In building structure, masonry structure is a relatively common form, especially in the last century. Since the masonry structure is a brittle structure, the wall is prone to cracks during use. According to the way of stress generated by cracks, it can be roughly divided into non-stressed cracks and stressed cracks. According to the survey, more than 95% of the cracks in the wall belong to non-stressed cracks. The reasons for the formation of cracks are generally insufficient bearing capacity or stability, temperature deformation, material shrinkage deformation, uneven settlement of the foundation, etc.

Non-stressed cracks can be divided into floor slab cracks (roof), wall cracks at the opening, vertical or oblique cracks in the wall, vertical cracks under the large window sill at the bottom, and uneven settlement cracks in the foundation according to the different positions of the cracks. Stress cracks can be divided into flexural cracks, compression cracks, shear cracks, tension cracks and local compression cracks, etc. Stress cracks are relatively rare in engineering.

Commonly used crack repair methods should include composite section reinforcement method, grouting method, external mesh method and replacement method. According to the needs of the project, these methods can be used in combination.

Composite section reinforcement method

The wall cracks are serious. In order to increase the overall rigidity of the house, reinforced concrete ring beams can be added on one or both sides of the house wall. The strength grade of concrete used for ring beam is C15～C20. The cross-section should be at least 120mm×180mm, the reinforcement can be 4Φ10～4Φ14, the steel bar Φ6@200～250, the anchors etc. extend into the wall every 1.5m～2.5m to be well tied with the wall, and bear the dead weight of the ring beam. When pouring the ring beam, the wall should be chiseled and moistened to strengthen the bond.

This method belongs to a kind of composite section reinforcement method. The advantages are that the construction process is simple, the adaptability is strong, the bearing capacity is greatly improved after the masonry is reinforced, and it has mature design and construction experience. It is suitable for the reinforcement of columns and walls. The disadvantage is that the wet operation time of on-site construction is long, which has a certain impact on production and life, and the clearance of the reinforced building is reduced to a certain extent.

grouting method

Scope of application: The grouting method is the pressure grouting method, which is suitable for treating cracks with a width greater than 0.5mm and a deep depth.

Material selection: The material of grouting can be non-shrinking cement-based grouting material, epoxy-based grouting material, etc.

The operation of the grouting method should meet the following requirements:

1. Carefully observe the length and width of the cracks, whether they are connected, whether there is water leakage, and analyze the reasons for the formation of cracks;

2. Basic treatment: clean the dust and oil on the crack surface;

3. Determine the injection port: generally set an injection port at a distance of 20-750px. The position of the injection port should be set as far as possible in the part with wider cracks and smooth openings, stick tape and reserve;

4. Sealing cracks: use quick-drying sealant, smear and scrape along the surface of the crack, leaving the injection port;

5. Install the plastic base: remove the tape on the injection port, and stick the base to the injection port with seam sealant;

6. Install the grouting device: inject the prepared grouting resin into the hose, and screw the grouting device with resin on the base;

7. Grouting: Loosen the spring of the grouting device and confirm the injection state. If the resin is insufficient, it can be replenished and then continue to inject;

8. The injection is completely closed: when the injection speed is reduced and it is confirmed that the glue is no longer injected, the grouting can be removed and the base is blocked with a plug;

9. After the resin is cured, knock off the base and plug, and clean the surface sealant.

extra mesh method

Scope of application: The extra mesh method is suitable for enhancing the crack resistance of masonry, limiting the development of cracks, and repairing weathered and eroded masonry.

Material selection: The materials used for the extra mesh should include steel mesh, steel mesh, composite fiber fabric mesh, etc. When using steel mesh, the diameter of the steel bar should not be greater than 4mm. When using non-woven fabrics instead of fiber composite materials to repair cracks, it is only allowed to be used for closed repair of static fine cracks in non-load-bearing components.

Construction operation: In addition to the area covered by the mesh, which should be determined according to the area of cracks or weathered and eroded parts, the anchorage length of the mesh should also be considered. The size of the short side of the mesh should not be less than 500mm.

The number of layers of mesh: for steel bars and steel mesh, it should be a single layer; for composite fiber materials, it should be 1 to 2 layers; the design can be determined according to the actual situation.

permutation

Scope of application: The replacement method is suitable for the cracked parts where the masonry is not under stress, the masonry block and mortar strength is not high, and the reinforcement of local weathering and denudation parts.

Material selection: The masonry blocks used for replacement can be original masonry materials or other materials, such as reinforced concrete solid blocks.

Construction operation: When replacing masonry, the following requirements should be met:

1. Remove the plastering layer on the surface of the masonry that needs to be replaced and the surrounding masonry, and then chisel off the replaced masonry along the plaster seam. During the chiseling process, disturbance of the masonry that does not replace the part should be avoided.

2. Carefully remove the mortar adhered to the masonry, and fully wet the wall after removing the floating dust.

3. During the repair process, it should be ensured that the filling masonry material is reliably embedded with the original masonry.

4. After the masonry repair is completed, do the plastering layer.