Effect of Aggregate Gradation on Cold Bituminous Mix Performance

Abstract

Aggregate gradation is the skeleton of a bituminous mixture and is responsible for the load carrying capacity of the pavement. This paper presented a study on variation in aggregate gradation, which is based on and adapted from the concept of the Bailey method, to evaluate the property of cold mixes. A total of 14 cold mixes were studied for dense (BC) and gap (SMA) graded mix. For each dense and gap gradation, one initial aggregate gradation was taken as per available standard specifications. From each type of initial gradation (BC and SMA), six aggregate gradations were developed. The Marshall test and indirect tensile strength (ITS) test of all cold mixes were conducted. Then the static creep test was conducted for each type of cold mix prepared with initial gradation, and the developed gradation performed best in the former two tests. The test results were compared with hot mix asphalt (HMA) performance with initial gradations (BC and SMA). The study indicated that though all of the developed gradations increased the Marshall stability of cold mixes, the most significant improvement compared with the HMA mixes was found in the case of the increased coarse aggregate (CA) ratio among the Bailey parameters. It was also observed that the modification of aggregate gradation resulted in substantial improvements in Marshall properties, ITS, and creep resistance.