Linear Viscoelastic Domain for Bituminous Mixtures

It is widely admitted that the behaviour of bituminous materials may be considered as linear for small strain and becomes nonlinear when the strain (stress) amplitude level increases. In this research, the "small" nonlinearities (when the applied strain amplitudes are lower than about 10^-4 m/m) are investigated. An improved complex modulus test campaign has been carried out for a large range of temperatures and frequencies on two types of mixtures (GB3 and GB5®). From experimental results, nonlinearity of mixes is observed - even at small strain amplitudes - for both norm and phase angle of complex modulus. Nonlinearity evolution changes follow the considered values of temperature and frequency. A key output of the study is that the Time Temperature Superposition Principle (TTSP)is valid even in the nonlinear domain. A master curve of the estimated linear viscoelastic strain limit could be plotted as a function of equivalent frequency.