Characteristics of cement mortar with nano-SiO2 particles

The amorphous or glassy silica, which is the major component of a pozzolan, reacts with calcium hydroxide formed from calcium silicate hydration. The rate of the pozzolanic reaction is proportional to the amount of surface area available for reaction. Therefore, it is plausible to add nano-SiO 2 particles (NS) to make high-performance concrete. The compressive strengths of cement mortar were evaluated at various water-cementitious material ratios (w/cm). Five different w/cm were used, including 0.23, 0.25, 0.32, 0.35, and 0.48 and four contents of NS, 3, 6, 9, and 12% by weight of cement. The compressive strengths of cement mortar with the addition of silica fume were also evaluated at a w/cm of 0.35 to compare with mortar containing nano-SiO 2 particles and three contents of silica fume were: 5, 10, and 15% by weight of cement. The experimental results show that the compressive strengths of mortars with NS were all higher than those of mortars containing silica fume at 7 and 28 days. It was demonstrated that the nano-particles were more valuable in enhancing strength than silica fume. This paper also analyzes some available examinations to monitor the hydration progress continuously, such as SEM observation, residual quantity test for Ca(OH) 2 , and the rate of heat evolution. The results of the examinations indicate that the SiO 2 in nano scale behave not only as a filler to improve the microstructure, but also as an activator to promote pozzolanic reactions.