NUNZIUM

The ancient Romans were masters of engineering, constructing vast networks of roads, aqueducts, ports, and massive buildings, whose remains have survived for two millennia. They built many of these structures with concrete. For instance, the Pantheon - AD 128 - is still intact, and some ancient aqueducts still deliver water to Rome today. In contrast, many modern concrete structures have crumbled after a few decades.

The reason for such extraordinary resilience was still unknown until a recent study published in Science, the fruit of collaboration between the University of Udine (IT) and the Massachusetts Institute of Technology (US). In their research, the authors analyzed the chemical composition of 2000-year-old concrete samples obtained from the archaeological site of Privernum, Italy. The observations are based on cutting-edge electron microscopy and x-ray technologies. They discovered that ancient concrete-manufacturing strategies had incorporated several key self-healing functionalities. The unknown self-healing capabilities of ancient concrete are due to the so-called "lime clasts" - white microscopic minerals that are a typical mark of Roman concrete. The lime clasts develop a brittle architecture thanks to a specific hot-mixing manufacturing protocol, creating an easily fractured and reactive calcium source. As tiny cracks start forming within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water (like the one that would penetrate a cracked surface on a rainy day), creating a calcium-saturated solution that recrystallizes and fills the crack.

It is worth noting that concrete is the most ubiquitous construction material in the world, but its production has serious environmental consequences. One method to reduce the carbon footprint - which accounts for up to 8% of total global greenhouse gas emissions - is to improve the longevity of concrete. The resulting extended use life, combined with a reduced need for repair, could reduce the environmental impact and improve the economic life cycle of modern constructs. Such a relevant innovation may now be at hand - not thanks to modern science, but to our ancestors' inheritance.