Concrete Crack Classification

(1) Structural stress cracks
Cracks in concrete structures under the action of load are called stress cracks. Ordinary concrete members may appear stress cracks when they bear 30% ~ 40% of the design load, and the ultimate failure load of such members is often more than 1.5 times of the design load value. Such cracks will not affect structural safety as long as the width meets the requirements of the code.
(2) Temperature crack
There are two reasons for temperature cracks. First, concrete produces temperature stress under the joint action of temperature deformation and constraint. When the temperature stress exceeds the structural resistance, cracks are produced. Second, after the concrete is heated, the physical and mechanical properties deteriorate, coupled with free water evaporation and cement stone dehydration shrinkage, will also produce cracks.
(3) dry shrinkage crack
When concrete hardens in the air, its volume will gradually shrink (dry shrinkage or contraction), and the cracks produced at this time are called dry shrinkage cracks. Dry shrinkage cracks are most common in the construction of concrete surface drying too fast, the surface of the member produces large tensile stress, when the tensile stress exceeds the ultimate tensile strength of concrete, that is, dry shrinkage cracks.
(4) Cracks caused by quality problems of raw materials
More common is the poor quality of raw materials such as cement or gravel, after the completion of concrete pouring, condensation process or use process due to insufficient strength, resulting in cracks.
(5) settlement crack
Settlement cracks are mostly caused by uneven and soft soil quality of structural foundation, or backfill soil is not solid or flooded and caused by uneven settlement. The crack width is usually proportional to the settlement amount, and the crack tends to be stable after the foundation deformation is stable.
(6) Construction cracks
Construction cracks cause, one is the concrete mix ratio is not allowed, the construction of any water or arbitrary increase in the strength of concrete. Second, the template construction scheme is improper, water leakage, leakage, template and support stiffness is insufficient. Third, inadequate curing of concrete, especially early curing quality. Four is the prefabricated structure of the installation sequence, installation process, welding process and other reasons.