Increasing the efficacy of recycling agents with simultaneous addition of zinc diethyldithiocarbamate as an antioxidant

Abstract

Recycling agents are commonly used to enhance the properties of aged asphalt binder. The aged asphalt binder found in reclaimed asphalt pavement is considerably oxidized and has lost a significant amount of its volatiles during its service life. Therefore, its performance characteristics need to be improved before it can fully function in new–pavement construction. Recycling agents are intended to modify performance characteristics; however, typical recycling agents are prone to oxidation, which renders them ineffective. It is hypothesized that the efficacy of recycling agents can be enhanced by simultaneous addition of antioxidants to the binder system. Therefore, in this paper, the synergy between three types of recycling agents (paraffinic oil, triglycerides and fatty acids, and tall oil) and zinc diethyldithiocarbamate (ZnDEC) as an antioxidant is examined using rheological characterization at high, ambient, and sub-zero temperatures. The study results show that the efficacy of recycling agents was improved with the addition of ZnDEC; however, the efficacy of the ZnDEC varied depending on the recycling agent used. The latter was attributed to the susceptibility of recycling agents to oxidation as well as the extent of synergy between a recycling agent and ZnDEC.