|A study in the journal Science Advances found that calcium-rich mineral deposits called “lime clasts,” commonly found in Roman-era concrete, gave buildings and structures “a previously unrecognized self-healing capability.” The deposits are not found in modern concrete. Such deposits are viewed as impurities by today’s concrete manufacturing standards. Aided by spectroscopic examinations and high-resolution, multiscale imaging and chemical mapping, researchers showed how lime clasts were used by Roman concrete-makers. The team produced samples of “hot-mixed concrete” using Roman and modern methods. After the materials hardened, scientists cracked the samples and ran water through the cracks.|
Sunken structures off the Italian coast doesn't sound impressive but the marvel is in the material.
|Roman concrete, 'opus caementicium', was a material used in construction until the fading of the Roman Empire. Roman concrete was based on a hydraulic-setting cement. Roman builders constructed seawalls and harbour piers that outlasted the empire. Tests revealed a rare chemical reaction, with aluminous tobermorite crystals growing out of another mineral called phillipsite.|
The concrete, a mixture of volcanic ash and quicklime, has withstood the sea for two millennia.
|The key ingredient proved to be seawater. As seawater percolated in the cracks in the Roman concrete it reacted with phillipsite found in the volcanic rock and created 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. It is even stronger than when it was first mixed.
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 strong enough.|