Effect of chloride ion migration behaviour on the microstructure and mechanical properties of ultra-high performance concrete: A review

This study summarizes the durability of ultra-high performance concrete (UHPC) under chloride ion erosion in marine and saline-alkali environments. The influence of chloride ion migration on the performance of UHPC is the focus of this study, with various factors affecting the microstructure of chloride ion migration in UHPC being summarized, including mineral admixtures, water binder ratio, fibres, curing temperature, and chloride exposure environment. The impact of these factors on the chloride ion diffusion coefficient and mechanical properties of UHPC is also discussed, and methods to improve the chloride ion permeability are proposed. Furthermore, an overview of research progress on chloride ion migration in UHPC components is provided, and the corrosion behaviour of reinforcement in UHPC members is discussed. Through the review, it was revealed that corrosion of reinforcement or fibres in UHPC is primarily caused by chloride ions, thereby reducing the stability of the structure. Raw materials and external environments played a significant role in the chloride ion migration process of UHPC. Steel fibres could enhance UHPC's resistance to chloride ion penetration and help reinforcement resist corrosion. Finally, addressing the limitations and deficiencies in current research, several directions and approaches for further studying the chloride ion permeability of UHPC were proposed, including strengthening research on the coupling effects of multiple factors, deepening the understanding of the influence of steel fibres and mineral admixtures on chloride ion migration, establishing a unified chloride ion migration testing standard, and focusing on chloride ion migration in components and structures. These findings and suggestions hold important innovative significance for promoting the application of UHPC in special environments such as marine and saline-alkali areas.