Method for evaluating crack resistance of asphalt cement based on asphalt-aggregate constraint simulation

Abstract

The invention relates to the technical field of road engineering asphalt pavement material performance detection, in particular to an asphalt cement anti-cracking performance evaluation method based on asphalt-aggregate constraint simulation, which comprises the following steps: preparing a cylindrical asphalt test piece completely bonded with circular bonding surfaces of a top die and a bottom die; placing the test piece at a preset temperature, and keeping the temperature constant until the temperature is uniform and stable; mounting the test piece subjected to heat preservation on a tensile testing machine, performing uniaxial stretching on the test piece in a preset loading mode in a constant-temperature environment consistent with S2 until the test piece is completely snapped, and continuously collecting real-time load and displacement in the whole stretching process; calculating an anti-cracking index based on the collected load and displacement, and evaluating the anti-cracking performance of the asphalt cement; a rigid constraint interface is constructed through a standardized test piece preparation process, a multi-dimensional constraint stress state and a real cracking mechanism of asphalt among aggregates are reproduced in a uniaxial stretching process, and a whole-process standardized system from test piece preparation, constant-temperature loading to data evaluation is constructed.

Description

Technical Field

[0001] This invention relates to the field of performance testing technology for asphalt pavement materials in road engineering, and in particular to a method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation. Background Technology

[0002] In the field of road engineering, low-temperature cracking and fatigue cracking of asphalt pavements are the most common early-stage defects on high-grade highways in my country. The crack resistance of asphalt binders directly determines the service life and long-term durability of asphalt pavements. Currently, the evaluation of the crack resistance of asphalt binders mainly relies on experimental methods based on linear viscoelastic theory, such as the Dynamic Shear Rheology (DSR) and Bending Beam Rheology (BBR) tests in the American Superpave system. These methods can effectively characterize the basic rheological properties of asphalt's high-temperature rutting resistance and low-temperature crack resistance, and are widely used in the global road engineering field.

[0003] However, in long-term engineering practice and academic research, there are core defects that cannot be overcome: First, existing rheological testing methods cannot simulate the multidimensional constrained stress state and stress concentration effect of asphalt binder in actual asphalt mixtures when it is wrapped by rigid aggregates. The test conditions are fundamentally different from the actual service conditions of asphalt pavement, and cannot truly reflect the nonlinear failure behavior of materials with significant nonlinear characteristics such as modified asphalt and recycled asphalt under complex stress conditions. Secondly, existing fatigue cracking and low-temperature cracking tests mostly use rheological indicators as the core of evaluation. During the test, the actual cracking of asphalt specimens is not induced, which is completely inconsistent with the actual cracking morphology and fracture evolution process of the pavement. It is difficult to accurately quantify the fracture resistance of asphalt binder under constrained conditions. Third, existing methods for testing modified asphalt and recycled asphalt exhibit large dispersion, poor repeatability, and poor reproducibility, failing to provide reliable technical basis for the research, screening, and incoming quality control of high-durability pavement asphalt materials, thus severely restricting the development of long-life asphalt pavement technology.

[0004] While traditional uniaxial tensile tests can achieve tensile fracture of asphalt specimens, they often use dumbbell-shaped free specimens. During the tensile process, the specimens can shrink laterally without restriction, resulting in a pure uniaxial stress state, which is completely inconsistent with the constrained stress state of asphalt in the mixture. The test results have a very low correlation with the actual cracking performance of the pavement. On the other hand, tensile tests with sidewall confinement introduce additional interference factors due to the frictional resistance of the sidewalls, leading to distorted test data and failing to accurately characterize the crack resistance of asphalt itself.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] This invention provides a method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation. By constructing a rigid constraint interface through a standardized specimen preparation process, the multidimensional constraint stress state and actual cracking mechanism of asphalt between aggregates are reproduced during uniaxial tensile testing. A standardized system for the entire process, from specimen preparation and isothermal loading to data evaluation, is constructed to solve the problems of distorted stress state, inconsistent evaluation logic, and poor result stability in traditional methods, thereby achieving accurate evaluation of the nonlinear crack resistance of asphalt binders.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation includes: S1 Prepare cylindrical asphalt specimens that are fully bonded to the circular bonding surfaces of the top and bottom molds; S2 Place the specimen at a preset temperature and keep it at a constant temperature until the temperature is uniform and stable; S3 installs the heat-insulated specimen on the tensile testing machine. Under the same constant temperature environment as S2, the specimen is subjected to uniaxial tension in a preset loading mode until the specimen is completely broken. Real-time load and displacement are continuously collected throughout the tensile process. S4 calculates crack resistance indices based on collected loads and displacements to evaluate the crack resistance performance of asphalt binders.

