Concrete is rationally chosen mixture of cement, fine aggregate, coarse aggregate and water. River sand, which is generally used as fine aggregate in concrete, has become very expensive due to rapid depletion of river bed, high transportation cost etc. In order to meet the global demand and control concrete cost, now more focus are being given to Non-Conventional and recycled materials which could be used as a replacement of river sand. Copper Slag, which is a by-product (having Silica SiO₂ as a major chemical composition) obtained during matte smelting and refining process of copper production, is abundantly available and even possesses low risk to health and environment and could be considered as an alternative to river sand. Utilizing these waste slags in Concrete also helps in resolving the dumping or disposal problem of the industrial waste which is a major concern today.

Chandana Sukesh et.al (2013) investigated the partial replacement of sand with quarry dust in concrete and found that the replacement of sand with quarry dust shows an improvement in the compressive strength of concrete. The results also showed that, as the replacement of the sand with quarry dust increases, the workability of the concrete decreases due to the absorption of water by the quarry dust. Omar M. Omara et.al (2012) studied the influence of limestone waste as partial replacement material for sand and marble powder in concrete properties and found that compressive strength of concrete has increased with increasing percentages of M.P additions at all curing ages. The highest compressive strength appears during the highest proportion of M.P specimen, especially at early curing ages. Sree Krishnaperumal Thanga Ramesh et.al (2013) have investigated the use of furnace slag and welding slag as replacement for sand in concrete and found a better performance towards compressive strength. The results showed that 5% of Welding Slag and 10% of Furnace Slag replaced with sand is very effective for practical purpose. Saveria Monosi et al (2010) used Foundry Sand in Cement Mortars and Concrete Production and found that structural mortar and concrete can be manufactured with UFS as a partial replacement of natural sand. A suitable recycling of the discarded foundry sand as building construction material was suggested. Ion Dumitru et.a (2013) did Field Trials Using Recycled Glass as Natural Sand Replacement and Powdered glass as Cementitious Materials Replacement in Concrete pavement and found that, recycled sand glass can be used to partially replace natural sand in concrete, producing concrete with atleast equivalent fresh and hardened properties. The compressive strength of the concrete pavement has achieved minimum 35MPa as per specification requirements. Flexural strength has achieved the required 4.5MPa at 91 days. Al-Jabri et.al (2005) investigated the effect of Copper Slag (CS) and Cement by-Pass Dust (CBPD) as replacements on the strength of cement mortars. The results indicated that, the mixture containing 5% CBPD + 95% cement yielded the highest 90 days compressive strength of 42 MPa in comparison with 40 MPa for the mixture containing 1.5% CBPD + 13.5 CS + 85% cement. The optimum CS and CBPD used was 5%. In addition, it was determined that, using CBPD as an activating material would operate better than using lime. Washington Almeida Moura et.al (2007) investigated the strength properties of copper slag admixed concrete and found that an addition of copper slag to concrete results in an increase on the concrete's axial compressive, splitting tensile strength and decrease in the absorption rate by capillary suction, carbonation depth and hence improved its durability. Brindha et.al (2010) studied the effect of replacing fine aggregate by copper slag on the compressive strength and split tensile strength and found that the percentage replacement of sand by granulated copper slag were 0%,5%,10%,15%,20%,30%,40% and 50%. The compressive strength was observed to increase by about 35-40% and split tensile strength by 30-35%. The experimental investigation showed that percentage replacement of sand by copper slag shall be upto 40%. Ishimaru et al (2005) investigated the fundamental properties of concrete using copper slag and class II fly ash as fine aggregates and the following conclusion was drawn. The results indicated that, upto 20% (in volume) of copper slag or class II fly ash as fine aggregates substitution can be used in the production of concrete. Binaya et al (2014) investigated the optimum usage of Copper Slag as Fine Aggregate in Copper Slag Admixed Concrete and found that for M20 grade mix of concrete, the compressive strength of concrete is comparable to the control mix up to 40% of Copper slag substitution, but they decrease with a further increase in Copper Slag contents (due to the increase of free water content in the mix). Joshua et al (2014) have studied the effect of partial replacement of sand with lateritic soil in sandcrete blocks. Tests have been conducted to evaluate the suitability of lateritic soils within the boundaries of Ota and its effect on the strength of sandcrete blocks when used to replace the conventional fine aggregate. The study recommends that block moulding industries within Ota need to adhere strictly to standard practice by incorporating lateritic soil not greater than 20% of the aggregate used in their sandcrete block production as a way of reducing the production cost as well as a corresponding reduction in the market price of sandcrete blocks.

Ordinary Portland cement of 53 grade having specific gravity of 3.094, fineness modulus of 4.62% and normal consistency of 32% was used. The Cement used has been tested for various proportions as per IS 4031-1988 and found to be confirming to various specifications of 12269- 1987.

