Research on Concrete Pumping Technology for Super High-rise Buildings

The pumping construction of commercial concrete has been widely used in building projects. However, for the pumping of super high-rise buildings over 300 meters in height, due to the excessively high pumping pressure, the concrete used has high strength and viscosity, making the pumping particularly difficult. This brings a series of technical problems that need to be explored to the pumping construction. With the popularization and rapid development of pumped concrete, continuous research on the pumping technology of high-strength concrete for super high-rise buildings has considerable practical value and economic significance for improving the construction quality and efficiency of super high-rise buildings.

The main building of the Hong Kong International Finance Centre has 88 floors and is 420 meters high. It is the fifth tallest building in the world and the second tallest in Asia. The maximum height of its concrete pumping is 408 meters, which poses high requirements for construction safety, reliability, environmental protection and the degree of automation. To ensure the quality of the project and structural strength, the main building uses C60 concrete entirely. All these pose severe challenges to the concrete conveying equipment. For this reason, some measures conducive to pumping have also been taken in the concrete formula, and the mixing plant has been built within the construction site, about 300 meters away from the concrete pump, to ensure that the concrete reaches the pouring surface within 20 minutes and reduce the loss of slump.

The concrete consumption for each floor of this project is approximately 240 cubic meters, and it is carried out in two phases. Two HBT90CH-2122D ultra-high pressure concrete pumps from Sany Heavy Industry are used, and two sets of the same pipeline are arranged simultaneously. Both pumps can pump at the same time. During the pumping process at a height of 400 meters, the working pressure of the concrete pump's hydraulic system is 24 to 25MPa, the outlet pressure of the concrete is 16MPa, and it changes direction 10 to 11 times per minute, with a conveying capacity of approximately 40m ³ /h.

2 Equipment Condition

2.1HBT90CH Concrete pump

2.1.1 Technical Features

1) Dual power structure

To ensure the reliability of the construction process, the entire machine is powered by two diesel engines, each driving two sets of pump groups. By applying the dual-power combined flow technology, the two pump sets operate simultaneously under normal circumstances. When one set malfunctions, it can be cut off, while the other set still maintains a 50% displacement and continues to work, thus avoiding losses caused by construction process interruption.

2) Fully automatic high and low voltage switching

The entire process of switching between high and low pressure pumping modes in the hydraulic system is fully controlled by a computer. Just press one button and the switch can be completed instantly without the need to stop the machine and without causing pollution.

3) High-pressure concrete piston

Due to the maximum pumping height reaching 408 meters, the concrete inside the pipeline exerts an extremely high back pressure on the concrete piston. In response to this critical working condition, a high-pressure concrete piston suitable for super high-rise pumping structures was developed using reinforced polyurethane materials.

4) Eyeglass plates, cutting rings

The counter-thrust of the high and low pressure pump glasses in the hydraulic system causes the seal to fail, and the sealing between this pair of coupling parts is the key to ensuring the pumping in super high-rise buildings. The HBT90CH concrete pump reduces the reverse thrust by optimizing the streamline of the S pipe. Meanwhile, it adopts a high preload technology to ensure a tight fit between the cutting ring and the eyeglass plate, guaranteeing reliable sealing.

5) Water washing

In the 408m super high-rise pumping project, the HBT90CH concrete pump still adheres to the legendary technology of the same water washing height as the pumping height, which has set the world record for the highest water washing. The waste of concrete is minimized, and the entire project can save 2,640 cubic meters of concrete, equivalent to 1.9 million Hong Kong dollars. In addition, as there is no remaining concrete, the burden of construction waste treatment and management is reduced, and the workload and cost during the construction process are lowered. ?

2.2 Auxiliary Equipment

A fabric radius of 32 was designed in accordance with the engineering requirements. The main parameters of a 5-meter tailless drag automatic climbing fabric rod

The fabric radius (m) is 32.5

Tower height (m)31

The climbing mode is automatic continuous climbing

Climbing speed (m/s)0.5

The overall power of the machine (kW) is 30

The overall machine mass (t) is 24

The fabric rod is driven by four hydraulic motor reducer units. Through the gear rack, the fabric rod and the support frame are lifted alternately to achieve the automatic continuous climbing of the entire machine. The entire climbing process can be operated by one person. Due to the limitations of the building structure, the maximum support span of the fabric rods can reach 10 meters, while the minimum is only 3.5 meters. For this reason, Sany Heavy Industry specially designed large-span luffing beams.

2.3 Conveying Pipe

At the pump outlet, 100m horizontal pipes, 4 90° elbow pipes, 1 45° elbow pipe and 2 15° elbow pipes are arranged. On the 32nd floor, which is 140 meters high, three 30-meter horizontal pipes and three 90° elbow pipes are arranged. Two 90° elbow pipes are arranged on the 45th floor, which is 200 meters high. Two 90° elbow pipes are arranged on the 55th floor, which is 240 meters high. Then keep going upwards. The entire pipeline system includes 10 meters of exposed tower body of the placing machine, 32 meters of arm length, and 44 meters of elbow converted, with a total length of 622 meters. Both ends of the straight pipe are firmly fixed with rigid supports.

The key to pumping construction technology

There are many technical problems in the concrete pumping construction of super high-rise buildings, and measures should be taken from the following aspects.

3.1 Pumping capacity of the equipment

The maximum pumping capacity of the equipment should have a certain reserve to ensure smooth transportation and avoid pipe blockage. During the pumping process at a height of 408 meters this time, the working pressure of the hydraulic system of the concrete pump was 24 to 25MPa, and the pressure at the concrete outlet was 16MPa. However, the working pressure of the hydraulic system of the HBT90CH ultra-high pressure concrete pump can reach 35MPa, and the maximum pressure at the concrete outlet can reach 22MPa. This is also a crucial factor for the HBT90CH to successfully complete the pumping at the 400m super high-rise.

