An experimental investigation into the bond-slip behaviour between CFRP composite and lightweight concrete

• Factors affecting the bond-slip interface of the CFRP/lightweight concrete joints are investigated.
• Epoxy bonded CFRP on lightweight concrete specimens failed due to concrete debonding.
• Lightweight and normal weight concrete shows the same effective bond length.
• CFRP can be successfully applied in strengthening of lightweight concrete structures.

Epoxy bonded fibre reinforced polymer (FRP) composites are widely used for the retrofit of ailing reinforced concrete structures, for both shear and flexure. The behaviour of retrofitted concrete structures is governed by the bond strength and the material characteristics of the epoxy bonded FRP and the concrete. Previous studies show that lightweight concrete (LWC), which uses Pulverised Fuel Ash (Lytag) instead of coarse granite aggregates, has significantly lower tensile strength and aggregate interlock compared to normal weight concrete. Performance of shear retrofitted concrete elements is primarily governed by the aggregate interlock and tensile strength. Thus the study of FRP enhancement techniques in LWC is paramount for limit state design. Many studies have been conducted to understand the bond-slip behaviour between normal weight concrete (NWC) and FRP composites, where the increasing interfacial (shear) and normal stresses with increasing plastic deformation lead to FRP debonding and/or FRP rupture failures. This paper presents the experimental pull-off test results obtained from lightweight concrete prisms with various configurations of epoxy bonded Carbon FRP (CFRP) sheets. The experimental results show that the LWC can successfully be applied in the strengthening of lightweight concrete structures. However, the lightweight concrete prisms failed due to a diagonal crack within the concrete materials. This was due to a lower tensile strength compared to normal weight concrete specimens where peeling or rupture of FRP is the dominant failure mechanism.