A quantitative characterization method for the thermally reversible aging properties of asphalt mixtures

Abstract

This invention discloses a quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures, relating to the field of quantitative asphalt characterization. The method defines the degree of thermally reversible aging of the asphalt mixture by the ratio of the calculated temperature stress change to the estimated temperature stress change. The product of the corresponding asphalt binder grading loss and the calculated temperature stress change is used as the grading loss of the asphalt mixture, thus establishing quantitative characterization parameters for the thermally reversible aging characteristics of asphalt mixtures. This invention addresses the long-standing neglect of thermally reversible aging characteristics in engineering practice for controlling early cracking of asphalt pavements; it establishes the correlation between asphalt binder and the low-temperature performance of the mixture; and it proposes quantitative characterization parameters for the thermally reversible aging characteristics of asphalt mixtures, laying the foundation for the adjustment of the extreme low-temperature grading of road-use asphalt binders (including modified asphalt).

Description

Technical Field

[0001] This invention relates to the field of quantitative characterization of asphalt, and specifically to a method for quantitative characterization of the thermally reversible aging properties of asphalt mixtures. Background Technology

[0002] Under prolonged low-temperature conditions, asphalt pavements often face the risk of low-temperature cracking. This cracking not only disrupts the integrity and continuity of the pavement structure and significantly shortens its service life, but also seriously affects driving safety and comfort. Numerous studies have shown that asphalt undergoes reversible thermal aging under sustained low-temperature conditions. That is, without significant oxidation reactions, physical hardening leads to increased material stiffness and decreased stress relaxation capacity, resulting in the accumulation of tensile stress when thermal contraction is hindered, thus inducing early cracking.

[0003] To improve the low-temperature cracking resistance of asphalt pavements, engineering practices typically employ measures such as selecting superior base asphalt, using polymer- or rubber-modified asphalt, appropriately increasing asphalt content, and optimizing aggregate gradation. Among these, improving the low-temperature rheological properties of asphalt binders is considered the most crucial technical approach. Currently, asphalt performance grading systems primarily rely on the bending beam rheometer (BBR) test to classify asphalt binders into low-temperature grades. The core indicators include creep stiffness and creep rate, with failure temperature serving as the grading criterion.

[0004] In practice, road engineers typically employ methods such as selecting superior asphalt, modifying asphalt, increasing asphalt content, and adjusting mixture gradation to improve the low-temperature cracking resistance of asphalt pavements. Improving the performance of asphalt binders is the primary approach to resisting low-temperature cracking.

[0005] However, the existing evaluation system has obvious limitations. On the one hand, BBR and its extended methods are only applicable to pure asphalt binders and cannot directly reflect the low-temperature response of asphalt mixtures containing coarse and fine aggregates, mineral powder, and complex interface structures under actual service conditions. On the other hand, although researchers have proposed various low-temperature performance evaluation indicators for asphalt mixtures, such as indirect tensile strength, fracture energy, and thermal stress, a quantitative correlation mechanism between the low-temperature performance of binder layers and mixture layers has not yet been established. As a result, the thermal reversible aging characteristics of asphalt mixtures lack effective quantitative characterization indicators, and the selection of asphalt binders for road use is not conducive to effectively controlling early cracking of asphalt pavements due to the lack of adjustment of low-temperature limit grading that considers thermal reversible aging characteristics.

[0006] Therefore, under current technological conditions, there is a lack of unified, quantifiable, and engineering-applicable characterization indicators for the thermal reversible aging characteristics of asphalt mixtures. Asphalt pavements designed based on a single index of binder may still experience unexpected early cracking in actual low-temperature environments, which restricts the accurate design and long-term service of high-performance asphalt pavements.

[0007] In summary, there is an urgent need for a quantitative characterization method that can directly quantify the degree of thermal reversible aging of asphalt mixtures and effectively connect the grading loss of asphalt binders with the actual performance of the mixture, so as to provide a scientific basis for the selection of asphalt materials and the adjustment of low-temperature PG grading. Summary of the Invention

[0008] One objective of this invention is to provide a quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures, which uses the ratio of the calculated temperature stress change to the estimated temperature stress change. Defined as the degree of thermally reversible aging of asphalt mixtures, it relates the corresponding asphalt binder grading loss to... The product of these factors is used as the grading loss of asphalt mixtures, thus establishing a quantitative characterization parameter for the thermally reversible aging characteristics of asphalt mixtures.

[0009] A quantitative characterization method for the thermally reversible aging properties of asphalt mixtures includes the following steps:

[0010] First, cylindrical specimens of asphalt mixture were prepared and divided into two groups. For the asphalt binder derived from the same source as the asphalt mixture, BBR beam specimens were prepared and divided into two groups. The asphalt mixture is composed of asphalt binder and aggregates. The asphalt binder derived from the same source as the asphalt mixture refers to the original asphalt material used to prepare the asphalt mixture, without aggregate dilution or physical separation.

[0011] Using asphalt mixtures and asphalt binders of the same origin to prepare specimens ensures that the basic materials of the two are consistent, providing a basis for establishing the correlation between the thermally reversible aging characteristics of the binder and the mixture. The two types of specimens are grouped separately to set different low-temperature curing time variables. By comparing the performance differences under different curing times, the influence of thermally reversible aging on material properties can be accurately captured.

