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10 ways to get the most out of your mix

OAPC mapped the path to asphalt excellence at the annual Good Roads Conference.

July 8, 2024  By  Jack Burton


Photo: jimfeng / E+ / Getty Images

Celebrating its 150th year, the Good Roads Annual Conference landed at Toronto’s Fairmont Royal York from April 21 to 24.

The event connected municipal leaders with key suppliers and decision-makers in all things transportation infrastructure, with a trade show floor of 120-plus booths as well as appearances from provincial political leaders such as Premier Doug Ford and the Ontario Liberal Party’s Bonnie Crombie. 

The Ontario Asphalt Pavement Council (OPAC) presented a panel discussion on hot-mix asphalt (HMA) best practices for maximizing project effectiveness and road longevity in its technical briefing session titled “The Quality of Asphalt in Ontario.”

OAPC’s board chair Steve Manolis, of GIP’s materials engineering division, past chair Peter Hamstra of Dufferin Construction and vice chair Christopher Campbell of Imperial Oil were joined by Middlesex, Ont.’s county engineer Chris Traini to explain and explore a list of the top 10 ways to get more durable asphalt pavements.

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1. Do your homework
For Peter Hamstra, knowledge is power in ensuring durable asphalt mixes. Before making any decisions, he recommended collecting a solid foundation of data on the project at hand, including the existing conditions, ideal thickness and the appropriate mix for the project’s goals. 

“Starting by doing a proper pavement design is the first thing: understanding your subsurface, what the soil type is and the drainage is important,” said Peter Hamstra. “If it’s a rehab or an overlay, you need to look at the existing pavement layer to see what’s going on there – is it rutting, is it cracking? These are all things that will help to determine the type of treatment that you’re going to do, and what type of mix you need.”

Result-driving data is not just limited to pre-project circumstances, but should also be based on the long-term intentions of the project and the appropriate maintenance, said Hamstra.

“The other thing is thinking ahead about your future maintenance on this road: what are you anticipating this road is going to need in 10, 20 or 30 years? Will it be something that you’re going to want to mill and resurface? Is it something that you’re going to do a cold recycle on?”

2. Encourage mixes that have higher asphalt concrete (AC) content
Chris Traini spoke to the decades of experience – and success – that Middlesex County has experienced in applying HMA mixes with a higher AC ratio. 

“We’ve seen a marked improvement in the life of our asphalt pavements, especially in our rural areas, where the small bump in the cost of providing a richer asphalt mix gave us an extended life in years – in some cases, five to seven years of additional life, on average. That means we’re seeing roads we don’t have to touch for 20 to 23 years.”

This increased longevity, Traini explained, comes from the protective benefits that increased AC provides against common sources of wear, such as weather and extended UV exposure. 

“The enemy to the durability and longevity of asphalt pavements is the sun and its ultraviolet light, and the breakdown it causes over time,” he said. “If you have a well-constructed road, a small bump in your AC content can prevent the types of deficiencies we see in our pavements generally caused by the degradation of the asphalt itself.”

Middlesex county engineer Chris Traini and OAPC board members Peter Hamstra, Steve Manolis and Christopher Campbell discussed how to maximize durability in your HMA mixes at this year’s Good Roads conference, with Doubra Ambaiowei moderating the panel.

3. Specify a finer gradation for your mix type
Another adjustment to HMA mixes for extra mileage on your road projects is selecting finer sizes of aggregate when possible, said Steve Manolis, especially when a higher AC content is also being employed. 

“We found through experience that fine-graded mixes, using smaller aggregate sizes, can be more durable and crack-resistant than their coarse-graded counterparts,” Manolis said. “One of the big reasons for this is that we can put a more effective amount of asphalt cement content into a fine-graded mix.”

While finer aggregate excels as a sidekick to higher AC ratios, these mixes also support durability by allowing a high degree of compaction to be applied, according to Manolis. 

“The other really important reason is that fine-graded mixes can be compacted, and are easier to compact than coarse-graded mixes. Compaction is hugely important to the pavement’s longevity: a well-compacted road is less permeable to air and less permeable to water, as these elements are less able to penetrate the pavement and cause the damage process.”

4. Don’t overheat the mix
“I think that one’s pretty self-explanatory: just don’t do it,” joked Traini.

Despite providing the ‘H’ in HMA mixes, keeping the heat below a high-degree threshold can prevent a range of longevity problems, including premature oxidization and cracking, he explained. 

“The thing to understand about hot mix asphalt paving is the key component – they’re hot. We need to dry our aggregates so that they effectively bind to the liquid, and we need to heat up our liquid asphalt high enough that its viscosity allows it to mix with the aggregates. But that extra heating you put in the liquid can be detrimental to the life of the liquid: you’re adding oxygen and making the asphalt a little bit more brittle.”

Being mindful of temperature can help in avoiding these high-heat drawbacks, but Traini also recommended looking toward using warm-mix asphalt (WMA) when possible, such as on late-season projects. 

