Why Roman concrete can heal its own cracks after two thousand years

No rebar. Two thousand years. Modern concrete cracks, leaks and falls apart, yet Rome's is still here. Crack it open and you find weird white chunks everywhere, which researchers long wrote off as sloppy mixing. In 2023 an MIT team found the clue: quicklime, mixed into a scorching-hot batch. When a crack cuts through one of those lime chunks, water dissolves calcium out and fresh crystals fill the gap. In their test, the quicklime block sealed its crack in two weeks; the control block kept leaking. Sources: • MIT News — https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106 • Seymour et al. 2023 — https://www.science.org/doi/10.1126/sciadv.add1602 • EurekAlert — https://www.eurekalert.org/news-releases/778694