Ancient Roman structures built with concrete have withstood centuries, inspiring researchers to uncover the secret behind their resilience. Unlike today’s Portland cement-based concrete, Roman concrete is known for its incredible durability and even a self-healing ability. This strength has led scientists to seek ways to replicate it, hoping to craft stronger, more sustainable materials for modern use.

Portland cement, developed in the 19th century, is the basis of today’s concrete, but it lacks the robustness of Roman concrete and has a high environmental cost due to its complex production process. Engineers are now exploring concrete alternatives that reduce or eliminate the use of traditional cement.

What truly distinguishes Roman concrete is its unique capacity to repair itself, unlike the cheaper, crack-prone concrete we use today. However, replicating Roman concrete’s formula has been a challenge. For years, scientists assumed that clasts—chunks found in Roman concrete samples—were merely impurities or evidence of poor mixing. But recent research suggests these clasts may have played an essential role in Roman concrete’s self-healing ability.

Roman concrete derived its strength from a mixture known as calcium aluminate silicate hydrates (CASH), created by combining heated limestone with water and volcanic ash, which added the necessary silicon and aluminum. This process produced calcium oxide, or quicklime, which, when mixed with water, became calcium hydroxide. Scientists are now investigating if the presence of clasts, once thought to be “mistakes,” might have been the intentional key to the concrete’s self-healing properties.

Though it’s difficult to prove whether the Romans intended these clasts, researchers are actively developing modern additives that mimic the ancient concrete’s properties. With self-healing concrete already emerging today, there’s hope that this ancient resilience can soon bolster modern structures, bringing new strength and sustainability to the buildings of the future.

By Impact Lab