation of 0.77 vol.% of S-NCB/CNT and 0.39 vol.% of L-NCB/CNT can achieve 4.82 and 4.93 times of increase in reflectivity of blank cement-based composites, respectively. Figures 5.40 and 5.41 show the electromagnetic parameters of cement-based nanocomposites without/with S-NCB/CNT and L-NCB/CNT, respectively. It can be seen from Figs. 5.40 and 5.41 that the real part of the dielectric constant of cement-based nanocomposites increases with as the content of NCB/CNT, which indicates that the degree of dielectric polarization of electromagnetic wave on the paste increases. Meanwhile, the imaginary part of the dielectric constant and the electrical loss tangent of cement-based nanocomposites also increase with NCB/CNT content, leading to the increase of the dielectric loss of the paste to electromagnetic waves. However, the imaginary part of magnetic permeability and magnetic loss tangent of cement-based nanocomposites with NCB/CNT are basically zero, which indicates that NCB/CNT have no magnetic loss ability to electromagnetic waves.

5.5 Application of Cement-Based Nanocomposites with Electrostatic …

193

Fig. 5.35 Electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT at different relative water content. a Without L-NCB/CNT. b With 0.39 vol.% of L-NCB/CNT. c With 0.77 vol.% of L-NCB/CNT. d With 1.41 vol.% of L-NCB/CNT. e With 2.14 vol.% of L-NCB/CNT

5.5 Application of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/CNT 5.5.1 Application for Structural Health Monitoring Due to the excellent mechanical and self-sensing properties of cement-based nanocomposites without/with NCB/CNT, they were devised as sensors in acquiring dynamic responses a five-story building model, for the purposes of structural modal

194

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.36 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with L-NCB/CNT under ultimate load. a Stress and fractional change in resistivity. b Strain and fractional change in resistivity. c The maximum fractional change in resistivity

identification and damage detection, as shown in Fig. 5.42a. The dynamic performances of the cement-based nanocomposite sensor were evaluated by the application of sinusoidal compression at a frequency of 2 Hz. As shown in Fig. 5.42b, the voltage variation as a function of time shows a similar change trend as the time histories of applied stress/strain, indicating superb response and recovery properties. The peak values of voltage variation can accurately identify the amount of the applied stress/strain, thus featuring the best pressure-sensitive reproducibility and stability. Figure 5.42c shows the time histories of the measured acceleration, strain

5.5 Application of Cement-Based Nanocomposites with Electrostatic …

195

Fig. 5.37 Sensitivity of cement-based nanocomposites without/with L-NCB/CNT under ultimate load. a Stress sensitivity. b Strain sensitivity

Fig. 5.38 Electromagnetic shielding properties of cement-based nanocomposites without/with NCB/CNT. a Without/with S-NCB/CNT. b Without/with L-NCB/CNT

Fig. 5.39 Reflectivity of cement-based nanocomposites without/with NCB/CNT in the frequency of 2–18 GHz. a Without/with S-NCB/CNT. b Without/with L-NCB/CNT

196

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.40 Electromagnetic parameters of cement-based nanocomposites without/with SNCB/CNT. a Real part of the dielectric constant. b Imaginary part of the dielectric constant. c Real part of the magnetic permeability. d Imaginary part of the magnetic permeability. e Dielectric loss angle of tangent. f Electromagnetic loss angle of tangent

response and voltage variation during hammer impact tests. The strain signal was obtained by taking an average of the outputs from the two strain gauges positioned in the vicinity of the cement-based nanocomposite sensor. It is apparent that the three different types of sensors reacted to the impact simultaneously, varying with the different impact intensities. The signal from the cement-based nanocomposite sensor was gradually attenuated over time, showing a low noise level and a comparatively long decay time, which makes it proper for damping estimation. To verify the authenticity of the responses, the modal frequencies were identified using the

5.5 Application of Cement-Based Nanocomposites with Electrostatic …

197

Fig. 5.41 Electromagnetic parameters of cement-based nanocomposites without/with LNCB/CNT. a Real part of the dielectric constant. b Imaginary part of the dielectric constant. c Real part of the magnetic permeability. d Imaginary part of the magnetic permeability. e Dielectric loss angle of tangent. f Electromagnetic loss angle of tangent

data from the three different types of sensors. It can be observed from Fig. 5.42d that the cement-based nanocomposite sensor can well identified modal frequencies of the five-story building model. As shown in Fig. 5.43, nine scenarios including one healthy state and eight damaged states were examined. In Case 1, the structure is healthy; in Cases 2 to 5, the lighter iron brick was bolted tightly to the centre of the 5th floor, 4th floor, 3rd floor and 2nd floor, respectively; in Cases 6 to 8, the heavy iron brick is bolted

198

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.42 Simulated damage scenarios

tightly to the centre of the 3rd floor, 4th floor and 5th floor, respectively; In Case 9, the 3rd floor and 4th floor are simultaneously equipped with a light iron brick each. The identified modal frequencies for each scenario are illustrated in. Changes in the modal parameters were not the same for each mode since the changes depend on the nature, location and severity of the damage. It is found that the results from the cement-based nanocomposite sensor were perfectly consistent with them from the accelerometer with no difference being observed, indicating that the cement-based nanocomposite sensor was sufficiently sensitive to capture the dynamic response of the structure and is, therefore, applicable to structural health monitoring. Note that the vibration modes higher than the first one showed increased sensitivity to local damage, which should be used in damage detection to attain a higher level of identification precision (Table 5.5).

5.5.2 Application for Oil Well Infrastructure Traditional cement-based composites are usually unsatisfied for the high requirements such as high strength, high stiffness, and low elastic modulus of oil well infrastructures. In view of the enhanced strength and stiffness and strong water adsorption of cement-based nanocomposites with NCB/CNT, they can also be applied for oil

5.5 Application of Cement-Based Nanocomposites with Electrostatic …

199

Fig. 5.43 Simulated damage scenarios Table 5.5 Identified modal frequencies and their changes using accelerometer and the cementbased nanocomposite sensor in different damage scenarios Damage Sensor Natural frequency (Hz) case M1 M2 M3 M4 1 2 3 4 5 6 7 8 9

Natural frequency change (%) M5

M1 M2

Acc

7.813 23.93 40.04 51.76 58.59 –

SSCC

7.813 23.93 40.04 51.76 58.59

Acc

7.813 24.41 39.55 49.80 57.13 0

SSCC

7.813 24.41 39.55 49.80 57.13

Acc

7.813 23.93 38.57 51.76 57.13 0

SSCC

7.813 23.93 38.57 51.76 57.13

Acc

7.813 23.44 39.06 50.29 57.62 0

SSCC

7.813 23.44 39.06 50.29 57.62

Acc

7.813 23.44 37.11 49.32 58.11 0

SSCC

7.813 23.44 37.11 49.32 58.11

Acc

7.813 22.46 39.55 49.32 57.62 0

SSCC

7.813 22.46 39.55 49.32 57.62

Acc

7.813 23.44 38.09 51.76 56.15 0

SSCC

7.813 23.44 38.09 51.76 56.15

Acc

7.813 24.41 39.55 48.83 56.64 0

SSCC

7.813 24.41 39.55 48.83 56.64

Acc

7.813 22.95 38.57 50.78 56.64 0

M3

M4

M5

+ 2.01 − 1.22 − 3.79 − 2.49 0

− 3.67

0

− 2.49

− 2.05 − 2.45 − 2.84 − 1.66 − 2.05 − 7.32 − 4.71 − 0.82 − 6.14 − 1.22 − 4.71 − 1.66 − 2.05 − 4.87

