Abstract
Traditional pavement design process involves limiting the strain on top of the subgrade layer to ensure that the pavement will not fail by rutting. The recently released Mechanistic-Empirical Pavement Design Guide (M-E PDG) and the associated „AASHTOWare Pavement ME Design” software of the United States considers permanent deformations in all the rut- susceptible layers (asphalt concrete and unbound granular material layers) on the overall cumulative rutting in the pavement. However, the rutting models incorporated in the design do not consider the influence of reduction of air voids during design life and the effect of confinement pressure.This investigation explores the influence of air voids reduction and confinement pressure on the rut depth prediction using AASHTOWare for a typical Indian pavement cross-section. An asphalt concrete mixture, Bituminous Concrete (Grade-1) confirming to the Ministry of Road Transport and Highways (MoRTH) specifications was cast at three air voids contents of 7, 4 and 2%. The dynamic moduli of these samples were determined at 5, 15, 20, 40 and 55°C for frequencies ranging from 0.01 to 25Hz at 0 and 200kPa confinement pressure. In addition, the dynamic modulus values of Dense Bituminous Macadam (Grade 2) mix at these temperature and frequencies for an air voids content of 4% were determined in the unconfined condition. A typical pavement cross-section as given in the Indian Roads Congress guidelines corresponding to 10% CBR and 150 msa traffic was chosen. Simulations were carried out for this pavement cross-section using the material properties measured for asphalt layers. Air voids and confinement pressure exhibited considerable influence on the rutting predicted for the asphalt layers of the pavement.While the AASHTOWare pavement design software may not be directly applicable to Indian conditions due to the use of considerable amount of data pertaining to USA and Canada, such exercise as carried out here, clearly showcases the limitations of the cross-sections used in India and provides guidelines on the directions India should take when it comes to material characterisation.
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