The use of warm mix asphalt (WMA) in the construction of Ontario highways is gaining momentum.
But there are challenges that have to be met and learning curves asphalt plant operators and contractors have to master, said the keynote speaker at the Ontario Asphalt Pavement Council’s (OAPC) recent fall seminar.
The hot mix technical service manager for The Miller Group and a member of several OAPC committees, Justin Baxter stressed the need for the industry and the Ministry of Transportation to collaborate as they negotiate through the provisions and requirements of a soon-to-be published specification document.
Known as Non-Standard Specific Provisions (NSSP) 0029, it sets the stage for an implementation plan for the wider use of WMA on provincial highways.
WMA technology allows for asphalt mixes to be produced in conventional asphalt plants at considerably lower temperatures than current standard hot mix asphalt with the result being less fuel is used and less greenhouse gases emitted.
In the production of traditional hot mix asphalt, the technology can also be used to improve compaction, extend the paving season, and increase long haul distances, although there is no greenhouse gas emission reductions.
But asphalt plant operators and contractors have faced some hurdles and operational barriers in using it. At the urging of and with input by OAPC, the Ministry of Transportation began working on the NSSP earlier this year. This past June the council sent a letter of support to the ministry, with a couple of key recommendations.
“WMA asphalt should be ministry driven and clearly specified in low-bid tenders in order to encourage its use,” the letter stated.
Another point was that the task of measuring and reporting emission data should be conducted by an environmental consultant.
Explaining the specification’s provisions and requirements and how the industry can adapt to them was the purpose of Baxter’s presentation, which was called A Collaborative Approach to Warm Mix Implementation — A Contractor/Producer Perspective.
“There is a need to continue working together through this as partners,” said Baxter, referring to both the industry and ministry.
As an example, he pointed out the ministry has taken into account many of the issues raised by the OAPC, most notably asphalt plant start-up challenges.
The maximum temperature for producing WMA is set at 130 C or at least 20 degrees below the production temperature of the control hot mix and not exceeding 150 C. But the ministry is prepared to allow a 15-degree increase above that threshold for a maximum one-hour start-up period, he said.
“In my mind this (exception) demonstrates the ministry recognizes the operational challenges involved in delivering this product and shows how they are willing to work with the industry to ensure that implementation is successful. It (the one-hour temperature increase) is a realistic identification of a challenge and a pragmatic approach to finding a workable solution.”
If production temperatures were to exceed the maximum allowable temperature, the mix would be deemed non-conforming.
Still, the ministry is prepared to make an allowance.
The non-conforming mix would still be accepted, but the contractor would be penalized with a three per cent payment discount penalty, he said.
The NSSP recognizes five warm mix technologies (CWM, Evotherm M1, Rediset LQ-1200A, WarmGrip N1, Zycotherm SP2) and the contractor would have the flexibility of choosing which one they wanted to use, he said.
A critical component of the NSSP is that projects involving the use of WMA would require a series of emission measurements plus moisture and performance tests.
To be conducted at both the asphalt plant and jobsite by an environmental consultant, the testing would include details such as visual observations of emissions from asphalt pavement hoppers and plant operational data such as production and fuel rates.
“There would also be control tests with sections of hot mix asphalt for a true performance comparison.”
But this testing shouldn’t be any more onerous than the scores of other tests contractors conduct on projects, said Baxter, who also believes most Ontario plants are capable of producing WMA.
“We’re known for our adaptability.”
Meeting and overcoming the challenge of warm mix implementation is not unlike society’s rapid, and successful, pivot from in-person conferences and meetings to ZOOM ones and webinars in the face of the pandemic, Baxter told the virtual audience.
“Interesting enough I have noticed the industry, as most others, have adapted quickly to conducting our business remotely or at least the communication part of the work. If we can employ the same adaptability in implementing WMA, we will be in good shape.”
Later in the meeting, a second speaker stressed that advances have been made in the utilization of WMA. More than 1.5 million tonnes of WMA have been paved on provincial highway since 2008, said Ministry of Transportation’s bituminous section head Gelu Vasiliu.
Nine to 10-year performance tests of WMA test sections compared to hot mix asphalt control sections have shown both are performing equally, said Vasiliu.
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