Predicting Field Permeability from Testing Hot-Mix Asphalt Specimens Produced by Superpave Gyratory Compactor (05-1285)**
Kunnawee Kanitpong, Asian Institute of Technology, Thailand
Hussain U. Bahia, University of Wisconsin, Madison
Jeffrey S. Russell, University of Wisconsin, Madison
Robert Schmitt, University of Wisconsin, Platteville

This study was conducted to develop laboratory and field permeability testing procedures for design and quality control of Superpave mixtures in Wisconsin. A total of 16 mixes used on 9 field projects, including fine-graded and coarse-graded mixes, were evaluated. The in-place field permeability was measured by using the NCAT device; field cores were taken for measuring permeability in the laboratory by using the ASTM D5084 method; and laboratory compaction was used to prepare and test samples from loose mixtures recovered from the field. Two compaction procedures, called Method A and Method B were used in this study to produce Superpave Gyratory Compacted (SGC) specimens that have similar thickness, air voids, and aggregate orientation of the field cores. The result indicates that Method B, which is based on using Ndesign gyrations for different sample sizes, can be used to produce samples that give permeability values similar to values measured for field cores. The results of this study also indicate a good relationship between field permeability (using the NCAT device) and lab permeability measured on field cores of fine-graded mixes with amount of passing No. 8 sieve (P8) higher than 45%. However, the relationship between field permeability and lab permeability measured on field cores of coarse-graded mix (P8 lower than 40%) is very poor. It is therefore concluded that the NCAT permeability device could possibly be used in the field for fine-graded mix (with P8 higher than 45%) to measure a permeability index that is related to the true permeability of field cores as measured by the ASTM D5084. However, to measure the field permeability of coarse-graded mix (P8 lower than 40%), an approach to prevent water leakage along the sealant due to rough pavement surface should be established. For coarse graded mixtures, there appears to be no current alternative better than taking field cores and testing them in the laboratory. For estimating permeability during mixture design, a simple method for preparing and testing permeability of SGC specimens and interpolating based on expected field density is introduced. The results represent a good estimate of the expected in-place field permeability.