Zhuojin Pipe Fitting Co., LtdPumping and Jacking Self-Compacting Concrete Construction for Steel Tube Arches
Literature Overview
This paper by Jiang Zhengwu, Pan Wei Wang, Li Xiangtao, and Zhang Changgui, published in Construction Technology (2011, Vol. 42, No. 2, pp. 134-137), describes the construction methodology for filling steel tube arches with self-compacting concrete (SCC) using a continuous pumping and jacking technique. The study was conducted in the context of a steel tube concrete arch bridge project in Zhejiang Province, China, and was supported by the Zhejiang Provincial Major Science and Technology Program and the National Natural Science Foundation of China. The authors address performance specification requirements, pumping sequence, construction preparation, emergency response measures, and key construction techniques.
Construction Technology Framework
The pumping and jacking method for SCC placement in steel tube arches represents a significant advancement over traditional vibration-based concrete placement methods. The approach leverages the self-compacting property of the concrete to eliminate the need for mechanical vibration, which is particularly advantageous in thin-walled steel tubes where vibration could cause tube deformation or damage to the internal reinforcement cage.
| Construction Parameter | Specification / Requirement |
|---|---|
| Concrete type | High-strength compensating shrinkage SCC |
| Placement method | Continuous pumping with jacking |
| Flowability | Self-compacting, no external vibration required |
| Shrinkage compensation | Expansive admixture to counteract drying shrinkage |
| Pumping sequence | Designed to minimize air entrapment and ensure full filling |
Technical Analysis of the Pumping and Jacking Process
The continuous pumping and jacking process involves the coordinated operation of concrete pumping equipment and mechanical jacking devices. As SCC is pumped into the steel tube, jacking equipment advances the tube or the pumping point, ensuring continuous and uniform filling. This method addresses several critical challenges associated with steel tube concrete arch construction:
- Air entrapment prevention: The continuous pumping sequence is designed to push air ahead of the concrete front, preventing void formation within the tube. For arch-shaped tubes, the pumping must start from the lowest point and progress upward, with the jacking mechanism controlling the rate of advance to maintain a continuous concrete column.
- Concrete segregation control: SCC mixes are inherently more susceptible to segregation and bleeding compared to conventional concrete, particularly during long pumping distances. The high-strength compensating shrinkage SCC mix designed for this project was carefully proportioned to maintain stability during pumping while achieving adequate flowability.
- Temperature and curing management: The environmental and climatic conditions at the construction site must be monitored and controlled throughout the pumping process. Temperature differentials between the fresh concrete and the steel tube can cause thermal stresses that may lead to cracking, particularly in high-strength concrete where the coefficient of thermal expansion is relatively high.
Quality Control and Emergency Response
The authors emphasize the importance of construction monitoring and emergency response planning. During the pumping and jacking process, the following quality control measures are critical:
- Slump flow and T500 time measurement at each batch to verify that the SCC maintains its specified flowability throughout the pumping duration.
- Pressure monitoring at the pumping equipment to detect blockages or flow restrictions in the delivery pipeline.
- Temperature logging of both the concrete and the steel tube to ensure that the temperature differential remains within acceptable limits.
- Joint management in case of pumping interruptions, with pre-planned procedures for restarting the pumping sequence without compromising the structural integrity of the composite member.
From a welding and fabrication standpoint, the steel tube arch segments must be fabricated and assembled to tight tolerances to ensure that the internal geometry is uniform and free of obstructions that could impede concrete flow. Weld seams within the tube interior must be smooth and flush, as any protruding weld beads could create flow restrictions or stress concentrations in the composite section.
Study Insights and Engineering Practice
This case study provides valuable practical guidance for engineers involved in steel tube concrete arch construction. The success of the pumping and jacking method depends on the careful integration of material design, construction sequencing, and real-time monitoring. The use of compensating shrinkage SCC is particularly important for arch structures, where drying shrinkage can induce significant internal stresses and potentially lead to cracking or deformation of the composite section. For engineers working on pipeline or structural projects involving concrete-filled steel tubes, the key lesson is that the concrete mix design and construction methodology must be developed in parallel, with the pumping and jacking sequence optimized based on the specific geometry and environmental conditions of the project.