Recommendations for Minimizing Poor Quality Coarse Aggregate in Asphalt Pavements

The Texas Department of Transportation has experienced problems with inconsistent performance of the coarse aggregate fraction of hotmix asphalt pavements. This project was initiated to address problems associated with variations in hotmix coarse aggregate quality. More specifically, the researchers wanted to identify simple tests that can be performed at the aggregate quarries to assess the durability of aggregates and determine what percentage of an aggregate is poor quality. The researchers surveyed civil engineering and geological literature to identify simple tests that can identify poor performing aggregates and can be performed in the field with a minimal amount of skill. Following the identification of potential tests, the researchers visited several quarries in Texas and used these techniques to differentiate good and poor quality coarse aggregates. The researchers identified several simple tests that inspectors can perform in the field to identify poor quality aggregates, including: aggregate angularity (more rounded = poorer quality), water absorption (more absorbed = poorer quality), hardness (soft = poorer quality), and fines content (more fines = poorer quality). Things that can be done at the aggregate quarries include: constructing smaller stockpiles, selective quarrying of good rock, and utilizing a wash system to remove some of the poorer quality aggregates. The preceeding tests and quarry recommendations can be utilized by inspectors to regulate the quality of coarse aggregate used in hotmix applications.