Crack treatment method
Option 1:
① Chisel off the upper leveling layer of the floor and clean it.
②Clean the surface of the concrete to be repaired, and after drying, use a brush or brush to repeatedly apply epoxy resin on the cracks, once every 3-5 minutes, with a coating thickness of about 1mm. until.
③Use 1:2 cement mortar to touch the surface.
Option 2:
① Remove the leveling layer on the upper part of the floor and clean it.
②Use a cutting machine to cut the cracks and cut them into V-shaped grooves
③The specific method is according to item ② of Plan 1.
④ Arrange the steel bars according to the diagram
⑤ Pour C30 fine stone concrete, add 2%-5% expanded cement into the concrete, and have a dedicated person guard and polish it within 4 hours after the concrete is poured, and Send someone to maintain the concrete.
Option 3
① Remove the leveling layer on the upper part of the floor and clean it.
② Cut a V-shaped groove with a width of 5~8mm along the direction of the crack. The specific method is according to item ② of Plan 1.
③ Arrange φ8@150 steel bars in both directions along the floor, specifically See the detailed drawing for the layout. The steel bars are embedded in the wall 5cm all around.
④ Use C30 fine stone concrete to pour the floor slab, with a thickness of 5cm..
Note: If there are irregular small cracks on the local floor surface, use the plan 1 to deal with the local penetration cracks on the floor. In the second treatment, if penetrating cracks appear in the mid-span of the floor slab, adopt the third treatment.
Let’s first look at the classification of cracks: cracks can be divided into stressed cracks and non-stressed cracks. Stress cracks are caused by factors such as uneven settlement of the foundation, concrete strength, and plate thickness; non-stress cracks are caused by factors such as temperature, shrinkage of concrete, construction, etc. They appear early or late, and early drying Shrinkage cracks will appear about 2 to 4 hours after pouring is completed, and some temperature cracks will only appear three months to half a year after completion acceptance. Among them, the main construction factors are that the protective layer of the negative reinforcement of the slab is too large (the steel bars are severely stepped down), the concrete protective layer at the bottom of the slab is insufficient, or the chloride salt content of the sand exceeds the standard.
Now let’s analyze the treatment methods for various types of cracks:
(1) For destructive cracks caused by unqualified cement stability in concrete or chemical reactions caused by mixing different types of cement, It must be treated thoroughly, that is, the concrete must be knocked out and re-poured.
(2) For cracks caused by stress, targeted reinforcement measures can be taken based on the cause of the cracks.
If there are cracks in the floor that have affected the structural safety, in addition to cutting V-shaped grooves along the cracks and cleaning them, pouring epoxy resin liquid into the cracks under pressure to seal them, flat steel must also be used to seal them. Or carbon fiber cloth and other measures to reinforce the floor. When reinforcing with carbon fiber cloth, for a single crack, in addition to pasting along the seam, it must be pasted at a spacing perpendicular to the seam direction; for multiple intersecting seams, it must be pasted in a tic-shaped pattern, with the spacing being the same as the cloth width. (The cloth width is about 300mm)
(3) The treatment of non-stressed cracks caused by temperature, shrinkage of concrete, construction and other factors is as follows:
1. For general concrete For cracks on the floor surface, the cracks can be cleaned first, and after drying, the cracks can be filled with epoxy resin liquid or sealed with surface painting. If cracks are found before final setting during construction, they can be treated by applying pressure.
2. For the treatment of other general cracks (with a width between 0.05mm and 0.2mm), the construction sequence is: clean the board joints, then use 1:2 or 1:1 cement mortar to smear the joints, and press Just maintain it flat and close it to restore the look and feel. (Limited to a small number of seams and not full-length or through seams)
3. When the cracks (width greater than 0.2mm) are large, an eight-shaped groove should be cut along the cracks, and then rinsed , smooth it with 1:2 cement mortar, or use epoxy cement to inlay it. (Limited to a small number of joints that are not full-length or through joints)
4. When cracks appear on the floor with a large area, a static load test should be carried out on the floor to check its structural safety. If necessary A layer of steel mesh can be added to the floor to improve the integrity of the slab. Or seal the seams with epoxy resin liquid on the board surface (a layer of waterproofing is also acceptable), and paste carbon fiber cloth on the bottom of the board into a tic-shaped shape, with the spacing being the same as the width of the cloth.
