Effects of CSF content on rheology and cohesiveness of mortar

Abstract

It is widely known that the addition of condensed silica fume to a concrete mix would improve the cohesiveness and hence segregation stability. However, quite often, this would also impair the flowability. To study the overall effects of condensed silica fume, an experimental programme was launched, whereby 45 mortar samples with different condensed silica fume contents and water/solid ratios, each representing the mortar portion of a concrete mix, were tested for their rheological properties, cohesiveness and packing densities. Their rheological properties were measured in terms of flow spread, flow rate, yield stress and apparent viscosity, while their cohesiveness and packing densities were measured using the sieve segregation and wet packing tests respectively. It was found that the effect of condensed silica fume on flowability could be positive or negative, depending on the water/solid ratio, and when the water/solid ratio is low, the addition of condensed silica fume would improve the flowability by increasing the packing density. It was also found that the effect of condensed silica fume on cohesiveness is always positive. Put together, the overall flowability-cohesiveness performance would be improved by the addition of condensed silica fume. Thomas Telford Ltd © 2011.