The secret to making concrete that will last 1000 years
Masic’s article is the latest in a series of studies on Roman concrete. Last year, he published a study with Marie Jackson, a researcher at the University of Utah, that examined the 70-foot grave by the first-century Roman noblewoman Caecilia Metella on the Appian Way, an ancient Roman road through Italy. Their investigation revealed that the special form of Roman concrete used in the tomb interacts with rain and groundwater, becoming more resistant over time.
And in earlier work, Jackson and her colleagues made a replica of the same concrete used 1,900 years ago to build Trajan’s Markets in Rome, and developed innovative fracture test to better measure its resilience, showing that it is much less brittle than modern concrete. Jackson also studied cores drilled from concrete in Roman harborsdetermining that seawater passing through the concrete reacts with it, creating new minerals that make the concrete more cohesive and elastic over time.
However, Jackson has some concerns about Masik’s new article. The sample she analyzed is undated and contains sand instead of the commonly used volcanic tephra — so the sample is not representative of Roman concrete, she says. In response, Masik says his team plans to analyze other sites “to confirm our hypothesis” that the Romans used quicklime in their concrete recipe, known as hot mix. Masik’s team also wants to take a closer look at the impact of hot mixing on how the Romans built their structures.
So did Masik really solve the mystery of how Roman concrete was made? “Who knows?” He says. “What I do know for sure is that we were able to bring some of these concepts to the real world. That’s what really excites me the most.” There is now the potential to create better concrete, whether it is purely “Roman” or not.
This recipe and process has been lost for over a millennium. Concrete like this did not exist before Joseph Aspdin from UK in 1824 he received a patent for a material made from a mixture of limestone and clay. He named it Portland cement because it resembled Portland stone, the limestone used for building in England.
Modern concrete is made from rock fragments combined with Portland cement, a mixture of limestone, clay or shale and other ingredients, ground and fired at 1450 degrees Celsius (2642 degrees Fahrenheit). This process creates huge amounts of greenhouse gases and leaves behind concrete that is not durable and breaks down in sometimes as little as 50 years, especially in marine environments. Roman concrete, by comparison, is strong and does not require steel reinforcement, unlike its modern counterpart. And it’s relatively cheap.
King notes that today, concrete infrastructure such as roads cost six to ten times their original price when considering lifetime repairs. So extending the life of concrete made today, even just a few times longer than expected life, would drastically reduce demand and reduce greenhouse gas emissions. “When you build a new freeway, potholes appear every three years,” says King. “If you now have to patch potholes every 10 or 20 years, this is the best material.” Having concrete that can last 2,000 years won’t necessarily make a big difference.
On this front, Masik and Jackson Laboratories are working with entrepreneurs interested in bringing their versions of Roman concrete to market. Jackson’s team, for example, partnered with an industry partner to create a synthetic version of volcanic tephra mined by the Romans due to the sheer volume that would be required.
After years of searching for an answer, Jackson is happy that the quest is generating interest. “What is really important and valuable is that the topic of Roman concrete is now in the media,” she says. “It’s incredibly complex and complex material. The people who did this were so brilliant and so precise in their actions that it took us 15 years of work to decipher most of it. And we’re confused about how much more we have to learn.”