Reasons why the cracks can appear on any concrete surface

Hairline or Construction cracks can appear on concrete surface for various reasons.
These cracks, although small, can eventually become lager, causing problems with the entire concrete structure.
One of the reasons for hairlines to appear is when the concrete mixture is too dry while pouring (not enough water was added when mixture was being prepared).
Concrete mixture that is too dry is further harmed when poured in hot temperature (water content is evaporating too fast).
Concrete must be allowed to dry and cure at slow rate to prevent this problem. In such situation watering the fresh poured concrete might help to prevent cracks forming.
If the concrete is poured on the windy day the top surface dries quicker then at the core and that too can cause hairline cracks forming.
The cracks can also appear on the concrete surface if the ground is not prepared properly (uneven, not compacted).
Steel reinforcement not sitting properly on the plastic chairs can also cause concrete cracks. Steel should be sited 35mm from the top of the surface for the reinforcement to work properly.
Another reason for concrete cracks to appear is when the construction joints are not deep enough and not placed properly. Construction joints should be at least 25mm deep and on intervals 25 to 30 times the depth of the concrete.