With 8% of global greenhouse gas emissions, modern cement is far from green. Its demand continues to grow while strategies to reduce its impact are insufficient. To find a way to reduce the emissions needed to make it, researchers at the Massachusetts Institute of Technology (MIT) looked at the craftsmanship of ancient Roman builders. A study published this Friday in the journal Science Advances reveals the self-healing properties of ancient Roman concrete, known for its longevity. Its authors claim that these ancient recipes could reduce the carbon footprint of the material.
Water and the magic happens
“I lived in Italy for many years and have always been fascinated by the ancient world and cultural heritage. When I joined the Department of Civil and Environmental Engineering at MIT, I started thinking about the concept of design inspired by antiquity,” says Amir Masic, co-author of the article. In the summer of 2016, Linda Seymour and her colleagues traveled to the ancient city of Privernum, located near Rome, Italy. The researchers analyzed ten fragments of a concrete wall to learn more about its composition. They came to an astonishing conclusion: the concrete was produced with quicklime. This “hot mixing” technique gives it a special property, it repairs its cracks and pores over the long term.
The team reproduced Roman concrete with a modern preparation comprising Portland cement, sand, water, ash and quicklime, all molded into cylinders. The blocks were mechanically fractured and then their fragments placed side by side, at very short distances, so that the researchers could observe their repair. Result: after letting a constant flow of water flow through the cracks, the concrete sealed again after a month.
Large-scale use?
Known for its strength and durability, concrete allowed ancient Rome to build large, complex structures that survived for millennia on earth, such as aqueducts.
On a large scale, using the method of ancient Rome would open the way to better durability, a reduction in the need for repairs and would therefore, the researchers believe, reduce the environmental impact of constructions. “Whether the damage occurs years after construction or centuries later, as long as the structure remains, these self-healing features remain active,” the paper explains. In future studies, Linda Seymour and her colleagues will explore the practical applications of their surprising discovery, both for reinforced and unreinforced concrete.