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In the process of service, reinforced concrete structures have to bear both load and multi-environmental factors. The deterioration of reinforced concrete beams is critical to the durability, safety, and sustainability of reinforced concrete structures. The main aim of the present research is to determine the degradation mechanism of reinforced concrete beams subjected to sustained loading and multi-environmental factors. Reinforced concrete beam specimens were prepared, loaded and then exerted multi-environmental factors. At the end of each degradation period, the degradation of concrete (chemical contents of concrete beam surfaces, carbonation depth, compressive strength and maximum cracks) and the corrosion of steel bars (corrosion ratio and tensile strength) were continuously measured. Moreover, degraded reinforced concrete beams were flexural loaded in four-point bending failure tests. The degradation mechanism of reinforced concrete beams subjected to sustained loading and multi-environmental factors was analyzed. Thus, this study can promote a comprehensive understanding of reinforced concrete beams subjected to sustained loading and multi-environmental factors. [ABSTRACT FROM AUTHOR]

The interfacial bonding behavior of textile reinforced concrete (TRC)-confined concrete and corroded steel bars was studied by central pull-out testing using three types of specimens (not strengthened, strengthened after corrosion and strengthened before corrosion). The results show that without the TRC constraint, the ultimate bond strength between the concrete and corroded steel bar decreases with increasing corrosion ratio, especially after the concrete cracks due to reinforcement corrosion, at which point the ultimate bond strength rapidly decreases. However, the ultimate bond strength of the specimens strengthened after corrosion can be three times greater than the strength of the specimens not strengthened when the concrete cracks due to reinforcement corrosion. For the specimens strengthened before corrosion, the TRC strengthening layer effectively limits the decrease in the ultimate bond strength between the corroded steel bars and concrete, which results in specimens with a high interfacial bond strength at high corrosion ratios. Thus, compared to the other two types of specimens, this case comparatively yielded the best results. Finally, for all three types of specimens and according to the experimental data, a calculation model of the ultimate bond strength was established considering changes in the corrosion ratio. [ABSTRACT FROM AUTHOR]

The issue of steel bar corrosion has seriously affected the working performance of concrete structures. Reinforcement is an effective measure to restore the mechanical properties and prolong the service life of concrete structures. Determining the bond properties between textile-reinforced concrete (TRC)–confined concrete and a corroded steel bar is one of the main issues in evaluating the effect of TRC reinforcement. Based on the results of electrochemical corrosion and pullout tests, the bond properties between concrete and a steel bar under unconfined and TRC–confined conditions were comparatively analyzed in terms of the corrosion-induced cracking, failure mode, bond-slip curve, bond strength, and bond failure mechanism. The empirical calculation formula of the ultimate bond strength between unconfined concrete and a corroded steel bar was obtained, and the confinement effects of TRC and fiber-reinforced polymer (FRP) were compared by collecting data from the relevant literature. The research results indicated that TRC confinement can effectively improve the bond properties between concrete and a corroded steel bar and limit the development of corrosion-induced cracks. Furthermore, TRC confinement controlled any further crack expansion during the pulling out of the steel bar. After TRC confinement, the brittle failure characteristic of the bond behavior between concrete and a corroded steel bar was improved, and the failure mode was changed from splitting to splitting–pullout. The confinement effect of TRC using a lower fiber-reinforcement ratio is similar to that of FRP. [ABSTRACT FROM AUTHOR]

• Degradation of the bond performance between composite limestone powder concretes and steel bars under a sulfate freeze–thaw environment was explored. • Contrary to slag, limestone powder and fly ash reduced the ultimate bond strength and increased the peak slip of split failure. • The bond performance decreased with the increase of anchorage length. • Limestone powder exacerbated the degradation of the bonding performance, while slag slowed the reduction of ultimate bond strength and corresponded with lower peak slip and more brittle failure. • The correction factor for the critical anchorage length of the sulfate freeze–thaw environment was derived. An experimental investigation was conducted to explore the degradation of the bond performance between five types of composite limestone powder concretes and steel bars under a sulfate freeze–thaw environment. The failure model, ultimate bond strength, peak slip and bond–slip curve were researched. Three types of anchorage lengths were adopted in the investigation. The results indicated that limestone powder and fly ash reduced the ultimate bond strength and increased the peak slip of split failure. Slag increased the ultimate bond strength and reduced the peak slip. The bond performance between the composite limestone powder concrete and steel bars decreased with increasing anchorage length. Limestone powder exacerbated the degradation of the bonding performance of concrete under freeze–thaw cycles, while slag slowed the reduction in ultimate bond strength and corresponded with lower peak slip and more brittle failure. The constitutive relationship between the conventional environment τ (s, d/L) and the sulfate freeze–thaw environment τ (s, f ts) was established, and the correction factor for the critical anchorage length of the sulfate freeze–thaw environment was derived. Thus, the influences of limestone powder, fly ash and slag on the critical anchorage lengths were analysed. [ABSTRACT FROM AUTHOR]