Analysis Of Synergetic Deformation Of Optical Fiber Sensors And Asphalt Mixture Under Mesoscopic Numerical Simulation

It is a difficulty in the application of distributed optical fiber sensor in monitoring the internal strain information of pavement structure to evaluate pavement performance.As an anistrope multi-phase material,the strain of the asphalt concrete(AC)is hard to be measured by optical fiber sensor exactly,which is of small size and high modulus.Thus,the algorithm for randomly-generating a virtual specimen of AC implanted with optical fiber sensor was developed.The three points bending test was simulated under the discrete element(DE)method.The characteristics of the synergetic deformation of optical fiber sensors and asphalt concrete were illustrated and the effects of compositions on the optical fiber measurement results were also investigated from the micro-scale perspective.First of all,an aggregate generation algorithm for autonomous control of polyhedral morphology was developed with Matlab through the minimum bounding box method.Then the virtual optical fiber sensor model was generated based on the geometrical properties of compact optical fiber.On the basis of the above algorithms,the methodology for randomly reconstructing a virtual specimen of AC with the heterogeneous(coarse aggregates,asphalt mastic,air voids and optical fiber sensor)and multilayer(aggregate gradation)morphological features was implemented.Secondly,suitable stiffness and bond models were adopted for the contacts between the components according to the mechanical properties of materials as well as the characteristics of each built in model of PFC3D.A series of laboratory tests were developed to determine the material properties of aggregate and mastic.Then the availability and stability of the simulation results were demonstrated with the experimental results.Thirdly,the influences of macro mechanical properties were explored by simulating the three points bending test.After analyzing the micro crack development process in the specimen and partitioning the specimen,it proved that the case of detachment slip initially appeared close to the cracking position and developed to the beam ends with the experiment.The relationship between the difference of the measured strain of optical fiber and AC with the deflection in the midspan after cracking is established according to the characteristics of the actual measurement of optical fiber sensor.The length of single side detachment slip of fiber and absolute percentage error(the ratio of the strain difference between optical fiber and AC and the strain of AC)were adopted to evaluation of optical fiber slip level.The absolute percentage error was 20.5%,and the slip length was 15mm while taking the AC-13 beam specimen as an example.Finally,the aggregate gradation,the regular variation of asphalt mastic,the air voids microstructures,and the mineral aggregate morphology characteristics were studied to investigate their impacts on measurement results.The variation law of variation rate of the difference(the gradient of the curve of absolute percentage error and midspan deflection)was obtained.The results indicated that the stronger the ability of aggregate squeeze and the bond strength of asphalt mortar and the smaller the radius of single gap was,the smaller error was.The aggregate gradation and the bond strength of asphalt mortar were the main influences of optical fiber measurement results.The strain on the difference of absolute percentage error calculated by the lower limit and higher limit of gradation was 5.6%,the result calculated by the lower limit and higher limit of bond strength was 9.8%,significantly higher than the influence of other factors.