In the mountainous area of the Hokuriku region, bridges are experiencing early deterioration caused by salt damage, alkali-silica reaction (ASR), and frost damage. Survival time analysis was carried out using the inspection data to study the relationship between the degradation tendency of bridges and the regional characteristics. In addition, the causes of the degradation of the reinforced concrete (RC) slab of a road bridge, which deteriorated early, were investigated using cylindrical core extraction. Polarizing microscopic observation of the specimens collected from the slab confirmed that ASR was the cause of the deterioration. The reduction in the mechanical properties of concrete due to ASR was also studied and reported. Moreover, vehicle running tests using a test truck were carried out. Then, long-term monitoring of the responses of the test bridge due to live load based on the bridge weigh-in-motion method was also performed for ordinary vehicles. The stiffness of the RC slab was evaluated by comparing the results obtained from the tests and the numerical analyses. It was found that the current stiffness of the slab remarkably decreased as compared with the results when the slab was sound. Finally, this study proposes an approach for the soundness evaluation of RC slabs.

<p>In order to improve the maintenance and management of the highway bridge deck, a test equipment was developed for grasping the rigidity of the deteriorated deck using the deformation of the deck obtained by the impact load. A soundness evaluation system of the bridge deck using the impact test result has been constructed, and this evaluation system utilizes the curvature of the neighbourhood of the load application point. The degradation degree was evaluated from the relationship between curvature and Young’s modulus calculated using deflection. When any abnormality is observed in the periodic inspection of the highway bridge deck, load bearing performance can be evaluated at an early stage by applying this system.</p>

In the mountainous area of the Hokuriku region, bridges are suffering early deterioration caused by salt damage, alkali-silica reaction (ASR) and frost damage. Under such a regional situation, the load carrying capacity evaluation of these bridges has become an urgent issue. In this study, a statistical method–survival analysis–was carried out by using inspection data for bridges in the Hokuriku region, and the relationship between degradation tendency of bridges and regional characteristics causing salt damage, ASR and frost damage has been studied. In addition, the degradation causes of the reinforced concrete deck of a road bridge which deteriorated early in the mountainous area of the Hokuriku region were investigated. Cylindrical core extraction was carried out to analyze the degradation causes. Polarizing microscopic observation of specimens collected from RC slabs confirmed that cracks developed from the andesite particles and cracks were confirmed to be filled with ASR gels. Therefore, ASR was a cause of the deterioration. Moreover, the degradation in the mechanical properties of concrete due to ASR was also studied and reported. The results show that the reduction in compressive strength and static elastic modulus of both dry and leakage-water parts affected the load bearing capacity of the structure.