Cement and Concrete: Design, Performance and Structure 9798886978315

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Kong Fah Tee Siew Choo Chin and Koorosh Gharehbaghi Editors

Cement and Concrete Design, Performance and Structure

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Library of Congress Cataloging-in-Publication Data ISBN: 979-8-88697-831-5

Published by Nova Science Publishers, Inc. † New York

Contents

Preface

.......................................................................................... vii

Chapter 1

The Performance of Green Self-Compacting Concrete Using Industrial Wastes....................................1 Pawan Kumar and Navdeep Singh

Chapter 2

Infrared Thermography Analysis of Sulfur Polymer Concrete Exposed to Accelerated Aging .......................................................45 Milica Vlahović and Tatjana Volkov Husović

Chapter 3

The Structural and Environmental Performance of Fly Ash Amended Cement ...................93 Lokeshappa Basappa and Anil Kumar Dikshit

Chapter 4

The Effect of Nanomaterials (Nano SiO2 and Nano Al2O3) on the Strength Properties of Self-Compacting Concretes ......................................117 Sarella Venkateswara Rao, Padakanti Rakesh and Nandipati S. M. Ravi Kumar

Chapter 5

Pertinency of Geopolymer Concrete for the Australian Construction Industry: A Broader Contextual Appraisal .................................153 Koorosh Gharehbaghi, Kong Fah Tee, Ken Farnes and Laura Blackburne

Chapter 6

A Novel Method of Improving the Gradation of Multi-Recycled Aggregate Using the Particle Packing Approach .........................................................191 Madhavi Latha Kasulanati and Rathish Kumar Pancharathi

vi

Contents

Chapter 7

Bamboo Fibre Composites: Potential and Challenges ...............................................213 Yu Xuan Liew, Sheh Ching Khong, Jia Jun Yee, Siew Choo Chin and Kong Fah Tee

Index

.........................................................................................257

Editors' Contact Information ..................................................................265

Preface

Cement and Concrete: Design, Performance, and Structure presents advances in cement and concrete research and development. In dealing with cement and concrete, this book investigates different aspects of their design, performance, and structure. The covered topics include green concrete and tomographybased concrete ageing analysis, as well as the use of natural fibres, geopolymers, and nanomaterials in concrete. The book is intended for academics, researchers, and engineers, and will serve as an invaluable guide or reference that encourages undergraduate and postgraduate students to look beyond normal procedures when developing and constructing innovative and sustainable building materials. This edited book is divided into the following seven chapters. In Chapter 1, the utilization of industrial waste is employed to evaluate the performance of green and self-compacting concrete. While Chapter 2 deals with infrared thermography analysis of sulfur polymer concrete exposed to accelerated ageing, in Chapter 3 various structural and environmental performances of fly ash-amended cement are evaluated and presented. The mechanical properties of concrete are carefully examined in Chapter 4 through the determination of the effect of nanomaterials on the strength properties of self-compacting concrete. To understand the current practices of geopolymer concrete, Chapter 5 deals with the pertinency of geopolymer concrete for the Australian construction industry. In Chapter 6, a novel method of improving the gradation of multi-recycled aggregate using a particle packing approach is prudently presented. Finally, in Chapter 7, bamboo fibre composites are dealt with to better understand their overall potential and challenges.

Chapter 1

The Performance of Green Self-Compacting Concrete Using Industrial Wastes Pawan Kumar and Navdeep Singh* Department of Civil Engineering, Dr. B R Ambedkar National Institute of Technology, Jalandhar, Punjab, India

Abstract Encompassing waste by-products in concrete such as recycled concrete aggregates (RCA), fly ash (FA) and coal bottom ash (CBA) are nowadays one of the most critical approaches, essential for green and sustainable development. To meet the necessities of green and sustainable development in concrete engineering construction, an attempt has been made to prepare high volume fly ash-coal bottom ash self-compacting concrete (HVFA-CBA-SCC) combinations with the inclusion of RCA (0% to 100%). In total five numbers of SCC mixes were prepared in which different substitution levels of natural coarse aggregates (NCA) with RCA (0%-100%) were used. In parallel, for the same mixes a constant substitution level of natural fine aggregates (NFA) and Portland cement (PC) with CBA (10%) and FA (50%) was introduced respectively. This study presents an experimental finding on the mechanical as well as durability properties such as compressive strength, tensile strength and flexural strength, initial surface absorption test, accelerated carbonation and capillary suction absorption test of proposed HVFACBA-SCC mixes prepared with recycled concrete aggregates (RCA).

*

Corresponding Author’s Email: [email protected].

In: Cement and Concrete Editors: Kong Fah Tee, Siew Choo Chin and Koorosh Gharehbaghi ISBN: 979-8-88697-831-5 © 2023 Nova Science Publishers, Inc.

2

Pawan Kumar and Navdeep Singh The outcomes revealed that, despite of the noticed decrement(s) in the overall performance due to the involvement of RCA, all the mixes have reasonable strengths comparable with the reference SCC mix such as after 28 days of curing the maximum decrement of 40% in overall strength has been experienced in HVFA-CBA-SCC mixes having RCA in relation to the reference mix without RCA. In addition to the above, lesser carbon emissions were noticed for the mixes containing RCA in relation to mixes containing NCA resulting in the promotion of green SCC.

Keywords: coal bottom ash, high volume fly ash, recycled concrete aggregates, self-compacting concrete

1. Introduction Self-compacting concrete (SCC) has been truly phenomenal since coming in limelight from the past two decades as it is a type of concrete that compacts under its own weight. Usually, the superiority of the concrete depends/relies on its compaction and curing process (Kumar and Singh 2020; Navdeep Singh, Kumar, and Goyal 2019; Navdeep Singh and Singh 2018). Recently, sustainability has become a major problem for Civil Engineers, due to the large usage of Natural resources (NR) by the building/construction sector further resulting in significant amount of construction and demolition waste (Cachim 2009; Ghorbani et al. 2018; Kwan et al. 2012). The construction sector is regarded as one of the primary consumers of raw materials. The large utilization/consumption of NR substantially causes pollution and affects environmental degradation (Ghorbani et al. 2019; Tabsh and Abdelfatah 2009). With the growth of the concrete sector in recent times, the production of construction and demolition waste (C&DW) has increased. Nowadays without any doubt, C&DW is the main emphasis for the researchers to make green and sustainable concrete (Soares et al. 2014). Reusing and recycling C&DW in various applications can be regarded as the most effective path of diminishing environmental impacts and consumption of NR. The recycled concrete aggregate (RCA) obtained using C&DW can be utilized in various civil engineering practices. India is among the largest producer of C&D waste. As per the data reported by Central Pollution Control Board, India generates more than 45 million tons of solid waste out of which around 12–15 million tons have been generated by construction industry. According to a report published

The Performance of Green Self-Compacting Concrete …

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in 2010 the production of C&D waste was around 12 million tons which accounts for 8.3–10 kg per capita per year. Whereas the metro cities of India like Chennai alone produce 175 kg per capita per year of C&D waste. The case is worst with the developed countries like USA which alone produces around 484 million tons of C&D waste (Joshi and Ahmed 2016; De Brito, Agrela, and Silva 2018; Shrivastava and Chini 2005; Saini and Singh 2020). One of the most commonly used supplementary cement materials (SCMs) in concrete is fly ash (FA), which is a primary by-product of coal combustion in thermal power plants. Usually, concretes prepared with ≥ 30% of FA are described as High-volume fly ash (HVFA) based concretes. In the year 2012 it has been reported that countries like China, India, Japan and Russia, etc. consumes near about 50.2%, 11.7%, 8.0% and 3.3% of coal (Yao et al. 2015). India, China, and Australia are projected to contribute 64% of the world coal production in 2040, a growth of about 4% compared to the 2012 coal production (Rafieizonooz et al. 2016). Due to the increase in demand of coal, the industrial waste has also been generated at a rapid rate. Fly ash makes up 70–80% of the total coal ash wastes, and the remaining 10–20% is bottom ash (Yao et al. 2015; Rafieizonooz et al. 2016; Navdeep Singh, Shehnazdeep, and Bhardwaj 2020). Of the millions of tons of coal ash waste generated annually, 100 million metric tons (Mt) is bottom ash, and the remainder is fly ash (Ahmaruzzaman 2010). The World of Coal Ash (WOCA) estimated that coal thermal power plants generate 780 million metric tons of coal bottom ash (CBA), of which 66% is by Asian countries, followed by Europe and the United States (Heidrich, Feuerborn, and Weir 2013). Also in 2012, the worldwide generation of FA per year was roughly about 750 million tons (Blissett and Rowson 2012), but only about one-fourth of FA has been recycled or reused. In the year 2015, 130 million tons of FA were produced in the United States yet only 50% is utilized (Yao et al. 2015). A low consumption rate of FA means that material might end up in landfills and further results in soil and water pollution (Yao et al. 2015). Generally, FA act as a pozzolanic material (Zhang and Canmet 1995), typically contributing to enhancing the workability and cost economy of concrete. Usually, the unburnt matter of coal incineration is regarded considered as coal bottom ash (CBA) (Kumar and Singh 2020; Navdeep Singh, Kumar, and Goyal 2019). It is produced at a boiler and constitutes nearly about 10-20% of coal ash. This ash is a complicated blend of metal carbonates and oxides in terms of chemical composition. As CBA is treated as a waste material, it is also thrown in ponds and landfills (Navdeep Singh, Mithulraj, and Arya 2018; Navdeep Singh, Kumar, and Goyal 2019; Navdeep Singh, Shehnazdeep, and Bhardwaj 2020).

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Pawan Kumar and Navdeep Singh

The disposal of coal ashes (FA and CBA) in the open air poses a threat to both the environment and humans (Navdeep Singh, Mithulraj, and Arya 2018; Kumar and Singh 2020). Kumar & Singh, 2020; Singh et al., 2019, 2020 further explains the increased risk of health problems such as lung, bladder, and skin cancer due to the presence of coal bottom ash linked to skin, lung, and bladder cancer. The thorough predictions are already present in literature wherein NCA has been successfully replaced with RCA. Also, the literature dictates that the mechanical and durability characteristics are significantly affected by the behavior/performance of SCC containing RCA at various proportions (Khodair and Bommareddy 2017; Khodair and Luqman 2017; Kurda, de Brito, and Silvestre 2017; Navdeep Singh and Singh 2016a). In most of the earlier studies, the addition of RCA instead of NCA has reduced compressive strength, split tensile strength and flexural strength, etc. of concretes (Evangelista et al. 2015; Gesoǧlu et al. 2014; Zoran et al. 2010). A decrement of up to 30% has been noted in the mechanical properties with full/fractional alteration of NCA in place of RCA (Akabari, Parikh, and Tejas 2016; Panda and Bal 2013). The usage of non-conventional aggregates (RCA) has led to comparable conduct in mechanical properties in some studies (Nischay T G, S Vijaya, and B Shiva Kumaraswamy 2015), while minor improvements in mechanical properties have also been noticed in some cases. In a few cases, an increase in compressive strength and tensile strength has been experienced with the involvement of RCA in place of NCA (Faisal et al. 2018; S. C. Kou and Poon 2009; Tuyan, Mardani-Aghabaglou, and Ramyar 2014a). Further with the involvement of RCA, the adverse effect has been noted in the case of long-term properties of SCC. For example, with the introduction of fine RCA, the chloride ion intrusion has been inflated (S. C. Kou and Poon 2009; Tuyan, Mardani-Aghabaglou, and Ramyar 2014b). On the other hand, the absorption/sorptivity values in the case of capillary water absorption have been improved with the addition of RCA (Gesoǧlu et al. 2014; Pereira-De-Oliveira et al. 2014). Due to additional pozzolanic properties and identical particle size as that of NFA, the use of CBA is in high demand in the construction sector (Aggarwal and Siddique 2014). Several successful SCC investigations have been performed to replace NFA with CBA (Ibrahim et al. 2015; Kumar and Singh 2020; Navdeep Singh, Mithulraj, and Arya 2018). The existing literature indicates that a common replacement range of substitution of CBA varied from 10-30% in place of NFA (Siddiquea, Aggarwalb, and Aggarwalb 2012). Also, it has been observed that a substitution level of 10% (by weight) is an ideal alteration level of NFA with

The Performance of Green Self-Compacting Concrete …

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CBA for fulfilling the essential fresh, mechanical, and durability requirements (Ibrahim et al. 2015; Kumar and Singh 2020; Navdeep Singh, Mithulraj, and Arya 2018). In a few of the studies, the beneficial outcome of CBA has been observed as most of the mechanical properties have been enhanced for SCC mixes containing 10%-20% of CBA as substitution of NFA (Abidin et al. 2014; Ibrahim et al. 2015; Paul and P.U 2014). Likewise, with 10% inclusion of CBA in place of NFA, an enhancement in long-term behavior such as carbonation resistance, chloride ion penetration, water absorption, capillary water absorption, etc. has also been witnessed (Abidin et al. 2014; Kasemchaisiri and Tangtermsirikul 2008; Rafieizonooz et al. 2017).

2. Research Significance The principal objective of this experimental program is to study the impact of RCA on HVFA-CBA-SCC mixes. This experimental study includes different mechanical (Compressive strength, Tensile strength, and Flexural strength) and durability properties (Accelerated carbonation and Capillary suction absorption test) of HVFA-CBA-SCC mixes comprising RCA. Also, different parameters such as cost analysis and global warming potential have been performed. In other terms, the current investigation used a practically oriented criterion in minimizing the degradation of natural resources and preventing excessive landfilling by using entirely waste materials. The outcomes observed in this study provide a quantitative information to understand the potential use of RCA in HVFA-CBA-SCC mixes as less CO2 emissions are detected while using non-conventional aggregates (RCA) in relation to conventional aggregates (NCA).

3. Industrial Wastes 3.1. Fly Ash Fly ash is a waste by-product attained from coal thermal power plants (Khodair and Luqman 2017; Hyeong Ki Kim 2015). Previous observations have revealed that the existence of FA significantly distresses/affects the abrasion resistance, strength and further helps in overcoming the moisture barriers already present in concrete pavements. This effect is imposed by the

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Pawan Kumar and Navdeep Singh

reaction between cement hydrates and FA, which further alters the concrete microstructure (Navdeep Singh and Singh 2016b; Kumar and Singh 2020). The consumption of FA in the concrete industry is also a significant energy saving and sustainable activity. The disadvantages of using fly ash concrete relative to traditional concrete may be attributed to its low alkalinity. Low alkalinity might lead to interference in the passivation film on the steel reinforcement bar in both NVC (normal vibrating concrete) and SCC. FA is primarily used as a binder as an alteration of PC in low as well as high volume. The principal benefits of its use are the reduction of CO2 emissions from the cement industry and the improvement in the workability of concrete (Anjos, Camões, and Jesus 2014; Rashad 2015). Also, the usage of high-volume FA precisely in mass concreting applications such as bridge abutments, piers and dams, etc. results in low hydration heat in comparison to PC based concretes (Khalifah et al. 2016; S.-G. Kim 2010; Moser, n.d.). As per ASTM C618-12(a), FA is classified as either Class C or Class F and its classification mainly depends on the chemical composition. Usually, Class FFA comprises calcium (1% to 12%) in the form of calcium hydroxide, calcium sulfate, etc., whereas Class C-FA has high levels of calcium oxide (30% to 40%) (Moser, n.d.; Ledbetter et al. 1981). The most familiar use, apart from different FA applications, is its usage in the manufacture of concrete and cement. Apart from this, FA has also been effectively integrated into the making of geopolymer concrete and backfilling, etc. The key benefit of using FA in SCC is its capability to decrease the superplasticizer amount needed to achieve the desired workability. In general, FA practice promotes rheological activity and curtails the risk of cracking at later ages due to lower hydration heat (Khalifah et al. 2016; S.-G. Kim 2010; Moser, n.d.).

3.2. Coal Bottom Ash Coal is a primary source of generating heat and electricity through the combustion process. Coal ash is a residue arising from the thermal power plant (Baite et al. 2016; Nikbin et al. 2016). The burned coal causes smoke that goes into the air and is collected as fly ash. The burned coal left at the bottom is thereafter cooled and recognized as bottom ash (H. K. Kim and Lee 2015). CBA is a waste product produced at Thermal plants. Near about 65-70% of electricity is still generated in India from thermal power plants based on coal. The combustion of nearly 20 tons of coal typically generates around 1 MW of

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electricity, along with the generation of 15%-20% of CBA (Navdeep Singh, Mithulraj, and Arya 2018). The ampleness of CBA has led to different concerns such as dumping and utilization due to land deficiency (Kumar and Singh 2020; Navdeep Singh, Kumar, and Goyal 2019). Due to similar size with fine aggregates, CBA has been successfully used as an alternative material in both normally vibrated and self-compacting concretes from the last couple of decades. CBA also embraces pozzolanic content (Navdeep Singh, Shehnazdeep, and Bhardwaj 2020; Kumar and Singh 2020) when produced/formed from other products such as lignite, sub-bituminous and anthracite, etc. The benefit of additional pozzolanic character facilitates its use in the concrete industry, which focuses mainly on minimizing carbon footprints. Generally, the size of the CBA depends on the source of the coal produced or the quality of the coal. The overall concrete behavior varies with the varying size of the CBA (British Standard 1992; Navdeep Singh, Mithulraj, and Arya 2018).

3.3. Recycled Concrete Aggregates The safety of the environment is a fundamental aspect, which is interconnected with the survival of humans. Parameters such as sustainability, environmental awareness, and the conservation of natural resources play an important role in modern construction requirements. In our lives, construction materials are very important because we invest 90% of our time on buildings or facilities (roads, highways, bridges, etc.). Usually, the construction sector (Mane et al. 2018) harms the nearby surroundings by: • • •

Creating 50% of total waste. Consuming 40% of total energy. Taking 50% of raw materials from nature.

The key reasons for the rise in concrete wastes are the demolition of many old buildings, generation of building waste from natural disasters such as earthquakes, storms, etc. The rough quantity of several construction materials in demolition waste is demonstrated in Figure 1.

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Pawan Kumar and Navdeep Singh

Ceramic 10%

Concrete 30%

10% 5% 5%

Metal Plastic Wood

40%

Various

Figure 1. Approximation data of demolition waste.

Nowadays in construction works, the use of RCA is a subject of higher priority throughout the globe. In Great Britain, 10% of the used aggregates are generally RCA (Collins RJ 1996) whereas in 1994 approximately 80,000 tons of RCA has been used in Holland (de Vries 1996). Further, the experts acknowledged that usage of 20% of RCA (coarse RCA) results accordingly on fresh and hardened properties. One of the key reasons for using RCA in structural concrete is to make the environment green and eco-friendly. As reported by Oikonomou 2005 (Oikonomou 2005) few major environmental problems are connected with construction as “construction consumes nearly half (50 percent) of raw materials from nature, takes 40 percent of total energy and produces 50 percent of total waste.” The consumption of RCA might help in reducing the effects of construction and stopping natural aggregates from being harvested.

4. Environmental and Health Issues Fly ash is released in the environment from the combustion of fossil fuels. The raised fly ash particles are generally irregular in shape and comprise various elements like thallium, selenium, cadmium, calcium, iron, silica, and aluminum, etc. (Navdeep Singh, Mithulraj, and Arya 2018; Navdeep Singh, Kumar, and Goyal 2019). Depending upon the harmfulness/morbidity, concentration in air, and chemical properties, FA particles might cause an inhalation threat to exposed workers which further leads to birth defects, permanent mutilation/defacement to respiratory systems and lungs, etc. (Lockwood et al., n.d.). Similarly, CBA encompasses a variable quantity of

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heavy metals which are characterized as ‘Group-I human carcinogenic metals’. The occurrence of such metals is the main source for bladder, lung, and skin cancers. After coming in contact with the surface water, the coal ashes percolate and fuse with surface water. Also, the rise in urbanization has put a great burden on the available natural resources (Ruhl et al. 2009; L. F. O. Silva and Da Boit 2011). The development of new Infrastructure schemes has contributed to creating the new structures instead of renovating the older structures which further leads to an increase of construction and demolition waste. Furthermore, sustainability in the construction sector has upstretched an extra worry/concern to mankind. The growing rate of landfills and the lack of available natural resources have forced the researchers/investigators to reuse the C&DW and solve the aforesaid worries (Akhtar and Sarmah 2018; Durmisevic 2009; Jain, Singhal, and Jain 2018). The superlative management of this increasing quantity of C&DW wastes will help in resolving the ecological imbalance.

5. Materials In all the HVFA-CBA-SCC mixes, Portland cement (PC) 43-Grade was the main binder, and it was combined with Class F FA. The reference SCC mix was prepared by using 50% PC + 50% FA along with 90% NFA + 10% CBA and 100% NCA. SCC combinations encompassing RCA were attained by substituting NCA with RCA at 25%, 50%, 75%, and 100% levels. The RCA used (maximum of 10 mm size) during the investigation was gained by crushing the left-over waste specimens from the author’s institute.

5.1. SCC Mix Proportions The proportions of various HVFA-CBA-SCC mixes are mentioned in Table 1. The mix design of the HVFA-CBA-SCC mixes including the RCA and CBA as replacement of NCA and NFA was achieved using equivalent mix proportions (Table 2). All the HVFA-CBA-SCC mixes were prepared with a binder content of 615 Kg/m3 and a constant water/binder of 0.45 after meeting the EFNARC guidelines. The conventional (natural aggregates), as well as non-conventional aggregates (recycled aggregates), were soaked in water for

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Pawan Kumar and Navdeep Singh

a period of 24 hours before casting. By using a tilting drum mixer, all the HVFA-CBA-SCC mixes were prepared. Table 1. Mix designations and description of HVFA-CBA-SCC mixes S no 1. 2. 3. 4. 5.

Mix designation CHFB-0R (Reference) CHFB-25R CHFB-50R CHFB-75R CHFB100R

Mix explanation in detail PC50%+FA50%+CBA10%+NFA90%+RCA0%+NCA100% PC50%+FA50%+CBA10%+NFA90%+RCA25%+NCA75% PC50%+FA50%+CBA10%+NFA90%+RCA50%+NCA50% PC50%+FA50%+CBA10%+NFA90%+RCA75%+NCA25% PC50%+FA50%+CBA10%+NFA90%+RCA100%+NCA0%

Table 2. Detailed proportions used in HVFA-CBA-SCC mixes Mix designation

W/B

SP

Water

FA

CHFB-0R (Reference) CHFB-25R CHFB-50R CHFB-75R CHFB100R

0.45

2.1

277

232

0.45 0.45 0.45 0.45

2.41 2.62 3.04 3.36

277 277 277 277

232 232 232 232

RCA CBA Kg/m3 0 62 151 301 452 602

62 62 62 62

PC

NCA

NFA

308

652

738

308 308 308 308

489 326 163 0

738 738 738 738

In order to obtain the desired workability superplasticizer of the brand name ‘Sika A (Sika Viscocrete 2002)’ was added. For estimating the mechanical and durability behavior sufficient number of specimens were cast: 100 mm x 100 mm x 100 mm x 100 mm cubes were cast for compressive strength, accelerated carbonation tests. Tensile strength was performed on cylindrical specimens having a diameter of 100 mm and a length of 200 mm. Flexural strength test was done on 100 mm x 100 mm x 500 mm size beams. Initial surface absorption test (ISAT) was performed on cubes having dimensions 150 mm x 150 mm x 150 mm. For performing the Capillary suction absorption test (CSAT), cylindrical specimens having a size of 100 ± 6 mm Ø with a length of 50 ± 3 mm were used. After 24 hours, the specimens were demolded and henceforth moist cured for their respective period.

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5.2. Details and Curing Methods The number of the specimens casted for different tests and curing period for each test are presented in Table 3. Table 3 also presents the exposure period to CO2 in case of carbonation tests. The specimens were cured in ‘Temperature controlled curing tanks’ having temperature of 27 ± 2°C for the desired curing period. Figure 2 shows the temperature-controlled curing tank used in the investigation. Table 3. Specimen details and curing and exposure periods for different tests Test Compressive strength Tensile strength Flexural strength Initial surface absorption test Accelerated carbonation Capillary suction absorption test

Number of specimens 81 81 54 54

Curing period (days) 7, 28, 56, 90 7, 28, 56, 90 28, 90 28, 90

108

28, 90

54

28, 90

Figure 2. Temperature controlled curing tank.

Exposure period (weeks) 28 and 90 days (exposure of 28 and 90 days) -

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Pawan Kumar and Navdeep Singh

6. Test Methods 6.1. Compressive Strength As recommended by Indian Standard 516-1959 on a 2000 KN ‘Compression Testing Machine’, compressive strength tests of all the HVFA-CBA-SCC mixes were performed after curing ages of 7, 28, 56, and 90 days. The approximate load was applied at a rate of 14 N/mm2/minute until the failure. Figure 3 (a) showing compressive strength on 100 mm x 100 mm x 100 mm size cubes.

6.2. Tensile Strength According to Indian Standard 5816:1999 on a 2000 KN ‘Compression Testing Machine’, the tensile strength of all HVFA-CBA-SCC combinations was performed after the curing age of 7, 28, 56, and 90 days on cylindrical specimens. The approximate load was applied at a rate of 1.2 N/mm2/minute to 2.4 N/mm2/minute until the failure. Figure 3 (b) presentation tensile strength on cylindrical specimens having a diameter of 100 mm and a length of 200 mm.

6.3. Flexural Strength As recommended by ASTM C293/C293M, a flexural strength test was performed on beams specimens after curing ages of 28 and 90 days. Flexural tests evaluate the tensile strength of concrete indirectly. It tests the ability of unreinforced concrete beam or slab to withstand failure in bending. Figure 3 (c) showing flexural strength on 100 mm x 100 mm x 500 mm size beams.

6.4. Initial Surface Absorption Test As recommended by BS 1881- 208:1996, the Initial Surface Absorption Test of all the HVFA-CBA-SCC mixes was performed after curing ages of 28 and 90 days. The initial surface absorption test gives the rate of flow of water into concrete per unit area at a stated interval from the start of the test and at a

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constant applied head. The water contact area is defined by a plastic cell sealed onto the concrete surface of the test specimen and is not kept less than 5000 mm2. Water is introduced into the cell via a connecting point and pressure is maintained at a head of 200 mm using a filter. A second connection point to the cap leads to a horizontal capillary tube. The readings are taken at intervals of 10 min, 30 min and 60 min from the start of the test. Figure 3 (d) demonstrating ISAT values on cubes having dimensions 150 mm x 150 mm x 150 mm.

6.5. Accelerated Carbonation In accordance with RILEM CPC-18, accelerated carbonation tests were performed on cubical specimens. Further, the specimens were introduced to a carbonation chamber where the concentration of CO2 was kept at 4% for 4 and 12 weeks after curing time of 28 and 90 days. During the exposure period, relative humidity was kept between 40 percent and 70 percent. The carbonation phenomenon increases with increase in temperature, and it generally varies from 25 ± 2°C. Figure 3 (e) showing carbonation chamber having cubes of size 100 mm x 100 mm x 100 mm.

6.6. Capillary Suction Absorption Test In compliance with ASTM - C - 1585 – 04, the initial rate of absorption (IRA) and secondary rate of absorption (SRA) values were assessed. Capillary suction test is used to determine the rate of absorption (sorptivity) of water by hydraulic cement concrete by measuring the increase in the mass of a specimen resulting from absorption of water as a function of time when only one surface of the specimen is exposed to water. Discs of 100 mm diameter and 50 mm thickness will be cut from the 100 mm × 200 mm cylinders and kept for oven drying till constant mass is achieved. The sides of the specimens must be suitably sealed. The mass of the specimen will be recorded with a precision balance. During the course of the tests the specimens must be supported in such a way that the exposed end of each specimen will be in touch with water. The setup used is shown in Figure 3 (f).

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Pawan Kumar and Navdeep Singh

(a) Compressive strength

(b) Tensile strength

(c) Flexural strength

(d) Initial Surface absorption test

(e) Accelerated carbonation

(f) Capillary suction absorption test

Figure 3. Pictorial view of the test (s) performed.

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7. Outcomes and Discussion The following segment represents the observed findings of the HVFA-CBASCC mixes. The HVFA-CBA-SCC mixes have been tested at several curing periods prepared with the constant amount of CBA, FA, and a varying amount of RCA. The findings of the different conducted tests such as compressive strength, tensile strength, flexural strength, initial surface absorption test accelerated carbonation and capillary suction absorption test are mentioned below.

