The primary objective of developing laboratory-produced asphalt mix designs is to establish conditions that as best as practicable replicate plant production, field operations, and quality 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. 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 11 laboratories across Canada to compare the potential variability of 5 key metrics employed in asphalt mix design: 1) fine aggregate relative density; 2) coarse aggregate relative density; 3) maximum relative density of uncompacted asphalt; 4) bulk relative density of compacted asphalt; and 5) addition of dust or baghouse fines in the lab to replicate the inadvertent creation of dust by the plant.
Outcomes from the study were compiled and reviewed and a summary is presented with commentary on the potential biases that may exist. The study concluded that there are variables in the basic materials testing we do that can have dramatic effects on asphalt mix design results and by better understanding and controlling those variables, asphalt mix designs can produce more repeatable results.
