Industrial use of waste carbon dioxide gas as an upcycled feedstock into concrete has realized 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 the hydration have not been previously explored.A model oil well cement paste was subjected to carbon dioxide gas during mixing.The carbonate reaction products and hydration reactions were characterized.The materials science impacts were assessed using isothermal calorimetry, Quantitative X-Ray Diffraction, and scanning electron microscopy.The analysis identified the nature and timing of mineral phase development resulting from carbonation and subsequent hydration of the cement.Changes at the microstructural level were documented including reaction product grain size, morphology, paste porosity and pore filling.It was concluded that the formation of calcite does not inhibit the formation of the amorphous calcium silicate hydrate gel over the span of the observations (to 24 hours).The initial calcite formation consists of nano-sized particles that mature in size as hydration proceeds.These nano-sized particles may improve the mechanical strength of the fully cured cement paste.