1. Phenomenon (1) The workability of mortar is not good, and the mortar is not easy to spread and squeeze during masonry, which affects the fullness of mortar joint and weakens the bonding force between mortar and brick. (2) Mortar has poor water retention, and is prone to delamination and bleeding. (3) The mortar in the ash tank will be stored for too long, and finally the mortar will sink to the bottom and harden. Even if water is added to re-mix, the strength of mortar will be seriously reduced.
2. Cause analysis (1) Cement mortar with low strength grade uses high strength grade cement and ultra-fine sand, which reduces the amount of cementing material-cement which plays a lubricating role between sand particles, so the friction between sand particles is large and the workability of mortar is poor. When building, it is difficult to thin mortar joint. Moreover, due to the lack of sufficient cementing materials between sand particles to play the role of suspension support, mortar is prone to precipitation and surface flooding. (2) Plasticizing materials such as lime putty mixed in cement mortar are of poor quality, contain more ash and sundries, or are dried and polluted due to poor preservation, which cannot improve the workability of mortar. (3) The mortar mixing time is short and the mixing is uneven. (4) The mixed mortar is stored for too long, or the mortar in the ash tank is not cleaned for a long time, which makes the mortar sink hard. (5) The mixing mortar is unplanned and cannot be used up within the specified time. The remaining mortar shall be mashed and mixed with water for later use. 3. Precautions Low-strength mortar should use (1) cement mixed mortar. If it is really difficult, the workability of mortar can be improved by adding micro foaming agent or fly ash with cement dosage of 5% ~ 10%. (2) Plasticizing materials in cement mixed mortar should meet the quality requirements of laboratory trial. The lime paste and clay paste on site should be properly stored in the pool to prevent sun exposure, air drying and hardening, and often watered to keep them moist. (3) Cement and medium sand with low strength grade should be used for mixing mortar. When mixing, the construction mixture ratio should be strictly implemented to ensure the mixing time. (4) Mortar in the ash tank should be stirred frequently, cleaned with a shovel, scraped off the mortar in the corner of the ash tank, piled aside for later use, or mixed with fresh mortar. (5) Mixing mortar should be planned, and the mixing amount should be determined according to the needs of masonry. As far as possible, mix it with it and store it in a small amount, so that there is always fresh mortar in the ash tank. The service time of mortar is related to the variety and temperature conditions of mortar. Under general temperature conditions, cement mortar and cement mixed mortar must be used up within 3 hours and 4 hours after mixing. When the temperature exceeds 30℃ during construction, it must be used up within 2h and 3h respectively. Excess mortar exceeding the above time shall not be used again.
Second, the strength of masonry mortar fluctuates greatly.
1. Phenomenon Most mortars have low strength, which affects the strength and quality of masonry.
2. Cause analysis: Some construction sites have no mixing ratio of mixing mortar, and some mixing ratios are not measured, so water consumption and cement are added or subtracted at will; Some construction sites directly pour cement on the sand pile, and sand and cement are randomly injected into the mixer for mixing. The strength of mixed mortar fluctuates greatly, and most of them are low. Some construction sites eat "small stoves" when making mortar test blocks, which leads to the inconsistency between the strength of mortar test blocks and the actual mortar strength.
3. Strengthen the preventive measures of construction management. According to the specification for design of mortar mixture ratio (JGJ/T 98-20 10), the mixture ratio is determined.
4. Treatment method (1) If it is found that the mixing mortar has no mixture ratio or has not been measured, it must be stopped immediately and mixed again after correction. (2) If the wall has been built with low-strength mortar, it must be removed and replaced with qualified mortar for re-building.
Third, brick masonry group build by laying bricks or stones chaos
The size error of 65438+ brick has great influence on the decorative wall, such as improper assembly form and uneven vertical joint width, which affects the appearance.
2. Cause analysis Because the plastering of the mixed water wall is easy for the operator to ignore the assembly form, the phenomenon of straight joint and "double skin" of multi-layer bricks appears. Masonry brick columns need a large number of seven-divided bricks to meet the requirements of staggered joints between inner and outer brick layers. Making seven-divided bricks will increase the workload, affect the masonry efficiency, and the brick loss is great. When the operator does not pay enough attention to it and lacks strict inspection, Sanqi brick column is used to using core-cladding method.
