Study On The Long-term Performance Deterioration Characteristics Of Epoxy Porous Asphalt Pavement Based On All-weather Conditions

Porous asphalt pavement is a versatile,ecologically oriented pavement that possesses attributes such as drainage,noise abatement,skid resistance,rainwater purification,and regulation of surface temperature and humidity.Its primary composition involves high viscosity asphalt and other thermoplastic asphalts.Due to the deficit in oxidation resistance and under the prolonged multi-field coupling of load,temperature,and water,porous asphalt is susceptible to aggregate spalling,scattering,and fatigue cracking,among other problems.These issues become particularly pronounced in areas with high horizontal shear force and frequent braking-start-stop activities.In contemporary times,countries such as Europe and Japan have turned to the use of epoxy asphalt and other thermosetting materials noted for their strength,adhesion,and durability.These materials are gradually replacing high viscosity asphalt in order to fortify the porous asphalt mixture and enhance the overall performance of porous asphalt pavement structures.Nonetheless,research in this field remains limited and superficial.This study aims to provide a comprehensive analysis of the weathering ability,road performance,and functional degradation of porous epoxy asphalt mixtures.To attain a more profound and holistic understanding of the degradation patterns of each basic performance aspect of porous epoxy asphalt pavement in service,this research initially conducts a comprehensive comparison of the impacts of thermal and oxygen aging（both short and long term）,damp heat aging,ultraviolet light aging,and all-climate aging.The results reveal notable variations in the sensitivity of different binders to aging factors,with damp heat deterioration on thermosetting materials being particularly significant.Following that,the deterioration pattern of epoxy asphalt under multi-factor,all-climate coupled aging conditions,such as temperature-humidity-lighting,is proposed.This is achieved through macroscopic and microscopic methods based on the decay characteristics of binder properties under different single-factor aging conditions.The study reveals that the resin in the epoxy asphalt is more susceptible to the full-climate aging effect than the asphalt as aging time extends.Concurrently,the similarity of Fourier transform infrared reflection（FTIR）spectra progressively decreases,and certain absorption peaks undergo consistent modifications in relative intensity and peak shape.This suggests that an extension in aging time would impact the coating structure of epoxy resin and asphalt,leading to the degradation of epoxy resin.Observations from the atomic force microscope（AFM）reveal that the resin material lacks a continuous undulating bee-type structure,and its roughness significantly surpasses that of the asphalt material.Metrics such as R_q,R_a,R_max,and image surface area difference（ISAD）all steadily increase with the advancement of aging time.This is primarily attributed to the post-curing behavior induced by aging.The co-existence of material property enhancement and weakening is predominantly caused by the combined impact of this post-curing behavior and environmental degradation.The scanning electron microscope（SEM）images demonstrate that the originally closed micropore structure on the specimen’s surface gradually opens,enlarges,and develops microcracks that extend outward from wide to narrow.Consequently,it can be inferred that the coupling effect of multiple factors peels off the surface coverings,exposes the interiors of the micropores as the aging weak zone,and ultimately triggers the formation of cracks.Through the analysis facilitated by molecular dynamics simulation,full-atom models of both matrix asphalt and epoxy asphalt,pre and post-aging,are developed.These models qualitatively and visually depict the concentration and distribution of the oxygen element,which has the most significant change across different models.They also facilitate the computation of mechanical parameters across these models,such as free volume fraction,diffusion coefficient,cohesive energy density,bulk modulus,shear modulus,and Young’s modulus.This further enables the exploration of molecular motion characteristics from a mechanical properties standpoint.The study reveals that complex cross-linking bonds contribute to the reduced activity of epoxy-curing products.Post-aging,the structure contains numerous short-chain small molecules with robust diffusion activity,along with a minimal quantity of water molecules.This leads to increased diffusion coefficient,and the heightened content of polar oxygen,coupled with the enhanced electrostatic force,results in stronger adsorption between the asphalt and the epoxy curing products.To further investigate the degradation pattern of the porous epoxy asphalt mixture’s performance,an initial gradation test was first conducted using the uniform design method.Following that,considering the initial viscosity of the epoxy asphalt system is determined by the base asphalt and the later viscosity is influenced by the cross-linking degree between the epoxy resin and the curing agent,the asphalt film thickness was selected.This selection takes into account its time-temperature characteristics,and optimizes the calculation method for instances where no apparent inflection point and intersection of dispersion loss and precipitation loss occur.Subsequently,the volume index evaluation method of porous epoxy asphalt mixture was corroborated by systematically comparing the volumetric method,the vacuum plastic sealing method,and the X-ray computed tomography（CT）scanning method.In terms of road performance,the degradation pattern of road performance under the combined effect of multiple fields was studied,with the aging of the binder being the key influencing factors.The research indicated that the high strength and strong bond of epoxy asphalt significantly enhanced the high-temperature stability,water stability,anti-flaking,fatigue resistance,and crack resistance of EPA-13.Although it also maintained commendable low-temperature performance,it exhibited greater sensitivity to lower temperatures.Furthermore,it was observed that during the two-stage continuous loading process of the four-point bending fatigue test,the loading interval was conducive to internal damage healing.The loading sequence had a significant impact on fatigue damage accumulation,especially for HPA-13,and the fatigue life when transitioning from low to high strain in stage II was considerably lower than when shifting from high to low strain.In the Overlay Test,whether at the standard temperature of 25°C or a lower temperature of 10°C,the epoxy asphalt mixture necessitated greater stress and more energy to form the initial crack.This suggests that the epoxy asphalt binder could significantly enhance the crack resistance of the porous structure.The grey correlation ranking of each evaluation index was as follows:allowable damage number J>cumulative fracture energy G>displacement at the maximum load of the first cycle L_F>first cycle fracture energy G_F>average fracture energy G^*>first cycle maximum load F.The study recommends using the number of loading cycles N,J,and G to evaluate crack resistance performance.Regarding functionality,the degradation pattern was explored using the reduction of void fraction as the indicative variable of functional decay.The change in the permeability coefficient with a void ratio under the same hydraulic gradient was examined using a custom-developed normal head permeability tester.The acoustic impedance tube method was employed to determine the sound absorption coefficients of specimens with varying void ratios.The degradation pattern of slip resistance was identified using a custom-developed small accelerated wear tester.The oil resistance of the porous epoxy asphalt mixture was assessed through an oil immersion simulation test.The heat and smoke release characteristics of epoxy asphalt were analyzed using thermogravimetry-mass spectrometry（TG-MS）and cone calorimeter（CONE）tests.Additionally,the gasoline escape rate and burning time under different void ratio conditions were investigated through unconstrained and semi-constrained combustion tests.In conclusion,the decay characteristics of slip resistance,oil corrosion resistance,and fire resistance of porous epoxy asphalt mixes markedly differ from those of conventional porous asphalt mixes.