7.1. Compressive Strength Compressive strength is usually the most common and fundamental property of concrete examined in almost every research on concrete (Fan et al. 2015; Pin, Ashraf, and Cao 2018; Navdeep Singh, M, and Arya 2019) (Fan et al. 2015; Pin et al. 2018; Singh et al. 2019b). The compressive strength is performed after curing ages of 7, 28, 56, and 90 days respectively. After a curing period of 28 days, the reference mix CHFB-0R revealed the most compressive strength among the remaining mixes. The fundamental test was performed to study the behavior of RCA as a substitution of NCA on several SCC combinations. The average compressive strength of reference SCC mix (CHFB-0R) and SCC mixes comprising RCA (CHFB-25R, CHFB-50R, CHFB-75R, and CHFB-100R) increased from 19.5-31.2 MPa and 16.2-30.4 MPa respectively. Compared to 28 days, the compressive strength of reference SCC mix and SCC mixes encompassing RCA increased by 45% to 60% [i.e., 28.4 and 31.2 MPa] and 44% to 62% [i.e., 24.6 and 30.4 MPa] respectively, after curing time of 56 and 90 days. The variation in compressive strength of HVFA-CBA-SCC mixes is represented in Figure 4. Usually, compressive strength is related to the microstructure of the hardened concrete (Behera et al. 2014; Evangelista et al. 2015; Rafieizonooz et al. 2017). The strength of any concrete also depends on the strength of the aggregate, cement matrix, and the ITZ between the matrix and the aggregate (Behera et al. 2014; Mohammed, Dawson, and Thom 2014; Nassar and Soroushian 2012; Wu, Shi, and Khayat 2016).

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Compressive strength (N/mm2)

35 7 Days

30

28 Days

56 Days

90 Days

25 20 15 10 5 0 CHFB-0R

CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 4. Compressive strength values of HVFA-CBA-SCC mixes comprising RCA.

The experienced loss in compressive strength of SCC mixes containing RCA when related to reference mix CHFB-0R might be due to the availability of weak characters like porous nature, micro and macro cracks, higher absorption rates, and old Interfacial Transfer Zone (ITZ), etc. Also, compressive strength is disturbed by the size and types of aggregates, waterto-cement ratio, and the addition of mineral and chemical admixtures (Kumar and Singh 2020; Navdeep Singh, Kumar, and Goyal 2019; Navdeep Singh, M, and Arya 2019). Despite the decrements in the compressive strength due to the involvement of RCA, all the mixes have reasonable strengths compatible with the reference SCC mix. For example, the SCC mix prepared with 100% RCA showed a compressive strength of 22.7 MPa after 28 days of curing i.e., 14% lower than the reference mix (26.7 MPa). Further, the presence of CBA as a replacement of NFA leads to weak and porous interfacial transition zone and higher water absorption. However, at prolonged curing ages, the pozzolanic activity of CBA comes into consideration that leads to the formation of CSH gel and filling the voids (M. Singh and Siddique 2015; Kumar and Singh 2020).

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7.2. Tensile Strength Apart from the above-mentioned, tensile strength is another important mechanical property of concrete that significantly distress/distracts the size and extent of cracking in concrete structures (Gesoglu et al. 2015; Siddiquea, Aggarwalb, and Aggarwalb 2012; Navdeep Singh, M, and Arya 2019; Tuyan, Mardani-Aghabaglou, and Ramyar 2014a). As concretes are frequently poor in tension, therefore, the valuation of tensile strength of concretes is of great importance. The variation in tensile strength of the different HVFA-CBA-SCC mixes at curing times of 7, 28, 56, and 90 days are presented in Figure 5. Tensile strength was executed to assess the performance of RCA on HVFACBA-SCC mixes. Similar to the compressive test, the tensile strength for all SCC combinations has also been enhanced with time but the same has been declined when compared with the reference SCC mix CHFB-0R.

Tensile strength (N/mm2)

8 7 Days

7

28 Days

56 Days

90 Days

6 5 4 3 2 1 0 CHFB-0R

CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 5. Tensile strength values of HVFA-CBA-SCC mixes comprising RCA.

For example, the tensile strength rises from 4.6-6.7 MPa and 3.1-6 MPa for the reference SCC mix and SCC mixes encompassing RCA respectively but when compared to reference mix maximum decrement of 33% has been witnessed for SCC mix CHFB-100R. Comparable performance has been noticed for SCC mix CHFB-25R containing 25% of RCA with a maximum decrement of 13% at all curing ages. Former investigations have already concluded that fusion of FA with PC results in a disadvantageous effect on tensile strength at different curing periods (Nehdi, Pardhan, and Koshowski

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2004). The decline in tensile strength might be due to free and porous hydrates of RCA (Kapoor, Singh, and Singh 2018; Navdeep Singh, Mithulraj, and Arya 2018; Navdeep Singh and Singh 2019). Split tensile strength also depends largely on the superiority of the paste, which is worsening due to the physical nature of CBA (Over and States 1996; M. Singh and Siddique 2014). The primary/main reason for the reduction in the values of HVFA-CBASCC mixes is principally due to the existence of a high amount of RCA which leads to the occurrence of weak intrinsic parameters between new and old ITZ along with weak microstructure (Behera et al. 2014; Nassar and Soroushian 2012; Wu, Shi, and Khayat 2016). The already present pores in nonconventional aggregates (RCA) astonishes/overcome/dismantle the pore refining action of CBA at all ages and further promoting the expansion of the cracks thus reducing the split tensile strength (Over and States 1996; M. Singh and Siddique 2014; Navdeep Singh and Singh 2016b).

7.3. Flexural Strength A flexural test is commonly used for determining the modulus of rupture of specimens (Mastali and Dalvand 2016; Wu, Shi, and Khayat 2016). The flexural strength was achieved after curing ages of 28 and 90 days respectively. The distinction in flexural strength for HVFA-CBA-SCC mixes at several substitution levels of NCA in place of RCA (0% to 100% with an increase of 25% throughout) together with the same amount of binder (PC+FA) and CBA as substitution of NFA respectively was recognized. The witnessed results directly specify that with the inclusion of RCA in HVFACBA-SCC mixes the flexural strength has been declined. The flexural strength rises from 7.11-8.69 MPa and 4.67-7.03 MPa for the reference HVFA-CBASCC mix and HVFA-CBA-SCC mixes containing RCA respectively. The maximum decrement of 41% has been observed in SCC mix CHFB-100R comprising 100% of RCA whereas a minimum reduction of 19% has been noticed for SCC mix CHFB-25R after 90 days of curing. Similar to the compressive strength, all the SCC mixes have reasonable strength compatible to reference SCC mix CHFB-0R despite the continuous reduction in flexural strength due to the presence of RCA. The distinction in flexural strength of HVFA-CBA-SCC mixes prepared with RCA and CBA at different curing periods is presented in Figure 6. The trends of all the mechanical properties are analogous as all the values of SCC mix comprising RCA keep on decreasing when related to reference SCC mix containing NCA.

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Also, the reasons behind the decrement in flexural strength are similar to that are observed for compressive strength and split tensile strength (Behera et al. 2014; Nassar and Soroushian 2012; Otsuki, Miyazato, and Yodsudjai 2003; Xiao et al. 2013).

Flexural strength (N/mm2)

10 28 Days

90 Days

8 6 4 2 0 CHFB-0R

CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 6. Flexural strength values of HVFA-CBA-SCC mixes comprising RCA.

7.4. Initial Surface Absorption Test Initial surface absorption test exhibits the flow rate of water in concrete per unit area for a given time interval (Kapoor, Singh, and Singh 2018; 2016). The ISA values were evaluated by testing standard size cubes having dimensions 150 mm x 150 mm x 150 mm at a curing period of 28 and 90 days. Before the start of testing, the specimens were oven-dried to a constant weight and left in a desiccator to cool. During testing water is introduced into the cell and pressure was maintained at 200 mm head using a filter funnel. Figure 7 shows the ISA 10, ISA 30, ISA 60 values of HVFA-CBA-SCC mixes comprising RCA after 28 days of curing. To determine the influence of RCA on CBA-based SCC, an absorption test has been performed. The surface absorption is increased with an increment in the levels of RCA (25% - 100%). For example, after a curing time of 28 days, ISA 10 values have been increased by about 15%, 23%, 38% and 58% for all the SCC mixes CHFB-25R, CHFB-50R, CHFB-75R, and CHFB-100R respectively in relation to mix CHFB-0R. Similarly, increments were noticed

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for ISA 30 values (Figure 7). Following the earlier trends, ISA 60 values were further increased by about 10%, 32%, 36%, and 45% for the aforesaid mixes in comparison to the control HVFA-CBA-SCC mix. Higher ISA values designate higher advancements in surface porosity. The noticed behavior allocates to the poor performance of the RCA (specifically due to weak residual mortar and formation of additional boundaries) which further convert the matrix into a more permeable form consequently become vulnerable to water permeation (Mcneil and Kang 2013; Otsuki, Miyazato, and Yodsudjai 2003; Yaragal 2017).

0.9 0.8

10 min

30 min

60 min

Initial surface absorption (ml/m2.se)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

CHFB-0R

CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 7. ISAT values of HVFA-CBA-SCC mixes comprising RCA after 28 days of curing.

Likewise, the ISA 10, ISA 30, ISA 60 values of CBA-SCC after a curing time of 90 days are represented in Figure 8. The observations indicate that RCA is having a damaging as well as the dominant effect on ISA values of all CBA-SCC mixes. Also, the outcomes of the surface absorption indicate a direct relation with RCA. As RCA increases the absorption also starts increasing (Evangelista et al. 2015; Kurda, de Brito, and Silvestre 2019; Zoran et al. 2010). The least ISA values have been obtained for the SCC mix containing 25% RCA (CHFB-25R), while maximum values have been experienced for the SCC mix containing 100% RCA (CHFB-100R) in comparison with the control SCC mix.

Initial surface absorption (ml/m2.sec)

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0.6 0.5

10 min

30 min

60 min

0.4 0.3 0.2 0.1 0 CHFB-0R

CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 8. ISAT values of HVFA-CBA-SCC mixes comprising RCA after 90 days of curing.

7.5. Accelerated Carbonation After an exposure period of 4 and 12 weeks of accelerated carbonation, the cured specimens (cured for 28 and 90 days of curing) were split about 50 mm from the edge perpendicular to the exposed surface to measure carbonation depth. Further, carbonation depth was estimated by spraying phenolphthalein solution on the recently broken surfaces (Kumar and Singh 2020; Navdeep Singh, Shehnazdeep, and Bhardwaj 2020). The test results attained after 4 and 12 weeks of CO2 treatment at 28 days of curing are represented in Figure 9. The increment in carbonation depth has been quite significant in all the HVFA-CBA-SCC mixes prepared with alteration of NCA with RCA after the same curing time. The maximum increase of 43% and 40% in carbonation depths has been observed for mix CHFB-100R after 4 and 12 weeks of exposure in comparison with reference SCC mix CHFB-0R. The results of carbonation depths observed after curing time of 90 days having exposure period of 4 and 12 weeks are presented in Figure 10. The observed findings demonstrate that the gap between CHFB-0R and CHFB-25R is minimal/slight as maximum increase in carbonation depth has been limited up to 8% and 10% after 4 and 12 weeks of exposure at 90 days of curing time. The increment in carbonation depth is substantial when >25% RCA has been replaced with NCA as the maximum increase of 35% and 33%

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in carbonation depth have been noticed after 4 and 12 weeks of exposure at 90 days of curing time. The poorer behavior has been noted for SCC mixes having ≥ 75% of RCA (CHFB-75R and CHFB-100R) in place of NCA in comparison to reference SCC mix CHFB-0R. 60.0 4 Weeks

12 Weeks

Carbonation depth (mm)

50.0 40.0

30.0 20.0 10.0 0.0 CHFB-0R

CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 9. Carbonation depth of HVFA-CBA-SCC mixes comprising RCA after 28 days of curing.

Carbonation depth (mm)

35.0 30.0

4 Weeks

12 Weeks

25.0

20.0 15.0 10.0 5.0 0.0 CHFB-0R CHFB-25R CHFB-50R CHFB-75R CHFB-100R Mix designation

Figure 10. Carbonation depth of HVFA-CBA-SCC mixes comprising RCA after 90 days of curing.

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After experimental investigation, it has been concluded that after extended exposure periods (12 weeks), the increase in carbonation depth has been experienced to more comparable than noticed at initial exposure periods (4 weeks). The observed trends of HVFA-CBA-SCC are somewhat similar to the trends noticed for NVC prepared with NCA (Arredondo-Rea et al. 2012; Shi Cong Kou and Poon 2013; Thomas et al. 2013). The primary cause for this low carbonation resistance might be due to the water content of cementitious matrix, physical nature, and pore structure of RCA (N Singh and Singh 2016; Navdeep Singh and Singh 2016b; Navdeep Singh, Kumar, and Goyal 2019). Also, the more the porosity, the more will be the dispersion rate of CO2. Other factors like, low density of CBA (Siddiquea, Aggarwalb, and Aggarwalb 2012; Navdeep Singh, Kumar, and Goyal 2019; Ankur and Singh 2021), a higher water absorption rate of RCA in comparison to NFA and NCA are also responsible for such trends.

7.6. Capillary Suction Absorption Test Capillary suction absorption test was executed to assess the absorptivity coefficient (I in mm) of several HVFA-CBA-SCC mixes at curing times of 28 and 90 days respectively. The lower the absorption, the greater is the resistance of concrete towards the absorption of water. The observations up to 6 hours were considered for evaluation of initial absorption rates (IRA) while after 6 hours, the observations were noted to assess the secondary rate of absorption (SRA). Figure 11 and Figure 12 demonstrate the absorption resistance of HVFA-CBA-SCC mixes after 28 days and 90 days of curing respectively. It has been experienced from the outcomes that with the enhancement in the levels of RCA instead of NCA, there is a further decrement in the resistance of capillary water penetration. The water absorption has been increased proportionally for each HVFA-CBA-SCC mix compared to reference SCC mix CHFB-0R. The IRA values after 28 days have been noticed to be increased by 28%, 66%, 33% for HVFA-CBA-SCC mixes CHFB-25R, CHFB-50R, and CHFB-75R in comparison to control SCC mix CHFB-0R. The IRA value for SCC mix CHFB-100R was 2.3 times higher than the value observed for control HVFA-CBA-SCC mix CHFB-0R for the same curing period. Correspondingly, after 90 days, the IRA values were increased by 15%, 19% and 24% for HVFA-CBA-SCC mixes CHFB-25R, CHFB-50R, and CHFB-75R in comparison to control HVFA-CBA-SCC mix CHFB-0R.

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Further, IRA value was increased by 39% for HVFA-CBA-SCC mix CHFB100R compared to the control CHFB-0R mix (Figure 12).

Absorption coefficient (I in mm)

12 10

CHFB-0R

CHFB-25R

CHFB-75R

CHFB-100R

CHFB-50R

8 6 4 2

0 0

8

17

24

35

42

60

85 104 120 134 147 294 416 510 587

(Time in sec) ^ 1/2 Figure 11. CSAT values of HVFA-CBA-SCC mixes comprising RCA after 28 days of curing.

Absorption coefficient (I in mm)

10 CHFB-0R CHFB-50R

8

CHFB-25R CHFB-75R

6 4 2 0 0

8

17 24 35 42 60 85 104 120 134 147 294 416 510 587 (Time in sec) ^ 1/2

Figure 12. CSAT values of HVFA-CBA-SCC mixes comprising RCA after 90 days of curing.

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The SRA values (obtained after 4 days) for all the HVFA-CBA-SCC mixes CHFB-25R, CHFB-50R, CHFB-75R, and CHFB-100R were increased further by a maximum of 48% after 28 days of curing. However, after 90 days the increments were restricted to merely 15% in SRA values when compared to the reference HVFA-CBA-SCC mix. The porous network of RCA composed of old cement paste was characterized with higher porosity and was probably responsible for such IRA and SRA rates (Kumar and Singh 2020; Y. F. Silva et al. 2016; Navdeep Singh, M, and Arya 2019). In fact, the wateraccessible porosity is interrelated with the water/binder ratio and the porosity of RCA which subsequently leads towards a highly porous microstructure (Yüksel, Bilir, and Özkan 2007).

7.7. Co-Relation between Mechanical and Durability Properties Usually, the performance of concrete can be also well assessed by co-relating mechanical properties (compressive strength, tensile strength, and flexural strength) with durability properties [water absorption (surface absorption) and accelerated carbonation]. Regression analysis is a general technique of statistical modeling that is used to evaluate the relationship between known variables (Navdeep Singh and Singh 2016a). The said approach is commonly used for prediction and forecasting, where there are substantial risks of overlapping experimental findings. Further, the observed co-relations in the midst of independent and dependent variables can be effectively obtained using regression analysis (Scott 2012). Several proposals like linear, exponential, and power equation relationships amongst these properties can be put forward in the literature. In the present study, a finite number of unknown parameters were considered from the experimental data with more accuracy related to other approaches through the linear regression process (Cook 1982). To generalize relationship (s) amid these parameters, the results of the compressive strength, tensile strength, and flexural strength with water absorption and accelerated carbonation of all HVFA-CBA-SCC mixes were used. The linear relationship of compressive strength/tensile strength/flexural strength with water absorption and accelerated carbonation are presented in Table 4, Table 5, and Table 6 respectively.

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From the observations, it has been found that mechanical properties have a strong relationship with water absorption (surface absorption) and accelerated carbonation as most of the R2 values (Figure 13-21) are observed to be more than 0.8 for all the above-said properties. Table 4. Co-relation of compressive strength and durability properties Compressive strength vs Water absorption Compressive strength vs Accelerated carbonation

28 days curing (ISA 30)

90 days curing (ISA 30)

y = -0.0594x + 1.9948

y = -0.0322x + 1.3022

28 days curing 4 weeks exposure y = -2.5894x + 92.674

90 days curing 4 weeks exposure y=0.9461x + 44.253

12 weeks exposure y = -3.5839x + 131.94

12 weeks exposure y = -1.4151x + 68.681

Table 5. Co-relation of tensile strength and durability properties Tensile strength vs Water absorption Tensile strength vs

Accelerated carbonation

28 days curing (ISA 30) y = -0.1134x + 1.0723 28 days curing 4 weeks 12 weeks exposure exposure y=y = -7.0113x + 5.0762x + 77.074 53.084

90 days curing (ISA 30) y = -0.0892x + 0.8699 90 days curing 4 weeks 12 weeks exposure exposure y = -2.659x y = -4.0577x + 31.81 + 50.527

Table 6. Co-relation of flexural strength and durability properties Flexural strength vs Water absorption Flexural strength vs

Accelerated carbonation

28 days curing (ISA 30) y = -0.0818x + 0.9994 28 days curing 4 weeks 12 weeks exposure exposure y = -3.5234x y = -4.9218x + 49.023 + 71.782

90 days curing (ISA 30) y = -0.0472x + 0.677 90 days curing 4 weeks 12 weeks exposure exposure y=y=1.4234x + 2.1889x + 26.166 42.024

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60.0 50.0

R² = 0.9543

40.0 30.0 R² = 0.9611

20.0 10.0

4 Weeks

12 Weeks

0.0 22

23

24

25

26

27

Figure 13. Correlation amongst compressive strength and accelerated carbonation after 28 days of curing.

36.0 31.0 R² = 0.9083

26.0 21.0 16.0

R² = 0.9359 11.0 4 Weeks

12 Weeks

6.0 25

26

27

28

29

30

31

32

Figure 14. Correlation amongst compressive strength and accelerated carbonation after 90 days of curing.

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Pawan Kumar and Navdeep Singh

0.7 R² = 0.9819

0.6 0.5

R² = 0.9541

0.4 28 Days

0.3

90 Days

0.2 22

24

26

28

30

32

Figure 15. Correlation amongst compressive strength and water absorption.

53.0 48.0

R² = 0.9871

43.0 38.0 33.0 R² = 0.9982

28.0

23.0

4 Weeks

12 Weeks

18.0 3.5

4

4.5

5

5.5

6

6.5

Figure 16. Correlation amongst tensile strength and accelerated carbonation after 28 days of curing.

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40.0

30.0 R² = 0.9922 20.0 R² = 0.9821 10.0 4 Weeks

12 Weeks

0.0 4.5

5

5.5

6

6.5

7

Figure 17. Correlation amongst tensile strength and accelerated carbonation after 90 days of curing.

0.7 0.6

R² = 0.9675

0.5 0.4 R² = 0.9698 0.3 28 Days

90 Days

0.2 3.5

4

4.5

5

5.5

6

6.5

Figure 18. Correlation amongst tensile strength and water absorption.

7

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Pawan Kumar and Navdeep Singh 60.0 50.0

R² = 0.9161

40.0 30.0 R² = 0.9058

20.0 10.0 4 Weeks

12 Weeks

0.0 4

4.5

5

5.5

6

6.5

7

7.5

Figure 19. Correlation amongst flexural strength and accelerated carbonation after 28 days of curing.

35.0 R² = 0.9704

30.0 25.0

R² = 0.9459

20.0 15.0 4 Weeks

12 Weeks

10.0 4.5

5.5

6.5

7.5

8.5

9.5

Figure 20. Correlation amongst flexural strength and accelerated carbonation after 90 days of curing.

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0.7

R² = 0.9488

0.6 0.5 0.4 R² = 0.9133 0.3

28 Days

90 Days

0.2 4

5

6

7

8

9

Figure 21. Correlation amongst flexural strength and water absorption.

7.8. Cost Analysis Usually, coarse aggregates (NCA) obtained from NR are used to produce concrete which upon demolition is further dumped in landfills. The present study largely focuses on attaining sustainable HVFA-CBA-SCC that comprises supplementary materials either in the form of non-conventional and binders. In other words, the current investigation used a practice-oriented criterion in minimizing the degradation of natural resources and preventing excessive landfilling. The non-conventional aggregates (RCA) were acquired by mashing the remaining left-over concretes available in the testing laboratory. The equivalent volume (per cubic meter) approach has been applied for the cost analysis for all the HVFA-CBA-SCC mixes. The analysis includes the cost of the material (including taxes) and transport charges. The free-of-cost (only transportation charges) industrial by-products (FA and CBA) are obtained from Thermal power plant Ropar, Punjab. Table 7 highlights the cost of all the HVFA-CBA-SCC mixes. The optimum cost value has been observed for the SCC mix CHFB-0R having 100% of NCA in comparison to all other SCC mixes (Table 7). The difference in the cost is due to involvement of labor and machinery required to convert C&DW waste into comparable size of natural aggregates (NCA). Based on the cost analysis the mixes can be

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arranged in decreasing order as CFHB-R100 > CFHB-R75 > CFHB-R50 > CFHB-R25 > CFHB-R0. Table 7. Cost analysis of HVFA-CBA-SCC mixes S no

Materials

1. OPC 2. FA 3. CBA 4. NCA 5. RCA 6. NFA 7. SP 8. Water Total

Cost (Rs per Kg) 7.5 0.52 0.52 1.31 1.95 1.45 200 0.05

CHFB0R 2310 120.6 32.2 854.1 0 1070.1 420 13.9 4821

SCC mix Combinations CHFB- CHFB- CHFB25R 50R 75R 2310 2310 2310 120.6 120.6 120.6 32.2 32.2 32.2 640.6 427.1 213.50 294.5 587 881.4 1070.1 1070.1 1070.1 482 524 608 13.9 13.9 13.9 4963.9 5084.8 5249.8

CHFB100R 2310 120.6 32.2 0 1173.9 1070.1 672 13.9 5392.7

7.9. Global Warming Potential (GWP) The Global Warming Potential (GWP) was matured/advanced to allow comparisons of the global warming impacts of different gases. Precisely, it is a measure of Greenhouse gas (GHG) contribution to the processing of a material in terms of CO2 equivalent. The larger the GWP, the more that a given gas warms the Earth compared to CO2 over that time period. Usually, the CO2 equivalent is the count of gases formed in terms of carbon dioxide during the processing of machinery, material, and transportation, etc. The distinction in GWP usually depends upon various aspects such as boundary condition, country, and other factors considered/examined for the processing of ingredients of concrete (Mastali et al. 2018; Mithun and Narasimhan 2016). The values of CO2 equivalent for the different SCC ingredients have been taken from previous literature (Kurad et al. 2017; Pavlu, Kocí, and Hájek 2019; Roh et al. 2020; Simalti and Singh 2021) as presented in Table 8. The main emphasis of recognizing the GWP was to just relate the effect of NCA and RCA on HVFA-CBA-SCC mixes. It is visible from the figure (Figure 22) that SCC mix CHFB-0R comprising 100% of NCA highlights the maximum value (309.7 Kg CO2 e/m3) of carbon emission. Further, the value of carbon emission kept on decreasing as the amount of RCA is increasing in the remaining SCC mixes. The minimum value of 292.1 Kg CO2 e/m3 has

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been observed for SCC mix CHFB-100R having the full replacement of NCA. The preceding information shows that using RCA in place of NCA in HVFACBA-SCC mixes is a sustainable solution as less CO2 emissions are observed for SCC mixes having RCA (CHFB-25R to CHFB-100R) when related to reference SCC mix CHFB-0R. Table 8. Global warming potential of HVFA-CBA-SCC mixes S no

Materials

Co2 (Rs per Kg)

1. OPC 0.93 2. FA 0.004 3. CBA 0 4. NCA 0.0282 5. RCA 0.0012 6. NFA 0.0051 7. SP 0.0019 8. W 0.0008 Total CO2 equivalent 315

SCC mix combinations CHFB- CHFBCHFB25R 50R 75R 286.4 286.4 286.4 0.9 0.9 0.9 0.0 0.0 0.0 13.8 9.2 4.6 0.2 0.4 0.5 3.8 3.8 3.8 0.0 0.0 0.0 0.2 0.2 0.2 305.3 300.9 296.5

CHFB100R 286.4 0.9 0.0 0.0 0.7 3.8 0.0 0.2 292.1

309.7

310

Axis Title

CHFB0R 286.4 0.9 0.0 18.4 0.0 3.8 0.0 0.2 309.7

305.3

305

300.9

300

296.5 292.1

295 290 285 280 CHFB-0R

CHFB-25R

CHFB-50R

CHFB-75R CHFB-100R

Axis Title

Figure 22. Global warming potential of HVFA-CBA-SCC mixes for per m3.

Conclusion The average compressive strength of reference SCC mix (CHFB-0R) and SCC mixes comprising RCA (CHFB-25R, CHFB-50R, CHFB-75R, and CHFB-

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100R) increased from 19.5-31.2 MPa and 16.2-30.4 MPa respectively. The tensile strength rises from 4.6-6.7 MPa and 3.1-6 MPa for the reference SCC mix and SCC mixes encompassing RCA respectively but when compared to reference mix maximum decrement of 33% has been witnessed for SCC mix CHFB-100R. The maximum decrement of flexural strength for 41% has been observed in SCC mix CHFB-100R comprising 100% of RCA whereas a minimum reduction of 19% has been noticed for SCC mix CHFB-0R after 90 days of curing. Similar to the compressive and tensile strengths, all the SCC mixes have reasonable strength compatible to reference SCC mix CHFB-0R despite continuous reduction in flexural strength due to the presence of RCA. The surface absorption is increased with increment in the levels of RCA (25% 100%). For example, after a curing time of 28 days, ISA 10 values have been increased by about 15%, 23%, 38% and 58% for all the SCC mixes CHFB25R, CHFB-50R, CHFB-75R, and CHFB-100R respectively in relation to mix CHFB-0R. A maximum increase of 43% and 40% in carbonation depths has been observed for mix CHFB-100R after 4 and 12 weeks of exposure in comparison with reference SCC mix CHFB-0R. The observed findings demonstrate that the gap between CHFB-0R and CHFB-25R is minimal/slight as maximum increase in carbonation depth has been limited up to 8% and 10% after 4 and 12 weeks of exposure at 90 days of curing time. The IRA value for SCC mix CHFB-100R was 2.3 times higher than the value observed for control HVFA-CBA-SCC mix CHFB-0R for the same curing period. Correspondingly, after 90 days, the IRA values were increased by 15%, 19% and 24% for HVFA-CBA-SCC mixes CHFB-25R, CHFB-50R, and CHFB-75R in comparison to control HVFA-CBA-SCC mix CHFB-0R. However, after 90 days the increments were restricted to merely 15% in SRA values when compared to the reference HVFA-CBA-SCC mix. It has been noticed that the mechanical properties in relation to durability properties represent overall strong linear relationships as most of the regression coefficients (R2) are observed to be more than 0.8 which further validates an agreeable performance of CBA-based SCC mixes. The optimum cost value (Rs 4821) has been observed for the SCC mix CHFB-0R having 100% of NCA in comparison to all other SCC mixes. The preceding information shows that using RCA in place of NCA in HVFACBA-SCC mixes is a sustainable solution as less CO2 emissions are observed for SCC mixes having RCA (CHFB-25R to CHFB-100R) when related to reference SCC mix CHFB-0R.

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Acknowledgments The authors acknowledge the Department of Civil Engineering of Dr B R Ambedkar National Institute of Technology, Jalandhar, India for all kinds of support.

