This paper presents the results of an experimental investigation that focused on the failure properties of asphalt binders at low temperatures. A novel test method was developed, based on the use of the dynamic shear rheometer equipped with 4 mm parallel plates. The method entails the application of constant shear strain rates at various temperatures until failure. Test data are modelled by means of the elasticviscoelastic correspondence principle and by thereafter referring to the shear stress at failure, to a purposely defined brittleness index and to a critical brittleness temperature. Results discussed in the paper, which refer to a preliminary set of experimental data, indicate that the proposed methodology may be very effective in evaluating and comparing low temperature failure properties of asphalt binders of various types and origins.

The research described in this paper deals with the experimental evaluation and modeling of physical hardening in asphalt binders. The term physical hardening refers to a reversible phenomenon occurring at low temperatures that causes time-dependent changes in viscoelastic properties. The experimental approach, followed to quantitatively assess physical hardening, was based on flexural creep tests carried out by means of the Bending Beam Rheometer at various temperatures and conditioning times. The results obtained confirmed that hardening phenomena have a significant influence on the creep response of asphalt binders, to an extent that can be quantitatively assessed by referring to the appropriate rheological parameters and by applying the loading time–conditioning time superposition principle. The experimental data were fitted to a mechanical model proposed in the literature (composed of a single Kelvin–Voigt element) and thereafter to an improved model (with two Kelvin–Voigt elements in series). Both models were assessed in terms of their prediction accuracy. The improved model was found to better describe physical hardening effects in the case of both short- and long-term conditioning. Practical implications of the study were finally highlighted by referring to possible ranking criteria to be introduced in acceptance procedures for the comparative evaluation of asphalt binders.

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