[0008] This invention achieves a multiaxial stress response consistent with actual road conditions by rigidly bonding the top and bottom molds to the asphalt specimen across its entire cross-section. This restricts the lateral free shrinkage of the asphalt specimen during uniaxial tensile testing, perfectly simulating the multidimensional constrained stress state of asphalt binder encased in rigid aggregate within the mixture. This reproduces the true cracking mechanism of the road surface. Compared to existing rheological tests that can only characterize linear viscoelastic properties, this invention can directly capture the nonlinear failure behavior of asphalt binder through the entire process of specimen stretching to fracture, thus overcoming the shortcomings of existing technologies.

[0009] Furthermore, the method for preparing the specimen includes: S11 Clean the bonding surfaces of the top mold and bottom mold, and preheat the top mold, bottom mold and spacer pins in an oven at 157~163℃; More specifically, cleaning the bonding surface thoroughly removes surface oil, dust, and residual asphalt, ensuring a high-strength, gapless bond between the asphalt and the rigid bonding surface, preventing interface debonding during the tensile process and thus test failure. Simultaneous constant-temperature preheating of the top mold, bottom mold, and spacer pins ensures uniform temperature for all mold components, preventing localized cooling of the asphalt due to temperature differences when in contact with hot asphalt, which could lead to incomplete bonding. It also ensures stable spacer pin dimensions, providing a prerequisite for precise control of the asphalt bonding layer thickness. The preheating time for the top mold, bottom mold, and spacer nails is 45 minutes. By using the above preheating temperature and time, it is possible to avoid problems such as local temperature drop when the mold comes into contact with hot asphalt, failure of the asphalt to cool and solidify and cover the entire bonding surface, and poor interface bonding effect. It is also possible to avoid local overheating and aging of the asphalt during subsequent contact, volatilization of lightweight components, and alteration of the crack resistance of the asphalt itself, which would lead to distorted test results. S12 Heat the asphalt binder to be tested to a fluid state, pour it into a silicone mold, and then cool it. More specifically, by pre-forming with silicone molds, asphalt disc specimens with regular dimensions, no air bubbles and no internal defects can be obtained, avoiding problems such as asphalt overflow, uneven thickness and interface bubbles caused by direct pouring, laying the foundation for subsequent full-section bonding with the top and bottom molds. Preferably, after the asphalt sample in S12 is poured into the silicone mold, it is cooled at room temperature for no less than 0.5 hours. If the cooling time is too short, the asphalt will not be fully set, and deformation and damage will easily occur during demolding, making it impossible to obtain specimens with regular dimensions. If the cooling time is too long, it will reduce the test efficiency but will not affect the specimen molding effect. S13 Place the cooled asphalt binder into the preheated bottom mold, and put the bottom mold back into the S11 oven for heating until the asphalt binder is completely melted and covers the entire bonding surface of the bottom mold. More specifically, the oven temperature is the same as in S11, and the pre-formed asphalt specimen is reheated and melted, which allows the asphalt to be evenly spread across the entire circular bonding surface, forming a cylindrical specimen that perfectly matches the size of the bonding surface. This ensures that the asphalt and the bottom mold bonding surface are 100% in contact, without gaps or missing material, providing a basis for the effective application of subsequent lateral constraints. S14 With the center of the bottom mold bonding surface as the center, place the preheated spacer pins evenly in the middle position of the top surface of the bottom mold in an equilateral triangle pattern. Then put the bottom mold back into the S11 oven for heating. Then use the positioning rod to coaxially close the top mold and the bottom mold. More specifically, the oven temperature is the same as in S11. The horizontally placed spacer pins are the only rigid limiting reference for the thickness of the asphalt bonding layer. After the cylindrical spacer pins are placed horizontally, the vertical distance between the highest point of its outer circle and the bottom mold is exactly equal to its own diameter. After the mold is closed, the vertical net distance between the top mold and the bottom mold can be accurately locked, which is the thickness of the asphalt bonding layer. The three spacer pins are evenly arranged in an equilateral triangle to form a stable three-point support plane, ensuring that the top mold and the bottom mold are completely parallel after the mold is closed, avoiding the appearance of wedge-shaped specimens, ensuring that the thickness of the asphalt bonding layer is uniform across the entire cross section, and ensuring that the entire cross section is subjected to consistent force during subsequent tensile testing, thus achieving uniform lateral constraint. Preferably, there are three spacer pins with a diameter of 1.5 mm or 3.0 mm, the diameter of which is exactly equal to the thickness of the asphalt bonding layer of the asphalt specimen. If the diameter of the spacer pin is too small, the asphalt bonding layer will be too thin, and it will be prone to instantaneous fracture during tension, making it impossible to capture the post-peak deformation characteristics. If the diameter of the spacer pin is too large, the asphalt bonding layer will be too thick, and it will be impossible to effectively simulate the real stress state of the asphalt film between aggregates, and the test results will be out of sync with the actual working conditions. Preferably, after placing the spacer pins, the bottom mold is returned to the oven for heating time of no less than 5 minutes to ensure that the spacer pins and the mold are at the same temperature, so as to avoid local cooling of the asphalt due to temperature difference after the mold is closed, which would affect the bonding effect. S15 After the mold is closed and locked, the specimen is placed horizontally in the oven in S11 and heated. After being taken out and cooled until fully set, the specimen is obtained. More specifically, by calibrating the specimen to a horizontal state using a level bubble, it can be ensured that the center axis of the bottom mold is completely perpendicular to the horizontal plane, and the bonding surfaces of the top and bottom molds are completely parallel to the horizontal plane. This prevents the molten asphalt from flowing to the lower side under the action of gravity, ensures that the thickness of the asphalt bonding layer is uniform across the entire cross section, prevents asphalt from overflowing the bonding surface and triggering specimen scrapping, and also eliminates residual internal stress inside the specimen, ensuring the authenticity of asphalt performance. Preferably, the oven temperature is the same as in S11. In S15, the oven heating time for the specimen after mold closing is about 15 minutes to ensure that the asphalt flows fully in the mold-closed state, filling the space between the top mold and the bottom mold, forming a standard cylindrical specimen without defects or bubbles. After heating, the specimen is cooled to room temperature until it is fully set. If the asphalt sample overflows the bonding surface, the test needs to be repeated.