5. For long and penetrating dangerous structural cracks with a crack width greater than 0.2mm, the treatment method is as follows: in addition to cutting V-shaped grooves along the cracks and flushing them clean, fill the epoxy resin liquid with pressure In addition to sealing the internal joints, the floor slabs must also be reinforced with sticky flat steel or carbon fiber cloth. When reinforcing with carbon fiber cloth, for a single crack, in addition to pasting along the seam, it must be pasted at a spacing perpendicular to the seam direction; for multiple intersecting seams, it must be pasted in a tic-shaped pattern, with the spacing being the same as the cloth width. (The width of the cloth is about 300mm.)
6. When the whole length, through and non-through length, and through cracks have the same composition and there are many, the bottom of the board can only be pasted vertically and horizontally.
3. Treatment plan for non-structural cracks in concrete floor slabs
Based on the nature of non-structural cracks, the following treatment plans are proposed:
1. For general concrete floor cracks If the cracks are cracked, the cracks can be cleaned first, and after drying, they can be filled with epoxy slurry or sealed with surface painting. If cracks are found before final setting during construction, they can be treated by applying pressure.
2. For other general crack treatment, the construction sequence is: clean the board joints, then use 1:2 or 1:1 cement mortar to smear the joints, flatten and maintain.
3. When the crack is large, an eight-shaped groove should be cut along the crack. After cleaning, it can be smoothed with 1:2 cement mortar or epoxy cement can be used to inlay it.
4. For cracks with surface width ≤0.3mm, small depth and large number of cracks, epoxy slurry can be applied to the surface of the cracks;
5. Surface width >0.3mm The cracks will cause corrosion of the steel bars and affect the durability of the structure. Epoxy gel waterproofing material is used to seal the cracks and grout.
6. When the crack area of ??the floor is large, a static load test should be carried out on the floor to check its structural safety. If necessary, a layer of steel mesh can be added to the floor to improve the overall strength of the floor. sex.
Cause analysis and countermeasures for concrete cracks in floor slabs and cracks in filling walls
Published time: 2010-04-15 Author of the article: Source: China Concrete and Cement Products Network
< p> At present, cracks in concrete floors and filled walls in residential projects are relatively common. Based on relevant information and combined with the situation of our company, the causes and countermeasures of cracks in cast-in-place concrete floors and block filled walls are analyzed as follows for everyone to use at work. Reference.1. Types of cracks in residential cast-in-place concrete floors
1. Longitudinal cracks: cracks along the longitudinal direction of the building. Most of them appear under the slab, and some of them run through the top and bottom.
2. Transverse cracks: that is, cracks along the transverse direction of the building within 1/3 of the span, most of which appear under the slab, and some of them run through the top and bottom.
3. Corner cracks: Oblique cracks that appear at the four corners of the room, mostly on the surface of the board. 4． Irregular cracks: cracks with irregular distribution and direction.
5. Transverse cracks at the root of the floor slab: cracks that occur within 30cm from the supports and are located on the upper surface of the slab. 6． Cracks along the direction of the embedded electrical conduit. 2. Reasons for cracks in floor slabs 1. Design aspect
1.1 When designing the structure, the safety reserve is too small, the reinforcement is insufficient or the cross-section is small, resulting in poor stiffness of the beam plate after forming and large overall deflection. Causes cracks at the corners of the board.
1.2 The designed plate thickness is not enough, and the deflection calculation is not performed. The overall deflection is too large, causing cracks at the four corners of the plate.
1.3 When the house is long, expansion joints are not installed, causing shrinkage cracks in weak links. (According to the American Concrete Institute, concrete has two types: dry shrinkage and temperature deformation. The dry shrinkage deformation shrinks about 19mm every 30.48m. The deformation caused by temperature changes is that the temperature change of 37°C shrinks or extends about 19mm every 30.48m. Some people in China It is believed that the longitudinal shrinkage of a 40m-long floor due to hardening and solidification is 8-20mm.)
1.4 Improper foundation design can cause uneven settlement, causing additional stress on the superstructure, resulting in cracks in the floor.
1.5 The floor slab is stressed in two directions and is reinforced as a one-way slab, causing cracks.
2. Reasons for commercial concrete
2.1 The water-cement ratio is large and the cement consumption is large.
2.2 If the dosage of high-efficiency retarder is too large, the stones will sink before solidification, causing settlement cracks, which often occur at the intersection of beams and slabs.
2.3 The quality of sand and gravel is not good, the gradation is not good, the mud content is high, and the powder content is high.
