Load accumulation evolution tracking test and analysis method and device for interlayer state of pavement

Abstract

The application discloses a load cumulative evolution tracking test and analysis method and device for pavement interlayer state, and belongs to the technical field of road engineering test detection. The method comprises the following steps: preparing an interlayer composite test piece, extracting volume characteristics, thickness distribution characteristics and porosity gradient characteristics of an interlayer action area as reference values; integrally transferring a positioning base fixed with the test piece to a loading device; applying a stage cumulative load to the test piece; when the cumulative load action times reach a preset observation node, the positioning base together with the test piece is taken out without damage for scanning; spatially registering each node scanning data and initial data, segmenting the interlayer action area and calculating evolution values of multi-dimensional characteristic parameters; decoupling analysis of load effect and structure effect is carried out, and a load cumulative-interlayer state quantitative evolution model is established. The application realizes a methodological transition from "static evaluation" to "dynamic tracking", and provides systematic test and analysis method support for revealing the evolution mechanism of the interlayer state.

Description

Technical Field

[0001] This invention belongs to the field of road engineering testing and inspection technology, specifically relating to a method and apparatus for tracking and analyzing the load accumulation evolution of pavement interlayer conditions. Background Technology

[0002] Asphalt pavements employ a multi-layered structural design, and the interlayer contact state is a key factor affecting the overall mechanical response and service life of the pavement. Extensive engineering practice shows that poor interlayer bonding and pavement distress are interdependent and mutually reinforcing. Interlayer damage undermines the structural integrity, exacerbating pavement distress; conversely, pavement distress alters the stress state between layers, accelerating interlayer damage development, creating a vicious cycle. Therefore, a deep understanding of the evolution of interlayer conditions under traffic loads is crucial for pavement structure design and maintenance decisions.

[0003] However, existing interlaminar studies suffer from fundamental methodological limitations. Whether it's macroscopic mechanical tests like direct shear and tensile tests, laser scanning analysis based on failure surface morphology, or microstructural observations based on tomography, all treat the interlaminar state as a static attribute at a specific point in time, evaluating only a single node after specimen formation or failure. This "initial-to-final state comparison" approach fails to answer the following key scientific questions: When do interlaminar properties begin to degrade? How does the degradation rate change with load history? Is there a critical point for accelerated damage? How do different initial structural states affect the evolution path? The objective reason for these limitations lies in the constraints of technology. Tomography is currently an important means of non-destructively obtaining the internal three-dimensional structure of materials, but the scanning process requires the specimen to be in a static state, making real-time scanning impossible during loading. Existing road material loading equipment is all closed or semi-closed structures, and once the specimen is loaded, it cannot be removed for scanning without disrupting the stress state. Even if it is forcibly removed, the micron-level repositioning accuracy cannot be guaranteed when reloading, resulting in the inability to compare the scan data before and after in the same spatial coordinate system, making evolution tracking impossible.

[0004] It is important to note that current research contains misconceptions regarding the physical mechanism of "interlayer damage." Some studies equate it to material fatigue, attempting to study it using continuous cyclic loading fatigue testing methods. However, the damage between pavement layers under traffic loads is essentially the accumulation of residual plastic strain generated with each loading cycle, belonging to a plastic damage accumulation process, rather than the crack propagation process of high-cycle fatigue. The two have fundamentally different physical mechanisms, sensitivity to loading continuity, and experimental method requirements.

[0005] Therefore, there is an urgent need to develop an experimental and analytical method and supporting device that can achieve multi-time point tracking of the same specimen, has precise positioning capabilities, and establish a systematic quantitative index system, so as to break through the methodological bottleneck of current interlayer research. Summary of the Invention

[0006] To address the aforementioned shortcomings in existing technologies, this invention provides a method and apparatus for tracking and analyzing the load accumulation evolution of pavement interlayer states, achieving a methodological leap from "static evaluation" to "dynamic tracking," and providing systematic experimental and analytical methodological support for revealing the evolution mechanism of interlayer states.

[0007] To achieve the aforementioned objectives, the present invention employs the following technical solution: a method for tracking and analyzing the cumulative load evolution of pavement interlayer states, comprising the following steps: S1: Prepare interlayer composite specimens, fix the specimens to a CT-compatible positioning base to form a rigid whole, obtain initial three-dimensional volume data of the interlayer through initial tomographic scanning, and extract the volume characteristics, thickness distribution characteristics and porosity gradient characteristics of the interlayer interaction area as evolution benchmark values. S2: The positioning base with the specimen fixed is transferred as a whole to the loading device. The positioning structure at the bottom of the base cooperates with the positioning element of the loading device to achieve precise spatial positioning. S3: Apply a phased cumulative load to the specimen using a loading device, dividing the total number of load applications into multiple loading phases, and pausing loading after each phase is completed; S4: When the cumulative number of load applications reaches the preset observation node value, the loading is paused and the base and specimen are removed without damage for tomographic scanning to obtain the three-dimensional volume data corresponding to the observation node. S5: Spatial registration is performed between the three-dimensional volume data corresponding to the observation node and the initial three-dimensional volume data. The interlayer interaction region is segmented in the registered data, and the volume characteristics, thickness distribution characteristics and porosity gradient characteristics of the current node are calculated. S6: Repeat S3 to S5 to complete the acquisition of all observation nodes and obtain the sequence data of multi-dimensional characteristic parameters as a function of the cumulative load application times; S7: Based on the sequence data, perform load effect analysis and structural effect analysis respectively, and quantify the contribution rate of each influencing factor to the inter-layer state evolution; S8: Using multivariate nonlinear regression or response surface methodology, construct the functional relationship between the change of characteristic parameters and axle load, frequency, number of accumulations, and initial state, establish a quantitative evolution model of load accumulation and interlayer state, and realize the load accumulation evolution tracking test and analysis of the interlayer state of the pavement.

