Asphalt mixture salt loss gradient characterization method based on DMA test

Abstract

The invention belongs to the field of road engineering, and particularly relates to an asphalt mixture salt loss 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 A group test piece are waterproof; step 3, soaking the test piece of the group A in a salt solution; step 4, transversely cutting the group A and the group B into N sheets along the radial direction respectively; step 5, performing wide temperature scanning test on the thin sheet test pieces at different positions by using a dynamic mechanical analyzer DMA to obtain a relation curve of a loss factor and scanning temperature, and obtaining the glass transition temperature Tg of each thin sheet; 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 to obtain a salt damage gradient coefficient K at the position; according to the method, the problem that salt damage of the pavement structure at different depths is not considered during existing pavement salt damage evaluation is solved, and a scientific basis is provided for asphalt pavement salt damage analysis.

Description

Technical Field

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

[0002] During winter in northern my country, using sodium chloride deicing agents to melt snow and de-icer is a common method for ensuring normal highway operations. Asphalt mixture is a complex material composed of a multiphase system consisting of aggregate, asphalt mortar, and voids. During the deicing process, sodium and chloride ions in the deicing agent contact the surface of the asphalt mixture and enter its internal structure through the voids, damaging the asphalt mortar and the asphalt-aggregate interface, thereby reducing the asphalt mixture's road performance. This damage caused by deicing agents to the asphalt mixture is known as salt damage.

[0003] Conventional methods for measuring the degree of damage to salt-damaged pavement include manual / machine vision, lidar scanning, and core sampling. However, manual / machine vision and lidar scanning mainly focus on evaluating the damage to the pavement surface. After core sampling, in addition to directly observing the core sample, tests such as compressive strength and splitting strength are usually conducted to evaluate the bearing capacity and overall performance of the pavement. However, there is a lack of salt damage evaluation for pavements of different depths.

[0004] In fact, compared with the salt damage on the surface of the asphalt mixture, the degree of salt damage to its internal structure gradually decreases along the depth direction. This is mainly due to the uneven diffusion of sodium and chloride ions within the asphalt mixture. The deeper the asphalt pavement structure, the lower the concentration of sodium and chloride ions in the asphalt mixture, which will cause asphalt mixtures of different structural depths to have different degrees of salt damage. However, current asphalt pavement maintenance measures lack a deep understanding of the salt damage gradient effect, resulting in the inability to formulate effective and scientific maintenance strategies. It is impossible to determine the depth to which the pavement surface needs to be milled, and the pavement surface is often milled excessively, resulting in a serious waste of natural resources and economic costs.

[0005] Current Chinese asphalt pavement design specifications use dynamic modulus as a design and evaluation indicator for pavement structures. However, the salt damage gradient effect causes the modulus of the asphalt mixture to exhibit a gradually increasing gradient along the depth of the pavement structure, resulting in nonlinear mechanical responses of the asphalt pavement structure. This makes it difficult to accurately and objectively evaluate the true load state of the asphalt pavement structure. Therefore, to more realistically reflect the salt damage gradient behavior of asphalt mixtures, it is particularly important to develop a test evaluation method that can accurately characterize the salt damage gradient of asphalt mixtures. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for characterizing the salt damage gradient of asphalt mixture based on DMA testing to more accurately characterize the degree of salt damage at different depths within the asphalt mixture, thereby providing a basis for asphalt mixture design and asphalt pavement maintenance decision-making.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: A method for characterizing salt loss gradient of asphalt mixture based on DMA test 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 specimens into Group A and Group B. The bottom and sides of the specimens in Group A are waterproofed, while the specimens in Group B are not treated. Step 3: Immerse the specimens of group A in a salt solution for salt damage treatment; place the specimens of group B vertically at room temperature for the same period of 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: Set fixed strain and frequency, and use the dynamic mechanical analyzer DMA to perform wide temperature scanning tests on thin-film specimens at different positions to obtain the relationship curve between loss factor and scanning temperature. By analyzing the peak position of the curve, the glass transition temperature T can be determined. g , that is, 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 salt damage gradient coefficient of the asphalt mixture at that location is obtained by the ratio of , and the calculation formula of the salt damage gradient coefficient 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.

