Low temperature performance of asphalt binders: New specification grading methods and improved polymer-modified systems

The goal of this thesis was to provide more insight into the low temperature failure mechanisms experienced by pavements in cold climates. It was an attempt to identify and correct those aspects that were relevant to thermal cracking and that were not adequately addressed in the current specifications. Further more, new polymer-modified binders with improved low-temperature properties were successfully designed and characterized.; Steps were taken towards the finalization of a new fracture mechanics based asphalt grading method. This included the development of a new mould that decreased the amount of material required for one test by approximately 90 percent. The starter notch was reduced to only a few microns thick ensuring that the sample is tested under the, most severe conditions. The results correlated well with the field performance of test sections constructed in Canada, showing that the newly proposed method offers a viable alternative to the currently used grading protocols.; A second project investigated the effect of physical hardening on asphalt pavements. Field correlation studies showed that physical hardening explains many of the observed field performances. A method was developed to assess the physical ageing susceptibility of asphalt binders. The method was accepted by the Ministry of Transportation of Ontario as a new laboratory standard under the designation "LS-308 Laboratory Standard for Determination of Performance Grade of Physically Aged Asphalt Cements Using the Extended BBR Method". Physical hardening is an important factor and binders that would harden excessively and would thus be prone to early cracking should be identified and eliminated.; The final part of this thesis dealt with the development of new polymer-modified systems with improved fracture properties. Fifteen different binders were prepared, some using methods available in the patent literature and others according to a new method developed at Queen's University. The performance in terms of resistance to fracture varied widely among the binders investigated. Two particular binders made according to the new method showed significant improvement in performance. The improvement was as high as a 250% increase in fracture toughness and a 10 and 15 fold increase in fracture energy compared to the control.