Asphalt mixture aging gradient characterization method based on DMA test

Abstract

The invention belongs to the field of road engineering, and particularly relates to an asphalt mixture aging gradient characterization method based on DMA (direct memory access) test, which comprises the following steps: step 1, selecting raw materials to prepare a test piece; 2, dividing the test pieces into a group A and a group B; the bottom surface and the side surface of the test piece of the group A are coated with sealant; step 3, performing thermo-oxidative aging on the group A test piece in a drying oven; step 4, transversely cutting the group A and the group B into N sheets along the radial direction; 5, carrying out temperature scanning tests on the slices at different positions by utilizing DMA (Direct Memory Access) to obtain the glass transition temperature Tg of the damaged slice test piece; and 6, calculating the ratio of the glass transition temperatures Tg of the A group of sheet test pieces to the B group of sheet test pieces at the same position, wherein the ratio is the aging gradient K of the asphalt mixture at the position. The thin sheet is cut according to the height direction of the test piece; therefore, the obtained test parameters are more consistent with the actual mechanical response of the asphalt pavement structure, and the defect that the aging gradient of the asphalt mixture is evaluated by an existing nanoindentation method is overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering, and in particular relates to a method for characterizing the aging gradient of asphalt mixture based on DMA testing. Background Art

[0002] Asphalt mixture is a complex material composed of a multiphase system consisting of aggregate, asphalt mastic, and voids. Asphalt mixture applied to the pavement surface is exposed to the elements for extended periods, allowing a large number of air molecules to contact the surface of the asphalt mixture and enter its interior through the voids. Under the influence of external factors such as atmospheric temperature, the asphalt mastic undergoes a complex series of thermo-oxidative aging reactions, generating numerous chemical functional groups such as carbonyl and sulfoxide groups. Lighter components such as saturated and aromatic compounds in the asphalt mastic gradually transform into more stable components such as asphaltenes. Consequently, thermo-oxidative aging causes the asphalt mastic to harden, increasing the modulus of the asphalt mixture.

[0003] Research has been conducted using nanoindentation testing to evaluate the aging gradient characteristics of asphalt mixtures under the effects of thermo-oxidative aging. The patent "In-situ Characterization Method for Asphalt Mixture Aging Gradient Based on Indentation Testing" (CN114527024A) discloses a method for evaluating the aging gradient of asphalt mixtures by obtaining modulus from nanoindentation testing. While this method achieves the goal of characterizing the aging gradient behavior of asphalt mixtures, it suffers from several insurmountable drawbacks. Firstly, the asphalt mortar modulus at the interface obtained by nanoindentation testing depends on the area of ​​the asphalt mortar. The limited asphalt mortar area in the AC-type dense-graded asphalt mixtures commonly used in asphalt pavements currently does not meet the testing requirements of nanoindentation testing. The use of SMA open-graded asphalt mixture specimens in the examples of this invention also demonstrates these drawbacks. If the aging gradient behavior of AC-type graded asphalt mixtures, commonly used in pavement structures, cannot be characterized, the practical engineering significance will be lost. Secondly, the current Chinese asphalt pavement design specifications use dynamic modulus as a design and evaluation indicator for pavement structures. Nanoindentation testing measures the static microscopic creep modulus, which is inconsistent with the macroscopic dynamic modulus used in current design specifications. This leads to questions about the reliability and scientific validity of the resulting gradient behavior of asphalt mixtures undergoing aging. Furthermore, the cumbersome preparation of nanoindentation specimens and the high surface roughness requirements make this method impractical for large-scale engineering applications. Therefore, it is necessary to develop a more accurate and feasible method for characterizing the gradient behavior of asphalt mixtures undergoing aging.

