Ancient Rome was quite advanced in the use of concrete thousands of years ago, thanks to interesting production strategies. Using this technology, Roman engineers built an extensive network of roads, aqueducts, ports, and massive buildings. Most structures were built using concrete and are still standing. Among these structures; The Roman Pantheon, which has the world’s largest unsupported concrete dome, and the ancient Roman aqueducts that still carry water to Rome today. Today, many modern concrete structures crumble after a few decades.
For years, researchers have worked to unravel the secret of ultra-durable ancient concrete, which is used in special areas such as structures that endure harsh conditions or those built in seismically active locations. Recently, however, a research team has made significant progress in this area and discovered ancient concrete production strategies. Research has revealed that the concrete used by the ancient Romans had some important properties, such as self-healing. These important findings were published in the journal Science Advances.
Research on Ancient Roman Concrete
For many years, researchers; They thought that the key to the durability of the old concrete was due to pozzolanic materials, such as volcanic ash from the Pozzuoli site in the Bay of Naples. This particular ash was shipped all over Rome for the concrete used for construction at that time. Ash was considered an important component of concrete by many architects and historians. However, closer examination of the concrete samples on the small millimeter scale revealed that the Roman concretes contained bright white mineral features all over. These white bits are often referred to as “lime shards” and originate from lime, another key component of the ancient concrete mix.
Researchers note that these properties have always caught their attention, especially since they began working on Ancient Roman concrete. The absence of these properties in modern concrete formulations raises the question of how they occur in older concretes. Researcher Masic, “Since I started working with ancient Roman concrete, these properties have always fascinated me. They are not found in modern concrete formulations, so why are they in these older materials?” says.
The new study shows that tiny bits of limestone, previously undetected, found in Roman concrete have acquired the ability to heal themselves. This feature was previously only seen as a result of careless mixing practices or poor quality raw materials. Researcher Masic, “The idea that the presence of these limescale crumbs is simply attributed to poor quality control has always bothered me. If the Romans spent so much effort following all the optimized detailed recipes over the centuries to make an outstanding building material, why should they spend so little effort to ensure the production of a well-mixed final product? There had to be more to this story.” says.
How Does Roman Concrete Heal Itself?
The researchers performed chemical analyzes to get a more precise idea of the formation of limescale in Roman concrete. The analyzes showed that the lime was used directly as quicklime and was formed as a result of the breaking of small crystals formed as a by-product during the hydration of the lime. When cracks form during the hardening process of concrete, these tiny crumbs allow water to penetrate those cracks, allowing the lime to restart the hydration reaction and repair the cracks. Therefore, the self-healing property of Roman concrete can be explained by the presence and function of lime crumbs.
The researchers discovered that the lime residues in the old concrete samples were made from different forms of calcium carbonate. Spectroscopic examination showed that it was formed at extreme temperatures as a result of an exothermic reaction produced using quicklime instead of or in addition to slaked lime. According to this study, hot mixing is the key to an extremely durable material.
masic, “The benefits of hot mixing are twofold. First, when general concrete is heated to high temperatures, it produces high temperature-related compounds that would not otherwise form, allowing chemicals that are not possible when you use slaked lime alone. Second, this increased temperature significantly reduces curing times because all reactions are speeded up and construction can be done much faster as a result.” says.
During the hot mixing process, the researchers determined that the lime crumbs develop a brittle nanoparticulate architecture, thereby creating a reactive source of calcium that can provide a critical self-healing function. This material can react with water to form a calcium-saturated solution that can recrystallize as calcium carbonate and quickly fill the crack. Or it can react with pozzolanic materials to further strengthen the composite material. As these reactions automatically heal cracks, the material becomes durable. In addition, to support this hypothesis, previous Roman concrete samples were also examined and calcite-filled cracks were found to be exhibited.
Experiment with Roman Concrete
Using both old and modern concrete formulations, the team produced samples of hot mix concrete and deliberately cracked them. Then they ran water through the cracks and found that within two weeks the cracks were completely healed and the water could no longer flow. An identical piece of concrete made without quicklime did not heal and water continued to flow through the sample. As a result of these successful tests, the team is working to commercialize this modified cement material.
masic, “It is exciting to consider how these more durable concrete formulations can not only extend the service life of these materials, but also increase the durability of 3D-printed concrete formulations.” says.
Masic hopes these efforts can help reduce the environmental impact of cement production, through the development of extended functional life and lighter concrete forms. This sector accounts for about 8 percent of global greenhouse gas emissions.
