MIT researchers used Raman confocal microscopy to directly visualize, for the first time, the chemical sequence triggered when CO₂ is injected into fresh cement paste. The process unfolds in three stages: CO₂ first sequesters calcium as calcium carbonate, causing silicates to form a distributed silica gel network; then, as normal hydration resumes, this gel reacts with calcium hydroxide via a pozzolanic reaction to produce calcium silicate hydrate (C-S-H) spread uniformly throughout the matrix; finally, the more evenly distributed C-S-H yields a stronger microstructure. Cement mixed with 1% CO₂ by weight achieved 13% higher compressive strength at 24 hours. The findings, published in the Journal of the American Ceramic Society in collaboration with CarbonCure Technologies, also clarify that calcium carbonate crystals are passive bystanders rather than active seeds for C-S-H growth, opening new avenues to optimize CO₂ dosage and potentially offset a meaningful fraction of cement production emissions.