[0004] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for characterizing the aging gradient of asphalt mixture based on DMA test, which uses dynamic mechanical scanning test to obtain the temperature and damage factor-scanning temperature test curves of thin slice specimens at different depths, and uses the glass transition temperature T g Characterize the aging gradient at different locations of asphalt mixture and construct the glass transition temperature T g The statistical relationship model between the aging depth of asphalt mixture and the pavement structure is used to accurately characterize the aging gradient behavior of asphalt mixture.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for characterizing the aging gradient of asphalt mixture based on DMA testing includes the following steps: Step 1: Select asphalt mixture raw materials that are the same as the target and make asphalt mixture cylindrical specimens; Step 2: Divide the test pieces into Group A and Group B. Apply sufficient anti-aging sealant to the bottom and sides of the test pieces in Group A, and leave the test pieces in Group B untreated. Step 3: Place the test pieces of group A vertically in an oven for thermal oxidative aging for a specified time; place the test pieces of group B vertically at room temperature for the same time; Step 4: Cut N thin slices from the specimens in the radial direction, which are recorded as the thin slices in group A; cut N thin slices from the specimens in group B at the same height as the thin slices in group A, which are recorded as the thin slices in group B; Step 5: Use DMA to conduct temperature scanning tests on the thin film at different positions to obtain the loss factor-scanning temperature test curve, and use the temperature corresponding to the peak of the curve to determine the glass transition temperature T of the thin film specimen. g ; Step 6: Calculate the glass transition temperature T of the thin slice specimens of group A and group B at the same position g The aging gradient of the asphalt mixture at that location is obtained by the ratio of , and the calculation formula of the aging gradient K is: (1); In formula (1), is the glass transition temperature of the thin film specimens of group A, is the glass transition temperature of the thin film specimens in group B.

[0007] Furthermore, the asphalt mixture aging gradient characterization method based on DMA test also includes step seven, calculating the asphalt mixture aging gradient at different positions, and constructing a statistical relationship model between the aging gradient and the slice height.

[0008] Furthermore, in step 1, the thickness of the aging-resistant sealant is 1-2 mm.

[0009] Furthermore, in step 3, the oven temperature is 150-170° C., and the thermal oxidation aging time is 3-5 days.

[0010] Furthermore, in step 4, N is 7 to 9.

[0011] Furthermore, in step 4, the specimen has a diameter of 100 mm and a height of 150 mm; the specimens of group A and group B are first cored and then sliced ​​transversely, with an interval of 8 to 12 mm between adjacent slices, and a thickness of 3 mm; the reserved distance from the slice at the top to the upper surface of the specimen is not less than 5 mm, and the reserved distance from the slice at the bottom to the bottom surface of the specimen is not less than 5 mm.

[0012] Furthermore, in step 4, the length of the sheet is 30 mm to 35 mm, the width is 10 mm to 14 mm, and the thickness is 2 mm to 3 mm.

[0013] Furthermore, in step five, the DMA test selected the strain control mode, the applied strain was 25 με, the loading frequency was 10 Hz, and the scanning temperature range was -20°C to 80°C.

[0014] Furthermore, in step 1, the gradation of the asphalt mixture raw material is AC-13.

[0015] Furthermore, in step 2, each group of parallel specimens is 3 to 5.

[0016] The working principle of the present invention is that asphalt mixture is a typical viscoelastic material, which will show three mechanical states: glassy state, viscoelastic state and even viscous flow state in a wide temperature range. g ) is the critical characteristic temperature of asphalt mixture transitioning from glassy state to viscoelastic state, which is closely related to its low temperature performance. Specifically, the glass transition temperature T g The higher the glass transition temperature T, the worse the low temperature performance of asphalt mixture. g It can also effectively reflect the aging characteristics of asphalt mixture. Under the action of thermal oxidative aging, the aromatic and saturated components of asphalt mixture gradually decrease, while the proportion of colloid and asphalt increases. Asphalt mixture shows a significant decrease in low temperature performance and glass transition temperature T g Therefore, the glass transition temperature T of asphalt mixture at different depths of pavement structure is g There will be significant differences, so the present invention uses the glass transition temperature T g It is feasible to characterize the aging gradient behavior of asphalt mixtures.

