Study on the hydration of slag-belite calcium sulfoaluminate-Portland cement composite cementitious system

In this paper, the slag powder (SP) and belite calcium sulfoaluminate (BCSA) were added into Portland cement (PC) to study the properties of composite cementitious system (SBP). The hydration mechanism of the SBP was studied by the setting time, the heat of hydration, X-ray diffraction (XRD), thermogravimetric (TG), and Fourier transform infrared (FTIR) spectroscopy. The properties of the SBP mortar were tested by mechanical properties, drying shrinkage, and pore size distribution. The microscopic morphology of the SBP mortars was observed by scanning electron microscopy (SEM). The results showed that the setting time of the SBP paste was increased and then decreased with the increase in SP dosage. The increase in SP dosage promoted the pozzolanic effect, it led to a higher generation of the calcium silicate hydrate (C -S -H) gel and the Ettringite (AFt) under the excitation of the fluorine gypsum (FG). The porosity of the SBP mortar was reduced, and the density was increased with the increase in SP dosage. However, when the SP dosage exceeds 25%, the excess generation of the AFt leads to micro-cracks, increases the volume of the macro pores, and decreases the mechanical and drying shrinkage properties of the mortar. This study can provide a theoretical basis for applying the SBP in engineering.