Effect of particle size of silica nanoparticles on hydration reactivity and microstructure of C-S-H gel

The most interesting aspect of research related to chemical reaction during cement hydration is the fundamental principles underlying these reactions and the rate of reaction expressed as evolution of degree of hydration over the time. Presently, several additives are used by concrete technologists to improve the performance and service life of cementitious materials. Application of nanomaterials, especially silica nanoparticles (SNPs), in construction has brought a new revolution by improving the properties of traditional building materials. However, the early age reactivity with cementitious system and is impact on the structure of hydrated products with the change in size and physical form (colloidal or powder). The present work is focused on the effect of particle size and form (i.e., colloidal and powder) of SNPs on its early age reactivity. Three different types of commercially available SNPs (i.e., Elk microsilica (100-300 nm), colloidal SNPs (8-15 nm) and powder SNPs (10-70 nm)) were used for the study. The results showed that the colloidal and powder SNPs have higher reactivity than the microsilica. Furthermore, Fourier transform infrared spectroscopy and ²⁹Silicon-nuclear magnetic resonance results revealed that in the presence of the colloidal and powder SNPs, the structure of C-S-H gel was more ordered as the Q² and Q³ peaks were very shaper and intense. However, with microsilica, unreacted silica peak Q⁴ was present, showing the slower reactivity of microsilica. These results show that SNPs not only accelerate the hydration rate significantly but are also helpful in the formation of more ordered and polymerized C-S-H, which is responsible for the higher compressive strength at the early age of hydration.