Finding Solutions of the 21st Century Transportation Problems Through Research and Innovations (Sustainable Civil Infrastructures) 303079637X, 9783030796372

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Sustainable Civil Infrastructures

Zahid Hossain Musharraf Zaman Jiupeng Zhang   Editors

Finding Solutions of the 21st Century Transportation Problems Through Research and Innovations Proceedings of the 6th GeoChina International Conference on Civil & Transportation Infrastructures: From Engineering to Smart & Green Life Cycle Solutions – Nanchang, China, 2021

Sustainable Civil Infrastructures Editor-in-Chief Hany Farouk Shehata, SSIGE, Soil-Interaction Group in Egypt SSIGE, Cairo, Egypt Advisory Editors Khalid M. ElZahaby, Housing and Building National Research Center, Giza, Egypt Dar Hao Chen, Austin, TX, USA

Sustainable Civil Infrastructures (SUCI) is a series of peer-reviewed books and proceedings based on the best studies on emerging research from all fields related to sustainable infrastructures and aiming at improving our well-being and day-to-day lives. The infrastructures we are building today will shape our lives tomorrow. The complex and diverse nature of the impacts due to weather extremes on transportation and civil infrastructures can be seen in our roadways, bridges, and buildings. Extreme summer temperatures, droughts, flash floods, and rising numbers of freeze-thaw cycles pose challenges for civil infrastructure and can endanger public safety. We constantly hear how civil infrastructures need constant attention, preservation, and upgrading. Such improvements and developments would obviously benefit from our desired book series that provide sustainable engineering materials and designs. The economic impact is huge and much research has been conducted worldwide. The future holds many opportunities, not only for researchers in a given country, but also for the worldwide field engineers who apply and implement these technologies. We believe that no approach can succeed if it does not unite the efforts of various engineering disciplines from all over the world under one umbrella to offer a beacon of modern solutions to the global infrastructure. Experts from the various engineering disciplines around the globe will participate in this series, including: Geotechnical, Geological, Geoscience, Petroleum, Structural, Transportation, Bridge, Infrastructure, Energy, Architectural, Chemical and Materials, and other related Engineering disciplines. SUCI series is now indexed in SCOPUS and EI Compendex.

More information about this series at http://www.springer.com/series/5140

Zahid Hossain Musharraf Zaman Jiupeng Zhang •

•

Editors

Finding Solutions of the 21st Century Transportation Problems Through Research and Innovations Proceedings of the 6th GeoChina International Conference on Civil & Transportation Infrastructures: From Engineering to Smart & Green Life Cycle Solutions – Nanchang, China, 2021

123

Editors Zahid Hossain Civil Engineering Arkansas State University Jonesboro, AR, USA

Musharraf Zaman Civil Engineeeing University of Oklahoma Norman, OK, USA

Jiupeng Zhang School Highway Chang’an University Xian, China

ISSN 2366-3405 ISSN 2366-3413 (electronic) Sustainable Civil Infrastructures ISBN 978-3-030-79637-2 ISBN 978-3-030-79638-9 (eBook) https://doi.org/10.1007/978-3-030-79638-9 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 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 Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Introduction

This volume contains eleven papers that were accepted and presented at the GeoChina 2021 International Conference on Civil and Transportation Infrastructures: From Engineering to Smart and Green Life Cycle Solutions, held in Nanchang, China, from September 18 to 19, 2021. It presents data, discussions, conclusions, and recommendations drawn from research and innovations for solving transportation problems of the twenty-first century. In particular, it provides directions in tackling challenges in highway infrastructures, transportation geotechniques, advancements in recycling, soil stabilization, and reinforcement, and assessments of roadway conditions through experimental and modeling perspectives, numerical analyses, and case studies. Information presented in this volume is expected to help practicing transportation engineers, professionals, and researchers to build longer-lasting and economically sustainable transportation infrastructures, and thus save taxpayers’ money.

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Contents

Experimental Study on Strength Behavior of Clayey Soil Reinforced with Glass Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suchit Kumar Patel and Baleshwar Singh

1

Process for the Development of a Digital Twin of a Local Road – A Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wynand JvdM Steyn and André Broekman

11

Capturing the Moving Deflection Basin Under a Traffic Speed Deflectometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dominik Duschlbauer and Jeffrey Lee

23

Unconfined Compressive Strength of Compacted Tropical Soil Bio-treated with Bacillus Megaterium . . . . . . . . . . . . . . . . . . . . . . . . . . . Adrian Eberemu

34

Properties of Tropical Black Clay Treated with Selected Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. J. Osinubi, A. O. Eberemu, P. Azige, and P. Yohanna

52

Geothermal Pavements: An Experimental and Numerical Study on Thermal Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Xiaoying Gu, Nikolas Makasis, Yaser Motamedi, Arul Arulrajah, Suksun Horpibulsuk, and Guillermo A. Narsilio Mechanistic Performance Analysis of Fiber-Reinforced Asphalt Pavement Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nitish R. Bastola, Mena I. Souliman, Ashish Tripathi, and Alexander Pearson Effect of Using Copper Tailings as Replacement of Fine Aggregate for Concrete Pavement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Meng-Yao Gao, Sung-Ching Chen, and Wei-Ting Lin

65

83

91

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viii

Contents

Research Progress of Fiber Reinforced Soil . . . . . . . . . . . . . . . . . . . . . . 102 Changgen Yan and Yinsen Tang Empirical Study of Warm Mix Asphalt Incorporating Recycled Asphalt Pavement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Ronald Fabrice Pouokam Kamdem, Jacob Adedayo Adedeji, and Mohamed M. H. Mostafa A Feasibility Study Towards the Application of Municipal Waste Pyrolysis Oil in Bituminous Pavement . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Swanand B. Kulkarni and Mahadeo S. Ranadive Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

About the Editors

Dr. Zahid Hossain serves as an associate professor and co-director of Civil Engineering at Arkansas State University (A-State). He also serves as an associate director of the Transportation Consortium of the South-Central States (TranSET). He has over 20 years of diversified experience in teaching, leadership, scholarship, and professional development activities with an emphasis on analyzing and developing sustainable geotechnical and transportation materials and technologies through fundamental science and applied approaches. He has taught about 25 different graduate and undergraduate level courses at multiple institutions in the USA and overseas. He has received and managed about $3.0M of research funds from various sources that include the National Science Foundation, National Aeronautics and Space Administration, and Departments of Transportation. He has authored/co-authored over 150 peer-reviewed chapters, journal articles, and conference papers. He has delivered over 100 technical presentations at local, regional, national, and international conferences and symposia. He received multiple prestigious awards including the 2019 A-State Faculty Award for Advising, the 2014 Ralph E. Powe Jr. Faculty Enhancement Award from Oak Ridge Associated Universities, the 2014 A-State Faculty Award for Scholarship, and the 2012 University Transportation Center Award from the US Department of Transportation for his outstanding contribution in transportation research, professional service, and academic excellence. He has served the professional societies in various capacities such as editors and reviewers of professional journals and conferences, and members of several scientific boards that include the National Academy of Sciences. He is a professional engineer (PE) in Arkansas. Dr. Musharraf Zaman holds the Aaron Alexander Professorship in Civil Engineering and Alumni Chair Professorship in Petroleum and Geological Engineering at the University of Oklahoma (OU), Norman. He has been serving as Director of the Southern Plains Transportation Center (SPTC)—a consortium of eight universities in U.S. DOT Region 6—for more than six years. He served as Associate Dean for Research and Graduate Programs in OU Gallogly College of Engineering for more than eight years. He is Prolific Teacher and highly ix

x

About the Editors

accomplished Researcher. During his tenure at OU, he has received several prestigious national-level teaching awards from the American Society of Engineering Education. He also received the David Ross Boyd Professorship, the highest lifelong teaching award given by OU. During his tenure at OU, he has received more than $30 million in external funding from various state and federal agencies and the industry. He has published over 350 peer-reviewed journal and conference papers. Several of his papers have won prestigious awards from international societies and organizations. He has supervised more than 80 master theses and doctoral dissertations to completion. In 2011, he won the prestigious Outstanding Contribution Award, given by IACMAG, for lifelong contributions in geomechanics. Dr. Jiupeng Zhang is a professor of Transportation Infrastructure Engineering and the vice dean of School of Highway at Chang’an University, China. He is a professionally registered pavement engineer with a research interest in pavement mechanics, pavement materials, construction, and maintenance. He completed both his undergraduate and graduate studies at the Southeast University, China. He has authored and co-authored more than 100 peer-reviewed journal articles, and about 30 referred conference papers, and served as the editor board member of the International Journal of Transportation Science and Technology, the China Journal of Highway and Transport, and the journal of Advances in Civil Engineering. Recently, he received eight S&T Awards from Jiangsu province, Henan province and China Highway and Transportation Society (CHTS) for his outstanding contributions to paving materials and construction. He won the FokYingTung Youth Teacher Award, the Wufu-Zhenhua Excellent Teacher Award, and the Shaanxi Youth S&T Nova Award for his contributions in transportation infrastructures research, professional service, and academic excellence.

Experimental Study on Strength Behavior of Clayey Soil Reinforced with Glass Fiber Suchit Kumar Patel1(B) and Baleshwar Singh2 1 Department of Transport Science and Technology, Central University of Jharkhand,

Ranchi 835205, India [email protected] 2 Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India [email protected]

Abstract. This study demonstrates the strength characteristics of a clayey soil reinforced with randomly distributed glass fibers by means of unconfined compression (UC) and California bearing ratio (CBR) tests for its application as a subgrade material for flexible road pavement. A low plastic clayey soil (CL) was mixed with 20 mm glass fibers in different proportions up to 1% by dry weight of soil. The test results show that the UCS and soaked CBR values of the clayey soil improve markedly with glass fiber inclusion along with modulus and energy absorption capability (EAC). Inclusion of glass fiber significantly reduces brittle behavior of the clayey soil by increasing the failure axial strain and decreasing post-peak strength loss, and this can be noted from the specimen failure mode. The UCS, CBR and subgrade modulus values are noted to increase with fiber content and reach their optimum values at 0.75% fiber content. The soil ductility increases continuously with fiber content. Increasing EAC indicates that the reinforced soil needs higher energy for its deformation, and has better bearing capacity. The glass fiber is found to be a good reinforcing material with the clayey soil for its application as subgrade material of low-volume flexible road pavement. Keywords: UCS test · CBR test · Glass fiber · Subgrade modulus · Failure mode

1 Introduction With rapid worldwide development, there is an increasing demand for the construction of new infrastructures facilities including roads and embankments which have led to the utilization of marginal sites. Local soils which are abundantly available at construction sites may not be capable of meeting the engineering requirements for their use in road pavements. The use of randomly distributed short fibers as reinforcement can significantly enhance the engineering aspects of such soils for their application in road pavements. Fiber-reinforced soil is relatively new soil reinforcement method. Similar to the root-reinforced soil, fiber increases the soil shear strength by added mobilized cohesion (Waldron 1977). © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 1–10, 2021. https://doi.org/10.1007/978-3-030-79638-9_1

2

S. K. Patel and B. Singh

Fiber-reinforced soil is different than traditional planar reinforcement. It retains strength isotropy of soil mass by eluding the formation of any possible weak plane. Fibers can be used even in places where the application of planar reinforcement is restricted due to space limitation (Zornberg 2002). Researchers have revealed that the inclusion of discrete fibers effectively enriches the stress-strain behavior, shear strength parameters, load bearing capacity and ductility of soils (Tang et al. 2007; Estabragh et al. 2011; Li and Zornberg 2013; Patel and Singh 2017, 2020). The different factors influencing the strength and deformation aspects of fiber-reinforced soil are fiber properties (fiber type, fiber length and content, fiber orientation), soil properties (particle size, shape and gradation), specimen molded states (Patel and Singh 2017, 2020), soil-fibers surficial interaction (Li et al. 2014). Several fibers (palm, polypropylene, polyethylene, polyester, linen fibers, rubber products and plastic strip) of varying length and content have been used with sand, clay and fly ash to investigate their CBR values for possible field applications (Benson and Khire 1994; Kumar et al. 1999; Kumar et al. 2005; Kumar and Singh 2008; Pradhan et al. 2012; Rao and Nasar 2012; Muntohar et al. 2013; Jha et al. 2014; Sarbaz et al. 2014; Priyadarshee et al. 2018), and the CBR values are noted to enhance significantly. Due to high tensile strength, stiffness, chemical resistance, non-biodegradability and thermal resistance, glass fibers have been used in the manufacture of different polymeric composites. These properties of glass fiber make it an exciting material to be used as a reinforcing element in soils. To this aim, an attempt has been made to investigate the use of glass fibers as reinforcement in a clayey soil for their application in road pavements by conducting unconfined compression (UC) and California Bearing Ratio (CBR) tests.

2 Materials and Methods A clayey soil containing sand size, silt size and clay size particle fractions, respectively as 21%, 54% and 25%, was used. The values of liquid limit, plastic limit, specific gravity, OMC and MDU of the soil were 46%, 25%, 2.63, 19.4% and 16.8 kN/m3 , respectively. As per Unified Soil Classification System (ASTM D2487–06), the soil was classified as low plasticity clay (CL). Glass fibers of 0.15 mm diameter and 20 mm length with four different fiber contents (f c = 0.25, 0.5, 0.75 and 1% by dry weight of soil) were used as reinforcement. The glass fibers has 2.57 as specific gravity, 1.53 GN/m2 as tensile strength, 112.3 GN/m2 as modulus of elasticity and zero as water absorption capability. The soil and glass fibers were mixed manually at the OMC of parent soil by segregating individual fibers in order to make a homogeneous soil-fiber mix. During manual mixing of fibers, it was noted that as the fiber percentage increased, the homogeneous mixing of soil-fiber became progressively difficult, and soil-fiber mixing took more time. At higher fiber content, soil-fiber lumps started to appear, particularly at 1% fiber content and above. Due to this reason, maximum fiber content was kept as 1%. Specimens of 38 mm diameter and 76 mm length were prepared for UC tests by compacting soil-fiber mix statically in a cylindrical mold. UC test was conducted as per ASTM D2166/D2166M-13 with an axial strain rate of 1.25 mm/min, and vertical loading was done maximum up to 15% axial strain. For CBR tests, the soil-fiber mix was compacted in a CBR mold and then kept for soaking in a water tank for four days (96 h) prior to

Experimental Study on Strength Behavior of Clayey Soil Reinforced with Glass Fiber

3

axial loading. Soaked CBR test was conducted as per ASTM D1883–16 with an axial strain rate of 1.25 mm/min.

3 Results and Discussion 3.1 Unconfined Compression Test 3.1.1 Stress-Strain Response Figure 1 presents the stress-strain behavior showing the effect of fiber content. With fiber addition, the stress-strain response has changed significantly in the form of increased peak stress and failure axial strain. There is a noticeable reduction in post-peak stress loss, showing inducement of plasticity to the unreinforced soil and transformation of brittle behavior to ductile gradually with added fibers. Fiber reinforcement benefit is mainly influenced by the bond strength between soil and fibers, as well as surficial friction between soil particles and fibers (Tang et al. 2007). With gradual deformation of the specimen due to the applied load, there is greater soil-fiber interfacial interaction, and the fibers get stretched causing development of tensile stress resistance. The peak stress is found out to be the maximum for 0.75% fibers, and addition of more fibers results in reduction of strength. This specifies the occurrence of an optimal fiber percentage for which there is maximum reinforcement advantage in the form of bond strength and surficial friction. For 1% fiber content, the number of fibers in soil is maximum, and the quantity of available soil matrix for holding the fibers may not become adequate to develop proper bond between all soil-fiber interfaces. Consequently, this hinders the mobilization of fiber tensile strength, causing reduction of peak UCS with 1% fiber. At the time of soil-fiber mixing, it was also noted that with 1% fibers, uniform mixing of fibers became difficult and formation of fiber lumps started to appear which hindered the specimen uniformity. However, the UCS of reinforced specimen with 1% fibers is greater than that of the specimen with 0.5% fibers. The UCS values are in the decreasing order with fiber contents of 0.75%, 1%, 0.5% and 0.25%. The average UCS value and the average failure strain of the three specimens for any soil-fiber mix are listed in Table 1. The UCS of the unreinforced soil is 138 kPa, whereas the corresponding maximum UCS values of the reinforced soil is 280 kPa with 0.75% fibers. The strength of any soil specimen is found to improve with increasing confinement in triaxial tests (Ranjan et al. 1996; Sivakumar Babu and Vasudevan 2008; Patel and Singh 2020). It can be inferred that in UC tests, an increase in fiber content increases internal interlocking effect causing enhancement in axial stress similar to an increase in confinement effect in triaxial test. The presence of fibers restrains the horizontal deformation of specimen and results in strength improvement in unconfined compression tests (Park 2011). 3.1.2 Specimen Failure Mode Typical effect of fiber content on failure mode of specimens has been shown in Fig. 2. For the unreinforced specimen, a single shear plane is noted at failure (Fig. 2a), representing brittle behavior. This brittle behavior of unreinforced specimen can also be observed from

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S. K. Patel and B. Singh

300

Axial stress (kPa)

250 200 150 100 50 0

fc = 1%

fc = 0.75%

fc = 0.5%

fc = 0.25%

fc = 0%

0

3

6 9 Axial strain (%)

12

15

Fig. 1. Stress-strain response of reinforced soil in UC tests

Table 1. Summary of UCS test results f c (%)

UCS (kPa)

Failure axial strain (%)

DR

EAC (KJ/m3 )

0

138

2.65

–

318

0.25

182

5.26

1.98

843

0.5

239

7.89

2.98

1456

0.75

280

9.86

3.72

2080

1.0

261

11.36

4.29

2818

the stress-strain curve (Fig. 1), where a sudden post-peak drop can be seen. For specimen reinforced with relatively lower fiber contents (0.25% and 0.5%), multi-shear planes appear from one end of the specimen (Figs. 2b & 2c), indicating some reduction in brittle nature. With 0.75% and 1% fiber contents, specimens show primarily bulging with the development of smaller cracks on the surface (Figs. 2d & 2e), showing ductile behavior of specimen. The bridging effect of fibers restricts the development of predominant shear planes, causing redistribution of stresses within a larger part of specimen.

Experimental Study on Strength Behavior of Clayey Soil Reinforced with Glass Fiber

5

3.1.3 Deformation Behavior The specimen deformation behavior has been examined from the failure axial strain values obtained from the stress-strain response depicted in Fig. 1. The values of failure axial strain of all the specimens have been presented in Table 1. With increasing fiber content, the failure axial strain of soil is noted to increase indicating that the fiber inclusion gradually increases the soil ductile behavior. The UCS and failure axial strain values for the unreinforced specimen are 138 kPa and 2.65%. The maximum UCS of 280 kPa (fiber contribution of 142 kPa) is with 0.75% fibers with corresponding increase in failure axial strain from 2.65% to 9.86% (Table 1). Nevertheless, the maximum failure axial strain is 11.36% with 1% fibers having a UCS value of 261 kPa. For UC tests, the performance of fiber-reinforced specimen has been quantified in terms of ductility, which characterises the deformation ability of reinforced specimen prior to its failure. Increasing failure axial strain is an indication of more ductile behavior of soil specimen. The deformation feature of fiber-reinforced soil has been examined in terms of ductility ratio (DR) expressed as:

Fig. 2. Failure mode of fiber-reinforced specimens: (a) f c = 0%; (b) f c = 0.25%; (c) f c = 0.5%; (d) f c = 0.75%; (e) f c = 1%

DR =

r u

(1)

where r is failure axial strain of reinforced soil and u is failure axial strain of parent soil. The DR values of all specimens have been summarized in Table 1. With increasing fiber content, the DR value increases continuously. This indicates that fiber-reinforced soil has the capacity to resist the external load up to a greater deformation prior to failure. Thus, it provides ample time for taking required precautionary steps for user safety and structure remedy in their field applications. At fiber contents of 0.25, 0.5, 0.75 and 1%, the noted DR values are 1.98, 2.98, 3.72 and 4.29, respectively. 3.1.4 Energy Absorption Capability The area under the stress-strain curve gives the energy absorption capability (EAC) of the soil specimen in triaxial test (Consoli et al. 2002). Similarly, the EAC values of

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S. K. Patel and B. Singh

both unreinforced and fiber-reinforced specimens under UC tests have been calculated up to failure axial strain. The effects of fiber content on the EAC values have been summarized in Table 1. The EAC improves continuously with fiber content, indicates that the fibers distributed in the soil have caused added energy absorption till the specimen failure. Further, increasing EAC indicates that the reinforced soil needs higher energy for its deformation, and thus has better bearing capacity. The maximum EAC is found as 2818 kJ/m3 for the specimen reinforced with 1% fiber, with UCS of 261 kPa and axial failure strain of 11.36%. However, among all reinforced specimens, the maximum UCS value of 280 kPa (at axial failure strain of 9.86%) is with 0.75% fiber content (Table 1), having corresponding EAC value as 2080 kJ/m3 . 3.2 CBR Test 3.2.1 Load-Penetration Response Typical load-penetration response showing the effect of fiber content, obtained from CBR tests on the clayey soil specimens, is presented in Fig. 3. The load bearing capacity of the specimens improves with fiber content up to 0.75%, indicating that fibers can significantly increase the load-penetration behavior. The load bearing capacity increases continuously with specimen penetration up to 12.70 mm for all fiber contents, indicating that the peak strength of specimen has not been reached even at 12.70 mm penetration, and that the fibers are still in tension without complete pullout or rupture. However, with higher penetration above 5.08 mm, the slope of the curves reduces indicating that the rate of bearing capacity improvement is decreasing. The interfacial interaction between fibers and soil mass restricts the movement of soil particles, and the fiber indentations caused by the soil particles allow to develop adhesion within the soil (Falorca and Pinto 2011), resulting in enhanced load carrying capacity of the fiber-reinforced soil. The initial stiffness of the specimen has increased with reinforcement up to 0.75% fiber content, whereas a reduction of initial stiffness is noted with 1% fiber. The decrease in stiffness is due to the alteration in soil fabric produced by the greater fiber concentration, which produces non-uniform voids inside the soil specimen and prevents dense packing (Chandra et al. 2008). 3.2.2 CBR Value The CBR values have been calculated from the load-penetration curves at penetration values of 2.54 mm and 5.08 mm. The CBR value at 5.08 mm penetration was noted to be greater than that at 2.54 mm penetration. Therefore, the tests were repeated and for the repeated tests, CBR value at 5.08 mm penetration was again higher than that at 2.54 mm penetration. Thus, the CBR value reported in this study is for 5.08 mm penetration. The CBR values of all specimens are presented in Table 2. CBR value increases gradually with fiber content up to 0.75% and afterwards drops at 1% fibers. The CBR value of polypropylene fiber-reinforced highly plastic silt was also found to enhance up to 0.75% fiber content (Zaimoglu and Yetimoglu 2012).

Experimental Study on Strength Behavior of Clayey Soil Reinforced with Glass Fiber

1500

fc = 1% fc = 0.75% fc = 0.5% fc = 0.25% fc = 0%

1200

Load (kPa)

7

900 600 300 0 0.00

2.54

5.08 7.62 Penetration (mm)

10.16

12.70

Fig. 3. Load-penetration response of reinforced soil in CBR tests

Table 2. Summary of CBR test results f c (%) CBR (%) I CBR BPR k s (MN/m3 ) 0

2.89

–

1

0.25

4.98

0.72

2.12

12.43

6.68

0.5

7.62

1.63

2.53

15.51

0.75

8.23

1.85

2.83

16.61

1.0

6.89

1.38

2.17 12 .77

The contribution of glass fibers to bearing capacity improvement of the clayey soil can be quantified in terms of CBR improvement factor (I CBR ) expressed as: ICBR =

CBRr −1 CBRu

(2)

where CBRr is the CBR value of reinforced specimen and CBRu is the CBR value of unreinforced specimen. The CBR improvement factors for all specimens, calculated for 5.08 mm penetration depth, are summarized in Table 2. Maximum enhancement in CBR is with 0.75% fiber inclusion with maximum I CBR value of 1.85.

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S. K. Patel and B. Singh

Determination of optimum soil-fiber mixture is essential for field applications. The CBR value of the unreinforced soil is 2.89%, and it increases to a maximum value of 8.23% with 0.75% fibers. Thus, as per IRC:SP:72–2007, the unreinforced soil is classified as very poor quality subgrade material (soaked CBR less than 3%), which can be modified to that of good quality (soaked CBR between 7% and 9%). Further, as per IRC:37–2001, a minimum soaked CBR value of 6% is necessary for use in the subgrade layer of low-volume flexible pavements. Thus the soil mix with 0.5, 0.75% and 1% glass fibers (having corresponding CBR values of 6.89%, 8.23% and 7.62%), can be used in practice (Table 2). Increase in bearing pressure of soil due to fiber reinforcement at the maximum penetration depth of 12.70 mm has also been evaluated in terms of bearing pressure ratio (BPR), defined as: BPR =

Pr Pu

(3)

where Pr is the piston load for fiber-reinforced specimen at 12.70 mm penetration and Pu is the corresponding piston load for the unreinforced specimen. The bearing pressure ratios of all specimens are presented in Table 2. The BPR value is noted to increase with fiber content and become maximum 2.83 times with 0.75% fiber. 3.2.3 Subgrade Modulus The deformation capacity of the reinforced soil when used as pavement subgrade can be evaluated from the variation of secant subgrade modulus, as it replicates the deformation response under wheel loads and other concentrated loads. The subgrade modulus (k s ) is expressed as the ratio of the bearing pressure (σδ ) to the corresponding penetration depth (δ): ks =

σδ δ

(4)

The penetration depth for calculating secant subgrade modulus for all specimens is considered as 5.08 mm, at which design CBR value has been considered. The secant subgrade modulus is summarized in Table 2. The subgrade modulus is noted to increase with fiber content, reaches the highest value of 16.61 MN/m3 with 0.75% fiber, and thereafter decreases with 1% fiber inclusion.

4 Conclusions From the unconfined compression and CBR tests on glass fiber-reinforced clayey soil, it has been observed that the application of optimum doses of glass fiber as soil reinforcement material, can significantly upgrade the engineering properties of the clayey soil in terms of improved unconfined compressive strength, CBR value, subgrade modulus, specimen ductility and EAC values. The conclusions drawn from the present experimental study are as:

Experimental Study on Strength Behavior of Clayey Soil Reinforced with Glass Fiber

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1 The unconfined compressive strength, CBR and subgrade modulus of clayey soil increase with glass fiber content to reach maximum value with 0.75% fibers. The UCS value increases maximum about two times (from 138 to 280 kPa), the CBR value about three times (from 2.89 to 8.23%) that of unreinforced soil, and the subgrade modulus about 2.5 times (from 6.68 to 16.61 MN/m3 ). 2 The specimen failure strain, ductility and EAC increase continuously with glass fiber content indicating higher bearing capacity and greater deformability of glass fiberreinforced clayey soil. 3 Glass fibers inclusion transforms the brittle failure mode of unreinforced clayey soil progressively to ductile mode with increasing fiber content. 4 Glass fibers of 0.5% and 0.75% contents can be effectively used as a subgrade material for low-volume flexible road pavement.

References ASTM D2487. Standard practice for classification of soils for engineering purposes (Unified Soil Classification System). ASTM International, West Conshohocken, PA, US (2006) ASTM D2166/D2166M. Standard test method for unconfined compressive strength of cohesive soil. ASTM International, West Conshohocken, PA, USA (2013) ASTM D1883. Standard test method for California Bearing Ratio (CBR) of laboratory-compacted soils. West Conshohocken, PA, USA (2016) Benson, C.H., Khire, M.V.: Reinforcing sand with strips of reclaimed high-density polyethylene. J. Geotech. Eng. 120(5), 838–855 (1994) Chandra, S., Viladkar, M.N., Nagrale, P.P.: Mechanistic approach of fiber-reinforced flexible pavements. J. Transp. Eng. 134(1), 15–23 (2008) Consoli, N.C., Montardo, J.P., Prietto, P.D.M., Pasa, G.S.: Engineering behavior of a sand reinforced with plastic waste. J. Geotech. Geoenviron. Eng. 128(6), 462–472 (2002) Estabragh, A.R., Bordbar, A.T., Javadi, A.A.: Mechanical behavior of a clay soil reinforced with nylon fibres. Geotech. Geol. Eng. 29, 899–908 (2011) Falorca, I.M.C.F.G., Pinto, M.I.M.: Effect of short, randomly distributed polypropylene microfibres on shear strength behaviour of soils. Geosynth. Int. 18(1), 2–11 (2011) IRC:SP:72. Guidelines for the design of flexible pavements for low volume rural roads. The Indian Road Congress, New Delhi, India (2007) IRC:37. Guidelines for the design of flexible pavements. The Indian Road Congress, New Delhi, India (2001) Jha, J.N., Choudhary, A.K., Gill, K.S., Shukla, S.K.: Behavior of plastic waste fibre-reinforced industrial wastes in pavement applications. Int. J. Geotech. Eng. 8(3), 277–286 (2014) Kumar, P., Singh, S.P.: Fibre-reinforced fly ash subbases in rural roads. J. Transp. Eng. 134(4), 171–180 (2008) Kumar, R., Kanaujia, V.K., Chandra, D.: Engineering behaviour of fibre-reinforced pond ash and silty sand. Geosynth. Int. 6(6), 509–518 (1999) Kumar, P., Mehndiratta, H.C., Chandranarayana, S., Singh, S.P.: Effect of randomly distributed fibres on flyash embankments. J. Inst. Eng. India Part CV Civil Eng. Div. Board 86(3), 113–118 (2005) Li, C., Zornberg, J.G.: Mobilization of reinforcement forces in fiber-reinforced soil. J. Geotech. Geoenviron. Eng. 139(1), 107–115 (2013)

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Li, J., Tang, C., Wang, D., Pei, X., Shi, B.: Effect of discrete fibre reinforcement on soil tensile strength. J. Rock Mech. Geotech. Eng. 6(2), 133–137 (2014) Muntohar, A.S., Widiyanti, A., Hartono, E., Diana, W.: Engineering properties of silty soil stabilized with lime and rice husk ash and reinforced with waste plastic fiber. J. Mater. Civ. Eng. 25(9), 1260–1270 (2013) Park, S.: Unconfined compressive strength and ductility of fibre-reinforced cemented sand. Constr. Build. Mater. 25, 1134–1138 (2011) Patel, S.K., Singh, B.: Strength and deformation behavior of fiber-reinforced cohesive soil under varying moisture and compaction states. Geotech. Geol. Eng. 35(4), 1767–1781 (2017) Patel, S.K., Singh, B.: Shear strength and deformation behaviour of glass fibre-reinforced cohesive soil with varying dry unit weight. Indian Geotech. J. 49(3), 241–254 (2019) Patel, S.K., Singh, B.: A comparative study on shear strength and deformation behaviour of clayey and sandy soils reinforced with glass fibre. Geotech. Geol. Eng. 38(5), 4831–4845 (2020). https://doi.org/10.1007/s10706-020-01330-5 Pradhan, P.K., Kar, R.K., Naik, A.: Effect of random inclusion of polypropylene fibres on strength characteristics of cohesive soil. Geotech. Geol. Eng. 30, 15–25 (2012) Priyadarshee, A., Kumar, A., Gupta, D., Pushkarna, P.: Compaction and strength behavior of tire crumbles-fly ash mixed with clay. J. Mater. Civ. Eng. 30(4), 04018033 (2018). https://doi.org/ 10.1061/(ASCE)MT.1943-5533.0002171 Ranjan, G., Vasan, R.M., Charan, H.D.: Probabilistic analysis of randomly distributed fiberreinforced soil. J. Geotech. Eng. 122(6), 419–426 (1996) Rao, S.V.K., Nasar, A.M.A.: Laboratory study on the relative performance of silty-sand soils reinforced with linen fibre. Geotech. Geol. Eng. 30, 63–74 (2012) Sarbaz, H., Ghiassian, H., Heshmati, A.A.: CBR strength of reinforced soil with natural fibres and considering environmental conditions. Int. J. Pavement Eng. 15(7), 577–583 (2014) Sivakumar Babu, G.L., Vasudevan, A.K.: Strength and stiffness response of coir fiber-reinforced tropical soil. J. Mater. Civil Eng. 20(9), 571–577 (2008) Tang, C., Shi, B., Gao, W., Chen, F., Cai, Y.: Strength and mechanical behavior of short polypropylene fibre reinforced and cement stabilized clayey soil. Geotext. Geomembr. 25, 194–202 (2007) Waldron, L.J.: The shear resistance of root permeated homogeneous and stratified soil. Soil Sci. Soc. Am. Proc. 41, 843–849 (1977) Zaimoglu, A.S., Yetimoglu, T.: Strength behavior of fine grained soil reinforced with randomly distributed polypropylene fibers. Geotech. Geol. Eng. 30(1), 197–203 (2012) Zornberg, J.G.: “Discrete framework for limit equilibrium analysis of fibre-reinforced soil. Geotechnique 52(8), 593–604 (2002)

Process for the Development of a Digital Twin of a Local Road – A Case Study Wynand JvdM Steyn(B) and André Broekman Department of Civil Engineering, EBIT, University of Pretoria, Pretoria, Gauteng, South Africa [email protected], [email protected]

Abstract. Virtual replicas of infrastructure can be used to run simulations and optimize the construction, management and maintenance of such assets throughout its entire lifecycle. These Digital Twins (defined as integrated multi-physics, multiscale, and probabilistic simulations of a complex product) mirror the behavior and environmental responses of its corresponding twin. Digital reconstruction techniques using optical sensor technologies and mobile sensor platforms are providing viable, low-cost alternatives to develop Digital Twins of physical infrastructure. In previous work, the digital twinning of asphalt pavement surfacings using visual Simultaneous Localization And Mapping (vSLAM) was investigated and successfully demonstrated on a small area of an asphalt surfacing. In this paper, a larger study was pursued to demonstrate the successful implementation of micro-twinning and macro-twinning of a local road. Light Detection And Ranging (LIDAR), Unmanned Aerial Vehicles (UAVs) and traffic counting Artificial Intelligence (AI) allows for quantification of the road geometry and infrastructure utilization over large areas (macro-twinning), whereas the photogrammetric reconstruction technique based on a Neural Network (NN) and a proprietary environmental condition sensor (SNOET) were used to acquire the surface texture and environmental conditions respectively (micro-twinning). These entry-level instrumentation and techniques accurately measured the geometry, surface characteristics and utilization of the generic road section. The addition of advanced environmental monitoring sensors provide management data that can assist in the maintenance of such roads. Keywords: Digital twin · Local roads · LIDAR · LoRaWAN · Transportation engineering

1 Introduction Tao et al. (Tao et al., 2017) defines a Digital Twin as “an integrated multi-physics, multiscale, and probabilistic simulation of a complex product and uses the best available physical models, sensor updates, etc., to mirror the life of its corresponding twin”. For engineering practitioners, cyber-physical data better serves the lifecycle management of infrastructure and assets. These cyber-physical systems and Big Data implementations (Núñez et al. 2014) increasingly serve as the primary lifecycle management systems for engineering practitioners, particularly during the 4th Industrial Revolution (4IR). These © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 11–22, 2021. https://doi.org/10.1007/978-3-030-79638-9_2

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Digital Twins are underpinned by powerful and intelligent sensor platforms alongside network connectivity at the physical edge of the sensor platform. Improved wireless sensor capabilities, decreasing power consumption and costs drive the accelerating adoption of such sensor platforms. This fusion of electronic engineering, information technology, materials science and computer science – together with traditional civil engineering theory – is collectively referred to as Civiltronics (Broekman and Steyn 2020). Intricate engineering challenges benefit from this transdisciplinary approach and revolutionary new technologies supporting the seamless integration of cyber-physical systems. Examples include the development of a 3D printed ballast particle (Kli-Pi) that can measure the in-situ, threedimensional acceleration and rotation characteristics of a discrete particle (Broekman and Gräbe 2018; 2019). This contrasts with traditional instrumentation techniques that consider only the macroscopic response of the track structure, ignoring the driving mechanism of permanent settlement on a mesoscale (discrete) level.

2 Current Understanding 2.1 Quantification of Road Performance and Surface Textures Pavement roughness is defined as the irregularities of a pavement surface as measured over a fixed distance between two points in space (Sayers and Karamihas 1998). The roughness of the surfacing affect long-term vehicle maintenance and operating costs and fuel-consumption with its own associated environment impacts. The development of comparatively accurate laser-based scanning systems automated the process of measuring pavement surface texture (Sengoz et al. 2012). During the last decade, low-cost tri-axis acceleration sensor platforms were employed, notably in the agricultural sector in Southern Africa, for collection of pavement roughness data. The data-driven approach for road maintenance improves the operational efficiencies through optimized blading of unpaved roads when riding quality deteriorates below a certain threshold (Pretorius and Steyn 2019). Telematics devices installed within vehicles can be exploited for the same application, alongside existing communications infrastructure that relays the data to a centralized storage, processing and visualization service (Wessels and Steyn 2018). This methodology utilizes calibrated response type algorithms to provide Class 3-level road roughness data continuously. Additionally, the measurements are independent of the vehicle dimensions and suspension characteristics, speed and operation conditions (Wessels and Steyn 2018). Even though these devices provide an approximated geolocation alongside a quality classification and failure identification of short sections of roadway, poor signal coverage and obstructions in rural areas provide limited definition and resolution of the in-situ road geometry. On a much smaller dimensional scale, existing measurement techniques of the pavement surface texture is qualitative and prone to operator bias. While the method of calculating the Mean Profile Depth (MPD) and Mean Texture Depth (MTD) are clearly defined (ASTM E1845–01 2003; ASTM E965–96 2006; Van Zyl and Van der Gryp 2015), the execution thereof lends itself to digital technologies. Experimental evidence supports the notion of obtaining quality measurements surpassing that of the traditional sand patch method when employing laser-based 3D scanning techniques (Sengoz et al.

