Simulation method for microscopic fatigue cracking behavior of semi-flexible pavement

Abstract

The invention provides a simulation method for a microscopic fatigue cracking behavior of a semi-flexible pavement. The simulation method comprises the following steps: step 1, forming a large-gap matrix asphalt mixture test piece; 2, a cement grouting material is poured; step 3, acquiring an SFP mesoscopic image; step 4, obtaining a binary image of the SFP; 5, constructing a pavement structure model; 6, determining the thickness and the thickness proportion; step 7, constructing a mesoscopic finite element model; 8, constructing a pavement structure finite element model containing the SFP microstructure; step 9, determining CZM model parameters; step 10, inserting a CZM unit; step 11, setting CZM model parameters; 12, simulating a traffic load; and step 13, simulating the fatigue cracking behavior of the SFP in the pavement structure, and quantifying the damage and the change process thereof. According to the method, the normal and tangential CZM parameters and the difference thereof in the CZM model are considered at the same time, the CZM parameters of the two-phase cementing materials with different thicknesses and thickness ratios are determined through the self-designed pull-out test and direct shear test, and the fatigue cracking behavior of the SFP can be simulated and analyzed more accurately.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of road engineering, and relates to a semi-flexible pavement, in particular to a simulation method for micro fatigue cracking behavior of a semi-flexible pavement. BACKGROUND

[0002] The semi-flexible pavement (SFP) is a kind of high-performance pavement material with excellent anti-rutting performance formed by pouring cement grouting material in a large-void base asphalt mixture (PAC). However, cracking is the main failure mode of the SFP. Due to the complex material composition of the SFP, which contains two-phase cementing materials of asphalt mortar and cement mortar, cracking may occur at the asphalt mortar-coarse aggregate interface, the asphalt mortar-cement mortar interface, the internal part of the asphalt mortar, and the internal part of the cement mortar under the action of vehicle load and environmental factors, and the cracking behavior is complex.

[0003] In order to clarify the fatigue cracking mechanism of the SFP, researchers introduce the cohesive zone model (CZM) to establish a finite element mechanics model to study the initiation and propagation process of cracks in the SFP and the damage characteristics. However, there are still the following research deficiencies:

[0004] Firstly, the CZM parameters are divided into normal and tangential adhesion / cohesion CZM parameters, and there is a significant difference between the normal and tangential adhesion / cohesion CZM parameters. However, the existing cohesive zone model only obtains the normal adhesion / cohesion CZM parameter through experiments, and ignores the tangential adhesion / cohesion CZM parameter, considering that the tangential and normal adhesion / cohesion CZM parameters are the same, which leads to a large gap between the actual situation and the model, and cannot truly represent the cracking behavior of the SFP.

[0005] Secondly, the thickness and thickness ratio of the two-phase cementing materials have an important influence on the adhesion / cohesion performance and failure mode, and further affect the size of the CZM parameter. However, the existing simulation does not consider the influence of the different thickness distribution of the asphalt mortar and cement mortar in the SFP and the thickness ratio of the asphalt mortar and cement mortar, and considers that the two-phase cementing materials with different thicknesses have the same adhesion / cohesion performance, thereby not considering the different distribution of the two-way adhesion / cohesion performance and the different values of the CZM parameter caused by the different thickness and thickness ratio of the two-phase cementing materials.

[0006] Thirdly, the existing research usually constructs the SFP finite element model based on the indoor test specimen to study the cracking behavior of the SFP, which is significantly different from the stress state of the actual pavement structure, and cannot simulate the stress state of the SFP in the actual pavement structure.

[0007] Fourth, the cracking of the SFP is caused by repeated load, the fatigue adhesion / cohesion damage evolution process of the two-phase cementitious material in the SFP cannot be obtained through the macroscopic fatigue test, the normal adhesion damage, the normal cohesion damage, the tangential adhesion damage and the tangential cohesion damage of the SFP under the fatigue load are not quantified and the damage distribution is not considered, the tangential and normal adhesion / cohesion damage characteristics of the two-phase cementitious material in the SFP under the fatigue load cannot be accurately obtained, and thus the fatigue cracking mechanism of the SFP is not clear. SUMMARY

[0008] In view of the problems in the prior art, the purpose of the present application is to provide a simulation method for the mesoscopic fatigue cracking behavior of a semi-flexible pavement, which solves the technical problem that the accuracy of the simulation method in the prior art needs to be further improved.

[0009] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0010] A simulation method for the mesoscopic fatigue cracking behavior of a semi-flexible pavement, comprising the following steps:

[0011] Step one, forming a large-void base asphalt mixture test piece.

[0012] Step two, pouring cement grouting material.

[0013] Step three, obtaining a SFP microscopic image.

[0014] Step four, obtaining a binary image of the SFP.

