Causes Of Distress In Cement Concrete Pavement On Black Cotton Soil And Remedy

Abstract

Black Cotton (BC) soil is present in large parts of India. This soil absorbs lot of water while getting wet and swells even more than 50% which is called Free Swelling Index (FSI). If swelling is prevented, it exerts lot of pressure on the pavement and causes all types of cracks. The CBR of this soil is between 2% to 3.5%. Indian design guidelines provide for Cement Concrete Pavement (CCP), a minimum of 8% CBR for subgrade. While constructing CCP on BC soils special precautions are needed, otherwise distresses will develop. If the new pavement is to be constructed, the remedy lies in removal of the BC soil up to a depth of about 2m from Natural Ground Level (NGL), and treating the underlying soil in construction prism with lime and cement ensuring 12% CBR and 98% compaction. In this case study a 10m wide CCP was built on existing 7m wide flexible pavement by removing the bituminous layer overlaid with Granular Sub-base and Roller Compacted Concrete. Fresh shoulders 1.5m wide on each side were added. The road failed prematurely. Study involved investigation of reasons for the failure of CCP on a highway. The distress is found to be in the form of wide and long longitudinal cracks with faulting at a few places, as well as transverse cracks, multiple cracks and corner breaks in some panels. In-situ stabilisation of Black Cotton Soil is suggested as an effective remedy to mitigate the problem to a large extent.