Crushed angular granite metal of 20mm size having the specific gravity of 2.637 and fineness modulus of 7.102 was used. Bulk Density in loose state and compacted state was found to be 1414 kg/m³ and 1550 kg/m³ respectively. The water absorption was 1.1%.

Rivers having the specific gravity of 2.601and fineness modulus 2.43 was used. Bulk Density in loose state and compacted state was found to be 1597 kg/m³ and 1700kg/m³ respectively. The water absorption was 1.20%.

Copper Slag with specific gravity 3.476 and fineness modulus 3.301 was used. Bulk Density in loose state and compacted state was found to be 1898 kg/m³ and 2024 kg/m³ respectively. The water absorption was 0.24%. As per the chemical analysis of Copper Slag, Silica content in Copper Slag was found to be 33.52%.

Test specimens consisting of cube specimens of size 150X150X150 mm were casted and tested as per IS 516 and 1199.

The aim of the present investigation was to study the relationship between the Compressive Strength of M30 grade of concrete mix with percentage of Copper slag used as replacement of Fine aggregate in Copper slag admixed concrete. M30 grade mix concrete was used and the mix proportion chosen was 1: 2.01: 3.326 with Water/Cement ratio of 0.5 as shown in Table 1. As per the partial replacement of Sand with Copper Slag, the mix proportions were modified. Cube specimens of dimension 150 x 150 x 150 mm were tested as part of the study. Sand was replaced with Copper Slag from 0% to 50% (0%, 10%, 20%, 30%, 40%, and 50 %). The cubes were tested at 28 and 90 days for compressive strength and a mathematical equation was derived between Compressive strength and % of copper Slag used as a partial replacement of Sand.

Table 1. Concrete Mix Design Details – M30 Mix

Table 1gives the quantities required for I m³ of concrete mix of M 30 grade of concrete mix. The mix proportions are made by replacing fine sand with Copper Slag at various percentages ranging from 0% to 50 %.

From Table 2, it can be observed that the compressive strength of concrete increased when copper slag was replaced up to 40%. However, the compressive strength decreased rapidly for mixtures with 50% copper slag replacement. For M30 Grade Mix Concrete with 40% of copper slag replacement at 28 days and 90 days, compressive strength were 47.41 N/mm² and 57.24 N/mm² compared with 41.16 N/mm² & 51.28 N/mm² for the control mixture.

Table 2. Compressive Strength of M30 Mix concrete

In comparison to sand, Copper Slag has a lower water absorption capacity. The lower water absorption capacity causes increased free water content there by decreasing in compressive strength. This further causes increase in the workability.

Figure 1 gives the mathematical equations arrived from the data for 28 days and 90 days, compressive strength values with percentage of Copper slag used as replacement of Fine aggregate in Copper slag admixed concrete.

At 28 days, the Mathematical Equation is as

Compressive Strength = -46.268(% Copper Slag)² + 33.771(% Copper Slag)+40.837                                                             (1)

At 90 days, the Mathematical Equation is as

Compressive Strength = -33.643 (% Copper Slag)²+27.124 (% Copper Slag ) + 51.143                                                          (2)

Figure 1. Compressive Strength of M30 Grade Mix at various % of Copper Slag Replacement at 28 and 90 days

• Replacement of Copper Slag as fine aggregate in concrete mixes reduces the cost of concrete production.
• The utilization of Copper Slag in Concrete production provides additional environmental as well as effective waste management technique for all the related Industries.
• Copper Slag behaves similar to River Sand as it contains Silica (SiO₂) similar to sand.
• The density of concrete increases by addition of Copper Slag thereby increasing the Self-weight.
• The measured water absorption of Copper Slag (0.24%) is less than that of Natural Sand (1.2%). This suggests that Copper Slag would demand less water than that required by natural sand in the concrete mix. Therefore, it is expected that the free water content in concrete matrix will increase as Copper Slag content increases, which consequently lead to increase in the workability of concrete.
• The results showed that the workability of Concrete increased substantially with increase of Copper Slag content in the concrete mixture due to low water absorption, coarser (in nature than sand) and glassy surface of Copper slag, thereby the strength properties are also improved.
• The compressive strength of Concrete is comparable to the control mix upto 40% of Copper slag substitution, but they decrease with a further increase in Copper Slag contents (due to the increase of free water content in the mix).
• The early compressive strength of Concrete was not adversely affected by Copper Slag addition upto the proportion of 40%.
• Compressive strength of Copper Slag admixed Concrete increased due to high toughness of Copper Slag.
• For longer curing periods (i.e. 90-Days), no detrimental effect (i.e. Strength reversal) was observed, when using Copper Slag.
• The coefficient of determination for 28 days & 90 days compressive strength were found to be 0.9753 and 0.9748 which indicates that the model has a good fit.