Failure-mode analysis of macro-synthetic and hybrid fibre-reinforced concrete beams with GFRP bars using acoustic emission technique

Abstract

Replacement of steel rebars with fibre-reinforced polymer (FRP) bars in concrete members has become prominent in recent years to avoid the corrosion issues. To improve the shear behaviour of glass FRP (GFRP) bars reinforced concrete (RC), macro-synthetic polyolefin (PO) fibres and a hybrid combination of PO with steel fibres are added. The influence of these fibres on the failure mode of GFRP beams are studied by applying acoustic emission (AE) technique. Seven full-scale GFRP-RC beams are cast by varying fibre dosages of 0.35%, 0.70% and 1.0% by the volume of concrete and tested under three-point bending with the shear span to effective depth ratio (a/d) of 2.2. Experimental results reveal that the addition of fibres increases the post-cracking stiffness, peak load and ductility, compared to the control beam. The increase in AE events, average RA values and shear-to-tensile crack-ratios indicate the effects of fibres on improving the shear capacity and ductility of the beams. The failure zones localised by AE events correlate well with crack patterns observed in the experiments. In particular, cracks (AE sources) distribute close to the loading point in the control specimen. The crack angle increases with the increase in fibre dosage, indicating the change in failure modes. With the addition of moderate and high fibre dosages, the failure mode is converted from shear to flexure-shear and flexure respectively, thereby producing more tensile fracture modes.