Structures such as the Pantheon and Trajan’s Markets in Rome are testament to the strength that the mineralization brings to the concrete, but it was a mystery how structures in the sea survive the constant onslaught of waves.
Scientists now discovered that when saltwater mixes with the volcanic ash and lime used by Roman builders, it leads to the growth of interlocking minerals, which bring a virtually impenetrable cohesion to concrete. Prof Marie Jackson, a geology and geophysics research Professor at the University of Utah who led the study.
Roman engineers made concrete by mixing volcanic ash with lime and seawater to make a mortar, and then added chunks of volcanic rock.
For the new study researchers studied cores of concrete from the ancient Roman pier, Portus Cosanus in Orbetello, Italy using high-powered light beam x-rays and discovered the minerals had grown into the cracks caused by tidal erosion, proving that the saltwater reaction continues even after the concrete has set. In contrast most modern concrete is a mix of Portland cement – limestone, sandstone, ash, chalk, iron, and clay, among other ingredients, heated to form a glassy material that is finely ground – mixed with sand or crushed stone that are not intended to chemically react, and so do not cause mineralization when mixed with saltwater.
If the research team succeeds, it will allow builders to construct sea defences, which last for centuries while also being beneficial for the planet. The research was published in the journal American Mineralogist.
Image source: unews.utah.edu