Influence of interfacial characteristics on the shear bond behaviour between concrete and ferrocement

Interfacial bond behaviour between concrete substrate and strengthening materials is crucial for achieving the aims of structural strengthening or repair. This paper presents an experimental investigation on shear bond behaviour between concrete substrate and ferrocement through direct shear tests. Various interfacial characteristics, including surface roughness, type of shear keys and use of wire mesh in the overlay, are considered as test variables. Test results indicate that both surface roughness and shear keys significantly affect the shear bond behaviour between concrete and ferrocement. Specimens with highly roughened concrete surfaces obtained using jet hammer achieve higher shear bond strength and interfacial fracture energy than those with slightly roughened concrete surfaces obtained using needle gun. Installation of shear keys at concrete-ferrocement interfaces can significantly improve the post-peak shear bond behaviour as well as alter the failure mode from brittle to ductile. Shear keys have negligible influence on shear bond strength of specimens with properly roughened surfaces, but can significantly enhance their interfacial fracture energy. As compared with expansive shear keys, adhesive shear keys are more reliable to resist interfacial shear between concrete and ferrocement. Among others, L-shaped or end-extension adhesive anchors are the most effective shear keys for improving interfacial shear bond behaviour between concrete and ferrocement. In addition, the use of wire mesh has negligible influence on shear bond strength but can prevent brittle failure of the overlay. Overall, it is recommended to prepare the concrete substrate with a highly roughened surface and to provide adhesive shear keys with end extension anchored in ferrocement.