[0008] Furthermore, the CT-compatible positioning base is made of aerospace aluminum or carbon fiber composite material; the bottom surface of the base is provided with at least three positioning steel balls distributed in a non-isosceles triangle; the four corners of the base are embedded with scanning markers made of titanium alloy; the specimen is fixed by low-density filling material or adjustable sidewalls to ensure that the relative position of the specimen and the base remains unchanged throughout the entire test cycle.

[0009] Furthermore, the molding method of the interlayer composite specimen includes at least one of the following: Marshall compaction molding, rotary compaction molding, rut plate cutting molding, and on-site core drilling sampling molding; the specimen scanning surface is a circular interface or a rectangular interface, and the size matches the molding method.

[0010] Furthermore, the method of applying the phased cumulative load is as follows: vertical pulse pressure and horizontal reciprocating motion are coupled for loading; a specimen installation station is set up on the horizontal track, the surface of the specimen is flush with the transition section of the track to form a continuous travel belt, and the wheels reciprocate along the track to simulate the travel load.

[0011] Furthermore, the step of segmenting the interlayer interaction region in the registration data and calculating the volume characteristics, thickness distribution characteristics, and porosity gradient characteristics of the current node includes the following sub-steps: S51: Based on the grayscale threshold and watershed algorithm, the volume data is segmented into aggregate phase, asphalt mortar phase and void phase; S52: Based on the theoretical interlayer interface, a preset thickness range along the interlayer normal is defined as the interlayer action area; S53: Calculate the volumetric expansion rate by counting the number of void phases in the interlayer interaction region and obtaining the volumetric expansion rate. S54: The asphalt mortar phase in the interlayer action area is skeletonized to generate the central axis surface. The distance from each point on the central axis surface to the void boundary is calculated to obtain the thickness distribution cloud map and statistical characteristic values, including the average effective contact thickness, thickness standard deviation and 95th percentile thickness. S55: Slice the material with a fixed step size along the interlayer normal, calculate the pore area fraction of each slice to obtain the gradient characteristics of porosity as a function of depth, including peak porosity, peak position offset and porosity distribution half-peak width.

[0012] Furthermore, the load effect analysis is as follows: with the initial inter-story state fixed, axle load, frequency, and cumulative number of times are used as independent variables, and the change in characteristic parameters is used as the dependent variable, a multi-factor analysis of variance is performed to calculate the contribution rate of the main effect and interaction effect of each factor.

[0013] Furthermore, the structural effect analysis is as follows: under fixed load conditions, with the initial inter-story state type as the independent variable, the differences in the evolution of characteristic parameters under different initial states are compared, and the significance of the differences is determined by multiple comparison methods.

[0014] A test and analysis device for tracking the cumulative evolution of loads between pavement layers includes: The load-bearing frame system is a gantry structure, including a bottom load-bearing platform, four vertically fixed column guide rails, an upper crossbeam that rises and falls vertically along the column guide rails, and a protective cover. The bottom load-bearing platform is made of cast iron and has T-slots machined on its upper surface. The upper crossbeam is a box-type welded structure. A precision positioning system is fixed to the upper surface of the bottom support platform, including a pallet support plate. Three tapered pin positioning sleeves are distributed on the pallet support plate, and lateral wedging mechanisms are installed on both sides of the pallet support plate. The hydraulic loading system, installed on the upper part of the protective cover, includes a servo actuator, a wheel set slide frame, a steering and retraction converter, and a loading rubber wheel. The servo actuator has a built-in LVDT displacement sensor, the wheel set slide frame is connected to the piston rod of the servo actuator, and the steering and retraction converter is connected to the wheel set slide frame. A CT-compatible positioning base is used to fix the test specimen. It includes a base body, a positioning base plate, positioning steel balls, and titanium alloy scanning markers. The inner cavity size of the base body is customized according to the test specimen specifications. The positioning base plate is fixed to the bottom of the base body, and three positioning steel balls are embedded in the bottom surface, with their positions corresponding to the conical pin positioning sleeves. The titanium alloy scanning markers are embedded in the four corners of the bottom of the CT-compatible positioning base. The train track system includes a horizontal track, a specimen installation station located in the middle of the horizontal track, and a transition section connecting the specimen installation station and the horizontal track. The surface of the specimen is flush with the track to form a continuous train track. The measurement and control system, used for load control and data acquisition, includes a force sensor, a laser displacement sensor, a temperature sensor, and an industrial control computer. The force sensor is installed between the servo actuator and the wheel set sliding frame, and the laser displacement sensor and temperature sensor are installed on the upper crossbeam.

