Roman Concrete

“The benefits of hot mixing are twofold,” Masic says. “First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction.”

Roman concrete was (or I guess, still is) self-healing. The compound contains small calcium clusters which react to pressure and water. If a crack starts to form, these clusters react and fill the crack as it tries to start.

Riddle solved: Why was Roman concrete so durable? | MIT News | Massachusetts Institute of Technology