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Ancient Roman cement the best?

Once built a building in ancient Rome you could forget about it. They were meant to last forever and most of them did. A stroll through Rome, the eternal city, is enough to appreciate the efforts of the human kind against the deterioration caused by time.

Why have roman buildings lasted longer than the most recently built ones? The “secret” of the Roman cement durability has finally been discovered, as a team of researchers from Italy and the United States analysed a sample of concrete which dates back to 37 B.C. The sample was taken from a breakwater in Italy’s Pozzuoli Bay, at the northern tip of the Bay of Naples.

The international team of researchers worked at the laboratory of U.C. Berkeley, as well as in Saudi Arabia and Germany and discovered that the Romans made concrete by mixing lime and volcanic rock to form a mortar. Their discovery might now revolution modern architecture.  

To build underwater structures the Romans created an exceptionally strong calcium-aluminum-silicate-hydrate (C-A-S-H) bond.

The secret of the Romans lays in a chemical reaction triggered off by seawater. The Romans packed into wooden forms mortar and volcanic tuff to build underwater. Water molecules hydrated the lime and reacted with the ash to cement everything together.

So what’s the difference from our present day cement? 

Portland cement, (the most common modern concrete blend) used for almost two centuries, wears particularly quickly in seawater, lasting on an average of less than 50 years.

Roman concrete bound better than Portland cement which lacks the lime-volcanic ash combination. Moreover, Roman cement was also more sustainable to produce as the production of Portland cement produces a sizable amount of carbon dioxide, one of the most damaging for the environment. To manufacture Portland cement, carbon is emitted by the burning fuel used to heat a mix of limestone and clays to 1,450 degrees Celsius (2,642 degrees Fahrenheit) as well as by the heated limestone (calcium carbonate) itself.

7 percent of the carbon dioxide that industry puts into the air is generated by the 19 billion tons of Portland cement we use every year on a worldwide scale.

To make their concrete, Romans used much less lime, and made it from limestone baked at 900 degrees Celsius (1,652 degrees Fahrenheit) or lower, a process that used up much less fuel.

Recovering the Roman technique might be a challenge worth taking into consideration for a more stable and ecological future.   

Giulia Lombardo

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