Making Roman concrete produces as much CO2 as modern concrete
Martinez et al. tested three different Roman concrete recipes with varying slaked lime-to-pozzolan ratios (1:2, 1:3, and 1:4), and assessed greenhouse gas and air emissions for each production stage based on known Roman construction practices. Specifically, the Romans used oak and fir wood as fuel for their lime kilns. (Processes like loading, transportation, and mixing were done by human and animal labor and thus fell outside the scope of the analysis.) The team also assessed greenhouse gas and air emissions for modern concrete production, taking into account variability in equipment efficiency and energy sources for the kiln, among other factors.
The results surprised the scientists. Per volume of concrete, the production process for Roman concrete ended up emitting as much and in some cases more CO2 than modern formulations. On the other hand, Roman concrete emits much lower volumes of such air pollutants as nitrogen oxide and sulfur oxide—between 11 percent and 98 percent less, depending on whether the energy source was fossil fuels, biomass, or renewable energy (which had the biggest reductions).
Roman concrete is also more durable and hence would require less maintenance and replacement over time, which might further offset any negative environmental impacts. However, the authors caution that it’s a difficult comparison, given that ancient Roman structures didn’t use steel bars for reinforcement, unlike modern concrete construction methods. It’s the corrosion of those steel reinforcements that primarily causes deterioration of modern concrete.
“Contrary to our initial expectations, adopting Roman formulations with current technology may not yield substantial reductions in emissions or energy demand,” said Martinez. “Using biomass and other alternative fuels to fire kilns may prove more effective in decarbonizing modern cement production than implementing Roman concrete formulations.” However, “there’s a lot of lessons 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.”
DOI: iScience, 2025. 10.1016/j.isci.2025.113052 (About DOIs).
