Ettringite and Monosulfoaluminate in Polycarboxylate Type Admixture Dispersed Fresh Cement Paste

摘要

The influence of polycarboxylate type admixture (PCA) on ettringite (AFt) and calcium monosulfoaluminate (AFm) formation in cement paste hydrated within two hours was investigated. It was found that PCA can accelerate initial AFt and AFm formation evidently. Chemical analysis and TGA results indicate that the amount of AFt and AFm in PCA dispersed cement paste hydrated for fifteen minutes are approximately 13.5 and 3 time of those in control pastes, respectively. FTIR and XRD spectra also verified this phenomenon. Consequently, adsorption amount of PCA to cement is lower for more AFt and AFm present in the hydration system, and it was confirmed by experiments and was compared with naphthalene formaldehyde sulphonate condensate high range water reducer. Relative flow area and relative flow area retention after two-hour hydration of cement paste which had w/c of 0.30 and was dispersed by PCA employed in the present paper are both more than 30. It is a key factor that PCA promotes initial AFt and AFm formation for better compatibility between PCA and cement other than steric hindrance mechanism.