Ancient Roman concrete offers lessons for sustainable building

Concrete is everywhere – beneath our feet, around our buildings, and across our cities. It’s one of the most used materials in the world, but it’s also a major contributor to pollution and climate change.

As the construction industry pushes to cut carbon emissions, some scientists are looking thousands of years into the past for ideas.

Researchers from Universidad del Norte, UC Davis, and UC Berkeley recently explored whether the techniques behind ancient Roman concrete could help us build in a more sustainable way today. The findings shed light on a surprising trade-off between emissions and durability.

What made Roman concrete different?

Modern concrete is made of cement mixed with sand, gravel, and water. Roman builders used a different formula. They combined limestone, volcanic ash known as pozzolan, and even rubble from demolished structures.

The key ingredient in both types of concrete is limestone, which must be heated to very high temperatures. This process releases carbon dioxide and produces calcium oxide, which then reacts with other minerals to form a strong binding paste.

Despite the clear differences in recipe, the energy and water required to produce Roman concrete today would be similar to that of modern concrete. Even the carbon emissions would be roughly the same – or in some cases, slightly higher.

“Contrary to our initial expectations, adopting Roman formulations with current technology may not yield substantial reductions in emissions or energy demand,” said study lead author Daniela Martinez of Universidad del Norte.

The research team ran models comparing different Roman concrete recipes and modern methods. They factored in not just ingredients but also production techniques and energy sources – like fossil fuels, biomass, or renewables. The goal was to measure the environmental impact from all angles.

Less pollution, more durability

While Roman concrete didn’t offer a big drop in carbon emissions, it did produce significantly lower levels of other pollutants – especially nitrogen oxide and sulfur oxide, which are known to damage human health.

Depending on the fuel source, these pollutants were reduced by anywhere from 11 to 98 percent. Renewable energy made the biggest difference.

And while emissions may be comparable today, Roman concrete’s potential lies in how long it lasts. The ancient structures built with it – bridges, aqueducts, public buildings – have stood the test of time.

That kind of durability could translate into serious sustainability gains, especially in places where concrete needs frequent repair or replacement, like roads and highways.

“Studying Roman concrete can teach us how to use materials in a way that can maximize the longevity of our structures, because sustainability goes hand-by-hand with durability,” said Martinez.

Concrete that lasts, and less waste

There’s growing awareness in the building industry that durability matters just as much as emissions. If we can build things that last longer, we don’t have to rebuild as often – and that reduces the environmental cost over time.

“When we take concrete’s service life into consideration, that’s when we start seeing benefits,” explained Martinez.

“In cases where prolonging the use of concrete can reduce the need to manufacture new materials, more durable concrete has the potential to reduce environmental impact,” noted study co-author Sabbie Miller of UC Davis.

But comparing ancient Roman concrete to modern concrete isn’t simple. Modern formulas have only been used for about 200 years, while Roman buildings have lasted over two millennia.

More importantly, modern concrete often includes steel reinforcement bars, which Roman builders didn’t use. That adds another layer of complexity to the comparison.

“Corrosion of steel reinforcement is the main cause of concrete deterioration, so comparisons should be made with great care,” noted study co-author Paulo Monteiro of UC Berkeley.

Looking to the future

The research team plans to continue comparing performance and longevity between Roman and modern concrete in real-world scenarios. Their hope is to better understand how lessons from the past can help solve problems we face today.

“We were interested in how we can draw lessons from their methods to inform some of the climate-mitigation challenges that we currently face in our built environment,” said Martinez.

“There’s a lot of lessons that we can draw from the Romans. If we can incorporate their strategies with our modern innovative ideas, we can create a more sustainable built environment.”

The full study was published in the journal iScience.

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