Performance Evaluation of Aggregate Gradations Adjusted Through the Bailey Method

Abstract

In asphalt mix design, the aggregate structure of the compacted mix is an important factor to evaluate, that contributes to the performance of Hot-Mix Asphalt (HMA). Bailey method provides a systematic way of blending coarse and fine mineral aggregates based on the concepts of aggregate interlock. This research is carried out with primary objective to determine if the Bailey Method can be a useful tool to design mixtures with improved performance for mixes commonly used in Pakistan. Four (04) asphalt concrete wearing course mixtures were chosen for redesign with the Bailey Method, including National highway authority gradations NHA-A and NHA-B, Superpave SP-1 and asphalt institute manual series MS-2 gradations. The Bailey parameters for the original mixtures were calculated and the gradations were redesigned to fall within the recommended ranges. The aggregates structures designed using Bailey method and the original mixes were applied in Marshall Mix design method to obtain the Marshall properties. The Hamburg wheel tracker test is employed on Superpave gyratory compactor (SGC) specimens for checking their rutting susceptibility. For this purpose, specimens were tested at a test temperature of 40 oC. All the redesigned mixtures did show an increase in rutting resistance, however significant improvement is observed in rutting for NHA-A and MS-2 gradations i.e. 9% and 10 % respectively. Two Non-linear regression models were also developed to explain the, VMA as a function of Bailey parameters (CA, FAc and FAf) and Rutting as a function of FAc and NMPS. Overall, this research project concluded that Bailey method can be a useful tool in the evaluation and design of HMA mixtures.