Author: Ehsan Sheikh,Seyed Roohollah Mousavi,Iman Afshoon
Publication: Journal of Cleaner Production
Publisher: ElsevierDate: 25 September 2022
Improving the concrete mechanical properties/durability indicators and reducing its costs and environmental damage by using waste materials have always been strategies for the growth and development of the concrete industry, waste management and environmental protection. This research studied the effects of using fine copper slag (CS) aggregates on the strength and microstructural properties of roller compacted concretes (RCC) by testing a total of 7 mix-designs including 0–60% fine copper slag aggregates and the results showed that the best compressive strength performance, about 23.58% more than that of the control design, was related to the 91-day concrete containing 40% CS. An increase in the CS increased the RCC's tensile and flexural strength. Different-age, 40% copper-slag specimens had the lowest surface and capillary water absorption and penetration rates, and 60% ones had about 7% increase in the unit weight and 26.8% reduction in the production costs. The mechanical properties were studied by scanning electron microscope (SEM) images and the results showed that this research can help collect copper slag waste from the nature, produce nature-friendly RCCs, reduce pollutants and waste depot spaces, save energy and preserve the environment.
Producing one ton of pure copper produces about 2.2–3 tons of copper slag (CS) as a waste by-product that has high FeO2 and low SiO2, Al2O3 and CaO (Gorai et al., 2003), and is released into the nearby environment (Shi et al., 2008). In 2015, the major CS production was by China, Japan, Chile, Russia and India (about 56%) (Sharma and Khan, 2018), but such factors as the expansion of cities, population growth and urban development led to its more production compared to 2015; the average annual CS production is about 30 million tons which is stored in the nature often unused (Shen and Forssberg, 2003). From the environmental protection point of view, storage of this volume of waste in the nature is not justified due to high costs and environmental hazards as well as the required land and space (Khanzadi and Behnood, 2009). Although part of this waste is used in producing engineering materials (tiles, cement, glass, mortar, concrete, etc.), making abrasive/cutting tools and constructing roads, railways, airport runways, embankments and drainages (Shi et al., 2008; Nazer et al., 2016), large amounts of it are still stored in the environment with no specific use.
Cost-effectiveness and rapid production are among the reasons why the roller compacted concrete (RCC) is used in the construction of hydraulic structures and pavements of various roads and highways. During the 1970s, RCC pavements replaced the conventional asphalt types due to their higher construction costs (ACI 325.10R-95, 2001). Compared to the ordinary concrete: 1) RCC has less water content, more mineral additives (e.g., fly ash), and different manufacturing/execution processes (Wang et al., 2018), and 2) about 70–80% of its volume is composed of aggregates letting more voids to be filled with fine aggregates (ACI 325.10R-95, 2001). As RCC is spread with bulldozer in horizontal layers and is compacted by vibrating rollers (Liu et al., 2015), its post-curing behavior depends on how accurately and qualitatively the layers are implemented, compacted and controlled. Various parameters that should be considered to achieve an ideal RCC density include the speed and frequency of the roller vibration, number of its passes and the compressed thickness (NEAPRC, 2009). Compared to asphalt pavements, the RCC strength and durability are higher and show better performance against such oily elements as gasoline, diesel and grease (Rao et al., 2016), and compared to conventional concrete/embankment dams, construction of RCC dams is faster and more cost-effective, and involves material savings and less spillway cost due to smaller size and dimensions (Karimpour, 2010).
The industry growth and construction progress around the world have boosted the need for large volumes of natural aggregates leading to the disposal of the related wastes and by-products and, hence, to potential environmental damage (Prem et al., 2018). Reducing the volume of waste materials and improving their recycling conditions are important issues in the waste and environmental management because natural resources are preserved and the required disposal space is reduced (Sharifi et al., 2015). About 3.7 billion tons of various aggregate types are used annually in the world (Association, 2018), and their production and consumption are still highly increasing compared to the past due to the concrete performance and special properties, and the increasing need of the related industries. As the concrete industry highly depends on natural resources for natural sand, much effort has been made in recent decades in many researches to reduce this dependence (Dhar et al., 2018). Introducing materials to replace natural aggregates can help limit the potential environmental damage and hazards due to the frequent use of natural resources (Mousavi et al., 2021). Therefore, approved, technical, economic waste collecting and disposing solutions can help keep the environment clean. The construction industry depends on the production of different-type/-quality concretes causing the annual consumption rate of which to be about 25 × 109 tons (IEA and WBCSD, 2009). Almost 55–80% of the concrete volume consists of aggregates most of which are produced either from riverbeds or by crushing mountain boulders that damage the environment seriously (Al-Jabri et al., 2009a). Only in 2015, aggregates used in the concrete industry amounted to about 48.3 × 109 tons (Freedonia, 2012). The need for large volumes of natural aggregates, mass production of industrial by-products/wastes and the related environmental degradation make it a task to see if it is possible to use various waste materials such as the CS as a substitute for natural aggregates in concrete. Certainly, the construction industry can, by the use of waste materials, proceed successfully and hopefully in future (Ambily et al., 2015). Replacing natural fine aggregates with the copper slag waste in concrete has economic, environmental, and practical benefits because the energy consumption and CO2 emissions are reduced, destruction of natural resources, due to their high consumption, is prevented and green, clean concretes are produced.
