Performance of Rubberized Asphalt Mixes in Alaska

Abstract

A study was conducted to compare the fatigue, thermal cracking, and permanent deformation resistance of several Alaskan crumb rubber–modified (CRM) asphalt mixtures with that of conventional mixes. Alaska Department of Transportation and Public Facilities–designated sites in Fairbanks and Anchorage were sampled to conduct flexural beam fatigue tests, thermal stress restrained specimen tests (TSRSTs) and Georgia loaded wheel tests (GLWTs) on both rubberized and conventional mixes. Condition surveys were also conducted at the sampled sites to assess the field performance of these mixes in terms of fatigue, rutting, and low-temperature cracking. Fatigue testing results combined with multilayer elastic analyses for typical Alaskan conditions indicated an enhanced fatigue resistance for the CRM mixes when compared with conventional mixes. However, field performance observations at both conventional and CRM sections indicated no signs of fatigue distress, suggesting similar field performance for both types of mixes. TSRST results indicated an improved thermal cracking resistance for the CRM mixes, especially when the wet process was used. These results were consistent with observed field thermal cracking performance. At a given site, the section with the largest transverse crack spacing had the mix with the coldest TSRST fracture temperature. Conventional mixes outperformed CRM mixes in resisting permanent deformation, in both the lab and the field. GLWT results indicated that CRM mixes deform more and at a faster rate than conventional mixes. This may be due to the dense-graded aggregate used in some of the highly modified CRM mixes, where aggregate-to-aggregate contact and interlock were absent.