Failure mechanism of silica coated polypropylene fibres for Fibre Reinforced Concrete (FRC)

This work investigates the effect of a fast, acid-catalysed sol-gel silica nano-coating on the mechanical performance of draw-wire Polypropylene (PP) fibres used as dispersed reinforcement in Fibre Reinforced Concrete (FRC). The failure mechanism is investigated. To this aim, the role of curing time is also considered. Mechanical performance is assessed in pull-out and three-point bending tests of un-notched beams. Coating deeply affects the post-cracking behaviour of FRC, which shifts from brittle (plain concrete), to softening (uncoated) and finally to plastic-softening (coated fibres). Remarkably, 28-day curing improves over 8-day curing in terms of energy dissipation capability for coated fibres only. This suggests that fibre-to-matrix bond enhancement moves the failure mechanism from delamination at the interface to failure in the interphase zone. In the former case, failure is inconsistent and occurs independently from the curing time while in the latter failure depends on the matrix quality.