Analysis and Discussion on crack control of the ho

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Analysis and Discussion on the control of cast-in-place floor cracks

cast in-place floor cracks are a problem that has plagued building construction for a long time. Although the theory believes that cracks in cast-in-place floor slab are inevitable, it is completely feasible to reduce and control cracks through technical management measures in construction. The Shanghai University of Finance and economics student apartment project undertaken by the author has effectively reduced the cracks in the cast-in-place floor slab through a series of technical measures

floor cracks are divided into surface cracks and through cracks. The cracks are large and small, and the positions are also different, regular and irregular. Facts have proved that surface cracks can be completely removed by taking certain measures during construction, and relatively regular and concentrated cracks can also be relatively reduced

through theoretical analysis and practical exploration, grasping three main links in the construction is the key to control and reduce the cracks in the cast-in-place floor slab:

first, reinforcement engineering:

because of its intellectualization and the improvement of consumer requirements, the embedding of pipelines has become an essential measure. However, due to too many pipelines, the bond between reinforcement and concrete is reduced, resulting in uneven stress of cast-in-place floor after concrete forming, showing some small regular cracks. The artificial or mechanical collision of reinforcement during construction makes the thickness of protective layer of reinforcement too large, which indirectly leads to the formation of cracks. In addition, due to the large change of outdoor temperature difference, especially the East and West gables of buildings that have experienced hot summer and cold winter, have become the concentration of 45 regular cracks

in view of the causes of cracks in the design and construction of the above reinforcement, corresponding measures can be taken to prepare for a rainy day, which can be prevented. It is inevitable that there are too many embedded pipelines, but if the upper and lower parts of the pipeline are covered with 4 @ 100 wide 600 reinforcing steel sheets, and the spacing between the water and electricity pipelines is controlled at more than 20 mm, the decrease of the bonding force between the reinforcement and the concrete caused by too many pipelines is avoided. During construction, in order to prevent people from stepping on the pedal reinforcement, a reinforced horse stool with a spacing of 1 meter can be set under the reinforcement, and more gangways for people to walk can be set to minimize human or mechanical damage and stepping on the reinforcement

the 45 cracks at the East and West gables of the building are concentrated in the floor cracks. Due to the large temperature difference between the inside and outside of the building, the shrinkage properties of reinforcement and concrete are different, which is inevitable. However, if the cracks are concentrated in this place during the construction, the design will be carried out together, and the cracks can be reduced by placing 8 @ 100 reinforcement with a length of one third of the beam at the corner of the outer wall

II. Formwork engineering:

in the construction market under the market economy, profit and cost are the long-term thinking topics of construction enterprises. The number of sets equipped with templates and the length of their turnover period are directly related to the size of the cost. However, due to the early removal of formwork, the concrete strength is not reached or the formwork support system is not firm, the floor load will cause the floor slab to deflect beyond its value, which may also cause full-length cracks in the slab

general residential projects should be equipped with a sufficient number of formwork according to the requirements of the construction period. The bottom formwork can be removed only when the concrete meets the requirements of formwork removal strength. Considering that when installing the upper formwork and its support of the cast-in-place structure, the lower formwork should have the bearing capacity to bear the upper load. Therefore, ensure that the two floors on the structure can bear the construction load, and work together with domestic and foreign car companies to expand the new energy vehicle market. The bottom floor can be used as a turnover installation. (that is, after the concrete pouring of the construction layer is completed, the next layer bears the load of the construction layer, and the last set of formwork can be removed to ensure the construction progress.)

in addition, the vertical tie rods in the formwork support should be set reasonably, and the supporting vertical rods should be 48 steel pipes with a wall thickness of not less than 3.5, with a spacing of not more than 900 mm. In the process of formwork removal, throwing steel pipes at random to impact the floor may also cause unrecoverable cracks and deformation, which should be avoided as far as possible

III. concrete engineering:

with the promotion and popularization of commercial concrete, the concrete vibration technology is also gradually improved, and the cracks caused by uneven vibration are gradually reduced or even eliminated. Therefore, the maintenance of concrete vibration and final setting has become the top priority. Before the final setting of concrete, the cast-in-place concrete slab is also prone to cracking if the wood crab is not pressed and plastered in time or times. During the curing period, the concrete strength does not reach 1.2MPa, and the construction of subsequent processes, especially the collision of heavy objects, is also prone to irregular cracks on the slab surface

practice has proved that after concrete pouring and tamping, three times of pressure plastering with wooden crab before its final setting can eliminate the surface cracks caused by shrinkage deformation in the plastic shrinkage stage. The project department will assign special personnel to supervise the implementation of wooden crab plastering

when the temperature is high (more than 30 ℃), watering and curing is the key to ensure the formation of concrete. The construction site shall set up vertical water pipes according to the actual situation on site, and be equipped with water pumps with sufficient lift. The concrete shall be covered with plastic film for curing within 12 hours of concrete pouring and tamping. Membrane curing should use disposable materials to ensure that all floors are covered, and there is always condensate in the plastic film. The subsequent processes should try to avoid damage to the plastic film

in addition, during the concrete curing period, for the floor slab with large bay span, try to avoid hoisting and stacking heavy objects to avoid external forces impacting the floor slab. When the concrete strength does not reach 1.2mp, the subsequent process construction shall not be carried out

in the construction of the student apartment project of Shanghai University of Finance and economics, we have taken a series of technical measures in the above three links. The project has been completed for nearly a year. After two summers and one winter, it has been observed that the floor cracks have been effectively controlled. In particular, the open room can be used to carry out experimental cracks such as stretching, tightening, bending, peeling, tearing, puncturing, bursting, shearing, low cycle fatigue, etc. after different attachments are selected according to the products, Basically eliminated, and the 45 cracks at the East and West Gables have also been significantly reduced. Practice has proved that the common problem of floor cracks can be controlled and reduced by taking a series of technical measures

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