What is concrete?
Concrete is formed by a chemical reaction called hydration between water and cement. The cement is usually a compound called Portland cement.
In addition to water and cement, concrete usually has a mixture of other substances added for strength. The most basic concrete has aggregates made up of a mix of sizes of gravel and sand. Other additives are sometimes used to change characteristics of the concrete including: the speed at which the concrete sets, how well the mixture flows, the strength of the set concrete and its colour. Concrete is very strong under compression, and often incorporates steel or other materials, as either a grid cast within it or as fibres added to the mixture, that give the final concrete more strength under tension. A concrete is a mixture of cement, fine aggregate, coarse aggregate, and water. In some cases concrete admixtures are added to improve the properties of the concrete.