Introducing additives to concrete manufacturing processes could reduce the sizeable carbon footprint of the material without altering its bulk mechanical properties, an MIT study shows. (Image: The researchers)

Despite the many advantages of concrete as a modern construction material, its production currently accounts for approximately 8 percent of global carbon dioxide emissions.

Recent discoveries by MIT engineers have revealed that introducing new materials into existing concrete manufacturing processes could significantly reduce this carbon footprint without altering concrete's bulk mechanical properties.

Approximately half of the emissions associated with concrete production come from the burning of fossil fuels, which are used to heat up a mix of limestone and clay that ultimately becomes the familiar gray powder known as ordinary Portland cement (OPC). While the energy required for this heating process could eventually be substituted with electricity generated from renewable solar or wind sources, the other half of the emissions is inherent in the material itself; as the mineral mix is heated to temperatures above 2,552 °F (1,400 °C), it undergoes a chemical transformation from calcium carbonate and clay to a mixture of clinker (consisting primarily of calcium silicates) and carbon dioxide — with the latter escaping into the air.

When OPC is mixed with water, sand, and gravel material during the production of concrete, it becomes highly alkaline, creating a seemingly ideal environment for the sequestration and long-term storage of carbon dioxide in the form of carbonate materials (carbonation). Despite this potential of concrete to naturally absorb carbon dioxide from the atmosphere, when these reactions normally occur, mainly within cured concrete, they can both weaken the material and lower the internal alkalinity, which accelerates the corrosion of the reinforcing rebar.

These processes ultimately destroy the load-bearing capacity of the building and negatively impact its long-term mechanical performance. Thus, these slow late-stage carbonation reactions, which can occur over timescales of decades, have long been recognized as undesirable pathways that accelerate concrete deterioration.

“The problem with these postcuring carbonation reactions is that you disrupt the structure and chemistry of the cementing matrix that is very effective in preventing steel corrosion, which leads to degradation,” said Professor Admir Masic.

However, the team's new carbon dioxide sequestration pathways rely on the very early formation of carbonates during concrete mixing and pouring, before the material sets, which might largely eliminate the detrimental effects of carbon dioxide uptake after the material cures.

The key to this new process is the addition of sodium bicarbonate — more commonly known as baking soda. In lab tests, 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 — enough to potentially make a significant difference in its global carbon footprint.

In addition, the resulting concrete sets much more quickly via the formation of a previously undescribed composite phase, without impacting its mechanical performance.

The composite, a mix of calcium carbonate and calcium silicon hydrate, “is an entirely new material,” said Masic. “Furthermore, through its formation, we can double the mechanical performance of the early-stage concrete.

“While it is currently unclear how the formation of these new phases will impact the long-term performance of concrete, these new discoveries suggest an optimistic future for the development of carbon neutral construction materials.”

“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,” added Masic.

For more information, contact Abby Abazorius at This email address is being protected from spambots. You need JavaScript enabled to view it.; 617-253-2709.