Long-Term Monitoring for ASR-Deteriorated PC Rigid-Frame Bridge

Reactive aggregates are widely distributed throughout Japan. In the Noto region, andesite is widespread, which causes alkali-silica reaction (ASR) degradation in concrete structures. For the maintenance of local bridges, it is necessary to observe the expansion trends of cracking caused by ASR in health assessments.

In this study, remote long-term monitoring of a four-span prestressed concrete (PC) rigid-frame bridge was performed to investigate the expansion of cracks by ASR. To evaluate the health of this degraded bridge, instead of focusing only on the locations of cracks, it was also necessary to monitor simultaneously the displacement behaviors over time of the bridge and to obtain the crack expansion trends, which could not be identified by regular visual inspections alone. Therefore, long-term monitoring and loading experiments using large vehicles are utilized to reveal the correlation between cracking due to ASR and displacement of the overall structure due to variations of diurnal temperature and the live load.

As a result of the loading tests using test trucks, by long-term monitoring of the relationship between the temperature and the crack displacement due to ASR, the expansion trend of the crack due to seasonal variations was obtained. A particularly rapid growth trend from spring to summer was recognized. In addition, the vertical displacement of the Gelber hinge, which could be obtained from the inclination angle using the correlation between the inclination angle and the vertical displacement of the static loading tests, was estimated at approximately 30–40 mm during summer. Moreover, as another conclusion of the study, it was found that changes in diurnal temperature and the displacement behavior of the entire bridge had significant consequences on the types of crack expansion in this bridge.