Today’s production of concrete and cement generates large emissions of carbon dioxide. One way to reduce the climate impact of cement is to take advantage of the material’s natural ability to capture carbon dioxide through carbonation. It is a natural process that can be enhanced by the smart design of concrete structures.
Carbonation is a natural process where carbon dioxide emitted from the limestone in the production of cement is reabsorbed. When cement is used as a binder in concrete, the concrete absorbs carbon dioxide from the air over the entire lifetime of the concrete, i.e. the cement undergoes carbonation. This means that bridges, buildings and other concrete structures reabsorb and convert the concrete into limestone. This has long been considered problematic since it also means the material erodes, but in light of climate change, the ability to bind large amounts of carbon dioxide through carbonation can also be seen as beneficial.
Unexpectedly large effect
Katarina Malaga, who researches sustainable concrete at RISE, says that many in the industry were surprised by new figures showing that concrete structures capture large amounts of carbon dioxide:
– “The latest IPCC report describes the role of cement in carbon dioxide emissions, but it also shows that, over their lifetime, concrete structures absorb 50 percent of the carbon dioxide emitted during cement production. This demonstrates the chemical reactivity of cement-based materials and can be incredibly important.”
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Amplifies positive effects
RISE has implemented several initiatives to develop methods to further strengthen and take advantage of the positive effects of concrete carbonation. According to conservative calculations, concrete structures in Sweden absorb around 300,000 tonnes of carbon dioxide per year, but according to Malaga, there is great potential to significantly increase uptake. For example, by handling demolition materials better, absorption could be doubled to 600,000 tonnes a year. When construction waste is crushed, the waste should be spread out so that it is exposed to air for maximal carbonation. Then it becomes a carbon sink while the material can be used for new concrete and other products.
– “When designing structures, it’s also important to understand how carbonation works,” says Malaga. “The material must be reactive, which means it’s important in the design process to leave surfaces open so that they can absorb carbon dioxide from the air.”
It’s important in the design process to leave surfaces open so that they can absorb carbon dioxide from the air
Utilising a natural process
RISE develops strategies for concrete carbonation with the goal of speeding up the natural carbonation process. By enhancing these types of methods, it is possible to create carbon sinks that have a time span of no less than 100-150 years. It thus becomes a relatively simple and inexpensive form of carbon capture and storage (CCS).
According to researchers at RISE, to make progress in this it is important to systematise measurement methods and calculations of carbonation capacity depending on the concrete composition and exposure environment. And knowledge among customers and decision-makers needs to increase.
– “One way would be to ensure that calculations of natural carbonation are included in the climate declarations that serve as a basis for standards bodies,” says Malaga.
