Effect of Nano-SiO2 Content on the Setting Time and Mechanical Properties of Tricalcium Silicate

Using analytically pure calcium carbonate and silica as raw materials, high purity tricalcium silicate (C3S) is prepared by solid-state reaction. The tricalcium silicate was sintered at a temperature of 1550°C with the heat preservation time of 6 h. The final sample needs three times of calcination circles. Ultrasonic cleaning machine was used to disperse the water and different amount of nano-SiO2 (0, 1, 2, and 3 wt%) for 5 min, then mixed with C3S, and formed into standard blocks. The setting time and compressive strength of each age (1, 3, 7, and 28 days) was measured to investigate the effect of nano-SiO2 on the setting time and mechanical properties of C3S. The results show that the content of free calcium oxide (f-CaO) in C3S sample is lower than 0.8% tested by glycol ethanol method sensitive, C3S crystal type is triclinic system T1 by X ray diffraction (XRD). The nano-SiO2 cut down the setting time of C3S and the setting time of C3S is decreasing with the increasing content of nanoSiO2. The initial setting time of C3S with different content of nano-SiO2 (0, 1, 2, and 3 wt%) are 187, 129, 105, and 85 min, respectively, the final setting time are 219, 194, 158, and 130 min. The addition of nano-SiO2 can significantly improve the early compressive strength of C3S, but the effect of nano-SiO2 on improving compressive strength of C3S is gradually weakened with the hydration of C3S.