14. Maintenance method for prestressed concrete sleepers according to the installation environment

For the maintenance of PC sleepers, visual inspection is used to check the surface condition to determine the need for replacement. In recent years, the number of PC sleepers that have exceeded their designed service life of 50 years is increasing, so systematic maintenance based on engineering evidence is required more than ever before. Therefore, we have proposed a method to quantitatively evaluate the soundness of PC sleepers, as well as a maintenance method according to the installation environment.

For the soundness judgment, we have proposed a method to evaluate the soundness of PC sleepers based on their natural frequencies, which can be obtained by hammering sound, and the degree of deformation caused by frost damage and salt injury. For example, in the case of 3PR-sleepers specified in JIS E1201, in an environment where there is a possibility of frost damage, we found that the standard thresholds for soundness judgment were the natural frequency to be 750 to 800 Hz, and the area where scaling (deterioration of concrete accompanied by flaking and falling) occurred due to frost damage to be 40% of the top surface of the PC sleeper. Furthermore, taking the differences in the environment in which PC sleepers are installed into consideration, we have proposed a maintenance flow by categorizing the areas into general environment and areas with a high risk of frost damage and salt injury (Fig. 1). In areas where scaling due to frost damage (Fig. 2) is observed, the soundness of the sleepers is determined based on scaling and natural frequencies. For other frost damage, salt injury, and general environments, we have proposed replacement criteria based on the cumulative passing tonnage as an index, indicating that the sleepers can no longer satisfy the JIS standard values for bend tests (Table 1).

This enables maintenance according to the installation environment and can be utilized to formulate a replacement plan of PC sleepers.

Other Contents