Rheological modeling of asphalt binder and asphalt mortar containing recycled asphalt material

The use of recycled materials in asphalt pavements has increased significantly over the years, with well-known environmental and economic benefits. However, the mechanism governing the interaction between the virgin asphalt binder and the aged binder contained in recycled asphalt pavement (RAP) is not entirely understood. In this paper, the effect of RAP on the rheological properties of asphalt binders and mortars was experimentally investigated and modeled with the objective of defining a relationship between the linear viscoelastic properties of binders and those of the corresponding mortars. First dynamic shear rheometer tests were performed on binders and mortars, prepared with a selected fraction of RAP, for measuring the complex modulus over a wide range of temperatures and frequencies. Then, the effective rheological properties of the combined virgin and RAP binder in the mortar were evaluated with a new approach based on a modified version of the Nielsen model, avoiding extraction and recovery. Finally, the material response was modeled using the analogical 2S2P1D model, consisting of one spring, two parabolic and one-dashpot elements combined in series and then assembled together with a second spring in parallel. A significant stiffening effect due to RAP was observed both on asphalt mortar complex modulus and on the corresponding asphalt binder parameter back-calculated with the modified Nielsen model. At the end, binder and mortar characteristic time, which is one of the 2S2P1D model parameter, was linked to the recycled material content through a simple exponential expression experimentally derived.