By Amma Wakefield, P.Eng.

Asphalt mix design is a delicate process of choosing and balancing the appropriate aggregates, asphalt binder and their proportions to obtain an asphalt mixture that is deformation resistant, fatigue resistant, low temperature crack resistant, durable, moisture damage resistant, skid resistant and workable.

The quality of the asphalt mix and its ability to perform is evaluated through set parameters for aggregates, asphalt binder, recycled materials and volumetric properties such as: Air voids (Pa), Voids in Mineral Aggregate (VMA), Voids Filled with Asphalt (VFA), and dust proportion. The parameters are set because they have historically provided a good indication of a mixture’s probable performance.

By Mike Anderson, P.E.

Since 2005 the Asphalt Institute (AI) has coordinated a little-known (even in the world of asphalt) proficiency sample program for roofing asphalt binders. The idea started with Paramount Petroleum who coordinated nine round-robin studies from 1999 to 2003.

Those studies focused on four common tests used by labs involved in testing roofing asphalt binders: Cleveland Open Cup (COC) Flash Point, Ring and Ball (R&B) softening point, penetration at 77°F (25°C), and rotational viscosity at 400°F (204°C). In 2004, AI agreed to assume the responsibility of continuing the program.