This is because compaction reduces the volume of air in HMA. In-place air void measurements are used as a measure of compaction (Figure 2). In-place Density MeasurementĪs previously discussed, theoretical maximum specific gravity is needed to calculate air void content therefore, it is involved in in-place air void determination during HMA pavement construction. The volume is calculated by weighing the mass of the water displaced by the sample and dividing by the unit weight of water. The mass is determined by measuring the dry mass of the sample either at the beginning of the test or after it has been dried at the end of the test. The basic premise of the maximum specific gravity is to divide the mass of the sample by the volume of the sample excluding the air voids. It is also used to calculate the amount of asphalt absorbed in a HMA mixture (Vba), which is then used in determining the effective asphalt content (Pbe). Theoretical maximum specific gravity is used along with bulk specific gravity values from field cores and laboratory compacted specimens to calculate air voids and the in-place air voids of a HMA pavement. The theoretical maximum specific gravity test is integral to Superpave mix design as well as field quality assurance. Maximum theoretical specific gravity sample.
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