Technical Paper ISSN 1997-1400 Int. J. Pavement Res. Technol. 5(3):142-152 Copyright @ Chinese Society of Pavement Engineering 142 International Journal of Pavement Research and Technology Vol.5 No.3 May 2012 A Laboratory Investigation into the Effect of Long-Term Oven Aging on RAP Mixes Using Dynamic Modulus Test Dharamveer Singh 1+ , Musharraf Zaman 2 , and Sesh Commuri 3 ─────────────────────────────────────────────────────── 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 o C, 21 o C, 40 o C and 55 o 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. Key words: Dynamic modulus; Hot mix asphalt; Reclaimed asphalt pavement. ─────────────────────────────────────────────────────── Introduction 12 Reclaimed asphalt pavement (RAP) is a recycled pavement material containing coated aggregates with asphalt binder [1-3]. According to the U.S. Environmental Protection Agency and the Federal Highway Administration, about 90 million tons of asphalt concrete is reclaimed each year, and over 80 percent (73 million tons) of it is reused in the production of hot mix asphalt (HMA) [3]. The use of RAP in a HMA mix has been favored over the use of virgin materials because it saves cost of raw materials and reduces the environmental impact of discarded pavement materials [1, 3-5]. Furthermore, the addition of RAP is beneficial in resisting permanent deformation at higher temperature [6-12]. On the other hand, excessive RAP content may reduce the resistance to cracking at low temperatures [13]. Many studies have been done to evaluate the effect of RAP on the performance of asphalt mix. McDaniel et al. [14] reported that adding small amounts of RAP does not significantly alter mix properties. As RAP content increases, some effects on mix 1 School of Civil Engineering and Environmental Science, University of Oklahoma, 202 W. Boyd Street, Norman, Oklahoma, USA, 73019. 2 College of Engineering, University of Oklahoma, Norman, Oklahoma, USA, 73019. 3 School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma, USA, 73019. + Corresponding Author: E-mail dvsinghchauhan@gmail.com; dvsingh@ou.edu Note: Submitted September 7, 2011; Revised November 22, 2011; Accepted November 23, 2011. properties were noted. However, the change was not in proportion to the amount of added RAP. Similarly, Kandhal et al. [15] found that up to 15% RAP can be used without changing the PG binder grade. In general, most studies on laboratory-produced mixes conclude that the effect of RAP on mixes’ properties is negligible at RAP contents within 15% to 20% [13-14, 16-17]. A low RAP content does not significantly affect the stiffness and strength of a mix at low and high temperatures. However, an increase in RAP content beyond 20% increases the mix’s stiffness and strength, resulting in an increase in its rutting resistance [2, 7, 13-14, 18]. Limited studies have been conducted thus far to investigate the effect of long-term oven (LTO)-aging on plant produced HMA mixes prepared with RAP. Daniel et al. [19] and Francken et al. [20] studied the effect of aging on HMA mixes. Specimens were compacted and subjected to three different levels of long-term aging. It was reported that LTO-aging increases dynamic modulus (|E*|) of the compacted samples significantly. However, they did not study the effect of aging on mix containing RAP. Evaluation of the effect of short-term and long-term aging on the performance of RAP-containing mixes would be helpful in understanding the response (stress-strain behavior) of a flexible pavement. Furthermore, it is known that for a given virgin HMA mix (without any RAP), a mix with stiffer binder grade (i.e., PG 76-28) is expected to result in a higher |E*| compared to a mix with a softer binder grade (i.e., PG 64-22). However, such behavior may not be reflected in a mix containing RAP, because it changes the rheological property and grade of the binder (compared to the virgin mix). Hence, it becomes important to evaluate the performance of RAP-containing HMA mixes at the design phase of a flexible pavement.