Research on Influences of Ultrasonic Vibration Agitation Stirring on Carbonation Resistance of Cement-Based Materials after Absorption of CO2

To disclose influences of ultrasonic vibration agitation on the carbonation resistance of cement-based materials after absorption of CO2, the variation laws in internal carbonization zone were explored by the testing carbonization depth and carbonization range (pH variation range) of cement mortar after CO2 absorption at different ages. Results demonstrated that when CO2 absorption volumes of the cement mortar before carbonization were 0.44%, 0.88%, 1.32%, 1.76%, and 2.20% (28 d), the carbonization depth under ultrasonic vibration decreased by 5.5%, 12.3%, 21.7%, 20.7%, and 26.7% compared to those under mechanical stirring, respectively. When the ultimate CO2 absorption volume increased to 2.2% of cement mass, the extended degree of cement mortar was 103.23 mm, which decreased by 5.4% compared to that before CO2 absorption. pH variation values of the carbonization range under ultrasonic vibration presented a rising trend with the increase of CO2 absorption volume of cement mortar before carbonation. This indicated that, with the increase of CO2 absorption volume of cement mortar before carbonation increases under ultrasonic vibration, the carbonization process of the hardened body of cement mortar might be decelerated to some extent. Additionally, changes in internal composition and physical images of cement-based materials after absorption of CO2 were analyzed through microtest means like SEM and XRD. A carbonation resistance model was constructed, thus enabling disclosure of the variation mechanism of carbonation resistance of cement-based materials after absorption of CO2 under mechanical stirring and ultrasonic vibration. Results demonstrated that the higher CO2 absorption volume of fresh slurry generated more “nano-level” CaCO3 crystal nucleus. Accordingly, it could improve the porous structure of the cement mortar, decrease the quantity of capillary tubes significantly, improve the compaction degree of cement-based materials effectively, and lower the diffusion rate of CO2 in the cement paste base, thus improving the carbonation resistance. Research conclusions have important significance to decrease CO2 emissions and improve carbonation resistance of concrete.