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Resources, Conservation and Recycling, 138 (July), 257–71. https://doi.org/10.10 16/j.resconrec.2018.07.025. Singh, Navdeep, Mithulraj, M., and Shubham, Arya. (2019). “Utilization of Coal Bottom Ash in Recycled Concrete Aggregates Based Self Compacting Concrete Blended with Metakaolin.” Resources, Conservation and Recycling, 144 (February), 240–51. https://doi.org/10.1016/j.resconrec.2019.01.044. Singh, Navdeep, Pawan Kumar, and Paresh Goyal. (2019). “Reviewing the Behaviour of High Volume Fly Ash Based Self Compacting Concrete.” Journal of Building Engineering, 26 (April), 100882. https://doi.org/10.1016/j.jobe.2019.100882. Singh, Navdeep, Shehnazdeep, and Anjani Bhardwaj. (2020). “Reviewing the Role of Coal Bottom Ash as an Alternative of Cement.” Construction and Building Materials, 233, 117276. https://doi.org/10.1016/j.conbuildmat.2019.117276. Soares, D., De Brito, J., Ferreira, J., and Pacheco, J. (2014). “Use of Coarse Recycled Aggregates from Precast Concrete Rejects: Mechanical and Durability Performance.” Construction and Building Materials, 71, 263–72. https://doi.org/10.1016/j.conbui ldmat.2014.08.034. Tabsh, Sami, W., and Akmal S. Abdelfatah. (2009). “Influence of Recycled Concrete Aggregates on Strength Properties of Concrete.” Construction and Building Materials, 23 (2), 1163–67. https://doi.org/10.1016/j.conbuildmat.2008.06.007. Thomas, C., Setién, J., Polanco, J. A., Alaejos, P., and Sánchez De Juan, M. (2013). “Durability of Recycled Aggregate Concrete.” Construction and Building Materials, 40, 1054–65. https://doi.org/10.1016/j.conbuildmat.2012.11.106. Tuyan, Murat, Ali Mardani-Aghabaglou, and Kambiz Ramyar. (2014a). “Freeze-Thaw Resistance, Mechanical and Transport Properties of Self-Consolidating Concrete Incorporating Coarse Recycled Concrete Aggregate.” Materials and Design, 53 (August), 983–91. https://doi.org/10.1016/j.matdes.2013.07.100. Tuyan, Murat, Ali Mardani-Aghabaglou, and Kambiz Ramyar. (2014b). “Freeze-Thaw Resistance, Mechanical and Transport Properties of Self-Consolidating Concrete Incorporating Coarse Recycled Concrete Aggregate.” Materials and Design, 53, 983– 91. https://doi.org/10.1016/j.matdes.2013.07.100. Vries, P de. (1996). “Concrete Recycled: Crushed Concrete Aggregate.” In Proc. of the International Conference: Concrete in the Service of Mankind, 121–30. Wu, Zemei, Caijun Shi, and Khayat, K. H. (2016). “Influence of Silica Fume Content on Microstructure Development and Bond to Steel Fiber in Ultra-High Strength CementBased Materials (UHSC).” Cement and Concrete Composites, 71 (May), 97–109. https://doi.org/10.1016/j.cemconcomp.2016.05.005. Xiao, Jianzhuang, Wengui Li, Zhihui Sun, David A. Lange, and Surendra P. Shah. (2013). “Properties of Interfacial Transition Zones in Recycled Aggregate Concrete Tested by Nanoindentation.” Cement and Concrete Composites, 37 (1), 276–92. https://doi.org/ 10.1016/j.cemconcomp.2013.01.006. Yao, Z. T., Ji, X. S., Sarker, P. K., Tang, J. H., Ge, L. Q., Xia, M. S., and Xi, Y. Q. (2015). “A Comprehensive Review on the Applications of Coal Fly Ash.” Earth-Science Reviews, 141, 105–21. https://doi.org/10.1016/j.earscirev.2014.11.016.

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Yaragal, and Subhash. (2017). “Performance Studies on Concrete with Recycled Coarse Aggregates,” Advances in Concrete Construction, 4(4), 263-281. https://doi.org/10. 12989/acc.2016.4.4.263. Yüksel, Isa, Turhan Bilir, and Ömer Özkan. (2007). “Durability of Concrete Incorporating Non-Ground Blast Furnace Slag and Bottom Ash as Fine Aggregate.” Building and Environment, 42 (7), 2651–59. https://doi.org/10.1016/j.buildenv.2006.07.003. Zhang, M. H., and Canmet. (1995). “Microstructure, Crack Propagation, and Mechanical Properties of Cement Pastes Containing High Volumes of Fly Ashes.” Cement and Concrete Research, 25 (6), 1165–78. https://doi.org/10.1016/0008-8846(95)00109-P. Zoran, J. G., Gordana, A. T., Iva, M. D., and Nenad, S. R. (2010). “Properties of SelfCompacting Concrete Prepared with Coarse Recycled Concrete Aggregate.” Construction and Building Materials, 24, 1129–1133.

Chapter 2

Infrared Thermography Analysis of Sulfur Polymer Concrete Exposed to Accelerated Aging Milica Vlahović1,* and Tatjana Volkov Husović2 1 Department

of Electrochemistry, Institute of Chemistry, Technology and Metallurgy, National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia 2 Department of Metallurgical Engineering, Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia

Abstract In the presented research, secondary sulfur was used as a binding agent in concrete. The starting point was that sulfur is known as a binder and that it can quite possibly be used as a binding agent in building materials. The next step was the development of technology, i.e., the process of sulfur polymer concrete manufacturing in order to optimize the technological parameters for producing high-quality material. Sulfur polymer composites, concretes and mortars, are high-performance environmentally sustainable and durable thermoplastic materials made of mineral aggregates, filler and modified sulfur binder which replaces cement and water in conventional Portland cement composite at temperatures above the hardening point of sulfur (120°C). Various additives were used to modify sulfur by its polymerization, whereby one *

Corresponding Author’s Email: [email protected].

In: Cement and Concrete Editors: Kong Fah Tee, Siew Choo Chin and Koorosh Gharehbaghi ISBN: 979-8-88697-831-5 © 2023 Nova Science Publishers, Inc.

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Milica Vlahović and Tatjana Volkov Husović of them is dicyclopentadiene which reacts with elemental sulfur thus forming long-chain polymeric polysulfides. Unlike conventional Portland cement-based concrete, sulfur polymer concrete is produced without water and achieves its final strength in a few days. State-of-the-art research indicates that composite materials with modified sulfur binder instead of cement and water have significant chemical and physico- mechanical advantages compared with Portland cement-based composites. The technological procedure for sulfur polymer concrete synthesis is followed by the research related to the examination of the material’s properties as well as testing the new material quality during the exploitation, which is far more important due to the fact that the influence of various environmental factors causes a certain degree of destruction and, therefore, degradation of the basic properties of all materials, including the building materials. These processes of accelerated corrosion or aging processes are caused by high atmospheric, water, and soil pollution, so the investigation of the newly obtained material- sulfur polymer concrete is directed towards the analysis of its behavior in the presence of the induced destruction agent. One of the key elements is a selection of methodologies for monitoring the resulting changes. For testing the material behavior under the influence of the induced destruction agent, more precisely for examining its thermal properties, infrared thermography was applied. The infrared thermography analysis results pointed out significant structural differences among the sulfur polymer concrete samples treated by the accelerated aging agent during the different time periods. Also, the same analysis showed noticeable differences in thermal properties between sulfur polymer concrete and Portland cement concrete samples owing to the structural changes during the exposure to the agent.

Keywords: sulfur polymer concrete, modified sulfur, Portland cement concrete, infrared thermography

1. Introduction 1.1. Safety and Environmental Management of Secondary Sulfur Sulfur is an element that was being removed from the atmosphere by slow natural processes during eons whereby it was binding to metals giving ores or to organic materials through food chains leading to its storage in crude oil.

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This made sulfur the 16th most abundant element in nature. Due to the technological revolution in the last 200 years, these natural processes were reversed towards restoring extremely huge amounts of sulfur to the environment mainly by exploiting minerals and crude oil. Now, the people and the planet are facing a serious problem regarding the treatment of waste sulfur. Unfortunately, the global trends in environmental protection put the focus on solving the problem of carbon dioxide emissions and greenhouse effects (Vlahović, 2012a). During the 1960s, there was a remarkable investment in environmental protection against sulfur deposal into the atmosphere, thus making sulfur a surplus commodity on the market, particularly in the United States of America and Canada. Therefore, extensive research programs concerning further development of using sulfur as a structural binder as well as characteristics of the obtained material including durability were initiated. The rapidly expanding world economies required a sharp increase in energy demand which still dominantly comes from oil. The sulfur content in crude oil principally varies from 5 wt. %. Crudes with approximately up to 0.5 wt. % sulfur are considered sweet, and those with more than 0.5 wt. % sulfur are considered "sour." High-sulfur crudes, especially those with a sulfur content >0.5 wt. %, complicate and make refining more expensive. At the same time the world’s regulatory agencies are enacting increasingly stringent environmental regulations. These regulations not only apply to emissions from the refining complex itself, but on the products produced by the refinery as well. These regulatory and market dynamics have created a challenging environment for a refiner to operate in, especially with respect to recovery and disposition of sulfur (sulfur management) (Vlahović et al., 2013; Gracia, Vàzquez and Cramona, 2004). Mostly owing to the current strict global environmental regulations regarding the petroleum and gas refining processes limiting the maximum quantity of sulfur present in combustibles, the availability of sulfur has considerably grown in many countries during the last decades, so it is evident that there will be a continuous abundant supply of sulfur in the future. There has been a significant increase in sulfur availability in many parts of the world during the last few decades. The main reasons for that are strict environmental regulations limiting allowable sulfur content in combustibles during the oil and gas refining, which leads to future permanent and enormous sulfur supply. Waste sulfur from oil refining is stored, while waste sulfur from ore processing, in the form of gaseous sulfur oxides, is usually converted into

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sulfuric acid which is afterward used for the artificial fertilizers production. Modern industrial production still requires further development of technologies that would provide incorporating waste sulfur into useful products. In all cases of producing large quantities of waste, building materials represent media that should be examined as potential waste acceptors. The fact is that a wide range of hazardous waste can be inerted by their incorporating into usable building materials. Building materials are preferred recipients because of large amounts of secondary sulfur and, on the other hand, because of their enormous practical application. Consuming sulfur for the production of sulfur polymer composites- concretes and mortars is a relatively new technology that has to be proven in practice. These materials are already in use, but improving their quality for further application is still needed. They have a relatively simple composition and manufacture, and interesting properties; also, they continue to receive more attention since they are environmentally friendly and cost-effective. Due to their mechanical strength, fast hardening and corrosion resistance, they belong to high performance materials suitable for numerous applications, especially those in which other materials fail (Vlahović and Martinović, 2018). From another point of view, polymeric materials based on inorganic components can have an important role in various technological processes. Although their production on an industrial scale is still problematic, inorganic polymers combined with other materials can generate sustainable high-quality and usable composite materials. Among inorganic materials that are able to form polymer chains under certain conditions, special attention should be paid to sulfur. Sulfur itself tends to polymerize to a large extent while chemical modification increases this tendency or prolongs the time required for the polymerization. Owing to its physico-chemical characteristics such as chemical passivity, excellent resistance to aggressive agents (acids and salt solutions) and hydrophobicity, sulfur can replace Portland cement to form a new, stable, hard composite product (Vlahović, 2012a). Although composites with sulfur as a binder have to be heated during manufacturing, they release far fewer greenhouse gas emissions compared with Portland cement composites. Namely, the Portland cement composite production process achieves nearly zero carbon emissions, but, when it comes to carbon footprint the true problem is the Portland cement. The gases liberated in the calcination during clinker fabrication at temperature of 1450°C as well as the combustion emissions generated to supply heat to the calcination process are avoided if sulfur binder is used (Vlahović et al., 2013).

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1.2. Development of Using a Sulfur Binder for Composite Materials Production Introducing sulfur for composites production has started with elemental sulfur as a binder. However, in spite of the excellent mechanical properties after production, the material showed low stability, so spalling and failure occurred after a short period. Also, exposure to repeated cycles of freezing and defrosting in terms of high humidity or immersion into water caused its degradation and failure. This can be explained by sulfur transformation. Namely, on cooling of casted liquid mixture, sulfur crystallizes as monoclinic Sβ at 114°C with volume contraction of 7%. Below 95.5°C, it transforms entirely to rhombic Sα within 20 hours. Higher density of Sα compared with Sβ provokes stresses and micro-cracking within the material. This causes easier moisture penetration into the material that therefore fails quickly (Mohamed and El Gamal, 2010). The development of a modified sulfur binder contributed to better endurance of sulfur polymer composite, which focused its application for roads construction and repairing and as a building material (Diehl, 1976; Beaudoin and Feldmant, 1984; Sullivan, McBee and Blue, 1975; Gregor and Hackl, 1978). Except the prevention of sulfur transformation from monoclinic to orthorhombic form, the degree of sulfur polymerization is increased and long chains are created due to modification. Modified sulfur has much lower thermal expansion coefficient compared with elemental one, therefore shrinkage and residual stresses upon cooling are lower. The polymer prevents the growth of macro- sulfur crystals. Long-term durability of modified sulfur polymer composite lies in the stability of microcrystalline sulfur (Vlahović and Martinović, 2018). Sulfur polymer composites, concretes and mortars, are high performance thermoplastic materials made of mineral aggregates, filler, and modified sulfur binder, instead of cement and water as in conventional Portland cement composites at temperatures above the hardening point of sulfur (120°C). Using sulfur to make modified sulfur binder is based on its physico-chemical characteristics. According to our own terminology, the term modified sulfur binder means a mixture of elemental sulfur and modified sulfur- sulfur polymer. Recent experience all over the world shows that composite materials produced with modified sulfur binder instead of cement and water have significant chemical and physico-mechanical advantages comparing with Portland cement composites (Mohamed and El Gamal, 2010).

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Although sulfur polymer composite is a commercial product in the United States of America, Canada, and Poland, neither its production is precisely defined process, nor its composition determined accurately. In general, beside sulfur, sulfur polymer composites contain mineral aggregates (rock, limestone, gravel, slag, dolomite, crushed concrete with Portland cement, calcium silicate, fibers of glass wool, sand, synthetic aggregates, volcanic material, ceramic material, etc.), filler (sand, fly ash, coal, dolomite, gypsum, limestone, pyrite, ground granite, calcite, barite, etc.), and various additives for polymerization or modification of sulfur, suppression of crystallization, suppression of forming and releasing sulfur gases, removing the odor of the composite material, increasing mechanical strength, etc. For a given aggregate, which is selected to be the closest to the application place, it is necessary to define the size and shape of particles, the optimal amount of sulfur in the mixture and the amount and type of additives and fillers. The production of sulfur polymer composite does not include water that is somewhere in deficiency (the Middle East) or available but contaminated and with an excess of mineral salts, which negatively affects the properties of Portland cement composite (Vlahović and Martinović, 2018; Diehl, 1976).

1.3. Sulfur Polymer Concrete Mixture Design and Manufacturing Procedures Contemporary tendencies desire production of materials with required characteristics based on combining constituents with different properties and in various proportions, as well as on the application of diverse manufacturing procedures and additional material processing. The mixture of sulfur polymer composite has to be designed to provide the best balance between mechanical strength, density, and workability. A limited absorption into the solidified material will lead to good durability even in extreme conditions. In order to obtain sulfur polymer composite with appropriate physicochemical and mechanical properties depending on the application, the initial components should satisfy certain requirements: •

Precisely defined grain size distribution to provide maximal dense packing of aggregates grains and minimize the amount of binder;

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• •

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Spherical shape of aggregates grains to achieve maximal dense particle packing with the reduced number of voids and pores, and therefore greater strength of the material; High resistance to aggressive chemical agents and sudden temperature changes enabling good stability of the material; Low porosity in order to provide low absorption of moisture.

The function of fillers in concrete is based mainly on their size and shape. Small fraction (≤ 75 μm) of filler improves particle packing by fulfilling free space among aggregates grains, thus increasing homogeneity and fluency of mixture which leads to obtaining dense product with a minimum content of voids and pores. They provide better properties of composite, even reducing the amount of binder without strength loss. During cooling and hardening, filler prevents forming large cyclic sulfur crystals thus improving mechanical properties of the composite (Mohamed and El Gamal, 2009; Report 548.2R93, 1993; Dotto et al., 2004; Moosberg-Bustnes, Lagerblad and Forssberg, 2004). Sulfur polymer concrete is produced by mixing aggregate, filler, and binder in the temperature range 130°-150°C. Mechanical mixers that can keep required temperature are adequate for this purpose. The proportion of aggregate, filler, and binder for the preparation of sulfur polymer concretes may vary depending on the application. Different procedures for sulfur polymer concrete production are schematically presented in Figures 1-6 (Mohamed and El Gamal, 2010): 1) Aggregate and filler are preheated and the molten modified sulfur is added, Figure 1.

Figure 1. Early Chempruf mixing scheme (Mohamed and El Gamal, 2010).

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2) All components are mixed at ambient temperature and then stirred along with heating until melting, Figure 2.

Figure 2. Sulkret mixing scheme (Mohamed and El Gamal, 2010).

3) Aggregate and filler are preheated and solid modified sulfur is added, Figure 3.

Figure 3. 4K A/S mixing scheme (Mohamed and El Gamal, 2010).

4) Aggregate is preheated and mixed with simoultaneous adding filler and modified sulfur, Figure 4.

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Figure 4. Later Chempruf scheme (Mohamed and El Gamal, 2010).

5) Aggregate is preheated. Solid modified sulfur is added and stirred until molten state is achieved and aggregate is completely covered with sulfur. Cold filler is added in the flowing mixture, heated and stirred continuously, until the concrete is homogenous, Figure 5.

Figure 5. ACI mixing scheme (Mohamed and El Gamal, 2010).

6) Elemental sulfur and modifiers are heated at temperature 130°-150°C. Molten sulfur is mixed with modifier forming modified sulfur. Filler is preheated to higher temperature, compared with the temperature of sulfur mixing, and transferred to form sulfur cement after mixing it with modified sulfur. Aggregate is preheated similarly to filler and mixed with sulfur cement forming homogenous product, Figure 6.

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Figure 6. Mohamed and El Gamal mixing scheme (Mohamed and El Gamal, 2010).

1.4. Application of Sulfur Polymer Concrete Sulfur polymer concrete can be used as a highly durable replacement for constructional materials at places within the industrial plants where the acids and salts cause premature destruction and cracking, as well as at locations with frequent cyclic freezing and melting. It has the most frequent usage: in food processing plants and chemical industry where aggressive materials are produced and stored, in plants for sewage treatment, on farms for domestic animals, for elements designed for sea area, drainage channels and sewage pipes, paving the pedestrian paths, curbs, sidewalks, roof tiles, railway and tramway sleepers, etc. (Vlahović et al., 2011). Sulfur polymer concrete can be used for solidification and encapsulation of different waste materials, such are fly ash, cement kiln dust, phosphogypsum, mercury, thus obtaining the sustainable development of construction and industrial sectors and for corrosion protection of reinforcing steel and concrete (Mohamed and El Gamal, 2012; Mohamed and El Gamal, 2011; Lopez et al., 2011; Adams, Bowerman and Kalb, 2001).

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1.5. Infrared Thermography for Real Time Inspection of Composite Materials During the service life of all materials, including composites, various environmental conditions affect them thus causing a certain degree of destruction and therefore degradation of their basic properties. In examining the properties of the material and quantifying their changes resulting from these processes of accelerated corrosion or aging, various non-destructive methods can be successfully implemented. Knowledge of the thermal processes can be of great significance because thermal phenomena are a rich source of information about various processes and changes or irregularities occurring during them, which allows for the control of these processes and the necessary modification. In non-destructive testing, temperature is usually assessed by analyzing the thermal, or infrared, radiation released by investigated specimens. Infrared thermography is a non-invasive, non-contact and inexpensive method of detecting, registering, processing, and afterward visualizing infrared radiation. The obtained thermogram represents the temperature distribution on the surface of the investigated material or object. The nondestructive and contactless measurement of the observed objects in most applications is the basic criterion for the use of thermal imaging techniques. When it comes to the early history of infrared science, there are some dilemmas, but it is certainly known that the ideas about the practical application of infrared radiation appeared in the late nineteenth century and the first applications of infrared technology date from the beginning of the twentieth century. Thermal non-destructive testing is gaining in importance due to its wide range of applications, high inspection rate and relatively affordable prices, so that infrared thermographic diagnostics and thermal non-destructive testing today represent a developed technology area that brings together advances in heat conductivity, materials science, infrared technology and computer data processing. In order to overcome the lack of every non-destructive method, it is possible to assemble them, so that thermal non-destructive testing can be complemented by the other techniques such as ultrasonic, eddy current, and laser, whereby similar physical principles and hardware may be implemented. Thermal non-destructive testing is usually compiled with ultrasonic testing particularly when the later has problems with detection. Principally, this technique is applicable to all types of materials, which makes it very flexible

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and versatile compared to other conventional non-destructive technologies (Vavilov and Burleigh, 2020; Jorge Aldave et al., 2013). The thermal non-destructive testing method can detect different types of faults in composite materials including voids, porosity, delaminations, foreign matter inclusions, trapped water, variations in thermal and physical properties as well as in thickness and other geometric features. The clear correlation between the thermal properties measurement and the detection of defects lies in the fact that a certain fault, like delamination, provokes a modification of the local characteristics of the material, whereby the disseminated concentration of micro-defects, like porosity, produces changes in the bulk thermal properties (Vavilov and Burleigh, 2020). The first reported researches in active thermal non-destructive testing appeared in the sixties of the 20th century in reviews written by Willburn (1961) and a few years later by Mc Gonnagle and Park (1964). Pulsed thermal non-destructive testing of composites was summarized twenty years later by Milne and Reynolds (1984), while a literature survey and bibliography on thermal non-destructive testing of composite materials was prepared by Burleigh in (1987). Periodic thermal waves in application to thermal nondestructive testing were reported by Almond and Patel (1996). General principles of active thermal non-destructive testing of composites were described by Vavilov and Taylor (1982) and Maldague (2001) and summarized in the ASNT IR handbook (2001). The recent papers covering thermal non-destructive testing were written by Vavilov (2007, 2014) and Vavilov and Burleigh (2015). The principle of infrared thermography is based on the physical phenomenon that any body that is at a temperature above absolute zero emits electromagnetic radiation in the range of wavelengths of 0.1-100 m known as thermal radiation. The surface of an object and the intensity and spectral composition of the radiation that it emits are in an understandable relationship. All areas of the electromagnetic spectrum carry certain information about the object or process where they were generated, Figure 7. While the visible portion of the spectrum provides data on the morphological properties of objects, as well as colors, the thermal properties of processes or objects are manifested in the infrared part of the electromagnetic radiation spectrum. Infrared thermography or thermovision is a traditional method for temperature mapping of objects, i.e., for visualization of temperature distributions (Grinzato, Bison and Marinetti, 2002).

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Figure 7. Electromagnetic radiation spectrum (Scribrr, no date).

The electromagnetic spectrum is arbitrarily divided into a large number of parts, strips, with reference to the wavelengths. The bands differ depending on the methods used to cause and detect radiation. There are no significant variations between radiations in various bands of the spectrum; everything is subject to the same laws and the only difference is in the wavelengths. As mentioned, thermography uses the infrared part of the spectrum, Figure 8. At shorter wavelengths of the infrared part of the spectrum, the end of the spectrum lies in the visible region, and at longer wavelengths, the infrared end of the spectrum borders microwaves. For practical reasons, the infrared part of the spectrum is divided into four smaller areas, with the border being chosen arbitrarily. The infrared spectrum includes the following spectral regions: • • • •

Near-infrared (wavelengths from 0.75 to 3 m), Mid-infrared (wavelengths grom 3 to 6 m), Far-infrared (wavelengths from 6 to 15 m), and Extreme-infrared (wavelengths from 15 to 100 m).

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Figure 8. Electromagnetic spectrum with its IR part used for thermal imaging (Meléndez, 2010).

Thermal imaging takes place in the infrared range of 7.5-13 m, with a spectral resolution of 1.3 mrad. The infrared spectrum in this area provides information on the temperature distribution on the surface of the observed object or process. Unlike other infrared analyses, the result of these analyses is an image, visual information, whereby the intensities of the measured infrared radiation are represented by color. It should be noted that the obtained thermal images (thermograms) are pseudo images, delivered using the appropriate LUT tables, i.e., by programmatically correlating the temperature to the paints or color valers. In this way, current information on the temperature distribution on the observed object is obtained in the form of visual information, Figure 9. Infrared thermography or thermal imaging as a non-destructive and contactless testing method is applicable for the detection of subsurface features, that is, subsurface defects, anomalies, etc., owing to temperature differences observed on the examined surface during monitoring by an infrared camera. It can offer information about the precise physical location of an occurring defect, which enables the subsequent electrical identification of an issue. This measurement technique is based on the detection of the emitted radiation in the infrared range of the electromagnetic spectrum, usually in the 2-5.6 m and 8-14 m regions, because of the low atmosphere absorption of these two spectral bands. This corresponds to wavelengths longer than the visible light portion of the electromagnetic spectrum.

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Figure 9. Thermal imaging of ceramic cups during firing.

Today's thermal imaging systems use the third generation of microbolometric semiconductor sensors that do not require cooling, which is a significant improvement when used in various applications. The new detectors enable recording at higher wavelengths, which enables better image quality, measurements of higher precision and elimination of the solar reflection influence. The resolution of the obtained image is 640x480 pixels, which corresponds to modern image processing systems. Contactless measurement in the temperature range from -40° to 2000°C is enabled, with an average measurement accuracy of ±2°C. The emissivity of an object can be defined either by a special set of measurements or it can be selected automatically from the emissivity list of the most frequently analyzed materials (Balaras and Argiriou, 2002; Albatici and Tonelli, 2010). The material testing using infrared thermography methodology encompasses measurement and analysis of the temperature field. The infrared camera as a detecting device accepts varying amounts of infrared radiation from the surface of the material and forms a thermographic image or thermogram that presents a map of its distribution. The inconsistent interior structure or presence of defects produce a various thermal conduction in the investigated material, thus having an influence on the heat flow, which means that it will cool down or warm up at different ratio. Consequently, the definitely acquired thermographic image will exhibit various thermal contrasts. As a simple and inexpensive imaging technique, infrared thermography is widely applicable in a variety of research fields and industries. In most of its

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applications, testing is carried out in a passive way, that is, the camera detects the thermal radiation emitted by objects. Detection of defects by means of infrared thermography is an active method, which implies that the heat flow required to produce the temperature differences in the tested material is enabled by providing additional energy. Active infrared thermography applies few excitation methods for producing thermal waves in the material without destruction, which rely on optical, mechanical, and inductive processes. The selection of the excitation method is determined by the type of defect or investigated material (Jorge Aldave et al., 2013).

1.6. Research Objectives Having in mind that while in service use, all materials are exposed to different external impacts that provoke some type of response, the idea of this study was to examine the quality of manufactured sulfur polymer concrete in extreme conditions, during the accelerated aging testing in hydrochloric acid solution. Since sulfur polymer concretes are relatively new building materials that can possibly replace conventional material made with Portland cement as a binder in many branches of construction, it was found plausible to choose Portland cement concrete as a reference material. In order to quantify the changes in the material structure as its response to the specific imposed stimulus, one non-destructive technique, infrared thermography testing, as a very fast non-destructive tool for examination of a wide range of materials, including composites, was applied as an addition to previous analyses that included image analysis, mathematical morphological analysis, ultrasonic pulse velocity testing, and SEM analysis.

