Polymers are added to asphalt binders primarily to stiffen the binder at higher
temperatures and thus to protect the pavement against rutting at summertime
temperatures early in the pavement's life. Also, it has been noted that polymers typically
increase the ductility of a binder and that some polymer-asphalt combinations are
especially effective. Furthermore, it is hypothesized that enhancing a binder's ductility,
and maintaining this enhancement with binder oxidative aging, contributes to enhanced
binder durability in pavements. However, polymer-asphalt interactions and how they
might contribute to improved binder performance is not well understood. The goal of
this work was to probe the relationship of polymer morphology on asphalt binder
rheology and mixture durability.
Experiments were conducted on asphalt mixtures and binders, and as a function
of oxidative aging. PFC mixtures, which are an open mixture designed to allow
enhanced water drainage, were of specific interest. These mixtures were tested for
Cantabro Loss, an indicator of a mixture's likelihood of failure by raveling. Asphalt
binders were tested using dynamic shear rheometry (DSR), which provided the DSR
function, (G' /η'/G'), a measure of binder stiffness that includes both the elastic modulus
and the flow viscosity), ductility (used to measure the elongation a binder could
withstand before failure), gel permeation chromatography (GPC), used to estimate the
relative amount of polymer) and fluorescence microscopy (used to image the polymer
morphology in the asphalt binder). From these data, relationships were assessed between binder morphology and
binder rheology and between binder rheology and mixture durability, all as a function of
binder oxidative aging. Polymer morphology related to ductility enhancement. Polymer
morphology related to a change in the DSR function, relative to the amount of polymer,
as measured by the polymer GPC peak height. Cantabro loss correlated to the DSR
function (R2=0.963). The overall conclusion is that polymer morphology, as indicated by
fluorescence microscopy, relates to both the rheological properties of the binder and the
Cantabro loss of the mixture. These relationships should yield a better understanding of
polymer modification, increased mixture durability (decreased raveling) and improved
rheological properties (DSR function and ductility)