[0008] Furthermore, the asphalt mixture salt damage gradient characterization method based on DMA testing also includes step seven, calculating the salt damage gradient coefficient of the asphalt mixture at different positions, and constructing a statistical relationship model between the salt damage gradient coefficient and the slice height based on these data.

[0009] Furthermore, in step 2, the waterproofing treatment is to wrap the sides and bottom of the specimen with plastic wrap / plastic bag or apply waterproof glue to prevent the sides and bottom from being immersed in the salt solution.

[0010] Furthermore, in step three, the salt damage treatment is to vertically place the specimen in a 0-5°C, 15%-18% sodium chloride salt solution and soak it at a constant temperature for 36-48 hours.

[0011] Furthermore, in step 4, N is 7 to 9.

[0012] Furthermore, the specimens of Group A and Group B were 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 was not less than 5 mm, and the reserved distance from the slice at the bottom to the bottom surface of the specimen was not less than 5 mm.

[0013] 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.

[0014] Furthermore, the DMA scan selected the strain control mode, with an applied strain of 25 με, a loading frequency of 10 Hz, and a scanning temperature range of -20 °C to 80 °C.

[0015] Furthermore, in step 1, the gradation of the asphalt mixture raw material is AC-13.

[0016] Furthermore, in step 2, each group of parallel specimens is 3 to 5.

[0017] The working principle of the present invention is: As a typical viscoelastic material, asphalt mixture can present 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. Salt damage can cause the road performance of asphalt mixture to deteriorate, especially the low temperature performance is significantly reduced and the glass transition temperature T g In other words, under the action of salt damage, the greater the degree of salt damage to the asphalt mixture, the higher the glass transition temperature T g Therefore, the glass transition temperature T of asphalt mixture at different pavement structure depths is g There are obvious differences, using the glass transition temperature T g It is feasible to characterize the salt damage gradient behavior of asphalt mixture.

[0018] In order to accurately describe the salt damage gradient behavior of asphalt mixture, this patent proposes a salt damage gradient characterization method based on Dynamic Mechanical Analyzer (DMA) testing. Using DMA to conduct temperature scanning tests to obtain the specimen damage factor-test temperature test curve, the glass transition temperature T of asphalt mixture at different depths is obtained. g Characterize the salt damage gradient behavior. This method has the advantages of simple specimen molding and applicability to asphalt mixtures of different gradations, providing a scientific basis for the design and subsequent maintenance decisions of salt-damage-resistant asphalt mixtures.

[0019] The beneficial effects of the present invention are: The present invention proposes a method of using the glass transition temperature T of the slice at different depths to determine the glass transition temperature T of the slice at different depths. g A new method for characterizing the salt damage gradient of asphalt mixture. Compared with the existing technology, the present invention is consistent with the diffusion and migration behavior of sodium ions and salt ions in asphalt mixture during snow melting and de-icing and their concentration gradient effect, accurately describing the salt damage gradient at different positions inside the asphalt mixture; it helps to accurately evaluate the degree of salt damage in each layer of the pavement, and provides a scientific basis for the optimal design of asphalt mixture and the precise maintenance of asphalt pavement. 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 immersing a test piece according to an embodiment of the present invention in a saline solution.

[0021] Figure 2 Schematic diagram of the position of the slice in the test piece according to an embodiment of the present invention.

[0022] Figure 3 This is the asphalt mixture loss factor-scanning temperature test curve of an embodiment of the present invention.

[0023] Figure 4 Statistical model of salt damage gradient coefficient K and different thicknesses h according to an embodiment of the present invention.

[0024] In the figure: specimen-100, waterproof layer-200. DETAILED DESCRIPTION

[0025] 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.

