Sample Size Requirements for Field Permeability Measurements of Hot-Mix Asphalt Pavements

The permeability of coarse-graded asphalt mixtures has been of great concern in recent years. Asphalt mixes that are permeable are susceptible to a number of distresses, such as moisture damage, raveling, cracking, and binder oxidation. In this study, seven sites were mapped according to the vacuum permeameter method to determine the location and distribution of permeable voids. The variability of the sites was evaluated to determine an appropriate sample size for permeability testing. Relatively impermeable pavements were consistent; pavements with moderate or high permeability were more variable. Relationships between sample size, reliability, and testing discrimination are presented. Based on the range of standard deviations measured in this project, a minimum sample size of 10 is recommended for pavements with marginal densities or variable consistency. On the basis of the results of this study, permeability test results are highly dependent on the placement of the permeameter during testing, the effective testing area of the permeameter, and the variability of the pavement. Field permeability testing may have value as a forensic tool, but the large sample size required is not conducive to standard quality control procedures.