Utilization potential of fly ash and copper tailings in concrete as partial replacement of cement along with life cycle assessment

Waste Management 99 (2019) 90–101

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Utilization potential of fly ash and copper tailings in concrete as partial replacement of cement along with life cycle assessment Rahul Dandautiya, Ajit Pratap Singh ⇑ Civil Engineering Department, Birla Institute of Technology and Science, Pilani 333031, India

a r t i c l e

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Article history: Received 28 March 2019 Revised 13 July 2019 Accepted 23 August 2019

Keywords: Copper tailings Environmental impacts Fly ash Life cycle assessment Sustainable utilization

a b s t r a c t Fly ash (FA) and copper tailings (CT) both are, anthropogenic wastes, spread all over the globe due to rapid growth in thermal power plants and progressive increase in the demand of copper. This study examines the feasibility of combined utilization of FA and CT in concrete as a partial replacement of cement by assessing compressive strength, cost, and environmental impact. Morphology and constituent minerals of FA and CT have been identified to understand the utilization potential. Subsequently, the concrete has been designed for 30 MPa target strength as per IS 10262:2009 for different mix proportions of FA and CT. Improvement (up to 8.27% compared to the control mix) in the compressive strength has been observed at combined replacement of 10% FA and 5% CT. The cost of concrete can also be reduced up to 16% without compromising its compressive strength. The environmental impact assessment of the modified concrete mix proportions has also been performed using life cycle assessment (LCA) as per ISO 14040:2006. Effect of all raw materials, electricity, and water consumption have been considered from their cradle to grave approach. One cubic meter concrete has been taken as a functional unit in LCA. Notable reduction has been observed in the chosen midpoint categories up to 38% in climate change, up to 32.6% in human toxicity, up to 33.6% in ozone depletion, up to 31.9% in agriculture land occupation, water depletion up to 34.3%, fossil depletion up to 34.8%, particulate matter up to 35.4%, and metal depletion up to 25.2%. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Concrete, at the micro level, considered as a heterogeneous mixture of cement, sand, aggregate, and water (Gagg, 2014; Sadowski and Mathia, 2016) and second largest global per capita consumed material after water. Due to the serious need of growth in infrastructure, the developing nations are investing exponentially, and the developed countries are putting their efforts to upgrade their existing aged infrastructure to make them more sustainable and cope up with the current structural requirement. Cement is the most essential ingredient in a concrete mix that binds and solidify the aggregates in the presence of water (Hewlett, 2003). In the manufacturing of cement, the limestone and clay need to be heated up to 1450 °C, and a large volume of CO2 (900–1000 kg/ton of cement production) has been released, which is estimated at about 5–7% of the total global emissions (Monteiro et al., 2017; Andrew, 2018; Benhelal et al., 2013). With about 280 million ton of yearly cement production (Indian Bureau of Mines, 2018), India ranked second largest cement ⇑ Corresponding author. E-mail address: [email protected] (A.P. Singh). https://doi.org/10.1016/j.wasman.2019.08.036 0956-053X/Ó 2019 Elsevier Ltd. All rights reserved.

producer around the globe, and a significant portion of this contributed to greenhouse gas emission, thus, requiring a sustainable approach of production of cement. Copper is extensively used in different industries due to its high electric and thermal conductivity and less corrosive property (Mardones et al., 1985). It is well known for its ability to make alloys and high malleability. Being the most used metal, its demand has been increasing with the increase in population. This everlasting and increasing demand escalated the manufacturing of copper, which accounts to be 19.7 million tons of purified copper globally in 2017 (Ober, 2018). CT is one of the major wastes generated (@ 128 ton/ton production of purified copper) during the manufacturing of copper, which is produced at the floatation and concentration stage in the process of copper extraction (Gordon, 2002; Beniwal et al., 2015). CT generally composed of different compounds made of iron, silica, aluminum, magnesium, zinc, lead, cadmium, different oxides, hydroxide, and other materials, which may adversely impact the environment and human health at the vicinity of the dumping site (Yang et al., 2013; Kundu et al., 2016). Many researchers (Castilla, 1996; Dudka and Adriano, 1997; Rösner, 1998; Sharma and Al-Busaidi, 2001) have highlighted the ill effects of CT on the surface and groundwater, sur-

