Influence of Aggregate Packing and Asphalt Binder Characteristics on Performance of Stone Matrix Asphalt

摘要

Stone matrix asphalt (SMA) is valued for its high resistance to rutting and durabilitycharacteristics. These characteristics of SMA mixtures are mainly the result of the rich asphaltmastic and the good stone-on-stone contact provided by its coarse, gap-graded aggregatestructure. SMA has been used in Virginia since 1995 with overall excellent performance.However, with the introduction of the 9.5 mm SMA mix in 2003, the field performance of thismix has been variable. This paper focuses on the laboratory evaluation of asphalt binder andaggregate packing effects on the rutting resistance of SMA, the primary failure mechanism forthe SMA-9.5. The objective was to identify defining characteristics of SMA mixtures thatimpact field performance. Four SMA-9.5 mixtures with known field performance – two goodperformers, one marginal performer, and one poor performer - were reproduced in the laboratoryand tested. Rutting resistance of the mixtures was evaluated using the flow number (FN)obtained from repeated load permanent deformation tests and the asphalt pavement analyzer. Inaddition, dynamic shear rheometer, bending beam rheometer, and dynamic modulus testing wereconducted to characterize the asphalt binder and mixtures stiffness. The results indicated thatrutting resistance of SMA was dependent on binder stiffness, binder content, and aggregatestructure (gradation, VCA, and Abrams fineness modulus). Mixtures with history of good fieldperformance showed significantly higher FN than the poor performers. Both binder content andaggregate packing (fineness modulus and VCA_(mix)) were lower for the good performing mixturesbut binder content appears to have more significant influence on FN – a one percentage pointincrease over VDOT minimum binder content of 6.3 percent resultant in significant decrease inrutting resistance irrespective of aggregate packing characteristics. It was concluded thatcombination of traffic characteristics (slow-moving, turning, or stopped), aggregate packing(higher VCA_(mix), lower Abrams modulus, higher percent passing No. 4 sieve), and binderamount, may have contributed to the observed poor SMA field performance.