Roman structures built more than 1500 years ago still stand strong – in fact, stronger than ever before if the new findings have any credibility. In contrast, the modern method of making concrete appear to be way inferior as our structures, especially those that are in contact with sea water such as harbors, piers, and breakwaters, begin to disintegrate in less than 50 years.
The Roman author, Pliny the Elder wrote in his Naturalis Historia around 79 C.E, that the concrete structures in harbors “become a single stone mass, impregnable to the waves, and every day stronger,” despite constant exposure to the elements and endless assault by saltwater sea waves.
So, how did the Romans make their super concrete? Scientific analyses of material taken from Roman made structures show that their recipe was a blend of volcanic ash, lime (calcium oxide), chunks of volcanic rock and seawater. Their piers, breakwaters, and harbors built with this material have withstood the ravages of the elements and time – in fact, time and seawater have behaved as their allies making them stronger over the centuries.
Why, then, have seawater and the passage of time been detrimental to our structures and a friend to theirs? Scientists attribute this to the way seawater reacts with the volcanic ash and rocks present in the cement of the Roman era to create new minerals that keep reinforcing the concrete as time goes by.
That same seawater, on the other hand, has proved to be our nemesis, corroding the steel in our concrete and damaging the structures from the inside out in about a fraction of the time and wave-battering that the Roman structures have withstood. Ironically, the steel in modern day concrete is there for reinforcement purposes and not for structures to implode on.
Marie Jackson, a geologist at the University of Utah and co-author of a study in Roman structures said: “They spent a tremendous amount of work [on developing] this – they were very, very intelligent people.”
The latest findings published in the journal American Mineralogist claim to have largely worked out the winning formula of the Romans. Marie Jackson and co-researchers explain how they were able to achieve that by analyzing concrete cores from Roman piers, breakwaters, and harbors.
Earlier studies had confirmed the presence of lime particles within the cores which also showed traces of the rare and difficult-to-make mineral, aluminous tobermorite.
According to Jackson, the aluminous tobermorite formation goes back to the early history of the concrete when the ingredients of the concrete mix – lime, seawater, and volcanic ash – chemically reacted with each other generating heat and the resultant mineral.
The latest studies, however, have led to another more significant discovery. “I went back to the concrete and found abundant tobermorite growing through the fabric of the concrete, often in association with phillipsite,” she said.
This happened over a period of time as seawater seeped into the porous concrete, dissolving the volcanic crystals and glasses causing the formation of crystalline aluminous tobermorite and phillipsite – the two main benefactors that helped reinforce the concrete and prevented cracks from expanding dangerously.
The Portland cement used in modern constructions is not supposed to undergo any sort of chemical reaction after it sets. On the contrary, any change or reaction to the hardened concrete means the material is faulty and may cause damage.
“I think [the research] opens up a completely new perspective for how concrete can be made – that what we consider corrosion processes can actually produce extremely beneficial mineral cement and lead to continued resilience, in fact, enhanced perhaps resilience over time,” observes Jackson.
If/when the findings do lead to the development of the exact Roman formula, and if it is feasible in the modern era considering the long curing time it needs – reportedly – we are looking at a revolutionary discovery. It will radically change the way we build today.
However, the researchers say that it could be years before the exact Roman combination is worked out.