Research On The Ultraviolet Radiation Ageing Characteristics Of Asphalt

Oxidation degradation causes hardening of asphalt and, consequently, may make a contribution to the deterioration of asphalt pavements. The principal reason of asphalt oxidation and embrittlement during service period is ultraviolet radiation in sunlight, especially in the high elevation areas where there is intensive ultraviolet radiation. The profound researches on the mechanism of photooxidation, rheological properties, service performance and retained fatigue life of asphalt binder, under the condition of ultraviolet radiation, are important for evaluating and forecasting the photooxidation resistance of asphalt.(1) Fourier Transform Infrared (FTIR) and Dynamic Shear Rheometer (DSR) were used to investigate the dominant effect factors in the indoor accelerated ultraviolet radiation (UV) ageing test, including ultraviolet radiation intensity, temperature, sample thickness and ageing time. Based on the estimation of the environmental conditions, a suitable ultraviolet radiation ageing condition was chosen for UV test. The higher the ultraviolet radiation intensity was, the faster the speed of carbonyl index increased. The effect of UV radiation was dominant, in particularly when the film thickness was smaller than 100μm.(2) By methods of four components analysis and FTIR, the influences of ultraviolet radiation ageing on chemical structural evolutions of asphalt binders were investigated. Results indicated that the carbonyl and sulphoxide indices of asphalt increased remarkably, resulting in more polar groups and the fraction of asphaltenes after ultraviolet radiation ageing as well as the formation of gels. With respect to the aging of SBS modified asphalt, there were more carbonyl and sulphoxide groups but less chain segments of butadiene. The analysis of FTIR spectra demonstrates that oxidation of base asphalt and degradation of SBS modifier occurs in parallel during ageing, which contribute to the changes on the chemical structure of SBS modified asphalt after ageing.(3) By ~1H Nuclear Magnetic Resonance (~1H NMR), test results show that during the ultraviolet radiation ageing process, several chemical reactions were occurred including isomerization, dealkylation and dissociation.(4) Using Atomic Force Microscopy (AFM), test results indicate that the distinct changes of asphalt in surface morphology occurred as a result of chemical structure changes during ageing. Due to ageing, asphaltene aggregates in base asphalt become larger, and network structure in SBS modified asphalt was disappeared and the surface morphology of SBS modified asphalt became close to base asphalt. The existence of SBS can only partly improve the dispersion of asphaltenes in bitumen after ageing, in consistence with the results of four components analysis, FTIR and ~1H NMR analysis.(5) Based on Brookfield viscosity and DSR tests, the effects of ultraviolet radiation ageing on the rheology and pavement performances of asphalt were investigated. Results indicate that viscosity of asphalt was enhanced, particularly in low temperature when compared to high temperature. The temperature sensibility was weakened after ultraviolet radiation ageing. The complex modulus was increased, while the phase angle was decreased, and the aged asphalt became hard. The flat area of phase angle of SBS modified asphalt was moved to high temperature area and then disappeared with the extension of the ageing time.(6) DSR time sweep fatigue test in constant strain was conducted to study the fatigue life of asphalt. Results indicate that ultraviolet radiation ageing caused the decrease of fatigue performance distinctly, and the influence of ultraviolet radiation on fatigue life of asphalt was the greatest among other factors.(7) SBS modifier improved the performance of base asphalt, while the improvement effect reduced gradually with the ageing time, whereas the property of SBS modified asphalt was still better than that of base asphalt.(8) The short-term ultraviolet radiation ageing may be stronger than PAV ageing that is recommended to assess the long-term ageing effect. It is especially true in the high latitude regions where the solar radiation is expected to be very strong. At the same time, compared with the PAV experiment, the UV test has a better corresponding relationship with the outdoor Natural Exposure Ageing (NEA) test.