Concrete is the world’s second most consumed material, after water. However, despite its many advantages as a modern construction material – including its high strength, low cost, and ease of manufacture – large quantities of carbon dioxide are released during the production of concrete. In fact, concrete production accounts for approximately eight percent of global CO2 emissions.
In an effort to overcome this problem, a team of researchers led by the Massachusetts Institute of Technology (MIT) has found that introducing new materials into concrete manufacturing processes could significantly reduce its carbon footprint, without changing its mechanical properties.
Over half of the emissions linked to concrete production are caused by the burning of fossil fuels that are used to heat up a mixture of limestone and clay which then becomes the gray powder known as ordinary Portland cement (OPC). Although the energy required for this process could eventually be substituted with electricity from renewable sources, the other half of the emissions is inherent in the material itself. As the mineral mix heats up to over 1,400C, it changes from calcium carbonate and clay to a mixture of calcium silicates and CO2, which is released into the atmosphere.
Although concrete has the potential to naturally absorb CO2 from the atmosphere through a process called carbonation, when these reactions normally occur, mainly within cured concrete, they can weaken the material, leading to long-term deterioration. By contrast, the new process introduced by the MIT team relies on the formation of carbonates during the early stages of concrete production, before the material sets. This approach can potentially eliminate the detrimental effects of CO2 uptake after the material cures and accelerate construction times.
The key to the new process is the addition of sodium bicarbonate (baking soda), an inexpensive ingredient that could help mineralize during the early stages of the manufacturing process up to 15 percent of the total amount of CO2 associated with cement production – enough to significantly reduce the material’s global carbon footprint. Moreover, the resulting concrete sets much more quickly, without impacting its mechanical performance, thus allowing the construction industry to be more productive.
“Our new discovery could further be combined with other recent innovations in the development of lower carbon footprint concrete admixtures to provide much greener, and even carbon-negative construction materials for the built environment, turning concrete from being a problem to a part of a solution,” concluded co-author Admir Masic, a professor of Environmental Engineering at MIT.
The study is published in the journal PNAS Nexus.
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