After the fall of the Roman Empire in 476 A.D., the art of making cement was lost. It was 13 centuries later that John Smeaton pioneered the use of hydraulic concrete.
The British engineer was commissioned by the parliament to rebuild the Eddystone Lighthouse situated off the coast of Cornwall, England. For this project, he started looking for a building material that would not be affected by any sorts of weather conditions.
He had carried out his research into various materials which could withstand the sea until he discovered a mix of lime, clay and crushed slag from iron-making. This conglomerate could form a quick-drying material known as hydraulic concrete when using pebbles and powdered brick as aggregate. This is generally regarded as the first use of modern concrete in engineering.
Hydraulic lime (HL) is a general term for varieties of lime (calcium oxide) or slaked lime (calcium hydroxide), used to make lime mortar which set through hydration. These contrast with varieties of air lime, the other common types of lime mortar, which set through carbonation (re-absorbing carbon dioxide (CO2) from the air).
Until the advent of artificial cements and especially the advent of Portland cement, lime was used almost exclusively and it has never entirely disappeared. Even if the term ‘hydraulic lime’ covers materials which vary in properties such as setting times and strength development, they all have main common features:
- ability to set under water;
- great workability;
- low shrinkage;
- salt and frost resistance;
- adequate compressive and flexural strengths;