1. The workability of masonry mortar is poor
1. Phenomenon (1) The mortar has poor workability. It is difficult to spread and squeeze grout during masonry, which affects the mortar joints. The fullness of the mortar also weakens the bonding force between the mortar and the bricks. (2) The mortar has poor water retention and is prone to delamination and bleeding. (3) If the mortar is stored in the ash tank for too long, the mortar will eventually sink to the bottom and harden. Even if water is added and mixed again, the strength of the mortar will be seriously reduced.
2. Cause analysis (1) Due to the use of high-strength cement and excessively fine sand in low-strength cement mortar, the amount of cement, the lubricating material between sand particles, is reduced, so the sand problem The friction force is large, the workability of the mortar is poor, and it is very difficult to thin the mortar joints during masonry. Moreover, due to the lack of sufficient cementing material between sand grains to act as a suspension support, the mortar is prone to sedimentation and surface flooding. (2) The plasticizing materials such as lime paste mixed into the cement mixed mortar are of poor quality, contain a lot of ash and debris, or are dry and contaminated due to poor storage, and cannot improve the workability of the 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, causing the mortar to sink to the bottom and become hard. (5) The mortar is mixed without a plan and cannot be used up within the specified time. The remaining mortar is crushed and mixed with water before continued use. 3. Prevention and control measures (1) Low-strength grade mortar should be made of cement mixed mortar. If there is any difficulty, microfoaming agent or fly ash with an amount of 5% to 10% of cement can be added to improve the workability of the mortar. . (2) The plasticized materials in cement mixed mortar should meet the quality requirements during trial preparation in the laboratory. On-site lime plaster, clay plaster, etc. should be properly kept in the pool to prevent exposure to the sun, drying and hardening, and should be watered frequently to keep them moist. (3) It is advisable to use cement with lower strength grade and medium sand to mix the mortar. When mixing, the construction mix ratio should be strictly followed and the mixing time should be guaranteed. (4) The mortar in the ash trough should be stirred frequently with a shovel during use, the bottom should be cleaned, and the mortar at the corners of the ash trough should be scraped off, piled on one side for continued use, or mixed with fresh mortar for use. (5) The mixing of mortar should be planned, and the mixing amount should be determined according to the masonry needs. Try to mix it for ready use and store it in small quantities, so that there is always fresh mortar in the ash trough. The usage time of mortar is related to the type of mortar, temperature conditions, etc. Under general temperature conditions, cement mortar and cement mixed mortar must be used up within 3h and 4h respectively after mixing; when the temperature exceeds 30°C during construction, they must be used up within 2h and 4h respectively. Use up within 3 hours. Excess mortar that exceeds the above time must not be used any further.
2. The strength of masonry mortar fluctuates greatly
1. The phenomenon is that most mortars have low strength, which affects the strength and quality of masonry.
2. Reason analysis: Some construction sites mix mortar without a mix ratio, while others have a mix ratio and do not measure it. They add or subtract water and cement arbitrarily; in some construction sites, cement is poured directly on the sand pile. , randomly inject sand and cement into the mixer and mix. The strength of the mixed mortar fluctuates greatly, and most of it is low. Some construction sites use "small stoves" when making mortar test blocks, causing the strength of the mortar test blocks to be inconsistent with the actual mortar strength.
3. Take preventive measures to strengthen construction management. The mix ratio is determined in accordance with the regulations on mortar mix ratio in the "Masonry Mortar Mix Proportion Design Regulations" JGJ/T 98-2010.
4. Treatment methods (1) If it is found that the mixing mortar has no mix ratio or is not measured, the machine must be stopped immediately and corrected before mixing. (2) If mortar with low strength has been used to build the wall, it must be removed and rebuilt with qualified mortar.
3. The assembly of brick masonry is chaotic
1. Phenomenon: The assembly method of the mixed water wall is chaotic, the brick joints are irregular, straight seams and "second skin" appear, and the bricks The column adopts the core-covering method, and the inner and outer brick layers do not bite each other, forming a circumferential seam, which reduces the strength and integrity of the masonry. The size error of the bricks has a greater impact on the clear wall surface. If the assembly form is improper, the formation of The uneven width of vertical seams affects the appearance.
