Effect of Aggregate Degradation on Volumetric Properties of Georgia's Hot-Mix Asphalt

• Published in: Transportation research record 2007-01, Vol.1998 (1), p.123-131
• Main Authors: Lynn, Todd, James, Robert S., Wu, Peter Y., Jared, David M.
• Format: Article
• Language: English
• ISSN: 0361-1981; 2169-4052
• DOI: 10.3141/1998-15

Various degrees of degradation of aggregate particles can occur in hot-mix asphalt (HMA) production during the mixing and compaction process. This breakdown may significantly increase the dust fraction of the aggregate gradation relative to that of laboratory specimens. This increased dust fraction could cause a loss of voids in the mineral aggregate (VMA) and air voids. After evaluation of 22 variations of HMA mixtures during production and construction, it was determined that aggregate degradation did result from plant mixing and field compaction activities. Aggregate degradation varied somewhat with respect to where the mixture was sampled within the production and construction processes. Aggregate degradation resulting from binder extraction that uses the ignition method, relative to the solvent extraction method, was also examined. Mixture volumetric properties (i.e., air voids and VMA) were significantly affected by aggregate degradation. On the basis of this study, before a volumetrics specification for mixture acceptance is investigated for future implementation in Georgia, a change in the Georgia Department of Transportation's mix design specification is recommended. The minimum VMA values for Superpave® mix design should be increased by 1% for all dense-graded mixes to compensate for the amount of aggregate degradation and loss of VMA during HMA production and construction. It is believed that this research-based policy change for mix design will better maintain the balance between proper durability and rut resistance of asphalt pavements in Georgia.