[0026] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0027] A method for characterizing salt loss gradient of asphalt mixture based on DMA test includes the following steps: Step 1: Select asphalt mixture raw materials identical to the target asphalt mixture and prepare asphalt mixture cylindrical specimens. In this embodiment, the target asphalt mixture is an AC-13 gradation, comprising 70# matrix asphalt, basalt aggregate, and limestone powder. The basalt aggregate is divided into four sizes: 0-3 mm, 3-5 mm, 5-10 mm, and 10-15 mm. The cylindrical specimens are 100 mm in diameter and 150 mm in height, prepared in accordance with the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering." Step 2: Divide the specimens into Group A and Group B, with each group consisting of 3 to 5 parallel specimens. The bottom and sides of the specimens in Group A are waterproofed, while the specimens in Group B are not. The waterproofing treatment involves wrapping the sides and bottom of the specimens with plastic wrap / plastic bags or coating them with waterproof glue to prevent them from being immersed in the salt solution. In this embodiment, the waterproof layer 200 is formed by placing the specimens 100 in a plastic bag and enhancing the sealing effect with waterproof glue (the upper opening of the plastic bag is bonded to the top of the side of the specimen with waterproof glue and then wrapped with rope or tape to tighten it).

[0028] Step 3: Figure 1 As shown, the specimens in Group A were vertically immersed in a 15%-18% sodium chloride salt solution at 0-5°C for 36-48 hours for salt damage treatment; the specimens in Group B were placed vertically at room temperature for the same period of time. The sodium chloride salt solution is made of sodium chloride crystals and distilled water, and its composition is basically the same as the deicing agent used for snow removal on asphalt pavements on highways. The road surface temperature during snow melting is generally 0-5°C. On the other hand, according to the "Road Deicing and Deicing Agents" (GBT 23851-2017), the concentration of sodium chloride deicing agents is generally 18%. Therefore, the salt damage test conditions are a constant temperature of 0-5°C and a salt solution concentration of 15%-18%.

[0029] Step 4: Figure 2As shown, N thin slices are cut into the radial direction of the specimens of group A, which are recorded as thin slices of group A; N thin slices are cut into the same height as the thin slices of group B, which are recorded as thin slices of group B; N is 7 to 9, and the more thin slices are cut, the more accurate the result is. However, the more slices are cut, the longer it takes. Considering the time efficiency and model accuracy, the preferred number of thin slices in each group of the present invention is 9; the specimens of group A and group B are first cored and then thin slices are cut horizontally, with an interval of 8 to 12 mm between adjacent thin slices and a thickness of 3 mm; the reserved distance between the thin slice at the top and the upper surface of the specimen is not less than 9. The distance between the thin sheet at the bottom and the bottom surface of the specimen is not less than 5 mm. 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 thin sheet is less than 2 mm, it is difficult to cut. Therefore, the sheet size (length, width and thickness) is designed to be 30 mm × 10 mm × 2 mm to 35 mm × 14 mm × 3 mm; preferably 30 mm (length) × 10 mm (width) × 3 mm (thickness).

[0030] Step 5: Figure 3 As shown in the figure, fixed strain and frequency are set, and a dynamic mechanical analyzer DMA is used to perform a wide temperature sweep test on thin-film specimens at different positions to obtain the relationship curve between loss factor and scanning temperature. By analyzing the peak position of the curve, the glass transition temperature T can be determined. g , that is, the glass transition temperature T of the thin film specimen g DMA scanning selected strain control mode, applied strain was 25με, loading frequency was 10Hz, and scanning temperature range was -20℃~80℃.

[0031] 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 salt damage gradient coefficient of the asphalt mixture at that location is obtained by the ratio of , and the calculation formula of the salt damage gradient coefficient 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. g The test results are shown in Table 1.

[0032] Table 1 T of thin-film specimens at different positions in group A and group B g and salt damage gradient coefficient

[0033] The salt damage gradient in the present invention is the glass transition temperature T before and after salt damage. gThe smaller the K value, the more serious the salt damage of the asphalt mixture. The "Technical Specifications for Highway Asphalt Pavement Construction" (JTG F40-2004) stipulates that the salt damage resistance of asphalt mixture after immersion in water shall not be lower than 0.8 of the original performance. Referring to the requirements of salt damage, the present invention regards thin slices with a salt damage gradient lower than 0.8 as severely salt damaged, and requires milling and re-surfacing the asphalt pavement. According to the results in Table 1, in this embodiment, the salt damage coefficient K of the thin slices in layers 1, 2, and 3 is less than 0.8, and the salt damage gradient of the thin slice in layer 4 is 0.802, which is close to the critical value of 0.8. At least 56.381 mm of the road surface needs to be milled off. In actual operation, for safety reasons, the milling thickness is 6 cm.