[0015] Step five, constructing a pavement structure model:

[0016] The pavement structure layer of the pavement structure model comprises an upper layer, a lower layer and a base layer; in the pavement structure model, the upper layer adopts the microscopic binary image obtained in step four to construct a non-homogeneous microscopic finite element model; the lower layer and the base layer both adopt a homogeneous linear elastic body model.

[0017] Step six, determining the thickness and the thickness ratio:

[0018] Based on the pavement structure model constructed in step five, the thickness distribution of the asphalt mortar and the cement mortar is obtained from the asphalt mortar binary image and the cement mortar binary image obtained in step four through Matlab programming.

[0019] The two-phase cementitious material image is evenly divided into 5 layers in the height direction and 30 parts in the length direction, a total of 150 regions, the thickness of the asphalt mortar and the cement mortar in each region is determined, and the thickness ratio of the asphalt mortar to the cement mortar in each region is calculated.

[0020] Step seven, constructing the mesoscopic finite element model:

[0021] The images of the 150 regions obtained in step six are processed by vectorization through the Algolab Photo Vector image processing software to obtain vector images of the asphalt mortar, cement mortar and coarse aggregate. The vectorized images are adjusted using Photoshop to ensure that the contours of the various materials do not intersect.

[0022] The asphalt mortar and cement mortar are created as surface domains using Photoshop software, and the coarse aggregate is created as a whole surface domain. The asphalt mortar, cement mortar and coarse aggregate components are then imported into the finite element software Abaqus as the mesoscopic finite element model of the upper surface layer in the pavement structure model.

[0023] Step eight, constructing the pavement structure finite element model containing the SFP mesoscopic structure:

[0024] The mesoscopic finite element model obtained in step seven is pre-processed using the finite element pre-processing software Hypermesh. The mesh-processed mesoscopic model is exported as an.inp file and imported into the Abaqus software for subsequent processing to establish the pavement structure finite element model containing the SFP mesoscopic structure.

[0025] Step nine, determining the CZM model parameters:

[0026] Step 901, preparing the combined test specimen:

[0027] Based on the thickness distribution of the asphalt mortar and cement mortar within the SFP obtained in step six, as well as the thickness ratio of the asphalt mortar and cement mortar in each region, a combined test specimen of "metallic drawing head-coarse aggregate-asphalt mortar-cement mortar-metallic drawing head" containing all thicknesses and thickness ratios of the two-phase cementitious material is prepared.

[0028] Step 902, determining the CZM model parameters of different two-phase cementitious material thicknesses and thickness ratios in the combined test specimen, including the normal adhesive CZM parameter, the normal cohesive CZM parameter, the tangential adhesive CZM parameter and the tangential cohesive CZM parameter.

[0029] The normal adhesive CZM parameter and the normal cohesive CZM parameter are determined by the drawing test.

[0030] The tangential adhesive CZM parameter and the tangential cohesive CZM parameter are determined by the direct shear test.

[0031] Step ten, inserting the CZM unit.

[0032] Step eleven, setting the CZM model parameters.

[0033] Step twelve, simulate the traffic load.

[0034] Step thirteen, simulate the fatigue cracking behavior of SFP in pavement structure, quantify the damage and its changing process:

[0035] According to the fatigue cracking behavior of SFP surface layer simulated in step twelve, the normal adhesion damage D na , the normal cohesion damage D nc , the tangential adhesion damage D ta , the tangential cohesion damage D tc and their distribution of each finite element unit of two-phase cementing material under different action times are respectively calculated according to formula III-1 to formula III-4; when the model reaches the peak stress, the damage is 0, and when the stress drops to 0, the damage is equal to 1, and the material is completely destroyed; the changing process of each damage in the SFP fatigue cracking process is obtained.

[0036]

[0037] In the formula:

[0038] delta na , delta nc , delta ta and delta tc respectively represent the effective loading displacement of the normal adhesion, the normal cohesion, the tangential adhesion and the tangential cohesion in the loading process;

[0039] and respectively represent the relative displacement of the normal adhesion, the normal cohesion, the tangential adhesion and the tangential cohesion of the crack surface when the cohesive force reaches the cracking strength;

[0040] and respectively represent the relative displacement of the normal adhesion, the normal cohesion, the tangential adhesion and the tangential cohesion of the crack surface when the cracking is completed.

[0041] Compared with the prior art, the present application has the following technical effects:

[0042] (Ⅰ) Existing SFP fatigue cracking simulation methods usually only obtain the adhesive / cohesive performance of the binder in the normal direction through experiments, so that only the normal CZM parameters can be obtained, and the tangential CZM parameters are considered to be the same as the normal, which weakens the influence of the tangential adhesive / cohesive performance on the CZM parameters. The adhesive / cohesive performance of the two-phase binder is not explored from both the normal and tangential directions, so that the real cracking evolution process cannot be obtained, and the absence of the tangential CZM parameters will lead to the neglect of the influence of shear cracking on SFP fatigue cracking. Compared with the existing simulation methods of SFP pavement material cracking behavior, the method of the application simultaneously considers the normal and tangential adhesive / cohesive CZM parameters in the CZM model and their differences, and the normal and tangential adhesive / cohesive CZM parameters of the two-phase binder are determined through self-designed pull-out test and direct shear test, which provides more perfect and accurate material parameters for the finite element model simulation, and helps to more accurately simulate the cracking behavior of the material.

