A low-CO₂ concrete mix could last 50 years in one location but deteriorate sooner elsewhere, according to a new ETH Zurich model. Announced on September 7, the approach could support wider use of greener concrete without creating additional maintenance problems.
The team tested three mixes using weather data from Zurich, Bergen in Norway, Manaus in Brazil, and Huailai in China. Its model tracks moisture changes inside concrete and calculates how quickly the reinforcing steel corrodes.
Moisture emerges as the decisive factor
Concrete is indispensable to modern construction, but producing cement releases large quantities of CO₂. Lower-emission cements could make building greener, although concrete made with them often carbonates faster than conventional mixes.
During carbonation, atmospheric CO₂ penetrates concrete and changes its chemical composition. This can remove the protection surrounding the embedded steel, allowing it to rust.
Current standards focus on delaying carbonation, which researchers said disadvantages low-CO₂ mixes by overlooking how quickly steel corrodes afterward.
Moisture mattered more than differences among the three mixes. According to Cristhiana Albert of ETH Zurich’s Institute for Building Materials, steel can rust up to 100 times faster in wet concrete than in dry concrete.
Four locations tell different stories
Despite their different climates, European standards place all four locations in the same “alternating wet and dry” category. The model indicated that identical concrete could perform very differently at each one.
“Climate plays a much larger role than we expected. The same concrete can behave completely differently in a different climate,” said Ueli Angst, Professor of Durability of Materials at ETH Zurich.
Bergen and Manaus offered a clear example. Both received around 2,500 millimeters of precipitation annually, yet the calculations produced different corrosion rates.
Timing explained the difference. Concrete absorbs water quickly but dries slowly, making the sequence of rainy and dry periods more important than annual rainfall or average humidity alone.
Some low-CO₂ concrete types could consequently last 50 years or longer in certain locations but deteriorate sooner under other conditions.
The model still needs real-world verification
The findings do not suggest that low-CO₂ concrete is automatically less durable or unsafe. It can match conventional concrete in strength, and even when carbonation occurs faster, the steel may rust slowly if the material does not remain damp.
“We need to better understand how climate-friendly types of concrete behave under different weather conditions in the long term,” said Albert.
Future projects may therefore need to select concrete according to the local climate instead of applying the same rules everywhere. Particularly humid regions may also require additional measures to limit water penetration.
“The current standards can therefore become an obstacle for new and more environmentally friendly materials,” Angst added.
The method is not ready for routine planning. Its calculations remain complex and require further verification on real buildings before the researchers can develop a simpler way to assess new concrete types.
A future climate test could also account for climate change. Shifts in the frequency and duration of rain and dry periods could alter corrosion rates and determine which low-CO₂ concrete remains suitable for a location over the long term.