[0010] The above-mentioned specimen preparation method ensures the compatibility between the mold and asphalt through clean synchronous constant temperature preheating, avoiding interface debonding and local performance degradation of asphalt from the source. The silicone mold preforming process avoids defects such as asphalt overflow, uneven thickness, and internal air bubbles caused by direct casting. The reheating and spreading process achieves 100% gapless bonding between asphalt and the bottom mold bonding surface. The three-point equilateral horizontally placed spacer pins precisely lock the thickness of the asphalt bonding layer and the parallelism of the top and bottom molds. The horizontal constant temperature heating and shaping process eliminates the problems of residual internal stress and uneven thickness in the specimen. Finally, it can stably prepare standardized constrained asphalt specimens with complete interface bonding, uniform and controllable thickness, no initial defects, and no residual stress. This perfectly meets the requirements of subsequent aggregate constrained tensile tests, ensuring the authenticity of the asphalt binder crack resistance test data from the source.

[0011] Furthermore, the cleaning method in S11 is to wipe the bonding surface with alcohol, which can achieve efficient cleaning without damaging the precision of the mold. Moreover, alcohol is volatile and leaves no residual impurities that affect the asphalt bonding effect.

[0012] Furthermore, in S12, the asphalt binder to be tested is placed in a covered sample container and then heated. The sealed heating with a cover can isolate oxygen in the oven, prevent the asphalt binder from undergoing thermo-oxidative aging, and at the same time prevent the volatilization of light oils in the asphalt, thus preserving the original properties of the asphalt to the greatest extent and ensuring that the test results truly reflect the crack resistance of the material itself.

