Cement

Types of Cement Cement materials can be classified into hydraulic cements and nonhydraulic cements. Hydraulic cements require water for setting and hardening, while nonhydraulic cements can set under air. Hydraulic cements, such as Portland cement, consist of silicates and oxides. The main mineral phases of hydraulic cements are alite, belite, tricalcium aluminate, and brownmillerite. Nonhydraulic cement sets as it dries and reacts with carbon dioxide in the air. Nonhydraulic cement does not require water for setting and hardening. Nonhydraulic cement is resistant to chemical attack after setting. Chemistry of Cement Hydraulic cement hardens through hydration of clinker minerals when water is added. The main mineral phases of hydraulic cement are responsible for its mechanical properties. The limestone is burned to produce lime in a calcination reaction. Lime reacts with silicon dioxide to form dicalcium silicate and tricalcium silicate. Lime also reacts with aluminum oxide to form tricalcium aluminate. Calcium oxide is obtained by thermal decomposition of calcium carbonate. The chemistry of these reactions is still the subject of research. Ancient Alternatives to Cement Bitumen was used by the Babylonians and Assyrians to bind burnt brick or alabaster slabs. Ancient Egyptians used sand and burnt gypsum mortar for cementation. Ancient Greeks used crushed potsherds as a pozzolan for hydraulic cement. Roman engineers used volcanic ash and lime for hydraulic cement. Crushed brick or pottery was used as a substitute for pozzolanic ash. Historical Use of Cement Lime was used by the Ancient Greeks and Minoans for cementation. The Greeks used volcanic tuff from Thera as a pozzolan. Roman engineers used crushed volcanic ash with lime for hydraulic cement. The material was called pozzolana and was extracted from Pozzuoli. Roman concrete was extensively used in structures like the Pantheon and Baths of Caracalla. Hydraulic cement actively used by medieval masons and military engineers in the Middle Ages. Structures such as canals, fortresses, harbors, and shipbuilding facilities were constructed. Lime mortar and aggregate with brick or stone facing material used in the Eastern Roman Empire and Gothic period. German Rhineland utilized hydraulic mortar with local pozzolana deposits. Development of Cement Techniques Tabby, a building material made from oyster shell lime, sand, and whole oyster shells, introduced in the 16th century. Concrete formed using tabby. French and British engineers formalized technical knowledge for making hydraulic cement in the 18th century. John Smeaton’s contribution to cement development for Eddystone Lighthouse construction. Parkers Roman cement developed by James Parker in the 1780s. Louis Vicat identified the principle of combining chalk and clay for cement production in the 19th century. Vicat devised a method for intimate mixture of chalk and clay. Burning process used in cement production. Roman cement replaced by Portland cement in the 1850s. Smeaton’s work on hydraulic cement apparently unknown to Vicat.