Ultrasonic-detected damage and bending behavior of reinforced PP-ECC beams after coupled action of freeze-thaw cycles and constant flexural load

Considering the performance degradation of structures in cold regions, the frost resistance and flexural performance of reinforced PP-ECC beams under the coupled action of freeze-thaw cycles and constant flexural load are investigated in this study. During the coupling test, the ultrasonic wave speed of the beams is recorded and the freeze-thaw damages in different regions of the beam are analyzed. Then, the flexural performance test is conducted on the beams, and the failure mode, number of cracks, maximum crack width, and flexural load-bearing capacity of the beams are measured. It is found that, with the increase of the number of freeze-thaw cycles, the freeze-thaw damage in the PP-ECC beam is more severe, and the flexural load-bearing capacity gradually decreases. Also, the number of cracks and cracking strength of the beams decrease, and the maximum crack width increases. With the increase of the flexural load, the frost resistance of both the tension zone and the bending shear zone of the beam is getting weaker, aggravating the freeze-thaw damage. Applying the constant load with a stress ratio of 0.25 results in the improvement of the frost resistance of the compression zone, thus reducing the freeze-thaw damage and increasing the load-bearing capacity of the beam. However, if the constant load is too large (stress ratio = 0.5), the freeze-thaw damage in the compression zone is aggravated, and the load-bearing capacity of the beam is reduced. Regardless of different degrees of freeze-thaw damage, the ductile failure of the beam is shown.