MIT study reveals how CO2 injection makes cement stronger by rewiring its chemical setting process

Researchers at MIT have used Raman confocal microscopy to directly observe the chemical reactions that occur when CO2 is injected into fresh cement paste. The study, published in the Journal of the American Ceramic Society, shows that CO2 initially captures calcium from the clinker, forming calcium carbonate and temporarily slowing normal hydration. This allows a silica gel network to form throughout the paste, which later reacts with calcium hydroxide to produce calcium silicate hydrate (C-S-H), the main binding compound in cement. This distributed formation of C-S-H results in a stronger, more uniform microstructure, with CO2-injected paste achieving 13 percent higher compressive strength at 24 hours compared to reference mixes. The findings clarify the mechanism behind CO2-injected concrete's improved early-age strength and open the door to optimizing the process. While the theoretical carbon offset potential is up to 40 percent of cement production emissions, the practical offset is likely lower but still significant. The study was conducted by the MIT Concrete Sustainability Hub in collaboration with CarbonCure Technologies and IIT Jodhpur.