Potential of Using Stone Matrix Asphalt (sma) for Thin Overlays

i DISCLAIMER The contents of this report reflect the views of the authors who are solely responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views and policies of the National Center for Asphalt Technology of Auburn University. This report does not constitute a standard, specification, or regulation. ii ABSTRACT Stone matrix asphalt (SMA) has been used within the U.S. since 1991. To date almost all of the SMA mixes have had either a 12.5 or 19.0 mm nominal maximum aggregate size (NMAS). These two NMASs have been predominant because they conform to information obtained from European experiences with SMA. However, the existence of a " fine " SMA mix could be beneficial because it can be placed in thinner lifts, could be used as part of a preventative maintenance program, and should be more workable. For the purpose of this study, a " fine " SMA was defined as a SMA having either a 4.75 or 9.5 mm NMAS. This research study was conducted to evaluate the potential of designing fine SMAs and to compare these fine SMAs to more conventional SMA mixes (larger NMAS). Data accumulated from this study showed that these fine SMAs could be successfully designed to have stone-on-stone contact. Rut susceptibility testing with the Asphalt Pavement Analyzer confirmed that the designed fine SMA mixes were rut resistant. Permeability testing indicated that these fine SMA mixes were less permeable than conventional SMA mixes, at similar air void levels, and thus should be more durable. Based upon all information from this study, it was concluded that fine SMAs are a viable option for thin overlays.