2. Background Research The research started with series of experiments performed in the laboratory conditions with the aim to conquer basic techniques and to define the order of operations in the process of mixing sulfur, aggregate and fillers, as well as to establish proportions in the consumption of sulfur and aggregate for the synthesis of sulfur polymer concrete. The fine fraction of the classical building mixture of sand and gravel, as well as a variety of other materials, such as slag,

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ash, and coal dust were used as an aggregate. At the same time, different types of fillers were used. Application of the modified sulfur is of exceptional importance for obtaining sulfur polymer concrete because it provides solidification of sulfur in open, entangled long chains thereby preventing brittleness of the composite material. For the selection of modifier decisive factor was the market availability and price. Although the literature dealing with sulfur polymer concrete production already exists, the performed experimental work provided developing our own technologies for sulfur polymer concrete manufacture as well as for sulfur modification. Also, the applied terminology differs from the one offered in the literature. Modified sulfur means polymerized sulfur, which is obtained by the addition of chemical additives- modifiers to elemental sulfur. Modified sulfur binder means a mixture of elemental and modified sulfur. By mixing it with a mineral aggregate of a suitable composition, and filler added, at sulfur melting point temperature, during solidification sulfur polymer concrete is obtained. After obtaining the material, very important in defining the applicability of sulfur polymer concrete is the examination of its properties. In the presented research, the emphasis is placed on modern methods and methodologies for quantifying the properties of materials based primarily on the principles of planning experiments and defining working models. In essence, the engineering approach to analysis is applied- the development potentials of materials are determined while the phenomena that occur within the material are not defined. Experiment planning is a methodology that defines in advance the purpose of setting up experiments so that experiments are performed with a clearly defined goal. In addition to defining the experiments, it was necessary to determine the procedures as well as the methodology for quantifying the properties that need to be examined. The basis of the plan was a selection experiment that defined the parameters of the material, as well as the ways of examining its changes during the time. Initial methods were based on methods applied to the same or similar group of materials to which sulfur polymer concrete belongs. It was quite logical to choose Portland cement concrete, produced with the same aggregate and Portland cement binder, as a referent material. The reason for this is in the fact that characterizations of sulfur polymer concrete and Portland cement concrete are quite the same because of their similar possible applications. With the aim to assess durability, or quality of the obtained sulfur polymer concrete, in other words its life cycle, accelerated destruction technique was

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applied. This methodology is based on the influence of an agent which may cause material damage, i.e., the change of physical, chemical, and mechanical properties. Accelerated destruction agent is used in increased concentrations in order to cause changes as quickly as possible. Therefore, the destruction of the sulfur polymer concrete with various fillers in three different aggressive environments during a period of one year was monitored. Change of mass, compressive strength, and apparent porosity served as parameters for estimating destruction of the material (Vlahović et al., 2011; Vlahović et al., 2010). These examinations represented the selection experiments. Based on the results of selection experiments, the composition of the sulfur polymer concrete in terms of filler choice, as well as the aggressive agent for further investigation was determined. Accordingly, in the experiments that followed, sulfur polymer concrete samples with alumina as filler were immersed in 10% hydrochloric acid solution as an accelerated destruction agent. The next step was the choice of adequate methods for monitoring changes. Since destructive test methods are not reliable for non-homogenous systems, methods based on non-destructive testing of changes in the material were selected. The use of non-destructive methods requires the existence of a standard, material, or system whose properties are known, or which can be used for making comparisons with a new material (system). Further activity was focused on defining changes in the structure of the investigated material, sulfur polymer concrete, and their comparing with the referent material Portland cement concrete. Macroscopic observation of the sulfur polymer concrete samples after six months of accelerated aging in the solution of hydrochloric acid confirmed the absence of any signs of surface damage or deterioration. There was also no significant mass loss or surface roughness. On the contrary, Portland cement concrete samples exhibited strong damage after 60 days, so further accelerated destruction testing in the same solution was not possible. Therefore, the examination of the Portland concrete was performed on the samples after up to 21 days of immersion (Vlahović et al., 2014). Image analysis of microphotographs taken through a microscope was applied as a conventional way of these examinations, whereby the samples were cut and changes of the obtained slices were quantified. The question of the resolution necessary for observing the surface or the interior of the samples

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in this case was solved by using two types of microscopes, optical and scanning electron microscope (SEM). Image analysis of the sample surface is an important non-destructive method for assessing the damage of the materials. Due to image analysis, more systematic and more accurate measurements have become possible (Vlahović et al., 2012b). Therefore, more objective characterization of concrete from the aspect of material properties is provided. Evaluation of various properties, as well as the effect of external influences on the microstructure of composite materials, can be investigated using these non-destructive methodologies. This methodology was successfully applied to quantify the damages of the composite materials exposed to different extreme conditions (Vlahović et al., 2013; Martinović et al., 2013; Martinović et al., 2014, Martinović et al., 2015). Surface defects are expressed as damage level, which presents the ratio of the damaged area and the initial ideal area. All synthesized composite samples have a certain damage level before exposure to various external influences and its value increases during the treatment. The image analysis results showed a very low destruction level of sulfur polymer concrete and indicated that the detected places of defects did not have a significant influence on macro destruction, whereby the destruction level of Portland cement concrete was very high (Vlahović et al., 2012b). In addition, a mathematical morphological analysis of the materials’ structures was performed. For that purpose, the samples were cut into slices which were analyzed in order to define the way of accelerated destruction agent influence throughout the entire volume of the material. Examinations were directed towards choosing structure parameters that would adequately represent changes throughout the volume. According to the trends of selected parameters variations throughout the volume of the samples, it was concluded that homogenization of sulfur polymer concrete sample occurred during the time of accelerated destruction. The greatest homogeneity increase happened on the 21st day of treatment. The influence of the accelerated destruction agent was towards rearranging sulfur, which was the main factor of homogeneity changes. On the contrary, according to a similar analysis, the homogeneity of the Portland cement concrete samples decreased. Changes in both materials were observed after 21 days of the agent action. After this period, it can be assumed that the complete penetration of accelerated destruction agent occurred through the volume of the samples. Mutually opposite materials’ responses to the influence of the accelerated destruction agent can be explained by structure rearranging and by the enhanced influence of sulfur as a binder on the

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properties of sulfur polymer concrete after a certain time, while the existence of the initial Portland cement composite samples is questionable (Vlahović and Martinović, 2018). The analysis of SEM microphotographs indicated evident structural differences between sulfur polymer concrete and Portland cement concrete samples and their quite the opposite responses to changes caused by the action of the accelerated destruction agent. Accelerated destruction agent provoked changes on micro scale in the structure of both materials (Figure 10).

Figure 10. SEM images: a) Sulfur polymer concrete untreated, b) Sulfur polymer concrete after 21 days of accelerated aging, c) Portland cement concrete untreated, d) Portland cement concrete after 21 days of accelerated aging.

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In the case of sulfur polymer concrete, binder phase- sulfur rearranged and conditionally homogenized the structure. As a result of the treatment, secondary bonding of the aggregate, which additionally homogenized the material, was noticed. It can be concluded that introducing an external disturbance leads to a new quality of the material in terms of its exploitation. Chemical activation of sulfur polymer concrete, precisely sulfur as a binder, resulted in structural changes of the material. On the contrary, unlike sulfur polymer concrete, the treated structure of Portland cement concrete was completely degraded, whereby the binder phase was destroyed owing to the accelerated destruction agent influence (Vlahović, Martinović and Volkov Husović, 2015). This methodology is good for homogeneous structures but does not satisfy completely when analyzing composite inhomogeneous materials such as sulfur and Portland cement concretes. Therefore, two other available nondestructive methods were applied in these tests. One of these methods, the ultrasonic pulse velocity testing is based on measuring the change in the properties of the input signal in all three directions (x, y, z). Homogeneity of the material can be discussed based on mutual differences in values of ultrasonic pulse velocities in three directions thus providing insight into the levels of inhomogeneity variation of the examined and reference material during treatment (Martinović et al., 2015). Differences between maximum and minimum values of ultrasonic pulse velocities for sulfur polymer concrete and Portland cement concrete, longitudinal (Vp) and transverse (Vs) are presented in Figure 11. It indicated a homogeneity change after a certain period of exposure to accelerated destruction agent influence (Vidojković et al., 2014). Bigger differences between the highest and the lowest values of ultrasonic pulse velocities of untreated sulfur polymer concrete samples compared to those treated for 180 days indicate that material after acid treatment became more homogeneous (Figure 11a). Since those differences for the treatment period of 21 days are negligible, the material can conditionally be considered as homogenous. For that treatment period compressive strength was the highest (Vlahović et al., 2011). All observed homogeneity changes are the result of material structure rearrangement caused by the influence of acid. The differences increase during Portland cement concrete treatment up to a time of 14 days, which means that homogeneity decreases during this period (Figure 11b). After 14 days there is a slight increase in homogeneity. It can be concluded that the observed changes in homogeneity, as well as the reduced homogeneity of the samples after 21 days of treatment in relation to untreated

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samples are the consequences of evident degradation of the material due to the action of acid.

Figure 11. Differences between maximum and minimum values of ultrasonic pulse velocities: a) Sulfur polymer concrete, b) Portland cement concrete.

The results of the other used method, infrared thermography where materials, sulfur polymer concrete and Portland cement concrete, are excited and themselves represent sources of information about changes within them, will be presented in the following text.

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3. Experimental Methodology Experimental work encompassed preparation of sulfur polymer concrete samples and the reference Portland cement concrete samples followed by their characterization. Both materials were afterward subjected to accelerated aging testing in acid solution during six months. Thermal properties of the materials were performed using infrared thermography measurements.

3.1. Samples Preparation Starting components used in the technological procedure of sulfur polymer concrete synthesis were aggregate, modified sulfur binder, and filler. The same aggregate, cement, and water were used for Portland cement concrete synthesis.

3.1.1. Aggregate Locally available classic mixture of sand and gravel sieved to a maximum grain size of 2 mm was used as an aggregate. Chemical analysis of the aggregate indicated that it mainly consisted of silicon oxide (89.98%), aluminum oxide (3.61%), calcium oxide (0.84%), iron oxide (0.62%), potassium oxide (0.59%), sodium oxide (0.57%), and magnesium oxide (0.19%). 3.1.2. Sulfur Sulfur, the basic component for the preparation of a modified sulfur binder, was a by-product from the oil refining process in the NIS Pančevo Oil Refinery, Serbia according to the Claus’s procedure and its purity was 99.9%. Dicyclopentadiene (DCPD), a cyclic hydrocarbon, was used for sulfur modification. The modification procedure was performed according to the literature [46] and consisted of mixing DCPD with molten sulfur in the temperature range from 120° to 140°C at ambient pressure for 30 min, followed by rapid cooling and solidification of the resulting product. Elementary sulfur and the obtained product were investigated by scanning electron microscope (SEM), type JEOL JSM-5800 with EDX, Figure 12.

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Figure 12. SEM images of: (a) Elementary sulfur, (b) Sulfur polymer (Vlahović et al., 2013).

The analysis of the obtained SEM images revealed significant differences in their microstructures. Namely, elementary sulfur consisted of dense orthorhombic crystals of the alpha form (Sα), Figure 12a, while plate monoclinic crystals of the beta form (Sβ), partially polymerized in zigzag chains, constitute modified sulfur, Figure 12b. Thus, it was proved that modification of sulfur was successful and that sulfur polymer was produced.

3.1.3. Filler The filler used in this research was alumina (Almatis, Germany). The filler and sulfur make a paste that coats and bonds the aggregate particles. The predominant roles of filler are to control the viscosity of the sulfur- filler paste and provide nucleation sites for crystal formation and growth, fill the voids in the aggregate thus reducing the required amount of sulfur and shrinkage during hardening as well as reinforcing the matrix which contributes the strength increasing (Mohamed and El Gamal, 2010). To meet these requirements, the filler particle size must be below 75 μm. Chemical composition and density of applied filler is given in Table 1. Table 1. Chemical composition and density of alumina Chemical composition (mass. %) Al2O3 Na2O SiO2 CaO 99.3 0.40 0.15 0.03

K2O 0.03

Fe2O3 0.02

TiO2 0.02

MgO 0.004

Bulk density (g/cm3) 3.86

3.1.4. Cement Ordinary Portland cement composed of 65.5% CaO, 21.9% SiO2, 5.4% Al2O3, 2.2% Fe2O3, 1.1% K2O, 0.1% Na2O, 1.3% MgO, and 3.9% SO3 was used for Portland cement concrete production.

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3.2. Technological Procedure of Sulfur Polymer Concrete Manufacturing Sulfur polymer concrete was synthesized according to the described manufacturing technological procedure (Vlahović, 2012a). This process consisted of mixing both melted elemental sulfur and modified sulfur into preheated and homogenized dry mixture of aggregate and filler at sulfur melting temperature, 132-141°C. The heated aggregate and alumina filler were then properly mixed with the molten modified sulfur binder until a homogenous viscous mixture was obtained. The alumina filler content of 7% was chosen in accordance with its influence on rheology, and to provide the maximum density of the concrete mixture. The temperature control was necessary because the viscosity of the concrete mixture had to allow its workability and handling whereby at the same time the thermal degradation of the thermoplastic material had to be avoided. After two minutes of homogenization and mixing, the concrete mixture was cast into molds preheated at 120°C and shaken on a vibration table for 10 seconds to compact the product in the molds. The samples surfaces were finished and left to harden at room temperature in the molds for 3 hours. Afterward, they were demolded and cured at room temperature for 24 hours. The mechanical properties were measured after 75 hours. For the purpose of this investigation, prism- shaped samples with dimensions (4 x 4 x 16) cm and cube- shaped samples (4 cm) were prepared. The applied technological procedure for sulfur polymer concrete production is schematically presented in Figure 13.

Figure 13. Technological procedure for sulfur polymer concrete production.

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3.3. Technological Procedure of Portland Cement Concrete Manufacturing The Portland cement concrete samples were made with the same aggregate as sulfur polymer concrete, Portland cement and water to cement ratio w/c of 0.5. The technological procedure consisted of mixing the aggregate with a certain quantity of tap water in the Hobart mixer and afterward the cement and the rest of the mixing water were added and the mixer was reoperated, whereby the total mixing time was about 6 min. The Portland cement concrete mixture was poured into molds and compacted by a vibrating table to settle the product in the molds. The samples were removed from the molds 24 h after casting and then cured in a moist room at a temperature of 20 ± 2°C with 95–98% relative humidity for 27 additional days, before being subjected to the tests. For this investigation, prism simples with dimensions (4 x 4 x 16) cm and cube samples (4 cm) were prepared.

3.4. Characterization of Concrete Samples For investigating physico-mechanical characteristics of the concrete materials and further testing, prism samples with dimensions (4 x 4 x 16) cm were used. Each reported value is the average of three readings obtained from three different samples, to ensure the reliability of the test results. Mechanical strength (compressive and flexural) of the composite samples was conducted using the "Amsler" press with maximum load of 200 kN, and method for testing the strength of concrete according to the standard (2008). The composition and relevant starting physico-mechanical properties of the prepared reference samples are shown in Table 2. Table 2. Composition and physico-mechanical properties of reference sulfur polymer concrete samples after 3 days of curing and Portland cement concrete samples after 28 days of curing Sample

SPC PCC

Composition (%) Aggregate Binder

Filler

Water

63 63

7 -

13

30 24

Bulk density (g/cm3) 2.34 2.18

Mechanical strength (MPa) σc σf 49.2 8.4 46.3 6.9

SPC = sulfur polymer concrete, PCC = Portland cement concrete, σc = compressive strength, σf = flexural strength.

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The proper size distribution matching of the aggregate and filler, and the right choice of the manufacturing technological process yielded sulfur polymer concrete particulate material with extremely low porosity, a tight microstructure and high compression and flexural strength.

3.5. Methods 3.5.1. Accelerated Aging Testing Sulfur polymer concrete was subjected to different degrees of accelerated aging by exposing five series of the samples to the same acid environment. The various levels of accelerated destruction were provoked by immersing the samples with dimensions of (4 x 4 x 16) cm in 10% HCl solution for 7, 14, 21, 60 and 180 days. Portland cement concrete samples with identical dimensions were subjected to the same acid environment for the reason of comparing. Since serious deterioration was noticed on those samples, immersion tests were terminated after 21 days. 3.5.2. Infrared Thermography Measurements As a final investigation, an analysis of the thermal properties of sulfur polymer concrete, which withstood a certain time of exposure to the accelerated aging agent, was performed. An initial sulfur polymer concrete sample and samples treated for 21 days and 180 days were analyzed, as well as an initial, untreated sample of the reference, Portland cement concrete. Active infrared thermography methodology consists of stimulating the surface of the tested material by providing a heat source, t.e. thermal impulse in a controlled manner or inducing this effect by means of acoustic activation, including ultrasound or microwaves, and then observing the path of its propagation by detecting the dynamic response of the generated thermal wave along the material surface using a thermal imaging camera which records the temperature evolution over time. This type of infrared thermography is especially used in defectoscopy. In this examination, an infrared camera GTS S100 Hotfind manufactured by GORATEC, with a temperature range of -20° to 250°C and sensitivity of ±1°C, was used. The samples were tested in a hotplate chamber, shown in Figure 14, and recorded over a period of 60 minutes, whereby the hotplate was heated up to a temperature of 40 ± 5°C.

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Figure 14. Scheme of the thermal imaging chamber (Vlahović, 2012a).

4. Results and Discussion 4.1. Infrared Thermography Analysis Modern thermal imaging systems use a new type of volumetric detectors thus enabling their wide range of applications. Detectors that give a twodimensional temperature distribution on the surface of the object have a high resolution (up to 0.01°C), which ensures adequate recording of the processes that take place in the tested sample. This type of non-destructive testing is based on the use of external stimuli of materials, thermal, with known intensities and monitoring of material responses to these stimuli. In that case, the material itself is a source of information about the changes that are detected by measurements of appropriate radiation.

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The application of thermal imaging systems to monitor changes in thermally excited systems such as sulfur polymer concrete and Portland cement concrete is a very reliable method. Analogously, it can be considered that the action of the accelerated destruction agent is in some way an external excitation of the material so that monitoring structural changes on the material surface can provide insight into the level of changes in the material itself during the treatment. The experimental paradigm in this research implies that the thermal load would destroy the sulfur polymer concrete samples, which was based on the hypothesis that sulfur was "grouped" within the structure, i.e., parts of the structure with increased sulfur content were created during the action of the accelerated aging agent. This led to a change in the mechanical properties of the material. It was assumed that under thermal loading, sulfur, as the most thermally unstable part of the structure, would be degraded in a relatively short period of time. The time changes were monitored by thermal recording, i.e., recording the temperature distribution per sample, which was supposed to prove or deny the presented hypothesis. The complete process was monitored through an integrated thermal imaging system with real-time infrared thermal data collection and designed software intelligence. It should be observed that by applying thermal imaging, another dimension, time, was added to the investigation; namely the samples, chemically treated for some time, were afterward thermally loaded during a certain period. An example of a thermogram and profile analysis is shown in Figure 15. Figure 15 shows the method of thermogram processing, i.e., the possibility of different line temperature changes. This analysis is useful for determining the parts of the surface where the greatest or smallest temperature changes have occurred. For the final analysis, it is best to use the overall two-dimensional analysis of the distributions and temperature changes on the test sample. Recent technical developments apply thermal infrared image (2D images) onto spatial information (3D images) to obtain 3D temperature distribution model. In this way, 3D-graphs that clearly indicate the level and character of changes are obtained.

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Figure 15. Thermogram and temperature profiles.

4.2. Analysis of Results Obtained for Sulfur Polymer Concrete Figure 16 presents the behavior of the initial sulfur polymer concrete sample during the heating period of 50 min when softening and deformation occurred, which was the reason for terminating the recording.

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Figure 16. Thermograms of the initial sample of sulfur polymer concrete during the heating period of 50 min (temperature in °C).

Figure 17 shows the behavior of sulfur polymer concrete, previously treated for 21 days by the accelerated aging agent, during 50 min of heating when the sample softened and deformed and therefore the recording was interrupted.

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Figure 17. Thermograms of a sulfur polymer concrete sample treated for 21 days during a heating period of 50 min (temperature in °C).

Thermograms reveal that after a heating time of 20 min, temperatures above 40°C were detected, which indicates the fact that secondary, exothermic reactions occurred within the mass of the sample thus causing its softening and deformation.

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Figure 18 illustrates the thermograms of a sulfur polymer concrete sample treated for 180 days during a heating period of 25 min when the sample softened and deformed and therefore further recording was suspended.

Figure 18. Thermograms of a sulfur polymer concrete sample treated for 180 days during a heating period of 25 min (temperature in °C).

Increased temperatures compared with samples treated for 21 days are observed. This can be explained by more intense secondary, exothermic reactions due to rearrangement of sulfur or forming unstable sulfur compounds

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during destruction under the action of the accelerated aging agent, which led to faster destroying of samples under thermal load.

4.3. Analysis of Results Obtained for Portland Cement Concrete Figure 19 presents the behavior of the initial Portland cement concrete sample during the heating period of 60 min.

Figure 19. Thermograms of the initial sample of Portland cement concrete during the heating period of 60 min (temperature in °C).

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The given images do not show fields with elevated temperature, but point inhomogeneities that most likely correspond to the components of Portland cement concrete with different thermal conductivities. A temperature increase in the mass of the sample over time is present as well, which also indicates the existence of a certain number of secondary, exothermic reactions. These changes are significantly less pronounced than with sulfur polymer concrete and obviously without visible macro consequences. Unlike sulfur polymer concrete, the Portland cement concrete sample shows higher thermal stability. Since it is a reference material that did not exhibit any significant changes after 60 minutes of thermal loading, the recording was interrupted.

4.4. Comparison of Changes in Sulfur Polymer Concrete and Portland Cement Concrete during Thermal Loading Figures 20 and 21 illustrate the graphs of the measured maximum temperatures of the tested sulfur polymer concrete and Portland cement concrete samples during the time of thermal loading, respectively. The graphs show differences in the behavior of the samples, which is understandable because there are actually four different materials. Regarding sulfur polymer concrete, thermal imaging tests have shown that the action of accelerated aging agent for different periods of acid exposure induces transformations that lead to changes in the thermal properties of the material. The dependences obtained by regression analysis of the initial samples of sulfur polymer concrete and those treated for 21 days are linear and with a relatively low rate of thermal properties degradation. The fact is that after a certain time of thermal loading (up to 50 min) a change in the material structure occurs. This is manifested as softening of the samples and further thermal imaging recordings are interrupted. In samples treated for 180 days, the thermal load has an even more intense effect on the change within the sample and its deformation in a shorter time. In this case, the regression analysis showed a nonlinear degree dependence with a relatively large gradient of changes in thermal properties within the sample volume. Therefore, this sample was transformed faster; it was softened compared to samples that were treated with an accelerated aging agent for a shorter time.

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Figure 20. Measured maximum temperatures of sulfur polymer concrete samples during the thermal load time.

Figure 21. Measured maximum temperatures of Portland cement concrete samples during the thermal load time.

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Reference material, Portland cement concrete, showed good thermal stability even after the time in which the sulfur polymer concrete samples were deformed. Despite the observed local exothermic reactions, no deformation of the Portland cement concrete sample occurred. The dependence obtained by regression analysis is linear and it correlates with the dependences obtained for sulfur polymer concrete samples treated for up to 21 days. These tests also showed that after a certain time of treatment with the accelerated aging agent, qualitative and quantitative changes in the structure of the material occurred. For easier comparison, a summary graph of the measured maximum temperatures of all tested samples during the thermal load time is presented in Figure 22.

Figure 22. Summary graph of measured maximum temperatures of sulfur polymer concrete and Portland cement concrete samples during thermal loading time.

In order to determine, more precisely to quantify the changes in the thermal properties of the material due to exposure to the agent of accelerated aging, a regression analysis was performed, i.e., fitting of the obtained

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maximum temperatures on the sample during the time of thermal load recording. The fitting was done with the assumption that in the first approximation it is possible to use a linear model to compare the rates of change of the response of the material samples to the thermal load, i.e., gradients. Figure 23 shows the gradient values for the tested samples.

Figure 23. Gradients of changes in sulfur polymer concrete and Portland cement concrete samples due to thermal loading.

From the graph in Figure 23, it is clear that the gradients increase significantly in samples that were previously treated with the accelerated aging agent for a longer time. This means that a change due to the unit thermal load occurred in a shorter time. This fact indicates the possible existence of secondary reactions in the already rearranged structures of the samples chemically treated for 21 and 180 days in relation to the untreated samples. These considerations, in addition to their consistence with the fact that sulfur polymer concrete is not thermally resistant unlike Portland cement concrete, also indicate that after 21 days of chemical treatment, sulfur takes the lead in changes.

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4.5. 3D Temperature Distribution Graphs The infrared thermography method made it possible to analyze the temperature field of the impact surface. The use of the infrared camera as a temperature transducer in various applications is convenient and widespread. However, the infrared data are available in the form of 2D images. The next stage of this analysis was attempted to determine the 3D temperature distribution. On the basis of the presented thermograms, the overall two-dimensional analysis of temperature distributions and changes on the examined samples was performed, and the results are given as 3D graphs. It means that the surface temperature data obtained from an infrared camera are converted into 3D visualization. The method is based on feature extraction, i.e., extraction of points. Figures 24-27 show 3D graphs of temperature distribution in the sulfur polymer concrete and Portland cement concrete samples, where the temperature is given on z-axis, while the positions of the points is presented on the x- and y- axes. Figure 28 shows 3D graphs of the temperature distributions in the sulfur polymer concrete and Portland cement concrete samples, whereby the heating time of all samples was 20 min.

Figure 24. Temperature distribution in the initial, chemically untreated sulfur polymer concrete sample thermally loaded for 50 min.

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Figure 25. Temperature distribution in a sulfur polymer concrete sample chemically treated for 21 days and thermally loaded for 50 min.

Figure 26. Temperature distribution in a sulfur polymer concrete sample chemically treated for 180 days and thermally loaded for 25 min.

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Figure 27. Temperature distribution in the initial, chemically untreated sample of Portland cement concrete thermally loaded for 60 min.

Figure 28. Comparative presentation of temperature distributions in sulfur polymer concrete and Portland cement concrete samples during a thermal load of 20 min.

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The increase in temperature indicates a higher reactivity of the sample, i.e., its weaker thermal stability. Essentially, a quantitative difference in the behavior of the samples after treatment with the accelerated aging agent was detected.

Conclusion Technological procedure for sulfur polymer concrete manufacturing consisted of mixing molten sulfur and modified sulfur at melting point temperature of sulfur into a dry heated mixture of aggregates and fillers. Mixing lasted until forming a homogeneous viscous mixture which was cast into preheated molds and vibrated. Modification of sulfur was realized by mixing the molten sulfur with cyclic hydrocarbon, dicyclopentadiene (DCPD). In that way, a material with appropriate value-in-use was obtained, sulfur polymer concrete, from the secondary, waste substance, sulfur originating from oil refining, which is in line with modern tendencies in the world to utilize materials obtained from alternative landfills as raw materials for new products (land mining). In order to assess the quality of sulfur polymer concrete accelerated aging method was applied, whereby the samples were immersed in 10% hydrochloric acid solution as an accelerated destruction agent. Portland cement concrete was chosen as reference material. The focus was put on modern methods and methodologies for quantifying the properties of the materials. Based on the previously performed investigations, changes in both materials were observed after 21 days of exposure to the impact of the accelerated destruction agent. It can be assumed that after this period, total penetration of the chemical agent throughout the volume of the samples is happening. Namely, a homogenization of sulfur polymer concrete occurred during the time of accelerated destruction. The greatest homogeneity increase happened on the 21st day of treatment. The influence of the accelerated destruction agent was towards rearranging sulfur, which was the main factor of homogeneity changes. On the contrary, the homogeneity of the Portland cement concrete decreased. The materials' responses to the influence of the accelerated destruction agent were mutually opposite. This can be explained by structure rearranging and by the enhanced influence of sulfur as a binder on the properties of sulfur polymer concrete after a certain time. After 21 days of treating Portland cement concrete samples, the existence of the initial material is questionable.

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This chapter presents the analysis of the thermal loading of sulfur polymer concrete samples, where the thermal imaging analysis, i.e., the analysis of the two- dimensional temperature distribution on the surface of the tested sample, was used as the methodology for quantifying changes. The obtained results indicated significant differences between the sulfur polymer concrete samples treated for 0, 21 and 180 days, which showed the existence of structural differences during this testing period. It should be mentioned that a softening of the sulfur polymer concrete samples occurred during the thermal load testing. Sulfur, as the most thermally unstable concrete ingredient, is responsible for this softening. The results of the analysis of the material behavior under thermal loading verified the relevance of this methodology to obtain complementary information about the investigated material. In addition to confirming the well-known fact that sulfur polymer concrete is not thermally stable, it was shown that the assumption of sulfur concentration and rearrangement during the action of a accelerated aging agent is reasonable. Thermal imaging tests pointed out that the initial, untreated sulfur polymer concrete sample, which didn’t undergo significant rearrangement of sulfur is much more thermally stable compared with the sample in which the rearrangement occurred (sample treated for 180 days). This confirms the assumption that the chemical agent induces structural changes in the material, which reflect on its mechanical properties. The applied analyses on the micro-level revealed that the initial structure of sulfur polymer concrete was rearranged. As a macro result, a material with better resistance to accelerated aging compared with the reference material, Portland cement concrete was obtained. The results of thermal imaging tests have confirmed the assumption that in the case of sulfur polymer concrete, the chemical agent of accelerated aging can be considered an analogue of stress input to improve the properties of prestressed concrete. It is interesting to note that the processing of material before its use, the so-called preprocessing, is increasingly present in the world. This trend is particularly pronounced in case of recycled materials, as well as materials that are officially declared as waste. According to the presented research, it can be concluded that the methodology of accelerated aging can be used to induce modifications in the structure of materials and thus properties changes. The method used for this investigation, infrared thermography, adequately demonstrates the possibility

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of detecting accelerated destruction influence on the structure of sulfur polymer concrete. The performed analysis proves that in both sulfur polymer concrete and Portland cement concrete structure changes on a micro-scale exist. These changes are the result of interactions with the accelerated destruction agent, which lead to different scenarios of sulfur polymer concrete and Portland cement concrete service life.

Acknowledgments This work was financially supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grant No. 451-0347/2023-01/200026).