[0015] The beneficial effects of this invention are: 1. This invention establishes for the first time a multi-node tracking method system for the cumulative evolution of interlayer state loads on pavements. By fixing the specimen on a CT-compatible positioning base with a spatial positioning reference, and combining it with the precision reset mechanism of the loading device and the design of a separable frame, the scanning and data registration of the same specimen at multiple load history nodes are realized. This solves the fundamental problem that traditional methods cannot track the evolution process and provides a "full-process tracking" research approach for the study of interlayer evolution mechanisms.

[0016] 2. This invention clearly distinguishes between "load accumulation effect" and "material fatigue," providing a scientific physical basis for the staged loading test method. Based on the physical mechanism of interlayer plastic damage accumulation, the rationality of staged cumulative loading is demonstrated, making the "loading-stopping-scanning-reloading" test process scientifically self-consistent, and also expanding the application boundaries of tomographic scanning technology in pavement material research.

[0017] 3. This invention proposes a multi-dimensional quantitative index system for interlayer state. By defining the interlayer interaction region and extracting complementary quantitative indicators such as volume expansion rate, effective thickness distribution spectrum, and porosity gradient curve, the vague concept of "interlayer state" is transformed into numerical parameters that can be accurately calculated, statistically compared, and mathematically modeled, thus achieving a methodological upgrade from qualitative observation to quantitative analysis.

[0018] 4. This invention establishes a decoupled analysis framework for load effects and structural effects. Through multi-factor variance analysis and response surface modeling, it can quantify and distinguish the independent contributions and interactions of load parameters and initial structural characteristics to the evolution rate, providing a statistical basis for identifying key control factors of inter-layer damage.

[0019] 5. The method of this invention has good versatility and transferability. Through a unified CT-compatible positioning base design, it covers commonly used specimen types in road engineering, such as Marshall compaction, rotary compaction, rut slab cutting, and on-site core drilling sampling; the loading design of the continuous driving belt more realistically simulates the stress state of the actual road surface. The three-parameter quantification system can be applied to interlayer composite specimens with different material combinations and interface treatments, and the evolutionary analysis method can be extended to other multilayer structural systems subjected to cumulative loads. Attached Figure Description

[0020] Figure 1 This is a flowchart of a test and analysis method for tracking the cumulative load evolution of pavement layers.

[0021] Figure 2 This is a structural diagram of a load accumulation evolution tracking and analysis device for interlayer road surfaces.

[0022] Figure 3 This is a schematic diagram of the structure for fixing the specimen to a CT-compatible positioning base.

[0023] Figure 4 This is a schematic diagram showing the assembly of specimens with different molding methods and positioning bases.

[0024] The components are as follows: 101. Bottom support platform; 102. Column guide rail; 103. Upper crossbeam; 104. Protective cover; 201. Pallet bearing plate; 202. Lateral wedging mechanism; 301. Servo actuator; 302. Wheel set sliding frame; 303. Steering and retraction converter; 304. Loading rubber wheel; 401. Base body; 402. Positioning base plate; 403. Positioning steel ball; 404. Titanium alloy scanning marker point; 405. Guide rail; 501. Force sensor; 502. Laser displacement sensor; 503. Temperature sensor; 504. Industrial control computer; 601. Horizontal track; 602. Specimen installation station; 603. Transition section; 4. Specimen; 5. Filling material; 6. Interlayer interface; 7. Bottom positioning plate of track. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, a method for tracking and analyzing the cumulative load evolution of pavement layers includes the following steps: S1: Prepare interlayer composite specimens, fix the specimens to a CT-compatible positioning base to form a rigid whole, obtain initial three-dimensional volume data of the interlayer through initial tomographic scanning, and extract the volume characteristics, thickness distribution characteristics and porosity gradient characteristics of the interlayer interaction area as evolution benchmark values. The CT-compatible positioning base is made of aerospace-grade aluminum or carbon fiber composite material to avoid severe scattering artifacts caused by steel materials during tomographic scanning. The base's bottom surface has at least three positioning steel balls arranged in a non-isosceles triangle as spatial positioning references. Titanium alloy scanning markers, each 1-2 mm in diameter, are embedded at the four corners of the base for precise registration of multi-temporal images. The specimen is fixed using low-density filler material or adjustable sidewalls to ensure that the relative position of the specimen and the base remains unchanged throughout the entire testing cycle. Once the specimen is fixed to the positioning base, it is not disassembled during subsequent loading and scanning processes; the specimen and base are transferred and manipulated as a unified rigid unit.

