Is normal distribution the most appropriate statistical distribution for volumetric properties in asphalt mixtures?

Volumetric properties are essential for a better understanding of how to design the mixtures. Due to the irregularity of aggregate shape, these properties vary randomly with the same gradation. In this paper, the volumetric properties [bulk specific gravity (7f), air voids (W), voids in mineral aggregate (VMA), and voids filled with asphalt (VFA)] were determined on two mixtures types, namely, A and B. These mixtures were statistically analyzed using different distribution methods. Seventy-two samples of Mixture A and 52 of Mixture B were fabricated using the Marshall design method. Results of the study showed that the Weibull distribution could reflect the probability distribution law of the volumetric properties of the mixtures. The two-parameter Weibull distribution function appears to be more appropriate or use with γ_f and VFA, whereas the three-parameter Weibull distribution function was most appropriate for W and VMA. The analysis of test results also revealed that there are significant differences in the volumetric properties of the two mixtures tested at the same confidence level. The confidence interval decreases with a decrease in reliability.