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2012). Steyn et al. (2019, 2020) details the methodology required to digitize small areas of in-situ pavements using a commercial scanner. While the areas are small when compared to the size of the road, the calibrated accuracy of 10 to 15 µm is unparalleled. Significantly, digitization of a defined section of the road serves as a Digital Twin to measure the progressive inter-particle orientation and settlement as a byproduct of either road traffic or Accelerated Pavement Testing (APT) applications evaluating different materials and modifiers (Jordaan et al. 2017). These changes in the micro-twin can be described statistically using a Probability Mass Function (PMF) for the roughness and curvature properties. This method is currently slow and labor intensive. 2.2 Autonomous and Dynamic Road Maintenance An online Digital Twin of a road section serves as the necessary interface to implement dynamic maintenance schemes. In these schemes, autonomous and dynamic scheduling is supported by a continuous stream of road condition data from a variety of sources (Steyn 2018; 2019). This ranges from more complex, yet sparsely implemented continuous vehicle response tracking, to automatic vehicle counting and classification measuring the traffic load over a defined section of road. Automation of mining haul roads, confined to a more controlled environment, have successfully demonstrated automatic road grading systems with improvements tied to the adoption of ever-more accurate and sophisticated technology (Heikkilä and Jaakkola, Heikkilä and Jaakkola, 2002; Thompson et al. 2019). Incorporation of existing mine communications and assets management systems have advanced the autonomy of dispatching maintenance equipment to priority areas, to near real-time implementation (Marais et al. 2008). For unpaved road applications of primarily used for agricultural industries, regression models that combine the road roughness, associated maintenance history and historical rainfall data (local weather stations) was able to successfully model the deterioration (Swanepoel et al. 2020). With the current expansion of Internet of Things (IoT) devices and coverage network in rural areas, real-time maintenance and robust asset management systems will soon come to fruition to the benefit of local communities.

3 Methodology Digital twinning (in this paper) is sub-divided into micro-twinning and macro-twinning applications. For macro-twinning, the geometry of the road and road utilization is considered using two optical instrumentation systems: high accuracy LIDAR (Light Detection And Ranging) and photogrammetry using a UAV/drone. The media acquired with the drone was used for traffic counting applications. For micro-twinning applications, a novel three-dimensional neural network reconstruction technique is investigated alongside environmental and air quality measurements that are indicative of factors that affect the surrounding roads. For all the methods considered, the digitization process of the Digital Twins was divided in to three steps, namely sample preparation or identification, data acquisition and digital processing (in conjunction with interpretation). Figure 1 provides a reference map of the Engineering 4.0 campus (located in Pretoria, South Africa), highlighting the location of the various points of interest mentioned in the paper. It shows

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locations of the central receiving antenna, as well as three locations where data were collected that are discussed in the paper.

Fig. 1. Overview of Engineering 4.0 and various data collection locations

3.1 Macro-twinning In the macro-twinning category, the paper evaluates a concept where the LiDAR, SNOET, Photogrammetry and traffic AI work are done on a wider scale on the specific campus. The objective of this work is to place the whole of the 106 hectare campus inside the digital twin. This is followed by more frequent micro-twinning steps using some of the same sensors, as well as additional photogrammetry techniques. An overall schematic of the process is shown in Fig. 2. An example of the LiDAR imaging of the first section of road is shown in Fig. 3. LiDAR data consists of a point cloud indicating the physical infrastructure that was scanned. This data are converted into standard CAD packages to become part of the digital model. The photogrammetry reconstruction is currently based on a drone scan using high-resolution photographs of the buildings and features on the campus (Fig. 4). Both the LiDAR and photogrammetry scans can be combined in the digital twin to ensure that not only high quality data clouds with better than 50 mm accuracy are available for detailed analysis, but also 3D imaging information. SNOET (SNiffing Omgewing/Environmental Tester) is a multi-component combination of sensors that was developed as a proof-of-concept prototype, integrating available sensor breakout boards that could be sourced commercially with a low-cost microcontroller based on Arduino architecture. The measurement parameters include temperature, relative humidity, barometric air pressure, Total Volatile Organic Compound (TVOC)

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Fig. 2. Overall schematic indication of digital twinning process for local road application

Fig. 3. LiDAR captured macro-twinning road details

concentration, CO2 concentration, air quality, geolocation, infrared temperature, light intensity and UV radiation. On the macro-twinning model, SNOET scans are conducted using mobile options along the roads and paths on the campus (Fig. 5), providing accurate environmental data at various times of the day along these routes. These data are combined with a static network of devices where continuous data are collected to develop environmental timelines. This static network communicates using a LoRa network to enable continuous and current data in the central database.

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Fig. 4. Photogrammetry reconstruction of storage building

Fig. 5. SNOET-based TVOC and CO2 data collected using mobile options on selected roads

As the traffic data source for the digital twin, an OpenDataCam open source tool is trialed as a potential low-cost, readily scalable solution to count and classify vehicles along the highway. It is specifically designed for deployment on power efficient, edge processing hardware that feature real-time inference. Screenshots of the analysis indicates the observations with identification of the various vehicles (Fig. 6). A counting accuracy of 5% was realized compared to actual traffic counts. Average speed could be approximated as the scale of the road is known.

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3.2 Micro-twinning Neural networks are ideal for applications where programming rules and algorithms are impossible to define explicitly. Current photogrammetric pipelines are computationally expensive, particularly for the dense 3D point reconstruction and meshing components. MVSNet (Yao et al. 2019) was developed as a deep learning architecture for depth map inference from unstructured multi-view images. The network is pre-trained on calibrated datasets (e.g. Broekman and Gräbe 2020). It accelerates the depth map inference with sufficient accuracy when provided with a minimum of three images, each with known intrinsic and extrinsic camera properties. In this paper, a section of road in Pretoria with visible signs of damage and deterioration to the seal was selected. 45 photographs were captured on a Samsung Galaxy S9 cellphone in a circular pattern from three different heights.

Fig. 6. OpenDataCam interface illustrating real-time object detection and inference confidence scores

Thereafter, structure-from-motion was computed (using COLMAP) from the photographs to calculate the relative orientation and location of the cameras. The camera properties, together with the photographs, where processed through the neural network. While the resolution is limited (768 × 576 pixels), the reconstruction is accomplished in approximately four seconds when executed on a workstation computer. Figure 7 illustrates the depth map (Fig. 7, top) and point cloud (Fig. 7, bottom) generated from only three input images provided (Fig. 7, right), each captured from a slightly different perspective. The metal pins serve as a scale, with the pins spaced 2.5 mm apart. SNOET was installed around various locations on the Engineering 4.0 campus (Fig. 8), close to the adjacent highway (Fig. 1). Of interest is the TVOC concentration, CO2 emissions and air quality that are all associated with vehicle traffic. Clear patterns could be observed during peak morning and afternoon traffic (Fig. 9), where concentrations increased above the background levels that were recorded during the night and over weekends.

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Fig. 7. MVSNet generated depth map and point cloud generated from cellphone photographs

Fig. 8. SNOET prototype installed adjacent to the N4 freeway

The SNOET prototype has been improved significantly since its inception, with the construction of four additional, identical sensor platforms. The new generation of Arduino MKR1310 microcontrollers used for SNOET include a LoRaWAN (Long Range, Wide Area networking protocol) radio module that sets the global standard for low power wide area IoT networks. More specifically, LoRaWAN uses a Media Access Control (MAC) protocol to establish wide area networks, allowing low-powered devices to

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Fig. 9. Air pollution and organic molecule concentrations measured by SNOET

communicate with Internet-connected applications over long-rage, low-bandwidth wireless connections. These devices communicate with a dedicated router gateway installed on the Engineering 4.0 campus (Fig. 1), with the network traffic sent to The Things Network (TTN). TTN uses an open-source, decentralized network to exchange data with applications. These applications receive the data payloads, decodes them and routes the formatted data to 3rd party service providers such as Google Cloud or Ubidots (Fig. 10) for storage, analysis and visualization.

Fig. 10. Ubidots dashboard backed of SNOET1 illustrating the sensor measurements

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4 Applications The paper describes the process of collecting infrastructure and operational condition data of a local road to develop a digital twin of the scenario. The objective of such a digital twin is to improve the management process of local (and by extension any other) roads, through a combination of detailed infrastructure information (LiDAR scans) and continuous data emanating from the local road (environmental and traffic data). Such a road management process means that the road owner does not have to wait for a typical 1-year snap-shot data-set regarding the conditions on the road, but that continuous data submission to the model can improve the continuous management and maintenance of the road. Through such continuous monitoring, local instantaneous changes in aspects such as traffic levels and emissions, or pavement conditions (e.g. asphalt temperature) can be incorporated into the road condition models to improve the maintenance expectations and planning for future actions on the specific road.

5 Conclusions The paper shares some of the potential benefits of having a macro- and micro-twin of physical infrastructure available. These digital twins can seamlessly integrate with the Pavement/Building Management System (PMS/BMS) of an infrastructure owner, providing continuous and objective data regarding the physical condition and environmental elements around the infrastructure. This can support continuous management decisions in an objective way. The implementation of OpenDataCam’s AI-assisted traffic counting proved effective to deploy a low-cost traffic quantization solution. With the addition of a dedicated IPcamera, the system will soon record the traffic of the adjacent freeway on a permanent, real-time basis for longer-term trend monitoring, improving existing design guidelines through this data-driven approach. Significant improvement exists for the classification of vehicles, particularly for public transportation vehicles such as minibus taxis. The aggregation of data from SNOET and vehicle statistics on a single cloud provides provide additional insight into interrelated variables. Compared to traditional 3D scanners, AI-assisted reconstruction techniques have the benefit of operating in nearly any illumination condition with significantly faster processing capabilities and at a lower cost. With the implementation of more accurate geolocation services, these platforms can be integrated with geospatial macro-twin for long-term monitoring of the pavement surface texture. This approach is simple enough for autonomous robotic systems that could perform the task, independent of human operators. Additional experiments are underway to determine the viability of integrating SNOET with asset management systems of unpaved roads. The air quality measurements associated with dust in the air could be used dynamic blading maintenance. The addition of LoRaWAN capabilities could see the installation of such miniaturized devices on vehicles themselves that continuously traverse the same section of road.

References American Society for Testing Materials (ASTM). Standard practice for calculating pavement macro-texture mean profile depth, ASTM E 1845-01, Pennsylvania, USA (2003)

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American Society for Testing Materials (ASTM). Standard test method for measuring pavement macro-texture depth using a volumetric technique, ASTM E 965-96, Pennsylvania, USA (2006) Broekman, A., Gräbe, P.J.: Development and calibration of a wireless, inertial measurement unit (Kli-Pi) for railway and transportation applications. In: Proceedings of the 37th Annual South African Transport Conference (SATC), Pretoria, South Africa, 9–12 July 2018 (2018) Broekman, A., Gräbe, P.J.: Analysis, interpretation and testing of mesoscale ballast dynamics using Kli-Pi. In: International Heavy Haul Association (IHHA) Conference, Narvik, Norway, 12–14 June 2020, pp. 151–157 (2019) Broekman, A., Gräbe, P.J.: PASMVS: a perfectly accurate, synthetic, path-traced dataset featuring specular material properties for multi-view stereopsis training and reconstruction applications. Data Brief 32 (2020). https://doi.org/10.1016/j.dib.2020.106219. Heikkilä, R., Jaakkola, M.: The efficiency of a 3-D blade control system in the construction of structure layers by road grader automated design - build of road construction in Finland. In: Stone, W.C. (ed.) ISARC 2002: 19th International symposium on Automation and Robotics in Construction. NIST Special Publication 989, Gaithersburg, Maryland 23–25 September 2002, U.S. Department of Commerce (2002) Jordaan, G.J., Kilian, A., Du Plessis, L., Murphy, M.: The development of cost-effective pavement design approaches using minerology tests with new nano-technology modifications of materials. In: Proceedings of the 36th Southern Africa Transportation Conference (SATC), Pretoria, South Africa, 10–13 July 2017 (2017) Marais, W.J., Thompson, R.J., Visser, A.T.: Managing mine road maintenance interventions using mine truck on-board data. In: Proceedings 7th International Conference on Managing Pavement Assets, Paper 6–18, Calgary, Canada, 25–28 June 2008 (2008) Núñez, A., Hendriks, J., Li, Z., De Schutter, B., Dollevoet, R.: Facilitating maintenance decisions on the Dutch railways using big data: the ABA case study. In: IEEE International Conference on Big Data, Washington, DC, USA, pp. 48–53 (2014) Pretorius, C.J., Steyn, W.J.M.: Quality deterioration and loss of shelf life as a result of poor road conditions. Int. J. Postharvest Technol. Innov. 6(1) (2019). ISSN: 1744–7569, https://doi.org/ 10.1504/IJPTI.2019.104178. Sayers, M.W., Karamihas, S.M.: The Little Book of Profiling, s. l, The Regent of the University of Michigan, Michigan (1998) Sengoz, B., Topal, A., Tanyel, S.: Comparison of pavement surface texture determination by sand patch test and 3D laser scanning, pp. 73–78. Periodica Polytechnica Civil Engineering, USA (2012) Steyn, W.J.M.: Intelligent infrastructure and data science in support of road maintenance. In: Proceedings of Advances in Materials and Pavement Performance Prediction (AM3P), Doha, Qatar, 16–18 April 2018 (2018) Steyn, W.J.M.: Optimization of gravel road blading. J. Test. Eval. 47(3), 2118–2126 (2019). https:// doi.org/10.1520/JTE20180022, ISSN 0090–3973 Steyn, W.J.M., Jordaan, G.J., Broekman, A., Marais, A.: Evaluation of novel chip seals applications during periods of low temperatures. In: Proceedings of 12th Conference on Asphalt Pavements for Southern Africa, Sun City, South Africa, 13–16 October 2019 (2019) Steyn, W.J.M., Broekman, A.: Civiltronics: fusing civil and electronics engineering in the 4IR Era. In: Civil Engineering, Magazine of the South African Institution of Civil Engineering, South Africa (2020). ISSN 1021–2000 Steyn, W.J.M., Broekman, A., Jordaan, G.J.: Digital twinning of asphalt pavement surfacings using visual simultaneous localization and mapping. In: Advances in Materials and Pavement Performance Prediction (AM3P) 2020, Virtual Conference, San Antonio, Texas, 3–7 August 2020 (2020) Swanepoel, T., Maina, J.W., Steyn, W.J.M.: Deterioration trends of unpaved roads from real data. South Afr. Inst. Civil Eng. J. (2020). (in press)

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Thompson, R., Peroni, R., Visser, A.T.: Mining Haul Roads, Theory and Practice. CRC Press, Boca Raton (2019). ISBN 9780367620608 Tao, F., Cheng, J., Qi, Q., Zhang, M., Zhang, H., Sui, F.: Digital twin-driven product design, manufacturing and service with big data. Int. J. Adv. Manuf. Technol. 94(9–12), 3563–3576 (2017). https://doi.org/10.1007/s00170-017-0233-1 Wessels, I., Steyn, W.J.M.: Continuous, response-based road roughness measurements utilizing data harvested from telematics device sensors. Int. J. Pavement Eng. (2018). https://doi.org/10. 1080/10298436.2018.1483505 Yao, Y., Luo, Z., Li, S., Shen, T., Fang, T., Quan, L.: Recurrent MVSNet for high-resolution multiview stereo depth inference. In: Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pp. 5525–5534 (2019). https://arxiv.org/abs/1902.10556

Capturing the Moving Deflection Basin Under a Traffic Speed Deflectometer Dominik Duschlbauer1 and Jeffrey Lee2(B) 1 SLR Consulting, North Sydney, Australia 2 ARRB, Melbourne, Australia

[email protected]

Abstract. In recent years, several different high-speed deflection testing devices have become available worldwide. One such device is the Traffic Speed Deflectometer (TSD). ARRB owns and operates two TSDs in Australia and New Zealand and they are also known as iPAVE (intelligent Pavement Assessment Vehicle). This study benchmarks iPAVE results against results obtained with an in-situ array embedded in the pavement at a site established in the state of Queensland, Australia. The embedded array allows for capturing the moving deflection basin under the iPAVe’s wheel(s). The study also focuses on signal processing techniques that can be used to work with geophone data and the integration of pavement velocities to pavement displacements which is the metric commonly used for pavement evaluations.

1 Introduction In 2014, ARRB acquired its first Traffic Speed Deflectometer (TSD) manufactured by Greenwood Engineering. It was then upgraded by ARRB, making it the first integrated road surface and sub-surface condition assessment system in the world. This device is known as the Intelligent Pavement Assessment Vehicle or iPAVE system. Since 2014 the iPAVE has been conducting annual network surveys in Queensland, New South Wales, Western Australia and New Zealand. In order to improve the understanding of data collected with the iPAVe, the ARRB Group has been carrying out detailed comparative studies comprising multiple sites in Australia (Lee and Duschlbauer (2017)) where the results of different non-destructive deflection testing equipment (including the iPAVe, Falling Weight Deflectometers (FWDs) and embedded sensor arrays) are compared against each other. In this study the results from an embedded array of geophones are presented. The study also details the signal processing techniques used to estimate the in-situ displacements of the pavement as the iPAVe is travelling over the array at traffic speeds. The measured pavement velocities and corresponding displacements as evaluated by the iPAVe and their correlation with the pavement velocities and displacements measured with the embedded array are discussed.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 23–33, 2021. https://doi.org/10.1007/978-3-030-79638-9_3

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2 Description of the Site, Instrumentation and Traffic Speed Deflectometer 2.1 Site Deception Bay Road is an arterial road located about 40 km north of the Brisbane CBD with 13,864 vehicles per day per carriageway in 2018. At the location where the instrumentation was installed, Deception Bay Road is two lanes per carriageway and the posted speed limit is 70 km/h. The number of heavy vehicles is approximately 3% of the total traffic. Based on the information available from the pavement management system, the pavement comprises of 70 mm of asphalt over 375 mm of unbound granular pavement. The location was selected because it is in good structural and surface conditions (NASSRA roughness 44 counts/km, rutting 5.6 m, and the TSD maximum deflection measured were 0.27 mm). The array is located along a straight road section to allow the TSD to align with the instrumented array and maintain a consistent test speed. There is no asphalt resurfacing work scheduled in the next 5 years, which is essential for this work because the installed sensors are located within the asphalt wearing course and will be destroyed during the next asphalt resurfacing work. 2.2 Embedded Array Both geophones (sensors measuring velocities) and accelerometers (sensors measuring accelerations) have been installed and a schematic diagram of the instrumentation array is shown in Fig. 1. Based on previous experience of similar instrumentation sites in Western Australia (Lee et al. (2019)), the sensor array has been strategically designed to maximise the number of wheels travelling directly over the array. The array extends ±250 mm laterally from what is considered the most frequently taken wheel path and the array extends 1000 mm in the longitudinal direction.

Fig. 1. The layout of ground instrumentation sensors.

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Holes A, B, E, and F only have a single geophone installed. Holes C and D accommodate both a geophone and an accelerometer. These combined holes have been included to validate the measurement accuracy of both sensor types. Hole G has a single highprecision accelerometer located 1 m away from Hole C. Holes F and G, due to their known longitudinal offset from hole C mainly serve the purpose to allow for the accurate determination of the instantaneous speed of vehicles at the time they travel past the array (in case their axle spacing is unknown). 2.2.1 Geophones The geophone model used was HG6-UB manufactured by HGS (India) Limited. The chosen model range has a nominal sensitivity of 30 V/m/s, a nominal corner frequency of 4.5 Hz, and nominal damping (ξ) of 0.56. The white circles in Fig. 2 are the discrete calibration points as identified in the calibration sheet of the geophone located in hole C (referred to as geophone C). The sensitivity at 100 Hz is 29.6 V/m/s. For this particular geophone, the calibration sheet identified a corner frequency fn of 4.64 Hz and a damping value ξ of 0.56. The black curves in Fig. 2 are the magnitude (left) and phase (right) of the geophone’s transmissibility based on the analytical solution of a damped, single degree of freedom oscillator (Collette et al. 2012). The transmissibility not only applies to velocities but also to displacements and accelerations (in case the geophone’s output is differentiated or integrated).

Fig. 2. Transmissibility of geophone C.

2.3 Traffic Speed Deflectometer: iPAVe As part of the commissioning, a number of tests were carried out, including FWD tests and repeated runs of a TSD. In 2014, ARRB acquired its first Traffic Speed Deflectometer (TSD) manufactured by Greenwood Engineering. It was then upgraded by ARRB, making it the first integrated road surface and sub-surface condition assessment system in the world. This device is known as the iPAVE system and referred to as iPAVe in this paper. The iPAVe utilises Doppler lasers to measure the vertical surface velocity of the deflected pavement at six locations along the mid-line of the rear left dual tyres, directly under the rear axle and in front of the dual tyres at distances of 100, 200, 300, 600 and 900 mm. The seventh Doppler laser, known as the reference laser, is positioned

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3,500 mm in front of the rear axle. The reference laser is presumed to remain relatively unaffected by the load applied by the axles and the vertical pavement deflection velocity of the reference laser is assumed to be zero. Figure 3 shows photographs of the iPAVE used in the tests. Its axle spacings are 3.6 m and 8 m, respectively.

Fig. 3. ARRB’s iPAVe.

3 Data Analysis and Results In this paper, one iPAVE run is discussed in detail. For the investigated run the iPAVE truck was travelling at a speed of 65 km/h over the array. The position of the laser beam (which is visible on the pavement) was located by studying slow-motion videos. The wheel path (as defined by the centreline of the dual tyre rear wheels) for the investigated pass-by is indicated in red on the right-hand side in Fig. 4. The centreline of the iPAVE rear dual tyres travelled over the array between geophones B and C with the offset from array’s centerline (holes C-F-G) being approximately 150 mm. Geophones B and C were directly under the inside tyre and outside tyre of the dual tyre rear wheel of the iPave.

Fig. 4. Path of the iPAVe relative to the embedded sensor array (hole location visually marked with masking tape).

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27

The sensors’ outputs were recorded synchronously with a 24-bit data acquisition system in DC-coupled mode. The sampling frequency was 5,000 Hz. The top graph in Fig. 5 shows the “weighted velocity” as measured by the geophone in hole C (referred to as geophone C). The weighted velocity is directly proportional to the measured voltage, the proportionality being the geophone’s nominal sensitivity. The three axles travelling over the array are clearly discernible visually and their spacing allowed for calculating the velocity the iPAVe truck was travelling at, since its axle spacings were known. The iPAVe’s speed was also recorded by its onboard GPS system and matched exactly. A weighted velocity trace does not account for the geophone’s non-linear characteristics near its resonant frequency of 4.5 Hz (refer to Fig. 2). The bottom graph in Fig. 5 shows the corresponding weighted velocity spectrum which indicates dominant energy in the frequency bandwidth of 4 Hz to 12 Hz for this particular pass by of the iPAVe. The geophone’s resonant frequency falls into the range of dominant frequencies, and as a consequence, compensating for the geophones’ non-linear effects requires consideration.

Fig. 5. Weighted velocity time trace (top) and corresponding spectrum (bottom).

In order to calculate unweighted velocities1 and the associated deflections the following analysis steps were taken: 1. Select a time segment: The effect of time slices of different durations is one focus of interest in this study. For that purpose, short time slices coinciding with only one axle rolling over the sensor to longer time slices which included all three axles of the iPAVe were studied. For each time segment, the following post-processing steps were taken: 1 The term unweighted velocity indicates that the effects of the geophone’s non-linear character-

istics have been (at least partially) compensated for.

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2. The measured voltage was detrended. 3. The voltage was converted to an unweighted velocity using the inverse FFT method. In this method at each frequency bin, the complex FFT of the time signal is divided by the geophone’s complex transmissibility and then converted back into the time domain using the inverse FFT. 4. The unweighted velocity was integrated into displacements in the time domain. The analysis steps have been carried out for each geophone individually using each geophone’s individual characteristics as per its factory calibration sheet. Results are presented for geophone C (its weighted velocity is shown in Fig. 5). Figure 6 shows the unweighted velocities for the three studied time slices. The pass-bys of the first two axles (duration 0.7 s) and the last axle (duration 0.5 s) are shown as the black dotted and black continuous lines, respectively. They overlap by approximately 50 ms. The time slice containing the pass-by of all three axles is shown in red (duration 1.2 s). A detail of the overlap region is shown in the rectangular insert in Fig. 6. Focusing on the two time segments which contain the pass-by of the last axle (the solid black and the solid red lines), the unweighting process results in essentially identical unweighted velocities as the last axle travels over the geophone (−0.1 s to +0.1 s). Only from approximately +0.1 s onwards do small but steadily increasing differences in unweighted velocities develop. Both time segments share the identical weighted data (Fig. 5) and the small differences in unweighted velocities are a direct result of the employed signal processing methodology due to slightly different detrending adjustments and different frequency bins being used in the inverse FFT conversion step. Correspondingly, when comparing the ‘all axles’ unweighted velocity (red line) against the ‘front axles’ unweighted velocity (dashed black line), similar differences in unweighted velocities are evident in the beginning (−0.8 s to −0.75 s).

Fig. 6. Calculated unweighted velocities.

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29

The unweighted velocities presented in Fig. 6 have been integrated to displacements which are presented in Fig. 7. The displacements using the two short time segments (black curves) overlap smoothly with the offset in the overlap region being less than two microns. The maximum deflection for the first and last axle, based on the short time segments, are −297 μm and −344 μm, respectively. Neither of the two deflection traces has significant uplift. The maximum positive displacement is less than +4 μm. Contrary, the integration of the longer time segment (comprising all three axles, red curve) yields noticeably different results and is affected by, what could be called, the effects of a “low frequency drift”. This is a well-known problem and arises from a combination of two effects namely the geophone unweighting procedure which amplifies low-frequency energy below the geophone’s corner frequency. This effect is further compounded by the subsequent integration to displacements. Different methods of dealing with these effects have been developed.

Fig. 7. Calculated displacements.

Arraigada and Partl (2006) double integrate accelerations to displacements and describe a baseline correction method where the low-frequency drift is removed via subtraction of polynomials. The authors do acknowledge that the results are sensitive to the definition of the start and stop periods of the applied corrections. Crespo-Chacon et al. (2016) are employing a process called ‘zero-restoration’. Details of the zero-restoration process are not discussed but, based on a visual inspection of the results, an approach similar to that used by Arraigada and Partl appears to have been used. A short-coming of the Crespo-Chacon et al. approach is that all positive deflections (ie uplift) are set to zero and consequently any real uplift that may be contained within the signal will not be detected.

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Duong et al. (2018) and Bahrani et al. (2019) have developed analysis techniques in which the geophone signal is high-pass filtered before the integration to displacements. While the high-pass filter is eliminating low-frequency drift issues, the resulting displacements are found to oscillate around zero and the Hilbert transform is used to calculate non-oscillating displacement envelopes. Two shortcomings of this technique are that (1) displacements will always be negative, and uplift (if present) cannot be detected and that (2) the high-pass filtered data requires amplification to compensate for the energy removed in the filtering step. It is not understood how the right amplification factor can be reliably chosen or whether calibration displacements are needed. Velarde et al. (2017) and Rada et al. (2016) are working with short time segments of 0.5 s duration. While this method is not eliminating the issues causing the low frequency drift, it significantly reduces their effects. As the duration of the time segment under investigation decreases, the frequency resolution of the FFT increases which avoids recovering geophone information well below its corner frequency where the signal to noise ratio is low. For example, for 1 s and 0.5 s long time segments the unweighting factors of the first frequency bin for geophone C (refer to Fig. 2) would be: 1. 1 s: First bin at 1 Hz where the sensitivity is 1.4 V/m/s requiring an amplification by a factor of 21.1 (29.6/1.4); and 2. 0.5 s: First bin at 2 Hz where the sensitivity is 5.8 V/m/s requiring an amplification by a factor of 5.1 (29.6/5.1). 3.1 Comparison with iPAVe The deflection and velocity slope parameters were recorded with the iPAVe’s onboard system (amongst other metrics) and the results are compared against the in-situ array using the results obtained for the last axle only (i.e. time segment duration is 0.5 s). The velocity slopes as measured with the embedded array were calculated by dividing the unweighted vertical pavement velocity by the speed of the iPAVe. The iPAVe report results every 10 m and the two result sets closest to the array are used which were recorded with GPS stamps 8.1 m before the array and 1.9 m after the array, respectively. The iPAVe results were recorded at discrete offsets from the rear axle and the velocity slopes and displacements are presented as symbols in Fig. 8. The maximum deflections estimated by the iPAVe range from −245.5 μm to −280.7 μm, depending on the transverse location and the evaluation method. The D0 deflections as calculated with geophones B and C were −336 μm and − 345 μm, respectively. The error is of the order of 15% to 30%. This discrepancy appears large and is not understood. While not explicitly discussed in this paper, significant variations – as measured in the embedded array and with the iPAVe truck – between individual runs were observed which were greater than the observed discrepancy between embedded array and iPAVe. The variation between individual runs were believed to be caused by the difficulty to align the iPAVe perfectly with the embedded array, which is particularly severe when measuring deflection on comparatively stiff pavements (ie in the low deflection range).

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Fig. 8. Comparison of the iPAVe data against geophones B (dash-dot) and C (solid) of the embedded array.

3.2 Visualisation The array utilises five sensors which are staggered transversally and longitudinally by known amounts. Since one embedded sensor allows for visualising a longitudinal slice of the deflection bowl, the shape of the deflection bowl can be partially reconstructed and visualised by appropriately arranging the slices measured by each sensor. Figure 9 shows contour plots of the vertical velocities and displacements of the particular iPAVe pass-by discussed. The horizontal lines at −0.5, −0.25, 0, +0.25 and + 0.5 coincide with data as measured by the geophones E, D, C, B and A, respectively.

Fig. 9. Velocities (left) and displacements (right).

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The dashed grey line is the path of the iPAVe’s laser beam as estimated from videos. Transverse data points between geophones have been linearly interpolated. One benefit of a three-dimensional representation of the deflection bowl is that it can be studied not only based on its curvature in the longitudinal plane but also on the transverse plane.

4 Conclusions ARRB has installed a permanent, in-situ pavement array on a site in Queensland, Australia. The array extends 1 m in the transverse direction and 1 m in the longitudinal direction. In the transverse direction, measurements are taken at five discrete offsets to maximise the chance to align the iPAVe with the array. In the longitudinal direction two sensors are used (one sensor suffices for estimating the speed of vehicles of unknown axle spacings). The design of an array with high resolution in the transverse direction allows for visualising the deflection bowl three-dimensionally. The array has been instrumented with geophones and accelerometers. In this study, only resultsmeasured with geophones are discussed. The signal processing steps taken to linearise the geophones’ frequency responses and to subsequently calculate the pavement deflections are presented. Measurement results for one iPAVe pass-by are discussed in detail and the vertical pavement deflections and velocity slopes as obtained with the in-situ array are compared against those of the iPAVe’s onboard system. The comparison revealed some discrepancies. While not presented in this study, the observed discrepancies between the pavement array and the iPAVe’s onboard system are smaller than the variation between separate iPAVe pass-bys over the array. Investigations into this intra-run variability are ongoing. Acknowledgments. The research was funded by the NACOE project. The NACOE program is an initiative between the Queensland Department of Transport and Main Roads (TMR) and the Australian Road Research Board (ARRB). The authors wish to thank Soheil Nazarian (University of Texas at El Paso) for in-depth discussions.

References Arraigada, M., Partl, M.: Calculation of displacements of measured accelerations, analysis of two accelerometers and application in road engineering. In: STRC 2006 ( (2006)) Bahrani, N., Blanc, J., Hornych, P., Menant, F.: Pavement instrumentation for condition assessment using efficient sensing solutions. In: International Conference on Smart Infrastructure and Construction 2019 (ICSIC) (2019) Collette, C., et al.: Review: inertial sensors for low-frequency seismic vibration measurement. Bull. Seismol. Soc. Am. 102(4), 1289–1300 (2012) Crespo-Chacón, I., García-de-la-Oliva, J.L., Santiago-Recuerda, E.: On the use of geophones in the low-frequency regime to study rail vibrations. Procedia Eng. 143(2016), 782–794 (2016) Duong, N., Blanc, J., Hornych, P., Menant, F., Lefeuvre, Y., Bouveret, B.: Monitoring of pavement deflections using geophones. Int. J. Pavement Eng. 21(9), 1103–1113 (2018). https://doi.org/ 10.1080/10298436.2018.1520994

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Lee, J., Duschlbauer, D., Chai, G.: Ground instrumentation for traffic speed deflectometer (TSD). In: Western Australian Road Research and Innovation Program (WARRIP) report (2019) Lee, J., Duschlbauer, D.: Pavement vibration measurements for Falling Weight Deflectometer and Moving Vehicle Loads. In: 17th AAPA International Flexible Pavements Conference 2017 (2017) Rada, G., Nazarian, S., Visintine, B., Siddharthan, R., Thyagarajan, S.: FHWA-HRT-15–074 report Pavement Structural Evaluation at the Network Level: Final Report (2016) Velarde, J.A., Rocha, S., Nazarian, S., Rada, G., Thyagarajan, S., Siddharthan, R.V.: Use of embedded sensors to evaluate performance of traffic speed deflection devices. Journal of Testing and Evaluation, 45(4) (2017)

Unconfined Compressive Strength of Compacted Tropical Soil Bio-treated with Bacillus Megaterium Adrian Eberemu(B) Department of Civil Engineering and Africa Centre of Excellence on New Pedagogy in Engineering Education, Ahmadu Bello University, Zaria, Kaduna State, Nigeria

Abstract. The environmental problem associated with the manufacturing and use of cement and other chemicals for soil stabilisation has led to an innovative and a more environmentally friendly technique called microbial induced calcite precipitation (MICP). MICP utilizes a biological process in soil improvement. Specimens of soil were bio-treated with 1/3 pore volume of stepped Bacillus megaterium (B. megaterium) suspension density 0, 1.5 × 108 cells/ml, 6 × 108 cells/ml, 12 × 108 cells/ml, 18 × 108 cells/ml and 24 × 108 cells/ml, respectively. The specimens were prepared at −2, 0, +2 and +4% moulding water content (MWC) relative to optimum moisture content (OMC) and compacted with British Standard light, BSL (or standard Proctor) energy. 2/3 pore volume of cementation reagent was injected into the compacted specimens in 3 cycles at 6 h interval and allowed to flow by gravity until partial saturation was achieved. The results obtained indicate that the unconfined compressive strength (UCS) increased with increase in B. megaterium suspension density and with decrease in MWC relative to OMC. Typically for the specimens prepared at OMC, the UCS of specimens treated with stepped B. megaterium suspension density of 1.5 × 108 cells/ml, 6 × 108 cells/ml, 12 × 108 cells/ml, 18 × 108 cells/ml and 24 × 108 cells/ml increased by 33.83%, 40.76%, 52.24%, 58.06%, 59.06%, respectively, compared to the UCS of the untreated specimen (i.e., with 0 cells/ml). Overall, higher calcite content precipitated in specimens resulted in increased UCS and dry density values. The phase structure, composition and morphology characterized using the scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) and Fourier transformation infra-red (FTIR) spectroscopy, indicated that calcite print was induced within the soil matrix. Specimens treated with B. megaterium suspension densities of 6 × 108 cells/ml, 12 × 108 cells/ml, 18 × 108 cells/ml and 24 × 108 cells/ml and prepared compacted at MWC −2, 0 and +2 OMC, respectively, satisfied the minimum 200 kN/m2 design criterion for the use of materials in municipal solid waste (MSW) containment application.

