Evaluation of New Test Procedures for Determining Bulk Specific Gravity of Fine Aggregate by Automated Methods

Two automated methods were evaluated for determining the dry bulk specific gravity (G_sb) of fine aggregates: Thermolyne SSDetect and InstroTek CoreLok. Each proposed method was evaluated against the standard method described in AASHTO T-84. The evaluation was based on a round-robin study with 12 laboratories and six materials, four crushed fine and two uncrushed (natural) fine aggregate sources. The CoreLok and SSDetect methods of determining fine aggregate specific gravity offer significant timesavings over AASHTO T-84. Both the CoreLok and SSDetect methods generally produce G_sb results similar to AASHTO T-84. It is believed that AASHTO T-84 may not produce accurate results for angular materials with high dust contents. More frequent statistical differences exist between the CoreLok and SSDetect apparent specific gravity (G_sa) and water absorption results than those produced by AASHTO T-84. However, G_sa and water absorption are not used in volumetric calculations for hot-mix asphalt. SSDetect offers improved precision over AASHTO T-84. The precision of the CoreLok method is slightly worse than that of AASHTO T-84, but it is expected to improve as technicians become more familiar with the procedure.