Hydration behaviors, workability, and strength variations in direct aqueous carbonation (DAC) of Portland cement paste.

This study investigates the mechanisms behind direct aqueous carbonation in concrete manufacturing, focusing on its effects on workability and strength. Through an analysis of cement paste under varying water-to-cement ratios (0.5, 0.55, and 0.6) and CO additive amount (0%, 0.1%, and 1%), the results demonstrate that early carbonation accelerates the setting process. Higher CO additive amounts and lower w/c ratios further reduce setting time and fluidity, also increase free water consumption, which negatively affects the pore structure and compressive strength. However, as the transformation of amorphous calcium carbonate to calcite, enhancing hydration during curing and ultimately improving the final compressive strength. This study elucidates the various effects of CO addition to cement paste on fresh and hardened paste during the direct aqueous carbonation process, shedding light on how it influences hydration, workability, and strength, contributing to sustainable concrete production.