Concrete is a composite construction material composed of fine and coarse aggregate embedded in a hard, cementitious matrix which primarily comprises oxides of calcium, silicon, aluminum and iron. It is mainly made up of cement and cement paste. Cement consists of a mixture of calcium, silicon, aluminum, and iron oxides, which are commonly present in the forms of calcium silicate (CaO·SiO2) and calcium aluminate (CaO·Al2O3). Cement is a type of inorganic binder, which hardens when mixed with water and forms a robust and durable material. Cement paste, on the other hand, is a mixture of cement, water and fine aggregate (such as sand). The main compounds in concrete are calcium silicate hydrate, calcium hydroxide, and calcium aluminate hydrate, which are formed as a result of the reaction between cement and water.