The Secrets of the Romans Unlocked And None Too Soon.

This lovely seawall? Yeah, the Romans built it.

Roman ruins remain everywhere in Europe and North Africa. Some of them, aqueducts for example, are still functioning. The secret to their longevity is the Roman development of concrete.

The knowledge of making concrete was lost during the Dark Ages. We imagined we had unlocked the secrets of ancient Rome in the mid-19th century with the development of Portland cement.

While we often attribute cheap, abundant fossil fuels as the key to launching the Industrial Revolution the reintroduction of concrete played a critical role. We used it to build roads, harbours, bridges, water and sewer lines, buildings, and airports - most of our modern infrastructure.

Only we never really got it right. Modern concrete isn't nearly as durable as the Romans'. Ours lasts about 120-years. It weakens and cracks and crumbles with time and exposure to the elements. Roman concrete doesn't do that. It lasts.

Now it seems we have finally cracked the secrets of Roman concrete by looking at how their marine construction actually improves with age and exposure to seawater.

The Roman recipe – a mix of volcanic ash, lime (calcium oxide), seawater and lumps of volcanic rock – held together piers, breakwaters and harbours. Moreover, in contrast to modern materials, the ancient water-based structures became stronger over time.

Scientists say this is the result of seawater reacting with the volcanic material in the cement and creating new minerals that reinforced the concrete

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[T]he Romans were aware of the virtues of their concrete, with Pliny the Elder waxing lyrical in his Natural History that it is “impregnable to the waves and every day stronger”.

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Over time, seawater that seeped through the concrete dissolved the volcanic crystals and glasses, with aluminous tobermorite and phillipsite crystallising in their place.

These minerals, say the authors, helped to reinforce the concrete, preventing cracks from growing, with structures becoming stronger over time as the minerals grew.

So, big deal, why should you care? Simple. Because our dependence on concrete isn't going away. If anything it's going to grow as we have to replace already crumbling but vital infrastructure. Part of that is because our crappy, new concrete doesn't hold a candle to ancient Roman concrete. Why keep paying for a product that might, if you're lucky, last a century when Roman concrete can last for thousands of years.

There's another reason. The environmental imperative. New concrete is a major source of greenhouse gas emissions. It is generally thought responsible for 7% of total CO2 emissions. Portland concrete is heated to 1450 degrees Celsius. Roman concrete has to be heated to just 900 C. That's a huge energy and emissions savings.

So now that we know what the Romans knew why would our governments squander countless billions of dollars on short term replacement of new concrete infrastructure?