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rounding soil, vegetation, and aquatic life, which further lead to affect the other living bodies adversely. The groundwater aquifers become susceptible to contamination due to leaching action of such products along with other anthropogenic sources and their hydrogeochemical processes (Bhakar and Singh, 2019). Many possibilities have been investigated, and solutions are proposed by the researchers to make the tailings productive. Onuaguluchi and Eren (2012) replaced cement with CT to make high conductivity concrete and recommend it for making easy ice removable roads. Gupta et al. (2012) tested the clayey soil stabilization property of CT and suggested that a mixture of 30% CT and 70% clayey soil give good bearing capacity. It is also used as a partial replacement of fine aggregates in concrete in some studies (Beniwal et al., 2015; Gupta et al., 2016). Besides this, the feasibility of utilizing it as a partial replacement of cement is studied in a few of the research works (Ahmari and Zhang, 2012; Kundu et al., 2016; Onuaguluchi and Eren, 2016). ASTM C 618 classified FA into two categories (i.e., Class C and Class F). Both are enriched with SiO2, Al2O3 and Fe2O3 with nearly 50% in Class C and around 70% and higher in Class F fly ash. India alone generates about 170 million tons of class F coal FA from the thermal power plans annually (Central Electricity Authority Report, 2017). Utilization of FA as a pozzolanic additive in concrete has been commenced in early 1914 (Halstead, 1986). FA is used broadly in the cement manufacturing process and has been utilized extensively in partial replacement of cement in concrete. It is also proven for its application in soil stabilization (Dermatas and Meng, 2003), as landfill liner (Mollamahmutog˘lu and Yilmaz, 2001; Cokca and Yilmaz, 2004; Çoruh and Ergun, 2010), manufacturing of bricks (Reidelbach, 1970; Cultrone et al., 2004; Shakir et al., 2013), as an adsorbent (Sen and De, 1987; Rio and Delebarre, 2003; Banerjee et al., 2005; Kuncoro and Fahmi, 2013; Li et al., 2017), backfilling of mines and road subbase (Shen et al., 2009; Yao and Sun, 2012), enhancement of soil properties in agriculture (Ukwattage et al., 2013; Ram and Masto, 2014) etc. Wang et al. (2016) used FA in concrete along with coal gangue (as aggregate) and suggested a notable reduction in the permeability when this modified concrete utilized in farmland drainage ditches. High volume fly ash concrete has been compared with natural aggregate concrete and recycled aggregate concrete by Tošic´ et al. (2018) for the application in the reinforced concrete beam. Kurda et al. (2018) also utilized high content fly ash along with recycled concrete aggregate with different proportions and found that at low water binder ratio both shows better result compared to higher water binder ratio. Although it is being used widely for many applications, a significant amount of it, which is being disposed in valuable land, led to various kinds of pollution (Fulekar and Dave, 1986; Borm, 1997; Walia and Mehra 1998; Ribeiro et al., 2014; Dandautiya et al. 2018; Zhang et al., 2018). In the concrete, subsequent to the addition of water to cement, exothermic hydration reaction will initiate and will lead to the release of lime. This lime imparts porosity to the structure and responsible for the development of microcracks, leads to degradation in bond strength and results from an adverse effect on the concrete durability (Deschner et al., 2012). Though Hewlett (2003) experimented and confirmed that pozzolanic materials (FA) reacts with excessive lime and improves the strength of the concrete, but the combined effect of FA and CT on the strength of concrete by partial replacement of cement is a matter of investigation. This has motivated authors to explore the performance of concrete for said purpose. The optimal utilization of FA and CT is not only useful to reduce cement requirement in the construction industry and infrastructure development but also beneficial for the surroundings (Schuhmacher et al., 2004). About 40% of the greenhouse gases are released through the development of the built environment

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(Vieira and Horvath, 2008; BED, 2011). Life cycle assessment (LCA) method demonstrates very proven results in relation to the quantification of these adverse environmental impacts (Bhakar and Singh, 2018). It facilitates a diverse, accurate, and quick estimate of the environmental impact of material while considering all its constituent associated with the process of procurement, transportation, manufacturing, utilization, and disposal. Nisbet et al. (2000) and Corinaldesi (2010) have defined life cycle inventories for different kinds of Portland cement concrete and performed LCA analysis. Knoeri et al. (2013) have studied the effect of individual of concrete production units using LCA from transportation, manufacturing, utilization, and demolition. The LCA analysis of magnetized fly-ash compound fertilizer was assessed systematically by Wang et al. (2017). The study clearly demonstrates how nonrenewable energy depletion becomes one of the highest affected category. Li and Wang (2018) investigated the severe impact on the environment due to the utilization of flue gas desulfurization gypsum in soil improvement through LCA combined with Technique for Order Preference by Similarity (TOPSIS) and found that the water consumption and soil toxicity are most impacted categories. Zhang et al. (2018) evaluated the environmental impact of Yimin opencast coal mine (China) using LCA considering 100 tons of coal as a functional unit and concluded that the dust is most serious category than the other selected categories. Although wide ranges of studies have also been conducted to investigate the feasibility of utilization of FA and CT, most of the studies are confined to assess the effectiveness of individual waste material. FA is extensively used as a replacement of cement, and various standards have recommended maximum replacement limit of 30% of cement in concrete (Thomas, 2007). Also, with a production of 280 million ton (Choudhary et al., 2019) of cement annually, India ranked second largest cement producer in the world and this cement production responsible for the release of 150 million ton of CO2 emissions annually (Andrew, 2018). Hence the utilization of CT along with FA with partial replacement of cement in concrete will cut a massive amount of CO2 releasing into the atmosphere during the cement manufacturing process and also help to reduce the adverse environmental impact caused by the heaps of FA and CT worldwide. In the current research work, LCA has been applied in all the mix proportions of concrete, and their environmental impact has been assessed along with the compressive strength and cost analysis.

