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We all know that the main constituent of concrete is cement, which is obtained by breaking down calcium carbonate (limestone). When carried out on a large scale, the process leads to the generation of high amounts of carbon dioxide (about 7% of global CO₂ emissions) into the air.
This has serious environmental consequences as carbon dioxide is a greenhouse gas that is the leading cause of global warming.
To reduce carbon dioxide emissions from the concrete industry, the C4S (Calcium Carbonate Circulation System for Construction) project manager Prof. Takafumi Noguchi and Ippei Maruyama have developed a new type of concrete known as calcium carbonate concrete. The research was funded by the NEDO Moonshot Project, C4S Research and Development Project, Calcium Carbonate Circulation System for Construction.
Taking a cue from the process of hardening of aquatic fossils into calcium carbonate over time, the researchers found out that the same process could be applied to concrete. Calcium is an essential part of the reaction between cement and water to form concrete, and a less carbon-intensive method to get the same results would be beneficial to the environment.
The researchers developed a technique in which, instead of burning, limestone calcium is made from the discarded concrete and combined with carbon dioxide from industrial exhaust or air at a very low temperature.
Despite the newly found concrete being highly environmentally friendly, it is not strong as the typical concrete, and its use is limited only to small construction projects. Till now, it has been used to make only small blocks of few centimeters in length.
Prof. Maruyama sees the new development as a welcome step to control global warming up to some extent and aims to replace the typical concrete by increasing strength and size limits and reducing energy used in the production.