Roman Concrete's Longevity Traced to a Second Chemistry: Carbonation

Roman structures routinely survive two millennia while modern concrete tends to degrade within a century, and researchers have long credited the pozzolanic reaction — volcanic ash reacting with lime and water — for that durability. A new study in Science Advances argues that a second process, carbonation, deserves equal billing. The team sampled untouched concrete from beneath a toilet seat at Hadrian’s Villa near Rome, a 1,900-year-old latrine chosen precisely because nobody ever restored it, leaving the material as an undisturbed long-term experiment.

Microscopy, X-ray scans, and chemical analysis confirmed the expected ash-lime-water signature, but the primary binding agent in the sample’s pores and fractures turned out to be calcite. As atmospheric carbon dioxide reacts with calcium compounds in the concrete, it forms calcium carbonate that fills micro-cracks and pores, letting the structure effectively self-heal and strengthen as it ages. The finding builds on 2023 research showing Roman concrete could repair cracks via calcium-rich deposits from quicklime, and reframes carbonates as a dynamic, central mechanism rather than a marginal side effect.

The practical stakes are environmental. Cement production accounts for roughly 8 percent of global CO2 emissions, and with about half of the buildings expected by 2050 not yet built, the researchers see reverse-engineering Roman techniques as a path to more durable, lower-carbon construction materials.