2. Materials and methods 2.1. Methodology FA, CT, Ordinary Portland Cement (OPC), fine aggregate and coarse aggregate have been used in this study to prepare concrete along with admixture. Tricalcium silicate (C3S ? 3CaO.SiO2), dicalcium silicate (C2S ? 2CaO.SiO2), tricalcium aluminate (C3A ? 3CaO.Al2O3) and tetra calcium alumino ferrite (C4AF ? 4CaO.Al2O3.Fe2O3) are the chief mineral phases found in the OPC (Struble et al., 2011). The hardening process of OPC takes place as a result of the reaction between these compounds with water. In the processes of hydration, lime is released which is a surplus and not utilized in the hardening process (Sharma and Pandey, 1999). This excess lime causes an adverse impact on the durability of the hardened concrete due to the formation of microcracks and weakened the bonding with concrete (Massazza, 1998). Addition of pozzolanic material will act as a solution to this problem because such material will react with surplus lime and provide similar binding property as given by cement. Thus, in present study, focus has been given to introduce the optimal quantity of pozzolanic material so that the strength of concrete can be improved/main-

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tained especially when such pozzolanic material reacts with residual lime. The materials (FA and CT) were collected and characterized to assess the feasibility of the samples as per the ASTM requirement. The subsequent sections explain more inside about the steps adopted in the proposed study. 2.2. Sampling and process The samples of FA were collected from the disposal site (29°100 31.37100 N and 73°590 21.06600 E) from Suratgarh Super Thermal Power Plant with the capacity of 1500 MW located near Suratgarh, district Sri Ganganagar, Rajasthan, India (Fig. 1). The plant has produced about 169.25 megatons of coal FA from the combustion of 509.46 megatons of coal in the year 2016-17 (Central Electricity Authority Report, 2017). The CT samples were taken from CT pond (Fig. 1) near Khetri Copper Complex, Hindustan Copper Limited (HCL) district Jhunjhunu, Rajasthan, India. The sampling site (27° 490 590 ’ N, 75° 460 00 ’ E) is located in the hot semi-arid region of Aravalli fold of western India majorly having older alluvial soil (Ground Water Brochure, 2008). The ores in the region are enriched with gold (Au), silver (Ag), cobalt (Co), iron (Fe), uranium (U) and rare earth elements along with Cu (Sarkar and Gupta, 2012). Both FA and CT samples have been stored in an airtight container, and as they were in uniform powder form, hence no further milling is required. The average specific gravity of samples were measured as 2.1 and 3.2 for FA and CT respectively. Ordinary Portland cement (OPC) of grade 43 complying with IS 8112 (2013) and specific gravity 3.15 has been used as a binder. River sand (specific gravity 2.74) confirming to Zone-I as prescribed in IS 383:2016 has been used as fine aggregate. The crushed stone (specific gravity 2.74) with the proportion of 2:3 of 10 mm and 20 mm size has been used as coarse aggregate that is complying with the IS 383 (2016). To increase the workability along with the reduction in water content in the mix design of concrete, ULTRACON 58 HP admixture (specific gravity 1.24) has been used as per IS 9103 (1999). From the literature and standards, it has been suggested that the maximum replacement limit of cement with FA should be 30% of cement (Thomas, 2007). This replacement marginally increases the compressive strength of concrete, and beyond 30% replacement of cement, the strength of concrete has been found to reduce. Optimum partial replacement of CT suggested by Kundu et al. (2016) is 10% of cement in concrete to attain acceptable compressive strength and suggested that beyond 10% replacement, the compressive strength reduces gradually with addition of CT due to its low reactiveness. A total of 14 different mix design proportions have been prepared for a target strength of 30 MPa as per IS 10262, 2009 (detailed in Table A1 of the appendix). These mix proportions have been considered for the casting of 126 cubes of 150 mm size (@ 9 cubes per mix proportion) for two different water-cement (w/c) ratios (i.e. 0.45 and 0.5) according to the guidelines given in IS 456 (2000). For each of the w/c ratio (out of all mix proportions) one control specimen mix has also been prepared. Considering the view of earlier findings of the researchers and code provisions, FA has been replaced with cement from 10%, 20% and 30% by weight of cement combined with 5% and 10% CT respectively. These mix proportions were labelled as M1 (FA 10% and CT 5%), M2 (FA 10% and CT 10%), M3 (FA 20% and CT 5%), M4 (FA 20% and CT 10%), M5 (FA 30% and CT 5%), and M6 (FA 30% and CT 10%) for two different w/c ratio 0.45 and 0.5. All mix specimens have been immersed in the water tank for curing purpose for the prescribed duration as the specified code provision. As the compressive strength has been used extensively in the literature to

