An estimation of the diffusivity of silica fume concrete

Deterioration and durability of concrete structures mainly depend on diffusivity and permeability of concrete. Silica fume (SF) influences concrete diffusivity in several ways. As a mineral admixture for high performance concrete, SF develops diffusivity and permeability of concrete as well as strength by densifying the microstructure of interfacial transition zone (ITZ) of concrete and by producing less diffusible and less permeable pozzolanic CSH gel than conventional CSH gel of normal concrete during cement hydration and also reducing the overall (bulk and ITZ) capillary porosity for fixed degree of cement hydration. Based on a microstructure model, a procedure for predicting the diffusivity of high strength SF concrete is developed by considering water-to-binder ratio, SF replacement ratio, and degree of hydration as major influencing factors. Results of the diffusivity calculated using the procedure is verified with results of several experiments. Subsequently, effects of SF on the diffusivity of concrete are evaluated. Finally, an optimum SF replacement ratio which can reduce reasonable diffusivity of concrete is proposed for durable concrete.