1 Introduction Due to pollution of groundwater, the scope of barrier system in engineered sanitary landfill has extended into researches on materials that have the potentials to mitigate the advection and diffusion of noxious waste into the underlying subsurface soil. Researches © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 34–51, 2021. https://doi.org/10.1007/978-3-030-79638-9_4

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have revealed that compacted clay liner (CCL), Geosynthetic Clay Liner (GCL), and different types of reclaimed, re-used, reprocessed and recycled wastes have potential as hydraulic barrier materials in engineered waste containment facility [11, 23]. However, the continued reliance on the existing industrially manufactured geosynthetic liners and covers materials for construction of hydraulic barriers in landfill sanitary systems has resulted in higher cost of constructing landfill sanitary systems. This has become even more worrisome due to the growing number in population, industrialization and sustainable development which has further resulted to the rising scale of unsystematic and unwholesome practice of wastes disposal within cities. The widespread deposits of lateritic soil in tropical regions, including Nigeria, makes the material a good candidate for use in the construction of barrier systems in engineered municipal solid waste (MSW) containment facilities. Researches have established acceptable results which show that, lateritic soils either singly or stabilized with processed agricultural and industrial wastes (e.g., bagasse ash, groundnut shell ash, waste wood ash, fly ash, foundry slag or cement kiln dust, etc.) can be used as barrier materials in sanitary landfills. The integrity of these materials as barrier material were based on the satisfactory chemical resistance, enhanced workability, lowered susceptibility to desiccation cracks and shrinkage, shear strength, hydraulic conductivity, diffusion and compatibility characteristics [18, 22, 27, 32, 35, 42, 47]. The high cost of improving unstable soils through stabilization with lime and or cement is also associated with the negative impact of greenhouse effect and global warming caused by vast CO2 emissions into the atmosphere during production of cement, that contribute significantly to environmental degradation and climate change [31]. Therefore, the paradigm shift towards sustainable and green technology (ecofriendly) of soil improvement has diverted the attention of researchers from hitherto conventional stabilizers, and pozzolanic agro-industrial wastes, which are either not economical, nonenvironmental friendly, and hence not sustainable to an innovative, new, economic and environmentally friendly Microbial Induced Calcite Precipitation (MICP) technique. MICP method of soil improvement involves the use of micro-organisms and chemicals to stimulate the formation of calcite within the soil matrix thereby forming bonds/links within the pores and surface of the soil grains that stiffen the soil. MICP has found application in remediation of cracks in rocks [19], fortification of concrete [44], contaminant immobilization [21], bio-remediation [2], mitigation of saturation and liquefaction in soil [45], improved soil properties [15, 24, 26, 39, 40, 52], and hydraulic conductivity reduction [24, 41]. The operational integrity of a structured landfill is guaranteed when the compacted materials for liner and cover constructions have satisfactory strength to hold high imposed stress caused by weights of waste [38]. Therefore, compacted soil strength is estimated as a function of the UCS. The minimum UCS value of 200 kN/m2 for compacted soil was reported by Daniel and Wu [12]. In the light of this, a number of studies have reported a general upgrade in UCS of soils using the MICP techniques but very few have related their results to the criteria for liners and covers as barrier systems [39, 40]. This study focused on the evaluation of the suitability of lateritic soil - B. megaterium mixture for use in the design of MSW containment system. Therefore, if the UCS of the bio treated soil satisfy the design criterion it would enable the construction

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of engineered landfill, particularly in developing countries, using the eco-friendly and sustainable MICP technique. The study also evaluated the micro morphological structure of the treated soil using scanning electron microscopy (SEM) and Fourier transformation infra-red (FTIR) spectroscopy.

2 Materials and Methods 2.1 Materials 2.1.1 Soil Sample It was obtained by disturbed sampling from Agulu (Latitude 6° 3 14 N and Longitude 7° 6 17 E), Anaocha Local Government Area, Anambra State, Nigeria. 2.1.2 Bacteria Bacillus species micro-organism (B. megaterium) was used. It is a rod-like, Grampositive, mainly aerobic spore forming and urease positive which was cultured and grown from the sample of lateritic soil used in this study. 2.1.3 Cementation Reagent The cementation reagent composition of 3 g Nutrient broth, 2.8 g CaCl2 , 10 g NH4 Cl, 2.12 g NaHCO3 and 20 g urea per litre of distilled water reported by researchers [15, 39, 40, 51] was adopted for the study. 2.2 Methods 2.2.1 Index Properties Studies on natural and treated soil were performed based on [5] and [6], respectively. 2.2.2 Compaction The procedure outlined in [5] was adopted and BSL compaction energy (or standard Proctor) was used. 2.2.3 Calcite Content The calcite content (CC) for the various B. megaterium suspension density was measured using acid wash test [9, 28]. 5 g natural lateritic soil and soil mixed with varying B. megaterium suspension density (cell/ml) were dissolved in 20 ml of 1-M HCl (gravimetric acid washing). The solvent was then filtered using filter paper with minute openings corresponding to No. 200 sieve (75 µm aperture). The filtrate on the filter paper was then rinsed and washed for about 10 min with distilled water to completely remove dissolved calcium from the soil grains. Thereafter, particles on the filter paper were oven-dried at 105 °C for 24 h and weighed. The change in masst between the original sample (W1 ) and

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37

after washing (W2 ) was calculated as the mass of calcium carbonate (CaCO3 ) content (%) using Eq. (1). The test was repeated in triplicate and the average taken for the various mixture considered. CC = 100 −

W1 × 100 W2

(1)

2.2.4 Unconfined Compression The test was carried out in accordance with the procedure outlined in [5]. The soil was mixed with the requisite MWC relative to OMC (i.e., −2, 0, 2 and 4%) containing 1/3 pore volume of B. megaterium suspension densities (i.e., 0, 1.5 × 108 , 6 × 108 , 1.2 × 109 , 1.8 × 109 and 2.4 × 109 cells/ ml) recommended by [46]. The specimens were compacted in 1,000 cm3 standard moulds and 2/3 pore volume of cementation reagent (ml) was injected into the specimen in 3 cycles at 6 h interval to percolate and partially saturate the specimens. After the 3rd cycle the specimens were left for 6 h to allow for continuous hydrolysis towards calcite precipitation as well as to establish constant interval of percolation of cementation reagent. The specimen for UCS test (76 mm × 38 mm) were cored and further allowed to air-cure for 12 h and wrapped for another 12 h before testing for UCS. 2.2.5 Micro-analysis of Specimens The morphological investigation of specimen was done using Phenom world scanning electron microscopy (SEM) fitted with an inbuilt X-ray Energy Dispersive Spectroscopy (EDS) as a complement to the micro-morphological feedbacks focused on instant semiquantitative chemical evaluations. FTIR studies were used to characterize the natural soil and bio treated specimens. The FTIR (Agilent Technologies) spectra is based on the transmittance method obtained at specimen scans of 30, resolution of 8 cm−1 and wave number in the range of 650–4000 cm−1 .

3 Results and Discussion 3.1 Index Property The natural soil was classified as A-4(3) soil using American Association of state Highway and Transportation Officials (AASHTO) [1] or SC soil using Unified Soil Classification System (USCS) [4]. The particle size plot and summary of the properties of the natural lateritic soil are presented in Fig. 1 and Table 1, respectively. 3.2 Effect of B. Megaterium on Calcite Content The properties of soil improved with MICP technique is directly linked to the formation of calcite, which stiffens and bind the soil particles together. The B. megaterium suspension density (cells/ml) is a function of population of cell of microbes per ml in liquid suspension. The amount of calcite as a function of the B. megaterium cells/ml is shown

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Fig. 1. Particle size distribution curve for the natural lateritic soil

Table 1. Properties of the natural lateritic soil Property

Quantity

Percentage passing 0.075 mm sieve 35.3 Natural moisture content (%)

11.6

Liquid limit (%)

36.7

Plastic limit (%)

13.0

Plasticity index (%)

23.7

Linear shrinkage (%)

9.0

Specific gravity

2.65

AASHTO classification

A-4(3)

USCS classification

SC

Maximum dry density Mg/m3

1.72

Optimum moisture content (%)

17.16

Colour

Reddish-brown

in Fig. 2. The calcite formed, slightly increased with increase in the B. megaterium suspension densities from 2.1% at 0 cells/ml to the maximum value of 4.4% (i.e., 52.3% increase) at 2.4 × 109 cell/ml. The recorded increase might not be unconnected with the higher B. megaterium suspension density that produced more urease enzyme for the hydrolysis of urea [33]. Also, the higher B. megaterium suspension density provided more nucleation sites on the surfaces of the microbes which then enabled the formation of calcite [51].

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Fig. 2. Variation of calcium carbonate content of lateritic soil with B. megaterium suspension density

3.3 Effect of B. Megaterium on Unconfined Compressive Strength The unconfined compressive strength (UCS) of compacted lateritic soil bio-treated with B. megaterium at different moulding water content, MWC (i.e., −2, 0, +2 and +4%) relative to OMC is shown in Fig. 3. The UCS values increased with increasing B. megaterium suspension density/ml as well as with the decreasing range/order of MWC relative to OMC from +4 (wet) to −2% (dry) OMC: −2 > 0 > +2 > +4%. Using the specimens prepared with OMC of 14.4% as example, the UCS values of specimens increased with B. megaterium suspension densities of 1.5 × 108 /ml, 6 × 108 /ml, 12 × 108 /ml, 18 × 108 /ml and 24 × 108 /ml increased by 33.83%, 40.76%, 52.24%, 58.06%, 59.06%, respectively, compared to the UCS of the untreated specimen (i.e., 0 cell/ml). The growth and cumulative capacity of B. megaterium provided site for the nucleation and formation of greater quantity of CaCO3. Similar findings were reported by [34, 39, 40]. Typically, microbes have sizes in the range 0.5–3.0 µm [3], therefore the 0.002 to 2.36 mm particle range (see Fig. 1) provides the enabling pore throat size for the movement of pre-mixed B. megaterium suspension/ml through the soil [45]. This provides adequate distribution of nucleation spots which attracted more of the formed calcite and free Ca2+ . Also, the relative increase in UCS with decreasing order of MWC from +4 to −2% relative to OMC can be attrinuted to fines fraction which offered a compact assembly and provided additional grain-to-grain contact for adequate bonding [39, 40]. The grain-to-grain contact could vary and in turn provided space that accommodated higher CaCO3 content that considerable increased strength that satisfied the minimum 200 kN/m2 design criterion for MSW containment facilities.

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Fig. 3. Variation of unconfined compressive strength of lateritic soil prepared at different moulding water content relative to optimum moisture content with B. megaterium suspension density

3.4 Unconfined Compressive Strength of Lateritic Soil - B. Megaterium Mixture as a Function of Moulding Water Content The UCS values shown in Fig. 4 decreased from the dry to wet sides of OMC. Higher UCS values were recorded for all bio treated specimens at lower MWC, but the values reduced correspondingly with increasing MWC for the varying B. megaterium suspension density. Similar findings were reported by [35, 39, 40]. The effect of increased MWC on one hand could be explained based on the principle of surface thermodynmics: (1) the average water layer in the soil composite became thick and expanded its diffuse double layer (DDL), (2) the force of attraction between the clay minerals reduced and the soil phase was unduly destroyed or simply altered and (3) the shear resistance and stiffness of the bio-treated soil was drastically reduced [13, 29, 30]. This resulted in the linear reduction of UCS values with higher MWC (see Fig. 4). Also, as B. megaterium suspension density increased, UCS values slightly increased. This probably suggests that, while B. megaterium tends to stimulate strength and stiffening process through the formation as well as deposition of calcite within the voids of the soil, the relative volume of water available in the soil preceding compaction had tremendously modified the bio treated specimen by reducing its stiffening potential [39, 40, 48]. 3.5 Relationship Between Unconfined Compressive Strength and Dry Density Lateritic Soil - B. Megaterium Mixtures The variation of UCS of lateritic soil - B. megaterium mixtures is showm in Fig. 5. Generally, UCS values increased with increase in dry density due to the increased bonding and filling of voids in the soil by calcite precipitated by the B. megaterium urease positive bacteria in cementation reagent medium [8, 36, 39, 40, 53]. The trend showed

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Fig. 4. Variation of unconfined compressive strength of lateritic soil - B. megaterium mixtures with moulding water content relative to optimum moisture content

Fig. 5. Variation of unconfined compressive strength of lateritic soil - B. megaterium mixtures with dry density

some relative complexity with slight deviations where UCS increased with decrease in dry density. The observed deviations were specific to specimens prepared on the dry side (−2%) of OMC for specimens treated with B. megaterium of 1.5 × 108 , 6 × 108 , 12 × 108 , 18 × 108 and 24 × 108 cells/ ml. However, specimens prepared at OMC and wet side of OMC (i.e., +2 and +4%) recorded relatively positive linear correlation between the dry density and UCS of the treated soil [11, 39, 40].

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3.6 Scanning Electron Microscopy and Energy Dispersive Spectroscopy of Specimens The scanning electron microscopy (SEM) and quantifications of element identified by energy dispersive spectroscopy (EDS) of micro-morphological pecimens are presented in Figs. 6, 7 and 8 for the natural lateritic soil, lateritic soil - B. megaterium of 0 cells/ml (i.e., cementation reagent only) and lateritic soil - B. megaterium of 24 × 108 cells/ml, respectively. The morphologies show that the cacite (CaCO3 ) distributions were not uniform at the 100 µm resolution and x500 magnification level. This suggests that the grain size of soil or extent of voids is a controlled factor than the soil fabrics (solid content) upsetting the uniformity in the CaCO3 formation and distribution [43]. It is important to state that, while the observed pore filling calcite precipitate in 24 × 108 cells/ml bio-treated soil (see Fig. 8a), was due to the urea hydrolysis of higher B. megaterium suspension density [3, 43], the precipitates in soil with B. megaterium suspension density 0 cell/ml could be due to the stimulation of indigenous bacteria swamp in the soil by cementation reagent [7, 14]. Generally, the variations in calcite precipitations might be due to the circulation, saturation and or absorption of urea source (cementation media) relative to the nucleation site proffered by bacterial cells [3]. Consequently, the variations in atomic and weight quantifications of element identified from EDS of natural soil, 0 cell/ml and 24 × 108 cells/ml bio treated soil (see Fig. 6a, 7a and 8a), further shed more light on the potentials of possible calcite formation. 3.7 Fourier Transformation Infra-red Characterisation of Natural and Bio-Amended Soil Fabric The technique of Infrared (IR) analysis is now frequently applied in geotechnical assessments of various kinds of clay and their modifications [17, 20, 49, 50]. These modifications were observed from various methods of soil improvement techniques such as stabilization [20, 50] and biogeochemical reaction [54]. The Fourier transformation infra-red (FTIR) spectra of natural lateritic soil and soil bio-treated with B. megaterium suspension densities of 0 cell/ml, 12 × 108 cells/ml and 24 × 108 cells/ml are presented in Figs. 9, 10, 11 and 12. The structural series of kaolinites is identified by alterations in orientation and intensity of its IR spectrum [25]. For all specimens, there were common various bands/phases in all schemes observed by FTIR transmittance bands. The bands at 3652 and 3693 cm−1 wave number represent the various degree of OH groups which are consistent with quite a number of studies [17, 20, 25, 49] reporting that the OH bands in kaolin characteristically exhibit clear stretching bands that are in the range 3600–3700. The wave numbers 685.8, 689.6, 693.3, 752.9 and 779 cm−1 correspond to Si-O perpendicular stretching; 790.2 cm−1 , 793.3 cm−1 relates to Si-O; 913.2 cm−1 , 909.5 cm−1 represent OH deformation of inner hydroxyl group; 1002.7, 1006.4, 1028.7, 1032.5 and 1036.2 cm−1 are associated with in-plane Si-O stretching and 1114.5 cm−1 is the Si-O longitudinal stretching mode as shown in Figs. 9, 10, 11 and 12 [17, 20, 25, 50]. The presence of 1423 cm−1 band (asymmetric stretch) in 12 × 108 , and 24 × 108 /ml bio-treated specimen (see Figs. 11 and 12) correlate with CO3 2− ions [10]. This suggest that CO3 2− is available and is easily mobilised to the nucleation site of the microorganism throughout its bonding activity with Ca2+ founded in calcite crystal

Unconfined Compressive Strength of Compacted Tropical Soil

43

Fig. 6. (a) Micrograph of natural lateritic soil at x500 magnification with complementary EDS (b) Atomic and weight quantifications of element identified from EDS of natural lateritic soil.

[53]. The various wave numbers depicted by weak intensity bands (i.e., 1636.3, 2050, 2885, 2791.8, 2322.1 and 1986.7 cm−1 ) might be related to cemented sediment having either magnesium, manganese, iron or aluminum as carbonates polymorphs [15, 16].

44

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Fig. 7. (a) Micrograph of lateritic soil - B. megaterium of 0 cell/ml (i.e., cementation reagent only) at x500 magnification with complementary EDS (b) Atomic and weight quantifications of element identified from EDS of lateritic soil - B. megaterium of 0 cells/ml (i.e., cementation reagent only) mixture

Unconfined Compressive Strength of Compacted Tropical Soil

45

Fig. 8. Micrograph of lateritic soil - B. megaterium of 24 × 108 cells/ml at x500 magnification with complementary EDS (b) Atomic and weight quantifications of element revealed by EDS spectra for lateritic soil - B. megaterium of 24 × 108 cells/ml mixture

46

A. Eberemu

Fig. 9. FTIR spectrum of natural soil

Fig. 10. FTIR spectra of natural lateritic soil - B. megaterium suspension density of 0 cell/ml specimen

Fig. 11. FTIR spectra of natural lateritic soil - B. megaterium suspension density of 12 × 108 cells/ml specimen

Unconfined Compressive Strength of Compacted Tropical Soil

47

Fig. 12. FTIR spectra of natural lateritic soil - B. megaterium suspension density of 24 × 108 /ml specimen

4 Conclusion The unconfined compressive strength (UCS) of lateritic soil was improved with B. megateruim using the microbial induced calcite precipitation technique (MICP). The UCS values increased from 161, 178, 371, 408 kN/m2 for the untreated soil (i.e., at 0 cell/ml) to peak values of 546, 745, 910 and 1011 kN/m2 at 24 × 108 cells/ml for specimens prepared at 4, 2, 0 and −2% moulding water content relative to optimum moisture content and compacted with BSL energy, respectively. Higher calcite content and dry density of specimens were responsible for the high UCS values recorded. The SEM/EDS and FTIR spectrometry results provided qualitative and effective methods for the examination of the morphologies and precipitates in the pores of the soil fabrics. The UCS design criterion of 200 kN/m2 for barrier material was satisfied by specimens treated with B. megaterium suspension densities of 6 × 108 cells/ml, 12 × 108 cells/ml, 18 × 108 cells/ml and 24 × 108 cells/ml prepared at MWC of −2, 0 and +2% relative to OMC, respectively, and compacted with BSL energy. Therefore, the bio-treated soil is recommended for use as barrier material in sanitary landfill based on the strength values recorded. Further experimental studies are suggested to estimate the effect of B. megateruim on hydraulic conductivity and desiccation crack reduction in the design of MSW containment facility. Conflict of Interest. On behalf of all authors, the corresponding author states that there is no conflict of interest.

References 1. AASHTO. Standard Specification for Transportation, Material and Methods of Sampling and Testing. 14th Edition. Amsterdam Association of State Highway and transportation officia Washington D.C. (1986) 2. Achal, V., Pan, X., Lee, D.J., Kumari, D., Zhang, D.: Remediation of Cr (VI) from chromium slag by biocementation. Chemosphere 93(7), 1352–1358 (2013)

48

A. Eberemu

3. Al Qabany, A., Soga, K., Santamarina, C.: Factors affecting efficiency of microbially induced calcite precipitation. J. Geotech. Geoenviron. Eng. 138(8), 992–1001 (2012). https://doi.org/ 10.1061/(ASCE)GT.1943-5606.0000666 4. ASTM. Annual Book of Standards. Vol. 04.08, American Society for Testing and Materials, Philadelphia (1992) 5. BS 1377. Method of Testing Soils for Civil Engineering Purpose. British Standard Institute, BSI, London (1990) 6. BS 1924. Method of Test for Stabilized Soils. British Standard Institute BSI London (1990) 7. Burbank, M.B., Weaver, T.J., Green, T.L., Williams, B.C., Crawford, R.L.: Precipitation of calcite by indigenous microorganisms to strengthen liquefiable soils. Geomicrobiol. J. 28(4), 301–312 (2011). https://doi.org/10.1080/01490451.2010.499929 8. Cheng, L., Shahin, M.A., Cord-Ruwisch, R., Addis, M., Hartanto, T., Elms, C.: Soil stabilisation by microbial induced calcium carbonate precipitation: investigation of some important physical and environmental aspects. In: 7th International Congress on Environmental Geotechnics, Australia (2014) 9. Choi, S.G., Park, S., Wu, S., Chu, J.: Methods for calcium carbonate content measurement of biocemented soils. J. Mater. Civil Eng. Tech. Note Eng. 29(11), 06017015 (2017). https:// doi.org/10.1061/(asce)MT.1943-5533.0002064 10. Cizer, Ö., Rodriguez-Navarro, C., Ruiz-Agudo, E., Elsen, J., Gemert, D.V., Balen, K.V.: Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime. J. Mater. Sci. 47, 6151–6165 (2012). https://doi.org/10.1007/s10853-012-6535-7 11. Daniel, D.E., Benson, C.H.: Water content density criteria for compacted soil liners. J. Geotech. Eng. ASCE 116(12), 1811–1830 (1990) 12. Daniel, D.E., Wu, Y.K.: Compacted clay liners and covers for arid sites. J. Geotech. Engrg. ASCE 119(2), 223–237 (1993) 13. Defay, R., Prigogine, I., Sanfeld, A.: Surface thermodynamics. J. Colloid. Interface Sci. 58, 498–510 (1977) 14. Dejong, J.T., Soga, E., Kavazanjian, S., et al.: Biogeochemical processes and geotechnical applications: progress, opportunities, and challenges. Geotechnique 63(4), 287–301 (2013). https://doi.org/10.1680/geot.SIP13.P.017 15. DeJong, J.T., Fritzges, M.B., Nusslein, K.: Microbially induced cementation to control sand response to undrained shear. J. Geotech. Geoenviron. Eng. 132(11), 1381–1392 (2006). https:// doi.org/10.1061/(asce)1090-0241(2006)132:11(1381) 16. Dhami, N.K., Reddy, M.S., Mukherjee, A.: Biomineralization of calcium carbonate polymorphs by the bacterial strains isolated from calcareous sites. J. Microbiol. Biotech. 23, 707–714 (2013) 17. Djomgoue, P., Njopwouo, D.: FT-IR spectroscopy applied for surface clays characterization. J. Surf. Eng. Mater. Adv. Technol. 03(04), 275–282 (2013). https://doi.org/10.4236/jsemat. 2013.34037 18. Eberemu, A.O.: Evaluation of bagasse ash treated lateritic soil as a barrier material in waste containment application. Acta Geotechnica 8(4), 407–421 (2013). http://www.springerlink.com/openurl.asp?genre=article&id=doi:https://doi.org/10.1007/ s11440-012-0204-5, https://doi.org/10.1007/s11440-012-0204-5, ISSN 1861–1125 19. Ersan, Y.C., Hernandez-Sanabria, E., Boon, N., de Belie, N.: Enhanced crack closure performance of microbial mortar through nitrate reduction. Cement Concr. Compos. 70, 159–170 (2016) 20. Etim, R.K., Attah, I.C., Yohanna, P.: Experimental study on potential of oyster shell ash in structural strength improvement of lateritic soil for road construction. Int. J. Pav. Res. Technol. 13(4), 341–351 (2020). https://doi.org/10.1007/s42947-020-0290-y 21. Fujita, Y., et al.: Stimulation of microbial urea hydrolysis in groundwater to enhance calcite precipitation. Environ. Sci. Technol. 42, 3025–3032 (2008)

Unconfined Compressive Strength of Compacted Tropical Soil

49

22. Goswami, R.K., Mahanta, C.: Leaching characteristics of residual lateritic soils stabilised with fly ash and lime for geotechnical applications. Waste Manag. 27, 466–481 (2007). https://doi. org/10.1016/j.wasman.2006.07.006 23. Hassan, A.A.: Hydraulic Performance of Compacted Clay Liners (CCLS) Under Simulated Landfill Conditions. M.sc Thesis Department of Civil and Environmental Engineering Carleton University, Ottawa-Carleton Institute of Civil and Environmental Engineering (2014) 24. Ivanov, V., Chu, J.: Applications of microorganisms to geotechnical engineering for bioclogging and biocementation of soil in situ. Rev. Environ. Sci. Bio/Technol. 7(2), 139–153 (2008). https://doi.org/10.1007/s11157-007-9126-3 25. Madejová, J., Komadel, P.: Baseline studies of the clay minerals society source clays: Infrared methods. Clays Clay Miner. 49(5), 410–432 (2001). https://doi.org/10.1346/CCMN.2001.049 0508 26. Mitchell, J.K., Santamarina, J.C.: Biological consideration in geotechnical engineering. J. Geotech. Geoenviron. Eng. ASCE 131(10), 1222–1233 (2005). https://doi.org/10.1061/(ASC E)1090-0241(2005)131:10(1222) 27. Mollamahmutoglu, M., Yilmaz, Y.: Potential use of fly ash and bentonite mixture as liner or cover at waste disposal areas. Environ. Geol. 40(11), 1316–1324 (2001). https://doi.org/10. 1007/s002540100355 28. Mortensen, B.M., Haber, M.J., DeJong, J.T., Caslake, L.F., Nelson, D.C.: Effects of environmental factors on microbial induced calcium carbonate precipitation. J. Appl. Microbiol. (2011). https://doi.org/10.1111/j.1365-2672.2011.05065.x 29. Mutaftschiev, B.: Surface thermodynamics. In: Mutaftschiev, Boyan (ed.) Interfacial Aspects of Phase Transformations, pp. 63–102. Springer Netherlands, Dordrecht (1982). https://doi. org/10.1007/978-94-009-7870-6_3 30. Neumann, A.W., David, R., Zuo, Y.: Applied surface thermodynamics. Focus Surf. 2011, 6 (2011) 31. Neville, A.M.: Properties of Concrete, 4th ed. (low-price ed.). Pearson Education Asia Publication, England, Produced by Longman Malaysia (2000) 32. Nik Daud, N.N., Muhammed, A.S., Kundiri, A.M.: Hydraulic conductivity of compacted granite residual soil mixed with palm oil fuel ash in landfill application. Geotech. Geol. Eng. 35(5), 1967–1976 (2017). https://doi.org/10.1007/s10706-017-0220-1 33. Okwadha, G.D., Li, J.: Optimum conditions for microbial carbonate precipitation. Chemosphere 81(9), 1143–1148 (2010) 34. Venda Oliveira, P.J., Neves, J.P.: Effect of organic matter content on enzymatic biocementation process applied to coarse-grained soils. J. Mater. Civil Eng. 31(7), 04019121 (2019). https:// doi.org/10.1061/(ASCE)MT.1943-5533.0002774 35. Oluremi, J., Eberemu, A., Ijimdiya, S., Osinubi, K.: Lateritic soil treated with waste wood ash as liner in landfill construction. Environ. Eng. Geosci. 25(2), 127–139 (2019). https://doi. org/10.2113/EEG-2023 36. Osinubi, K.J., Eberemu, A.O., Ijimdiya, T.S., Yakubu, S.E., Sani, J.E.: Potential use of B. Pumilus in microbial induced calcite precipitation improvement of lateritic soil. In: Proceedings of the 2nd Symposium on Coupled Phenomena in Environmental Geotechnics (CPEG2), Leeds, United Kingdom, 6–8 September 2017. Session: Clean-ups, Paper #64, pp. 1–6 (2017) 37. Osinubi, K.J., Eberemu, A.O., Amadi, A.A.: Compacted Lateritic soil treated with blast furnace slag as hydraulic barrier in waste containment systems. In: Proceedings International Conference on Infrastructure Deviations & the Environments (ICIDEN 2006), Abuja, Nigeria (2006)

50

A. Eberemu

38. Osinubi, K.J., Moses, G., Oriola, F.O.P., Liman, A.S.: Influence of molding water content on shear strength influence of molding water content on shear strength characteristics of compacted cement kiln dust treated lateritic soils for liners and covers. NIJOTECH. 34(2), 265–271 (2015). https://doi.org/10.4314/njt.v34i2.8 39. Osinubi, K.J., Yohanna, P., Eberemu, A.O., Ijimdiya, T.S.: Unconfined compressive strength of lateritic soil treated with bacillus coagulans for use as liner and cover material in waste containment system. IOP Conf. Ser. Mater. Sci. Eng. 640, 012081 (2019). https://doi.org/10. 1088/1757-899X/640/1/012081 40. Osinubi, K.J., Gadzama, E.W., Eberemu, A.O., Ijimdiya, T.S.: Comparative evaluation of strength of compacted lateritic soil improved with microbial-induced calcite precipitate. In: Proceedings 3rd International Engineering Conference (IEC 2019). Federal University of Technology, Minna, Nigeria (2019) 41. Osinubi, K.J., Yohanna, P., Eberemu, A.O., Ijimdiya, T.S.: Evaluation of hydraulic conductivity of lateritic soil treated with Bacillus coagulans for use in waste containment applications. In: Zhan, L., Chen, Y., Bouazza, A. (eds.) Proceedings of the 8th International Congress on Environmental Geotechnics (ICEG 2018), “Towards a Sustainable Geoenvironment”, Hangzhou, China, 28th October–1st November, vol. 3, pp. 401–409. Springer, Cham (2019). https://doi.org/10.1007/978-98113-2227-3_50 42. Osinubi, K.J., Nwaiwu, C.M.O.: Design of compacted lateritic soil liners and covers. J. Geotech. Geoenviron. Eng. ASCE 132(2), 203–213 (2006). https://doi.org/10.1061/(ASC E)1090-0241(2006)132:2(203) 43. Pan, X., Chu, J., Yang, Y., Cheng, L.: A new biogrouting method for fine to coarse sand. Acta Geotech. 15(1), 1–16 (2019). https://doi.org/10.1007/s11440-019-00872-0 44. Ramachandran, S.K., Ramakrishnan, V., Bang, S.S.: Remediation of Concrete Using MicroOrganisms. ACI Mater. J. 98(1), 3–9 (2001) 45. Rebata-Landa, V., Santamarina, J.C.: Mechanical limits to microbial activity in deep sediments. Geochem. Geophys. Geosyst. 7(11), 1–12 (2006) 46. Rowshanbakhta, K., Khamehchiyana, M., Sajedib, R.H., Nikudela, M.R.: Effect of Injected bacterial Suspension Volume and Relative Density on Carbonate Precipitation Resulting from Microbial Treatment. J. Ecol. Eng. 89, 49–55 (2016). https://doi.org/10.1016/j.ecoleng.2016. 01.010 47. Rubinos, D.A., Spagnoli, G.: Utilization of waste products as alternative landfill liner and cover materials – a critical review. Crit. Rev. Environ. Sci. Technol. (2018). https://doi.org/ 10.1080/10643389.2018.1461495 48. Sabat, A.K., Mohanta, S., Swain, S.: Effect of moulding water content on geotechnical properties of rice straw ash stabilized expansive soil. ARPN J. Eng. Appl. Sci. 10(22), 10427–10432 (2015) 49. Saikia, B.J., Parthasarathy, G.: Fourier transform infrared spectroscopic characterization of kaolinite from Assam and Meghalaya, north eastern India. J. Modern Phys. 1, 206–210 (2010) 50. Sharma, L.K., Sirdesai, N.N., Sharma, K.M., Singh, T.N.: Experimental study to examine the independent roles of lime and cement on the stabilization of a mountain soil: a comparative study. Appl. Clay Sci. 152, 183–195 (2017) 51. Stocks-Fischer, S., Galinat, J.K., Bang, S.S.: Microbiological precipitation of CaCO3 . Soil Biol. Biochem. 31(11), 1563–1571 (1999) 52. Umar, M., Kassim, K.A., Zango, M.U., Muhammed, A.S.: Performance evaluation of lime and microbial cementation in residual soil improvement. IOP Conf. Ser.: Mater. Sci. Eng. 527, 012005 (2019)

Unconfined Compressive Strength of Compacted Tropical Soil

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53. Wang, Z., Zhang, N., Cai, G., Jin, Y., Ding, N., Shen, D.: Review of ground improvement using microbial induced carbonate precipitation (MICP). Mar. Georesour. Geotechnol. (2017). https://doi.org/10.1080/1064119X.2017.1297877 54. Wen, K., Li, Y., Amini, F., Li, L.: Impact of bacteria and urease concentration on precipitation kinetics and crystal morphology of calcium carbonate. Acta Geotech. 15(1), 17–27 (2019). https://doi.org/10.1007/s11440-019-00899-3

Properties of Tropical Black Clay Treated with Selected Admixtures K. J. Osinubi1 , A. O. Eberemu2(B) , P. Azige1 , and P. Yohanna3 1 Department of Civil Engineering, Ahmadu Bello University Zaria, Zaria, Nigeria 2 Department of Civil Engineering and Africa Centre of Excellence On New Pedagogies

in Engineering Education (ACENPEE), Ahmadu Bello University Zaria, Zaria, Nigeria [email protected] 3 Department of Civil Engineering, University of Jos, Jos, Nigeria

Abstract. The properties of tropical black clay (also known as black cotton soil, BCS) treated with cement kiln dust (CKD) and locust bean waste ash (LBWA) was studied. Tests performed include index and compaction using British Standard light (BSL); West African Standard (WAS) (or Intermediate) and British Standard heavy (BSH) energies. Statistical analysis was performed using two-way analysis of variance (ANOVA) incorporated in Microsoft excel software. Results obtained show that the specific gravity value of the natural BCS (2.4) reduced to a minimum value of 2.33 at 2% CKD/10% LBWA treatment. Peak liquid limit (LL) value of 55.6% was recorded at 3% CKD/6% LBWA treatment, minimum plastic limit (PL) value of 15.6% recorded for 3% CKD/6% LBWA treatment, while plasticity index (PI) value recorded a peak value of 40.0% at 3% CKD/6% LBWA treatment. The compaction characteristics, that is, maximum dry density (MDD and optimum moisture content (OMC) decreased and increased, respectively, with higher CKD/LBWA treatment. Generally, ANOVA results show that CKD and LBWA had significant effects on BCS. Although CKD/LBWA treatment improved the properties of BCS; however, the Nigerian General Specifications requirements of LL ≤ 35.0% and PI ≤ 12.0% for sub-base material in road construction were not met. It is recommended that BCS be minimally treated with 1% CKD/10% LBWA for use as subgrade material for the construction of low-volume roads. Keywords: Atterberg Limits · Black cotton soil · Compaction · Cement kiln dust · Locust bean waste ash · Specific gravity

1 Introduction Black cotton soil (BCS) is a high swelling soil. It fits into the smectite group which contains montmorillonite; an extremely expansive and troublesome clay mineral when come across during the course of construction processes (Osinubi et al. 2010). BCS are usually dominant in semi-arid provinces of hot and mild climate regions and places in which the yearly evaporation surpasses the rainfall. The major group encompasses sedimentary rock of volcanic source; these are predominant in North America, South Africa and Israel, whereas the plain igneous rocks are the subsequent group of parent © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 52–64, 2021. https://doi.org/10.1007/978-3-030-79638-9_5

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materials that originate from Nigeria, U.S.A. and also India (Plait 1953). In Nigeria, BCS are domiciled in the North-east region of the country and causes major failure in roads/structures constructed within the region. Replacement of the entire soil is not economical and time consuming thus, the need for soil improvement within such regions to attain the basic requirement for use in flexible pavement is necessary. The quantity of waste produced worldwide has increased due to industrialisation as well as population and economic growths (Oluremi et al. 2012; Rajesh et al. 2015). Most people in households and industries are worried merely about the disposal of wastes from direct locality, with no knowledge of the effect of these wastes on the environment (Reddy 2014). Hoyos et al. (2015) and Rajesh et al. (2015) explained the environmental impact of improper wastes disposal and numerous strategies for its improvement. Thus, it is necessary to come up with an appropriate disposal technique for agro - industrial wastes with respect to their beneficial reuse in soil improvement. Researchers reported that several of these wastes are agro-based (Pourakbar et al. 2015; Fasihnikoutalab et al. 2016), industry generated wastes (Jha and Sivapullaiah 2016) and bio-solids (Disfani et al. 2016). Research is on-going on the use of agricultural waste and industry generated waste such as LBWA, Sawdust ash (SDA), Plantain peel ash (PPA), Rice husk ash (RHA), Bagasse ash (BA), Cement kiln dust(CKD), etc., because their pozzolanic behaviour in treatment of deficient soils have recorded positive results (Phanikumar 2004; Moses 2008; Moses and Folagbade 2010; Eberemu 2011; Osinubi et al. 2015; Yohanna et al. 2016; Etim et al. 2017;Osim 2017). The increasing cost of conventional soil stabilization additives has been a problem and the improvement of BCS with LBWA/CKD blend having pozzalanic properties may be relatively cheaper. The enhanced engineering characteristics of BCS due to treatment with CKD and LBWA may be very suitable for bringing together environmental and sustainability benefits. This laboratory study focused on the evaluation of the impact of LBWA/CKD treatment on the plasticity and compaction properties of BCS. The objective was to determine changes in the modified soil using LBWA and CKD in stepped concentrations of 0, 2, 4, 6, 8 and 10% and 0, 1, 2, 3 and 4% content, respectively.

2 Materials and Methods 2.1 Materials 2.1.1 Black Cotton Soil BCS was sourced from Gombe State, Nigeria. Disturbed sample was collected at about 0.5 m depth. The sample was dried and pulverized prior to sieving through BS No. 4 sieve (4.76 mm aperture) before laboratory tests were conducted. 2.1.2 Locust Bean Waste Ash LBWA was obtained by the atmospheric combustion of locust bean husk collected from Duduguru in Nasarawa State, Nigeria. The husks were burnt in temperature in the range 500 – 650°C measured with a thermocouple and allowed to cool before being sealed in polythene bags to avoid carbonation. The ash was sieve through No 200 sieve (0.075 mm aperture) before laboratory tests were conducted.