[0013] Furthermore, the preset temperature in S2 is 24.5~25.5℃. In order to improve the temperature uniformity, it is necessary to keep it warm for about 1.5 hours.

[0014] More specifically, the temperature range mentioned above corresponds to the temperature range in which fatigue cracking is most likely to occur during the actual service of asphalt pavement, which can make the test results more consistent with the actual working conditions of the pavement.

[0015] Furthermore, the preset loading mode in S3 is a graded loading mode, which is as follows: first, axial tension is applied in the displacement control mode of 0.8~1.2mm / min. When the tension reaches 40N, it switches to the load control mode of 1.8~2.2N / s to continue uniform tensioning until the specimen is completely broken.

[0016] More specifically, by first loading to 40N using low-speed displacement control, the specimen can be completely fitted with the testing machine fixture, eliminating assembly gaps and avoiding distortion of displacement data in the initial loading stage. Then, by switching to uniform load control mode to stretch until fracture, the stress process of asphalt pavement under traffic load can be stably simulated, capturing the full curve details of the asphalt specimen from elastic deformation, plastic deformation to final fracture, and fully characterizing the entire crack resistance process of asphalt binder.

[0017] Furthermore, the crack resistance indicators include at least tensile strength, elongation after peak, and strain energy index; the formula for calculating tensile strength is: ; in, The value represents tensile strength, expressed in MPa, and is rounded to four decimal places. The maximum tensile force is expressed in N, and the value is rounded to one decimal place; D is the diameter of the bonding surface, expressed in mm, and the value is rounded to two decimal places. The formula for calculating tensile strength is based on an axial tensile mechanical model of a circular bonding surface, using the maximum tensile force P collected during the tensile process. ult The ultimate tensile stress that the asphalt specimen can withstand per unit bond area is calculated using the bonding surface diameter D. In the formula, 4 / (πD) 2 The area of ​​the circular bonding surface is the reciprocal of the area of ​​the circular bonding surface, which perfectly matches the stress form in which the asphalt specimen and the circular bonding surfaces of the top and bottom molds are completely in contact in this invention; tensile strength is the core basic indicator characterizing the ultimate bearing capacity of asphalt binder against tensile fracture, and can directly reflect the basic strength characteristics of asphalt materials. The formula for calculating post-peak elongation is: ; in, The value is the post-peak elongation, with one decimal place. δ is the post-peak elongation deformation value in mm, which is the displacement of the sample when it reaches the tensile strength and then decays to 80% of the tensile strength. The value is retained to three decimal places. The adhesive thickness is the same as the spacer pin diameter, and the unit is mm. The value is retained to two decimal places. The post-peak elongation calculation formula focuses on the nonlinear failure behavior of asphalt binders after reaching their ultimate tensile strength. It uses the post-peak elongation deformation value δ, which is the value of the asphalt specimen after reaching its tensile strength and the tensile force decays to 80% of the peak strength, as the numerator and the original bond thickness t of the asphalt specimen as the denominator. The absolute elongation deformation is converted into relative elongation and presented as a percentage. This formula differs from the conventional fracture elongation in that it accurately captures the plastic deformation capacity of asphalt binders after reaching their peak strength, quantifies its toughness characteristics of cracking without breaking, and can effectively distinguish the fatigue cracking resistance and low-temperature cracking resistance of different asphalt materials. The formula for calculating the strain energy index is: ; in, The strain energy index is dimensionless and its value is retained to 3 decimal places. and The value represents the unit change (%) of the elongation rate of the specimen along the horizontal axis, and is rounded to one decimal place. This represents the average action intensity corresponding to the unit change in elongation, in MPa, with the value retained to 4 decimal places. The tensile strength at the i-th measuring point is expressed in MPa, and the value is rounded to four decimal places. The strain energy index calculation formula is divided into two forms: a continuous integral form calculated by adaptation theory and an engineering summation form based on discrete measurement point data from adaptation tests. Both use the ratio of real-time tensile strength to peak tensile strength as the core calculation term throughout the tensile process, with the unit change in elongation as the calculation step size. The final result is a dimensionless index characterizing the crack resistance and energy dissipation capacity of asphalt binder throughout the entire process from loading to fracture. This formula eliminates the interference of differences in the basic strength of different asphalt materials on the evaluation results by normalization by dividing by the peak tensile strength, and focuses more on the deformation energy dissipation characteristics of the material. The calculated strain energy index integrates the strength characteristics, plastic deformation capacity, and energy dissipation characteristics of asphalt, and can comprehensively and quantitatively reflect the nonlinear crack resistance performance of asphalt binder, effectively distinguishing the differences in crack resistance performance of different types of materials such as modified asphalt and recycled asphalt.