3. Preventive measures should make the operator understand that brick wall assembly is not only for the beauty of the wall, but also to meet the needs of load transfer. Therefore, regardless of the clear water and mixed water wall, the lap joint of brick joints in the wall shall not be less than 1/4 brick length; At most, every five layers of bricks should have a layer of Ding Brick Rachel (Five Shun and One Ding). In order to save, half a brick is allowed, but it should also meet the requirement of 1/4 brick length, and half a brick should be dispersed in the mixed water wall. The assembly method of brick column should be considered according to the section of brick column and the actual use, but the core masonry method should not be adopted. Mortar for horizontal and vertical mortar joints of brick columns must be full. After each layer of brick is built, a vertical joint scraping and joint filling work should be carried out to improve the strength of masonry. The selection of wall assembly form should be based on the mechanical properties of the parts to be built and the size error of the bricks: generally, the methods of one smooth and one ding and Ding Meihua are often used for fair-faced walls; In earthquake areas, in order to strengthen the tensile strength of tooth joints, the method of riding and assembling can be adopted; Brick reservoirs should adopt the method of combining three shun and one ding; Double-sided clean-water walls, such as enclosure walls and fences of industrial plants, can be assembled with Sanqi section. Because there are many positive deviations in the length and negative deviations in the width of general bricks, the vertical joint width of the wall can be uniform with plum blossom ding group. In the same building project, bricks from the same brick factory should be used as much as possible to avoid frequent changes in assembly form due to dimensional errors of bricks.
Four, brick joint mortar is not full
1. The plumpness of horizontal mortar joint in brick layer is less than 80%; There is no mortar (blind joint) in vertical joints, especially in hollow brick walls, and there are often more transparent joints; When laying drywall, the depth of large necking joint is more than 2cm, which affects the fullness of mortar. Before bricklaying, it is not watered and wet, and the dry brick is on the wall, which leads to the weak bond between mortar and brick.
2. Cause analysis: For the mortar below M2.5, if cement mortar is used, it is difficult to squeeze the mortar during masonry due to its poor workability. After the operator spreads and scrapes the mortar with a shovel or tile knife, there will be holes in the bottom ash and the mortar will not be full. Using dry bricks to build walls will reduce the strength of mortar due to early dehydration. However, the powder crumbs on the surface of dry brick play an isolation role, which weakens the bond between brick and mortar. When paving mortar with push ruler, sometimes because the mortar is too long, the laying speed can't keep up, and the moisture in the mortar is absorbed by the bottom brick, which makes the brick and mortar on the masonry lose their bonding. When building drywall, in order to save the scraping process, the method of building mortar with large shrinkage is adopted, so that the shrinkage depth of masonry brick joints reaches 2 ~ 3 cm, which not only reduces the fullness of mortar, but also increases the workload of jointing.
3. Preventive measures to improve the workability of mortar are the key to ensure the fullness of mortar joints and improve bond strength. Improve the masonry method. It is not appropriate to use the method of pushing ruler to spread ash or build bricks, but to promote the "three-in-one brick laying method", that is, to adopt the masonry method of "one brick, one shovel of ash and one kneading and squeezing". It is forbidden to build walls with dry bricks. Bricks should be wetted 1 ~ 2 days before masonry, so that the moisture content of bricks can reach 10% ~ 15% during masonry. In winter construction, before laying under the condition of positive temperature, the brick surface should be properly wet. When the negative temperature construction can't pour bricks, the consistency of mortar should be increased appropriately. For the earthquake area with seismic fortification intensity of 9 degrees, it is not suitable for masonry in the case that bricks cannot be poured in severe winter.
Five, clear water wall tile seam skew
1. Phenomenon On a large area of fair-faced wall, the vertical joints of T-shaped bricks are often skewed and uneven in width, and the T-shaped bricks are not pressed in the middle (the T-shaped bricks are not centered on the lower bricks), and the vertical joints between the windowsill and the window wall are dislocated, which becomes elastic and directly affects the beauty of fair-faced wall.
