We can call cracks always as the headache for civil engineer’s but it can be prevented if several measures are taken.
Generally cracks may form in plastic stage or in harden stage of concrete. In case of plastic stage the climate plays vital role,to prevent cracks in early stage of concreting you have to consider the temperature variation of that area and you may vary W/C ratio accordingly.
In area of high temperature one can use wet gunny bags after the intial setting is reached it will reduce the escape of water causing shrinkage cracks. And it will be better to concreting in early morning or evening as the temperature be low.
Good workmenship and proper supervision is necessary if you are preparing concrte manually of machine mix at site,and it is not required in ready mixed conrete.
Sometimes improper mixing conrete becomes porous and sometimes it becomes very stiff due to defficiency of water so that it must be mixed throughly as per mix desing.
If there is discontinuity in placing of concrete then the crack may form at that place so whenever discontinuity exist cement slurry must be poured up to 1 cm.
Removal of voids is also necessary for that compaction of fresh concrete must be done sufficiently and over compaction should be avoided.
Pozzolanic materials can be used and suitable admixutre can be added and nowadays there is many synthetic binders are available in market which will increase the tensile strength of concrete and it depends on work condition and desired quality of the work.
After all you have to take technical approach to avoid cracking of concrete and it includes
- Proper mix desing of concrete.
- Preparation of concrete according to mix desing
- Placing of concrete before final setting takes place and avoiding the free fall of concerete when placing.
- Sufficient compaction by adopting proper method.
- Providing minimum specified cover by IS code.
- Providing minimum reinforcements as per IS code.
- Arranging proper formwork for the specified duration with proper supports.
- By avoiding the placing of any load before final setting time.
- Proper curing for at least seven days.