AN EVALUATION OF SELECTED METHODS FOR MEASURING THE BULK SPECIFIC GRAVITY OF COMPACTED HOT MIX ASPHALT (HMA) MIXES

The measurement of the bulk specific gravity of compacted hot mix asphalt (HMA) mixes is the basis for volumetric mix design and quality process control procedures. Among the items, which are dependent upon the measured mix bulk specific gravity, are air voids and voids in mineral aggregate. In this study, four methods of mix bulk specific gravity are evaluated. The methods include the water displacement, dimensional analysis, parafilm, and the vacuum sealing method. The evaluation consisted of measuring samples of the four mix types (fine and coarse Superpave, Stone Matrix Asphalt, and Open Graded Friction Course), three compactive efforts (low, medium, and high), and two aggregate types (limestone and granite). Additionally, all samples were cut into cubical shaped samples and the mix bulk specific gravity determination was repeated with all the methods. The results indicated that the vacuum sealing method appeared to provide the best measurement of the specific gravity of the samples in all instances. The ability of the other methods to accurate measure the specific gravity was found to be dependent upon the parameters (type, compactive effort, and sample state) of the mix being tested.