[0012] Secondly, the first and third groups of specimens were placed in an environment of -30 to -10℃ for constant temperature curing for 1 hour, and the second and fourth groups of specimens were placed in an environment of -30 to -10℃ for constant temperature curing for 72 hours.

[0013] Preferably, the curing temperature is -18℃, which is the typical critical temperature for low-temperature cracking of asphalt pavement. Curing at this temperature can simulate the low-temperature service environment of actual pavement. The two curing durations of 1 hour and 72 hours are chosen because thermal reversible aging intensifies with the extension of low-temperature curing time. 1 hour curing can be regarded as the initial state of thermal reversible aging, while 72 hours curing can be regarded as the state of significant development of thermal reversible aging. By comparing the two, the degree of development of thermal reversible aging can be clearly characterized.

[0014] The selection of curing temperature and duration in this method is in line with engineering practice, ensuring that the test results have engineering reference value. The setting of two curing durations forms a clear aging gradient, which can effectively amplify the differences in the impact of thermally reversible aging on material properties, improve the discrimination and sensitivity of subsequent characterization parameters, and solve the problem of low characterization accuracy caused by the unclear aging gradient in existing methods.

[0015] Furthermore, this invention conducts indirect tensile creep tests on the first and second groups of specimens respectively to obtain the original data of the two groups of asphalt mixtures. Based on the original data of the asphalt mixtures, creep compliance functions of the asphalt mixtures after 1 hour and 72 hours of curing are obtained. and ;

[0016] Among them, two sets of raw data were obtained from two sets of cylindrical specimens through indirect tensile and creep tests. The first set of raw data is... The second set of original data is: i = 1, 2, ..., n; i = 1, 2, ..., n; and The lateral and vertical deformations of the first and second groups of specimens are respectively. and This represents the horizontal displacement.

[0017] Based on the above data, we can further calculate:

[0018] Axial strain at time t of the first set of specimens , ;

[0019] Axial strain at time t of the second set of specimens , ;

[0020] The heights of the first and second groups of specimens;

[0021] The average stress at time t of the first group of specimens , ;

[0022] The average stress at time t in the second group of specimens , ;

[0023] ;

[0024] ;

[0025] ;

[0026] Based on the first and second sets of raw data, the creep compliance of the two sets of cylindrical specimens at time t was obtained. and ;pass And a power function model was used for fitting. The instantaneous creep compliance after 1 hour of curing was obtained by fitting. Creep amplitude coefficient Regression coefficient ;pass And a power function model was used for fitting. The instantaneous creep compliance after 72 hours of curing was obtained by fitting. Creep amplitude coefficient Regression coefficient .

[0027] The complete creep test can be calculated through indirect tensile and creep tests. and curve, i.e. Creep compliance varies with time from 0 to 1000 s.

[0028] pass and Calculate the creep stiffness after 1 hour and 72 hours of curing, respectively. and ;

[0029] pass Calculate the creep stiffness after 1 hour of curing , ;pass Calculate the creep stiffness after 72 hours of curing. , .

[0030] Will and The calculated temperature stress of the asphalt mixture after 1 hour of curing was obtained by substituting the values ​​into the Hopkins-Hamming method. Calculated temperature stress of asphalt mixture after 72 hours of curing Among them, the linear shrinkage coefficient of the mixture in the Hopkins-Hamming method Actual pavement constant .

[0031] The core advantage of indirect tensile creep testing lies in its ability to generate a horizontal tensile stress field within the specimen. Since low-temperature cracking of pavement is mainly caused by transverse shrinkage tensile stress, this testing method can accurately simulate the low-temperature cracking stress state of actual pavement, ensuring that the test results are consistent with engineering realities. Creep compliance is a key parameter characterizing the deformation capacity of a material under constant stress. Thermally reversible aging leads to a decrease in the low-temperature deformation capacity of the material. By comparing creep compliance curves at different curing times, the impact of thermally reversible aging on the low-temperature performance of the mixture can be directly reflected. Using a power function model to fit the calculated data can eliminate the influence of experimental errors on the results, obtaining a continuous and stable creep compliance function, providing a reliable basis for subsequent quantitative calculations.

[0032] Compared to traditional low-temperature testing methods for mixtures, the indirect tensile creep test used in this step is closer to the actual cracking mechanism, solving the problem that the stress state of existing testing methods does not match reality. By fitting the model, a complete creep compliance curve is obtained, avoiding the limitations of discrete original data and improving the accuracy of parameter calculation. At the same time, the test is performed directly on the mixture level, avoiding the uncertainty of extrapolating the properties of the binder to the properties of the mixture, and providing core data support for the accurate characterization of the thermal reversible aging of the mixture.

[0033] Preferably, during the indirect tensile creep test, the load is controlled so that the average deformation of the first and second groups of specimens is between 0.00250 mm and 0.00900 mm. This range is the critical deformation interval for the elastic-plastic transition of asphalt mixtures at low temperatures, which can accurately capture the changes in deformation capacity caused by reversible thermal aging; it can avoid the problems of insufficient deformation leading to insignificant test signals and excessive deformation leading to irreversible damage to the specimens, ensuring the validity and reliability of the test data.

