Across Canada, roads are being expected to meet higher performance expectations. Heavier traffic loads, intensified freeze–thaw cycles and a warming climate are placing unprecedented stresses on pavement structures. At the same time, highway agencies face increasing pressure to reduce environmental impacts, extend service life and control long-term costs. These challenges have converged into a single, pressing question: how can we build asphalt pavements that are both more durable and more sustainable?

High-performance asphalt concrete (HPAC) has emerged as one of the most promising answers. Unlike conventional hot-mix asphalt, HPAC is engineered to deliver superior resistance to rutting, cracking and long-term aging. Recent Canadian research is now demonstrating that HPAC can be achieved not only through expensive polymer-modified binders, but also by repurposing waste and low-value materials already available in abundance. By intelligently combining by-product asphaltenes from oil sands processing with recycled polyethylene terephthalate (PET) fibres, researchers are redefining what resilient, climate-ready pavements can look like.

Rethinking the Role of Asphalt Binder

Asphalt mix performance depends on the interactions among aggregates, asphalt binder and the mixture structure, with the binder playing an important role in temperature sensitivity and durability. In cold regions such as Canada, asphalt binders must strike a delicate balance: stiff enough at high temperatures to resist rutting, yet flexible enough at low temperatures to avoid cracking. Traditional polymer-modified binders can achieve this balance, but they come at a high cost and may suffer from storage stability and phase separation issues.

An alternative approach gaining attention is the use of asphaltenes, high-molecular-weight fractions recovered as a by-product during oil sands bitumen upgrading and refining that currently has limited commercial value. However, when blended into conventional asphalt binders, asphaltenes significantly increases binder stiffness and high-temperature performance.

Laboratory studies conducted at the University of Alberta in Canada have shown that adding approximately 12 per cent asphaltenes by binder weight can elevate a typical performance grade (PG) 70 binder to a much stiffer grade suitable for high-modulus and high-performance applications, i.e. PG 82. This stiffness gain translates directly into improved rutting resistance and structural capacity, critical attributes for heavily trafficked corridors.

Yet stiffness alone is not enough. Increasing binder stiffness often comes at the expense of cracking resistance, particularly at low and intermediate temperatures. Without mitigation, asphaltenes-modified binders may become more brittle, increasing the risk of thermal and fatigue cracking. Addressing this trade-off has been a central focus of recent HPAC research.

Fibre Reinforcement: A Simple Idea with Powerful Effects

Fibre reinforcement is not new to pavement engineering, but its role has evolved. Historically, fibres were used primarily to control drain down in stone mastic asphalt. Today, fibres are increasingly recognized as mechanical reinforcements that can bridge cracks, redistribute stresses and enhance energy dissipation within asphalt mixtures.

Among the many fibre types explored, glass, basalt, aramid and cellulose, polyethylene terephthalate (PET) fibres stand out for both performance and sustainability. Derived from recycled plastic bottles, PET fibres offer high tensile strength, excellent thermal stability and strong resistance to chemical degradation in the context of pavement engineering. Just as importantly, they provide a practical recycling pathway for one of the world’s most prevalent plastic waste streams.

In asphalt mixtures, PET fibres act as microscopic reinforcements. When cracks initiate, fibres resist crack opening and promote pull-out mechanisms rather than brittle fracture. This process absorbs energy and delays crack propagation, particularly under repeated traffic loading and temperature cycling.

Why Fibre Length Matters

While fibre dosage has been widely studied, fibre length has received far less attention, yet it plays a critical role in performance. Fibres that are too short may not effectively bridge cracks, while excessively long fibres can clump during mixing, leading to poor dispersion and construction challenges.

Recent research at the University of Alberta has systematically examined PET fibre lengths ranging from 6 to 18 mm in HPAC mixtures containing asphaltenes-modified binders. The results are compelling. Among the tested lengths, 12-mm PET fibres consistently delivered the best balance of performance.

At intermediate temperatures, mixtures reinforced with 12-mm fibres showed the highest cracking tolerance index and fracture energy, indicating superior resistance to crack initiation and growth. At low temperatures, the same fibre length provided significant gains in fracture energy and tensile strength, even when tested well below freezing. Shorter fibres improved performance compared to unreinforced mixtures, but not to the same extent. Longer fibres offered no additional benefit and, in some cases, introduced dispersion challenges.

These findings highlight a crucial lesson for practitioners: fibre reinforcement is not a one-size-fits-all solution. Optimizing fibre length is essential to unlocking the full performance potential of HPAC.

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