Scientists have unlocked the secret of what's allowed the Roman Empire's mortar to endure 2,000 years of earthquakes and floods while modern concrete can begin to crumble in as few as 50 years.
An ingredient makes Roman marine concrete actually grow stronger, a team of researchers has found, Science Magazine reported.
Writing in the journal American Mineralogist, the scientists began with the ancient Roman recipe for mortar, laid down by engineer Marcus Vitruvius in 30 BCE (Before Common Era), that called for a blend of volcanic ash, lime, and seawater, mixed together with volcanic rocks and spread into wooden molds that were immersed in more sea water.
Science Magazine noted the Roman mortar's durability has been well-documented; a note from 79 BCE described concrete exposed to seawater as "a single stone mass, impregnable to the waves and everyday stronger."
But researchers, hoping to discover why that's so, studied drilled cores of a Roman harbor from Pozzuoli Bay near Naples, Italy, Science Magazine reported. And when they analyzed it, they found the seawater had dissolved components of the volcanic ash, allowing new binding minerals to grow.
Within a decade, a very rare hydrothermal mineral called aluminum tobermorite (Al-tobermorite) had formed in the concrete. Although Al-tobermorite – long known to give Roman concrete its strength – can be made in the lab, it's difficult to incorporate into concrete.
The researchers, however, writing in American Mineralogist, found that when seawater percolates through a cement matrix, it reacts with volcanic ash and crystals to form Al-tobermite and a porous mineral called phillipsite.
"Because both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement," Science Magazine reported.
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