[0018] Furthermore, when the asphalt binder is modified asphalt, its qualification requirement is a strain energy index (SEI) ≥ 5.0; when the asphalt binder is recycled asphalt, its qualification requirement is a strain energy index (SEI) ≥ 5.5.

[0019] Furthermore, the data acquisition method in S3 is as follows: record the displacement of the specimen and the corresponding load during the test at a rate of at least 2 points per second.

[0020] Preferably, the displacement data acquisition accuracy is not less than 0.001 mm, the load data acquisition accuracy is not less than 0.1 N, and the number of parallel tests is not less than 2 to ensure the accuracy and repeatability of the test data; Furthermore, the allowable error for the repeatability test of tensile strength is 5% of the average value, and the allowable error for the reproducibility test is 10% of the average value; The permissible error for repeatability testing of post-peak elongation is 7% of the average value, and the permissible error for reproducibility testing is 12% of the average value. The permissible error for repeatability testing of strain energy index is 7% of the average value, and the permissible error for reproducibility testing is 12% of the average value.

[0021] Furthermore, the method for mounting the specimen on the tensile testing machine includes: fixing the bottom mold to the base plate of the tensile testing machine, assembling the top mold with a fisheye joint, installing a Y-type joint on the main shaft of the testing machine and then slowly pressing it down, completing the connection of the two joints by a pin, and then removing the positioning rod; More specifically, by using the fisheye joint and the Y-type joint, the coaxiality error between the testing machine spindle and the specimen can be completely eliminated, ensuring that the axial tensile force acts vertically and evenly on the entire bonding surface of the asphalt specimen, avoiding abnormal fracture of the specimen caused by uneven load and local stress concentration during the tensile process; after clamping, removing the positioning rod can release the rigid constraint between the top mold and the bottom mold, ensuring that only the asphalt specimen bears the axial tensile force during the tensile process.

