Use of crumb rubber in lieu of binder grade bumping for mixtures with high percentage of reclaimed asphalt pavement

Abstract

Use of recycled/reclaimed asphalt pavement (RAP) leads to economic as well as environmental benefits. However, increasing the percentage of RAP in a new asphalt pavement may hinder the economic benefits due to the necessity of expensive softer binders used to compensate for RAP stiffening effect. Alternatively, this problem may potentially be overcome by use of another recycled material: crumb rubber (CR). In this study, linear viscoelastic, thermal and fatigue cracking properties of mixtures prepared with different rubberised asphalt binders were compared with the soft binders. The scope of the testing included asphalt mixtures produced from the following binders; (i) devulcanised rubber, (ii) CR terminally blend, (iii) CR wet process, (iv) soft binder (PG 58-34) and (v) base (control) binder (PG 58-28). The results of the fatigue tests indicated that CR-modified asphalt mixtures made with the base binder (PG58-28) outperformed the mixture made with grade bumped (PG58-34) binder. Similar results were observed in low-temperature cracking tests. The results indicated that the CR-modified binders can be used in lieu of grade bumping of binders in high RAP mixtures. In fatigue cracking tests, among the three CR technologies, wet process outperformed terminally blend and devulcanised rubber at high temperatures and high strain levels at low temperatures. At relatively low strain levels, terminally blend was the best performer in low temperature. In low-temperature cracking tests, devulcanised rubber exhibited highest tensile strength, but lowest fracture energy. Wet process exhibited highest fracture energy and lowest strength.

Keywords:

• Rubber softening effect
• devulcanised binder
• low-temperature cracking
• fatigue cracking
• visco-elastic continuum damage
• binder grade bumping

ORCID

Salih Kocak http://orcid.org/0000-0002-6049-5266

M. Emin Kutay http://orcid.org/0000-0002-0575-1917

Additional information

Funding

The authors would like to thank the Michigan Department of Environmental Quality (MDEQ) for their financial support of this study through the scrap tire market development grant. Valuable comments of Michael Marshall and Rhonda Oyer of MDEQ during the research project are also greatly appreciated.