Why Concrete Cracks?
Generally, it is assumed that cracks are due to some problems in the foundation, whereas it is not always correct and should not be considered failure
of structure or improper design or bad quality work.
Generally, 1/16 to 1/4-inch-wide cracks is acceptable limits. Even the best construction and concreting cannot prevent cracking in concrete, and 0% cracks is unrealistic.
Causes of cracks in concrete can be summarized as:
- Concrete expands and shrinks due to temperature differences
- Settlement of structure
- Due to load applied
- Due to loss of water from concrete surface shrinkage occurs
- Insufficient vibration at the time of laying the concrete
- Improper cover provided during concreting
- High water cement ratio to increase workability
- Due to corrosion of reinforcement steel
Types of Cracks in Concrete
The following figure shows types of cracks in concrete:
How to Prevent Cracks in Concrete Structures?
Preventive measures to avoid creation of cracks:
Preventive measures must be taken at the time of concreting and later to reduce cracks after concrete formation. Main factors are:
(1) Reduce Water Content in Concrete:
Water cement ratio affects the quality of concrete in no small way. W/C ratio is weight of water to the weight of cement used. A lower w/c ratio leads to high strength in concrete and lesser cracks.
W/C ratio shall not exceed 0.5 in concreting, which reduces the workability of concrete which can be covered by use of plasticizer or superplasticizer. Less water content increases the durability of concrete
Concrete expands and shrinks with changes in moisture and temperature. The overall tendency is to shrink. Shrinkage is the main cause of cracks, when concrete hardens it evaporates the excess water and thus shrinks, so lesser the water content, lesser is the shrinkage.
Shrinkage in slabs is ½ inch per 100 ft. The shrinkage of concrete pulls the slab apart showing it as cracks on surface.
To Be Continued....
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