0

− 4.17

− 2.01 − 1.22 − 5.66 − 3.33 − 4.10 − 3.67 − 1.89 − 3.33

200

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Table 5.6 Mix proportions of oil well cement-based nanocomposites without/with NCB/CNT (mass ratio) Code

Cement

Water

NCB/CNT (%)

Dispersant (%)

Retarder (%)

W0

1

0.44

0

0

0.3

W0.5

1

0.44

0.5

0.4

0.3

W1

1

0.44

1

0.5

0.3

W1.5

1

0.44

1.5

0.6

0.3

W2

1

0.44

2

0.8

0.3

M0

1

0.44

0

0

0

M1

1

0.44

1

0.2

0

M3

1

0.44

3

0.7

0

well infrastructures. The mix proportions of the cement-based nanocomposites with NCB/CNT for oil well infrastructures are shown in Table 5.6. As shown in Table 5.7, the addition of NCB/CNT slightly increases the densities of oil well cement-based nanocomposites. Moreover, the workability and free water of all the cement-based nanocomposites meet the requirements of oil well infrastructures. The oil well cement-based nanocomposites with NCB/CNT exhibited less free fluid than the neat cement, i.e., better static stability, which may derive from the strong water adsorption of NCB. The rheology of oil well cement-based nanocomposites without/with NCB/CNT was measured at 22 and 80 °C, respectively. The results indicate that oil well cement-based nanocomposites thicken with the increase of temperature. At 22 °C, the viscosity of the oil well cement-based nanocomposites decreases after adding NCB/CNT, while the viscosity increases with increasing NCB/CNT content at 80 °C. The rheology of oil well cement-based nanocomposites without/with NCB/CNT can be well described by the Hershel Bulkley rheology model (τ = τ y + k n ) with τ y , n and k values presented in Table 5.7. Table 5.8 shows the triaxial compressive strength, ultimate compressive strain, and elastic modulus of oil well cement-based nanocomposites without/with NCB/CNT. Table 5.7 Properties of oil well cement-based nanocomposites without/with NCB/CNT Code

W0

Density Initial Free fluid 22 °C, 40 MPa setting time

k (Pa sn ) τ y (Pa) n

(g/cm3 ) (min)

(ml)

n

1.890

5.22

0.65 0.83

110

80 °C, 40 MPa

3.71

k (Pa sn ) τ y (Pa)

0.33 10.00

0.50

W0.5 1.890

120

4.55

0.84 0.19

0.78

0.49

2.07

1.42

1.895

123

3.68

0.93 0.09

2.38

0.24 15.00

5.00

W1.5 1.900

126

3.5

0.94 0.08

0.58

0.24 18.03

13.58

1.900

149

3.81

0.87 0.21

0.43

0.43

11.69

W1 W2

5.20

5.6 Summary

201

Table 5.8 Mechanical properties of oil well cement-based nanocomposites without/with NCB/CNT under triaxial test Code

Triaxial compressive strength

Compressive ultimate strain

Elastic modulus

Absolute value (MPa)

Absolute value

Absolute value (GPa)

Relative value (%)

Relative value (%)

Relative value (%)

M0

55.45

0

0.71

0

10.45

0

M1

66.62

20

1.38

94

8.11

− 22

M3

62.77

13

1.50

113

7.86

− 25

The presence NCB/CNT generally increases the triaxial compressive strength, ultimate compressive strain, and meanwhile, decreases elastic modulus of oil well cement-based nanocomposites. The triaxial compressive strength/ultimate strain increases by 20%/94% and 13%/113% when 1 wt% and 3 wt% of NCB/CNT are incorporated, respectively. In contrast, the elastic modulus of oil well cement-based nanocomposites decreases by 22 and 25% after adding 1 and 3 wt% of NCB/CNT. These phenomena indicate the high potential for NCB/CNT as a modifying filler for oil well cement-based composites. Figure 5.44 shows the morphology of oil well cement-based nanocomposites without/with NCB/CNT. As shown in Fig. 5.44a, the NCB/CNT fills the pores in oil well cement matrix, diminishing the space required for CH crystals to grow, compared with oil well cement-based nanocomposites without NCB/CNT (Fig. 5.44b). Moreover, NCB/CNT can exert bridging and pinning effects during fracture process, as depicted in Fig. 5.44c, d, thus modifying the mechanical properties of cement-based nanocomposites.

5.6 Summary In this chapter, a new-generation cement-based nanocomposite with NCB/CNT is introduced. The self-sensing properties together with the mechanical, electrical, and electromagnetic shielding and absorption properties of the developed nanocomposites as well as their applications in frame and oil well structures are presented. The conclusions can be summarized as below. (1) The addition of NCB/CNT undermines the strength of cement-based nanocomposites, which may stem from the NCB that adsorbs on the surface of binder grains and inhibits the hydration of binders. Meanwhile, the presence of CNT can exert bridging effect during fracture process. (2) NCB/CNT can endow cement-based nanocomposites with excellent electrical properties. The percolation interval of cement-based nanocomposites with

202

5 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 5.44 Morphology of oil well cement-based nanocomposites without/with NCB/CNT. a Without NCB/CNT. b With NCB/CNT. c Bridging effect. d Pinning effect

NCB/CNT ranges from 0.39 to 1.41 vol.%. The DC/AC resistivity of cementbased nanocomposites can be as low as 176/48 Ω cm, respectively, implying the formation of conductive pathways composed of NCB/CNT. (3) Cement-based nanocomposites with NCB/CNT possess excellent self-sensing properties. The maximum resistivity change, stress sensitivity and strain sensitivity of the nanocomposites increase and then decrease with the increase of NCB/CNT content. The maximum resistivity change, stress sensitivity and strain sensitivity of the nanocomposites reach 22.18%, 3.21%/MPa, and 704, respectively. Moreover, the self-sensing performance is quite stable at different loading amplitude, loading rate, and moisture content. (4) Cement-based nanocomposites with NCB/CNT possess good electromagnetic shielding and adsorption properties. The electromagnetic shielding effectiveness and reflectivity of the nanocomposites reach 7.5 and 23.91 dB, increased by 230.7 and 393% compared with that of blank cement-based composites.

References

203

(5) The identified modal frequencies from the cement-based nanocomposite sensors were highly consistent with the accelerometer and strain gauge results. In addition, the cement-based nanocomposite sensors offered more high-frequency components than the strain gauge. The identified modal frequencies and their changes due to in various damage cases obtained by the cement-based nanocomposite sensors were perfectly consistent with those obtained by the accelerometer, indicating that the cement-based nanocomposite sensor was sensitive enough to capture the dynamic response. (6) The presence of NCB/CNT increases the triaxial compressive strength and the corresponding strain, and simultaneously, reduces the elastic modulus of cement-based nanocomposites, which fully meets the requirement of the construction materials for oil well infrastructures. In summary, the cement-based nanocomposites with NCB/CNT can be smart/multifunctional, strong, durable, and low environmental footprint(e.g., carbon footprint), showing great potential in developing smart/multifunctional, resilient, high-requirement, and special infrastructures.

