Effects of ultraviolet (UV) radiation on thermal, chemical, and rheological properties of rubber-modified asphalt binders

This research aims to investigate the thermal, chemical and rheological properties of UV-aged asphalt binders containing recycled tire rubber (RTR) powder. The UV Aging process changes the chemical composition and physical properties of asphalt and causes distress on pavement. It is known that the presence of crumb rubber (CR) reduces the susceptibility of asphalt to aging, but its mechanism is not fully understood. Moreover the rheological performance of a crumb rubber modified binder are still partially unknown. In this research, the effect of ultraviolet (UV) rays on samples of asphalt binder mixed with crumb rubber is studied. One neat binder and two sets of rubber-modified samples with 16.6 and 20 %wt. are prepared and then inserted inside a QUV Accelerated Weathering Tester for 100 hours. The samples are then collected and changes in their thermal conductivity, chemical indices and rheology are studied using Nanoflash, differential scanning calorimeter, FTIR, and dynamic shear rheometer (DSR), respectively. Results show that addition of rubber leads to a reduction of specific heat for the two rubberized binders. Specific heat capacities of the three UV aged samples are larger than those of their unaged counterparts, and the 16.6%-aged has the highest value. FTIR spectra of the three unaged samples are very similar, whereas distinct changes occur after UV aging. The normalized absorbance of peak associated with S=O group increases and the peak for the aliphatic group decreases after UV aging, showing some evidences of oxidation due to UV aging. Using crumb rubber in the binder decreases the thermal conductivity and 20% wt. sample is even less conductive compared to the 16.6%wt. At all temperatures above 25°C, aged samples have lower thermal conductivity than the unaged ones, except neat binder which was opposite. Rheological measurements show that complex modulus of the samples increases with addition of rubber particles and also aging.