DSpace JSPUI

India has taken up an ambitious programme of construction of four-lane and six-lane national highway sections under the National Highway Development Programme. Several stretches of bituminous pavements constructed under this program have already been opened to traffic. Premature surface cracks were observed on some stretches within a year or two of construction and these cracks were found to initiate from top and progress downwards. These have been identified in literature as top-down cracking. Such cracking in bituminous pavements has also been reported to be a major mode of failure in many other countries. In the present study, an effort was made to examine the causes of the top-down cracking susceptibility of bituminous layers using 3D finite element analysis. Uniform contact pressure and circular tire contact area are usually considered for analysis of flexible pavements. For computing the mechanistic parameters at locations close to the pavement surface, it is necessary to consider realistic contact shape and pressure conditions. Evaluation of non-uniform contact stresses at the tyre-pavement interaction was made in this study by developing a 3-Dimensional finite element model considering typical properties of tyre components. The resulting distribution of surface stresses within the contact area was used for analysis. The finite element model developed in this study for analysis of bituminous pavements was validated by comparing the computed strains with measured surface strains. A number of pavement sections were analysed using the finite element model to evaluate the effect of different parameters on the top-down cracking susceptibility of bituminous pavements. Octahedral shear stress failure criterion was adopted to assess the top-down cracking potential. Bituminous pavements in most parts of India are subjected to high pavement temperatures, especially in summer. Temperature within the bituminous layers is not uniform. Temperature gradients within typical bituminous layers were measured in the field as well as in the laboratory. Different pavements were analysed for surface temperatures of 35°C, 45°C and 55°C. Similarly, the influence of heavy axle loads, different interface conditions of bituminous layers, surface tractive forces and binder type were considered for evaluation of top-down cracking susceptibility. It was seen from the analysis that the combination of high surface temperatures and soft binder grade is highly conducive to development of top-down cracking.