Due to the high construction demands of structures like bridges and sea squares, the use of high-grade concrete is essential. However, due to space limitations and logistical challenges, much of this concrete has to be transported over long distances. For instance, in the construction of two buildings at Qingdao Court Plaza, the HBT60A concrete pump was used to deliver high-grade concrete over extended distances. This case serves as a good example to discuss the challenges and techniques involved in pumping high-strength concrete over long distances.
One notable project is the Zhong Court Sea Square, where helicopter landings are planned, making the strength requirements particularly strict. At that time, C60 high-strength concrete was used, with a slump of 12–14 cm, a horizontal conveying distance of 300 meters, and a vertical lift of 10 meters. Four 90° bends with a radius of 1000 mm were also included, and each pumping operation involved about 400 m³ of concrete.
Pumping high-strength concrete presents significant challenges, including low slump, high viscosity, long-distance delivery, and high pumping pressure, all of which can lead to reduced efficiency or even blockages. To address these issues, several key steps must be taken:
1. **Pre-pumping equipment checks**
Before starting, ensure all equipment is fully inspected. The main system pressure should be adjusted to 32 MPa, taking into account the high pumping pressure and potential overflow from the main relief valve. The main pump displacement should be set to minimum, while the sequence valve pressure should not drop below 10.5 MPa. It's important to have sufficient nitrogen in the accumulator to maintain stability.
2. **Sliding valve cylinder maintenance**
Ensure there is no internal leakage in the sliding valve cylinder. The buffer should be appropriately small, and lubrication must be adequate to prevent sluggish movement caused by high-viscosity concrete. If the gate wears too much, it may lead to leakage and blockage in the Y-tube or adjustable pipe.
3. **Sealing of Y-tube and upper shell**
The Y-tube and upper shell must be tightly sealed. Any leakage can cause slurry to seep out, leading to blockages and unnecessary delays during construction.
4. **Pipe requirements for long-distance pumping**
Minimize pipe bends to reduce resistance. Each additional 90° bend (R1000) is equivalent to adding 5 meters of horizontal pipe. In one project, only four φ125A 90° elbows were used, with the rest being straight pipes totaling 310 meters. Reinforcement of the pipeline and clamps is crucial to prevent pipe beating, bursting, or jamming.
5. **Proper water usage before pumping**
Avoid over-lubricating the pipeline with excessive water. Some operators mistakenly believe more water leads to better lubrication, but this can cause blockages. Instead, a proper amount of water should be used to lubricate the pipeline without compromising the mix.
6. **Concrete pumping challenges**
High-strength C60 concrete has a fine aggregate size under 30 mm, a sand ratio of 39%, and a cement content that meets pumping needs. However, the low water-cement ratio (0.2–0.3) results in a slump of around 12 cm, reducing fluidity. Increasing the sand ratio improves pumpability but may affect strength. The best solution is to adjust the water content without compromising strength. Initially, without superplasticizer, the pumping pressure was 26–28 MPa, with slow performance. After adding a certain amount of superplasticizer (NF-2), the slump increased to 18–20 cm, and the pressure dropped to around 18 MPa, doubling the pumping efficiency.
7. **Post-pumping pipeline cleaning**
After pumping, the pipeline should be cleaned promptly. Disconnect the pipeline in the middle and clean it in two sections to ensure safety. When using a sponge ball, place a cement bag and two sponge balls ahead of the cleaning piston to avoid damage.
By following these guidelines, the challenges of pumping high-strength concrete over long distances can be effectively managed, ensuring smooth and efficient operations.
600-800KG/h Production Line
600-800KG/h Production Line
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