Compressive strength and microstructural development of cement paste incorporating nanosilica with different particle sizes

Nanosilica particles are among the most studied nanomaterials in cementitious mixtures. However, literature on the effect of nanosilica particle size on the performance of these mixtures is still limited, with sometimes inconsistent findings. This study aims to address this gap by including the synthesis and application of different-sized nanosilica particles in one study. A uniform synthesis method was used to achieve nanosilica with four distinct average particle sizes (10, 35, 65, and 90 nm), covering the whole nanoscale range. The nanosilica particles were then fully characterized and utilized in cement paste at 1, 2, and 3 wt% of the cement. The compressive strength, heat evolution, microstructure, and rheological behaviour of the resultant pastes were investigated. The results revealed that the smallest particle size of nanosilica (10 nm) provided the highest compressive strength enhancement (over 100 % enhancement when used at 2 wt% of cement). The high pozzolanic reactivity of such small nanosilica particles at 2 wt%, together with their acceleration effect on cement hydration and densification of the paste microstructure, all contributed to this strength improvement. Overall, the enhancing effects of the nanosilica particles on the compressive strength of the pastes were less substantial when their particle size increased from 10 to 90 nm at any given concentration. All the nanosilica particles also increased the viscosity of the paste. This increasing effect was higher for smaller-sized nanosilica particles and at higher concentrations.