Exploring the Potential of Copper Slag and Quartz as Fine Aggregate Replacements in Concrete: A Comprehensive Study ^†

Abstract

In the realm of civil construction, river sand is an essential ingredient that cannot be overlooked. With the ever-increasing surge in construction activities, the demand for river sand has surged in tandem, resulting in its escalating scarcity, and subsequently, its price surge across the entire nation. This study delves into the utilization of copper slag as a viable alternative in the production of cement mortars, particularly as a partial replacement for fine aggregates. Experiments were conducted on concrete cubes and cylinders to determine the compressive strength and split tensile strength, respectively. Five cubes and cylinders were tested after 7, 14, and 21 days of curing. The extensive characterization of copper slag was conducted, encompassing its chemical composition, mineralogical attributes, and size distribution. The findings highlight that mortars containing copper slag exhibit superior compression resistance compared to the river sand-based mortars. Specifically, the 50% replacement of river sand with a blend of copper slag and quartz demonstrates the highest strength, surpassing the other compositions. Notably, the partial substitution of sand with copper slag outperforms both quartz and sand individually, with the optimal strength achieved at a 50% replacement rate. 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 caused by industrial by-products, and exploring natural alternatives.

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 SiO₂, 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. Values of mass of ingredients required for 1:3 ratio, where natural sand is replaced with copper slag/quartz.

% Replacement	Cement in Kg	Sand in Kg	CS/Quartz in Kg
0	0.188	0.565	0
25	0.188	0.424	0.141
50	0.188	0.2825	0.2825
75	0.188	0.141	0.424
100	0.188	0	0.565

. 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.

3. Results and Discussion

3.1. Sieve Analysis of Fine Aggregate

The sieve analysis of sand and copper slag was performed as discussed earlier.

From

Table 2. Observations and calculations for sieve analysis of sand.

Sl. No.	IS Sieve Number	Weight Retained in gm	Cumulative Mass Retained	Cumulative % Retained (C)	% Finer (100 C)
1	4.75	35	35	3.5	96.5
2	2.36	60	95	9.5	90.5
3	1.18	213	308	30.8	69.2
4	0.60	258	566	56.6	44.4
5	0.30	311	877	87.7	12.3
6	0.15	101	978	97.8	2.2
7	0.075	121	999	99.9	0.01
8	Pan	1	1000	100	0

and Figure 2 show the details of sieve analysis conducted for sand, also from

Table 3. Observations and calculations for sieve analysis of copper slag.

Sl. No.	IS Sieve Number	Weight Retained in gm	Cumulative Mass Retained	Cumulative % Retained (C)	% Finer (100 C)
1	4.75	0	0	0	0
2	2.36	4	4.02	0.402	99.58
3	1.18	147	151.75	15.17	84.82
4	0.60	584	738.68	73.86	26.13
5	0.30	247	986.92	98.69	1.30
6	0.15	10	996.97	99.69	0.30
7	0.075	1	997.97	99.79	0.20
8	Pan	2	1000	100	0

and Figure 3 it is observed that copper slag, being an industrial by-product, exhibits a different particle size distribution compared to that of natural sand. In this case, the data show that no material was retained on the 4.75 mm sieve. This indicates that the copper slag particles are predominantly smaller. Since copper slag was not retained on the larger sieve, this means that it is 100% finer than 4.75 mm.

The data show that they consist of a range of fine-to-coarse particles, which are suitable for use as a fine aggregate in concrete. The sieve analysis of copper slag indicates that it primarily consists of fine particles, with most of the material passing through the sieves as shown in Figure 3. This suggests that copper slag can be a potential replacement for fine aggregates in concrete, provided it has the other required properties. The sieve analysis of quartz shows a mix of particle sizes, including both fine and coarse particles. These data imply that quartz may not be an ideal candidate for a fine aggregate replacement in concrete without further processing to obtain a more consistent particle size distribution.