References 1. D. Tasis, N. Tagmatarchis, A. Bianco, M. Prato, Chemistry of carbon nanotubes. Chem. Rev. 106, 1105–1136 (2006) 2. J. Hilding, E.A. Grulke, Z.G. Zhang, F. Lockwood, Dispersion of carbon nanotubes in liquids. J. Disper. Sci. Technol. 24, 1–41 (2003) 3. B. Han, S. Ding, J. Wang, J. Ou, Nano-Engineered Cementitious Composites: Principles and Practices (Springer, Singapore, 2019) 4. B. Han, L. Zhang, S. Sun, X. Yu, X. Dong, T. Wu, J. Ou, Electrostatic self-assembly NCB/CNT composite fillers reinforced cement-based materials with multifunctionality. Compos. A Appl. Sci. Manuf. 79, 103–115 (2015) 5. L. Zhang, S. Ding, L. Li, S. Dong, D. Wang, X. Yu, B. Han, Effect of characteristics of assembly unit of NCB/CNT composite fillers on properties of smart cement-based materials. Compos. A Appl. Sci. Manuf. 109, 303–320 (2018) 6. B. Han, S. Sun, S. Ding, L. Zhang, X. Yu, J. Ou, Review of nanocarbon-engineered multifunctional cementitious composites. Compos. A Appl. Sci. Manuf. 70, 69–81 (2015) 7. V.K. Vadlamani, V.B. Chalivendra, A. Shukla, S. Yang, Sensing of damage in carbon nanotubes and carbon black-embedded epoxy under tensile loading. Polym. Compos. 33, 1809–1815 (2012) 8. X. Yu, E. Kwon, A carbon nanotube/cement composite with piezoresistive properties. Smart Mater. Struct. 18, 55010 (2009) 9. A.L. Materazzi, F. Ubertini, A.D. Alessandro, Carbon nanotube cement-based transducers for dynamic sensing of strain. Cement Concr. Compos. 37, 2–11 (2013) 10. B. Han, J. Ou, Embedded piezoresistive cement-based stress/strain sensor. Sens. Actuators A 137, 294–298 (2007) 11. H. Li, H. Xiao, J. Ou, Effect of compressive strain on electrical resistivity of carbon black-filled cement-based composites. Cement Concr. Compos. 28, 824–828 (2006) 12. Z. Zhang, Functional Composites (Chemical Industry Press, 2014) 13. E. García-Macías, D.A. Alessandro, R. Castro-Triguero, D. Pérez-Mirad, F. Ubertini, Micromechanics modeling of the electrical conductivity of carbon nanotube cement-matrix composites. Compos. B Eng. 108, 451–469 (2017)

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14. A. Loukili, A. Khelidj, P. Richard, Hydration kinetics, change of relative humidity, and autogenous shrinkage of ultra-high-strength concrete. Cem. Concr. Res. 29, 577–584 (1999)

Chapter 6

New-Generation Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT

6.1 Introduction CNT can modify the mechanical properties and durability as well as electrical conductivity of cement-based nanocomposites, which is highly related to the dispersion state of CNT [1, 2]. Previous studies have been proven the addition of second phase into CNT can greatly improve its dispersion [3–5]. TiO2 , as an inexpensive industrial material with high dielectric constant and excellent functionality, shows great potential as the second phase with CNT [6, 7]. The addition of TiO2 , on the one hand, may notably improve the dispersibility of CNT in cement-based nanocomposites. On the other hand, the presence of TiO2 can endow cement-based nanocomposites with excellent electromagnetic shielding and absorption properties due to its high dielectric constant [8, 9]. This chapter introduces the mechanical properties and microstructures of cementbased nanocomposites with TiO2 /CNT as well as their functional/smart properties including electrical, self-sensing and electromagnetic shielding and absorption properties.

6.2 Preparation of Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT The raw materials used to fabricate cement-based nanocomposites with TiO2 /CNT include Portland cement, silica fume, standard quartz sand, SP, and TiO2 /CNT. The properties and morphology of TiO2 /CNT are shown in Table 6.1 and Fig. 6.1, respectively. The properties of other raw materials refer to Sect. 2.2. The mix proportion and fabrication process of cement-based nanocomposites in this chapter are shown in Table 6.2 and 6.3, respectively.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_6

205

206

6 New-Generation Cement-Based Nanocomposites with Electrostatic …

Table 6.1 Properties of TiO2 /CNT TiO2 :CNT (mass ratio)

Conductivity (Ω cm)

Specific surface area (m2 /g)

OD of CNT (nm)

Average particle size of TiO2 (m2 /g)

Contact angle (°)

10:90

50

450

76.96

Fig. 6.1 Morphology of TiO2 /CNT

Table 6.2 Mix proportions of cement-based nanocomposites without/with TiO2 /CNT (mass ratio) Cement

Silica fume

Water

Sand

SP

TiO2 /CNT (vol.%)

0.9

0.1

0.40

1.5

0.002

0

0.9

0.1

0.40

1.5

0.002

0.19

0.9

0.1

0.40

1.5

0.002

0.38

0.9

0.1

0.40

1.5

0.002

0.76

0.9

0.1

0.40

1.5

0.002

1.15

0.9

0.1

0.40

1.5

0.004

2.25

0.9

0.1

0.40

1.5

0.006

2.98

0.9

0.1

0.40

1.5

0.012

3.69

0.9

0.1

0.40

1.5

0.015

4.40

0.9

0.1

0.40

1.5

0.020

5.78

6.3 Mechanical Properties of Cement-Based Nanocomposites …

207

Table 6.3 Fabrication process of cement-based nanocomposites without/with TiO2 /CNT Dispersion method

Shear mixing + non-covalent surface modification by SP

Fabrication process Feeding order

Technology

Molding

Method

Time (s)

Method

Size (mm)

Method

Time (d)

Shear mixing (140 r/min)

30

Vibration

40 × 40 × 160

Standard condition

1

Water + SP Shear mixing (140 r/min)

30

W (20 °C)

28

Half of Cement

Shear mixing (140 r/min)

60

Shear mixing (285 r/min)

30

Shear mixing (140 r/min)

60

Shear mixing (285 r/min)

30

TiO2 /CNT + Silica fume

Half of Cement

Curing

6.3 Mechanical Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT 6.3.1 Compressive Strength Figure 6.2 presents the compressive strength of cement-based nanocomposites without/with TiO2 /CNT at 3 and 28 d. It can be seen from Fig. 6.2 the addition of TiO2 /CNT generally decreases the compressive strength of cement-based nanocomposites. However, after the content of TiO2 /CNT reaching 1.15 vol.%, the change of compressive strength of cement-based nanocomposites with TiO2 /CNT ranges within ± 10% compared with that of blank cement-based composites, indicating the TiO2 /CNT shows little effect on the compressive strength.

208

6 New-Generation Cement-Based Nanocomposites with Electrostatic …

Fig. 6.2 Compressive strength of cement-based nanocomposites without/with TiO2 /CNT

Fig. 6.3 Flexural strength of cement-based nanocomposites without/with TiO2 /CNT

6.3.2 Flexural Strength Figure 6.3 shows the flexural strength of cement-based nanocomposites without/with TiO2 /CNT at 3 and 28 d. Similar with compressive strength, the flexural strength of cement-based nanocomposites is less affected by the addition of TiO2 /CNT.

