Quasi-static characterisation of asphalt mixtures
A modern road pavement is a highly complex structure. Paving materials can exhibit non-linear and time dependent material properties whilst subjected to complicated three-dimensional loading conditions that are functions of the specific construction of each pavement. Nevertheless, empirical or linear elastic techniques, which cannot fully describe such factors, are often used in road engineering to assess pavement deterioration. An alternative approach is the use of finite element techniques, incorporating more complex constitutive models, to describe the response of asphalts and other paving materials. This thesis is concerned with the experimental determination of the model parameters necessary for the characterisation of two UK asphalt mixtures, for use in a dynamic plasticity based constitutive model to simulate paving material response. The constitutive model is under development at Delft University of Technology in the Netherlands, where it will be implemented in a three-dimensional finite element code. The thesis describes the constitutive framework for the material response model. It also details the experimental work and numerical verification undertaken in the study to enable the determination of the basic model parameters required to describe a 10 mm dense bitumen macadam and 30/10 hot rolled asphalt mixture, for use in the constitutive model. The characterisation of the mixtures has been undertaken through a series of quasi-static uniaxial compression and tension tests, which due to the significant influence of strain rate and temperature on the response of the asphaltic materials, were undertaken over a range of displacement rates and temperatures. Through specification of key model parameters as functions of material strength, temperature and strain rate, and the development of relationships describing the hardening and softening characteristic of the mixtures, the constitutive model has been successfully utilised to simulate the temperature and rate dependent stress-strain response of the asphalt mixtures to compressive loads.