Experimental and analytical study on interfacial shear resistance of prefabricated ultra-high performance concrete-post-cast normal concrete interface

Abstract

Although the interface performance of prefabricated NC and post-cast UHPC (abbreviated as NC-UHPC) has been well investigated, only few studies focus on the interface performance of prefabricated UHPC and post-NC (abbreviated as UHPC-NC). The UHPC-NC interface appears when UHPC was prefabricated offsite and transported to the construction site as a permanent formwork to cast composite members. The present study conducts Z-shaped direct shear tests on the UHPC-NC specimens to investigate their interfacial shear resistance. The main interface treatments include smooth, chiseling, grooving, planting rebars, and combined grooving and planting rebars, among which the latter is a relatively new interfacial treatment for the UHPC-NC interface. Three typical failure modes, namely, pure interface failure, combined interface and NC shear failure, and NC splitting failure are identified from the test results. The interface roughness dominates the interfacial cracking load. The planted rebars significantly improve nominal shear resistance and ductility and show synergistic effect with grooving when the rebars are in the grooves. In accordance with failure mechanisms and existing codes, comprehensive modified calculation formulas for nominal shear resistance of the UHPC-NC interfaces are proposed, and the calculation results agree with test results well with relative errors less than 10%.