Durability Evolution of In-Service Inland Ship Lock Concrete: A Multiscale Case Study with Mix Proportion Back-Analysis

In-service inland ship lock concrete is exposed to persistent humidity, cyclic wetting-drying, carbonation, and ship-induced surface abrasion, resulting in pronounced zone-dependent deterioration. This study investigated two representative inland ship locks to clarify the governing factors of long-term durability evolution under real service conditions. Field inspection, core-based testing, X-ray computed tomography, SEM/EDS, XRF/XRD/TG-DTA analyses, and mix proportion back-analysis were combined to establish a multiscale evidence chain linking original material system, pore structure, phase evolution, and macroscopic durability performance. The two ship locks still retained adequate compressive load-bearing capacity, whereas clearer divergence was observed in durability-related properties. Compared with Lock A, Lock B showed lower charge passed, higher splitting tensile strength, and a denser internal structure, which was associated with a higher total amount of cementitious materials, better fine-aggregate grading, a higher sand ratio, and the incorporation of approximately 40 kg/m 3 fly ash. Continued hydration and carbonation jointly governed the long-term reconstruction of the cement paste. In addition, the fluctuating water zone exhibited a carbonation-mechanical abrasion coupled deterioration mode rather than carbonation alone. This case study provides field-based evidence for condition assessment and maintenance decision-making for aging ship lock concrete.