This document analyzes the compressive strength of concrete with partial replacements of sand with ground granulated blast furnace slag (GGBS) and cement with fly ash. Samples of M25 grade concrete were prepared with 0-20% replacements of sand with GGBS and 0-10% replacements of cement with fly ash. The compressive strength and workability (slump) of the samples were tested at 7 and 28 days. The results indicated that additions of GGBS and fly ash improved the workability and compressive strength of the concrete, enhancing the mechanical properties. The optimal replacements were determined to be 10-15% GGBS and 5-10% fly ash.