What are the specific conditions for crack prevention and control in masonry projects? The following Zhongda Consulting and Bidding Teachers will give you answers for your reference.
1. The foundation design of residential projects should focus on controlling deformation values. Foundation deformation calculations should be carried out in accordance with the relevant provisions of the "Code for Design of Building Foundations" GB50007, and settlement deformation observations should be carried out in accordance with the requirements of the specification.
2. When the length of the residence is greater than 40m, expansion joints should be installed. When reliable technical measures are adopted, they can be appropriately relaxed within the scope allowed by the regulations.
3. At the connection point between the reinforced concrete structural columns and the load-bearing wall of the masonry structure, 2φ6 horizontal steel bars and φ4 distributed short bars should be installed every 500mm along the wall height. A knotted mesh or φ4 composed of in-plane spot welding The spot welded steel mesh should not extend less than 1000mm into the wall on each side. In the bottom 1/3 of the floor for 6 or 7 degree seismic fortification, the above-mentioned tied steel mesh should be installed along the horizontal length of the wall. In masonry structures, at the connection points between non-load-bearing rear partition walls and load-bearing walls and columns, 2φ6 tie steel bars should be installed every 500 to 600mm along the wall height, and each side should not extend less than 500mm into the wall or column.
4. For masonry-filled walls and main structures in reinforced concrete structures, 2φ6 tie bars should be installed every 500mm to 600mm along the wall height. The length of the tie bars extending into the wall should comply with the design and relevant Standards require that 6 and 7 degree seismic fortifications should be installed in full length.
5. At the window sill elevations of the bottom and top floors (including jump floors) of masonry structures, horizontal cast-in-situ reinforced concrete waist beams with the length of the vertical and horizontal walls should be set up. The height should be the height of the masonry block. Modulus, and not less than 80mm, concrete strength grade should not be less than C20, longitudinal bars should be no less than 4φ10, stirrups φ6@200, longitudinal steel bars should be reliably connected to the structural columns; exterior windows on other floors should be equipped with cast-in-place or Precast concrete window sill plate, the height is not less than 60, the longitudinal reinforcement is not less than 2φ10, the single-leg stirrup is φ6@200, the window sill plate is embedded in the wall between windows, and each side is not less than 600 mm.
6. For lightweight infill walls such as small concrete hollow blocks and autoclaved aerated concrete blocks, when the wall length is greater than 5m, structural columns should be installed with a spacing of no more than 3m, and the top of the wall and the beam should be There should be ties; when the wall height exceeds 4m, a reinforced concrete waist beam with a height of not less than 120mm and the same thickness as the wall should be set at half the height of the wall; reinforced concrete structural columns should be set at the unconstrained end of the masonry.
7. At the intersection of masonry infill walls and reinforced concrete beams, columns, shear wall piers and other two different substrates, hot-dip galvanized welded mesh (diameter ≥ 1.0mm) should be used on the outer and inner walls. ) or reinforced alkali-resistant glass mesh cloth coated with polymer mortar and anchored with reinforced strips for anti-cracking treatment. The width of the reinforced strips from the joints: each side of the interior wall should not be less than 150mm, and each side of the exterior wall should not be less than 250mm. . The masonry infill walls in stairwells and pedestrian passages should be reinforced with hot-dip galvanized welded mesh mortar surfaces. Autoclaved aerated concrete block filled walls, lightweight partition boards and other walls that are prone to cracks should be covered with hot-dip galvanized welded mesh (diameter ≥1.0mm) or reinforced alkali-resistant glass mesh cloth with polymer Mortar and anchor anti-crack treatment.
8. When the concrete walls, column edges, doors and window stacks are less than 240mm and the walls between windows are less than 360mm, they should be poured with reinforced concrete.
9. Reinforced concrete structural columns should be installed on both sides of openings larger than 2m wide in masonry structure load-bearing walls or back-built infill walls.
10. The infill wall should be set on the beam and not directly on the floor. When unavoidable, it must meet the structural calculation requirements, otherwise the bottom structure of the wall should be strengthened.
11. For masonry roof parapets and window sills with full-length windows on the exterior walls, reinforced concrete capping and crack-resistant columns should be installed. The spacing between the crack-resistant columns should not exceed 3m, and there should be no crack-resistant columns inside. Less than 4φ12 longitudinal bars and φ6@200 stirrups; the overlap and anchoring length of the top and anti-cracking columns shall not be less than 500mm.
