DEVELOPMENT OF A MIXTURE DESIGN PROCEDURE FOR STONE MATRIX ASPHALT (SMA)
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 were 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% 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 U.S. since 1991. However, for the pavements with air voids falling below the 3% range, some rutting was observed. (7) A voids in mineral aggregate (VMA) significantly lower than specified VMA can be obtained due to aggregate breakdown. Hence, the mix designer must consider aggregate type, compactor type and compactive effort along with the gradation in meeting the required VMA criteria. Specifying a minimum asphalt content can result in different requirements for aggregates with different specific gravity. (8) Fifty blows of Marshall hammer were found to be approximately equal to 100 revolutions of the Superpave gyratory compactor in terms of resultant density. The Superpave gyratory compactor was found to produce less aggregate breakdown than the Marshall hammer. (9) Fiber stabilizers were found to be more effective in reducing draindown than polymer stabilizers. However, mixes modified with polymer showed better resistance to rutting in laboratory wheel tracking tests.
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Corporate Authors:
National Center for Asphalt Technology
Auburn University, 277 Technology Parkway
Auburn, AL United States 36830 -
Authors:
- Brown, E R
- Haddock, J E
- Mallick, R B
- Lynn, T A
- Publication Date: 1997-3
Language
- English
Media Info
- Features: Figures; References; Tables;
- Pagination: 34 p.
Subject/Index Terms
- TRT Terms: Aggregate gradation; Air voids; Asphalt content; Binders; Compaction; Compactors; Fibers; Fillers; Hammers; Mix design; Polymers; Properties of materials; Rutting; Stabilizers; Stiffness; Stone matrix asphalt
- Identifier Terms: Los Angeles Abrasion Test
- Uncontrolled Terms: Gyratory compactors; Voids in mineral aggregate
- Old TRIS Terms: Air voids content; Fillers
- Subject Areas: Highways; Materials; I31: Bituminous Binders and Materials;
Filing Info
- Accession Number: 00750980
- Record Type: Publication
- Report/Paper Numbers: NCAT Report No. 97-3
- Files: NTL, TRIS
- Created Date: Jul 14 1998 12:00AM