After 28 days of hydration, it could be clearly seen from Fig. 12 (c-e) that there were more pores in the microstructure of pure cement (WPS), and the overall structure was loose. However, with the addition of NS, the number of pores in the system decreased, the hydration products were refined, and the overall structure compacted. The system mixed with particle size of 15 nm NS (WNS15) had the most obvious effect on microstructure improvement, which was attributed to the better pozzolanic activity, filling effect and nucleation effect of the smaller particle size of NS.