“Many ancient civilizations came up with lime-based cementlike materials to use as mortar in construction, from the gypsum-based plaster used on the pyramids in Egypt to sticky rice/lime mortar employed in parts of the Great Wall of China, but it was the Greeks and Romans who got lucky by adding locally abundant volcanic ash to their cement mix. This formula resulted in a mortar that not only set up quickly and with great strength but could also harden under water and then survive 2,000 years of crashing seas, as the seawall in Italy’s Pozzuoli Bay has. When the Romans mixed in bits of brick and gravel, they got opus caementicium, which we now know as concrete from the Latin, concretus, which means “to grow together.” Ever visited the Pantheon in Rome? That amazing freestanding dome with a 142-foot diameter is made of the stuff. Unreinforced. It has survived 1,890 years and multiple earthquakes with little or no maintenance. So why can’t our roads and bridges survive a tiny fraction as long?
Research just released in February by MIT, Georgetown University, the French National Center for Scientific Research, and the Concrete Sustainability Hub aims to provide some answers. For all these millennia, nobody has fully understood the atomic-level crystal grain structure of this miraculous material that upon adding water becomes a paste that can flow into complex forms and then harden into a strong solid in a matter of hours or weeks depending on the formula used.”