Effects of the pozzolanic reactivity of nanoSiO2 on cement-based materials

The aim of this work is to understand the characteristics of the pozzolanic reactivity of nanoSiO(2) from studies of its pozzolanic reaction kinetics, morphology and structure of the hydrates and the influences of these features on the properties of cement-based materials, so as to explore a more targeted way of using nanoSiO(2) in cement or concrete. It revealed that the pozzolanic reaction of nanoSiO(2) is of the first-order and the apparent reaction rate constant of nanoSiO(2)-4 nm is about one order of magnitude bigger than that of silica fume, but the specific reaction rate constant is about one half to that of silica fume. A compacter gel structure and poorer crystallinity of the hydrates of nanoSiO(2) to those of silica fume are found, as well. The rate of hydration of cement at very early ages is enhanced by nanoSiO(2), but the rate slows down with aging due to the compact gel structure. To make the use of the high pozzolanic reactivity and ultrafine particle size of nanoSiO(2), as well as its resulting compact gel structure, colloidal nanoSiO(2) was applied onto the hardened cement mortar by brushing technique and a less permeable surface was resulted, which shows the potential of using nanoSiO(2) as a surface treatment material for cement-based materials. (C) 2014 Elsevier Ltd. All rights reserved.