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Why Is The 2,000-Year-Old Roman Concrete Still Stands Today, More Durable Than The Modern Concrete?

Elaine Hannah
First Posted: Jul 06, 2017 04:29 AM EDT
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The ancient Roman concrete harbor structures still stand today and seem stronger than before. The secret lies on their concrete that is more durable compared to the concrete of today. So, why is this so?

The findings of the study were published in American Mineralogist. The work was led by geologist Marie Jackson from the University of Utah and other colleagues. The researchers examine the minerals and micro scale of Roman concrete. They discovered that the seawater sieving in the concrete interlocked the minerals that contribute to the cohesion of the concrete, according to Phys.org.

The Roman concrete was used in different edifices such as the Pantheon and Trajan's markets in Rome. It is also widely used in harbors from the open sea that acts as extensive anchorage for ships and warehouses. Most of it could still be seen today and even gets stronger.

This concrete was made of volcanic ash with lime and seawater to come up with a mortar. Then, it was incorporated with the more volcanic rock "aggregate" in the concrete. This made the Roman concrete more durable.

Meanwhile, the modern concrete is made of Portland cement, a mixture of silica sand, limestone, clay, chalk and other components that are melted together at intense temperatures. These bind the aggregates, which are chunks of rock and sand. The aggregate must be lethargic because if there is any chemical reaction in the cement paste, there would be cracks in the concrete. This could lead to erosion and collapse or damage of the structure. This is the reason why this concrete does not have the endurance of the natural rocks.

In the study, the researchers collected samples of Roman marine concrete from many ports along the Italian coast. They used an electron microscope to map the samples. With the X-ray microdiffraction and Raman spectroscopy, they could determine the mineral grains created in the Roman concrete for over centuries.

They discovered that there was abundant aluminous tobermorite in the concrete. This is a tough silica-based mineral that is rare and difficult to make in the laboratory. There was another related mineral found called phillipsite. The seawater splattered on them and slowly dissolving the volcanic ash within the concrete. This led to the development of reinforced structure from these interlocking components.

Jackson said the Romans produced a rock-like concrete that flourishes in open chemical exchange with seawater. Meanwhile, in modern concrete, it erodes as salt water rusts the steel bars and washes away the components that bind the materials together, according to Science Alert. 

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