Shear-bond behaviour between concrete and hybrid fibre-reinforced cementitious composites for repairing: Experimental and modelling

Hybrid fibre-reinforced cementitious composites (HFRCC), with high toughness and ductility, have great potential for repairing damaged concrete in complex service environments. The per-formance of repairing largely depends on the bond between repairing materials and existing concrete. In this study, the direct shear-bond tests of cubic specimens were carried out to explore the shear-bond behaviour between existing concrete and HFRCC for repairing concrete structures. Then, the effects of polyvinyl alcohol (PVA)/steel fibre volume fraction and water/binder ratio of HFRCC on the bond behaviour were analyzed. The experimental results show that the failure mode of specimens changed from HFRCC fracture to interfacial fracture with the increase of PVA fibre content in HFRCCs. Additionally, the failure mode of specimens transformed from interfacial fracture to hybrid fracture with the increase of steel fibre content in HFRCCs. However, water/ binder ratio of HFRCCs only marginally affected the failure mode. The shear specimens with a water/binder ratio of 0.35, PVA fibre volume fraction of 1.5% and steel fibre volume fraction of 0.75% (e.g., S0.75P1.5W0.35) exhibited the highest shear strength. With the increase in loading, the strain concentration on the interface obtained by three-dimensional digital image correlation (3D-DIC) technology moved from the loading end to the free end and the strain at the loading end increased gradually. Finally, the shear strength model and bilinear bond-slip model of HFRCC-concrete were proposed to predict shear strength and shear stress-slip curve, respectively.