Shrinkage cracks mostly appear in a

Shrinkage cracks mostly appear in a period of time after the completion of concrete curing or about a week after the completion of concrete pouring. The evaporation of water in the cement slurry will produce dry shrinkage, and this shrinkage is irreversible. The occurrence of shrinkage cracks is mainly due to the difference in the degree of moisture evaporation inside and outside the concrete, which results in different deformations: the concrete is affected by external conditions, the surface moisture loss is too fast, the deformation is large, the internal humidity change is small, the deformation is small, and the deformation is large. The surface shrinkage deformation is restrained by the concrete, resulting in large tensile stress and cracks. The lower the relative humidity, the greater the shrinkage of the cement paste, and the easier it is to produce shrinkage cracks. Shrinkage cracks are mostly superficial parallel linear or net-like shallow cracks, with a width between 0.05 and 0.2 mm. They are more common in the plane parts of large-volume concrete, and are distributed along the short direction in thinner beams and slabs. Shrinkage cracks usually affect the impermeability of concrete, cause the corrosion of steel bars and affect the durability of concrete, and under the action of water pressure, hydraulic fracturing will affect the bearing capacity of concrete and so on. The shrinkage of concrete is mainly related to the water-cement ratio of concrete, the composition of cement, the amount of cement, the nature and amount of aggregate , and the amount of admixtures.