Roman concrete is notoriously strong. Roman structures have lasted for thousands of years, and many of them look no worse for wear than they did when they were built. Many of these ancient Roman buildings are made from a specific type of concrete that has left scientists and engineers scratching their heads for centuries. Not only has this concrete stood the test of time, but it has also been used in incredible shapes like free-standing domes and arches are still impressive.
Modern concrete is cheap and widely available, but it is not very durable. Many concrete buildings have a shelf life of a century, maybe two centuries. After that, modern concrete starts to crack and crumble. That means that, currently, there will be few buildings from our present era that survive into the distant future.
So how is it that people two thousand years ago made a building material more durable than the one we have today? We might finally know the answer to that question.
Is Heat The Key?
For decades, scientists and historians have been stuck on the formula of ancient Roman concrete. People thought that the Romans must have found some special additive to boost the strength of their concrete. With modern chemistry and the entire global supply chain at their fingertips, engineers believed if the Romans had had a special formula, modern science would have found it.
Instead, it turns out that the formula was not the key to success but how the formula was mixed together. The leading theory is now that the Romans used a process called “hot mixing” to superheat the concrete as it was being made. The high heat changed the chemical composition and makeup of many of the key ingredients leading to additional strength.
Modern concrete is cold-mixed. Portland cement is added to water, rocks, and gravel to create a thick concrete paste. This paste is kept at room temperature and transported in trucks. Heat is not a part of the final concrete mixing process. Can this simple detail make the difference between concrete that lasts thousands of years and concrete that merely lasts a hundred?
A Better Concrete
This new theory is currently being tested by scientists at MIT. They are trying to apply ancient Roman concrete methods to modern concrete formulas to create a brand-new product. Stronger concrete could transform the building industry by making buildings more durable, longer lasting, and safer.
One of the critical ingredients in concrete is lime, and lime changes dramatically when mixed and heated in certain ways. Lime that is heated and mixed into concrete is much stronger and could even have the ability to “self heal.”
For years, scientists studying Roman concrete believed that the presence of this heated lime was the result of crude or ancient building practices rather than something intentional. Now people think that the presence of this lime is the result of superheating the concrete. It was very intentional.
The more things change, the more they stay the same. Now, scientists are rediscovering Roman concrete. In the future, more buildings could be built out of the same material that raised ancient Rome from the Earth.
These discoveries also highlight how ancient people were just as smart and just as capable as their modern equivalents. The fact that ancient Roman engineers could create a product that outperforms our own is incredible. The fact that we might relearn how to create this material and start using it earnestly once more is even more incredible.
This story is the perfect blend of science, archeology, history, and engineering, and it will be interesting to see where it goes from here.