Ancient Roman Concrete Was Self-Healing Thanks to Volcanic Ash
Romans used volcanic ash in their concrete, creating a material that actually gets stronger over time and can heal its own cracks when exposed to seawater.
About this fact
Ancient Roman concrete has puzzled scientists for centuries because structures like the Pantheon and harbor docks have grown stronger over 2,000 years while modern concrete crumbles in decades. The secret was their use of volcanic ash (pozzolanfrom Pozzuoli) mixed with lime and seawater. When seawater enters tiny cracks in Roman concrete, it reacts with the volcanic ash to create new calcium-aluminum-silicate-hydrate compounds that actually fill and seal the cracks. This process continues indefinitely, making the concrete self-healing. Additionally, the volcanic ash creates a more durable matrix than modern Portland cement. Recent studies by MIT have shown that Roman concrete continues to evolve chemically, becoming stronger and more crack-resistant over time. Modern engineers are now trying to recreate this ancient recipe to build more sustainable infrastructure.