Effective incorporation of asphalt mixture properties in the structural design of asphalt pavements as a precursor for implementing performance-based design -

Abstract

Despite its numerous limitations and its empirical nature, the 1993 AASHTO Design Guide for Pavement Structures is, to date, the most widely used pavement design manual by highway agencies and consultants around the world. As defined in the 1993 design guide, the structural coefficient of a pavement layer is an abstract measure of the relative ability of a unit thickness of a given material to function as a structural component of the pavement. The structural coefficient of the asphalt layer ‘a1’ is typically assumed to be 0.44 for dense graded asphalt mixes, or is acquired from a relationship that ties ‘a1’ to the resilient modulus (MR). The main shortcoming of the design guide is that the assumed ‘a1’ value of 0.44 and the relationship between ‘a1’ and the resilient modulus (MR) relationship do not account for the effect of mix type and properties, traffic volume and speed, layer thicknesses (thin versus thick pavements), climate, and unbound layer properties. Recently, pavement design needs have prominently evolved, owing to significant changes in traffic volumes and truck configurations, materials, material characterization models, performance prediction models, mix design methods, mix fabrication and construction procedures. These developments have rendered the 1993 design guide unsuitable in numerous design scenarios. The objective of this research is to enhance the design methodology for asphalt pavements incorporated in the 1993 AASHTO design guide by integrating asphalt mixture properties in the design process. The aim is to provide a more accurate estimate of the structural coefficient ‘a1’ of the asphalt layer by establishing a new relationship between the structural coefficient and the effective dynamic modulus (⌠E*⌠eff.) eff.) of the asphalt mix. The methodology employed to develop the relationship entails back-calculating the structural layer coefficient of the asphalt layer for a number of design scenarios (mix type, traffic v