More than 2000 years ago, the Roman Empire invented a unique marine concrete that allowed for the construction of enormous, durable structures – even underwater. Incredibly, the exact chemical properties of this concrete mixture have eluded scientists to this day – but now, researchers from the University of Utah believe they may have finally cracked the code. According to the findings in the journal American Mineralogist, the secret lies in the chemical properties of two of the mixture’s components: lime and volcanic ash, which contained a rare mineral known as aluminium tobermorite. When exposed to sea water, the substance would crystallize in the lime while curing. Rather than be eroded by the water, its presence actually gave the material additional strength. Using an electron microscope, X-ray micro-diffraction and Raman spectroscopy, the researchers were able to map the distribution of elements in remaining Roman architectural works. What they found was significant amounts of tobermorite growing through the composition of the concrete, and a related, porous mineral called phillipsite. Through continued exposure to seawater, the scientists predict, the crystal were able to keep growing over time, reinforcing the concrete and preventing cracks from forming.
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