| SMA-13 asphalt mixtures are widely used as the upper-layer of road structures because of the excellent road performance.However,in seasonal frozen regions,the upper-layer structure is directly affected by freeze-thaw cycles,leading to performance degradation and cracking issues.These issues adversely affect the safety of travel and the service life of pavement,while increasing the maintenance costs.To improve the service conditions of asphalt pavement in seasonal frozen regions,understanding the evolution and damage mechanisms of asphalt mixture performance is crucial.This study,funded by the National Natural Science Foundation,focuses on SMA-13 asphalt mixture,uses molecular dynamics simulation,physicochemical characterization,rheological analysis,mechanical analysis,X-ray tomography,and three-dimensional finite element analysis,and reveals the evolution patterns and damage mechanisms of asphalt mixture performance(rheological properties of asphalt binder and mastic,mechanical properties of asphalt mixture).The main researches are as follows:(1)The formation mechanism of asphalt-quartz/calcium carbonate interfacial adhesion was analyzed through molecular dynamics calculations,and the deterioration and failure mechanisms of asphalt-quartz/calcium carbonate interfacial adhesion under water temperature and loading were revealed.At the same time,the microscopic physicochemical characteristics of asphalt binder,asphalt mastic,and asphalt mortar under a freeze-thaw cycle were analyzed by Fourier transform infrared spectroscopy(FTIR)and scanning electron microscope(SEM)tests,which further revealed the freeze-thaw damage mechanism.The results showed that under the action of the freeze-thaw cycle,the asphalt-mineral interface adhesion decreased significantly,the asphaltcalcium carbonate interface had poor resistance to water temperature damage,the content of the asphalt recombination fraction increased relatively,the surface of the asphalt materials appeared to have microscopic cracks,and the asphalt film on the surface of mineral particles peeled off.(2)The rheological properties of asphalt binder and mastic under the action of freeze-thaw cycles were investigated by multiple stress creep recovery(MSCR)test,frequency scanning(FS)test,linear amplitude scanning(LAS)test and bending beam rheology(BBR)test,combined with viscoelastic theory and modeling.The results showed that with the increase of the number of freeze-thaw cycles,the elastic deformation resistance of asphalt binder was significantly enhanced,the fluidity was significantly reduced,and the permanent deformation resistance was enhanced.The change trend of the elastic deformation resistance,fluidity and permanent deformation resistance of asphalt mastic had inflection points at 10 to 15 freeze-thaw cycles,and the change trend was opposite to that of asphalt binder as a whole.The influence of asphalt-mineral powder interface adhesion damage on the rheological properties of asphalt mastic was reflected.The fatigue damage resistance of asphalt binder and mastic decreased significantly,the rutting resistance increased significantly,and the low-temperature cracking resistance decreased.(3)Based on the rheological property of asphalt binder and mastic,and combined with the Palierne model and Einstein model,the effect of the freeze-thaw cycle on asphalt-mineral powder interface interaction was analyzed.Meanwhile,the asphalt-coarse/fine aggregate interfacial interaction and interfacial mechanical behavior under the freeze-thaw cycle were analyzed by using the quantitative water-boiling method,photoelectric colorimetry,and the interfacial oblique shear test.In addition,the evolution of pore structure characteristics of asphalt mixtures with the number of freeze-thaw cycles was discussed by X-ray tomography.The results showed that the asphalt-aggregate/mineral powder interface interaction and mechanical behavior were damaged under freeze-thaw cycles,and the larger the coarse aggregate particle size,the greater the degree of damage to the adhesion interface.The asphalt mixture pore structure appeared to be a connected phenomenon and showed characteristics from the surface to the inside as well as accelerated expansion.(4)The static and dynamic characteristics of asphalt mixtures under freeze-thaw cycles were analyzed by conventional mechanical tests,uniaxial creep tests,dynamic modulus tests,and indirect tensile fatigue tests,combined with Hopman energy ratio and other theories and methods.Subsequently,the effects of asphalt binder and mastic rheological properties,asphalt-aggregate interface interaction,and asphalt mixture pore structure characteristics on the mechanical properties of asphalt mixtures were analyzed by using the grey relation analysis(GRA)algorithm and the GM(1,N)model,and the performance prediction was carried out.The results showed that,under the action of the freeze-thaw cycle,the high-temperature compression damage resistance,elastic deformation resistance,viscous deformation resistance,fatigue damage resistance,and long-term creep deformation resistance of SMA-13 asphalt mixtures decreased significantly,the time of appearance of tiny fatigue cracks was significantly advanced,and viscous deformation and fatigue damage failure were more likely to occur.From the perspectives of material performance and structural characteristics,suggestions to improve the mechanical behavior of asphalt mixtures in the seasonal frozen regions were targeted.(5)The mechanical and full-field strain characteristics of asphalt mixtures’ bending-tensile fracture under the freeze-thaw cycle were investigated by semicircular bending(SCB)tests and digital image correlation analysis(DIC)technology.Then,based on X-ray tomography,digital image processing and three-dimensional reconstruction technology,combined with the material properties and structural characteristics under freeze-thaw cycle,a three-dimensional heterogeneous finite element model of asphalt mixture was constructed,and the influence mechanism of freeze-thaw damage on the crack resistance of asphalt mixture was revealed.The results showed that,under the action of the freeze-thaw cycle,the surface horizontal strain of the SMA-13 asphalt mixture decreased,the toughness decreased,the serviceability with cracks decreased significantly,and it was more prone to brittle failure,which was caused by the decline of the deformation resistance of the asphalt material and the stress transfer efficiency between aggregate particles.Using high-modulus asphalt materials,improving the asphalt-aggregate adhesion ability,and enhancing the pore drainage ability are effective ways to reduce the cracking disease of asphalt pavement in seasonal frozen regions.This research contributes experimental and theoretical references for analyzing damage mechanisms and predicting the performance of asphalt mixtures under freeze-thaw cycles.It also offers targeted suggestions for the evaluation,prediction,and maintenance of asphalt pavement performance in seasonal frozen areas. |
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