Influence of loading amplitude on viscoelastic properties of bitumen, mastic and bituminous mixtures

Abstract

Bituminous materials are considered as linear viscoelastic for a small number of applied cycles at low strain amplitudes. Their behaviour can be represented considering the complex modulus and the complex Poisson’s ratio (isotropic case), which are obtained for sinusoidal loading. These two properties are independent of strain/stress amplitude in the case of linear viscoelasticity (LVE). However, when increasing amplitude, nonlinearity induces a strain dependence of the measured complex modulus. This paper investigates the phenomenon of nonlinearity in bitumen, mastic and bituminous mixture (BM). Strain amplitude sweep (SAS) tests were performed at different temperatures and frequencies. From LVE characterisation results, it was possible to observe relationships between the rheological behaviours of bitumen, mastic and bituminous mixture. Nonlinearity results show that BM presents non-negligible nonlinearity even for very small strain (few tens of µm/m). Nonlinearity effect is temperature- and frequency- dependent. The LVE limit decreases with temperature for BM and increases for bitumen and mastic. LVE limit in terms of stress amplitude changes following the same factor for all materials, suggesting that the nonlinearity observed on bituminous mixtures is inherited from the bitumen.