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.

In order to explore the influence of green coir fiber on the fundamental properties of ultra-high performance concrete (UHPC), this paper performed experimental research on the effects of fiber content and length on the expansion behavior, compressive strength, elastic modulus, and flexural strength of UHPC. Additionally, the typical failure characteristics of UHPC reinforced by coir fibers were also analyzed by using scanning electron microscopy. The experimental results indicate that the workability and compressive strength of UHPC significantly decrease with the content and length of coir fiber increase, while the performance of UHPC can meet requirements within acceptable thresholds. On the other hand, adding coir fibers significantly improves the flexural strength and ductility of UHPC, and a reasonable upper limit exists for both fiber dosage and length. Compared with other plant-based fibers, coir fiber demonstrates a more pronounced capacity to improve the flexural performance of UHPC.