3 Reasons for construction
3.1 Insufficient maintenance. Mandatory regulations require concrete curing to be covered and watered. Nowadays, most of them are not covered and watering cannot be guaranteed. Sexually moist.
3.2 The construction speed is too fast and the load is loaded too early, especially for brick-concrete residential floor slabs. The slabs are poured the day before, and the bricks are loaded and rolled out the next day, causing early concrete damage.
3.3 Suffering from freezing during winter.
3.4 The formwork is removed too early or the formwork support system is not rigid enough.
3.5 The laitance on the concrete surface is too thick and the surface strength is not enough.
3.6 During construction, the concrete slab reinforcements were bent and knocked down, the protective layer was too thick, and the bearing capacity was reduced.
Three Measures to Prevent Cracks in Floor Concrete
1. Design aspects
1.1 When using small-diameter steel bars, appropriately increasing the reinforcement ratio can increase the ultimate tensile strain of concrete.
1.2 The negative reinforcements at the corners are arranged in two directions, and the one-way boards are also equipped with negative reinforcements on all four sides.
1.3 Under the same reinforcement ratio, using smaller diameter steel bars and reducing the spacing between steel bars can improve the crack resistance of cast-in-place slabs.
2. Construction aspects
2.1 Try to set expansion joints in cast-in-place floor slabs. The spacing between expansion joints can be about 14m or the longitudinal length of a unit in a residential building. They are located at the floor supports with a joint width of 10mm and software in the middle. Material, concrete is broken but the ribs are continuous.
2.2 When tying the steel bars, ensure even spacing and ensure that the position of the negative reinforcement remains unchanged. When pouring concrete, set up a horse track to avoid stepping on the negative reinforcement.
2.3 Use a flat vibrator to apply pressure twice, the second time before final setting.
2.4 Add a steel mesh under the embedded wire pipe, and try to arrange the embedded pipe in the direction of the stressed steel bar.
2.5 Use the method of covering and watering for maintenance. Covering and watering are mandatory requirements. At present, most of us only water without covering. After the water dries, we cannot guarantee timely replenishment and maintenance. During this period, the concrete cannot be guaranteed to be in a continuously moist state and the proper curing effect cannot be achieved.
2.6 If the concrete does not reach 1.2mpa, no one is allowed to enter, but the formwork should be removed early, or an early removal system should be adopted, and vertical support should be maintained after the formwork is removed.
3 Mixing station aspects
3.1 Ensure production according to the designed slump. If segregation is found on site, secondary mixing will be performed. 3.2 Ensure the quality of cement, sand and gravel, and ensure that the mix ratio is scientific and reasonable.
3.3 Shrinkage reducing agents will be available soon. Shrinkage cracks can be reduced by mixing shrinkage reducing agents into concrete.
4. Treatment of cracks in floor slab concrete
4.1 Cracks with a width less than 0.3mm can be sealed with 6202 cement.
4.2 If the crack width is greater than 0.3mm, perform chemical grouting treatment. The method is as follows:
(1) Chiseling: Chisel along the cracks, and chisel out the width and depth according to the cracking situation. V-grooves of 15~20mm each.
(2) Bury grouting pipes: Drill holes every 50cm along the direction of the crack, bury grouting nozzles, and fix them with glue.
(3) Seal cracks: Use structural glue The riding seams are repeatedly scraped and solidified, while surrounding cracks and branch cracks are sealed.
(4) Blow air to test pressure: seal the leaking parts.
(5) Grouting: Prepare the grouting liquid and inject it into the grouting device, which is pressurized by an air compressor to 0.2mpa. Grouting starts from one end of the grouting nozzle. Generally, the grouting stops after the grouting liquid overflows from the adjacent grouting nozzle and is closed. Grouting mouth, proceed with next grouting in sequence.
(6) Remove the mouth and close the grouting mouth.
5. Crack analysis of block-filled walls
1. Types of cracks
1.1 Cracks at the intersection between masonry and columns and beams, horizontal or vertical joints.
1.2 Cracks in the masonry itself, vertical joints or cracks along the mortar joints.
2. Causes of cracks
2.1 The impact of block drying shrinkage: The drying shrinkage value of blocks is generally less than 0.4mm/m. Tests have proven that after curing at room temperature for one month, the total shrinkage rate is 30~ 40%. After curing for about two months, the shrinkage rate is about 95%. If the construction speed is too fast and the blocks with a stagnation period of less than 28 days are used, shrinkage cracks will occur in the block wall.
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