Concrete carriageway is  normally  classified  into  two  types:  Reinforced  and Unreinforced Concrete pavement.

The reinforcement in reinforced carriageway (in the form of mesh) is used for controlling cracking.Then one may query how unreinforced pavement can control cracking without the use of mesh reinforcement. 

To answer this question, one should pay attention to the features of unreinforced concrete pavement. In accordance with Highways Standard Drawing No. H1109 [kindly refer to Standard drawings for your area/country], an approximately 3mm wide groove with a depth of about one-third to one-fourth of slab thickness is designed with a  regular spacing (normally 5m) . The grooves are designed to be too narrow for stones to fall into when the cracks are open  due to concrete contraction. 

The sectional area in which the groove is located is a plane of weakness and thus this groove acts a potential crack-inducing device in  which  any  potential  cracks  due  to  shrinkage  and  thermal  contraction  may  form. Consequently, the cracks are formed at the base of the groove and thus it would not cause any  unpleasant  visual  appearance  on  the  exposed  surface  of  unreinforced   concrete pavement.