Design and Load Management Method for Restraint Jigs for Considering Applied Load in Concrete Freeze–Thaw Tests

Loads applied to concrete structures or members, such as prestressing load, connection load, and restraint load, affect the deterioration caused by frost damage. In particular, frozen concrete exhibits expansion. The freezing expansion of deteriorated concrete accumulates gradually, and previous research has suggested that it is related to frost damage. However, the relationship between loading and freeze–thaw resistance has not been clearly identified yet. In this study, restraint jigs were designed for freeze–thaw tests using restrained concrete specimens. The restraint jigs applied compressive load to specimens by tightening the bolt at the top of the jig. Four methods to monitor the bolt loads were investigated, and the strain gage method was most appropriate. The design of the restraint jig was reconsidered based on the test results, and the accuracy of the strain gage method was confirmed. The bolt loads and the specimen loads were also monitored during freeze–thaw cycles in air and water. Due to the complex behavior of unfrozen water in concrete, the bolt load should be managed with the bolt strain at the maximum concrete temperature.