NCAT Report 97-03 DEVELOPMENT OF A MIXTURE DESIGN PROCEDURE FOR STONE MATRIX ASPHALT ( SMA ) By
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 successfully in Europe for over 20 years to provide better rutting resistance and to resist studded tire wear. Since 1991, the use of SMA has increased steadily in the United States. At present, some states routinely use SMA even though a standard mixture design procedure is not available. A mixture design procedure that provides guidance on material properties, aggregate gradation, determination of optimum asphalt content, and mixture properties is needed. This paper presents a mixture design procedure for SMA mixtures developed by the National Center for Asphalt Technology. Data for the development of the procedure was collected from a laboratory study conducted with various samples of aggregates, fillers, asphalt binders, and stabilizing additives. Compacted mixtures were tested to evaluate the effects of aggregate structure, asphalt binder, and binder-fine aggregate mortar. Specific conclusions from this study were: 1) The Los Angeles abrasion loss showed good correlation with aggregate breakdown; 2) it appeared that the 3:1 or 2:1 flat and elongated particles provided much better classification for the various aggregates than a 5:1 ratio; 3) the flat and elongated particle ratio showed excellent correlation with aggregate breakdown; 4) in a SMA mix, the percent passing the 4.75 mm sieve must be below 30 percent to ensure proper stone-on-stone contact; 5) the percent passing the 0.02 mm sieve did not show a correlation with mortar stiffness. However, the dry compacted volume, as obtained from the Penn State test method, did show a good correlation with mortar stiffness and can be utilized to characterize the shape of fillers. Generally, a more angular filler tends to produce a higher air voids result in this test; 6) In-place results from about 86 projects showed that very little rutting has occurred in SMA pavements constructed in the United States since 1991. However, for the pavements with air voids falling below the 3 percent range, some rutting was observed; 7) a VMA significantly lower than specified VMA can be obtained due to aggregate breakdown. Hence, the mix designer must consider …
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