Some of the buildings built in ancient Rome 2,000 years ago still defy decay to this day. A recent study has now revealed the secret behind the longevity of ancient Roman concrete: Contrary to previous assumptions, the Romans heated their concrete while mixing it. The resulting chemical composition of Roman concrete gave it self-healing abilities.
If water penetrates the concrete through a crack, chemical processes take place that strengthen the material and fill the cracks, material scientists report Friday in the journal “Material Science”. For the study, the researchers took samples from a 2,000-year-old Roman concrete wall in Priverno and examined them with special X-ray equipment. The analyzes showed that the Romans had mixed the concrete hot and used so-called burnt lime. This created lime lumps with a large surface area in the concrete.
Mixed with volcanic rock
According to the researchers, these clumps of lime serve as a source of calcium, which fills voids that form when it comes into contact with water. In addition, penetrating water causes the lime to react with another special component of Roman concrete: the pozzolana. In previous studies, the scientists found that this volcanic rock was mixed with concrete in ancient Rome.
Self healing for thousands of years
As the limestone reacts with the pozzolana, crystalline structures are formed that become progressively harder over time. This strengthens the concrete. Because the calcium in the lime lumps is stored until it comes into contact with water through cracks, the self-healing ability of Roman concrete lasts for thousands of years.
Researchers develop new cement mixture
Inspired by the concrete of ancient Rome, the researchers developed a new cement mixture. “Their self-healing potential paves the way for more durable, resilient and sustainable concrete designs,” the authors wrote in the study.
Source: Krone
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