Outstanding features of the CS and its use in cement and concrete industries, especially in areas where it is in abundance, can have many environmental and economic merits (Shi et al., 2008). The use of copper slag powder as a cement substitute and its effects on the properties of different types of concrete have been investigated in different researches [freshness (Afshoon and Sharifi, 2014); durability (Najimi et al., 2011; Sharifi et al., 2020a, Sharifi et al., 2020b); mechanical properties (Mobasher et al., 1996; Afshoon and Sharifi., 2017; Mirhosseini et al., 2017); thermal properties (Afshoon and Sharifi, 2020); fracture (Arino, and Mobasher, 1999)].
Al-Jabri et al. (2011) claimed that replacing 50% of the natural fine aggregates of cement mortars with the CS will increase the compressive strength by about 70%. Al-Jabri et al. (2009b) reported that when fine copper slag aggregates were used in high-performance concretes (0–100%), the density increased slightly (<5%), but the flowability increased considerably. According to them, up to 50% replacement improved the mechanical parameters, but above that (80–100%) reduced the compressive strength by 16%. Sharma and Khan (2017a) reported that increasing fine copper slag aggregates (0–60%) in the SCC increased the compressive and tensile strengths compared with those of the control mix design. They believed that about 20% replacement was the best to achieve the highest compressive strength and showed, by microstructural studies, that increasing the CS volume increased the pores, micro-cracks and capillary channels. Al-Jabri et al. (2009a) observed that while increasing the volume of copper slag aggregates improved the strength and durability of the high strength concrete (HSC), the water demand was reduced by about 22% at 100% replacement.
Wu et al. (2010a) believed that the improved flowability, efficiency and dynamic behavior of high strength concretes containing fine copper slag aggregates were related to the latter's smooth, polished surfaces and their less water absorption. They attributed the compressive, tensile and flexural strength drop of these concretes at more than 40% FeO2 to the presence of excess water and higher CS fineness that caused micro-cracks and cavities to develop in the concrete microstructure. Wu et al. (2010b) reported that the desirable performance of concretes containing up to 40% fine copper slag aggregates under dynamic compressive strength was due to their improved mechanical properties. Achudhan and Vandhana (2018) observed that the compressive strength of RC beams improved by about 8.2% at maximum 40% CS replacement for natural fine aggregates. Sharma and Khan (2018) stated that using 100% fine copper slag aggregates and 10% metakaolin in the SCC not only increased its compressive and tensile strengths, but also reduced the carbonation depth, surface water absorption and sorptivity to achieve the desired quality (based on the UPV test). They recommend the use of such concretes in constructing tall buildings, bridge piers, in-situ and prefabricated piles, shallow and deep foundations and gravity dams. Examining the microstructure of SCCs containing fine copper slag aggregates, Gupta and Siddique (2019) concluded that the strength drop occurred above 30% replacement; formation of ettringite at 40% replacement and presence of pores and micro-cracks at 50 and 60% were other reasons for the strength drop. Vijayaraghavan et al. (2017) confirmed the significant improvement in the strength and mechanical properties of concretes containing 40% CS, 40% iron slag and 10% recycled concrete aggregates. After examining the properties of SCCs containing 0–100% fine copper slag aggregates, micro-silica and fly ash, Sharma and Khan (2017b) concluded that the compressive and tensile strengths increased in a 20–60% range of CS replacement. Using the scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), they examined the microstructure of specimens containing CS and confirmed the production of C–S–H compact gel after 120 days with a Ca/Si in the 0.77–1.11 range. Ambily et al. (2015) reported a 15–20% drop in the compressive strength of high-performance concretes (HPC) containing 100% fine copper slag aggregates, but believed that their use in producing these types of concretes was still cost-effective. Previous studies have reported improvements in the energy absorption, flexural capacity and fracture toughness parameters of flexural concrete beams containing fine copper slag aggregates (Prem et al., 2018). According to Khanzadi and Behnood (2009), coarse copper slag aggregates' suitable strength properties and strong bond could improve the strength properties of high strength concretes (HSC). Rezaei Lori et al. (2019) proposed a 60% CS replacement in the production of pervious concretes and believed that the results of the pull-off adhesion test resembled those of the slag-free concretes. According to their report, increasing the CS in such concretes increased their porosity and permeability. Sharifi et al., 2020a, Sharifi et al., 2020b reduced the W/C in SCCs containing coarse copper slag aggregates and improved the mechanical properties up to 100% replacement; the concrete production cost reduced by about 19% at full replacement. Gupta and Siddique (2020) claimed that the effects of using fine copper slag aggregates on the chlorine ion permeability were more evident at higher curing ages (90 and 365 days) and believed that the surface water absorption and capillarity reduced considerably in concretes containing less than 40% CS compared to the control mix design.
