BASE OF CONCRETE PAVEMENT SHOULD BE MADE SMOOTH, BEFORE LAYING THE CONCRETE SO AS TO REDUCE THE CO-EFFICIENT OF FRICTION BETWEEN THE CONCRETE SLAB AND THE BASE.

CEMENT CONCRETE ROADS :-- It is very essential to have a good solid foundation of well consolidated and non -absorptive materials under a concrete road .A concrete slab , being a rigid type of construction,is liable to crack over a yielding and flexible base when loaded .The sub grade support is necessary to bearing the load and subgrade failure is a common cause of cracking and subsequently tilting or the disruption of the slab as such the base ,sub base or subgrade together act as a unit for supporting the concrete pavement.Except for WBM ,the base of concrete pavement should be made smooth before laying the concrete so as to reduce the co-efficient of friction between the concrete slab and the base. The width of the base should project out atleast 30 centimetres beyond the proposed edge of the concrete slab if kerbs are not set on the slabs .The base under the concrete pavement must be properly levelled,hollow patches filled up and consolidated with hard core ,cambered , and cross falls and longitudinal slopes given .There should be no soft spots in the base or subgrade.The base can one of the following (1) One layer of WBM over a layer of soling stones filled with sand and for which a minimum depth of fifteen cm of metalling or 22.5 cm thickness of metalling and soling combined.(11) Two layers of WBM under the action of water ,well consolidated and when a concrete pavement is laid over a WBM surface,the concrete slab is bonded with the rough and uneven surface of the WBM base .To obtain a good bond ,the surface of this base should be well cleaned with wire brushes to a depth of about 15 to 20 mm so as to remove all loose materials and clean surface of the WBM may be given a wash of cement slurry prior to laying the concrete @2.75 kg of cement/sqm.Ten cm concrete slabs laid over 15 cm well consolidated existing WBM crust have been found adequate to stand an axle load of 8100 kg (or single wheel load of 4100 kg) . Theoretically 7.5 cm thickness of slab is too small for this intensity of load but the endurance of these slabs may be due to the bonding of the slabs to the existing road which virtually increases the thickness of the slab, and also due to the higher modulus of subgrade reaction of the thick and consolidated old road crust .These slabs are without reinforcement.( For concrete pavements the minimum modulus of subgrade reaction of the under surface (base or subgrade) obtained with a plate bearing test should be 5.5kg /cu. cm.