Cement and plaster

Abstract

The essential characteristic of cement and plaster is that they are calcined materials which harden on reaction with water when mixed as a paste. Such materials have been known and exploited since ancient times. The Egyptians used cement when building the Pyramids, and the Romans and Greeks used a cement produced from a mixture of volcanic ash and lime, which still forms the basis of some modern cement formulations (pozzolanic cements). The most widely used cement type, Portland cement, was patented in England in 1824 by Joseph Aspdin who produced it by calcining impure (argillaceous) limestones, some of which have become known subsequently as cementstones. The name Portland cement arises from the similarities in appearance of concrete made from the cement to Portland stone. Portland cement is stronger than pozzolanic cement, and has improved setting characteristics. The cementstones which were initially used to make Portland cement are widespread throughout the geological succession, and it is interesting to speculate whether they were exploited by the Romans in the northern extremities of the Roman empire, far from Mediterranean sources of volcanic ash. Plaster was also introduced to Britain by the Romans, but was lime-based; ‘modern’ gypsum-based Plaster of Paris was introduced in 1254.