What performance trait does the PG grading system primarily measure?

The PG grading system, which stands for Performance Grade, is designed to classify asphalt binders according to their performance characteristics at various temperatures and loading conditions. The primary focus of the PG grading system is to measure the binder's resistance to deformation at both high and low temperatures.

At high temperatures, a binder must resist flow and rutting under the stresses imposed by heavy traffic loads. Conversely, at low temperatures, it must maintain flexibility to avoid cracking. The PG grading system assigns specific grades based on the performance of the asphalt binder in these temperature ranges, ensuring that the selected binder will withstand the thermal and mechanical stresses encountered in specific geographic locations and climate conditions.

This emphasis on temperature-related performance is what makes the PG grading system critical for ensuring the longevity and effectiveness of hot mix asphalt pavement. Therefore, it serves as a guide for selecting the appropriate binder for the expected environmental conditions and traffic demands.