This summer, Italy's Ministry of Culture announced the discovery of a new room in the ruins of Pompeii, previously inaccessible to the public. The walls feature vibrant blue paint—a costly pigment used in special rooms—and frescoes depicting agricultural scenes, preserved for nearly 2,000 years. However, the most intriguing find for scientists is a coarse-grained material, pivotal to understanding one of ancient Rome's greatest technological achievements: concrete.
Admir Masic, a chemist from the Massachusetts Institute of Technology (MIT), studied the Pompeian material, revealing it as a precursor to Roman concrete, essential for the infrastructure of the Roman Empire. This concrete enabled Romans to construct aqueducts, supplying fresh water to cities and supporting hygiene in populous areas like Pompeii.
While modern concrete remains a primary building material worldwide, it has significant drawbacks, including cracking over time and contributing to approximately 8% of global carbon dioxide emissions due to cement production. Investigating the secrets of Roman concrete could lead scientists to develop more sustainable and durable building materials.
Roman concrete was renowned for its unique self-healing properties. Masic and his colleagues discovered that white lumps of lime—known as clusters—were crucial components. Previously thought to indicate poor mixing, Masic argues these clusters were a deliberate choice by ancient engineers. These unburned lime pieces acted as reservoirs of calcium, which would dissolve upon contact with water, filling cracks and restoring the integrity of the concrete.
The longevity of Roman concrete, according to Masic, stemmed from a process called 'hot mixing,' where unburned lime was added during preparation. This reaction generated heat, accelerating the setting of the concrete and creating localized high-temperature zones where lime remained in small chunks, facilitating self-healing.
Not all scientists agree with the 'hot mixing' theory. Geologist Maria Jackson from the University of Utah believes that the durability was due to a specific reaction between lime and volcanic ash known as pozzolana. This substance contributed to the formation of rare minerals that fortified the concrete structure, preventing crack propagation. Jackson and her team replicated the ancient recipe and tested it in seawater, proving that the concrete only grew stronger over time.
Modern researchers are working to adapt Roman concrete recipes to contemporary conditions. For instance, Varda Ashraf from the University of Texas has developed a concrete suitable for underwater use, ideal for constructing durable bridges and marine fortifications. By substituting clay for pozzolana, her formulation significantly reduces energy consumption and lowers the carbon footprint by up to 70%.
Thus, the secrets of ancient Roman concrete may unlock the potential for more eco-friendly construction in the future. Scientists hope their research will lead to materials that not only endure for centuries, like Roman aqueducts, but also pose less harm to the environment.