There is something unusual about Roman sea walls: they last for a very long time. In fact, while modern concrete erodes when exposed to seawater and eventually requires replacement, Roman concrete grows even stronger.
Professor Marie Jackson at the University of Utah investigated the old concrete using imaging techniques called electron microscopy, X-ray micro-diffraction, and Raman spectroscopy. The Romans made concrete out of a mixture of lime and volcanic ash. Jackson and her teammates noticed a rare mineral, aluminium tobermorite, in the ancient concrete. They hypothesized that when water interacts with the concrete heat is produced, which allows the mineral to crystallize and strengthen the structure.
Sean Wei, a recent graduate from Harvard’s Weiss Institute, confirms that materials often change with exposure to the environment, as proposed in Professor Jackson’s research. He suggests that the hypothesis could be tested by comparing the mechanical strength of an ash and lime mixture exposed to salt water to an identical mixture not exposed to the salt trigger.
These findings are relevant for modern construction because current methods of concrete production are resource and energy intensive, composing 5% of the world’s carbon emissions. Decreasing the need to replace degrading concrete could alleviate environmental effects. Professor Jackson has proposed that the ancient method could be used in the construction of the Swansea lagoon, a large man-made body of water designed to provide hydropower, which is being built in the United Kingdom.
Acknowledgments: Many Thanks to Sean Wei, a recently graduated graduate student from Harvard SEAS
Managing Correspondent: Emily Kerr