Quick point of clarification - concrete is about 40% sand. PortlandPortland cement is one of the other parts of concrete - it’s what actually holds concrete together. Other pozzolons, like fly ash, can make up 25-50% of the cementitious material.

FWIW, Cement is wildly energy intensive to create and produces a huge amount of CO2. We don’t have a lot of replacement options for cement (or concrete generally) because of its unique durability.