ABSTRACT
Various studies have shown that the addition of silica fume, even in moderate quantities, can have a very significant effect on the course of the hydration of Portland cement. This chapter discusses the effect of silica fume on the cement pastes in terms of porosity, density, permeability and pore-size distribution, their interrelationships with some mechanical properties, and frost resistance. Published data on physical properties of Portland cement-silica fume blend pastes are sparse. Three types of techniques may be used to determine the total porosity: helium comparison pycnometry, mercury porosimetry, and mercury porosimetry and helium pycnometry. Porous materials tend to have a heterogeneous microstructure involving a wide range of particles and pore sizes and may also vary widely in composition. Microhardness measurements may thus vary from region to region and, to be representative of the bulk, many readings should be taken.
