A method for pouring concrete into tall, narrow cavities

Abstract

A method for pouring concrete into tall, narrow cavities addresses the issue of blind spots and insufficient compaction that can occur when pouring concrete into such cavities with varying cross-sections. The method includes the following steps: S1, concrete selection; S2, pouring height control, employing layered continuous pouring with each layer being 50cm thick, preceded by a 50mm layer of mortar of the same grade; S3, pouring time control, placing test blocks every 1 meter for observation and controlling the initial setting time; when the pouring height reaches 3 meters, the bottom 50cm of concrete must be at least partially set, while the concrete at the contact surface must not be at least partially set; S4, vibration control during pouring, using auxiliary vibration to compact the concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete pouring technology, and more particularly to a method for pouring concrete into a large, narrow cavity. Background Technology

[0002] In the construction of prefabricated hollow components in the water system prefabrication field, there are often problems such as incomplete pouring, poor concrete quality, and cold joints, which result in a high risk of water tank leakage.

[0003] Prefabricated waterworks buildings use fully prefabricated components. Considering seepage prevention performance, prefabricated components with cavities are often selected. When pouring concrete in a confined space, it is necessary to ensure the quality of concrete construction while avoiding damage to the prefabricated components with cavities. Traditional concrete pouring methods result in issues such as incomplete compaction, poor concrete quality, and cold joints. Furthermore, waterworks pool walls have variable cross-sections, a height of 7-9 meters, and cavities of 0.2-0.6 meters. Vibrators cannot effectively vibrate from below within these confined cavities. Additionally, the pool walls have variable cross-sections—the outer wall is sloping, while the inner wall is flat—and a water-stop steel plate is present at the bottom sill connection. Therefore, if the vibrator is lowered into position, it can only vibrate the inner wall, leaving the outer wall unvibrated. This easily leads to incomplete compaction of the concrete on the outer wall.

[0004] In addition, because the vertical cavity structure of the pool wall is 7-9 meters long, the concrete cannot be poured into the cavity due to its small size. During the free fall of the concrete, segregation and bleeding are likely to occur, which will cause the coarse aggregate to sink and the mortar to float. This will result in severe delamination of the cavity concrete, forming local weak layers. Moreover, the bond between the hardened concrete and the precast cavity wall is not dense due to the presence of water film formed by bleeding, which will seriously damage the quality of the concrete. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a concrete pouring method for tall and narrow cavities, which effectively solves the problem that blind spots are easy to exist when pouring concrete for tall and narrow cavities with variable cross sections, which will result in incomplete pouring.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a method for pouring concrete into a tall and narrow cavity, comprising the following steps:

[0007] S1, Concrete selection: High-flowability concrete or self-compacting concrete;

[0008] S2, pouring height control, adopts layered continuous pouring, with a layer thickness of 50cm, and before the first layer is poured, 50mm of the same grade of mortar is poured.

[0009] S3, control the pouring time. Leave a test block every 1 meter for observation and control the initial setting time. When the pouring height reaches 3 meters, ensure that the bottom 50cm of concrete has set initially, and the concrete on the contact surface must not set initially.

[0010] S4, pouring vibration control, to assist in the vibration of concrete.

[0011] Preferably, the high-fluidity concrete in S1 requires coarse aggregate particle size control on the basis of conventional concrete, with the maximum particle size ≤20mm, the initial slump controlled within 220±20mm, and the slump maintained at ≥200mm for 2h.

[0012] Preferably, the concrete test blocks in S3 are used to determine their strength using a test needle.

[0013] Preferably, in step S4, an attached vibrator or a high-frequency vibrator is used for auxiliary vibration of the concrete.

[0014] Preferably, step S5 is also included, which involves observing the pouring process using a visual device located below the cavity to observe the density of the concrete inside the cavity.

[0015] Preferably, in step S2, a string tube is arranged at the outlet of the discharge pipe to distribute the material into the cavity, and a steel wire is wound around the string tube to control the angle between the string tube and the discharge pipe.

[0016] Preferably, the spool is a damped pipe.

[0017] Preferably, the tubing is a fiber nylon water bag.

[0018] This invention can effectively solve the risks of incomplete compaction and leakage in precast hollow concrete pouring for waterworks, and the construction is simple and convenient to operate, with good construction quality. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the internal structure of the cavity in this invention;

[0020] Figure 2 This is a schematic diagram of the casting duct structure of the present invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings. The drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0022] When selecting concrete materials, if the cavity of the double-layer wall allows for normal entry of the pump truck's placing pipe and vibrator during construction, high-flowability concrete can be used. Strict control of coarse aggregate particle size is required, with a maximum particle size ≤20mm. The initial slump should be controlled within 220±20mm, and the slump should be maintained at ≥200mm after 2 hours to ensure the workability of the concrete. Emphasis should be placed on measuring the concrete slump, air content, and density. If the cavity is small, self-compacting concrete should be used. During the mix design and on-site testing, the following concrete conditions must be carefully controlled: initial slump / spread, 2-hour slump / spread, initial collapse time, 2-hour collapse time, J-ring height difference, T500 time, segregation rate, and workability.

[0023] Self-compacting concrete refers to freshly mixed concrete that has high fluidity without segregation or bleeding, and can fill every corner of the formwork with its own weight without vibration or with minimal vibration, achieving full compaction and optimal performance.

