Cement is the primary binding material used in concrete, a vital construction material. But the production of cement is very polluting. The cement industry is the third largest source of industrial air pollution, including sulfur dioxide, nitrogen oxides and carbon monoxide. Moreover, cement currently accounts for around 8% of global carbon dioxide emissions.
Many of the emissions from concrete production are attributed to the burning of fossil fuels such as oil and natural gas, which heat up the limestone and clay that becomes Portland cement. Mixing these minerals creates a chemical transformation that creates clinker and carbon dioxide, which inevitably ends in the air. When the cement is mixed with water, sand, and gravel material, it becomes highly alkaline, which can, in theory, create an ideal environment for the sequestration and long-term storage of carbon dioxide. However, over time these reactions will weaken the material and lower the internal alkalinity, which will destroy the load-bearing capacity of the building and negatively impact its long-term mechanical performance. As a result, these slow late-stage carbonation reactions will accelerate concrete deterioration and inevitably release carbon back into the air.
MIT researchers may have found a way to make cement and concrete less damaging to our health and the environment. They discovered that adding new materials into existing concrete manufacturing processes can reduce carbon emissions without changing the concrete’s properties. They use sodium bicarbonate, commonly known as baking soda. While testing this in the lab, the researchers found that up to 15 percent of the total amount of carbon dioxide associated with cement production could be mineralized during the early stages of the development process. This could be enough to reduce the material’s global carbon footprint significantly. Adding baking soda with limestone and clay creates a new material that seems to set more quickly than without the baking soda, without impacting its mechanical performance.
It is currently unclear how the formation of these new phases will impact the long-term performance of concrete. Still, this study suggests that introducing pre-cure stage carbonation could simultaneously be harnessed as a critical carbon sink while potentially mitigating some of the mechanical consequences seen during late-stage carbonation. Shifting these reactions earlier can relieve the internal stresses before they can destructively accumulate.
The idea of making cement and concrete less environmentally damaging isn’t new. Many companies are exploring the approach to taking out the carbon dioxide from the concrete. Still, this new research stresses how important these efforts are and can be for the environment. The researchers believe that combined with other recent innovations, their discovery could help lower the construction industry’s carbon footprint and turn concrete from being part of the problem into a solution.