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Dotto, JMR; De Abreu, AG; Dal Molin, DCC; Műller, IL. Influence of silica fume addition on concretes physical properties and on corrosion behaviour of reinforcement bars. Cem Concr Compos. 2004, 26, 31–39. Gracia, V; Vàzquez, E; Cramona, S. Utilization of by-produced sulfur for the manufacture of unmodified sulfur concrete, International RILEM Conference on the Use of Recycled Materials in Buildings and Structures, Barcelona, Spain, 2004, 1054–1063. Gregor, R; Hackl, A. A new approach to sulfur concrete. In New Uses of Sulfur-II; Bourne, DJ; Ed.; American Chemical Society, Washington, D.C., US, 1978, Vol. 165, 54–78. Grinzato, E; Bison, PG; Marinetti, S. Monitoring of ancient buildings by the thermal method. J Cult Herit. 2002, 3 (1), 21–29. Institute for Standardization of Serbia. Methods of testing cement- Part 1: Determination of strength, Serbian standard SRPS EN 196-1:2008. 2008. Jorge Aldave, I.; Venegas Bosom, P.; Vega González, L.; López de Santiago, I.; Vollheim, B.; Krausz, L.; Georges, M. Review of thermal imaging systems in composite defect detection. Infrared Phys Technol. 2013, 61, 167–175. López, FA; Gázquez, M; Alguacil, FJ; Bolívar, JP; García-Díaz, I; López-Coto, I. Microencapsulation of phosphogypsum into a sulfur polymer matrix: physicochemical and radiological characterization. J Hazard Mater. 2011, 192 (1), 234–245. Maldague, X. Theory and Practice of Infrared Technology for Nondestructive Testing, Wiley Series in Microwave and Optical Engineering, Wiley, New York, 2001. Maldague, X.P.V., P. O. Moore. Nondestructive Testing Handbook: Infrared and Thermal Testing (Volume 3), Third Edition, Techn. ed., American Society for Nondestructive Testing, USA, 2001. Martinovic, S; Vlahovic, M; Boljanac, T; Dojcinovic, M; Volkov Husovic, T. Cavitation resistance of refractory concrete: influence of sintering temperature. J Eur Ceram Soc. 2013, 33, 7–14. Martinovic, S; Vlahovic, M; Boljanac, T; Majstorovic, J; Volkov-Husovic, T. Influence of sintering temperature on thermal shock behavior of low cement high alumina refractory concrete. Compos Part B: Eng. 2014, 60, 400–412. Martinović, S; Vlahović, M; Majstorović, J; Volkov Husović, T. Anisotropy analysis of low cement concrete by ultrasonic measurements and image analysis. Sci Sinter. 2016, 48, 57–70. Martinović, S; Vlahović, M; Stević, Z; Volkov-Husović, T. Influence of sintering temperature on low level laser (LLL) destruction of low cement high alumina refractory concrete. Eng Struct. 2015, 99, 462–467. McGonnagle, W.; Park, F. A discussion of theory and various methods including eddycurrent testing. International Science and Technology. 1964, 31 (14). Meléndez, J; Foronda, A; Aranda, JM; López, F; López del Cerro, FJ. Infrared thermography of solid surfaces in a fire. Meas Sci Technol. 2010, 21 (10), 1–10. Milne, JM; Reynolds, WN. The Non-Destructive Evaluation of Composites and Other Materials by Thermal Pulse Video Thermography, Proceedings of SPIE 520, Thermosense-VII: Thermal Infrared Sensing for Diagnostics and Control, Cambridge Symposium, Cambridge, United States 1984, 119–122. Mohamed, AMO; El Gamal, MM. Hydro-mechanical behavior of a newly developed sulfur polymer concrete. Cem Concr Compos. 2009, 31, 186–194.

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Mohamed, AMO; El Gamal, MM. Solidification of cement kiln dust using sulfur binder. J Hazard Mater. 2011, 192 (2), 576–584. Mohamed, AMO; El Gamal, MM. Sulfur bazed hazardous waste solidification. Environ Geol. 2012, 53(1), 159–175. Mohamed, AMO; El Gamal, MM. Sulfur Concrete for the Construction Industry, A Sustainable Development Approach, J. Ross Publishing, USA, 2010. Moosberg-Bustnes, H; Lagerblad, HB; Forssberg, EE. The function of fillers in concrete. Mater Struct. 2004, 37, 74–81. Scribbr (no date). Available at: https://www.leonardodrs.com/commercial-infrared/abo ut/thermal-101/ (Accessed: 18 October 2021). Sullivan, TA; McBee, WC; Blue, DD. Sulfur in coatings and structural materials. In New Uses of Sulfur; West, JR; Ed.; Advances in Chemistry Series; American Chemical Society, Washington, D.C., US, 1975; Vol. 140, pp 55–74. Vavilov, V; Burleigh, D. Infrared Thermography and Thermal Nondestructive Testing, Springer Nature, Switzerland AG, 2020. Vavilov, V; Taylor, R: Theoretical and practical aspects of the thermal NDT of bonded structures. In: Sharpe, R., Ed., Res. Techn. in NDT, Volume 5, Academic Press, London, 1982, pp.239–280. Vavilov, VP. Pulsed thermal NDT of materials: Back to basics. Nondestruct Test Eval. 2007, 22(2–3), 177–197. Vavilov, VP. Thermal NDT: historical milestones, state-of-the-art and trends. Quantit Infra Red Thermogr J. 2014, 11(1), 66–83. Vavilov, VP; Burleigh, DD. Review of pulsed thermal NDT: physical principles, theory and data processing. NDT & E Int. 2015, 73, 28–52. Vidojković, V; Đorđević, N; Boljanac, T; Vlahović, M; Martinović, S; Branković, A. Procedure for Cooling Molten Sulphur Modified by Dicyclopentadiene on a Flat Metal Surface, Registered Serbian Patent 53412, 2014. http://www.zis.gov.rs/upload/doc uments/pdf_sr/pdf/glasnik/GIS_2014/GIS_2014_5.pdf. Vlahović, M. Doctoral dissertation. University of Belgrade, Faculty of Technology and Metallurgy, 2012a. Vlahović, M; Boljanac, T; Branković, A; Vidojković, V; Martinović, S; Đorđević, N. The influence of filler type on the corrosion stability of the sulfur concrete. Hem Ind. 2010, 64 (2), 129–137. Vlahović, M; Jovanić, P; Martinović, S; Boljanac, T; Volkov-Husović, T. Influence of Chemical Stress on Sulfur-Polymer Composite Structure. In New Developments in Polymer Composites Research; Laske, S; Witschnigg, A; Eds.; Polymer Science and Technology; Nova Science; Publishers, Inc., New York, United States of America, 2013; pp 257-278. Vlahović, M; Jovanić, P; Martinović, S; Boljanac, T; Volkov-Husović, T. Quantitative evaluation of sulfur-polymer matrix composite quality. Compos. Part B: Eng. 2013, 44, 458–466. Vlahovic, M; Martinović, S. The synthesis of sulfur-polymer matrix composite and morphological analysis of the samples in extreme conditions. In Polymer-Matrix Composites, Materials, Mechanics and Applications; Rice, E; Sparks, B; Eds.;

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Polymer Science and Technology, Nova Science Publishers, Inc., New York; United States of America, 2018; pp 1-55. Vlahovic, M; Martinović, S; Boljanac, T; Jovanic, P; Volkov-Husovic, T. Durability of sulfur concrete in various aggressive environments. Constr Build Mater. 2011, 25, 3926–3934. Vlahović, M; Martinović, S; Jovanić, P; Boljanac, T; Volkov-Husović, T. Image Analysis Technique for Evaluating Damage Evolution and Predicting Mechanical Strength of Concrete Structures under Corrosion. In Advances in Image Analysis Research; Ed. Roger M. Echon, RM; Ed.; Computer Science, Technology and Applications; Nova Science Publishers, Inc.: New York, US, 2014; pp 147-169. Vlahović, M; Martinović, S; Volkov Husović, T. Valorization of secondary sulfur from oil refining process for sulfur concrete production, Plenary lecture, XXIII International Conference, “Ecological Truth” Eco -Ist’ 15, Kopaonik, Serbia 17-20 June 2015, Proceedings, 12–28. Vlahović, M; Savić, M; Martinović, S; Boljanac, T; Volkov-Husović, T. Use of image analysis for durability testing of sulfur concrete and Portland cement concrete. Mater Des. 2012b, 34, 346–354. Willburn, D.K. Survey of infrared inspection and measurement techniques. Mater. Res. Stand. 1961, 1.

Chapter 3

The Structural and Environmental Performance of Fly Ash Amended Cement Lokeshappa Basappa1 and Anil Kumar Dikshit2, 1 Department

of Civil Engineering, University BDT College of Engineering, Davangere, India 2 Environmental Science and Engineering Department, Indian Institute of Technology Bombay, Powai, Mumbai, India

Abstract Fly ash is a byproduct from thermal power plants. It contains toxic metals that are released into the environment through leaching during dry disposal, wet storage and reuse of fly ash. To develop scientific basis for optimal methods of disposal and reuse of fly ash, the studies are needed for establishing the potential for the mobilization of metals as function of the chemical speciation of fly ashes and also during its dry/wet disposal. Comprehensive studies are also required in order to understand the leaching of potentially harmful metals from fly ash-blended cement as fly ashes are being extensively utilized in cement/construction industries. The main scope of the present study was to assess the structral strength as well leaching behaviour of toxic metals and metalloids present in fly ashes as discharged and as used in blending cement. The fly ash samples (A, B and C) from three thermal plants were collected from three different thermal power plants located in Maharshtra, India. A set of 70.6 mm x 70.6 mm x 70.6 mm mortar cubes were casted using cement-fly ash in ratios as 100:0 (M0), 80:20 (M1), 60:40 (M2), 30:70



Corresponding Author’s Email: [email protected].

In: Cement and Concrete Editors: Kong Fah Tee, Siew Choo Chin and Koorosh Gharehbaghi ISBN: 979-8-88697-831-5 © 2023 Nova Science Publishers, Inc.

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Lokeshappa Basappa and Anil Kumar Dikshit (M3) and 5:95 (M4) for all three fly ashes using 43 grade Ordinary Portland Cement (OPC) and Indian standard sand. These cubes were cured in ultrapure water for period of 3, 7, 14, 28 and 90 days. Subsequentially, the cured cubes were tested for compressive strengths while the curing waters were monitored for variation in pH and metal leaching of As, Cr, Pb, Se and Zn. The fly ash A and C being F class fly ashes showed compressive strengths of blended mixes (M1, M2, M3 and M4) higher than those of pure cement cubes casted with OPC alone (M0). However, compressive strengths of C class fly ash blended cement cubes were lower than those of pure cement cubes. Optimum blending of fly ash with ordinary Portland cement was found to be up to 40% for class F ashes while C class fly ashes were not at all fit to be used as a building material due to lack of bonding strength. Also, it was found that the ultimate compressive strengths of F class fly ash amended cubes were much more than those of unamended cubes (M0). Thus, the addition of fly ash led to enhancement in compressive strength. pH of curing water reached to 11 soon after the immersion of mortar cubes in curing water. Declining trend of pH was observed after 7 days up to 90 days. pH at the end of 90 days was in the range of 8.59.5. Concentrations of As, Pb and Se in curing water was found to increase with increase in the blending percentage of fly ashes for the first three days and then decreased with curing age. Thus, pH of leaching water became neutral and the leaching of metals decreased with the age of cubes. Overall, substitution of up to 40% fly ash was observed to beneficial both with respect to compressive strength as well as leaching of metals.

Keywords: blended cement mix, fly ash, leaching, metals, mobility

1. Introduction Forty percent of global electricity is generated from coal fired thermal power plants that consume over 5 billion tons of coal annually (Mukherjee et al., 2008). India is the world’s fourth largest economy and has a fast growing energy market. Coal occupies an important position in energy sector in India since it has vast reserves of thermal grade coal and is the third largest producer of coal. Coal based thermal power plant installations contribute to about 70% of the total installed capacity for power generation in India (Shivpuri et al., 2011). These plants emit enormous amount of air pollutants and also generate coal combustion solid residues such as bottom ash and fly ash, where fly ash

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is the major solid waste. Fly ash, having a complex heterogeneous mixture of amorphous and crystalline phases, is generally fine powdered ferroaluminosilicate material with Al, Ca, Mg, Fe, Na and Si as the predominant elements (Adriano et al., 1980; Aitken and Bell, 1985; Mattigod et al., 1990). Toxic metals, such as lead, selenium, chromium, nickel, cadmium, zinc and mercury that are naturally present in coal, are enriched in fly ash as a result of combustion in the thernal power plants (Dayan et al., 2001; Sonmez et al., 2005). The potential of readily leaching out of several of these metals out of fly ash and contaminating exposed soils, surface waters and ground waters or being otherwise bioavailable, leads to growing environmental concerns regarding disposal and utilization of fly ashes (Singh, 2005). Fly ash is a pozzolanic material and therefore, exhibits cementitious properties when combined with water and/or calcium hydroxide. This property of fly ash is widely used as a replacement for cement or an admixture in the cement industry (Rostami and Brendley, 2003; Poon et al., 2006). This chapter presents the behaviour of fly ash blended cement in various mix proportions for the purpose of evaluating pH and leaching of metals in curing water vis-avis the compressive strength of cement fly ash mortar cubes. All assessments were done using fly ash samples collected from three thermal power plants situated in Maharashtra, India. Fly ashes were mixed in pre chosen ratios with Ordinary Portland Cement and Indian Stanard Sand and curing was carried for duration of 3, 7, 14, 28 and 90 days.

2. Alteration of Metals in Portland Cement Fly Ash Mixtures Exploitation of resources of environment is the greed of human kind. Cement is no exception for this. Domestic cement consumption in India is around 235 kg per capita against global average of 520 kg per capita. India stands second in the world in the production of cement (Statista, 2022). Exploitation of raw materials of cement is the concern of the day and the sustainability of the cement industry requires the blending of mineral admixtures with OPC. Fly ash has been found to be a major contributor in the cement industry in saving resources of raw materials of cement. The reuse provides an alternative to storing the coal combustion products in ash ponds, ash dykes and landfills. Also, pozzolanic based stabilization/ solidification is an effective remediation technology to immobilize toxic metals present in fly ash (Dermatas and Meng, 2003). The knowledge of leaching behaviour of fly ash blended cement is important to know the amount

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of leachable constituents of environmental importance, as their availability may affect the biological system. To understand the environmental risks associated with fly ash as a replacement for cement, it is important to understand the mechanisms by which the mobility of metals in the fly ash may be increased or decreased. The binding mechanisms of the metals in the fly ash determine their mobility under exposure to different solutions and conditions. These binding mechanisms include the ion exchangeable, outer and inner sphere complexation, precipitation and co-precipitation (Noel et al., 2007). Portland cement and fly ash binder may solidify the toxic metals but the subsequent chemical conditions may or may not result in long term sequestration of these metals (Giammar et al., 2009). The metal speciation and mobility that can occur might limit reuse of fly ash in cement production. The trace metals in the fly ash are very immobile and could be extracted using the most aggressive solution. Mixing metal rich materials with cement is actually an established waste treatment technology (Means et al., 1995) and such technologies use mixtures of cement and fly ash to permanently sequester metal contaminants (Roy et al., 1991; Parsa et al., 1996). When nitrates of metals are added to cement, the metals are expected to precipitate as insoluble hydroxides due to the high pH of the binder (Roy et al., 1991). It can also chemically react with the fly ash and binder. The carbon content in fly ash has an adverse effect on workability, thus variation in carbon content may lead to erratic behaviour with respect to workability and also air entraining agents become absorbed by the porous particles (Shi and Spence, 2004). The amount of trace metals leached from cement solidified by fly ash depends on the kind of fly ash rather than their content in fly ash (Noel et al., 2007).

3. Characteristics of Fly Ashes, Ordinary Portland Cement and Other Materials 3.1. Physical and Chemical Properties of Fly Ashes 3.1.1. Fly Ash Samples Three fly ash materials, named as A-Ash, B-Ash and C-Ash, were collected from dust hoppers of electrostatic precipitators of three full-scale thermal power plants (TPP-A, TPP-B, TPP-C) situated in Maharashtra, India. These

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power plants use bituminous and sub-bituminous coals from India and those imported from Indonesia. The ashes were classified based on their calcium oxide content. B-Ash belonged to class C being calcium-rich (greater than 10% calcium oxide) while A-Ash and C-Ash were silica-rich belonging to class F (less than 10% calcium oxide). Characteristics of thermal power plants considered in the study are given Table 1. Table 1. Characteristics of thermal power plants S. No.

1 2 3

Name of Thermal Power Plant (Type of Ash) TPP-A (A-Ash) TPP-B (B-Ash) TPP-C (C-Ash)

Total Coal Consumption (MT/year) 2,394,315 1,803,700 10,284,627

Avg. Ash Content in Coal (%) 24.96 1.87 38.57

Ash Generation (MT/year) 578,714 33,729 3,966,423

Fly ash samples were analysed for various constituents and properties as discussed below.

3.1.2. Physical Characteristics 3.1.2.1. Particle Size Distribution Beckman Coulter Laser Diffraction Particle Analyser (Model LS 13320, Japan) was used for particle size analysis of fly ash samples. Laser diffraction technique for particle size analysis works on scattering of light at an angle that is directly related to their size. As particle size decreases, the observed scattering angle increases logarithmically. Scattering intensity also depends on particle size, diminishing with particle volume. Large particles, therefore, scatter light at narrow angles with high intensity whereas small particles scatter at wider angles but with low intensity. All fly ashes were analysed for the particle size distribution and mean particle diameters were observed to be 17.03 µm, 3.25 µm and 2.14 µm respectively for A, B and C-Ash. 3.1.2.2. Specific Surface Area The surface area was determined with the help of BET surface area analyzer (Smart Instruments, India) and was found as 0.65 m2/g, 1.2 m2/g and 0.97 m2/g respectively for A, B, and C-Ashes. There was no correlation of surface area with mean particle size.

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3.1.2.3. pH pH of the fly ash samples was measured as follows. The sample was prepared by mixing fly ash with ultrapure water with a ratio 1:20 solid/solution ratio in orbital shaker (Trishul Equipment, India) at 184 rpm. pH of the supernatant of mixed sample was measured within 10 minutes of mixing using Thermo Scientific pH meter (Orion, 3 Star, Singapore) and gave the representative pH of fly ashes as 9.77, 11.54 and 9.75 respectively for A, B, and C-Ash. Summary of the above parameters is tabulated in Table 2. Table 2. Physical parameters of fly ashes Parameters Mean particle size (µm) Specific surface area (m2/g) pH

A-Ash 17.03 0.65 9.77

B-Ash 3.25 1.2 11.54

C-Ash 2.14 0.97 9.75

Usually fly ashes are classified based on percent contents of silica and calcium. Class C ashes are calcium-rich with greater than 10% calcium oxide while class F ashes are silica-rich having less than 10% calcium oxide. Thus, B-Ash belonged to class C and A-Ash and C-Ash were class F ashes.

3.1.3. Chemical Composition Philips X-Ray Fluorescence Spectrometer (Model 2404, Netherlands) was used to ascertain chemical composition of the fly ash sample. Major oxides in the fly ashes were evaluated on percent weight basis and are reported in Table 3. It can be observed that silica and alumina were the major oxides in all the fly ashes. However, the amount of silica was almost double the amount of alumina for A-Ash and C-Ash. Iron oxide was the third prominent oxide while calcium oxide was only 1 to 2% in A-Ash and C-Ash. All other oxides were in very trace amounts. Table 3. Chemical composition of fly ashes in terms of major oxides (% by weight) Parameters SiO2 CaO Al2O3 Fe2O3 MgO

A-Ash 61.00 2.18 23.67 7.51 1.02

B-Ash 35.32 18.81 27.82 10.64 3.00

C-Ash 62.00 1.03 26.3 5.50 0.75

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Parameters A-Ash B-Ash C-Ash Na2O 0.17 1.03 0.10 P2O5 0.25 0.14 0.35 TiO2 1.66 0.72 1.61 K2O 0.65 0.63 0.41 BaO 0.08 0.12 0.06 SrO 0.12 0.12 0.13 MnO 0.04 0.08 0.05 SO3 0.25 0.47 0.11 LOIa 1.40 1.10 1.60 Total 100.00 100.00 100.00 a LOI is loss on ignition, which represents the unburned carbon content in the fly ash samples.

3.1.4. Mineralogy Mineralogical studies of the fly ashes were analysed by Rigaku Geigerflex Powder X-Rray Diffraction Spectrophotometer (Japan) with graphite monochromator and Cu-Kα radiation with 0.02 to 20 steps and 1 second count time per step to identify the crystalline phases present in fly ash for physical characterization. XRD patterns for mineralogical analysis of all the fly ash samples are shown in Figure 1. XRD patterns indicate several distinct peaks. Amongst them, quartz (SiO2) was the most predominant crystalline phases present in the all three fly ash samples. A-Ash and C-Ash contained mullite (3Al2O3 2SiO2) while hematite and magnesia were additional minerals present in B-Ash.

Figure 1. Crystalline phases in the XRD patterns of fly ashes.

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3.1.5. Morphology The microstructure characteristics of fly ash samples were studied using JOEL Scanning Electron Microscope (Model JSM-5600, Japan) with Energy Dispersive X-ray Spectroscopy (EDS) analysis facility. Morphology of all fly ash samples is shown in Figure 2. It is controlled by combustion temperature and the cooling rate during their production. The variation in the size of particles was observed to range from less than 1 µm to greater than 20 µm. SEM-EDS reveals that the predominant elements in all fly ash samples were silicon, aluminum, iron and calcium. Aluminum was primarily associated with silicon. Lesser amounts of the elements like potassium, magnesium, sodium, titanium and sulfur were observed with aluminum and silicon.

(a)

(b)

(c)

Figure 2. Morphology of (a) A-ash, (b) B-ash, and (c) C-ash.

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Micrographs also showed that most of the particles were spherical in shape and some of them were ceno-spherical in nature. Usually, smaller sized particles adhered to bigger sized particles. The polarisation effect of particles was seen from the pattern of spreading in the micrographs. The surfaces of fly ash particles were observed to be very smooth. Hollow spears due to spherical nature of fly ash particles could be responsible for high porosity.

3.1.6. Total Extractable Concentration of Toxic Metals Jobin Yvon Horib Inductively Coupled Plasma-Atomic Emission Spectroscopy (Model ULTIMA 2000, France) shown in Figure 3 was operated with Argon as plasma and purge gas. The operating conditions maintained during ICP analysis are referred in Table 4. Elements were determined with suitable wavelength adjustments. Extract solutions were analyzed in the instrument with an initial dilution factor of 1:20 for microwave digestion step samples. Multi-element ICP standards in 2% nitric acid were used as base for multi-point calibration of ICP-AES. Depending upon the sample matrix, ICP was also calibrated with ICP standards prepared in identical matrix.

Figure 3. Horiba Jobin Yuan Ultma ICP-AES used for metal speciation.

Quality control (QC) samples were analysed as part of the ICP-AES analytical runs to check for instrument drift, accuracy and precision. Spiked blanks of the custom standard were used as surprise control for ICP-AES during experiments. Secondary standards were also used frequently to check accuracy. Extraction and analysis of blank samples and standard reference fly

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ash material (NIST 1633b) were performed. All analytical and sampling results recorded were the averages of at least two experiments. Minimum detectable limit for the metals ranged from 0.01 ppb for minor metals to 1 ppb for major metals. Table 4. ICP-AES instrumental and operational conditions Parameters RF generator power RF frequency Plasma Auxiliary Nebulizer type Nebulizer make Nebulizer pressure Nebulizer flow rate Spectrometer Analyzer

Value/Type 1.0 kW 40 MHz 12.0 L/minutes 0.75 L/minutes V-type Glass concentric 2.90 bars 0.85 L/min Monochromator PMT

Data on all 25 elements viz. Ca, Mg, Mn, Na, K, Ag, Ba, Bi, Li, As, Fe, Al, Si, Pb, Cd, Se, As, Zn, Hg, Ni, Cu, and Cr was provided by ICP-AES analysis. However, As, Cr, Pb, Se and Zn as minor metal and Ca, Si, Fe and Al as major metals were taken as metals of interest in the present study.

3.1.6.1 Total Extractable Metals Milestone Microwave Digester (Model MLS 1200, USA) was used for the determination of total extractable metals present in any fly ash sample (Figure 4). It represents the maximum amount of metals that was present in a sample as the most aggressive acid environment ensured complete extraction. The operational conditions of the digester are shown in Table 5. Table 5. Operating conditions of Milestone Microwave Digester Steps 01 02 03 Ventilation

Power (w) 250 400 500 -

Pressure (bars) 03 06 10 -

Time (minutes) 05 05 04 03

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Figure 4. The Milestone Microwave Digester used for digestion.

0.5 g fly ash was digested with 4:1 mixture of concentrated HNO3 (10 mL) and HCl (2.5 mL) in pressure vessels for 14 minutes at high pressure and temperature conditions as per details given in Table 5. Sample was ventilated for 3 minutes and was allowed to cool down for 30 minutes. Digested sample was opened in a fume chamber to vent away acid fumes. This sample was diluted with 50 mL ultrapure water and the suspension was centrifuged for 10 minutes at 10,000 rpm. 10 mL supernatant was decanted and filtered with the 0.2 µm PTFE filter. Sample, thus, extracted was diluted to 1:20 for further analysis of metals with ICP-AES. Table 6 lists the metal extracted using microwave acid digestion technique in descending order of their concentration for all the fly ashes under consideration. Table 6. Total extractable metals in fly ashes Metals Barium Chromium Zinc Arsenic Copper Lithium Selenium Cadmium Cobalt Bismuth Lead Silver Strontium Nickel

Metal Concentration (µg/g) A-Ash B-Ash 621 419 159 184 152 156 137 140 135 140 122 116 104 144 83 84 76 90 70 79 61 59 50 43 35 46 31 50

C-Ash 638 148 144 129 138 118 153 81 92 95 72 95 45 101

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It can be seen that Ba, Cr, Zn, As, Cu, Li, Se, Cd, Co were the toxic metals, which were present in significant amounts (638 to 92 µg/g) in all ashes. There would be serious concern should these leach out from fly ashes during the life cycle of fly ash in storage, reuse and disposal. The effect of toxic metals viz. As, Cr, Pb, Se and Zn should need attention as the fly ashes are stored on-site in ash ponds for prolonged periods. At present, ashes are also being considered as component of many alternative building materials.

3.2. Ordinary Portland Cement Commercially available 43 grade Ordinary Portland cement (Vasadatta make, India) conforming to IS: 8112-1989 was used for casting fly ash blended cement cubes. Cement was stored as per standard procedure specified in IS code.

3.3 Other Materials 3.3.1. Glassware All glassware of Borosil make were used. Glassware was washed with chromic acid, followed by neutralization with dilute alkali, followed by deionised water and ultrapure water. Then, clean glassware was dried in an oven prior to each experiment. 3.3.2. Chemicals All chemicals used were of analytical reagent (AR) grade from Merck Chemicals, India. Stock solutions of the reagents of 1000 mg/L were prepared. The metallic grade (acids free from metals) nitric acid and hydrochloric acids were used in the experiments and for the operating solutions for the ICP-AES. Ultrapure water produced by Siemens Water Kit (Model TWF EDI UV TM, Singapore) was used in all experiments. 3.3.3. ICP Standards ICP-AES was calibrated using 25 element aqueous custom standard in 5% HNO3 (ZOASIS 1004) from VHG Labs, Manchester, USA. Calibration standards were prepared in the same matrices as that of the samples.

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3.3.4. Indian Standard Sand Indian standard sand procured from Tamil Nadu Minerals Ltd., Ennore, Chennai, India conforming to IS: 650-1991 was used. Three different grades of particle sizes viz., grade-1 (> 1 mm), grade-2 (1 mm to 500 µ) and grade-3 (90 to 500 µ) were provided. For cube experiments, equal proportions of each grade were utilised.

4. Fly Ash Blended with Ordinary Portland Cement The changes in metal speciation and leaching potential during blending of fly ashes with cement were assessed and compared with those from fly ashes and cement alone. Emphasis was also given to study the leaching of metals with curing age ranging from 0 to 90 days. To find optimum percentage of fly ashes for blending with cement, the mix proportions as represented in Table 7 were chosen. The proportions used here were in good agreement with other leaching and strength studies of mortar (Jewell et al., 2009; Jain et al., 2009). Table 7. Mix designs for fly ash blended with cement Set No. M0 M1 M2 M3 M4

Cement to fly ash ratio 100:0 80:20 60:40 30:70 5:95

Sand (grams) 600 600 600 600 600

Cement (grams) 200 160 120 60 10

Fly ash (grams) 0 40 80 140 190

Water (grams) 83 83 83 83 83

W/C 0.42 0.42 0.42 0.42 0.42

The water to cement ratio was maintained at 0.42 for all mix proportions based on the consistency of the cement. Blended cubes were prepared in accordance with IS: 4031-1988 (part 6) as cubes of size 70.6 mm x 70.6 mm x 70.6 mm conforming to IS: 10086-1992. Standard moulds were lined with mould oil. Predetermined amounts of constituents viz., cement, fly ash, and sand were correctly weighed and mixed with a trowel for about a minute till it showed uniform colour. Calculated quantity of ultrapure water to maintain water cement ratio of 0.42, as per IS: 4031–1998 (Part-6), was added and mixed for 5 minutes. Mould was placed on a table vibrator conforming to IS: 4031-1988 and mortar, thus, prepared was filled in the moulds in three layers with required tamping. A set of 3 moulds were filled for each mortar mix for

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all three fly ashes. Moulds were kept in a humidity chamber for 24 h. After 24 h, all cubes were removed from moulds and were submerged in ultrapure water for required curing period. The curing was continued for 3, 7, 14, 28 and 90 days in separate curing chambers. However, 0 and 1 day’s cubes were not submerged in water since de-moulding period was 24 h. The pH and the metals leached in curing water were monitored at the end of each curing periods. The compressive strengths of blended cubes were also determined for each curing period for each fly ash. Cement OPC cubes were taken as control for comparing the impact of blended fly ashes on compressive strength and metal leaching. The experimental methodology of the protocol of the cement fly ash blended cubes is shown in the Figure 5.

