The white chunks previously had been overlooked as evidence of sloppy mixing or poor-quality raw material.Lime clasts and concrete's durabilityConcrete is essentially artificial stone or rock, formed by mixing cement, a binding agent typically made from limestone, water, fine aggregate (sand or finely crushed rock ) and coarse aggregate (gravel or crushed rock)."First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form.To investigate whether the lime clasts were responsible for Roman concrete's apparent ability to repair itself, the team conducted an experiment.Their findings suggest that the lime clasts can dissolve into cracks and recrystallize after exposure to water, healing cracks created by weathering before they spread."