Abstract Manager

The primary objective of developing laboratory-produced asphalt mix designs is to establish conditions that as best as practicable replicate plant production, field laydown and compaction, and quality control and assurance processes. The ability to replicate these conditions provides confidence that the asphalt mixture will demonstrate similar material qualities in both the laboratory and field and will provide the selected performance characteristics. Recent experience suggests current asphalt mix design processes do not always provide material characteristics correlating to those produced in the field following plant production and laydown. This paper presents the findings of a study investigating laboratory testing variability of key asphalt mix properties and how this variability could influence quality, performance, and overall cost of asphalt production.

A study was undertaken in 10 laboratories across 7 Canadian provinces and territories to compare the potential variability of 5 key metrics employed in asphalt mix design: 1) fine aggregate specific gravity, 2) coarse aggregate specific gravity, 3) Theoretical Maximum Specific Gravity of uncompacted asphalt, 4) bulk specific gravity of compacted asphalt, and 5) addition of dust in the lab to replicate the inadvertent creation of dust by the plant.

The study focused on three key components of each of the five mix design metrics:

1) How test property variation in the lab compares to measured material property in the field.

2) How potential test property variability can influence mix design performance in the field.

3) Potential economic implications of the inherent variability.

Asphalt mix and aggregate from a single source was sent to 10 independent laboratories for evaluation. Outcomes from the study for the five key metrics were compiled and reviewed. A summary of resultant variability is presented with commentary on the potential biases that may exist within a specific test type or testing procedure between independent laboratories.

These performance metrics studied are arguably the most impactful as they are used in the volumetric calculations in quality control and assurance reporting. Combined, these metrics are used to calculate optimal binder content and absorption and represent the strength, flexibility, and durability of the asphalt mix over its intended lifespan. Testing that accurately represents in-place conditions can result in a more cost-efficient mix design.