[0017] Furthermore, in practice, due to the uneven diffusion of air molecules, there are significant differences in the air concentration within the asphalt mixture at different depths in the pavement structure. The deeper the pavement structure, the lower the oxygen concentration in the asphalt mixture, which will cause asphalt mixtures at different depths to be affected by different degrees of thermal oxidative aging effects. The conventional method of directly using the entire cylindrical specimen to obtain test parameters makes it difficult to accurately and objectively evaluate the true state of the asphalt pavement structure at different depths, which is not conducive to conducting asphalt pavement structure analysis and maintenance decisions. Therefore, the present invention obtains multiple thin slices along the height direction of the specimen for analysis.

[0018] The beneficial effects of the present invention are: The present invention carries out temperature scanning test based on DMA method to obtain loss factor-scanning temperature curve of asphalt mixture slices of different depths, and proposes a method to use glass transition temperature T g A method for characterizing the aging gradient behavior of asphalt mixtures. This method has the advantages of simple specimen molding and applicability to asphalt mixtures of different gradation types. It helps to more accurately analyze the mechanical behavior of pavement structures and make optimal maintenance decisions. It can reflect the degree of thermal oxidative aging of asphalt mixtures at different depths through indicators, thereby reducing maintenance and repair problems caused by improper milling depth.

[0019] When cutting thin slices, the present invention follows the height direction of the specimen, which is equivalent to the depth direction of the road surface. The test parameters obtained using these thin slices are more consistent with the actual mechanical response of the asphalt pavement structure, which makes up for the shortcomings of the existing nanoindentation method in evaluating the aging gradient of asphalt mixtures, and helps to provide a reliable basis for accurate analysis of the mechanical behavior of pavement structures and making optimal maintenance decisions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them: Figure 1 Schematic diagram of the position of the slice in the test piece according to an embodiment of the present invention.

[0021] Figure 2 This is the asphalt mixture loss factor-scanning temperature test curve of an embodiment of the present invention.

[0022] Figure 3 Statistical model of the aging gradient K and different depths h according to an embodiment of the present invention.

[0023] In the figure: specimen-100, slice-200. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0025] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0026] A method for characterizing the aging gradient of asphalt mixture based on DMA testing includes the following steps: Step 1: Select asphalt mixture raw materials identical to the target and prepare cylindrical asphalt mixture specimens. In this embodiment, the target asphalt mixture is an AC-13 gradation, and the raw materials include 70# matrix asphalt, basalt aggregate, and limestone powder. The basalt aggregate is divided into four sizes: 0mm-3mm, 3mm-5mm, 5mm-10mm, and 10mm-15mm. According to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering," cylindrical asphalt mixture specimens with a diameter of 100 mm and a height of 150 mm are prepared. Step 2: Divide the specimens into Group A and Group B. Apply sufficient anti-aging sealant to the bottom and sides of the specimens in Group A. The purpose of applying the anti-aging sealant is to ensure that air in the oven enters the asphalt mixture from the top, preventing the thermal oxidative aging effect on the sides and bottom from affecting the aging gradient behavior of the asphalt mixture. The specimens in Group B are not treated and serve as the control group. Step 3: Place the test pieces of group A vertically in an oven for thermal oxygen aging for a specified time; place the test pieces of group B vertically in an indoor environment for the same time, without the need to place them in a special light-shielding environment; the aging temperature and time are 150°C~170°C and 3d~5d respectively; in this embodiment, based on the results of preliminary experimental exploration, the oven temperature is set to 163°C and the thermal oxygen aging time is 3d; the oven is required to have a stable heat preservation function, and the maximum setting temperature must not be lower than 200°C. It is not necessary to use a rotary film oven; Step 4: Cut N thin slices from the test pieces of group A along the radial direction, recorded as group A slices; cut N thin slices from the test pieces of group B at the same height as the slices of group A, recorded as group B slices; test The core is first taken from the specimen and then thin slices are cut horizontally. The interval between adjacent slices is 8-12 mm, and the thickness of the slices is 3 mm. The "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" T0738-2011 requires the shaping of core samples in the uniaxial dynamic modulus test of asphalt mixtures. Accordingly, in this embodiment, the position of the slices at the edge is limited: the distance between the slice at the top and the upper surface of the specimen is not less than 5 mm, and the distance between the slice at the bottom and the bottom surface of the specimen cannot be less than 5 mm. Step 5: Use DMA to carry out temperature scanning tests on slices at different positions to obtain the loss factor-scanning temperature test curve, and use the temperature corresponding to the peak of the curve to determine the glass transition temperature T of the slice specimen.g ;like Figure 2 As shown in the figure, the DMA test uses the strain control mode, the applied strain is 25με, the loading frequency is 10Hz, and the scanning temperature range is -20℃~80℃; the number of parallel runs of each test is 3, and the average value of the three runs is taken as the final test result; the present invention cuts 9 thin slices, and the T values ​​of the rectangular specimens at different positions of group A and group B are g The test results are shown in Table 1. The depth in Table 1 refers to the depth from the upper surface of the slice to the upper surface of the test block, which is used to indicate the specific position of the current slice. Figure 1 The positions of nine thin slices 200 in the cylindrical specimen 100 are schematically shown in FIG.

