Effect of the particle size of nanosilica on the compressive strength and the optimum replacement content of cement mortar containing nano-SiO2

•We present effect of nanosilica particle size on compressive strength.•We investigate effect of nanosilica particle size on optimum content.•We found that particle size affected directly on the compressive strength.•Microstructure results support compressive strength and optimum content results.

This research presents the compressive strengths and the microstructure photographs of cement mortars containing nanosilica (NS) with various sizes of 12, 20 and 40 nm and then compared with cement mortar with silica fume (SF). Tested results indicated that NS significantly improved compressive strength of cement mortar and the strength improvement was also dependent on the NS particle size. Cement mortar containing NS 40 nm gave higher compressive strength compared with NS 12 and 20 nm due to their agglomeration and ineffective dispersion. By varying the replacement contents of 3%, 6%, 9% and 12% NS by weight of cement, the optimum replacement content was 9% for all NS particle sizes and SF. These results indicate that the particle size of nanosilica affected only the compressive strength of cement mortar, but it had no effect on the optimum replacement content. The results of microstructure photographs are also supported the compressive strength and optimum replacement content results. NS particles presented high pozzolanic activity and could fill up pores, resulting in homogeneous, dense and compact microstructures.