Figure 5. Experimental methodology for leaching protocol for blended cubes.

4.1. Curing of Fly Ash Blended Cement Mortar Cubes Fly ash blended mortar cubes, casted as per schedule given in Table 4, were cured in curing chambers filled with ultrapure water for 3 to 90 days. The casted cubes were named as MA1, MB1, MC1; MA2, MB2, MC2; MA3,

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MB3, MC3; and MA4, MB4, MC4 correponding to A-Ash, B-Ash, C-Ash, with mortar cubes with only cement cubes (M0) being the reference. The cured cubes were tested for compressive strength as per section 4.2 while curing waters were tested for variation of pH and metals as discussed in section 4.3.

4.2. Compressive Strength of Fly ash Cement Mortar Cubes Compressive strengths of cubes were measured using Compressive Testing Machine (AIMIL, India) having least count of 10 kN. Specimen was gradually loaded till its failure to calculate its compressive strength as given in equation 1. Care was taken to load the specimen axially. A set of three cubes were used in all calculations for averaging compressive strength in each case. Compressive Strength = Load taken by the specimen at failure / Cross-section area

(1)

4.2.1. Variation in Compressive Strengths Gaining of compressive strength of cement blended with fly ash is represented in Figures 6 to 9 respectively for 80:20 (M1), 60:40 (M2), 30:70 (M3), and 5:95 (M4) for all the fly ashes. The trend of compressive strength of cement alone i.e., 100:0 (M0) was taken as reference to compare any given combination of blending. Figure 6 shows gain of compressive strength for combination of M1 mixes for all ashes. With reference to cement strength of M0, all fly ash blended cements showed lower strength up to 28 days of curing. However, the strength gaining pattern with increasing curing time remained similar. A-Ash (MA1) and C-Ash (MC1) showed increased strength beyond 28 days till 90 days as compared to cement. In the case of B-Ash (MB1), the strength was found to be lower than that of cement. It is also clear from the figure that A (MA1) and C-Ashes (MC1) tended to gain strength beyond 90 days, but B-Ash (MB1) and cement (M0) did not. Hence, increasing the percentage of blending may achieve higher strengths beyond 28 days. As stated earlier, silicates present in A and C-Ashes might have reacted with calcium released from cement as well as calcium available within fly ash itself. This might have resulted in a gain in strength in MA1 and MC1 beyond 28 days.

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1 Day

3 Day

7 Day

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Figure 6. Comparison of compressive strengths of M1 mix (80% cement and 20% fly ash) with respective to M0 (100% cement). M0

MA2

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1 Day

3 Day

7 Day

14 Day

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Figure 7. Comparison of compressive strengths of M2 mixes (60% cement and 40% fly ash) with respective to M0 (100% cement).

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Figure 7 shows gain of compressive strength for combination of M2 (60:40) mixes for all ashes. With reference to cement strength (M0), all blended cements for this combination showed lower strength up to 28 days of curing like Figure 6. However, strength gained at the end of every curing period was lower than that corresponding strength in case of M1 mixes. All other observations were the same as those discussed above. Figure 8 shows gain of compressive strength for combination of M3 (30:70) mixes for all ashes. With reference to cement strength (M0), all blended cements (MA3, MB3 and MC3) showed significantly lower strengths at all curing periods including 90 days. It clearly indicates increased blending was detrimental to strength. Hence, it can be inferred that the optimum percentage of blending of cement with fly ash lies between 20 and 40%. M0

MA3

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50

40

30

20

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0 0 Day

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Figure 8. Comparison of compressive strengths of M3 mix (30% cement and 70% fly ash) with respective to M0 (100% cement).

Figure 9 shows gain of compressive strength for combination of M4 (5:95) mixes for all fly ashes. With reference to cement strength (M0), all blended cements did not develop any appreciable strength. It is expected as fly ashes do not have binding property. Lack of cement in mixes was the main cause of lack of compressive strengths in M4 mixes.

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MA4

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Compressive strength (N/mm2)

50

40

30

20

10

0 0 Day

1 Day

3 Day

7 Day

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Curing age (days)

Figure 9. Comparison of compressive strengths of M4 mix (5% cement and 95% fly ash) with respective to M0 (100% cement).

4.3. Curing Water Analysis for pH and Leaching of Metals The water in curing tanks was monitored for pH and leached metals for each corresponding mix design for fly ashes for each curing period. Care was taken to measure its pH in every instance of sampling. Leaching of metals in the curing water was evaluated by extracting 30 mL of samples from the curing tanks maintained for 3, 7, 14, 28 and 90 days for each of the mix proposed in Table 7. A sample of 10 mL was filtered using 0.2 µm PTFE filter and acidified to 2% by mass nitric acid for ICP-AES analysis.

4.3.1. Variation of pH pH of the ultrapure water used for curing was 6.58. It was monitored after 3, 7, 14, 28 and 90 days of curing. Variations of pH with curing time for all mixes M0, M1, M2, M3 and M4 for all three ashes are shown in Figure 10. pH was found to reach to 11-11.5 immediately after imersion of fly ash blended cubes for curing.

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A declining trend of pH was observed significantly after 7 days. This might be due to the release of alkalies from fly ash blended cubes during the reaction with water. The pH of solution went on reducing with increase in curing times. Drastic reduction in pH was observed at end of 90 days curing to ~8.5-9.5.

Figure 10. Variations of pH in curing waters for various mix designs (M0, M1, M2, M3 and M4) for all three fly ashes at the end of various curing periods.

4.3.2. Variation of Metals Metal releasing patterns in the curing water is shown in Figures 11 to 15 for the curing periods of 3, 7, 14, 28 and 90 days for As, Cr, Pb, Se and Zn. Concentration of arsenic, lead and selenium increased with increase in the blending percentage of fly ashes for the first three days and then, decreased with increase in curing period. However, Zn showed increase in concentration with curing period till 28 days, it completely disappeared at the end of 90 days of curing. This pattern remained same for all the fly ashes. In the case of chromium, trends of increased concentration were seen for only cement (M0) but not for any blended mix for the entire curing period. It may be concluded that fly ash blended cubes consumed / absorbed all the Cr and Se at end of 90 days and made curing water free from Cr and Se.

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Figure 11. Metals released in the curing water from fly ash blended cement mixes (M0, M1, M2, M3, M4) for all fly ashes (A, B, C) after 3 days of curing.

Figure 12. Metals released in the curing water from fly ash blended cement mixes (M0, M1, M2, M3, M4) for all fly ashes (A, B, C) after 7 days of curing.

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Figure 13. Metals released in the curing water from fly ash blended cement mixes (M0, M1, M2, M3, M4) for all fly ashes (A, B, C) after 14 days of curing.

Figure 14. Metals released in the curing water from fly ash blended cement mixes (M0, M1, M2, M3, M4) for all fly ashes (A, B, C) after 28 days of curing.

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MO

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MA2

MA3

MA4

MB1

MB3

MB4

MC1

MC2

MC3

MC4

MB2

60

Metal relese (µg/L)

50 40 30 20 10 0

As

Cr

Pb

Se

Zn

Figure 15. Metals released in the curing water from fly ash blended cement mixes (M0, M1, M2, M3, M4) for all fly ashes (A, B, C) after 90 days of curing.

Conclusion Based on the experiments carried out for the fate of metals in fly ash blended with Ordinary Portland cement, the F class fly ash blended cement cubes with fly ash A and C showed compressive strengths higher than those of pure cement cubes (M0) at the end of 90 days. However, compressive strengths of C class fly ash blended cement cubes with fly ash B were lower than those of pure cement cubes. The maximum blending of fly ash with ordinary Portland cement was found to up to 40% for class F ashes i.e., fly ash A and C. Class C ash i.e., fly ash B was not fit to be used as a building material due to lack of bonding strength. Blended cements continued to gain strength beyond 28 days. However, ordinary Portland cement did not gain strength after 28 days. The ultimate compressive strength of F class fly ash amended cubes was much more than that of unamended cubes. Thus, the addition of fly ash led to enhancement in compressive strength. Curing water pH reached to 11 after the commencement of curing of mortar cubes. A declining trend of pH was observed from 7 days onwards. Concentrations of As, Pb and Se increased with increase in the blending

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percentage of fly ashes for the first three days and then decreased with curing age.

References Adriano, D. C., Page, A. L., Elseewi, A. A., Chang A. C. and Straughan, I. (1980). Utilization and Disposal of Fly Ash and Other Coal Residues in Terrestrial Ecosystems: A Review. Journal of Environmental Quality, 9: 333–344. Aitken, R. L. and Bell, L. C. (1985). Plant Uptake and Phytotoxicity of Boron in Australian Fly Ash. Journal of Plant and Soil, 84: 245-257. Dayan, A. and Paine, A. (2001). Mechanisms of Chromium Toxicity, Carcinogenicity and Allergenicity. Journal of Human Toxicology, 20: 439-510. Dermatas, D. and Meng, X. (2003). Utilization of Fly Ash for Stabilization/ Solidification of Heavy Metal Contaminated Soils. Engineering Geology, 70: 377-394. Giammar, D., Biswas, P., Catalano, J. G., Dikshit, A. K. and Hao, J. (2009). Life cycles of Metals in Coal Combustion: Metal Release and Capture, Speciation in Fly Ash and Transformations during Ash Reuse and Storage. Report Submitted to the Consortium for Clean Coal Utilization, Washington University, Saint Louis, USA. IS 10086 (1992). Specification for Moulds for Use in Tests of Cement and Concrete. Bureau of Indian Standard, New Delhi. IS 4031 (Part-6) (1998). Methods of Physical Tests for Hydraulic Cement. Bureau of Indian Standard, New Delhi. Jain, J. and Neithalath, N. (2009). Analysis of Calcium Leaching Behavior of Plain and Modified Cement Pastes in Pure Water. Cement and Concrete Composites, 31: 176185. Jewell, R. B., Rathbone, R. F., Robl, T. L. and Henke, K. R. (2009). Fabrication and Testing of CSAB Cements in Mortar and Concrete that Utilize Circulating Fluidized Bed Combustion Byproducts. 2009 World of Coal Ash Conference, Lexington, KY, USA. Mattigod, S. V., Rai. D., Eary. L. E. and Ainsworth. C. C. (1990). Geochemical Factors Controlling the Mobilization of Inorganic Constituents from Fossil Fuel Combustion Residues: Review of the Major Elements. Journal Environmental Quality, 19: 188201. Means, J. L., Smith, C. A., Nehring, K. W., Brauning, S. E., Gavaskar, A. R., Sass, B. M., Wiles, C. C. and Mashni, C. I. (1995). The Application of Solidification/ Stabilization to Waste Materials. Journal of Hazardous Materials, 44: 103-104. Mukherjee, A. R., Zevenhoven, R., Bhattacharya, P., Sajwan, K. S. and Kikuchi, R. (2008), Mercury Flow Via Coal and Coal utilization Byproducts: A Global Perspective. Resource Conservation and Recycling, 52: 571-591. Noel, J. D., Biswas, P. and Giammar, D. E. (2007). Evaluation of a Sequential Extraction Process Used for Determining Mercury Binding Mechanisms to Coal Combustion Byproducts. Journal of the Air and Waste Management Association, 57: 856-867.

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Parsa, J., Staurt, H., Mcgee, M. and Steiner, R. (1996). Stabilization/Solidification of Hazardous Wastes using Fly Ash. Journal of Environmental Engineering, 122(10): 935-940. Poon, C. S., Qiao, X. C., Cheeseman, C. R. and Lin, Z. S. (2006). Feasibility of Using Reject Fly Ash in Cement Based Stabilization/Solidification Processes. Environmental Engineering, 23: 14-23. Rostami, H. and Brendley, W. (2003). Alkali Ash Material: A Novel Fly Ash-Based Cement. Environmental Science and Technology, 37: 3454-3457. Roy, A., Eaton, H. C., Cartledge, F. K. and Tittlebaum, M. E. (1991). Solidification/ Stabilization of a Heavy Metal Sludge by a Portland Cement/ Fly Ash Binding Mixture. Hazardous Waste and Hazardous Materials, 8(1): 33-41. Shi, C. and Spence, R. (2004). Designing of Cement-Based Formula for Solidification/Stabilization of Hazardous, Radioactive and Mixed Wastes. Critical Reviews in Environmental Science and Technology, 34: 391-417. Shivpuri, K. K., Lokeshappa, B., Deepak, A. K. and Dikshit, A. K. (2011). Metal Leaching Potential in Coal Fly Ash. American Journal of Environmental Engineering, 1(1): 2127. Singh, G. (2005). Environmental Assessment of Fly Ash from Some Thermal Power Stations for Reclamation of Mined Out Areas, IV: 9.1-9.10, Fly Ash Utilization Programme, TIFAC, DST, New Delhi. Sonmez, O. and Pierzynsk, G. M. (2005). Phosphororus and Manganese Oxides Effects on Soil Lead Bioaccessibility: PBET and TCLP. Journal of Water, Air and Soil Pollution, 166: 3-16. Statista (2022). Consumption volume of cement in India. https://www.statista.com/statis tics/269322/cement-consumption-in-india-since-2004/ (accessed on 20 July 2022).

Chapter 4

The Effect of Nanomaterials (Nano SiO2 and Nano Al2O3) on the Strength Properties of Self-Compacting Concretes Sarella Venkateswara Rao Padakanti Rakesh and Nandipati S. M. Ravi Kumar Department of Civil Engineering, National Institute of Technology Warangal, Warangal, Telangana, India

Abstract Utilizing nanoparticles in concrete improves many of the novel functions, including the mechanical properties of specimens, besides improving the microstructure and pore structure. Nanoparticles act as heterogeneous nuclei for cement paste, accelerating cement hydration because of their high reactivity. Because of the effective dispersion, the performance of any concrete can be better with nano inclusions. The demand for active finer particle additions to self-compacting concrete (SCC) is also satisfied. This indirectly improves the mechanical properties better than conventional concrete. In this study, three grades of self-compacting concrete with characteristic strength 25, 40, 60 MPa were developed using rational mix design (Modified Nan Su method). In the present study, two nano inclusions, nanosilica in a colloidal state with 30% nano content and nanoalumina in an amorphous state, were investigated. It was concluded from the study that the SCC containing nanosilica and nanoalumina particles performed better than normal SCC. 

Corresponding Author’s Email: [email protected].

In: Cement and Concrete Editors: Kong Fah Tee, Siew Choo Chin and Koorosh Gharehbaghi ISBN: 979-8-88697-831-5 © 2023 Nova Science Publishers, Inc.

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Keywords: self-compacting concrete, nanoalumina, nanosilica

1. Introduction Self-compacting concrete (SCC) is flowable concrete and does not require any compaction during casting. It has such a viscosity that the air bubbles can migrate to the outer surface of the fresh concrete. The fundamental idea of SCC is to lubricate the aggregate grains with a thin layer of cement paste so that the shear stresses between them in the fresh mixture can be decreased, and the mixture can become flowable (Okamura and Ouchi, 2003), (Jalal, Teimortashlu, and Grasley, 2019). The stability of SCC can be enhanced by incorporating fine materials such as fly ash (FA) and silica fume as increase in cement content leads to a significant rise in material cost. This has other negative effects on concrete properties (Khayat and Guizani, 1997). The use of such admixtures may provide greater cohesiveness by improving the grain-size distribution and particle packing (Sonebi and Bartos, 1999). Alternatively, a Viscosity Modifying Admixture (VMA) along with a Super Plasticizer (SP) may be used to impart high fluidity accompanied by adequate viscosity (Khayat, 1999). Use of chemical admixtures, increases the material cost and the savings in labour cost might offset the increased cost. Use of mineral admixtures not only reduces the material cost but also improves the fresh and hardened properties of SCCs (Bouzoubaa and Lachemi, 2001). Nanotechnology is a very active research field and has applications in a number of areas. Nowadays nanomaterials are used in construction along with the traditional building materials. Incorporation of nanomaterials in SCC is a most promising concept for developing concrete having certain desirable properties. The extremely fine size of the nanoparticles can alter the specific surface area and hence the properties of SCC, better than micro level properties as fly ash and silica fume. Nanoparticles added in cement composites can increase the workability, strength and durability characteristics (Li et al. 2004), (Askari Dolatabad, Kamgar, and Gouhari Nezad, 2020). Nanoparticles can also improve the bond between the aggregates and cement paste. There are a small number of studies that have been performed on the incorporation of nanoparticles in SCCs to achieve improved physical and mechanical properties. Nanoparticles can act as heterogeneous nuclei for cement pastes, further accelerating cement hydration, because of their high reactivity, as a nano-reinforcement, and as a nano-filler,

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making the microstructure denser, and thereby leading to a reduced porosity. The most significant issue with the use of nanoparticles is effective dispersion. In this study, two different types of nanoparticles, nanosilica and nanoalumina were included in SCC. Nanosilica in colloidal state with 30% nano content was added to SCC in three percentages (1%, 1.5% and 2%). Nanoalumina in amorphous state was added in two percentages (0.25% and 0.5%). This study investigates influence of these nanoparticles in SCC. The rheological and strength properties have been presented.

2. Research Significance The use of nano inclusions in SCC solves the dual purpose of improving the finer particles requirement in SCC and also improve the reactivity at the hydration level, enhance the strength properties. The studies on use of nano inclusions in SCC are rare and hence the present study gains good significance.

3. Mechanism for Achieving Self-Compactability Simply increasing the water content in a mix to achieve a flowable concrete like SCC is obviously not a viable option. Instead, the challenge is to increase the flowability of the particle suspension and at the same time avoid segregation of the phases. The main mechanism controlling the balance between higher flowability and stability are related to surface chemistry. The development of SCC has thus been strongly dependent on surface active admixtures as well as on the increased specific surface area obtained through the used fillers. The method for achieving self-compactability involves not only high deformability of paste or mortar, but also resistance to segregation between coarse aggregate and mortar when the concrete flows through the confined zone of reinforcing bars. (Hajime et al. 2003 and Ozawa, 1989) have employed the following methods to achieve self-compactability. a. Limited aggregate content b. Low water-powder ratio c. Use of Super Plasticizer (SP)

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The frequency of collision and contact between aggregate particles increases as the relative distance between the particles decreases and the internal stress increases when concrete is deformed, particularly near obstacles. It has been revealed that the energy required for flowing is consumed by the increased internal stresses, resulting in blockage of aggregate particles. Limiting the coarse aggregate content, whose energy consumption is particularly intense, to a level lower than normal proportions is effective in avoiding this kind of blockage. Highly viscous paste is also required to avoid the blockage of coarse aggregate when concrete flows through obstacles. When concrete is deformed, the paste with high viscosity also prevents localized increase in the internal stress, due to the approach of coarse aggregate particles. High deformability can be achieved only by the employment of a superplasticizer, keeping the water-powder ratio at a very lower level.

4. Nanotechnology “Nanotechnology is the art and science of manipulating matter at the nano scale.” Nanotechnology is the creation of materials and devices by controlling of matter at the levels of atoms, molecules, and super molecular (nano scale) structures. In other words, it is the use of very small particles of materials to create new large-scale materials.

4.1. Nanosilica (Nano SiO2) Nanosilica (NS) is the first nano product that replaced the micro silica. It has a specific surface area near to 1,00,000 m2/kg (micro silica has only 20,000 m2/kg) and a particle size of 5 nm to 250 nm. NS can contribute to efficient ‘Particle Packing’ in concretes by densifying the micro and nanostructure leading to improved mechanical and durability properties. NS can control degradation (through blocking of water entry on account of pore refinement) of the fundamental binder system of hydrated cement i.e., C-S-H gel caused usually due to calcium leaching out when immersed in water. NS improves behavior of freshly mixed cement concretes by imparting segregation resistance and by enhancing both workability and cohesion of the matrix.

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4.1.1. Production Methods of Nanosilica There are different methods to produce nanosilica products. One method is based on a sol-gel process (organic or water route) at room temperature. In this process, the starting materials (mainly Na2SiO4 and organometallics like TMOS/TEOS) are added in a solvent, and then the pH of the solution is changed, reaching the precipitation of silica gel. The produced gel is aged and filtered to become a xerogel. This aerogel is dried and burned or dispersed again with stabilized agent (Na, K, NH3, etc.) to produce a concentrated dispersion (20 to 40% solid content) suitable for use in concrete industry. An alternative production method is based on vaporization of silica between 1500 to 2000°C by reducing quartz (SiO2) in an electric arc furnace. Furthermore, nanosilica is produced as a byproduct of the manufacture of silicon metals and ferro-silicon alloys, where it is collected by subsequent condensation to fine particles in a cyclone. Nano-silica produced by this method is a very fine powder consisting of spherical particles or microspheres with a main diameter of 150 nm with high specific surface area (15 to 25 m2/g). Finally, nanosilica can also be produced by precipitation method. In this method, nanosilica is precipitated from a solution at temperatures between 50 to 100°C (precipitated silica). It was first developed by Iller in 1954. This method uses different precursors like sodium silicates (Na2SiO3), burned rice husk ash (RHA), semi-burned rice straw ash (SBRSA), magnesium silicate and others. In addition, nanosilica (NS) is being developed via an alternative production route. Basically, olivine and sulphuric acid are combined, whereby precipitated silica with extreme fineness but agglomerate form is synthesized (nano-size with particles between 6 to 30 nm), and even cheaper than contemporary micro-silica. 4.1.2. Effects of Nanosilica Addition in Concrete and Mortars Micro-silica can fill the voids in the young and partially hydrated cement paste, increasing its density. Some researchers found that the addition of 1 kg of micro-silica permits a reduction of about 4 kg of cement, and this can be higher if nanosilica is used. Optimizing the PSD will increase the properties (strength, durability) of the concrete due to the acceleration effect of nanosilica in cement paste. Nanosilica addition in cement paste and concrete can result in different effects. The accelerating effect in cement paste is one such effect. The main mechanism of this working principle is related to the high surface area of nanosilica, because it works as nucleation site for the precipitation of C-S-H

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gel. Also, the accelerating effect of nanosilica addition was established indirectly by measuring the viscosity change (rheology) of cement paste and mortars. The viscosity test results have shown that cement paste and mortar with nanosilica addition needs more water in order to keep the workability of the mixtures constant.

4.1.3. Applications of Nanosilica 1. Nanosilica is only used in the High-Performance Concretes (HPC), Eco-Concrete and Self-Compacting Concretes (SSC) because of their high cost. 2. Nanosilica is applied in HPC and SCC concrete mainly as an antibleeding agent. 3. It is also added to increase the cohesiveness of concrete and to reduce the segregation tendency. 4. It is used as an additive in eco-concrete mixtures and tiles one of the problems of these mixtures is their low compressive strength and long setting period. This disadvantage is solved by adding nanosilica to eco-concrete mixes to obtain an accelerated setting and higher compressive strength. 5. The inclusion of nanosilica reduces the setting time and increases the strength of the resulting cement.

4.2. Nanoalumina (Nano Al2O3) Binders are made from Portland ‘clinker’ ground together with a little calcium sulfate, and frequently also contain fine mineral powders such as limestone, pozzolana (typically volcanic ash), fly ash (usually from coal burning power plants) and granulated blast furnace slag. Such powders are referred to as Supplementary Cementitious Materials (SCMs) since they are used to replace some of the more expensive clinkers. Chemical admixtures such as super plasticizers and air-entraining agents can be added in small amounts to modify the properties of a concrete for specific applications. Another type of admixtures recently used are nanoparticles. The reason for using Al2O3 as a partial replacement by cement is the C-A-H (lime alumina- calcium sulfate) gel formation in concrete. The major constituent of a pozzolana is the alumina that can be amorphous or glassy. This component reacts with calcium hydroxide produced from the hydration

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of calcium aluminates. The rate of the pozzolanic reaction is proportional to the amount of surface area available for reaction. Therefore, it is possible to add nano-Al2O3 of a high purity (99.9%) and a high Blaine fineness value (60 m2/g) in order to improve the characteristics of cement mortars.

5. Mix Proportions of SCC Self-compacting concrete (SCC) has many benefits associated with the high workability of fresh concrete. The high flow ability, good stability and low blockage of the SCC are characteristics obtained with high fluidity, moderate viscosity and cohesion. This depends on the components and their proportions in the mixture. Nan Su method is the new mix design method for selfcompacting concrete (SCC). First, the amount of aggregates required is determined and the paste of binders is then filled into the voids of aggregates to ensure that the concrete thus obtained has flow ability, self-compacting ability and other desired SCC properties. As per Nan Su’s method of mix design of SCC, the parameters that influence the mix proportions are packing factor, fine aggregate–total aggregate ratio and powder content. However, as per Nan Su’s method assumptions in lieu of packing factor, cement content, fly ash content and fine aggregate/total aggregate ratio were made. From the strength and workability studies conducted on SCC, it was noted that there is a significant change in the mix proportions with respect to packing factor, effective size of aggregate, fine aggregate–total aggregate ratio, fly ash content, cement content and water content. It was hence felt that these parameters, which were otherwise assumed, are of reasonable importance. Hence, it was felt that there is a need for a rational mix design methodology for SCC. The existing Nan Su method has been suitably modified based on experimental investigation.

5.1. Modified Nan Su Method: Rational Mix Design The strength and workability studies conducted on SCC (Su, Hsu and Chai, 2001), confirmed that the parameters viz., packing factor, effective size of aggregate, fine aggregate/total aggregate ratio, fly ash content, cement content and water content influence the mix proportion to a great extent. It was hence felt that these parameters, which were assumed in case of Nan Su method of mix design, are of reasonable importance and a rational mix design

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methodology modifying the existing Nan Su method was proposed (Su, Hsu and Chai, 2001), (Venkateswara Rao, 2010). This rational mix design procedure can be adopted for designing any grade of self-compacting concrete. It is a simplified and direct mix design methodology for SCC based on experimental observations. The concept of this methodology is to develop various charts and equations that will help to arrive at the mix proportion of SCC having particular strength. The problem in selection of trial values such as packing factor, cement content, fly ash content etc., as required in existing Nan Su method can be eliminated using the rational mix design method (Venkateswara Rao, 2010).

6. Fresh Properties of SCC 6.1. Requirements of Self-Compacting Concrete SCC mixes must meet three key properties: 1. Ability to flow into and completely fill intricate and complex forms under its own weight. 2. Ability to pass through the congested reinforcement under its own weight. 3. High resistance to aggregate segregation. Due to the high powder content, SCC shows more plastic shrinkage or creep than ordinary concrete mixes. These aspects should therefore be considered during designing and specifying the SCC. By definition of SCC, it is clear that fresh concrete has to fulfill various properties. First, the SCC must be adequately free flowing so that the coarse aggregate particles can float in mortar, but the air can still rise and escape sufficiently. Second, sedimentation of the coarse aggregate particles and upward movement of fine mortar, paste or water before the concrete sets must be avoided. Otherwise, the SCC components will be resulting inhomogeneous compositions that can adversely affect their durability and fitness for use. Third, the paste volume and grading curve must be chosen so that the concrete fills the form work and is not held back in front of the gaps between the reinforcement. Suitable test methods by which the corresponding

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requirements can be verified were developed to ensure that the SCC meets these requirements. Many different test methods have been developed to characterize the properties of SCC. So far, no single way or combination of techniques has achieved universal approval and most of them have their adherents. Similarly, no single method has been found which characterizes all the relevant workability aspects. Each mix design should be tested by more than one test method for different workability parameters. The requisite test methods are described in Table 1. Table 1. List of test methods for fresh properties of SCC S. NO 1 2 3 4 5 6 7 8 9 10

Method

Property

Slump flow test T50cm Slump flow V-funnel test V-Funnel at T5 minutes L-Box test U – Box test Fill box apparatus test J-Ring Orimet test GTM screen stability test

Filling ability Filling ability Filling ability Segregation resistance Passing ability Passing ability Passing ability Passing ability Filling ability Segregation resistance

For the initial mix design of SCC all three workability parameters need to be assessed to ensure that all aspects are fulfilled. A full-scale test should be done to verify the self-compacting characteristics of the chosen design for a particular application. For site quality control, two test methods are generally sufficient to monitor production quality. Typical combinations are Slumpflow and V-funnel or Slump-flow and J-ring.

6.2. Workability Criteria for the Fresh SCC Filling ability, passing ability and segregation resistance are the requirements for judging the workability criteria of fresh SCC. These requirements are to be fulfilled at the time of placing of concrete. Typical acceptance criteria for Selfcompacting concrete with a maximum aggregate size up to 20 mm are shown in Table 2.

