There are two thousand years, the Roman builders built walls and huge docks for maritime embarkation. Concrete was used outstripped the empire – and it continues to make lessons for modern engineers, scientists say.
A lot of structures simmering off the Italian coast may seem less impressive than a gladiatorial coliseum. But underwater, the wonder is in the material.
Port of concrete, a mixture of volcanic ash and quicklime, has been resisted the sea for two millennia and counted. On the other hand, it is stronger than when mixed.
Roman things are “an extraordinarily rich material in terms of scientific opportunities,” said Philip Brune, a researcher at DuPont Pioneer who studied the engineering properties of Roman monuments. “This is the most sustainable building material in human history, and I say it as an engineer not to be a hyperbole.”
The mystery was why the old hardware lasted. “Archaeologists say they have the recipe,” said Marie Jackson, an expert on ancient Roman concrete and the University of Utah.
(Pliny the Elder wrote an ode to the concrete “as soon as it comes into contact with the waves of the sea and submerges, it becomes a mass of stone, impenetrable to the waves”).
But this is not the whole picture: it is one thing to gather the ingredients, another to learn how to bake the cake.
To that end, Jackson and his colleagues have studied the microscopic structures of concrete samples, extracted from dikes and pillars in the context of a project called Study of the Roman Maritime Concrete. “This rocklike concrete is in many ways like volcanic deposits in underwater environments,” Jackson said.
When modern concrete is designed to ignore the environment, kiss concrete Roman. As scientists indicate in a study published Monday in the American mineralogist magazine, Roman concrete is filled with tiny crystal growth. Crystals, such as tiny shield plates, can prevent concrete from fracturing.
Scientists subjected the concrete samples to a battery of advanced imaging and spectroscopic tests. The tests revealed a rare chemical reaction with crystals of tobermorite alumina from another mineral called philipsite.
Brown, who did not participate in the study, called the work a “significant achievement.” He compared it to scientists who are bitten into a mysterious flavor of the cake and determined that the baker uses black chocolate made from organic origin.
In this case, the key ingredient turned out to be seawater. As the sea water has leaked into small cracks in Roman concrete, Jackson said he reacts with it naturally found in philipsite volcanic rock and crystals created from tobermorite.
“Tobermorite aluminum is very difficult to produce,” she said, and requires very high temperatures to synthesize small quantities. Shoring the ancient Romans could lead to better production of tobermorite, which is valued for its industrial applications, he noted.