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Shrinkage crack in RCC slab can appear due to ________
1. Improper curing 
2. Improper loading
3. Improper formwork 
4. Improper mixing of concrete

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Correct Answer - Option 1 : Improper curing 

Concept:

If the proper curing is carried out as soon as initial set has taken place and is continued for at least 7 to 10 days then the initial shrinkage is comparatively less.

When the hardening of concrete takes place under moist environment there is initially some expansion which offsets a part of subsequent shrinkage.

So shrinkage crack in RCC slab can appear due to improper curing.

Other causes of Shrinkage crack in RCC slab-

Cement content – It increases with richness of mix

Water content – Greater the water quantity used in the mix, greater is the shrinkage.

Maximum size, grading & quality of aggregate – With use of largest possible max. size of aggregate in concrete and with good grading, requirement of water for desired workability is reduced, with consequent less shrinkage on drying due to reduction in porosity

Presence of excessive fines in aggregates – The presence of fines increases specific surface area of aggregate & consequently the water requirement for the desire workability, with increase in initial shrinkage.

Chemical composition of cement – Shrinkage is less for the cement having greater proportion of tri-calcium silicate and lower proportion of alkalis i.e. rapid hardening cement has greater shrinkage than ordinary port-land cement.

Temperature of fresh concrete and relative humidity of surroundings – With reduction in the surrounding temperature the requirement of water for the same slump/workability is reduced with subsequent reduction in shrinkage.

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