An asphalt mixture fatigue life prediction method based on initial modulus index

Abstract

The application discloses a kind of based on initial modulus index asphalt mixture fatigue life prediction method, the present application includes the following steps: S1, the standard test piece of asphalt mixture is made;S2, the three-point bending fatigue test of asphalt mixture under different stress levels is carried out to the standard test piece made under setting parameter;S3, according to test data fitting asphalt mixture stress strain hysteresis curve;S4, based on the stress strain hysteresis curve obtains the initial modulus and failure modulus of asphalt mixture;S5, based on the initial modulus and failure modulus described above constructs the fatigue damage factor model of asphalt mixture based on initial modulus;S6, based on the fatigue damage factor model constructed predicts the fatigue life of asphalt mixture in use.The present application is more reasonable by introducing failure modulus and constructing damage factor model, so that the residual life of asphalt mixture can be more accurately and quickly predicted.

Description

Technical Field

[0001] This invention relates to asphalt life prediction, specifically a method for predicting the fatigue life of asphalt mixtures based on initial modulus. Background Technology

[0002] Under cyclic traffic loads, the service performance of asphalt pavements gradually deteriorates. When the service performance of an asphalt pavement is about to decrease to the failure threshold, it needs to be repaired or maintained to extend its service life. Fatigue life is one of the most important service performance parameters of asphalt pavements, and the ability to accurately predict the remaining service life significantly affects the maintenance and repair strategies. Currently, phenomenological fatigue models ignore the damage evolution process of asphalt mixtures and cannot obtain accurate fatigue life. Using the relationship between cumulative dissipated energy and fatigue life to predict the fatigue performance of mixtures is a commonly used method, but it requires long-term loading tests to obtain the dissipated energy, which is not conducive to practical engineering applications.

[0003] Generally speaking, the fatigue damage process of asphalt mixtures is essentially a process of modulus decay with the number of loading cycles, which can be simplified into a curve model of the relationship between modulus and fatigue load. Obtaining the characteristic parameters of the modulus decay curve is an effective means of predicting the remaining service life of asphalt mixtures. Considering the fatigue damage evolution process of asphalt mixtures, using the initial modulus index of asphalt mixtures to predict the remaining service life of asphalt mixtures is accurate and fast, and has practical significance for scientifically guiding the maintenance of actual asphalt pavements. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned shortcomings by providing a method for predicting the fatigue life of asphalt mixtures based on the initial modulus index, thereby solving the problems existing in the current fatigue model.

[0005] The technical solution adopted in this invention is:

[0006] A method for predicting the fatigue life of asphalt mixtures based on initial modulus index includes the following steps:

[0007] S1. Prepare standard specimens for asphalt mixtures;

[0008] S2. Under the set parameters, conduct three-point bending fatigue tests on the prepared standard specimens of asphalt mixtures under different stress levels.

[0009] S3. Fit the stress-strain hysteresis curve of the asphalt mixture based on the test data;

[0010] S4. Obtain the initial modulus and failure modulus of the asphalt mixture based on the stress-strain hysteresis curve;

[0011] S5. Based on the above initial modulus and failure modulus, construct a fatigue damage factor model for asphalt mixture based on the initial modulus;

[0012] S6. Based on the constructed fatigue damage factor model, predict the fatigue life of asphalt mixtures in use.

[0013] As a further optimization, in step S1, the standard specimen is required to be a prism beam with a length of 250mm±2.0mm, a width of 30mm±2mm, and a height of 35mm±2mm, cut after being formed by roller rolling, and its span is 200mm±5mm.

[0014] As a further optimization, in step S2, the set parameters are a single loading frequency of 10Hz and a single test temperature of 15℃.

[0015] As a further optimization, in step S2, when conducting the three-point bending fatigue test of the asphalt mixture, the load, displacement at the mid-span of the specimen and the number of times the load was applied when the specimen fractured were recorded in each test, and the number of times the load was applied when the specimen fractured was taken as the fatigue life of the asphalt mixture.

[0016] The conversion formula for the recorded measured bending tensile stress is as follows:

[0017]

[0018] The recorded displacement parameters are converted into bending tensile strain using the following formula:

[0019]

[0020] Where: σ m —Measured bending tensile stress (MPa);

[0021] ε m —Measured bending tensile strain;

[0022] d—Specimen span (mm);

[0023] F — Measured load (N);

[0024] b — Width of the cross-interruption interview piece (mm);

[0025] h — Height of the intervening test piece (mm);

[0026] l — Mid-span displacement of the specimen (mm).

