How to deal with cracks in the wall after the external wall is insulated with rock wool and stained with dust

Cause analysis and prevention methods of cracks in brick-concrete structure floor and wall At present, some engineering floors are changed from precast to cast-in-place, and there are cracks in windowsill, floor and top wall. The common quality problems are described as follows. 1. Cause analysis of oblique cracks under windowsill and cast-in-place concrete floor slab 1 cracks. The causes of oblique cracks in the wall under the windowsill and cracks in the cast-in-place concrete floor can be summarized as follows. (1) cracks caused by shrinkage of mixed expansive soil; Because the volume of concrete shrinks when it condenses and hardens in the air, when it is consolidated around and cannot shrink freely, it will produce tensile stress and cracks. ⑵ Because the prefabricated residential building is changed to full cast-in-place floor, the integrity of the project is greatly strengthened, and the stiffness of some walls is relatively increased, while the thickness of cast-in-place floor is still between 8- 10cm. Although the strength meets the requirements, the stiffness of the floor relative to the wall decreases, so some weak parts, such as sudden changes in section, construction joints, threading pipes, etc., often crack first. ⑶ Temperature stress crack: At the joint of cast-in-place concrete floor and wall, the floor elongation caused by temperature rise exerts horizontal thrust on the wall, resulting in cracks in the wall. The distribution of cracks is closely related to the mechanical characteristics of the wall, and cracks are more likely to appear at the openings of doors and windows, plane turning points and due to stress concentration. (4) At present, the structural forms of residential buildings are basically the same, and there is not much change. Designers often only pay attention to strength and ignore deformation. There are no joints where expansion joints are set, and the foundation treatment is not careful, which often leads to excessive settlement and deformation of residential projects, resulting in cracks in walls and floors. 5] Because the construction period is too short, the project will be put into use before the foundation and the main project are settled. In the process of use, the foundation and the main project will be constantly deformed. Some fatal projects are delivered without cracks, but cracks will appear after a period of use. This phenomenon often occurs in the engineering of artificial foundation treatment. [6] In order to catch up with the construction period, some construction units removed the formwork when the concrete failed to meet the required strength, and the construction load was added too early and too large, which led to internal cracks in the hardening process of concrete, which is also one of the reasons that cannot be ignored. 2. Precautions (1) Designers should consider foundation treatment and superstructure treatment when deciding the foundation reinforcement and treatment scheme. The treatment methods of superstructure include: developing architectural modeling, simplifying architectural plane, setting settlement joints reasonably, strengthening the overall stiffness of the building, etc. , as far as possible to avoid uneven degradation of foundation leading to cracking of the upper body. You can consider adding a waist beam under the window sill of the external wall. According to the foundation conditions, waist beams shall be set under the window sill of the first floor or other floors. (3) For brick-concrete structures with more than 5 floors (including warehouses with no more than 6 floors), the external walls and floors below 2 floors should minimize the sudden changes, and the sudden changes should be appropriately strengthened. (4) The expansion joint spacing can be shortened appropriately. The specification stipulates that the expansion joint should be set at ≥50m, and it is suggested to change it to 40-45m. 5] constructional column and ring beam shall be set in strict accordance with specifications, and wall width, wall height-thickness ratio and window wall width shall be calculated and determined according to specifications. [6] The construction joint of cast-in-place floor slab should be located on the resident wall, not in the middle of the room 1/3. Once the reasonable arrangement of the construction period, can't blindly fast, especially the artificial foundation, must strictly control the construction progress, in case of uneven settlement of the foundation after the completion of the upper main structure and cracks. Being the main project construction should be carefully organized and reasonably arranged, especially in the cast-in-place floor construction, the mixed soil must reach the specified strength before it can be removed; The upper construction load should not be added too early, too large or too concentrated, and it is forbidden for lifting objects to collide; When pouring mixed expansive soil, the pipeline should be buried to a proper depth. When the thickness is less than or equal to ≤80mm and the pipe diameter is greater than or equal to ≥25mm, a layer of steel wire mesh with a width of 500mm and the same length as the pipe can be added to the bottom and surface of the plate. Second, the cause analysis of cracks in the top wall 1. Cracks in the top wall are more obvious at the top of the building. Cracks are caused by many factors, which can be summed up in the following aspects. ⑴ Temperature stress: Because the building is in a natural environment, it is greatly influenced by natural conditions such as temperature, season, wind and rain, and there are many exposed water surfaces on the top floor, which leads to large expansion and contraction range and high frequency of the wall and cast-in-place concrete floor. The expansion and contraction coefficients of the two are quite different, and the temperature stress caused by mutual restriction is also large, which is the main reason for wall cracking. ⑵ Improper design: When designing, the design unit often considers that the structure is stressed more and deformed less. Although there are many factors that cause wall cracks, one of the reasons is that no corresponding measures are taken in the design. For example, the height-thickness ratio of brick-concrete structure wall is not strictly controlled, the thickness of roof insulation layer is not enough, there is no overhead layer, and the hole in the longitudinal wall of the end room is too large, which are the reasons for the wall cracking. ⑶ Improper construction: The poor construction quality of brick masonry is also an important factor for wall cracking. Masonry mortar strength can't meet the design requirements, mortar joint is not full, mortar joint is not correct, dry brick on the wall, will lead to cracks in the wall. 2. Prevention and control measures From the design point of view, the control measures for temperature stress in the design are small, and the following measures are recommended. (1) The minimum thickness of roof insulation layer should be higher than the current practice, and slag inclusion should be avoided as far as possible, and the quality and moisture content of insulation materials should be strictly controlled. When necessary, on the basis of thermal insulation layer, add an overhead thermal insulation layer on the roof. (2) The thickness of the external wall is 370mm, the cross section of the constructional column at the corner of the external wall can be 370mm, and the structure at the corner of the external wall is% d% a..