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2.1.3 Cement Kiln Dust CKD is a product of dry kiln process. The material was collected from Benue Cement Company, Gboko, Benue State, Nigeria. The CKD was sieved through No 200 sieve (0.075 mm aperture) before laboratory tests were conducted. 2.2 Methods 2.2.1 Index Properties All tests on the natural BCS and BCS – LBWA/CKD mixtures were performed in agreement with BS 1377 (1990) and BS 1924 (1990), respectively. Soil samples were treated with 0, 2, 4, 6, 8 and 10% LBWA and 0, 1, 2, 3 and 4% CKD content by dry weight of soil, respectively. 2.2.2 Oxide Composition of Samples Oxide tests for BCS, LBWA and CKD were conducted at the National Research Institute for Chemical Technology (NARICT) using Energy Dispersive X-Ray Fluorescence (Nuclear Energy Test) techniques. 2.2.3 Specific Gravity Specific gravity (Gs ) test on the soil was carried out in accordance with the procedure outlined in BS 1377 (1990). The procedure was repeated to obtain three values from which the average specific gravity values of BCS and LBWA were determined. In the case of CKD, kerosene was used instead of water. 2.2.4 Atterberg Limits The tests include liquid limit (LL), plastic limit (PL), and plasticity indices (PI) of the natural and modified soil samples. Tests were performed based on Test 1(A) BS 1377 (1990) Part 2 and BS 1924 (1990) for untreated and modified soils, respectively. Soil samples were treated with LBWA and CKD as described in Sect. 2.2.1. The plasticity index of the natural and treated soils was determined as the difference in values between the LL and PL. 2.2.5 Compaction The compaction tests method used was carried out in accordance with the procedure described in BS 1377 (1990) for varying BCS – LBWA/CKD mix ratios using stepped concentrations of 0, 2, 4, 6, 8 and 10% LBWA as well as 0, 1, 2, 3 and 4% CKD by dry weight of soil. Three compactive efforts (i.e., BSL, WAS or Intermediate and BSH) were considered. WAS compaction is the effort obtained from a 4.5 kg rammer falling through 45 cm onto five layers in a BS (Proctor) mould, each receiving 10 blows.

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3 Results and Discussion 3.1 Properties of the Natural Black Cotton Soil Preliminary test on natural soil showed that 68.5% of the material passed sieve with 0.075 mm opening. The natural soil had a liquid limit 52.8%, plastic limit 19.16% and plasticity index 33.64%. The soil is classified as CH (ASTM 1992) or A-7–6(13) (AASHTO 1986). The properties of the natural soil are summarised in Table 1. Compositions of oxides for the soil and the additives are summarized in Table 2. The soil-grading curve is shown in Fig. 1 Table 1. Natural soil properties Property

Quantity

Natural moisture content, %

18.6

Percentage passing BS No 200 sieve 68.5 Specific gravity

2.4

Free swell, %

85

AASHTO classification

A-7–6 (13)

USCS

CH

Liquid limit, %

52.8

Plastic limit, %

19.16

Plasticity index, %

33.64

Maximum dry density, Mg/m3 British standard light

1.68

West African standard

1.76

British standard heavy

1.82

Optimum moisture content, % British standard light

17.2

West African standard

13.4

British standard heavy 13.4 Colour Greyish-black

3.2 Specific Gravity The variation of specific gravity of BCS – CKD mixtures with LBWA content is shown in Fig. 2. Specific gravity (Gs) of the soil decreased with increase in LBWA content except for the 6% LBWA content. Addition of CKD reduced the Gs value from 2.4 for the natural soil to the least value of 2.33 at 2% CKD/10% LBWA treatment. The combined effect of increased percentages of LBWA and CKD marginally increased the specific gravity

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Table 2. Composition of Oxides of black cotton soil (BCS), locust bean waste ash(LBWA) and cement kiln dust(CKD) Oxide

Compositions % BCS

LBWA CKD

CaO

3.58

1.78

59.84

SiO2

49.00

57.21

5.80

Al2 O3 15.1

11.75

2.4

Fe2 O3 14.23

5.01

3.776

MnO

0.23

0.58

0.15

Na2 O

–

0.013

–

K2 O

2.23

1.03

1.01

SO3

–

–

0.92

P2 O5

–

0.23

–

Ag2 O

2.17

–

2.82

TiO2

2.09

–

0.32

Cr2 O3 0.022

–

0.01

Eu2 O3 0.16

–

–

CO2

–

–

0.022

V2 O5

0.10

–

0.02

LOI

11.1

10.13

0.04

100

Percentage passing

90 80 70 60 50 40 30 20 0.001

0.01

0.1

Sieve size (mm)

1

Fig. 1. Particle size distribution curve of the natural black cotton soil

10

Properties of Tropical Black Clay Treated with Selected Admixtures

57

of BCS. The slight increase may be due to CKD’s higher Gs (2.6) and rearrangement of soil particles in more or less face-to-face structures due to cation exchange reactions in the mixtures. The high Gs recorded for 1% CKD with increase in LBWA may be due to initial densification accompanying pozzolanic reaction of LBWA in the mixture. The peak Gs value for BCS was obtained at 1% CKD/2% LBWA treatment.

Fig. 2. Variation of specific gravity of BCS – CKD mixtures with LBWA content

Statistical analysis of the test results using analysis of variance (ANOVA) showed that the effect of CKD on BCS was significant (FCAL = 15.06 > FCRIT = 2.87), while LBWA had an insignificant effect (FCAL = 0.37 < FCRIT = 2.71). The engineering implication of the statistics is that CKD greatly affected the Gs of the modified BCS which is linked to its density. This shows that Gs will greatly control the amount of CKD applied during field application since it influences the density of the compacted BCS in the field than the LBWA. 3.3 Atterberg Limits Liquid Limit: The variation of LL of BCS – CKD mixtures with LBWA content is shown in Fig. 3. The value of LL of the natural BCS increased from 52.8% to the peak value of 55.6% at 3% CKD/6% LBWA treatment and thereafter decreased with increase in LBWA content. The observed increase may be due to higher quantity of the additives that required more water for pozzolanic reaction in the mixture. On the other hand, the decrease in LL value may be linked to flocculation and agglomeration due to cation exchange reactions in which Ca2+ in the additives reacted with ions of lesser valence in the clay structure. Similar trend was reported by Osinubi et al. (2015) and Etim et al. (2017). The ANOVA results showed that CKD (FCAL = 15.57 > FCRIT = 2.87) and LBWA (FCAL = 14.47 > FCRIT = 2.71) had significant effects on the LL of BCS with the impact

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Liquid limit(%)

56.00 55.00 0% CKD

54.00

1% CKD

53.00

2% CKD

52.00

3% CKD 4% CKD

51.00 0

2

4

6

8

10

LBWA content(%) Fig. 3. Variation of liquid limit of BCS – CKD mixtures with LBWA content

of CKD being statistically greater. Also, it implies that CKD is more potent than LBWA in improvement the LL of BCS. Therefore, it is recommended that CKD content should be controlled during field application because of its potential to alter the compaction characteristics. Plastic Limit: The variation of plastic limit of BCS – CKD mixtures with LBWA content is shown in Fig. 4. The plastic limit (PL) values of the BCS – CKD mixtures initially decreased to minimum values at 6% LBWA content and thereafter increased. The least PL value of 15.6% was recorded for 3% CKD/6% LBWA treatment which corresponds to a 3.6% reduction of the 19.2% recorded for the natural BCS. The result could be attributed to cation exchange reaction within the mixture led to flocculation and aggregation of the soil particles (Osinubi 1995). The ANOVA results showed that PL of BCS was significantly affected by CKD (FCAL = 12.96 > FCRIT = 2.87) and LBWA (FCAL = 48.58 > FCRIT = 2.71) with the impact of LBWA being more statistically significant. Plasticity Index: The variation of plasticity index (PI) of BCS – CKD mixtures with LBWA content is shown in Fig. 5. Generally, peak PI values for BCS – CKD mixtures were recorded at 6% LBWA content and thereafter decreased up to 10% LBWA content. The highest PI value of 40% recorded for BCS - 3% CKD/6% LBWA treatment was not significantly higher than the 33.6% obtained for the natural soil because not much silt particles might have precipitated during flocculation and agglomeration process. ANOVA results showed that PI values of BCS were significantly impacted by CKD (FCAL = 25.39 > FCRIT = 2.87) and LBWA (FCAL = 49.99 > FCRIT = 2.71) with LBWA being more statistically significant.

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20

Plastic limit(%)

19 0% CKD

18

1% CKD 17

2% CKD 3% CKD

16

4% CKD

15 0

2

4

6

8

10

LBWA content(%) Fig. 4. Plot of plastic limit of soil – CKD mixtures with LBWA content

42

Plasticity index(%)

40 0% CKD

38

1% CKD 36

2% CKD

34

3% CKD 4% CKD

32 0

2

4

6

8

10

LBWA content(%) Fig. 5. Variation of plasticity index of BCS – CKD mixtures with LBWA content

3.4 Compaction Characteristics Maximum Dry Density The variation of maximum dry density (MDD) of BCS - CKD mixtures with LBWA content for BSL, WAS and BSH compaction are shown in Fig. 6ac. Both CKD and LBWA marginally impacted the MDD values which reduced with increase in CKD and LBWA content for the compactive efforts considered due to flocculation and accumulation of the soil particles. Similar findings were reported by Osinubi et al. (2015) and Etim et al. (2017).

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Maximum dry density(Mg/m3)

1.7 1.68 1.66

0% CKD BSL

1.64

1% CKD BSL 2% CKD BSL

1.62

3% CKD BSL 1.6

4% CKD BSL

1.58 0

2

4

6

8

10

A

LBWA content(%)

Maximum dry density(Mg/m3)

1.80 1.78 1.76

0% CKD WAS

1.74

1% CKD WAS

1.72

2% CKD WAS

1.70

3% CKD WAS 4% CKD WAS

1.68 1.66 0

2

4

6

LBWA content(%)

8

10

B

Maximum dry density(Mg/m3)

1.95 1.90 0% CKD BSH 1.85

1% CKD BSH 2% CKD BSH

1.80

3% CKD BSH 1.75

4% CKD BSH

1.70 0

2

4

6

LBWA content(%)

8

10

C

Fig. 6. Variation of MDD of BCS – CKD mixtures with LBWA content for different compactive effort (A) BSL (B) WAS (C) BSH

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Optimum moisture content(%)

22 21 20 0% CKD BSL

19

1% CKD BSL

18

2% CKD BSL

17

3% CKD BSL

16

4% CKD BSL

15 0

2

4

6

8

10

LBWA content(%)

A

Optimum moisture content(%)

18 17 16 0% CKD WAS

15

1% CKD WAS

14

2% CKD WAS

13

3% CKD WAS

12

4% CKD WAS

11 10 0

2

4

6

8

10

LBWA content(%)

B

Optimum moisture content(%)

17 16 15 0% CKD BSH 14

1% CKD BSH

13

2% CKD BSH

12

3% CKD BSH 4% CKD BSH

11 10 0

2

4

6

LBWA content(%)

8

10

C

Fig. 7. Plot of OMC of soil – CKD mixtures for (A) BSL Compaction (B) WAS Compaction (C) BSH Compaction with LBWA contents

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For BSL compaction, the ANOVA results showed that BCS was significantly impacted by CKD (FCAL = 14.33 > FCRIT = 2.87) and LBWA (FCAL = 58.74 > FCRIT = 2.71 for LBWA) with LBWA being more statistically significant. For WAS compaction BCS was significantly impacted by CKD (FCAL = 3.69 > FCRIT = 2.87) and LBWA (FCAL = 43.52 > FCRIT = 2.71) with LBWA also being more statistically significant. Finally, for BSH compaction, the ANOVA results showed that BCS was significantly impacted by CKD (FCAL = 12.82 > FCRIT = 2.87) and LBWA (FCAL = 11.18 > FCRIT = 2.71) with CKD being more statistically significant. A comparison of the statistical results for the three energies showed that only specimens compacted with BSH had trends similar to those established for Gs and LL with CKD being more statistically significant. It implies that, in order to achieve the desired MDD in the field, BCS has be compacted to 100% relative density of BSH energy for the optimally treated soil. Optimum Moisture Content The variation of optimum moisture content (OMC) of BCS – CKD mixtures with LBWA content for BSL, WAS and BSH is shown in Fig. 7a-c. The OMC values increased with higher CKD and LBWA content. Peak OMC values of 20.0% at 4% CKD/6%LBWA treatment(see Fig. 7a), 14.7% at 3% CKD/8%LBWA treatment(see Fig. 7b) and 16.0% at 1% CKD/8% LBWA treatment (see Fig. 7c) for BSL, WAS and BSH compaction, respectively. The increase in OMC with higher CKD and LBWA is not unconnected with the greater demand of water required to provide more OH− for cation exchange reaction and the increase in specific surface area resulting from the additives that may need extra water to lubricate the whole soil matrix. The results are in agreement with the findings reported by Osinubi (1999), Stephen (2005), Moses (2006), Akinmade (2008) and Osinubi et al. (2007, 2011).

4 Conclusion The plasticity and compaction properties of BCS treated with some selected admixtures (i.e. LBWA and CKD) was studied. The untreated soil was classified as CH or A-7– 6(13) according to the USCS and AASHTO classification, respectively. Based on the tests results obtained which showed that CKD and LBWA improved the properties of black cotton soil, the following deductions were made: 1. Specific gravity of the soil reduced from 2.4 to 2.34 with increase in LBWA content except for the 6% LBWA, while CKD reduced the specific gravity from 2.4 for the natural to least value of 2.33 at 2% CKD/10% LBWA treatment. 2. Peak value for liquid limit value of 55.6% was recorded for 3% CKD/6% LBWA treatment. Minimum plastic limit of 15.6% was recorded for 3% CKD/6% LBWA treatment, while peak plasticity index value of 40.0% was recorded at 3% CKD/6%LBWA treatment. 3. MDD generally decreased, while OMC increased with admixtures content. 4. Statistical evaluation of the test results using ANOVA showed that the admixtures generally had statistically significant effects on the treated black cotton soil.

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5. It is recommended that BCS be treated with 1% CKD/10% LBWA can be used as material for the construction of low-volume roads.

References AASHTO: Standard Specification for Transportation, Material and Methods of Sampling and Testing, 14th edn. Amsterdam Association of State Highway and Transportation Official, Washington, D.C. (1986) Akinmade, O.B.: Stabilization of Black Cotton Soil using locust bean waste ash. Unpublished M.Sc thesis, Civil Engineering Department, Ahmadu Bello University, Zaria (2008) ASTM Annual Book of Standards, vol. 04.08. American Society for Testing and Materials, Philadelphia, 1992 (1992) BS 1377: Method of Testing Soils for Civil Engineering Purpose. British Standard Institute, BSI, London (1990) BS 1924: Method of Tests for Stabilized Soils. British Standard Institute (BSI), London (1990) Disfani, M.M., Arulrajah, A., Maghoolpilehrood, F., Bo, M.W., Narsilio, G.A.: Geotechnical characteristics of stabilised aged biosolids. Environ. Geotech. 2(5), 269–279 (2016). https:// doi.org/10.1680/envgeo.13.00054 Eberemu, A.O.: Consolidation properties of compacted lateritic soil treated with Rice Husk Ash. Geomaterials 1, 70–78 (2011). https://doi.org/10.4236/gm.2011.13011 Etim, R.K., Eberemu, A.O., Osinubi, K.J.: Stabilization of Black cotton soil with lime iron ore tailings admixture. J. Transp. Geotech. 10, 85–95 (2017). Elsevier.https://doi.org/10.1016/j. trgeo.2017.01.002 Fasihnikoutalab, M.H., Asadi, A., Huat, B.K., et al.: Utilisation of carbonating olivine for sustainable soil stabilisation. Environ. Geotech. 4(3), 184–198 (2016). https://doi.org/10.1680/jenge. 15.00018 Hoyos, L.R., DeJong, J.T., McCartney, J.S., et al.: Environmental geotechnics in the US region: a brief overview. Environ. Geotech. 2(6), 319–325 (2015). https://doi.org/10.1680/envgeo.14. 00024 Jha, A.K., Sivapullaiah, P.V.: Role of gypsum on microstructure and strength of soil. Environ. Geotech. 3(2), 78–89 (2016). https://doi.org/10.1680/envgeo.13.00084 Moses, G.: Stabilization of Black Cotton Soil with ordinary Portland Cement using Bagasse Ash as Admixture. Unpublished M.Sc. Thesis, Department of Civil Engineering, Ahmadu Bello University, Zaria (2006) Moses, G.: Stabilization of black cotton soil with ordinary Portland cement using bagasse ash as admixture. IRJI J. Res. Eng. 5(3), 107–115 (2008) Moses, G., Folagbade, O.: Groundnut shell ash stabilization of black cotton soil. Electron. J. Geotech. Eng. 15, 415–442 (2010) Oluremi, J.R., Adedokun, S.I., Osuolale, O.M.: Stabilization of poor lateritic soils with coconut husk ash. Int. J. Eng. Res. Technol. (IJERT) 1(8), 1–9 (2012) Osim, A.R.: Compacted Cement Kiln Dust Treated Black Cotton Soil as Suitable Liner and Cover Material in Waste Containment Facilities. Unpublished Ph.D Thesis. Department of Civil Engineering, Ahmadu Bello University Zaria (2017) Osinubi, K.J.: Lime modification of black cotton soil. Spectr. J. 2(1 and 2) (1995) Osinubi, K.J.: Evaluation of admixture stabilization of Nigerian black cotton soil. Niger. Soc. Eng. Tech. Trans. 34(3), 88–96 (1999)

64

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Osinubi, K.J., Bafyau, V., Eberemu, A.O.: Bagasse ash stabilization of lateritic soil. In: Proceedings of the First International Conference on 114 Environmental Research, Technology and Policy “ERTEP 2007” under the Auspices of International Society of Environmental Geotechnology, Accra, Ghana, 16–19 July, Category E: State-of-the-Art Technologies for Environmental Performance and Protection, pp.1–17 (2007) Osinubi, K.J, Sani, E.J., Ijimdiya, T.S.: Lime and slag admixture improvement of tropical black clay road foundation. In: Transportation Research Board (TRB) 89th Annual Meeting CD-ROM, Washington, D.C., USA. Jan 10–14. Subject: Recycled Materials in Transportation Infrastructure, Session 243: AFP40 – Physico-chemical and Biological Processes in Soils Committee, Paper # 10–0585, pp. 1–18 (2010) Osinubi, K.J., Eberemu, A.O., Oyelakin, M.A.: Improvement of black cotton soil with ordinary Portland cement - locust bean waste ash blend EJGE. Bund. F. 16, 619–627 (2011) Osinubi, K.J., Yohanna, P., Eberemu, A.O.: Cement modification of tropical black clay using iron ore tailing as admixture. J. Transp. Geotech. 5, 35–492015Elsevier Publishing Company. https://doi.org/10.1016/j.trgeo.2015.10.001 Phanikumar, B.R., Sharma Radhey, S.: Effect of flyash on engineering properties of expansive soil. J. Geotech. Geoenviron. Eng. 130(7), 764–767 (2004) Plait, R.M.: Determination of swelling pressure of black cotton soil–a method. In: Proceedings of the Third International Conference on Soil Mechanics and Foundation Engineering. Zurich, Switzerland, 16th–27th Aug, vol. 1, pp. 170–172 (1953) Pourakbar, S., Asadi, A., Huat, B.K., Fasihnikoutalab, M.H.: Soil stabilisation with alkali-activated agro-waste. Environ. Geotech. 2(6), 359–370 (2015). https://doi.org/10.1680/envgeo.15.00009 Rajesh, S., Rao, B.H., Sreedeep, S., Arnepalli, D.N.: Environmental geotechnology: an Indian perspective. Environ. Geotech. 2(6), 336–348 (2015). https://doi.org/10.1680/envgeo.14.00047 Reddy, K.R.: Evolution of geoenvironmental engineering. Environ. Geotech. 1(3), 136–141 (2014). https://doi.org/10.1680/envgeo.13.00088 Stephen, A.T.: Stabilization Potential of Bagasse Ash on Black cotton Soil. Unpublished M.Sc. Thesis, Department of Civil Engineering, Ahmadu Bello University, Zaria (2005) Yohanna, P., Mannir, I., Osinubi, K.J.: Reliability assessment of black cotton soil stabilized with sawdust ash admixtures for use in road construction. Niger. J. Eng. 23(1), 44–57 (2016)

Geothermal Pavements: An Experimental and Numerical Study on Thermal Performance Xiaoying Gu1 , Nikolas Makasis1,2 , Yaser Motamedi1 , Arul Arulrajah3 , Suksun Horpibulsuk4 , and Guillermo A. Narsilio1(B) 1 Department of Infrastructure Engineering, The University of Melbourne, Parkville, Australia

[email protected]

2 Engineering Department, University of Cambridge, Cambridge, UK 3 Department of Civil and Construction Engineering, Swinburne University of Technology,

Melbourne, Australia 4 School of Civil Engineering, and Center of Excellence in Innovation for Sustainable

Infrastructure Development, Suranaree University of Technology, Nakhon Ratchasima, Thailand

Abstract. One of the greatest challenges society faces today is the provision of clean and renewable energy to both meet the over-growing energy demand and reduce our carbon footprint. Ground source heat pump (GSHP) systems can efficiently heat and cool buildings using shallow geothermal energy and can therefore contribute towards the above goals. Significant attention has been given to energy geo-structures in the last few years, that is, using subsurface structures to exchange heat with the ground. Thus, these geo-structures provide structural support and thermal energy. The majority of literature relating to energy geo-structures focuses on piles, but only limited research exists on geothermal pavements. This work developed a detailed 3D finite element (FE) model to explore the thermal performance of geothermal pavement systems. This 3D FE model has been successfully validated against a full-scale experimental test undertaken in Adelaide, South Australia. The validated model is then used to evaluate the long-term performance of geothermal pavement systems under both a traditional system configuration and as a hybrid system configuration. The performance of the geothermal pavement system is analysed under three thermal loading cases including balanced, heating dominated and, cooling dominated cases, showing the potential and identifying possible limitations for geothermal pavements.

1 Introduction Meeting worldwide increasing energy demand and reducing carbon footprint has become a key challenge of the 21st century. Moving towards clean and renewable energy resources is a top priority. Heating and cooling accounts for nearly 50% of the global energy consumption and fossil fuels are the main resources for supplying heating and cooling for buildings and industries (REN21 2019). Ground source heat pump (GSHP) systems are considered one of the most efficient and environmentally benign solutions to be used in space heating and cooling (Kim et al. 2016; Johnston et al. 2011; Li et al. 2019). The typical coefficient of performance (COP) value of a GSHP system is around © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 65–82, 2021. https://doi.org/10.1007/978-3-030-79638-9_6

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four to five, which indicates that every 1 kW electricity input can produce 4 to 5 kW heating/cooling energy (Narsilio et al. 2014). A typical GSHP system consists of three parts: the ground heat exchanger, the heat pump unit and the heat distribution system (Jeon et al. 2018). The ground heat exchanger (GHE) is formed by a series of embedded pipes or loops (usually high-density polyethylene, HDPE pipe) that circulate a carrier fluid, typically water or antifreeze solution. In heating mode, GHEs extract heat from the ground via a heat pump, which then upgrades the thermal energy and delivers it through the building distribution system. The reverse process occurs in the summer where heat is returned to the ground through the GHEs. Traditionally, the GHEs can be installed in either vertical boreholes (Hepbasli et al. 2003) or horizontal trenches (˙Inallı and Esen 2004). Restrictions to the wider utilisation of GSHP systems include the typically high capital costs mainly due to the costly installation of the GHEs such as the cost of drilling boreholes for vertical GSHP systems (Qi et al. 2019), or the need for a large installation area for horizontal GSHP systems. Detailed studies on GSHP systems can be found in (Sarbu and Sebarchievici 2014; Florides and Kalogirou 2007; Lund and Boyd 2016). Recent advances on energy geo-structures have been increasingly gaining attention due to their strong potential for cost savings of GSHP systems as well as the adoption of GHEs into urban environments to solve the land availability issue (Bidarmaghz and Narsilio 2018; Brandl 2006; Xia et al. 2012). Energy geo-structures incorporate HDPE piping to underground structures primarily designed for stability, to also exchange heat. Hence, these underground structures such as foundation piles, retaining walls and tunnel linings can serve as GHEs with little additional cost, and achieve a dual purpose of structural stability and thermal provision (Lu and Narsilio 2019; Abdelaziz et al. 2011; Brandl 2006; Adam and Markiewicz 2009). Compared to traditional GSHP systems, the installation of GHEs highly depends on the site layout and geometry of the underground structures which constrains the flexibility of designing the GHEs. Moreover, the heat transfer between GHEs can cause additional stress on structural stability and needs to carefully considered in the design (Batini et al. 2015; Katzenbach et al. 2014). These limitations can raise complexity in designing geothermal systems that can provide the entirety of the desired thermal loads. Therefore, for some geothermal systems, it is more beneficial or necessary to be used in combination with an auxiliary energy system to fulfil the thermal demand, thus forming a hybrid system. Most of the available research investigates the thermal performance of the energy geo-structure and how to enhance their thermal load providing capabilities, as well as exploring the impact of GHE heat transfer on the structural stabilities (Makasis et al. 2018; Makasis and Narsilio 2020; Bourne-Webb et al. 2016). In this research study, the focus is placed on the energy provision, while the structural stability is expected to be further investigated in future works. GHEs play a key role in the heat exchange mechanisms of a GSHP system, therefore, it is significant to accurately model the GHE behaviour. In the past decades, both analytical and numerical studies have been carried to provide an understanding of GHE behaviour. There are three widely accepted analytical methods for modelling (vertical) GHEs: the infinite line source (ILS) model (Carlslaw and Jaeger 1959), the infinite cylindrical source (ICS) model (Ingersoll 1950) and the finite line source (FIS) model (Eskilson 1987). A detailed review of these can be found in (Philippe et al. 2009). Numerical modelling has been introduced to gain further

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understanding of the heat transfer process and performance stemming from different design configurations. There were some simplified 2D numerical models for studying the performance of GHEs (Tarnawski et al. 2009; Kayaci et al. 2015), however, most of the studies focused on developing 3D numerical models to fully capture the 3D heat exchange process between the ground and the carrier fluid (Ozudogru et al. 2014; Kayaci and Demir 2018; Makasis et al. 2018; Han et al. 2017; Selamat et al. 2016). For instance, Han et al. (2017) created a 3D finite element (FE) model to assess the thermal performance of various horizontal GSHP system configurations, as well as exploring the importance of using local geological data (measured ground temperatures and properties) as design inputs for improving modelling accuracy. Apart from numerical models for traditional GSHP systems, there also exist numerical modelling works for energy geo-structures (Sterpi et al. 2018; Di Donna and Laloui 2015; Makasis and Narsilio 2020; Makasis et al. 2020; Muñoz-Criollo et al. 2016). Bidarmaghz and Narsilio (2018) built a 3D model to analyse the performance of energy tunnel by considering the interactions between the tunnel GHEs, the ground, and the air. As opposed to analytical solutions, numerical modelling is more flexible and has fewer constraints, however it may also involve significant computational expense. Geothermal pavement systems are a GSHP system application that, unlike other energy geo-structures, has not received much attention. The majority of the existing research focuses on using these pavements for road maintenance purposes, such as deicing and cooling road surface (Eugster 2007; Gao et al. 2010; Muñoz-Criollo et al. 2016). Eugster (2007) summarised a number of pilot-scale experiments of road/bridge geothermal snow melting and/or de-icing systems and concluded geothermal road systems for surface heating is feasible, renewable and with lower maintenance requirements. Gao et al. (2010) also performed a small-scale experimental study of slab solar collection on the hydronic system of road. Their results showed that an ice-snowing melting system in the road with seasonal thermal energy storage is sustainable and functional, and the solar collector could obtain around 30% solar heat in summer, therefore, could lower the pavement surface temperature as well. Muñoz-Criollo et al. (2016) further developed a numerical model to deepen understanding on the inter-seasonal ground energy collection and storage pavement system and concluded that the significance of meteorological conditions and boundary conditions on the system performance. There is now substantial research related to shallow geothermal energy systems and their performance has been studied extensively with the help of numerical modelling. However, there is limited research related to the design of geothermal pavement system for the thermal control of buildings. Geothermal pavements incorporate horizontal GHEs at a relatively shallow depth (Traditional horizontal GSHP systems generally placed GHEs deeper, 1–3 m depth), to take advantage of existing excavations for the road construction and thus substantially reduce capital costs for the GHE installation. The ground is used as a heat source/sink and a GSHP unit can provide heating and cooling to nearby buildings. To bridge this gap, this study creates an experimentally validated 3D FE model of a geothermal pavement. Showing the potentials of this pavement systems, the long-term performance of both standalone and hybrid geothermal pavements is analysed under three thermal loading cases: balanced, heating, and cooling dominated cases.

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2 Methodology This research develops a validated numerical model for a geothermal pavement system with the main aim of using this model to investigate the system thermal performance. Detailed 3D finite element numerical modelling approaches are utilised, incorporating the governing equations to simulate the thermal performance of the system under annual thermal loads of a typical residential dwelling in Adelaide, SA considering three different scenarios: a heating dominant case (most typically encountered given climate and building envelopes of Adelaide), a balanced load case and a cooling dominant load case. These studies are undertaken to explore the thermal potential of geothermal pavements under different load scenarios. Furthermore, the thermal performance of the system under aforementioned thermal load cases is assessed by introducing a hybrid system approach, which incorporates the geothermal pavement system with an auxiliary heating/cooling system such as a reverse cycle air conditioner (RCAC) or an air conditioner (AC) to provide the required thermal loads. 2.1 Finite Element Model The modelling of the geothermal pavement system is implemented in the finite element (FE) package, COMSOL Multiphysics, focusing on the GHEs embedded in the pavement. This 3D numerical FE model has been developed within The University of Melbourne, and validated herein with both data from literature and experimental data from a full-scale field study in Adelaide, SA (Motamedi-Ghahfarokhi et al. 2021a and 2021b). The governing equations for fluid flow and heat transfer are numerically coupled to capture the heat transfer between the carrier fluid in the pipes and surrounding ground. The momentum and continuity Eqs. (1) and (2) are used for modelling the incompressible fluid flow inside the HDPE pipes. Both heat conduction and convection are considered for modelling the heat transfer between carrier fluid and the ground. Conductive heat transfer mainly occurs in the solid materials, including ground, GHE pavement structure backfills and the HDPE pipe walls, while convective heat transfer dominates in the carrier fluid within the HDPE pipes. In the absence of groundwater flow, the conductive heat transfer equation of the soil, HDPE pipe walls and GHEs was modelled by Eq. (3). In addition, the conductive-convection energy equations for heat transfer in the fluid flow are listed in Eq. (4) and (5) (Lurie 2008). ∇.Aρw v = 0  ρw

∂v ∂t



ρm Cp,m ρw ACp,w

= − ∇p − fD

(1) ρw |v |v 2dh

∂Tm = ∇ · (λm ∇Tm ) ∂t

∂T ρw A  2 |v v + Qwall + ρw ACp,w v∇T = ∇(Aλw ∇T) + fD ∂t 2dh   Qwall = f Tm, pipe wall , T

(2) (3) (4) (5)

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69

where A is the inner cross-section of the HDPE pipe [m2 ], ρw is the carrier fluid density [kg/m3 ], v is the fluid velocity field [m/s] within the pipes, t is time [s], p is pressure [Pa ], fD represents the Darcy friction factor [−], dh is the hydraulic diameter of the pipe [m], ρm is the solid material density [kg/m3 ], Cp,m is the specific heat capacity of a solid material [J /kgK], Tm stands for the temperature of a solid material, λm is the thermal conductivity of a solid material [W /mK], Cp,w is the specific heat capacity of the fluid [J /kgK], λw is the thermal conductivity of the fluid [W /mK], Qwall is the external heat exchange rate through the pipe wall [W /m], and a function of the temperature of the pipe outer wall, Tm, pipe wall [K] and the temperature of the carrier fluid T[K]. 2.2 Model Geometries and Model Parameters This research aims to investigate the long-term thermal performance of geothermal pavement systems based on a validated numerical model. The finite element model, geometry and configuration can be seen in Fig. 1 and the relevant material properties are summarised in Table 1. The geothermal pavement system consists of a 0.05 m surface layer (asphalt), 0.30 m thickness of base layer with a mix of gravel (0.25 m) and fine sand (0.2 m) and the remaining layer is a highly plastic clay which is the subgrade layer of the pavement. A single GHE circuit consisting of 8 legs of HDPE pipes, and having an outer diameter of 25 mm (SDR11) is placed at a depth of 0.5 m below the surface and connected in series meandering in an area of approximately 4 m × 20 m. The total length of the HDPE pipes is 160.4 m with a spacing of 600 mm between the centre of the pipes. Moreover, the constant fluid flow rate through the inlet of the circuit is 12 L/min. Since this model is based on the conditions of a site in Adelaide, and given the shallow depth, groundwater flow is not considered in this research. Table 1. Material properties Materials

Description

Density (kg/m3 )

Specific heat capacity [J/(kg·K)]

Thermal conductivity [W/(m·K)]

Thickness (m)

Asphalt

Road surface

2400

Gravel

Base

2200

850

1.3

0.05

944

1.4

0.25

Fine sand

Base

2240

1185

1.8

0.20

Clay

Subgrade

2100

840

1.9

10

Water

Carrier fluid

998

4158.5

0.58

-

2.3 Model Assumptions, Initial and Boundary Conditions Appropriate assumptions, initial and boundary conditions are crucial to obtaining meaningful results. The geothermal pavement system including boundary conditions is shown in Fig. 1(a) and is summarised below:

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Fig. 1. Model geometry: a) meshed 3D FE numerical model; b) top view of the model; c) section view of the model (not to scale)

• The fluid flow within the pipes is assumed to be fully developed, therefore, the fluid flow and heat transfer occurring in the fluid are analysed as a 1D problem. • The initial temperature of both ground and the farfield boundaries are equal to the measured undisturbed ground temperature for different depths Tfarfield (z), which can be seen in Table 2. • Thermal insulations which renders a zero net-flux is prescribed to the farfield side boundaries of the numerical model. The distance between the edge of GHEs and the outer boundary is determined as 10 m, to ensure there is sufficient distance to avoid any boundary influences (similar results are achieved while assuming fixed temperatures over the simulation period at the boundaries). The temperature of the model bottom is set as a prescribed temperature on the boundary. • Since the effect of seasonal ground temperature variation generally reaches depths of 5–10 m, and deeper ground temperature remains relatively constant, then, the surface boundary of the model is prescribed as a time-dependent ambient temperature Tair (t). The ambient air temperature data are the recorded air temperature in Adelaide, SA.

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• The time-dependent inlet fluid temperature Tin (t) is determined through a function of carrier fluid temperature at the outlet point of GHE Tout (t) and the input annual thermal loads of a typical residential house in Adelaide, SA.

Table 2. Measured farfield initial ground temperatures Depth (m)

Farfield temperature (°C)

0.0

16.1

0.3

16.5

0.5

16.8

1.0

17.3

1.5 and below 17.5

2.4 Thermal Performance Evaluation General GSHP systems can be defined as efficient and functional if the operating fluid temperature in the pipes is within a reasonable temperature range (typically between −5 and 40 °C) for the life of the project (typically 20–25 years) (Makasis et al. 2018). These temperatures are based on a number of parameters importantly, the thermal load distribution, which defines the thermal energy the GSHP system needs to extract from/reject to the ground, the system geometry and the site conditions amongst others. Since the GHEs of the geothermal pavement system are located at a shallower depth than traditional horizontal GSHP systems, these temperatures (and thus the overall system performance)

Fig. 2. Daily thermal load of a typical residential building and weather data for Adelaide, South Australia (heating dominant) and additional balanced and cooling dominant variants studied herein.

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can also be more sensitive to the ambient ground temperature. In this study, annual thermal loads of a typical residential house in Adelaide, SA, as shown in Fig. 2, are used with the FEM numerical model to determine the carrier fluid temperatures. The base Adelaide load case, which is typically heating dominant, is further adjusted to provide two additional load scenarios: a balanced load case and a cooling dominant load case by diminishing the original heating loads to gain further understanding of the system performance. In this study, the average fluid temperature Tfluid (average from Tin and Tout ) is used to quantify the circulated fluid temperature within the pipe.

