Effect of Flat and Elongated Coarse Aggregate on Characteristics of Gyratory Compacted Samples

Abstract

The effect of various levels of flat and elongated (F&E) particles on the gyratory compaction characteristics in a standard bituminous mixture was examined. Compaction characteristics involve the effect of F&E particles on the void development in the gyratory compactor as well as the break-down characteristics. F&E particles could also affect the performance characteristics of the compacted mixtures. F&E particles in typical Illinois surface mixtures were examined. Two coarse aggregate sources, a dolomite and crushed gravel, were used. A cubical mixture was prepared in which all particles had an F&E ratio < 3:1 and baseline compaction characteristics were established. Coarse aggregates were individually measured to produce aggregate particles with measured F&E ratios < 3:1, between 3:1 and 5:1, and > 5:1. The coarse aggregates in the cubical gradation were replaced with various percentages of the same-sized aggregate with F&E ratios in the 3:1 and 5:1 range. These mixtures were compacted and the volumetric and gyratory characteristics were compared. Solvent extractions and binder ignition samples were obtained to indicate the relative breakdown in aggregates achieved with the different percentages of the F&E particles. The testing indicates the changes produced when different percentages of F&E particles are introduced into a mixture. When combined with performance testing, these data will provide a valid base upon which to recommend levels of allowable F&E particles in an asphalt mixture.