“Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability.”
The Pantheon’s dome has stood since 128 C.E., while modern concrete crumbles in decades. MIT’s team says the Romans hot-mixed quicklime, and the white lime chunks everyone wrote off as sloppiness seal cracks when water gets in. Cracked test samples healed within two weeks. Cement is about 8 percent of global greenhouse emissions, and for decades engineers assumed the Romans were the ones being careless.