Fracture Characterization Of Asphalt Mixtures Based On Acoustic Emission Parameters

With the implementation of major national strategies such as the “Belt and Road Initiative”,“Northeast Revitalization” and “Yangtze Economic Belt” and the continuous advancement of the reform and opening up process,the construction of transportation infrastructure has developed rapidly,and a new journey of building a powerful transportation country has been launched in the new era.As the main structural form of road pavement in China,asphalt concrete pavement(flexible pavement)is prone to various diseases such as rutting,cracks and loose road surface due to its remarkable viscoelastic characteristics under the combined effects of vehicle load and environmental factors.Temperature cracks,fatigue cracks,and reflection cracks are all related to the fracture characteristics of asphalt mixture.,The reliable fracture characterization of asphalt mixture presents important theoretical and practical values both in improving asphalt pavement design and ensuring the safe operation of pavement structure.The existing methods for characterizing the fracture characteristics of asphalt mixtures mainly include two categories: theoretical analysis methods(fracture mechanics,numerical simulation,etc.)and microscopic morphology analysis methods(digital image correlation,scanning electron microscopy,etc.).The theoretical analysis method relies on the assumptions of material parameters and boundary conditions,which cannot truly reflect the fracture process of asphalt mixture.Microscopic morphology analysis methods cannot realize the real-time monitoring of internal damages in asphalt materials.As a passive non-destructive testing method,acoustic emission(AE)technology presents unique advantages.It has high sensitivity and can effectively detect invisible cracks in the micrometer range.It can be more authentic and reliable to reflect time-dependent changes of materials and internal damage of structures.This thesis was studied based on the supports of National Natural Science Foundation project “Study on the damage model and meso-characteristics of asphalt concrete freeze-thaw cycle in the seasonal frozen area” and the key scientific and technological research and development project of the Science and Technology Department of Jilin Province,“Research and application of ecological green permeable pavement materials in severe cold regions”.Considering the effects of mineral distribution,test temperature and fiber parameters,etc.on the fracture process and fracture mode of asphalt mixture,the fracture characterization of asphalt mixtures based on acoustic emission parameters were conducted.The specific research works carried out in this thesis is demonstrated as follows:1.The fracture behavior of asphalt concrete was characterized by acoustic emission technology.The AE parameters of AC,SMA and OGFC asphalt concrete were studied under indirect tensile test.The effect of grading and maximum nominal particle size on the fracture behavior of asphalt concrete was analyzed.With test temperature effect on the fracture behavior considered,the influence of temperature on AE parameters of different mineral grade asphalt concrete was clarified through the indirect tensile test of Marshall specimen.It is demonstrated that different AE parameters and corresponding cumulative AE parameters are sensitive to the fracture behavior.And the influence mechanism of different mineral gradation and temperature on the fracture behavior of asphalt concrete was verified.2.Based on AE and Digital Image Correlation(DIC),the indirect tensile test at-10 °C was used to study the effect of glass,basalt and steel fibers on the low temperature crack resistance of asphalt concrete,of which the results were compared with the control asphalt concrete.The evolution of AE parameters(amplitude,ringing count,duration and rise time,and their corresponding cumulative acoustic emission parameters)was obtained during the indirect tensile failure process of asphalt concrete.The fracture behavior between the fiber reinforced asphalt concrete and the control asphalt concrete using AE is realized.The effects of different fiber types and fiber lengths on the low-temperature crack resistance of asphalt concrete were analyzed,and the toughening mechanism of the fiber was clarified.Comparing with the static displacement and strain results obtained by DIC test,AE parameters were verified to be more sensitive and superior for characterizing the fracture behavior of asphalt concrete.3.The effect of fiber on the compression resistance of asphalt concrete under normal temperature of 20 °C was studied,which was reinforced by glass,basalt and steel fibers,respectively.At the same time,the AE technique was used to monitor the damage process of the specimen in real time.Compared with the variation of AE parameters(amplitude,counts and corresponding cumulative parameters)of asphalt concrete with different types and lengths of fibers,the effect of different fiber types and lengths on the compressive properties of modified asphalt concrete was clarified.And it demonstrated the modification mechanism of different fibers.At the same time,the acoustic emission parameters and the change of load level with time are combined to determine the damage and fracture stages of different fiber modified asphalt mixtures under normal temperature and pressure conditions,which provided a basis for the monitoring of asphalt mixture failure process based on acoustic characteristics.4.The SBS modified pervious asphalt concrete was prepared by Marshall compaction method.The fracture process characterization and fracture mode identification of pervious asphalt mixture under compression and indirect tension were realized based on AE parameters.Through the variation of AE parameters(amplitude,ringing count,duration,energy and rise time),cumulative AE parameters and load levels with time,the fracture process of the pervious asphalt concrete under compression and indirect tensile loads was analyzed.The fracture stage division and fracture process characterization of pervious asphalt concrete were realized through the variation rule of AE parameters.The rising angle(RA value)and the average frequency(AF value)calculated by the AE parameters,using the RA-AF correlation analysis method and k-medoids clustering,the fracture mode(shear and tensile cracks)of the pervious asphalt concrete were identified and the failure mechanism of the permeable asphalt mixture in the compression and splitting tests was clarified.In addition,the effects of different test temperatures on the damage process and fracture mode of the permeable asphalt mixture specimens were clarified.