12. Autoclaved lime sand bricks, autoclaved fly ash bricks, and autoclaved aerated concrete blocks should be constructed with special masonry mortar that matches the characteristics of the wall material.
13. The crack-resistant design of load-bearing walls of small concrete hollow blocks (hereinafter referred to as blocks) should meet the following requirements:
1) Between the reinforced concrete roof panels and walls A horizontal sliding layer is set at the contact surface of the ring beam. The sliding layer can be made of two layers of linoleum sandwiched with talc powder or rubber sheets. For long longitudinal walls, it can be set only in 2 to 3 bays at both ends. For transverse walls, it can be set only in 2 to 3 bays at both ends. Set within the range of L/4 at both ends (L is the length of the transverse wall).
2) When a cast-in-place reinforced concrete ring beam is set under the top roof panel and stretched along the internal and external walls, the height of the ring beam should not be less than 190mm, and the longitudinal steel bars should not be less than 4φ12. Horizontal ribs should be appropriately installed in the wall under the ring beams at both ends of the house.
3) Three welded steel mesh sheets are installed in the mortar joints of the lower wall at the root of the top beam (the longitudinal steel bars should not be less than 2φ4, and the spacing between transverse bars should not be greater than 200mm). The steel mesh should extend from the root of the beam. The penetration into the walls on both sides shall not be less than 1m.
4) 2φ4 welded steel mesh should be installed in each horizontal mortar joint of the masonry on the lintel of the door and window openings of the top wall, and should extend into the wall at both ends of the lintel for no less than 600mm.
5) The parapet should be equipped with reinforced concrete core columns or structural columns. The spacing between structural columns should not be greater than 3m (or set in each bay). The spacing between reinforced core columns should not be greater than 600mm. The spacing between structural columns or core columns should not be greater than 600mm. It should extend to the top of the parapet and be poured together with the cast-in-place reinforced concrete top.
6) Strengthen the tie between the top core column (or structural column) and the wall. The vertical spacing of the tie steel mesh should not be greater than 400mm, and the length extending into the wall should not be less than 1000mm.
7) When the length of the internal longitudinal walls of the first and second bays at both ends of the top-floor house is greater than 3m, reinforced concrete core columns should be added to the wall, and transverse horizontal steel mesh sheets should be installed.
8) The gable wall of a house can be installed with horizontal steel mesh or reinforced concrete core columns or structural columns added to the gable wall. When installing horizontal steel mesh sheets in the gable wall, the spacing should not be greater than 400mm; when adding reinforced concrete core columns or structural columns in the gable wall, the spacing should not be greater than 3m.
9) Use small block infill walls. At both ends of the top floor of the house and on both sides of the door and window openings of the first and second bays on the ground floor, no less than 1φ12 steel bars should be installed in no less than one hole. The steel bars should be anchored to the floor ring beams or foundations and filled with no less than C20 perforated concrete; in the horizontal mortar joints of the wall on both sides of the door and window openings, a 2φ4 welded steel mesh with a length of no less than 900mm and a vertical spacing of 400mm should be set piece.
10) The base wall of the block building should increase the stiffness of the foundation and ring beams; the foundation part of the block wall should be filled with C20 concrete in the block holes.
Materials
1. The variety, specification, strength level and other related properties of wall materials should meet the design requirements, and there should be product qualification documents and on-site re-inspection reports. It is strictly prohibited to use products that are banned or eliminated by the state.
2. Before entering the site using cement for masonry mortar, its strength and stability should be retested in batches. Different types of cement must not be mixed.
3. Use medium-coarse sand for masonry mortar. Coarse sand should be used for rough stone masonry. The mud content of the sand is:
1) For cement mortar and strength grade no less than M5 cement mixed mortar should not exceed 5%;
2) For cement mixed mortar with a strength level lower than M5, it should not exceed 10%;
3) Artificial sand, mountain Sand and extra-fine sand should be tested and prepared to meet the technical requirements of masonry mortar.
