Here's what you should know about Roman concrete, the strongest concrete on Earth. What is Roman concrete? Roman concrete, or opus caementicium, was developed over 2,000 years ago. It was used in a variety of structures, many of which still survive today.

The production of crystallisation leads to more and more calcium silicate hydrate forming and thickening until the water molecules' path is blocked and there are no longer any empty, weak spaces in the mixture. This results in a very low porous, and therefore very strong, structure.

Suspended slabs, beams, and girders (as often found in bridges) require 3,500 to 5,000 psi. Traditional concrete walls and columns tend to range from 3,000 to 5,000 psi, while 4,000 to 5,000 psi is needed for pavement.