Lessons Learned from 60 Years of Pavement Trials in Continental Climate Regions of Canada and Future Perspective
During the early 1960s,Canadian road authorities began using stiffer asphalt to address the issue of early rutting in the wheel track zone of asphalt pavements,which was caused by the growing traffic volumes.Pavements constructed with stiffer asphalt commonly exhibit evenly spaced transverse cracks due to the significant internal stresses caused by low temperatures and the inadequate resistance of the asphalt to cracking under such conditions.Research conducted on asphalt pavements with cracks caused by low temperatures has verified the significant impact of asphalt's consistency,temperature sensitivity,phase uniformity,and durability.In order to tackle the difficulties presented by the utilization of modified asphalt in the current asphalt performance evaluation system,the Canadian asphalt pavement test section during the 1990s was used to examine and assess the dependability of the U.S.Superpave™ specification.The results reveal that blown asphalt exhibits inadequate durability,while polymer modifiers only improve the durability of soft asphalt.In the early 21st century,the Ontario municipality commissioned studies on asphalt pavement test sections to enhance the current asphalt performance test specifications.These studies mainly considered the occurrences of phase separation,phase transformation,and thermally reversible aging(gelation)of asphalt,as well as the impact of polymers and fibers on the durability of asphalt.The results find that using different types of colloids(sol,gel,and sol-gel)in the same Superpave level can result in asphalt pavements with benefit/cost ratios varying by up to 2‒3 times.By assessing and choosing the appropriate type of asphalt,such as Alberta oil sand asphalt(sol),the service life of asphalt pavements can be prolonged.Compared with polymer-modified asphalt with high content,more oxidized recycled asphalt,or asphalt with higher wax content(gel),Alberta oil sand asphalt has lower wax content.The service life of asphalt pavements can be further improved by incorporating small quantities of polymer or fiber modification.Improved test specifications for asphalt cement will help save costs and meet the maintenance needs of 25 million km of asphalt pavements under global climate change.On the basis of summarizing the research of asphalt pavement trials in Canada in the past 60 years,new prospects and suggestions on the future research content and key technical problems of pavements in cold areas are put forward,which can provide a reference for future research.
pavement test sectionasphalt specificationrheological typeslife-cycle cost analysislong-life pavement