## 5 Freeze-Thaw Erosion Test of the Fatigue Damaged Reinforced Components
### Fatigue Characteristics of Strengthened Components under Freeze-Thaw Cycles
#### 5.3.2 Fatigue Test Procedure for Freeze-Thaw Reinforcement of the Test Plate  
Fatigue tests were conducted using a test plate corroded by freeze-thaw cycles to investigate the effect of freezing and thawing cycles on the fatigue properties of the reinforced components. The fatigue test comprised a hydraulic fatigue testing machine with trisection loading. Each test plate was fatigued for 2 million cycles, and a static load test was performed after every 5.0 \(\times\)\(10^{5}\) fatigue cycles to test the deflection and strain. (1) Fatigue test process after the freezing and thawing of the carbon fiber cloth reinforced test plates. As shown in Figure 11, the damage cracks that appeared in the early stage of the fatigue test plate were covered after grinding and strengthening with carbon fiber cloths, and the occurrence of the original crack was unclear in the fatigue process. However, in the fatigue test, after the freeze-thaw cycle of the plate reinforced with carbon fiber cloths, several cracks appeared on its top plate. A transverse through the crack was gradually generated. After 2 million cycles of fatigue loading, several pits appeared on the concrete roof, and local peeling between the carbon fiber cloths and the concrete occurred. Figure 10: Surface rust on the affixed steel plate after freeze–thaw erosion. Figure 9: Pasting a carbon fiber cloth reinforced component interface after freeze–thaw erosion. (2) Fatigue test process for the prestressed hollow slab strengthened using bonded steel plates after the freeze-thaw cycle  
After 50 freeze-thaw cycles, fatigue tests on the bonded steel plate reinforced specimens were performed. It was found that during the fatigue test, the development of the original cracks was nearly unobservable, and there existed no phenomenon whereby a crack was opened and then closed. The oblique sticking steel method exhibited a good inhibition effect on the development of cracks. The data for the fatigue test process are shown in Tables 7-9. After 50 freeze-thaw cycles, the components strengthened using carbon fiber cloths and steel plates could withstand 2 million cycles of fatigue loading. During the 2 million cycles of fatigue loading, the original cracks in the carbon fiber cloth strengthened specimens after freeze-thaw damage were not evident, the roof was significantly damaged, and local debonding between the carbon fiber cloth and the concrete occurred. However, cracks hardly developed in the strengthened members with bonded steel plates during the 2 million cycles of fatigue loading, and the specimens exhibited good crack resistance. 3.3 Force Characteristics during the Fatigue Process of the Freeze-Thaw Erosion of the Reinforced Test Plate  
With an increase in the number cycles of fatigue loading, the strains of the reinforced test slabs after freeze-thaw erosion under a constant load were significantly higher than those prior to freeze-thaw erosion. For example, the tensile strain of the bonded carbon fiber reinforced reinforcements, which were passed through 20.0 \(\times\) 10\({}^{5}\) cycles of fatigue, under a loading of 200 kN, was 260.3 \(\upmu\)\(\varepsilon\) at the bottom of the span prior to freezing and thawing. The tensile strain of the reinforced specimen with freeze-thaw cycle erosion was 360.6 \(\upmu\)\(\varepsilon\). Freeze-thaw erosion increased the strain level of the prestressed hollow slab. Under the two reinforcement methods, the deflection obtained for a constant fatigue cycle was greater than that obtained in the prestressed hollow slab prior to freeze-thaw erosion. For example, when a weight of 200 kN was applied after 20.0 \(\times\) 10\({}^{5}\) fatigue cycles, the deflection in the reinforced component with steel plates was 1.43 mm prior to freezing and thawing, and that of the steel plate reinforced component after undergoing freeze-thaw cycles was 1.76 mm. Freeze-thaw erosion increased the deformation of the reinforced components.