Eccentric Compression Behavior of Square Steel Tube Basalt Fiber Recycled Concrete Short Columns

Literature Overview and Research Innovation

This study, published in Engineering Mechanics in 2022 by researchers from the State Key Laboratory of Building Safety and Environmental Protection, Henan Polytechnic University, and Xi'an University of Architecture and Technology, investigates the eccentric compression performance of square steel tube basalt fiber recycled concrete (SBRRC) short columns. The research is supported by multiple funding sources including the National Natural Science Foundation (Grant No. U1904188) and the Henan Provincial Key R&D Program. This work represents an important advancement in sustainable construction technology, combining recycled aggregate concrete with basalt fiber reinforcement within a steel tube confinement system. From a steel pipe engineering perspective, the study addresses the mechanical behavior of a novel composite system where the steel tube serves as both a structural component and a confinement element for a sustainable concrete mix.

Experimental Program and Design Parameters

Eight short column specimens were designed and tested under eccentric compression loading, with four key parameters varied: recycled coarse aggregate replacement ratio, basalt fiber dosage, recycled concrete strength grade, and eccentricity. The test results provide insight into how each parameter influences the load-bearing capacity, deformation characteristics, and failure modes of the composite columns.

The use of recycled coarse aggregate is driven by environmental and sustainability considerations, as it reduces the demand for natural aggregates and diverts construction and demolition waste from landfills. However, recycled aggregates typically exhibit lower strength and higher water absorption than natural aggregates, which can reduce the concrete's compressive strength and bond with the steel tube. The addition of basalt fiber addresses some of these deficiencies by improving the concrete's tensile properties and crack resistance.

Mechanical Behavior and Failure Analysis

All specimens exhibited three distinct loading stages: elastic, elastic-plastic, and plastic-descending. The load-lateral deflection curves at mid-height showed similar shapes across all specimens, with a rapid increase in lateral deflection after the peak load. This behavior is characteristic of short columns under eccentric compression, where the transition from elastic to plastic behavior is governed by the yielding of the steel tube and the crushing of the concrete core.

The peak load capacity was found to decrease with increasing recycled aggregate replacement ratio or eccentricity, and to increase with increasing recycled concrete strength grade. These trends are physically intuitive: higher replacement ratios introduce more heterogeneous interfaces and weaker aggregate particles, reducing the concrete's effective strength; greater eccentricity increases the bending moment, which shifts the neutral axis and reduces the compressive zone; and higher concrete strength directly increases the axial load capacity.

The basalt fiber contribution to the mechanical behavior is primarily through crack control and post-crack ductility enhancement. While the fiber does not significantly increase the peak load capacity, it improves the energy dissipation capacity and reduces the spalling of the concrete cover. From a steel pipe engineering standpoint, this improved concrete behavior translates to better confinement effectiveness and more uniform stress distribution within the composite section.

Finite Element Modeling and Design Formula

The authors developed a finite element model capable of analyzing the full-range mechanical behavior of SBRRC short columns under eccentric compression. The model was validated against the experimental results and demonstrated good agreement in predicting the load-deflection curves and failure modes. Based on the experimental and numerical results, a design calculation method for the eccentric compression capacity was proposed.

The finite element model incorporates the following key elements:

• Steel tube: Modeled with a bilinear elastic-plastic material model, accounting for strain hardening and the Bauschinger effect under cyclic loading.
• Recycled concrete: Modeled with a damage-plasticity model that accounts for the reduced strength and modified stress-strain behavior due to recycled aggregates.
• Basalt fiber: Modeled as a smeared reinforcement with a linear elastic stress-strain relationship, contributing to the tensile resistance of the concrete matrix.
• Interface: Modeled with a cohesive zone model that captures the bond behavior between the steel tube and the recycled concrete core.

Quality Control and Material Specification Considerations

The use of recycled aggregates and basalt fibers introduces additional quality control requirements compared to conventional concrete:

The welding of steel tube components in SBRRC columns follows the same quality control procedures as conventional STC columns, but with additional attention to the interface with the recycled concrete. The recycled concrete's higher water absorption can affect the weld quality if moisture from the concrete core reaches the weld zone during fabrication. Adequate drying and moisture barrier measures should be implemented before welding operations.

Study Insights and Sustainability Implications

This research contributes significantly to the advancement of sustainable construction technology by demonstrating that recycled aggregate concrete, when combined with basalt fiber reinforcement and steel tube confinement, can achieve acceptable mechanical performance for structural applications. The steel tube serves a dual role: it provides structural load-bearing capacity and lateral confinement that compensates for the reduced strength of the recycled concrete core. The basalt fiber enhances the concrete's crack resistance and post-crack ductility, which is particularly beneficial for the heterogeneous recycled concrete matrix.

From a steel pipe engineering perspective, the study validates the feasibility of using steel tubes in sustainable construction applications without compromising structural safety. The quality control requirements for the steel tube components are essentially the same as for conventional applications, but the additional attention required for the recycled concrete and basalt fiber materials represents a new dimension in construction quality management. Engineers should ensure that the full supply chain — from recycled aggregate production to basalt fiber manufacturing to steel tube fabrication — is subject to rigorous quality assurance procedures to maintain the reliability of the composite system.