cement

Any bonding agent used to unite particles in a single mass or to cause one surface to adhere to another. Portland cement is a powder which when mixed with water and sand or gravel turns into mortar or concrete.

In geology, cement refers to a chemically precipitated material such as carbonate that occupies the interstices of clastic rocks.

The term ‘cement’ covers a variety of materials, such as fluxes and pastes, and also bituminous products obtained from tar. In 1824 English bricklayer Joseph Aspdin (1779-1855) created and patented the first Portland cement, so named because its colour in the hardened state resembled that of Portland stone, a limestone used in building.

Cement is made by heating limestone (calcium carbonate) with clay (which contains a variety of silicates along with aluminium). This produces a grey powdery mixture of calcium and aluminium silicates. On addition of water, a complex series of reactions occurs and calcium hydroxide is produced. Cement sets by losing water.

Cement kilns contribute to some extent to the world's output of carbon dioxide. It was estimated in 1997 that by 2000 cement works could be responsible for 10% of all emissions of carbon dioxide. Cement production is growing fastest in East Asia, with rapid construction of buildings and roads.