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Deep beneath the Mediterranean Sea, an ancient Roman breakwater has withstood 2,000 years of relentless ocean erosion and remains intact. What makes it so durable? A recent study by the Physics Organization Network revealed that an international team from the Lawrence Berkeley National Laboratory uncovered a surprising fact: the Romans developed a method to produce concrete that not only lasted centuries but also significantly reduced COâ‚‚ emissions. How did they do it?
The Secret Behind Marine Concrete
Researchers from the University of California, Berkeley, King Abdullah University of Science and Technology, and the Deutsches Elektronen-Synchrotron (DESY) in Berlin used advanced tools like the Advanced Light Source (ALS) to analyze the composition of ancient Roman marine concrete. Their findings showed that the Romans used a different approach compared to modern practices—two key differences stood out.
First, instead of using Portland cement, which forms calcium silicate hydrate (CSH), the Romans incorporated aluminum into their mix, creating a compound called calcium aluminosilicate hydrate (CASH). This compound is more stable and resistant to seawater damage. Through spectral analysis at the ALS, scientists found that the way aluminum replaces silicon in CASH may be the secret behind the concrete’s strength and durability.
Another important distinction was the formation of hydration products. In modern concrete, CSH tends to form low-crystalline structures, which lack the stability seen in nature. However, in Roman seawater concrete, researchers identified xonotlite—a crystalline mineral known for its rigidity. This discovery highlights how the Romans’ methods created a more resilient material.
How Did the Romans Achieve This?
Today, concrete is the most widely used building material, but its production is a major environmental concern. The manufacturing of Portland cement releases large amounts of COâ‚‚, contributing to about 7% of global greenhouse gas emissions. Additionally, transportation and use of concrete add to its environmental footprint.
“Modern concrete is very effective, with over 19 billion tons produced annually,†said Professor Paul Monteiro from UC Berkeley. “But the problem lies in the carbon emissions from cement production.†Portland cement requires heating limestone and clay to around 1,450°C, which releases significant CO₂.
The research team discovered that the Romans used less lime and baked their materials at much lower temperatures—around 900°C. This process required less fuel and emitted far less CO₂. Their recipe included less than 10% lime by weight, and the combination of lime with volcanic ash created highly stable compounds like CASH and aluminosilicates, ensuring long-term strength and resilience.
A Model for Green, High-Performance Concrete
Monteiro noted that many modern structures are designed to last only 50 to 120 years, while Roman ports have endured over 2,000 years of harsh conditions. This durability offers valuable insights for future construction.
One of the main challenges with modern concrete is its low tensile strength and tendency to crack. As cities expand, there's a growing need for sustainable, high-performance materials that minimize environmental impact. Volcanic ash, first documented by Vitruvius, played a crucial role in Roman concrete. These natural pozzolans helped create a stronger, more durable mix when combined with lime.
The Romans mixed volcanic ash with lime to make mortar, then filled wooden frameworks with volcanic rock and submerged them in seawater. This triggered a rapid chemical reaction, producing a strong, long-lasting structure.
“Volcanic ash has practical value today,†Monteiro explained. “By learning from the Romans, we can develop modern concrete that uses less energy and emits fewer greenhouse gases. This could lead to a greener, more sustainable future.â€
Green, high-performance concrete is no longer just a dream—it represents a real opportunity to build better, cleaner, and more environmentally friendly structures. By combining ancient wisdom with modern science, we can create materials that not only meet functional needs but also protect our planet. The lessons from Rome show us that innovation doesn’t always mean starting from scratch. Sometimes, looking back can help us move forward. (Reporter: Hualing)
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