The environmental impact of concrete
As we have seen, the most common building materials are complex compounds. This makes it difficult to measure exactly the environmental impact of their production, because it requires an analysis of each substance used. However, we can get a clear idea of the size of the environmental impact of concrete from the environmental impact of cement.
Graphics 1 by F. Seganfreddo
The most recent estimates were published in November 2023 by Andrew Robbie and Peters Glen, two researchers at the Center for International Climate Research in Oslo involved in the Global Carbon Project (GCP). The GCP is an international research project that has been monitoring CO2 emissions from countries around the world since 2001. Their work consists of creating a searchable data set that collects data from various scientific publications around the world. It is a big data synthesis project, similar to the effort led by the IPCC to synthesize scientific studies on climate change.
According to this data set, in 2021, cement production was responsible for the emission of 1.6 billion tons of CO2 into the atmosphere, a 120% increase in just 20 years (754.33 million tons in 2001). This impressive increase is well shown in the graph produced by the Oxford program, Our World in Data.
Graphics 2 by F. Seganfreddo
To better understand these data, it is important to consider how they were calculated. The impact of cement, in fact, is measured on the basis of CO2 emissions from the chemical processes of production alone, that is, without counting emissions from the use of cement, such as fossil fuels used for its transportation, the impact of building construction, land consumption, etc.
During the cement production stage, limestone and clay are melted at high temperatures (about 1450°C), leading the limestone to decompose into calcium oxide and carbon dioxide. About half of the total CO2 emissions from cement production are due to this chemical reaction (CaCO3 + heat → CaO + CO2). The other half comes from emissions during production and transportation. According to estimates by the independent organization Fakta o Klimatu, if cement emissions are considered as a whole, together with the fossil fuels burned in the production process, it comes to a total emission of about 2.8 billion tons of CO2, or 8% of global emissions. As Fakta o Klimatu researchers explain, if the cement industry were a country, its emissions would come only after those of China and the United States.
Carbi Crete
One possible solution for reducing the environmental impact of concrete production comes from a Canadian start-up, CarbiCrete. Founded by a team of engineers from McGill University, based in Montréal, the company is involved in concrete production by following a new production method based on removing excess CO2 from the atmosphere. Specifically, production takes place in two stages:
- During the first stage, concrete is produced not from a cement mix, but from a mix of metal slag, waste from the metallurgical industry. Using this mix of metals avoids emissions from cement production, which, as we have seen, are responsible for nearly half of the Co2 emissions in concrete production;
- The second step is to treat the concrete products with CO2. CO2 is captured from the atmosphere to mineralize the calcium in concrete products. During this treatment, the GHG reacts with the metal slag to form calcium carbonate. This process alters the properties of the initial concrete, effectively making it similar to traditional concrete and suitable for use in construction.
The first stage, avoiding the use of cement, reduces CO2 emissions to zero. The second stage, on the other hand, reduces the amount already in the atmosphere by encapsulating the greenhouse gas in the building material. Thanks to this new process, CarbiCrete’s products are called “carbon-negative”, since more CO2 is removed in their production than is produced.
Co2 removal or emissions reduction?
CarbiCrete is not the only company in the field, in fact there are many companies in recent years that are moving to address this issue, using different technologies to reduce the emissions generated by the production of concrete products.
Graphics 3 by F. Seganfreddo
Each company is focusing on different aspects of concrete production, looking for new technologies to reduce emissions from that part of the process. The company Sublime System, for example, replaces the initial cement burning stage with an electrochemical process, thus avoiding emissions from burning fossil fuels.
The main difference between CarbiCrete and other companies is that the latter do not use technologies to extract CO2 from the atmosphere, but rather seek technologies that produce fewer and fewer emissions. According to proponents of this method, this would be the true path to “green” cement production, as stated by Sublime System‘s founder in an interview for Musingsmag: “The long-term sustainability of ‘green cement’ depends on cement production technologies that avoid CO2 emissions, rather than those that rely on CO2 capture. We call these technologies ‘true-zero,’ not ‘net-zero,’ which instead involves some additions and subtractions to achieve zero”.
Conclusions
High-temperature treatment of cement is responsible for about half of the CO2 emissions during the production of concrete, the most widely used construction material in the world. The first way to reduce these emissions is to replace cement with other materials. The company CarbiCrete uses steel scraps instead of cement and treats its products with CO2 extracted from the atmosphere. In this way, the entire process not only reduces emissions, but allows excess CO2 that would otherwise remain in the atmosphere to be encapsulated in a building material, creating harm to human and planetary health. Although there are alternative approaches, it is difficult to say which approach to reducing emissions is better. What is certain is that efforts must be made to reduce the environmental impact of the entire industry, and any effort in this direction deserves attention.
After graduating with a Master’s degree in Philosophy from the University of Padua, he attended a Master’s degree in Science Communication at the University of Trento. He currently works as a science communicator for foundations and research centres in Italy. He collaborates as a writer for Atmosphera Lab.
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