Experimental Study of Cold Joint Performance in a Scaled Fiber-Reinforced Self-Compacting Concrete Diaphragm Wall Model Using: Effects of Geometric Profiles and Chemical Treatments

Abstract This study investigates the influence of longitudinal cold joints on the structural performance of self-compacting concrete diaphragm walls reinforced with polypropylene fibers. Experimental quasi-static four-point bending tests were conducted on eight small-scale specimens (60 * 900 * 2600)mm to evaluate various joint configurations: flat (reference), keyed, trapezoidal, triangular, and semi-circular geometries, alongside chemical treatments (epoxy bonding) and ultra-high-performance concrete (UHPC) shear pocket retrofitting. The instrumentation strategy utilized five strategically positioned strain gauges and a mid-span LVDT to capture localized deformation patterns at the interface and monitor vertical deflection. This setup enabled a comprehensive analysis of stiffness, ductility, and post-cracking response, providing insights into how interfacial treatments alter failure modes compared to the control. Results demonstrate that joint geometry and chemical treatments fundamentally redefine load-transfer mechanisms. The UHPC-filled shear pockets achieved the most significant performance enhancement, yielding a 29% increase in ultimate load through high-strength dowel action and the activation of a compression strut mechanism. Geometrically, triangular profiles maximized load capacity by 40% but exhibited brittle failure, whereas semi-circular joints provided superior ductility and optimized stress distribution via a hinge-like response. Furthermore, epoxy bonding enhanced interfacial shear resistance while preserving yield characteristics. The findings highlight a critical trade-off between strength and ductility; specifically, trapezoidal and keyed joints effectively restricted transverse dilation. Ultimately, advanced configurations (UHPC and semi-circular) ensured structural continuity by shielding the central wall region and inhibiting crack propagation from lateral panels.