Use of Crumb Rubber in Performance Graded Binder

About four billion scrap tires currently reside in landfills and stockpiles across the nation. Most markets which use recycled tires as a raw material cannot support additional expansion. One of the available expanding markets for scrap tires is crumb rubber modified (CRM) asphalt for use as pavement. During production of CRM binders, there are two concerns relative to property measurement. The first is testing the appropriate properties to ensure quality control during binder production. The second is testing of binder properties to determine performance characteristics of the pavement. This study investigates the effects of various crumb rubber materials on binder performance-related parameters evaluated using performance graded testing procedures. The study also examines the interaction process variables of time and temperature to determine the appropriate parameters for producing CRM binders with specific performance related properties. Two types of interactions were evaluated. The first was short term interactions, which models actual binder production. The second was intermediate term interactions extending for up to several hours, which models a storage period. This study summarizes the effects of polymer modifiers as supplemental additives to improve the performance, stability and workability of CRM binders. The study includes recommendations for production processes and conditions, as well as suggestions for performance-related specifications pertaining to CRM asphalt production