3.2. Compressive Test of the Cube for Partial Replacement of Fine Aggregate with Copper Slag

Compressive strength tests were conducted at two curing periods, 7 days, and 21 days. These durations represent the short-term and longer-term strength characteristics of concrete, respectively. The percentage of copper slag replacement varied (0%, 0.25%, 0.50%, and 0.75%). This variation allowed for the assessment of different replacement levels that affect the compressive strength. From

Table 4. The following compressive strength results were obtained after curing cubes for 7 and 21 days for different proportions of copper slag, as given below.

Curing Period	% of Replacement	Compressive Strength of Cube (in N/mm2) for 7 days	Compressive Strength of Cube (in N/mm2) for 21 days
1	0	17.77	38.50
2	0.25	24.44	42.20
3	0.50	36.88	54.22
4	0.75	28.88	46.22

and Figure 4, the compressive strength of concrete with copper slag replacement increases as the percentage of replacement increases, up to a maximum of 0.50% replacement (36.88 N/mm²). Similar to the 7-day results, the 21-day data indicate that the maximum compressive strength was achieved at 0.50% replacement (54.22 N/mm²).

3.3. Compressive Test of the Cube for Partial Replacement of Fine Aggregate with Quartz

The following compressive strength results were obtained after curing the cubes for 7 and 21 days with different proportions of quartz, as given below in

Table 5. The compression strength of the cube filled with sand partially replaced with quartz.

Curing Period	% of Replacement	Compressive Strength of Cube (in N/mm2) for 7 days	Compressive Strength of Cube (in N/mm2) for 21 days
1	0	17.29	24.30
2	0.25	18.27	27.90
3	0.50	20.38	28.80
4	0.75	16.50	26.20

.

The copper slag tests and compressive strength tests for quartz-replaced concrete were conducted at 7 days and 21 days. The percentages of quartz replacement (0%, 0.25%, 0.50%, and 0.75%) varied to assess their impact on the compressive strength. From Table 4 and Figure 5, the compressive strength generally increases with increasing quartz replacement up to 0.50% (20.38 N/mm²). This trend is similar to the copper slag replacement results and suggests that quartz can be an effective partial replacement for fine aggregates. At 21 days, the maximum compressive strength is also observed at 0.50% quartz replacement (28.80 N/mm²).

3.4. Split Tensile Strength of Cylinders for Partial Replacement of Sand with Copper Slag

The following split tensile strength results were obtained after curing the cylinders for 7 and 21 days for different proportions of copper slag, as given below in

Table 6. Split tensile strength of cylinder filled with sand partially replaced with copper slag.

Curing Period	% of Replacement	Compressive Strength of Cube (in N/mm2) for 7 days	Compressive Strength of Cube (in N/mm2) for 21 days
1	0	1.63	2.15
2	0.25	2.21	2.81
3	0.50	2.76	3.91
4	0.75	2.29	2.75

.

The split tensile strength tests were performed at 7 days and 21 days to assess the tensile properties of concrete with the copper slag replacement. Varying percentages of copper slag replacement (0%, 0.25%, 0.50%, and 0.75%) were tested. The split tensile strength increased as the percentage of copper slag replacement increased, with the maximum at 0.50% replacement (2.76 N/mm²) as shown in Figure 6. This suggests that copper slag enhances the tensile properties of concrete. The trend continued at 21 days, with the highest split tensile strength observed at 0.50% replacement (3.91 N/mm²). As the percentage replacement of copper slag increased, the split tensile strength of concrete increased gradually up to 50%, and then decreased. The maximum strength was typically achieved at the 0.50% replacement level for both the materials. The strength gains observed at 21 days indicate the durability and long-term performance of concrete with these replacements.

3.5. Comparative Study of Comparative Study of Compressive Strength When Fine Aggregate Is Partially Replaced with Copper Slag and Quartz for 7 Days

From Figure 7 and Figure 8, it can be observed that the increase in compressive strength over time (from 7 days to 28 days) for both the materials indicates the importance of longer curing periods for achieving optimal concrete strength. The 50% replacement level consistently produces the highest compressive strength for both the copper slag and quartz replacements, highlighting the potential for optimizing concrete mix designs with these materials.

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.