The uses of Recycled Concrete Aggregate (RCA) as a substitute for natural aggregates in concrete has gained attention in recent years due to its economic and environmental benefits. However, the quality of RCA may vary, affecting its performance in concrete. This study investigates the effect of different replacement of RCA with and without SKY Glenium B8777, a viscosity-modifying admixture, on the properties of concrete. The research objectives were to evaluate the compressive strength, split tensile strength and flexural strength of concrete mixtures with different proportions of RCA and SKY Glenium B8777. The experimental program prepared the concrete specimens with different RCA replacement levels (0%, 10%, 20%, 30%, 40%, and 50%) and with and without SKY Glenium B8777. The results showed that the compressive, split tensile strength and flexural strength of the concrete decreased with increasing the RCA content, but the addition of SKY Glenium B8777 helped to improve the strength properties. These findings suggest that partial replacement of RCA with SKY Glenium B8777 can be a viable option to enhance the fresh properties as well as hardened properties of concrete.