[0027] The molding method for the interlayer composite specimen includes at least one of the following: Marshall compaction molding, rotary compaction molding, rut slab cutting molding, and on-site core sampling molding. For Marshall compaction molding, the specimen is cylindrical, compacted on both sides, with a diameter of 101.6 mm or 152.4 mm; for rotary compaction molding, the specimen is cylindrical, controlled by the number of compaction cycles or the compaction height, with a diameter of 100 mm or 150 mm; for rut slab cutting molding, the rut slab is first molded, and then cut into cubic specimens of the required size; for on-site core sampling molding, a core sample containing the interlayer interface is drilled from the actual road surface. All different types of specimens are fixed on a standardized positioning base to achieve standardization of spatial positioning reference. The scanning surface of the specimen is a circular or rectangular interface, with dimensions matching the molding method.

[0028] S2: The positioning base with the specimen fixed is transferred as a whole to the loading device. The positioning structure at the bottom of the base cooperates with the positioning element of the loading device to achieve precise spatial positioning. S3: Apply a phased cumulative load to the specimen using a loading device, dividing the total number of load applications into multiple loading phases, and pausing loading after each phase is completed; The phased cumulative load is applied by coupling vertical pulse pressure with horizontal reciprocating motion. A specimen installation station is set up on the horizontal track, with the specimen surface flush with the track transition section to form a continuous travel belt. The wheels reciprocate along the track to simulate the travel load. The track length can be adjusted according to the number and size of the specimens to ensure that the wheels have a stable speed and a complete load pulse when passing over the specimen surface.

[0029] It should be particularly noted that the "staged cumulative loading" proposed in this invention is fundamentally different from traditional material fatigue testing, and this difference is key to understanding the scientific basis of this invention.

[0030] In terms of physical mechanisms: fatigue tests study the nucleation and propagation of microcracks in materials under high-cycle stress. This process is highly sensitive to the continuity of the loading history; interruptions in the test introduce crack closure effects, significantly altering the subsequent crack propagation rate. However, the interlayer damage in asphalt pavement studied in this invention is primarily caused by irreversible reorientation of aggregate particles, plastic extrusion of the asphalt film, and compaction and propagation of microvoids—all processes of cumulative plastic deformation. Their progression depends on the cumulative number of load applications, rather than the continuity of loading. The stress relaxation effect occurring during loading interruptions is consistent with the intermittent characteristics of vehicle loads on real road surfaces.

[0031] Therefore, the staged cumulative loading method adopted in this invention is physically consistent with the actual service state between layers, and the obtained evolution law can reflect the load accumulation effect of the interlayer state. This method is clearly distinguished from traditional fatigue tests in terms of physical essence, experimental logic, and engineering significance.

[0032] S4: When the cumulative number of load applications reaches the preset observation node value, the loading is paused and the base and specimen are removed without damage for tomographic scanning to obtain the three-dimensional volume data corresponding to the observation node. Observation node value N i Based on the predetermined experimental objectives, the experiment includes an initial node, at least one intermediate node, and a final node to cover the complete evolution process from the initial state to the target damage state. For example, to capture the full-cycle evolution characteristics, nodes such as N=0, 50,000, 100,000, 200,000, and 500,000 can be used; to quickly screen for parameter influences, only the initial and final nodes can be set; to accurately locate critical points, nodes can be densified in the estimated critical region. This invention does not limit the specific node values.

[0033] S5: Spatial registration is performed between the three-dimensional volume data corresponding to the observation node and the initial three-dimensional volume data. The interlayer interaction region is segmented in the registered data, and the volume characteristics, thickness distribution characteristics and porosity gradient characteristics of the current node are calculated. The process of segmenting the interlayer interaction region in the registration data and calculating the volume characteristics, thickness distribution characteristics, and porosity gradient characteristics of the current node includes the following steps: S51: Based on the grayscale threshold and watershed algorithm, the volume data is segmented into aggregate phase, asphalt mortar phase and void phase; S52: Based on the theoretical interlayer interface, a preset thickness range along the interlayer normal is defined as the interlayer action area. This range is usually 2-5mm above and below the interface. S53: Calculate the interlayer void volume by counting the number of void phases within the interlayer interaction region, and obtain the volume expansion rate ΔV. This index reflects the degree of expansion of interlayer voids and loose regions. ΔV=(V i -V0) / V0×100% Among them, V i V represents the volumetric characteristics of the i-th stage, and V0 represents the interlayer void volume; S54: The asphalt mortar phase in the interlayer interaction area is skeletonized to generate a central axial surface. The distance from each point on the central axial surface to the void boundary is calculated to obtain the thickness distribution cloud map and statistical characteristic value T. i Including average effective contact thickness T mean Thickness standard deviation T std and the 95th percentile thickness T 95 ; where T 95 It is most sensitive to the expansion of local void regions, thickness standard deviation T std It reflects the degree of unevenness in the contact state; S55: Slice the material at a fixed step size along the interlayer normal, and calculate the pore area fraction of each slice to obtain the gradient characteristic P of porosity as a function of depth. i Including peak porosity P peak Peak position offset ΔZ peak And the full width at half maximum (FWHM) of the porosity distribution. Where ΔZ peak FWHM reflects the directionality of damage propagation to one or both sides of the interface, while FWHM reflects the degree of concentration of damage along the depth direction.