[0022] The technical solution of this invention can achieve the following technical effects: (1) This invention uses the rigid bonding of the top mold, bottom mold and asphalt specimen across the entire cross section to restrict the lateral free shrinkage of the asphalt specimen during uniaxial tension, thereby stimulating multiaxial stress response. This perfectly simulates the multidimensional constrained stress state of asphalt binder wrapped by rigid aggregate in actual mixture, reproduces the real cracking mechanism of pavement, and fundamentally overcomes the core defect of existing rheological tests that can only characterize linear viscoelastic properties and are out of touch with actual working conditions. (2) This invention uses three core indicators—tensile strength, post-peak elongation, and strain energy index—to comprehensively quantify the crack resistance of asphalt binders from three dimensions: ultimate bearing capacity, plastic toughness, and energy dissipation capacity throughout the process. In particular, it can effectively characterize the post-peak failure behavior of materials with significant nonlinearity, such as modified asphalt and recycled asphalt, filling the industry gap where existing technologies cannot reflect the nonlinear failure characteristics of asphalt. The correlation between the test results and the actual cracking performance of the pavement is significantly better than that of existing methods. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the top mold and bottom mold structure; Figure 2 This is a cross-sectional view of the top mold and the bottom mold; Reference numerals: 1. Top mold; 2. Protrusion; 3. Bottom mold; 4. Groove; 5. Spacer pin. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0027] In this embodiment of the invention, the instruments and equipment used include: a constant temperature oven, a high-precision electronic balance (accuracy 0.01g), a universal tensile testing machine (with a temperature control box, force sensor accuracy 0.1N, displacement accuracy 0.001mm), a spirit level, a circular silicone mold, a rigid metal top mold, a bottom mold, spacer pins (two types with diameters of 1.5mm and 3.0mm), a positioning rod, a fisheye connector, and a Y-type connector; Reference Figure 1 and Figure 2The top mold 1 is a horizontal rigid plate. The bottom center of the plate extends downward to form a cylindrical protrusion 2 that is coaxial with the bottom mold 3. The lower end surface of the protrusion 2 is a flat circular bonding surface that has been polished with high precision. The edge of the plate has three positioning holes that are coaxial with the bottom mold 3. These holes are used to insert positioning rods to achieve precise mold closing and locking with the bottom mold 3. The top of the plate has a threaded connection structure that is compatible with the fisheye joint, which can form a rigid force transmission connection with the main shaft of the tensile testing machine. The bottom mold 3 is a high-rigidity alloy steel circular plate component with the same material and outer contour size as the top mold 1. A cylindrical groove 4 is recessed inward on the upper surface of the plate to accommodate the asphalt binder. When the mold is closed, the protrusion 2 extends into the groove 4. Positioning holes corresponding to the top mold 1 are provided on the edge. The bottom is provided with a slot-type fixing structure that matches the bearing base plate of the tensile testing machine, which can completely lock the bottom mold 3 onto the base plate of the testing machine. The spacer pin 5 is a cylindrical high-rigidity stainless steel pin, available in two fixed diameter specifications: 1.5mm and 3.0mm. The diameter machining tolerance is controlled within ±0.01mm, and its nominal diameter is exactly equal to the design bonding layer thickness of the asphalt specimen. When in use, it is placed horizontally with its own central axis parallel to the bonding surface. Three of them are evenly arranged in an equilateral triangle on the top surface of the bottom mold 3. After the mold is closed, it is movably clamped between the top mold 1 and the bottom mold 3, and the vertical clearance d between the two molds is precisely locked by its own fixed diameter.

[0028] The asphalt samples used included: Example 1 was SBS modified asphalt (ID grade), Example 2 was plant-mixed hot recycled asphalt, and Example 3 was No. 70 base asphalt. Example 1:

[0029] This embodiment provides a method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation, used to evaluate the crack resistance of SBS modified asphalt (ID grade), including the following steps: Preparation of S1 cylindrical asphalt specimens; S11 uses anhydrous alcohol to wipe and clean the circular bonding surfaces of the top mold and bottom mold, and then lets them dry for later use; place the top mold, bottom mold, and 3 spacer pins with a diameter of 1.5mm in a constant temperature oven at 160℃ and preheat for 45 minutes. S12 The SBS modified asphalt sample was placed in a covered sample container and heated in a constant temperature oven at 150℃ until it became a uniformly flowing viscous liquid. 4.5±0.05g of the asphalt sample was weighed and poured into a circular silicone mold. It was cooled at room temperature for 0.5h to obtain a pre-formed asphalt disc specimen. S13 Take out the pre-formed asphalt disc specimen from the silicone mold, place it on the preheated bottom mold bonding surface, put the bottom mold back into the constant temperature oven at 160℃ and heat for 15 minutes until the asphalt is completely melted and covers the entire circular bonding surface of the bottom mold. S14. Using the center of the bottom mold bonding surface as the center, place three preheated spacer pins horizontally in an equilateral triangle at the middle position of the top surface of the bottom mold. Then, put the bottom mold back into a constant temperature oven at 160℃ and heat for 5 minutes. Take out the top mold and bottom mold, insert two positioning rods into the positioning holes of the bottom mold, align the positioning holes of the top mold with the positioning rods, and slowly press down until they are completely in contact with the spacer pins. Insert the third positioning rod to complete the mold closing and locking. S15 The specimen after mold closing and locking is placed on a tray, and the specimen is calibrated to a horizontal state with a bubble level (the center axis of the bottom mold is perpendicular to the horizontal plane). It is then placed in a constant temperature oven at 160℃ and heated for 15 minutes. After being taken out, it is cooled at room temperature until it is completely set. The asphalt is checked and there is no overflow. A qualified constrained asphalt specimen is obtained. Three sets of specimens are prepared in parallel.