3 Results and Discussion This section introduces the results of the model validation and presents analysis results of evaluating the thermal performance of the geothermal pavement system. The model validation is discussed in Sect. 3.1, and then the thermal performance of different model configurations under various thermal load cases, including a standalone geothermal pavement system design and a hybrid system, are presented in Sect. 3.2. To determine the functionality and efficiency of geothermal pavement systems, the coefficient of performance (COP) for each system is calculated and discussed in Sect. 3.3. 3.1 Model Validation with Field Observations in Adelaide A geothermal pavement system field study was conducted in 2019 at a carpark in Adelaide, SA. To explore the thermal benefits of geothermal pavement systems, this field study carried out a Thermal Response Test (TRT) for 1.5 days with a constant heat power of 4.5 kW and a flow rate of 16.8 L/min. The geometry and instrumentation of the field setup is illustrated in Fig. 3 and are further discussed in Sect. 2.2 with the material details. In addition to the measured inlet and outlet temperatures from the TRT unit, thermistors were installed along the length of the pipes to the soil to help gain understanding on the heat transfer. Further details have been reported in (Gu et al. 2021; Motamedi-Ghahfarokhi et al. 2021a and 2021b). Figure 4 displays the comparison between modelled and measured outlet fluid temperature, which shows an excellent agreement. The (arguably insignificant) inconsistencies in the results could be attributed to the fact that the sensors used to record the inlet and outlet fluid temperatures were attached to the outside of the pipes rather in direct contact with the water. These attached sensors could be more susceptible to the ambient air temperatures. For example, fluctuations in the measured Tout that can be seen around the 15th hour of the test occurred in the middle of the day when the air temperature was higher compared to the rest of the day. The effects of these are seen on the upper right part of Fig. 4(b). Moreover, inconsistencies observed at the initial stage of the test could also be because of modelling initialisation errors. Soil temperatures at thermistor locations sensor 1, 2 and 4 (Fig. 3) are computed for a more complete validation, results for which can be seen in Fig. 5. The modelled temperatures at both T1 and T2 have very well captured the measured results. The sensor at location T4, however shows a lesser agreement. Even though the largest variation between measured and modelled at location T4 is less than 1 °C, the overall trend of the

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Fig. 3. Instrumentation of the field-scale geothermal pavement system: a) Plan view, b) cross section view

Fig. 4. Comparison between simulated numerical results and experimental data

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modelled soil temperature for the T4 sensor is consistently lower than the measured data with lower fluctuations. Since the GHE of geothermal pavement system is located at a shallow depth of 0.5 m, the soil temperatures can be strongly influenced by the surface temperature, and unlike locations T1 and T2 the effect of the GHE operation is less dominant at this depth. In summary, the 3D numerical model is capable of simulating the performance of the geothermal pavement system while also showing a very acceptable agreement with measured data.

Fig. 5. Comparison between numerical results and thermistor readings for different locations

3.2 Investigation on the Thermal Performance of the Geothermal Pavement Systems In this section, the validated numerical model is employed to evaluate the long-term thermal performance of the geothermal pavement system. To ensure there are no thermal accumulation effects on the ground due to imbalanced thermal loads like a traditional vertical GSHP system does (Li et al. 2018; Bidarmaghz et al. 2016), a five-year thermal load case (yearly repetition of the loads in Fig. 2) is simulated. Based on the results shown in Fig. 6, it is evident that there are no accumulation thermal effects on the horizontal GHE performance, since the Tfluid shows a yearly cyclic performance. Thus, an annual (one year) thermal demand of a typical residential dwelling in Adelaide, SA is used in this research to represent the performance throughout the system’s design life. Two geothermal system configurations are analysed: a standalone geothermal pavement system, details are discussed in Sect. 3.2.1; and a hybrid system (using the geothermal pavement to provide the base thermal loads (6 kW) and an RCAC system to support shortfalls). Results are analysed in Sect. 3.2.2.

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Fig. 6. Average fluid temperature ((Tin + Tout )/2) distribution for five-year geothermal pavement GHE operation

3.2.1 Thermal Performance of the Pavement System The thermal load defines the thermal energy that the pavement systems will be storing to/drawing from the ground to provide comfort space temperatures to the building. To investigate the potential of the geothermal pavement system, three thermal load cases are utilised in this study, which has been shown in Fig. 2 (and included indicated in Fig. 7). Amongst these load cases, the cooling demand remains constant and only the heating demands are varied for each thermal load case, this represents an extreme case where inhabitants of the building have different temperature set points and comfort levels during the heating season (winter). As discussed in Sect. 2.4, the design of geothermal pavement systems is considered acceptable only if the average fluid temperatures T fluid over the simulation are within a reasonable operating range. Based on the provided thermal load profiles, it was found that four identical GHE circuits can meet the thermal loads. The heating dominant case resulted in the most extreme fluid temperatures, showing the highest T fluid value of 39.8 °C and lowest of 0 °C while maintaining a suitable T of about 1.5 °C between inlet and outlet of the ground heat exchangers (and GHSP) for optimal system operation. As for the balanced load case, the highest T fluid changes little to 39.1 °C since the cooling demand remained unchanged. However, the lowest T fluid of the balanced load case has increased to 3.5 °C which is due to the reduction in heating demand. Compared with the heating dominant case, the required heat load is only two-third of this demand. As the heating demand is decreased further (one-third of the heating demand of the heating dominant case) to now render a cooling dominant load case, the resulting ground loop temperatures results in the least extreme values, 37.4 °C and 3.1 °C respectively. In addition to the cooling dominant case having the lowest annual thermal demand, this specific case study shows farfield ground temperatures around 16.8 °C, which leads the ground conditions to be more favourable for cooling purposes. If the farfield ground temperatures were much higher, the preferable dominant load case might be heating dominant instead of cooling dominant.

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Fig. 7. Average fluid temperature resulting from a GSHP system with three thermal load profiles: heating dominant load; balanced load, and cooling dominant load.

3.2.2 Thermal Performance of the Hybrid Geothermal Pavement System In the common scenario of a large residential development with multiple dwellings and a finite pavement area available, it may not be possible to assign four GHE circuits per dwelling. In this case, a hybrid system may be considered and result in a more economical solution and better operation of the system. Here one must find the maximum amount of thermal energy that the geothermal pavement can provide (per dwelling). To this aim, an iterative process varying the peak heating and cooling capacity of a GSHP such that the resulting average fluid temperature is found to be within operational ranges is undertaken. As a result of this multiple successive forward simulations, the hybrid system considered in this study uses the geothermal pavement system to supply a “baseload” of thermal demands that are lower than 6 kW (for both heating and cooling), while the exceeding thermal loads are supplied by an auxiliary system. The resulting Tfluid values for the geothermal pavement system comprising of a hybrid design under three load cases are displayed in Fig. 8. Compared to the four GHE circuit design as discussed in Sect. 3.2.1, the hybrid system requires only two GHE circuits, which would significantly reduce the capital costs of geothermal pavements. The heating dominant case, which is shown in Fig. 8(a), is the only scenario that sees Tfluid going below 0 °C, thus, an anti-freeze solution (instead of just plain water) may be required, in this case, 15% of Propylene Glycol is recommended by IGSHPA guidelines (IGSHPA 2009). Given the “peaky” thermal load pattern found in Adelaide, despite the modest baseload (33 to 40%), the hybrid system (an RCAC system) can provide 78% of the annual thermal load using the geothermal pavement system, requiring the use of the auxiliary system for 137 days per year. In both balanced and cooling dominant load cases, the geothermal pavement system alone can provide the entire heating load therefore, only an auxiliary cooling air conditioning system (AC) is more suitable to provide the peak cooling load instead of using an RCAC system. It is noticed that the cooling dominant case has the lowest Tfluid among all the three cases, this is because the geothermal pavement system is not being used to its full

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capacity. The proposed hybrid system is capable of providing 85% and 80% of the total annual load in balanced load case and cooling dominant load case respectively, while the auxiliary cooling system is only used to provide 30% of the cooling demand in both the above cases. One should note here that the GSHP component of the hybrid system is actually satisfying the thermal load shown in grey in Fig. 8, while the overall building loads are heating dominant, balanced and cooling dominant, the GSHP is now satisfying

Fig. 8. Average fluid temperature of the hybrid geothermal pavement system. A baseload (in grey colour) is satisfied by the GSHP system, while the balance load, by smaller auxiliary systems: a) heating dominant load case; b) balanced load case; c) cooling dominant load case

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slightly heating dominant cases (for the overall heating dominant and balanced load cases) but still a cooling dominant load (for the overall cooling dominant case). 3.3 System Performance Comparison with Coefficient of Performance While evaluating the feasibility and effectiveness of a geothermal system, apart from assessing whether the carrier fluid temperatures remains a reasonable range, ensuring the system operates within an optimal range of COP (coefficient of performance) is also important. The daily COP values of the geothermal pavement systems were computed based on the water temperatures entering into the GSHP along with the technical specifications provided by Climate Master™ (Climate Master™ TC Series 50 Hz TCH/V072 – HFC410A). In addition, it should be noted that while calculating the COP of the geothermal pavements within the hybrid system, a smaller heat pump is used (Climate Master™ TC Series 50 Hz TCH/V030 – HFC410A), and the COP values of RCAC and AC are obtained from literature. The COP of RCAC for heating and cooling purposes are 3.0 and 2.5 (Qi et al. 2019) and COP for the AC system for cooling is 3.4 (Hu and Huang 2005). The calculated COP for both standalone geothermal pavement system and hybrid systems under different load cases are listed in Table 3. The average annual COP are presented in Fig. 9. Table 3. Calculated COP of different heating/cooling systems with various loading cases Dominant load case

System

COP (heating)*

COP (Cooling)*

Heating

Geothermal pavements

4.06

4.25

Hybrid system (pavement and RCAC)

3.84†

4.84†

Geothermal pavements

4.17

4.26

Hybrid system (pavement and AC)

4.09†

4.97†

Geothermal pavements

4.26

4.25

Hybrid system (pavement and AC)

4.18†

4.95†

Balance

Cooling

* Averaged heating/cooling coefficient of performance. † Weighted average between COP of the auxiliary system and geothermal pavement system.

Compare the hybrid systems with standalone geothermal pavements, amongst all three load cases, the annual COP of hybrid system is always higher than using standalone geothermal pavement system. Heating dominant case has the lowest COP because it has the highest thermal loads which results in more extreme fluid temperatures that degrades the system performance. Because the RCAC has a heating COP value of 3.0, that leads the lowest heating COP observed in the hybrid system under the heating dominant case. Similarly, since the cooling COP of AC is higher than RCAC, the cooling efficiency of hybrid system with both balanced and cooling dominant are slightly greater

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than the heating dominant case. Additionally, as shown in Fig. 9, it is noticed that as the thermal load is reduced going from heating dominant case to balanced case and further from balanced case to cooling dominant case, the average annual COP for hybrid system increases. As discussed above, the cooling dominant load case was generated by decreasing the building the heating load causing the ratio of cooling to heating load to increase in the resulting total load. Since the mechanical specifications of selected heat pump indicates a better system performance in cooling mode, the system is expected to render higher overall COP values as the cooling load increases in proportion. It bears mentioning that the enhancement in COP in case of cooling dominant case is not as pronounced as in the balanced load case. Based on this, it can be inferred that a balanced system may have a better performance than the cooling dominant case as the geothermal system for the balanced case studied here provides more thermal energy.

Fig. 9. Averaged annual COP for different loading cases under both a traditional geothermal system configuration as well as for a hybrid geothermal system

4 Summary and Conclusions Energy geo-structures are gaining more attention for providing space heating and cooling along with also contributing towards the continuous efforts regarding mitigating climate change. Geothermal pavements as a novel technology in energy geo-structures has been largely overlooked in the literature. This research developed a 3D FE numerical model that has been successfully validated with experimental data, and this numerical model is further utilised to evaluate the geothermal pavement long-term performance under various load cases. Annual thermal demand of a typical residential house in Adelaide, SA is utilised to investigate the long-term performance of the system. This study focuses on the performance of the following two system design configurations: one is using a standalone geothermal pavement system to satisfy the overall thermal demand, and the second consists of a geothermal system to satisfy a baseload and an auxiliary RCAC system to supply the balance of the thermal demand. The performance of these two system configurations under three load cases are evaluated for: a) a heating dominant

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case (the typical Adelaide thermal load case); b) balanced load case; and c) a cooling dominant load case. Key findings are summarised as below: • A developed FE modelling methodology has been presented and validated against a field TRT test undertaken in Adelaide, South Australia. • Under design thermal loads cases, four GHE circuits (having total HDPE pipe length of 640 m) of the geothermal pavement system can fulfil the thermal demands. • Adopting a hybrid system can reduce the required GHE circuits from four to two, thus can reduce the capital costs related to material and installation of the system. In addition, using an auxiliary system also results in higher COP compared with standalone GHE system. • Geothermal pavements have a great potential for satisfying thermal loads under various tested load cases: heating dominant, balanced, and cooling dominant cases. The annual COP values for both standalone geothermal pavements and the hybrid systems are found to be greater than 4.0. Overall, this paper carries out a comprehensive study of exploring the thermal performance of geothermal pavement systems, and results indicate that it is worthwhile to investigate these systems in detail. Further study could explore the cost implications, and optimisation of this system by considering geometrical arrangements and material parameters. Acknowledgements. Funding from the Australian Research Council (ARC) (project number LP170100072) and the University of Melbourne is much appreciated. Moreover, the fifth and sixth authors would also like to acknowledge the support from the National Science and Technology Development Agency (NSTDA), Thailand, under Chair Professor program (P-19-52303). Assistance from the City of Mitcham (SA), Dr Mahdi Disfani and Mr Ramin Raeesi in the fieldwork is much appreciated.

References Abdelaziz, S.L., Olgun, C.G., Martin, J.R., II.: Design and operational considerations of geothermal energy piles. Am. Soc. Civ. Eng. (ASCE) 211, 450–459 (2011) Adam, D., Markiewicz, R.: Energy from earth-coupled structures, foundations, tunnels and sewers. Géotechnique 59, 229–236 (2009) Batini, N., Rotta Loria, A.F., Conti, P., Testi, D., Grassi, W., Laloui, L.: Energy and geotechnical behaviour of energy piles for different design solutions. Appl. Therm. Eng. 86, 199–213 (2015) Bidarmaghz, A., Narsilio, G.A.: Heat exchange mechanisms in energy tunnel systems. Geomech. Energy Environ. 16, 83–95 (2018) Bidarmaghz, A., Narsilio, G.A., Johnston, I.W., Colls, S.: The importance of surface air temperature fluctuations on long-term performance of vertical ground heat exchangers. Geomech. Energy Environ. 6, 35–44 (2016) Bourne-Webb, P., Burlon, S., Javed, S., Kürten, S., Loveridge, F.: Analysis and design methods for energy geostructures. Renew. Sustain. Energy Rev. 65, 402–419 (2016) Brandl, H.: Energy foundations and other thermo-active ground structures. Géotechnique 56, 81–122 (2006)

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Carlslaw, K., Jaeger, J.: Conduction of Heat in Solids. CLarendon Press, Oxford (1959) Di Donna, A., Laloui, L.: Numerical analysis of the geotechnical behaviour of energy piles. Int. J. Numer. Anal. Meth. Geomech. 39, 861–888 (2015) Eskilson, P.: Thermal analysis of heat extraction boreholes. Department of Mathematical Physics, Lund Institute of Technology (Sweden) (1987) Eugster, W.J.: Road and bridge heating using geothermal energy. overview and examples. In: Proceedings European Geothermal Congress (2007) Florides, G., Kalogirou, S.: Ground heat exchangers—a review of systems, models and applications. Renew. Energy 32, 2461–2478 (2007) Gao, Q., Huang, Y., Li, M., Liu, Y., Yan, Y.Y.: Experimental study of slab solar collection on the hydronic system of road. Sol. Energy 84, 2096–2102 (2010) Gu, X., Makasis, N., Motamedi, Y., Narsilio, G.A., Arulrajah, A., Horpibulsuk, S.: Geothermal pavements: field observations, numerical modelling and long-term performance. Géotechnique (2021) Han, C., Ellett, K.M., Naylor, S., Yu, X.: Influence of local geological data on the performance of horizontal ground-coupled heat pump system integrated with building thermal loads. Renew. Energy 113, 1046–1055 (2017) Hepbasli, A., Akdemir, O., Hancioglu, E.: Experimental study of a closed loop vertical ground source heat pump system. Energy Convers. Manage. 44, 527–548 (2003) Hu, S.S., Huang, B.J.: Study of a high efficiency residential split water-cooled air conditioner. Appl. Therm. Eng. 25, 1599–1613 (2005) IGSHPA: Ground Source Heating Pump Residential and Light Commerical Design and Installation Guide. Oklahoma State University (2009) ˙Inallı, M., Esen, H.: Experimental thermal performance evaluation of a horizontal ground-source heat pump system. Appl. Therm. Eng. 24, 2219–2232 (2004) Ingersoll, L.R.: Theory of Earth Heat Exchangers for the Heat Pump, Heat Conduction. American Society of Heating and Ventilating Engineers, Journal section, Heating, Piping, and Air Conditioning (1950) Jeon, J.-S., Lee, S.-R., Kim, M.-J.: A modified mathematical model for spiral coil-type horizontal ground heat exchangers. Energy 152, 732–743 (2018) Johnston, I.W., Narsilio, G.A., Colls, S.: Emerging geothermal energy technologies. KSCE J. Civ. Eng. 15, 643–653 (2011) Katzenbach, R., et al.: New technologies and applications: materials and equipment in near surface geothermal systems. J. Deep Found. Inst. (DFI J.) 8, 93–107 (2014) Kayaci, N., Demir, H.: Numerical modelling of transient soil temperature distribution for horizontal ground heat exchanger of ground source heat pump. Geothermics 73, 33–47 (2018) Kayaci, N., Demir, H., Atayılmaz, S.Ö., ¸ A˘gra, Ö.: Long-term simulation of horizontal ground heat exchanger for ground source heat pump. In: ASME 2015 International Mechanical Engineering Congress & Exposition, vol. 6B (2015) Kim, M.-J., Lee, S.-R., Yoon, S., Go, G.-H.: Thermal performance evaluation and parametric study of a horizontal ground heat exchanger. Geothermics 60, 134–143 (2016) Li, C., Mao, J., Peng, X., Mao, W., Xing, Z., Wang, B.: Influence of ground surface boundary conditions on horizontal ground source heat pump systems. Appl. Therm. Eng. 152, 160–168 (2019) Li, W., Li, X., Wang, Y., Tu, J.: An integrated predictive model of the long-term performance of ground source heat pump (GSHP) systems. Energy Build. 159, 309–318 (2018) Lu, Q., Narsilio, G.A.: Cost effectiveness of energy piles in residential dwellings in Australia. Curr. Trends Civ. Struct. Eng. 3, 1–6 (2019) Lund, J.W., Boyd, T.L.: Direct utilization of geothermal energy 2015 worldwide review. Geothermics 60, 66–93 (2016)

82

X. Gu et al.

Lurie, M.V.: Modeling and Calculation of Stationary Operating Regimes of Oil and Gas Pipelines, pp. 73–108 (2008) Makasis, N., Narsilio, G.A.: Energy diaphragm wall thermal design: the effects of pipe configuration and spacing. Renew. Energy 154, 476–487 (2020) Makasis, N., Narsilio, G.A., Bidarmaghz, A., Johnston, I.W.: Ground-source heat pump systems: the effect of variable pipe separation in ground heat exchangers. Comput. Geotech. 100, 97–109 (2018) Makasis, N., Narsilio, G.A., Bidarmaghz, A., Johnston, I.W., Zhong, Y.: The importance of boundary conditions on the modelling of energy retaining walls. Comput. Geotech. 120, 103399 (2020) Motamedi-Ghahfarokhi, Y., Makasis, N., Arulrajah, A., Horpibulsuk, S., Gu, X., Narsilio, G.: Investigating the thermal behaviour of geothermal pavements using Thermal Response Testing (TRT). Transp. Geotech. 29, 100576 (2021a) Motamedi-Ghahfarokhi, Y., Makasis, N., Arulrajah, A., Horpibulsuk, S., Narsilio, G.: Thermal performance of the ground in geothermal pavements. In: International Conference on Energy Geotechnics (2021b) Muñoz-Criollo, J.J., Cleall, P.J., Rees, S.W.: Factors influencing collection performance of near surface interseasonal ground energy collection and storage systems. Geomech. Energy Environ. 6, 45–57 (2016) Narsilio, G., Johnston, I., Bidarmaghz, A., Colls, S., Mikhaylovaa, O., Kivi, A., Aditya, R.: Geothermal energy: introducing an emerging technology. In: Advances in Civil Engineering for Sustainable Development, ACESD 2014, pp. 1–14 (2014) Ozudogru, T.Y., Olgun, C.G., Senol, A.: 3D numerical modeling of vertical geothermal heat exchangers. Geothermics 51, 312–324 (2014) Philippe, M., Bernier, M., Marchio, D.: Validity ranges of three analytical solutions to heat transfer in the vicinity of single boreholes. Geothermics 38, 407–413 (2009) Qi, D., Pu, L., Ma, Z., Xia, L., Li, Y.: Effects of ground heat exchangers with different connection configurations on the heating performance of GSHP systems. Geothermics 80, 20–30 (2019) REN21: Renewables 2019 Global Status Report (2019) Sarbu, I., Sebarchievici, C.: General review of ground-source heat pump systems for heating and cooling of buildings. Energy Build. 70, 441–454 (2014) Selamat, S., Miyara, A., Kariya, K.: Numerical study of horizontal ground heat exchangers for design optimization. Renew. Energy 95, 561–573 (2016) Sterpi, D., Angelotti, A., Habibzadeh-Bigdarvish, O., Jalili, D.: Assessment of thermal behaviour of thermo-active diaphragm walls based on monitoring data. J. Rock Mech. Geotech. Eng. 10, 1145–1153 (2018) Tarnawski, V.R., Leong, W.H., Momose, T., Hamada, Y.: Analysis of ground source heat pumps with horizontal ground heat exchangers for northern Japan. Renew. Energy 34, 127–134 (2009) Xia, C., Sun, M., Zhang, G., Xiao, S., Zou, Y.: Experimental study on geothermal heat exchangers buried in diaphragm walls. Energy Build. 52, 50–55 (2012)

Mechanistic Performance Analysis of Fiber-Reinforced Asphalt Pavement Overlays Nitish R. Bastola, Mena I. Souliman(B) , Ashish Tripathi, and Alexander Pearson Department of Civil Engineering, The University of Texas at Tyler, 3900 University Blvd, RBS 1008, Tyler, TX 75701, USA [email protected]

Abstract. Among the various distresses in flexible pavement structures, fatigue cracking can be accounted for as one of the major distresses that need to be addressed by pavement engineers. Numerous construction practices are introduced to reduce the effect of fatigue in pavement structures. One of such methods is applying fibers to the asphalt mixture to prolong the serviceability and the performance of the pavement structures. The use of fibers is applicable to freshly constructed pavements as well as in pavement rehabilitation and maintenance work, such as overlay. This paper primarily analyzes the application of fibers in pavement overlay structures. The two major pavement cases with original asphalt overlay and the one with fibers mixed asphalt overlay are considered utilizing a developed testing program where mechanistic analysis is evaluated. It was found that the fiber mixture pavement overlay had a higher pavement life than the ordinary asphalt overlay.

1 Introduction There are diverse types of cracks in asphalt pavement. However, it is crucial to understand that once the pavement develops interconnected cracks generated from the bottom of HMA and transferred to the hot mixed asphalt layer, it is then referred to as fatigue cracking. When acted upon by traffic loading, these multiple cracks will form a pattern similar to the pattern on an alligator’s back, which is where alligator cracking gets its name from. Patching is one type of solution that often can repair and remove fatigue cracking. However, if the crack surfaces are significant, it will need an overlay. The overlay is the best way for the rehabilitation of large amounts of fatigue cracking. Distress in the pavement likely occurs overtime after the construction of the pavement structure has finished. Fatigue cracking is a significant concern when there is a need for the economical design of the pavement. Among the various options for enhancing and rehabilitating the pavement, fibers are often thought of, but they are an entirely new concept, causing a concern related to their long-term performance. The use of fibers as a material to reinforce the pavement has been practiced for many decades. Moreover, the use of fibers in preventing the drain-down of binders in aggregate particles is observed regularly. However, they are rarely used to rehabilitate several cracks in the asphalt pavement structures, such as fatigue cracking. Numerous varieties of fibers are used nowadays. This study also utilizes fibers in overlays to determine the improved © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 83–90, 2021. https://doi.org/10.1007/978-3-030-79638-9_7

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performance of pavement overlays to improve fatigue cracking resistance of flexible pavements. The use of fiber is a cost-effective method of strengthening the pavement structures for prolonged service life [1]. The background for this study was initiated in 2008 when FORTA Corporation and the City of Tempe in Arizona used a Type C-3/4 base, and surface course layers were selected for the pavement of Evergreen Drive (East of the Loop 101 and North of University Drive). Two main asphalt mixtures were used for the most deteriorated section of the Evergreen Drive, where the 2 mm overlay was used after milling the edge of the pavement. The overlay was done on 64.31 m of the pavement for the study. In this study, laboratory samples of 150 mm diameter gyratory specimens were prepared, which includes the compaction for repeated load deformation testing or flow number testing [1]. AASHTO TP8 test protocols were used for the preparation of beam specimens and compaction. The air void level was 7%. Various properties such as dynamic modulus, triaxial shear strength, and repeated load for flexural beam tests for fatigue and evaluation of rutting resistance were tested. These tests were useful in providing ASTM Ai-VTSi consistency-temperature relationships [2].

2 Literature Review Flexible pavements refer to the kind of pavement that bend when acted by the force of the tire. There will be a specific design objective of preventing excessive failure in any layer in flexible pavements. The load distribution patterns also change from layer to layer in flexible pavement. With this loading and variable environmental conditions, flexible pavements are very prone to distress, such as alligator cracking. Among various methods to rehabilitate the pavement, one of the most known processes is the use of fibers. The use of fibers in the pavement did not start until the late 1950s. The JohnsManville Company, US Army Corps of Engineers, and the Asphalt Institute initiated the first evaluation of asbestos fibers in HMA [3]. This study concluded an increase in tensile strength, compressive strength, stability, ability to sustain load after reaching maximum stability, and resistance to weathering. This study was performed on pavement construction, but fibers in the overlay have a much shorter history. Von Quintus et al. 2007 [4] performed a research study to determine the difference between Polymer-modified Asphalt (PMA) and conventional unmodified HMA mixture to reduce the occurrence of distress increasing pavement life. Various conditions were identified to have the effect of PMA, maximizing the overlay life. The use of fibers led to the minimization of fatigue cracking, transverse cracks, and rutting with an adequate increase in service life. Similarly, Severo and Ruwer [5] performed research to determine hot mixed asphalt rubber overlay performance. The mix was 88% asphalt and 12% ground tire rubber. A distressed section of the road was taken for the study and analyzed for two years. The effect of using the rubber mixed overlay was investigated for two years and found that the overlay was crack-free with no maintenance required. Research by Jaskula et al. 2017 [6] was also focused on the overlay construction with the various mixtures of asphalt and polymer fibers. The use of Aramid-Polyalphaolefin fibers was notable. Low-temperature cracking and resistance to permanent deformation

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were illustrated. Various performances related to high temperatures were analyzed by using the curve of dynamic modulus. The results throughout the research indicated that the evaluated fibers could improve low-temperature pavement performance. This extensive literature review facilitated learning the uses of fibers in the construction of flexible pavement and overlays. It provides guidance for knowing the mechanistic analysis of the HMA pavement as the analysis explains the phenomena caused due to the numerous physical actions such as stresses, strains, and deflection within a structure. Multiple mechanistic studies are performed with time; for example, Coleri et al. 2018 [7] used recycled materials on mechanical-empirical simulations. Similarly, Souliman et al. 2016 [8] conducted a mechanistic analysis using 3D-Move, which was based on the fatigue performance on unmodified asphalt rubber and polymer modified mixture resulting in higher performance on the modified mixture.

3 Objectives The objective of this study is to determine the performance of fiber-reinforced asphalt overlay when it accounts for the distress conditions of fatigue. Various results from mechanical laboratory evaluations and long-term mechanistic performance were utilized in evaluating the benefits of reinforcing an overlay with the fibers in this study.

4 Mechanistic Analysis Using the 3-D Move Software Package A comprehensive concept for the design of a pavement layer thickness is referred to as mechanistic-empirical pavement design. The phenomenon caused by physical activities such as stress, strain, and deflection within the structure is explained by mechanisticempirical pavement design. Climatic conditions, properties of the materials of the pavement structure, and loads are the cause of these phenomena. Empirical parameters are used along with the mechanistic approach for defining the life of a pavement structure based on the above-described phenomenon. Analysis of asphalt pavement requires various technological software packages, in which 3-D Move analysis was deemed most powerful. University of Nevada, Reno, under the cooperative agreement with Federal Highway Administration Agency, released the software [9]. Continuum finite layer approach is applied for computing pavement responses, which leads the program to handle complex surface loadings such as multiple loads and non-uniform tire pavement contact stresses. Loading configuration and tire are adjustable according to path requirements. Estimation of damage under off-road farm vehicles and estimation of pavement performance at the intersection are some of the 3-D Move software’s advanced applications. Similarly, some of the salient features regarding the software are the modeling of 3D surface stresses, analyzing the imprints of any shape, analyzing non-generic axle and tire configuration, and accounting for viscoelastic material characterization utilizing symmetrical conditions. Figure 1 represents the 3-D Move software and its various application. In this study, the approach of the empirical equation based upon the physical effects and the failure of the pavements was implemented to estimate the performance of the

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Fig. 1. 3-D Move software and its application

original mixture and fiber-reinforced mixture based on fatigue characteristics. Two pavements overlay structures of 25 mm and 50 mm characterized as thin and thick, respectively, were included for the analysis. Three vehicular speeds of 16, 72, and 120 kph and the parameters such as material properties, pavement layer thickness, and single axle traffic load of 80 KN over dual tires spaced at 304.8 mm were utilized for the analysis of the pavement overlay in terms of fatigue lives.

5 Fatigue Mechanistic Analysis When an HMA pavement is exposed to repeated traffic loading under various conditions of the environment, it results in tensile stress. This tensile stress initiates cracking at the bottom of the HMA surface, which eventually leads to fatigue cracking after the continuous traffic loads. Fatigue cracking is often rehabilitated using an overlay. The use of fibers in overlay results in the strengthening of HMA pavements. It is essential to reinforce the overlay of the pavement structure against fatigue cracking. For analyzing the pavement for fatigue cracking, 36 individual 3-D move analyses were performed. The analysis cases were two mixtures types, two pavement structures types, 3-speed types, and three pavement temperatures, summing up to 36 cases. Maximum tensile strains were identified by analyzing tensile strains at the bottom of the asphalt concrete layer under the center point between the dual tires. The strains obtained from 3-D move analysis were used in calculating the fatigue life NF using the following relationship, as presented as Eq. 1 [1].    NF = k1 1 ∈t k2 (1) Where k1 and k2 are the regression constants, and the values of these constants are presented in Table 1. The fatigue ratio was then calculated as follows: Fatigue Ratio =

NF of Fiber − reinforced mixture NF of original mixture

(2)

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Table 1. The regression coefficient for two different types of mixtures for fatigue [10] Mixture type

K1

K2

Unmodified original mixture 4E-14 4.95 Fiber-reinforced mixture

4E-18 5.98

Table 2, given below, summarizes the NF cycles derived from strains for both original and fiber-reinforced mixture. Table 2. Mechanistic fatigue analysis results for original mixture and fiber-reinforced mixtures for overlay pavement structures Pavement layer thickness

Thin

Speed (kph)

Original mixture

Fiber-reinforced mixture

NF (Cycles)

NF (Cycles)

– 12

35,637,609

148,214,363

4.16

22

634,094

2,955,500

4.66

(˚C) 16

72

120

Thick

Temp

16

72

120

Average fatigue ratio

Fatigue ratio

38

74,490

134,506

1.81

– 12

42,390,662

186,547,889

4.4

22

1,260,856

7,145,845

5.67

38

124,740

360,645

2.89

– 12

55,656,490

210,000,034

3.77

22

1,985,318

11,730,583

5.91

38

202,582

661,878

3.27

– 12

112,130,179

688,038,164

6.14

22

1,156,952

8,198,969

7.09

38

86,468

200,181

2.32

– 12

139,696,815

797,519,376

5.71

22

2,663,465

21,846,873

8.2

38

179,953

692,913

3.85

– 12

175,829,706

927,883,904

5.28

22

4,058,175

33,393,097

8.23

38

303,979

1,175,680

3.87 4.8

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As stated earlier, fatigue mechanics analysis was conducted with 3D move software. For both the mixture of two HMA overlay layers, the NF cycle was determined at the various speeds of 16, 72, and 120 kph, respectively, and a temperature of –12, 22, and 38 °C with Eq. 1, tensile strain and regression constant. Fatigue ratios were also calculated, and it is noticed that the fiber-reinforced mixture had a higher NF cycle compared to the ordinary mixture. It is explicitly noticed that the fatigue performance of the fiber-reinforced mixture was 4.8 times more than controlled unmodified mixtures. Similarly, the tensile strain at the bottom of the HMA layer is given below in Fig. 2.

Fig. 2. Tensile strains at the bottom of the asphaltic layers for different pavement structures and vehicle speeds for overlay pavement structures

Figure 2 shows that with the increase in the pavement thickness in the same mixture, tensile strain decreased at the bottom of HMA. Similarly, concerning the vehicular speed from lower the higher, the tensile strain decreased, and for the temperature increment, the strain value also increased. Figure 3 below represents the NF cycle of modified and fiber-reinforced mixture, and it shows that a thick pavement, when acted with higher vehicle speed, has higher pavement life within the mixture. The control mixture and fiber-reinforced mixture has an average NF of 31,892,919 cycles and 169,261,133 cycles, respectively, as shown in Fig. 3. This indicates that the fiber-reinforced mixture has a higher fatigue life than the controlled mixture.

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Fig. 3. NF cycles for unmodified original mixture and fiber-reinforced mixture for different temperatures for overlay pavement structures

6 Conclusions and Recommendations The calculated NF cycles illustrated the life of pavement with fiber-reinforcement is higher than the unmodified mixtures concerning mechanistic fatigue analysis. The fatigue performance (NF ) of the fiber-reinforced mixture was 4.8 times greater than that of the unmodified mixture in an overlay. The results of this study conclude that the use of fibers in the HMA overlay will enhance and improve pavement performance in terms of fatigue. Therefore, it is recommended to determine the most cost-efficient fiber contents for different traffic loading conditions and pavements thickness as further research.

References 1. Kaloush, K.E., Biligiri, K.P.: Evaluation of FORTA Fiber-Reinforced Asphalt Mixtures Using Advanced Material Characterization Tests –Evergreen Drive, Tempe, Arizona, Research Report (2008) 2. Putman, B.J.: Effects of Fiber Finish on the Performance of Asphalt Binders and Mastics, Research Article: Advances in Civil Engineering (2011) 3. AASHTO Designation: T32103. Determining the Fatigue Life of Compacted Hot-Mix Asphalt (HMA) Subjected to Repeated Flexural Bending, Washington DC (2003) 4. Von Quintus, H.L., Mallela, J., Buncher, M.: Quantification of the effect of polymer modified asphalt on flexible pavement performance. Transp. Res. Rec. J. Transp. Res. Board 2001, 141–154 (2007). Transportation Research Board of the National Academies, Washington, DC 5. Severo, L., Ruwer, P.: Performance of Asphalt-Rubber Hot Mix Overlays at Brazilian Highway

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6. Jaskula, P., Stienss, M., Szydlowski, C.: Effect of polymer fibres reinforcement on selected properties of asphalt mixtures. Modern Building Materials, Structures, and Techniques (2017) 7. Coleri, E., Zhang, Y., Wruck, B.: Mechanistic-empirical simulations and life cycle cost analysis to determine the cost and performance effectiveness of asphalt mixtures containing recycled materials. Transp. Res. Board J. Transp. Res. Board, 2672(40), 143–154, 2018 8. Souliman, I.M., Mamlouk, M., Eifert, A.: Cost-effectiveness of rubber and polymer-modified asphalt mixtures as related to fatigue performance. Transp. Res. Board J. Transp. Res. Board (2016) 9. Siddharthan R.V., Yao, J., Seebaly, P.E.: Pavement strain from moving dynamic 3D load distribution. J. Transp. Eng. 124(6), 557–566 (1998) 10. Souliman I.M., Tripathi, A., Isied, M.: Mechanistic analysis and economic benefits of fiberreinforced asphalt mixtures. J. Mater. Civ. Eng. 31(8), 04019142 (2019)

Effect of Using Copper Tailings as Replacement of Fine Aggregate for Concrete Pavement Meng-Yao Gao1 , Sung-Ching Chen1(B) , and Wei-Ting Lin2 1 School of Civil and Architectural Engineering, East China University of Technology,

418 Guanglan Avenue, Nanchang, Jiangxi, China [email protected] 2 Department of Civil Engineering, National Ilan University, No. 1, Section 1, Shennong Road, Yilan City, Yilan County, Taiwan

Abstract. The accumulation of copper tailings in China has reached 2.4 billion tons, with much, and the comprehensive use rate was only 8.2%. Natural river sand was a non-renewable in a short time. Natural river sand distribution has strong regional limits. This study was focused on prepared C30 concrete pavement with copper tailings as fine aggregate. It could not only ease the pressure of natural sand shortage but also improve the comprehensive use rate of copper tailings and reduce environmental pollution. The range of copper tailings particles was 0.15–0.075 mm, which belongs to ultra-fine sand. There were still obvious differences between copper tailing and natural sand in compositions, shape, and particle grading. In this study, copper tailings were mixed with natural river sand as fine aggregates to mix the mixture of C30 concrete. The particle graduation and MB value of mixed sand after replacement of 30 wt.% and 100 wt.% copper tailings in river sand were conducted. The effect of 0 wt.%, 30 wt.%, and 100 wt.% replacement rate on the mechanical properties of C30 concrete, dry shrinkage performance, resistance to sulfate erosion durability were studied and evaluated. The experimental results show that: 30 wt.% and 100 wt.% mixed sand has more fine aggregate, poor grading, and the measured MB value is greater than 1.4. With the increase of the content of copper tailings, the dry shrinkage rate increased to 15.94 µm, and the compressive strength decreased by 55.7%. Keywords: Copper tailings · Fine aggregate · Mixed sand · C30 concrete

1 Introduction Copper tailing was composed of fine sand particles left after crushing and cleaning of ore, which was much industrial solid waste (Zhang et al. 2019). There were many copper tailings in China. According to relevant statistics, by the end of 2013, the accumulation of copper tailings in China has reached 2.4 billion tons. On the one hand, Much tailings not only occupy much agricultural land, but also cause serious environmental pollution due to fine tailings particles; on the other hand, the comprehensive use rate of copper tailings in China is only 8.2%, which is far lower than the world advanced level (the © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 91–101, 2021. https://doi.org/10.1007/978-3-030-79638-9_8

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average use rate of foreign tailings could reach 60%), and most valuable parts in tailings were not effectively utilized (Zhang et al. 2020; Zhang et al. 2020; Zou et al. 2014). Many building materials were often consumed in highway engineering. The application of copper tailings as fine aggregate in pavement concrete preparation could not only reduce the project cost but also improve the comprehensive use rate of copper tailings (Tao et al. 2019; Gao 2017). Previous studies had shown that two main reasons restrict the widespread use of copper tailings concrete in Engineering: first, the particle size distribution and physical properties of copper tailings in different areas were different; second, the mechanical properties of copper tailings in the concrete application in different areas were different (Zhan et al. 2018; Pyo et al. 2018; Sharma et al. 2017). However, given the strong needs of the state on the sustainable development of green environmental protection and the environmental pollution caused by the massive store of copper tailings, it is necessary to research replace natural sand with copper tailings in different areas in practical application. In this experiment, copper tailings replace natural sand in different proportions as a fine aggregate to prepare pavement concrete. By studying the mechanical properties and durability of concrete, we try to find out the influence law, which can provide a reference for the wide application of copper tailings in road engineering in the future.

