Asphalt mixture water damage gradient characterization method based on DMA test

Abstract

The invention belongs to the field of road engineering, and particularly relates to an asphalt mixture water damage 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 pieces in the group A in water; 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 water damage gradient coefficient K at the position; according to the method, the defect that the water damage gradient is not considered in an existing water stability evaluation method is overcome, and a scientific basis is provided for asphalt pavement water damage analysis.

Description

Technical Field

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

[0002] Asphalt mixture is a complex material composed of a multiphase system of aggregate, asphalt mortar, and voids. Asphalt mixture applied to the surface of a pavement structure is exposed to the elements for extended periods, allowing a large number of water molecules to contact the surface and penetrate its internal structure through the voids. Under the continuous erosion of water molecules, the molecular structure of asphalt is gradually destroyed, reducing its rheological properties and long-term durability. Furthermore, the thin film formed by water molecules between the asphalt and aggregate hinders direct contact between the asphalt and aggregate, resulting in a decrease in asphalt-aggregate interfacial adhesion and an increased risk of delamination between the asphalt and aggregate. Compared to water damage to the surface layer of asphalt pavement, the extent of internal damage is generally less severe, primarily due to the uneven diffusion of water molecules within the asphalt mixture. Significant differences in water concentration exist within the asphalt mixture at different depths within the pavement structure. The deeper the pavement structure, the lower the water concentration in the asphalt mixture, resulting in varying degrees of water damage to the asphalt mixture at different depths. Currently, asphalt pavement maintenance measures fail to consider the impact of the water damage gradient effect, assuming that the deterioration of asphalt pavement structural layers at different depths is uniform. This prevents the development of objective and reliable maintenance strategies, resulting in a significant waste of natural resources and economic costs. Furthermore, the water damage effect causes the modulus of the asphalt mixture to exhibit a gradient behavior that gradually increases along the depth of the pavement structure, resulting in nonlinear mechanical responses of the asphalt pavement structure and making it difficult to accurately and objectively evaluate the true stress state of the asphalt pavement structure. In summary, it is necessary to accurately characterize the water damage gradient behavior of asphalt mixtures caused by the water damage effect. This is of great engineering significance for achieving more scientific analysis of the mechanical behavior of pavement structures and formulating optimal maintenance measures.

[0003] The "Testing Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" uses the immersion Marshall test or freeze-thaw splitting test as methods for evaluating water damage in asphalt mixtures. The patented "Method for Evaluating Water Stability of Asphalt Mixtures Based on Complex Modulus Damage of Slice Specimens" uses slice modulus to analyze water damage in asphalt mixtures based on dynamic mechanical testing. However, this method assumes that water damage within the asphalt mixture specimen is uniform and fails to consider the gradient effect of water damage within the asphalt mixture. Consequently, its evaluation results differ significantly from the actual water damage of the asphalt mixture.

[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 water damage gradient of asphalt mixture based on DMA testing, which can more accurately characterize the degree of water damage at different positions of asphalt mixture, thereby providing a basis for asphalt pavement water damage analysis and treatment.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for characterizing water damage 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 test pieces into Group A and Group B. Apply sufficient waterproof glue to the bottom and sides of the test pieces in Group A, and leave the test pieces in Group B untreated. Step 3: Immerse the specimens of group A in water; 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 water damage gradient coefficient of the asphalt mixture at that position is obtained by the ratio of . The calculation formula of the water 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.

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

[0008] Furthermore, in step 2, the thickness of the waterproof glue is 1 mm to 2 mm, and the test pieces of group A are immersed in water after the waterproof glue is completely dried.

[0009] Furthermore, in step three, the immersion treatment is to place the specimen vertically in a constant temperature water tank at 50°C to 60°C, with the water covering the specimen to a height of no less than 1 cm, and the immersion time is 36h to 48h.

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

[0011] Furthermore, 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 mm 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. Preferably, the size of the sheet is 30 mm × 10 mm × 3 mm.

