|Two thousand years ago, Roman builders constructed vast seawalls and harbour piers. The concrete they used outlasted the empire — and still holds lessons for modern engineers. Half-sunken structures off the Italian coast might not sound impressive but the marvel is in the material. The harbour concrete, a mixture of volcanic ash and quicklime, has withstood the sea for two millennia and counting. It is even stronger than when it was first mixed.|
|Scientists subjected the concrete samples to a battery of advanced imaging techniques and spectroscopic tests. The tests revealed a rare chemical reaction, with aluminous tobermorite crystals growing out of another mineral called phillipsite.|
The key ingredient proved to be seawater. As seawater percolated within the tiny cracks in the Roman concrete it reacted with the phillipsite naturally found in the volcanic rock and created the tobermorite crystals.
Microscopic image shows the lumpy calcium-aluminum-silicate-hydrate (C-A-S-H) binder material that forms when volcanic ash, lime, and seawater mix.
Caesarea Concrete Bath
|The Romans mined a specific type of volcanic ash from a quarry in Italy. Modern seawalls require steel reinforcement. The Romans didn’t use steel. Their reactive concrete was more than strong enough on its own.|