Environmental Considerations in the AASHTO Mechanistic-Empirical Pavement Design Guide: Impacts on Performance

Abstract

This paper is a continuation of an earlier overview on the subject and presents the results of a sensitivity analysis that assessed the ability of the new design guide to portray the impact of temperature and moisture content on flexible pavement performance. The study used the most common asphalt concrete (HL3) and unbound materials (granular A and silty sand) used in Canada. Two binders [performance grade (PG) 52-34 and PG 58-28] and three moisture conditions (dry, wet, and optimum) were chosen. Designs performed using Level 3 analysis for unbound materials and Level 1 for asphalt concrete showed that the new design guide is sensitive to binder performance grades and climatic zones (cold versus warm); however, the new design guide showed limited sensitivity to the state of unbound materials: permanent deformation showed negligible changes between wet, dry, and optimum conditions. Model simulations indicated that rutting that accumulated throughout the 20-year design life for the warm region (Long Beach, California) was 50% more than that in the relatively cold region (New York). Using different soil conditions for unbound materials showed that the increase in resilient modulus from wet to dry conditions increases total rutting by 27%. Results also demonstrated good sensitivity to the type of asphalt binder and agreed with the binder type objective: the HL3 mix prepared with the PG 58-28 binder substantially decreased rutting (by 271%) compared with the mix prepared with the PG 52-34 binder.