Quicklime: Rome’s construction secret

[guy]

There have been numerous posts (see below) on the use of quicklime in Roman construction. Here is a very informative short video on the topic, explaining Roman concrete’s durability.

Ancient Romans used quicklime (calcium oxide) because it was the essential reactive binder that made their mortars and concretes harden into durable, stone‑like masses. When quicklime was produced by heating limestone and then combined with water, it transformed into calcium hydroxide, which could then react with volcanic ash to form the calcium‑aluminum‑silicate hydrates that gave Roman concrete its strength and centuries-old longevity.

Recent analyses of Pompeian construction sites show that Romans often used hot mixing, adding dry quicklime directly to ash and aggregate (the solid, inert material—such as stones, gravel, sand, crushed brick) before hydration. 

This produced intense localized heat and left behind lime clasts (the bright white, calcium‑rich chunks of partially reacted quicklime embedded throughout ancient Roman concrete) that later dissolved and recrystallized, effectively “self‑healing” cracks in the structure over centuries. These white clasts can be seen in the video.
 

 

 

 

https://www.scientificamerican.com/article/pompeii-house-frozen-mid-renovation-reveals-secrets-of-roman-cement/

 

An earlier short video explaining the Pantheon’s durability:

 

Edited 2 hours ago by guy