Concrete is a mixture of cement blended with water and various sizes of aggregates. The cement and water form a paste that glues the aggregates together when it hardens. Concrete, in its freshly mixed state, is a plastic, workable mixture that can be formed into almost any desired shape. It starts to slowly stiffen when mixed, but remains workable for several hours. This is a long enough period to allow it to be placed and finished. After the initial set, it continues to gain strength for months, sometimes years if moisture continues to be present.

Cement and water combine chemically to bond the sand and coarse aggregate together. The volume of water added to a certain volume of cement determines, to a large extent, how string the hardened concrete will be. Most concretes are designed with a certain cement content and enough water to make the mass workable. Providing workability is adequate, reducing the mixing water content makes the batch stronger and the addition of water makes the batch weaker.