4. The lime paste used in masonry mortar should be fully matured, and the curing time should not be less than 14 days. It is strictly prohibited to use dehydrated and hardened lime plaster. The curing time of finely ground quicklime should not be less than 2 days. Slaked lime powder should not be used directly. In masonry mortar.
5. The early strength agent, retardant, antifreeze, etc. added to the masonry mortar should be inspected and tested to meet the requirements before use.
6. The storage period of autoclaved lime sand bricks, autoclaved fly ash bricks, and autoclaved aerated concrete blocks after leaving the kiln should be more than 45 days (not less than 28 days). Small hollow concrete The product age of the building blocks should not be less than 28 days. After the blocks are brought into the site, reliable rainproof measures should be taken at the on-site storage yard.
7. The moisture content of autoclaved aerated concrete blocks should be controlled within 15% before they are laid.
8. The strength grade of concrete small hollow blocks used in load-bearing walls of five-story and above residential buildings should not be lower than MU7.5, and the strength grade of concrete porous bricks should not be lower than MU10; The moisture content shall not be greater than 15%; the strength grade of the top layer of masonry mortar shall not be less than Mb10, and the other layers shall not be less than Mb7.5.
9. The strength grade of non-load-bearing concrete small hollow blocks, autoclaved aerated concrete blocks, etc. used for exterior walls is not less than MU5.0, and the strength grade used for interior walls is not less than MU3. .5; the moisture content during masonry shall not be greater than 15%; the strength grades of special masonry mortar used for exterior and interior walls shall not be less than Mb5 and Mb3.5 respectively.
Construction
1. Autoclaved lime sand bricks, autoclaved fly ash bricks, small hollow concrete blocks, aerated concrete blocks and autoclaved fly ash blocks, etc. The transportation and stacking of materials should avoid collisions and prevent missing edges and corners. After entering the site, they should be stacked neatly according to varieties and specifications, and the stacking height should not exceed 2m. Aerated concrete blocks should be protected from rain. Bricks and blocks of different types must not be mixed.
2. Pre-mixed mortar should be preferred for masonry mortar. When mixed with a mortar mixer, the mixing time should be no less than 2 minutes. When admixtures are added, the mixing time should be no less than 3 minutes. When mixing admixtures, the admixtures should first be dissolved in water according to the specified concentration, and the admixture solution should be added when the mixing water is added. The admixtures should not be directly added to the mixed mortar. Mortar should be mixed and used immediately. Cement mortar and mixed mortar must be used within 3 hours and 4 hours respectively after mixing. If the maximum temperature during construction exceeds 30°C, they must be used within 2 hours and 3 hours respectively.
3. Watering and moisture content of bricks and blocks:
1) Under normal temperature, sintered bricks should be watered and moistened 1 to 2 days before laying, and the moisture content should be 10% to 15%. It is strictly prohibited to use dry bricks on walls;
2) Under normal temperature, autoclaved lime sand bricks and autoclaved fly ash bricks should be watered and moistened 1 to 2 days before construction. , the moisture content should be 8% to 12%, and it is strictly prohibited to put dry bricks or bricks soaked in rainwater on the wall;
3) Ordinary concrete hollow blocks must not be watered, and should be wet concrete with natural moisture content. Hollow blocks shall not be constructed.
4) Aerated concrete blocks and autoclaved fly ash blocks can be sprinkled with appropriate amounts of water on the masonry surface;
5) When special masonry mortar is used for masonry, Whether and how to water should be determined according to the material characteristics and the requirements of special masonry mortar.
Masonry construction method:
1) The thickness of the mortar joints of the masonry should be consistent and the mortar should be full. There should be no transparent seams, blind seams or false seams in the vertical mortar seams.
2) When filling the wall close to the bottom of the beam or slab, a gap of 30mm to 80mm should be left, and an interval of not less than 7 days should be left, and then filled with fine stone concrete and expansion agent. ; If comb bricks are used for repair, they should be laid symmetrically along the direction of the wall. The inclined bricks should be 60 degrees. The triangular gaps on both sides and in the middle should be filled with dry-hard expansion mortar and repaired tightly. The masonry at the lower opening of the sloping roof beam should be built in a stepped shape, and the gap filling method is as described above.
3) When the distance from the top of the door and window opening to the bottom of the beam is less than 200mm, the door and window lintels should be cast integrally with the structural beams. When the loading port and construction hole are blocked, the top should be filled with fine stone concrete and expansion agent.
