New methodology to analyze the steel-concrete bond in CFST filled with lightweight and conventional concrete

The construction sector is constantly seeking for new building systems that are cheaper, faster and with a reduced generation of residues. In this way, the use of concrete-filled steel tubes (CFST) increased due to its fast and clean execution, and its high mechanical strength, durability and ductility. The performance of this system depends on the steel-concrete interaction that occurs in the form of a natural bond. The present work evaluates the natural bond mechanisms manifested in thin-walled steel tubes filled with three types of concrete: conventional, lightweight and lightweight with expansive admixture. Push-out tests were realized in the CFSTs and the results were compared with bond strength values prescribed by international standards. Finally, the residual concrete adhered to the CFST interface was evaluated by a new methodology using visual resources. Results indicated that the lower modulus of elasticity of the lightweight concretes contribute to the enhancement of the confinement effect and microlocking. And the expansive admixture improved the adhesion performance of the filling core. Additionally, the new methodology presents a good correlation with the other tests and it is easy to apply.

Automated summary

The construction sector is continuously exploring new building systems that are cost-effective, fast, and reduce waste generation, with concrete-filled steel tubes being widely used. This study evaluated the natural bond mechanisms in thin-walled steel tubes filled with different types of concrete, highlighting the benefits of lightweight concrete's lower modulus of elasticity in enhancing the confinement effect and the improved adhesion performance of the filling core with expansive admixture. Additionally, the new methodology for evaluating residual concrete on CFST interfaces showed good correlation with other tests and easy application.