2. Cause analysis: There are large errors in the length and width of bricks, such as positive deviation in length and negative deviation in width. When laying bricks piece by piece, it is not easy to master the width of vertical joints, and if you don't pay attention, there will be deviation joints. When building walls and bricks, the influence of window position on vertical joints of bricks is not considered. When the window sill is built to the size of a window, the edge of the window is not in the vertical seam position, which makes the vertical seam of the wall between the windows move up and down. Exterior drywall built by hand with inner feet needs to be worn frequently to see the verticality of vertical joints of external walls. When it is built to a certain height, it is inconvenient to sew through the wall, and it is easy to make mistakes. A slight negligence will lead to wandering seams.
3. The prevention and control measures for masonry drywall should be bricks with neat edges and uniform colors. Before drywall masonry, the bottom should be placed evenly. First, measure the size of the bricks on site to determine the masonry method and adjust the width of the vertical joints. When swinging the bottom, the window position should be led out, so that the vertical seam of the brick should be as flush as possible with the window. If it can't be installed, you can move the window position appropriately (generally not more than 2cm). When the width of the window does not match the modulus of the brick, seven separate bricks should be left in the lower center of the window to keep the vertical joints between the windows in a good position. Youding's walking joint is mainly caused by Ding Brick swimming. Therefore, when laying, it must be emphasized that the midline of Tintin coincides with the midline of the lower brick. When laying large-area drywall (such as gables), in the first few layers of bricks, the verticality of vertical joints shall be hung along the corner at 1m, and the height of at least one step shall be maintained, and the verticality shall be accurate. At regular intervals along the wall, play chalk lines at the vertical joints, and measure the chalk lines with theodolite or pendant. When the masonry reaches a certain height (one-step frame or one-story wall), it will extend upward based on the chalk line to control the joint of oil ding.
Sixth, whether the wall is optional.
1. Phenomenon: Leave gaps at will when building, and leave more gaps. If the gap is filled with brick slag, the wall section will weaken seriously. If the mortar in the shade is lax, the mortar joint will not be straight.
2. Cause analysis: the operator lacks understanding of the problem of keeping straight windows and is used to keeping straight windows; There are too many leaves due to inconvenient operation and improper construction organization. After the masonry 12cm thick partition wall is retained, if it is not straight, it will bite deeply, which makes the mortar joint on the upper part of the brick not easy to be blocked. The lien method of oblique if is not uniform, the workload of lien large oblique if is large, and the straightness of oblique if mortar joint is difficult to control, thus making the joint uneven. Construction holes are left at will, and concrete and mortar are scattered to the left of the holes by transport vehicles, which affects the connection quality. The color of the brick filling the construction hole is inconsistent with the original wall, which affects the beauty of the fair-faced wall.
3. The prevention and control measures in the arrangement of construction organization plan, should consider the construction. Exterior wall large angle shall be built synchronously as far as possible, leaving no gaps, or one-step frame shall be built with gaps, and two-step frame shall be built synchronously, so as to strengthen the integrity of the corner. At the junction of vertical and horizontal walls, synchronous masonry should be arranged as far as possible when conditions permit. For example, the vertical wall can be built synchronously with the outer feet, and the working faces will not interfere with each other, so as to minimize the gaps and contribute to the integrity of the house. Inclined if appropriate to take 18 layer inclined if build by laying bricks or stones method, in order to prevent the operation is not skilled, make the horizontal if seam is not straight, you can add a small amount of leather rod. If it is a drywall, if there are doors and windows, the left-behind part should be built to the corner doors and windows, and multiple poles should be set at the door and window frame to control the elevation. In the non-seismic fortification area, when it is really difficult to leave an oblique gap, a straight gap should be left to lead out the wall 12cm, and Rachel bars should be set according to the regulations, so as to make it easy to connect the brick joints, so as to ensure the quality of the gap and enhance the integrity of the wall. Attention should be paid to the quality of the connection. First, clean the joints, and then water them wet. When the joint is connected, the joint surface shall be filled with mortar and the mortar joint shall be kept straight.