[0043] (Ⅱ) The existing simulation method does not consider the influence of the thickness and thickness ratio of the asphalt mortar and cement mortar in the SFP, and considers that the adhesive / cohesive performance of the two-phase binder with different thicknesses is the same, so that the different distribution of the two-way adhesive / cohesive performance of the two-phase binder caused by the thickness and thickness ratio of the two-phase binder is not considered. Compared with the existing model, the method of the application considers the different distribution of the normal and tangential adhesive / cohesive performance caused by the thickness and thickness ratio of the asphalt mortar and cement mortar in the SFP, and according to the different thickness ratio of the two-phase binder, the normal and tangential adhesive / cohesive performance of the two-phase binder with different thicknesses and thickness ratios is accurately determined through indoor test, and then the normal adhesive CZM parameter, normal cohesive CZM parameter, tangential adhesive CZM parameter and tangential cohesive CZM parameter of the two-phase binder with different thicknesses and thickness ratios are accurately obtained, and in the model construction, the corresponding CZM parameters are given according to the different thickness and thickness ratio of the two-phase interface, and the model considers the different distribution of the normal and tangential adhesive / cohesive performance of the two-phase binder in the SFP.

[0044] (Ⅲ) The existing model studies the cracking behavior of SFP through simulation indoor test, which is significantly different from the stress characteristics of the actual SFP pavement structure. In addition, the existing pavement structure model mostly uses a homogeneous model, and the materials of each structural layer are homogeneous elastic bodies, without considering the influence of the microstructure of the pavement material. The model established by the application considers the microstructure of the material, and a pavement structure model containing the SFP microstructure is established by embedding the SFP microstructure model, which can not only study the damage and cracking characteristics of the SFP microstructure, but also simulate the complex stress state of the actual pavement structure.

[0045] (IV) According to the thickness and thickness ratio of the two-phase cementing material, the normal adhesion CZM parameter, the normal cohesion CZM parameter, the tangential adhesion CZM parameter and the tangential cohesion CZM parameter are respectively set, then the normal adhesion damage, the normal cohesion damage, the tangential adhesion damage and the tangential cohesion damage are obtained by simulating the action of the moving vehicle load, and the change process of the normal adhesion damage, the normal cohesion damage, the tangential adhesion damage and the tangential cohesion damage with the action times is explored, and the mesoscopic fatigue mechanism of the SFP is clarified. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is a schematic diagram of the mesoscopic finite element model of the present application.

[0047] Figure 2 It is a schematic diagram of the adhesion / cohesion CZM unit in the mesoscopic finite element model of the present application.

[0048] Figure 3 It is a schematic diagram of the specimen forming of the pull-out test and the direct shear test designed in the present application.

[0049] Fig. 4(a) is a schematic diagram of the pull-out test in the indoor test in the present application.

[0050] Fig. 4(b) is a schematic diagram of the direct shear test in the indoor test in the present application.

[0051] The specific content of the present application is further explained and described in detail in combination with the following embodiments. DETAILED DESCRIPTION

[0052] It should be noted that all the materials, equipment, models and software in the present application, if not specially stated, all use the known materials, equipment, models and software in the prior art.

[0053] The application provides a simulation method of mesoscopic fatigue cracking behavior considering bidirectional adhesion / cohesion performance and different distribution of two-phase cementitious material in SFP. First, by obtaining the real SFP mesoscopic structure, the thickness distribution of two-phase cementitious material in SFP is obtained, and a combined test piece of'metal drawing head-coarse aggregate-bituminous mortar-cement mortar-metal drawing head' which can accurately control the thickness of the cementitious material is prepared. Second, by a series of drawing and direct shear tests, the relationship between the thickness and thickness ratio of two-phase cementitious material and the normal and tangential adhesion / cohesion performance under different temperature conditions is established, and the normal adhesion CZM parameter, normal cohesion CZM parameter, tangential adhesion CZM parameter and tangential cohesion CZM parameter of two-phase cementitious material with different thickness and thickness ratio are determined. Finally, according to the real mesoscopic structure of SFP, a two-dimensional finite element model of SFP pavement structure is constructed. The mesoscopic model of SFP surface layer is divided into several parts, and zero-thickness CZM units are inserted into the two-phase cementitious material inside and at the boundary of the SFP mesoscopic model, and different CZM parameters are given according to the different thickness and thickness ratio of the two-phase cementitious material in each part, so that the characteristics of the different distribution of the adhesion / cohesion performance of the two-phase cementitious material in the test piece with different thickness distribution can be realized. The repeated vertical moving load and horizontal stress are applied to the model to simulate the moving vehicle load, and the normal adhesion damage, normal cohesion damage, tangential adhesion damage and tangential cohesion damage of the two-phase cementitious material in SFP and the damage distribution are determined, and the normal and tangential adhesion / cohesion damage degree and damage evolution process of the two-phase cementitious material under different load action times and the fatigue cracking initiation and propagation process are studied, and the SFP pavement fatigue cracking mechanism is determined.

