Quasi-Static and Dynamic Interfacial Bond Performance Between Ultra-Early-Strength Unsaturated Polyester Polymer Concrete and Ordinary Portland Concrete Under Flexural Loadings.

Unsaturated polyester polymer concrete (UPPC) is a promising rapid repair material for pavement engineering, while the age-dependent and rate-dependent bonding behaviors between UPPC and ordinary Portland concrete (OPC) substrate remains poorly understood, restricting its application in heavy-traffic scenarios. This study systematically investigates the quasi-static and dynamic bond performance of the UPPC-OPC interface at four curing ages (1 d, 3 d, 7 d, 28 d) under flexural loads. Quasi-static three-point bending tests show that the 28 d interfacial bond strength reaches 4.62 MPa, 97% higher than that of the OPC-OPC control group. Dynamic flexural tests via a 100 mm diameter split Hopkinson pressure bar reveal the strain-rate effect of the dynamic increase factor (DIF). DIF decreases below 1.0 at low strain rates (<10 s-1) due to weakened viscoelastic stress relaxation of partially cured unsaturated polyester resin, while it rises above 1.0 at higher strain rates induced by polymer hardening and inertial confinement. Combined with scanning electron microscopy characterization, the coupling relationship between curing age, strain rate and interfacial failure mode is further clarified. This work provides fundamental insights into the rate-dependent behaviors of polymer-cement heterogeneous interfaces, and offers theoretical guidance for the design of UPPC-based rapid repair systems.