| The application of fibers to asphalt mixture is an effective way to improve the durability and prolong the service life of pavement.New interfaces between fibers and asphalt mastic will be formed by introducing the fibers into the asphalt mixture,which affects the properties of asphalt mastic,the interface interaction between asphalt mastic and aggregate will be also changed simultaneously.The mechanical response of the fiber asphalt mixture is significantly determined by those multiple and complex interface behaviors,and then affect the service life and durability of the pavement.At present,the bonding-failure behavior of fiber asphalt mixture interface and its influence on the properties of mixture are still unclear.In this study,the action mechanism of fiber-asphalt mastic-aggregate interface was clarified,bond ability and failure mode of the interface were explored by adopting multi-scale research methods.Furthermore,a machine learning-based prediction model for cracking performance of fiber asphalt mixture was established with the interface performance parameters and raw material performance indicators.First,to explore the interface transition zone(ITZ),action behavior and mechanism of fiber-asphalt mastic-aggregate interface,the characteristic elements gradient distribution and micro-structure variation of interface were characterized by using X-ray energy dispersive spectrometer(EDS)and fourier transform infrared spectrometer(FTIR).The results indicated that the width of ITZ between fiber and asphalt mastic is about 3.5-4.5μm,the widest ITZ is between polyester fiber and asphalt mastic,followed by basalt fiber and glass fiber.the width of ITZ between aggregate and asphalt mastic is 30-40μm,the widest ITZ is between limestone and asphalt mastic,followed by basalt and granite.In terms of microstructure,it was found that the asphalt binder is mainly in the form of saturated aliphatic and aliphatic rings,and there are fewer aromatic structures.With the addition of fiber and filler,the sulfoxide functional group index of asphalt showed an increasing trend.The action mechanism of fiber-asphalt mastic-aggregate interface is mainly physical adsorption,without significant chemical bonds.Second,to quantify the bonding-failure behavior of the interface between fiber and asphalt mastic,the micro-mechanics test platform including micro-tensile system,data acquisition system,temperature control system and microscopic system was self-developed,the loading rate was determined to be 1mm/min,fiber pullout test was carried out based on this.The results showed that the peak load of the load-displacement curve of basalt fiber and asphalt mastic was the largest,and the displacement at peak load of polyester fiber was the largest.Bond-slip model of fiber-asphalt mastic was established based on Popovics equation,and the correlation coefficient is over 0.89.The micromechanical process of viscoelastic deformation,softening and debonding,debonding of fiber in asphalt mastic was visualized for the first time with the help of a microsystem.Within the test conditions,the interface shear strength(IFSS)of basalt fiber and asphalt mastic is greater than that of glass fiber,polyester fiber.The bond property of modified asphalt mastic to fiber is better than that of matrix asphalt,and IFSS increases gradually with the decrease of temperature.Based on the experimental study and the stress transfer behavior analysis with the shear-lag theory,it was found that the interface failure mainly includes three modes:fiber pulling out,fiber fracture and matrix failure,matrix failure is more likely to occur under high temperature,whereas fiber fracture is more likely to occur.Furthermore,a guideline for the occurrence of different interface failure modes was established.In addition,the adhesion work of fiber-asphalt mastic was calculated based on the theory of surface energy,and the correlation between the experimental values and the theoretical values was analyzed.Third,to investigate the bonding-failure behavior of the interface between fiber asphalt mastic and aggregate,the bond performance and failure mode of the interface were assessed based on bond strength test and digital image technology.The results showed that the addition of fiber can improve the interface bond strength(IFBS)of asphalt mastic-aggregate interface,which significantly increased the cohesion strength of the interface,but had a certain negative effect on the adhesive strength.The effects of asphalt type on IFBS are not consistent under different temperature conditions due to the different failure modes of the interface.The aggregate type also has an effect on IFBS,limestone is the best,followed by basalt and granite.Temperature has a significant effect on IFBS,and IFBS of asphalt mastic and aggregate is 3.44-8.01MPa at-10℃,which is much larger than 0.42-0.91MPa at 25℃.The cohesive failure of interface mainly occurs at low temperature,while at medium temperature,mixed failure mainly occurs at the interface between SBS modified asphalt mastic and aggregate.And then,the influence of fiber on the properties of asphalt mastic was studied by lowtemperature stretching,temperature scanning and frequency scanning tests,and the interaction ability between fiber and asphalt mastic was quantified.It can be found that the addition of fiber can significantly improve the ultimate tension and tensile fracture energy of asphalt mastic at low temperature,and the failure mode of SBS modified asphalt mastic changed from "brittle failure" to "ductile failure".Basalt fiber has the greatest advantage in increasing the ultimate tension,while polyester fiber has the greatest advantage in increasing the tensile fracture energy.At the same time,the phase angle of asphalt mastic was decreased,the rutting factor was increased,and the effect of polyester fiber was significantly improved.The complex shear modulus of asphalt mastic with different types of fiber is more significantly different at low frequency.The coefficient of complex shear modulus can well characterize the interaction between fiber and asphalt mastic,and it is affected by the test temperature,fiber type and other factors.Finally,the crack resistance of the fiber asphalt mixture was studied based on the diskshaped compact tension test,and a neural network-based prediction model of the fracture energy of the mixture was established considering interface and raw materials-related parameters.It can been found that the the crack mouth opening displacement at the end of the test and ductility of asphalt mixture increased after adding fibers.Fiber,asphalt,aggregate and gradation type all affect the crack resistance of fiber asphalt mixture.The addition of fiber,application of modified asphalt and selection of alkaline aggregate can improve the fracture energy of fiber asphalt mixture,and the mixture with smaller nominal maximum aggregate size has better crack resistance.A neural network structure containing 7 inputs,1 output and 8 hidden layers was constructed based on IFSS,IFBS,useful temperature interval,complex shear modulus of asphalt mastic,optimum asphalt content,modulus of fiber and nominal maximum aggregate size,the accuracy of the established prediction model is over 0.94,which can well predict the crack resistance of the mixture from the perspective of interface.The results provide theoretical basis and scientific guidance for the high performance design and application of fiber asphalt mixture. |
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