[0054] The specific embodiments of the application are given below, and it should be noted that the application is not limited to the following specific embodiments, and any equivalent variations made on the basis of the technical solutions of the application fall within the protection scope of the application.

[0055] Embodiment:

[0056] The embodiment gives a simulation method of mesoscopic fatigue cracking behavior of semi-flexible pavement, which comprises the following steps:

[0057] Step one, forming a large-void base bituminous mixture test piece:

[0058] The aggregate of the base bituminous mixture is basalt, and the asphalt is SBS modified asphalt, and the large-void base bituminous mixture cuboid test piece is prepared by wheel rolling method.

[0059] In step one, the size of the test piece is 60cm long x 60cm wide x 5cm thick.

[0060] Step two, pouring cement grouting material:

[0061] After the test piece in step one is cooled, the test piece is sealed around, cement grouting material of the semi-flexible pavement is mixed with water and stirred uniformly, and is slowly poured into the test piece. After pouring, the test piece is placed on the vibration table for high-frequency vibration for 2 minutes, so that the cement grouting material is uniformly poured into the test piece, and the cement grouting material is timely supplemented until the cement grouting material no longer enters the inside of the test piece. After the cement grouting material is poured, the test piece is placed in a standard curing room for curing, and an SFP rutting plate is obtained.

[0062] In step two, the cement grouting material is mixed with water at a water-material ratio of 0.34.

[0063] Step three, SFP microscopic image acquisition:

[0064] After the SFP rutting plate obtained in step two is completely hardened, the SFP rutting plate is vertically cut to obtain a longitudinal section, and a high-precision digital camera is used to take a photograph of the longitudinal section to obtain an SFP microscopic image.

[0065] In step three, a longitudinal section with a length of 60 cm and a height of 5 cm is obtained.

[0066] In this embodiment, the high-precision digital camera is a commonly used high-precision digital camera known in the art.

[0067] Step four, obtaining a binary image of the SFP:

[0068] The SFP microscopic image obtained in step three is preprocessed by Photoshop image analysis software combined with Matlab. A gray scale transformation function is used to enhance the contrast of the image and increase the gray scale value difference between the voids, asphalt mortar, cement mortar and coarse aggregates in the image. Then, the image is binarized by Matlab to obtain the binary images of the coarse aggregates, asphalt mortar, cement mortar and voids in the SFP, respectively.

[0069] Step five, constructing a pavement structure model:

[0070] As shown in Figure 1 , the pavement structure layer of the pavement structure model includes an upper layer, a lower layer and a base layer. In the pavement structure model, the upper layer uses the microscopic binary image obtained in step four to construct a non-homogeneous microscopic finite element model; the lower layer and the base layer both use a homogeneous linear elastic body model.

[0071] Figure 1 In the formula, P represents the vertical force, and F represents the lateral force.

[0072] In step five, the upper layer is an SFP upper layer with a thickness of 5 cm; the lower layer is a dense-graded asphalt mixture AC-20 lower layer with a thickness of 8 cm, and the base layer is a cement stabilized gravel base layer with a thickness of 30 cm.

[0073] Step six, determine the thickness and thickness ratio:

[0074] Based on the pavement structure model constructed in step five, the thickness distribution of asphalt mortar and cement mortar is obtained from the binary images of asphalt mortar and cement mortar obtained in step four respectively by Matlab programming.

[0075] The two-phase binder image is evenly divided into 5 layers along the height direction and 30 parts along the length direction, a total of 150 regions, and the thickness of asphalt mortar and cement mortar in each region is determined, and the thickness ratio of asphalt mortar and cement mortar in each region is calculated.

[0076] In step six, the specific way to obtain the thickness distribution of asphalt mortar and cement mortar is: based on the pavement structure model constructed in step five, a sampling mask image with the same size as the binary images of asphalt mortar and cement mortar is established, and the sampling mask image and the binary two-phase binder image are multiplied respectively, the white two-phase binder area is converted into white lines with equal spacing, and the length of the line is the thickness of the corresponding binder; the white line has only two states of connection and disconnection, the pixel length of each white line is counted, and then the actual length of each white line, i.e. the thickness of the binder, is calculated by converting the pixel size and the actual size ratio of the image, and the thickness distribution of asphalt mortar and cement mortar is obtained respectively.

[0077] Step seven, construct a mesoscopic finite element model:

[0078] The images of the 150 regions obtained in step six are processed by vectorization through the Algolab Photo Vector image processing software to obtain the vector graphs of asphalt mortar, cement mortar and coarse aggregate, and the vectorized graphs are adjusted by Photoshop to ensure that the contours of each phase material do not intersect.