[0030] S2 constant temperature insulation; The prepared specimens were placed in a temperature-controlled chamber at 25℃±0.5℃ and kept at a constant temperature for 1.5 hours until the internal temperature of the specimens was uniform and stable. The tensile speed of the tensile testing machine was checked at the same time, and the force sensor and displacement sensor were zeroed.

[0031] S3 constrained tensile fracture test; S31 removes the heat-insulated specimen, quickly fixes the bottom mold to the bearing base plate of the tensile testing machine, assembles the top mold with a fish-eye joint, and slowly presses down after installing the Y-type joint on the main shaft of the testing machine, completing the rigid connection between the two joints through the pins, and then removes the 3 positioning rods; S32 starts the tensile testing machine, first applying axial tension in the displacement control mode of 1 mm / min. When the tension reaches 40 N, switch to the load control mode of 2 N / s to continue uniform tensioning until the asphalt specimen is completely broken. The S33 records the real-time displacement and corresponding load data of the specimen during the tensile process at a sampling frequency of 2 points per second.

[0032] Quantitative evaluation of S4 crack resistance performance; Based on the collected load-displacement full curve data, tensile strength, post-peak elongation and strain energy index were calculated, and the results are recorded in Table 1. Example 2:

[0033] This embodiment provides a method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation, used to evaluate the crack resistance of plant-mixed hot recycled asphalt. The only difference from Embodiment 1 is: The diameter of the spacer pins is 3.0 mm; The asphalt sample was plant-mixed hot recycled asphalt, and the heating temperature of S12 was 165℃. The remaining steps are exactly the same as in Example 1, and the test results are recorded in Table 1. Example 3:

[0034] This embodiment provides a method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation, used to evaluate the crack resistance of No. 70 base asphalt. The only difference from Embodiment 1 is that: The asphalt sample was No. 70 Grade A road petroleum asphalt, and the heating temperature of S12 was 145℃. The displacement control rate is 0.8 mm / min, and the load control rate is 1.8 N / s; The remaining steps are exactly the same as in Example 1, and the test results are recorded in Table 1.

[0035] Comparative Example 1: The only difference between this comparative example and Example 1 is that no spacer pins were placed during the specimen preparation process. The remaining steps are completely consistent with Example 1, and the test results are recorded in Table 1.

[0036] Comparative Example 2: This comparative example uses the existing Superpave system DSR test to test the crack resistance of the SBS modified asphalt in Example 1. The test temperature is 25℃, and the test results are recorded in Table 1.

[0037] The test results of the above embodiments and comparative examples were summarized, and the repeatability error of parallel tests and the correlation between the test results and the actual cracking of the same batch of asphalt mixture pavement after six months were statistically analyzed. The results are shown in Table 1: Table 1 Summary of Asphalt Crack Resistance Test Results Note: In the correlation with actual road surface cracking, R 2 The closer the result is to 1, the higher the degree of match between the test results and the actual cracking of the road surface, and the stronger the engineering applicability of the method.

[0038] Examples 1-3 all adopted the three-step specimen preparation process, graded loading mode and multi-dimensional index evaluation system of the present invention, and all showed excellent test stability and engineering applicability. The repeatability error of parallel tests was far lower than the industry general requirements, and the correlation between the test results and the actual cracking of the pavement was greater than 0.9. They can accurately and realistically reflect the actual crack resistance of asphalt binder.

[0039] Comparative Example 1, due to the absence of spacer pins, could not accurately control the thickness of the asphalt bonding layer, resulting in poor parallelism between the top and bottom molds after mold assembly, uneven asphalt layer thickness, and severe eccentric load fracture during tensile testing. The test results showed extremely high dispersion, with a repeatability error as high as 18.7%, and were almost uncorrelated with the actual cracking of the road surface, making it completely impossible to effectively evaluate the crack resistance performance of asphalt.

