Abstract
While the necessity for cost effective and sustainable replacements for virgin paving mixtures is becoming more and more evident in recent years, particularly with asphalt binder and aggregate economics and the obligations for using greener alternatives, contradictory performance results of high percentages of reclaimed asphalt pavement (RAP) in Superpave mixtures have made the addition of RAP to hot mix asphalt (HMA) quite challenging. Obtaining RAP involves milling and processing that produces an excessive amount of fine aggregates, making it difficult to control the final HMA volumetric properties, especially when higher amounts of RAP are used. In addition, segregation in RAP stockpiles is a common phenomenon which causes difficulties in air void control of the final mix due to higher asphalt content of fine aggregates. Fractionation is a process in which RAP is separated into at least two sizes, typically one coarse and one fine fraction, in order to ensure consistency of RAP. Fractionation is now being increasingly specified for inclusion of higher volumes of RAP in Superpave mixtures; however, whether any improvements of mechanical properties of HMA can be obtained by fractionation is virtually unknown. In this study, the effect of increasing RAP percentage, source of RAP, and replacing RAP with fractionated RAP on the performance of Superpave HMA mixtures was investigated in terms of rutting, freeze-thaw resistance, and cracking resistance by conducting Hamburg wheel track device (HWTD), moisture susceptibility, and complex modulus tests. HMA mixtures in this study were made with the same virgin aggregates and virgin binder using two different sources of RAP by increasing RAP amount from 20 to 40 %. Results showed that the performance can be different based on the aged binder and quality of aggregates in RAP; moreover, the fractionation effect was found to be insignificant on enhancing the performance of Superpave mixtures with RAP.
