Effects of silica fume on dry-process sprayed concrete Available to Purchase

This paper presents and discusses data on the effects of using silica fume (in powdered form) in dry-process sprayed concrete. A series of spraying trials were carried out using 3:1 and 4:1 (aggregate:cement) mixes, with up to 15% of the cement being replaced by silica fume on a weight-for-weight basis. Measurements of material rebound were made, and in situ mix proportions were determined. Compressive strength, flexural strength and water absorption tests were carried out on specimens extracted from the hardened test panels. The presence of silica fume in the dryprocess sprayed concrete mixes produced substantial (up to 50%) reductions in rebound losses; this in itself is a very significant advantage in this production process, and this fact alone may be adequate justification for use of silica fume in dry-process sprayed concrete. The reduction in rebound appears to be largely a result of the increased water demand caused by the inclusion of silica fume powder, as opposed to its cohesive properties. The work also shows that the benefits (in terms of strength and durability) normally associated with the use of silica fume in more conventional cast concrete should not be expected automatically with dry-process sprayed concrete due to the effects of water demand.