The Romans’ self-healing concrete

One of the secrets to the success of Rome: self-healing concrete:

Photo by Life Of Pix on

Now, an international team has discovered ancient concrete-manufacturing techniques that incorporated several key “self-healing” properties. For years, researchers believed the key to the ancient concrete’s durability was one ingredient: pozzolanic material, such as volcanic ash from the area of Pozzuoli, on the Bay of Naples…

Historians say this specific kind of ash was shipped all across the Roman empire for use in construction projects, being described as a key ingredient for concrete at the time. After closer examination, these ancient samples also contain small, distinctive, millimeter-scale bright white mineral features. They were common component of Roman concretes. The white chunks — often called “lime clasts” — come from lime, another key ingredient in ancient concrete mix.

Masic adds that, during the hot mixing process, lime clasts develop a characteristically brittle nanoparticulate architecture. This creates an easily fractured and reactive calcium source, which could provide a “critical” self-healing ability for building materials. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts.

Prof. Masic explains that the material can then react with water, creating a calcium-saturated solution. It then recrystallizes as calcium carbonate and quickly fills the crack, or reacts with pozzolanic materials to further strengthen the material.

What I often wonder about inventions and techniques of the ancient world is how exactly they came about. How did Romans discover that a particular component – pozzolanic material – made concrete better in the long-term? I would guess there is evidence to suggest when this emerged and how it was dispersed but we may not know exactly how this formula developed.

If this could be incorporated into modern materials, could this make concrete even more important? I remember reading about the importance of concrete in How the World Really Works. Could this mean roads that do not need to be repaired as often, buildings that last longer, and numerous other applications?

This is also a reminder that infrastructure mattered for ancient empires and continues to matter today for modern everyday life. Even small improvements to basic materials or processes could have a tremendous effect given the scale and speed of today’s world.

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