Concrete Cracking
Concrete Cracking
(OP)
What causes concrete to crack, expansion or contraction? Does concreet expand enough to caused cracking due to heaving?
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RE: Concrete Cracking
RE: Concrete Cracking
If the slab was on a pure, frictionless surface, i.e. grease or teflon -no cracks.
RE: Concrete Cracking
RE: Concrete Cracking
As JAE noted, shrinkage cracks only develop from restraint. Unfortunately, almost all concrete placements have some restraint, either from friction at the subgrade interface or from geometry. In general, expansion does not cause cracking. If expansion is extensive, heaving of thin sections can occur, or in drastic cases, shearing will occur at joints in thick sections.
See FAQ in Concrete Engineering Forum for additional info.
RE: Concrete Cracking
also cracking causes would be increased heat of hydration due to excessive cement, poor mix proportions .
diagonal crack-diagonal tension,
web shear crack, and secondary cracks in web are commonin flexural memebers.
regds
Raj
RE: Concrete Cracking
1. Shrinkage crack occurs due to the differential shrinkage between the free and the constrained portions of concrete. Shrinkage occurs when the free water available in excess of the water consumed in hydration of cement evaporates. This shrinkage is prevented by the friction on the constrained surfaces.
2. Three is also thermal cracking occuring in thick concrete masses due to temperature gradient caused by dissipation of heat of hydration. In thick sections, the exposed surfaces cool faster and they act as insulating layers thus preventing the heat of hydration generated in the interior portions from dissipation. This causes a temperature gradient across the section, causing the cracking of concrete. This is minimized by controlling the temperature during placement by chilling of the course aggregates before placement or adding ice cubes to the aggregate so that the steep temperature gradient is avoided.
The above cracks occur during the curing period and before the concrete gets loaded.