2. Cause analysis: Since the water-contaminated wall needs to be plastered, operators tend to ignore the assembly form, so the phenomenon of straight joints and "double skin" of multi-layer bricks appears. Building brick columns requires a large number of three-quarter bricks to meet the staggered joint requirements of internal and external brick layers. Making three-quarter bricks will increase the workload and affect the efficiency of masonry. Moreover, the brick loss is very large. When the operator does not pay enough attention to the thought and lack of Under strict inspection, Sanqi brick columns are accustomed to using the core-laying method.
3. Preventive and control measures should make the operator understand that the form of brick wall assembly is not just for the beauty of the wall, but also to meet the needs of transmitting loads. Therefore, regardless of whether it is a clear or concrete wall, the overlapping joints of the bricks in the wall must not be less than 1/4 brick length; the inner and outer skin bricks should be tied with a layer of D bricks at most five layers apart (five straight and one Ding). For the sake of economy, the use of half bricks is allowed, but the overlap requirement of 1/4 brick length should also be met, and the half bricks should be scattered in the mixed water wall. The assembly method of brick columns should be uniformly considered based on the cross section of the brick columns and the actual use conditions, but the core-laying method shall not be used. The mortar in the horizontal and vertical mortar joints of the brick columns must be full. After each layer of bricks is laid, the vertical joints must be scraped and filled with mortar to improve the strength of the masonry. The selection of the wall assembly form should be based on the stress properties of the parts to be built and the size error of the bricks: Generally, the one-shun-one-ding and plum-shaped ding assembly methods are often used for clear water walls; in earthquake areas, in order to strengthen the teeth To determine the tensile strength of the seams, the riding seam assembly method can be used; the brick reservoir should be built using the three-shun-one-ding assembly method; double-sided clear water walls, such as industrial factory building enclosure walls, fences, etc., can be built using the three-seven seam assembly method. method. Since bricks generally have positive deviations in length and negative deviations in width, the vertical joint width of the wall can be made uniform by using plum blossom tiles. In the same building project, bricks from the same brick factory should be used as much as possible to avoid frequent changes in the assembly form due to errors in brick specifications.
4. The mortar in the brick joints is not full
1. The phenomenon is that the mortar fullness of the horizontal mortar joints of the brick layer is less than 80%; there is no mortar in the vertical joints (blind joints), especially for hollow bricks Walls often have more transparent joints; when building fair-faced walls, large shrinkage joints with a depth greater than 2cm are used, which affects the fullness of the mortar. The bricks were not watered and moistened before laying, and the dry bricks were put on the wall, resulting in poor bonding between the mortar and the bricks.
2. Cause Analysis For mortar of M2.5 or smaller than M2.5, such as cement mortar, due to poor workability of cement mortar, it is difficult to squeeze out the mortar during masonry. The operator must use a large shovel or tile knife to lay the mortar. After scraping the mortar, cavities are created in the bottom ash and the mortar is not full. Build walls with dry bricks so that the mortar loses strength due to early dehydration. The dust on the surface of dry bricks acts as an isolation and weakens the bond between bricks and mortar. When laying ash using the pusher method, sometimes the ash spread is too long and the masonry speed cannot keep up. The moisture in the mortar is absorbed by the bottom bricks, causing the bricks to be laid and the mortar to lose their bond. When building exposed walls, in order to save the process of scraping joints, a large shrinkage mortaring method was adopted, so that the depth of the joints of the masonry bricks reached 2 to 3 cm, which not only reduced the fullness of the mortar, but also increased the workload of jointing.
3. Preventative measures to improve the workability of mortar are the key to ensuring that the mortar of the mortar joints is full and improving the bonding strength. Improve masonry methods. It is not advisable to use the push rule method to spread ash or place bricks for masonry. The "three-one bricklaying method" should be promoted, that is, using a large shovel, "one brick, one shovel of ash, and one squeeze" masonry method. It is strictly forbidden to use dry bricks for walls. Bricks should be wetted 1 to 2 days before masonry, so that the moisture content of the bricks reaches 10% to 15% during masonry. During winter construction, the brick surface should be properly moistened before laying even under positive temperature conditions. When it is impossible to pour bricks during construction at negative temperatures, the consistency of the mortar should be appropriately increased. For earthquake areas with a seismic fortification intensity of 9 degrees, it is not appropriate to carry out masonry work when bricks cannot be poured in severe winter.