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Table 2. Acceptance criteria for self-compacting concrete S. No

Method

Unit

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Slump flow test T50 cm Slump flow J – Ring V – Funnel V – Funnel at T5 minutes L – Box U – Box Fill Box GTM Screen stability test Orimet test

mm sec mm sec sec h2/h1 (h2-h1) mm % % sec

Typical range of values Minimum Maximum 650 800 2 5 0 10 6 12 6 15 0.8 1.0 0 30 90 100 0 15 0 5

6.3. Test Methods It was observed that none of the test methods for SCC has yet been standardized, and neither of the tests described are yet to be perfected or definitive. Therefore, a brief description of the tests has been presented below. They are mainly ad-hoc methods, which have been devised specifically for SCC.

6.3.1. Slump Flow Test and T50cm Test The slump flow is used to assess the horizontal free flow of SCC in the absence of obstructions. It was first developed in Japan for use in assessment of underwater concrete. The diameter of the concrete circle is a measure of the filling ability of concrete. Slump Flow is definitely one of the most commonly used SCC tests at present. This test involves the use of slump cone with conventional concretes as described in ASTM C 143 (Standard Test Method for Slump of HydraulicCement Concrete). The main difference between Slump Flow Test and ASTM C 143 (Standard Test Method for Slump of Hydraulic-Cement Concrete) is that the Slump Flow Test measures the spread or flow of concrete sample, once the cone is lifted rather than the traditional slump (drop in height) of the concrete sample. The T50 test is also determined during the Slump Flow Test. It is simply the amount of time that the concrete takes to flow to a diameter of 50 centimeters. The slump flow test procedure is as shown in Figure 1.

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Figure 1. Slump flow test procedure (SCC mixes).

6.3.1.1. Slump Flow Apparatus The mould used is in the shape of a truncated cone with internal dimensions 200 mm diameter at the base, 100 mm diameter at the top and a height of 300 mm. The base plate is of a stiff non- absorbing material of at least 700 mm square, marked with center location for the slump cone, and further concentric circle of 500 mm diameter. The other apparatus required are trowel, scoop, ruler, and a stop watch. 6.3.1.2. Procedure About 6 liters of concrete is needed to perform the test. First, the base plate and the inside of the slump cone were moistened. Next, the base plate was placed on level stable ground, and the slump cone was placed centrally on the base plate and held down firmly. The concrete was filled into the cone with the scoop without tamping. The excess material on the top of slump cone was removed and leveled with a trowel. The surplus concrete around the base of the cone was removed. The slump cone was raised vertically upwards, allowing the concrete to flow out freely. The time taken for concrete to reach the 500 mm spread circle was recorded using the stopwatch. This is the T50 time. After the flow of concrete was stopped, the final diameter of concrete in two perpendicular directions was measured. The average of the two measured diameters is called slump flow in mm. 6.3.2. L – Box Test This test, based on a Japanese design for underwater concrete, has been described by Peterson, 1999. This test assesses the flow of concrete, and also

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the extent to which it is subjected to blocking by reinforcement. The apparatus is shown in Figure 2.

Figure 2. L – Box test apparatus (SCC mixes).

The apparatus consists of a rectangular-section box in the shape of an ‘L’, with a vertical and horizontal section, separated by a moveable gate, in front of which, vertical lengths of reinforcement bars are fitted. The vertical section is filled with concrete, and then the gate is lifted to let the concrete flow into the horizontal section. When the flow has stopped, the height of the concrete at the end of the horizontal section is expressed as a proportion of that remaining in the vertical section called as H2/H1 ratio or blocking ratio. It indicates the slope of the concrete when the concrete is at rest. This is an indication of passing ability, or the degree to which the passage of concrete through the bars is restricted. The horizontal section of the box can be marked at 200mm and 400mm from the gate and the time taken to reach these points measured. These are known as the T20 and T40 times and are indicators of the filling ability.

6.3.2.1. Procedure About 14 liters of concrete is needed to perform the test. The apparatus was placed on the level ground. It was ensured that the sliding gate could open and close freely. The inside surfaces of the apparatus were moistened and surplus water was removed. The vertical section of the apparatus was filled with the concrete sample. The sliding gate of the vertical section was lifted and concrete has allowed flowing out into the horizontal section. The time taken for concrete to reach the 200 and 400mm marks in the horizontal section was measured simultaneously by using the stopwatch. The distances H1 and H2 were measured when the concrete stops flowing and the blocking ratio H2/H1is

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calculated. The maximum time required for performing this L – box test is 5 minutes.

6.3.3. V – Funnel Test and V – Funnel Test at T5 Minutes This test was developed in Japan and used by Ozawa et al, 1989. The equipment consists of a V-shaped funnel, shown in Figure 3. The V-funnel test is used to determine the filling ability of the concrete with a maximum aggregate size of 20 mm. The funnel was filled with about 12 liters of concrete and the time taken for it to flow through the apparatus measured. After this the funnel was refilled concrete and left for 5 minutes to settle. If the concrete shows segregation, then the flow time increases significantly.

Figure 3. V – funnel test apparatus (SCC mixes).

6.3.3.1. Procedure for Flow Time About 12 liters of concrete was needed to perform this test. The V-funnel apparatus was placed on the firm ground. The inside surfaces of the V – funnel was moistened and the surplus water in funnel was drained through trap door by opening it. Before starting the test, the trap door was closed and a bucket was placed underneath. The V – funnel apparatus was completely filled with concrete without any compaction. The top surface was leveled with the trowel. The trap door was opened and concrete was allowed to flow out under gravity. By using the stopwatch, the time taken for the complete discharge of concrete from the funnel was measured. The whole test has to be performed within 5 minutes.

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6.3.3.2. Procedure for Flow Time at T5 Minutes After measuring the flow time, the trap door of the V-funnel was closed and a bucket was placed underneath. Again, the concrete was filled into the apparatus completely without any compaction. The top surface was leveled with the trowel. The trap door was opened after 5 minutes and the concrete was allowed to flow out under gravity. The time for the complete discharge of concrete from the funnel was recovered. 6.3.4. J – Ring Test The J – Ring test has been developed at the University of Paisley. The test is used to determine the passing ability of the concrete. The equipment consists of a rectangular section (30 mm x 25 mm) open steel ring, drilled vertically with holes to accept threaded sections of reinforcement bar. These sections of bar can be of different diameters and spaced at different intervals in accordance with normal reinforcement considerations. The diameter of the ring of vertical bars is 300mm, and the height 100 mm as shown in Figure 4.

Figure 4. J – Ring apparatus (SCC mixes).

The J – Ring can be used in conjunction with the Slump flow test. These combinations judge the flowing ability and the passing ability of the concrete. The slump flow spread was measured to assess flow characteristics. The J – Ring bars can be set at any spacing to impose a more or less severe test of the passing ability of the concrete. After the test, the difference in height between the concrete inside and that just outside the J – Ring is measured. This is an

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indication of passing ability, or the degree to which the passage of concrete through the bars is restricted.

6.3.4.1. Equipment The mould used is in the shape of a truncated cone with the internal dimensions 200mm diameter at the base, 100mm diameter at the top and a height of 300mm. The base plate is of a stiff non- absorbing material, at least 700mm square, marked with center location for the slump cone, and further concentric circle of 500mm diameter. A rectangular section (30mm x 25mm) open steel ring, drilled vertically with holes is called as J - ring. The holes can be screwed threaded sections of reinforcement bar. The other apparatus required are trowel, scoop, ruler, and a stop watch. 6.3.4.2. Procedure About 6 liters of concrete is needed to perform this test. Moisten the base plate and inside of slump cone, place the baseplate on level stable ground. The slump cone was placed on the level ground and the J – ring was placed centrally inside the slump cone and was held down firmly. The concrete was filled into the cone with the scoop without any compaction. The top surface of the cone was leveled with the trowel. The surplus concrete around the base of the cone was removed. The slump cone is raised vertically upwards to allow the concrete to flow out freely through the rings. The difference in height between the concrete just inside the bars and that just outside the bars was measured. The average difference in height at four locations (in mm) was measured. 6.3.5. U – Box Test This test was developed by the Technology Research Centre of the Taisei Corporation in Japan. This test is also called a box-shaped test. It is used to measure the filling ability of self-compacting concrete. The apparatus consists of a vessel that is divided by a middle wall into two compartments, shown by R1 and R2 in Figure 5. An opening with a sliding gate was fitted between the two sections. Reinforcing bars with nominal diameters of 13 mm are installed at the gate with centre-to-centre spacings of 50 mm. This creates a clear spacing of 35 mm between the bars. The left-hand section was filled with about 20 liters of concrete. The gate was lifted and the concrete flows upwards in the other section. The height of the concrete in both sections is measured.

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Figure 5. U – Box apparatus (SCC mixes).

6.4. Size of Test Specimen Used The self-compacting concrete mixes with nanomaterials, after having checked for the satisfaction of the fresh properties of self-compacting specifications as per EFNARC, 2005 was cast into cube moulds of size 150 mm x 150 mm x 150 mm, beam moulds of size 100 mm x 100 mm x 500 mm and cylindrical moulds of 300 mm height x 150 mm diameter. The moulds were fabricated with steel sheets. It is easy for assembling and removing the mould specimen without damage. Moulds were provided with base plates, having smooth surface to support. The mould is filled without leakage. Care was taken to ensure that there were no leakages.

6.5. Curing of Test Specimens After 24 hours of casting, the specimens were removed from the moulds and immediately dipped in clean fresh water. The specimens were cured for 3 days, 7 days and 28 days respectively depending on the requirement of age of curing. The fresh water tanks used for the curing of the specimens were emptied and cleaned once in every fifteen days and were filled once again. All the specimens under immersion were always kept well under water and it was seen that at least about 15 cm of water was above the top of the specimens as shown in Figure 6.

Fig.6.

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Figure 6. Demoulded specimens and curing process.

7. Tests on Hardened Concrete Testing of hardened concrete plays an important role in controlling and confirming the quality of self-compacting concrete with nanomaterials.

7.1. Compressive Strength Compressive strength of a material is defined as the value of uniaxial compressive stress reached when the material fails completely. In this investigation, the cube specimens of size 150 mm x 150 mm x 150 mm are tested in accordance with IS 516 – 1969 (method of test for strength of concrete). The testing was done on a compression testing machine of 300tonne capacity. The machine can control the rate of loading with a control valve. The machine has been calibrated to the required standards. The plates are cleaned; oil level was checked and kept ready, in all respects for testing. After 28 days of curing, cube specimens were removed from the curing tank and cleaned to wipe off the surface water. The specimens were transferred on to the swiveling head of the machine such that the load was applied centrally. The smooth surfaces of the specimen are placed on the bearing surfaces. The top plate was brought in contact with the specimen by rotating the handle. The oil pressure valve was closed and the machine was switched on. A uniform rate of loading 140 kg/cm2/min was maintained. The maximum load to failure at which the specimen breaks and the pointer starts moving back

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was noted. The test was repeated for the three specimens and the average value was taken as the mean strength. The test set up is shown in Figure 7.

Figure 7. Compressive strength test setup.

7.2. Flexural Strength Standard beam test (Modulus of rupture) was carried out on the beams of size 100 mm x 100 mm x 500 mm as per IS: 516 (Method of test for strength of concrete), by considering that material is homogeneous. The beams were tested on a span of 400 mm for 100 mm specimen by applying two equal loads placed at third points. To get these loads, a central point load has applied on a beam supported on steel rollers placed at third point as shown in Figure 8 (a) and (b). The rate of loading is 1.8 kN/minute for 100 mm specimens and the load was increased until the beam failed. Depending on the type of failure, appearance of fracture and fracture load, the flexural tensile strength of the sample was estimated. If ‘a’ be the distance between the line of fracture and the nearer support, then for finding the modulus of rupture, these cases should be considered. •

When a > 133 mm for 100 mm specimen , where P = total load applied on the beam

•

When 110 mm < a < 133 mm,

•

When a < 110 mm, the result should be discarded.

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(a)

(b) Figure 8. (a) Schematic diagram for flexure test setup; (b) Flexural strength test.

7.3. Split Tensile Strength This is also sometimes referred as “Brazilian Test” as this test was developed in Brazil in 1943. This comes under indirect tension test methods. The test was carried out by placing a cylindrical specimen horizontally between the loading faces of a compression testing machine and the load was applied until failure of the cylinder, along the vertical diameter as shown in Figure 9. A concrete cylinder of size 150mm diameter and 300mm height was subjected to the action of a compressive force along two opposite edges. The cylinder was subjected to compression near the loaded region and the length of cylinder is subjected to uniform tensile stress.

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Figure 9. Split tensile strength test.

where P= Compressive load on the cylinder. L= Length of cylinder. D= Diameter of cylinder.

8. Materials The materials used in the experimental investigation are locally available cement, sand, coarse aggregate, mineral and chemical admixtures. The chemicals used in the present investigation are of commercial grade.

8.1. Cement Ordinary Portland cement of 53 grade (IS: 12269-1987, Specifications for 53 Grade Ordinary Portland cement) has been used in the study. It was procured from a single source and stored as per IS: 4032 – 1977. Care has been taken to ensure that the cement of the same company and same grade is used throughout the investigation. The cement thus procured was tested for physical properties in accordance with the IS: 12269 – 1987.

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Table 3 shows the physical characteristics of cement used, tested in accordance with IS: 4031-1988 (methods of physical tests for hydraulic cement). Table 3. Physical properties of Ordinary Portland cement S. No 1. 2.

Property Normal consistency Specific gravity

3.

Initial setting time

Test Method Vicat Apparatus (IS: 4031 Part - 4) Sp. Gr bottle (IS: 4031 Part - 4) Vicat Apparatus (IS: 4031 Part - 4)

Fineness

5.

Specific surface area Soundness

6.

Compressive Strength 3 Days 7 Days 28 Days

IS Standard

3.10

Sieve test on sieve no.9 (IS: 4031 Part – 1)

1.6%

Not less than 30 minutes Not less than 10 hours 10%

2900 cm2/gm

2250 cm2/gm

Le-Chatlier method (IS: 4031 Part – 3) Mortar cubes (1:3) (IS: 4031.Part - 6

1.8 mm

Not more than 10 mm

Final setting time 4.

Test Results 29.5%

90 minutes 220 Minutes

29 M Pa 43 M Pa 53.3 M Pa

8.2. Fine Aggregates The fine aggregate used was locally available river sand without any organic impurities and conforming to IS: 383 – 1970 (methods of physical tests for hydraulic cement). The fine aggregate was tested for its physical requirements such as gradation, fineness modulus, specific gravity and bulk density in accordance with IS: 2386 – 1963 (methods of test for aggregate for concrete) and is shown in Table 4. The sand was surface dried before use.

8.3. Coarse Aggregate The coarse aggregate chosen for SCC was typically round in shape, wellgraded and smaller in maximum size than conventional concrete. The size of

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coarse aggregate used in self- compacting concrete was between 10 mm to 20mm. The rounded and smaller aggregate particles provide better flowability and deformability of concrete and also prevent segregation. Graded aggregate is also essential mainly to cast concrete in highly congested reinforcement or formwork having small dimensions. Crushed granite metal of sizes 20 mm to 10 mm graded obtained from the locally available quarries was used in the present investigation. These were tested as per IS 383-1970 (Methods of physical tests for hydraulic cement). The physical properties like specific gravity, bulk density, flakiness index, elongation index and fineness modulus are shown in Table 4. Table 4. Physical properties of coarse and fine aggregate S.No

Property

Method

1.

Specific gravity

2.

Bulk density

Pycnometer IS:2386 Part 3-1986 IS:2386 Part 3-1986

Loose Compacted 3. 4. 5. 6.

Bulking Flakiness index Elongation index Fineness modulus

IS:2386 Part 3-1986 (IS:2386 Part 2-1963) (IS:2386 Part 2-1963) Sieve Analysis (IS:2386 Part 2-1963)

Fine Aggregate 2.55

Coarse Aggregate 2.65 1442 kg/m3

1567 kg/m3 1713 kg/m3 6% w c ---

-6.15% 7.1%

2.19

7.16

8.4. Water Water used for mixing and curing was potable water, which was free from any amounts of oils, acids, alkalis, sugar, salts and organic materials or other substances that may be deleterious to concrete or steel confirming to IS: 3025 – 1964 part22, part 23 and IS: 456 – 2000 (code of practice for plain and reinforced concrete). The pH value should not be less than 6. The solids present were within the permissible limits as per clause 5.4 of IS: 456 – 2000.

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8.5. Fly Ash Fly ash is one of the most extensively used supplementary cementitious materials in the construction field resembling, Portland cement. It is an inorganic, non-combustible, finely divided residue collected or precipitated from the exhaust gases of any industrial furnace. Most fly ash particles are solid spheres and some particles, called cenospheres, are hollow and some are the plerospheres, which contain smaller spheres inside. The particle sizes in fly ash vary from less than 1 μm to more than 100 μm, with the typical particle size measuring less than 20 μm. Their surface area is typically 300 to 500 m2/kg, although some fly ashes can have surface areas as low as 200 m2/kg and as high as 700 m2/kg. Fly ash is primarily silicate glass containing silica, alumina, iron, and calcium. Fly ash’s relative density or specific gravity generally ranges between 1.9 and 2.8 and the color is generally grey. Fly ash used in this investigation was procured from National Thermal Power Corporation, Ramagundam, Telangana State, India. It confirms with grade I of IS: 3812 – 1981 (Specifications for fly ash for use as pozzolana and admixture). It was tested in accordance with IS: 1727 –1967 (Methods of test for pozzolana materials). A typical oxide composition of Indian fly ash is shown in Table 5. Table 5. Typical oxide composition of fly ash (Class – F) S. No 1. 2. 3. 4. 5. 6. 7. 8.

Characteristics

Percentage

Silica, SiO2 Alumina Al2O3 Iron oxide Fe2O3 Lime CaO Magnesia MgO Sulphar Trioxide SO3 Loss on Ignition Surface area m2/kg

49-67 16-28 4-10 0.7-3.6 0.3-2.6 0.1-2.1 0.4-1.9 230-600

The chemical composition and physical characteristics of fly ash used in the present investigation were given in Tables 6 and Table 7.

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Table 6. Chemical requirements of fly ash S No. 1. 2. 3. 4. 5. 6. 7.

Characteristics Silicon dioxide (SiO2) plus aluminium oxide (Al2O3) plus iron oxide (Fe2O3) Silicon dioxide (SiO2) Magnesium Oxide (MgO) Total sulphur as sulphur trioxide (SO3) Available alkalies as sodium oxide (Na2O) Loss on ignition Chlorides

Requirements (% by weight) 70 (minimum)

Fly Ash Used (% by weight) 94.46

35 (minimum) 5 (max.) 2.75 (max.) 1.5 (max.)

62.94 0.60 0.23 0.05

12 (max.)

0.30 0.009

Table 7. Physical requirements of fly ash S. No

Characteristics

1.

Fineness by Blain’s apparatus in m2/kg Lime reactivity (MPa) Compressive strength at 28 days as percentage of strength of corresponding plain cement mortar cubes Soundness by autoclave expansion

2. 3.

4.

Requirements for Grade of Fly Ash (IS:3812-1981) Grade – I Grade – II 320 250

Experimental Results

4.0 3.0 Not less than 80%

9.8 86%

335

Nil

8.6. Silica Fume Silica fume gives a very good improvement of the rheological, mechanical as well as chemical properties. The particles of silica fume are spherical with average size 0.1mm and its amorphous silica could exceed 90% of the total. Thus, silica fume is one of the most common additives for producing high and super high strength concretes. Silica fume used in this investigation was a product of Elkem. The general physical requirements and dosage are given in the Table 8.

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Table 8. Physical requirements of silica fume S. No. 1. 2. 3. 4. 5. 6. 7. 8. 9.

Property

Result

Form or state Colour Odour Melting point (°C) Specific gravity Bulk Density (kg/m3) Specific Surface (m2/g) Particle size, mean (µm) Silicon Dioxide

Ultra fine amorphous powder Gray Odourless 1550 – 1570 2.2 – 2.3 150 – 700 15 – 30 ≈0.5 > 85%

8.7. Super Plasticizer High range water reducing admixture called as super plasticizers are used for improving the flow or workability for lower water-cement ratios without sacrifice in the compressive strength. These admixtures when they disperse in cement agglomerates significantly decrease the viscosity of the paste by forming a thin film around the cement particles. In the present work, waterreducing admixture Conplast SP 430 conforming to IS 9103: 1999 (specification for admixtures for concrete), ASTM C – 494 (Standard Specification for Chemical Admixtures for Concrete) types F, G and BS 5075 part.3 (British Standards Institution) was used. Conplast SP 430 is a Sulphonated Naphthalene based Formaldehyde (SNF), super plasticizer and it was manufactured by Fosroc.

9. Experimental Program The experimental program consisted of casting and testing of SCC specimens. Though basically modified Nan Su method of mix design (Venkateswara Rao, 2010) was adopted, number of trials was made in producing SCC satisfying the EFNARC specifications (EFNARC, 2005). A total of three grades of concrete viz. M25, M40 and M60 were investigated, representing ordinary, standard and high strength concrete respectively as per IS 456-2000 (code of practice for plain and reinforced concrete) (Arefi, Jahaveri and Mollaahmadi,

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2011). The characteristic strengths of these concretes are respectively 25, 40, 60 MPa. The properties of the constituent materials used in the present investigation are given in Table 9. The adequate Super Plasticizer (SP) dosage was used to improve the flowability, self-compacting ability and segregation resistance of fresh SCC to meet the design requirements. The water content of the SP can be regarded as part of the mixing water. In the present work, Sulphonated Naphthalene Formaldehyde (SNF) based water-reducing admixture (Super Plasticizer) was used. The dosage of SP was fixed based on trial and error to suit the requirements of EFNARC Specifications (2005). Table 9. Material property of ingredients used for SCC Cement – OPC 53 grade Specific gravity Normal consistency

3.10 29.5%

Coarse aggregate Specific gravity Bulk density (kg/m3) Fineness modulus

2.65 1442 7.16

Super plasticizer – Conplast SP 430 Specific gravity 1.22 Chloride content Nil

Fly Ash Fineness Silicon Dioxide (SiO2) Lime reactivity Fine aggregate Specific gravity Bulk density (kg/m3) Fineness modulus

335 m2/kg 62.94% 9.8 MPa 2.5 5 1713 2.19

For compressive strength, standard cube moulds of 150mm x 150mm x 150mm made of cast iron were used. For split tensile strength, standard cylinder moulds of 150 mm φ x 300mmmade of cast iron were used. For flexural strength 100 x 100 x 500 mm of standard prism moulds were used. The program consisted of casting and testing M25, M40 and M60 grade concrete specimens of SCC with addition of nanosilica, nanoalumina and without nanoparticle additions. A total of 54 cubes, 36 cylinders and 36 prisms were cast and tested. The parameters of investigation included, different types of nano inclusions (silica and Alumina), grade of concrete (M25, M40 and M60) and age of concrete (3, 7 and 28 days). Nanosilica (30% nano content) with addition of 1, 1.5 and 2% by weight of cement and nanoalumina with 0.25%, 0.5% by weight of cement was adopted in the study.

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9.1. Nanosilica (Nano SiO2) Nanosilica (NS) is the first nano product that replaced the micro silica (Ozawa et al. 1989). It has a specific surface area near to 1, 00,000 m2/kg (micro silica has only 20,000 m2/kg) and a particle size of 5 nm to 250 nm. Nanosilica (NS) can contribute to efficient ‘Particle Packing’ in concretes by densifying the micro and nanostructure leading to improved mechanical and durability properties.

9.2. Nanoalumina (Nano Al2O3) The reason for using Al2O3 as a partial replacement by cement in SCC is the C-A-H (lime alumina- calcium sulfate) gel formation in concrete (EFNARC, 2005). The principal constituent of a pozzolana is the alumina that can be amorphous or glassy. This component reacts with the calcium hydroxide produced from the hydration of calcium aluminates. The rate of the pozzolanic reaction is proportional to the amount of surface area available for reaction. Therefore, adding nano-Al2O3 of high purity (99.9%), particle size 15 ± 3 nm and a high Blaine fineness value (165-175 m2/gm) improves the characteristics of cement mortars. The details of the mixed proportions of the three SCC mixes M25, M40 and 60 are shown in Table 10. SCC 1, SCC 2 and SCC 3 correspond to M25, M40 and M60 grade concretes. In each of these three grades nanosilica (NS) of 1, 1.5 and 2% additions and nanoalumina (NA) of 0.25% and 0.5% additions were done. Table 10. Mix proportions of SCC mixes Type of mix SCC 1 SCC2 SCC3

w/b

Coarse Aggregate 754.16

Water

S.P

0.36

Quantities (kg/m3) Cement Fly Fine Ash Aggregate 315.12 330.25 1078.29

232.72

11.62

Silica Fume --

0.30 0.26

468.00 677.34

794.08 799.30

244.71 256.40

14.78 17.6

-54

353.05 677.34

946.48 304.31

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9.3. Fresh Properties of SCC Mixes In order to validate the mixes designed, rheology studies have been conducted and the details of the Slump flow, L – box, V funnel test, V funnel at 5 minutes are shown in Tables 11, 12 and 13 for SCC mixes of grade M25, M40 and M60 respectively. Table 11. Fresh properties of M25 grade of SCC Grade Type of test

M 25 SCC1

Slump Flow (mm) T50 (sec) V-Funnel (sec) V-Funnel at 5 min (sec) H2/H1 ratio

*NS 1

NS 1.5

NS 2

770 2.6 6.53 7.8

760 2.85 7.35 9.85

740 3.54 8.16 11.3

1

1

1

EFNARC Specifications

NA 0.5

660 4.87 9.35 12.6

** NA 0.25 710 3.78 8.33 9.75

670 4.83 9.56 12.6

650 – 800 2–5 6 – 12 6 – 15

0.97

1

0.95

0.8 – 1.0

Table 12. Fresh properties of M40 grade of SCC Grade Type of test

M 40 SCC2

Slump Flow (mm) T50 (sec) V-Funnel (sec) V-Funnel at 5 min (sec) H2/H1 ratio

740 2.4 5.73 7.25

*NS 1 727 2.5 6.65 8.53

NS 1.5 710 3.12 7.65 10.8

NS 2 690 4.59 8.27 12.3

**NA 0.25 725 3.78 7.14 10.4

NA 0.5 690 4.75 8.24 12.7

1

1

1

0.98

1

0.98

EFNARC Specifications 650 – 800 2–5 6 – 12 6 – 15 0.8 – 1.0

Table 13. Fresh properties of M60 grade of SCC Grade Type of test

M 60 SCC3

Slump Flow (mm) T50 (sec) V-Funnel (sec) V-Funnel at 5 min (sec) H2/H1ratio

780 2.6 6.53 7.85

*NS 1 770 2.85 7.35 10.25

NS 1.5 750 3.54 8.16 11.3

NS 2 675 4.87 9.35 12.5

**NA 0.25 725 3.78 8.33 11.4

NA 0.5 680 4.83 9.56 13.2

1

1

1

0.97

1

0.95

NS – nano-silica **NA – nano-alumina.

*

EFNARC Specifications 650 – 800 2–5 6 – 12 6 – 15 0.8 – 1.0

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It can be noted that all the mixes are satisfying the EFNARC specifications.

10. Discussion of Test Results In the present study, hardened properties compressive strength, split tensile and flexural strength were determined for all grades of SCC with and without nano particle additions (SiO2 & Al2O3). The compressive strengths of SCC were determined at the end of 3, 7 and 28 days and the results are shown in Table 14. The spilt tensile and flexural strengths of SCC were conducted at the end of 7 and 28 days and the results are shown in Table 15 and Table 16 respectively. Table 14. Compressive strength of SCC with and without nano additions S. No

1 2 3 4 5 6

Type of Concrete

SCC NS 1 NS 1.5 NS 2 NA 0.25 NA 0.5

Compressive Strength (MPa) M 25 M 40 3 7 28 3 Days Days Days Days 17.06 25.23 32.48 18.12 21.94 26.42 37.42 23.81 23.65 28.33 39.47 23.90 20.48 26.08 38.15 24.05 22.79 25.76 34.00 24.80 24.00 34.80 43.42 25.50

7 Days 32.34 41.12 44.19 43.13 34.32 38.13

28 Days 48.61 53.67 60.14 57.34 52.04 58.91

M 60 3 Days 28.40 34.06 36.10 34.26 32.61 35.53

7 Days 44.00 49.88 52.38 50.21 49.44 51.72

Table 15. Split tensile strength of SCC with and without nanoparticle additions S. No

1 2 3 4 5 6

Type of Concrete SCC NS 1 NS 1.5 NS 2 NA 0.25 NA 0.5

Split tensile Strength (MPa) M 25 M 40 7 Days 28 Days 7 Days 1.7 2.77 1.98 1.91 2.92 1.65 1.73 3.01 1.82 1.51 2.55 1.90 1.65 2.58 1.82 1.66 3.13 1.97

28 Days 3.6 3.89 4.10 3.80 3.21 3.98

M 60 7 Days 2.3 2.68 2.83 2.73 2.66 2.77

28 Days 4.03 4.20 4.42 4.19 4.0 4.4

28 Days 67.50 70.94 75.45 72.80 69.52 73.80

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Table 16. Flexural strength of SCC with and without nanoparticle additions S. No

1 2 3 4 5 6

Type of Concrete SCC NS 1 NS 1.5 NS 2 NA 0.25 NA 0.5

Flexural Strength (MPa) M 25 M 40 7 Days 28 Days 7 Days 3.13 4.14 4.38 3.04 4.54 5.12 2.87 5.34 5.46 2.57 4.34 5.62 2.97 5.20 4.81 3.04 6.30 5.02

28 Days 4.62 5.35 6.75 6.18 6.98 7.12

M 60 7 Days 5.10 5.56 6.89 5.72 5.89 6.83

28 Days 8.08 8.30 10.44 8.74 8.96 10.30

From Figure 10 and 11, it can observe that the optimum dosage of nanosilica is 1.5% and 0.5% in case of nanoalumina based on the 28 days compressive strength. The percentage increase of compressive strength is however more in nanosilica based SCC. This can be attributed to better hydration with nanosilica. Figure 12 shows the variation of the compressive strength vs the split tensile strength for different types of concrete including SCC, SCC-NS and SCC-NA. For comparison trend lines are drawn for NC on the same figure.