[0079] Photoshop software is used to create a surface domain for asphalt mortar and cement mortar respectively, and a surface domain for coarse aggregate as a whole, and then the asphalt mortar, cement mortar and coarse aggregate parts are imported into the finite element software Abaqus as the mesoscopic finite element model of the upper surface layer in the pavement structure model.

[0080] In this embodiment, the schematic diagram of the adhesion / cohesion CZM unit in the mesoscopic finite element model is as shown in Figure 2 .

[0081] Step eight, construct a pavement structure finite element model containing SFP mesoscopic structure:

[0082] The mesoscopic finite element model obtained in step seven is pre-processed by the finite element pre-processing software Hypermesh, the mesoscopic model after mesh division is exported as an.inp suffix file, and then imported into Abaqus software for subsequent processing to establish a pavement structure finite element model containing the SFP mesoscopic structure;

[0083] Step nine, determine the CZM model parameters:

[0084] Step 901, prepare the combined specimen:

[0085] According to the thickness distribution of the SFP internal asphalt mortar and cement mortar obtained in step six, and the thickness ratio of the asphalt mortar and cement mortar in each region, a combined specimen of "metal pulling head-coarse aggregate-asphalt mortar-cement mortar-metal pulling head" containing all thicknesses and thickness ratios of the two-phase cementitious material is prepared.

[0086] In step 901, the specific preparation process of the combined specimen is as follows: first, bond the coarse aggregate and the metal pulling head together and place them in an oven for heating for 1 h, then pour the asphalt mortar, accurately control the thickness of the mortar with a micrometer, pour the cement grout after it cools down, the cement grout hardens to form the cement mortar, polish the cement mortar to the specified thickness, bond it with another metal pulling head, and after curing and shaping, the combined specimen with different thicknesses and thickness ratios is obtained.

[0087] In this embodiment, the specific preparation process is shown in FIG. 8. Figure 3 For each total thickness of the two-phase cementitious material (including 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm), the thickness ratio of the asphalt mortar to the cement mortar varies from 0:10 to 10:0, covering all thicknesses and thickness ratios.

[0088] In this embodiment, the asphalt mortar is mainly composed of asphalt, mineral powder, and fine aggregate with a particle size less than 1.18 mm. In order to ensure that the thickness of the asphalt wrapped around the surface of the fine aggregate in the asphalt mortar is consistent with that of the asphalt mixture in the large void matrix, the gradation composition of the asphalt mortar is calculated based on the gradation of the asphalt mixture. At the same time, based on the specific surface area method and the principle of the same thickness of wrapped asphalt, the asphalt content (Pb 砂浆 ) of the mortar is calculated to be 29%. The cement grout and water are uniformly mixed at a water-cement ratio of 0.34, and the cement grout is mainly composed of sulphoaluminate cement, fly ash, water reducing agent, early strength agent, and other additives. First, the cement grout and water are stirred at a low speed of 300 r / min to ensure complete mixing, and then the stirring speed is gradually increased to 2000 r / min for two minutes to ensure complete mixing and form a uniform slurry with good fluidity.

[0089] Step 902, determine the CZM model parameters of different thicknesses and thickness ratios of the two-phase cementing material in the combined test piece, and the CZM model parameters include the normal adhesion CZM parameter, the normal cohesion CZM parameter, the tangential adhesion CZM parameter and the tangential cohesion CZM parameter.

[0090] The normal adhesion CZM parameter and the normal cohesion CZM parameter are determined by the pull-out test.

[0091] The tangential adhesion CZM parameter and the tangential cohesion CZM parameter are determined by the direct shear test.

[0092] In this embodiment, the normal adhesion / cohesion performance of the combined test piece is obtained by the pull-out test, and the tangential adhesion / cohesion performance is obtained by the direct shear test. The force-displacement curve and the failure mode during the test process are recorded, and the pull-out test and the direct shear test are shown in FIGS. 4(a) and 4(b). By repeating the pull-out test and the direct shear test by controlling the temperature, the adhesion / cohesion performance at different temperatures can be obtained. The failure modes are mainly divided into normal and tangential cohesion failure (internal damage of asphalt mortar and internal damage of cement mortar), and adhesion failure (interface damage of asphalt mortar-coarse aggregate and interface damage of asphalt mortar-cement mortar).

[0093] The specific process of step 902 is as follows:

[0094] The peak force in the force-displacement curve of the pull-out test and the direct shear test can be used to calculate the adhesion / cohesion strength, as shown in formula I.

[0095]

[0096] In the formula:

[0097] T represents the adhesion / cohesion strength, and the unit is MPa;

[0098] F represents the peak force, and the unit is kN;

[0099] A represents the cross-sectional area of the combined test piece, mm 2 .

