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First, the reasons for the crack analysis 1, the material problem due to the light weight of lightweight blocks, used as a non-load-bearing wall has a greater advantage than the red brick, but also has its shortcomings, one shrinkage than the clay brick, with the When the water volume decreases, the material will have a large shrinkage deformation, which will easily cause different degrees of cracks. Second, the block will undergo secondary shrinkage after dampening. After the shrinkage, the material will expand after being wet, and the dry shrinkage will occur again after dehydration. Deformation caused cracks in the wall; third, the tensile strength and shear strength of the block masonry were poor, only 50% of the clay bricks. Fourth, the quality of the blocks was unstable. Due to the defects of the block itself, some cracks are caused, such as the inverted eight-character cracks symmetrically distributed in the middle and outer walls of the house, oblique cracks or vertical cracks appearing on the ledges of the first to second floors of the building, and horizontal seams and levels appearing under the roof beams. Cracks in corners, heavy weights appearing on large walls, vertical cracks on lighter parts, etc.
2. Design issues (1) Designers pay attention to strength design and neglect crack resistance construction measures. For a long time, people have become accustomed to various types of cracks in masonry structures. Designers generally make necessary calculations in terms of strength, and most of them refer to national standards or standard atlases for structural measures, and they rarely put forward cracking requirements separately. Measures, not to investigate or summarize the feasibility of these measures.
(2) The designer is not familiar with the application of new material blocks. The design unit's application of new material blocks' performance and new standards is still under scrutiny and exploration, and therefore there are more or less design flaws. The main ones are: 1 The non-load bearing concrete block wall is a post-laying and filling envelope structure. When the size of the wall is not matched with the specifications of the block, it is difficult to completely fill up with the blocks, which results in excessive cracking in the joints of the beam-column columns of the masonry and crucible frame structure; 2 the stress of the door windows and the reserved hole and other parts are concentrated. District, without effective measures to strengthen the knot, will be cracked due to impact vibration; 3 wall thickness is too small and masonry mortar strength is too low, so that the wall is not easy to crack the rigidity; 4 wall openings installed pipeline or crane Hanging weights all cause wall deformation and cracking; 5 Wall contact with water does not consider construction measures such as anti-drainage and flooding and dripping to allow wall leakage.
(3) Construction problems The construction unit lacks training and practice. The construction methods, tools, and mortar all follow the practice of clay fired bricks. They lack experience in masonry height and humidity control, plus horizontal and grey ash joints during construction. Insufficient seams, weakening the wall's ability to resist shear, and the inability of workers to masonry, all lead to cracks in the walls.
Second, the crack prevention and control measures 1, the quality of material control Lightweight block quality and performance indicators, the impact of wall cracks is the largest contraction, and the relative moisture content is an important indicator of contractility. For this reason, it is required that lightweight blocks, especially light aggregate concrete small blocks, must be delivered by the 28-day maintenance party, and the use unit must insist on product acceptance and prevent the use of substandard products.
2. Putting Structural Design Closer Preventing cracks in new lightweight block walls must focus on architectural design. The designer shall take effective construction measures in accordance with the requirements of the Technical Specifications for Non-load-bearing Concrete Block Masonry, the Construction of Non-load-bearing Concrete Block Masonry Structure, and related regulations, combined with the functions of the building and various materials. In order to avoid wall cracking and leakage.
3. Construction prevention and control measures (1) The construction unit should select qualified local manufacturers with permits. When signing a contract, it is necessary to clarify the time for the block to enter the construction site. The manufacturer must ensure the age of the problem and take corresponding responsibility.
(2) The construction unit shall strengthen the inspection of the incoming blocks.
(3) After entering the site, the blocks shall be transported to the construction floor where the line has been laid out as soon as possible, scattered and piled up to the masonry site, and waterproof measures shall be taken in advance to ensure the water conservation of the main structure and the rainwater does not flow into the floor. In order to increase the age of the block as much as possible, masonry should be performed after one week interval, and the moisture content of the block should be measured by the electric heating method. When the moisture content is lower than 15%, construction is allowed.
(4) According to the characteristics of blocks, water should not be moistened in advance before masonry, so as to avoid increasing water content of the blocks due to uneven watering. The method of watering the masonry surface before laying the mortar should be taken.
(5) Strengthen the installation of ring beam and structural column. If the wall length exceeds 4 meters, the structural column should be set. If the wall height exceeds 3 meters, ring beams shall be provided. When the wall length and height are large and there are openings, the construction of the structural column should first ensure that both sides of the opening are in order to avoid shrinkage cracks at the corners of the opening. When the main structure is not reinforced, or when the position is misaligned, planting bars must be used.
(6) Due to the influence of air humidity and the difference in deformation between the frame structure, it is recommended to pull the tie bars on both sides of the wall to increase the crack resistance.
(7) In strict accordance with the operating procedures, ensure the strength of mortar, and the fullness of the mortar (especially the vertical joint).
(8) After the masonry is completed, it is necessary to adhere to the sprinkler maintenance to reduce the drying shrinkage of the mortar.
To sum up, there are many reasons for the cracking of various lightweight brick walls. Only the strict implementation of relevant masonry standards, and the effective control measures in various aspects of production, design and construction, and careful construction against cracking of masonry blocks In order to eliminate the problem of the quality of cracking in new block walls,
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