Effects of particle size of colloidal nanosilica on hydration of Portland cement at early age

The aim of this study is to evaluate the effects of different particle sizes colloidal nanosilica (30, 60, and 140 nm) on the early performance of Portland cement. Flowability, mechanical property, and microstructural characterization tests were conducted to investigate the macroscopic and microscopic properties. The results revealed that the flowability of the paste decreased with the reduction of the particle size of colloidal nanosilica. The main reason was that the sol may form flocculation restricting a part of free water under ion environment, and this phenomenon became more serious as the particle size decreased. The compressive strength with 60-nm sol was higher than that of the other two, and hydration activities under different situations were further proved by hydration heat analysis. The reasons causing this result were mainly because flocculation limited the original chemical activity like pozzolanic and seeding effects of nanomaterials. Through thermogravimetric analysis and X-ray diffraction, it can be concluded that the seeding and pozzolanic effects of nanomaterials dominated the hydration process at different periods. Comparing images from scanning electron microscopy, the microstructure was most compact when incorporated into 60-nm sol, and filling effects also contributed to the performance during hardening.