Evaluation of locally available synthetic macro fibres in a single-fibre pullout test in concrete

Abstract

There is increasing use of synthetic macro fibres in concrete applications. However, the performance of these fibres varies, based on various factors. This study investigates the fibre/ matrix interface performance of four types of synthetic macro fibres locally available in the South African construction market. The influence of water-cement ratio (w/c), fibre embedment length, fibre properties and fibre snubbing angle on the single-fibre pull-out behaviour is studied in this paper. The influence of some of these properties on the compressive strength is also evaluated. Three mix designs and four fibre types were used for the investigation. All tests were performed in a controlled climate room. Specimens with single fibres were tested in a Universal Testing Machine. Scanning Electron Microscope (SEM) images of pulled out fibres were examined for inferences. The results have shown that w/c has no influence on the pull-out load of synthetic macro fibres. However, the pull-out load increases with increase in fibre embedment length and equivalent fibre diameter. Pull-out load increases for flat fibres bent along their strong axis as the fibre snubbing angle increases. While crimped fibres with improved geometry show optimum pull-out performance when pulled out perpendicularly to the crack plane, flat fibres performed better at the snubbing angles tested. SEM images also show more surface damage on fibres with irregular geometry.