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For the past number of years the Michigan State Highway Dept. has been investigating voids in bituminous mixtures. During this study a method was developed which consists of placing a bituminous mixture in a large pycnometer and introducing a solvent that dissolves the asphalt, thereby liberating the air voids in the mass. From the weights of the sample and the solvent used, the specific gravity of the voidless bituminous mixture can be determined by calculation. The pycnometer consists of a 1000-ml Erlenmeyer flask with a 1 1/2-in. ground glass opening in which is fitted a top with a restricted neck for more precise volume measurement. Volume measurements must be precisely controlled at specific temperatures in order to minimize errors due to the thermal volume changes of the solvent. The paper describes the procedure and illustrates the calculation. Data are presented to show the repeatability of the method on the different types of materials from which bituminous mixtures are normally made. Also a comparison is made with the conventional method of determining specific gravity of aggregates.
Serafin, Paul J.
Bituminous Testing Engineer, State Highway Laboratory, Ann Arbor, Mich.