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 only a range of cementititous compositions but also a methodology for particle size 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 concrete made using pure OPC. In that way, concrete made using Roman Cement™ more closely resembles ancient Roman concrete than concrete made using pure OPC.
Roman Cement™ compositions containing mixtures of particle size optimized Portland cement and fly ash have been tested extensively since May 2009. Binary cement-pozzolan blends containing 20% and 35% SCM (80% and 65% Portland cement), respectively, have been shown by rigorous NIST testing (according to ASTM C-109) to have compressive strengths at 1-56 days that are equal or greater than the strength of a control cement containing 100% OPC at the same water to cement ratio (w/c). Ternary cement-pozzolan blends containing 75% SCM and 25% Portland cement were shown by a university test lab to have similar compressive strength at 1-28 days as 100% OPC and significantly greater compressive strength than an interground blend of 75% SCM and 25% OPC. The data prove that the underlying science behind particle size optimization of the Portland Cement and SCM fractions is sound and can yield cement-pozzolan blends that perform the same or better than 100% OPC.