This document discusses a study on the effect of using different substitutes for partial replacement of cement and aggregate on the strength of concrete. Concrete cubes with M20 design mix were cast using fly ash, marble powder, M-sand and concrete waste to partially or fully replace cement and sand. The concrete cubes were tested after 28 days to determine their compressive strength. It was found that fly ash and marble powder can partially replace cement at 15% and 10-15% respectively without reducing strength. M-sand was found to increase strength even at 15% replacement of sand. Concrete waste also provided satisfactory strength when used to fully replace coarse aggregate and partially replace sand.