1. Introduction
Cement mortar, a crucial construction compound composed of sand, cement, and water, heavily relies on river sand as a primary fine aggregate. However, the soaring demand for infrastructure development, particularly in developing nations, has put a strain on the supply of natural sand, leading to its rapid depletion. This scarcity has spurred the search for alternative fine aggregates with manufactured sand produced using crushers, which are emerging as a promising substitute. This artificial sand must adhere to the accepted gradation standards, as it can reduce the voids and cement consumption, enhancing the cost-effectiveness. In response to the escalating demand for alternatives to river sand, experts in the construction field have identified various options, including waste glass, crushed rock, limestone powder, and fly ash. Notably, materials, such as copper slag (CS) and quartz, that were previously overlooked as fine aggregate replacements are now considered promising due to their comparable properties to traditional sand.
Copper slag, a by-product of copper smelting and refining, holds promise as a construction material, serving as a partial or full substitute for the conventional aggregates. Widely used in sandblasting and abrasive tool manufacturing due to its hardness, density, and low free silica content, copper slag is finding favor as a filler material in the building industry. Every ton of copper production generates 2.2–3.0 tons of copper slag. Its physical properties include a pH of 5, an electrical conductivity of 5.5 s/m, a hardness rating of seven on the Mohs scale, a bulk density of 1.88 g/cc, a specific gravity of 3.53, and a minimal moisture content (<0.001) [
1,
2,
3]. Numerous studies have explored copper slag’s potential as a partial replacement for fine aggregates in concrete. Experiments using M25-grade concrete have investigated replacement percentages ranging from 10% to 20% [
1,
2,
3]. In-depth investigations into strength, workability, and durability have identified the optimal proportions of copper slag as a substitute material [
4,
5,
6,
7]. Other research on high-strength concrete (HSC)-incorporating copper slag has shown improved strength and durability with less than 40% copper slag as a sand substitute, especially when coupled with superplasticizer additives [
8,
9,
10,
11]. Additionally, the use of quartz sand as a sand replacement has been explored, presenting an economical substitution for weather-resistant concrete [
6].
Quartz, the most abundant silica mineral, is typically colorless and transparent. It forms in various rock types, including igneous, metamorphic, and sedimentary formations. Composed mainly of SiO
2, quartz boasts a Mohs hardness of seven and remarkable resistance to both mechanical and chemical weathering. Its durability renders it a dominant mineral in mountain regions and the primary component of beaches, riverbeds, and desert sands. Quartz’s ubiquity, abundance, and robustness make it an invaluable geological feature [
4,
12,
13,
14]. Numerous studies have explored quartz’s potential as a partial replacement for fine aggregates in construction materials. Sandstone comprising predominantly smooth and rounded quartz grains has been the subject of research into compressive strength, providing valuable insights [
8]. Investigations into Ultra High-Performance Concrete have delved into the effects of quartz powder (Qp) and quartz sand (Qs), employing mathematical models based on coded variables and ANOVA techniques. These models apply to variable ranges, such as quartz powder substitution (0–20% by cement weight), quartz sand substitution (0–50% by crushed limestone weight), and water curing temperatures (from 25 °C to 95 °C) [
15,
16,
17]. In this study, an attempt has been made to find out the compressive strength of the cube with different proportions of copper slag and quartz with a cement–concrete mix design [
18,
19,
20,
21].
2. Materials and Methods/Methodology
Materials are usually categorized into two sources: natural and manmade. Materials such as stone and wood are natural, and concrete, masonry, and steel are manmade. But both must be prepared and treated before they are used in a building. Structural materials consist of a hard, chemically inert particulate substance known as aggregate (usually sand and gravel), bonded together by cement and water.
2.1. Cement
Ordinary Portland cement of 53 grade conforming to IS 8112-1989 [
22] was used. Tests on various physical properties, such as specific gravity, fineness, and initial and final setting times, were performed as per IS 269-1989 [
23].
2.2. Fine Aggregate
Commercially available river sand was used in this study. Grain size distribution was carried out as per IS 383-1970 [
24].
2.3. Water
Potable water was used for the entire project.
2.4. Copper Slag and Quartz
The copper slag and quartz used in this work were bought from Megha metallizers, Bommasandra, Karnataka, India. Tests on various physical and chemical properties were performed.
