Zhuojin Pipe Fitting Co., LtdC60 Pumped Jacking Self-Compacting Steel Tube Concrete Preparation and Engineering Application
Literature Overview
This paper by Chen Jing, Xu Tingbo, Xia Yuanying, and Li Donglai from China Construction Ready-Mixed Concrete Co., Ltd., published in 2014 in the journal Concrete, presents the development and engineering application of C60 pumped jacking self-compacting steel tube concrete (SCC). The study addresses the challenges of pumping high-strength self-compacting concrete through steel tubes during jacking construction of super-high-rise buildings, specifically applied in the Chengdu Huazhi Plaza project.
Core Technical Challenges
The development of C60 self-compacting concrete for steel tube concrete (SRC) column jacking construction involves several interrelated technical challenges:
Material Design Parameters
| Parameter | Target Specification | Technical Challenge |
|---|---|---|
| Compressive strength | C60 (60 MPa) | High strength with workability |
| Slump flow | 650-750 mm | Self-compacting without vibration |
| Passing ability | ≥80 mm (J-ring) | Flow through steel tube constraints |
| Viscosity loss | ≤50 mm in 30 min | Long-duration pumping stability |
| Pumpability | Through steel tube jacking system | High pressure, long distance |
| Air content | Controlled | Strength and durability |
| Water-binder ratio | Low | High strength requirement |
Key Technical Solutions
- Super-absorbent polymer (SAP) — The use of ultra-high absorption resin (SAP) addresses the long-duration slump retention challenge. SAP particles absorb water and swell, releasing moisture gradually to maintain workability during extended pumping operations. The absorption capacity of SAP can reach 20-30 times its dry weight.
- Pump additive optimization — The selection and dosage of pump additives (viscosity-modifying agents, water reducers, and retarders) are critical for achieving the required pumpability while maintaining high strength. The study systematically evaluates different pump additive formulations.
- Sand ratio optimization — The sand ratio (sand-to-aggregate ratio) directly influences the paste volume, which governs the flowability and passing ability of the concrete. Higher sand ratios increase paste volume and improve flowability but may reduce strength.
Connection with Steel Pipe Engineering
This research has significant implications for steel pipe engineering in several ways:
- Steel tube inner surface quality — The pumpability of high-viscosity C60 self-compacting concrete through steel tubes is sensitive to the internal surface condition of the tubes. Surface irregularities, weld protrusions (from longitudinal or circumferential welds), and internal scale can create flow restrictions and pressure drops. Internal surface roughness should be controlled to Ra ≤ 12.5 μm for optimal pumping performance.
- Weld seam geometry — Longitudinal weld seams in welded steel tubes (ERW, HFW, or LSAW) create internal protrusions that can obstruct concrete flow and create stress concentrations. The internal weld protrusion height should be limited to ≤ 0.5 mm for pumped concrete applications.
- Steel tube dimensions — The internal diameter of the steel tube must accommodate the aggregate size and flow characteristics of the self-compacting concrete. The minimum internal diameter should be at least 3 times the maximum aggregate size to prevent blockage.
- Tube-jacking interface — The friction between the steel tube and the jacking system affects the pumping pressure requirements. The surface treatment and lubrication of the tube exterior are critical for efficient jacking operations.
Engineering Application Analysis
The Chengdu Huazhi Plaza project represents a significant application of this technology in super-high-rise construction. The jacking construction method involves:
- Casting the SRC column in sections within the steel tube
- Pumping self-compacting concrete through the tube from the bottom
- Jacking the completed column section upward to create space for the next section
- Repeating the process for successive column sections
The C60 grade is selected to achieve high load-bearing capacity with relatively compact column cross-sections, which is essential for maximizing usable floor area in super-high-rise buildings. The self-compacting property eliminates the need for internal vibration, which is impractical within the confined space of a steel tube during jacking operations.
Key Insights and Reflections
The successful development of this concrete mix design demonstrates the importance of interdisciplinary collaboration between concrete technology and steel structure engineering. The concrete mix must be designed not only for strength and durability but also for compatibility with the steel tube geometry and the jacking construction method.
From a quality control perspective, the following measures are essential:
- Batch consistency — Automated batching systems with real-time moisture correction should be used to maintain mix uniformity throughout the pumping operation.
- Pump pressure monitoring — Continuous monitoring of pump pressure can detect early signs of blockage or flow restriction, allowing timely intervention.
- Steel tube inspection — Pre-pouring inspection of the steel tube interior for surface defects, weld protrusions, and dimensional accuracy is critical.
Reference Value and Outlook
This paper provides valuable guidance for the design and application of high-strength self-compacting concrete in SRC column jacking construction. The systematic approach to material optimization, particularly the use of SAP for slump retention, represents a significant advancement in concrete technology for challenging construction applications. For steel pipe engineers, the key takeaway is that the internal quality of steel tubes is not merely a manufacturing concern but a functional requirement that directly impacts construction feasibility and structural performance.