Lessons learned from 60 years of pavement trials in continental climate regions of Canada

Abstract

In the early 1960s, increasing traffic demanded that transportation agencies use progressively harder asphalt binders to prevent premature wheel path rutting. Using stiffer binders increased stress from cold temperature shrinkage, typically manifesting, for the first time, as rather regularly spaced transverse cracks. Trials to investigate this phenomenon confirmed the importance of binder consistency, temperature sensitivity, phase homogeneity and durability. Studies in the 1990s focused on evaluating the new Superpave™ specification, developed in the United States, to address the increasing use of modified binders in preceding decades. Air-blown materials were found to perform poorly and polymer modifiers only provided benefits in softer grades. Current trials, commissioned by the Ontario government in the 2000s, were designed to refine binder specification tests, by accounting for well-documented phase separation and transformation, associated thermoreversible changes in rheology (gel formation), and to investigate high polymer and fiber modification. Benefit/cost ratios vary by 2–3 fold for test sections of equal Superpave design but different rheological type (sol, sol/gel or gel). Long-life pavements can be designed through a judicious and balanced choice of binder properties. Albertan binders of high phase angle (sol-type), which are low in wax and modified with small amounts of polymer or fiber, outperform less stable materials, such as those with too much polymer, oxidized residue, or wax (gel-type). Improved binder specification will provide substantial savings and prepare the world’s 25 million kilometers of asphalt pavements for climate change.