Figure 10. Compressive strengths of SCC with different dosages of nanosilica.

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Figure 11. Compressive strengths of SCC with different dosages of nanoalumina.

The trend line for Normal Concrete (NC) shown in Figure 12 is based on the assumption that the split tensile strength is 10% of the compressive strength. It can be found that at higher grades the values of split tensile strength are less than 10% of compressive strength values. The graphs seem to converge at higher grades of concrete. The difference between NC and SCC (different types) are diverging as the grades of concrete are increasing.

Figure 12. Compressive strength vs split tensile strength at age of 28 days.

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Figure 13 shows the relationship between flexural and compressive strength for different types of concretes including SCC, SCC-NS and SCCNA. As per IS: 456 – 2000 the flexural strength is 0.7 x (√characteristic compressive strength). A trend line of the variation of the flexural strength and compressive strength is plotted on the same figure. It can be noted from Figure 13 that SCC with nano-alumina (SCC-NA) performed better than the flexural strength of SCC.

Figure 13. Compressive strength vs flexural strength at age of 28 days.

Conclusion With the increase in the dosage of nanomaterials, the rate of increase of compressive strength increased as compared to SCC of identical grade without nano inclusions. This is true with both SiO2 and Al2O3 nano additions. The early compressive strength (3 and 7 days) in case nano-based SCC is 20–40% more compared to normal SCC. This may be due to the early age hydration of cement. This is true with all the three grades of concrete. The optimum dosage of nanosilica is 1.5% and 0.5% in case of nanoalumina based on the 28 days compressive strength. The percentage increase of compressive strength is however more in nanosilica based SCC. This can be attributed to better hydration with nanosilica. It has been observed that the 28 days split tensile and flexural strengths are more in case of 1.5%

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addition of nanosilica and with 0.5% addition of nanoalumina in SCC. The percentage of increase of these strengths are more in nanosilica based SCC. A relationship between compressive strength and split tensile strength has been established and it was noted that at higher grades of self-compacting concrete the split tensile strength was less than 10% of the compressive strength. A relationship between compressive strength and flexural strength has been established and it was noted that of all the mixes SCC-NA performed well.

References Al Ghabban. A, Al Zubaidi. A. B., Jafar. M. Fakhri. Z., Effect of nano SiO2 and nano CaCO3 on the mechanical properties, durability and flowability of concrete. In: IOP Conference Series: Materials Engineering and Science, (Istanbul, Turkey, 2018), 454, (1), IOP Publishing, p 012016, doi: https://iopscience.iop.org/article/10.1088/1757899X/454/1/012016. Arefi. M. R., Jahaveri. M. R., Mollaahmadi. E., Silica nanoparticle size effect on Mechanical properties and microstructure of cement mortar, J. Am. Sci., (2011) doi: http://www.jofamericanscience.org/journals/am-sci/am0710/029_6985am0710_231_ 238.pdf. Ashwani Rana. K., Shashi B Rana, Anjna Kumari and Vaishnav Kiran, Significance of Nanotechnology in Construction Engineering. I. J. Rec. Tre. Eng., l (1), (2009), doi: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.381.6406&rep=rep1&type =pdf. Askari Dolatabad Y, Kamgar R, and Gouhari Nezad I, Rheological and Mechanical Properties, Acid Resistance and Water Penetrability of Lightweight Self-Compacting Concrete Containing Nano-SiO2, Nano-TiO2 and Nano-Al2O3. Iran J. Sci. Technol. Trans. Civ. Eng. 44, 603–618, (2020). doi: https://doi.org/10.1007/s40996-019-00 328-1. Azad Faez, Arash Sayari, Salar Manie, Mechanical and Rheological Properties of SelfCompacting Concrete Containing Al2O3 Nanoparticles and Silica Fume, Iranian J. Sci. and Tech., doi: https://link.springer.com/article/10.1007/s40996-019-00339-y Bouzoubaa N., Lachemi M, Self-compacting concrete incorporating high volumes of class F fly ash preliminary results, Cem. Con. Res., 31, 413–420, (2001). doi: https://doi. org/10.1016/S0008-8846(00)00504-4. Diab. A. M., Elyamany. H. E., Elmoaty AEMA, Sreh M. M. Effect of nanomaterials additives on performance of concrete resistance against magnesium sulfate and acids. Constr. Build. Mater. (210), 210–231, (2019), doi: https://doi.org/10.1016/j.conbu ildmat.2019.03.099. EFNARC European guidelines for self-compacting concrete. – Specifications, production and use, (2005) doi: https://www.theconcreteinitiative.eu/images/ECP_Documents/E uropeanGuidelinesSelfCompactingConcrete.pdf.

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Ehsan Mohseni and Konstantinos Daniel Tsavdaridis, Effect of Nano-Alumina on Pore Structure and Durability of Class F Fly Ash Self-Compacting Mortar, American Journal of Engineering and Applied Sciences, 2016, 9(2), 323 – 333. doi: 10.38 44/ajeassp.2016.323.333. Faez. A, Sayari. A and Manie. S. Mechanical and Rheological Properties of SelfCompacting Concrete Containing Al2O3 Nanoparticles and Silica Fume. Iran J Sci. Technol. Trans. Civ. Eng., 44, 217–227 (2020). doi: https://doi.org/10.1007/s40996019-00339-y. Furqan Farooq, Sardar Kashif Ur Rahman, Arslan Akbar, Rao Arsalan Khushnood, Muhammad Faisal Javed, Rayed alyousef, Hisham alabduljabbar, Fahid aslam, A comparative study on performance evaluation of hybrid GNPs/CNTs in conventional and self-compacting mortar, 2020, https://doi.org/10.1016/j.aej.2019.12.048. Grzeszczyk S., Jurowski K., Bosowska K., Grzymek M., The role of nanoparticles in decreased washout of underwater concrete. Constr. Build. Mater. (203), 670–678, (2019), doi: https://doi.org/10.1016/j.conbuildmat.2019.01.118. IS: 10262-2009, Concrete Mix Proportioning- Guidelines, Bureau of Indian Standards-New Delhi, India, https://law.resource.org/pub/in/bis/S03/is.10262.2009.pdf. IS: 12269-1987, Specifications for 53 grade ordinary Portland cement, Bureau of Indian Standards-New Delhi, India, doi: https://law.resource.org/pub/in/bis/S03/is.12269.19 87.pdf. IS: 15388, Part-II (2003), Specification for Silica Fume. Guidelines, Bureau of Indian Standards-New Delhi, India, https://law.resource.org/pub/in/bis/S03/is.15388.2003. pdf. IS: 3812 Part-II (2003), Specification for Pulverized Fly ash in concrete. Guidelines, Bureau of Indian Standards-New Delhi, India, https://law.resource.org/pub/in/bis/ S03/is.3812.2.2003.pdf. IS: 383-1970 (Reaffirmed 2002), Specification for coarse and fine aggregates from natural sources for concrete, Bureau of Indian Standards-New Delhi, India. doi: https://www. iitk.ac.in/ce/test/IS-codes/is.383.1970.pdf. IS: 456-1957 (Reaffirmed 2005), Code of practice for general construction of plain and reinforced concrete, Bureau of Indian Standards-New Delhi, India, https://www.iitk. ac.in/ce/test/IS-codes/is.456.2000.pdf. IS: 516-1959(Reaffirmed 1999), Method of test for strength of concrete, Bureau of Indian Standards-New Delhi, India, https://www.iitk.ac.in/ce/test/IS-codes/is.516.1959.pdf. IS: 9103-1999 Concrete Admixtures-Specification, Bureau of Indian Standards-New Delhi, India, https://law.resource.org/pub/in/bis/S03/is.9103.1999.pdf. Ismael. R., Silva. J. V., Carmo. R. N. F., Soldado E., Lourenco C., Costa H., Júlio E., Influence of nano-SiO2 and nano-Al2O3 additions on steel-to-concrete bonding. Constr. Build. Mater., (125),1080–1092, (2016). https://doi.org/10.1016/j.conbuildm at.2016.08.152. Jaishankar. P., Karthikeyan. C., Characteristics of cement concrete with nano alumina particles. In: IOP Conference Series: Earth and Environmental Science, (80), 1, p 012005, (2017). https://doi.org/10.1088/1755-1315/80/1/012005. Jalal M, Teimortashlu E, and Grasley Z, Performance-based design and optimization of rheological and strength properties of self-compacting cement composite incorp-

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orating micro/nano admixtures, J. Compos. Part B: Eng., 163, 497-510, 2019. doi: https://doi.org/10.1016/j.compositesb.2019.01.028. Khanzadi. M., Tadayon. M., Sepehri. H. and Md. Sepehri, Influence of Nano-Silica Particles on Mechanical Properties and Permeability of Concrete, second international conference on sustainable construction materials and technologies, (Ancona, Italy), ISBN 978-1-4507-1490-7, (2010), http://www.claisse.info/2010%20papers/l46.pdf. Khayat K. H., Guizani Z, Use of viscosity-modifying admixture to enhance stability of fluid concrete, ACI Mate. J., 94(4), 332–340, (1997) doi: https://trid.trb.org/view/577181. Khayat K. H., Workability, testing, and performance of self-consolidating concrete, ACI Mater. J., 96(3),346–353,(1999),doi: https://www.researchgate.net/publication/2799 02414_Workability_testing_and_performance_of_self-consolidating_concrete/stats. Li. H, gang Xiao H, Yuan J and Jinping Ou, Microstructure of cement mortar with nanoparticles, Nano compos., Part B – Eng., 35, pp. 185-189, (2004), doi: https://doi. org/10.1016/S1359-8368(03)00052-0. Magsoudi. A. A., Magsoudi. M and Noori. M, Effect of Nanoparticles on SCC, Second International Conference on Sustainable Construction Materials and Technologies, ISBN 978-1-4507-1488-4, (2010). Mahmud Sami Döndüren, Mohammed Gamal Al-Hagri, A review of the effect and optimization of use of nano-TiO2 in cementitious composites, Research on engineering structures and materials, 2022, http://dx.doi.org/10.17515/resm2022. 348st1005. Niewiadomski. P, Domian Stefaniuk, Jerzy Hola, Microstructural Analysis of Selfcompacting Concrete Modified with the Addition of Nanoparticles, Proce. Eng.,172, (2017), doi: https://doi.org/10.1016/j.proeng.2017.02.122. Okamura H, Ouchi M, Self-Compacting Concrete, J. Adv.Concr.Technol. 1, (1), 5-15, (2003) doi: https://doi.org/10.3151/jact.1.5. Ozawa. K, Kunishima. M, Maekawa. K, and Ozawa. K, Development of High Performance Concrete Based on the Durability Design of Concrete Structures, Proceedings of the second East-Asia and Pacific Conference on Structural Engineering and Construction (EASEC-2, 1989), 1, p. 445-450. Ozyildirim C. and Zegetosky C., Research Report on Laboratory investigation of Nanomaterials to improve the strength and permeability of Concrete, (2010), doi: http://www.virginiadot.org/vtrc/main/online_reports/pdf/10-r18.pdf. Quercia. G. and Brouwers. H. J. H. Application of Nano-Silica (nS) in Concrete Mixes, (8th fib OhD symposium in Kgs. Lyngby, Denmark), (2010), doi: https://josbrouwers. bwk.tue.nl/publications/Conference61x.pdf. Rabar H Faraj, Hemn Unis Ahmed, Serwan Rafiq, Nadhim Hamah Sor, Dalya F Ibrahim, Shaker M A Qaidi, Performance of Self-Compacting Mortars Modified with Nanoparticles: A Systematic Review and Modeling, Cleaner Materials, 2022. https://doi.org/10.1016/j.clema.2022.100086. Sonebi M., Bartos P. J. M., Hardened SCC and its bond with reinforcement, Proceedings of the First International RILEM Symposium on Self-Compacting Concrete. (Stockholm, Sweden, 1999), p 275, doi: https://www.rilem.net/publication/publicatio n/12.

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Su. N., Hsu. K. C., Chai. H. W. A simple mix design method for self-compacting concrete, Cem. and Concr. Res., 1799-1807, (2001). doi: https://doi.org/10.1016/S0008-884 6(01)00566-X. Venkateswara Rao S., Jorge de Brito, Experimental study of the mechanical properties and durability of self-compacting mortars with nanomaterials (SiO2 and TiO2), Constr. and Build. Mater., (2018), doi: : 10.1016/j.conbuildmat.2015.08.049. Venkateswara Rao S., Seshagiri Rao M. V., Ramaseshu D. and Ratish Kumar P., A rational Mix design procedure for self compacting concrete, J. Cem. Wap. Bet., 5, 271 – 280, (2013). Venkateswara Rao S., Seshagiri Rao M. V., Rathish Kumar P. “Effect of Size of Aggregate and Fines on Standard And High Strength Self compacting Concrete,” J of App. Sci. Res., 6(5), 433-442, (2010), doi: http://www.aensiweb.com/old/jasr/jasr/2010/433442.pdf. Venkateswara Rao. S. Experimental studies on the effect of size of aggregate and fines on the strength and durability properties of Self Compacting Concrete, PhD thesis of JNTUH, India, (2010). Zhang A., Yang W., Du Y. and Liu. P., Effects of nano-SiO2 and nano-Al2O3 on mechanical and durability properties of cement-based materials: A comparative study, J. Build. Eng., ISSN: 2352-7102, 2020.

Chapter 5

Pertinency of Geopolymer Concrete for the Australian Construction Industry: A Broader Contextual Appraisal Koorosh Gharehbaghi1 Kong Fah Tee2,3, Ken Farnes1 and Laura Blackburne4 1 RMIT

University, Melbourne, Australia of Civil and Environmental Engineering, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia 3 Interdisciplinary Research Center for Construction and Building Materials, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia 4 University of New South Wales, Sydney, Australia 2 Department

Abstract Innovative engineering materials, such as geopolymer concrete, have emerged with the potential to reduce carbon emissions globally and lead to a sustainable concrete industry. Using polymers to supplement or replace Portland cement as a binder, geopolymer concrete exhibits a smaller greenhouse footprint when compared to Portland concrete products. With the appropriate mix design and formulation, the material can offer superior chemical and mechanical characteristics when compared with Portland concrete for several applications at a competitive cost.



Corresponding Author’s Email: [email protected].

In: Cement and Concrete Editors: Kong Fah Tee, Siew Choo Chin and Koorosh Gharehbaghi ISBN: 979-8-88697-831-5 © 2023 Nova Science Publishers, Inc.

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Koorosh Gharehbaghi, Kong Fah Tee, Ken Farnes et al. However, despite the potentially advantageous engineering properties and commercial attributes and the potential benefits of geopolymer concrete, many challenges and obstacles await such as market resistance before this type of concrete can be acknowledged as a conventional building material. As with any revolutionary product, the successful implementation of geopolymer concrete in the Australian construction industry is influenced by a variety of technical, environmental, and commercial factors, that will be investigated in this chapter. The objective of this chapter is to explore the applicability of geopolymer concrete in the Australian construction and engineering industry. It is found that, although geopolymer concrete has been gradually utilized within the Australian construction sector, particularly for high-rise buildings, more encouragement is needed for the general acceptance of geopolymer concrete in the construction sector. Therefore, the main considerations that will contribute to the implementation of more geopolymer concrete usage within the Australian industry, will be investigated.

Keywords: geopolymer concrete, Portland concrete, construction industry

1. Introduction The main aim of this chapter is to explore the future of geopolymer concrete within the Australian construction industry. The investigation will consider areas such as the history of the material, its advantages, and disadvantages in commercial applications, other alternative materials that must be regarded as substitutes to geopolymer concrete, and barriers to its successful implementation in the construction and engineering industry. Through this chapter, the Australian construction industry has the potential to gain valuable insight into the benefits of geopolymer concrete as an alternative to other materials. Innovative engineering materials, such as geopolymer concrete, have emerged with the potential to influence the future of an environmentally sustainable construction product industry by using geopolymers to supplement or replace Portland cement as a binder. Geopolymer concrete exhibits a smaller greenhouse footprint when compared to Portland concrete products. With the appropriate mix design (commonly incorporating monomers and resins such as polyester-styrene, acrylics, and epoxies) and formulation development, the material can offer superior chemical and mechanical

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characteristics (compared with Portland cement) for several applications, at a competitive cost. However, despite the potentially advantageous engineering properties and commercial and potential benefits of geopolymer concrete, many challenges and obstacles await, such as more complex commercial production, some physical and chemical properties being substantially different, and market resistance before this type of concrete can be acknowledged as a conventional building material. As with any revolutionary (as opposed to evolutionary) product, the successful implementation of geopolymer concrete in the Australian construction industry will be influenced by a variety of technical, environmental, and commercial factors, as will be investigated in this chapter. The overall process of this chapter is shown in Figure 1.

Figure 1. The overall process of the chapter.

The chapter is aimed at the Australian construction industry, presenting the target audience with the potential to gain valuable insight into the benefits of geopolymer concrete as an alternative to Portland cement. Furthermore, the potential advantages of this research to the construction industry may be to inform future business decisions (i.e., considerations into alternative material selections), assist in policy formation (such as an Australian standard for the specification and supply of geopolymer concrete), and encourage further research into the applications and benefits of this material. Furthermore, an inductive research approach was undertaken as a result of the degree of uncertainty that the answer to the research question will deliver, and due to the conclusion most likely being based on a premise (i.e., argument or theory

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building). A representation of the inductive research approach is shown in Figure 2.

Figure 2. The method of the research - inductive approach.

Research undertaken for this chapter utilized a qualitative method using secondary data collected from journals, articles, books, and primary data from an interview with a recognized industry expert. This research method was employed to gain insight into various aspects of the construction industry, such as the cultures, attitudes, values, concerns, and motivations that will potentially influence the future of geopolymer concrete in Australia.

2. Background of Geopolymer Concrete Geopolymer technology is a rapidly developing field of development with many commercial applications including in the construction industry. Geopolymer is the generic name for a wide range of engineered aluminosilicate products that have the potential for use as a replacement for Portland cement in the production of structural and non-structural concretes. Geopolymer concrete is one of the building materials that has become more popular in recent years due to the perception that these materials are more environmentally friendly and that they have potentially advantageous engineering properties and commercial attributes in comparison to Portland concrete.

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Globally, the construction industry is becoming more frequently focused on creating buildings that meet the need for more space on limited land while having an environmentally low impact (Hirvonen et al., 2019; Charalambides et al., 2019; Blackburne et al., 2023). The increase in population results in a higher demand for buildings that have been getting taller and more sustainable as technology and innovation proves that it is possible to create more available space while meeting environmental, economic, and societal sustainability demands (Iacovidou et al., 2017; Dumlao-Tan and Halog, 2017; Dimitriou et al., 2020) on a smaller footprint (Harris et al., 2023). Over the past decade, as environmental regulations begin to overlay building design, it has become popular to use greener materials in construction, swapping non-renewable materials for materials that can be regrown in just 10-30 years whilst reducing CO2 and its footprint across the globe (De Luca et al., 2021; Gharehbaghi et al., 2022a) or using recovered byproducts of commercial processes. Figures 3a and 3b represent the CO2 emission by the industry sector and environmental predicaments of waste diminution in construction projects.

Figure 3a. The CO2 emission by industry sector (Warburton, 2019).

Figure 3b. The environmental predicaments of waste diminution in construction projects (Gharehbaghi and Scott-Young, 2018).

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Within the construction industry, the use of green building materials is one of the most common strategies to reduce CO2 (Bovea and Powell, 2016; Samad et al, 2017; Tee et al, 2019; Gharehbaghi et al., 2022b). Green building materials very often have nontoxic properties and are made from recycled materials. This means they are in most cases created from renewable resources in comparison to non-renewable resources. The use of recycled concrete and the use of sustainable materials is also gaining support within the construction industry (Hahladakis et al., 2020). The use of recycled concrete aggregates and similar strategies needs to be constantly reviewed as a strategy for the reduction of CO2 and conserving energy (Maduabuchukwu et al., 2020; Iacovidou and Purnell, 2016; Samad et al, 2018). Braga et al., (2017) highlighted that one way to conserve energy during concrete production is using recycled concrete aggregate. Further, in their research, Gharehbaghi et al., (2020a) compared fibrereinforced concrete and geopolymer concrete for high-rise construction. They determined that geopolymer concrete has some environmental advantages when compared with traditional binders which are used in Portland cement. In his experimental research, Davidovits (2002) extensively highlights the geopolymeric binders and their composite applications. Davidovits (2002) particularly notes that a new grade of materials is expected to have a wideranging impact on construction, architectural, and engineering applications. He further demonstrated that quazite which is a mixture of mineral aggregates together with polymers and monomers is used to form the first breakthrough in history called Geopolymer concrete. This was also supported by a private company Zeobond and the ACO Group, who credit their success in being a world leader in modern large-scale geopolymer concrete production to Davidovits’ research and invention (Zeobond, 2010; ACO Group, 2021). Figure 4 presents the Poly structures according to Davidovits. Regarding the chemical designation of Geopolymer, the name “polysialates” was suggested by Davidovits, in which sialate is an abbreviation for aluminosilicate. Zeobond quoted their success and development of Geopolymer concrete to Davidovits’ research and invention. However, Zeobond mentioned that a similar composite to Geopolymer concrete was first trailed in some concrete applications by G.V. Glukhovsky and co-workers in the Soviet Union post-World War Two, around 1954.

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Figure 4. Poly (sialates) structures according to Davidovits (Pacheo-Torgal, et al., 2007).

This was an alkali-activated slag and not the geopolymer concrete formula developed by Davidovits (Domone and Illston, 2010). Rafi (2019) noted that alkali-activation was performed using corrosive chemicals for the making of concrete known as ‘soil cement’ and not sold to third parties as commercial cement. Geopolymer technology on the alternative side from the beginning was aimed at manufacturing binders and cement for various types of applications throughout the concrete industry (Geopolymer Institute, 2021).

2.1. Alternatives and Innovations in the Concrete Industry 2.1.1. The Need for Alternatives and Innovations Widely used for its advantageous features such as durability, versatility, high compressive strength, cost-effectiveness, and availability, it cannot be denied that concrete will continue to be an essential material required to satisfy global construction and infrastructure needs. As a result, the concrete industry worldwide is confronted with many growing challenges, including the preservation and management of material and energy resources, along with

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minimizing associated CO2 emissions (Schneider et al., 2011l Blackburne et al., 2022). Juenger et al., (2010) also agree that the construction materials industry, in particular manufacturers of concrete, is under increasing pressure to reduce the energy consumption of concrete production and the related environmental impacts, i.e., greenhouse gas emissions. This issue is further highlighted by Yang et al., (2010) who emphasize that the negative environmental effects of concrete originate from matters such as the depletion of reserves of natural resources, high energy consumption, and disposal concerns. Hence, there are apparent consistencies in the concerns that surround the environmental impacts of Portland concrete, which justify the rising interest in the development and implementation of alternative materials to Portland cement as a binder in concrete. The following section will detail the alternative cement binders currently available as a substitute to Portland cement, focusing mainly on Calcium Aluminate cement, Calcium Sulfoaluminate cements, Alkali-Activated Binders (Inorganic Polymers), and super sulfated cement. Table 1 shows the comparison of Portland cement to alternative cement/binders.

2.1.2. Calcium Aluminate Cement Calcium aluminate cement is a unique category of cement that contains the primary component of monocalcium aluminate. When compared to Portland cement it offers superior early strength, fire resistance, abrasion resistance, and acid resistance (Fentiman et al., 2008). The advantages of this type of cement are further emphasized by Juenger et al., (2010) who highlight that the production of calcium aluminate cement results in lower CO2, in comparison with Portland cement. The two current primary uses of calcium aluminate cement are in refractory applications of concrete. They are typically used in industries involving high temperatures (e.g., steel making), and other building applications such as floor screeds and rapid-hardening mortars. Other diverse areas of use for this type of cement also exist, such as the storage of toxic wastes. Applications of calcium aluminate cement are typically selected for their durability in severe conditions (Scrivener, et al., 1999; Wang, et al., 2014).

Table 1. Comparison of Portland cement to alternative cement/binders (Juenger, et al., 2010)

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Despite the numerous advantages of calcium aluminate concrete, Juenger et al., (2010) state that it is not used as extensively as Portland cement, as it is limited by two main barriers: 1. Through the process of “conversion” in calcium aluminate cement (whereby metastable hydrates convert to stable hydrates), increases in porosity and decrease in strength occur. 2. Cost efficiency is also an evident barrier, as calcium aluminate cement is more expensive in comparison to Portland cement; with the cost attributed to the limited supply of bauxite, the main source of alumina in this type of cement’s production.

2.1.3. Calcium Sulfoaluminate Cement Calcium sulfoaluminate cement is gaining attention in the construction industry, due to its capacity to provide a lower CO2 alternative to Portland cement. This type of cement contains ye’elimite (C4A3Ŝ) a naturally occurring form of calcium sulfoaluminate as a major component (generally consisting of 30-70%), along with other materials for clinker production, such as sulfoaluminate belite (containing primarily C4A3Ŝ and C2S) and ferrialuminate clinker (containing primarily C4A3Ŝ and C4AF and C2S). These clinkers are incorporated with different levels of calcium sulfate through the grounding process, to produce rapid-hardening, high-strength, expansive, or self-stressing cement (Juenger et al., 2010). There are inconsistencies relating to the origins of this type of cement, as Juenger et al., (2010) suggest that it was developed in the 1960s during which time it was patented by Alexander Klein as an expansive or shrinkage compensating addition to cementitious binders; referred to as “Klein’s compound.” However, Pera and Ambroise (2004) and Shi, et al., (2011); Jimenez and Palomo (2011) suggest that calcium sulfoaluminate cement was developed by the China Building Materials Academy in the 1970s, with the objective of manufacturing self-stressed concrete pipes, as a result of their swelling properties. Furthermore, it is in China that calcium sulfoaluminate cement has been commonly used, as evident in applications such as bridges, leakage, and seepage prevention projects, concrete pipes, precast concrete elements (e.g., columns and beams), pre-stressed concrete elements, waterproof layers, glass fibre-reinforced cement products, low-temperature construction, and shotcrete treatments (Juenger et al., 2010).

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Koorosh Gharehbaghi, Kong Fah Tee, Ken Farnes et al.

2.1.4. Alkali-Activated Binders (Inorganic Polymers) Alkali-activated binders are composed of two primary constituents, including a cementitious component and alkaline activators. Figure 5 shows a diagrammatic representation of the geopolymer atom structure. The cementitious binders in this form of concrete can take the form of several industrial by-products and wastes, as well as aluminosilicate raw materials such as granulated blast furnace slag, granulated phosphorus slag, steel slag, coal fly ash, and volcanic glass among others (Shi et al., 2011).

Figure 5. Diagrammatic representation of the geopolymer atom structure. Red: Oxygen, Purple: Aluminum, Yellow: Silicon, Green: Sodium (Concrete Institute of Australia, 2021).

Like calcium sulfoaluminate cement, Juenger et al., (2010) state that alkali-activated binders are gaining increasing attention as an alternative to Portland cement, due to the material’s high strength and durability, and lower environmental impact in comparison. This view is shared by Shi et al., (2011), who further maintain that this form of cement is a necessary transition from today’s Portland cement to the cement of the future. Although geopolymer concrete is one form of alkali-activated binders, other alternatives include: •

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Polymer-Impregnated concrete: Produced by “impregnating” hydrated Portland cement, with a low viscosity monomer, such as methyl methacrylate, which was later polymerized by radiation, or other catalytic processes. Polymer-Modified concrete: Produced by combining Portland cement with a polymer modifier such as acrylic, styrene-butadiene latex, or polyvinyl acetate (Fowler, 1999; Behera, et al., Maiti 2014).

Pertinency of Geopolymer Concrete …

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2.1.5. Super Sulfated Cement Super sulfated cement is composed of various amounts of ground granulated blast furnace slag, gypsum or heat-activated gypsum and Portland cement, consequently, it is almost free of Portland cement, consisting primarily of granulated blast furnace slag (70-90%), calcium sulfate (10-20%), and other low quantities (generally