Asphalt is widely used in road engineering, but asphalt pavement is exposed to the external environment for a long time and is affected by many different factors, such as ultraviolet, moisture, oxidation and so on. According to the different causes of asphalt aging, the aging of asphalt materials can be divided into thermal oxygen aging, light aging and water aging.

The aging of asphalt mainly occurs in the process of contacting with the external environment, and the main factors are oxygen and temperature. In the process of production and putting into use, asphalt begins to have different degrees of thermal oxygen aging reaction. At present, it is generally believed that thermal oxygen aging can be divided into three stages: the first stage is the transportation and storage link after production. In this stage, the contact area between asphalt and air is very small, and the thermal oxygen aging is not serious; The second stage is the mixing, paving and rolling process of asphalt and aggregate. In this process, the temperature of mixed asphalt will reach about 170 ° C, the performance index will be greatly reduced and serious thermal oxygen aging reaction will occur. This stage is the main stage of thermal oxygen aging; The third stage is the aging reaction of asphalt pavement under the influence of temperature change, ultraviolet radiation and other factors, which is also the main process of aging.  

The ultraviolet wavelength of sunlight on the surface through the atmosphere is 290-400nm, and its energy is higher than that of C-C bond and C-H bond connected with benzene ring and other stable groups in asphalt. Therefore, ultraviolet will destroy the asphalt structure and form free radicals, resulting in chemical reactions such as condensation and dehydrogenation of asphalt molecules, so that some aromatic components are transformed into colloids, Part of the colloid is transformed into asphaltene, and the final proportion of asphaltene increases significantly. The aged asphalt gradually becomes brittle and hard, and the low-temperature crack resistance and fatigue durability of the pavement are significantly reduced. There are many factors affecting the photoaging of asphalt, including UV irradiation intensity, irradiation time, asphalt film thickness, etc. among them, UV irradiation intensity is the most important factor affecting the photoaging rate. The photoaging rate of asphalt accelerates with the increase of UV irradiation intensity and irradiation time. After asphalt mixing, the asphalt film wrapped on the aggregate is very thin. Under UV irradiation, the thinner the asphalt film is more prone to aging and the more serious the aging is.