Comparing Superpave and Marshall Mix Design methods for Trunk Road: A Study of Volumetric Properties, Mechanical Performance, and Life Cycle Cost analysis

Abstract

The Marshall mix design method has been used for asphalt pavements in Ethiopia for decades, but its use in trunk roads has resulted in unsatisfactory highway performance, with a shorter pavement lifespan than anticipated. The Superpave mix design approach has been developed to address these drawbacks and provides better performance, particularly for roads exposed to high climatic changes and traffic loadings. To conduct this study, crushed basalt aggregate, asphalt binder with a penetration grade of 60/70, and hydrated lime were used as materials for both mix designs. A quality test was conducted on the selected material to ensure that they met acceptable specification criteria for Ethiopian roads. Using each mix design method, the samples are mixed and compacted individually to determine their volumetric properties. Optimum binder content was determined using a national pavement association method, and samples are prepared for performance tests. The Superpave and Marshall mix designs are compared on the basis of their volumetric properties, mechanical performance, and Life Cycle Cost. Volumetric properties are determined by measuring the air voids, voids in mineral aggregate, and voids filled with asphalt. Their mechanical performance was also evaluated by conducting wheel tracking tests, indirect tensile strength tests, and retained stability tests. The Life Cycle Cost is determined by analyzing the pavement’s initial cost, maintenance and rehabilitation cost, salvage value, and road user cost. The results of all tests indicated that the Superpave mix design outperformed the Marshall mix design in terms of volumetric properties, mechanical performance, and on life cycle cost. Therefore, adopting the Superpave mix design procedure in Ethiopia can help enhance the performance of trunk road, resulting in longer-lasting, more durable pavements that can potentially save costs in the long term.