Effect of polyacrylamide on the carbonation behavior of cement paste

This work investigated the influence of polyacrylamide on carbonation behaviors of cement pastes by measuring carbonation depth and pH value. Electrochemical impedance spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry were performed to monitor changes in hydrates and microstructure of cement pastes to dissect underlying mechanisms. The results show that polyacrylamide decreases the amount of portlandite (CH) and alters its morphology from a larger size with parallel-stacked lamellar structure to a smaller size with edge-corroded structure, thereby enhancing CH reactivity with CO2 during carbonation. Higher Ca/Si ratios of C-S-H phases with a higher carbonation rate form in the presence of polyacrylamide. Polyacrylamide reduces porosity and improves pore refinement by transferring capillary pores to gel pores due to filling effect of CaCO3 grains with a small crystal size during carbonation. Overall, polyacrylamide yields an accelerating effect on the carbonation of cement paste in a dosage dependent manner.