Producing High Quality Recycled Hot Asphalt with Increased Reclaimed Asphalt Content – Qatar Experience

Abstract

Under the Public Works Authority (PWA) maintenance framework contract in the State of Qatar, road rehabilitation and maintenance generate considerable amounts of Reclaimed Asphalt (RA) than can be used in recycled Hot Mix Asphalt (HMA). Therefore, there is a great necessity to develop a national experience to understand the constraints and limitations of increasing RA content in recycled HMA while aligning this with the PWA initiatives on using and increasing RA in HMA. This paper sets out a guideline on how to increase RA content in HMA, considering the RA and virgin material characteristics, setup and capabilities of the asphalt plant. The study aimed to produce several recycled HMA mixes with increased RA contents using a dense-graded 19.0 mm Nominal Maximum Aggregate Size (NMAS) PEN 60/70 mix. Instead of performing design for each RA content, adjustments on the blending proportions were made accordingly as such to meet the same Job Mix Formula (JMF) of an approved HMA mix. Characterizing the RA besides data of the virgin material properties helped in adjusting the proportion during the HMA production as such to meet the control JMF. Qatar Construction Specification (QCS) 2014 was used to benchmark the results of various HMA mixtures that were prepared according to the Marshall mix design method. This paper draws a practical guideline and best practices on how to produce and optimize RA content in recycled HMA, in addition to highlighting and improving key parameters surrounding the production, from milling to laying, to produce stable, workable yet performing mixes.