The Secret of Making 1000-Year-Life Concrete

Masic’s article is the latest in a series of investigations into Roman concrete. Last year, she, along with Marie Jackson, a researcher at the University of Utah, published research examining the 22-foot tomb of Caecilia Metella, a first-century Roman noblewoman on the Appian Way, an ancient Roman road through Italy. Their research revealed that the special Roman concrete used in the tomb became more flexible over time by interacting with rainwater and groundwater.

In their previous work, Jackson and colleagues produced an exact replica of a similar concrete used to build Trajan’s Markets in Rome 1,900 years ago and developed an innovative fracture test to better measure its flexibility and showed it to be much less brittle. More than modern concrete, Jackson also studied the cores opened from concrete in Roman ports, determining that seawater passing through the concrete reacts with the concrete to form new minerals that make the concrete more cohesive and flexible over time.

But Jackson has some concerns about Masic’s new paper. The sample analyzed is undated and contains sand instead of the typically used volcanic tephra – so the sample is not representative of Roman concrete, he says. In response, Masic said his team plans to analyze other sites “to confirm our hypothesis” that the Romans used quicklime in their concrete recipe, known as hot mix. Masic’s team also wants to look in more detail at the effect the hot mix had on how the Romans built their structures.

So did Masic really solve the mystery of how Roman concrete was made? “Who knows?” says. “What I do know is that we’ve been able to translate some of these concepts into the real world. That’s what excites me the most.” Certainly “Roman” or not, there is now the potential to build better concrete.

This recipe and process was lost more than a thousand years ago. Similar concrete did not exist until Joseph Aspdin of Great Britain received a patent in 1824 for a material made from a mixture of limestone and clay. He named it Portland cement because it resembled Portland stone, a limestone used for construction in England.

Modern concrete is made from chunks of rock combined with Portland cement, a mix of limestone, clay or shale, and other ingredients, and is ground and burned at 1,450 degrees Celsius (2,642 degrees Fahrenheit). This process creates massive amounts of greenhouse gases and leaves you with non-durable concrete, which degrades in as little as 50 years, especially in marine environments. By contrast, Roman concrete is strong and, unlike its modern counterpart, does not require steel to reinforce it. And relatively cheap.

Concrete infrastructure, such as roads, today costs six to 10 times its original price when repairs are taken into account over its lifetime, King says. Therefore, extending the life of concrete produced today by only a few times its expected life will significantly reduce demand and reduce greenhouse gas emissions. “When you lay a new highway, every three years, potholes appear,” King says. “Now if you only need to fill your pits every 10 years or every 20 years, this is the better material.” Having concrete that lasts 2,000 years isn’t necessary to make a big difference.

On this front, Masic’s and Jackson’s labs are working with entrepreneurs interested in launching their own versions of Roman concrete. For example, Jackson’s team collaborated with an industry partner to create a synthetic version of the volcanic tephra mined by the Romans because of the enormous volume that would be needed.

After years of chasing an answer, Jackson is happy that the search has sparked interest. “The really important and valuable thing is that the topic of Roman concrete is now in the media,” he says. “This is an incredibly sophisticated and complex material. The people who made it were so brilliant and so precise in what they did that it took us 15 years to decipher most of it. And we are humbled that we still have so much more to learn.”

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