Science has explained why Roman concrete lasted for nearly 2,000 years.

(Dan Tri Newspaper) - A structure built nearly 2,000 years ago provides further evidence of the secret behind the durability of ancient Roman concrete, which has withstood the test of time.

Prior to the supposed collapse of Pompeii in 79 AD, archaeologists discovered a perfectly preserved, "frozen" structure of Roman construction techniques beneath the volcanic ash that buried it.

The dome of the Pantheon in Rome currently holds the record for being the largest unreinforced concrete structure still in existence in the world (Photo: Getty Images).

Here, they found neatly stacked piles of materials, including the components used to mix the famously durable concrete, behind monuments like the Pantheon, where the massive unreinforced concrete dome has stood for millennia.

"Hot mixing" technology reveals the reason behind the extraordinary durability of Roman concrete.

Recently, a completely new analysis has revealed that the secret lies in a technique that materials scientist Admir Masic of the Massachusetts Institute of Technology (MIT) calls "hot-mixing."

This method involves directly mixing the concrete components, including a pozzolanic volcanic ash mixture with quicklime, which reacts with water to generate a large amount of heat within the mixture.

When the entire concrete is heated to high temperatures, it creates chemical reactions that would not occur with lime alone, forming compounds characteristic of high-temperature conditions.

Some building materials found at Pompeii (Photo: Pompeii Archaeological Park).

However, the increased temperature significantly shortens the setting and curing time because all reactions occur faster, allowing for high-speed construction.

In particular, the remaining quicklime particles in the mixture gave Roman concrete the ability to "self-heal" cracks over time.

When concrete cracks, the cracks tend to spread to the lime particles, which have a larger surface area than other matrix particles.

When water penetrates the cracks, it reacts with the lime to create a calcium-rich solution, which, upon drying, forms calcium carbonate, sealing the crack and preventing it from spreading.

"This material has both historical and scientific value when properly deciphered. It has the ability to self-repair over thousands of years, functioning flexibly and durably."

"Roman concrete withstood earthquakes, volcanic eruptions, survived underwater, and resisted harsh environmental erosion," Masic said in the journal Nature Communications.

Although the hot mixing technique helped explain much of the mystery surrounding the durability of Roman concrete, this finding does not match the actual formula described in the architect Vitruvius's treatise De architectura.

A wall at the site in Pompeii and a compositional analysis is overlaid on the right. (Photo: Pompeii Archaeological Park)

According to Vitruvius's description, lime had to be slaked with water before being mixed with pozzolan; this discrepancy between ancient records and archaeological evidence has baffled scientists.

The works of Vitruvius are considered the most comprehensive source of information on Roman architecture and opus caementicium (Roman concrete) technology, but the specimens are revealing a completely different story.

Under the microscope, the mortar samples in the wall showed clear signs of hot mixing, cracked lime fragments, a calcium-rich reactive layer spreading into volcanic ash particles, and tiny calcite and aragonite crystals formed in the cavities of the pumice.

Raman spectroscopy confirmed mineral alteration, while isotopic analysis revealed carbonation processes occurring over time.

Applications of self-healing concrete in modern times.

According to Masic, the results show that the Romans prepared the binder by taking quicklime, grinding it to a certain size, mixing it dry with volcanic ash, and then adding water to create the binding agent.

According to researchers, this knowledge could be applied to modern concrete production, demonstrating the wisdom of our ancestors.

Modern concrete is one of the most popular building materials in the world, but it is not very durable and easily deteriorates after only a few decades.

The manufacturing process also harms the environment, consumes resources, and emits greenhouse gases. Improving the durability of concrete could help make it more sustainable.

"The way the voids in volcanic material are filled through recrystallization is something amazing that we want to replicate. We want materials that can self-heal," Masic shared.

Source: https://dantri.com.vn/khoa-hoc/khoa-hoc-da-ly-giai-vi-sao-be-tong-la-ma-ben-vung-gan-2000-nam-20251212000408505.htm