Opus caementicium exposed in a very characteristic Roman arch. In distinction to modern day concrete constructions, the concrete used in Roman structures was generally protected with brick or stone. The Romans utilised concrete extensively from 300 BC to AD 476.[18] In the Roman Empire, Roman concrete (or opus caementicium) was https://gregoryj7mjg.blogspothub.com/34841238/concrete-reinforced-wall-fundamentals-explained