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 …
STONE MATRIX ASPHALT PROPERTIES RELATED TO MIXTURE DESIGN
The objectives of this Stone Matrix Asphalt (SMA) study were to: (1) find the interlaboratory average values and the standard deviations of voids in mineral aggregates (VMA), theoretical maximum density and optimum asphalt content; (2) develop a draindown test and evaluate the effects of various factors on draindown of asphalt in SMA mixes; (3) develop a comparison of laboratory densities of SMA mixes prepared by a gyratory machine to those prepared by the mechanical Marshal hammer; and (4) develop a method to evaluate stone-on-stone contact in SMA mixes.
VARIATION IN HOT MIX ASPHALT MIX DESIGN PROPERTIES (WITH DISCUSSION)
The objective of this study was to determine the expected variability within laboratories and between laboratories for tests commonly conducted on HMA materials. The evaluated HMA properties include: (a) Bulk specific gravity of aggregates, (b) Effective specific gravity, (c) Optimum asphalt content at 4 percent air voids, (d) Marshall stability, (e) Marshall flow, (f) Bulk density of lab compacted mix, (g) Voids in mineral aggregates (VMA) based on bulk and effective specific gravities, (h) Theoretical maximum (Rice) specific gravity. The primary goal was to evaluate the variability of optimum asphalt content determined between a number of laboratories for a given aggregate and asphalt cement. The optimum asphalt contents were determined using Corps of Engineers gyratory, Texas gyratory, Hveem, manual Marshall, mechanical Marshall, and mechanical Marshall with slanted foot and rotating base.