Determining Air Voids Content of Compacted Stone Matrix Asphalt Mixtures

This study compared the difference in air voids, optimum asphalt content, and voids in mineral aggregate (VMA) by using the saturated surface dry (SSD) and CoreLok methods for determining bulk specific gravity of the compacted specimen. The critical air voids level at which stone matrix asphalt (SMA) mixtures are considered to become permeable was also determined for the gradations used in this study. Some of the pertinent conclusions are as follows. (a) There is a significant difference between air voids content measured by the SSD method and the CoreLok method, (b) The CoreLok method resulted in a higher optimum asphalt content and VMA than designs based on the SSD method. (c) The CoreLok method may have a system error that overestimated the air voids content at zero to low air voids levels; therefore, a correction factor was suggested to apply to the CoreLok results if needed. (d) At a permeability threshold of 125 X 10^-5 cm/s, the critical air voids contents are 4.5%, 5.7%, and 7.8% by the SSD method for 19-, 12.5-, and 9.5-mm nominal maximum aggregate size (NMAS) SMA mixtures, respectively, (e) Both the SSD and corrected CoreLok methods can be used for SMA 9.5-mm NMAS mixtures. For SMA 12.5-mm NMAS mixtures with 6.0% or more air voids and for SMA 19-mm NMAS mixtures with more than 4% air voids, there is a greater potential for error by the SSD method, and the corrected CoreLok method should be used.