6.3.3 Modification Mechanisms Figure 6.4 shows the SEM images that indicate the modification mechanisms of TiO2 /CNT on cement-based nanocomposites. It can be seen from Fig. 6.4

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Fig. 6.4 SEM images of cement-based nanocomposites without/with TiO2 /CNT. a Without TiO2 /CNT. b With TiO2 /CNT

the TiO2 /CNT is uniformly distributed in the matrix, which confirms the well dispersibility of TiO2 /CNT.

6.4 Functional/Smart Properties of Cement-Based Nanocomposites with Electrostatic Self-Assembly TiO2 /CNT 6.4.1 Electrical Properties Figure 6.5 shows the DC resistivity of cement-based nanocomposites without/with TiO2 /CNT at 3, 7 and 28 d. The DC resistivity slightly increases with TiO2 /CNT content and then decreases. At the content between 0.76 and 2.25 vol.%, the DC resistivity of cement-based nanocomposites decreases sharply with increasing TiO2 /CNT content; While the DC resistivity changed little when the CNT content was smaller than 0.76 vol.% or larger than 2.25 vol.%. Therefore, the percolation interval of cement-based nanocomposites with TiO2 /CNT is 0.76–2.25 vol.%. When 1.16 vol.% of TiO2 /CNT was incorporated, the DC resistivity of cement-based nanocomposites decreases by 95.1%, 96.2%, and 95.3% at 3, 7, and 28 d, respectively. In addition, the DC resistivity does not change significantly with the curing age. Figure 6.6 shows the AC resistivity of cement-based nanocomposites without/with TiO2 /CNT at the curing age of 3, 7, and 28 d. The AC resistivity shows similar trend with DC resistivity. The percolation interval of cement-based nanocomposites with TiO2 /CNT is 0.76–2.25 vol.%. At the same curing age, the AC resistivity of cement-based nanocomposites decreases with the increase of the test frequency. This phenomenon is particularly evident for cement-based nanocomposites with doping

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Fig. 6.5 DC electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT

levels less than 0.76 vol.% of TiO2 /CNT. This is mainly due to the fact that the polarization phenomenon is more pronounced in cement-based nanocomposites with low content of TiO2 /CNT. The AC resistivity of cement-based nanocomposites also increases with curing age. However, the growth rate of AC resistivity with curing age is smaller for the cement-based nanocomposites with high-content TiO2 /CNT than that with low-content TiO2 /CNT, as with the increase of TiO2 /CNT content, the conductive network is gradually improved so that it is less affected by the hydration of cement. AC impedance spectra and equivalent circuits were used to analyze the conductivity mechanism of cement-based nanocomposites with TiO2 /CNT. In the blank cement-based composites, the bulk cement matrix, pore solution and electrode affect the AC impedance spectrum. Hence the equivalent circuit can be viewed as a series connection of three parts: pore solution Rs , bulk cement matrix (capacitor original Q1 and resistor R1 ) and electrode (capacitor original Q2 and resistor R2 ), denoted as Rs (Q1 R1 )(Q2 R2 ), as shown in Fig. 6.7a. In cement-based nanocomposites with TiO2 /CNT, the bulk cement matrix, the pore solution, the electrodes and the conductive TiO2 /CNT affect the AC impedance spectrum. The equivalent resistance at this point can be considered as a four-part series connection of the pore solution Rs , the

Fig. 6.6 AC electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT at the curing ages of a 3 d, b 7 d, and c 28 d

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Fig. 6.7 The equivalent circuits of cement-based nanocomposites without/with TiO2 /CNT. a Without TiO2 /CNT. b With TiO2 /CNT

bulk cement matrix (capacitor original Q1 and resistance R1 ), the electrode (capacitor original Q2 and resistance R2 ) and the conductive TiO2 /CNT (capacitor original Q3 and resistance R3 ), denoted as Rs (Q1 R1 )(Q2 R2 ) (Q3 R3 ), as shown in Fig. 6.7b. As in the analysis above, the measured AC impedance spectra are fitted to the equivalent circuits of Rs (Q1 R1 )(Q2 R2 ) for the blank cement-based composites and Rs (Q1 R1 )(Q2 R2 ) (Q3 R3 ) for the cement-based nanocomposites with TiO2 /CNT. The measured and fitted values of the AC impedance spectrum are represented by Nyquist plots, as shown in Fig. 6.8. As shown in Fig. 6.8, all the Chi-squared values are less than or equal to 1.32 × 10−3 . This indicates that the iterative error between the measured and fitted AC impedance values is small, and also shows that the selected equivalent circuit can accurately describe the composite AC impedance spectrum. The topology of the AC impedance spectrum of the cement-based nanocomposites with TiO2 /CNT first stabilizes, then changes and then stabilizes with the change of TiO2 /CNT content. The two turning content level of the AC impedance spectra are 0.15 vol.% and 0.45 vol.%, respectively. The two content level are exactly the boundary of percolation region. With the increase of TiO2 /CNT content, the circular arc in the high frequency band gradually decreases, while the linear part in the low frequency band gradually becomes circular. When the TiO2 /CNT content is 0.45 vol.%, the linear part of the low frequency band disappears and becomes a complete arc indicating that the AC impedance is controlled by charge diffusion to electron conductivity. This indicates that the structural unit consisting of TiO2 /CNT and bulk cement matrix has played a major role in the conductive pathway. This is consistent with the resistivity test results above.

6.4.2 Self-Sensing Properties Figure 6.9 shows the relationship between the resistivity rate of change and stress/strain for cement-based nanocomposites without/with TiO2 /CNT under seven cyclic loads with a maximum loading amplitude of 8 MPa. It can be seen from

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Fig. 6.8 AC impedance spectrum of cement-based nanocomposites without/with TiO2 /CNT. a Without TiO2 /CNT. b With 0.19 vol.% of TiO2 /CNT. c With 0.38 vol.% of TiO2 /CNT. d With 0.76 vol.% of TiO2 /CNT. e With 1.15 vol.% of TiO2 /CNT. f With 2.25 vol.% of TiO2 /CNT. g With 2.98 vol.% of TiO2 /CNT. h With 3.69 vol.% of TiO2 /CNT. i With 4.40 vol.% of TiO2 /CNT. j With 5.78 vol.% of TiO2 /CNT

