Exploring the Durability Specification of Coarse Aggregate Used in Airport Asphalt Mixtures

Coarse and fine aggregate constitutes approximately 93% of dense graded airport asphalt and the aggregate properties can affect asphalt surface performance. Despite a general trend towards performance-related specification of asphalt mixtures, prescriptive aggregate properties are generally still retained. This primarily reflects the absence of reliable performance-based laboratory test methods for determining the effect of aggregates on asphalt weathering and erosion. Historical airport asphalt specifications included a broad range of aggregate durability properties and the aggregate supply industry has questioned whether coarse aggregate durability testing can be simplified to combinations of just two properties. To determine whether a reduction in aggregate durability testing is appropriate for Australian airport asphalt, eight sources of aggregate were tested for wet strength, wet-dry strength variation, Los Angeles abrasion, sodium sulphate soundness and water absorption. The different tests were associated with different levels of variability and the correlation between the various tests results was generally low, except for Los Angeles abrasion and wet strength. The industry recommended combinations of aggregate durability testing were found to be inconsistent and ineffective. Consequently, the current range of aggregate durability tests must be retained. The only exception was the potential to omit Los Angeles abrasion when the wet strength is high. Furthermore, there was no significant difference between the results associated with the various coarse aggregate fraction sizes, indicating it may be appropriate to allow only one sized fraction per quarry source to be tested. Further work is required to correlate the various aggregate durability tests to asphalt field performance.