Climate data could unlock more low-carbon concrete

Cristhiana Albert (left) and Thilo Schmid (right), the two PhD students and first authors of the study, are investigating the behaviour of various concrete mixes in the laboratory. Image: Oliver Lang / ETH Zurich)

The researchers used detailed weather data to show how moisture affects the rate at which steel reinforcement corrodes inside concrete.

They found that the same concrete can have very different lifespans depending on the climate, even though the sites studied would be classified in the same way under current European standards.

The research looked at three concrete mixes in four locations with different climatic conditions: Zurich in Switzerland, Bergen in Norway, Manaus in Brazil and Huailai in China.

The team fed detailed weather data into a model that simulates fluctuations in moisture levels within concrete over time. This allowed them to assess how quickly steel reinforcement would rust after carbonation had taken place.

Carbonation occurs when CO₂ from the air penetrates concrete and changes its chemical composition. In reinforced concrete, that can reduce the natural protection around the steel, allowing corrosion to begin.

This is particularly important for low-carbon concrete, which can carbonate more quickly than conventional concrete. Current durability standards tend to focus heavily on this first phase, which can put lower-carbon mixes at a disadvantage.

But ETH Zurich said the more important question is how quickly the steel corrodes afterwards.

Cristhiana Albert, of the Institute of Building Materials at ETH Zurich, said moisture plays a decisive role. If concrete is wet, the corrosion process can take place up to 100 times faster than when it is dry.

Impact of climate on concrete

Ueli Angst, professor of durability of engineering materials at ETH Zurich, said, “The climate plays a much bigger role than we expected. The same concrete can behave completely differently in a different climate.”

The researchers said this is not always reflected in current standards. Zurich, Bergen, Manaus and Huailai would all fall into the same European exposure category of “alternating wet and dry”, despite having very different weather patterns.

Rainfall alone was also found to be a poor guide to corrosion risk. Bergen and Manaus both receive around 2,500mm of rain a year, but the model showed different corrosion rates because concrete absorbs water quickly and dries out slowly.

The key factor is the pattern of wet and dry periods, rather than annual rainfall or average humidity alone.

How reinforced concrete deteriorates. Illustration: Ueli Angst / ETH Zurich)

The results do not mean that low-carbon concrete is necessarily less durable or unsafe. ETH Zurich said some of the low-carbon concrete types examined could last 50 years or more, depending on the location.

Albert said, “We need to gain a better understanding of how environmentally friendly types of concrete behave over the long term under different weather conditions.”

The researchers said greater consideration should be given to a structure’s location and climate, rather than applying the same rules everywhere. In particularly damp regions, additional measures may be needed to reduce water ingress.

Angst said current standards could become a barrier to lower-carbon materials if they fail to account for their specific properties.