The 2016 auditor general’s report on the state of Ontario’s road infrastructure brought a lot of attention to hot mix asphalt pavement practices.
That focus, combined with concerns about how pavement performs on roads after being laboratory tested, is the catalyst for an intensive study now taking place at the University of Waterloo and multiple third-party testing laboratories across the province.
The review has been underway since last summer and will continue to 2019. The study is jointly sponsored by the university’s Centre for Pavement and Transportation Technology and the Ontario Asphalt Pavement Council (OAPC).
It is intended to measure the properties and performance of asphalt by analyzing “recovered” asphalt collected from eight highway construction sites earlier this year.
Asphalt cement is the “glue” that binds together the aggregate in an asphalt pavement mix which typically consists of five per cent asphalt cement and 95 per cent aggregate (stone, sand, gravel), says Steve Manolis, general manager of Coco Asphalt Engineering.
A member of OAPC’s technical committee, he was one of two industry representatives who elaborated on the study’s “why and how” at the council’s fall seminar in a Woodbridge-Ont. area convention centre.
Samples of liquid asphalt cement have been traditionally taken from asphalt mix plants and then tested for compliance to performance specifications such as the ability to resist deforming (or rutting) under heavy traffic loads in the summer.
Now some Ontario municipalities — although so far not the Ministry of Transportation — have added another layer of testing by sampling the actual asphalt mix or pavement with the intent of recovering the asphalt cement, he says.
This is a procedure where the mixing process is reversed with use of a solvent so the asphalt cement components are separated from each other and can then be individually tested for load bearing and cracking properties. But there are also a lot of variables to consider, he says.
“Some of the technical matters which need to be better understood are whether the properties of the recovered asphalt are the same as the original cement,” he explains.
“In other words, how does the extraction and recovery process change the properties of the asphalt cement?”
It’s also important to realize there is the potential for variable results between two laboratories using the same samples, he says.
In North America, there are two standardized test methods that serve as the basis for specification testing.
As part of the talk at the fall seminar, Manolis summarized the standard test methods published by the American Association of Testing Materials and the American Association of State Highway Transportation Officials which serves as the basis for specification testing in North America.
His presentation was followed by a second one on the actual study methodology by Amma Wakefield, the lead researcher and PhD candidate specializing in asphalt at the University of Waterloo.
“This study has a few phases, within an overarching objective to develop a framework to evaluate asphalt pavement and mixture properties to predict performance,” he says.
In the first phase, the researchers will be looking at how the recovery process impacts asphalt cement properties, while evaluating the variability in testing between laboratories.
Evaluating the asphalt mixes with performance tests that measure “fundamental material engineering properties” will be the objective of the second phase.
A long-term third phase to be conducted by the Ministry of Transportation, OAPC, and the research team will monitor the performance at the actual eight test sites and then compare the results with what is been observed in the laboratories, says Wakefield.
Recent Comments
comments for this post are closed