Concrete porosity with polypropylene fibres and silica fume

Purpose This research examines the effects of Type 1 and Type 2 synthetic polypropylene fibres in concrete, with and without silica fume, regarding porosity. The raison d’être for the research is to examine the porosity of fibre concrete where the concrete may be subject to a hydrostatic pressure from water. The use of silica fume defines the positive benefits that can be achieved by utilising a waste/by product in a concrete mix. Methodology The standard for determining the penetration depth of water under pressure (BS 12390: part 8 2009) in concrete was used with two types of synthetic fibre (Type 1 and Type 2) and plain concrete, with and without silica fume were subject to a water pressure test over 72 hours to determine the depth of water penetration. Findings The findings showed that synthetic fibres when added to a concrete mix increase the porosity of the concrete when compared to plain concrete, however when additional silica fume is used at a dry rate of 10% to the dry mass cement content or 20% slurry content, the porosity of the concrete is significantly reduced. Originality Designers and contractors use fibre reinforced concrete to create water retaining structures. Low permeability equates to more consistent and better stored water quality. This research demonstrates the effectiveness of silica fume, which improves the performance of the concrete with regard to porosity and mitigates the effects of the synthetic fibre inclusion. Low absorption in concrete equates to low life cycle costs and good sustainability credentials through the use of a by product.