COMPARATIVE EVALUATION OF MARSHALL AND SUPEPRAVE MIX DESIGN METHODS USING NHA ASPHALTIC CONCRETE MIXTURES

Abstract

The primary objective of any asphalt mix design method is to establish an economically efficient combination of bitumen and aggregates in an appropriate proportion such that it yields a paving mix with sufficient amount of asphalt binder, desirable percentage of air voids, VMA, VFA, suitable workability and satisfactory performance. Moreover, the asphalt mix composition, i.e. proportion of asphalt cements (Optimum Asphalt Content), aggregate and mineral filler has a substantial impact on its resistance against pavement distresses. With the advancement in technology, the traditional Marshall mix design method which was introduced in 1939 has become obsolete and outdated. The impact compaction technique implemented in Marshall method is considered a poor reflection of actual field compaction in view of the fact that pavements are subjected to gradually applied compressive loads by compaction rollers and traffic. On the other hand, Superpave mix design technique, which was established in 1993, is gaining attraction of many state highway departments due to its better simulation of field compaction characteristics and incorporation of environmental conditions, heavy traffic loading etc. In general, asphalt concrete mix is designed in such a way that it possesses enough stiffness to prevent major deformations without compromising its flexibility. Since the Indirect Tensile Strength (ITS) and Resilient Modulus (MR) are reliable indicators of asphaltic pavements’ stiffness, both these parameters (MR and ITS) are considered in this research work to characterize the permanent deformation behavior of asphaltic mixtures. This comparative study is aimed to analyze both design methods on the basis of volumetric properties and performance evaluation by using the materials procured from same source and adopting identical aggregates’ gradation complying with NHA specifications which are most commonly used all across Pakistan for pavements design. The results of performance testing were quite propitious and the implementation of Superpave mix design approach is strongly recommended.