Experimental study on the effect of nano-SiO2 on long-term properties of negative-temperature cement paste

The current research on the application of nanomaterials in concrete is mainly carried out under positivetemperature curing conditions, while research under negative-temperature curing conditions is very scarce. This paper investigated the effect of nano-SiO2 on long-term strength and chloride diffusivity of cement pastes cured at negative temperature (-5 degrees C). Thermogravimetric analysis (TGA) confirms that the low-dosage nanoSiO2 can still exert the pozzolanic effect within negative-temperature cement paste even after 120 days. The macro results show that low-dosage nano-SiO2 effectively shortens the curing age required for strength and durability development. It is further proved that compared to the promotion effect of nano-SiO2 on hydration, the optimization of internal pore structure by nano-SiO2 plays the dominant role in shortening the curing age required. Furthermore, it is found that the low sensitivity of strength to the microstructure results in the insignificant effect of nano-SiO2 on the long-term strength. In contrast, nano-SiO2 can effectively improve the long-term chloride permeability resistance through increasing the tortuosity of pore structure and decreasing the critical pore diameter and threshold pore diameter.