Research on Ultra Violet (UV) aging depth of asphalts

UV radiation contains high energy which could excite asphalt molecules to excited states or break the covalently bond of asphalt. It leads to the asphalt aging on surface of asphalt pavement during servicing period. However, UV aging principle of asphalt is not quite clear. Even the thickness of asphalt that researchers used in UV aging simulation experiments were not unified. So in this paper, the UV aging depth of asphalt was investigated by Ultraviolet Spectrophotometer tests (UST) and peeling method. In the UST, the statistics presented that the transmittance of asphalt reached 0% when the thickness of asphalt was around 4.5 μm. And in the peeling method, the aged asphalt was peeled layer by layer using carbon disulfide. Then the properties of peeled aged asphalts were evaluated by temperature sweep test (carried by Dynamic shearing rheometer) and four components test. And the changing properties of peeled aged asphalts showed that the aged asphalt on the top surface was diffused to the underpart asphalt. And the diffusion depth of UV aged asphalt could be nearly 2200 μm at 10 d UV aging time. And finally, the UV aging model asphalt was built. All the results indicated that UV radiation could only age the limited depth of asphalt and the aging phenomenon of lower asphalt (under 4.5 μm) was caused by diffusion of the surface aged asphalt within 4.5 μm thickness.