[0027] Table 1 Glass transition temperature results at different positions of group A and group B asphalt mixtures

[0028] Step 6: Calculate the glass transition temperature T of the thin slice specimens of group A and group B at the same position g The aging gradient of the asphalt mixture at this location is obtained by the ratio of , and the calculation results are shown in Table 2. The calculation formula of the aging gradient K is: (1); In formula (1), is the glass transition temperature of the thin film specimens of group A, is the glass transition temperature of the thin film specimens in group B.

[0029] Table 2 Aging gradient coefficients at different positions of the specimen

[0030] Furthermore, the DMA test-based asphalt mixture aging gradient characterization method also includes step seven, calculating the asphalt mixture aging gradient K at different locations, and constructing a statistical relationship model between the aging gradient K and the slice height h; using the model to characterize the aging gradient behavior of the asphalt mixture at different depths in the asphalt pavement structure; inputting the known thickness of the asphalt pavement structure into the model to obtain the aging gradient at that location. In this embodiment, the constructed statistical relationship model between the aging gradient K and the slice height h is as follows: Figure 3 As shown, we can see that K=-2.4501E-5h 2 +0.0079h+0.3525, where E represents an exponential with base 10, and 2.4501E-5 is a number expressed in scientific notation, representing 0.000024501; the coefficient of determination of this statistical relationship model is R 2 The value is 0.9818, which indicates that the model has a very good fitting effect.

[0031] The present invention adopts the glass transition temperature T before and after aging g The ratio of K to Asphalt Pavement represents the degree of aging of the asphalt mixture, which is referred to as the aging coefficient K in this article. The smaller the K value, the greater the degree of aging of the asphalt mixture. Referring to the "Technical Specifications for Highway Asphalt Pavement Construction" (JTG F40-2004), the water damage resistance of the asphalt mixture after immersion in water shall not be less than 0.8 of the original performance. That is, when the K value at a certain position of the asphalt pavement structure layer is less than 0.8, the mechanical properties of the asphalt mixture are significantly attenuated, and it can be judged that the asphalt mixture at this thickness needs to be milled and recycled; similarly, the present invention stipulates that when the K value is lower than 0.8, it is necessary to carry out maintenance and recycling. According to the aging gradient results of the specimens in Table 2, in this embodiment, the aging coefficient K of the thin slices of layers 1, 2, 3, and 4 is less than 0.8, and the critical position of the aging coefficient K of 0.8 is between layers 4 and 5. At least 73.509 mm of the road surface needs to be milled off. In actual operation, for the sake of safety, 7.5 cm of the road surface needs to be milled off.

[0032] Furthermore, the aging-resistant sealant has the characteristics of high temperature resistance, heat insulation, and strong sealing. According to preliminary tests, the thickness of the sealant can be set to 1mm~2mm; the specific coating method is to apply the fluid sealant on the surface of the cylindrical specimen until it is cured and dry.

