Asphalt Pavement Magazine, July / August 2015
Richard Willis, PhD & Nam H. Tran, PhD, P.E., NCAT, Auburn, AL
When asphalt binder is exposed to oxygen and the sun’s ultraviolet rays, it begins to age and oxidize. The changes that occur to asphalt binders are primarily due to the chemical composition of the asphalt. Asphalt pavement changes occur in two stages: short-term and long-term. Short-term aging is mainly due to volatilization, oxidation, and/or absorption of oily components. Long term aging happens in the field and is mainly due to changes in composition through reaction between asphalt constituents and atmospheric oxygen.
These aging processes leave binders stiffer, less ductile, and with lower temperature susceptibility than conventional paving grade asphalts.
The aging process reduces the ratio of oily maltenes in the binder, leaving a greater ratio of stiffer asphaltenes, which cause the asphalt binder to become less ductile. These viscosity and elasticity changes result in a hardened, brittle asphalt binder.
