Adding sodium bicarbonate—baking soda—in powder form to concrete production could reduce the carbon footprint of the ubiquitous building material by 15%, without compromising mechanical performance, according to a study at the Massachusetts Institute of Technology. In addition to sequestering carbon, an advantage to adding baking soda is a faster-setting concrete mix that can allow formwork to be removed earlier, reducing the time required to complete a structure, says Admir Masic, the study's lead researcher and an associate professor in MIT’s department of civil and environmental engineering.
“The importance of this research is our understanding of the capacity of cement to mineralize CO2 in the early stages of making concrete,” without affecting the material’s mechanical properties, says Masic, lead author of the article "Cementing CO2 into C-S-H: A step toward concrete carbon neutrality," published March 28 in the journal PNAS Nexus.
He cautions that the research is preliminary. “Work is needed to commercialize the process,” Masic says.
The research team—also including MIT professor Franz-Josef Ulm, MIT postdoctoral student Damian Stefaniuk, doctoral student Marcin Hajduczek and James Weaver from Harvard University’s Wyss Institute—introduced baking soda and alite, an impure form of tricalcium silicate, in certain proportions and produced calcium silicon hydrate (CSH) and calcium carbonate.
The “key discovery” is the production of a “new material, which is a CSH carbonate composite,” Masic explains. The caveat is that the additive works to reduce embodied carbon by up to 15% only if the calcium carbonate is added in the fresh stage of mixing, when the material is still in a slurry form, say the researchers.
The process is simpler than some carbon sequestration technologies, which first harvest CO2, turn it into a liquid under pressure and inject it into a mix. There is no special equipment needed for the baking soda additive, for it is naturally in a soluble solid form, says Masic. “That simplifies the [potential for] translation into industrial applications,” he adds.
The team is already trying other soluble carbonates and bicarbonates and introducing them into more complex mixes.
“There are a lot of additives for concrete,” says Masic. “We have to make sure this system doesn’t affect the performance of other ingredients.”