[0034] Furthermore, the asphalt mixture salt damage gradient characterization method based on DMA test also includes step seven, calculating the salt damage gradient coefficient of the asphalt mixture at different positions, and constructing a statistical relationship model between the salt damage gradient coefficient and the slice height based on these data; Figure 4 As shown, K=-2.0911E-5h 2 +0.0069h+0.4784, where E represents an exponential with base 10, and 2.0911E-5 is a number expressed in scientific notation, representing 0.000020911; the coefficient of determination R of this statistical relationship model 2 The value of h is 0.98815, indicating that the model has a very good fitting effect. This model can be used to quantitatively describe the gradient salt damage behavior of asphalt mixtures at different depths in asphalt pavement structures. By inputting the thickness of the known asphalt pavement structure into the model, the salt damage gradient at that location can be obtained. The depth h can also be solved based on the required salt damage gradient coefficient.

[0035] This paper proposes a new method for characterizing the salt damage gradient of asphalt mixtures based on the Dynamic Mechanical Analyzer (DMA) test. First, thin slices were cut from the salt-damaged asphalt mixture at different locations. Then, the loss factor-scanning temperature curve of the thin slices was recorded using the DMA test to obtain the glass transition temperature (T) at different depths of the asphalt mixture. g . Finally, a relationship model between the salt damage coefficient and the depth at different positions was constructed to accurately characterize the salt damage gradient behavior of the asphalt mixture. The present invention provides a scientific basis for the design of asphalt mixtures, the formulation of maintenance decisions for asphalt pavements, and structural mechanics analysis. This method is suitable for the characterization of AC-type graded asphalt mixtures commonly used in asphalt pavements, which is conducive to the structural analysis and maintenance decision-making of asphalt pavements, and has important engineering significance for achieving more accurate pavement structure design and the formulation of optimal maintenance measures.

[0036] 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 salt loss gradient of asphalt mixture based on DMA test, characterized in that: The following steps are involved: Step 1: Select asphalt mixture raw materials that are the same as the target and make asphalt mixture cylindrical specimens; Step 2: Divide the specimens into Group A and Group B. The bottom and sides of the specimens in Group A are waterproofed, while the specimens in Group B are not treated. Step 3: Immerse the specimens of group A in a salt solution for immersion treatment; place the specimens of group B vertically at room temperature for the same period of 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: Set fixed strain and frequency, and use the dynamic mechanical analyzer DMA to perform wide temperature scanning tests on thin-film specimens at different positions to obtain the relationship curve between loss factor and scanning temperature. By analyzing the peak position of the curve, the glass transition temperature T can be determined. g , that is, 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 salt damage gradient coefficient of the asphalt mixture at that location is obtained by the ratio of , and the calculation formula of the salt damage gradient coefficient 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 method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1 is characterized in that: The method further includes step seven, calculating the salt damage gradient coefficient of the asphalt mixture at different positions, and constructing a statistical relationship model between the salt damage gradient coefficient and the slice height based on these data.

3. The method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1 is characterized in that: In step 2, the waterproofing treatment is to wrap the sides and bottom of the specimen with plastic wrap / plastic bag or apply waterproof glue to prevent the sides and bottom from being immersed in the salt solution.

4. The method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1 is characterized in that: In step three, the salt damage treatment is to vertically place the specimen in a 0-5°C, 15%-18% sodium chloride salt solution and soak it at a constant temperature for 36-48 hours.

5. The method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1, characterized in that: In step 4, N is 7 to 9.

6. The method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1 is characterized in that: For Group A and Group B specimens, cores were first taken and then thin slices were cut horizontally. The interval between adjacent slices was 8 to 12 mm, and the thickness of the slices was 3 mm. The reserved distance from the slice at the top to the upper surface of the specimen was not less than 5 mm, and the reserved distance from the slice at the bottom to the bottom surface of the specimen was not less than 5 mm.

7. The method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1, 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 method for characterizing salt loss gradient of asphalt mixture based on DMA test according to claim 1, characterized in that: The DMA scan selected the strain control mode, with an applied strain of 25 με, a loading frequency of 10 Hz, and a scanning temperature range of -20 °C to 80 °C.

9. The method for characterizing salt loss gradient of asphalt mixture 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 method for characterizing salt loss gradient of asphalt mixture 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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