[0034] The quantitative indicators of interlayer state also include at least one of the following: aggregate orientation distribution characteristics (reflecting the degree of reorientation of aggregate particles under shear action), asphalt mortar area fraction (reflecting the migration and redistribution of the asphalt film at the interface), and connectivity porosity (reflecting the degree of interconnection of pores). This invention uses volumetric characteristics, thickness distribution characteristics, and porosity gradient characteristics as core characterization indicators, but does not exclude the combined use of other supplementary parameters. Researchers can choose appropriate parameter combinations according to specific research objectives.

[0035] S6: Repeat S3 to S5 to complete the acquisition of all observation nodes and obtain the sequence data of multi-dimensional characteristic parameters as a function of the cumulative load application times; S7: Based on the sequence data, perform load effect analysis and structural effect analysis respectively, and quantify the contribution rate of each influencing factor to the inter-layer state evolution; The load effect analysis involves fixing the initial interlayer state, using axle load, frequency, and cumulative load count as independent variables, and the change in characteristic parameters as the dependent variable, conducting a multi-factor analysis of variance to calculate the contribution rates of the main effects and interaction effects of each factor, and plotting the main effect diagram and interaction effect diagram. Based on the physical mechanism of interlayer plastic damage accumulation in asphalt pavement, the expected axle load and the cumulative load count are the dominant factors affecting the evolution rate. This method provides a statistical tool for quantitatively identifying key control factors.

[0036] The structural effect analysis is as follows: under fixed load conditions, with the initial inter-story state type as the independent variable, the differences in the evolution of characteristic parameters under different initial states are compared, and the significance of the differences is determined by multiple comparison methods (such as Tukey HSD method).

[0037] S8: Using multivariate nonlinear regression or response surface methodology, construct the functional relationship between the change of characteristic parameters and axle load, frequency, number of accumulations, and initial state, establish a quantitative evolution model of load accumulation and interlayer state, and realize the load accumulation evolution tracking test and analysis of the interlayer state of the pavement.

[0038] like Figure 2 and Figure 3 As shown, a test and analysis device for tracking the cumulative evolution of loads between pavement layers includes: The load-bearing frame system is a gantry structure, comprising a bottom support platform 101, four vertically fixed column guide rails 102, an upper crossbeam 103 that rises and falls vertically along the column guide rails 102, and a protective cover 104. The bottom support platform 101 is made of cast iron and has T-slots machined on its upper surface. The upper crossbeam 103 is a box-type welded structure, subjected to aging stress relief treatment, with linear bearings at its four corners engaging with the column guide rails 102. The protective cover 104 covers the columns. The lifting hydraulic cylinder has a mechanical locking structure for locking the height of the upper crossbeam 103 after it is lowered to the working position. The precision positioning system is fixed on the upper surface of the bottom support platform 101, including a pallet support plate 201. Three tapered pin positioning sleeves are distributed on the pallet support plate 201, and lateral wedge clamping mechanisms 202 are installed on both sides of the pallet support plate 201 to press the positioning base from the side during loading. The hydraulic loading system, installed on the upper part of the protective cover 104, includes a servo actuator 301, a wheel set sliding frame 302, a steering and retraction converter 303, and a loading rubber wheel 304. The servo actuator 301 has a range of ±10kN, a built-in LVDT displacement sensor, and a frequency response of 0-20Hz. The wheel set sliding frame 302 is connected to the piston rod of the servo actuator 301, and the actuator is confined beside the guide rail 405. The steering and retraction converter 303 is connected to the wheel set sliding frame 302. The loading rubber wheel 304 has a diameter of 200mm, a width of 50mm, and is made of polyurethane. Its hardness can be changed to simulate different tire ground contact conditions. A CT-compatible positioning base is used to fix the specimen 4. It includes a base body 401, a positioning base plate 402, positioning steel balls 403, and titanium alloy scanning markers 404. The inner cavity size of the base body 401 is customized according to the specimen specifications. The positioning base plate 402 is fixed to the bottom of the base body 401, and three positioning steel balls 403 are embedded on the bottom surface, with their positions corresponding to the conical pin positioning sleeves. The titanium alloy scanning markers 404 are embedded in the four corners of the bottom of the CT-compatible positioning base. like Figure 4 The diagram shown is an assembly diagram of specimens and positioning bases for different molding methods in this embodiment. It mainly includes cylindrical specimens with circular bases, cubic specimens with square bases, and core drill specimens with arc-shaped plate bases.

[0039] The trolley track system includes a horizontal track 601, a specimen installation station 602 located in the middle of the horizontal track 601, and a transition section 603 connecting the specimen installation station 602 and the horizontal track 601. The surface of the specimen is flush with the track, forming a continuous trolley belt. After the positioning base is placed in the station, the surface of the specimen is flush with the transition section 603 and the track, forming a continuous trolley belt. The loading rubber wheel 304 reciprocates along the entire length of the track, and the stroke can be adjusted according to the number of specimens and the track length.

