The research aimed to investigate the mechanical and durability qualities of concrete mix designs by incorporating copper slag (CS) as a substitute for fine aggregate of natural sand (NS). Eleven concrete mixtures were casted, including the control mix, with varying concentrations of CS ranging from 0% to 100% at an increment of 10%. Tests were conducted to evaluate the mechanical properties of the concrete mixes, including flexural strength, compressive strength and split tensile strength. In addition, the durability of the concrete was assessed by conducting tests for water absorption and rapid chloride penetration test. (RCPT). The results indicated at 30% replacement of CS as NS, the maximum improvement in flexural, compressive, and split tensile strength of concrete is achieved. Addition upto 60% still resulted in concrete mixtures with comparable strength to the control mix. Beyond this replacement rate, the concentration of CS increases the amount of free water in the mixture, leading to a decrease in strength. Therefore, it is recommended that 30 wt% of CS can used as replacement of NS in order to obtain concrete with good strength and durability properties.