Abstract
In the Marshall test, the percentage of air voids has been used as a basis to determine the asphalt content. But, it is not easy to determine accurately the value of air voids of a compacted asphalt mixture. According to the author's experience, it is not rare to have the case that the calculated value of air voids content becomes negative.
In this paper, in order to clarify the reason why the value of air voids content sometimes becomes too small an attempt was made to determine the effects of the following three factors on the calculated value of air voids content: (1) Method of measuring the volume of specimens, (2) method of measuring the specific gravity of aggregates, and (3) difference between the specified and the true asphalt content of compacted test specimens.
From the results of the investigation, the following conclusions were drawn.
(1) The method of measuring the volume of compacted specimens affects the calculated value of air voids content. A minimum value was obtained when the volume was measured with paraffin coating.
(2) The method of measuring the specific gravity of aggregates also affects the value of air voids content. A minimum value was obtained when the bulk specific gravity was used.
(3) When a large amount of asphalt is used, some of it adheres to the mixing and molding apparatus during the preparation of specimen. As the result, the value of air voids content calculated using the specified asphalt content is smaller than the true air voids.