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Fig. 6.9a–j the resistivity change rate increases with increasing stress/strain and decreases with decreasing stress/strain showing a regular variation, but the overall resistivity change rate shows an increasing trend. This rising trend is due to the polarization effect. This indicates that ionic conductivity still plays a larger role in the conductive mode of cement-based nanocomposites when the TiO2 /CNT content is low. As can be seen from Fig. 6.9k–t, the resistivity variation of cement-based nanocomposites increases with increasing stress/strain and decreases with decreasing stress/strain with no polarization, showing good synchronization and repeatability. As shown in Fig. 6.9u, the maximum resistivity change of cement-based nanocomposites reaches −9.50% after adding 4.40 vol.% of TiO2 /CNT. Figure 6.10 shows the stress and strain sensitivity of cement-based nanocomposites without/with TiO2 /CNT under cyclic loading with amplitude of 8 MPa. The stress sensitivity and strain sensitivity of cement-based nanocomposites both show a trend of increasing and then decreasing with the increase of TiO2 /CNT content. The stress and strain sensitivities reach 1.18%/MPa and 317, respectively, when 4.40 vol.% of TiO2 /CNT is incorporated. Noteworthily, the highest strain sensitivity is about 158 times higher than that of ordinary strain gauges (approximately 2). Figure 6.11 shows the compressive stress/strain and fractional change in electrical resistivity to compressive strain of cement-based nanocomposites without/with TiO2 /CNT under compressive stress amplitudes of 2, 4, and 6 MPa. From Fig. 6.11a– t, it can be seen that the rate of change of resistivity increases with the stress/strain. The resistivity change rate of cement-based nanocomposites has an overall increasing trend when the TiO2 /CNT content is less than 2.25 vol.%, indicating the presence of polarization. Meanwhile, the resistivity change rate of cement-based nanocomposites with 2.25–5.78 vol.% of TiO2 /CNT shows good synchronization and repeatability. The maximum resistivity change rates of cement-based nanocomposites were −0.04%/−0.21%/−0.61%, −0.02%/−0.10%/−0.21%, −0.07%/−0.27%/−0.44%, −0.18%/−0.30%/−0.37%, −0.60%/−1.14%/−1.60%, −0.64%/−1.42%/−2.25%, −1.34%/−3.16%/−4.59%, −1.27%/−3.01%/−4.73%, −2.74%/−4.96%/−6.92%, and −0.46%/−2.09%/−4.12% at the loading amplitude of 2 MPa/4 MPa/6 MPa, when 0 vol.%, 0.19 vol.%, 0.38 vol.%, 0.76 vol.%, 1.15 vol.%, 2.25 vol.%, 2.98 vol.%, 3.69 vol.%, 4.40 vol.%, and 5.78 vol.% of TiO2 /CNT are incorporated, respectively. Overall, the maximum resistivity variation increases with the increase of loading amplitude. Figure 6.12 shows the stress and strain sensitivities of cement-based nanocomposites without/with TiO2 /CNT under compressive stress amplitudes of 2, 4 and 6 MPa. The stress and strain sensitivities of cement-based nanocomposites with 2.25–5.78 vol.% of TiO2 /CNT increase with the loading amplitude. The stress/strain sensitivities of cement-based nanocomposites with 4.40 vol.% of TiO2 /CNT reach 1.35%/MPa/364, 1.22%/MPa/329, and 1.14%/MPa/308 at the loading amplitude of 2 MPa, 4 MPa and 6 MPa, respectively. Figure 6.13 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT under 7 times of cyclic loading at loading rate of 0.2, 0.4, 0.6 and 0.8 mm/min. The resistivity rates of change with stress/strain of cement-based nanocomposites with 2.25–5.78 vol.%

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Fig. 6.9 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT under repeated compressive loading with stress amplitude of 8 MPa. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.19 vol.%, c 0.38 vol.%, d 0.76 vol.%, e 1.15 vol.%, f 2.25 vol.%, g 2.98 vol.%, h 3.69 vol.%, i 4.40 vol.%, and j 5.78 vol.% of TiO2 /CNT. Strain-FCR of cement-based nanocomposites with k 0 vol.%, l 0.19 vol.%, m 0.38 vol.%, n 0.76 vol.%, o 1.15 vol.%, p 2.25 vol.%, q 2.98 vol.%, r 3.69 vol.%, s 4.40 vol.%, and t 5.78 vol.% of TiO2 /CNT. u The maximum FCR of cement-based nanocomposites without/with TiO2 /CNT

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Fig. 6.10 Sensitivity of cement-based nanocomposites without/with TiO2 /CNT under 7 times of cyclic compressive loading. a Stress sensitivity. b Strain sensitivity

of TiO2 /CNT show good synchronization and repeatability at loading rates of 0.2, 0.4, 0.6 and 0.8 mm/min. As shown in Fig. 6.13t, the maximum resistivity change rate of cement-based nanocomposites with TiO2 /CNT decreases with the loading rate. Figure 6.14 shows the sensitivity of cement-based nanocomposites without/with TiO2 /CNT under 7 times of cyclic compressive loading at loading rate of 0.2, 0.4, 0.6 and 0.8 mm/min. The stress and strain sensitivities of cement-based nanocomposites are little affected by the loading rate when the TiO2 /CNT content is less than 2.98 vol.%. Moreover, the loading rate shows influence on the sensitivity of cement-based nanocomposites with 3.69–5.78 vol.% of TiO2 /CNT. The stress/strain sensitivities of cement-based nanocomposites with 4.40 vol.% of TiO2 /CNT are 1.13%/MPa/303, 1.05%/MPa/281, 1.00%/MPa/269, and 0.97%/MPa/259 at the loading rates of 0.2 mm/min, 0.4 mm/min, 0.6 mm/min, and 0.8 mm/min, respectively. Figure 6.15 shows the compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT under ultimate load. The change of resistivity of cement-based nanocomposites increases with the stress/strain, showing good synchronization. The change rates of resistivity of cement-based composites at ultimate load are −5.48, −5.68, −4.64, −8.62, −30.79, −74.82, −73.82, −75.33, −75.33 −84.09, and −83.12% when 0 vol.%, 0.19 vol.%, 0.38 vol.%, 0.76 vol.%, 1.15 vol.%, 2.25 vol.%, 2.98 vol.%, 3.69 vol.%, 4.40 vol.%, and 5.78 vol.% of TiO2 /CNT are incorporated, respectively. In particular, the resistivity change varies synchronously with stress/strain during compression to damage when the TiO2 /CNT content exceeds 1.15 vol.%. Figure 6.16 shows the stress and strain sensitivities of cement-based nanocomposites without/with TiO2 /CNT under ultimate load. As shown in Fig. 6.16, the stress and strain sensitivities of cement-based nanocomposites with TiO2 /CNT generally increase with the TiO2 /CNT content. The stress/strain resistivities of cement-based nanocomposites at ultimate load are 0.06%/MPa/12, 0.07%/MPa/17, 0.06%/MPa/17, 0.11%/MPa/28, 0.37%/MPa/78, 1.03%/MPa/182, 0.95%/MPa/206, 0.95%/MPa/182, 1.04%/MPa/217, 1.04%/MPa/200 when 0 vol.%, 0.19 vol.%, 0.38

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Fig. 6.11 Compressive stress/strain and fractional change in electrical resistivity to compressive strain of cement-based nanocomposites without/with TiO2 /CNT under compressive stress amplitudes of 2, 4, and 6 MPa. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.19 vol.%, c 0.38 vol.%, d 0.76 vol.%, e 1.15 vol.%, f 2.25 vol.%, g 2.98 vol.%, h 3.69 vol.%, i 4.40 vol.%, and j 5.78 vol.% of TiO2 /CNT. Strain-FCR of cement-based nanocomposites with k 0 vol.%, l 0.19 vol.%, m 0.38 vol.%, n 0.76 vol.%, o 1.15 vol.%, p 2.25 vol.%, q 2.98 vol.%, r 3.69 vol.%, s 4.40 vol.%, and t 5.78 vol.% of TiO2 /CNT. u The maximum FCR of cement-based nanocomposites without/with TiO2 /CNT