2.5. Mix Design Calculation for Mortar Specimen (as Specified by IS 456:2000) [25]
The process of selecting suitable ingredients for concrete and determining their relative amounts to produce concrete of the required, strength, durability, and workability as economically as possible is termed the concrete mix design.
Volume = 70 × 70 × 70; density of mortar = 2200 Kg/m3; mass = 2200 × 0.07 × 0.07 × 0.07 = 0.7546 Kg; cement/sand ratio= 1:3; weight of cement = 1/4 × 0.7546 × 1 = 0.188 Kg; weight of sand = ¼ × 0.7546 × 3 = 0.565 Kg; w/c = 0.5; water = 0.5 × 1.88 = 0.094 L.
2.6. Casting of Cubes
The cube must be cast as per the details given in
Table 1. The number of mortar cubes that were cast is 5. The replaced copper slag mortar cubes contained different replacement quantities. The contents of copper slag totaled 0%, 25%, 50%, 75%, and 100%. Five cubes were cast for each replacement. The total number of cubes cast was 15. The ratio 1 (cement):3 (fine aggregate) was achieved by completely mixing 94 mL of water. The size of mould cubes was 70 × 70 × 70 cubic mm, and they were made of plywood as shown in
Figure 1. For the casting of mortar in plywood cube moulds, the moulds were coated with grease so that mortar could be easily removed out of mould.
2.7. Casting of Cylinders
The cylinders must be cast as per the details given in
Table 1. The number of mortar cylinders that were cast is 5. The replaced copper slag mortar cylinders contained different replacement quantities. The contents of copper slag were 0%, 25%, 50%, 75%, and 100%. Five of the cylinders were cast for each replacement. The total number of cylinders cast was 15. The ratio 1 (cement):3 (fine aggregate) was achieved by completely mixing 94 mL of water. The size of mould cylinder was 70 mm in diameter, and it was made of PVC. For the casting of mortar in the moulds, the moulds were coated with grease so that mortar could be easily removed from the mould.
2.8. Curing of Cubes and Cylinder
After casting and allowing the cubes to set, it is essential to begin the curing process before conducting any tests, except in cases where a 24-h test is specifically required. These freshly cast cubes should be promptly placed into a curing tank. To ensure proper water circulation and effective curing, it is important to maintain adequate spacing between the individual specimens. When utilizing a mist room for curing, it is crucial to provide ample space around the specimens. This arrangement ensures that all the surfaces of the cubes remain consistently moist throughout the curing period. The compressive strength of cubes was tested for 5 different cubes after 7, 14, and 21 days of curing.
2.9. Experimental Setup
The experiments were conducted on concrete cubes and cylinders to determine the compressive strength and split tensile strength, respectively. The cubes and cylinders used for experiments were cast as per IS 516 [
26] and IS 5816 [
27]. Five cubes and cylinders were tested after 7, 14, and 21 days of curing. A Universal Testing machine was used to conduct compressive strength tests.
4. Conclusions
This study covered sieve analysis, water absorption, and compressive and split tensile strength tests on concrete mixtures with varying replacement percentages. The key conclusions drawn from the study include the following: The compressive strength increased as the percentage of copper slag replacement increased, with the maximum strength achieved with the 0.50% replacement after both 7 and 21 days of curing. An increased copper slag content also improved the workability. The compressive strength generally increased with increasing quartz replacement up to 0.50% after both 7 and 21 days of curing. The split tensile strength increased with more copper slag replacement, peaking at 0.50% replacement after both 7 and 21 days of curing. The tensile properties of concrete were enhanced by the copper slag.
Both copper slag and quartz can effectively replace fine aggregate in concrete, leading to improved compressive and split tensile strengths. The maximum strength was typically achieved at the 0.50% replacement level for both materials. Longer curing periods (28 days) resulted in increased strength, indicating the durability and long-term performance of these replacements. In conclusion, this study demonstrates that both copper slag and quartz can be viable alternatives for fine aggregate in concrete mixtures. Copper slag, with its pozzolanic properties, showed a greater strength-enhancing potential, while quartz also exhibited positive effects. These findings are promising for optimizing concrete mix designs, reducing the environmental impacts of using industrial by-products, and exploring natural alternatives.