Performance Evolution of High-Slump Concrete Under Vibration: Influence of Vibration Timing on Mechanical,...

High-slump concrete is highly sensitive to vibration due to its low viscosity and weak cohesion, factors that critically influence its performance development and long-term durability. In practice, vehicle-bridge coupled vibrations during half-width bridge construction represent a typical condition that intensifies these effects. This study investigates performance deterioration of high-slump concrete subjected to simulated vibration modes reflecting construction scenarios. Mechanical and durability properties were evaluated, and microstructural changes were analyzed using SEM. Results show that early vibration enhances compressive strength at early ages, but this benefit diminishes with curing. The bonding performance at the new-old concrete interface is highly sensitive to vibration timing, casting-to-final setting vibration greatly reduces bond strength, while initial-to-final setting vibration causes minor damage or slight improvement. Vibration modes also differently affect durability: initial-to-final setting weakens frost and abrasion resistance, whereas casting-to-final setting enhances pore structure and chloride resistance. SEM analysis reveals vibration-induced dispersion of hydration products, reduced C-S-H gel formation, and increased microcracks at the fresh-old interface. Both vibration modes further promote microcracks and porosity after freeze-thaw cycles, damaging the gel structure. Overall, this study clarifies the mechanisms by which vibration timing governs the performance evolution of high-slump concrete and provides a scientific basis for optimizing vibration procedures to ensure durability and interfacial reliability in engineering applications.