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Fig. 6.12 Sensitivity of cement-based nanocomposites without/with TiO2 /CNT under compressive stress amplitudes of 2, 4 and 6 MPa. a Stress sensitivity. b Strain sensitivity

vol.%, 0.76 vol.%, 1.15 vol.%, 2.25 vol.%, 2.98 vol.%, 3.69 vol.%, 4.40 vol.%, and 5.78 vol.% of TiO2 /CNT are incorporated, respectively. Figure 6.17 shows the thermal sensitivity of cement-based nanocomposites without/with TiO2 /CNT. It can be seen from Fig. 6.17 that the resistivities all decrease with temperature and show good repeatability. Moreover, the resistivity change rate generally decreases with TiO2 /CNT content. From −30 to 60 °C, the resistivities of cement-based composites with 0, 0.19, 0.38, 0.76, 1.15, 2.25, 2.98, 3.69, 4.40, and 5.78 vol.% of TiO2 /CNT decrease by 98.68%, 98.44%, 98.50%, 97.63%, 78.09%, 41.72%, 41.34%, 41.00%, 38.55%, 38.55%, and 43.81%, respectively. When the TiO2 /CNT content is less than 1.15 vol.%, the conductivity of cement-based nanocomposites is mainly dominated by ionic conductivity that is greatly influenced by temperature. With the increase of TiO2 /CNT content, the conductivity of cementbased nanocomposites converts from ionic to electronic conductivity. Hence, the conductivity is less affected by temperature when the TiO2 /CNT content exceeds 2.25 vol.%. Figure 6.18 shows the thermal sensitivity of cement-based nanocomposites without/with TiO2 /CNT under −30 to 60 °C. The thermal sensitivity of cement-based nanocomposites generally decreases with TiO2 /CNT content. The thermal sensitivities of cement-based nanocomposites are 1.10%/°C, 1.09%/°C, 1.09%/°C, 1.08%/°C, 0.87%/°C, 0.46%/°C, 0.46%/°C, 0.46%/°C, 0.43%/°C, and 0.49%/°C when 0 vol.%, 0.19 vol.%, 0.38 vol.%, 0.76 vol.%, 1.15 vol.%, 2.25 vol.%, 2.98 vol.%, 3.69 vol.%, 4.40 vol.%, and 5.78 vol.% of TiO2 /CNT are incorporated, respectively. Based on the results, the percolation threshold zone ranges from 0.15 to 0.45 vol.%.

6.4.3 Electromagnetic Shielding and Absorption Properties Figure 6.19 shows the electromagnetic shielding properties of cement-based nanocomposites with different content of TiO2 /CNT. As depicted in Fig. 6.19,

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Fig. 6.13 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT under 7 times of cyclic loading at loading rate of 0.2, 0.4, 0.6 and 0.8 mm/min. Stress-FCR of cement-based nanocomposites with a 0 vol.%, b 0.19 vol.%, c 0.38 vol.%, d 0.76 vol.%, e 1.15 vol.%, f 2.25 vol.%, g 2.98 vol.%, h 3.69 vol.%, i 4.40 vol.%, and j 5.78 vol.% of TiO2 /CNT. Strain-FCR of cement-based nanocomposites with k 0 vol.%, l 0.19 vol.%, m 0.38 vol.%, n 0.76 vol.%, o 1.15 vol.%, p 2.25 vol.%, q 2.98 vol.%, r 3.69 vol.%, s 4.40 vol.%, and t 5.78 vol.% of TiO2 /CNT. u The maximum FCR of cement-based nanocomposites without/with TiO2 /CNT

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Fig. 6.14 Sensitivity of cement-based nanocomposites without/with TiO2 /CNT under 7 times of cyclic compressive loading at loading rate of 0.2, 0.4, 0.6 and 0.8 mm/min. a Stress sensitivity. b Strain sensitivity

the presence of TiO2 /CNT increases the electromagnetic shielding effectiveness of cement-based nanocomposites. The electromagnetic shielding effectiveness of cement-based nanocomposites with 5.78 vol.% of TiO2 /CNT reaches 0.49 and 3.4 dB at 2 GHz and 18 GHz, respectively, increased by 220 and 30% compared with that of blank cement-based composites. Figure 6.20 exhibits the reflectivity of cement-based nanocomposites without/with TiO2 /CNT in the frequency range of 2–18 GHz. As shown in Fig. 6.20, the reflectivity of cement-based nanocomposites decreases with the content of TiO2 /CNT. The incorporation of 5.78 vol.% of TiO2 /CNT can achieve −5.26, −3.82, −12.85, and −32.01 dB of reflectivity at the band of 2–4 GHz, 4–8 GHz, 8–12.5 GHz, and 12.5–18 GHz, respectively, increased by 230, 120, 160, and 690% compared with the reflectivity of blank cement-based composites. Figure 6.21 shows the electromagnetic parameters of cement-based nanocomposites without/with TiO2 /CNT. It can be seen from Fig. 6.21 that the real part of the dielectric constant of cement-based nanocomposites increases with as the content of TiO2 /CNT, which indicates that the degree of dielectric polarization of electromagnetic wave on the mortar increases. Meanwhile, the imaginary part of the dielectric constant and the electrical loss tangent of cement-based nanocomposites also increase with TiO2 /CNT content, leading to the increase of the dielectric loss of the paste to electromagnetic waves. However, the imaginary part of magnetic permeability and magnetic loss tangent of cement-based nanocomposites with TiO2 /CNT are basically zero, which indicates that TiO2 /CNT have no magnetic loss ability to electromagnetic waves.

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Fig. 6.15 Compressive stress/strain and fractional change in electrical resistivity of cement-based nanocomposites without/with TiO2 /CNT under ultimate load. a Stress and fractional change in resistivity. b Strain and fractional change in resistivity. c The maximum fraction change in electrical resistivity

6.5 Summary This chapter demonstrates the effect of TiO2 /CNT on the mechanical properties and function/smart properties, including electrical, self-sensing, and electromagnetic shielding and absorption properties of a new-generation cement-based nanocomposite with TiO2 /CNT. The conclusions can be summarized as below.

6.5 Summary

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Fig. 6.16 Sensitivity of cement-based nanocomposites without/with TiO2 /CNT under ultimate load. a Stress sensitivity. b Strain sensitivity

(1) The compressive/flexural strengths of cement-based nanocomposites range within ± 10% compared with that of blank cement-based composites. Therefore, the addition of TiO2 /CNT shows little effect on the strength of cement-based nanocomposites. (2) TiO2 /CNT can endow cement-based nanocomposites with excellent electrical properties. The percolation interval of cement-based nanocomposites with TiO2 /CNT ranges from 0.76 to 2.25 vol.%. The DC/AC resistivity of cementbased nanocomposites can be as low as 14,549/717 Ω cm, respectively, implying the formation of conductive pathways composed of TiO2 /CNT. (3) Cement-based nanocomposites with TiO2 /CNT possess excellent self-sensing properties. The maximum resistivity change, stress sensitivity and strain sensitivity of the nanocomposites increase and then decrease with the increase of NCB/CNT content. The maximum resistivity change, stress sensitivity and strain sensitivity of the nanocomposites reach 9.50%, 1.18%/MPa, and 317, respectively. Moreover, the self-sensing performance is quite stable at different loading amplitude, loading rate, and moisture content. (4) Cement-based nanocomposites with TiO2 /CNT possess good electromagnetic shielding and adsorption properties. The electromagnetic shielding effectiveness of cement-based nanocomposites with TiO2 /CNT reaches 0.49 and 3.4 dB at 2 GHz and 18 GHz, respectively, increased by 220 and 30% compared with that of blank cement-based composites. Moreover, the presence of TiO2 /CNT can achieve −5.26, −3.82, −12.85, and −32.01 dB of reflectivity at the band of 2–4 GHz, 4–8 GHz, 8–12.5 GHz, and 12.5–18 GHz, respectively, increased by 230, 120, 160, and 690% compared with the reflectivity of blank cement-based composites. In summary, the cement-based nanocomposites with TiO2 /CNT possess outstanding self-sensing properties to stress, strain, and temperature on the promise of good mechanical properties. These merits enable the developed nanocomposites’ broad application potential for developing multifunctional/smart infrastructures.

