# Effects of Freeze-Thaw and Wet-Dry Cycles on Tension Stiffening Behavior of Reinforced RAC Elements
## 1 Introduction
The presence of RCAs increased the porosity of the concrete and, consequently, decreased the freeze-thaw durability of RACs. Some researchers [18; 19; 20] conducted pull-out tests to investigate the bond behavior between RAC and steel bars after freeze-thaw cycles. [PERSON] et al. [18] found that the bond strength of steel-RAC decreases as the freeze-thaw cycles increase: the interface between the steel bar and the concrete deteriorates with the cycles, the formation and propagation of interfacial cracks occurs and the chemical bond between the steel bar and the concrete is reduced. According to [PERSON] et al. [19], the bond behavior reduction with freeze-thaw cycles was more pronounced for plain steel than for deformed steel bars. As for the latter, the bond strength tends to decrease as the diameter of the bar increases. [PERSON] et al. [20] highlighted that as concrete subjected to freeze-thaw cycles deteriorates, the frictional force and the mechanical force between bar and concrete are weakened and, hence, the bond strength is reduced. Additionally, the researchers noticed that there was a greater reduction in steel-RAC bond by increasing the number of cycles. In general, freeze-thaw damage occurs in the concrete due to its porosity. When freezing, water exhibits an expansive behavior and, if the volume available in the pores is not sufficient and the pressure exerted by ice exceeds the strength of the material, micro-cracks can be formed in concrete. In the wetting and drying process, evaporation of water from the pores during the drying stage causes shrinkage and micro-cracks in the concrete. When experiencing another wetting stage, the microstructure recovers water and swells; however, some of the changes that occurred in the previous drying stage are not reversible. The periodicity of this cyclical process leads to cracking and fragmentation of the concrete surface [21]. [PERSON] et al. [22] analyzed the physical and mechanical performance of structural concrete made with either natural or recycled aggregates after exposure to wet-dry cycles. The investigation results revealed that the degradation of RAC was greater than in natural concretes, mainly after a high number of cycles. It is believed that this occurs because of the presence of AM, so that RAC presents fragmentation in both the new mortar and the old mortar attached to the RCA particles, suffering, therefore, greater damages than natural concrete, which undergoes the degradation process only in the new mortar. The researchers also concluded that RAC resistance to wet-dry degradation is governed by the initial open porosity of the concrete. Despite advances in research on RAC, there is little data on steel-concrete performance after aging. Therefore, the present paper presents the results of an experimental study aimed at assessing structural durability by analyzing tension stiffening performance, crack propagation, isolated matrix capacity and steel-RAC bond after exposing the reinforced elements to degradation processes, i.e., freeze-thaw and wet-dry cycles.