Evaluation of High Los Angeles Abrasion Loss Aggregate in Stone Matrix Asphalt

Abstract

Stone matrix asphalt (SMA) was developed in Germany over 40 years ago to resist rutting from studded tire wear. In recent years, there has been increased interest in SMA in the U.S.A. The foundation of SMA mixes is a coarse aggregate stone skeleton that forms a load-bearing matrix. Typical requirements of aggregate are between 30% and 40% loss measured by Los Angeles abrasion test. South Carolina’s granitic aggregate sources are mostly between 45% and 60% loss. In this study, sources with 44%, 53%, and 56% loss were evaluated for pavement rutting, moisture susceptibility, draindown, and cracking potential. The original plan started with designs using 12.5 mm nominal maximum aggregate size (NMAS) to increase macrotexture, from a safety standpoint, but eventually changed to 9.5 mm NMAS to be more consistent with typical coarse aggregate stockpile gradations in South Carolina. The designs were tested with and without fiber. The fiber designs met draindown requirements while the fiberless ones failed at elevated temperatures. The designs met the rut susceptibility criteria and the data indicated that moisture damage did not compromise the designs. The cracking test index (CT_index), a measure of cracking potential, showed good resistance for all of the designs with the exception of the 9.5 mm NMAS with fiber, which had poor results even when compared with high RAP (reclaimed asphalt pavement) dense-graded mixtures. The macrotexture for the 12.5 mm NMAS designs was comparable with other South Carolina open-graded friction course mixtures. Overall, the sources with 44% and 53% loss by Los Angeles abrasion test performed equivocally, with the 9.5 mm fiber design having lower cracking resistance.