performancegrade

Performance grade, often abbreviated as PG, is a system used to classify asphalt binder by its anticipated performance under temperature conditions encountered in service. The grade is written as PG XX-YY, where XX is the high-temperature grade in degrees Celsius and YY is the low-temperature grade in degrees Celsius. For example, PG 64-22 indicates a binder intended to perform adequately up to high pavement temperatures of about 64°C and down to low temperatures of about -22°C.

The PG system was developed during the SHRP program in the 1990s and subsequently adopted into the Superpave asphalt binder specification administered by AASHTO. It intends to predict binder behavior under thermal stress: high-temperature performance relates to resistance to rutting and flow under hot conditions, while low-temperature performance relates to resistance to cracking in cold climates. The designation helps engineers select binders appropriate for the climate and traffic of a given project.

Determination of a PG grade relies on laboratory testing. High-temperature performance is evaluated with the Dynamic Shear Rheometer (DSR), which assesses stiffness and relaxation behavior at elevated temperatures. Low-temperature performance is evaluated with the Bending Beam Rheometer (BBR), which assesses creep stiffness at low temperatures. Aging potential and compatibility with aggregates may also influence the final grade selection.

Practically, engineers use climate data, such as mean daily maximum and minimum temperatures and extremes, to assign an appropriate PG grade for binders used in asphalt mixtures. While useful, the PG designation is one tool among many, and field performance depends on material formulation, mixing, placement, and environmental factors.