[0034] Creep stiffness and creep compliance are reciprocals of each other and are core parameters characterizing a material's resistance to deformation. Thermally reversible aging increases the low-temperature stiffness of a material, and changes in stiffness can directly reflect the degree of aging. The Hopkins-Hamming method is an internationally recognized method for calculating low-temperature temperature stress in asphalt materials. Based on the material's creep stiffness characteristics, it can accurately simulate the stress accumulation process of the material during cooling. The linear shrinkage coefficient of the mixture and the pavement constant set by the method are calibrated based on a large amount of engineering calculation data to ensure the accuracy of the calculation results.

[0035] This invention transforms the deformation characteristics of creep flexibility into stress characteristics through creep stiffness, which better meets the stress control requirements for low-temperature cracking of pavement. The application of the Hopkins-Hamming method realizes the quantitative transformation from material mechanical parameters to actual temperature stress of pavement, solving the problem of the disconnect between material properties and pavement engineering applications in existing methods. The acquisition of actual temperature stress provides direct data for subsequent characterization of stress changes caused by thermally reversible aging.

[0036] On the other hand, this invention conducts Ex-BBR tests on the third and fourth groups of specimens respectively to obtain the original data of the two groups of asphalt binders. Based on the original data of the asphalt binders, the creep compliance functions of the asphalt binders after 1 hour and 72 hours of curing are obtained. and ;

[0037] Specifically, two sets of raw data were obtained from the Ex-BBR test for the two sets of BBR beams, and the third set of raw data was... The fourth set of original data is: i = 1, 2, ..., n i = 1, 2, ..., n; and for Mid-span deflection of the third and fourth groups of specimens at time t.

[0038] Based on the above data, we can further calculate:

[0039] Bending strain of the third group of specimens , ;

[0040] Bending strain of the fourth group of specimens , ;

[0041] L represents the beam height of the third and fourth sets of specimens, and L is the span of the support point.

[0042] Initial bending stress of the third group of specimens , ;

[0043] Initial bending stress of the fourth group of specimens , ;

[0044] ;

[0045] ;

[0046] ;

[0047] The creep compliance of the two sets of BBR beams at time t was obtained based on the third and fourth sets of raw data. and ;

[0048] pass And a power function model was used for fitting. The instantaneous creep compliance after 1 hour of curing was obtained by fitting. , Regression coefficient ;pass And a power function model was used for fitting. The instantaneous creep compliance after 72 hours of curing was obtained by fitting. , Regression coefficient .

[0049] pass and Calculate the creep stiffness after 1 hour and 72 hours of curing, respectively. and ;

[0050] pass Calculate the creep stiffness after 1 hour of curing , ;pass Calculate the creep stiffness after 72 hours of curing. , .

[0051] Will and The estimated temperature stress of asphalt binder after 1 hour of curing was calculated using the Hopkins-Hamming method. Calculated temperature stress of asphalt binder after 72 hours of curing Among them, the shrinkage coefficient of the binder in the Hopkins-Hamming method Calculate the pavement constant .

[0052] The shrinkage coefficient reflects the material's sensitivity to volume shrinkage at low temperatures. Asphalt binder is a single-phase organic material; at low temperatures, molecular chains freeze and wax crystals precipitate, leading to significant shrinkage. Therefore, a shrinkage coefficient is set... It is 0.00017 This matches the high shrinkage characteristics of its pure phase; while asphalt mixture is a multiphase composite system of aggregates and binders, with a rigid aggregate skeleton that shrinks very little, strongly constraining the shrinkage behavior of the binder, thus significantly reducing the overall shrinkage sensitivity. It is 0.00002 It conforms to the actual shrinkage pattern of the mixture.

[0053] The relationship between pavement constants, material stress transfer efficiency, and pavement structural constraints. The value is 18, which is set for the binder. Since the binder is the bonding phase of the mixture, its dispersion state and stress transfer loss within the mixture need to be considered to simulate the contribution of the binder to the pavement stress under ideal conditions. The value of 1 is set for the mixture, because the mixture is directly used as the road structure layer, and the stress transfer is direct without additional dispersion loss. The value is close to the stress transfer mechanism of the actual road structure.

[0054] The Ex-BBR test is currently the most accurate testing method for evaluating the low-temperature creep performance of asphalt binders. It can accurately calculate the creep compliance and stiffness characteristics of binders by measuring the mid-span deflection of small beams, providing an accurate theoretical benchmark for the thermally reversible aging characteristics of binders. By using the same curing temperature and duration as the mixture specimens, it can ensure that the environmental conditions for thermally reversible aging of both are consistent, providing a basis for establishing the correlation between binder extrapolation and mixture calculation.

[0055] Meanwhile, the high precision of the Ex-BBR test ensures the reliability of the binder layer data, providing an accurate theoretical benchmark for subsequent calibration; the synchronous curing condition settings eliminate the interference of environmental variables on the test results, ensuring the comparability of the aging degree of the binder and the mixture; and the creep compliance function of the binder is obtained through model fitting, providing a continuous and stable parameter basis for the subsequent calculation of temperature stress.

[0056] Creep stiffness is a core indicator of a binder's ability to resist low-temperature deformation. Thermally reversible aging leads to an increase in binder stiffness, and changes in stiffness can quantify the degree of aging of the binder. The shrinkage coefficient and pavement constant set by the Hopkins-Hamming method for binders are calibrated based on the single-phase characteristics of the binder. This method can accurately calculate the low-temperature stress accumulation law of the binder under ideal conditions, providing a theoretical reference for comparing the actual stress state of the mixture.