[0027] As a further optimization, in step S3, curve fitting is performed using Matlab software based on flexural stress and flexural strain to obtain the stress-strain hysteresis curve of the asphalt mixture, and the morphological parameters of the hysteresis curve are obtained: major axis, minor axis, center point coordinates, and the angle between the major axis and the x-axis of the coordinate system.

[0028] As a further optimization, in step S4, the tangent of the angle between the major axis of the hysteresis curve and the x-axis of the coordinate system represents the flexural modulus of the asphalt mixture, thereby obtaining the modulus evolution curve. The maximum value in the modulus evolution curve is taken as the initial modulus. The relative error between adjacent modulus values ​​after the initial modulus is calculated in turn. When the relative error exceeds 5%, the modulus value is taken as the failure modulus.

[0029] Wherein: the above formula for calculating the bending modulus is:

[0030]

[0031] Where: E——modulus (MPa);

[0032] σ max —Stress amplitude (MPa) during the loading process;

[0033] ε max —Strain amplitude during the loading process;

[0034] σ0 — Stress at the center point of the hysteresis curve (MPa);

[0035] ε0 — strain at the center point of the hysteresis curve;

[0036] θ — the angle between the major axis a and the x-axis;

[0037] The formula for calculating the above relative error value is:

[0038]

[0039] In the formula: R modulus —Relative error (%);

[0040] E n E n+1 — The modulus (MPa) at loading times n and n+1, and less than E1.

[0041] As a further optimization, in step S5, a damage factor model is constructed by introducing the failure modulus based on the classic fatigue damage factor model, and its calculation formula is as follows:

[0042]

[0043] In the formula: D—fatigue damage factor;

[0044] E i ——Load N i The modulus (MPa) after this step;

[0045] E1—Initial modulus (MPa);

[0046] E2—Failure modulus (MPa);

[0047] N i —Number of loads;

[0048] N f —Fatigue lifespan;

[0049] a, b, c — Model fitting parameters.

[0050] As a further optimization, in step S5, a relationship model between the initial modulus and the failure modulus is constructed, as shown in the following formula:

[0051] E2=kE1-W

[0052] Where: E1—initial modulus (MPa);

[0053] E2—Failure modulus (MPa);

[0054] k, m — Model fitting parameters;

[0055] Substituting the relationship model between the initial modulus and the failure modulus into the damage factor model, we obtain the relationship model between the damage factor and the initial modulus:

[0056]

[0057] In the formula: D—fatigue damage factor;

[0058] E i ——Loading N i The modulus (MPa) after this step;

[0059] E1—Initial modulus (MPa);

[0060] N i —Number of loads;

[0061] N f —Fatigue lifespan;

[0062] a, b, c — Model fitting parameters.

[0063] As a further optimization, in step S6, the initial modulus of the experimental asphalt mixture and the modulus of the asphalt mixture after service are obtained and substituted into the relationship model between the damage factor and the initial modulus to calculate the service life ratio of the asphalt mixture beam. The remaining life is calculated by using the design life and the service life ratio.

[0064] 10. The method for predicting the fatigue life of asphalt mixtures based on the initial modulus index according to claim 9, characterized in that:

[0065] In step S6, the formula for calculating the remaining lifetime is:

[0066]

[0067] In the formula: N—number of loading times;

[0068] N f —Fatigue lifespan;

[0069] N d —Design life;

[0070] N rsl — Remaining lifespan.

[0071] The present invention has the following advantages:

[0072] The fatigue life prediction method for asphalt mixtures of this invention, based on the classical fatigue damage factor model, introduces a failure modulus to construct a more reasonable damage factor model, thereby enabling a more accurate and rapid prediction of the remaining life of asphalt mixtures. This method considers the fatigue damage evolution process of asphalt mixtures and has advantages such as fewer calculation steps, a simple model form, and independence from load control modes, making it highly operable and practical. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0074] The present invention will be further described below with reference to the accompanying drawings:

[0075] Figure 1 This is a graph showing the relationship between modulus and the number of times the compound is applied. Detailed Implementation

[0076] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0077] It should be understood that in the description of the embodiments of the present invention, terms such as "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance, nor as indicating or implying order. In the embodiments of the present invention, "multiple" refers to two or more.