5. The brick joints of the clear-faced wall are skewed
1. Phenomenon: On large-area clear-faced walls, the vertical seams of the small bricks are often skewed, the width is uneven, and the bricks are not pressed in the middle (the small bricks are not pressed in the middle). If the strip bricks on the lower layer are not centered), the upper and lower vertical joints between the window sill of the clear wall and the wall between the windows will be misaligned or activated, which directly affects the beauty of the clear wall.
2. Reason analysis: The length and width of bricks have large dimensional errors. For example, the length of bricks has a positive deviation and the width has a negative deviation. When building a brick in a smooth manner, the width of the vertical joints is not easy to grasp if you are not careful. A gap will occur. When laying the bricks on the wall, the effect of the window position on the vertical joints of the bricks was not considered. When the window size was reached at the window sill, the edge of the window was not at the position of the vertical joints, causing the vertical joints of the wall between the windows to move and become misaligned. When building an exterior plain wall by hand, you need to often lean in to check the verticality of the vertical joints on the exterior wall. After the wall is built to a certain height, it is inconvenient to see through the wall joints and errors are prone to occur. A slight oversight may cause wandering. seam.
3. Preventive and control measures When building drywall, bricks with neat corners and uniform color should be selected. Before building the exposed wall, the bottom should be laid out uniformly, and the size of the bricks on site should be measured first to determine the assembly method and adjust the width of the vertical joints. When setting the bottom, the window position should be led out so that the vertical joints of the bricks are as aligned as possible with the window edge. If the installation cannot be opened, the window position can be moved appropriately (generally no more than 2cm).
When the width of the window does not meet the module of the brick, the three-quarter brick should be left in the center of the lower part of the window to keep the upper and lower vertical joints in the wall between the windows out of position. The running joints are mainly caused by the movement of the bricks. Therefore, when laying bricks, it is necessary to emphasize the center line of the bricks, that is, the center line of the bricks coincides with the center line of the lower strip bricks. When building a large-area plain wall (such as a gable), in the first few layers of bricks, use a line to hang the vertical joints 1m along the corner to maintain accurate verticality at least one step higher. At regular intervals along the wall, ink lines are drawn at the vertical joints, and the ink lines are measured using a theodolite or a line drop. When the brickwork reaches a certain height (one-step frame or one-story wall), extend the ink line upward to serve as a benchmark for controlling the seams.
6. Chasing is left at will on the wall
1. Phenomenon: Chasing is left at will during masonry, and most of the chasms are left in the shade. The mouth of the chasing is filled with brick slag to make the wall cross-section Suffered severe weakening. The mortar connection to the shaded area is not tight and the mortar joints are not straight.
2. Cause analysis: Operators lack awareness of the problem of retaining bars and are accustomed to leaving straight bars; due to inconvenient construction operations and improper construction organization, too many retaining bars are caused. The balconies left behind when building a 12cm thick partition wall are not straight. When connecting the tiles, the mortar joints on the upper part of the connecting tiles are difficult to seal due to the large depth of the tiles. The method of retaining the slanted beams is not uniform, and the workload of retaining large slanted beams is large. It is difficult to control the straightness of the ash joints of the slanted beams, causing the connecting parts to be out of line. Construction openings are randomly left open, and the material transport trolleys scatter concrete and mortar onto the openings, affecting the quality of the connections. The color of the bricks used to fill the construction holes is inconsistent with the original wall, which affects the beauty of the clear water wall.
3. Preventive and control measures When arranging the construction organization plan, the construction plan should be uniformly considered. For the large corners of the exterior walls, try to make sure that there are no hooks left at the same time, or that the first step is to leave hooks, and the second step is to be built synchronously to strengthen the integrity of the corner. At the junction of vertical and horizontal walls, try to arrange synchronous masonry if possible. For example, if the vertical walls are built with external scaffolding, the horizontal walls can be built simultaneously without interfering with each other on the working surfaces. This can minimize the remaining parts and is conducive to the integrity of the house. The 18-layer diagonal beam construction method should be adopted. In order to prevent the horizontal joints at the joints from being not straight due to unskilled operation, a small number of poles can be added. If there are doors and windows in the clear water wall, they should be built to the edge of the corner door and window, and a number pole should be erected next to the door and window frame to control the elevation. In non-seismic fortified areas, when it is really difficult to leave diagonal beams, straight beams extending 12cm from the wall should be left, and tie bars should be set up according to regulations to make the brick joints between the beams easy to join, so as to ensure the quality of the connections and strengthen the wall. of wholeness. Attention should be paid to the quality of the connection. First, the joints should be cleaned, then watered and moistened. When connecting, the joints should be filled with mortar and the mortar joints should be kept straight.
