archeology

Ancient Roman builders were “hot-mixing,” which means that they dumped volcanic ash and powdered quicklime together dry, then added water later, triggering a chemical reaction that cooked the mixture from the inside.

the heat unlocked chemical pathways impossible with the standard method of “slaking” lime first — “slaking” being the process where the lime is first mixed with water before it’s poured out.

The hot-mixing method has faster setting times, and most importantly, creates something called a lime clast, which are little white chunks of minerals common in ancient Roman concrete that was at one point thought to be a sign of poor mixing but is now being viewed as the key to its absurd durability. These lime clasts effectively give ancient Roman concrete a self-healing ability that can keep it going for generations.

Very interesting!