Concrete, one of the dirtiest substances ever concocted, could help save the planet | Aleksei Zotov/UCG/Universal Images Group via Getty Images No, Rome was not built in a day, but it was built at breathtaking speed, its temples, amphitheaters, and aqueducts rising with the help of a magical blend of volcanic ash and lime. Today, that miraculous mortar has a less than enchanting name: concrete. “Romans lived through a true architectural revolution, and at the foundation of this revolution, literally, was a concrete discovery,” said Admir Masic, a materials science professor at MIT who...