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Fig. 6.17 Thermal sensitivity of cement-based nanocomposites without/with TiO2 /CNT. a Without TiO2 /CNT. b With 0.19 vol.% of TiO2 /CNT. c With 0.38 vol.% of TiO2 /CNT. d With 0.76 vol.% of TiO2 /CNT. e With 1.15 vol.% of TiO2 /CNT. f With 2.25 vol.% of TiO2 /CNT. g With 2.98 vol.% of TiO2 /CNT. h With 3.69 vol.% of TiO2 /CNT. i With 4.40 vol.% of TiO2 /CNT. l With 5.78 vol.% of TiO2 /CNT

6.5 Summary Fig. 6.18 Thermal sensitivity of cement-based nanocomposites without/with TiO2 /CNT under −30 to 60 °C

Fig. 6.19 Electromagnetic shielding properties of cement-based nanocomposites with different content of TiO2 /CNT

Fig. 6.20 Reflectivity of cement-based nanocomposites without/with TiO2 /CNT in the frequency of 2–18 GHz

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Fig. 6.21 Electromagnetic parameters of cement-based nanocomposites without/with TiO2 /CNT. a Real part of the dielectric constant. b Imaginary part of the dielectric constant. c Real part of the magnetic permeability. d Imaginary part of the magnetic permeability. e Dielectric loss angle of tangent. f Electromagnetic loss angle of tangent

References 1. D. Tasis, N. Tagmatarchis, A. Bianco, M. Prato, Chemistry of carbon nanotubes. Chem. Rev. 106, 1105–1136 (2006) 2. J. Hilding, E.A. Grulke, Z.G. Zhang, F. Lockwood, Dispersion of carbon nanotubes in liquids. J. Disper. Sci. Technol. 24, 1–41 (2003) 3. B. Han, L. Zhang, S. Sun, X. Yu, X. Dong, T. Wu, J. Ou, Electrostatic self-assembly NCB/CNT composite fillers reinforced cement-based materials with multifunctionality. Compos. A Appl. Sci. Manuf. 79, 103–115 (2015) 4. L. Zhang, S. Ding, L. Li, S. Dong, D. Wang, X. Yu, B. Han, Effect of characteristics of assembly unit of CNT/NCB composite fillers on properties of smart cement-based materials. Compos. A Appl. Sci. Manuf. 109, 303–320 (2018) 5. B. Han, S. Sun, S. Ding, L. Zhang, X. Yu, J. Ou, Review of nanocarbon-engineered multifunctional cementitious composites. Compos. A Appl. Sci. Manuf. 70, 69–81 (2015)

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6. S. Park, J. Hwang, G. Park, J. Ha, M. Zhang, D. Kim, D.J. Yun, S. Lee, S.H. Lee, Modeling the electrical resistivity of polymer composites with segregated structures. Nat. Commun. 10, 2537 (2019) 7. L. Zhang, L. Li, Y. Wang, X. Yu, B. Han, Multifunctional cement-based materials modified with electrostatic self-assembled CNT/TiO2 composite filler. Constr. Build. Mater. 238, 117787 (2020) 8. Z. Li, S. Ding, X. Yu, B. Han, J. Ou, Multifunctional cementitious composites modified with nano titanium dioxide: a review. Compos. A Appl. Sci. Manuf. 111, 115–137 (2018) 9. G. Xiong, Cement-Based Composite Material for Microwave Absorbing (Nanjing University of Technology).

Chapter 7

New-Generation Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/GNP

7.1 Introduction Graphene nanoplatelet (GNP), as a typical 2-D nano carbon material, offers a possibility to develop high-performance and functional/smart cement-based nanocomposites through its excellent mechanical, electrical, and thermal properties [1–3]. Meanwhile, the cost-effective 0-D nano carbon material, carbon nano black (NCB), can endow cement-based nanocomposites with remarkable electrical conductivity and self-sensing properties [4, 5]. However, the cement-based nanocomposites with NCB always exhibit low mechanical properties as the water adsorption of NCB inhibits hydration of cement [6]. Therefore, NCB/GNP may perform synergistic effect that not only improve the dispersibility of GNP by the volume exclusion effect of NCB but play the short-range and long-range electrical conductivity [7–9], which may endow cement-based nanocomposites with excellent functional/smart performance without notably reducing their mechanical properties. In this chapter, the mechanical, electrical, self-sensing, and electromagnetic shielding and absorption properties of a new-generation cement-based nanocomposites with NCB/GNP are introduced and the corresponding modification mechanisms are described.

7.2 Preparation of Cement-Based Nanocomposites with Electrostatic Self-Assembly NCB/GNP The raw materials used to fabricate cement-based nanocomposites with NCB/GNP included Portland cement, SP, and NCB/GNP. The properties and morphology of NCB/GNP are shown in Table 7.1 and Fig. 7.1, respectively. The properties of other raw materials refer to Sect. 2.2. The mix proportion and fabrication process of cementbased composites in this chapter are shown in Tables 7.2 and 7.3, respectively. It is © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 S. Ding et al., New-Generation Cement-Based Nanocomposites, https://doi.org/10.1007/978-981-99-2306-9_7

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Table 7.1 Properties of NCB/GNP NCB:GNP (mass ratio)

Graphene layers

Lateral size (μm)

Graphene purity (wt%)

Particle size of NCB

Specific surface area of NCB/GNP (m2 /g)

Specific resistivity (Ω cm)

80:20

12) causes hydrogen to dissociate from the GO carboxyl sites. In addition to the cationic effect, GO reacts with hydroxide ions in alkaline solutions and loses the majority of its oxygen-bearing groups. The oxygen groups disappear in alkaline solutions, the overall force acting between the GO layers switches from repulsion to attraction, causing GO to aggregate [18]. For some particulate and hydrophobic nanofillers, they are generally poor load carriers in cement-based composite. In addition, strong matrix-filler bonds are hard to accomplish, leading to poor interfacial load transfer during mechanical deformation and high electron and phonon scatter, compromising electrical and thermal properties. (3) The features of multi-component, multi-phase, multi-scale, and heterogeneous caused by the presence of aggregates and interfacial transition zone compromise the enhancement/modification of cement-based composite with a low dosage of nanomaterials. In microscale level, cement-based composite is a porous material and consists of solid phases in contact and in equilibrium with a pore solution. The nano-reinforcement effect is very sensitive to the pore structures of cement-based composites as nanomaterials are more effective for reinforcing cement-based composites with low W/C (i.e., dense structure). Meanwhile, the thermodynamically metastable feature of cement-based composites may lead to time-dependent and environment-dependent performance of cement-based nanocomposites. The nano enhancement/modification effect is weakened and even invalid during the service period, for example, electrical conductivity of cement-based nanocomposites decreases with the increasing curing age. (4) Understanding on the nano enhancement/modification mechanisms is on the weak side because of the complex nature (mainly including heterogeneity and anisotropy) of cement-based nanocomposites with multi-component, multiphase, and multi-scale characteristics, in particular with the addition of complicated multiscale, hierarchical nanomaterials. The factors that affect the properties/performances of cement-based nanocomposites are also various, such as source of raw materials, W/C, curing condition, curing age, chemical admixtures, etc. This issue makes it extremely difficult to design the cement-based nanocomposites specifically for a certain set of specific properties or for particular applications from a scientific standpoint. Indeed, the design of the cementbased nanocomposites, more often, is based on high throughput screenings and empirical trials. Comprehensive and precise constitutive models for quantitatively describing and forecasting the behaviors of cement-based nanocomposites in different temporal and spatial conditions based on experiments and numerical simulations are rare. In addition to the challenges of figuring out the complex mechanisms, challenges still exist in accurately characterizing the properties/performances of cement-based nanocomposites. For example, the interfacial shear strength at CF-CNT-matrix interface is hard to measure, which

