Effect of nano admixtures on the engineering properties and microstructure of sulphoaluminate cement mortar at −10 °C

The traditional cement-based cementitious materials cannot hydrate at −10 °C, and the sulfoaluminate cement can hydrate, but the cement slurry has poor properties and low strength. Three kinds of nano admixtures (silica fume, nano-SiO2, nano-CaCO3) were selected as modified materials, and the effect of nano admixtures on the fluidity, strength, internal temperature, micro-morphology, mineral composition and pore structure of sulphoaluminate cement mortar were studied under the condition of mixing and curing of cooled materials at −10 °C. The results show that the fluidity, compressive strength and flexural strength of mortar increase first and then decrease with admixture content. When the content of silica fume, nano-SiO2 and nano-CaCO3 is 3 %, 0.5 % and 0.5 % respectively, the fluidity and strength of mortar are the maximum. With the optimum content of three kinds of nano admixtures, nano-SiO2 has the best improvement on the strength and internal temperature of mortar. The hydration of sulphoaluminate cement can continue at −10 °C. At the age of 1 d, ettringite is yielded in the mortar. After the addition of nano admixtures, the amount, characteristic diffraction peak and diffraction intensity of ettringite in mortar increase. The nano admixtures can optimize the pore structure of mortar with the age of 1 d. The fractal dimension of pore structure of mortar with 0.5% nano-SiO2 is the minimum.