define the strength of concrete, it has been measured for allabove specimens after 7, 28, and 56 days using universal testing machine (Aimil AIM-653, 1000 kN). The chemical compositions of FA and CT have been found out by X-ray Fluorescence (XRF) using Panalytical Epsilon-5 available at Instrumentation Research Laboratory in Jawaharlal Nehru University, New Delhi. The samples in XRF analysis are prepared by initially pressing the material to make uniform powder, and then binder (boric acid) is added to form pellets using cylinder type dies. The analysis of these prepared samples was done at 25 kV of voltage and 0.5 mA of current. The form shape and structure of cement were studied by using the Scanning Electronic Microscope (SEM) through FEI Apreo-S instrument at Birla Institute of Technology and Science Pilani, Rajasthan, whereas, for FA and CT, it was done at Instrumentation Research Laboratory in Jawaharlal Nehru University, New Delhi using Zeiss EVO40. All three materials are non-conductive; hence, before SEM analysis coating of silver was applied to the samples, and the instrument was operated at accelerating voltage of 15 kV and the working distance of 12.5 mm. 2.3. Life cycle assessment (LCA) analysis To perform LCA analysis, cradle to grave approach has been used to understand the possible environmental impact of the replacement of FA and CT in concrete. ISO 14040:2006 has been considered as a guideline for the analysis. LCA process is divided into four-part: (a) defining the goal and scope of the analysis; (b) inventory analysis; (c) impact assessment of the process, and (d) analysis of the results. The goal is to assess the environmental impact of the partial replacement of cement with FA and CT in concrete at different proportions and compare them with the control mix. UMBERTO NXT tool has been used to perform LCA analysis. The software helps to calculate the potential impact on the environment due to a different stage of a product. Graphical modeling is performed with the help of software for -analyzing the life cycle of the material. This helps to analyze, acquire, and visualize the environmental impact in the form of different midpoint and endpoint selected categories. Initially, the life cycle model is drawn in the form of a process map then the specification of the processes and activities are required to be defined. The attached data set in the software is used to evaluate the energy and material flow and corresponding impact assessment on the environment. The outcome of this analysis is represented in the form of tables and graphs. Cradle to grave approach is a primary generic LCA approach that includes extraction of raw materials, quantification of energy utilized, production of material, utilization, recycling and finally disposal which is suitable for the analysis of concrete as recommended in the literature (Rebitzer et al., 2004). Climate change (kg of CO2 equivalent), human toxicity (kg of 1,4 dichlorobenzene (DCB)), ozone depletion potential (CFC-11 equivalent), agriculture land occupation (m2 area annual crop equivalent), water depletion (in m3), fossil depletion (kg of oil equivalent), particulate matter (kg of PM2.5 equivalent) and Metal depletion potential (kg of Fe equivalent) are considered as midpoint categories in the LCA analysis of modified concrete. Eco inventory 3.0 dataset available with the UMBERTO NXT tool has been used to consider inventory data for cement, gravel, sand, water, inert waste, and electricity production. Both FA and CT have been considered as the inert material. It has been assumed that the density of the concrete remains uniform and the whole mass of it is considered as inert waste after its service life. In all the calculations, one cubic meter concrete is taken as the functional unit. The analysis is performed for all mix proportions (M1-M6 and control mix) and each of the w/c ratio (0.45 and 0.5). The Life cycle inventory (LCI) model for the LCA analysis is shown in Fig. 2. This framework is divided into three sections, viz. raw material, manufacturing process, and waste disposal. In the raw material section cement, sand

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Fig. 1. Location and topography of the study area.

Fig. 2. Framework of LCA approach used in the study.

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(fine aggregate) and gravel (coarse aggregate), used to produce concrete, are defined through process T1, T2 and T3 as shown in Fig. 2. P1, P4 and P7 (represented with 1green circle) show the input for initial phase of the processes T1, T2 and T3. P3, P6 and P9 are the end of the process and show the fraction of disposal of wastes during the above processes. Fly ash, copper tailings and the admixtures are considered as inert material which are essential component of the raw material section (shown by P10, P11, and P12). Next step in the model is the manufacturing section where ‘‘T” represents the concrete manufacturing process in which appropriate raw material quantity is mixed with water as per the mix design of concrete. Process for water is defined by T4 and electricity consumption for mixing is shown as T5. The consumption of electricity is uniform as it has been used only for the mixing of concrete with equal mixing time for all mix proportions. Final produced concrete is shown in the manufacturing section denoted as P22. After the completion of service life of concrete, it has been treated as an inert waste which is shown as process T6 in the waste disposal section. 3. Result and discussion 3.1. Material characterization The results of XRF show the chemical composition of OPC, FA, and CT as given in Table A2 of appendix. Both FA and CT are made of pozzolanic materials (SiO2, Al2O3, and Fe2O3) with a small amount of CaO, MgO, and other compounds. The combined weights of pozzolanic materials are found as 86.93% and 96.1% of their weights in CT and FA respectively. They are considerably higher than the recommended value (70%) given in ASTM C618-19 (2019). The values of loss on ignition and moisture have also been found below the ASTM C618-19 guidelines which makes them suitable to use in concrete by replacing cement partially. The SEM images of FA, CT and cement provide a detailed morphology of the materials as presented in Fig. A1 of the appendix. The particles of FA are spherical in shape, behaves like a ball bearing, which gave a greasy effect in concrete. It makes concrete more workable and easier to pump as these spherical particles reduced the friction between the ingredients of concrete. Replacing cement with the same weight and lesser density of FA leads to a reduction in concrete bleeding due to less water requirement and a higher volume of fine particles. The shape of particles of CT is not flaky, which may exhibit a higher interlocking capability, increase in the density of concrete and impart additional strength when it combines with the cement and FA particles. Thus, these materials, having nearly the same order of particle size, can be used effectively as cement replacement. 3.2. Compressive strength of the material The deformation and stresses developed in the casted cubes, after 7, 28 and 56 days, during the compressive strength test, have been measured for all the mix proportions. These results are presented in six graphs, as shown in Fig. 3. Each graph shows stressstrain curves after the specific time interval corresponding to the different w/c ratios. These stress-strain curves show non-linear behaviour for all mix proportions, which may be due to nonhomogeneity in concrete mass, and leads to the differential moment between binding material and aggregate. The elastic modules have been defined as secant modulus in the study. The values presented in Table A3 of appendix shows a comprehensive overview of all the mix proportions with regard to 1