[0078] In this embodiment of the invention, "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, or both A and B existing simultaneously. Furthermore, in this document, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0079] This invention provides a method for predicting the fatigue life of asphalt mixtures based on the initial modulus index, comprising the following steps:

[0080] S1. Prepare standard specimens for asphalt mixtures;

[0081] In this step, the standard specimen is required to be a prism beam with a length of 250mm±2.0mm, a width of 30mm±2mm, and a height of 35mm±2mm, cut after being formed by roller rolling, and its span is 200mm±5mm.

[0082] S2. Under the set parameters, conduct three-point bending fatigue tests on the prepared standard specimens of asphalt mixtures under different stress levels.

[0083] The specified parameters are a single loading frequency of 10 Hz and a single test temperature of 15 ℃.

[0084] In this step, when conducting the three-point bending fatigue test on the asphalt mixture, the load, displacement at the mid-span of the specimen and the number of times the load was applied when the specimen fractured were recorded in each test, and the number of times the load was applied when the specimen fractured was taken as the fatigue life of the asphalt mixture.

[0085] The conversion formula for the recorded measured bending tensile stress is as follows:

[0086]

[0087] The recorded displacement parameters are converted into bending tensile strain using the following formula:

[0088]

[0089] Where: σ m —Measured bending tensile stress (MPa);

[0090] ε m —Measured bending tensile strain;

[0091] d—Specimen span (mm);

[0092] F — Measured load (N);

[0093] b — Width of the cross-interruption interview piece (mm);

[0094] h — Height of the intervening test piece (mm);

[0095] l — Mid-span displacement of the specimen (mm).

[0096] S3. Fit the stress-strain hysteresis curve of the asphalt mixture based on the test data;

[0097] In this step, the stress-strain hysteresis curve of the asphalt mixture is obtained by curve fitting based on the bending tensile stress and bending tensile strain using Matlab software, and the morphological parameters of the hysteresis curve are obtained: major axis, minor axis, center point coordinates, and the angle between the major axis and the x-axis of the coordinate system.

[0098] S4. Obtain the initial modulus and failure modulus of the asphalt mixture based on the stress-strain hysteresis curve;

[0099] In this step, the tangent of the angle between the major axis of the hysteresis curve and the x-axis of the coordinate system represents the flexural modulus of the asphalt mixture, thereby obtaining the modulus evolution curve (modulus versus loading times, where the loading times are positive integers), such as... Figure 1 As shown, the maximum value in the modulus evolution curve is taken as the initial modulus. The relative error between adjacent modulus values ​​after the initial modulus is calculated sequentially. When the relative error exceeds 5%, the modulus value is taken as the failure modulus. According to... Figure 1 It can be seen that the modulus evolution curve is divided into three phases: Phase I, Phase II, and Phase III by the initial modulus and the failure modulus.

[0100] Wherein: the above formula for calculating the bending modulus is:

[0101]

[0102] Where: E——modulus (MPa);

[0103] σ max —Stress amplitude (MPa) during the loading process;

[0104] ε max—Strain amplitude during the loading process;

[0105] σ0 — Stress at the center point of the hysteresis curve (MPa);

[0106] ε0 — strain at the center point of the hysteresis curve;

[0107] θ — the angle between the major axis a and the x-axis;

[0108] The formula for calculating the above relative error value is:

[0109]

[0110] In the formula: R modulus —Relative error (%);

[0111] E n E n+1 — The modulus (MPa) at loading times n and n+1, and less than E1.

[0112] This embodiment selected eight test materials for testing, including four type A materials and four type B materials. The following is a statistical table of the fatigue life test results for the selected asphalt mixtures. Table 1 shows the fatigue life test results for type A asphalt mixtures, and Table 2 shows the fatigue life test results for type B asphalt mixtures.

