Identifying non-linear HMA behaviour from uniaxial creep and dynamic modulus test results

Abstract

Viscoelastic materials can be characterised using a number of tests of which the most commonly used for hot–mix asphalt (HMA) are creep and dynamic sinusoidal loading. For linear viscoelastic materials, the information obtained from these tests is essentially the same as the creep compliance and dynamic modulus are mathematically related through the convolution integral. In this paper, the non–linear response of HMA is studied by comparing uniaxial creep compliance and dynamic modulus test results. It is observed that non–linear behaviour occurs at high temperatures/reduced time. The specimen deformation response in the dynamic modulus test is used to confirm that the observed differences between the creep compliance and dynamic modulus test results are due to non–linearity and not just experimental error. Non–linear behaviour causes frequency modulation of the deformation response signal. The signal frequency is therefore non–stationary as illustrated by the instantaneous frequency calculated using the Hilbert–Huang transform.