| Asphalt pavement is widely used in all kinds of roads due to its advantages of smooth pavement,comfortable driving,short construction period and convenient maintenance.With the rapid development of traffic in China,the length of roads in forest areas,scenic spots and countryside is also increasing.Under the shady,humid or polluted environments,a large number of microorganisms exist on the asphalt pavement,which leads to the asphalt aging due to the degradation of the light component,resulting in the early destruction of the asphalt pavement.However,the current research mainly focuses on the thermal oxygen aging and ultraviolet aging,and few scholars pay attention to the microbial aging.The aging effects of microbial consortium on asphalt have not been paid enough attention.There were few studies on the aging mechanism by the microbial consortium.Therefore,this paper simulated the habitat for microorganisms and environment of asphalt aging,studied the aging behavior and mechanism of single bacteria and compound bacteria.The article also developed anti-aging agent and studied the effect of compound anti-aging agent on the performance of asphalt pavement,which is of great significance for improving the durability and extending its service life.First,select representative microorganisms of asphalt pavement in forest areas and rural areas for indoor culture,and then conduct microbial aging test.The aging behavior of single strain on asphalt was investigated by scanning electron microscopy(ESEM),infrared spectroscopy(FTIR),gel chromatography(GPC)and atomic force microscopy(AFM).The results showed that the microorganisms preferentially regard light components in asphalt as nutrient source to propagate on bituminous surface,forming some potholes.Further,BS and BL have a stronger degradation ability to light components,while PA can degrade more complicated structural components in asphalt.The molecular weight distribution of aged asphalt becomes more concentrated.The content of carbonyl and sulfoxide does not increase significantly,and the overall roughness of asphalt surface decreases.BS,BL and PA show the faster aging rates to light components,and are difficult to degrade resins and asphaltenes.BS has a higher prophase activity.The propagating rate of PA is between those of BS and BL and its prophase activity and aging rate are relatively stable.Secondly,BS,BL and PA were mixed in different proportions to form compound bacteria.A more suitable culture medium for the three microbial consortia is selected.ESEM,GPC,FTIR and AFM were used to investigate the aging behavior of compound bacteria on asphalt.Results indicated that the peptone content change of culture medium obviously affects the propagation of microbial consortia.The prepared culture medium II improved the degradation ability of compound bacteria.The compound bacteria preferentially degrade bituminous light components as their nutrient sources,and show weak degradation ability to macromolecular components.Moreover,the smaller molecules are decreased in aged asphalt and the molecular weight distribution of aged asphalt is narrowed.The carbonyl and sulfoxide contents are not changed obviously,but the methylene content is decreased.The compound bacteria of S2 show better synergistic effect to effectively degrade asphalt than those of S1 and S3.The maximum viscous force of aged asphalt is lowered,reflecting the decrease in bituminous viscidity.The elastic modulus of asphalt shows an increasing trend as the aging duration is prolonged.Then,according to the aging mechanism of compound bacteria,the anti-aging agent for bacteria was selected.The selected anti-aging agent was compounded,and the anti-aging properties of compound anti-aging modified asphalt were investigated by using FTIR,GPC,X-ray diffraction(XRD)and photoelectron spectroscopy(XPS).The results showed that the content of macromolecules in modified asphalt increases with the addition of compound anti-aging agent.The carbon element in asphalt mainly exists as C-H bond and C-C bond.With the aging duration is prolonged,the anti-aging agent components in the modified asphalt were decomposed continuously,which reduced the content of macromolecules,decreased the content of hydroxyl and the proportion of element C in hydrocarbons.The compound anti-aging agent can be dispersed evenly and maintain the complete crystal structure in asphalt.The anti-aging effect of FH1 is better than other two anti-aging agents.The addition of anti-aging agent inhibited the aging of asphalt by microorganisms.Finally,the influence of compound anti-aging agent on asphalt and its mixture pavement performance was studied through the test of asphalt conventional performance index,rutting test and freeze-thaw splitting test.The results showed that the compound anti-aging agent has no significant effect on the conventional properties of asphalt.The high temperature performance,low temperature performance and water stability of modified asphalt mixture meet the requirements of actual construction specifications.In a word,the paper reveals the aging mechanism of microorganisms on asphalt,and develops a compound anti-aging agent for microbial aging,which overcomes the microbial aging problem of asphalt pavement under the shady,humid or polluted environments.It is important to improve the aging mechanism of asphalt and improve the durability of asphalt pavement. |
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