When longitudinal cracks occur at the grass-roots level, steel mesh should be added at the height of13 from the bottom of the concrete slab in the whole panel where the longitudinal cracks are located, and the distance between the steel mesh and the crack end should not be less than 5m.
When the base is raised, it should be removed. If the base material becomes loose after removal, it should also be removed and repaired with plain concrete.
Sprinkler quantity should be determined according to the substrate, temperature, humidity, wind speed and other factors during construction. In a word, before pouring concrete, make sure that the base is wet and evenly spread, especially where the base is uneven. If the base is still dry after watering, it should be watered again to ensure that the base is wet.
Before pouring concrete, the garbage, paper, sundries, leaves and branches on the surface of the base should be cleaned up.
Reasons: insufficient curing period of concrete pavement, uneven settlement of foundation and uneven compaction of subgrade.
Settlement crack?
It can be divided into two situations: first, after concrete pouring, cement and aggregate naturally sink, and at the same time bleeding occurs, resulting in cracks in the settlement process; Second, after concrete pouring, when cement and aggregate are partially blocked by embedded parts such as steel bars, and the formwork moves, tensile stress and shear stress will be generated in concrete, and settlement cracks will be generated there. Cracks usually appear at 1~3 h after pouring, which belongs to pre-hardening cracks [. When the settlement is terminated, it should be dealt with quickly, and then the crack should be closed by pressure again. ?
Temperature crack?
After concrete pouring, the surface is not covered in time. In hot or windy weather, the surface free water evaporates too fast, and the volume of concrete shrinks sharply, leading to cracking. In the process of concrete hardening, cement releases a lot of hydration heat, the internal temperature rises continuously, and the surface produces tensile stress. In order to prevent temperature cracks, gradation should be reasonably selected, cement with low hydration heat should be used, the dosage of cement and water should be reduced, and the expansion value of concrete should be reduced. In the construction management, we should pay attention to the artificial cooling measures and cut the joints in time. ?
Dry shrinkage crack?
After pouring cement concrete, in the hardening process, because the volume of cement hydration product is smaller than the original substance, and the free water evaporates in the air, the gel shrinks due to water loss, and tensile stress is generated with the volume shrinkage of concrete. When the tensile stress is greater than the tensile strength of concrete at that time, dry shrinkage cracks are generated. Shrinkage cracks often occur in high temperature and hot season. The water on the surface of concrete loses quickly, the volume shrinks quickly, the internal temperature changes little and the shrinkage is small. Surface shrinkage deformation is constrained by internal concrete, which can also cause surface cracks.
Handling:
Water the cracks in the finished pavement.
Dig subgrade, treat foundation, and do a good job of drainage.
Re-compact the subgrade.