Impact of in-situ carbonation and slag replacement on hydration, microstructure and durability of cement paste

The present study examines the effect of in-situ carbonation on cement paste with varying slag replacement levels. CO₂ was injected during mixing, and the resulting performance of the samples was evaluated using various analytical methods. Results indicated that the phase assemblage of the pastes changed due to the introduction of CO₂ into the system. Calcium carbonate formed during the first 24 h after carbonation but did not fully crystallize until later dates. In-situ carbonation enhanced the early-age compressive strength by improving the degree of hydration of the paste, resulting in strength gains of 7.5 % to 17.3 % after 1 day. However, after 28 days, carbonated samples exhibited a strength reduction of up to 17.7 % in low and non-slag mixes, while higher slag samples maintained their performance. Moreover, the combined incorporation of slag and CO₂ significantly reduced the migration coefficient by as much as 68.6 %. These findings demonstrate the synergistic potential of slag and in-situ carbonation to enhance early age strength and refine the pore structure of the cement paste.