2 Materials and Methods 2.1 Material Portland Ordinary cement (P.O 42.5) conforms to GB 175-2007 “general Portland cement” in china. See Table 1 for the main physical properties. Table 1. The physical properties of cement. Cement sort

P.O 42.5

Specific surface area (m3 /kg)

358

Initial setting time (Min)

172

Final setting time (Min)

234

3d compressive strength (MPa)

27.2

28d compressive strength (MPa) 55.7 3d flexural strength (MPa)

5.5

28d flexural strength (MPa)

8.8

The coarse aggregate experiment is selected from Jiangxi Changxin cement building materials, with a diameter of 5–25 mm. The apparent density is 4275 kg/cm3 , and the bulk density is 1808 kg/cm3 . The grading curve is shown in Fig. 1. Natural river sand is from Jiangxi Changxin cement building materials, with fineness modulus of 2.7, belonging to medium sand. See Table 2 for physical properties and Table

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Fig. 1. The graduation curves of the crushed stone.

3 for particle size distribution. The copper tailing sand is from Daye tailing pond in Hubei Province, and the selected tailings are surface tailings. The fineness modulus is 1.2, which is ultra-fine sand, and the mud content in tailings is high. See Table 2 for its physical properties. The particles of copper tailings are mainly concentrated below 0.15 mm (see Table 3 and Fig. 2). Table 2. The properties of fine aggregates. Aggregates

Apparent density (kg/m3 )

Bulk density (kg/m3 )

Fineness modulus

River sand

2621

1656

2.7

Copper tailing

3094

1596

1.2

Table 3. The accumulated sieving residue of fine aggregates. Sieve size (mm)

4.75 2.36 1.18 0.60 0.30 0.15 0.075

River sand (%)

10.3 24.0 38.6 55.9 85.3 91.8 98.0

Copper tailing (%)

0.4

2.2

3.3

4.5

9.6 15.8 88.1

The chemical composition of copper tailings is mainly SiO2 , Al2 O3 , and less Cao, Fe2 O3 , MgO, etc. (see Table 4). XRD phase analysis (see Fig. 3) shows the mineral composition of copper tailings mainly includes quartz, calcite, albite, potash feldspar, diopside, etc. The dosage of retarding and water reducing agent is 0.2%–0.5%.

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Fig. 2. The particle size distribution of copper tailing. Table 4. The chemical compositions of the copper tailing (%). CaO Al2 O3 SiO2 Fe2 O3 MgO CuO TiO2 MnO 0.3

15.9

75.5

0.3

0.7

6.6

0.6

Fig. 3. XRD of copper tailings.

0.1

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2.2 Test Methods and Specimens A big difference between pavement concrete and industrial and civil building concrete mix proportion design. For industrial and civil buildings, the concrete mix proportion design follows JGJ 55-201 specification in china for mix proportion design of ordinary concrete, which takes the compressive strength of concrete as the main design index, while for road concrete, the mix proportion design follows JTG e30-2005 “Highway engineering cement and cement concrete test specification” in china and JTG d402011 “highway cement concrete pavement design specification” in china, is the concrete flexural strength as the primary design index. In this study, it is assumed that there is a third class highway with frost resistance requirements, and the traffic load level is low. According to the JTG d40-2011 code in china for design of highway cement concrete pavement, the safety standard of pavement design is grade III, and the standard value of 28d design bending tensile strength is 4.0 Mpa. At the same time, according to the highway grade and construction conditions, it is assumed that the cement concrete pavement is paved with three roller shaft units. According to JTG F30-2003 technical specification in china for construction of highway cement concrete pavement, the slump of cement concrete mixture is 30 mm–50 mm. To preliminarily study the influence of copper tailings on the mechanical properties and durability of C30 pavement concrete, and to provide reference and improvement suggestions for the next experiment. In this experiment, three groups of specimens with 0 wt.%, 30 wt.%, and 100 wt.% substitution is selected as the preliminary concrete configuration experiment. The final mix proportion is shown in Table 5. The flexural and compressive strength of the formed specimens after 7 d and 28 d curings, as well as the dry shrinkage and sulfate resistance of cement concrete, were tested. Table 5. The mixing proportions of concretes (kg/m3 ). The proportion Cement River sand Copper tailing Crushed stone Water Water reducer of copper sailing (wt.%) 0

336

671.0

0

1246

198

0.67

30

336

469.7

201.3

1246

208

0.67

100

336

0

671.0

1246

293

0.67

In the experiment, the particle size of copper tailings is fine, and most of them are concentrated in 0.075 mm. According to GB/T 14684-2011 “building sand” in china, the content of mud is defined as the content of particles less than 75 µm in natural sand, while the content of stone powder is defined as the content of particles less than 75 µm in manufactured sand. The soil in natural sand is harmful to both concrete and mortar, its content must be controlled, the suitable stone powder is helpful to both concrete and mortar. As shown in Table 3, the particles of copper tailings in the experiment are relatively fine, and most of them are concentrated in 0.075 mm and below. The MB value of copper

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tailings is determined by the methylene blue test and the stone powder content in tailings is determined, which will better explain the influence factors of copper tailings content on Mechanical properties and durability of C30 pavement concrete. As shown in Fig. 2, if the fine aggregate is all tailings, the fluidity of concrete mixture will be poor, and the dry shrinkage deformation of concrete will be serious in the later stage. To avoid the above situation, this experiment adopts the method that copper tailings gradually replace natural sand, which is, tailings gradually replace natural sand by 0 wt.%, 30 wt.% and 100 wt.%. At the same time, by increasing or decreasing the unit water consumption of each replacement batch, the slump of a concrete mixture is controlled within the standard range (30–50 mm), to optimize the mix proportion design of tailing sand concrete.

3 Results and Discussion 3.1 Methylene Blue Experiment According to the analysis in Table 6, the MB values of the mixed sand with different substitution amounts are all greater than 1.4, showing the mixed sand is mainly composed of mud powder. At the same time, it also reflects that in the dry screening method of mixed sand, still a high content of mud powder on the 0.075 mm sieve. Besides, the stone powder content in the mixed sand is far beyond the standard sand standard for pavement concrete. Previous studies have found that when the mass of stone powder in aggregate is higher than 8 wt.% of the total mass, the drying shrinkage of concrete will be more obvious. If the mixed sand is used to prepare concrete, the fluidity of concrete mixture will be decreased, the preparation strength of concrete will be reduced, and the dry shrinkage deformation of concrete will be increased (Yang 2014; Li 2014; Zhang et al. 2014). Table 6. Stone powder content of mixed sand. Stone powder content

JTG/T F30-2014

The proportion of copper MB Stone powder (%) Stone powder (%) sailing (wt.%) 30

2.1

9.01

100

4.6

23.67

MB < 1.40 or qualified

I

II

III

3.0 5.0 7.0

MB ≥ 1.40 or unqualified 1.0 3.0 5.0

3.2 Particle Size Distribution of Mixed Sand According to Fig. 4 and Fig. 5, the fineness modulus of natural river sand is 2.7, and the grading curve falls in zone II of the natural river sand grading curve, which meets the construction needs. When the proportion of tailings sand is 30 wt.%, part of the grading curve falls in zone II of the grading curve of natural river sand. However, the accumulated screen allowance of less than 0.6 mm is larger than that in the standard grading curve,

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so it belongs to the poorly graded sand. If the copper tailings sand is used as the fine aggregate of concrete, it is necessary to adjust the sand ratio properly and increase the water consumption per unit mixture to meet the workability of the construction concrete mixture. When the proportion of tailings sand is 100 wt.%, the fineness modulus is 1.2, which belongs to ultra-fine sand, and the grading curve is different from that of standard manufactured sand. If the tailing sand with this ratio is used as the fine aggregate of concrete, the poor design will lead to the high viscosity of concrete, difficult pumping, large shrinkage of concrete and easy to cause deformation cracks.

Fig. 4. The graduation curves of the mixed sand.

3.3 Mechanical Properties of Copper Tailings Concrete Table 7 gives the flexural strength and compressive strength of tailings concrete at 7d and 28d. From the table, we can see the 28d flexural strength of natural river sand concrete reaches the design flexural strength of 4.0, and the 28d flexural strength of concrete with 30 wt.% and 100 wt.% replacement of copper tailings sand fails to reach the design flexural strength. With the increase of tailing sand content, the flexural strength of concrete gradually decreases. Compared with the natural river sand concrete without copper tailings, the flexural strength of 30 wt.% and 100 wt.% tailings concrete decreases by 28% and 45%. In the 28d compressive strength, the compressive strength of natural river sand concrete and 30 wt.% copper tailings sand can reach the design value of C30 concrete, but the compressive strength of concrete is 43.5% lower than the design strength when the concrete is replaced by 100 wt.%. Because the mud content of tailing sand has a great influence on the strength of concrete. In this experiment, the stone powder content of

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Fig. 5. The fineness modulus of the mixed sand.

tailing sand used in this experiment is mainly mud powder, which is higher than the standard of standard sand. When the high mud content in the fine aggregate is used to prepare the concrete, the fine particles of the mud will adhere to the surface of the aggregate, which acts as a barrier layer reaction on the boundary between the cement paste and the aggregate, thus damaging the force of the aggregate wrapped by the cement paste, forming a weak part in the concrete, and affecting the strength of the concrete (Lan et al. 2012; Tian 2010). If we want to improve the replacement rate of tailings for concrete configuration, we need to reduce the mud content of copper tailings or adjust the concrete mix (Huang 2005; Sun et al. 2019). Table 7. The mechanical properties of the concretes. The proportion of copper sailing (wt.%)

Flexural strength (MPa)

Compressive strength (MPa)

7d

28d

7d

28d

0

3.14

4.49

30.3

34.5

30

3.03

3.23

12.2

30.8

100

2.09

2.47

14.9

20.9

3.4 Dry Shrinkage Properties of Copper Tailings Concrete Figure 6 shows the dry shrinkage strain of concrete with different tailing sands at 7d, 14d, and 28d. Before 28d, the dry shrinkage of concrete shows a rapid increase trend, and the dry shrinkage of concrete does not stop at 28d and still has a continuously increasing trend. Compared with the natural river sand concrete, the dry shrinkage rate of concrete is significantly increased with add copper tailings. When the age is 7 days, the dry shrinkage rate of 30 wt.% tailings concrete is the same as that of natural river

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sand concrete, and the dry shrinkage rate of 100 wt.% tailings concrete is 28.9% higher than that of natural river sand concrete. At the age of 14 d and 28 d, the dry shrinkage rate of tailings concrete is significantly higher than that of natural river sand concrete. The dry shrinkage rate of 100 wt.% tailings concrete is 1594 × 10–6 at 28 d, which is 77% higher than that of natural river sand concrete. Due to mineral processing technology, copper tailings often have high dust content. When used in concrete preparation, the content of concrete paste will be increased, so the tailing sand concrete has the potential harm of increasing dry shrinkage.

Fig. 6. The dry shrinkage ratio of the mixed sand.

3.5 Sulfate Resistance of Copper Tailings Concrete Table 8 shows that after a dry-wet cycle, the compressive strength ratio of concrete with 30 wt.% and 100 wt.% tailings sand in 5% sodium sulfate solution is reduced to 81% and 55.7%. The compressive strength of tailings concrete is greatly affected by sulfate attack. Besides, it is obvious from Fig. 7 that no obvious on the surface of natural river sand concrete, but obvious holes appear on the surface of 30 wt.% tailings concrete, and cracks are obvious on the surface of 100 wt.% tailing sand concrete. With the increase of the replacement amount of tailings sand, the ability of concrete to resist sulfate corrosion gradually weakens. Because this may be the MB value of the mixed sand is too large, and the mud powder in the tailings sand will absorb more free water in the concrete, which will lead to the decrease of the humidity in the concrete, resulting in more microcracks in the concrete, which creates a good condition for the permeability and diffusion coefficient of H+ and SO42− ions in the surrounding environment, which leads to the concrete The resistance to sulfate attack is decreased.

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The proportion of copper sailing (wt.%) MB 0

Times

Compressive strength and corrosion resistance coefficient (%)

–

1

94.7

30

2.1

1

81.0

100

4.6

1

55.7

Fig. 7. Appear the specimen after the sulfate attack.

4 Conclusions (1) In the methylene blue test of mixed sand, MB value was greater than 1.4, which is mainly mud powder. In 100 wt.% tailings, stone powder reaches 23.67%, which was far beyond the standard sand standard for pavement concrete. (2) When the proportion of tailings sand was 30 wt.%, part of the grading curve falls in zone II of the standard manufactured sand, but the accumulated screen allowance below 0.6 mm is larger than that in the standard grading curve, and the grading was poor. When the proportion of tailing sand was 100 wt.%, the grading curve is different from the standard curve. If the tailing sand with this proportion was used as the fine aggregate of concrete, if the design was not good, it will lead to the high viscosity of concrete, difficult pumping, large shrinkage of concrete and easy to cause deformation cracks. (3) The flexural strength of 30 wt.% and 100 wt.% tailing sand concrete can not reach the design flexural strength of 4.0, and the mud content of tailings has a great impact on the strength of concrete configuration. To improve the replacement rate of tailings sand for concrete configuration, it was necessary to reduce the mud content of copper tailings sand or adjust the concrete mix. (4) The dry shrinkage rate of concrete with copper tailings was higher than that of natural river sand concrete and increases with the increase of copper tailings content. When the content of copper tailings was 100 wt.%, the dry shrinkage rate of 28d concrete was as high as 15.94 µm, which is 77% higher than that of natural river sand concrete. (5) The compressive strength of concrete with 30 wt.% and 100 wt.% tailings sand in 5% sodium sulfate solution was 81% and 55.7% lower than that of natural river

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sand concrete. The compressive strength of tailings concrete was greatly affected by sulfate attack.

Acknowledgments. This research was supported by the East China University of Technology (Project No.: DHBK2019232).

References Zhang, J., Liu, J., Liu, Z.: Effect of copper tailings sand on mechanical properties and durability of C50 concrete. New Build. Mater. 46(08), 83–96 (2019) Zhang, W., Gu, X., Qiu, J., Liu, J., Zhao, Y., Li, X.: Effects of iron ore tailings on the compressive strength and permeability of ultra-high performance concrete. Constr. Build. Mater. 260, 119917 (2020) Zhang, Y., et al.: Experimental study on the utilization of copper tailing as micronized sand to prepare high performance concrete. Constr. Build. Mater. 244, 118312 (2020) Zou, X., Liu, D., Zili, L., Li, M., Zou, X., Shen, W.: Research on performance of machine-made sand-copper tailing composite sand commercial concrete. J. Wuhan Univ. Technol. 36(12), 27–31 (2014) Tao, Y., Wang, Y., Huang, X., Tara, Li, Y., : Research on macroscopic properties of tailings concrete under the action of engineering quality. Constr. Qual. JST 37(09), 69–72 (2019) Gao, C.: Research on road performance and technology of machine-made sand cement concrete. Chongqing Jiaotong University (2017) Zhang, Y., Ma, J., Liu, H.: Experimental study on road performance of iron tailing sand concrete. Concrete 12(350), 157–160 (2018) Pyo, S., Tafesse, M., Kim, B.-J., Kim, H.-K.: Effects of quartz-based mine tailings on characteristics and leaching behavior of ultra-high performance concrete. Constr. Build. Mater. 166, 110–117 (2018) Sharma, R., Khan, R.A.: Durability assessment of self-compacting concrete incorporating copper slag as fine aggregates. Constr. Build. Mater. 155, 617–629 (2017) Yang, Q.: Research on the characteristics and durability of the interface zone of mixed sand high performance concrete. Chongqing Jiaotong University (2014) Li, G.: Experimental Research on Substituting Iron Tailing Sand for Natural Sand. Yanshan University (2014) Zhang, X., Fu, B., Liu, J., Zhou, Z.: Study on the performance of high performance concrete prepared by iron tailings/machine-made sand. Concrete 3(293), 116–118 (2014) Lan, Q., Ma, H., Shen, W., Zili, L., Zhiyuan, X., Mai, W.: Research on performance of mixed tailings sand concrete. J. Wuhan Univ. Technol. 34(12), 19–23 (2012) Tian, J.: Study on the preparation and application of iron tailing sand concrete. Tsinghua University (2010) Huang, H.: Research on performance and application of mixed sand concrete. Chongqing University (2005) Sun, J., Wu, D., Cao, L., Shen, W., Lu, Z., Ji, X.: Research on performance of mixed sand high-strength and high-performance concrete. Concrete 9(359), 146–149 (2019)

Research Progress of Fiber Reinforced Soil Changgen Yan and Yinsen Tang(B) Chang’an University, Middle Section of South Erhuan Road, Yanta, Xi’an, China

Abstract. Based on the research results of fiber reinforced soil in recent decades, the mechanical properties and constitutive models of fiber reinforced soil were introduced. A large number of experiments on the engineering properties of fiber reinforced soil show that fiber reinforced soil can effectively improve the shear, tensile and compressive strength of soil and enhance the toughness of soil. The fiber content, fiber type and fiber orientation are the main factors affecting the strength and deformation of fiber reinforced soil. In addition, some research results on fiber corrosion are also introduced. In terms of constitutive model, the mechanical equilibrium model, energy equalization model, statistical model, elastic-plastic model and two-phase constitutive model of fiber-reinforced soil are introduced. Finally, the research status of fiber reinforced soil is summarized, and the future research direction and emphasis are put forward. It mainly includes the constitutive model that accurately reflects the stress-strain relationship of fiber-reinforced soil, the large-scale model experiment, the microscopic study of the interaction mechanism of fiber-soil interface, the study of the dynamics characteristics, and the systematic study of the special fiber-reinforced soil. Keywords: Fiber reinforced soil · Shear strength · Tensile strength · Compressive strength · Constitutive model

1 Introduction As a new type of soil improvement technology, fiber reinforced soil is a kind of composite soil whose mechanical properties can be enhanced by adding a certain amount of fiber to the soil. The principle of its action is to combine the tensile properties of fiber with the compressive properties of soil by using the friction between fiber and soil, so as to improve the strength of soil. Compared with some traditional reinforcing materials, fiber reinforced soil has the advantages of simple mix, random uniform distribution of fiber in soil and no potential weak structural surface. Compared with other soil improvement technologies, it has the advantages of low cost, environmental protection, simple construction technology and remarkable improvement effect. Therefore, fiber reinforced soil is considered as an effective and economical soil improvement technology, which has attracted wide attention in the field of geotechnical engineering and has been studied extensively. The study of the stress-strain relationship and the corresponding mechanical model of the fiber reinforced soil can predict the strength and deformation characteristics of the fiber reinforced soil and provide reference for engineering design, which is the focus of this field. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 102–115, 2021. https://doi.org/10.1007/978-3-030-79638-9_9

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In this paper, the research achievements of domestic and foreign scholars on fiber reinforced soil technology in recent decades, including the shear strength, compressive strength, tensile strength, constitutive model and other aspects of fiber reinforced soil are introduced.

2 Engineering Properties of Fiber Reinforced Soil 2.1 Shear Strength of Fiber Reinforced Soil The shear strength of soil refers to the ultimate resistance of soil to shear stress caused by external load. The addition of a certain amount of fiber into soil can improve the shear strength of soil. The shear strength properties of fiber reinforced soil are mainly studied by direct shear test, triaxial compression test and unconfined compression test. Direct shear test, the additional shear failure surface, ambiguous problems such as stress state and the end effect makes difficult to truly simulate the behavior of fiber reinforced soil model, despite these limitations, but direct shear apparatus because of its advantages of simple operation, most of laboratory research theory and practice both at home and abroad has been widely applied in the project (Xiao-nan Gong 2014). Gray and Ohashi (1983) conducted direct shear tests on dry sand containing different types of fibers, and found that fiber reinforcement increased the peak shear strength and limited the reduction of shear resistance after the peak, and the shear strength was proportional to the concentration or area ratio of the fibers. However, some scholars have shown that there is no obvious linear relationship between shear strength and fiber content. Yetimoglu (2003) found that fiber content has little influence on peak shear stress. Anagnostopoulos (2013) conducted direct shear tests on polypropylene fiber reinforced soil and found that fiber reinforcement significantly increased the residual strength of medium dense fine sand, on the contrary, the increase of strength of reinforced sand in high dense state was almost negligible. The reason has much to do with the kinds of sand, density and fiber used in the experiment. The results of Mirzababaei et al. (2017) Also show that the normalized shear strength of fiber reinforced soil under large shear displacement can be significantly improved even at 0.25% low fiber content. And they believe that the optimal fiber content is only related to the initial porosity of the soil, but has nothing to do with the stress history of the soil and the normal effective stress applied. Like fiber content, fiber orientation is also an important factor affecting the improvement of soil shear strength by fiber (Neeraja V S 2014). Kanchi (2015) studied the influence of anisotropic distribution on stress and strain and found that with the fiber direction gradient increases, the contribution of fiber to the strength of reinforced soil decreased. The influence of the fiber on the tensile direction is the greatest and the vertical fiber does not participate in the shear failure of soil. This is consistent with the results of Michalowski and Cermak (2002), who found that vertical fibers did not contribute to the strength of reinforced soil by triaxial tests on fiber reinforced soil. Subsequently, Wang (2017) also found that the contribution of fiber to the peak deviator stress almost linearly decreased with the increase of fiber orientation from 0° to 90°. In fact, the fiber distribution in different directions in the soil is different, and the fiber direction distribution function is often used to describe the fiber material distribution in each direction

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in quantitative analysis (Michalowski 1997). Fukuda and Chou (1982) studied the influence of fiber length and orientation distribution on the strength of short fiber composite materials by using probability method. According to the fiber length and orientation distribution function and the geometric and physical properties of composite materials, a general theory was proposed. However, the deformation inhomogeneity between the fiber and soil is not considered, and the influence of soil properties on the strength of the composite is not considered. Furtherly, Zhu (1994) proposed a strength analysis theory of randomly oriented short fiber composite materials, in which the non-uniform deformation inside the composite material was considered in the strength calculation. Villard et al. (1990) set a parameter in their constitutive model to reflect the influence of fiber distribution direction on fiber reinforcement. The reinforcing effect of different types of fibers is also different. Sun (2017) found through direct shear test that when the fiber length is 12 mm and the content is 0.3%, the internal friction Angle of carbon fiber reinforced soil is the largest, followed by glass fiber reinforced soil, polypropylene fiber reinforced soil is the smallest, and polypropylene fiber has the highest cohesive force. Boz (2018) found that the increase of strength of polypropylene fiber was greater than that of basalt fiber, and the 1% fiber content was more effective in enhancing the anti-freezing-thawing effect. Compared with the direct shear test, triaxial test can overcome the disadvantages of the shear plane not appearing on the weakest surface, the difficulty in controlling drainage conditions, the uneven distribution of shear stress on the shear plane, and the magnitude and direction change of principal stress (Xiao-nan Gong 2014). Based on triaxial test and statistical analysis, Ranjan et al. (1996) believed that fiber addition resulted in an increase in peak shear strength and a decrease in post-peak stress loss. Michalowski and Zhao (1996) based on triaxial test results, show that polyamide fiber produces an increase in peak shear stress under large confining pressures, which is related to a large loss in stiffness before failure and a large increase in failure strain. Li (1995) conducted a triaxial compression test on fiber-reinforced cohesive soil, and pointed out that fiber-reinforced cohesive soil significantly improved its mechanical properties, enhanced its shear strength, and increased its cohesive force value. In different test conditions, Priyadarshee (2019) triaxial test found that the greater the confining pressure, the greater the peak stress and stiffness. However, when the confining pressure is low, the enhancement of fiber strength is more significant because the increase of confining pressure inhibits the enhancement of fiber strength. In addition, some scholars have used unconfined compressive tests to study the shear strength of fiber reinforced soil. Taesoon Park (2004) conducted unconfined compression tests on fiber reinforced soil, which showed that the incorporation of fiber improved the shear strength of soil. Tang (2007) added different amounts of polypropylene staple fiber to the pure soil. Through unconfined compression test and direct shear test, it was shown that the addition of fiber improved the unconfined compression strength and shear strength of the plain soil, and the strength value increased with the increase of fiber content. Hu (2008) conducted direct shear test and unconfined compression test on cellulose fiber soil, and found that the reinforcement rate of cellulose fiber was 0.6%, which was the optimal reinforcement rate. At this time, the unconfined compression

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strength of clay increased by 20.8%. When the reinforcement rate of fiber was too high, the fiber had a weakening effect on the unconfined compression strength. Both direct shear test, triaxial compression test and unconfined compression test discuss the mechanical properties of shear strength of fiber reinforced soil on a macroscopic level. At present, a few scholars have carried out micromechanical studies on the shear strength of fiber reinforced soil. Tang et al. (2009) calculated the critical length of fibers in fiber reinforced soil and obtained the relation curve of fiber tension and displacement based on the shear strength measured at the interface of fiber reinforced soil in the single fiber drawing test. Subsequently, Tang et al. (2011) pointed out based on scanning electron microscope (SEM) experiments that the reinforcing effect of fiber depends on the interaction strength of the reinforcement/soil interface, and the mechanical interaction between the reinforcement/soil interface mainly has two forms: friction force and bonding force. The mechanical effects of bonding and friction depend on interface contact conditions and soil conditions. Li et al. (2014) showed that the shear strength of the corrugated fiber/soil interface was 2.78 times that of the linear fiber/soil interface. Zhang et al. (2015) divided the progressive failure process of fiber drawing interface into five stages based on the three-line model, and gave the analytical solutions of interface shear stress, shear displacement and fiber axial force at each stage. Liu (2020) carried out the mechanical properties test of the interface between the fiber reinforced soil and the structure under cyclic load, and found that the relation curves of the interface shear stress, normal stress and shear displacement developed in the shape of “hysterical loop” and “disc”, respectively. The attenuation rate gradually decreased with the increase of the number of cycles, and the peak value all appeared at the maximum displacement. The mechanical properties of fiber reinforced soil are mainly controlled by the interface force between fiber and soil, so it is of great significance to study the mechanical properties of fiber/soil interface. The size of fiber is small and the action mechanism of fiber in soil is not very clear, so there is no effective method to quantitatively measure the interface force between fiber and soil. 2.2 Compressive Strength of Fiber Reinforced Soil The compressive strength of soil is mainly studied by unconfined compressive tests. Kumar et al. (1999) conducted laboratory studies on the randomly distributed polyester fiber reinforced silt and ash specimens, and found that the fiber improved the peak compressive strength, California bearing ratio value, peak friction Angle and ductility of the specimens. Kaniraj (2001) pointed out that fiber reinforcement could greatly improve the unconfined compressive strength of cement cured clay, and the increase was related to fiber length and fiber content. In terms of fiber content, Zhou (2015) conducted unconfined compressive strength test on fiber silty reinforced clay and found that with the increase of fiber content, the unconfined compressive strength of reinforced soil increased continuously, but the increase extent decreased continuously, and the influence of fiber content on unconfined compressive strength was particularly significant. Tilak B (2015) carried out unconfined compressive tests on expansive soil, and the results showed that the compressive strength increased with the addition of lime and gypsum and the increase of curing period, while the compressive strength also increased before the content of coconut shell fiber was 1.5%, and then the trend was reversed. In terms

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of fiber length, Hu (2015) carried out unconfined compression tests on fiber reinforced soil, and pointed out that with the increase of fiber length, the unconfined compression strength of soil sample increased linearly, and the compression strength of soil sample after fiber addition was significantly increased. Festugato (2017) studies show that fiber length and porosity/cement ratio are the key parameters to evaluate the unconfined compressive strength of fiber-reinforced soil-cement. Wu (2010) found that fiber could increase the residual strength of soil samples after destruction, increase the failure toughness and reduce the failure. Tang (2007) carried out similar tests, and pointed out that the unconfined compressive strength and cohesion of fiber-reinforced soil increased first and then decreased with the increase of sand content, and the internal friction angle of fiber-reinforced soil was in direct proportion to the amount of sand mixed. Moreover, the SEM observation showed that under the impact or extrusion of sand in clay, the shape of fiber changed, thus increasing the roughness of fiber and strengthening the interface Mechanical action. Gao (2015) pointed out that adding carbon fiber can effectively improve the unconfined compressive strength of soil. The strength first increases and then decreases with the increase of the content, and the enhancement effect is most obvious when the content is 0.1%. 2.3 Tensile Strength of Fiber Reinforced Soil Studies on the tensile strength characteristics of fiber reinforced soil are generally conducted by bending test, splitting test and tensile test (Guo 2018). Compared with the compressive and shear strength of soil, the tensile strength is relatively small and is easy to be neglected. However, in civil engineering, failure caused by tensile stress is very common, such as tensile cracks in dry soil, which will have a negative impact on engineering activities. Therefore, the research of using fiber reinforced soil to improve the tensile strength of soil has been paid much attention by geotechnical experts and scholars. Li (1995) conducted tensile tests on the fiber-reinforced cohesive soil and found that the fibers could increase the plasticity and toughness of the cohesive soil under the action of tensile stress and show the property of cracking and continuous during tensile stress. Viswanadham (2010) bending tests show that the incorporation of geofibres increases tensile strain at different modulus. Festugato et al. (2017) conducted splitting test, and the results showed that the splitting tensile strength of fiber reinforced soil-cement increased with the increase of fiber length. Correia et al. (2015) conducted tensile test, bending test and splitting test, and the results showed that different test methods had different effects on the tensile strength of fiber reinforced soil by breaking the strain level. Zhang (1997) tested fiber reinforced soil with uniaxial static and dynamic tension and pressure tester, and found that compared with pure soil, the critical opening displacement of fiber reinforced soil could be increased by dozens of times. Tang (2009) conducted the pull-out test with the self-made fiber pull-out test device and found that after the fiber was pulled, the interaction between the interfaces did not completely disappear and there was still residual strength to a certain extent, indicating that fiber reinforcement could delay or prevent the further development of tensile cracks and improve the toughness of soil. Li (2012) conducted direct tensile tests in the laboratory and found that the tensile strength of soil was mainly determined by the cohesive force. The tensile strength of fiber reinforced soil increased with the increase of fiber content and dry density, and decreased

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with the increase of water content. Tang et al. (2016) Conducted direct tensile test, and the results showed that the peak tensile strength of soil could be greatly increased by fiber reinforcement, while the residual tensile strength could be reduced. 2.4 Fiber Corrosion In terms of fiber corrosion, Wang et al. (2006) found that the alkali resistance of basalt fiber is better than that of acid resistance. Due to the difference in acid-base resistance, the composite has corrosion characteristics: in acidic medium, the bending strength and bending modulus of the composite decrease synchronically. In alkaline medium, the bending strength of the composite decreases while the bending modulus remains almost the same. According to Xiao (2020) simulation of acid rain accelerated corrosion, the three kinds of eucalyptus fiber/PE wood and plastic composite materials (yellow, green and silver) would all fade, their mechanical properties would decrease, their water absorption would increase, and their surface cracks would increase and expand into holes. Xie (2016) used weight loss ratio analysis method and found that the corrosion degree of ECR glass fiber in different acids was as follows: nitrate > sulfate > hydrochloric acid, and the influence of acids on the corrosion of ECR glass fiber was completely different. Hydrochloric acid mainly destroys the network structure of alumina and sulfuric acid and nitric acid mainly destroys the network structure of silica. The acid resistance of ECR glass fiber is much better than that of E glass fiber due to the silicic acid gel produced by ECR glass fiber during ion exchange. Yu (2015) found that the corrosion resistance of different glass fibers varies greatly, and the acid corrosion of glass fibers is mainly due to the boron in its composition. The higher the boron content is, the more likely the fiber in acidic medium will fail. Cheng (2004) found that the fiber orientation had great influence on the stress corrosion behavior of fiberglass reinforced plastics, and the stress corrosion resistance of the three orientations of ±30°, ±45° and ±60° changed from strong to weak. Compared with unidirectional fiber glass reinforced plastics, the three orientations of fiberglass reinforced plastics have higher critical load values of stress corrosion, and the fiber/matrix interface plays an important role in the stress corrosion of the orientations of fiberglass reinforced plastics. Liu (2020) found that with the extension of soaking time in acid, alkali and salt solutions, the mechanical properties of glass fiber/polyurethane composites gradually decreased to the degree of alkali > acid > salt, and the tensile strength, bending strength and interlaminar shear strength perpendicular to the direction of glass fiber decreased more obviously. In terms of fiber material service life prediction, Wang (2019) analyzed from the perspective of macroscopic, microscopic morphology and mechanical property changes, and found that temperature, time and corrosion medium concentration were factors affecting the service life of the material, and established a 3-10-1 three-layer BP neural network life prediction model. In terms of fiber material protection, V.A. Rybin (2016) found that dense ZrO2 and TiO2 coating on the basalt fiber surface could significantly slow down the degradation of the fiber. Titanium dioxide coating has moderate protection against corrosion in calcium hydroxide solution, while zirconia coating can effectively protect the base fiber in both calcium hydroxide solution and sodium hydroxide solution.

