Proposed refinement of superpave high-temperature specification parameter for performance-graded binders

A semiempirical approach developed to predict the viscoelastic response of a binder in repeated creep recovery tests is described. This model provides an avenue to predict the rut resistance (R) as a function of loading (time and load) and temperature from data at a single frequency or frequency sweeps when needed. Thus, it can be used to develop a grading procedure for asphalt binders that not only accurately captures the delayed elasticity of modified binders but also accounts for the effect of traffic speed and traffic loading. The current Superpave binder specification attempts to capture the relative high-temperature performance (i.e., resistance to rut) of a binder via the inverse shear loss compliance, 1/J" or G*/sin delta, at 10 rad/s. This parameter represents an improvement over the absolute viscosity because it is measured at a defined rate of deformation and accounts to some degree for the viscoelasticity of the binder via the phase angle. The parameter would correctly predict the relative R for an ideally viscous (R alpha eta) material or an ideally elastic material (R = infinity). However, there is mounting evidence that at phase angles between 40degrees and 75degrees, the parameter may not fully capture the viscoelastic nature of many modified binders. Various authors have shown that the R of mixtures can be well described by models using data from dynamic creep experiments, in which the mix is subjected to a load followed by a relaxation period. More recently, Bahia proposed to capture their high-temperature performance by using a similar technique on neat binders.