[0040] Comparative Example 2 uses the existing DSR test technology, which can only obtain the rheological index of asphalt and cannot reflect the actual fracture behavior of asphalt. The correlation between the test results and the actual cracking of the pavement is only 0.45, which cannot provide a reliable basis for the selection of crack resistance performance of asphalt materials.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation, characterized in that, include: S1 Prepare cylindrical asphalt specimens that are fully bonded to the circular bonding surfaces of the top and bottom molds; S2 Place the specimen at a preset temperature and keep it at a constant temperature until the temperature is uniform and stable; S3 After heat preservation, the specimen is installed on the tensile testing machine. Under the same constant temperature environment as S2, the specimen is subjected to uniaxial tension in a preset loading mode until the specimen is completely broken. Real-time load and displacement are continuously collected throughout the tensile process. S4 calculates crack resistance indices based on collected loads and displacements to evaluate the crack resistance performance of asphalt binders.

2. The method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation according to claim 1, characterized in that, The method for preparing the specimen includes: S11 Clean the bonding surfaces of the top mold and bottom mold, and preheat the top mold, bottom mold and spacer pins in an oven at 157~163℃; S12 Heat the asphalt binder to be tested to a fluid state, pour it into a silicone mold, and then cool it. S13 Place the cooled asphalt binder into the preheated bottom mold, and put the bottom mold back into the oven in S11 for heating until the asphalt binder is completely melted and covers the entire bonding surface of the bottom mold. S14 With the center of the bottom mold bonding surface as the center, place the preheated spacer nails horizontally in an equilateral triangle at the middle position of the top surface of the bottom mold, and then put the bottom mold back into the oven in S11 for heating; then use the positioning rod to coaxially close the top mold and the bottom mold. S15 After the mold is closed and locked, the specimen is placed horizontally in the oven in S11 for heating. After being taken out, it is cooled until it is completely set, and the specimen is obtained.

3. The method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation according to claim 2, characterized in that, The cleaning method in S11 is to wipe the adhesive surface with alcohol.

4. The method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation according to claim 2, characterized in that, In S12, the asphalt binder to be tested is placed in a covered sample container and then heated.

5. The method for evaluating the crack resistance of asphalt binder based on asphalt-aggregate constraint simulation according to claim 2, characterized in that, The preset temperature in S2 is 24.5~25.5℃.

6. The method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation according to claim 1, characterized in that, The preset loading mode in S3 is the graded loading mode, which is as follows: first, axial tension is applied in the displacement control mode of 0.8~1.2mm / min. When the tension reaches 40N, the load control mode of 1.8~2.2N / s is switched to continue uniform tensioning until the specimen is completely broken.

7. The method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation according to claim 2, characterized in that, The crack resistance indicators include at least tensile strength, elongation after peak, and strain energy index; the formula for calculating tensile strength is: ； in, Tensile strength; D is the maximum tensile force; D is the diameter of the bonding surface; The formula for calculating post-peak elongation is: ； in, δ is the post-peak elongation, which is the post-peak elongation deformation value, i.e. the displacement of the sample when it decays to 80% of the tensile strength after reaching the tensile strength. The adhesive thickness is the same as the diameter of the spacer pin; The formula for calculating the strain energy index is as follows: ； in, The strain energy index; and This represents the unit change in the elongation of the specimen along the horizontal axis. The average action intensity corresponding to a unit change in elongation; Let be the tensile strength at the i-th measuring point.

8. The method for evaluating the crack resistance of asphalt binder based on asphalt-aggregate constraint simulation according to claim 7, characterized in that, When the asphalt binder is modified asphalt, its qualification requirement is a strain energy index (SEI) ≥ 5.0; when the asphalt binder is recycled asphalt, its qualification requirement is a strain energy index (SEI) ≥ 5.

5.

9. The method for evaluating the crack resistance of asphalt binders based on asphalt-aggregate constraint simulation according to claim 1, characterized in that, The data acquisition method in S3 is to record the displacement of the specimen and the corresponding load during the test at a rate of at least 2 points per second.

10. The method for evaluating the crack resistance of asphalt binder based on asphalt-aggregate constraint simulation according to claim 2, characterized in that, The method for mounting the specimen on the tensile testing machine includes: fixing the bottom mold to the base plate of the tensile testing machine, assembling the top mold with a fisheye joint, installing a Y-type joint on the main shaft of the testing machine and then slowly pressing it down, connecting the two joints with a pin, and then removing the positioning rod.

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