Asphalt is currently widely used in road engineering, but the asphalt pavement is exposed to the external environment for a long time and is affected by many different factors, such as: ultraviolet rays, moisture, oxidation and so on.
According to the different causes of asphalt aging, the aging of asphalt materials can be divided into thermo-oxidative aging, light aging and water aging.
1. Thermo-oxidative aging of asphalt
The aging of asphalt mainly occurs in the process of contact with the external environment, and the main factors are oxygen and temperature. In the process from production to putting into use, asphalt begins to undergo different degrees of thermo-oxidative aging reaction. It is generally believed that thermo-oxidative aging can be divided into three stages: the first stage is the transportation and storage link after production. The contact area is very small, and the thermal-oxidative aging is not serious; the second stage is the mixing, paving and rolling process of asphalt and aggregate. During this process, the temperature of the mixed asphalt will reach about 170°C, and the performance indicators will be severe. Reduce and produce serious thermo-oxidative aging reaction, this stage is the main stage of thermo-oxidative aging; the third stage is the aging reaction of the pavement under the influence of temperature changes, ultraviolet radiation and other factors after the asphalt pavement is completed, which is also aging the main process.
2. Photoaging of Asphalt
The wavelength of ultraviolet rays irradiated by sunlight on the surface through the atmosphere is 290-400nm, and its energy is higher than the C-C bond and C-H bond energy in the asphalt connected to the benzene ring and other stable groups, so the ultraviolet rays will have a destructive effect on the asphalt structure. The formation of free radicals causes chemical reactions such as condensation and dehydrogenation of asphalt molecules, so that some aromatic components are converted into colloids, and some colloids are converted into asphaltenes, and the final proportion of asphaltenes 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 that affect the photoaging of asphalt, including: ultraviolet light irradiation intensity, irradiation time, asphalt film thickness, etc. Among them, the ultraviolet light irradiation intensity is the most important factor affecting the photoaging rate. The increase of light irradiation intensity and the increase of irradiation time accelerated. After the asphalt is mixed, the asphalt film wrapped on the aggregate is very thin (usually only about 10 μm). Under the irradiation of ultraviolet light, the thinner the asphalt film is more prone to aging and the aging is more serious.
3. Water aging of asphalt
Asphalt is a hydrophobic material, and its internal soluble substances will be reduced due to the long-term penetration of water, resulting in an aging reaction. Since liquids such as water can penetrate into the interior of asphalt, and the PH value of such liquids is different, it has a great influence on asphaltenes in asphalt and the interfacial tension between oil and water.
There are relatively few studies on water aging at home and abroad. The 15 causes of asphalt aging include the effect of water, and it is found that water will accelerate the aging of asphalt under the combined effect of time, heating, oxygen and sunlight.
With the deepening of aging degree, the complex modulus of asphalt increases and the phase angle decreases. With the participation of water, the complex modulus of the asphalt has a larger increment than that without the participation of water, and its phase angle is smaller. The participation of water reduces the fatigue limit temperature of asphalt and reduces the fatigue resistance of asphalt. The stiffness modulus of the water pressure-aged asphalt is greater than that of the conventional pressure-aged asphalt, indicating that the effect of water makes the asphalt hard, the low temperature stiffness increases and the aging degree deepens, which reduces the low temperature crack resistance of the asphalt.
CN
MM
EN
AR
June 29, 2022 
