| With the advancement of industrialization,the phenomenon of acid rain is becoming increasingly prominent in China.Compared to simple water damage,acid rain can have a more adverse impact on asphalt pavements,and its erosive effect leads to a reduction in the service quality of asphalt pavements while also being detrimental to the green,ecological and sustainable development of road engineering.The damage caused by acid rain to asphalt pavements is mainly through the destruction of the adhesion capacity of the asphaltaggregate interface,so the change in the adhesion characteristics of the asphalt-aggregate interface under erosion is the key research element to study the effect of acid rain on the performance of asphalt pavements and the deterioration mechanism.To address these issues,this dissertation investigates the effects of acid rain on matrix asphalt and SBS(Styrene-butadiene-styrene)asphalt based on three levels: microscopic-fine-scopic-macroscopic.The macroscopic changes of asphalt,asphalt-aggregate interface and asphalt mixture under the effect of acid rain and the microscopic features are tested respectively.Firstly,we designed indoor vibration simulation method and wet and dry cycle method to simulate the actual environment of acid rain eroded pavement,then combined with the basic performance test of asphalt and FTIR(Fourier Transform Infrared),SEM(Scanning Electron Microscope),TGA(Thermogravimetric Analysis)and other tests to study the influence of acid rain erosion on the macroscopic properties and microscopic characteristics of asphalt;then,based on the surface free energy theory,we analyzed the wetting behavior of asphalt on the aggregate surface before and after acid rain erosion,and used the lying drop method to calculate the adhesion work of the system and the Then,the molecular interaction between asphalt-acid rain(water)-aggregate coexistence system was investigated by means of molecular dynamics simulation to further analyze the mechanism of the effect of acid rain on asphalt pavement.The results show that The test results show that:In asphalt,the softening point,ductility,and viscosity decreased after acid rain erosion,while the penetration increased;In the aspect of mixture,the impact of acid rain on its road performance is manifested as a significant weakening of high-temperature stability and water stability;As the erosion process progresses,the degradation rate of asphalt and its mixture performance slows down,because the accumulation of corrosion products in the later stages of erosion prevents acid ions from entering the asphalt and its mixture to a certain extent,mitigating the corrosion of acid rain on the sample.Acid rain mainly affects the component distribution and molecular action strength of asphalt.After erosion,asphalt will undergo dissolution,migration,and condensation,resulting in the destruction of its internal balance and reduced resistance to deformation.After acid rain erosion,the micromorphology of both asphalts has significantly changed.Irregular folds,pits,and microcracks have been observed on the surface of the base asphalt,while cracks first appear in SBS asphalt,and then continue to develop into cracks until blocky cracks occur.The TGA results show that the thermal stability of asphalt becomes worse after acid rain erosion,and there are phenomena such as lower initial decomposition temperature,faster mass loss rate,and larger mass loss rate.This is the result of the breaking and destruction of molecular bonds in asphalt under acidic conditions,as well as the accelerated expansion of cracks.Interfacial water is the key to weakening the interaction between asphalt and aggregate.Acid ions cause the components of asphalt to rearrange on the surface of the aggregate,while increasing the polarity difference between asphalt and aggregate,making it easier for acid rain molecules to break through the asphalt film and contact the aggregate,weakening the adhesion energy between the entire asphalt and the aggregate,leading to failure. |
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