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will determine the critical length of the fillers required for the most efficient load-transfer capability. The shortage of effective characterization methods, inevitably, constrains proper design of the cement-based nanocomposites that the extraordinary potential and multifunctionality of nanomaterials are fully realized. To address the above issues, the following strategies are suggested: (1) Designing delicate and feasible hierarchical nanostructured composites. Using hierarchical nanomaterials has become a major development for new-generation cement-based nanocomposites. Distinctive nanocomposites can be constructed via careful design and optimization, which would be beneficial for compensating the shortages of single nanoparticles and providing new functionalities such as stimuli-responsiveness, energy storage and conversion elements, real-time structural health monitoring, sensing, and vibrational damping in composites at the same time. For example, there has been substantial progress in synthesizing continuous fiber spinning with CNT and graphene, and also various yet controllable CNT and graphene 3D nanostructures. The continuous CNT or graphene spun fibers can exceed the mechanical properties of CF that are used for state-of-the-art structural reinforcements in cement-based composites [19, 20]. The best load-carrying capability ever reached yet could be achieved by engineering the continuous CNT or graphene fiber preforms in composite design with as high a loading of the filler as possible that is aligned in the direction of the load, which could provide the opportunity to translate the exceptional properties of the individual CNT and graphene into a variety of engineering applications, including structural applications, multifunctional composites, electrical and thermal management, energy-absorbing composites, and self-stiffening composites with the required properties as shown in Fig. 10.2. (2) Developing new cementitious system with tailored microstructure and performance. Cement is the most important component of cement-based nanocomposites. The microstructure and performance of cement-based nanocomposites can be controlled through the modulation and optimization of cement mineral compositions and cement manufacturing process. (3) Deeply exploring the mechanisms at multiscale. Based on experimental approaches, theoretical and numerical simulations, and nano-tomacroscale analysis, the hierarchical research paradigm should be used to analyze complex/multiscale structures/properties/performances of cementbased nanocomposites and establish theoretical models to elucidate the mechanisms occurring at the nanoscale to macroscale. First-principle calculations, molecular dynamics methods combined with the state-of-the-art characterization technologies such as cryo-electron microscopy, nano-CT, nanoindentation, synchrotron radiation, etc. are promising approaches to overcome this challenge. In addition, unified measurement standards with definite and repeatable processes are vital to evaluate the properties/performances of different cementbased nanocomposites in a reproducible way, and even to allow comparison

10.4 Bridging Nanomaterials to Macroscale Cement-Based Nanocomposites

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Fig. 10.2 Schematic of new-generation cement-based nanocomposites with various CNT/graphene composites for the prospective applications

among the characterizations using different technologies, which would be beneficial for ascertaining the underlying physical and chemical mechanisms of cement-based nanocomposite system. (4) Integrating design with multi-functionality. In addition to superior mechanical properties and durability, multifunctional integration is also an important development paradigm of new-generation cement-based nanocomposites. Implementing different functionalities and using microstructures to achieve special macroscopic properties and functionalities are gaining attention in the field of cement-based nanocomposites. Combining structural hierarchy with multidisciplinary integration is essential for the development of multifunctional new-generation cement-based nanocomposites, thus finding more real killer applications of new-generation cement-based nanocomposites. (5) Developing a materials innovation infrastructure. Due to the complexity, diversity and variability of cement-based nanocomposites, it is necessary to develop a materials innovation infrastructure based on materials genome engineering. To restructure or modify material structural units in nanoscale via interpreting material genetic code can draw the blueprint of nanoscale properties, thus providing

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Fig. 10.3 Discovery process of new-generation cement-based nanocomposites based on materials genome engineering

new theories and methods to develop new-generation cement-based nanocomposites. This new integrated design continuum, incorporating greater use of artificial intelligence, high throughput combinatorial processing, biotechnology, and digital data, will also replace lengthy and costly empirical studies with mathematical models and computational simulations, provide model parameters, validate key predictions, and supplement and extend the range of validity and reliability of the models. In addition, it will help to accelerate the discovery process and realize the scientific, informative, and standardized design, optimization, manufacturing, and deployment of new-generation cement-based nanocomposites, as shown in Fig. 10.3.

10.5 Summary Compared with other construction materials, the production of cement-based composites consumes the least amount of materials and energy, produces the least amount of harmful by-products, and causes the least amount of damage to environment. They are a responsible choice for sustainable development, and are still indispensable in the foreseeable future. In addition, the application room of cementbased compsites is constantly expanding. Some inherent weaknesses and the existing performances of cement-based composites make them impossible to fully meet

References

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the construction and creation of future human living space. The massive production and application of cement-based composites have an enormous impact on resources, energy as well as environment on earth. Nano science and technology is conducive to understand and tailor cement-based composites at a more fundamental level thus providing a transformative approach to solve the above issues and boosts the emergence and rapid development of cement-based nanocomposites. Cement-based nanocomposites can be smart/multifunctional, strong, durable, easy to fabricate, recyclable, eco-friendly, and low environmental footprint, in particular, carbon footprint, presenting the unlimited possibility for promoting sustainable development of cement-based composites. They have a wide application foreground in large/giant civil infrastructures (high-rise buildings, highway, bridges, runways for airport, continuous slab-type sleepers for high-speed trains, dam, nuclear power plant), resilent infrastructures in complex and extreme environments (ultra-low temperature, ultra-dry, vacuum, electromagnetic radiation, etc.), and extraterrestrial infrastructures, thus energizing the sustainable development of infrastructures for shaping and cementing human civilization. However, there exist some health, environmental, and safety concerns related to the fabrication and use of the cement-based nanocomposites. It is necessary not only to clarify the relationship between the composition, process, structure and performance of cement-based nanocomposites, but also to perform a life-cycle analysis (including economic, social and environmental aspects) to evaluate its sustainability. For this purpose, it is critical to study the basic theories (e.g., cementitious properties and mechanisms, quantitative relationship between composition-structure-process-performance) in depth from multiple disciplines (e.g., chemistry, physics, mathematics, materials, mechanics, civil engineering, mechanical engineering, computing science) and integrate advanced technologies (e.g., new nanotechnology, biotechnology, bionics, digital manufacturing/ construction, additive manufacturing, materials genome technology, metamaterial technology, artificial intelligence, digital twin technology, multi-scale/multiphysics simulation), to enrich the research paradigms, and to improve/develop rigorous standards/specifications for the development continuum of cement-based nanocomposites, i.e., discovery-development-property optimization-system design and integration-certification-manufacturing-deployment). Different engineering or scientific teams at different institutions. This system employs experienced teams at each stage of the process should work together and utilize and leverage their existing education infrastructure, experience, and expertise to further advance this goal.

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