The application of thermal analysis to study the hydration behavior of tricalcium aluminate-gypsum in the presence of polycarboxylate-based superplasticizers

The effect of polycarboxylate-based superplasticizers (PCE) on hydration behavior of tricalcium aluminate-gypsum system, which is a partial system of ordinary Portland cement, is investigated by means of isothermal calorimeter, thermal analysis and X-ray diffraction. The adsorption characteristics of PCE and morphology change of ettringite crystals upon PCE introduction are also examined by gel permeation chromatography and scanning electron microscope, respectively. Our results show that the initial hydration process and formation of crystalline monosulphate are significantly slowed down due to the presence of PCE. It is concluded that this retardation phenomenon is due to a stabilization effect induced by the adsorption of the PCE on ettringite precursor. Moreover, the morphology and size of ettringite crystals are found to be changed by the adsorption of PCE.