Asphalt concrete used in flexible highway pavements has 5-8% air voids immediately after laying of the roadway. Constitutive laws for asphalt concrete developed till now have modelled the mix as a linear elastic or viscoelastic material and have not taken into account the effect of voids concentration on the mechanical behaviour of the material. In the present study the theory of mixtures is used to model asphalt concrete. Asphalt concrete is considered to be a mixture of aggregate matrix, asphalt and air in a purely mechanical system in which the thermal effects and chemical reactions are ignored. Constitutive relation for each component of the mixture is assumed to be dependent only on the kinematical quantities associated with each component. The resulting hyperbolic conservation equations are solved by an upwind finite volume scheme coupled with an operator splitting technique for a quasi-static type of loading. The numerical scheme is used to simulate the variation of air voids content across the thickness of a typical road pavement.