Effects of mixing sequences of nanosilica on the hydration and hardening properties of cement-based materials

Effects of nanosilica (NS) on improving physicochemical property of cement is greatly dependent on its dispersion. This research aims to study the influences of mixing sequences of raw materials on the dispersion of NS and the properties of cement-based materials. Particle size distribution, hydration heat, setting time and compressive strength were measured to determine the optimal mixing sequence of NS in cement-based materials. Phase contents of calcium hydroxide (CH) and other hydrates, Ca/Si atom ratios of the C-S-H gel as well as microstructures of cement pastes were also analyzed to assess the effects of the nanosilica added at different mixing sequences on properties of cement-based materials. Smaller mean particle size of NS in cement solution and advanced induction period of cement hydration suggested that the mixing sequence of PCE's addition after NS was the best for the property gain features of cement-based materials, and the enhancement of 3d compressive strength could reach 42.5%. Protocol of combined mixing of NS under ultrasonication with PCE was better but this could be dependent on the PCE type. (C) 2020 Elsevier Ltd. All rights reserved.