Advanced constitutive modelling of bituminous materials

Abstract

Currently in the UK, the mechanical properties of bituminous (asphalt) mixtures are determined by means of a suite of tests (stiffness modulus, resistance to permanent deformation and resistance to fatigue cracking) performed by means of a pneumatic apparatus known as the Nottingham Asphalt Tester (NAT). This paper presents a methodology for an alternative experimental characterisation and modelling procedure for bituminous (asphalt) mixtures using a dynamic plasticity based constitutive model. The paper briefly describes the material response model and details the monotonic, uniaxial compression and tension testing at various temperatures and strain rates that are necessary to determine the basic model parameters. Two standard UK wearing course mixtures have been included in the testing programme comprising a continuously graded, Dense Bitumen Macadam (DBM), and a gap graded, Hot Rolled Asphalt (HRA). The uniaxial test data has been used to determine mathematical functions for the compressive and tensile strengths of the asphalt mixtures as well as functions describing their hardening and softening behaviour. Plots of the flow surface (or yield surface) have been produced for both mixtures over a range of temperatures and strain rates and the model has been successfully used to simulate the compressive response of asphalt mixtures. Once implemented in a finite element code, the constitutive model has been able to simulate the damage occurring in a flexible bituminous pavement under traffic loading.