Preventive measures for cracks in cast-in-place concrete floor slab;
(1) design measures
1, when doing architectural design, the plane layout should be as regular as possible to reduce sudden changes.
2, floor reinforcement, under the condition of the same reinforcement ratio, as far as possible to reduce the diameter and spacing of reinforcement, however, negative reinforcement should not be less than φ 10, spacing should not be greater than φ150 mm. ..
3. When the negative reinforcement of the floor is reinforced separately, the area without negative reinforcement of the floor should be provided with a two-way steel mesh with a length of not less than 200mm, and its length should not be less than Φ 6.5 @150. When conditions permit, floor negative reinforcement should usually be set.
4. The cast-in-place slab with a span of ≥3.9m shall be provided with double-layer bidirectional reinforcement at the external corner of the building, the corner of the external wall and the four corners of the room. The reinforcement spacing should not be greater than 100mm, and the reinforcement range should be greater than14 of the slab span. For the external corner of the building, reinforcement should be increased and radial reinforcement should be increased.
(2) Main technical measures taken in the construction process
1, double-layer two-way reinforcement of floor slab (including short reinforcement with negative bending moment) must be provided with stirrups, and the vertical and horizontal spacing should be no more than 700mm (i.e. no less than 2 pieces per square meter), especially φ 8 small reinforcement, and the stirrup spacing should be controlled within 600mm (i.e. no less than 3 pieces per square meter).
2. When pouring concrete, temporary movable pick plates should be laid in the areas prone to cracks and areas with large negative bending moment reinforcement stress to expand the contact surface. At the same time, arrange a sufficient number of steel workers to carry out timely renovation before and during concrete pouring, especially where cracks are most likely to appear on the floor.
3, to ensure that the template and its supporting system have enough stiffness, especially for the underlying template support point foundation to consolidate, the spacing should be appropriate, so that the template stiffness of the floor and beam will not differ too much. In the floor formwork where construction and transportation often pass, the support system should be properly strengthened.
4, to scientifically and reasonably arrange the crossover operation time of each type of work, after the bottom steel binding, pipeline embedded should be interspersed in time, leaving no or less tail, reducing the number of workers after the bottom steel binding.
5. In the construction, the management of concrete pouring operation should be strengthened, so that the cloth is uniform and vibrated tightly to prevent vibration leakage and excessive vibration. For a large area of board surface, the poured concrete is vibrated twice with a flat vibrator to increase the compactness of concrete and improve the crack resistance.
6. Strengthen concrete curing, cover and water within 12 hours after concrete pouring, and water curing shall not be less than 7 days. When the temperature is around 20℃, water it 4 times a day; When the temperature is above 25℃, water it 6 times; When the temperature is lower than 5℃, stop watering and cover with plastic film for maintenance. During the curing period, heavy objects shall not be piled on the cast-in-place board surface.
7. Don't dismantle the formwork support of the floor prematurely. Generally, the formwork shall be removed 14 days after the concrete pouring is completed, and the back roof shall be installed in the appropriate position after the formwork is removed if necessary.
8. Set φ6.5@ 100 steel mesh on the upper and lower parts of floors with dense pipelines, and the width in the pipeline area should be greater than 200mm. The outer diameter of various conduits shall not exceed 1/3 of the plate thickness, and staggered stacking of three or more layers of pipelines is strictly prohibited.
9. Control the slurry collection and calendering time of concrete. The first slurry collection should be carried out at the initial setting of concrete, and the second slurry collection and calendering should be carried out before the initial setting. After the second calendering, it is best to calender again and brush the hair. This not only prevents cracking, but also plays a beautiful role.
10, within 24 hours after the concrete pouring of the floor slab, it can be limited to the preparatory work such as measurement, positioning, elastic line, etc. After 24 hours, a small number of concealed columns and shear wall reinforcement can be arranged for binding operation, so as to unload and put down gently. On the third day, formwork construction of bulk materials such as steel pipes, wallboard and floor slab can be started.
The contents of the above measures to prevent cracks in cast-in-place concrete floors are collected and sorted by Zhong Da Consulting Company. For more information about "Measures to Prevent Cracks in Cast-in-place Concrete Floors" and other architectural knowledge, please visit the dynamic column of Zhong Da Consulting. For information about winning the bid, industrial and commercial information, the honor and qualification of the construction engineer under construction and the national construction enterprise, you can log in to the "Easy Winning Bid" Zhong Da Consulting & Construction link, or follow the official account of WeChat, and Zhong Da will consult the official website of WeChat.
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