Seven, small hollow block wall vertical cracks
1. Phenomenon Vertical cracks appear on the external wall, generally about 2m at the eaves before and after the gables.
2. Cause analysis Due to the temperature difference between indoor and outdoor, bending stress is generated in the wall, the high temperature side is compressed, the low temperature side is pulled, and the shrinkage and tensile stress are added, resulting in vertical cracks. The whole gable without doors and windows has vertical cracks in the middle of the wall due to the greater degree of restraint around it. The middle of the crack is wide and the upper and lower ends are getting smaller and smaller.
3. Preventive measures (1) to improve the tensile and shear strength of masonry, and add horizontal long steel bars and core columns. (2) Ensure the construction quality. Because the block wall is thin and the contact surface of horizontal mortar joint is small, mixed mortar with good plasticity should be prepared. In order to ensure the quality of masonry, horizontal mortar joint and vertical joint should be full; Lapping must be qualified, and joints are not allowed; The applied blocks must be kept in production for more than 28d before laying. When stacking and masonry, it should be rain-proof, reduce shrinkage and reduce cracks.
4. Treatment methods The cracks should be observed before treatment, and the cracks can only be repaired after they are basically stable. Remove loose, peeling and cracked decorative layers, and remove scum, scale and oil stains at cracks. Refer to the following treatment methods. 1) When it is confirmed as a temperature deformation crack, corresponding treatment shall be carried out according to the structural characteristics, environmental conditions, use requirements and possible hazards. 2) Temperature cracks generally do not affect the structural safety. After a period of observation, when the crack is widest, adopt the following methods of closed protection or local repair. (1) When the wall cracks are heavy and the maximum crack width is wt = 3 ~ 10 mm, corresponding treatment measures should be taken. When the wall cracks are serious, Wt> 10mm, the building reinforcement treatment scheme should be customized, and the reinforcement treatment should be carried out according to the scheme requirements after approval by the relevant departments. Remove the empty drum, shell and decorative layer at the gap, and brush and rinse. (2) When the crack width is less than 0.5mm, colorless waterproof agent or synthetic polymer waterproof coating can be directly sprayed on the wall twice, the coating thickness is not less than 2mm, and the coating range is 300mm around the crack. (3) When the gap width is between 0.5 and 3.0 mm, clean the floating ash, scum and dust in the gap, fill the sealing material in layers, and then spray the waterproof agent twice. ④ Reinforcement anchorage.
Eight, stairs and beams filled the cracks in the wall.
1. Phenomenon (1) There are vertical cracks in the stairwell and stair rest platform of a long multi-storey building adjacent to the floor. (2) Local cracks occur in the wall (window wall) at the bottom of the girder.
2. Cause analysis The local cracks in the wall under the beam are mainly caused by no beam pad or insufficient beam pad area and excessive local load on the brick wall. In addition, it is also related to the low grade of brick mortar and poor construction quality.
3. Preventive measures (1) Oblique cracks mainly occur on soft soil foundation. Due to the uneven settlement of foundation, the wall bears large shear force. When the structural stiffness is poor, the construction quality and material strength can not meet the requirements, cracks appear in the wall. (2) The window wall with concentrated beam load should have a certain width (or pile), and a concrete beam pad with sufficient area should be set under the beam; When the load of the main girder is large, the transverse reinforcement of the wall should be considered; For the wall between windows with small width, scaffolding holes should be avoided during construction. (3) Some wall cracks have regional characteristics, which should be comprehensively investigated and analyzed in conjunction with the design and construction units, combined with the local climate, environment, structural forms and construction methods, and then measures should be taken to solve them.
Nine, masonry foundation uneven subsidence caused by wall cracks.
1. Phenomenon (1) Inclined cracks generally develop upward. Due to the high rigidity (few openings) of the transverse wall, there is generally no large relative deformation, so this kind of crack rarely appears. Cracks are mostly in the lower part of the wall, and gradually decrease upward. The width of cracks is large and small, and often appears shortly after the building is completed, and its width and number gradually develop with time. (2) Horizontal cracks in the wall between windows. Generally, it appears in pairs on the upper and lower diagonal of the wall between windows, with cracks on the side with large settlement at the bottom and cracks on the side with small settlement at the top. (3) Vertical cracks appear on the upper and lower windowsills of the longitudinal wall, with the cracks being wide at the top and narrow at the bottom. When there is a reinforced concrete ring beam at the top of the longitudinal wall, there are fewer vertical cracks in the center of the top.
