Research | Major Contributions

Since the early 1990s we have evaluated a large number of pavement trials in Ontario (see above) and elsewhere. Our efforts have consistently explained why certain test sections show no distress while others crack severely. We have been able to conclude from this that gradual, reversible hardening (aging) processes at cold temperatures, such as wax crystallization, asphaltene aggregation and free volume collapse, are likely causing early and excessive distress. In addition, we have shown that short term reversible aging strongly correlates with long term irreversible aging (oxidative hardening). Those asphalts that are unstable in a colloidal sense harden rapidly due to both physical and chemical processes. Where these are not at fault, poor brittle and ductile failure properties are often to blame.

Our 1996 Canadian Technical Asphalt Association (CTAA) paper with Joseph Ponniah of the Ontario Ministry of Transportation (MTO), Use of Fracture Energy in Performance-Based Specifications of Asphalt Binders, discusses and documents the start of this effort and won an Editors Award for Best Written Paper out of 25 submissions. Our 2004 CTAA paper with Kai Tam of MTO, Improved Approach to Low-Temperature and Fatigue Fracture Performance Grading of Asphalt Cements, discusses and documents the basic ideas behind what would later become a series of four standard test methods and won another Editors Award for Best Written Paper out of 25 submissions. This early work has led to the publication and acceptance by the MTO of four laboratory standards, and the inclusion of associated acceptance criteria in numerous paving contracts.

In addition to our work on pavement trials, we have also investigated numerous incidents of premature and excessive cracking in large contracts for the central, eastern and northeastern regions of Ontario (Highways 11, 401, 407, 416, 417, and many others). All of these were affected by significant transverse and wheel path distress after only a single or few winter(s) in service. Our findings were reported to the MTO and published in several peer reviewed papers. We recently discovered that ~70-80% of the premature and/or excessive cracking in Ontario contracts is associated with the addition of waste engine oil residues to the asphalt cement. Our 2012 paper, Waste Engine Oil Residue in Asphalt Cement by Hesp and Shurvell, as recently presented in Auckland, New Zealand, and published in the Proceedings of the 7th International Conference on Maintenance and Rehabilitation of Pavements (MAIREPAV7), won another Best Paper Award out of 32 submissions.

In 2002, MTO awarded a contract to rebuild a stretch of Highway 655 north of Timmins. The contract contained a provision for the inclusion of seven test sections, each 500 m in length. We were asked to design the trial with the goal of validating our specification tests. Although trials existed in other places, none had, side-by-side, six highly modified binders of exactly the same Superpave™ grade in an area where air temperatures regularly fall below -40°C. In addition, other trials have previously been designed with too many confounding variables. Hence, the sections on Highway 655 have the exact same design except for the varying compositions of asphalt cements under study. In 2004, just 4 months after construction, the air temperature reached a record low of -48°C for the area and fell below -40°C on an additional 7 days. The pavement reached -34°C on two days, which, according to the pavement design software, should only happen once in 50 years! Early observations have shown very significant performance differences between the seven binders: section 655-2 showed 233 meters of cracks, 655-3 showed 111 meters, 655-4 showed 437 meters, 655-6 showed 80 meters, and 655-7 showed 93 meters when surveyed in 2008. Only 655-1 has shown virtually no distress so far. In recognition of the fact that current specifications need to be improved, MTO commissioned three additional trials (Highways 417 (2006), 655 (Phase II, 2007) and 427 (2008)).

In collaboration with many individuals at MTO, we have explored the possibility of using fundamental material properties for performance prediction. This effort started with Imperial Oil, MTO and NSERC support in the early 1990s and has resulted in the publication of many papers and four laboratory standards: LS-228, LS-298, LS-299 and LS-308. Since 2007, LS-308 and LS-299 have been implemented for reporting and acceptance of the asphalt cement on large numbers of paving contracts for the City of Kingston and MTO worth in excess of $300 million.

Numerous research groups from around the world have since published papers on laboratory tests that our group originally developed for asphalt cement specification. A three-point bend fracture toughness test we developed was refined into a standard under the direction of the European Committee for Standardization (CEN/TS 15963:2010, available online for $86), which recently conducted successful round robin tests.