Cement is one of the most common materials on Earth due to its high strength and low cost. However, its production is one of the main sources of carbon dioxide emissions. Washington State University researchers have developed a new technique for making cement that absorbs more carbon than it emits.
The problem of cement and CO2 emissions
Cement production requires high temperatures that are generally achieved by burning fuels, which emit CO2. This process also triggers chemical reactions that release huge amounts of CO2 into the atmosphere. In total, it is estimated that cement production is responsible for 8% of global carbon dioxide emissions.
The solution: biochar in cement
To reduce the environmental impact of cement production, researchers have been experimenting with substituting volcanic rocks for limestone or adding ingredients such as titanium dioxide, construction waste, baking soda or clay discarded during mining. Some teams have even used microalgae to grow the necessary limestone.
In this study, Washington State University researchers have investigated a new technique that involves the use of biochar (charcoal when used as a soil amendment), a type of carbon made from organic waste. Although biochar has been used in cement production before, this time the team first treated it with cement wash water. This increased its resistance and allowed a greater proportion of the additive to be mixed. But more importantly, the biochar was able to absorb up to 23% of its own weight in carbon dioxide from the surrounding air.
Carbon-negative cement
In experiments, the team created cement that contained 30% treated biochar and found that the resulting cement was carbon-negative: it absorbed more carbon dioxide than it emitted during its production. According to the researchers’ calculations, 1 kg of cement with 30% biochar removes around 13 g of CO2 more than is emitted during the production of the material. Considering that regular cement is typically responsible for emitting around 0.9kg of CO2 for every 1kg of material, the difference is noticeable.
Furthermore, biochar cement also maintains its strength. After 28 days, the compressive strength of the cement was 27.6 MPa, similar to that of normal cement.
Additional benefits of biochar in cement
Using biochar to produce cement not only reduces the carbon footprint, but also diverts biomass from other destinations that could potentially release more CO2.
Biochar cement is expected to continue to absorb CO2 throughout its multi-decade lifespan. Although more research is needed to optimize and scale up the method, this new technique for producing cement has great potential to reduce the carbon footprint of the construction industry.
The development of more sustainable construction techniques and materials is essential to achieve a more circular economy and reduce environmental impact. Cement production is one of the biggest challenges in this regard, so the development of carbon-negative cement is excellent news. In addition to reducing carbon dioxide emissions, this new technique can divert organic waste from other, less sustainable destinations and improve water quality by treating cement wash water.
It is important to note that although this new technique is a great improvement, reducing the environmental impact of cement production cannot be achieved through technological innovation alone. There is also a need for the construction industry, consumers and governments to adopt more sustainable practices and policies in the selection and construction of buildings, but that is another story.
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