For interpretation of color in Fig. 2, the reader is referred to the web version of this article.

durability. It is also observed that with the increase in w/c ratio, the strength of the concrete decreases and may result to develop cracks due to excess in shrinkage. The cubes of mix proportions M1 to M6 (w/c ratio 0.45) show relatively higher strength than cubes of w/c ratio of 0.5. Stress-strain ratio for cubes of mix M1 (w/c ratio 0.45) have been found for different duration concrete, which increases with increase in time duration of concrete (i.e. stress-strain ratio at 56 days > stress-strain ratio at 28 days > stress-strain ratio at 7 days), which have a similar gradient pattern as found in the control mix of w/c ratio of 0.45. A similar pattern has been observed in the case of w/c ratio of 0.5 also. It has been observed that mix M1 and mix M2 have a greater disparity in compressive strength at both w/c ratio of 0.45 and 0.50 unlike the rest of the concrete mixes. From the results of secant modulus, it has been seen that, though both M1 and M2 have similar content/quantity of FA (i.e., 10% of cement), the amount of CT varies as 5% of cement in mix M1 and 10% of cement in M2 which is the leading cause of disparity in the compressive strength at different w/c ratio. 7-days, 28-days, and 56-days compressive strength of six different FA and CT mix combinations, presented in Fig. 4, have been compared with the compressive strength of the respective control mix samples. The standard deviations (detailed in Table A4 of the appendix) of compressive strength results are very less dispersive. The results exhibit standard deviation of 0.18 N/mm2 to 1.4 N/mm2 for 7-days compressive strength, 0.19 N/mm2 to 1.27 N/mm2 for 28days compressive strength and 0.12 N/mm2 to 2.22 N/mm2 for 56days compressive strength. 7-days compressive strengths of mix M1 at 0.45 w/c ratio is the highest among the other mix samples. It reduces gradually for the other mix design samples, except control mix (C-Mix), which is slightly lower than M1. The 28-days compressive strength results indicate nearly similar trends as of 7 days, but the strength of M1, M2, M3, and M4 at 0.45 w/c ratio are higher than the target strength. It is to be noted that all mix design samples are unable to achieve 28-days target strength at 0.5 w/c ratio except control mix (C-Mix) which closely approaches the target strength as evident from Fig. 5. On the other hand, the results of the 56days unconfined compression test are very encouraging to demonstrate combined utilization of CT and FA to replace cement in concrete partially. In 56-days results, the compressive strength of all specimens with water cement ratio of 0.45 is higher than the target strength except for M6. For 0.5 w/c ratio, the compressive strength of M1, M2, and M3 are significantly higher than the target strength and M4 and M6 are merely close to the target strength. The compressive strength of M1 has been found about 8.27% and 1.75% higher than the control mix at 0.45 and 0.5w/c ratios, respectively. Although the compressive strength of M2 and M3 is relatively lower than the control mix but higher than the target compressive strength (30 MPa) for both the w/c ratios. The test results also reveal that the compressive strength of mix M1 at 0.45 w/c ratio for 28-days and 56-days compressive strength is higher than those of control mix under similar conditions. The increase in compressive strength is mainly due to certain reactions taking place in the modified mixes of cement and pozzolanic material (FA, CT), which can be described as follows (Papadakis, 1999): hydration

C 3 S þ H ƒƒƒƒƒ! C  S  H þ CaOH reaction between lime and silica from pozzolanic material CaOH þ S ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ! C  S  H In the current work, it has been observed that the replacement of cement with FA beyond 20% combined with CT of 10%, has an adverse effect on the compressive strength of concrete (Mallisa

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7 days , w/c = 0.45

7 days , w/c = 0.5

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32 Stress (N/mm2)

40

Stress (N/mm2)

