Study on bonding properties and constitutive model of steel bar and nano-SiO2 reinforced recycled aggregate concrete

Abstract

Optimizing design and ensuring the structural safety of recycled aggregate concrete (RAC) structures requires a thorough understanding of the bond-slip mechanism between steel bars and RAC. Previous studies have demonstrated the significant enhancement of the microscopic properties of RAC and its bond with steel bars due to nano-SiO2. However, the structural bonding mechanism between the steel bar and nano-SiO2-enhanced RAC remains unclear. Therefore, this study investigates the influence of nano-SiO2 on the bond performance between RAC and steel bars, elucidating the enhancement mechanism through microscopic techniques. Additionally, various factors affecting the bond-slip performance of RAC specimens are analyzed, leading to establishing a multifactorial coupling formula considering thickness-to-diameter ratio, concrete strength, and relative anchorage length. Furthermore, slip index correction formulas and a constitutive model are developed, considering these factors. Acoustic emission (AE) technology monitors the bonding process, clarifying the evolution of AE digital signals and bond damage history. Employing the finite element method, a numerical model of bond-slip behavior is established, revealing specimens' changing bond strength and failure modes. Experimental results indicate that increasing nano-SiO2 content reduces structural porosity, leading to denser and more homogeneous microstructures, thereby enhancing RAC's mechanical properties and bonding performance. Moreover, AE techniques effectively monitor bond damage at different stages. Finally, a bond-slip constitutive model is proposed for steel bar and nano-SiO2 reinforced RAC, offering insights for numerical calculations and engineering designs.