7. Vertical cracks in small hollow block walls
1. Phenomenon Vertical cracks occur on the exterior wall, usually about 2m away from the front and rear eaves of the exterior gable wall.
2. Cause analysis: Due to the temperature difference between indoor and outdoor, bending stress is generated in the wall. The high-temperature side is under pressure and the low-temperature side is under tension. Coupled with shrinkage and tensile stress, vertical cracks appear. The entire gable wall without door or window openings will have vertical cracks in the middle of the wall due to the greater degree of constraints around it. The crack is wide in the middle and becomes smaller at the upper and lower ends.
3. Preventive measures (1) Improve the tensile and shear strength of the masonry, add horizontal full-length steel bars, and add core columns. (2) Ensure construction quality. Because the wall of the block is thin and the contact surface of the horizontal mortar joint is small, a mixed mortar with good plasticity should be prepared. In order to ensure the quality of masonry, horizontal mortar joints and vertical joints should be full; overlapping and staggered joints must be qualified, and no through joints are allowed; the blocks used must be in production for more than 28 days before they can be laid. When stacking and masonry, avoid rain to reduce shrinkage and cracks.
4. Treatment methods: Cracks should be observed before treatment, and repairs can be made only after the cracks are basically stable. Remove loose, peeling and cracked trim and remove scum, dirt and oil from cracks. Please refer to the following management methods. 1) When temperature deformation cracks are confirmed, appropriate treatment should be carried out based on structural characteristics, environmental conditions, usage requirements and possible hazards. 2) Temperature cracks generally do not affect structural safety. After a period of observation, when the cracks are at their widest, use the following sealing protection or partial repair methods. ① When the cracks in the wall are severe, the maximum crack width Wt=3~10mm, corresponding treatment measures should be taken. When the cracks in the wall are serious and Wt>10mm, a building reinforcement treatment plan should be customized. After approval by the relevant departments, the reinforcement treatment should be carried out according to the plan requirements. Remove the hollow shell and decorative layer from the cracks, and sweep and rinse them clean.
② When the width of the crack is less than 0.5mm, a colorless or same-color waterproofing agent or synthetic polymer waterproof coating can be sprayed directly on the wall twice. The thickness of the coating should not be less than 2mm, and the coating range should be expanded to 300mm around the crack. ③ If the width of the crack is between 0.5 and 3.0mm, clean the floating debris, scum and dust in the crack, fill it with sealing materials in layers, and spray the waterproofing agent twice after filling it firmly. ④ Reinforced anchorage.
8. Filling wall cracks in stairs and beams
1. Phenomenon (1) Vertical cracks occur in the stairwells of long multi-story houses, where the stair rest platform and the floor are adjacent. Straight cracks. (2) Local cracks occur in the wall at the bottom of the girder (wall between windows).
2. Cause analysis: Local cracks in the wall under the beam are mainly caused by the lack of beam pads or insufficient beam pad area, and the local brick wall bears excessive load. In addition, it is also related to the low marking of bricks and mortar and poor construction quality.
3. Prevention and control measures (1) Oblique cracks mainly occur on soft soil foundations. Due to uneven subsidence of the foundation, the wall bears greater shear force. When the structural stiffness is poor and the construction quality is poor, When the material strength cannot meet the requirements, the wall will crack. (2) Walls between windows with concentrated loads from beams should have a certain width (or stacking), and a sufficient area of ??concrete beam pads should be installed under the beams; when the load of the beams is large, transverse reinforcement should be considered for the wall; For small-width window walls, scaffolding holes should be avoided during construction. (3) Some wall cracks have regional characteristics. We should work with the design and construction units to conduct a comprehensive investigation and analysis based on the local climate, environment, structural form, construction methods, etc., and then take measures to solve them.
9. Wall cracks caused by uneven subsidence of masonry foundation
1. Phenomenon (1) Oblique cracks generally develop upward. Due to the high stiffness of the transverse wall (and the few door openings), large relative deformation generally does not occur, so such cracks rarely occur. Cracks are mostly found in the lower part of the wall, and gradually decrease upward. The width of the cracks is larger at the bottom and smaller at the top. They often appear soon after the house is built, and their width and number gradually develop over time. (2) Horizontal cracks in the wall between windows. Generally, they appear in pairs at the upper and lower corners of the wall between windows. The cracks on the side with greater settlement are at the bottom, and the cracks on the side with smaller settlement are at the top. (3) Vertical cracks occur at the top of the center of the longitudinal wall and at the bottom window sill. The cracks are wide at the top and narrow at the bottom. When there are reinforced concrete ring beams on the top floor of the longitudinal wall, there will be fewer vertical cracks at the center top of the top floor.