[0024] High-flowability concrete and self-compacting concrete are both effective for the pourability of relatively small, closed structures and for ensuring good sealing of concrete, especially self-compacting concrete.

[0025] In this implementation case, the double-layer wall cavity has a height of 8 meters and relatively dense internal reinforcement, making it difficult to vibrate the concrete deep into the working surface. Therefore, SF2 self-compacting concrete with a spread of 660-755mm and a maximum particle size ≤16mm was used. Because the placing pipe could not enter the cavity, and the free fall height from the outlet to the pouring point exceeded the free fall height of the concrete by 2m, fiber nylon water bags were used as a guide tube (1) to place the concrete into the cavity to prevent segregation. This effectively buffered the concrete flow, providing friction to reduce the flow velocity. The distance between the fiber nylon water bags and the pouring point was controlled at 1-2 meters. Concrete pouring was carried out in layers, each 50cm thick. Before the first layer, a 50mm layer of mortar of the same grade was poured to prevent coarse aggregate from falling and bouncing, and to ensure the bonding between the new and old concrete. Furthermore, during this process, because the cross-section is variable, when the concrete falls directly to the bottom of the cavity, there will be a dead point at the bottom of the cavity. In this way, we can better achieve dead-point-free pouring by adjusting the angle between the tremie pipe 1 and the discharge pipe.

[0026] Because the double-layer wall slabs function as formwork, the concrete pouring speed must be controlled to avoid damage due to excessive pressure. The initial setting time of the concrete is generally 6-8 hours, depending on the trial mix design. In summer, the initial setting time may be earlier, so the layer interval should be controlled before the initial setting of the concrete. It is also necessary to ensure that the bottom 50cm of concrete reaches the initial setting state when the pouring height reaches 3 meters. Test blocks should be placed every meter for observation. The strength of the concrete test blocks is determined using the penetration resistance method: mortar is sieved from the concrete mixture for test blocks, and tests are conducted every 30 minutes. The testing interval should be shortened as the initial setting time approaches. For self-compacting concrete in special conditions, such as narrow vertical cavities, auxiliary vibration can be achieved using an attached vibrator or a high-frequency vibrator. During pouring, a visual monitoring device placed inside the cavity can be used to observe the pouring process, effectively ensuring the final quality of the concrete.

[0027] The embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom remain within the scope of this invention.

Claims

1. A method for pouring concrete into a tall, narrow cavity, characterized in that, In the construction process of prefabricated cavity components used in the field of prefabricated waterworks, the water tank wall has a variable cross-section, with a height of 7-9 meters and a cavity of 0.2-0.6 meters; the process includes the following steps: S1, Concrete selection: Use high-flowability concrete or self-compacting concrete; High-flow concrete requires coarse aggregate particle size control on the basis of conventional concrete, with a maximum particle size ≤20mm, and the initial slump controlled within 220±20mm, and the slump maintained at ≥200mm for 2h; self-compacting concrete uses SF2 self-compacting concrete, with a spread of 660~755mm and a maximum particle size ≤16mm. S2, pouring height control, adopts layered continuous pouring, with a layer thickness of 50cm, and before the first layer is poured, 50mm of the same grade of mortar is poured; to prevent coarse aggregate from falling and jumping and to ensure the bonding between new and old concrete. Because the placing pipe cannot enter the cavity for operation, the free fall height from the outlet pipe to the pouring point exceeds the free fall height of the concrete by 2m; in order to prevent concrete segregation, fiber nylon water bags are used as a tremie pipe (1) to place the concrete in the cavity, which plays a buffering role. It has a certain friction force and can reduce the flow rate of the concrete; the height of the fiber nylon water bag from the pouring point is controlled at 1 to 2 meters; the cross section is a variable cross section. When the concrete falls directly to the bottom of the cavity, there will be a dead point at the bottom of the cavity. By adjusting the angle between the tremie pipe (1) and the outlet pipe, it is better to achieve pouring without dead points; S3, Pouring Time Control: To avoid excessive pressure that could damage the blades, the concrete pouring speed should be controlled. The initial setting time of the concrete is generally 6 to 8 hours, depending on the trial mix, and may be earlier in summer. The layer interval should be controlled before the initial setting of the concrete, and it is necessary to ensure that the bottom 50cm of concrete reaches the initial setting state when the pouring height reaches 3 meters. Test blocks should be placed every 1 meter of pouring for observation, and the strength of the concrete test blocks should be determined using the penetration resistance method. Mortar should be sieved from the concrete mixture for test blocks, and tested every 30 minutes. The test interval should be shortened when the initial setting is approaching. S4, Pouring Vibration Control: Auxiliary vibration of concrete; For special working conditions, self-compacting concrete is subjected to auxiliary vibration by attached vibrators or high-frequency vibrators. S5, the pouring observation method, uses a visual device below the cavity to observe the density of the concrete inside the cavity, effectively ensuring the final quality of the concrete.

2. The method for pouring concrete into a tall, narrow cavity according to claim 1, characterized in that, The concrete test blocks in S3 are used to determine their strength using a test needle.

3. The method for pouring concrete into a tall, narrow cavity according to claim 1, characterized in that, A spool (1) is arranged at the outlet pipe, through which material is distributed in the cavity; and a steel wire is wound on the spool (1), through which the angle between the spool (1) and the outlet pipe is controlled; the spool (1) is a damped pipe or a fiber nylon water bag.

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