Experimental study on shear performance of thin-walled UHPC mold shell-concrete interface

To address the issue of collaborative performance failure caused by insufficient bond strength at the Ultra-High Performance Concrete (UHPC)-Normal Concrete (NC) interface in prefabricated mold shell systems, this study investigates 20 mm-thick UHPC mold shells. Double-sided direct shear push-out tests were conducted to explore the average ultimate load, load-slip curves, and interfacial shear strength of specimens subjected to different interfacial treatment techniques. The shear mechanisms of these techniques were analyzed, and a segmented bond-slip constitutive model was established based on the experimental data. The results indicate that: In the scouring treatment, a high-pressure water jet (pressure: 25 MPa, jet angle: 30°, duration: 9-10 h) was used to achieve a surface roughness of (1.5±0.2) mm, the interfacial shear strength is significantly enhanced to 1.35 MPa through the synergistic effects of interface roughening and steel fiber anchoring. For the grooving treatment, the optimal parameter combination is a groove density of $\rho$=1.25 (groove width: 20 mm, depth: 5 mm, spacing: 55 mm), achieving a maximum interfacial shear strength of 1.60 MPa. For the interface agent treatment, the optimal parameters involve adding cellulose ether (mass content: 0.1%-0.2%) to cement paste and applying it with a coating thickness of 2.0-3.0 mm, resulting in a maximum interfacial shear strength of 1.95 MPa. A comprehensive comparison of the experimental results from different interface treatment techniques shows the following ranking of interfacial shear performance: XWSM-0.2% > KC-5/5 > CM > GH. The cellulose ether interface agent (XWSM-0.2%) demonstrates significantly superior overall performance compared to traditional mechanical enhancement techniques due to its low dosage and high efficiency.