Nebraska LTAP
Date of this Version
5-31-2024
Document Type
Article
Citation
Bastola, N. R., Khedmati, M., Teixeira, J. E. S. L., and Haghshenas H.F. (2024) Effect of Antioxidant Additives and Recycling Agents on Performance of Asphalt Binders and Mixtures - Phase I. NDOT Research Report SPR-P1(20)M116.
Abstract
The use of reclaimed asphalt pavement (RAP) in asphalt mixtures has notably increased in recent times. Nevertheless, the inherent stiff and aged characteristics of RAP materials have consistently raised concerns regarding cracking performance. The use of recycling agents (RAs) has gained popularity in recent years since they can effectively modify the engineering properties of the aged asphalt binder. Besides that, the combination of RA with antioxidant (AO) additives has shown promise in enhancing the long-term performance of RAP mixtures. This research aims to investigate the effect of various RAs and one AO additive on performance of asphalt binders and high-RAP mixtures. Five RAs (paraffinic oil, naphthenic oil, aromatic extracts, triglycerides/fatty acids, and tall oils) and one AO (zinc diethyldithiocarbamate - ZnDEC) were selected. Initially, the effects of RA and AO were analyzed at the binder level considering chemical (SARA, FT-IR, CHNOS) and rheological as well as physical (DSR, BBR, and Wihelmy Plate) testing results. Secondly, following the findings at the binder level, two specific RAs (naphthenic oil and triglycerides/fatty acids) were chosen and utilized in combination with ZnDEC to modify the binder used in producing high-RAP mixtures. The studied mixtures were subjected to semi-circular bending test (SCB) and Hamburg wheel tracking test (HWTT) to evaluate cracking, rutting and moisture damage resistance of the mixtures, respectively. The chemical analysis of the RAs showed that those based on triglycerides/fatty acids and tall oils demonstrated pronounced peaks near the 1740 cm-1 region and a greater oxygen content relative to other RAs. As expected, the RAs had a softening effect on the binder blends. Additionally, ZnDEC helped retard the oxidation of the RA-modified binders, and its effectiveness depended on the RAs' susceptibility to aging. At the mixture level, the simultaneous use of RAs and ZnDEC in the high-RAP mixture improved cracking performance and reduced oxidative aging but might negatively affected rutting and moisture damage resistance.