[0040] The measurement and control system, used for loading control and data acquisition, includes a force sensor 501 (range 20kN, accuracy 0.05%FS), a laser displacement sensor 502 (range ±10mm, resolution 0.1μm), a temperature sensor 503 (PT100, ±0.1℃), and an industrial control computer 504. The force sensor 501 is installed between the servo actuator 301 and the wheel set sliding frame 302. The laser displacement sensor 502 and the temperature sensor 503 are installed on the upper crossbeam 103 to monitor the vertical displacement of the loading rubber wheel and the cumulative deformation of the specimen.

[0041] The working process of the device is as follows: prepare composite specimens and fix them on the positioning base → initial CT scan → place the positioning base in the work position, and position it with the tapered pin → lock it with the electromagnetic chuck and wedge it laterally → set the loading parameters and start cumulative loading → reach the observation node and stop the machine → release the lock and lift the upper frame → take out the positioning base and specimens, and perform a staged CT scan → reset and lower the frame → continue cumulative loading to the next node → cycle until all nodes are completed.

[0042] Example 1: Load Cumulative Evolution Tracking of Rotationally Compacted Specimens This embodiment includes the following steps: S1: Prepare an interlayer composite specimen, fix it on a CT-compatible positioning base, and perform an initial tomographic scan.

[0043] This embodiment uses a rotary compaction molding composite specimen. The lower layer is AC-20, and the upper layer is AC-13. The specimen diameter is 150mm, and the total height is 100mm. After molding and full curing, specimen 4 is removed from the metal mold and placed on a CT-compatible positioning base. The inner cavity diameter is 152mm, the sidewalls are adjustable, and three quenched positioning steel balls distributed at 120° are pre-placed on the bottom surface. Titanium alloy scanning markers 404 with a diameter of 1.5mm are embedded at the four corners. The gap between specimen 4 and the sidewalls of the base is filled with a filling material 5 (such as low-density rigid foam) to form a rigid whole that cannot move relative to the base.

[0044] The interface processing is set to multiple states: Type A (smooth) no processing, Type B (adhesive) spraying 0.3kg / m 2 SBS modified emulsified asphalt, Class C (rough), was roughened with a steel brush.

[0045] The positioning base with specimen 4 fixed on it was placed in the industrial CT scanning chamber for initial scanning (denoted as ScanT0). The scanning parameters were: voltage 180kV, current 200μA, and voxel resolution 25μm. After scanning, the initial three parameters were extracted: interlayer void volume V0, effective contact thickness distribution T0, and porosity gradient curve P0.

[0046] S2: The positioning base with specimen 4 fixed on it is transferred as a whole to the loading device. The positioning steel ball 403 cooperates with the tapered pin positioning sleeve on the pallet bearing plate 201 to achieve repeatable and precise spatial positioning. The reset accuracy is tested to be better than ±5μm.

[0047] S3: Apply a pre-defined staged cumulative load to specimen 4 on the loading device. The loading device adopts a continuous conveyor belt design with a total track length of 1200mm and a specimen installation station 602 in the middle. The surface of the specimen is flush with the track transition section 603. The wheels are 200mm in diameter and 50mm wide, and reciprocate along the entire track. The vertical direction uses a half-sine waveform, with a grounding pressure of 0.7MPa and a frequency of 10Hz. The preset observation nodes are N=0, 50,000 times, 100,000 times, 200,000 times, and 500,000 times.

[0048] S4: When the cumulative load application count reaches the preset observation node, loading is paused. Servo actuator 301 drives the wheel assembly sliding frame 302 and the steering and retraction converter 303 to rotate and rise, causing the loading rubber wheel 304 to detach from the specimen 4. The positioning base, along with the specimen 4, is removed without damage for scanning to obtain the three-dimensional volume data corresponding to this node (denoted as ScanT). i ).

[0049] S5: ScanT i Spatial registration with ScanT0 was performed. Using the titanium alloy scanning markers 404 at the four corners of the positioning base as the registration reference, the spatial coordinate system was unified, and the interlayer interaction region was segmented in the registered volume data. The volumetric feature V of the i-th stage was calculated. i Thickness distribution characteristics T i and porosity gradient characteristics P i The specific sub-steps include: The threshold range of the three phases is determined based on the gray-level histogram, and the watershed algorithm is applied to segment the aggregate phase, asphalt mortar phase and void phase.

[0050] Based on the theoretical interlayer interface position Z0, the interlayer action area is defined as [Z0-2mm, Z0+2mm].

[0051] The number of void phase voxels in the statistical region is multiplied by the volume of a single voxel to obtain the interlayer void volume, and the volume expansion rate ΔV is calculated as follows: ΔV = (V i -V0) / V0×100%.

[0052] The asphalt mortar phase is skeletonized to generate a central surface. The Euclidean distance from each point on the central surface to the void boundary is calculated to obtain a thickness distribution contour map. T is statistically extracted. mean T std and T 95 .

[0053] Orthogonal slices were generated along the Z-axis with a step size of 100 μm. The pore area fraction of each slice was calculated, and the porosity gradient curve was plotted. P was extracted. peak ΔZ peak And FWHM.