[0057] Based on the above, this invention obtains the calculated temperature stress change. This change directly reflects the cumulative increase in low-temperature stress of asphalt mixture from 1 hour to 72 hours during the thermally reversible aging process, and is a direct manifestation of the degree of thermally reversible aging of the mixture.

[0058] Obtain the estimated temperature stress change This change reflects the cumulative increase in thermally reversible aging stress of asphalt binder under ideal conditions, and is the theoretical benchmark for the degree of thermally reversible aging without structural constraints.

[0059] Thermally reversible aging refers to the increase in stiffness of asphalt materials due to physical hardening at low temperatures, such as wax crystallization and molecular chain freezing. This process can be partially or completely reversed after heating, which is different from irreversible aging caused by oxidation.

[0060] Calculation of parameters for thermally reversible aging , , ; The correction factor for the reversible thermal aging of the mixture is, in physical terms, the correction ratio of the temperature stress change caused by the reversible thermal aging of the mixture due to its internal structure, namely the aggregate skeleton, interfacial bonding, etc., relative to the calculated value of the pure binder.

[0061] The classification loss of asphalt binder was obtained through Ex-BBR testing. Through the parameter of thermal reversible aging and graded loss The thermally reversible aging characteristics of asphalt mixtures were quantitatively characterized. , It is a commonly used indicator to characterize the degree of reversible thermal aging of cementitious materials, reflecting the degree of deterioration of the low-temperature performance of cementitious materials after aging.

[0062] Calculate equivalent graded loss ;pass The thermally reversible aging characteristics of asphalt mixtures were quantitatively characterized. It is a comprehensive characterization parameter that corrects the thermal reversible aging index of the binder layer to the mixture layer, and directly reflects the thermal reversible aging characteristics of asphalt mixtures.

[0063] Through the parameter of thermal reversible aging and equivalent graded loss To achieve quantitative characterization of the thermally reversible aging properties of asphalt mixtures; among which, It is a core characterization parameter. The larger its value, the more severe the thermal reversible aging of the mixture and the worse its low-temperature crack resistance.

[0064] The introduction of this method enables a scientific mapping from binder performance to mixture performance, quantifies the influence of the internal structure of the mixture on thermally reversible aging, and solves the problem that existing methods cannot distinguish between binder aging and mixture structural response. pass For binders By performing calibration, the aging indicators under ideal conditions are transformed into aging indicators under actual conditions of the mixture, thus achieving the accurate transfer of thermally reversible aging characteristics from the binder level to the mixture level.

[0065] Therefore, compared with existing methods, which indirectly infer the aging characteristics of the mixture through the properties of the binder, neglecting the influence of structural effects, the present invention introduces [a new method] by simultaneously testing the thermally reversible aging properties of the mixture and the binder. The parameters enable quantitative correction of structural effects, accurately converting the aging index of the binder into the layer index of the mixture, thus significantly improving the characterization accuracy.

[0066] Existing low-temperature testing methods for road mixtures are difficult to simulate the horizontal tensile stress field of low-temperature cracking in road surfaces. This invention uses indirect tensile creep testing to create a horizontal tensile stress field inside the specimen that is consistent with the actual road surface. The test results can better reflect the thermally reversible aging behavior of real road surfaces and provide a more reliable basis for engineering applications.

[0067] Existing methods are mostly qualitative descriptions or single-index characterizations, which cannot compare the aging degree between different mixtures; the method proposed in this invention... The parameters are quantitative indicators that integrate the aging of binders and the structural effects of mixtures. They can be directly used to compare the degree of thermal reversible aging of mixtures with different gradations and compaction degrees, providing a clear basis for material selection and optimization.

[0068] Meanwhile, the present invention proposes For the first time, the parameters quantify the influence of internal structures such as aggregate skeleton and interfacial bonding on thermally reversible aging, which not only enables the characterization of thermally reversible aging characteristics, but also provides a new approach for optimizing the mix proportion of the mixture.

[0069] All the test methods in this invention are mature methods in the field of road engineering, the equipment is readily available, and they are easy to promote and apply in engineering projects. Furthermore, The parameters directly reflect the actual degree of thermally reversible aging of the mixture and can serve as a key indicator for assessing the risk of low-temperature cracking in pavement structure design. Furthermore, even using the same type of asphalt, mixtures with different gradations or compaction degrees may exhibit different characteristics. This value can directly guide the optimization design of the mix proportion of the mixture and improve the low-temperature service performance of the pavement.

[0070] This invention effectively eliminates the influence of factors such as material differences, environmental interference, and test dispersion on the results, ensuring the accuracy and reliability of the characterization parameters.

[0071] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0072] This invention addresses the long-standing neglect of thermally reversible aging characteristics in engineering practices aimed at controlling early-stage cracking of asphalt pavements. It selects reliable testing methods and provides detailed specimen preparation and testing parameters. Based on indirect tensile test data, it proposes a method for calculating the temperature stress of asphalt mixtures by introducing a power function model and improving the Hopkins & Hamming algorithm. It establishes the correlation between asphalt binder and the low-temperature performance of the mixture. Furthermore, it proposes quantitative characterization parameters for the thermally reversible aging characteristics of asphalt mixtures, laying the foundation for the adjustment of the ultimate low-temperature grading of road-use asphalt binders (including modified asphalt). Attached Figure Description

[0073] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0074] Figure 1 (a) is the power function model fitting of the indirect tensile creep compliance curves of base asphalt A asphalt mixture after curing at -10℃, -20℃, and -30℃ for 1h and 72h respectively. Figure 1 (b) is the power function model fitting of the indirect tensile creep compliance curves of rubber-modified asphalt mixtures after curing at -10℃, -20℃, and -30℃ for 1h and 72h respectively.

