Zhuojin Pipe Fitting Co., LtdAxial Compression Performance of Steel Tube Recycled Aggregate Short Columns
Literature Overview
This experimental study by Wu Bo, Liu Wei, Liu Qiongxiang, and Xu Zhe (South China University of Technology, 2010), conducted under the State Key Laboratory of Subtropical Building Science, investigates the axial compression performance of steel tube confined recycled aggregate short columns. Through 17 experimental specimens tested at both 7-day and 28-day ages, the study compares the mechanical behavior of recycled aggregate CFST columns with conventional CFST columns and proposes a bearing capacity calculation formula based on comparison with existing design standards.
Research Background and Sustainability Context
The integration of recycled aggregate from demolished concrete into new structural members represents a significant sustainability strategy in construction engineering. China's rapid urbanization and infrastructure renewal have generated enormous volumes of construction and demolition waste, much of which consists of concrete rubble. The incorporation of recycled coarse aggregate (RCA) into concrete mixes offers a pathway for waste valorization while reducing natural resource consumption.
However, recycled aggregate concrete (RAC) typically exhibits lower mechanical properties compared to natural aggregate concrete (NAC) due to:
- Residual old mortar on recycled aggregate surfaces reducing interfacial transition zone (ITZ) strength.
- Higher water absorption of recycled aggregate affecting workability and hydration.
- Greater porosity and weaker aggregate particles in recycled material.
The steel tube confinement in CFST columns provides a natural solution to these concerns by:
- Providing lateral confinement that compensates for reduced aggregate strength.
- Containing the concrete core against lateral expansion, enhancing post-peak ductility.
- Protecting the recycled aggregate concrete from environmental degradation.
Experimental Program Design
| Parameter | Specification | Rationale |
|---|---|---|
| Number of specimens | 17 total | Sufficient statistical basis |
| Testing ages | 7 days and 28 days | Early-age and mature strength behavior |
| Recycled aggregate content | 32%~35% by volume | Moderate replacement level |
| Column type | Short columns (slenderness ratio low) | Isolate material effects from buckling |
| Loading condition | Pure axial compression | Fundamental material behavior |
| Comparison specimens | Conventional CFST with natural aggregate | Baseline for comparison |
Experimental Results and Analysis
Strength Comparison
The key finding of this study is that steel tube recycled aggregate short columns incorporating 32%~35% recycled concrete aggregate exhibit axial compression performance comparable to fully cast conventional CFST short columns. This result is significant because it demonstrates that steel tube confinement effectively compensates for the inherent strength reduction associated with recycled aggregate.
| Property | Conventional CFST | Recycled Aggregate CFST | Ratio (Recycled/Conventional) |
|---|---|---|---|
| Peak axial strength | Baseline | 0.92~1.00× baseline | Essentially equivalent |
| Initial stiffness | Baseline | 0.85~0.95× |