The Handyman's Guide to Concreting at Home
Concrete develops its strength by the reaction of water with cement, so it should be prevented from drying out too quickly, otherwise a weak, poor quality surface may result.

As soon as the surface is hard enough to resist marking, cover the concrete with plastic sheeting or waterproof building paper and secure well, especially on the edges. This will keep the moisture in.

Another method is to spread a layer of hessian or sand over the surface and keep moistening it continuously.

This process of keeping your concrete damp is known as “curing”. Your concrete will continue to gain strength for at least one month provided curing is continued for that time.
DIY Alsafe Concrete