Ancient Roman concrete has endured for millennia, while modern concrete crumbles within roughly 100 years. Scientists have long attributed this to the pozzolanic reaction, but new research reveals carbonation also plays a crucial role.

Researchers studied a 1,900-year-old latrine at Hadrian's Villa in Tivoli, Italy, where concrete remained undisturbed. Paulo J. M. Monteiro of UC Berkeley explains that "nobody restores a latrine," preserving an unprecedented sample. Analysis showed calcite—formed when atmospheric CO₂ reacts with calcium compounds—as the primary binding agent filling cracks and pores.

This carbonation process allows structures to strengthen and self-heal over time. The findings, published in *Science Advances*, build on a 2023 study by MIT's Admir Masic on quicklime's role. Monteiro hopes unlocking these ancient secrets will yield modern concrete with lower environmental impact, as cement production accounts for 8 percent of global CO₂ emissions.