[0100] The area surrounded by the force-displacement curve of the pull-out test and the direct shear test can obtain the fracture energy, as shown in formula II.

[0101] G = ∫T(x)dx Formula II

[0102] In the formula:

[0103] G represents the fracture energy, and the unit is J / mm 2 ;

[0104] T represents the adhesion / cohesion strength, and the unit is MPa;

[0105] x represents displacement, and the unit is mm.

[0106] The normal adhesion CZM parameter, the normal cohesion CZM parameter, the tangential adhesion CZM parameter and the tangential cohesion CZM parameter of the two-phase cementitious material with different thicknesses and thickness ratios can be determined by comprehensively considering the adhesion / cohesion strength and the fracture energy and combining different failure modes.

[0107] In the embodiment, the elastic modulus of the aggregate and the two-phase cementitious material is obtained by nanoindentation test, and the Poisson's ratio is obtained by a material testing machine. The elastic modulus and the Poisson's ratio of other structural layers of the elastic layered system in the macroscopic model can be obtained by dynamic modulus test.

[0108] Step ten, inserting the CZM unit:

[0109] The batch insertion of the zero-thickness CZM unit is completed by the plug-in "Abaqus insert cohesive element" developed based on Abaqus, so as to batch insert the zero-thickness CZM unit in the internal and interface of the asphalt mortar and the cement mortar in the pavement structure finite element model containing the SFP microstructure obtained in step eight; the zero-thickness CZM unit includes the tangential adhesion CZM, the normal adhesion CZM, the tangential cohesion CZM and the normal cohesion CZM.

[0110] In the embodiment, the plug-in "Abaqus insert cohesive element" developed based on Abaqus is a known plug-in.

[0111] Step eleven, setting the CZM model parameter:

[0112] According to the different total thicknesses and thickness ratios of the two-phase cementitious material, different CZM model parameters are set at different positions of the pavement structure finite element model containing the SFP microstructure obtained in step ten according to the CZM model parameters determined in step nine, so as to realize the differentiated representation of the adhesion / cohesion performance of the two-phase cementitious material.

[0113] Step twelve, simulating the driving load:

[0114] The boundary conditions and the applied load of the model are set, the bottom of the model is set as completely fixed, and the facility load action area is set at the top of the model to simulate the action range of the driving load.

[0115] The application of the moving vertical load and the horizontal load is completed by the DLOAD subroutine and the UTRACLOAD subroutine, and the fatigue cracking behavior of the SFP surface layer is simulated by repeating the action of the driving load.

[0116] In the embodiment, the DLOAD subroutine and the UTRACLOAD subroutine are known DLOAD subroutine and UTRACLOAD subroutine.

[0117] In step twelve, the tire ground pressure is set to 0.7 MPa, the length of the load ground action is set to 17 cm, and the driving load speed is set to 60 km / h, 80 km / h and 100 km / h, respectively, during the simulation of the action range of the driving load.

[0118] Step thirteen, quantifying damage:

[0119] Step thirteen, simulating the fatigue cracking behavior of SFP in the pavement structure, quantifying damage and its change process:

[0120] According to the fatigue cracking behavior of the SFP surface layer simulated in step twelve, the normal adhesion damage D na , the normal cohesion damage D nc , the tangential adhesion damage D ta , the tangential cohesion damage D tc and their distribution of each finite element unit of the two-phase cementing material under different action times are calculated according to formula III-1 to formula III-4, respectively; when the model reaches the peak stress, the damage is 0, and when the stress decreases to 0, the damage is equal to 1, and the material is completely destroyed; the change process of each damage in the SFP fatigue cracking process is obtained.

[0121]

[0122] In the formula:

[0123] δ na , δ nc , δ ta and δ tc represent the effective loading displacement of the normal adhesion, normal cohesion, tangential adhesion and tangential cohesion during loading, respectively;

[0124] and represent the relative displacement of the normal adhesion, normal cohesion, tangential adhesion and tangential cohesion of the crack surface when the cohesive force reaches the cracking strength, respectively;

[0125] and represent the relative displacement of the normal adhesion, normal cohesion, tangential adhesion and tangential cohesion of the crack surface when the cracking is completed.

[0126] In this embodiment, by exploring the change process of the normal adhesion damage, the normal cohesion damage, the tangential adhesion damage and the tangential cohesion damage under different action times, the mesoscopic fatigue cracking mechanism of SFP is obtained.

