Cracking
Summary
Cracking - Often associated with the restraint to shrinkage.
Technical Information
There is a risk of cracking in all concrete floors. This risk increases with the size of the bays and distance between stress relief joints. There is a higher risk of cracks in jointless floors than in jointed floors, but in comparison to joints and their associated maintenance an acceptance of some cracking in a jointless floor might be considered to be preferable. Pile-supported floors, constructed in large areas with fewer stress relief joints, have a higher risk of cracking.
Cracking is often associated with the restraint to shrinkage, fine cracks generally having no structural significance. Less commonly, cracks can occur because of overloading or structural inadequacy, and some restraint-induced cracks could have structural implications because of their position in relation to applied loads.
The earlier the loads are applied, the greater the risk of cracking due to restraint to shrinkage and/or load-induced stresses. Loading at an early age will cause pinning of the slab to the sub-base. This can be mitigated by consideration of the following:
- Racking should remain unloaded for as long a period as possible.
- Loads should be partial and evenly spread.
- Loading should follow the floor bay construction sequence, oldest first.
- Phased loading from the centre of the bays outwards is advisable.
- Avoidance of bolting any base-plates that straddle joints.
Related Definitions
Crack Surveys , Wearing Slab , Expansion , Thermal Cracking , ContractionResources
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