I'm glad to see research into this. Sand for concrete is a specific type of sand (nice and bumpy so it likes to lock together like a jigsaw puzzle) and people get killed by what are basically sand cartels. This was the "legitimate" mob business in the last season of Barry.
Portland cement is about 2/5 sand, so we'll need to start drinking more coffee! I was glad to see they're testing other organic matter since coffee is very susceptible to climate change, ironically caused in a large part by cement production. Unless you believe the reader comment on the article begging people to realize climate change is a hoax...
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.