Those white lumps in Roman concrete may be part of a repair system. Researchers found calcium-rich inclusions, tiny features within the concrete, that can help fill small cracks when water enters.

Water can dissolve calcium from the inclusions, which can then form new minerals inside a crack. In tests, researchers deliberately cracked Roman-inspired concrete samples and ran water through them. Cracks in the tested mixture sealed within two weeks; a comparison without quicklime kept leaking.

Concrete with a built-in crack repair system

Roman remains at Privernum beside an elemental map of a concrete fragment — MIT / courtesy of the researchers. Original photograph / elemental map, resized.

Calcium-rich areas shown in red in the original elemental map — MIT / courtesy of the researchers. Original photograph / elemental map, resized.

Original experimental figure: cracked sample, water-flow test and mineral-filled crack — Seymour et al., Science Advances (2023), Figure 5. Original experimental figure; scale bars retained.

Concrete with a built-in crack repair system

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