[0075] Figure 2 (a) is the temperature stress change curve of the base asphalt (A) mixture, i.e., mixture A, after 1h / 72h of curing; Figure 2 (b) is the temperature stress change curve of the base asphalt (A) binder, i.e., A binder, after 1h / 72h of curing; Figure 2 (c) shows the temperature stress change curves of rubber-modified asphalt (A+CR) mixture, i.e., A+CR mixture, after curing for 1h / 72h; Figure 2 (d) shows the temperature stress change curves of rubber-modified asphalt (A+CR) binder, i.e., A+CR binder, after 1h / 72h of curing. Detailed Implementation

[0076] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. However, this does not limit the invention to the scope of the described embodiments. Test methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0077] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0078] Example 1

[0079] Step 1: Prepare cylindrical specimens of asphalt mixture and divide them into a first group and a second group of specimens; prepare BBR beam specimens of asphalt binder of the same origin as the asphalt mixture and divide them into a third group and a fourth group of specimens.

[0080] Step 11: Using base asphalt (denoted as asphalt A) as asphalt binder, mix asphalt A and limestone aggregate. After the asphalt mixture is mixed, use rotary compaction to form a specimen with a diameter of 150 mm and a height of 110 mm. Cut the specimen into cylindrical specimens with a diameter of 150 mm and a height of 40 mm. The upper and lower surfaces are flat and parallel, and the diameter direction is vertical and not tilted.

[0081] Step 12: Take the same batch of base asphalt and pour it into BBR beam specimens with dimensions of 125mm×12.5mm×6.25mm, and divide them into the third group of specimens and the fourth group of specimens.

[0082] Step 13: Place the first group of specimens and the third group of specimens in a -18℃ environment for constant temperature curing for 1 hour, and place the second group of specimens and the fourth group of specimens in a -18℃ environment for constant temperature curing for 72 hours.

[0083] Step 2: Perform indirect tensile and creep tests on the first and second groups of specimens respectively; perform Ex-BBR tests on the third and fourth groups of specimens respectively.

[0084] Indirect tensile test and creep test:

[0085] Load control: Ensure that the average level deformation is between 0.00250mm and 0.00900mm;

[0086] Loading time: 1000s;

[0087] Data acquisition: The sampling frequency is 10Hz for the first 10 seconds, and then decreases according to the specification.

[0088] Obtain the first set of raw data as The second set of original data is: i = 1, 2, ..., n; i = 1, 2, ..., n;

[0089] Ex-BBR test:

[0090] Load P: According to AASHTO T313-22 "Standard Test Method for Determining Low-Temperature Performance of Asphalt Cementitious Materials by Bending Beam Rheometer", the maximum bending stress generated at the mid-span of the BBR beam is 0.3 MPa by applying a constant load.

[0091] The span L = 102 mm, the beam width b = 12.5 mm, and the beam height h = 6.25 mm.

[0092] Record mid-span deflection Up to 240s.

[0093] Obtain the third set of raw data. The fourth set of original data is: i = 1, 2, ..., n i = 1, 2, ..., n;

[0094] Step 3, Data Processing and Calculation

[0095] Step 31, Axial strain at time t of the first set of specimens , ;

[0096] Axial strain at time t of the second set of specimens , ;

[0097] The heights of the first and second groups of specimens;

[0098] The average stress at time t of the first group of specimens , ;

[0099] The average stress at time t in the second group of specimens , ;

[0100] ;

[0101] Based on the first and second sets of raw data, the creep compliance of the two sets of cylindrical specimens at time t was obtained. and ; ; ;

[0102] pass And a power function model was used for fitting. The instantaneous creep compliance after 1 hour of curing was obtained by fitting. Creep amplitude coefficient Regression coefficient ;pass And a power function model was used for fitting. The instantaneous creep compliance after 72 hours of curing was obtained by fitting. Creep amplitude coefficient Regression coefficient .

[0103] The power function model is as follows: ; ;

[0104] In this embodiment, the instantaneous creep compliance during 1 hour of curing Creep amplitude coefficient Regression coefficient ;

[0105] Instantaneous creep flexibility during 72 hours of maintenance Creep amplitude coefficient Regression coefficient .

[0106] The complete creep test can be calculated through indirect tensile and creep tests. and curve, i.e. Creep compliance varies with time from 0 to 1000 s.

[0107] pass and Calculate the creep stiffness after 1 hour and 72 hours of curing, respectively. and ;

[0108] pass Calculate the creep stiffness after 1 hour of curing , ;pass Calculate the creep stiffness after 72 hours of curing. , .

[0109] Will and The calculated temperature stress of the asphalt mixture after 1 hour of curing was obtained by substituting the values ​​into the Hopkins-Hamming method. Calculated temperature stress of asphalt mixture after 72 hours of curing Among them, the linear shrinkage coefficient of the mixture in the Hopkins-Hamming method Actual pavement constant .

[0110] Calculated temperature stress of asphalt mixture after 1 hour of curing ;

[0111] Calculated temperature stress of asphalt mixture after 72 hours of curing = ;

[0112] Obtain the actual temperature stress change ;

[0113] Step 32: Two sets of raw data were obtained from the two sets of BBR beams through Ex-BBR tests. The third set of raw data is... The fourth set of original data is: i = 1, 2, ..., n i = 1, 2, ..., n; and for Mid-span deflection of the third and fourth groups of specimens at time t.

