Use of Zinc Diethyldithiocarbamate as an Antioxidant for Asphalt Binders

Asphalt aging imparts irreversible changes in the binder properties, leading to premature failure of pavements. Therefore, it is imperative to abate the aging process for improving the durability and serviceability of pavements. The use of antioxidants, which act as sacrificial agents and limit the growth of aging-propagating compounds in the asphalt binder, is an effective way to reduce the rate of aging in binders. This study examined the performance of zinc diethyldithiocarbamate (ZDC) as a potential antioxidant additive. The laboratory evaluation of ZDC modified binder was carried out using a dynamic shear rheometer (DSR) and Fourier transform infrared spectroscopy (FTIR) at various aging conditions. Three base binders of similar grade were modified with a single dosage of ZDC, and the influence of the modification on the stiffness, fatigue, and aging characteristics of asphalt binders was evaluated. It was found that irrespective of the binder source, ZDC modification enhanced the fatigue resistance of the binder without altering the stiffness characteristics. On average, the fatigue life of antioxidant-modified binders was found to be 4, 31, and 34 times higher than that of the base binders after 20-, 40-, and 60-h aging periods, respectively. The occurrence of new peaks in FTIR spectra indicated chemical interaction between the antioxidant and base binder. The inclusion of ZDC additive significantly lowered the aging indices derived from both rheological and chemical analysis. The Fraass breaking point temperature reduced by an average of 2°C for antioxidant-modified binders, indicating improvement in low-temperature properties. Statistical results showed that the performance of modified binder was not affected by varying the source of the base binder. The practical utilization of ZDC in pavement construction was studied using a multielastic layer pavement analysis tool. The results indicated that, compared with conventional asphalt binder, antioxidant modification led to a 17% reduction in the asphalt layer thickness, which is estimated to result in a 6.6% cost saving per lane per kilometer in construction. It was concluded that antioxidant modification is an economical method to prolong the service life of the pavement.