[0054] S6: Repeat steps S3-S5 to complete the data acquisition for all five observation nodes.

[0055] S7: Load effect and structural effect analysis based on sequence data. Load effect analysis uses a fixed A-type smooth interface, with axle load, frequency, and cumulative number of cycles as independent variables, to perform multi-factor ANOVA, calculate the contribution rate of each factor, and plot the main effects diagram. Structural effect analysis uses a fixed load case, with the initial state as the independent variable, to perform ANOVA and multiple comparisons.

[0056] S8: Establish a predictive model for the evolution of inter-story state. Using multivariate nonlinear regression or response surface methodology, construct the functional relationship between the change of characteristic parameters and axle load, frequency, cumulative load application times, and initial state type, and establish a quantitative evolution model of load accumulation-inter-story state.

[0057] The evolutionary trajectory exhibits typical three-stage characteristics: the initial compaction period, the stable damage accumulation period, and the accelerated deterioration period.

[0058] Example 2: Marshall compacted specimen This embodiment is similar to Embodiment 1, except that the composite specimen is formed using Marshall compaction molding. The specimen diameter is 101.6 mm, and it is compacted 75 times on both sides. After molding, specimen 4 is fixed in a positioning base with a matching inner diameter. The remaining steps are the same as in Embodiment 1.

[0059] Example 3: Test specimens cut and formed from rutted slabs This embodiment is similar to the scheme of Embodiment 1, except that the composite specimen is cut from a rutted slab. The cut size is a cube of 100mm×100mm×100mm, and the interlayer interface 6 is rectangular. The specimen 4 is fixed in a matching square positioning base in the inner cavity, and the remaining steps are the same as in Embodiment 1.

[0060] Example 4: On-site core sampling specimen This embodiment is similar to the scheme of Embodiment 1, except that the composite specimen is derived from core samples taken from actual road surfaces. The core sample has a diameter of 100mm. An arc-shaped base plate with positioning steel balls 403 is attached to the side of the core sample. Then, the core sample is placed in a positioning base with a matching inner diameter and fixed with filler material. The remaining steps are the same as in Embodiment 1.

[0061] Example 5: Equivalence Verification Experiment To further verify the reliability of the phased cumulative loading method, a comparative experiment can be set up: parallel specimens with the same initial state are selected. Group A is continuously loaded to the target cumulative number of times, while Group B is loaded in segments according to preset nodes, with appropriate pauses between each segment, accumulating to the same target number of times. The final vertical permanent deformation and interlayer three-parameter evolution of the two groups of specimens are compared. Based on the theory of plastic damage accumulation, it is expected that there will be no significant difference between the results of the two groups. This verification experiment can be selectively implemented according to research needs.

[0062] This invention, based on the concept of load accumulation and evolution tracking, collects three-dimensional volumetric data of the same interlayer composite specimen at multiple load history nodes. Through spatial registration and multi-dimensional parameter quantification, a complete evolutionary data chain from the initial state to the critical failure state is established. The multi-dimensional index system proposed in this invention achieves a leap from "fuzzy qualitative" to "precise quantitative" understanding of interlayer states. The established decoupled analysis framework of load effects and structural effects provides systematic methodological support for identifying key influencing factors of interlayer damage.

[0063] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the invention.

