Bond Stress-Slip Behaviour of Carbon Fibre Reinforced Polymer (CFRP) Anchors of Varying Geometries Under Direct Pullout Conditions

Ultra-High Performance Concrete (UHPC) is currently being considered for the construction of double wythe building wall panels, consisting of insulation sandwiched between two thin UHPC wythes. To enhance the structural performance of the panels, the two wythes need to be connected structurally, and composites are an excellent choice to avoid thermal bridging that can occur with metallic connectors. For the connectors to be effective, the bond between the connector and the UHPC is critical. Several studies have been conducted on the bond-slip behaviour of glass fibre reinforced polymer (GFRP) and carbon FRP (CFRP) bars in UHPC, but little effort has been directed towards studying the bond strength of CFRP composites fabricated from sheets. In this study, the tensile strength and bond-slip/anchorage behaviour of unidirectional CFRP sheets in UHPC are investigated. The sheets are formed into several types of anchors. Two main parameters, fibre content in UHPC and geometrical shape of CFRP sheets, are considered for this experimental investigation. UHPC mixes with 2% steel fibre and 2% POM fibre content are studied. The other four variable parameters (geometrical orientation) are CFRP sheets in straight, circular, round, and weave patterns. In total, 48 pullout specimens are fabricated and tested. The results of pullout test in specimens with anchors indicate that most of the anchors provide sufficient anchorage strength to allow tensile failure within the CFRP bars rather than anchorage failure/pullout failure. However, straight and weave patterns are not as effective, and the specimens fail with pullout and neck softening failure modes.