1. What are the causes of cracks in the new floor?
1, design reason
In structural design, the safety margin is too small, the reinforcement is insufficient or the cross section is too small, which makes the formed beam and slab have poor stiffness and excessive overall deflection, and then causes the four corners of the slab to crack. Or the design plate thickness is not enough, the deflection calculation is not done, and the overall deflection is too large, resulting in cracks in the four corners of the plate.
2, the reason of commercial concrete
The water-cement ratio is large, and the cement consumption is large. Then the content of high-efficiency retarder is too large, and the stones sink before solidification, resulting in sinking cracks, which often appear at the joint of beam and slab to cause floor cracks. 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.
3. Construction reasons
Maintenance is not in place, and mandatory specifications require concrete maintenance to be covered with water. At present, most of them are not covered with water, and there is no guarantee that frequent moisture will cause cracks in the floor. One of the reasons is that the construction speed is too fast and the load is early, especially 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 caused the early damage of concrete. Then there are cracks in the floor due to freezing in winter, premature formwork removal or insufficient rigidity of formwork support system. The laitance on the concrete surface is too thick and the surface strength is not enough. Finally, it may be that the concrete cover rib of the floor slab is bent and collapsed during construction, the protective layer is too thick, and the bearing capacity decreases, resulting in cracks in the floor slab.
Second, how to deal with cracks in the floor of new buildings in rural areas?
1, floor cracks caused by stress
(1) The self-built floor slab is cracked and needs targeted reinforcement.
(2) If cracks appear in the floor slab at key positions, that is, cracks that have affected the structural safety of the floor slab, the cracks should be cleaned up, V-shaped grooves should be chiseled along the cracks, epoxy resin liquid should be injected into the cracks every 20-30 mm with a needle or other items with pressure, the injector should be removed after injection, and the base should be blocked with a plug. After the resin is cured, knock off the base and plug, and clean up the residual glue on the surface.
(3) Strengthen the floor with carbon fiber cloth or glued flat steel.
Note: when strengthening the floor with carbon fiber sheets, if it is a single joint reinforcement, it should be pasted along the joint and also at the vertical part of the joint. If there are multiple intersecting seams, they should be glued into a grid, and the spacing should be based on the specifications of the seam width.
2. Non-stress-induced floor cracking
Cracks in the floor of rural self-built houses may also be caused by factors such as temperature and improper construction. In this case, they should be treated as follows:
(1) The number of floor cracks is small and not long, and the connection is good.
A, the width of the floor crack is less than 0.05 mm.
First, clean the self-built floor, and then seal it with epoxy resin liquid when the floor is dry. The pouring interval of epoxy resin liquid should be kept at about 20-30 mm If there are local cracks in the middle of construction, it can be plastered again.
B, the width of the floor crack is between 0.05 and 0.2 mm..
After the cracks are cleaned, plaster the cracks with cement mortar with the mixing ratio of 1:2 or 1: 1, flatten them after plastering, and maintain them well.
C, the width of the floor crack is greater than 0.2 mm.
When the width of the ground crack of the self-built building is greater than 0.2 mm, a splayed groove should be chiseled along the crack, then washed clean, leveled with cement mortar with the mixing ratio of 1:2, or filled with epoxy mastic.
(2) The dangerous floor cracks are long and well connected.
The treatment method of floor cracks in long and through dangerous structures is consistent with the treatment method of floor cracks caused by stress, which can be treated with reference to the first point method.
(3) The floor crack area is large.
A, when the floor crack area is large, structural safety inspection should be carried out to avoid affecting the living safety of residents. You can add a layer of steel mesh to the floor to improve the integrity of the floor.
B, you can also use epoxy resin liquid to seal the floor surface, and stick carbon fiber cloth at the bottom of the floor with the same spacing as the non-specifications.
3. The floor cracks caused by material problems.
(1) At present, the floor of self-built houses in rural areas is generally constructed by cast-in-place method, and cement is needed. If the stability of the cement contained in the floor is unqualified, that is to say, the uneven change of the hardened volume of cement leads to the cracking of the floor. In this case, the concrete can only be knocked off and poured again.
(2) Different kinds of cement will react chemically after mixing, resulting in cracks in the floor of the self-built house. In this case, the concrete can only be knocked off and poured again.
The above contents are about the causes of cracks in new floors and how to deal with cracks in new rural buildings. If the cracks are large, we should pay attention to them and deal with them in time to avoid more problems in the later stage.