Ancient Roman aqueducts and bridges have stood tall for more than 2,000 years. Now researchers suggest the durability of Roman concrete might make modern construction more sustainable.

The study published in iScience shows that, while the emissions and energy consumption of ancient Roman and modern concrete are similar, the Romans’ long-lasting concrete may have positive impacts on the environment.

“Studying Roman concrete can teach us how to use materials in a way that can maximise the longevity of our structures, because sustainability goes hand-by-hand with durability,” says author Daniela Martinez, an engineer at Colombia’s Universidad del Norte.

“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.”

Approximately 8% of human-contributed CO2 emissions come from the production of modern concrete. In 2022, global cement production produced 1.6 billion tons of this greenhouse gas.

Today, concrete is made by mixing cement with various types of sand and gravel. Ancient Romans made concrete by combining limestone, volcanic rocks called pozzolan and water.

Martinez’s team tested concrete recipes using models to compare the estimated number of raw materials required and the amount of CO2 and other air pollutants produced.

They compared multiple ancient Roman recipes as concrete was not made uniformly with the same ratios of ingredients.

The researchers were surprised to find that Roman concrete resulted in similar CO2 emissions per volume of concrete to modern concrete productions. In some cases, Roman concrete even produced more CO2 emissions than its modern-day counterpart.

“Contrary to our initial expectations, adopting Roman formulations with current technology may not yield substantial reductions in emissions or energy demand,” says Martinez.

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

CO2 is not the only greenhouse gas that is harmful to the environment.

The study findings show that Roman concrete may reduce the amount of other air pollutants like nitrogen oxide and sulphur oxide – two pollutants that can cause both short-term and long-term respiratory complications for humans.

This reduction was dependent on what ratio of materials the recipe used and whether the production was fuelled by fossil fuels, biomass or renewable energy.

For example, emissions of nitrogen oxides were reduced by 85% and sulphur oxides emissions were reduced by 98% when using electric fuel to produce the ancient Roman concrete which has a 1:4 ratio of limestone to pozzolan,.

The most positive environmental impact Roman concrete could have on production comes from its durability. 

“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,” says author Sabbie Miller from the University of California, Davis in the US.

Modern concrete roads and pavements typically last 30 to 40 years, but often require maintenance and repaving. Taking inspiration from Roman concrete could provide a more sustainable option

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

Additionally, Roman concrete, unlike modern concrete, was not reinforced with steel bars to increase its strength.

“Corrosion of steel reinforcement is the main cause of concrete deterioration, so comparisons should be made with great care,” says author Paulo Monteiro from the University of California, Berkeley in the US.

Modern concrete has only been produced for the past 200 years, so the researchers now plan to develop a more in-depth analysis to compare the materials in different environments.

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