Laboratory Tests and Numerical Simulations of Mixing Superheated Virgin Aggregate with Reclaimed Asphalt Pavement Materials

Abstract

The use of reclaimed asphalt pavement (RAP) in asphalt mix contributes to sustainable construction. However, a high percentage of RAP in asphalt mix causes concern about compromising the performance of asphalt pavement, especially cracking. The binder transfer and blending between RAP and virgin aggregate during production in an asphalt plant is a critical procedure that affects the performance of the asphalt mix. The heating of RAP by superheated virgin aggregate and the transfer of RAP binder can affect the degree to which virgin binder and RAP binder are blended and thus affect the performance of mixes containing RAP. Several parameters, such as RAP percentage, mixing time, and RAP moisture content, can affect the heating of RAP and the degree of blending between the virgin binder and RAP binder. To increase the understanding of RAP heating and RAP binder transfer, laboratory tests and numerical simulations that employed the discrete element method (DEM) were conducted for this study to investigate the temperature evolution and amount of RAP binder transfer during the mixing of superheated virgin aggregate and RAP materials in a laboratory drum mixer. The results indicated that a longer mixing time or higher superheated virgin aggregate temperature was needed for cases with a high RAP content and high RAP moisture content. The DEM simulations were found to be a promising method for studying the mixing process of superheated virgin aggregate blended with RAP materials. In the future, such DEM simulations could be applied to guide the mix production process for RAP mixes.

On the degree of binder activity of reclaimed asphalt and degree of blending with recycling agents

“…These concepts seem to be widely recognised by the scientific community, however the results of a literature review (Table 1) highlighted that practitioners have not yet achieved a general consensus on the terms related to the blending phenomena and authors use concepts and terms interchangeably. Amongst these: blending efficiency (Bowers, Huang, Shu, & Miller, 2014;Bowers, Moore, Huang, & Shu, 2014;Xu, Hao, Zhang, & Yuan, 2018), blending status (Zhao, Huang, Shu, & Woods, 2016), blending ratio (Delfosse, Drouadaine, Largeaud, & Dumont, 2016), rate of intermixing (Oliver, 2001), binder transfer (Zhang, Wen, & Hobbs, 2015), mobilization rate (Bressi et al, 2015;Ding, Huang, & Shu, 2018;Vassaux et al, 2018;Zhao, Huang, Shu, & Woods, 2015), meso-blending (Gundla & Underwood, 2015) and the most used terminology by far degree of blending (DoB) (Abd, Al-Khalid, & Akhtar, 2018;Al-Qadi et al, 2009;Booshehrian, Mogawer, & Bonaquist, 2013;Castorena, Pape, & Mooney, 2016;Cavalli, Partl, & Poulikakos, 2017;Coffey, Dubois, Mehta, & Purdy, 2013;Gaitan et al, 2013;Kriz et al, 2014;Liphardt, Radziszewski, & Król, 2015;Mogawer, Booshehrian, Vahidi, & Austerman, 2013;Mogawer et al, 2012;Navaro et al, 2012;Norton et al, 2014;Rinaldini, Schuetz, Partl, Tebaldi, & Poulikakos, 2014;Shirodkar et al, 2013Shirodkar et al, , 2011Stephens, Mahoney, & Dippold, 2001). (Vassaux et al, 2019) "Blend" presents the ability of two components to create a homogenous product where the chemical composition is identical everywhere at the scale observation of the study.…”

“…Furthermore, analysing the many factors identified, it was recognised that some are linked to the design and manufacturing of the asphalt mixture containing RA (Table 2), while some others are strictly related to the RA (Table 3). Kriz et al, 2014;Lo Presti et al, 2015;Nahar et al, 2013;Navaro et al, 2012;Oliver, 2001;Rad, Sefidmazgi, & Bahia, 2014;Stephens et al, 2001;Zhang et al, 2015;Zhao et al, 2015).…”

“…If the mixing time is prolonged, it can be possible that RA particles began to interact with each other increasing the amount of the available RA binder (Bowers, Moore, et al, 2014;Gaitan et al, 2013;Nahar et al, 2013;Navaro et al, 2012;Oliver, 2001;Rad et al, 2014;Zhang et al, 2015;Zhao et al, 2016).…”

Effect of Mixing Time and Temperature on Cracking Resistance of Bituminous Mixtures Containing Reclaimed Asphalt Pavement Material

“…Some studies investigated the temperature evolution 88 and the amount of RAP binder transfer during the mixing of the overheated new aggregates and 89 RAP; results showed that either a longer mixing time or higher overheated new aggregates is 90 necessary when high RAP contents are to be used, as stated by Zhang et al (2015).…”

Evaluation of the fatigue performance of fine aggregate matrices prepared with reclaimed asphalt pavements and shale oil residue

“…On the other hand, the stiffening process that occurs after the addition of a proportion of RAP can compromise the fatigue performance of the mixture (Zhang et al, 2015;Ghabchi et al 2016). In order to overcome such issue and to spread the use of larger proportions of RAP, soft binders and rejuvenating agents have been employed to produce new HMA mixtures.…”