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3 Progress in Constitutive Research of Fiber Reinforced Soil The constitutive model is the mathematical description of stress and strain of fiber reinforced soil under load, and it is the basis of soil stability evaluation and numerical calculation. However, the research results of constitutive model based on the stressstrain relationship of fiber reinforced soil are relatively few. The constitutive models of fiber reinforced soil include dynamic equilibrium model, energy homogenization model, statistical model, elastic-plastic model and two-phase constitutive model. In the last century, some scholars studied the effect of fiber on the shear strength of soil based on the principle of force balance. Gray (1983) studied the mechanical behavior of reinforced sand and pointed out that the failure envelope of randomly distributed fiber reinforced sand was a double-fold line. Considering the interaction between fiber and surrounding soil, the strength analysis model of fiber reinforced soil is established based on the mechanical balance between fiber reinforced body and soil. Waldron (1977) used the initial Mohr Coulomb criterion to describe the load-deformation characteristics of fiber reinforced soil. Jewell and Wroth (1987) analyzed the relationship between intercropping forces and shear strength of reinforced soil from the Angle of friction. Masher and Gray (1990) predicted triaxial shear strength of random discrete fiber reinforced soil based on the Poisson distribution of fiber. The energy dissipation theory is used to predict the strength of composite materials with uniform fiber distribution in all directions, and the energy dissipation model is based on the energy dissipation principle when considering the relative slip and friction between the fiber and soil or the tensile deformation of the fiber during failure (Michalowski 1996). In order to predict the failure stress of fiber-reinforced sand under triaxial compression, Michalowski and Cermak (2002) integrated the power dissipation in the composite with anisotropic fiber distribution, introduced the spherical integral space, then transformed the deformation of the composite element into the spherical integral space, and established the energy homogenization model considering fiber slip and fiber yield. Subsequently, Michalowski (2008) established an energy homogenization model considering the anisotropy characteristics of fiber reinforced soil. Jamei (2013) established an energy homogenization model for predicting shear failure of fibrous reinforced clay soils, taking into account specific clay/fiber interface behavior, and verified the model. Wang (2018) combined the stress superposition method and energy homogenization technology to establish a model method to predict the pre-failure and failure behavior of fiber reinforced clay under the action of triaxial compression. With the development of statistics, some scholars have measured the data through experiments, obtained the functional relationship between the variables of the fiber reinforced soil after loading through mathematical statistics, and established a statistical model. Ranjan (1996) conducted regression analysis on a large number of triaxial compression test data with different fiber parameters and confining stress, and established a shear strength prediction model that can quantify fiber characteristics, soil characteristics and confining stress on randomly distributed discrete fiber reinforced soil. Sivakumar Babu and Vasudevan (2008) based on experimental data results, the regression statistical model was used to predict the principal stress, cohesion, friction Angle and initial stiffness of the fiber reinforced soil during failure. Maliakal and Thiyyakkandi (2013)

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conducted regression analysis on the observed data of critical confining stress, and established a mathematical model with fiber content, aspect ratio, confining stress and soil characteristics as input parameters to predict the principal stress of clay fiber composite during failure. Mirzababaei (2018) established a nonlinear regression model to predict the relationship between effective shear stress ratio, deviator stress and axial strain of fiber reinforced soil samples with different fiber content under different initial effective consolidation stresses. In terms of the elastoplastic constitutive model, Jouve (1995) derived a highly operable elastoplastic constitutive formula for fibre-reinforced sand soil. Considering the approximation of stress expansion and the approximation of a point outside the yield surface, the rationality of the approximation is verified by triaxial compression test. Li (2019) regarded garbage soil as a complex composed of fibrous materials and mud, and the mechanical properties of garbage soil under load depended on the combined action of fibrous materials and mud, and proposed the concept of fiber action parameters. By constructing a new plastic potential function reflecting the action of fiber reinforcement, an elastoplastic constitutive model which can reasonably describe the mechanical stress-strain characteristics of garbage soil is established. Zornberg (2002) proposed a discrete method to characterize the effect of randomly distributed fibers on soil strength improvement. In the discrete method, fiber reinforced soil is composed of soil and fiber. Fiber is regarded as discrete element, and the stability is promoted by transferring tensile stress on the shear plane. The relationship of shear strength parameters prediction is given. At present, the idea of stress-strain calculation of fiber reinforced soil is to define the soil and fiber reinforced body as basic phase and reinforced phase respectively, establish their constitutive models respectively, and then overlay their models in a certain way (Prisco 1993). Lei Wang (2014) regarded the fiber reinforced soil as a combination of basic and fiber phases, respectively adopted modified Cambridge model and linear elastic model, and introduced the reasonable strength model of the reinforced soil as the failure criterion, which could analyze the yield of the fiber reinforced soil when the strain was great, and established a two-phase constitutive model of the fiber reinforced soil. Diambra (2010) based on the mixture principle of composite material mechanics, believed that the fiber had linear characteristics, and proposed a model that could predict the constitutive behavior of fiber reinforced soil under triaxial conditions. The generality of the model is highlighted by the fact that it allows the use of any fiber orientation distribution function to reproduce the strength anisotropy under triaxial compression and tensile conditions. Further, Diambra (2013) adopted a more complex Severn-Trent model when establishing the constitutive model of fiber-reinforced sand soil under the condition of axisymmetric triaxial axis, which combined the concepts of critical state theory, Mohr Coulomb strength criterion, critical surface plasticity and motion hardening, and considered the problem of dividing pores in fiber-reinforced soil. Subsequently, Diambra and Ibraim (2014) established the constitutive model of the cohesive soil of fiber reinforced soil based on the principle of stress superposition, and applied the theory of modified shear lag method to analyze the stress transfer mechanism at the fiber/soil interface. Finally, Diambra and Ibraim (2015) deduced the analytical expressions of strain ratios in fibers and composites, and then applied them to the stress superposition constitutive model.

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In addition, in practice, the overall deformation of fiber deformation and fiber reinforced soil will not be the same. When the deformation of reinforced soil is small and the stress level is low, the relative slip between the fiber and soil will occur, which will affect the stress transfer between the two and the effect of fiber reinforcement (Wang 2014). Therefore, Diambra (2010) model introduced a dimensionless fiber slip function mainly related to average stress, and Machado (2002) proposed a fiber slip function expression of the ratio between average stress and generalized shear stress. In the aspect of strength failure criterion of fiber reinforced soil, the traditional method assumes that the orientation of fiber in soil is random when establishing the failure model of fiber reinforced soil (Michalowski and Cermak 2002, Viswanadham 2010, Jewell 1987, Masher and Gray 1990). Due to the influence of fiber anisotropy, the actual shear failure behavior of fiber reinforced soil usually depends on the loading direction. Obviously, the traditional model cannot describe the characteristics of fiber reinforced soil very well. Accordingly, Michalowski and Cermak (2002) used fiber distribution function to characterize the anisotropy of fiber direction, thus describing the anisotropy strength of fiber reinforced soil. Subsequently, they introduced the concept of macroscopic Angle of internal friction to describe the failure criteria of fiber-reinforced sand, taking into account the influence of sand and fiber (Michalowski 2003). Diambra (2010) combined with the mixing theory to simulate the strength and deformation anisotropy of fiber reinforced soil. Gao and Zhao (2013) then proposed a criterion to describe the anisotropic strength failure of fiber reinforced soil under three-dimensional loading. In addition, some scholars take the role of the reinforced soil as the external force (equivalent additional stress) on soil skeleton. Therefore, the stress-strain relationship of reinforced soil can be calculated by the constitutive model of pure soil, and the constitutive model of composite material does not need to be established for reinforced soil composite, Jie (1999) proposed the equivalent additional stress method and worked out the finite element program to calculate a model retaining wall (Denver model). Duncan Zhang model was adopted for the element model of soil. In the calculation process, the effect of reinforcement was regarded as external force (equivalent additional stress) on the soil element surrounding the layer reinforcement. Subsequently, Jie (2007) improved the equivalent additional stress method and added an additional matrix to the elastic matrix or elastic-plastic matrix of the original soil to directly solve the problem. This makes it possible to apply equivalent additional stress method directly without iteration, which greatly simplifies the programming difficulty and improves the computational efficiency.

4 Summary In the past few decades, scholars have done a lot of research on fiber reinforced soil, especially on the study of engineering properties and constitutive models based on the relationship between stress and strain. In a nutshell, fiber reinforced soil can improve the shear, tensile and compressive strength of soil and the failure toughness of soil. The fiber content, fiber type and fiber orientation are the main factors affecting the strength and deformation of fiber reinforced soil. Compared with other soil improvement techniques, it has the advantages of simple incorporation, random and uniform distribution of fibers in

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soil, no potential weak structural surface and excellent improvement effect. These results show that fiber reinforced soil is an excellent soil improvement technology and has a broad application prospect. However, there are still some deficiencies in the research of fiber reinforced soil, which has not been widely applied yet. In the future, the following aspects should be studied. (1) Construct a constitutive model that can accurately reflect the stress-strain relationship of fiber-reinforced soil. In recent decades, many scholars have constructed corresponding constitutive models based on different principles. Generally speaking, most of these constitutive models can only be applied to the corresponding fibers, and they do not have good applicability to all kinds of fibers. Or the stressstrain relationship of fiber reinforced soil is not well described. In addition, most constitutive models are based on assumptions that do not reflect the actual situation well, such as the problem of fiber orientation. Traditional methods assume that the fiber orientation in soil is random and the effects of anisotropy are not well considered. Finally, there are some limitations in the construction of constitutive models under complex stress and strain, and there is a lack of constitutive models that can accurately reflect the stress-strain relationship of fiber-reinforced soil. (2) Carry out large-scale model test research and field test. At present, the research on the engineering properties of fiber reinforced soil mainly focuses on laboratory tests, which are restricted by scale and boundary conditions. Meanwhile, the research method mainly adopts macroscopic geotechnical tests of small soil samples, which cannot reflect the engineering properties of fiber reinforced soil comprehensively. Therefore, the research of large sample, large scale model test and field test will be the focus and direction of future research on engineering properties of fiber reinforced soil. (3) Microscopic study on the interaction mechanism of fiber-soil interface. The mechanical mechanism of the interaction between traditional geosynthetic materials and soil has been very mature and formed a systematic theory. In contrast, the research on the interaction mechanism of fiber-soil interface is still at the qualitative stage, both at the macro and micro levels. Quantitative research on the mechanism of fiber-soil mechanics from micro level and the development of instruments and equipment that can measure the mechanical parameters of fiber-soil interface are the key to the formation of the system theory of fiber-soil interface mechanism in the future. (4) Study of kinetic characteristics. From the perspective of domestic and foreign research and development trends, the static characteristic test is mainly used in the experimental study of fiber reinforced soil, with the focus on finding the appropriate fiber content, type and other engineering construction parameters. There are few studies on the dynamic triaxial test, but it is only the influencing factor of adding a cyclic dynamic load, which cannot well reflect the deformation property of fiber reinforced soil under traffic load. With the rapid development of traffic engineering in the future, fiber reinforced soil, as a new soil improvement technology, has a good prospect and market because of its many advantages. The key problems to be solved are to study the strengthening mechanism of fiber reinforced soil under

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traffic load and to form system theory in the study of dynamic characteristics of fiber reinforced soil. (5) Systematic study on special soil reinforced with fiber. Some properties of special soil, such as expansion and shrinkage of expansive soil and collapsibility of loess, often bring great harm to engineering. At present, the relevant studies on special soil reinforced with fiber are not mature. Only fiber can well inhibit the expansion and shrinkage of expansive soil, while the reinforcement effect, mechanical properties and action mechanism of fiber on other special soil are worthy of further study.

References Anagnostopoulos, C.A., Papaliangas, T.T., Konstantinidis, D., et al.: Shear strength of sands reinforced with polypropylene fibers. Geotech. Geol. Eng. 31(2), 401–423 (2013) Viswanadham, B.V.S., Jha, B.K., Pawar, S.N.: Influence of geofibers on the flexural behavior of compacted soil beams. Geosynthetics Int. 17(2), 86–99 (2010) Boz, A, Sezer, A.: Influence of fiber type and content on freeze-thaw resistance of fiber reinforced lime stabilized clay. Cold Reg. Sci. Technol. 151(JUL), 359–366 (2018) Ji-wei, C., Tian-min, W.: Stress corrosion cracking of oriented glass fibre reinforced plastics. Acta Materiae Compositae Sinica 21(6), 39–46 (2004) Correia, A.A.S., Venda Oliveira, P.J., Custodio, D.G.: Effect of polypropylene fibres on the compressive and tensile strength of a soft soil, artificially stabilised with binders. Geotext. Geomembr. 43(2), 97–106 (2015) Xie, J., et al.: Corrosion mechanism of e-glass of chemical resistance glass fiber in acid environment. J. Wuhan Univ. Technol.-Mater. Sci. Ed. 31(4), 872–876 (2016). https://doi.org/10.1007/ s11595-016-1461-1 Diambra, A., Ibraim, E., Russel, A.R., Muir, W.D.: Fiber reinforced sands: from experiments to modeling and beyond. Int. J. Numer. Anal. Meth. Geomech. 37(15), 2427–2455 (2013) Diambra, A., Ibraim, E., Wood, D.M., et al.: Fiber reinforced sands: experiments and modeling. Geotex. Geomembr. 28, 238–250 (2010) Diambra, A., Ibraim, E.: Fibre-reinforced sand: interaction at the fibre and grain scale. Geotechnique 65(4), 296–308 (2015) Diambra, A., Ibraim, E.: Modeling of fiber-cohesive soil mixture. Acta Getotechnica 9(6), 1029– 1043 (2014) Festugato, L., Menger, E., Benezra, F., et al.: Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotext. Geomembr. 45(1), 77–82 (2017) Fukuda, H., Chou, T.W.: A probabilistic theory of the strength of short-fibre composites with variable fibre length and orientation. J. Mater. Sci. 17(4), 1003–1011 (1982) Gao, L., Zhou, Q., Yu, X., et al.: Experimental study on the unconfined compressive strength of carbon fiber reinforced clay soil. Mar. Georesour. Geotechnol. 35(1), 151015051905004 (2015) Gao, Z., Zhao, J.: Evaluation on failure of fiber-reinforced sand. J. Geotech. Geoenvironmental Eng. 139(1), 95–106 (2013). https://doi.org/10.1061/(asce)gt.1943-5606.0000737 Gray, D.H., Ohashi, H.: Mechanics of fiber reinforcement in sands. J. Geotech. Eng. ASCE 109(3), 335–353 (1983) Panpan, G.: Study on influence mechanism and constitutive model of shear strength of fiber reinforced soil. Hefei University of Technology (2018) Da, H., Jili, Q.: Mechanical properties of cellulose fiber reinforced soil. J. Highw. Transp. Res. Dev. 35(1), 22-27+35 (2008)

Research Progress of Fiber Reinforced Soil

113

Xiaoqing, H., Liu, H., Guangli, X., Xin, Y., Guowu, J.: Effect of fiber content and length on strength of fiber reinforced soil. Saf. Environ. Eng. 22(2), 139–143 (2015) Jamei, M., Villard, P., Guiras, H.: Shear failure criterion based on experimental and modeling results for fiber-reinforced clay. Int. J. Geomech. 13(6), 882–893 (2013) Jewell, R.A., Wroth, C.P.: Direct shear tests on reinforced sand. Géotechnique 37(1), 53–68 (1987) Yuxin, J., Guangxin, L., Jiqin, Z.: New method for calculation of fiber reinforced soil. Eng. Mech. 16(3), 81–89 (1999) Yuxin, J., Nailong, W., Guangxin, L.: Improvement of equivalent additional stress method in reinforced soil calculation. Rock Soil Mech. 28(1), 129–132 (2007) Jouve, P., Bouzidi, R., Riou, Y.: Resolution of elastoplastic constitutive relations application to the fiber reinforced sand. Comput. Geotech. 17(3), 327–347 (1995) Kanchi, G.M., Neeraja, V.S., Babu, G.L.S.: Effect of anisotropy of fibers on the stress-strain response of fiber-reinforced soil. Int. J. Geomech. 15(1), 06014016.1–06014016.6 (2015) Kaniraj, S.R., Havanagi, V.G.: Behavior of cement-stabilized fiber-reinforced fly ash-soil mixtures. J. Geotech. Geoenvironmental Eng. 127(7), 574–584 (2001) Kumar, R., Kanaujia, V.K., Chandra, D.: Engineering behavior of fiber-reinforced pond ash and silty sand. Geosynth. Int. 6(6), 509–518 (1999) Guangxin, L., Lun, C., Jiqin, Z., et al.: Experimental study on fiber reinforced clay. J. Hydraul. Eng. 6, 31–36 (1995) Jian, L., Chaosheng, T., Deyin, W., Bin, S., Xiangjun, P.: Study on interface strength of corrugated fiber reinforced soil based on single fiber drawing test. Chin. J. Geotech. Eng. 36(09), 1696–1704 (2014) Jian, L.: Experimental study on tensile strength of fiber reinforced soil. Engineering geology committee of Chinese geological society. In: Proceedings of the ninth National Engineering Geology Congress. Engineering Geology Committee of Chinese Geological Society: Editorial Department of Engineering Geology, pp. 669–674 (2012) Xiulei, L., JinFeng, L., Jianyong, S.: Elastoplastic constitutive model of municipal solid waste soil with fiber reinforcement. Rock Soil Mech. 40(05), 1916–1924 (2019) Junwei, L., Yanping, Z., Jinpeng, H., Xin, L., Junjie, L.: Study on shear characteristics of fiber reinforced soil and structural interface under cyclic loading. Water Resour. Hydropower Eng. 51(01), 159–165 (2020) Zhi, L., Yong, Z., Bin, Z., Junshan, L., Jiheng, J.: Study on corrosion-resistance and UV-resistance of glass fiber/polyurethane composites. Polyurethane Ind. 35(1), 26–28 (2020) Machado, S.L., Carvalho, M.F., Vilar, O.M.: Constitutive model for municipal solid waste. J. Geotech. Geoenvironmental Eng. 128(11), 940–951 (2002) Maliakal, T., Thiyyakkandi, S.: Influence of randomly distributed coir fibers on shear strength of clay. Geotech. Geol. Eng. 31(2), 425–433 (2013) Masher, M.H., Gray, D.H.: Static response of sand reinforced with fibers. J. Geotech. Eng. ASCE 116(11), 1661–1677 (1990) ˇ Michalowski, R.L., Cermák, J.: Triaxial compression of sand reinforced with fibers. J. Geotech. Geoenvironmental Eng. 129(2), 125–136 (2003) Michalowski, R.L., Cermak, J.: Strength anisotropy of fiber-reinforced sand. Comput. Geotech. 29, 279–299 (2002) Michalowski, R.L.: Limit analysis with anisotropic fiber-reinforced soil. Géotechnique 58(6), 489–501 (2008) Michalowski, R.L., Zhao, A.: Failure of fiber-reinforced granular soils. J. Geotech. Eng. ASCE 122(3), 226–234 (1996) Michalowski, R.L.: Limit stress for granular composites reinforced with continuous filaments. J. Eng. Mech. 123(8), 852–859 (1997)

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Mirzababaei, M., Arulrajah, A., Horpibulsuk, S., et al.: Shear strength of a fibre-reinforced clay at large shear displacement when subjected to different stress histories. Geotext. Geomembr. 45(5), 422–429 (2017) Mirzababaei, M., Mohamed, M., Arulrajah, A., Horpibulsuk, S., Anggraini, V.: Practical approach to predict the shear strength of fibre-reinforced clay. Geosynth. Int. 25(1), 50–66 (2018) Neeraja, V.S., Manjari, K.G., Babu, G.L.S.: Numerical analysis of effect of orientation of fibers on stress-strain response of fiber reinforced soil. Int. J. Geotech. Eng. 8(3), 328–334 (2014) Prisco, C.D., Nova, R.: A constitutive model for soil reinforced by continuous threads. Geotext. Geomembr. 12(2), 161–178 (1993) Priyadarshee, A., Kumar, A., Sharma, V., Kumar, V.: A study on the influence of confining pressure on the behavior of fiber-reinforced soil. In: Agnihotri, A.K., Reddy, K., Bansal, A. (eds.) Sustainable Engineering. LNCE, vol. 30, pp. 293–301. Springer, Singapore (2019). https://doi. org/10.1007/978-981-13-6717-5_28 Ranjan, G., Vasan, R.M., Charan, H.D.: Probabilistic analysis of randomly distributed fiberreinforced soil. J. Geotech. Eng. ASCE 122(6), 419–426 (1996) Rybin, V.A., Utkin, A.V., Baklanova, N.I.: Corrosion of uncoated and oxide-coated basalt fibre in different alkaline media. Corros. Sci. 102, 503–509 (2016) Sivakumar Babu, G.L., Vasudevan, A.K.: Strength and stiffness response of coir fiber-reinforced tropical soil. J. Mater. Civ. Eng. 20(9), 571–577 (2008) Hao, S., Wenquan, F., Lei, Z., Fuquan, M., Yulong, H., Chunpeng, H.: Experimental study on the mechanical properties of different types of fiber reinforced soil. J. Chin. Foreign Highw. 37(03), 237–241 (2017) Park, T., Tan, S.A.: Enhanced performance of reinforced soil walls by the inclusion of short fiber. Geotext. Geomembr. 23(4), 348–361 (2004) Chaosheng, T.A.N.G., Bin, S.H.I., Yi, C.A.I., Wei, G.A.O., Fengjun, C.H.E.N.: Experimental study on soft soil reinforced by polypropylene fiber. Rock Soil Mech. 09, 1796–1800 (2007) Chaosheng, T., Bin, S., Wei, G., Yi, C., Jin, L.: Effect of sand content on the strength of polypropylene fibre-reinforced cohesive soil. Chin. J. Rock Mechan. Eng. S1, 2968–2973 (2007) Chaosheng, T., Bin, S., Wei, G., Jin, L.: Drawing test of single fiber in fiber reinforced soil and determination of critical reinforcement length. Rock Soil Mech. 30(08), 2225–2230 (2009) Chaosheng, T., Bin, S., Kai, G.: Microscopic study on the interfacial interaction between reinforcement and soil. J. Eng. Geol. 19(04), 610–614 (2011) Tang, C.-S., Jian, L., et al.: Tensile strength of fiber-reinforced soil. J. Mater. Civ. Eng. 28(7), 04016031 (2016) Tilak, B.V., Dutta, R.K., Mohanty, B.: Effect Of coir fibres on the compaction and unconfined compressive strength of bentonite-lime-gypsum mixture. Slovak J. Civ. Eng. 23(2), 1–8 (2015) Villard, P., Jouve, P., Riou, Y.: Modelissation du compertment mecanique du Texsol. Bull. Liaison Lab. 168, 15–27 (1990) Waldron, L.J.: Shear resistance of root-permeated homogeneous and stratified soil. Soil Sci. Soc. Am. Proc. 41, 843–849 (1977) Deyin, W., Chaosheng, T., Jian, L., Baosheng, L., Wei, T., Kun, Z.: Shear strength characteristics of fiber reinforced unsaturated cohesive soil. Chin. J. Geotech. Eng. 35(10), 1933–1940 (2013) Lei, W., Bin, Z., Junchao, L., et al.: A two-phase constitutive model for fiber reinforced soil. Chin. J. Geotech. Eng. 36(7), 1326–1333 (2014) Wang, M.C., Zhang, Z.G., Sun, Z.J., et al.: Corrosion resistance characteristic of continuous basalt fiber and its reinforcing composites. J. Beijing Univ. Aeronaut. Astronaut. 32(10), 1255–1258 (2006) Tao, W., Jun, W., Diyu, Z., et al.: Life prediction of glass-fiber reinforced plastics based on BP neural network under corrosion conditions. CIESC J. 70(12), 360–368 (2019) Wang, Y.X., Guo, P.P., Ren, W.X., et al.: Laboratory investigation on strength characteristics of expansive soil treated with jute fiber reinforcement. Int. J. Geomech. 17(11), 04017101 (2017)

Research Progress of Fiber Reinforced Soil

115

Jiling, W.: Fibre reinforced expansive soil strength and deformation characteristics research. Nanjing University of Aeronautics and Astronautics (2010) Yankai, W., Bin, N., Xiansong, S.: Experimental study on mechanical properties of randomly distributed sisal fiber reinforced soil. Hydrogeol. Eng. Geol. 39(06), 77–81 (2012) Shunren, X., Nixin, J., Yaoqiong, G., Caiyun, J., Chunxia, H.: Acid rain corrosion resistance of three colored eucalyptus/polyethylene wood plastic composites. J. Mater. Sci. Eng. 38(4), 674–679 (2020) Gong, X.-N., Kanghe, X.: Soil Mechanics, pp. 131–133. China Architecture & Building Press, Beijing (2014) Yetimoglu, T., Salbas, O.: A study on shear strength of sands reinforced with randomly distributed discrete fibers. Geotext. Geomembr. 21(2), 103–110 (2003) Wang, Y., Guo, P., Dai, F., Li, X., Zhao, Y., Liu, Y.: Behavior and modeling of fiber-reinforced clay under triaxial compression by combining the superposition method with the energy-based homogenization technique. Int. J. Geomech. 18(12), 04018172 (2018) Qiuxia, Y., Bin, L., Zongwen, L., et al.: Method for evaluating acid corrosion resistance of glass fibers. Fiber Glass (6), 7–13 (2015) Chengcheng, Z., Honghu, Z., Tang, C.-S., Bin, S.: Progressive failure model of fiber reinforced soil interface. J. Zhejiang Univ. Eng. Sci. 49(10), 1952–1959 (2015) Xiaojiang, Z., Keji, Z., Jingxing, Z.: Development of uniaxial static and dynamic tensile and compression test instrument and fracture characteristics test of fiber reinforced soil. Dam Obs. Geotech. Test 04, 37–40 (1997) Guofu, Z., Hao, S., Wenquan, F., Fuquan, M., Bin, Y.: Analysis of factors influencing unconfined compressive strength of different types of fiber soils. Shanxi Architect. 41(29), 47–49 (2015) Zhu, Y.T., Zong, G., Manthiram, A., et al.: Strength analysis of random short-fiber-reinforced metal matrix composite materials. J. Mater. Sci. 29(23), 6281–6286 (1994). https://doi.org/10. 1007/BF00354572 Zornberg, J.G.: Discrete framework for equilibrium analysis of fiber-reinforced soil. Géotechnique 52(8), 593–604 (2002)

Empirical Study of Warm Mix Asphalt Incorporating Recycled Asphalt Pavement Ronald Fabrice Pouokam Kamdem1(B) , Jacob Adedayo Adedeji2 , and Mohamed M. H. Mostafa3 1 Department of Civil Engineering, Central University of Technology, Bloemfontein 9301,

South Africa 2 Department of Civil Engineering, Durban University of Technology, Midland Campus,

Durban, Kwa-Zulu Natal, South Africa 3 Department of Civil Engineering, University of Kwa-Zulu Natal, Howard Campus, Durban,

Kwazulu Natal, South Africa [email protected]

Abstract. The depletion of natural resources along with the progressive change of climate due to high heat and harmful gas emission into the atmosphere are the concerns engineers, scientists and politicians have been addressing and cooperating toward finding efficient solutions to palliate to this global issue. Thus, the use of Warm Mix Asphalt (WMA) incorporating Recycled Asphalt Pavement (RAP) as part of a long-term solution has gained prominence in part of Europe, Asia and America and most recently in South Africa. Though the WMA–RAP possesses environmental benefits, yet it presents inconsistent mechanical performances related to many factors. Hence, this paper aims to evaluate the tensile strength, the rutting and the fatigue performance of WMA incorporating RAP, at 15% and 30%, and also to compare them against the performances of the traditional Hot Mix Asphalt (HMA). Consequently, laboratory experiments such as Indirect Tensile Strength (ITS), the Four-Point Beam Bending test and the Hamburg Wheel Tracking (were) carried out to evaluate the mechanical properties of the WMA–RAP. Results of the study show that, the control hot mix asphalt (HMACM) exhibits lower tensile strength and rutting performance than the WMA–RAP. As far as the fatigue cracking performance is concerned, the WMA (15% RAP) performs better than the HMA-CM and the WMA (30% RAP). Overall, the incorporation of RAP in the WMA at up to 30% may possess satisfactory mechanical performance and can be applied to the construction and the rehabilitation of medium traffic volume roads. Keywords: Warm mix asphalt · Recycled asphalt pavement · Hot mix asphalt · Fatigue cracking · Rutting failure · Indirect tensile strength

1 Introduction The crucial issues of global warming associated with the degradation of the natural resources have resulted in seeking alternative technologies, manufacturing, production © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 116–129, 2021. https://doi.org/10.1007/978-3-030-79638-9_10

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and construction techniques that are sustainable and safe to the environment (IPCC 2007). As far as, the pavement engineering industry is concerned, the introduction of warm mix asphalt incorporating recycled asphalt (WMA-RAP) to replace the traditional hot mix asphalt (HMA) has shown itself to be beneficial to the environment (Tao and Mallick 2009). Thus, the low energy consumption and emission at production, as well as, the reduction of the bitumen viscosity via the WMA additives are the environmental benefits the WMA offers (Gandhi and Amirkhanian 2007; Kandhal 2010; Ronald Fabrice et al. 2020). Gandhi and Amirkhanian (2007), Hurley and Prowell (2005) and Akisetty et al. (2009) add further advantages related to the utilisation of the WMA and these include the reduction of mixing temperature allowing longer haul distance, extended time for compaction in the cold season and the safer working condition. In addition, unlike the HMA, the WMA possesses higher workability property and therefore, can accommodate a higher amount of RAP (Dinis-Almeida et al. 2012). Overall, the incorporation of RAP in the WMA leads to more enormous benefits ranging from economic benefits to environmental benefits as the need for natural aggregates into the asphalt mix is reduced. Kheradmand et al. (2014) found that WMA incorporating RAP can possess similar or better mechanical performance than the HMA. Thus, this study aims to evaluate the tensile strength, the rutting performance and the fatigue cracking performance of the WMA incorporating RAP at 15% and 30% and therefore compare those performances against the HMA-CM containing only virgin aggregates. The study to evaluating and comparing the performances of the WMA–RAP against the HMA-CM was achieved through laboratory experiments which include comprehensive materials selection, mix design and fabrication of asphalt samples based on the Superpave design method and standard specifications. The laboratory experiment also includes performance tests such as the Four-Point Beam Bending test, the Hamburg Wheel Tracking test and the Indirect Tensile Strength test. These tests performed on the asphalt mix samples were based on the level II mix design that satisfies category B pavement structure (medium traffic volume of up to 10 million ESALs) forecasted to serve for 20 years. The mix designs, the production of asphalt samples and the performance tests were achieved following the South African, the Europeans and the American’s guidelines. The RAP used in the WMA was obtained from local deteriorated pavements. The dolerite used in the asphalt mixes as virgin aggregates were collected at the Lafarge Olivehill Crushers site in Bloemfontein. Furthermore, the Sasobit, which is a WMA organic additive, as well as the virgin 50/70 bitumen binder used in the asphalt mixtures, were obtained in Sasolburg.

2 Production of Asphalt Premix 2.1 Materials Selection and Grading Analysis The coarse dolerites particles (28 mm, 20 mm, 14 mm, and 10 mm), the fine dolerites particles (crusher dust), the fillers (lime) and the 50/70 grade bitumen were selected and used to design and produce the HMA-CM premix samples. Besides the coarse and fine particles of dolerite rocks, the lime and the virgin 50/70 grade bitumen, additional components which include the RAP and the Sasobit additive were used for the design and

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the production of the WMA–RAP premix samples. It should be noted that the amount of aged bitumen, extracted from 15% RAP and 30% RAP, was found to be 0.8% and 1.5% respectively. Table 1 shows the mix design percentages or the proportional representation of materials in the asphalt mixes. Table 1. Proportion representation of materials in the asphalt mix Agg size

Virgin aggregates

Filler RAP

28 mm

20 mm 14 mm 10 mm 7.1 mm C/DUST Lime Fine RAP

12.0%

12.5%

12.0%

8.5%

9.5%

44.0%

1.0% None

WMA (15% RAP) % Mix

5.0%

16.0%

10.0%

10.0%

43.0%

5.0%

1.0% 15%

WMA (30% RAP) % Mix

9.0%

16.0%

7.5%

7.5%

None

28.0%

1.0% 30%

HMA-CM % Mix

The gradation test was then carried out on the virgin aggregates and the virgin aggregates incorporating RAP to ensure that they are adequately distributed in the HMACM, the WMA (15% RAP) and the WMA (30% RAP). Inadequate distribution of the various sizes of aggregates in the fabricated asphalt mix samples may have adverse effects on its volumetric, Marshall and mechanical properties. Gradation tests performed on the virgin materials and the virgin materials mixed with RAP was achieved following the South African National Standard SANS 3001–AG1 (SANS 3001-AG1:2014 2014). The results of the gradation tests performed on the virgin aggregates materials, the virgin aggregates materials incorporating 15% RAP and 30% RAP were obtained and presented in Fig. 1. The upper limit and lower limit of the grading envelop represent the minimum and the maximum materials grading specification imposed by the SANS 3001–AG1. The SANS 3001–AG1 (2014) dictates that the curve of an ideal combined aggregates grading should not deviate the upper and the lower limit of the grading envelop. The results of the grading tests obtained on virgin aggregates and the virgin aggregates incorporating RAP exhibit adequate aggregates blending proportion as the curve of the combined aggregates grading falls within the grading envelop. Therefore, it implies that the HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) samples are expected to exhibit satisfactory volumetric properties and reliable mechanical performances. 2.2 Characterisation of Asphalt Premixes The HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) premixes were produced following the SANS 3001-AS11:2011 (2011) standard procedure. The HMA-CM and the WMA–RAP, produced at 150 °C and 120 °C respectively, were subjected to volumetric tests to determine: the binder content (BC); the void in the asphalt mix (VIM);

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Fig. 1. Grading curve and grading envelop: HMA-CM, WMA (15% RAP) and WMA (30% RAP)

the bulk density of the asphalt mix (BD); and the bulk density of aggregates (BDA). Other volumetric properties such as the air voids percent (Vv), the percent volume of the bitumen (VB), the volume of the aggregates (VA), the voids in mineral aggregates (VMA) and the percent voids filled with bitumen (VFB) were also determined. The characteristics of the HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) premixes were determined and reported in Table 2. The void in the control HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) was found to be 4%, 4.1% and 5.3% respectively. Sabita Manual 32, (2011) states that if a percentage of ±4.5% bitumen binder is used in the asphalt mix, the void in the mix (VIM) determined should not be lower than 4% and higher than 6%. Thus, HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) mixes fall within the asphalt design guideline specification. Furthermore, the voids in the mineral aggregates (VMA) as well as the voids filled with mineral aggregates (VFB), are reported to meet the requirements specified in the SANS 3001 AS11. In other words, the voids in the mineral aggregates found in HMACM, the WMA (15% RAP) and the WMA (30% RAP) is superior to 13% which according to the SANS 3001 meet the prescribed requirements. Also, the voids filled with mineral aggregates found in the HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) fall within the minimum 65% and the maximum 75%. This implies that the HMACM, the WMA (15% RAP) and WMA (30% RAP) meet the requirements indicated in SANS 3001 (SANS 3001 - AS10: 2011 2011; SANS 3001-AS11:2011 2011; SANS 3001-AS20:2011 2011; SANS 3001-AG1:2014 2014).

MVB (Kg/3 )

%BC

4.6

4.6

4.7

Type of mix

HMA-CM

WMA (15% RAP)

WMA (30% RAP)

2723

2732.8

2751.6

SANS 3001 AS11

Test methods SANS 3001 AS20

2938

2938 5.3

4.1

4.0

%VIM

BDA (Kg/3 )

2938

SANS 3001 AS11

SANS 3001 AG1

16.1

14.3

17.2

%VMA

SANS 3001 AS11

319.6

328.9

342.9

VA (cm3 )

SANS 3001 AS11

42.1

42.3

44.09

VB (cm3 )

SANS 3001 AS11

360.7

369.5

382.6

VDA (cm3 )

SANS 3001 AS11

Table 2. Properties of the HMA-CM and the WMA–RAP premixes

10.6

6.4

11.5

VBEF (cm3 )

SANS 3001 AS11

65.8

44.8

66.9

%VFB

SANS 3001 AS11

2579.3

2631.2

2543

BD (Kg/3 )

SANS 3001 AS10

120 R. F. P. Kamdem et al.

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2.3 Production and Preparation of Asphalt Mix Samples The fabrication of the HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) samples were undertaken while targeting air void between 4% and 6% recommended in Sabita Manual 35, (2014). The WMA (15% RAP) and the WMA (30% RAP) were mixed at 120 °C and the HMA-CM at 150 °C. The produced asphalt premixes were subjected to short term ageing in the oven during ±4 h at 110 °C for the WMA (15% RAP) and the WMA (30% RAP) and at 140 °C for the HMA-CM samples. The aged asphalt premixes intended for the fabrication of rutting test samples were immediately compacted in the Superpave Gyratory Compactor machine to produce cylindrical samples measuring 150 mm in diameter and 60 mm in thickness. Afterward, each cylindrical asphalt samples were sawn on one side to allow them to fit into a set of two high-density mould adaptors installed into the Hamburg Wheel Tracking machine. The asphalt mix samples intended for fatigue cracking performance test were fabricated using the Superpave Slab Compactor machine which produces slabs samples measuring 300 mm wide, 400 mm long and 70 mm thick. Thereafter, the asphalt slabs samples (300 × 400 × 70) were cut into four beams and carefully sawn to obtain beams with final dimensions of 65 mm wide, 400 mm long and 50 mm thick enabling them to be installed into the Four–Point Beam Bending machine. As far as the fabrication of asphalt mix samples aimed for the ITS test is concerned, the asphalt premixes were poured into a preheated cylindrical mould (100 °C) and immediately compacted using a Marshall Compactor machine. The fabricated cylindrical briquettes samples with dimensions 101.5 mm in diameter and 66 mm in thickness were compacted at 75 blows count to account for medium volume traffic.

3 Empirical Performance Tests 3.1 Indirect Tensile Strength Test (ITS) The indirect tensile strength (ITS) test was performed on the HMA-CM, the WMA (15% RAP) and WMA (30% RAP) to determine their tensile strength. The tensile strength of an asphalt mix is directly related to the fatigue cracking performance of that asphalt mix. In other words, a higher tensile strength is an indication which predicts higher resistance against cracking failure of the asphalt mix. The ITS tests were performed on the asphalt mix samples following the SANS 3001 - AS10: 2011 (2011). The compaction of specimens at 140 °C for the HMA-CM and 110 °C for the WMA (15% RAP) and the WMA (30% RAP) were achieved using a Marshall Drop Hammer weighting 4536 g, dropped at the constant height of 457.2 mm on each face of the specimens. The specimens subjected to a total number of 75 blows to account for the designed traffic load were conditioned at 25 °C in an oven before being subjected to loading in the Marshall Compression testing machine. The data entered in Table 3 are the dimensions of the asphalt mix samples and the recorded maximum loads causing the failure of the HMA-CM, the WMA (15% RAP) and the WMA (30% RAP). Those data were used as a variable in Eq. (1) to determine the indirect tensile strength of asphalt mixes. ITS =

2P π.L.∅

(Equation 1)

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ITS = Indirect tensile strength (KPa) P = Load causing failure (KN) L = thickness of the specimen (mm) Ø = diameter of the specimen (mm)

Table 3. Variables used for the determination of the indirect tensile strength Type of mix

Number of samples

Diameter of samples (mm)

Thickness of samples (mm)

Maximum load to failure (KN)

HMA-CM

1

101.5

63.5

14.3

2

101.5

63.0

13.3

3

101.5

62.4

13.4

4

101.5

63.1

12.7

1

101.5

63.1

16.5

2

101.5

62.9

15.4

3

101.5

63

17.3

4

101.5

63.2

16.4

1

101.5

63.2

16.7

2

101.5

63.0

17.6

3

101.5

64.7

13.6

4

101.5

62.8

15.9

WMA (15% RAP)

WMA (30% RAP)

3.2 Indirect Tensile Strength Results Analysis The ITS of the HMA-CM, the WMA (15% RAP) and the WMA (30% RAP) were determined and presented in Table 4. The Sabita Manual 32, (2011) specifies that an asphalt mix should be above 1000 kPa to be accepted in term of indirect tensile strength. Thus, the ITS results of the asphalt mixes in Table 4 were found to be satisfactory based on the design specification. Figure 2 shows the ITS performance of the HMA-CM against the WMA (15% RAP) and the WMA (30% RAP). It can be observed from Fig. 2 that, the HMA-CM exhibits lower tensile strength than the WMA (15% RAP) and the WMA (30% RAP). The higher stiffness strength of the WMA–RAP over the HMA-CM, predicts their ability to resist fatigue cracking better than the HMA-CM. It is, moreover, observed on Fig. 2 that the ITS of WMA–RAP is reduced with an increased amount of RAP in the WMA as the WMA (15% RAP) exhibit higher tensile strength than the WMA (30% RAP). Thus, this implies that an increased percentage of RAP in the WMA can negatively affect its stiffness performance.

