[kach22i]

Mystery of why Roman buildings have survived so long has been unraveled, scientists say
https://www.cnn.com/style/article/roman-concrete-mystery-ingredient-scn/index.html

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. The researchers said this self-healing potential could pave the way to producing more long-lasting, and thus more sustainable, modern concrete. Such a move would reduce concrete's carbon footprint, which accounts for up to 8% of global greenhouse gas emissions, according to the study.

For many years, researchers had thought that volcanic ash from the area of Pozzuoli, on the Bay of Naples, was what made Roman concrete so strong. This kind of ash was transported across the vast Roman empire to be used in construction, and was described as a key ingredient for concrete in accounts by architects and historians at the time.
Masic said that both components are important, but lime was overlooked in the past.