cement

Cement is a fine powder that, when mixed with water, binds together other materials to form concrete or mortar. The most widely used type is Portland cement, a hydraulic cement that hardens through hydration reactions with water.

Cement is produced by quarrying and preparing raw materials, typically limestone and clay or other silica-containing materials. These are heated in a kiln to form clinker, which is then ground to a powder and blended with small amounts of gypsum to regulate set. Variants of cement include ordinary Portland cement, rapid-hardening cement, sulfate-resisting cement, and white cement. Many mixes also incorporate supplementary cementitious materials such as fly ash, slag, or silica fume to improve performance and reduce clinker content.

Upon hydration, cement reacts with water to form compounds that bind aggregates in concrete. The primary hydration products are calcium silicate hydrates and calcium hydroxide, which impart strength and durability. The rate of strength development depends on fineness, temperature, and curing conditions. Cement is used to produce concrete, mortars, and grouts for buildings, roads, dams, and many other structures.

History and standards: The modern use of cement began in the 19th century, with the term Portland cement popularized after the name chosen by Joseph Aspdin in 1824. Earlier hydraulic cements existed in antiquity. Today, cement types and grades are specified worldwide (for example ASTM C150 in the United States and EN 197 in Europe), guiding composition, strength, and performance requirements.

Environmental considerations: Cement production is energy-intensive and releases CO2 from calcination of limestone and fuel use. Efforts to reduce environmental impact include improving energy efficiency, using alternative fuels, substituting clinker with supplementary cementitious materials, and developing lower-emission cements.