Using a single test to determine specific gravity and absorption of aggregate blends

The ability to measure the specific gravity of an aggregate accurately and consistently is paramount to transportation materials engineers. Current standard test methods (AASHTO T-84 and T-85) typically are not used for routine quality control purposes because of long testing times and questions about variability. Among new techniques developed for measuring specific gravity and absorption is a vacuum-sealing method, which eliminates the need for long soaking periods and for determining aggregate mass in a saturated-surface-dry moisture state. The vacuum-sealing method also has the potential to measure the specific gravity of a blend of aggregates in a single test. Specific gravity and absorption of six coarse and four fine aggregates composed of various mineralogy types were measured by both traditional and vacuum-seal methods. Ten blends, whose gradations generally met Superpave(R) hot-mix asphalt specifications, were created by using various combinations of aggregates and tested in a single vacuum-seal test. Five replicate tests were done on all individual aggregates and blends. Aggregate-blend single-test results (specific gravity and absorption) were compared with values obtained with traditional individual test results and mathematical combinations. The comparisons yielded generally strong correlations among methods, indicating the vacuum-seal procedure has promise as a relatively rapid method for determining specific gravity and absorption in a single test of an aggregate blend. However, some real differences in test values suggest that the vacuum-seal method needs refinement before it can be seamlessly substituted for traditional methods.