Experimental study on Portland cement/calcium sulfoaluminate binder of paste filling

The curing time and compressive strength of ordinary Portland cement have its limitations, which limits its application range. In this article, the ratio of ordinary Portland cement/CSA ratio is optimized by laboratory test, and the composition and structure of hydration products are changed to achieve the performance adjustment. Then, the microstructures of the optimized cementing materials at different stages were observed and compared by the analysis of hydration process and scanning electron microscopy. The experimental results show that the setting time decreases with the increase of sulphoaluminate cement content in the system and prolongs with the increase of gypsum content, and the change trend of initial setting time and final setting time is consistent. When the content of sulphoaluminate cement exceeds 14% or the content of gypsum exceeds 16%, the compressive strength of cementing material decreases greatly in the early and late stages, but the strength of cementing material does not increase beyond this range. Composite admixtures H3BO3 (0.3%) + Na2SO4 (0.1%) and H3BO3 (0.3%) + NaNO3 (0.1%) can not only improve the setting time of composite cementing materials, but also improve the strength of composite cement.