Experimental investigation of crack propagation and post-cracking behaviour in macrosynthetic fibre reinforced concrete

An experimental investigation on the fracture test response of notched concrete beams with two types of discrete macrosynthetic fibres is presented. The influence of high-modulus polypropylene macro fibres on crack propagation and opening was evaluated using the digital image correlation technique. The surface displacements measured close to the tip of the notch were analysed to evaluate the crack opening profile in concrete in relation to the observed load response. A method for precisely estimating the displacement discontinuity across the crack from measured surface displacements was developed. Post-peak softening in the flexural load response was found to be associated with crack advance in the cementitious matrix. The measured crack opening profiles in the post-cracking response indicated a hinge-type behaviour in the beam. The physical hinge in the post-cracking flexural response of the beam was directly determined from the surface measurements. It was found that the addition of macrosynthetic fibres up to 8 kg/m³ (0·9% by volume) did not significantly influence crack propagation but provided resistance to opening of the hinge, which resulted in an increase in toughness and significant load recovery in the post-peak flexural load response.