This chapter discusses the practical significance of the relative accuracy of the specific gravity determinations. The underlying question is, how close should the result from a revised test method be to that of the current method? To answer this question, two analyses were conducted. The first analysis was to determine if differences in the results of revised and current methods were within the acceptable range of the cur- rent methods. The second analysis assessed the sensitivity of the portland cement concrete and asphalt mixture volumet- ric properties to aggregate specific gravity values.
Repeatability Analysis
The first analysis was based on the repeatability of the cur- rent specific gravity tests. From a practical point of view, it is acceptable if differences in results from different procedures (i.e., alternative methods) are less than differences in results of duplicate specimens tested according to the current methods.
Precision estimates of the current methods are available in AASHTO T 84 and T 85 and also are determined annually by the Proficiency Sample Programs and reported on the AMRL website. The within-lab standard deviations (Sr) and accept- able range of two results (D2S) from AASHTO T 84 and T 85, respectively, are as follows: