Laser-induced breakdown spectroscopy (LIBS) analysis: "The Interdependent Roles of Chloride, Moisture and Dissolved Oxygen in Macro-voids at the Steel-Concrete Interface in Corrosion"

Corrosion of steel in concrete is a key durability issue for reinforced concrete structures, leading to significant economic costs and safety risks. Research suggests that moisture within voids at the steel-concrete interface (SCI) plays a critical role in corrosion. However, experimental evidence clarifying this role remains limited. Here, we systematically investigated the influence of macro-voids at the SCI by exposing reinforced concrete specimens to different wet-dry cycles and to continuous submersion in chloride solution, thereby generating distinct moisture conditions within the interfacial voids. X-ray computed tomography (XCT) was used to monitor the evolution of the gas-liquid configuration inside these voids along with steel corrosion over 9 months. Under wet/dry cycles, corrosion initiated at lower chloride levels than under continuous immersion. XCT revealed that interfacial voids became fully saturated after prolonged immersion but remained partially saturated during wet/dry exposure. These findings are interpreted through the lens of corrosion science and gas-liquid interactions in porous materials. We suggest a mechanism in which the dissolution of pressurized gas bubbles trapped within interfacial voids leads to an increase in dissolved oxygen concentration near the void, thereby locally elevating the steel corrosion potential (E_corr). Together with chloride accumulation, which gradually lowers the pitting potential, this shift in E_corr enhances the likelihood for local corrosion initiation under wet-dry cycles. Overall, this study contributes to understanding how different water exposure conditions affect the local environment at the SCI, providing insight into the mechanistic links between interfacial void gas-liquid content and corrosion in reinforced concrete.

混凝土中钢筋腐蚀是钢筋混凝土结构面临的核心耐久性问题，会造成显著的经济损失与安全风险。已有研究表明，钢-混凝土界面（steel-concrete interface, SCI）空隙内的水分对钢筋腐蚀起到关键作用，但阐明该作用机制的实验证据仍较为有限。本研究通过将钢筋混凝土试件置于不同干湿循环条件以及氯化物溶液中持续浸泡，构建界面空隙内不同的水分环境，系统探究了钢-混凝土界面宏观空隙对钢筋腐蚀的影响。研究采用X射线计算机断层扫描（X-ray computed tomography, XCT），在9个月的试验周期内监测了这些空隙内部的气液构型演化过程与钢筋腐蚀情况。试验结果显示，相较于持续浸泡工况，干湿循环条件下钢筋腐蚀在更低的氯化物浓度下便已启动。XCT扫描结果表明，持续浸泡工况下界面空隙会完全被水饱和，而干湿循环工况下空隙始终处于部分饱和状态。本研究结合腐蚀科学与多孔材料中气液相互作用理论对上述结果进行了解释，提出了如下作用机制：被困于界面空隙内的加压气泡发生溶解，使得空隙附近的溶解氧浓度升高，进而局部提升了钢筋的腐蚀电位（E_corr）。加之氯化物的累积会逐步降低钢筋的点蚀电位，腐蚀电位的正向偏移进一步提升了干湿循环条件下局部腐蚀启动的可能性。综上，本研究有助于理解不同水暴露条件对钢-混凝土界面局部环境的影响，为阐明界面空隙气液含量与钢筋混凝土腐蚀之间的机制关联提供了理论参考。