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A team of scientists from the Massachusetts Institute of Technology explored why ancient Roman concrete lasted so long. Their work, as reported in Science Advances, sheds light on a durable construction material that has puzzled engineers for generations.

The researchers point to a heating method called hot mixing as a key factor. In this approach, the concrete mixture is heated to high temperatures, triggering a cascade of chemical reactions within the cement matrix. The elevated heat drives processes that would not occur under normal curing conditions, altering the microstructure in ways that boost longevity.

This method appears to enable the concrete to self-heal over time. During hot mixing, lime particles evolve into a brittle, nanoparticle framework that can develop microcracks. When moisture enters these microcracks, calcium from the framework dissolves and forms a solution that rapidly seals the openings. Earlier explanations had suggested that poor mixing created lime-rich patches, but the new findings emphasize a chemical pathway where the heat-induced structure itself becomes a reservoir for healing agents when water is present.