Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85930
RoadScience layers, respectively. However, by special provision, fraction- ated RAP is allowed at up to 20, 30 and 40 percent in those same layers." Separately, RAP has to be chemically analyzed or char- acterized to determine its properties (below). That ben- efi ciation or fractionation of RAP that's been chemically characterized can permit signifi cantly higher levels of RAP in Superpave mixes is borne out in a paper from the 2012 Transportation Research Board meeting, Fractionation of High Recycled Asphalt Pavement Content in Asphalt Mixtures for Superpave Mix Design Compliance, by Cory Shannon, E.I.T.; Yongjoo Kim, Ph. D.; Thomas Glueckert and Hosin "David" Lee, Ph.D., P.E., they write. "First a sieve analysis was performed on the recovered aggregate materials from ignition oven burn- off testing to determine the aggregate and asphalt binder composition of the RAP materials. To remove excessive fi ne materials a fractionated RAP stockpile was produced by removing RAP materials passing the No. 30 (0.60 mm) sieve." In Wisconsin, pavement demolition concrete is crushed next to a construction site. The result- ing RCA will go back as base material below concrete pavement. The Superpave mix design was then performed with RAP inclusion levels of 30, 40 and 50 percent, based on virgin asphalt binder replacement for RAP materials randomly se- lected from the bulk stockpile (traditional RAP) and RAP ma- terials from the fractionated stockpile consisting of materials retained at No. 30 sieve and larger (fractionated RAP). The fractionated RAP materials produced a lower surface area requiring lower virgin asphalt content, they say, resulting in the increased asphalt fi lm thickness on aggregates. The fractionated RAP mixtures also exhibited higher indirect tensile strength than traditional RAP mixtures for all levels of inclusion. "It was determined that the use of the fractionation method to remove fi ne recovered aggregates contributed Department of Civil and Environmental Engineering Uni- versity of Iowa-Iowa City. "Due to the increased amount of fi nes created during the milling process and the corresponding increased surface area, high RAP content mixes have great diffi culty in meet- ing the volumetric requirements of the Iowa DOT," they write. "The fractionation method for this study focused on physical removal of RAP material below a certain sieve size to limit fi ne aggregate contribution." Current Iowa DOT specifi cations limit contractors to a maximum of 30-percent virgin asphalt binder replacement by RAP materials in the surface course for any state-regu- lated project, the authors write. "The main objective of this study is to develop quality standards for the inclusion of RAP contents higher than 30 percent in asphalt mixtures," 18 September 2012 Better Roads by the RAP materials is an effective method for improv- ing mix design criteria compliance while also reducing the requirement of virgin asphalt for asphalt surface mixtures with a high RAP inclusion level up to 50 percent," they conclude. Determining AC Content Lab testing requirements and testing frequency for binder (AC) content vary according to the category of RAP and the amount of RAP used in a mixture, Copeland writes in Reclaimed Asphalt Pavement in Asphalt Mixtures (download a copy by Googling "FHWA-HRT-11-021"). RAP from multiple sources may be subject to more rigor- ous testing than RAP from a single source, she writes. For all RAP stockpiles, the asphalt binder content and aggregate