Climate-Based Model Could Support Wider Use of Low-Carbon Concrete
Researchers at ETH Zurich have developed a modelling approach that predicts the service life of reinforced concrete using local weather data. The method could help architects and engineers use low-carbon concrete more widely while limiting future corrosion and maintenance problems.
A Challenge For Lower-Carbon Cement
Cement production generates large amounts of CO₂. Cements with a lower carbon footprint can therefore play an important role in reducing the environmental impact of construction. However, concrete made with these cements often carbonates faster than conventional concrete.
During carbonation, atmospheric CO₂ enters the material and changes its chemical composition. This can reduce the natural protection around the reinforcing steel, allowing corrosion to begin. Current building standards mainly focus on delaying this first phase. According to the researchers, however, the speed of subsequent steel corrosion is equally important.
Local Climate Strongly Affects Durability
The ETH Zurich team studied three concrete mixes in four locations: Zurich, Bergen, Manaus and Huailai. They combined detailed weather data with a model that simulates changes in moisture levels inside concrete over time. This allowed them to estimate how quickly the reinforcing steel would corrode.
Moisture proved to have a greater influence than the composition of the tested concrete mixes. When concrete is wet, the steel can corrode up to 100 times faster than when it is dry. Despite their very different climates, current European standards place all four locations in the same ‘alternating wet and dry’ category.
Annual rainfall alone does not provide an accurate prediction. Bergen and Manaus, for example, both receive around 2,500 millimetres of rain per year. Yet the model produced different corrosion rates. Concrete absorbs water quickly but dries slowly, making the sequence and duration of wet and dry periods especially important.
Matching Concrete To Its Location
The findings do not suggest that low-carbon concrete is automatically less durable or unsafe. Its strength can equal that of conventional concrete. Although carbonation may occur more quickly, the reinforcing steel may still corrode very slowly if the material does not remain wet.
Some of the low-carbon concretes in the study could last for at least 50 years in certain locations, while deteriorating sooner elsewhere. Designers and engineers may therefore need to select concrete according to the building’s climate and exposure. In particularly damp regions, additional measures could reduce water ingress.
The model is not yet ready for practical use. Its calculations remain complex and require validation on existing structures. The researchers ultimately aim to create a simpler assessment method for new concrete types. Such climate-based testing could also account for changing rainfall patterns caused by climate change and support more informed use of lower-carbon construction materials.
Source: ETH Zurich
Photo: Ueli Angst / ETH Zurich