The Romans used a pure pozzolanic cement made from volcanic ash pozzolana and quicklime. Portland cement was not used by the Romans because it was not invented until modern times. Roman concrete has withstood the test of time, with the Pantheon and aqueducts still standing after 2000 years. However, pure pozzolanic cement develops strength too slowly to be suitable in modern building practices and is mainly used to repair ruins.
Roman Cement™, as described herein, is not pure pozzolanic cement but a hybrid cementitious material that includes Portland cement and one or more SCMs. Roman Cement™ is not so much a cement composition as it is a methodology for optimizing Portland cement and SCMs for use with each other. This permits high SCM substitution levels while still providing high early strength, as required by modern building practices and codes.
The Portland cement fraction is designed to hydrate rapidly and provide high early strength. The SCM fraction reacts with and chemically stabilizes excess lime released during hydration of Portland cement to yield concrete that is more chemically balanced, durable, and resistant to chemical attack than pure OPC. In that way, concrete made using Roman Cement™ more closely resembles ancient Roman concrete than concrete made using pure OPC.