The five common reasons for concrete cracking are as follows:

1. Excess water in the mix

2. Concrete drying too fast

3. Improper strength concrete poured on the job 4. Lack of control joints (in concrete slab)

5. Foundations poured in the winter

please find the link below for further details

http://www.wisecracks.com/5-reasons-concrete-cracks/

In order to prevent concrete for cracking some of the Preventive Control Measures are as follows:

distress in concrete structure is cracking of concrete