Influence of sodium aluminate on cement hydration and concrete properties

The influences of sodium aluminate (SA) on cement hydration were studied. Heat evolution of cement pastes with and without SA was monitored by a differential scanning calorimeter (DSC). Hydration products were identified using scanning electron microscope (SEM), X-ray diffraction (XRD), thermal analysis (TG–DSC), and mass spectrum (MS). Pore structures of cement pastes were analyzed using nitrogen absorption method. Concrete strength and chloride penetration resistance were also evaluated. The mechanisms by which SA contributes to cement hydration and microstructure development were explored. The results indicate that addition of SA resulted in changed calcium sulfoaluminate morphology, form acicular AFt to tabular AFm. Adding of SA increased the volume of small capillary pores (5–30 nm) and reduced the volume of larger pores (>30 nm). Cement setting time reduced significantly as SA addition reached up to 4%. 1.5% SA addition can enhance concrete strength at early age but reduce it at later age. Addition of SA also improved chloride penetration resistance of concrete.