40

24

24

16

16 8

8 0

0 0

0.01 M-1

M-2

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M-6

0.02 Strain

0.03 M-3

0

0.04 M-4

C-Mix

0.005

M2

M5

M6

28 days , w/c = 0.45

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32 Stress (N/mm2)

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Stress (N/mm2)

0.015 Strain

0.02

0.025

M3

0.03 M4

C-Mix

28 days , w/c = 0.5

40

24

24

16

16

8 0

8 0

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M2

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M6

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0.04

0

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C-Mix

0.01 M1

M2

M5

M6

56 days, w/c = 0.45

0.02 Strain

0.03 M3

0.04 M4

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56 days, w/c = 0.5 40

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32 Stress (N/mm2)

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0.01

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24

24

16

16

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M2

M5

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Fig. 3. Stress-strain behavior for all the mix proportions.

and Turuallo, 2017). It may be due to non-availability of lime as all the extra lime released during the hydration process has been optimally utilized (Papadakis, 1999). For FA and CT there will not be any lime available beyond above limits of replacement due to the chemistry of concrete pore solution leading to reduced reaction with the pozzolanic materials and thus reduction in strength (Urhan, 1987). 3.3. Economic viability The economic feasibility of the concrete made by partial replacement of cement with FA and copper tailings has been assessed. The rate of each material has been taken from the schedule of rates followed in district Gwalior, Madhya Pradesh, India for

the year 2018 (detailed in Table A5 of appendix) and calculated for each kg of raw materials. The final cost of all the proposed combinations (detailed in Table A6 and A7 of appendix) is compared with the cost of the control mix. It is observed from the cost analysis that the partial replacement of cement with CT and FA results a significant reduction in the cost of concrete, as shown in Fig. 5. The production cost of one cubic meter of concrete as compared to control mix is reduced by about 6.72%, 8.81%, 11.36%, 13.44%, 16%, and 18.08% for M1, M2, M3, M3, M4, M5, and M6 respectively at a w/c ratio of 0.45. Similarly, the reduction in production cost has been found about 6.50%, 8.51%, 10.97%, 12.98%, 15.45% and 17.46% for mix composition M1, M2, M3, M4, M5, and M6 respectively than the control mix at a w/c ratio of 0.5.

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28 Days Compressive Strength in N/mm2

Compressive Strength in N/mm2

7 Days 42 36 30 24 18 12 6 0 M1

42 36 30 24 18 12 6 0

M2 M3 M4 M5 M6 C-Mix FA and CT Mix Praportion w/c ratio 0.45 0.5

M1

M2 M3 M4 M5 M6 C-Mix FA and CT Mix Praportion 0.45 0.5 w/c ratio

Compressive Strength in N/mm2

56 Days 42 36 30 24 18 12 6 0 M1

M2 M3 M4 M5 M6 C-Mix FA and CT Mix Praportion 0.45 0.5 w/c ratio

2700 Type of mix

2900

--15.45%

-12.98%

3100

-10.97%

3300

-8.51%

3500

w/c 0.5 -6.5%

3700

-17.46%

2900

Cost of 1 m3 of concrete (in Rs)

-18.08%

-16%

3100

-13.44%

3300

-11.36%

3500

w/c 0.45 -8.81%

3700

-6.72%

Cost of 1 m3 of concrete (in Rs)

Fig. 4. Compressive strength test results of all proportions.

2700 Type of mix

Fig. 5. Cost reduction in percentage in different category mix with respect to control mix.

From the bar charts presented in Fig. 4 and Fig. 5, it can be summarized that mix M1 at w/c ratio 0.45 can be the best alternative in terms of both cost and better compressive strength of concrete. M2 and M3 mixes may also be taken into consideration as a more economic concrete without compromising on compressive strength. 3.4. Environmental impact assessment Results of environmental impact assessment analysis using LCA technique have been summarized in the bar charts as shown in

Fig. 6, Fig. 7, and Fig. 8. A successive reduction in the point scale has been observed in the raw material part of both, midpoint and endpoint result due to a notable decrease in the cement consumption. The results of endpoint values (Fig. 6) show a fairly reduction in the adverse impact on the quality of the ecosystem, human health, and resources with the successive replacement of cement by FA and CT due to raw material. As for as ecosystem is concerned, the impact reduces from 20.6 points and 19.7 points for M1 at w/c ratio 0.45 and 0.5 respectively to 17.1 points and 16.5 points for M6 at w/c ratio 0.45 and 0.5 respectively compared

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Fig. 6. Endpoint environmental impacts for w/c ratio 0.45 and 0.5 for a different mix of concrete.

