Effect of nano-SiO2/CaSO4 whisker–silica fume on the strength, drying shrinkage, and capillary water absorption of cement mortar

To compensate for the defects of silica fume (SF), which aggravates drying shrinkage, and increase the strength and durability of cement mortar, it was modified using 1 wt% nanosilica (NS) or calcium sulfate whisker (CSW) compounded with 2 wt% SF. The strength, volume stability, and durability of the cement mortar were characterized using the compressive strength, drying shrinkage, and capillary water absorption. The physical composition and microstructure of the samples are discussed in detail based on thermogravimetry, mercury intrusion porosimetry, and scanning electron microscopy measurements. The combination of SF and NS increased the generation of C–S–H gels and reduced the total porosity, thus increasing the early strength of the cement mortar and decreasing the capillary water absorption. Notably, on combining SF and CSW, additional calcium aluminate hydrates (AFts) were generated, and the mesoporosity (10–50 nm) was reduced. The fibrous AFt phase increased the later strength of the cement mortar, and the presence of additional AFt increased the solid phase volume, which compensated for the drying shrinkage.