AASHTO T 326:05(2018) Standard Method of Test for Uncompacted Void Content of Coarse Aggregate (As Influenced by Particle Shape, Surface Texture, and Grading).
A calibrated cylindrical measure is filled with coarse aggregate of prescribed grading by allowing the sample to flow through a funnel from a fixed height into the measure. The coarse aggregate is struck off, and its mass is determined by weighing. Uncompacted void content is calculated as the difference between the volume of the cylindrical measure and the absolute volume of the coarse aggregate collected in the measure. Uncompacted void content is calculated using the bulk dry specific gravity of the coarse aggregate as received without special grading except as noted in Section 4.3.1. Two runs are made on each sample and the results arc averaged.
For a graded sample (Test Method A or C) the percent void content is determined directly, and the average value from two runs is reported.
3.1.2. For the individual size fractions (Test Method B), the mean percent void content is calculated using the results from tests of each of the three individual size fractions.
Methods A and B provide percent void content determined under standardized conditions, which depends on the particle shape and texture of a coarse aggregate. An increase in void content by these procedures indicates greater angularity, less sphericity, or rougher surface texture, or some combination of the three factors. A decrease in void content results is associated with more rounded, spherical, or smooth-surfaced coarse aggregates, or a combination of these factors.
4.2. Method C measures the uncompacted void Content of the fraction retained on a 4.75-mm (No. 4) sieve of the as-received material. This void content depends on grading as well as particle shape and texture.
4.3. The void content determined on the standard graded sample (Method A) is not directly comparable with the average void content of the three individual size fractions from the same sample tested separately (Method B). A sample consisting of single-size particles will have a higher void content than a graded sample. Therefore, use either one method or the other as a comparative measure of shape and texture, and identify which method has been used to obtain the reported data. Method C does not provide an indication of shape and texture directly if the grading from sample to sample changes.
4.3.1. The bulk dry specific gravity of the coarse aggregate determined by T 85 is used in calculating the void content. The effectiveness of these methods of determining void content and its relationship to particle shape and texture depends on the bulk specific gravity of various size fractions being equal. or nearly so. The void content is actually a function of the volume of each size fraction. If the type of rock or mineral or its porosity varies markedly in any of the size fractions, it may be necessary to determine the specific gravity of the size fractions used in the test.AASHTO T 326 pdf download.