Discovery at Pompeii reveals secret of Roman self-healing concrete

Researchers from the Massachusetts Institute of Technology have published in Nature Communications details of how the Romans made self-healing concrete.

In Pompeii, archaeologists made a rare discovery of an incomplete construction site whose building process was frozen in time by the eruption of the Mount Vesuvius volcano in 79CE. This provided an insight into how the Roman builders made concrete.

Modern concrete is mixed wet, whilst the Roman builders used a hot-mix process, which started with a dry mix of quicklime and volcanic ash with water added afterwards. This process generated high temperatures that created lime clasts, which are the secret to the long life of Roman concrete.

When cracks appear in the hardened concrete, water penetrates them and dissolves calcium in the clasts. The calcium recrystallises and transforms into calcite or aragonite, which plugs the cracks and prevents further decay. This self-healing process is why Roman structures like the Pantheon and aqueducts still stand after two thousand years.

Pompeii is an example of using high-quality concrete for building construction. However, researchers have found that good-quality concrete was not universally adopted by Roman builders. Poor quality concrete was sometimes used, which caused building failures.

Modern self-repair concrete uses bacteria, microcapsules with healing agents, or vascular networks to make sustainable, durable solutions for low-maintenance concrete flooring, columns and other structures designed to be strong and last a long time. This type of concrete is Ideal for inaccessible areas like tunnels, bridges, and underwater structures.