The construction joint is not a real "sew". It is just because the concrete is poured first before the initial setting time, and there is a joint surface with the concrete after the pouring. This joint surface is called a construction joint. Let's take a look at the construction joint problems and solutions.
What is a construction joint
Construction joints refer to the joints formed between pre- and post-concrete concretes due to design requirements or construction needs to be poured in stages during the concrete placement process.
The role of construction joints
As we all know, when we use concrete and steel to pour, we often do all the work in one shot. What we need to consider is the design requirements and the convenience of construction. This causes the concrete to be poured not to be completed at one time, but to be completed by stages. In the previous and next pouring process, the two pourings are different because of the time, so a small seam will be produced. This is the "construction joint" that people often say.
From this point of view, construction joints are not simply referring to this small joint, but to a section of concrete that has been poured first and that of post-cast concrete because of different setting times. This section (or joint) is the real construction joint.
Then why must construction seams be reserved in the construction process? This has to be explained from the unique role of construction joints.
Everyone knows a word, "The city of Rome was not built in one day." In fact, the construction of any building cannot be completed overnight. However, if the sub-construction is correct, there will be many follow-up problems. For example, when the foundation is hit, because the area of ​​the foundation to be hit is too large and needs to be carried out in stages, if it cannot be reasonably calculated The specific implementation of the construction, then the foundation of this house can not be strong, this house can not stand still.
Therefore, the role of construction joints can be seen by everyone, set aside construction joints, can accurately grasp the specific implementation of sub-time (or sub-construction), can effectively ensure the building's construction quality. In general, construction joints need to be reserved before the construction. Planning ahead where specific construction joints are reserved can make the building not appear to be insecure between the parts due to the division of construction. problem. When we reserve the construction joints, we need to calculate how long it takes for each segment to solidify the concrete, and then determine a reasonable time difference so that each part can be constructed in sections and firmly combined. This is the effect of construction joints and the significance of construction joints.
Construction joints leaving method:
The position of construction joints shall be set at the site where the structure is subject to small shear force and is convenient for construction. The following provisions shall be complied with: Columns shall be left horizontally, and vertical joints shall be left for beams, slabs and walls.
(1) Construction joints shall be placed under the top surface of the foundation, below the girder or crane girder leg, above the crane girder, below the pillarless column caps.
(2) Large cross-section beams that are integrated with floor slabs. Construction joints should be located 20mm to 30mm below the floor of the slab. When there is a beam under the board, stay in the lower part of the bracket.
(3) For unidirectional plates, construction joints should be placed at any position parallel to the short side of the plate.
(4) Floors with primary and secondary beams should be placed along the direction of secondary beams, and construction joints should be placed within the middle 1/3 of the secondary beam span.
(5) The construction joints on the wall shall be left in the middle 1/3 of the span of the lintel of the portal, and may also be left at the intersection of the vertical and horizontal walls.
(6) The construction joints on the stairs should be left at 1/3 of the tread board. The concrete of the stairs should be poured continuously. If it is a multi-story staircase and the upper floor is cast-in-place floor slab and not poured, the construction joint can be left; it should be left at 1/3 of the middle of the stair section, but it should be noted that the joint surface should be perpendicular to the axis of the stairs. direction.
(7) The construction joints of the pool pool wall should be left on the vertical wall 200mm to 500mm above the floor surface.
(8) Two-way forced floor slabs, massive concrete, arches, shells, silos, equipment foundations, multi-storey rigid frames, and other complex structures, the location of construction joints should be set according to design requirements.
Construction joint problems and solutions
1, vertical seam surface chiseling method
After the final coagulation, the baffle is removed and the surface is cut with a pickaxe or a steel rod to clean the loose stones. At this time, the strength of the crucible is very low, and the depth of cut is 20 to 30mm. When the second pouring crucible is used, the pressure water is used in advance. Rinse the seam surface and apply a brushing slurry together to enhance the occlusal force.
2, increase the coarse aggregate method
The large size of beams and plates results in thicker retention seams, and the surface layers of laitance and bleeding are correspondingly thicker. It is more difficult to deal with construction joints; for example, the effect of scraping or turbulent vibrating on the scraped surface is poor. The method of adding coarse aggregates can be used to spread the grading clean gravel into the laitance and re-vibration to prevent the concentration of stones. This will make the joints thicker and thicker when the concrete is poured in a larger volume, the cement slurry will not be lost and the strength will not be reduced, and the adhesive force and bite force of the old and new interfaces can also be improved.
3, clear laitance method
When the volume of carcasses is small, the simple method is to scrape the surface slush with iron trowels to a depth of <25 MM, and dig out the strips to improve the bonding quality of the horizontal construction joints, which is beneficial to the combination of old and new concrete. .
4, secondary development of vibration method
After a good grasp of time, after the first set of condensate, the second revitalization is performed before the final condensing. This will re-stir and combine the sinking stones and the levitation water once more to make it more uniform and compact. The practice of resurfacing the joints is effective. One of the measures.
The above points are the summary of this site for everyone to summarize what is the construction joints, construction joints and solutions related information, I believe we will have a certain understanding after reading, so that everyone will know a lot, if everyone There are those who want to know can check it out on our website.
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