Considering the harsh marine environment characterized by dry–wet cycles, freeze–thaw action, chloride penetration, and sulfate attack, four optimized ultra-high-performance concrete (UHPC) mix designs were developed. Durability was assessed via electric flux, dry–wet cycles, and rapid freeze–thaw tests to evaluate the effects of curing methods, aggregate types, and mineral admixtures on key durability indicators, including chloride ion permeability, compressive strength loss, and mass loss. Scanning electron microscopy (SEM) examined microstructural changes under various conditions. Results showed that curing method significantly affected chloride ion permeability and sulfate resistance. High-temperature curing (70 ± 2 °C) reduced 28-day chloride ion electric flux by about 50%, and the compressive strength loss rate of specimens subjected to sulfate attack decreased by 2.7% to 45.7% compared to standard curing. Aggregate type had minimal impact on corrosion resistance, while mineral admixtures improved durability more effectively. Frost resistance was excellent, with mass loss below 0.87% after 500 freeze–thaw cycles. SEM analysis revealed that high-temperature curing decreased free cement particles, and mineral admixtures refined pore structure, enhancing matrix compactness. Among all mixtures, Mix Proportion 4 demonstrated the best overall durability. This study offers valuable insights for UHPC design in aggressive marine conditions.

This study focuses on the development of high-performance composite cementitious materials for offshore engineering applications, addressing the critical challenges of durability, environmental degradation, and carbon emissions. By incorporating polycarboxylate superplasticizers (PCE) and combining fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) in various proportions, composite mortars were designed and evaluated. A series of laboratory tests were conducted to assess workability, mechanical properties, volume stability, and durability under simulated marine conditions. The results demonstrate that the optimized composite exhibits superior performance in terms of strength development, shrinkage control, and resistance to chloride penetration and freeze–thaw cycles. Microstructural analysis further reveals that the enhanced performance is attributed to the formation of additional calcium silicate hydrate (C–S–H) gel and a denser internal matrix resulting from secondary hydration. These findings suggest that the proposed material holds significant potential for enhancing the long-term durability and sustainability of marine infrastructure.

Shear damage at the base of seepage control walls in rock‐bound embankments presents a critical challenge in flood defense engineering. This study examines the shear behavior of plastic rubber concrete by varying rubber powder dosage (0–30 kg/m ³ ), water–binder ratio (0.6–0.8), and rubber particle size (40–80 mesh). Direct shear tests on Φ 150 × 150 mm specimens show that increasing the rubber dosage from 0 to 30 kg/m ³ nearly doubles the friction coefficient (0.4824 → 0.9634) while reducing cohesion (1.1829 MPa →0.7509 MPa). Lowering the water–binder ratio effectively offsets this cohesion loss; at W/B = 0.6, cohesion increases by up to 37.8%, and the friction coefficient reaches 1.8366. Particle‐size analysis indicates that 60‐mesh rubber provides the best balance, raising cohesion to 1.85 MPa and more than doubling friction relative to the control. Mechanism tests (ring‐shrinkage and SEM) reveal that rubber introduces compliant interfacial zones that redistribute stress, delay cracking, and enhance post‐peak shear resistance. The optimized mix (30 kg/m ³ , 60 mesh, W/B = 0.6) was successfully applied in a Yellow River cutoff wall and met all design requirements, with 2 years of monitoring confirming stable mechanical and hydraulic performance. This study provides practical insights and empirical evidence for the application of rubberized plastic concrete in seepage control structures, promoting sustainable use of waste rubber in civil infrastructure.