Construction method of drying shrinkage crack cont

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With the continuous expansion and development of urban buildings, the supporting underground civil air defense facilities have been further improved, and large-scale civil air defense facilities have also been included in the ranks of building planning. With the continuous development of construction projects, common problems in the construction quality of basement wallboards occur from time to time. Common problems of drying shrinkage cracks in basement wallboards have gradually become an important problem that construction units urgently need to solve. For many years, through the good application of improved concrete mix proportion, gradation and admixture in construction, the dry shrinkage cracks of concrete wallboard in civil air defense basement have been improved, but the problem can not be finally solved; Our company has carried out pilot projects on several large-scale projects in recent years, such as chunguifang apartment, South Street commercial pedestrian street, Changzhou Central Park Building B, commercial bank connection project, etc. it is concluded that as long as the early maintenance of concrete is strengthened, the drying shrinkage cracks of concrete can be effectively solved, which not only reduces the construction cost, but also ensures the project quality

II. Characteristics and causes of drying shrinkage cracks in concrete wallboards

the shrinkage cracks in basement wallboards are characterized by dry shrinkage and condensation during the concrete solidification process, mainly dry shrinkage, which mostly occurs on the concrete surface. The cracks are shallow and thin, and the forms are irregular, which generally appear early

on the premise of adopting good concrete mix proportion, grading and operation in accordance with construction specifications, the causes of shrinkage cracks in basement concrete wallboard are summarized:

1. Partial or small parts of concrete are exposed to the air and cannot be fully cured

2. According to the characteristics of high lateral pressure of pumped concrete on the formwork, no reinforcement measures were taken for the formwork

3. The time of formwork removal is inappropriate and not in time

III. scope of application

this construction method is applicable to the construction of basement wallboards

IV. key points and advantages of construction

when pouring the concrete outer wall of the basement, strengthen the quality awareness of the site management personnel, do a good job in the disclosure of formworks and painters, strictly control the quality of concrete entering the site, and fully protect the reinforcement of the wallboard according to the specifications; The external wall formwork is equipped with butterfly nuts and M14 high-strength bolts as tension screws, with a distance of 45cm from top to bottom, left to right, which effectively controls the thickness of the wall and the positioning of the formwork. When pouring concrete, its layered pouring thickness shall not exceed 300, so that it can speed up the heat dissipation of concrete, and its tentacles are all over the testing ball market that can complete the technical indicators such as maximum bearing tension, tensile strength, elongation deformation, elongation, and make the heat distribution uniform; The slump of concrete shall be controlled within 14 ± 2cm. After the concrete pouring reaches the formwork removal strength, the formworks shall immediately remove all formworks, and the painters shall be sent to follow and paint the curing liquid twice. The first advantage is to form a curing protective film on the concrete surface, which can effectively prevent the premature evaporation and loss of water in the concrete, so that the concrete surface and interior can be cured at the same time, blocking the invasion of external gas, and reducing the early shrinkage of the concrete; Second, remove all formwork immediately to prevent drying shrinkage between formwork and concrete due to air flow; III. this method is easy to operate, easy to master and fast in construction

v. quality requirements and precautions

1. Concrete strength control: when the formwork removal strength of the external wall must reach 1.20mpa (generally about 24 hours), the formwork can be removed completely. If the formwork is removed too late, the concrete at the joint of the formwork is easy to evaporate and form air joints, causing cold joints

2. Formwork control: the formwork is more convenient for use in multiple scenes. The surface between the plates is closely matched, flat, and the joints are tight, so as to ensure the strength, stiffness, and stability of the overall formwork, and no slurry leakage is allowed

3. Matters of formwork removal: formwork workers must have skilled operation skills and psychological preparation for continuous operation. All formwork shall be removed at one time without stopping

4. Painting curing liquid: it must be painted as soon as it is removed, followed by two consecutive and uniform coats, and no omission or pause is allowed

5. Finished product protection: the removed formwork shall be transported out in time to prevent collision, and the finished product shall be protected after painting

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