A Laboratory Investigation into the Effect of Long-Term Oven Aging on RAP Mixes Using Dynamic Modulus Test

Abstract

Reclaimed Asphalt Pavement (RAP) has been widely used in the construction and rehabilitation of flexible pavements. A proper understanding of the performance of hot mix asphalt (HMA) prepared with RAP is important to ensure better and longer lasting pavements. The present study was undertaken to evaluate the effect of long-term oven (LTO) aging of HMA mixes containing RAP using the dynamic modulus (|E*|) test. Two different HMA mixes, namely Mix-1 and Mix-2, were collected from asphalt plant. Mix-1 contains performance grade (PG) 64-22 unmodified binder mixed with 25% RAP, while Mix-2 includes PG76-28 styrene-butadiene-styrene (SBS)-modified binder mixed with 15% RAP. Both mixes have the same aggregate type (primarily limestone), aggregate gradation and binder content. Specimens were compacted using a Superpave Gyratory Compactor (SGC) at four target air voids of 6%, 8%, 10% and 12% (i.e., percentage compactions of 94% to 88% of the maximum theoretical density). LTO-aging of compacted specimens was done in accordance with AASHTO R30. |E*| tests were conducted on un-aged and LTO-aged compacted specimens at four different temperatures of 4°C, 21°C, 40°C and 55°C and at six different loading frequencies of 25 Hz, 10 Hz, 5 Hz, 1 Hz, 0.5 Hz and 0.1 Hz. Mix-1, with a softer grade binder (i.e., PG64-22) and a higher amount of RAP (25%), had a higher |E*| compared to Mix-2 with a stiffer grade binder (i.e., PG76-28) and lesser amount of RAP (15%). Furthermore, statistical analyses using the standard ”student t-test” revealed that, irrespective of binder grade, higher amounts of RAP result in stiffer mixes with higher |E*|. LTO-aging increased |E*| of the compacted samples by 42% to 60%, depending on the amount of RAP and air void content in the compacted specimen. It is expected that the present study will be helpful in understanding the behavior of HMA mixes containing RAP.