| Asphalt pavement has been exposed to the natural environment since it was built and is directly subjected to the influence of continuous climate changes such as solar radiation,external temperature and rainfall.At the same time,the new pavement has been damaged to a considerable extent in a short period of time with the rapid development of China’s transportation industry and thus affecting the performance of asphalt pavement.So it is urgent to take corresponding pre-conservation measures to extend the service life of asphalt pavement.The aging law and aging mechanism of asphalt must be analyzed and studied in order to make the asphalt pavement affected by aging get reasonable maintenance and regeneration.In this paper,we design an indoor"light,heat and water"multi-factor coupled cycle aging test by simulating the asphalt top layer in summer with high temperature,rain and intense UV radiation,and considering the temperature,UV and water factors based on the number of cycles.Based on the data collected at the National Meteorological Science Data Center,the climate distribution conditions of UV radiation intensity,temperature(high temperature in summer)and water(rainfall)in Nanjing,Jiangsu Province were analyzed to determine the indoor simulated accelerated aging environment conditions:irradiation intensity of 46.6 m W/cm~2,aging temperature of 70°C and single spraying time of 3 minutes and 53 seconds.The experimental study of the coupled cyclic aging of matrix asphalt was conducted in four aspects:change in morphological characteristics,change in macroscopic properties,change in adhesion properties and change in microstructure.A prediction equation model for the aging rate of macroscopic properties and adhesion properties and the corresponding microstructure aging kinetic index equation were established,and the correlation between microstructure and macroscopic properties and adhesion properties of matrix asphalt during coupled cycle aging was obtained by using gray correlation analysis.The analysis obtained the multifactor coupled cycle aging mechanism of matrix asphalt,i.e.,photothermal aging is a photothermal oxidation reaction in which all microscopic components of asphalt participate together.The oxidation reaction becomes intense at high temperature and then the ultraviolet light activates the polar groups generated by thermal oxygen aging,which further triggers the oxidation reaction.Hot water aging is an interactive,together hot water oxidation reaction.The polar groups in water cause asphaltenes at the reaction interface of asphalt and water.The polar groups in water make asphaltenes in the interface of asphalt and water reaction into a strong structural film and gradually harden and deteriorate.Light and water aging is the coupling reaction of ultraviolet light with water and oxygen.Ultraviolet radiation makes microstructure condensation effect,resulting in the aggregation of asphaltenes flocculation precipitation precipitation.Colloidal system from sol to gel,from colloid to solid transformation and water by dissolving part of the aging products downward penetration,which accelerating the asphalt aging.The role of light,heat and water coupling cycle lead the asphalt light components volatile oxidation,the microscopic components to change,such as aromatic fraction into gum,gum into asphaltene and saturated fraction to promote this transformation,which leads to a reduction in structural stability and ultimately the macroscopic properties of asphalt and adhesion performance decay.Through the analysis method of pre-conditioning timing based on aging index,the adhesion Ad of asphalt is selected as the decisive aging index and the best pre-conditioning timing of asphalt fog seal based on adhesion performance is analyzed in the"light,heat and water"multi-factor coupled cycle aging test by three groups of coupled cycle aging(L3).The optimal pre-conservation time for the adhesion-based fog seal is 1%-5%of the adhesion Ad value.The optimum amount of recycled raw materials was determined by the performance design method,and the optimum amount of silicone fog seal was 6%and the optimum amount of recycled fog seal was 4%.The effect of silicone fog sealer and regenerative fog sealer on aging asphalt maintenance and regeneration was evaluated and analyzed from three aspects:morphological characterization,macroscopic properties and adhesion performance.The coupled cycle aging mechanism of matrix asphalt studied in this paper can provide a practical and rigorous theoretical basis for the maintenance and regeneration of aging asphalt pavement and guide the actual project.The best pre-conservation timing of fog sealer based on asphalt adhesion performance analyzed in this paper can propose reasonable index and timing for the promotion and application of regenerative fog sealer technology in China. |
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