EFFECTS OF SILICA FUME ON DRY-PROCESS SPRAYED CONCRETE

This paper presents and discusses data on the effects of using silica fume (in powdered form) in dry-process sprayed concrete. A series of s praying trials were carried out using 3:1 and 4:1 (aggregate:cement) m ixes, with up to 15% of the cement being replaced by silica fume on a weight-for-weight basis. Measurements of material rebound were made, a nd in situ mix proportions were determined. Compressive strength, flex ural strength and water absorption tests were carried out on specimens extracted from the hardened test panels. The presence of silica fume in the dry process sprayed concrete mixes produced substantial (zip to 50%) reductions in rebound losses, this in itself is a very significa nt advantage in this production process, and this fact alone may be ad equate justification for use of silica fume in dry-process sprayed con crete. 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 ifs cohesive properties. The work also shows that the be nefits (in terms of strength and durability) normally associated with the use of silica fume in more conventional cast concrete should not b e expected automatically with dry-process sprayed concrete due to the effects of water demand.