Effects of colloidal nanoSiO2 on fly ash hydration

The influences of colloidal nanoSiO(2) (CNS) addition on fly ash hydration and microstructure development of cement-fly ash pastes were investigated. The results revealed that fly ash hydration is accelerated by CNS at early age thus enhancing the early age strength of the materials. However, the pozzolanic reaction of fly ash at later age is significantly hindered due to the reduced CH content resulting from CNS hydration and the hindered cement hydration, as well as due to a layer of dense, low Ca/Si hydrate coating around fly ash particles. The results and discussions explain why the cementitious materials containing nanoSiO(2) had a lower strength gain at later ages. Methods of mitigating the adverse effect of nanoSiO(2) on cement/FA hydration at later ages were proposed. (c) 2012 Elsevier Ltd. All rights reserved.