2026 Volume 79 Issue 1 Pages 208-216
The area stretching from the Noto region of Ishikawa Prefecture to the Echizen coast of Fukui Prefecture is heavily affected by salt carried in from the sea. Since around 1980, salt damage has caused significant deterioration in concrete structures near the coast. Furthermore, prestressed I-beams manufactured at a precast concrete plant in Nanao City, Ishikawa Prefecture, in compliance with JIS A 5313, have frequently suffered from alkali-silica reaction （ASR）effects in the three Hokuriku prefectures due to distribution issues. Consequently, it is presumed that I-beam bridges in coastal areas of the Hokuriku region are experiencing complex deterioration. This paper details the analysis of concrete deterioration from a pre-tensioned I-beam bridge exposed to airborne salt for 50 years along the Sea of Japan coast in Hakusan City, Ishikawa Prefecture. Core samples were extracted, and the chloride ion concentration distribution was analyzed. The deterioration status was examined in detail using a petrographic approach, including observation with a stereomicroscope, polarizing microscope, and electron microscope. The results revealed that the concrete exhibits combined deterioration due to carbonation, salt damage, and alkali-silica reaction, and that crevice corrosion has progressed in the PC strands. Furthermore, the paper examines the relationship between the combined deterioration of the concrete and presents several observations regarding the crevice corrosion observed in the PC stranded wire.
