The Effect of Recycled Asphalt Materials on Hot Mixed Asphalt Pavement Performance

Abstract

Rises in construction and asphalt binder costs, as well as the growing pressures on landfills, have contributed to the increased use of Recycled Asphalt Shingles (RAS) in Hot Mixed Asphalt (HMA) Pavement Mixtures. Initial incorporation of Manufacturers Waste Scrap Shingles (MWSS) into HMA pavements yielded encouraging results and prompted waste management organizations, industry and government to investigate incorporation of Tear-Off Scrap Shingles (TOSS). As of 2009, the Minnesota Department of Transportation (Mn/DOT) standard specifications only allowed a 5% MWSS replacement for the allowable Recycled Asphalt Pavement (RAP) and TOSS was permitted, only with, “prior approval from the engineer”. This need to get approval greatly reduced the willingness of local entities to use TOSS. Furthermore, a high-profile, pre-mature, and expensive, pavement failure prompted many to re-evaluate the benefits of using RAS in HMA pavement mixtures. A multi-agency research effort between Mn/DOT and the Minnesota Pollution Control Agency (MPCA) was initiated with the goal of making a recommendation on a comprehensive RAS specification, including the option of using TOSS that would allow agencies to realize the economic and environmental benefits without compromising pavement performance or durability. The research study (1) incorporated both controlled laboratory experiments and evaluations of in service pavements. Several producers submitted their ground RAS samples to the Mn/Dot laboratory for inclusion in the study. These RAS samples were tested for gradation, and deleterious materials (DM) content; these results were later used to assist in the development of an initial specification. In addition, the RAS samples were tested for the performance grade (PG) of the asphalt binder. Laboratory-produced HMA mixtures incorporating: Tear-Off Scrap Shingles (TOSS), or Manufacturer Waste Scrap Shingles (MWSS), and/or Recycled Asphalt Pavement (RAP) were tested for both asphalt binder PG grades and mixture dynamic modulus. It was concluded that the shingle properties, especially the fineness of the grind, and shingle type and the amount of recycled materials used in the HMA mixture had an impact on pavement performance. The knowledge gained from the collaborative research effort helped decision makers make an informed decision on a 2010 comprehensive RAP/RAS specification, which now allows the use of TOSS as a substitute for the total RAP content of the mix.