Cement is a material which when mixed with water sets into a strong paste. If aggregate is added to cement and water, the paste, which is formed by the combination of cement and water, bonds the aggregate particles together to produce concrete.
Normal cements are manufactured by heating a mixture of clay, or other argillaceous material(s), and limestone, or other calcareous material(s), which fuses into so called clinker. The clinker is ground and combined with a small amount of gypsum to make cement. Ordinary Portland Cement is the most common type of these cements. Rapid Hardening Portland Cement and Sulphate Resisting Portland Cement are other examples. The exact composition of their materials gives the cements their particular properties.
In mix design the most important property of a type of cement is its influence on the speed with which the concrete sets and develops strength and on the eventual strength of the concrete. The cement density also affects the mix proportions as calculated with the DOE Method.