3.2 Reliability of equipment Configuration

The configuration of equipment should be based on reliability as the primary principle. The reasonable layout of pipelines for the concrete transportation in super high-rise buildings is of vital importance. Once the pumping is stopped for more than 2 hours due to equipment failure, the concrete in the transportation pipes will experience bleeding and segregation, which will cause the concrete in the entire pipeline system to be scrapped and seriously affect the construction quality. The Sany HBT90CH pump is equipped with two engines. They can operate simultaneously to enhance work efficiency or work independently. Even if one engine malfunctions, the backup engine will continue to work, significantly improving the reliability of the construction process. In addition, two independent pump and pipeline systems are also a strong guarantee for the smooth construction.

3.3 Pipeline system resistant to ultra-high pressure

When performing ultra-high pressure pumping, the maximum pressure inside the pipeline can reach 22MPa, and a longitudinal tensile force of 27 tons will be generated. Therefore, a pipeline system that can withstand ultra-high pressure must be adopted. In addition, the conventional connection and sealing methods cannot meet the requirements either, and the following solutions need to be adopted.

1) Use ultra-high pressure pipes with a wall thickness of more than 9.5mm to ensure the anti-explosion capacity of the pipes.

2) The connection between pipes is guaranteed by the strength grade of the screw, and the longitudinal tension is borne by the screw, providing reliable protection at the joint.

3) The ultra-high pressure concrete sealing ring with a skeleton can prevent concrete from being squeezed out of the pipe clamp gap under a high pressure of 22MPa, ensuring a long-lasting and reliable seal.

4) The smaller the diameter of the conveying pipe, the greater the conveying resistance. However, overly large conveying pipes have poor anti-explosion capacity, and the flow rate of concrete in the pipe is slow and the residence time is long, which affects the performance of concrete. It is best to choose a conveying pipe with a diameter of 125mm.

3.4 Reasonable pipe layout

Pipe laying should be set up in accordance with the concrete pouring plan, and elbows and hoses should be used sparingly to shorten the pipeline length as much as possible. In this project, the pipelines are laid along the floor or wall. A series of supports are installed on the concrete floor or wall with expansion bolts, and each pipeline is fixed by two supports. To reduce the concrete back pressure inside the pipeline, a 100-meter horizontal pipe and several elbow pipes were arranged at the pump outlet, achieving good results.

3.5 Reasonable and applicable concrete mix ratio

The principle of mix proportion design is to not only meet the requirements of strength and durability, but also be economically reasonable and have good pumpability. Therefore, in addition to the usual factors to be considered, the following aspects must be well handled.

1) Cement dosage

The amount of cement used for pumping concrete in super high-rise buildings must take into account both strength and pumpability. If the amount of cement is too small, the strength will not meet the requirements. If it is too large, the viscosity of the concrete will be high, the pumping resistance will increase, which will increase the difficulty of pumping and reduce the suction efficiency. In this example, the amount of cement used was 375kg/m ³ +3, and excellent results were achieved during the construction.

2) Coarse aggregate

Conventional pumping operations require that the ratio of the maximum aggregate particle size to the pipe diameter not exceed 1:3. In the pumping of super high-rise buildings, due to the high pressure inside the pipeline, segregation is prone to occur. This ratio should be less than 1:5, and the number of sharp and flat stones should be small to avoid increasing the amount of cement used.

3) Slump

In ordinary pumping operations, a slump of concrete around 160mm is most conducive to pumping. A slump that is too high is prone to segregation, while a slump that is too low results in poor fluidity. In the pumping of super high-rise buildings, to reduce pumping resistance, the slump should be controlled at 180 to 200mm. Meanwhile, to prevent concrete segregation, zeolite powder can be added to reduce bleeding.

4) Fly ash and admixtures

The combined use of fly ash and admixtures can significantly reduce water consumption and improve the workability of concrete mixtures. However, due to the wide variety of admixtures, their adaptability to fly ash varies. The optimal dosage should be determined through experiments.

3.6 Ensure the continuous supply of concrete

In view of the good viscosity and fast setting of concrete, to ensure the homogeneity of concrete, the mixer truck should rotate at high speed in the reverse direction for 20 to 30 seconds before feeding the pump. During the pumping process, continuous and rapid stirring should be carried out without stopping to avoid the phenomenon of pipe blockage caused by the concrete remaining for too long during pumping.

3.7 Ensure the smooth pumping of concrete

Before pressure delivery, the hopper, pump chamber, conveying pipelines and other parts in contact with concrete of the pump should be moistened with water. Only after checking that there are no abnormalities in the pipelines can cement mortar be used for lubrication and pressure delivery.

When starting the pumping, the pump should be in a low-speed operation state. Pay attention to observing the pressure of the pump and the working conditions of each part. Only after the pumping is smooth can the normal transportation speed be increased.

When concrete pumping is difficult and the pump pressure suddenly rises, it will cause the pipeline to vibrate. You can strike the pipeline with a mallet, find the clogged section, and handle it by running the forward and reverse pumps in point or disassembling and cleaning. After checking and confirming that there is no blockage, continue pumping to avoid damaging the pump.

During construction, the method of receding pipes from far to near and the secondary pipe laying method are adopted. The direction of concrete pouring in this project is the same as the direction of pumping.

3.8 Other Precautions

1) Pipes with cracks or surface depressions must not be used. Pipe clamps must be tightly fastened to prevent pipe bursts from injuring people.

2) Timely handle faults and replace necessary vulnerable parts;

3) After the machine stops, it should be cleaned in time and the maintenance of the pump should be paid attention to.