4) It is strictly prohibited to dig transverse grooves and inclined grooves in load-bearing masonry; it is strictly prohibited to dig wire conduit grooves and junction box holes in the walls between door stacks and windows that have been completed; if there are arrangements in the design, Yes, holes must be embedded or left in place during masonry construction. Mechanical cutting should be used when grooving in masonry, and the grooving depth should not exceed 1/3 of the wall thickness.
5) Reinforced concrete lintels should be installed for reserved openings with a width greater than 300mm, and the length extending into the wall on each side should not be less than 250mm.
6) The corners and junctions of masonry should be built at the same time. Separate construction of internal and external walls without reliable measures is strictly prohibited. Temporary interruptions that cannot be built at the same time but must be left in place should be built as diagonal chalets. The horizontal projection length of the diagonal chalets should comply with the specifications and design requirements.
7) The tie bars left in the masonry of the infill wall should be reliably connected to the original structure. The placement location should be consistent with the mortar joints of the masonry and must not be bent. The ends of the tie bars should be 90° Hook.
8) The daily height of small hollow concrete blocks and autoclaved aerated concrete blocks should be controlled within 1.4m under normal temperature conditions.
9) Leave a temporary construction opening in the wall. The side of the opening should not be less than 500mm from the junction wall, and the net width of the opening should not exceed 1m. Temporary construction openings should be repaired. When repairing temporary construction openings and construction scaffolding holes, the mortar joints should be filled with mortar, and dry bricks should not be used.
10) Use autoclaved lime sand bricks, autoclaved fly ash bricks, small hollow concrete blocks, aerated concrete blocks and autoclaved fly ash blocks to connect the infill walls and frame columns. 15mm × 15mm wooden strips should be used to leave seams in advance, water them to moisten them before attaching the mesh, and then embed them with 1:3 cement mortar.
11) Relevant requirements for small concrete hollow blocks:
① The reverse masonry method should be used with the bottom facing upward.
② The thickness of horizontal mortar joints and the width of vertical mortar joints should be controlled between 8mm and 12mm. The mortar fullness of horizontal mortar joints and vertical mortar joints shall not be less than 90%;
③ Horizontal mortar joints shall be fully paved with mortar setting method to cover all wall ribs of small blocks or multi-row holes of small blocks. Bottom sealing surface; Vertical mortar joints should adopt the full-paved end-face method, that is, paving the small blocks with their end faces upward and squeezing the mortar onto the wall, then adding mortar and compacting, and hooking the mortar joints to 3mm to 5mm along with the masonry. concave seam.
④ The wall should be built with staggered holes and joints, and the overlap length should not be less than 90mm. When individual parts of the wall cannot meet the above requirements, tie steel bars or steel mesh sheets should be installed in the mortar joints, but the vertical joints should not exceed two small blocks.
⑤ It is strictly forbidden to use small broken blocks when used for load-bearing walls.
⑥ When pouring the concrete for the core column, special small block hole-filling concrete should be used. When ordinary concrete is used, the slump should not be less than 90mm. When pouring the core column concrete, the mortar and other debris in the hole should be removed and washed with water; the core column concrete can only be poured when the strength of the masonry mortar is greater than 1MPa; before pouring the core column concrete, an appropriate amount of the same amount as the core column concrete should be poured Remove the stone cement mortar and pour the concrete.
12) Requirements for non-load-bearing walls of autoclaved aerated concrete blocks:
① Horizontal mortar joints shall be paved by grouting method, and the length of one grouting shall not exceed the length of two blocks. Length; the vertical mortar joints adopt the full-laying end face method (the method is the same as above), and the mortar joints are hooked into concave joints 3mm to 5mm away from the wall surface as the masonry is built.
② Special masonry mortar should be used for masonry construction. The thickness of horizontal mortar joints should be 15mm and the width of vertical mortar joints should be 20mm.
③ The length of the building blocks should not be less than 1/3 of the length of the building blocks, and should not be less than 150mm. When individual parts of the wall cannot meet the above requirements, tie steel bars or steel mesh sheets should be installed in the mortar joints, but the vertical joints should not exceed two skin blocks.
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