| Asphalt pavements are unable to cope with the effects of complex and changing traffic and climatic conditions,and their roadworthiness can deteriorate too quickly.Nanomaterials are often used as asphalt modifiers to improve the high and low temperature performance and anti-aging properties of asphalt due to their unique surface effect,small size effect and macroscopic quantum tunneling effect.In order to study the performance of graphene oxide(GO)modified bitumen before and after ageing and its anti-ageing mechanism,this paper firstly tested the physical properties of bitumen before and after ageing,then tested and analyzed the high temperature viscoelastic properties,fatigue properties,low temperature thermal properties,component changes and colloidal structure,carbonyl functional group and sulfoxide group content,microstructure,nano adhesion and microstructure evolution of different bitumen before and after ageing.Finally,the ageing resistance mechanism of GO-modified bitumen was analyzed based on the free radical theory and combined with the structural properties of GO,the colloidal structure of bitumen and the content of oxygen-containing functional groups.The main research findings are as follows:(1)The test results of physical properties,high temperature viscoelastic properties,fatigue properties and low temperature thermal properties of GO modified asphalt before and after aging show that the addition of GO can reduce the temperature sensitivity of asphalt before and after aging,improve the high temperature stability and anti-aging properties,and extend the service life of asphalt.The GO/styrene-butadiene-styrene block copolymer(SBS)modified bitumen has the best fatigue resistance,however,GO reduces the low temperature stability of the bitumen,but the effect is minimal.Thermal oxygen ageing improves the three-dimensional mesh structure of the bitumen and increases the cross-link density of the bitumen.The addition of GO significantly increases the cross-link density of the bitumen and is better than SBS modified bitumen for 70#base bitumen.(2)The test results of the colloidal structure and chemical properties of GO-modified bitumen before and after ageing showed that the addition of GO transformed the aromatic fraction in the bitumen to colloidal and asphaltene,and also reduced the effect of thermal oxygen ageing on the content of bitumen components and colloidal stability.The addition of GO promotes the production of amides and facilitates the miscibility of GO with bitumen,while effectively inhibiting the increase of carboxylic acid and ketone content in bitumen and improving the ageing resistance of bitumen.(3)The microscopic properties of GO-modified bitumen before and after ageing were found that thermal oxidative ageing caused dramatic changes in the microscopic surface structure and bee-like characteristics of the bitumen,while the bee-like structure of GO-modified bitumen changed to a relatively small extent,and the boundary between the phases changed more obviously.The surface roughness of GO-modified bitumen is lower and the surface is flatter,resulting in less variation between phase states at the nanoscale,proving that GO-modified bitumen has a better component content ratio and a more stable colloidal structure.(4)The colloidal structure of the GO-modified bitumen is more stable and the aromatic content is slightly reduced,but the amount of change in the oil fraction after ageing is smaller,indicating that GO has a certain adsorption of lighter components and produces shielding protection for the components between the income layers,which in turn reduces their volatilization or the occurrence of polymerization and dehydrogenation,thus playing a role in improving the ageing resistance of the bitumen.Based on the free radical theory,GO can effectively reduce the amount and rate of O2 penetration,which on the one hand reduces the rate of free radical generation during chain initiation,and on the other hand reduces the reaction rate between O2 and the generated free radicals,prolongs the chain reaction time and inhibits the growth of carbonyl and sulfoxide groups,thus improving the ageing resistance of asphalt. |
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