[0114] Based on the above data, we can further calculate:

[0115] Bending strain of the third group of specimens , ;

[0116] Bending strain of the fourth group of specimens , ;

[0117] L represents the beam height of the third and fourth sets of specimens, and L is the span of the support point.

[0118] Initial bending stress of the third group of specimens , ;

[0119] Initial bending stress of the fourth group of specimens , ;

[0120] ;

[0121] ;

[0122] ;

[0123] The creep compliance of the two sets of BBR beams at time t was obtained based on the third and fourth sets of raw data. and ;

[0124] pass And a power function model was used for fitting. The instantaneous creep compliance after 1 hour of curing was obtained by fitting. , Regression coefficient ;pass And a power function model was used for fitting. The instantaneous creep compliance after 72 hours of curing was obtained by fitting. , Regression coefficient .

[0125] The power function model is as follows: ; ;

[0126] In this embodiment, , , ;

[0127] , , ;

[0128] pass and Calculate the creep stiffness after 1 hour and 72 hours of curing, respectively. and ;

[0129] pass Calculate the creep stiffness after 1 hour of curing , ;pass Calculate the creep stiffness after 72 hours of curing. , .

[0130] Will and The estimated temperature stress of asphalt binder after 1 hour of curing was calculated using the Hopkins-Hamming method. Calculated temperature stress of asphalt binder after 72 hours of curing Among them, the shrinkage coefficient of the binder in the Hopkins-Hamming method Calculate the pavement constant .

[0131] Calculated temperature stress of asphalt binder after 1 hour of curing ;

[0132] Estimated temperature stress of asphalt binder after 72 hours of curing ;

[0133] Obtain the estimated temperature stress change ;

[0134] Calculation of parameters for thermally reversible aging , , ; This is the correction coefficient for the reversible thermal aging of the mixture; due to factors such as aggregate skeleton, interface effect, and void structure, the amplification or transfer efficiency of the mixture to the reversible thermal aging response of the binder is only 35%. The closer to 1, the more significant the thermally reversible aging; The smaller the size, the more the mixture structure buffers against reversible thermal aging.

[0135] This embodiment The value is relatively low, indicating that the asphalt mixture has good structural buffering capacity and can effectively mitigate the adverse effects of low-temperature hardening of asphalt.

[0136] ;

[0137] Calculate equivalent graded loss =0.63℃;

[0138] At the compound level, the actual equivalent low-temperature performance degradation is only 0.63℃, far less than the 1.8℃ obtained from testing the binder alone. Therefore, if the binder is used directly... Using methods to assess the risk of low-temperature cracking in a mixture would severely overestimate the aging hazards; while using It is more in line with reality.

[0139] Example 2

[0140] Based on the above embodiments, two types of asphalt mixtures, base asphalt A and rubber-modified asphalt (A+CR), were subjected to different low temperatures (-10℃, -20℃, -30℃). The base asphalt A mixture included mixtures 1-6, and the rubber-modified asphalt mixture (rubber was 80-mesh waste tire rubber powder, with a mass fraction of 15%) included mixtures 7-12. After curing for 1 hour and 72 hours, mixtures 1-12 underwent indirect tensile creep tests to obtain the following results: Figure 1 The results of the indirect tensile creep test after fitting the power function model are shown.

[0141] Table 1 shows the power function model fitting parameters for the low-temperature creep compliance curves of two asphalt mixtures: base asphalt A and rubber-modified asphalt (A+CR).

[0142] Table 1

[0143]

[0144] The fitting results show that, All three fitting parameters are greater than 0.95, and the standard deviations of all three fitting parameters are less than 0.0025. The small standard deviations indicate that the model fits well and can be used for subsequent stiffness and temperature stress calculations.

[0145] contrast Figure 1 The creep compliance curves for 1 hour and 72 hours show that the creep compliance at 72 hours is generally lower than that at 1 hour, indicating that long-term low-temperature curing leads to increased stiffness, a typical manifestation of reversible thermal aging. As the temperature decreases from -10℃ to -30℃, compliance decreases while stiffness increases, consistent with the low-temperature hardening characteristics of asphalt materials. Therefore, within the range of -10℃ to -30℃, low-temperature constant-temperature curing can effectively induce measurable physical hardening, i.e., reversible aging, and this process can be quantified through creep compliance.

[0146] Therefore, the reversible thermal aging of asphalt mixtures cannot be directly represented by the properties of the binder; it must be assessed through… Perform quantitative correction.

[0147] Example 3

[0148] Based on Example 1, base asphalt (A) mixture, base asphalt (A) binder, rubber modified asphalt (A+CR) mixture, and rubber modified asphalt (A+CR) binder were tested in two groups. The materials were cured for 1 hour and 72 hours respectively, and then subjected to indirect tensile creep test and Ex-BBR test. The results were calculated using Hopkins-Hamming. The specific test information is shown in Table 2.

