Compared with Fig. 12 (a) and Fig. 12 (b), it could be seen that there were visible pores on the surface of C-S-H gel formed by pure cement hydration. However, after adding 1.0 wt.% 15 nm of NS into cement, the surface of C-S-H was dense and had no obvious pores, indicating that the addition of NS could be filled into C-S-H gel pore, and improving the microstructure of C-S-H gel.