Concrete is a compound material made from sand, gravel and cement. The cement is a mixture of various minerals which when mixed with water, hydrate and rapidly become hard, binding the sand and gravel into a solid mass. The oldest known surviving concrete is to be found in the former Yugoslavia and was thought to have been laid in 5,600 BC using red lime as the cement.
The Assyrians and Babylonians used clay as the bonding substance or cement. The first major concrete users were the Egyptians in around 2,500 BC and the Romans from 300 BC. The Romans found that by mixing a pink sand-like material which they obtained from Pozzuloli with their normal lime-based concretes they obtained a far stronger material. The pink sand turned out to be fine volcanic ash and they had inadvertently produced the first 'pozzolanic' cement. Pozzolana is anysiliceous or siliceous and aluminous material which possesses little or no cementitious value in itself but will, if finely divided and mixed with water, chemically react with calcium hydroxide to form compounds with cementitious properties.
The secret of concrete production was lost for many years until in 1756, British engineer, John Smeaton made the first modern concrete (hydraulic cement) by adding pebbles as a coarse aggregate and mixing powered brick into cement. In 1824, English inventor, Joseph Aspdin invented Portland Cement, which has remained the dominant cement used in concrete production. Joseph Aspdin created the first true manufactured cement by burning ground limestone and clay together. The burning process changed the chemical properties of the materials and created a stronger cement than just using plain crushed limestone would produce.
Concrete is the most widely used construction material in the world and with a 9000-year history it has played a major part in shaping modern civilization.
Modern concrete was developed after the discovery of Portland cement. First patented in 1824 but not developed in its present form until 1845 when higher kiln temperatures were achieved, Portland cement made new forms of construction possible.
Despite these advances attempts to supply the building trade with ready mixed concrete on-site floundered until the late 1920's when delivery trucks were fitted with a drum that agitated the concrete while on the move. In the UK, the first Readymix operation was set up in 1930 and by the 1960's a successful national network of concrete plants was firmly established.
Today, Readymix concrete comprises a mix of aggregates, cement, water and a variety of admixtures.