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Table 4. Indirect tensile strength test results Type of mix

ITS (KPa)

Ave. ITS (KPa)

HMA-CM

1412

1324.11

WMA (15% RAP)

1642.7

1535.62

WMA (30% RAP)

1657.35

1747.23

1346.89

1262.37

1336.34

1722.34

1627.57

1632.05

1317.44

1589.0

1577.75

Fig. 2. Indirect tensile strength: HMA-CM versus WMA–RAP

3.3 Hamburg Wheel Tracking Test The permanent deformation was simulated using the Hamburg Wheel Tracking machine to evaluate the capacity of the WMA (15% RAP) and the WMA (30% RAP) to resist rutting failure and then compare their rutting performances against the HMA-CM ones. The Hamburg Wheel Tracking test was performed following the AASTHO-T324 test procedures. The set of high-density mould adaptors containing the sawn asphalt mix samples were mounted and adequately fitted into the trays. The mounting trays were fastened into the Wheel Tracking machine containing a water bath preheated at 50 °C. Table 5 contains the diameter, the thickness, the compaction type, the bulk density and

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the void of the asphalt mix samples used as input data in the computer equipping the Wheel Tracking machine. The test was allowed to commence and was ended when failure has occurred. It is worthy to note that the properties which include the air voids determined in the WMA (15% RAP), WMA (15% RAP) and the HMA-CM samples were verified to ensure that the requirements specified in the Sabita Manual 32 (2011) to perform the Hamburg Wheel Tracking test are met. Table 5. Characteristics of the asphalt mix samples for the Hamburg wheel tracking test Type of mix

HMA-CM

WMA (15% RAP)

WMA (30% RAP)

Diameter (mm)

150

150

150

Thickness (mm)

60

60

60

Max density (Kg/m3 )

2512

2512

2490

Void in the mix (%)

4.0

4.1

4.8

Compaction type

Superpave gyratory

Superpave gyratory

Superpave gyratory

Water temperature (°C)

50

50

50

Max load cycle

1000

1000

1000

Wheel speed (Cycle/min)

26

26

26

3.4 Hamburg Wheel Tracking Test Results Analysis Figure 3 presents the typical rut depth of the WMA (15% RAP) and the WMA (30% RAP) against the HMA-CM when the load cycles reach 1000 passes. The observation made from Fig. 3 shows that the rut depths of the HMA-CM are higher than the WMA (15% RAP) and the WMA (30% RAP). This signifies a better rutting performance of the WMA (15% RAP) and the WMA (30% RAP) over the HMA-CM when the load cycles gradually increase. Past empirical studies conducted on the WMA alone have shown that the WMA usually has lower rutting performance than the traditional HMA. However, the finding made in this study is the experimental evidence that the rutting performance of the WMA can be improved and can even surpass the rutting performance of the traditional HMA if the RAP is added into the WMA. Further observations show that the WMA (15% RAP) has better rutting resistance when compared to the WMA (30% RAP). This implies that, though the addition of RAP into WMA may improve its resistance against rutting failure, yet it can slightly lower the rutting performance of the WMA with a significantly increased amount of RAP. 3.5 Four-Point Beam Bending Test The fatigue cracking failure of pavements in service occurs as a result of the repeated number of applied loads exceeding the allowable tensile strains of the asphalt mix (Sabita Manual 35, 2014). In this study, the Four-Point Beam Bending test was performed to

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Fig. 3. Rutting results: HMA-CM versus WMA–RAP

evaluate the fracture resistance of the WMA (15% RAP), the WMA (30% RAP) and therefore compare them against the HMA-CM and these using the Four-Point Bending machine. The Four-Point Beam Bending test was performed following the AASHTO-T321 test procedure. Thus, Table 6 shows the characteristics of the HMA-CM samples, the WMA (15% RAP) and the WMA (30% RAP) samples mainly needed not only to verify their suitability for the Four-Point Beam Bending test but also to use them as additional input data. The air void in the WMA (15% RAP), the WMA (30% RAP) samples and the HMA-CM sample were found to lie between 4%–6% air void. This indicates that the WMA (15% RAP), the WMA (30% RAP) and the HMA-CM samples meet the requirements imposed for the Four-Point Beam Bending test. The fatigue life of the WMA (15% RAP), the WMA (30% RAP) and of the HMACM beam samples were determined by allowing the repetition of the loading cycle to continue until the stiffness of the asphalt beam was reduced to 50% of the initial stiffness and when the first 50th load cycle was reached. The test was conducted with two variations of strain which include 200 µ1 and 400 µ1 at 20 °C and the frequency of 10 Hz was set to rest during a period of 10 s load time pulse. 3.6 Four-Point Beam Bending Test Results Analysis Table 7 and Table 8 present a summary of various conditions under which of the Four– Point Beam Bending tests were performed and a series of results obtained at 200 µ1 and at 400 µ1. AASHTO 321 defines the fatigue cracking as a 40% reduction of the initial stiffness measured at the first 50th cycle of loading. Based on this fundamental definition,

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R. F. P. Kamdem et al. Table 6. Characteristics of the asphalt mix samples for the four-point beam

Type of mix

HMA-CM

WMA (15% RAP)

WMA (30% RAP)

Description

Beam 1

Beam 2

Beam 1

Beam 2

Beam 1

Beam 2

Width (mm) Height (mm)

62

62

62

62

62

62

48

48

48

48

48

48

Length (mm)

380

380

380

380

380

380

Density (kg/m3 )

2463.8

2462.8

2456

2421

2430

2438

Void in the mix (%)

3.6

3.6

4.0

5.2

5.0

4.6

the results of the Four–Points Beam Bending tests plot in Fig. 4 show that the HMA-CM has the lowest fatigue cracking performance compared to the WMA (15% RAP) and the WMA (30% RAP) when tested at 200 µ1. However, the HMA-CM presents lower fatigue performances than the WMA (15% RAP) in one hand, but on the other hand, it presents a higher but very close fatigue performance to the WMA (30% RAP) when tested at 400 µ1. This indicates that the addition of RAP in the WMA prepared and produced in the same conditions reduces the fatigue life of the WMA technology. Table 7. Four-point beam bending test conditions and results at 200 µ1 Type of mix

HMA-CM

WMA (15% RAP)

WMA (30% RAP)

Description

Initial

Current

Initial

Current

Initial

Current

Load applied (KN)

0.5630

0.2811

1.531

0.762

1.354

0.676

Beam deflection (mm)

0.1108

0.1104

0.112

0.112

0.111

0.111

Phase angle (Deg)

10.9

15.6

8.5

17.0

9.0

9.1

Loading cycle 4 × 106 count

92570

4 × 106

844060

4 × 106

400000

Flexural stiffness (MPa)

12009

6021

18645

9318

16955

8461

Peak to peak stress (KPa)

2407

1203

3749

1865

3391

1693

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Table 8. Four-point beam bending test conditions and results at 400 µ1 Type of mix

HMA-CM

WMA (15% RAP)

WMA (30% RAP)

Description

Initial

Current

Initial

Current

Initial

Current

Load applied (KN)

1.8584

0.9311

2.482

1.235

1.772

0.86

Beam deflection (mm)

0.2220

0.2210

0.220

0.219

0.222

0.222

Phase angle (Deg)

11.4

22.6

11.2

15.2

11.1

15.1

Loading cycle 4 × 106 count

1870

4 × 106

18500

4 × 106

12160

Flexural stiffness (MPa)

11199

5631

14709

7354

10417

5213

Peak to peak stress (KPa)

4498

2252

5930

2942

4174

2082

Fig. 4. Fatigue cracking resistance: HMA-CM versus WMA–RAP

4 Conclusions The study attempts to evaluate the structural strength of WMA partially incorporating RAP over HMA using the laboratory experiments. Thus, indirect tensile strength, the rutting and the fatigue cracking performance of the WMA (15% RAP) and the WMA (30% RAP) and therefore compare them against HMA-CM. Furthermore, the laboratory work includes the selection of materials; the aggregates mix design; the materials grading tests; the production of asphalt premixes; the characterisation of the asphalt premixes; and the fabrication of asphalt samples. All of the procedures were conducted using the Superpave testing methods and other standard procedures.

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The result obtained reveals a stronger tensile strength and rutting resistance of the WMA (15% RAP) and the WMA (30% RAP) samples against the HMA-CM. This implies that the incorporation of RAP into the warm mix has the potential to improve its tensile strength and rutting performance, and this study result is in agreement with findings by Zaumanis (2010). As far as the fatigue cracking performance is concerned, the result shows that the WMA (15% RAP) and the WMA (30% RAP) perform better when compared to the HMA-CM at 200 µ1. Though at 400 µ1 the WMA (15% RAP) maintains its higher rutting performance over the HMA-CM, the WMA (30% RAP) loses it, just as highlighted by Sengoz et al. (2017). Nevertheless, according to Xiao and Amirkhanian (2010) the use of 15% RAP in the asphalt mix increases its stiffness; however, it can consequently leads to reducing its resistance to fatigue cracking failure. General analysis of the test results indicates a satisfactory tensile strength, rutting and fatigue cracking performance of the WMA (15% RAP) and the WMA (30% RAP) over the HMA-CM. However, the performance of the WMA tends to worsen when the amount of RAP, presents into the WMA, increases. The gradual reduction in the performance of the WMA, when the RAP increases, is explained by the fact that the dosage of the Sasobit organic additive into the warm mix incorporating recycled asphalt was based on the amount of virgin bitumen binder rather than the amount of recycled asphalt presents in the warm mix. Overall, the incorporation of RAP at 15% and 30% into the WMA has revealed satisfactory performances and can, therefore, be used for the construction, the maintenance and the rehabilitation of medium-traffic volume flexible roads. Further studies could be carried out on the optimum dosage of Sasobit organic additives needed to improve the performance of WMA incorporating RAP at 30% and above.

References Akisetty, C.K., Lee, S.-J., Amirkhanian, S.N.: Effects of compaction temperature on volumetric properties of rubberized mixes containing warm-mix additives. J. Mater. Civ. Eng. 21(8), 409– 415 (2009). https://doi.org/10.1061/(ASCE)0899-1561(2009)21:8(409) Dinis-Almeida, M., Castro-Gomes, J., Antunes, M.D.L.: Mix design considerations for warm mix recycled asphalt with bitumen emulsion. Constr. Build. Mater. 28, 687–693 (2012). https://doi. org/10.1016/j.conbuildmat.2011.10.053 Gandhi, T.S., Amirkhanian, S.N.: Laboratory investigation of warm asphalt binder properties - a preliminary analysis. In: Proceedings of the 5th International Conference on Maintenance and Rehabilitation of Pavements and Technological Control, MAIREPAV 2007 (2007) Hurley, G.C., Prowell, B.D.: Evaluation of Sasobit for Use in Warm Mix Asphalt, NCAT Report 05-06 (2005) IPCC, The Intergovernmental Panel on Climate Change 2007: Climate Change 2007 - The Physical Science Basis: Working Group I Contribution to the Fourth Assessment Report of the IPCC (October 2009) Kandhal, P.: Warm mix asphalt technologies: an overview. J. Indian Roads Congr. 71(2), 1–21 (2010) Kheradmand, B., Muniandy, R., Hua, L.T., Bt, R., Yunus, A.S.: An overview of the emerging warm mix asphalt technology. Int. J. Pavement Eng. 15(1), 79–94 (2014). https://doi.org/10. 1080/10298436.2013.839791

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Ronald Fabrice, P.K., et al.: Evaluating the performance of warm mix asphalt incorporating recycled asphalt pavement treated bases. Transp. Res. Procedia 45, 716–723 (2020). https://doi.org/ 10.1016/j.trpro.2020.02.106 Sabita Manual 32: Best Practice Guideline for Warm Mix Asphalt. Sabita, Cape Town (2011). http://www.sabita.co.za/wp-content/uploads/2017/08/Download-for-Manual-32.pdf Sabita Manual 35: Design and Use of Asphalt Road Pavements. Sabita, Cape Town (2014). http:// www.sabita.co.za/wp-content/uploads/2019/02/Sabita-asphalt-manual-35-TRH8-2019.pdf SANS 3001-AG1:2014: Civil Engineering Test Methods – Part AG1: Particle Size Analysis of Aggregates by Sieving. SABS, Pretoria (2014). https://store.sabs.co.za/pdfpreview.php?hash= 298d926aff49f51b02d8d05374c0cda36bbc135b&preview=yes SANS 3001-AS11:2011: Civil Engineering Test Methods – Part AS11: Determination of the Maximum Void-less Density of Asphalt Mixes and the Quantity of Binder Absorbed by the Aggregate. SABS, Pretoria (2011). https://store.sabs.co.za/pdfpreview.php?hash=6b007293d 590bb058b50bb8c8a91a9508c0b1c39&preview=yes SANS 3001-AS20:2011: Civil Engineering Test Methods – Part AS20: Determination of the Soluble Binder Content and Particle Size Analysis of an Asphalt Mix. SABS, Pretoria (2011). https://store.sabs.co.za/pdfpreview.php?hash=2172017708aca8e61bd81da0d667a4 15a2b1f783&preview=yes SANS 3001 - AS10: 2011: Civil Engineering Test Methods – Part AS10: Determination of Bulk Density and Void Content of Compacted Asphalt. SABS, Pretoria (2011). https://store.sabs.co. za/pdfpreview.php?hash=643fdd579c051fabb5cd69021c2f9e9f3f1800b8&preview=yes Sengoz, B., Topal, A., Oner, J., Yilmaz, M., Dokandari, P.A., Kok, B.V.: Performance evaluation of warm mix asphalt mixtures with recycled asphalt pavement. Periodica Polytech. Civ. Eng. 61(1), 117–127 (2016). https://doi.org/10.3311/PPci.8498 Tao, M., Mallick, R.B.: Effects of warm-mix asphalt additives on workability and mechanical properties of reclaimed asphalt pavement material. Transp. Res. Rec. J. Transp. Res. Board 2126(1), 151–160 (2009). https://doi.org/10.3141/2126-18 Xiao, F., Amirkhanian, S.N.: Effects of liquid antistrip additives on rheology and moisture susceptibility of water bearing warm mixtures. Constr. Build. Mater. 24(9), 1649–1655 (2010). https://doi.org/10.1016/j.conbuildmat.2010.02.027 Zaumanis, M.: Warm mix asphalt Investigation. Technical University of Denmark (2010). http:// www.warmmixasphalt.org/submissions/117_20100630_M.Zaumanis_WMA_Master_thesis. pdf

A Feasibility Study Towards the Application of Municipal Waste Pyrolysis Oil in Bituminous Pavement Swanand B. Kulkarni(B) and Mahadeo S. Ranadive Department of Civil Engineering, College of Engineering, Pune, MS, India

Abstract. In the search of modified bitumen in bituminous pavement, the feasibility of mixing pyrolysis oil of municipal solid waste into bitumen was examined to find an efficient, cost-effective and environmental friendly substitute. In case of addition of pyro-oil of low-density polyethylene municipal plastic waste by 5%, 7.5% and 10% into viscosity grade 30 (VG30) bitumen, considerable deviations in basic properties of bitumen were found. The physical and chemical characteristics of pyro-oil were determined and compared with the characteristics of bitumen and fuel oil. The average gross calorific value (GCV) of pyro-oil was found to be 10745 kcal/kg, which is very close to GCV of diesel 10800 kcal/kg. The other values, too, were within the range of the properties of diesel. Hence pyro-oil is a better substitute for diesel. The chemical characteristics such as Fourier-transform infrared spectra (FTIR) of pyro-oil were found to be similar to those of bitumen, which proves that blending of pyro-oil into bitumen is feasible. The cutback bitumen is being manufactured by mixing fuel in bitumen of penetration grade 80–100 and is used as tack coat in bituminous pavement. Therefore, pyro-oil can be considered as a substitute for diesel in cutback bitumen to prepare modified cutback bitumen. Keywords: Municipal plastic waste · Bituminous pavement · Calorific value · Carbon black · Modified cutback bitumen · Pyro-oil

1 Introduction Bitumen is a petroleum-based material and used as a binder in flexible pavement, but it has a severe adverse impact on the environment and living beings. The stock of petroleum is limited, petroleum prices are continuously increasing. Therefore, researchers are trying to find efficient and cost-effective modified bitumen. Over the years, bio-renewable natural resources including sugars, triglyceride oils, and proteins have been tested as alternative sources for producing adhesives and binders (Airey and Musarrat 2008). Municipal solid waste (MSW) is one of the major environmental problems of Indian cities. Improper management of MSW causes hazards to inhabitants. Various studies reveal that about 90% of MSW is disposed off unscientifically in open dumps and landfills, creating problems to public health and the environment (Mufeed et al. 2008). As per earlier researches, it is noticed that bio-oil extruded from biomass i.e. from switch © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 Z. Hossain et al. (Eds.): GeoChina 2021, SUCI, pp. 130–147, 2021. https://doi.org/10.1007/978-3-030-79638-9_11

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grass, oak wood, and corn stover is a renewable source of fuel from bioconversion that can be blended into the conventional bitumen as a modified binder (Raouf et al. 2010). Pyrolysis is an important thermo-chemical route, becoming an increasingly popular option for the disposal of municipal solid waste. In this method, thermal decomposition is achieved in the absence of oxygen. The bio-oil is produced along with carbon black (solid char) and uncondensed gas. The bio-oil obtained from pyrolysis of municipal solid waste can be utilized as a bio-binder in flexible pavement. Carbon black can be used to produce activated carbon and to reinforce fillers in plastic and rubber goods, as well as in the ceramic brick industry. Gaseous products can be used for heating purpose in boilers as well as in generators for the generation of electricity. Thus, problematic waste is completely converted into usable products. The oil obtained from pyrolysis of MSW is called bio-oil, whereas the oil obtained from municipal plastic waste is called pyro-oil. Figure 1 shows the flow diagram of the pyrolysis process for the conversion of MSW and municipal plastic waste into bio-oil or pyro-oil.

Fig. 1. Flow chart of Pyrolysis of Municipal Solid Waste.

Currently, the state of the art for the utilization of bio-oils is concentrated on its uses as bio-renewable fuels to replace fossil fuels (Peralta et al. 2012). Plastic wastes do not biodegrade in landfills, are not easily recycled, and degrade in quality during the recycling process (Pawar and Lawankar 2013). Instead of biodegradation, plastics waste goes through photo-degradation and turns into plastic dust which can enter the food chain and can cause complex health issues to earth habitats through the thermal treatment on the plastic waste the fuel can be derived. (Pawar and Lawankar 2013). By adopting the chemical process such as pyrolysis, plastic waste can be safely converted

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into hydrocarbon fuels and used for transportation (Pawar and Lawankar 2013). The bio-oil is a viscoelastic material, and after heat treatment, it has a viscosity similar to many types of asphalt used in the paving industry (Peralta et al. 2013). However, until now, almost no research has studied the applicability of utilizing bio-oils as a partial or full replacement alternative of bitumen in the pavement industry (Tayh et al. 2014). In this paper, it is proposed to use the bio-oil obtained by pyrolysis of MSW in flexible pavement, in various percentages, and to examine its effectiveness. Municipal plastic waste is the most important ingredient of MSW. It is non-biodegradable, and it creates extensive environmental pollution. Therefore, the pyrolysis of municipal plastic waste, particularly polypropylene (PP) and low-density polyethylene (LDPE), was carried out. The preliminary characteristics of modified bitumen prepared by blending of pyro-oil into VG30 were studied, as well as the physical and chemical characteristics of pyro-oil were examined to study the feasibility of blending it into bitumen.

2 Background The research activities for finding an alternative binder for bitumen in flexible pavement are noteworthy. It is found that the pyrolysis of MSW may be a future potential alternative source of liquid hydrocarbon fuels and chemical compounds feedstock (Islam et al. 2010). The bio-oil can be developed so that it can be best utilized as a bio binder by developing its procedure of heat pre-treatment, superpave specifications, determining temperature range, comparing the rheological properties of bitumen binder (Raouf et al. 2010). Researchers have confirmed that bio binder produced from biomass, specifically swine manure, is a promising candidate to be used as an alternative for asphalt binder (Fini et al. 2011). It was found that the addition of bio binder to base binder can improve the base binder’s low-temperature properties while improving its workability (Fini et al. 2011). The carbonization process of yard waste was carried out to explore the basic feasibility of recovering sufficient bitumen to support the production of bio asphalt (Daniel et al. 2011). The usage of bio-oil and waste cooking oil can bring a breakthrough result in the field of roads and highway construction material. The results exhibit very close similarity as bitumen in a mixture (Maniruzzaman et al. 2016). Using a bio-oil modified binder in asphalt pavements could also reduce mixing time, compaction temperatures, ageing and stiffening characteristics of the reclaimed asphalt pavements (RAPs) and virgin binders (Ramana et al. 2015). Yang et al. (2014) conducted experiments in a pilot-scale pyrolysis system and all products of palletized wood and barley straw were collected and analyzed. The liquid products were separated into an aqueous phase and an organic phase (pyrolysis oil) under gravity. The oil yields were 34.1% and 12.0% for wood and barley straw, respectively (Yang et al. 2014). By adopting this technology, municipal plastic waste is efficiently converted into 65% of useful liquid hydrocarbon fuels without emitting many pollutant. Engine tests carried out with plastic liquid fuel blends which are obtained from the pyrolysis of municipal plastic waste (Divakar Shetty et al. 2016).

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Recycling via pyrolysis is one of the promising methods for recycling plastic waste and involves thermochemical decomposition of organic and synthetic materials at elevated temperatures in the absence of oxygen to produce fuels. The process is usually conducted at higher temperatures between 500 °C–800 °C (Olufemi and Olagboye 2017). The Fourier transform infra-red (FTIR) test was conducted for MSW bio-oil. The FTIR spectra show aliphatic carboxylic acids and aliphatic hydrocarbon groups and the peaks are matching with the peaks of FTIR spectra of bitumen (Kulkarni and Ranadive 2018). Also, these groups are present in the chemical composition of bitumen. Therefore the MSW bio-oil can be considered for partial replacement of bitumen (Kulkarni and Ranadive 2018). It is observed that bitumen modified by pyro-oil of HDPE plastic waste, has more surface free energy than base bitumen (Khapne et al. 2020). There is hardly research available on the application of pyro-oil of LDPE plastic waste in the construction of flexible pavement. In this paper, attempts are made to study the feasibility of pyro-oil to prepare modified bitumen to be used in bituminous pavement.

3 Materials and Methods A pilot model of pyrolysis was set up at the College of Engineering Pune, India. (Kulkarni and Ranadive 2020). Various samples of MSW were segregated and processed for pyrolysis. The maximum quantity of pyro-oil obtained from different types of wastes was recorded. 3.1 Experimental Setup A laboratory-scale externally heated fixed-bed pyrolysis batch reactor of a capacity of 10 kg was prepared for pyrolysis of MSW at the College of Engineering, Pune (India). The main components of the pilot pyrolysis plant are the reactor, agitator inside the reactor, vapor pipeline, condenser, and receiver, oil collecting tap, heating coil, insulation, temperature sensor, pump, motor and gearbox, and control panel. Figure 2 shows the pilot pyrolysis plant installed at laboratory (Kulkarni and Ranadive 2020). This pilot pyrolysis plant is prepared exclusively for research into the pyrolysis of municipal solid waste and its effective utilization in flexible pavement. The reactor could be heated electrically to a maximum of 800 °C. This is the external body temperature of the reactor. The inside temperature of the reactor reaches a maximum of 325 °C, whereas the maximum vapour line temperature observed up to a maximum of 225 °C. The yield of bio-oil of MSW obtained was around 30% to 50% of the feedstock waste depending on its quality and pyrolysis temperature. The uncondensed gas was released and allowed to be mixed in water, and the carbon black was collected from the reactor after completion of the reaction and pyrolysis process cycle. 3.2 Pyrolysis of MSW and Municipal Plastic Waste The different samples of MSW were collected from Karad city, India. MSW contains organic waste, plastic waste, paper waste, and textile waste. The samples were dried in air and then segregated. The average proportions of organic waste, plastic waste,

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Fig. 2. Pilot pyrolysis plant

textile waste, and paper waste were found to be 69.86%, 9.74%, 8.98%, and 10.51%, respectively. The organic waste had a major contribution to MSW; it disintegrates easily, and can be converted into good manure by a composting method. Paper waste can also be recycled. In MSW, three categories of plastic waste were found. The household substances contain items such as coconut oil bottles, detergent, bleach and fabric conditioner bottles, snacks food boxes and cereal box liners, milk and non-carbonated drinks bottles, toys and buckets of plastic which fall into the category high-density polyethylene (HDPE). The category of low-density polyethylene (LDPE) consists of carry bags, milk bags, and grain storage plastic bags, etc. The category of polypropylene (PP) comprises bottle tops of ketcup and syrup bottles, yogurt and some margarine containers, potato crisp bags, biscuit wrappers, stationery plastic folders, and food pouches with metallic flickering coatings inside, etc. HDPE plastic waste can easily be segregated and taken out for recycling. PP plastic wastes, especially pouches, can’t be processed in a pyrolysis plant because of their metallic coatings. The rest of the plastic waste is LDPE. The environmental pollution issues arise due to LDPE mixed in MSW. Therefore, our study is focused on LDPE plastic waste. The plastic used in this study was milk bags, oil packing bags, and carry -bags, among others, segregated from MSW. This municipal plastic waste was dried in air and then cleaned. It was further cut into small pieces of about 100 mm to 150 mm using scissors. The pyrolysis was carried out for the combined MSW as well as for the different ingredients of MSW such as organic waste, plastic waste (LDPE, HDPE, and PP), and textile waste by using pilot pyrolysis plant The catalyst scolecite (zeolite), at 5% of the weight of the waste material, was fed to the reactor. Nitrogen purging was performed intermittently to remove oxygen from the reactor. Various 28 samples of MSW were processed through pyrolysis as shown in Table 1. The output of pyro-oil derived from various types of wastes such as combined MSW (mixed all ingredients of MSW without segregation), organic waste, textile waste, PP

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plastic waste, LDPE plastic waste, and HDPE plastic waste are shown in Table 1 and it was found that the maximum outputs of pyro-oil were 32.91%, 42.72%, 29.39%, 41.85%, 57.8%, and 34.02% respectively. The output of LDPE waste was comparatively higher. The physical properties of bio-oil of MSW were studied. Due to the higher water content in bio-oil of MSW, important characteristics such as kinematic viscosity and the flash point could not be determined (Kulkarni and Ranadive 2018). These are the important characteristics to be compared to examine the feasibility of applying bio-oil in bituminous pavement (Kulkarni and Ranadive 2018). The FTIR spectra show aliphatic carboxylic acids and aliphatic hydrocarbon groups, and the peaks match the peaks of the FTIR spectra of bitumen (Kulkarni and Ranadive 2018). Also, these groups are present in the chemical composition of bitumen. Therefore, MSW bio-oil can be considered a partial replacement for bitumen (Kulkarni and Ranadive 2018). The relatively high viscosity and reduced viscosity after aging of MSW pyrolysis oil has indicated its potential for application as a substitute of the light fraction in the bitumen for road construction (Yang et al. 2018). In this paper, the study concentrated on pyro-oil of LDPE plastic waste of 11 samples. It was observed that pyro-oil generation was around 40% to 45% of the waste processed, carbon black generation was around 25% to 30%, whereas the remaining approximately 30% was uncondensed gas released from the outlet. The average maximum external temperature of the reactor was observed to be around 600 °C. The uncondensed gas was allowed to mix in water to avoid air pollution in the surrounding area. The gas can be collected in a balloon and then reused for initial heating of the pyrolysis plant. The behavior of pyro-oil obtained from pyrolysis of municipal plastic waste was studied. The pyro-oil obtained from LDPE plastic waste was blended in proportions 5%, 7.5% and 10% into VG30, and pyro-oil of PP waste was blended in proportion 10% into VG30, to prepare modified bitumen. Two different samples of VG30 were used for the experiment. Preliminary tests to determine the characteristics of modified bitumen, such as penetration, ductility, flash point, softening point, and kinematic viscosity, were performed to examine feasibility.

4 Result and Discussion In this section, the test results of modified bitumen are discussed. Moreover, the physical characteristics of pyro-oil of municipal plastic were compared with those of fuel, and the chemical characteristics of pyro-oil were compared with those of bitumen. The physical characteristics of carbon black powder generated through pyrolysis of municipal plastic waste were determined. The application of pyro-oil and carbon black is discussed in light of the results. 4.1 Test Results of Modified Bitumen The experiments were conducted by mixing pyro-oil of LDPE plastic waste and PP plastic waste in different proportions into VG30 to examine feasibility. Important Preliminary tests were conducted, and the results are compared with the basic characteristics of VG30, as well as with the IS standards (IS 73: 2013).

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S. B. Kulkarni and M. S. Ranadive Table 1. Output of bio-oil/pyro-oil received through pyrolysis process

Sr. No.

Type of waste processed for pyrolysis

Quantity of waste in Quantity of kg bio-oil/pyro-oil obtained in %

Maximum external temperature of reactor observed in °C

1

MSW batch 1

2.8

13.39

585

2

MSW batch 2

5.6

14.48

515

3

MSW batch 3

3.727

13.42

550

4

MSW batch 4

3.624

13.32

540

5

MSW batch 5

2.963

4.42

555

6

MSW batch 6

4.605

25.52

550

7

MSW batch 7

2.916

15.81

583

8

MSW batch 8

3.048

32.91

543

9

MSW batch 9

2.017

18

586

10

Wet organic waste

3.265

36.97

502

11

Dry organic waste

1.8

47.72

500

12

Semidry organic 2.079 waste

43

546

13

Textile waste

0.871

29.39

597

14

PP batch 1

1.553

41.85

860

15

PP batch 2

3.3

20.76

800

16

HDPE batch 1

1.742

23

750

17

HDPE batch 2

2.469

34.02

541

18

LDPE batch 1

3.114

57.8

730

19

LDPE batch 2

2.283

32.85

645

20

LDPE batch 3

4.122

29.35

626

21

LDPE batch 4

1.830

53.82

577

22

LDPE batch 5

1.712

33

576

23

LDPE batch 6

2.090

44.88

584

24

LDPE batch 7

1.715

51.78

564

25

LDPE batch 8

1.527

17.88

596

26

LDPE batch 9

1.655

45

600

27

LDPE batch 10

1.655

18

610

28

LDPE batch 11

2.4

20.83

625

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4.1.1 Blending of Pyro-Oil of LDPE Plastic Waste into VG30 The pyro-oil of LDPE plastic waste was added by 5%, 7.5% and 10% in bitumen VG 30 to prepare three samples of modified bitumen. The tests for determining specific gravity, penetration, flash point, ductility, softening point, and kinematic viscosity were performed for these three samples. The results are given in Table 2 (Kulkarni et al. 2016). The properties of modified bitumen are compared with the test values of bitumen VG 30. The specific gravity of modified bitumen is slightly reduced, but there is no measurable difference. The penetration value of modified bitumen with a 5% addition of pyro-oil is decreased by 6%, whereas for 7.5%, and 10% addition of pyro-oil, it is increased by 39%, and 70% to that of the base bitumen respectively and also the penetration values found to be more than the maximum allowable limit 70 for VG30. The flash point is reduced by 41%, 40%, and 38%, ductility is reduced by 32%, 44%, and 56%, softening point is reduced by 15%, 23%, and 35%, and kinematic viscosity is reduced by 22%, 32%, and 46% respectively for 5%, 7.5%, and 10% addition of pyro-oil in VG 30. The penetration values at 7.5% and 10% addition pyro-oil are higher than the maximum limit allowed, whereas flash point, softening point and kinematic viscosity of modified bitumen are lower than the minimum limit allowed. Table 2. Test result of modified bitumen by using pyro-oil of LDPE plastic waste (Kulkarni et al. 2016) Sr. No.

Test description

Modified bitumen with addition of pyro-oil of LDPE plastic waste to VG 30

Test values of VG 30 Bitumen

Standards of VG30as per IS 73: 2013

5%

7.5%

10%

1

1.003

1.003

1.01

–

1

Specific gravity

2

Penetration at 25 °C, 100 g, 5 s, 0.1 mm, Min

61

90

110

64.6

Min 45

3

Flash point in °C

162

165

170

275

Min 220

4

Ductility in cm

39

32

25

57

Min 40

5

Softening point °C

44

40

34

52

Min 47

6

Kinematic Viscosity at 135°C, cSt

315

275

220

405.69

Min 350

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S. B. Kulkarni and M. S. Ranadive

4.1.2 Blending of Pyro-Oil of PP Plastic Waste IntoVG30 The pyrolysis oil waste PP plastic was added by 10% in another sample of VG30 bitumen to prepare modified bitumen. The tests for determining specific gravity, penetration, flash point and ductility were performed for modified bitumen mentioned above. The results are given in Table 3. The properties of modified bitumen are compared with the test values of VG 30 bitumen into which it was blended. The specific gravity of modified bitumen was slightly reduced, but there is no measurable difference. By addition of 10% pyro-oil to bitumen VG30, the value of penetration was increased by 2.5 times, whereas the flash point, softening point, ductility and kinematic viscosity were reduced by 17%, 36%, 71%, and 45% respectively. Flash point was higher than the minimum value allowed as per IS 73:2013. The penetration of modified bitumen was found to be higher than the maximum limit allowed, whereas the softening point, ductility and kinematic viscosity were found to be lower than the minimum limit allowed as per IS 73:2013. Thus, measurable deviations were noticed. Table 3. Test results of modified bitumen by using pyro-oil of PP plastic waste Sr. No.

Test description

Modified bitumen with addition of pyro-oil of PP plastic waste (10%) to VG 30

Test values of VG 30 Bitumen

Standards of VG30 as per IS 73: 2013

1

Specific gravity

1.043

1.06

–

2

Penetration at 25 °C, 100 g, 5 s, 0.1 mm, Min

132

53

Min 45

3

Flash point °C

275

330

Min 220

4

Softening point °C 33

49

Min 47

5

Ductility at 25 °C, 34 cm

68

Min 40

6

Kinematic viscosity at 135 °C cSt

378

Min 350

209

The properties of modified bitumen were compared with the test values of VG 30. The specific gravity of modified bitumen was slightly reduced, but there was no measurable difference. By addition of 10% pyro-oil to bitumen VG30, the value of penetration was increased by 2.5 times, whereas the flash point, softening point, ductility and kinematic viscosity were reduced by 17%, 36%, 50%, and 45% respectively. Flash point was found higher than the minimum value allowed as per IS 73:2013. The penetration of modified bitumen was found to be higher than the maximum limit allowed, whereas the softening

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139

point, ductility and kinematic viscosity were found to be lower than the minimum limit allowed as per IS 73:2013. Thus, measurable deviations were noticed. 4.2 Physical Characteristics of Pyro-Oil of LDPE Plastic Waste Initially, one sample of pyro-oil of municipal plastic waste was tested. The calorific value was found to be 10465 kcal/kg, which is as high as the calorific value of fuels such as light diesel oil, diesel, and kerosene. The calorific values of LDO, diesel and kerosene are 10700 kcal/kg, 10800 kcal/kg, and 11100 kcal/kg, respectively. Since the calorific value of pyro-oil falls within the range of these values, it was assumed that this pyro-oil can be very well applied in cutback bitumen because cutback bitumen is manufactured by mixing kerosene, diesel, and petrol in 80–100 penetration grade bitumen. Therefore, to concentrate the study on plastic waste, total of 11 samples of municipal plastic waste were processed through pyrolysis and checked physical characteristics. Out of that the characteristics of three samples showing higher calorific value were selected for chemical analysis and further research work. These samples were named as sample A, sample B, and sample C, respectively. Table 4 shows the test results of physical characteristics of these three samples. 4.2.1 Comparison of the Physical Characteristics of Pyro-Oil with Fuel The average values of the physical characteristics of the samples A, B and C were calculated and found to be density 813.4 kg/m3 , kinematic viscosity 1.9 cSt, gross calorific value 10745 kcal/kg, water content 1.3%, flash point