[0149] Table 2

[0150]

[0151] The calculated and estimated temperature stress results for the above materials are as follows: Figure 2 As shown, Figure 2 (a) is the temperature stress change curve of the base asphalt (A) mixture, i.e., mixture A, after 1h / 72h of curing; Figure 2 (b) is the temperature stress change curve of the base asphalt (A) binder, i.e., A binder, after 1h / 72h of curing; Figure 2 (c) shows the temperature stress change curves of rubber-modified asphalt (A+CR) mixture, i.e., A+CR mixture, after curing for 1h / 72h; Figure 2 (d) shows the temperature stress change curves of rubber-modified asphalt (A+CR) binder, i.e., A+CR binder, after 1h / 72h of curing. Figure 2 In the graph, the horizontal axis represents the cooling time, and the vertical axis represents the temperature stress.

[0152] Depend on Figure 2 It is known that the estimated temperature stress of the binder is greater than the actual temperature stress of the mixture. Therefore, the BBR data of the binder cannot be used directly to assess the cracking risk of the mixture.

[0153] Furthermore, the temperature stress after 72 hours of curing was greater than that after 1 hour of curing. This indicates that during the low-temperature constant-temperature curing process, as the curing time increases, there is an accumulation of temperature stress in the asphalt mixture and asphalt binder. In other words, thermal reversible aging phenomena have occurred in the asphalt mixture and asphalt binder.

[0154] Comparative Example 1

[0155] Using the same base asphalt (denoted as asphalt A) as in Example 1 as the asphalt binder, asphalt A and limestone aggregate were mixed to prepare asphalt mixture.

[0156] Following the method described in Example 1, IDT cylindrical specimens (ϕ150 mm × 40 mm) and homologous BBR beam specimens (125 mm × 12.5 mm × 6.25 mm) were prepared and cured at -18℃ for 1 hour and 72 hours, respectively.

[0157] In this embodiment, only the BBR beam was subjected to the Ex-BBR test, and the binder grading loss was calculated according to the Superpave method. According to the current PG rating system, The corresponding low temperature level is approximately The temperature is 64-18°C. Therefore, this material has a high risk of cracking below -18°C and is not recommended for use in areas where the minimum design temperature is above -18°C.

[0158] To verify the actual situation, another TSRST prism specimen (75 mm × 75 mm × 300 mm) was prepared from the same batch of asphalt mixture. After curing at -18℃ for 72 hours, a thermal stress-restrained specimen test was conducted according to ASTM D6723, and the actual cracking temperature was measured. The results indicate that the mixture actually meets the requirements of PG 64-16 and can be used in cold regions with a minimum design temperature of -16°C.

[0159] Therefore, if based on The decision would exclude the mixture from applications in regions with temperatures as low as -16°C, resulting in an overly conservative design and increased engineering costs.

[0160] This invention introduces a structural correction coefficient. The equivalent graded loss was calculated. The temperature at ℃ corresponds to a low-temperature performance degradation that is much smaller than the results of individual tests on the binder, and is highly consistent with the cracking temperature measured by TSRST.

[0161] In summary, ignoring the buffering effect of the internal structure of the mixture on the aging response, directly applying the binder... Using it for evaluating the performance of mixtures can lead to a serious overestimation of the risk of low-temperature cracking. The present invention proposes... The parameters effectively solve the above problems and have outstanding practical value and engineering guidance significance.

[0162] Comparative Example 2

[0163] The following five asphalt mixtures, all using AC-13 dense gradation, were selected, and the optimal asphalt content was determined according to the Marshall method:

[0164] Mixture M1: Base asphalt, limestone aggregate;

[0165] Mixture M2: Base asphalt, 20% rubber powder (CR) wet modification, limestone aggregate;

[0166] Mixture M3: High-wax crude oil asphalt (wax content 5.2%), limestone aggregate;

[0167] M4 mixture: recycled asphalt mixture (RAP content 30%, recycling agent content 8%), limestone aggregate.

[0168] For each mixture:

[0169] Preparation of IDT cylindrical specimens ( 150mm×40mm) and the same BBR beam (125mm×12.5mm×6.25mm);

[0170] The samples were divided into four groups according to the method of this invention, and cured at -18°C for 1 hour and 72 hours respectively.

[0171] Meanwhile, TSRST prism specimens (75mm×75mm×300mm) were prepared from the same batch of the mixture. After curing at -18℃ for 72h, thermal stress-restrained specimen tests were conducted according to ASTM D6723, and the cracking temperature was measured. ;

[0172] For each mixture:

[0173] (1) Calculate the graded loss of binder by Ex-BBR test and Superpave method ;

[0174] (2) Calculate the thermally reversible aging parameters by combining IDT creep and Ex-BBR analysis. And obtain the equivalent graded loss. ;

[0175] (3) The TSRST test yielded the true cracking temperature. ;

[0176] The experimental results are shown in Table 3:

[0177] Table 3

[0178]

[0179] The test results in Table 3 show that if only the grade loss of the binder is considered... Such an evaluation would lead to significant misjudgments. For example, the comparison between M1 (base asphalt) and M4 (high-wax asphalt). The values ​​were 1.8℃ and 1.5℃, respectively, which are close in magnitude, but the actual measured cracking temperatures differed by as much as 5.5℃. This difference stems from the fact that at low temperatures, wax crystallization in high-wax asphalt weakens the interfacial bond between the asphalt and aggregate, causing the aggregate skeleton to be unable to effectively restrain shrinkage deformation, thus significantly increasing the risk of cracking. However, traditional... The method completely ignores such structural effects and cannot reflect the true differences in the internal mechanical response of the mixture.

