Use concrete placing boom to pour high-rise buildings

1. Working performance of concrete

The working performance of concrete during pouring mainly includes workability, fluidity and water retention. The evaluation index currently used is slump.

Because the vertical structure (walls, columns, etc.) of high-rise buildings has dense steel bars, in order to ensure that the concrete can fill the formwork under vibration, the slump at the outlet of the pumped concrete should not be less than 150mm, and it should have good workability and water retention. Workability is mainly determined by visual inspection. The slurry should wrap the stones, and the stones should not be exposed or scattered; if the concrete is scattered halfway out of the spray, it means that the workability is not good. If the mortar splashes severely when sprayed on the ground, it means that the slump is too large.

Since the slump of concrete will be lost to a certain extent during transportation and transportation in the pump pipe, the slump of concrete when it is pre-mixed and transported out of the mixing station and when it enters the pump should be appropriately greater than the slump at the outlet of the pump pipe. The specific size should be determined according to the specific situation, such as the distance between the mixing station and the construction site, the temperature and humidity during construction, and the layout of the pipeline on the construction site (pipeline length, pumping height, number of turns, etc.). When the slump loss is large, the slump of the pump should be appropriately increased.

① The layout location of the pump should be selected in a place with a stable foundation and open surroundings that is conducive to the operation and parking of concrete transport vehicles. The pump pipe should also be placed on a stable steel pipe bracket, and sleepers should be added where necessary to reduce vibration.

② The position of the vertical pipe should be selected at a shorter straight horizontal distance from the pump, which should not be less than 1/4 of the pumping height and generally not less than 20m. The holes reserved for vertical pipes on the building structure should be selected on the plates with less structural stress, and structural reinforcement measures should be taken around the holes if necessary.

③ The elbow and vertical pipe should be tightly connected to the building structure every 3m, and there should be no vibration or shaking, otherwise it will affect the pumping effect.

④ The diameter of the pump pipe should generally be gradually transitioned from 150-125-100, connected by a reducer, and the transition length of the reducer should not be less than 500mm and 1500mm respectively.

⑤ The reverse flow valve should be installed on the horizontal pipe about 5m away from the pump outlet;

2.3 Concrete distributor

Concrete distributor is a special equipment for paving concrete and pouring it into the mold when concrete is transported to the casting surface. It is divided into movable distributor, fixed distributor and pump truck attached distributor according to the structure.

 The movable distributor is widely used in the concrete pouring construction of high-rise buildings. This type of concrete placing boom can be placed on the concrete pouring working floor. It consists of two sections of boom conveying pipes, rotating supports, balance arms, counterweights, base frames and legs. It has the advantages of simple structure, manual operation, easy use and low cost. Since the movable concrete placing boom is light in weight and simple in structure, it can be moved to different construction sites by a tower crane, which is very suitable for the needs of flow operations in multiple high-rise buildings.

 The fixed concrete placing boom can be installed in the elevator shaft inside the building or on the periphery of the building. It climbs up layer by layer as the construction progresses. It can be used in high-rise buildings with integral lifting scaffolding installed.

 The vertical conveying height of the concrete placing boom attached to the pump truck generally does not exceed 30m, and is only used for foundation and building structure concrete construction below 30m.