Claims

1. A method of simulating mesoscopic fatigue cracking behavior of a semi-flexible pavement, characterized by, The method comprises the following steps: Step one, forming a large-void base asphalt mixture test piece; Step two, pouring cement grouting material; Step three, SFP microscopic image acquisition; Step four, obtaining a binary image of the SFP; Step five, constructing a pavement structure model: The pavement structure layers of the pavement structure model include an upper layer, a lower layer and a base layer; in the pavement structure model, the upper layer adopts the microscopic binary image obtained in step four to construct a heterogeneous microscopic finite element model; the lower layer and the base layer both adopt a homogeneous linear elastic body model; Step six, determining thickness and thickness ratio: Based on the pavement structure model constructed in step five, the thickness distribution of the asphalt mortar and the cement mortar is obtained from the binary images of the asphalt mortar and the cement mortar obtained in step four through Matlab programming; The two-phase binder images are evenly divided into 5 layers along the height direction and 30 parts along the length direction, a total of 150 regions, the thickness of the asphalt mortar and the cement mortar in each region is determined, and the thickness ratio of the asphalt mortar to the cement mortar in each region is calculated; Step seven, constructing a microscopic finite element model: The images of the 150 regions obtained in step six are processed through vectorization by using the Algolab Photo Vector image processing software to obtain vector images of the asphalt mortar, the cement mortar and the coarse aggregate, and the vectorized images are adjusted by using Photoshop to ensure that the contours of the materials do not intersect; The asphalt mortar and the cement mortar are created as surface domains by using Photoshop software, and the coarse aggregate is created as a whole surface domain, then the asphalt mortar, the cement mortar and the coarse aggregate parts are imported into the finite element software Abaqus as the microscopic finite element model of the upper layer in the pavement structure model; Step eight, constructing a pavement structure finite element model containing the SFP microscopic structure: The microscopic finite element model obtained in step seven is preprocessed by using the finite element pre-processing software Hypermesh, the partially meshed microscopic model is exported as an.inp suffix file, and then imported into the Abaqus software for subsequent processing to establish a pavement structure finite element model containing the SFP microscopic structure; Step nine, determining the CZM model parameters: Step 901, preparing a combined test piece: According to the thickness distribution of the asphalt mortar and the cement mortar in the SFP and the thickness ratio of the asphalt mortar to the cement mortar in each region, a combined test piece of "metal pulling head-coarse aggregate-asphalt mortar-cement mortar-metal pulling head" containing all thicknesses and thickness ratios of the two-phase binder is prepared; Step 902, determining the CZM model parameters of different two-phase binder thicknesses and thickness ratios in the combined test piece, wherein the CZM model parameters include normal adhesion CZM parameters, normal cohesion CZM parameters, tangential adhesion CZM parameters and tangential cohesion CZM parameters; The normal adhesion CZM parameters and the normal cohesion CZM parameters are determined by the pulling test; The tangential adhesion CZM parameters and the tangential cohesion CZM parameters are determined by the direct shear test; Step ten, inserting a CZM unit; Step eleven, setting the CZM model parameters; Step twelve, simulating the traffic load; Step thirteen, simulating the fatigue cracking behavior of SFP in the pavement structure, quantifying the damage and its change process: According to the fatigue cracking behavior of the SFP surface layer simulated in step 12, the normal adhesion damage D of each finite element unit of the two-phase cementing material under different action times is calculated according to formula III-1 to formula III-4 na , the normal cohesion damage D nc , the tangential adhesion damage D ta , the tangential cohesion damage D tc and the distribution thereof; when the model reaches the peak stress, the damage is 0, and when the stress drops to 0, the damage is equal to 1, and the material is completely destroyed; the change process of each damage in the SFP fatigue cracking process is obtained; In the formula: δ na , δ nc , δ ta , and δ tc represent the effective loading displacement of normal adhesion, normal cohesion, tangential adhesion, and tangential cohesion, respectively, during loading; and and respectively represent the normal adhesion, normal cohesion, tangential adhesion and tangential cohesion relative displacement of the crack surface when the cohesive force reaches the cracking strength. and and represent the normal adhesive, normal cohesive, tangential adhesive and tangential cohesive relative displacement of the crack faces at the completion of cracking, respectively.

2. The method of claim 1, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. Step one, forming the large-void matrix asphalt mixture test piece: The aggregate of the matrix asphalt mixture is basalt, and the asphalt is SBS modified asphalt. The wheel rolling method is used to prepare the large-void matrix asphalt mixture cuboid test piece. Step two, pouring the cement grouting material: After the test piece in step one is cooled, the test piece is sealed around, the cement grouting material of the semi-flexible pavement is mixed with water and stirred uniformly, and is slowly poured into the test piece. After pouring, the test piece is placed on the vibration table for high-frequency vibration for 2 minutes, so that the cement grouting material is uniformly poured into the test piece. The cement grouting material is replenished in time until the cement grouting material no longer enters the test piece. After the pouring of the cement grouting material is completed, the test piece is placed in a standard curing room for curing to obtain the SFP rutting plate. Step three, obtaining the SFP microscopic image: After the SFP rutting plate obtained in step two is completely hardened, the SFP rutting plate is vertically cut to obtain a longitudinal section. A high-precision digital camera is used to take a picture of the longitudinal section to obtain the SFP microscopic image. Step four, obtaining the binary image: The SFP microscopic image obtained in step three is preprocessed by Photoshop image analysis software combined with Matlab. The gray scale transformation function is used to enhance the contrast of the image and increase the gray value difference between the voids, asphalt mortar, cement mortar and coarse aggregate in the image. Then, the image is binarized by Matlab to obtain the binary images of the coarse aggregate, asphalt mortar, cement mortar and voids in the SFP, respectively.