to 22.7 point and 21.6 points for C-Mix at w/c ratio 0.45 and 0.5. For human health endpoint category, the impact reduces from 23.5 points and 21.6 points for M1 at w/c ratio 0.45 and 0.5 respectively to 17.3 points and 16.1 points for M6 at w/c ratio 0.45 and 0.5 respectively compared to 27 point and 25 points for C-Mix at w/c ratio 0.45 and 0.5. In case of resources category, the impact reduces from 4.8 points and 4.4 points for M1 at w/c ratio 0.45 and 0.5 respectively to 3.6 points and 3.4 points for M6 at w/c ratio 0.45 and 0.5 respectively compared to 5.5 point and 5.1 points for C-Mix at w/c ratio 0.45 and 0.5. This variation is observed as at 0.5 water-cement ratios relatively less value for all mix proportions because the designed cement content is less as compared to w/c ratio 0.45. There is no notable variation observed due to the manufacturing process on the endpoints results with respect to w/c ratios of 0.45 and 0.5. In ecosystem quality, its value is 0.1 points; in human health, it is 0.36 points; and in resources, it is 0.07 points; for both

w/c ratio 0.45 and 0.5. Use of equal amount of energy in the manufacturing (mixing of ingredients) for all the mix proportions is the main reason behind similar trends. The disposal of material is also not much affected by this replacement (ecosystem quality 4.9 points; human health 68 points; resources 2.0 points for both w/ c ratio). The detailed midpoint results, shown in Fig. 7 and Fig. 8 summarize the effect on climate change, human toxicity, ozone depletion, agriculture land occupation, water depletion, fossil depletion, particulate matter and metal depletion due to the modified concrete mixes. The variation is observed chiefly in the raw part of all categories. Out of these categories, climate change and human toxicity are most influenced by the replacement of cement with FA and CT. In the control mix, the effect on climate change is observed as 445.64 kg of CO2 equivalent and 408.92 kg of CO2 equivalent for 0.45 and 0.5 w/c ratio respectively in the raw section. But in the

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Fig. 7. Midpoint lifecycle assessment of different concrete mixes at w/c ratio 0.45 with different proportion of FA, CT, and Cement.

modified mix it decreases to 382 kg of CO2 equivalent in M1 to 275.9 kg of CO2 equivalent in M6 for 0.45 w/c ratio and 350.85 kg of CO2 equivalent for M1 to 254 kg of CO2 equivalent for M6 for 0.5 w/c ratio. In the case of Human toxicity, it has been observed as 1543.19 kg of 1,4 DCB equivalent and 1436.6 kg of 1,4 DCB equivalent for 0.45 and 0.5 w/c ratios respectively for the raw section of control mix. However, it decreases to 1354.47 kg of 1,4 DCB equivalent in M1 to 1039.16 kg of 1,4 DCB equivalent for w/ c ratio of 0.45 and 1264.4 kg in M1 to 976.6 kg in M6 for 0.5 w/c ratio. As the production of cement is one of the major contributors of CO2 emission, being a major greenhouse gas, it depletes the ozone layer, resulting in an adverse effect on climate and human along with global warming potential (GWP). The inert concrete waste disposal has no severe impact on midpoint attributes except particulate matter and metal depletion. Equal consumption of electricity in concrete preparation is also not giving any variation in midpoint environmental impact for all the mix proportions.

However, the reduction of the quantity of cement in the raw material results in a very significant decrease in ozone layer depletion, climate change, and a reduced human toxicity effect. This variation in climate change further leads to a decrease in the water and fossil fuel depletion and the occupation of agriculture land.

4. Summary and conclusions This study examines the feasibility of combined utilization of CT and FA as an alternative to partially replace cement in concrete by assessing compressive strength, cost, and environmental impact. FA and CT were initially characterized, and their suitability for partial replacement of cement in concrete is identified through XRF and SEM. Various mix design proportions are synthesized for the partial replacement, and specimens are prepared. The performance of modified concrete proportion is evaluated in terms of strength,

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Fig. 8. Midpoint lifecycle assessment of different concrete mixes at w/c ratio 0.50 with different proportion of FA, CT, and Cement.

economic feasibility, and environmental sustainability. The conclusive remarks drawn from this study is presented below:  The Pozzolanic compounds found in FA and CT are above the ASTM requirement. Hence both can be used as a replacement of cement in concrete.  Replacing FA up to 20% with CT up to 5%, at w/c ratio 0.45, the 56-days have given higher compressive strength than the target strength. Beyond this limit, there is a reduction in compressive strength, which is due to the absence of cementing material available to react with pozzolanic compounds.  This replacement is also helped in reducing the cost of concrete production from 6.5% to 18.08%. It is found out that for better compressive strength and comparative economic, 10% FA replacement and 5% CT of cement at a w/c ratio of 0.45 is most favorable. 20% FA and 5% CT replacement with the cement is found a most economical mix without compromising compressive strength.

 The results of LCA analysis obtained through the extensive inherent data set in LCA tool shows a notable reduction in greenhouse gas emission which positively impacted and reduced the endpoint environmental impacts (ecosystem quality, human health, and resources).  The reduction in CO2 emission by lowering the cement consumption leads to a progressive decrement in global warming potential (GWP). As in the midpoint, environmental impact assessment climate change, human toxicity, ozone layer depletion, etc. all are lowered with the higher replacement of cement with FA and CT.