Examining 15, 30, 45, 60, 90 and 120 min RCC mixing-compaction times, Gharavi (2003) observed that increasing the delay time in relation to the optimized compaction time highly reduced the mix strength. Modarres and Hosseini (2014) studied the mechanical properties of RCCs containing recycled asphalt and rice husk ash (RHA) and claimed that the asphalt waste had negative effects on the mentioned properties and replacing cement with RHA by up to 5% reduced the rate of the strength drop. Fakhri and Saberi (2016) believed that using such cement additives as micro-silica by about 10% improved the RCC strength by about 20% while using only rubber wastes reduced it. Ali Ahmad et al. (2017) claimed that when the optimum moisture content was used to produce RCCs containing Lumachelle, the obtained strength was close to that of the concrete containing natural fine aggregates. Rooholamini et al. (2019) reported that increasing fine-grained Electric Arc Furnace (EAF) steel slag reduced the mechanical parameters of the RCC, but increasing coarse grains improved the mechanical and fracture parameters significantly due to the desired angularity and roughness.
If these wastes are used as cement or natural aggregate substitutes in concrete elements aiming at producing clean, nature-friendly products, their collection from the environment will help the nature to face less damage for a period of time equal to the useful life-span of concrete structures. Even after the concrete element's life-span ends, it can be crushed, graded and reused as recycled waste materials in the production of fresh concretes; this cycle can probably be repeated many times.
This research addresses the environmental problems, concerns and consequences of leaving large copper-slag volumes in the nature. It tries to eliminate the related natural-aggregate-production damage to the nature by studying the feasibility of replacing CS for natural fine aggregates in the nature-friendly RCC and investigating its mechanical and microstructural characteristics. To this end, the RCC's natural fine aggregates were replaced with 0, 10, 20, 30, 40, 50 and 60% CS and results of the mechanical tests were validated scientifically using SEM images. To the authors' best knowledge, this is the first comprehensive research on using fine copper-slag aggregates in the RCC, and the results have confirmed that green, nature-friendly RCCs containing CS can be produced to solve their related environmental waste problems.
This section addresses defining materials specifications, designing mix-design ratios, selecting dimensions, preparing specimens and performing tests.
Results and discussion
To evaluate the performance and behavior of various concrete types, it is necessary to perform strength tests (compressive, tensile and flexural) and review and analyze the related results. Studying other characteristics (surface and capillary water absorption, water penetration, and unit weight) and investigating the microstructural and economic aspects will also provide the consumer with a better understanding of the performance and application of the produced concrete. This section has
A thorough investigation and analysis of the experimental results of this study shows that if the copper slag (CS) is used in roller compacted concrete (RCC) instead of natural fine aggregates, the result will be an inexpensive, clean, green, and nature-friendly RCC. This study investigated the effects of using fine CS aggregates on the production costs, environmental merits, mechanical properties and microstructure of the RCC. To this end, 7 mix designs were prepared wherein 0, 10, 20, 30, 40,
Suggestions for future studies
Future studies need, for this type of concrete, to study and evaluate: 1) fracture parameters under different loading modes, 2) strength against heat, 3) performance in acidic environments, 4) electrical resistance, 5) effects of carbonation and 6) thaw/freeze cycles.
CRediT authorship contribution statement
Ehsan Sheikh: Writing – original draft, Data curation, Writing – original draft, preparation. Seyed Roohollah Mousavi: Conceptualization, Methodology, Investigation, Reviewing and Editing, Supervision, Project administration, Funding acquisition. Iman Afshoon: Resources, Methodology, Formal analysis, Writing – original draft, Data curation, Writing – original draft, preparation, Software.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CSCopper slagRCCroller compacted concreteSEMscanning electron microscopeRHArice husk ashEAFelectric arc furnaceSCCself-compacting concreteHSChigh strength concreteRCreinforced concreteUPVUltrasonic pulse velocityEDSenergy dispersive spectroscopyHPChigh-performance concretesSSDsaturated surface dryC–S–Hcalcium silicate hydrateITZinterfacial transition zoneEIeconomic index (strength/price)OPCordinary portland cementFAfine aggregateCAcoarse aggregateSFRCsteel fiber reinforced concrete SymbolsW/C
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