2. Cause analysis (1) Oblique cracks mainly occur on soft soil foundation. Due to the uneven settlement of foundation, the wall bears large shear force. When the structural stiffness is poor, the construction quality and material strength can not meet the requirements, cracks appear in the wall. (2) The reason for the horizontal cracks in the window wall is that the resistance of the upper part of the settlement unit makes the window wall suffer a large horizontal shear force, which leads to the horizontal cracks in the upper and lower positions. (3) The vertical crack under the window sill at the bottom of the building is due to the fact that the window sill wall acts as an anti-beam after being stressed, especially when a wide window or window sill wall bears a large concentrated load (such as auditorium, factory building and other projects), the window sill wall cracks due to excessive reverse deformation, which will crush the window in serious cases and affect the opening of the window sash. In addition, if the foundation is built above the frozen soil layer, cracks will occur at the window sill due to frost heaving.
3. Precautions (1) Reasonable setting of settlement joints. All houses with different loads (houses with large height difference), houses with long plane shape and different foundation treatment methods of the same building and some basements should be divided into several parts on the basis, and settlement joints should be set to make them settle separately to reduce or prevent cracks. Settlement joints should be wide enough. During operation, it is necessary to prevent the broken parts from being poured together when pouring the ring beam, or bricks, mortar and other sundries from falling into the joints, so as to avoid the phenomenon that the house cannot freely settle and the wall cracks. (2) Strengthen the rigidity of the superstructure and improve the shear strength of the wall. Due to the strong rigidity of the superstructure, the differential settlement of the foundation can be adjusted appropriately. Therefore, ring beams should be set at the top surface of foundation (+0.000) and doors and windows of each floor to reduce the number of buildings. Strictly implement the rules and regulations in operation, such as watering and wetting the brick, improving the workability of mortar, improving the fullness of mortar and the bonding degree of brick layer (improving the fullness of mortar joint can greatly improve the shear strength of the wall). If there is a temporary interruption in the construction, it should be kept as much as possible. When keeping a straight line, we should also tie a knot and resolutely put an end to the practice of yin without knot. (3) Strengthen the exploration of foundation trench. For complex foundation, drilling should generally be carried out after foundation trench excavation, and foundation construction can only be carried out after weak parts are reinforced. (4) The lower part of the wide window should be provided with a concrete ring beam or build by laying bricks or stones to turn against Shi Zhuan to adapt to the deformation of the window sill beam, so as to prevent vertical cracks on the window sill. In order to avoid cracks under the bottom windowsill of multi-storey residential buildings, in addition to strengthening the integrity of the foundation, the method of long reinforcement can also be adopted. In addition, the windowsill should not be built with too many half bricks.
Ten, masonry engineering summer-planting cracks
1. The straight masonry is the weak part that affects the overall stiffness of the building. In the subsequent construction, the connection is not handled well, and cracks appear in the main load-bearing parts of the structure.
2. Cause analysis The temporary breaks, corners and junctions of masonry internal and external walls should be kept straight at will.
3. Prevention measures When laying the corner of masonry or the junction of vertical and horizontal walls, they should be laid at the same time. If temporary breaks cannot be laid at the same time, an inclined gap should be left. The inclined length of solid masonry should not be less than 2/3 of the height of masonry at the temporary break. See the picture. In addition to the corner, such as temporary breaks, if it is difficult to stay obliquely, it can also be left straight, but it must be made into a square and set up Rachel bars. Rachel reinforcement is not less than 56mm. According to the wall thickness, put one root every 120mm and place it in layers. 500mm for a layer. The end of the Rachel bar should be bent into a 90-degree right-angle hook, and the length buried in the masonry is not less than 500mm from the left corner of the wall, and the length of the protruding end is not less than 500mm. When the freezing method is used for masonry, the length buried in masonry shall not be less than1000 mm. Each layer of Rachel not less than 2.
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