Bonding performance analysis of reinforcement bars in red mud concrete

This study systematically revealed the influence of red mud (RM) content on the bonding strength and mechanism at the reinforcement bar–concrete interface by pull-out tests. The effects of RM content, reinforcement bar diameter, and embedment length on bonding behaviour were discussed. The interfacial porosity measurements and hydration product analyses were further elucidated by microstructural observations to reveal the governing mechanisms. The results indicated that the bonding–slip curves of RM5, RM10, RM15, and RM20 specimens followed the classical bonding–slip model of RM0 concrete. The incorporation of RM slightly reduced the mechanical and bonding performance of concrete; however, this reduction could be partially compensated by optimising the dosage of the water-reducing admixture. The microstructure and hydration products at the reinforcement bar–concrete interface had significant influence on bonding strength, exhibiting a positive correlation with the compressive and splitting-tensile strengths of the RM concrete. Direct pull-out (DP) and splitting pull-out (SP) were observed, and the presence of RM had no significant effect on the type of failure mode. These findings provide new insights into the bonding mechanism of RM concrete and offer theoretical and practical guidance for its structural applications.