Good mixes, better evidence

Asphalt mix design in Ontario is good. It has produced pavements that perform well under demanding traffic and climate conditions, and the industry has built real technical depth around the Superpave volumetric framework over the past three decades.

So, when agencies and contractors started seeing premature cracking on pavements that met every specification requirement, it was worth paying attention to. The mix design was approved. The volumetrics were fine. The paving was done properly. And yet, a few years in, the surface was showing distress that nothing in the design process predicted. That pattern, consistent enough across enough jurisdictions to be hard to ignore, is what is driving interest in balanced mix design (BMD) here in Ontario and across North America.

The idea behind BMD is this: instead of designing an asphalt mix to meet volumetric targets and trusting that performance will follow, you add performance tests that directly measure how the mix behaves under the conditions that determine its service life. That includes rutting, cracking, moisture damage, and fatigue, evaluated in ways that are relevant to the climate, traffic, and position of the mix within the pavement structure. BMD does not replace volumetric design. It builds on it.

Where volumetrics falls short

Superpave was never meant to stop at volumetrics. The Strategic Highway Research Program (SHRP) that produced it in the early 1990s did include performance and strength testing recommendations. Those tests were set aside during implementation, judged at the time to be too complex or too equipment-intensive for routine use. The volumetric framework that remained, air void content, voids in the mineral aggregate (VMA), and voids filled with asphalt (VFA), served well, and the industry built considerable experience around it.

But volumetric parameters describe the geometry of a compacted specimen. They do not measure how that specimen responds to repeated loading at high temperatures, or how it fractures under thermal stress in a cold January in Sudbury. In a sense, BMD is the industry returning to something it always intended to do, with better tools and more field experience to draw on. As the Federal Highway Administration (FHWA) has documented across its regional BMD peer exchanges, a growing number of state agencies are reporting premature cracking in pavements that met every volumetric target.²

RAP is a big part of the conversation

Much of the practical motivation for performance testing comes down to the use of Reclaimed Asphalt Pavement (RAP). RAP is abundant in Ontario. Good Roads’ annual paving report, produced in collaboration with the Ontario Asphalt Pavement Council (OAPC) and the Municipal Engineers Association (MEA), estimates the province’s total RAP inventory at approximately 3.7 million tonnes, with current municipal utilization rates so low that the stockpile would take roughly 19 years to deplete.³ Under the current Ontario Provincial Standard Specification (OPSS), RAP is capped at 15 per cent in surface course mixtures and 30 per cent in base course.⁴

Those limits exist for a reason. As RAP content increases in the asphalt mix, the aged and oxidized binder in RAP material stiffens the blend in ways that volumetrics does not fully capture. Rutting resistance may improve, but resistance to low-temperature and fatigue cracking can be compromised if the design does not account for these effects. Performance testing gives mix designers a direct way to evaluate the tradeoffs in high-RAP mixes, and it gives agencies a technical basis for approving those designs.

What Ontario is actually doing

The Ministry of Transportation of Ontario (MTO) has been clear that the province will not move to full BMD and mix performance testing (MPT) without retaining volumetrics and binder-grade testing alongside it, and that more study is needed before implementation.⁵ That is the right approach. Several U.S. states that moved quickly to adopt BMD specifications reported instances where lab-designed mixes passed performance criteria but failed during plant production.⁶ Building the correlation data and lab capacity before setting the specifications is exactly the kind of groundwork that avoids those problems.

What this means going forward

For contractors, the conversation about asphalt mix quality is going to evolve. Volumetric compliance will remain necessary, but whether it remains sufficient on its own is what is being worked out now. Contractors who want to propose higher RAP contents, or who are working with additives or modified binders, will find that performance testing is the tool that makes that case on technical grounds. That is worth understanding early, because building in-house capacity to run and interpret these tests is not something that happens in a single paving season.

For owners and agency engineers, BMD offers more direct assurance that what is being specified will actually perform over the design life, and it provides a technical framework for evaluating higher RAP contents and innovative mix approaches that volumetrics alone cannot fully support. It also connects to the sustainability accounting that procurement processes are beginning to require, as Environmental Product Declaration (EPD) frameworks and RAP crediting increasingly intersect with how mixes are evaluated. Getting the threshold values right for Ontario’s climate and materials is the work that has to happen next, and it has to be done here, with Ontario data. 

Sources

1. AASHTO PP 105-20, Standard Practice for Balanced Mix Design. AASHTO, 2020. Via NAPA: asphaltpavement.org/expertise/engineering/resources/bmd-resource-guide
2. FHWA, Balanced Asphalt Mix Design: Eight Tasks for Implementation. FHWA-HIF-22-048, 2022. fhwa.dot.gov/pavement/asphalt/amdbmd/
3. Good Roads, OAPC, and MEA. 2025 Ontario Paving and RAP Report. Good Roads, 2025. goodroads.ca/news_articles/2025pavingreport/
4. Ontario Provincial Standard Specification OPSS.MUNI 310, Material Specification for Hot Mix Asphalt. Ontario Ministry of Transportation.
5. MTO-OAPC Hot Mix Asphalt Subcommittee. Meeting Notes, December 5, 2024. Ontario Ministry of Transportation Technical Consultation Portal. tcp.mto.gov.on.ca
6. FHWA. 2023 Rocky Mountain West Peer Exchange on BMD: Outcomes and Summary. FHWA-HIF-23-029, 2023. fhwa.dot.gov/pavement/asphalt/amdbmd/