Flat and Elongated Aggregates in Superpave Regime

Abstract

Some states have recommended changing the definition of flat and elongated aggregates from 5:1 to 3:1 and an increase in the maximum allowable percentage of flat and elongated (F&E) particles to 20% or higher in the Superpave aggregate specification. Engineering justification and performance data are required to rationally establish the criteria for this change. The objectives of this research included the statistical analysis of performance indicators of Superpave mixtures containing different levels of 3:1 particles. Three mixes were designed and tested using 0, 15, and 40% of 3:1 particles from a set of Kentucky limestone aggregates. This paper contains the findings, conclusions, and recommendations on the research. The mixtures did not differ significantly in their performance-related properties at lower and higher temperatures. However, at intermediate temperatures, significant differences were observed. A curve shifting analysis confirmed the presence of lower shear stiffness with an increase in the percentage of 3:1 F&E particles. The mix densification trends were inconclusive. Additionally, at low temperatures, the mixes with increasing percentages of 3:1 F&E particles seemed to have higher tensile strengths. This particular finding needs to be further investigated. Overall, increases up to 40% of 3:1 F&E particles did not adversely affect the performance potential of such mixes as measured by the Superpave methodology.