What are the causes of several cracks in concrete beams?
2. Causes of cracks in beams caused by concrete composition materials: Concrete shrinkage is an important reason for cracks, and the factors affecting concrete shrinkage are mainly aggregate varieties and contents. The size, shape and gradation of coarse aggregate itself do not affect the shrinkage of concrete; The elastic modulus of coarse aggregate has a great influence on the shrinkage of concrete: the greater the elastic modulus, the greater the inhibition on the shrinkage of concrete.
3. Concrete mixture ratio causes beam cracks: concrete mixture ratio, such as unit water consumption, unit cement consumption, water cement ratio, sand ratio, etc., has great influence on drying shrinkage. Their effects on drying shrinkage are: unit water consumption >; Unit cement dosage > water cement ratio > sand ratio.
4. Causes of cracks in beams caused by concrete curing: Prolonging the initial wet curing can only delay the drying shrinkage time, but it can not reduce the short-term drying shrinkage of concrete, but it has a certain impact on the final drying shrinkage value. If the concrete is cured in time at an early stage (mixed with fly ash 14d), the tensile strength of concrete can be effectively improved, and the carbonation depth of concrete outer surface can be reduced, thus reducing the shrinkage caused by carbonation of concrete.
5. Causes of cracks in beams caused by steel bar installation: For concrete cracks, steel bars play a role in limiting and restraining. The constraint of steel bars on concrete is mainly through the bond and friction between them.
6. Causes of cracks on the beam caused by formwork removal under surcharge: The early concrete strength was low (generally around 1.2MPa) and could not bear surcharge. Although theoretically, the slab's stacking load is all stressed by its formwork support system at this time, in practice, because the layout of the formwork keel is designed under the consideration of allowing the formwork panel to deform 1/250 (without considering the concentrated load force), cracks or "internal injuries" will inevitably appear at the concrete bottom of the slab under the action of large concentrated stacking load. If the formwork is removed too early, the concrete strength will not meet the requirements, and the load on the beam will have a destructive impact on the beam.