Variability and Normality Assumptions for Virginia Department of Transportation Volumetric Properties

Abstract

The paper investigates the statistical measures of process mean, standard deviation, correlation, and normality assumptions for the Virginia Department of Transportation volumetric properties of voids in total mix (VTM), asphalt content (AC), and voids in mineral aggregates (VMA) on the basis of 3 years of contractors' testing data. The VTM had an overall pooled standard deviation of 0.86%, but the data distribution was found not to follow the normal distribution. No difference based on mix type [base mix (BM), intermediate mix (IM), surface mix (SM), or stone matrix asphalt (SMA)] was observed. The average AC, however, was found to depend on mix type with three distinct groups: BM and IM (about 4.35%), SM (about 5.30%), and SMA (about 6.40%). The standard deviations for the combined BM and IM and that of the SM were found to be similar (about 0.30%) and different from the standard deviation of the SMA (about 0.42%). The AC data distribution passed one of the three tests of normality. The correlation between the VTM and AC was found to be equal to −0.28. The average of the VMA was found to depend on mix type and specifically on the maximum nominal aggregate size ranging from 13.84% for the BM to 18.18% for the SMA. The standard deviations was found to be independent of mix type (about 1.00%). Similar to the VTM, the VMA distribution failed all three normality tests. As expected, a high correlation between the VTM and VMA was observed (about 0.65). The correlation increased to 0.85 when the effect of the AC was removed.