Roman concrete, also called opus caementicium, was a material used in construction in Ancient Rome. It's unique feature allowed it to become stronger over the centuries, by forming a material known as Aluminum Tobermorite. Sea water reacts with Pozzolana (siliceous-aluminous material) in Volcanic ash to form Aluminum Tobermorite.
- 1:3 ratio of lime to Pozzolanic ash for cement used in regular buildings
- 1:2 ratio of lime to Pozzolanic ash for cement used in sea facing/shoreline buildings/walls
- possibly used sea water instead of regular water
Roman port at Cosa built using this pozzolana-lime method survived for over 2000 years. In contrast, modern concrete when exposed to salt-water/sea-water, deteriorates within decades.