Bulk Specific Gravity Measurements of 25.0-mm and 37.5-mm Coarse-Graded Superpave Mixes

Abstract

The measurement of specific gravity for hot-mix asphalt (HMA) is critical to almost every activity pertaining to asphalt mixtures. During design and construction, the bulk specific gravity (Gmb) of HMA mixes is used to calculate many properties that indicate pavement quality. Thus, it is important to measure this property accurately and precisely. This study evaluated four methods for measuring Gmb, including the traditional saturated surface dry (SSD) method, the CoreLok method, the height-diameter method, and the CoreReader method. Four aggregate sources were used to create mix designs for 25.0-mm and 37.5-mm nominal maximum aggregate sizes (NMASs). In addition, the level of compactive effort was varied to assess the comparisons for a range of air voids. Results indicate that the traditional method exhibited the lowest levels of variability. Strong correlations were developed to relate the test methods on the basis of the large NMASs. The strongest and most practical relationship was developed between the SSD and CoreLok methods. These models can be used to assess the effects of incorporating new test methods for both design and construction procedures. They can also be used to normalize data from different test methods, should alternative methods be desired. Although some recommend the use of an alternative test method (such as CoreLok), the studies on which these recommendations are based did not include large NMAS mixes (25.0 mm and 37.5 mm). Although alternative methods do possess significant advantages, the results of this study do not support the elimination of the traditional Gmb test method.