Effect of Type, Size, and Dosage of Nanosilica and Microsilica on Properties of Cement Paste and Mortar

Many studies attention are being devoted to use of nano-scale silica particles in cementitious materials by considering the success of using silica fume in concrete as an active pozzolan. The effect of various types of nanosilicas (NSs), both in powder and colloidal forms, with specific surface area (SSA) from 80 to 380 m²/g (0.016 to 0.078 ft²/lb) on the mechanical properties of cement paste and mortar were studied. Results showed a substantial reduction in the workability of mixtures by adding NS particles. The compressive strength of specimens was not affected by NS in powder and colloidal form, but was only sensitive to changing SSA. The use of NS enhanced the strength of cement paste compared to the control mixture, and the level of improvement increased for higher dosages of NS. However, by increasing the SSA more than 90 m²/g (0.018 ft²/lb), the compressive strength of specimens decreased. A low percent of various NSs did not affect compressive strength of mortar. However, adding a high dosage of NS particles created the same effect as using microsilicas.