Understanding Cement Carbonation As a Means of Carbon Dioxide Utilization

Industrial use of waste carbon dioxide gas as an upcycled feedstock into concrete has unlocked strength benefits when applied to masonry blocks and ready mixed concrete. The introduction of carbon dioxide to cement paste at the first moments of hydration produce thermodynamically stable carbonate reaction products. The carbonates are effectively formed in the fresh concrete mix and are homogenously distributed throughout the matrix prior to the development of any significant hydration products. The materials science impacts of the carbonation on cement hydration were studied as a means of understanding the physiochemical aspects of this CO₂ utlization approach. A model oil well cement paste was reacted with carbon dioxide gas during mixing. The materials science impacts were assessed through 24 hours of early hydration using isothermal calorimetry, Quantitative X-Ray Diffraction, and scanning electron microscopy. The carbonate reaction products and hydration reactions were characterized. The analysis identified the nature and timing of mineral phase development resulting from carbonation and subsequent hydration of the cement. It was concluded that the formation of calcite does not compromise the formation of the normal hydration products, including amorphous calcium silicate hydrate gel. The initial calcite formation consists of nano-sized particles that may improve the mechanical strength of the fully cured cement paste.