For nearly 2,000 years, Rome’s Pantheon has stood strong thanks to its unique pozzolanic concrete mix, which included volcanic ash and lime. However, new research suggests that Roman builders used a different technique called hot mixing, adding quicklime directly to the mix to create an even stronger and self-healing material.
A team of scientists from MIT discovered this secret by analyzing ancient samples of 2,000-year-old Roman concrete from Italy. They found tiny white chunks of lime embedded in the mix, which had previously been thought to be evidence of poor mixing. But materials scientist Admir Masic wasn’t convinced.
Masic and his team conducted advanced tests that revealed the Romans were using hot mixing, generating extreme heat that created high-temperature compounds and gave the concrete self-healing properties. This method allowed cracks to spread towards the lime clasts, where they would be sealed by a calcium-rich solution formed when exposed to water.
The research team tested their findings by creating Roman-style concrete using the hot mixing method and comparing it to modern concrete. Their results showed that cracks in the hot-mixed concrete healed completely within two weeks, while control concrete remained cracked. This self-repair mechanism could explain why ancient Roman structures have withstood harsh conditions for centuries.
The discovery of this ancient technique could lead to more sustainable construction methods. Modern concrete is a major contributor to global CO₂ emissions, and a stronger, self-repairing concrete could significantly reduce maintenance costs and increase the lifespan of infrastructure. The MIT team is now working on commercializing their Roman-inspired concrete as an eco-friendly alternative.
Source: https://dailygalaxy.com/2025/02/we-finally-know-the-mystery-behind-romes-millennia-old-concrete-durability