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Constant inspection, diligence needed for asphalt: expert

Dan O'Reilly
Constant inspection, diligence needed for asphalt: expert

In a day-long program featuring a diverse number of speakers, the need for continuous improvement, research, testing and innovation was the overarching theme of the Ontario Asphalt Pavement Council’s (OAPC) recent fall seminar.

In a keynote address, David Newcomb, principal investigator with the Texas A&M Transportation Institute, called for constant inspection and vigilance, keeping up to date with new technology and advances in machinery and equipment, plus avoiding the trap of becoming too lax.

“Do your homework. Sometimes I think we can all do a better job,” he told the approximately 450 delegates, noting that preparation and planning can avoid a lot of onsite mistakes.

“When you go out and look at the surface (of the asphalt) see the cracks below the surface.”

Newcomb defined homework as the use of preconstruction evaluations to uncover surface defects and subsurface conditions as well as to gauge material integrity.

Doing homework was at the top of his Top Ten List for More Durable Pavements presentation. Other pointers on that list included aiming for higher density, ensuring uniformity and consistency in asphalt mixes, preparing the surface correctly and using Reclaimed Asphalt Pavement (RAP) responsibly.

“We need to treat it (RAP) like any other material. It’s a resource not a waste,” he said.

RAP is produced by milling, a process that eliminates surface defects and creates a level pavement.

“Mill to the bottom of the cracks,” said Newcomb, linking that suggestion back to the need to properly prepare the surface.

Another one of his warnings was to avoid “five minute screw ups.” To underscore that message, he showed an image of a portion of his own street where there was gravel instead of asphalt pavement. An investigation revealed that a roller had actually gone over the curb.

 

The choice of procedure and solvent type used in the test method can have an impact

— Amma Wakefield

The Asphalt Institute

 

 

Preparation, planning, testing and monitoring are the key for more effective designs and better constructed roads, said Newcomb, who predicted there will be a greater use of constructability reviews. These are third-party audits or techniques to review construction projects before they actually commence to identify potential obstacles and problems.

An advocate for using higher asphalt content in mixes, he also said the use of performance tests to define asphalt content will become more important.

Immediately following that presentation, the Asphalt Institute’s Canadian regional engineer Amma Wakefield gave the OAPC audience both a progress update and a closeup view of the methodologies being used in a University of Waterloo study intended to measure the properties and performance of asphalt by analyzing “recovered” asphalt collected from eight highway construction sites in 2017.

The research involves reversing the mixing process with the use of a solvent so that the asphalt cement components are separated from each other and can then be individually tested for load bearing and cracking properties.

Wakefield is the lead researcher on the study, which is jointly sponsored by the university’s Centre for Pavement and Transportation Technology and OAPC and includes the participation of a number of independent testing laboratories.

“The choice of procedure and solvent type used in the test method can have an impact on the resulting physical properties of the recovered asphalt. However, most specifications don’t identify one extraction-recovery test method,” said Wakefield, in summarizing just one of the findings to date.

In an interview after the conference, Wakefield said a final report will be submitted to the OAPC sometime next spring. The council will use it as an information package when dealing with Ministry of Transportation and municipal governments.

Two other speakers also kept the spotlight on research and innovation by highlighting their respective organizations’ efforts of incorporating fibres into hot mix asphalt pavements to make roads stronger and last longer.

A number of different fibres have been used by the Ministry of Transportation and since 2016 it has tendered 10 contracts for aramid fibre-reinforced asphalt pavement trial sections, said bituminous section head Pamela Marks.

“Toronto Pearson International Airport is the busiest airport in Canada,” said Greater Toronto Airports Authority senior civil engineer Kevin Chee, pointing out there were more than 465,000 aircraft movements in 2017.

To prevent distress to the asphalt, the authority retained SNC-Lavalin to carry out an evaluation program to design and study a Superpave mix (P-401) using three different types of aggregates “which are commonly available in Ontario with and without (the) aramid fibre.”

As part of the study, three-fibre enhanced Superpave mixes were placed down on a taxiway earlier in 2018. They will be monitored on a long-term basis, said Chee.

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