One of the world’s most iconic historic destinations could hold the key to breakthroughs for modern architects seeking better building materials, according to a new study published in Nature Communications.
A research team at Pompeii—the ancient Italy city famously buried by a Mount Vesuvius eruption in 79 CE—uncovered an ancient, unfinished construction site among the ruins. The discovery of the half-built walls of a bakery and piles of unused pre-mixed building materials means the team of scientists was able to start to unlock the secret of how the Romans made concrete, a mystery that has long fascinated experts.
Roman structures, from the vast performance venue of Rome’s Colosseum and domed Pantheon temple, to huge infrastructure projects like aqueducts and harbours, were unprecedented at the time of construction. Their concrete could harden underwater, an essential property, and, even more impressively, could “self-heal” by dissolving and recrystallizing “lime clasts,” to seal up water damage, for example.
One of the important ingredients is pozzolan, a natural (or artificial) material that, when finely ground and mixed with water, chemically reacts with calcium hydroxide (lime) to make hard, resilient compounds.
The researchers explain that they analysed the microstructure and chemical make-up of the Pompeii finds, showing “unequivocally how quicklime was pre-mixed with dry pozzolan before adding water in the creation of Roman concrete. This construction method, also known as hot mixing, results in an exothermic reaction within the mortar and the formation of lime clasts, key contributors to the self-healing and post-pozzolanic reactivity of hydraulic mortars.”
“Studying it truly felt as if I had travelled back in time and was standing beside the workers as they mixed and placed their concrete,” said Admir Masic, Professor of Civil and Environmental Engineering and study lead from Massachusetts Institute of Technology.
As a site frozen in time, Pompeii provides unique insights into the past, Masic explained. “For studying ancient technologies, there is simply no parallel. It’s exceptional preservation offers a true ‘snapshot’ of Roman building practice in action.” But that does not mean we should see the past as a monolith. One of the important aspects of the latest discovery is the light it casts on the evolution of Roman technology, proving that the method used in the bakery is different from that used a century earlier by the Romans and described by the contemporary historian Vitruvius.
The way Romans adapted their building methods could hold value for construction projects today, as we seek materials that rot less easily and are less polluting than Portland concrete (responsible for 8% of world emissions). Masic said: “There is the historic importance of this material, and then there is the scientific and technological importance of understanding it. This material can heal itself over thousands of years, it is reactive, and it is highly dynamic. It has survived earthquakes and volcanoes. It has endured under the sea and survived degradation from the elements.”
He continued: “While the ancient process itself is not a direct replacement for modern standards, the principles revealed can inform the design of next-generation durable, low-carbon concretes.”