[0113]

[0114] Table 1: Fatigue life test results of type A asphalt mixture

[0115]

[0116]

[0117] Table 2: Fatigue life test results of type A asphalt mixture

[0118] S5. Based on the above initial modulus and failure modulus, construct a fatigue damage factor model for asphalt mixture based on the initial modulus;

[0119] In step S5, based on the classic fatigue damage factor model D=(E i -E1) / E i A damage factor model is constructed by introducing the failure modulus, and its calculation formula is as follows:

[0120]

[0121] In the formula: D—fatigue damage factor;

[0122] E i ——Loading N iThe modulus (MPa) after this step;

[0123] E1—Initial modulus (MPa);

[0124] E2—Failure modulus (MPa);

[0125] N i —Number of loads;

[0126] N f —Fatigue lifespan;

[0127] a, b, c — Model fitting parameters;

[0128] To facilitate calculation and simplify the formula, a relationship model between the initial modulus and the failure modulus is constructed, as shown in the following formula:

[0129] E2=kE1-W

[0130] Where: E1—initial modulus (MPa);

[0131] E2—Failure modulus (MPa);

[0132] k, m — Model fitting parameters;

[0133] Substituting the relationship model between the initial modulus and the failure modulus into the damage factor model, we obtain the relationship model between the damage factor and the initial modulus:

[0134]

[0135] In the formula: D—fatigue damage factor;

[0136] E i ——Loading N i The modulus (MPa) after this step;

[0137] E1—Initial modulus (MPa);

[0138] N i —Number of loads;

[0139] N f —Fatigue lifespan;

[0140] a, b, c — Model fitting parameters.

[0141] The fitting parameters of the damage factor model and fatigue life curve of asphalt mixture under different conditions are summarized in Table 3 below. As can be seen from the data in Table 3, the fitting accuracy of the fatigue damage concealment model based on modulus feature points under different conditions is greater than 0.9, and the model has high reliability.

[0142] Asphalt mixture types a b c <![CDATA[R 2 ]]> A1 0.027 2.627 0.002 0.964 A2 0.009 4.238 0.030 0.975 A3 0.017 3.912 0.006 0.929 A4 0.019 4.049 0.018 0.968 B1 0.031 2.654 0.010 0.925 B2 0.010 4.438 0.040 0.925 B3 0.021 3.952 0.028 0.939 B4 0.021 4.279 0.038 0.972

[0143] Table 3 Fitting parameters for the fatigue damage factor model

[0144] S6. Based on the constructed fatigue damage factor model, predict the fatigue life of asphalt mixtures in use.

[0145] In step S6, the initial modulus and the post-service modulus of the asphalt mixture to be tested are obtained. The initial modulus can be found in the design documents, or obtained by taking core samples from lanes without vehicle loads (such as overtaking lanes or emergency lanes, ensuring that the asphalt mixture modulus of the lane remains unchanged) for UTM dynamic modulus testing. The modulus of the post-service asphalt mixture is obtained by taking core samples from the driving lane for UTM dynamic modulus testing. These values ​​are then substituted into the relationship model between the damage factor and the initial modulus to calculate the service life ratio of the asphalt composite beam. The remaining service life is calculated by using the design life and the service life ratio. The formula for calculating the remaining service life is as follows:

[0146]

[0147] In the formula: N—number of loading times;

[0148] N f —Fatigue lifespan;

[0149] N d —Design life;

[0150] N rsl — Remaining lifespan;

[0151] Taking the A2 material as an example, the initial modulus in the design document and the initial modulus from the core sample are not significantly different. Therefore, the average of the two can be used as the input parameter for the damage factor model. Through calculation, the service life N of the asphalt mixture can be obtained. i / N f =0.716, substituting this into the remaining service life calculation formula, we can calculate the remaining service life of this asphalt mixture under standard axle load (100KN) as N. rsl =5.96×10 6 .

[0152]

