| With the increase of highway mileage in China,the status of preventive maintenance in pavement disease prevention and control engineering has been improved.In high altitude area,there are extreme climatic conditions such as strong ultraviolet radiation and large temperature difference between day and night.Asphalt materials are more prone to aging,which accelerates the attenuation of pavement performance of micro surfacing,and seriously affects the application effect of micro-surfacing in preventive maintenance in plateau area.A large number of simulation studies on ultraviolet aging of asphalt have been carried out at home and abroad.However,there is little research on the actual aging of asphalt in micro-surfacing maintenance in high altitude area.In view of this situation,raw materials were selected from the construction site to prepare micro surfacing specimens,and the samples were exposed to natural environment at 3500 m altitude for 6,12 and 18 months.The effects of mineral powder content,asphalt content,paving thickness,gradation,asphalt type and aging time on the natural aging process of micro surfacing binder were investigated.Then,asphalt with different aging degree was recovered through asphalt extraction experiment,and the rheological properties of asphalt after aging were tested by dynamic shear rheological test(DSR).Finally,the aging law of micro surfacing asphalt material in natural environment of high altitude area was explored by using infrared spectroscopy(FTIR).The research results have guiding significance for delaying the aging rate of micro surfacing overlay asphalt in high altitude and strong ultraviolet area,improving the service life of pavement and mix design of micro-surfacing.The results show that the longer the aging time of asphalt mixture is,the more serious the asphalt aging is.The aging rate of asphalt in summer and autumn is higher than that in spring and winter.The asphalt aging degree is the lowest when the mineral powder is5% and asphalt is 9%,and the asphalt aging degree is the largest when the mineral powder is 15% and asphalt is 6%.When the powder binder ratio is 1.3 ～ 1.6,G*,phase angle and rutting factor change little.The growth rate of asphalt rutting factor without SBR addition is higher than that of SBR modified asphalt,and the ability to resist aging is even worse.There is no significant difference in asphalt aging between 0.8cm and 1.2cm microsurfacing mixture,and 0.8cm micro-surfacing mixture can fully absorb ultraviolet radiation in the atmosphere.Compared with MS-II mixture,MS-III mixture has larger porosity,larger area exposed to air and more serious aging.The infrared spectrum analysis showed that the content of methyl and methylene decreased,the carbonyl absorption peak increased,and the light component transformed into the heavy component.Compared with the base asphalt,the carbonyl group of SBR modified asphalt did not show obvious absorption peak,and the sulfoxide group increased significantly,indicating that the sulfur bond in SBR was oxidized prior to the carbon oxygen double bond.The carbonyl absorption peak of asphalt in MS-III SBR asphalt mixture is stronger than that in MS-II SBR asphalt mixture,which indicates that asphalt aging in MS-III asphalt mixture is more serious.The change of functional groups is consistent with the macro rheological properties,which can better explain the aging behavior of asphalt in mixture.Based on the above conclusions,it is recommended to use SBR modified emulsified asphalt to pave the MS-II micro-surfacing mixture with a thickness of 0.8cm.According to the actual project,the amount of mineral powder is reduced and the asphalt content is increased. |
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