‘Concrete’ has had an illustrious past. Originally it was a term used by the philosophers to distinguish a real substance from an abstract one, then a school of poetry, then a type of electronic French music, and now just pavement material.
The word ‘concrete’ has only been used to mean gravel mixed with water and cement since about 1815.
Concrete is made of bits of hard material (aggregate), like sand or gravel, bonded together by mortar.
The ancient Assyrians and Babylonians used a form of concrete, with clay as the bonding substance. The Egyptians took it a step further, using lime and gypsum as binders.
The Romans discovered ‘pozzolana’, a form of cement made by grinding volcanic slag with powdered lime. Concrete made of pozzolana was extraordinarily strong and the Romans used it to construct buildings with spans of 75 feet or more. The Pantheon at Rome couldn’t have been built without it: the dome is solid concrete.
Modern concrete can be mixed and poured in quantity, but early Roman cement dried too quickly and had to be laid one course at at time. But about the time of the birth of Christ a slow drying mortar was discovered. This may have contributed to the burst of public building in Rome at the time of Augustus.
As the Roman Empire disintegrated, knowledge of concrete was forgotten and the great buildings of the late empire, such as St Sophia in Constantinople, were brick-built.