2. Cause analysis (1) Oblique cracks mainly occur on soft soil foundations. Due to uneven subsidence of the foundation, the wall bears greater shear force. When the structural stiffness is poor and the construction quality is poor, When the material strength cannot meet the requirements, the wall will crack. (2) The reason for the occurrence of horizontal cracks in the wall between windows is that resistance is encountered at the upper part of the settlement unit, which causes the wall between windows to be subjected to greater horizontal shear force, resulting in horizontal cracks at the upper and lower positions. (3) Vertical cracks under the window sill on the ground floor of the house are caused by the fact that after the window wall is loaded, the window sill wall acts as a reverse beam, especially when the wider window or the window wall bears a large concentrated load (such as an auditorium, Factory buildings and other projects), the window sill wall will crack due to excessive reverse deformation. In severe cases, the window will be squeezed and the window sash will be affected. In addition, if the foundation is built above the frozen soil layer, cracks will occur at the windowsill due to frost heave.
3. Preventive measures (1) Set up settlement joints reasonably. All houses with different loads (houses with huge height differences), too long, complex plane shapes, different foundation treatment methods for the same building, and houses with partial basements should be divided into several parts from the foundation, and settlement joints should be set to allow them to settle individually. , to reduce or prevent cracks. The settlement joints should be of sufficient width. During the operation, it is necessary to prevent the broken parts from being poured together when pouring the ring beams, or bricks, mortar and other debris falling into the joints to prevent the house from settling freely and causing 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 uneven settlement of the foundation can be appropriately adjusted. Therefore, ring beams should be installed at the top surface of the foundation (+0.000) and the doors and windows of each floor to reduce the number of doors at the end of the building. Strictly implement the specifications during operation, such as watering and moistening the bricks, improving the workability of the mortar, improving the fullness of the mortar and the bonding of the brick layer (increasing the fullness of the mortar joints can greatly improve the shear strength of the wall). Setbacks should be left as much as possible at temporary construction interruptions. When leaving straight branches, knots should also be tied, and the practice of hanging branches without knots should be resolutely eliminated. (3) Strengthen foundation trenching work.
For more complex foundations, extensive drilling should be carried out after the foundation trench is excavated. Foundation construction can only begin after the weak areas discovered are reinforced. (4) Concrete ring beams or counter-stone bricks should be considered at the lower part of large windows to adapt to the deformation of the window sill counter-beams and prevent vertical cracks at the window sill. In order to avoid cracks under the bottom window sill of a multi-story house, in addition to strengthening the integrity of the foundation, length-long reinforcement can also be used to strengthen it. In addition, it is not advisable to use too many half-bricks on the window sill.
10. Cracks at the joints of masonry projects
1. Phenomenon The straight joints of the masonry are the weakest parts that affect the overall stiffness of the house. During subsequent construction, the connections were not handled well and cracks appeared in the main load-bearing parts of the structure.
2. Reason analysis: Straight lines are left arbitrarily at the temporary breaks, corners and intersections of internal and external walls of masonry.
3. Preventive measures When masonry is built, the masonry corners or the intersections of vertical and horizontal walls should be built at the same time. If the temporary breaks cannot be built at the same time, diagonal sills should be left. The diagonal length of solid masonry should not be less than 2/3 of the height of the masonry at the temporary interruption. See picture. Except for corners, if it is difficult to leave diagonal rafters at temporary breaks, straight rafters can also be left, but they must be made into sun rafters and tie bars must be installed. The tie bars shall be steel bars no less than Φ56mm. Place one piece every 120mm according to the wall thickness and place them in layers. 500mm is one layer. The end of the tie bar should be bent into a 90° right-angle hook, and the length embedded in the masonry should be no less than 500mm from the left edge of the wall, and the length of the extended end should also be no less than 500mm. When using the freezing method for masonry construction, the length embedded in the masonry shall not be less than 1000mm. There should be no less than 2 tie bars per layer.
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