Image Credit: Archaeological Park of Pompeii

Pompeii Sheds New Light on the Secrets of Roman Concrete

A newly discovered construction site in Pompeii has given researchers unprecedented evidence about how the Romans produced their extraordinarily durable concrete — confirming that builders used a “hot-mixing” technique that helped structures survive earthquakes, eruptions, and centuries of weathering.
Roman concrete famously underpinned the empire’s architectural achievements, from aqueducts to massive domes. In recent years, MIT’s Admir Masic and colleagues proposed that its longevity came from mixing quicklime with volcanic ash in a dry state, then adding water. The heat generated by this reaction created small lime fragments that later dissolved into cracks, giving the material self-healing abilities.
But this idea conflicted with the writings of Vitruvius, who described adding water to lime first. The debate persisted — until archaeologists uncovered an active construction zone frozen in time by the eruption of Vesuvius in 79 CE.
The site contained raw material piles, tools, and walls mid-construction, allowing researchers to sample concrete at every stage. The evidence was conclusive: workers mixed dry quicklime and volcanic ash before adding water, exactly as the hot-mixing model predicts. Intact quicklime fragments were even found in the raw piles.
Chemical and isotope studies also revealed a diverse set of reactive volcanic minerals, including pumice, that continued strengthening the concrete long after it set. These dynamic processes created a cement that could repair itself for thousands of years.
For Masic, the Pompeii site was like opening a time capsule: “You felt as if the Roman builders could walk back in at any moment,” he said. The findings also help explain how Roman engineering achieved its legendary durability — a lesson modern researchers hope to apply in developing longer-lasting, more sustainable concretes.
The study, published in Nature Communications, suggests Vitruvius may have been misunderstood and that his references to heat align with the newly confirmed technique. The work is part of a broader effort to translate Roman knowledge into modern engineering without fully replicating ancient methods.

Published on: 09-12-2025

Edited by: Abdulmnam Samakie

Source: Massachusetts Institute of Technology