The word concrete comes from the Latin ‘concretus’ meaning grown together or compounded. However, the earliest concrete so far discovered, predates the Romans by many centuries and is thought to date from around 7000BC.
Very early concretes often consisted of a mixture of lime (quicklime) with sand, stones and water. The Romans discovered that if a fine volcanic ash found near Pozzuoli was mixed with the lime, a much stronger concrete could be produced, which set both under water and in air. This ash was what we today would call a pozzolana. Roman concrete (as seen in the core of Hadrian’s wall) was made by pouring the liquid mortar over a layer of broken stones, allowing it to harden before repeating the process. The Romans even experimented with reinforcing rods made from bronze, but this failed due to the widely differing thermal expansion properties of the bronze rods and the surrounding concrete
Whilst the Saxons and Normans possessed some knowledge of concrete making, it was not as widely used as in Roman times. There was a revival of interest in concrete in the 18th century, when engineers and scientists began to experiment with new cements culminating in the development of Portland cement by Joseph Aspdin and later by Isaac Johnson.