Zhuojin Pipe Fitting Co., LtdEccentric Compression Performance of Square CFST Columns with Basalt Fiber Recycled Concrete
Literature Overview
The paper by Zhang Xianggang, Yang Junna, Ding Yahong, Xue Jianyang, and Wang Xingguo, published in Engineering Mechanics in 2022 (Vol. 39, No. 1, pp. 45-58), investigates the eccentric compression behavior of square concrete-filled steel tube (CFST) short columns incorporating basalt fiber and recycled coarse aggregate concrete. This research, supported by multiple funding sources including the State Key Laboratory of Building Safety and Environmental Protection and the National Natural Science Foundation of China (U1904188), represents an important advancement in sustainable structural engineering by combining recycled materials with advanced fiber reinforcement technology.
Research Background and Motivation
The growing volume of construction and demolition waste has created an urgent need for recycled aggregate utilization in structural applications. Simultaneously, the demand for sustainable structural materials with improved performance characteristics has driven research into fiber-reinforced concrete. The combination of recycled coarse aggregate with basalt fiber reinforcement in CFST columns offers a promising pathway to reduce environmental impact while maintaining or improving structural performance. The study addresses the gap in knowledge regarding the mechanical behavior of this novel composite system under eccentric compression, which is a common loading condition in practical structures.
Experimental Program and Specimen Design
Eight short column specimens were designed and tested with the following variable parameters:
| Parameter | Variable | Design Consideration |
|---|---|---|
| Recycled coarse aggregate replacement rate | Multiple levels | Environmental sustainability |
| Basalt fiber dosage | Multiple levels | Toughness enhancement |
| Recycled concrete strength grade | Multiple grades | Structural capacity |
| Eccentricity ratio | Multiple values | Practical loading conditions |
The specimens were subjected to eccentric compression static loading tests, during which the load-displacement and load-strain relationships were recorded, and the failure processes and patterns were documented.
Key Experimental Results
| Observation | Finding |
|---|---|
| Loading stages | Elastic → Elastic-plastic → Plastic-descending |
| Load-deflection curve shape | Similar across all specimens |
| Post-peak behavior | Rapid increase in lateral deflection after peak load |
| Effect of replacement rate | Peak capacity decreases with increasing replacement rate |
| Effect of eccentricity | Peak capacity decreases with increasing eccentricity |
| Effect of concrete strength | Peak capacity increases with higher recycled concrete strength grade |
All specimens exhibited three distinct loading stages: elastic, elastic-plastic, and plastic-descending. The load-lateral deflection curves were relatively similar in shape across all specimens, indicating consistent deformation mechanisms regardless of the specific parameter combinations. After reaching peak load, the lateral deflection increased rapidly, reflecting the loss of load-carrying capacity.
Finite Element Analysis Model
The authors developed a finite element analysis model capable of performing full-process analysis of the eccentric compression mechanical behavior of square CFST columns with basalt fiber recycled concrete. The model was validated against experimental results and demonstrated good agreement in predicting both the peak capacity and the post-peak behavior. The validated model enables parametric studies beyond the experimental scope, providing additional design guidance.
Implications for Steel Pipe Engineering
The use of recycled concrete with basalt fiber in CFST columns introduces several considerations for steel pipe selection and fabrication:
| Consideration | Impact on Steel Pipe Requirements | Recommendation |
|---|---|---|
| Reduced concrete stiffness | Higher steel tube confinement demand | Select appropriate wall thickness to maintain confinement |
| Potential for increased concrete spalling | Steel tube must resist outward bursting pressure | Adequate steel tube yield strength specification |
| Fiber pull-out at concrete-steel interface | May affect composite action | Consider surface treatment of steel tube interior |
| Sustainability requirements | Steel tube should also be from recycled steel | Specify recycled content in steel tube procurement |
| Long-term durability | Recycled concrete may have different permeability | Ensure steel tube provides adequate corrosion protection |
The square geometry of the steel tube creates corner regions where stress concentrations develop under eccentric loading. The combination of recycled aggregate (which typically has higher water absorption and lower interfacial transition zone strength than natural aggregate) and basalt fiber (which provides crack-bridging capacity) creates a complex composite behavior that the steel tube must accommodate through its confinement action.
Design Method Recommendations
Based on the experimental and analytical results, the study proposes a design calculation method for the eccentric compression capacity of square CFST columns with basalt fiber recycled concrete. The method accounts for:
- The reduced compressive strength of recycled concrete compared to natural aggregate concrete at equivalent strength grades.
- The enhanced ductility provided by basalt fiber reinforcement.
- The confinement effect of the square steel tube on the recycled concrete core.
- The interaction between axial force and bending moment under eccentric loading.
Study Insights and Reflections
This research represents a meaningful step toward sustainable structural engineering by demonstrating that recycled materials, when properly designed and reinforced, can achieve acceptable structural performance in critical applications such as CFST columns. The consistent three-stage loading behavior across all specimens suggests that the fundamental deformation mechanisms remain unchanged by the use of recycled aggregate and basalt fiber, which is reassuring from a design perspective. The validated finite element model provides a powerful tool for further parametric studies and design optimization. For steel pipe engineers, the study highlights the importance of maintaining high-quality steel tube fabrication even when the concrete core incorporates recycled materials, as the steel tube's confinement effectiveness becomes even more critical in compensating for the potentially reduced concrete properties. The work contributes to the growing body of knowledge on green structural engineering and provides practical guidance for the adoption of recycled materials in composite structural systems.