Optimized Design for 4.75-mm NMAS Superpave Mix Thin Overlay

Transportation infrastructure facilities such as highways consume large quantities of materials in initial construction and periodic maintenance and rehabilitation. A Superpave asphalt mixture with 4.75-mm nominal maximum aggregate size (NMAS) is a promising, low-cost pavement preservation treatment that can be applied in thin lifts for low- to medium-volume facilities. This study evaluates the performance of 4.75-mm NMAS Superpave asphalt mixture and proposes an optimized mixture design for a long-lasting ultra thin hot-mix asphalt (HMA) overlay. Twelve different 4.75-mm NMAS mix designs were developed in the laboratory using two binder grades and three different percentages of natural (river) sand in combination with finer quarry materials. Test results from two laboratory performance tests show that rutting and moisture damage of such mixes during Hamburg Wheel Tracking Device and Lottman tests are aggregate-type and source specific. Anti-stripping agent affects moisture sensitivity test results irrespective of natural sand content and binder grade. Finally, optimum combinations of aggregates and binder were developed for 4.75-mm NMAS mixture based on the statistical analysis of performance data.