CHARACTERIZATION AND DESIGN ANALYSIS OF BITUMINOUS PAVEMENTS --PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON THE STRUCTURAL DESIGN OF ASPHALT PAVEMENTS HELD DEFLT UNIVERSITY OF TECHNOLOGY, AUGUST 23-26 1982. VOL 1 AND 2. -- NETHERLANDS

With rapid motorisation and industrialisation in India, bituminous pavement surfacings are becoming more and more common in the country. However, the design of bituminous pavement layers is still based on adhoc experience and empirical strength tests. This paper aims at developing an analytical method of design for bituminous pavements based on more realistic strength characterization tests simulating the stress environment in the pavement layer under actual traffic loads. Three types of bituminous pavement specifications commonly used in India viz bituminous concrete, bitumen bound macadam and sheet asphalt as recommended by the Indian roads congress (irc) have been included in the study. Water bound macadam comprising crushed stone aggregate/overburnt brick aggregate was employed as a base course. Local roorkee soil (i.s. Classification -sm) represented the subgrade soil. Stiffness moduli of pavement component materials were determined by the conventional triaxial tests. In certain cases where horizontal stresses developed at the bottom of the bituminous layers under traffic loads are tensile in nature, the stiffness modulus may be different from the case where the horizontal radial stresses are in compression. In order to simulate the radial stresses in tension, thick hollow cylindrical triaxial specimens were cast and tested under axial compression. Radial tension was simulated by inducing water pressure inside the central hole. Analysis of results of all pavement materials tested indicates nonlinear relationship between strength modulus and applied stress. Since stiffness is also dependent on duration of loading, creep tests in tension as well as compression have been carried out. The creep compliance is also dependent on stress level as well as duration of loading. Semi-full scale pavement sections were installed in the pavement testing laboratory employing the local soil as subgrade and the wbm and various bituminous specifications as the base and surface courses. Over each combination of base course/subgrade, three different thicknesses of bituminous pavement layers of each specification were installed and the load-deformation and pressure transmission characteristics of the pavement system were observed under static plate loads simulating the traffic loads. The results of semi-full scale testing exhibit supremacy of bituminous concrete layer over bitumen bound macadam and sheet asphalt in terms of its greater resistance to surface deformation and better pressure transmission characteristics. Axisymmetric finite element model has been developed for a multilayer pavement system which is based on the non-linear elastic stress-strain behaviour of the pavement component materials under simulated traffic loads. The stiffness of pavement materials as determined from laboratory characterization tests are used as design input into the analytical model to predict the load response.