HOW TO IMPROVE THE FOUNDATION UNDER THE CONCRETE PAVEMENT, LIABLE TO CRACK OVER A YIELDING AND FLEXIBLE BASE , WHEN LOADED.

It is very essential to have a good solid foundation of the non observative material under the concrete road .A concrete slab, being a rigid type of Construction , is liable to crack over a yielding and flexible base when loaded .The most important property of the required base or subgrade is its equal bearing strength all over the surface. The load carrying capacity of a concrete road Structure lies mainly in the structural rigidity of the slab and the uniformity of the subgrade support .It is therefore necessary to prepare the base in such a way that the concrete slabs are supported as uniformly as possible . Subgrade failure is a common cause of cracking. Except for WBM the base of the concrete pavement should be made smooth before laying the concrete so as to reduce the coefficient of friction between the concrete slab and the base .The width of the base should project at least 30 cm 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 or longitudinal slopes must be given and there should be no soft spots present either in the base or the subgrade.plate bearing test should be followed brought to the value of 5.5 kg /cu. cm .10 cm thick concrete slabs laid over 15 cm well consolidated existing WBM crust have been found adequate to stand an axle load of 8100 kg . Theoretically ,7.5 cm thickness 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 is 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.