Research On Mechanism And Characterization For Ultraviolet Aging Of Asphalt

Asphalt is complex compounds,which is composed of aromatic,saturated,asphaltene,colloidal and other polymer materials.In the service period of asphalt pavement,asphalt will be aged by the temperature,ultraviolet light,resulting in deterioration of its performance.So domestic and foreign scholars widely used thermal short term aging?TFOT and RTFOT?,thermal long term aging?PAV?and thermal accelerated aging method for asphalt mixture to simulate the aging process and predict changes of properties.However,the asphalt will also be aged by ultraviolet light during its service time.And there is no standard to gudie simulation of ultraviolet light aging for asphalt.So it is necessary to systematically study the aging behavior of asphalt and its mixture under ltraviolet light.Firstly,the maximum depth that UV rays could penetrate into asphalts was studied.Then,asphalt layer peeling experiment was used to remove the asphalt layer after UV aging.And the dynamic shearing rheometer?DSR?,four components experiment and Fourier transform infrared spectroscopy?FTIR?were used to study the UV aging depth of asphalt and the diffusion mechanism of UV aging.Then aging effects of UV aging time,sample thickness,temperature and UV light length was further studied.On this basis,a simplified diffusion model of UV aging was established to calculate the diffusion coefficient of UV aged asphalt by Fick's second law and different performance indexes?composite modulus,phase angle,carbonyl factor and asphaltene?.After that,the advantages and disadvantages of these methods were compared.Furturemore,the asphalt mixture with different asphalt and different structure was aged and studied by two kind of the ultraviolet aging methods?UV aging before molding and post-molding?.Finally,the mechanism of two kinds of UV aging methods was analyzed by a single gradation asphalt mixture.The main conclusions were as follows:?1?The results of the UV spectrophotometer and the asphalt surface peeling method showed that only about 0-5?m of the surface layer of asphalt could be directly aged by ultraviolet light.The directly aged asphalt would gradually diffuse to unaged asphalt below 5?m?not UV irradiated to depth?,while the unaged asphalt below 5?m would also gradually diffuse to the aging layer of asphalt.During the process of UV aging,the interdiffusion process of aged asphalt and unaged asphalt occurred.?2?The simple UV diffusion model was established.Then diffusion coefficient of the aged asphalt was calculated by using different parameters?Loglog complex modulus and phase angle model,carbonyl factor and asphaltene?.The diffusion coefficient of the aged layer calculated by the Loglog model and the asphaltene was in the order of 10^-1?m²/s,and the diffusion coefficient of the carbonyl factor is on the order of 10^-2?m²/s.The comparative analysis showed that the composite modulus of Loglog complex modulus and translation complex modulus were most suitable for the calculation of the aging diffusion coefficient of asphalt.?3?The relationship between the aging degree of asphalt and the time of UV aging was studied by using complex modulus,four components and carbonyl factor.The composite modulus ratio showed a good linear relationship with the UV aging time and asphaltene,colloid instability index Ic and carbonyl factor showed a logarithmic growth relationship with UV aging time.Then two prediction models of complex modulus and carbonyl factor of asphalt were established.Finally,two ways to shorten the UV aging time of asphalt were proposed.?4?According to the composite modulus and the carbonyl factor under the three different wavelengths of 380nm,320nm and 280nm,the principle of ultraviolet aging of asphalt was mainly based on molecular excitation theory and supplemented by breaking bond theory.?5?The mechanism of UV aging before molding and post-molding on the performance of asphalt mixture was completely different.And a single graded asphalt mixture was aged by the UV aging post-molding method.The results were showed that only the upper layer of ultraviolet light on a particle size of the asphalt played a significant role in aging.Compared by actual service situationa of sphalt pavement,it was considered that the UV aging of asphalt mixture was more realistic to study the aging of asphalt mixture.