3. The method of claim 2, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. In step one, the size of the test piece is 60 cm long x 60 cm wide x 5 cm thick. In step two, the cement grouting material is mixed with water at a water-to-material ratio of 0.

34. In step three, a longitudinal section with a length of 60 cm and a height of 5 cm is obtained.

4. The method of claim 1, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. In step five, the upper layer is an SFP upper layer with a thickness of 5 cm; the lower layer is a dense-graded asphalt mixture AC-20 lower layer with a thickness of 8 cm; and the base layer is a cement stabilized gravel base layer with a thickness of 30 cm.

5. The method of claim 1, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. In step six, the specific method for obtaining the thickness distribution of the asphalt mortar and the cement mortar is as follows: based on the pavement structure model constructed in step five, a sampling mask image with the same size as the binary images of the asphalt mortar and the cement mortar is established. The sampling mask image and the two-phase binder binary images are multiplied respectively, and the white two-phase binder area is converted into white lines with equal spacing. The length of the line is the thickness of the corresponding binder. The white line has only two states: connected and disconnected. The pixel length of each white line is counted, and the actual length of each white line, i.e. the thickness of the binder, is calculated according to the ratio of the image pixel size and the actual picture size. The thickness distribution of the asphalt mortar and the cement mortar is obtained respectively.

6. The method of claim 1, wherein, In step 901, the specific preparation process of the combined test piece is as follows: first, the coarse aggregate is bonded with the metal drawing head, and is placed in an oven for heating for 1 h, then the asphalt mortar is poured, the thickness of the mortar is accurately controlled by a micrometer, the cement grouting material is poured after the mortar is cooled, the cement mortar is hardened to form a cement mortar, the cement mortar is polished to a specified thickness, and is bonded with another metal drawing head, and the combined test piece with different thicknesses and thickness ratios is obtained after curing and forming; The specific process of step 902 is as follows: The peak force in the force-displacement curve of the pull-out and direct shear test can be used to calculate the adhesion / cohesion strength, as shown in formula I; In the formula: T represents the adhesion / cohesion strength, with the unit of MPa; F represents the peak force, with the unit of kN; A represents the cross-sectional area of the combined test piece, mm 2 ; The area surrounded by the force-displacement curve of the pull-out and direct shear test can be used to obtain the fracture energy, as shown in formula II; G == ∫ T (x) dx Formula II In the formula: G represents the breaking energy in J / mm 2 ; T represents the adhesion / cohesion strength, with the unit of MPa; x represents displacement, with the unit of mm; By comprehensively considering the adhesion / cohesion strength and the fracture energy, and combining different failure modes, the normal adhesion CZM parameters, the normal cohesion CZM parameters, the tangential adhesion CZM parameters and the tangential cohesion CZM parameters of the two-phase cementing material with different thicknesses and thickness ratios can be determined.

7. The method of claim 1, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. The specific process of step ten is as follows: the plug-in "Abaqus insert cohesive element" developed by Abaqus is used to complete the batch insertion of zero-thickness CZM units, so as to realize the batch insertion of zero-thickness CZM units in the asphalt mortar and the cement mortar inside and at the interface of the pavement structure finite element model containing the SFP mesostructure obtained in step eight; the zero-thickness CZM unit includes tangential adhesion CZM, normal adhesion CZM, tangential cohesion CZM and normal cohesion CZM.

8. The method of claim 1, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. The specific process of step eleven is as follows: according to the different total thicknesses and thickness ratios of the two-phase cementing material, and according to the CZM model parameters determined in step nine, different CZM model parameters are set at different positions of the pavement structure finite element model containing the SFP mesostructure obtained in step ten, so as to realize the differentiated representation of the adhesion / cohesion performance of the two-phase cementing material.

9. The method of claim 1, wherein the semi-flexible pavement meso fatigue cracking behavior is simulated by using a microstructure-based fatigue damage model. The specific process of step twelve is as follows: the boundary conditions and the applied load of the model are set, the bottom of the model is set as completely fixed, and the facility load action area is set at the top of the model to simulate the action range of the driving load; The moving vertical load and the horizontal load are applied through the DLOAD subprogram and the UTRACLOAD subprogram, and the fatigue cracking behavior of the SFP surface layer is simulated by repeatedly applying the driving load.

10. The method of claim 9, wherein the micro fatigue cracking behavior of the semi-flexible pavement is simulated by using a micro fatigue cracking model. In step twelve, during the simulation of the action range of the driving load, the tire ground pressure is set to 0.7 MPa, the length of the load ground action is set to 17 cm, and the driving load speed is set to 60 km / h, 80 km / h and 100 km / h, respectively.

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