Why modern mortar crumbles, but Roman concrete lasts millennia

Modern concrete –  used in everything from roads to buildings to bridges – could be demolished within 50 years. But thousands of years after Roman Empire crumbled to dust, its  concrete structure are still standing. Now, scientists have finally figured out  why: a special ingredient make cement grow stronger – not weaker – over time. Scientists have begun their search with an ancient recipe of mortar, laid down by Roman engineer Marcus Vitruvivus in 30 C.C.E.

It called for a concoction of volcanic ash, lime and seawater, mixed together with volcanic rocks and spread into wooden molds that were then immersed in more seawater. History contains many references to the durability of Roman concrete, including this cryptic note written in 79 BCE, depicting concrete exposed into seawater as: “a single stone mass, impregnable to the waves and everyday stronger”. To learn more, researchers surveyed drilled cores of a Roman harbor from Pozzuoli Bay near Naples, Italy. When they analyzed it, they found that sea water dissolved components of volcano ash, allowing new biding minerals to grow.

Within a decade, a very rare  hydrothermal mineral  is called tobermorite alumine formed in concrete. Al-tobermorite, long known to give Roman concrete its strength, can be made in laboratory, but it is very hard to incorporate it in concrete. However, researchers have found that, when seawater percolate into a cement matrix, it will react with volcanic ash and crystals to form Al-tobermortite and a porous mineral   dubbed phillipsite. So, will you be seeing stronger piers and breakwaters anytime soon? Because, both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement.

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