The structure of polymer modified binders and corresponding asphalt mixtures

As a part of the Strategic Highway Research Program (SHRP), the Danish Road Institute has developed an optical method for evaluation of asphalt mixtures by microscopy of thin and plane sections. The method is based on the technique used to examine and characterize the microstructure of Portland Cement Concrete. In this study, the preparation technique has been modified, making it possible to examine the structure of the polymer modified binder directly in the asphalt mixture. The structure is observed under a microscope with UV-light by illuminating the surface of cut and polished specimens of the asphalt mixture prepared as thin or plane sections. The polymers used were SBS and EVA type polymers. It is important to be able to examine the structure of the polymer modified binder in the asphalt mixture since the chemical interaction and structural build-up of the polymer phase is influenced by several factors. It is well known that mechanical treatment and mixing temperature affect the quality of the polymer modified binder. In addition, the cooling rate influences how the polymer structurizes in the binder during placement and compaction of the final asphalt pavement. The polymer modified binder will be subjected to oxidation and degradation during mixing, storage and transportation of the hot mix asphalt. This, together with chemical interactions of the polymer phase and the surface of the mineral aggregates, will greatly affect the structure of the polymer modified binder and finally the performance of the asphalt mixture. This effect is impossible to predict by only looking at the structure of the pure polymer modified binder. Consequently, it is not sufficient to know the structure of the pure polymer modified binder before mixing with aggregates. It is also necessary to know the structure of the polymer modified binder in the final asphalt mixture, since each mixture has undergone its own special shown in color during the technical session. It was not possible to publish these in color. Please contact the authors if you wish to obtain a set of the color slides.