FLOW CHARACTERISTICS AND VISCOSITY FUNCTIONS IN ASPHALT BINDERS MODIFIED BY WAX

Warm mix asphalt (WMA), obtained by means of special bitumen modifiers, such as wax or other organic additives, represents a promising technical solution to reduce the temperatures required for asphalt production and pavement construction. In this experience, an extended program of rheological analyses was carried out in order to evaluate the effects of different type of wax on bitumen viscous flow and dynamic properties at high pavement service temperatures. Five different organic additives, including both natural and synthetic waxes, were considered and eleven bitumen-wax blends were produced and studied using rheological testing. Viscosity measurements performed in the domain of the mixing and paving temperatures have shown essential changes in binders' rheological behavior mainly due to the crytallizing/melting properties of waxes. Changes in viscosity functions depended on the chemical structure of wax as well as on its physical characteristice. However, the viscosity of all blends at 120C was lower than the viscosity of the base bitumen and the consequent redutions in mixing and compaction temperatures were quantitatively evaluated for all binders. The study of the flow characteristics of the bitumen-wax blends at high pavement service temperatures was carried out using complex viscosity master curves evaluated in the linear viscoelastic domain. Increasing resistance to viscous deformation referable to wax modifications was recorded by analyzing viscoelastic properties in the low frequency domain and different contributions were found with regard to each type of wax. For the polyamidic wax-modified binders, the results indicated the presence of a complex behavior characterized by the absence of a Newtonian region of flow. The final contribution of the experience is related to the development of wax modification of asphalt binders in order to produce WMA for pavement engineering applications.