Experience with Thin Superpave Mixture Overlay of Small Aggregate Top Size in Kansas

Abstract

Superpave® asphalt mixture with small (4.75-mm) nominal maximum aggregate size (NMAS) is a promising, low-cost pavement preservation treatment for rural roads. This mixture has the potential to provide a smooth riding surface, be applied in thin lifts, correct surface defects, decrease construction time, and provide an economical surface mixture for low- to medium-volume facilities. Because of budget constraints in highway construction and preservation programs and the economic advantages of such a mixture, many highway agencies are considering implementing it for rural roads. Two rural highway pavements in Kansas were overlaid with a 15- to 19-mm-thick 4.75-mm NMAS Superpave mixture in 2007. Overall, the experience in Kansas with the 4.75-mm NMAS mixture was varied. Both projects had construction issues. Experience on one project showed that extended aggregate drying and drum cleaning would be necessary when producing these mixtures. Performance history on both projects after overlay construction showed that roughness of the road surface was significantly improved and was consistent for the 3 years after the overlay. Transverse cracks seem to be the major concern, although the rutting performance of this small-sized aggregate mixture is satisfactory. Crushed gravel aggregates seemed to perform better in the mixture than crushed limestone aggregates. A binder with a higher grade may be needed to address transverse cracking issues.