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Roman concrete, in many cases, has proven to be longer-lasting than its modern , which can deteriorate within decades. Now, scientists behind a new study say they have uncovered the mystery ingredient that allowed the Romans to make their construction material so durable and build structures in challenging places such as docks, sewers and earthquake zones.
They found that white chunks in the concrete, referred to as lime clasts, gave the concrete the ability to heal cracks that formed over time. The white chunks previously had been as evidence of sloppy mixing or poor-quality raw material. With further study, the researchers concluded that lime clasts arose because of the use of quicklime (calcium oxide) — the most reactive, and dangerous, dry form of limestone — when mixing the concrete, rather than or in addition to slaked lime. Additional analysis of the concrete showed that the lime clasts formed extreme temperatures expected from the use of quicklime, and "hot mixing" was key to the concrete's durable nature.