Functions of construction joints requirements for

2022-07-22
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Construction joint refers to the joint formed between the first and second poured concrete due to the design requirements or construction needs of segmental pouring during the concrete pouring process. Therefore, the construction joint does not really exist, it is only because the later poured concrete exceeds the initial setting time, and there is a joint surface with the first poured concrete, which is called the construction joint

construction joint refers to the joint formed between the first and second poured concrete due to the design requirements or the construction needs of segmental pouring during the concrete pouring process. Therefore, the construction joint does not really exist, it is only because the later poured concrete exceeds the initial setting time, and there is a joint surface with the first poured concrete, which is called the construction joint. The following editor will introduce the function of construction joints and the treatment requirements of construction joints

function of construction joints

construction joints can accurately grasp the specific implementation of sub construction (or subsection construction), and can effectively ensure the construction quality of buildings. Generally speaking, construction joints need to be reserved before the building. If you plan in advance where to reserve construction joints, you can make the building not be unstable and have problems because of the sub construction. When reserving construction joints, we need to calculate how long it takes for each section to set the concrete, and then determine a reasonable time difference, so that each part can be constructed in sections and firmly combined. This is the role of construction joints and the significance of their existence

retaining position of construction joint

1. The construction joint should be retained on the top surface of the foundation, below the bracket of the beam or crane beam, above the crane beam, and below the column cap of the beamless floor

2. For the large section beam connected with the floor slab, the construction joint should be left 20 ~ 30mm below the bottom of the slab. When there is a beam bracket under the plate, it shall be left at the lower part of the beam bracket

3. For one-way slabs with a length width ratio greater than 2, the construction joint should be left at any position parallel to the short side of the slab, and the construction joint should be left vertically, and cannot be made into an inclined tenon

4. The floor slab with primary and secondary beams should be poured along the direction of the secondary beam, and the construction joint should be left within the middle 1/3 of the span of the secondary beam

5. The construction joint on the wall should be left within 1/3 of the lintel span of the door opening, or at the junction of vertical and horizontal walls

6. The construction joint on the stairs should be left at 1/3 of the step board. The concrete of stairs should be poured continuously. If it is a multi-storey staircase, and the upper floor is a cast-in-place floor slab but not poured, the construction joint can be left; It should be left in the middle 1/3 of the stair section, but it should be noted that the joint surface should be inclined and perpendicular to the axis of the stair. (the reason for the dispute in the construction is that the old specification stipulates that the stair construction joint must be left in the middle 1/3 section, while the traditional construction is left in the upper and lower steps. When it is left in the middle of the ladder, the shear force is theoretically small, but the quality of the construction joint is not easy to control during the construction, and it is easy to form a short-term “ overhang ” at the poured part during the secondary formwork erection, which is not conducive to the quality control of the components.)

7. The construction joint of the pool wall should be left on the vertical wall 200 ~ 500 mm higher than the surface of the bottom plate

8. For two-way stressed floor slab, mass concrete, arch, shell, warehouse, equipment foundation, multi-storey rigid frame and other complex structures, the location of construction joints shall be reserved according to the design requirements

treatment requirements for construction joints

1. When the old concrete surface and exposed reinforcement (embedded parts) are exposed to cold air, the old concrete within 1.5m from the new and old concrete construction joints and the exposed reinforcement (embedded parts) within 1.0m in length shall be protected from cold and heat preservation

2. When the concrete does not need to be heated for curing and will not freeze within the specified curing period, the concrete can be poured directly for the non frost heaving foundation or the old concrete surface

3. When the concrete needs to be heated and cured, the temperature difference between the newly poured concrete and the adjacent hardened concrete or geotechnical medium shall not be greater than 15 DEG; C; The temperature of the subgrade surface in contact with the concrete shall not be less than 2° C。 11.3.11 the temperature of concrete at the beginning of curing shall be determined by thermal calculation according to the construction scheme, but shall not be lower than 5° C. The thin section structure should not be less than 10 DEG; C。

4. The cement mortar and weak layer on the poured concrete surface shall be chiseled off, and the area of fresh concrete exposed after chiseling shall not be less than 75%. When roughening, the concrete strength should meet the following requirements:

1) when roughening manually, it should not be less than 2.5MPa

2) when chiseling with pneumatic machine and other machinery, it shall not be less than 10MPa

5. The concrete surface that has been roughened shall be washed with water, but there shall be no ponding. Before pouring new concrete, for vertical construction joints, a layer of cement paste should be brushed on the old concrete surface. For horizontal construction joints, a layer of 10mm~20mm thick cement mortar with a cement sand ratio of 1:2 which is slightly smaller than the water binder ratio of the concrete should be paved on the old concrete surface, or a layer of concrete with a thickness of about 30cm should be paved, and its coarse aggregate should be reduced by 10% compared with the newly poured concrete

6. When the construction joint is an inclined plane, the old concrete should be poured or chiseled into a step shape

editor's summary: This is the introduction of the function of construction joints and the requirements for the treatment of construction joints. I hope it will be helpful to you. If you want to know more, you can pay attention to information

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