Acknowledgments The authors are thankful to BITS Pilani, India, for providing the necessary facilities to carry out this research work. Special thanks are due to Prof. K. S. Sangwan and Flexible Manufacturing Systems

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Laboratory, BITS Pilani for giving access of UMBERTO NXT software which has been used in this research. The support given by the research staff of the laboratory is fully acknowledged. Authors are grateful to Hindustan Copper Limited located in Khetri, Rajasthan, India for allowing to take sufficient samples of copper tailings and Ultra Tech Limited, Mumbai for providing admixture to perform this research. The references cited in this manuscript are also fully acknowledged. Authors express their sincere thanks to the anonymous reviewers and editors for their valuable suggestions and efforts. Declaration of Competing Interest The authors declare that they have no conflict of interest. Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.wasman.2019.08.036. References Ahmari, S., Zhang, L., 2012. Production of eco-friendly bricks from copper mine tailings through geopolymerization. Constr. Build. Mater. 29, 323–331. https:// doi.org/10.1016/j.conbuildmat.2011.10.048. Andrew, R.M., 2018. Global CO2 emissions from cement production. Earth syst. sci. data 10 (1), 195–217. https://doi.org/10.5194/essd-10-195-2018. ASTM C618–19, 2019. Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete. ASTM International, West Conshohocken, Pennsylvania, USA. https://doi.org/10.1520/C0618-19. Banerjee, S.S., Joshi, M.V., Jayaram, R.V., 2005. Removal of Cr (VI) and Hg (II) from aqueous solutions using fly ash and impregnated fly ash. Sep. Sci. Technol. 39 (7), 1611–1629. https://doi.org/10.1081/SS-120030778. BED, 2011. Buildings Energy Data Book: Energy efficiency and renewable energy. US Department of Energy. Benhelal, E., Zahedi, G., Shamsaei, E., Bahadori, A., 2013. Global strategies and potentials to curb CO2 emissions in cement industry. J. Clean. Prod. 51, 142– 161. https://doi.org/10.1016/j.jclepro.2012.10.049. Beniwal, P., Kumar, R., Usman, M., Sangwan, S., 2015. Use of copper tailings as the partial replacement of sand in concrete. Int. J. Res. Appl. Sci. Eng. Technol. 3 (12), 1–6. https://doi.org/10.1016/j.resconrec.2008.06.008. Bhakar, P., Singh, A.P., 2018. Life cycle assessment of groundwater supply system in a hyper-arid region of India. Procedia CIRP 69, 603–608. https://doi.org/ 10.1016/j.procir.2017.11.050. Bhakar, P., Singh, A.P., 2019. Groundwater quality assessment in a Hyper-arid region of Rajasthan. India. Nat. Resour. Res. 36 (2), 505–522. https://doi.org/10.1007/ s11053-018-9405-4. Borm, P.J.A., 1997. Toxicity and occupational health hazards of coal fly ash (CFA). a review of data and comparison to coal mine dust. Ann. Occup. Hyg. 41, 659– 676. https://doi.org/10.1093/annhyg/41.6.659. Castilla, J.C., 1996. Copper mine tailing disposal in northern Chile rocky shores: Enteromorpha compressa (Chlorophyta) as a sentinel species. Environ. Monit. Assess. 40 (2), 171–184. https://doi.org/10.1007/BF00414390. Central Electricity Authority Report, 2017. Report on Fly Ash Generation at Coal/ Lignite Based Thermal Power Stations and its Utilization in the Country for the Year 2016–17. (accessed 30.08.2018). . Choudhary, D., Tripathi, M., Shankar, R., 2019. Reliability, availability and maintainability analysis of a cement plant: a case study. Int. J. Quality Reliability Manage. 36 (3), 298–313. Cokca, E., Yilmaz, Z., 2004. Use of rubber and bentonite added fly ash as a liner material. Waste Manag. 24 (2), 153–164. https://doi.org/10.1016/j. wasman.2003.10.004. Corinaldesi, V., 2010. Mechanical and elastic behaviour of concretes made of recycled-concrete coarse aggregates. Constr. Build. Mater. 24 (9), 1616–1620. https://doi.org/10.1016/j.conbuild mat.2010.02.031. Çoruh, S., Ergun, O.N., 2010. Use of fly ash, phosphogypsum and red mud as a liner material for the disposal of hazardous zinc leach residue waste. J. Hazard. Mater. 173 (1–3), 468–473. https://doi.org/10.1016/j.jhazmat.2009.08.108. Cultrone, G., Sebastián, E., Elert, K., De la Torre, M.J., Cazalla, O., Rodriguez-Navarro, C., 2004. Influence of mineralogy and firing temperature on the porosity of bricks. J. Eur. Ceram. Soc. 24 (3), 547–564. https://doi.org/10.1016/S0955-2219 (03)00249-8. Dandautiya, R., Singh, A.P., Kundu, S., 2018. Impact assessment of fly ash on ground water quality: an experimental study using batch leaching tests. Waste. Manag. Res. 36 (7), 624–634. https://doi.org/10.1177/0734242X18775484.

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