Claims

1. A method for tracking and analyzing the cumulative load evolution of pavement interlayer conditions, characterized in that, Includes the following steps: S1: Prepare interlayer composite specimens, fix the specimens to a CT-compatible positioning base to form a rigid whole, obtain initial three-dimensional volume data of the interlayer through initial tomographic scanning, and extract the volume characteristics, thickness distribution characteristics and porosity gradient characteristics of the interlayer interaction area as evolution benchmark values. The CT-compatible positioning base is made of aerospace aluminum or carbon fiber composite material; the bottom surface of the base is provided with at least three positioning steel balls distributed in a non-isosceles triangle; the four corners of the base are embedded with scanning markers made of titanium alloy; the specimen is fixed by low-density filling material or adjustable sidewalls to ensure that the relative position of the specimen and the base remains unchanged throughout the entire test cycle. S2: The positioning base with the specimen fixed is transferred as a whole to the loading device. The positioning structure at the bottom of the base cooperates with the positioning element of the loading device to achieve precise spatial positioning. S3: Apply a phased cumulative load to the specimen using a loading device, dividing the total number of load applications into multiple loading phases, and pausing loading after each phase is completed; S4: When the cumulative number of load applications reaches the preset observation node value, the loading is paused and the base and specimen are removed without damage for tomographic scanning to obtain the three-dimensional volume data corresponding to the observation node. S5: Spatial registration is performed between the three-dimensional volume data corresponding to the observation node and the initial three-dimensional volume data. The interlayer interaction region is segmented in the registered data, and the volume characteristics, thickness distribution characteristics and porosity gradient characteristics of the current node are calculated. The process involves segmenting the interlayer interaction region in the registration data and calculating the volume characteristics, thickness distribution characteristics, and porosity gradient characteristics of the current node. It includes the following steps: S51: Based on the grayscale threshold and watershed algorithm, the volume data is segmented into aggregate phase, asphalt mortar phase and void phase; S52: Based on the theoretical interlayer interface, a preset thickness range along the interlayer normal is defined as the interlayer action area; S53: Calculate the volumetric expansion rate by counting the number of void phases in the interlayer interaction region and obtaining the volumetric expansion rate. S54: The asphalt mortar phase in the interlayer action area is skeletonized to generate the central axis surface. The distance from each point on the central axis surface to the void boundary is calculated to obtain the thickness distribution cloud map and statistical characteristic values, including the average effective contact thickness, thickness standard deviation and 95th percentile thickness. S55: Slice the layers with a fixed step size along the interlayer normal, calculate the pore area fraction of each slice to obtain the gradient characteristics of porosity as a function of depth, including peak porosity, peak position offset and porosity distribution half-peak width. S6: Repeat S3 to S5 to complete the acquisition of all observation nodes and obtain the sequence data of multi-dimensional characteristic parameters as a function of the cumulative load application times; S7: Based on the sequence data, perform load effect analysis and structural effect analysis respectively, and quantify the contribution rate of each influencing factor to the inter-layer state evolution; The load effect analysis is as follows: with the initial inter-story state fixed, axle load, frequency, and cumulative number of times are used as independent variables, and the change in characteristic parameters is used as the dependent variable. A multi-factor analysis of variance is performed to calculate the contribution rate of the main effect and interaction effect of each factor. The structural effect analysis is as follows: under fixed load conditions, with the initial inter-story state type as the independent variable, the differences in the evolution of characteristic parameters under different initial states are compared, and the significance of the differences is determined by multiple comparison methods. S8: Using multivariate nonlinear regression or response surface methodology, construct the functional relationship between the change of characteristic parameters and axle load, frequency, number of accumulations, and initial state, establish a quantitative evolution model of load accumulation and interlayer state, and realize the load accumulation evolution tracking test and analysis of the interlayer state of the pavement.

2. The method for tracking and analyzing the cumulative load evolution of pavement interlayer states according to claim 1, characterized in that, The molding method of the interlayer composite specimen includes at least one of the following: Marshall compaction molding, rotary compaction molding, rut plate cutting molding, and on-site core drilling sampling molding; the specimen scanning surface is a circular interface or a rectangular interface, and the size matches the molding method.

3. The method for tracking and analyzing the cumulative load evolution of pavement interlayer states according to claim 1, characterized in that, The phased cumulative load is applied by coupling vertical pulse pressure with horizontal reciprocating motion; a specimen installation station is set up on the horizontal track, and the surface of the specimen is flush with the transition section of the track to form a continuous travel belt, and the wheels reciprocate along the track to simulate the travel load.

4. An apparatus for tracking and analyzing the load accumulation evolution of pavement interlayer states as described in any one of claims 1-3, characterized in that, include: The load-bearing frame system is a gantry structure, including a bottom load-bearing platform (101), four vertical column guide rails (102) fixed to the bottom load-bearing platform (101), an upper crossbeam (103) that rises and falls vertically along the column guide rails (102), and a protective cover (104). The bottom load-bearing platform (101) is made of cast iron and has T-slots machined on its upper surface. The upper crossbeam (103) is a box-type welded structure. The precision positioning system is fixed on the upper surface of the bottom support platform (101) and includes a pallet support plate (201). Three tapered pin positioning sleeves are distributed on the pallet support plate (201), and lateral wedge clamping mechanisms (202) are installed on both sides of the pallet support plate (201). The hydraulic loading system is installed on the upper part of the protective cover (104) and includes a servo actuator (301), a wheel set slide frame (302), a steering and retraction converter (303), and a loading rubber wheel (304). The servo actuator (301) has a built-in LVDT displacement sensor. The wheel set slide frame (302) is connected to the piston rod of the servo actuator (301). The steering and retraction converter (303) is connected to the wheel set slide frame (302). A CT-compatible positioning base is used to fix the test specimen. It includes a base body (401), a positioning base plate (402), positioning steel balls (403), and titanium alloy scanning markers (404). The inner cavity size of the base body (401) is customized according to the test specimen specifications. The positioning base plate (402) is fixed to the bottom of the base body (401), and three positioning steel balls (403) are embedded on the bottom surface. Their positions correspond one-to-one with the conical pin positioning sleeves. The titanium alloy scanning markers (404) are embedded in the four corners of the bottom of the CT-compatible positioning base. The train track system includes a horizontal track (601), a specimen installation station (602) located in the middle of the horizontal track (601), and a transition section (603) connecting the specimen installation station (602) and the horizontal track (601). The surface of the specimen is flush with the track to form a continuous train track. The measurement and control system is used for load control and data acquisition, including a force sensor (501), a laser displacement sensor (502), a temperature sensor (503), and an industrial control computer (504). The force sensor (501) is installed between the servo actuator (301) and the wheel set sliding frame (302), and the laser displacement sensor (502) and the temperature sensor (503) are installed on the upper crossbeam (103).

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