Baking soda may help concrete absorb carbon, MIT researchers find

By Niall Patrick Walsh Apr 11, '23

New research from MIT has found that adding sodium bicarbonate, otherwise known as baking soda, to concrete mixtures may make a significant dent in the material’s carbon footprint. The findings, published recently in the journal PNAS Nexus, also suggest that the addition of sodium bicarbonate may accelerate construction times through quicker concrete setting.

The research was led by MIT professors of civil and environmental engineering Admir Masic and Franz-Josef Ulm, MIT postdoc Damian Stefaniuk, doctoral student Marcin Hajduczek, and James Weaver from Harvard University’s Wyss Institute. With concrete production accounting for approximately 8 percent of global carbon dioxide emissions, and concrete being the world’s second most consumed material after water, the team sees innovation in the material’s environmental performance as being a key component to reducing global greenhouse gas emissions.

Half of the emissions associated with concrete production come from the burning of fossil fuels to heat up a mix of limestone and clay to ultimately create cement powder; emissions which the team notes could be limited by increased adoption of renewable solar and wind sources. The other half of emissions are generated by the release of carbon dioxide from the limestone-clay mixture during the heating process, whose mitigation is less obvious.

According to the latest MIT paper, such emissions could be partially offset through the addition of sodium bicarbonate during concrete production, when the cement mixture is combined with water, sand, and gravel. According to the team, the addition of sodium bicarbonate to the mixture has proven to induce a carbon sequestration process, whereby CO2 is absorbed and crystalized within the concrete mixture before it dries, thus ‘locking in’ the CO2.

The concept of concrete absorbing CO2 is not new. Traditional concrete has the capacity to absorb carbon for decades after construction, claiming back up to 40% of the emissions released during the initial cement mixing process according to the MIT paper. However, the absorption of CO2 at this late stage is actively discouraged due to the potential for newly-formed carbon crystals to weaken the material’s performance, cause cracks, and accelerate the corrosion of steel reinforcement in concrete.

MIT’s new approach of adding sodium bicarbonate, by contrast, shifts the carbon absorption to the concrete mixing and curing phase, where the formation of carbon crystals occurs before the material dries, thus having no detrimental impact on its subsequent performance. In lab tests using the sodium bicarbonate substitution, the team demonstrated that up to 15 percent of the total amount of carbon dioxide associated with cement production could be mineralized during these early stages.

“It's all very exciting because our research advances the concept of multifunctional concrete by incorporating the added benefits of carbon dioxide mineralization during production and casting,” team leader Masic said about the study. “Furthermore, through its formation, we can double the mechanical performance of the early-stage concrete.”

News of the research comes one week after LEVER and Atelier Ten published a paper seeking to ‘debunk four mass timber myths,’ and one month after a new 3D printing factory was unveiled in Mexico that aims to cut construction times by 50 percent. Also in March, University of Michigan researchers merged 3D printing with computational design to create ‘ultra-lightweight, waste-free concrete,’ while in February, an IAAC/WASP team created a ‘solid and expressive’ 3D printed wall made from earth.

Source :

https://archinect.com/news/article/150345793/baking-soda-may-help-concrete-absorb-carbon-mit-researchers-find