Evaluation of Terminal Blend GTR Mixes with RAP

Abstract

This paper summarizes the results of a research study that involved the construction of four test sections as part of a pavement-resurfacing project to examine the performance of different ground tire rubber (GTR)–modified mixes and compare them to that of a conventional polymer-modified mix. In the first section (the control section), a styrene-butadiene-styrene (SBS) polymer-modified binder meeting performance grade (PG) 70-22M was used in the surface course mixture. Furthermore, the surface course mixtures used in the other three sections included a PG 64-22 asphalt binder modified with 7% cryogenic GTR (CR GTR), a PG 64-22 binder modified with 6% cryogenic GTR and 0.5% antisettling agent (CR GTR+ASA), and a PG 64-22 binder modified with 7% ambient GTR (AM GTR). All asphalt mixtures included 20% reclaimed asphalt pavement (RAP). Samples of the GTR-modified asphalt binders were obtained at the asphalt terminal and asphalt plant and were tested to evaluate the tendency of the different types of GTR particles to separate from the modified binder. In addition, samples of the GTR- and polymer-modified mixes were obtained during construction and were compacted in the laboratory. Tests were conducted on the compacted samples to evaluate their resistance to fatigue cracking, low-temperature cracking, moisture damage, and rutting. To this end, semicircular bending tests and indirect tensile strength tests were conducted on the field-produced lab-compacted samples to examine their fatigue-cracking resistance. In addition, the modified Lottman and the asphalt concrete cracking device experiments were performed to evaluate the mixes’ resistance to moisture damage and low-temperature cracking, respectively. Finally, the asphalt paving analyzer was conducted to evaluate the rutting of the samples of the GTR- and polymer-modified mixes. The field performance of the test sections was monitored for 30 months after construction. The results of the laboratory tests showed that the GTR- and polymer-modified mixes had acceptable resistance to low-temperature and fatigue cracking as well as to moisture-induced damage, which were in general similar to that of the mixes used in the polymer-modified PG 70-22M test section. Furthermore, the GTR mixes had better resistance to rutting. In general, the CR GTR mix had similar performance to that of the AM GTR mix. Finally, no distresses were observed in any of the polymer and GTR test sections in the first 30 months after construction.