A material exhibits a thixotropic behaviour if its apparent viscosity decreases in time under stress, and if it progressively recovers its initial viscosity when the stress is released. Methods for characterizing thixotropy for fluids are relatively well known, the situation is more difficult for viscoelastic materials. For bituminous binders, it corresponds to a decrease of material stiffness under cyclic loading by modification of its internal structure and to a recovery of this stiffness after rest. This property has been highlighted by simple shear tests, carried out using a controlled stress rheometer. An experimental procedure has been defined for studying the thixotropic behaviour of binders in dynamic mode. Then, it has allowed describing the corresponding curves of complex modulus versus the set stress and the rest period at different conditioning times of samples. This study has also permitted to demonstrate that stiffness variations are linked to re-arrangement of molecular structure and not to cracks formation and healing. Finally, based on specific indicators, it has been possible to compare different bituminous binders in order to estimate the ability of materials to restore their internal structures.
