Perhaps they had loads of the stuff lying around and found a use for it but conc doesn't work how most people think it does. It is a chemical reaction when you

Perhaps they had loads of the stuff lying around and found a use for it but conc doesn't work how most people think it does. It is a chemical reaction when you mix and pour it and it does not simply dry out. That's why it works underwater if you are careful to stop currents from winnowing out the cement from the aggregate. It also gives off a lot of heat in volume when curing if you are not careful.