[0033] Furthermore, the number of slices cut out in each group can be 7 to 9. The more slices cut out, the more accurate the statistical relationship model of the aging gradient and the height curve constructed in step 7. However, the more slices cut out, the longer it takes. Taking into account the time efficiency and model accuracy, the preferred number of slices in each group of the present invention is 9. The DMA instrument model used in this embodiment is DMA850. The fixture requires that the width of the specimen cannot exceed 15 mm. In the DMA single cantilever beam mode, the length of the specimen should not exceed 35 mm. In addition, when the thickness of the slice is less than 2 mm, it is not easy to cut. Therefore, the slice size is designed to be 30 mm to 35 mm (length) × 10 to 14 mm (width) × 2 to 3 mm (thickness); preferably 30 mm (length) × 10 mm (width) × 3 mm (thickness).

[0034] The present invention utilizes sealant to "protect" the surface of the cylindrical specimen, so that only the upper surface of the specimen is subjected to the heat-aging effect of the oven, simulating the situation in which a real asphalt pavement is only subjected to sunlight-heat-oxidative aging from the upper surface. Combined with the production of thin sections along the depth (height) direction, the aging gradient behavior of the asphalt pavement can be more realistically characterized, thereby more accurately and objectively evaluating the actual degree of damage to the asphalt pavement structure. It can also characterize the AC-type graded asphalt mixture commonly used in asphalt pavements, which is beneficial for conducting asphalt pavement structure analysis and maintenance decision-making, and has important engineering significance for achieving more accurate pavement structure design and formulating optimal maintenance measures.

[0035] The above description is only a preferred embodiment 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 are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for characterizing the aging gradient of asphalt mixture based on DMA test, characterized in that: The steps include: Step 1: Select asphalt mixture raw materials that are the same as the target and make asphalt mixture cylindrical specimens; Step 2: Divide the test pieces into Group A and Group B. Apply sufficient anti-aging sealant to the bottom and sides of the test pieces in Group A, and leave the test pieces in Group B untreated. Step 3: Place the test pieces of group A vertically in an oven for thermal oxidative aging for a specified time; place the test pieces of group B vertically at room temperature for the same time; Step 4: Cut N thin slices from the specimens in the radial direction, which are recorded as the thin slices in group A; cut N thin slices from the specimens in group B at the same height as the thin slices in group A, which are recorded as the thin slices in group B; Step 5: Use DMA to conduct temperature scanning tests on the thin film at different positions to obtain the loss factor-scanning temperature test curve, and use the temperature corresponding to the peak of the curve to determine the glass transition temperature T of the thin film specimen. g ; Step 6: Calculate the glass transition temperature T of the thin slice specimens of group A and group B at the same position g The aging gradient of the asphalt mixture at that location is obtained by the ratio of , and the calculation formula of the aging gradient K is: （1）； In formula (1), is the glass transition temperature of the thin film specimens of group A, is the glass transition temperature of the thin film specimens in group B.

2. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: The method further includes step seven, calculating the aging gradient of the asphalt mixture at different positions, and constructing a statistical relationship model between the aging gradient and the slice height.

3. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 1, the thickness of the aging-resistant sealant is 1 to 2 mm.

4. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 3, the oven temperature is 150° C. to 170° C., and the thermal oxidation aging time is 3 d to 5 d.

5. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 4, N is 7 to 9.

6. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 4, the specimen has a diameter of 100 mm and a height of 150 mm. The specimens of group A and group B are first cored and then sliced ​​transversely. The interval between adjacent slices is 8 to 12 mm, and the thickness of the slices is 3 mm. The reserved distance from the slice at the top to the upper surface of the specimen is not less than 5 mm, and the reserved distance from the slice at the bottom to the bottom surface of the specimen is not less than 5 mm.

7. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 4, the length of the sheet is 30 mm to 35 mm, the width is 10 mm to 14 mm, and the thickness is 2 mm to 3 mm.

8. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 5, the DMA test selected the strain control mode, the applied strain was 25 με, the loading frequency was 10 Hz, and the scanning temperature range was -20°C to 80°C.

9. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1, characterized in that: In step 1, the asphalt mixture raw material gradation is AC-13.

10. The asphalt mixture aging gradient characterization method based on DMA test according to claim 1, characterized in that: In step 2, each group of parallel specimens consists of 3 to 5 pieces.

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