- Low-CO₂ concrete durability is significantly affected by environmental humidity.
- Steel reinforcement in wet concrete can corrode up to 100 times faster than in dry concrete.
- The same concrete can perform very differently in various climates.
- Future projects may need to select concrete formulations based on local climate conditions.
A new model from ETH Zurich suggests that low-CO₂ concrete formulations could last up to 50 years in some locations but may deteriorate sooner in others. The model, published on September 7th, aims to promote the widespread use of environmentally friendly concrete without introducing additional maintenance issues. The research team tested three concrete formulations and utilized meteorological data from Zurich, Switzerland; Bergen, Norway; Manaus, Brazil; and Huailai, China. The model tracks humidity changes within the concrete and calculates the rate of steel reinforcement corrosion.
Humidity emerges as a critical factor.
The Impact of Humidity on Concrete
Concrete is indispensable in modern construction, but cement production releases significant amounts of CO₂. Low-emission cement helps create more environmentally friendly buildings, but concrete made with these cements often undergoes carbonation faster than traditional mixtures. During carbonation, CO₂ from the atmosphere penetrates the concrete and alters its chemical composition, which can remove the protective layer surrounding embedded steel reinforcement, leading to corrosion. Current standards focus on slowing carbonation, but researchers point out that this overlooks the disadvantage of low-CO₂ formulations in terms of the subsequent corrosion rate of the steel.
The impact of humidity far outweighs the differences between the three formulations. "Steel reinforcement in wet concrete can corrode up to 100 times faster than in dry concrete," said Cristhiana Albert from ETH Zurich's Institute for Building Materials.
Concrete Performance in Different Climates
Although the climate conditions in the four locations vary, the European standard categorizes all four under the same "alternating wetting and drying" classification. The model shows that the same concrete can perform very differently in each location. "The influence of climate far exceeded our expectations; the same concrete may perform completely differently in different climates," said Ueli Angst, a professor of material durability at ETH Zurich. Bergen and Manaus provide a clear example, with both locations having an annual precipitation of about 2,500 millimeters, yet the calculated corrosion rates differ.
This difference can be explained by the time factor, as concrete absorbs water quickly but dries slowly. The sequence of rainy and dry seasons has a greater impact on the annual precipitation or average humidity than the total amount. Therefore, some low-CO₂ concrete types may be sustainable for 50 years or more in certain locations but may deteriorate sooner in other environments.
The model still needs validation in real-world conditions. The findings do not mean that low-CO₂ concrete is inherently less durable or unsafe. Its strength can be comparable to traditional concrete, and even with faster carbonation, if the material does not remain wet, the rate of steel corrosion may still be slow. "We need to better understand the long-term behavior of environmentally friendly concrete under different climate conditions," Albert noted. Thus, future projects may need to select concrete based on local climate rather than applying the same standard across all regions. Particularly humid areas may also require additional measures to limit water penetration.
"Current standards may therefore become a barrier to new, more environmentally friendly materials," Angst added.
The method is not yet ready for routine planning; its calculations are still complex and require further validation in actual buildings before researchers can develop simpler methods for evaluating new concrete types. Future climate tests may also consider climate change, as changes in the frequency and duration of rainfall and dry periods could alter corrosion rates and determine which low-CO₂ concrete remains suitable for a given location in the long term.
Challenges and Responses for Eco-Friendly Concrete
As environmental awareness grows, low-CO₂ concrete is gaining attention, but its long-term durability faces challenges from climate factors. The study shows that the impact of humidity on steel corrosion far outweighs the concrete formulation itself, meaning that concrete performance may vary significantly under different climate conditions. This finding prompts the construction industry to rethink standards, and future concrete selection may need to consider regional climate characteristics to ensure the durability and safety of structures.