What are the causes of floor cracks? How to deal with floor cracks?

As the name implies, floor crack refers to the phenomenon that cracks appear in the floor part of the building structure. Floor crack is one of the most common and difficult quality problems at present. Although some floor cracks are not harmful to the structural safety, they will have leakage defects under special circumstances such as water supply, which is easy to cause residents' complaints. Let's take a look at the causes of floor cracks and how to deal with them.

Causes of floor cracks:

First, the causes of floor crack design

1. In structural design, the safety margin is too small, the reinforcement is insufficient or the section is too small, which makes the formed beam and slab have poor stiffness and excessive overall deflection, resulting in cracking at the four corners of the slab.

2. The thickness of the designed plate is not enough, and the deflection is not calculated, and the overall deflection is too large, resulting in cracking at the four corners of the plate.

3. When the building is long, there is no expansion joint, which leads to shrinkage cracks in the weak links. According to the data of American Concrete Society, there are two kinds of concrete: dry shrinkage and temperature deformation. Every 30.48mm, the dry shrinkage is about 19mm. When the deformation caused by temperature change is 37℃, the temperature change is about 19mm ... Some people in China think that the longitudinal shrinkage of 40m-long floor due to hardening and curing is 8-20 mm).

4. Improper handling of foundation design will lead to uneven settlement, additional stress of superstructure and floor cracks.

5. The floor slab is stressed in two directions and reinforced in one direction, resulting in cracks in the floor slab.

2. Causes of cracks in commercial concrete floor slab

1, high water-cement ratio and large cement consumption.

2. When the content of high-efficiency retarder is too large, the stones sink before solidification, resulting in sinking cracks, which often appear at the joint of beam and slab, causing cracks in the floor.

3. The quality of sand and gravel is not good, the gradation is not good, the silt content is large, and the powder content is large.

Three, the floor crack construction reasons

1, the maintenance is not in place, and the mandatory code requires that concrete maintenance should be covered with water, but now most of them are not covered with water, so there is no guarantee that frequent moisture will lead to cracks in the floor.

2, the construction speed is too fast, the load is early, especially for the floor of brick-concrete residential buildings. The floor slab was poured the day before, and the brick was put and the car was moved the next day, which led to the early damage of concrete.

3. Floor cracks caused by freezing in winter.

4, dismantle prematurely or template support system stiffness is not enough.

5. The laitance on the concrete surface is too thick and the surface strength is not enough.

6. During construction, the concrete cover rib of the floor slab bends and goes down the steps, the protective layer is too thick, and the bearing capacity decreases, resulting in cracks in the floor slab.

Treatment methods of floor cracks:

(1) The destructive floor cracks caused by unqualified cement stability or chemical reaction of different types of cement in concrete should be thoroughly treated, that is, the concrete should be knocked out and poured again.

(2) For floor cracks caused by stress, targeted reinforcement measures can be taken according to the causes of floor cracks. If there are cracks in the floor that have affected the structural safety, in addition to flushing the V-shaped groove along the cracks, epoxy resin liquid is poured into the cracks by pressure, and measures such as sticking flat steel or carbon fiber cloth are also adopted to strengthen the floor. When carbon fiber sheets are used to reinforce cracks in a single floor slab, they should be pasted at intervals perpendicular to the direction of cracks. For multiple intersecting seams, paste them into a hash shape with the same spacing and width. (The width of the cloth is about 300 mm)

(3) Non-stressed floor cracks caused by temperature, concrete shrinkage, construction and other factors shall be treated as follows:

1. For cracks on the surface of general concrete floor slab, the cracks on the floor slab can be cleaned first, and then filled with epoxy resin liquid or closed by surface painting after drying. If cracks are found before final setting during construction, they can be treated with plastering.

2. For the treatment of other common floor cracks (the width is between 0.05 mm and 0.2 mm), the construction sequence is as follows: after the floor cracks are cleaned, they shall be leveled and maintained with 1: 2 or1:kloc-0/cement mortar, and sealed to restore the look and feel. (Limited to a few short and non-penetrating joints)

3. When the floor crack (width greater than 0.2mm) is large, a splayed groove should be chiseled along the crack. After cleaning, smooth it with 1: 2 cement mortar, or repair it with epoxy putty. (Limited to a few short and non-penetrating joints)

4. When the crack area of the floor is large, static load test should be carried out on the floor to check its structural safety. If necessary, a layer of steel wire mesh can be added to the floor to improve the integrity of the floor. Or seal the board with epoxy resin liquid (waterproof layer is also acceptable), and stick carbon fiber cloth at the bottom of the board into a well shape with equal spacing and width.

5. For the long, through cracks in the floor slab of dangerous structure, the treatment method for cracks with a width greater than 0.2mm is: in addition to flushing the V-groove along the cracks, epoxy resin liquid is injected into the cracks under pressure to seal them, and flat steel or carbon fiber cloth is pasted to reinforce the floor slab. When strengthening with carbon fiber cloth, for a single crack, in addition to sticking along the seam, it is necessary to expand the width at intervals perpendicular to the direction of the seam; For multiple intersecting seams, paste them into a hash shape with the same spacing and width. (The width of the cloth is about 300 mm)

6. When there are a large number of cracks in the long, long and non-long floor slabs, only vertical and horizontal pasting is carried out at the bottom of the floor slab.

The above questions are about how to deal with floor cracks. If you have any questions about how to deal with floor cracks, you are welcome to pay attention to us at any time, and we will update the wonderful content for you from time to time!