[0180] In contrast, this invention introduces a parameter representing the degree of thermally reversible aging. The equivalent graded loss was calculated. This couples the material aging behavior with the structural response of the mixture. Data shows that M1's... And M4 This reflects the loss of structural buffering capacity in high-wax mixtures due to interfacial weakening. Correspondingly, The values ​​were 0.63℃ and 1.13℃, respectively, accurately capturing the performance difference between the two and highly consistent with the measured cracking temperature.

[0181] according to The order from smallest to largest corresponds to the cracking temperature from best to worst. And based on... The ranking is significantly biased, especially in the medium performance range where it is impossible to effectively distinguish the quality of materials.

[0182] Linear regression analysis further confirmed that

[0183] Will and Performing linear regression yields the regression equation:

[0184] , ;

[0185] Will and Performing linear regression yields the regression equation:

[0186] , ;

[0187] Correlation coefficient with cracking temperature far higher of This indicates that the parameters of the present invention have stronger predictive ability and engineering reliability.

[0188] In summary, traditional evaluation methods that rely solely on binder performance tend to lead to conservative designs or underestimated risks because they neglect the modulating effect of the multiphase structure of the mixture on thermally reversible aging. This invention, however, utilizes... This breakthrough represents a leap from single-material aging to material-structure synergistic response, enabling precise, quantitative, and universal characterization of the thermally reversible aging properties of different types of asphalt mixtures, and providing a scientific basis for the selection of pavement materials and life prediction in cold regions.

[0189] The above description is merely some specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A quantitative characterization method for the thermally reversible aging properties of asphalt mixtures, characterized in that, Includes the following steps: Step 1: Prepare cylindrical specimens of asphalt mixture and divide them into a first group of specimens and a second group of specimens; prepare BBR beam specimens of asphalt binder of the same origin as the asphalt mixture and divide them into a third group of specimens and a fourth group of specimens. Step 2: Place the first and third groups of specimens in an environment of -30 to -10℃ for constant temperature curing for 1 hour, and place the second and fourth groups of specimens in an environment of -30 to -10℃ for constant temperature curing for 72 hours. Step 3: Conduct indirect tensile and creep tests on the first and second groups of specimens respectively, and calculate the actual temperature stress of the asphalt mixture after 1 hour of curing using the Hopkins-Hamming method. Calculated temperature stress of asphalt mixture after 72 hours of curing ; Step 3 specifically includes: Step 31: Conduct indirect tensile creep tests on the first and second groups of specimens respectively to obtain the original data of the two groups of asphalt mixtures. Based on the original data of the asphalt mixtures, obtain the creep compliance functions of the asphalt mixtures after 1 hour and 72 hours of curing. and ; Step 32, through and Calculate the creep stiffness after 1 hour and 72 hours of curing, respectively. and ; Step 33, will and The calculated temperature stress of the asphalt mixture after 1 hour of curing was obtained by substituting the values ​​into the Hopkins-Hamming method. Calculated temperature stress of asphalt mixture after 72 hours of curing ; Step 4: Perform Ex-BBR tests on the third and fourth groups of specimens respectively, and calculate the estimated temperature stress of the asphalt binder after 1 hour of curing and the estimated temperature stress of the asphalt binder after 72 hours of curing using the Hopkins-Hamming method. Step 4 specifically includes; Step 41: Perform Ex-BBR tests on the third and fourth groups of specimens respectively to obtain the raw data of the two groups of asphalt binders. Based on the raw data of the asphalt binders, obtain the creep compliance functions of the asphalt binders after 1 hour and 72 hours of curing. and ; Step 42, through and Calculate the creep stiffness after 1 hour and 72 hours of curing, respectively. and ; Step 43, will and The estimated temperature stress of asphalt binder after 1 hour of curing was calculated using the Hopkins-Hamming method. Calculated temperature stress of asphalt binder after 72 hours of curing ; Step 5: Obtain the calculated temperature stress change. In step 5, the actual pavement constants are calculated. In step 8, the pavement constant is calculated. ; Step 6: Obtain the estimated temperature stress change. ; Step 7, Calculate the parameters of thermally reversible aging. , , ; Step 8: Obtain the grading loss of asphalt binder through Ex-BBR test. Through the parameter of thermal reversible aging and graded loss The thermal reversible aging characteristics of asphalt mixtures were quantitatively characterized, and the equivalent graded loss was calculated. ;pass The thermally reversible aging characteristics of asphalt mixtures were quantitatively characterized.

2. The quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures according to claim 1, characterized in that, In step 3, the linear shrinkage coefficient of the mixture in the Hopkins-Hamming method .

3. The quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures according to claim 1, characterized in that, In step 4, the shrinkage coefficient of the binder in the Hopkins-Hamming method .

4. The quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures according to claim 1, characterized in that, Step 4 specifically includes: pass Calculate the creep stiffness after 1 hour of curing , ;pass Calculate the creep stiffness after 72 hours of curing. , .

5. The quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures according to claim 1, characterized in that, pass Calculate the creep stiffness after 1 hour of curing , ;pass Calculate the creep stiffness after 72 hours of curing. , .

6. The quantitative characterization method for the thermally reversible aging characteristics of asphalt mixtures according to claim 1, characterized in that, In step 3, during the indirect tensile creep test, the load was controlled so that the average deformation of the first and second groups of specimens was 0.00250mm-0.00900mm.

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