5. Include adequate surface preparation in the plans
Proper time for surface preparation and examination is key in ensuring optimal smoothness in the finished roads, said Hamstra. 

Using finer aggregate blends in your mixes can help you get the most out of the compaction process, said the OAPC’s board chair, Steve Manolis.
Photo: Nastasic / E+ / Getty Images

“Any good road builder will realize that the surface mix you put on is only as good as what’s underneath it,” he said, adding that contracts should ensure that preparation processes can be carried out to an adequate degree. 

Following a number of pre-project steps before adding the mix, such as proper sloping, base solidity, examining for potential rutting and surface consistency and removing any loose materials, all make for a better asphalt application process and more importantly, a smoother road. 

6. Ensure adequate bond
Proper tack coat application, according to Manolis, “really is one of the simplest and most cost-effective ways we can employ to extend pavement [lifecycles.]”

By strongly bonding each layer, proper tack coat application increases performance and mitigates durability issues such as premature cracking and improper compaction. Manolis referenced studies from across North America that showed the impact of poorly-bonded layers on premature cracking, along with how strong bonding creates crack resistance. 

“Spraying the tack coat, which acts as a glue on the surface of the asphalt layer before being overlaid with the second lift, bonds the two layers together, and really makes them a strong and cohesive unit that resists cracking,” he said. 

7. Provide proper pavement density
Compacting the mix to the appropriate density supports durability across a number of practices, including proper coating application and creating the air space in the pavement needed for the material to adjust and adapt to weather effects, explained Chris Campbell.

“Obviously, HMA and WMA are combinations of aggregates, liquid and fillers that are all mixed together. Within that mixture, there are gaps and holes, and those holes are important, both in the sense that some liquid will get in there to ensure proper coating, but also, we need some of that air space so the liquid can expand and contract depending on the temperature and climate,” he said.

When miscalculated, an overly-loose density in the mixture can be too permeable and lead to increased oxidization and aging. For Campbell, finding the sweet spot means looking at the particulars and conditions of the mix, tools and demands of the location. 

“It’s about ensuring you understand what your mix design needs are for your area, that you understand the materials you’re using – the liquid type, and how the liquid interacts – and also the equipment you’re going to use in the field, the compaction methods the contractor is bringing to the table and the environment you’re trying to compact in.”

8. Produce mix that is uniform and consistent
A good road begins at the plant, according to Peter Hamstra, who emphasized that consistency in the production process creates consistency in mixes and, more importantly, road performance.

Christopher Campbell spoke of the benefits his company has seen from integrating on-site personnel into the quality assurance process.
Photo: kozmoat98 / E+ / Getty Images

“On the production side, we need to make sure that we’re running our plants consistently without a lot of starting and stopping, through things like making sure that your mixing speed is consistent with the material speed that’s coming into the plant, so you don’t have to stop making sure that your lay-down speed on the site is also consistent.”

Consistency in the production and output rate of plant-side mixing processes may support consistency in end results, but Hamstra highlighted that their impacts must also be tested for both before and after the mixing process. 

9. Use RAP responsibly
This focus on testing and quality assurance extends into the use of reclaimed asphalt pavements (RAP). When using RAP, Manolis urges all stakeholders to conduct proper testing to ensure the consistent results and yields necessary for it to be viewed as a viable alternative. 

“The design methodology and technology is fairly well understood. But the real key to this is a strong quality management program, both from the producer and the contractor side, and also on the municipality and owner side, to ensure that the mix is produced as per design.”

By ensuring that RAP is properly used to create good, durable roads, the industry can guarantee the enjoyment of RAP’s fiscal and environmental impacts for years to come.  

“It really is one of the most complex issues that we have, both for the industry and I think for all business owners today,” Manolis said. 

“The good news is it’s technically possible to incorporate appropriately-reclaimed asphalt pavement into pavements to achieve long-lasting and durable roads. This also has improved economic and environmental benefits.”

10. Complete QA testing and inspection
Investing in qualified technicians and inspectors to carry out proper quality assurance and inspection processes can help avoid a number of headaches regarding the long-term health of the road, along with any potential contract disputes arising from pavement performance, said Campbell.

“I can tell you that for a relatively small investment, [at Imperial Oil] we have likely prevented hundreds of claims or hundreds of challenges with our Canadian contractors by being able to provide a review in less than half a day of the AC content and the gradation of the asphalt that’s being placed on our roads,” Campbell said.

Imperial Oil’s QA strategy is multi-pronged, leveraging both the responsibilities of roadbuilding personnel and the goals of the project to ensure any problems in mix consistency are immediately dealt with, instead of deficiencies caught at the last minute setting projects back in both time and costs.

“We trained our inspectors to also act as lab techs, and we’ve dedicated resources to take asphalt samples first thing in the morning on a project, take them back to our shop, do a burn to determine AC content and do a gradation,” he said. 


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