[0153] Table 4 Modulus values ​​of material A2

[0154] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for predicting the fatigue life of asphalt mixtures based on initial modulus index, characterized in that, Includes the following steps: S1. Prepare standard specimens for asphalt mixtures; S2. Under the set parameters, conduct three-point bending fatigue tests on the prepared standard specimens of asphalt mixtures under different stress levels. S3. Fit the stress-strain hysteresis curve of the asphalt mixture based on the test data; S4. Obtain the initial modulus and failure modulus of the asphalt mixture based on the stress-strain hysteresis curve; In step S4, the tangent of the angle between the major axis of the hysteresis curve and the x-axis of the coordinate system represents the flexural modulus of the asphalt mixture. Thus, the modulus evolution curve is obtained. The maximum value in the modulus evolution curve is taken as the initial modulus. The relative error between adjacent modulus values ​​after the initial modulus is calculated in turn. When the relative error exceeds 5%, the modulus value is taken as the failure modulus. Wherein: the above formula for calculating the bending modulus is: ； Where: E—modulus, unit: MPa; σ max —Stress amplitude during loading, unit: MPa; ε max —Strain amplitude during the loading process; σ0 — Stress at the center point of the hysteresis curve, unit: MPa; ε0 — strain at the center point of the hysteresis curve; θ — the angle between the major axis a and the ε axis; The formula for calculating the above relative error value is: ； In the formula: R modulus —Relative error; E n E n+1 —The modulus at loading times n and n+1, and less than E1; S5. Based on the above initial modulus and failure modulus, construct a fatigue damage factor model for asphalt mixture based on the initial modulus; In step S5, a damage factor model is constructed by introducing the failure modulus based on the classical fatigue damage factor model. The calculation formula is as follows: ； In the formula: D—fatigue damage factor; E i ——Loading N i The modulus after this step, in MPa; E1—Initial modulus, unit: MPa; E2—Failure modulus, unit: MPa; N i —Number of loads; N f —Fatigue lifespan; a, b, c — Model fitting parameters; In step S5, a relationship model between the initial modulus and the failure modulus is constructed, as shown in the following formula: E2 = kE1 - m Where: E1 — initial modulus, unit: MPa; E2—Failure modulus, unit: MPa; k, m — Model fitting parameters; Substituting the relationship model between the initial modulus and the failure modulus into the damage factor model, we obtain the relationship model between the damage factor and the initial modulus: ； In the formula: D—fatigue damage factor; E i ——Loading N i The modulus after this step, in MPa; E1—Initial modulus, unit: MPa; N i —Number of loads; N f —Fatigue lifespan; a, b, c — Model fitting parameters; S6. Based on the constructed fatigue damage factor model, predict the fatigue life of asphalt mixtures in use; In step S6, the formula for calculating the remaining lifetime is: ； In the formula: N—number of loading times; N f —Fatigue lifespan; N d —Design life; N rsl — Remaining lifespan.

2. The method for predicting the fatigue life of asphalt mixtures based on the initial modulus index according to claim 1, characterized in that: In step S1, the standard specimen is required to be a prism beam with a length of 250mm±2.0mm, a width of 30mm±2mm, and a height of 35mm±2mm, cut after being formed by roller rolling, and its span is 200mm±5mm.

3. The method for predicting the fatigue life of asphalt mixtures based on the initial modulus index according to claim 1, characterized in that: In step S2, the set parameters are a single loading frequency of 10Hz and a single test temperature of 15℃.

4. The method for predicting the fatigue life of asphalt mixtures based on the initial modulus index according to claim 1, characterized in that: In step S2, when conducting the three-point bending fatigue test on the asphalt mixture, the load, displacement at the mid-span of the specimen and the number of times the load was applied when the specimen fractured were recorded in each test, and the number of times the load was applied when the specimen fractured was taken as the fatigue life of the asphalt mixture. The conversion formula for the recorded measured bending tensile stress is as follows: ； The recorded displacement parameters are converted into bending tensile strain using the following formula: ； Where: σ m —Measured bending tensile stress: Unit: MPa; ε m —Measured bending tensile strain; d—Specimen span, unit: mm; F — Measured load, unit: N; b — Width of the cross-interruption test piece, in mm; h — Height of the cross-interruption test piece, in mm; l — Mid-span displacement of the specimen, unit: mm.

5. The method for predicting the fatigue life of asphalt mixtures based on the initial modulus index according to claim 4, characterized in that: In step S3, the stress-strain hysteresis curve of the asphalt mixture is obtained by curve fitting based on the bending tensile stress and bending tensile strain using Matlab software, and the morphological parameters of the hysteresis curve are obtained: major axis, minor axis, center point coordinates, and the angle between the major axis and the x-axis of the coordinate system.

6. The method for predicting the fatigue life of asphalt mixtures based on the initial modulus index according to claim 1, characterized in that: In step S6, the initial modulus of the experimental asphalt mixture and the modulus of the asphalt mixture after service are obtained and substituted into the relationship model between the damage factor and the initial modulus to calculate the service life ratio of the asphalt mixture beam. The remaining life is calculated by using the design life and the service life ratio.

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