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Prevention and treatment of cracks in reinforced concrete cast-in-place board

The reinforced concrete cast-in-place board has the advantages of good integrity, seepage resistance and leakage resistance, and has been widely used in the house construction in recent years. Because the concrete is a kind of heterogeneous material, during the hardening process, the deformation of all kinds of materials is inconsistent, resulting in the micro cracks between aggregate and cement paste or cement itself.
The cause of cracks in reinforced concrete cast-in-place board
(1) the factor of material itself. The cast-in-place board material is steel and concrete, their quality is not qualified, is bound to cause cracks of cast-in-place plate, such as steel, in order to save costs, reinforcement for some small manufacturers of the cast-in-situ slab, the quality of serious failure of reinforced ductility, toughness and weldability are poor, low tensile strength, it is easy to crack; concrete aggregate (Sha Shi): the quality is not good, not good gradation, large amount of mud, containing large amount of powder, the use of fine stone and sand.
(two) design negligence. The roof panels are not provided with thermal insulation or thermal insulation layer, or with thermal insulation layer, but the thickness of the insulation layer is determined arbitrarily without calculation. The thickness of the insulation layer is not enough, and the deflection of the panel is not checked. The overall deflection is too large, causing four corner cracks. The design of structure safety is small, insufficient reinforcement or smaller section, the beam forming poor rigidity, the overall deflection, caused by the four corners of the board crack; building a long not set expansion joints, cracks in the weak link; foundation design of improper handling, caused by uneven settlement, the upper structure the additional stress, resulting in floor cracks; floor two-way force according to one-way slab reinforcement, causing cracks. In addition to the theoretical calculation of the reinforcement, the necessary parts are not reinforced.
(three) negligence of construction. Clogging due to pipeline reinforced concrete pouring process, especially to remove the pipe inside the concrete, not scattered in the pouring position, not easy to clean or not clean, leave no concrete due to vibration, loose or dense, concrete can not be set later and at the beginning of the new pouring combination form dry shrinkage and shrinkage cracks; the construction speed is too fast, the load on the early, especially brick residential floor, the day before pouring floor, second days on the brick, take the car, resulting in early concrete damage; maintenance is not in place, do not cover concrete curing, water can not be regularly moist; early form removal or template support the system stiffness is insufficient; the protection measures are not in place resulting in frozen concrete in winter construction.
(four) other aspects. The shrinkage cracks caused by concrete shrinkage of concrete will induration process, when the floor is restrained, shrinkage will produce internal force in the concrete slab, the concrete tensile stress, when the stress exceeds the tensile strength of concrete slab cracks, cracks and uneven settlement of foundation.
Two. Prevention and control measures for cracks in reinforced concrete cast-in-place board
(1) the guarantee measures for materials. The correct choice of cement is to control the ratio of water to cement and make it less than 0.4. In order to ensure that concrete mixture has a certain fluidity, high quality fly ash and superplasticizer can be added to ensure the pumping ability of concrete. While the use of superplasticizer, must do the test of compatibility with cement, superplasticizer and cement selection combined with good fluidity; selection of well graded aggregate, coarse aggregate amount of total volume of concrete from 65% to 75%, is an important factor affecting the quality of concrete, should pay attention to the quality of sand stone, stone should be used continuous grading macadam, the maximum particle size control in 15 ~ 20mm; choose a good transportation route to ensure smooth road, shorten the transportation time, avoid concrete delamination and segregation. At the same time, the transportation tools should be checked regularly to minimize the loss of cement slurry during the transportation of concrete mixture.