Zhuojin Pipe Fitting Co., LtdAxial Compression Performance of Steel Tube Sea Sand Recycled Concrete
Literature Overview
This 2018 paper published in the Journal of Building Materials by Huang Yijie, Wu Jida, Xiao Jianzhuang, Wang Qing, and Sun Huangsheng from Shandong University of Science and Technology and Tongji University investigates the axial compression performance of steel tube sea sand recycled concrete (STSSRC) specimens. The research was supported by multiple funding sources including the National Natural Science Foundation of China (Grant No. 51408346), the China Postdoctoral Special Funding Project (Grant No. 2016T0041), and other institutional grants. The study addresses the dual challenges of sustainable construction material utilization by combining recycled coarse aggregates and sea sand in steel tube concrete members.
Experimental Program
The authors conducted 18 axial compression tests on STSSRC specimens, with recycled coarse aggregate replacement rate and chloride ion (Cl-) content in sea sand as the main experimental parameters. The specimens were designed to systematically vary these parameters to isolate their individual effects on the structural behavior.
Experimental Parameter Matrix
| Parameter | Variations | Range |
|---|---|---|
| Recycled coarse aggregate replacement rate | Multiple levels | 0% to high replacement |
| Cl- content in sea sand | Multiple levels | Natural to elevated |
| Total specimens | 18 | Systematic matrix |
Key Experimental Findings
Failure Mode and Loading Stages
The STSSRC specimens exhibit a loading process similar to conventional steel tube concrete, consisting of three distinct stages: elastic stage, elastic-plastic stage, and failure stage. The primary failure mode is diagonal shear failure, which is consistent with the confinement mechanism of the steel tube on the concrete core.
Effect of Recycled Coarse Aggregate Replacement Rate
The peak load decreases slightly with increasing recycled coarse aggregate replacement rate. This is attributed to the lower strength and higher porosity of recycled aggregates compared to natural aggregates. However, the peak strain increases with the replacement rate, indicating improved ductility of the composite member.
Effect of Chloride Ion Content
The peak load decreases slightly with increasing Cl- content in sea sand. The peak strain exhibits a non-monotonic behavior with Cl- content: it first increases and then decreases. This suggests an optimal Cl- content range beyond which the corrosion effects on the steel tube begin to dominate.
Stress-Strain Full Curve Model
The authors compared the calculated peak loads from different code formulas with experimental values and fitted a stress-strain full curve model for STSSRC based on the experimental data. This provides a practical design tool for engineers considering the use of recycled aggregates and sea sand in steel tube concrete structures.
Engineering Practice Implications
From a steel pipe manufacturing and welding perspective, the use of sea sand recycled concrete in steel tube concrete members introduces additional considerations for steel tube selection and welding quality. The chloride ions from sea sand can potentially cause corrosion of the steel tube, particularly at the weld heat-affected zone where the microstructure may be more susceptible to corrosion attack.
Steel Tube Corrosion Risk Assessment
| Risk Factor | Mechanism | Mitigation Measure |
|---|---|---|
| Cl- diffusion from concrete | Electrochemical corrosion | Use of corrosion-resistant steel grades |
| Weld HAZ susceptibility | Microstructural changes reduce corrosion resistance | Post-weld heat treatment |
| Concrete cover quality | Incomplete compaction at tube-concrete interface | Proper concrete placement and vibration |
| Long-term durability | Cumulative corrosion damage | Regular inspection and maintenance |
The welding of steel tubes for STSSRC members should follow standard welding procedures while paying particular attention to the quality of circumferential welds. Any defects in these welds could serve as initiation sites for corrosion attack. Ultrasonic testing of all structural welds is recommended, and the weld metal composition should be selected to provide adequate resistance to chloride-induced corrosion.
Study Insights and Reflections
This research contributes to the field of sustainable construction by demonstrating the feasibility of using recycled coarse aggregates and sea sand in steel tube concrete members. The findings indicate that while there is a slight reduction in peak load capacity, the ductility characteristics remain acceptable, and the overall structural behavior is comparable to conventional steel tube concrete. The fitted stress-strain full curve model provides a valuable design tool. However, the long-term durability of STSSRC members under chloride exposure remains a critical concern that requires further investigation through accelerated corrosion testing and long-term monitoring of field installations. The study also highlights the importance of controlling the Cl- content within an optimal range to balance the beneficial effects on concrete workability against the detrimental effects on steel tube corrosion resistance.