Experimental Study on the Effects of Straight and Ring-Type Steel Fibres on the Bond Behaviour of Steel Bars in Rubber-Recycled Aggregate Concrete

The application range of rubber-recycled aggregate concrete (RRAC), a new type of green building material, is currently limited due to performance defects, including low hardness, high water absorption, and poor adhesion. To expand its application in reinforced concrete structures, it is crucial to enhance the bonding performance between RRAC and steel bars. In this study, the effects of adding straight steel fibres (SSFs) and ring-type steel fibres (RSFs) to RRAC were investigated, in order to enhance the bonding performance. To investigate the impact of steel fibres (SFs) on the bonding properties of RRAC and steel bars, a total of 51 specimens were subjected to pull-out tests to systematically examine the impact of SSF and RSF dosages on the bonding performance. The results demonstrated that incorporating the optimal amount of SSFs and RSFs can significantly improve the bond strength and bond stiffness. Moreover, the combined use of SSFs and RSFs yielded even better enhancement effects. The RRAC exhibited remarkable performance, when the total content of SFs was 1.2% and the proportion of RSFs 75%. In this case, the bond strength and bond stiffness were enhanced by 3.7% and 53.88%, respectively. Finally, a bond-slip constitutive model for RRAC and steel bar was established. The combined use of SSFs and RSFs minimizes the limitations of poor mechanical properties in traditional RRAC and holds significant value for the widespread adoption and application of RRAC.