Ancient Romans May Hold Clues to More Sustainable Concrete

The ancient Romans may have left behind more than ruins: their approaches to making sustainable concrete appear to have produced structures that can endure for thousands of years.

A new study has closely examined the inputs and energy requirements behind ancient Roman mortar and concrete, outlining several practical directions for improving modern cement.

What the study assessed

The analysis reached a counter-intuitive result: manufacturing Roman mortar and concrete can demand more water and generate more greenhouse gas emissions than Portland cement, which remains the most widely used cement type in today’s concrete.

Even so, the researchers argue that those higher upfront impacts do not necessarily mean Roman-style mixes are worse overall. If the concrete lasts much longer, the environmental balance can shift because replacement and repair would be needed less often.

Service life changes the emissions picture for Roman concrete

An international group of environmental engineers reports that, for buildings, Roman concrete blends would have to outlast modern counterparts by at least 41 percent to deliver the same cumulative emissions.

For infrastructure with shorter design lives-such as streets and motorways-the mixes would need to endure at least 29 percent longer.

"When we take concrete's service life into consideration, that's when we start seeing benefits," says lead author and engineer Daniela Martinez of the University of the North in Columbia.

"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."

Longevity is difficult to compare with steel-reinforced modern concrete

Setting Roman concrete alongside modern concrete is not straightforward, largely because many contemporary structures are strengthened with steel reinforcement.

As steel corrodes, it expands, which can force the surrounding concrete to crack and deteriorate in as little as a decade. Ancient Roman concrete, by contrast, can be capable of ‘self-healing’: when cracks form, they may be naturally sealed again as water infiltrates.

This self-repair is one reason Roman seawalls have survived for millennia, despite continual pounding by waves and exposure to corrosive saltwater.

Whether present-day concrete can reliably do the same remains uncertain.

"Corrosion of steel reinforcement is the main cause of concrete deterioration, so comparisons should be made with great care," explains author and engineer Paulo Monteiro of the University of California, Berkeley.

Martinez and colleagues also note that longer-lived cement structures "can only partially offset increased demand for new material," though they suggest Roman production practices may carry additional environmental advantages.

What Roman cement-making could change in modern production

Portland cement and Roman cement share the same key starting material. Heating limestone produces a highly reactive, caustic powder known as quicklime. When mixed with water, that quicklime becomes a strong mortar.

Concrete recipes across the ancient Roman Empire differed widely, but they typically combined this mortar with locally sourced volcanic rocks rather than the gypsum commonly used in modern concrete.

The study also indicates that Roman concrete leads to far fewer hazardous air pollutants-possibly because limestone was fired using oak and fir wood instead of fossil fuels.

Based on recent modelling, adopting Roman cement techniques could cut nitrogen oxide and sulphur oxide emissions by up to 98 percent compared with current methods.

"Using biomass and other alternative fuels to fire kilns may prove more effective in decarbonizing modern cement production than implementing Roman concrete formulations," says Martinez.

Why cement emissions matter globally

Today, concrete is the second most widely used material in the world, after water. Its manufacture is responsible for roughly 8 percent of global anthropogenic carbon emissions-around a quarter of all industrial carbon emissions.

According to Arizona State University materials scientist Narayanan Neithalath, if cement manufacturing were treated as its own country, it would rank as the third-largest carbon dioxide emitter globally, behind China and the United States.

"If we stand a reasonable chance of staying below the two degrees Celsius warming target set by the Paris Agreement, cement-related emissions will have to fall by more than 20 percent in the coming decade," Neithalath explained in 2023.

Examining ancient Roman concrete, the authors argue, could support progress towards those urgent climate targets.

The study was published in iScience.