Toward High Performance Asphalt Concrete (HPAC) for Cold
Climates: From a Material Viewpoint to Pavement Behaviour

Fatigue is one of the principal failure modes observed in pavement structures. One way to improve bituminous pavement fatigue performance is by reducing pavement deflection, which  can be done by increasing the stiffness of the asphalt base layer(s).

To minimize fatigue damage to the asphalt mixture and optimize pavement performance, a new type of asphalt mixture called EME, with a high modulus and good fatigue resistance, was introduced in France in early 1980s. EME mixes are usually produced with very hard bitumen (10–20, 15–25 or 20–30 pen). Specifications for EME mixes require very high stiffness, as  much as 14,000 MPa at 15°C and 10 Hz, with high fatigue performance. Until now, this technology has not been available in cold regions because of poor performance at low temperatures.

In cold regions, asphalt mixtures are usually designed with relatively soft bitumen to prevent
thermal cracking. Hard bitumen grades, such as those used in Europe to produce EME mixes, did not meet low temperature requirements for North American applications and  could therefore not be used in cold regions. The challenge for cold regions is to adapt traditional EME mix designs to improve low temperature resistance. Various avenues could  be explored to accomplish this. One possibility is to optimize the aggregate mix skeleton and use a new bitumen type based on a softened bitumen modified by adding polymer(s)  and/or additive(s) to extend the useable range 2 (new PG grade). These types of asphalt  concrete mixes, with high fatigue and low-temperature resistance, combined with a high  modulus, will be designated High Performances Asphalt Concrete, or HPAC.