[0013] Furthermore, in step five, the DMA scan 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. g ) is an important indicator for evaluating water damage in asphalt mixtures. The results of the literature "Study on the Mechanism of the Influence of Mineral Aggregate and Asphalt Adhesion on Water Damage in Mixtures" show that the glass transition temperature T g The higher the T, the worse the water damage resistance of the asphalt mixture. g It is closely related to its water damage resistance. Under the action of water molecules, the smaller the water damage of asphalt mixture is, the higher the 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, using the glass transition temperature T gIt is feasible to characterize the water damage gradient behavior of asphalt mixture.

[0017] In order to accurately describe the water damage gradient behavior of asphalt mixture, this patent uses a dynamic mechanical analysis (DMA) to conduct a temperature scanning test to obtain a specimen damage factor-test temperature test curve, which can obtain the glass transition temperature T of asphalt mixture at different depths. g The present invention is based on the glass transition temperature T g The correlation between T g Characterize the water damage gradient of specimens at different depths / thicknesses.

[0018] The beneficial effects of the present invention are: The present invention proposes a characterization method for the water damage gradient behavior of asphalt mixture based on the dynamic mechanical analyzer DMA test. It uses DMA to carry out temperature scanning test to obtain the specimen damage factor-test temperature test curve, and obtains the glass transition temperature T of asphalt mixture at different depths. g This method characterizes the water damage gradient, addressing the shortcomings of existing water stability assessment methods that fail to consider the water damage gradient. This invention provides a scientific basis for asphalt pavement water damage analysis, using indicators to reflect the degree of water damage at different thicknesses of asphalt mixtures, thereby reducing maintenance issues caused by improper milling depths. This method offers advantages such as simple specimen formation and compatibility with asphalt mixtures of varying gradations, facilitating more accurate analysis of pavement structural mechanical behavior and optimal maintenance decision-making. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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 a water immersion test according to an embodiment of the present invention.

[0020] Figure 2 Schematic diagram of the slicing position of the slice according to an embodiment of the present invention.

[0021] Figure 3 This is the asphalt mixture loss factor-scanning temperature test curve of an embodiment of the present invention.

[0022] Figure 4 Statistical model of water damage gradient coefficient K and different thicknesses h according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] 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.

[0024] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0025] The target road surface of this embodiment is AC-13 graded asphalt mixture.

[0026] A method for characterizing water damage gradient of asphalt mixture based on DMA test includes the following steps: Step 1. Select 70# matrix asphalt, basalt aggregate and limestone powder; basalt aggregate is divided into four grades: 0~3mm, 3mm~5mm, 5mm~10mm and 10mm~15mm; prepare AC-13 gradation and cylindrical asphalt mixture specimens with a diameter of 100mm and a height of 150mm in accordance with the requirements of the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" for indoor simulated water damage gradient tests.

[0027] Step 2: Divide the specimens into Group A and Group B. Each group of parallel cylindrical specimens consists of three, and the average of the three tests is used as the final test result. Apply sufficient waterproofing adhesive to the bottom and sides of the specimens in Group A for waterproofing. After application, place the asphalt mixture in a dry and ventilated environment and wait for the adhesive to completely dry, according to the adhesive's drying time. Specimens in Group B remain untreated. Select a commercially available waterproofing adhesive with high waterproofing properties, good adhesion, and durability.

[0028] Step 3: Figure 1 As shown, the specimens of group A were placed vertically in a constant temperature water tank at 50℃~60℃ and immersed in water for 36h~48h. The water surface must cover the top surface of the specimen by at least 1cm; the specimens of group B were placed vertically at room temperature for the same time.

[0029] Step 4: After soaking in water, use a cutting machine to core the cylindrical specimens of group A and group B and cut them into N slices from top to bottom. The cut specimens are marked as group A slices and group B slices respectively. The cutting process is as follows: Figure 2 shown.

[0030] Step 5: Perform temperature scanning tests on the thin film specimen at different positions through DMA to obtain the relationship curve between the loss factor and the scanning temperature; by analyzing the peak value of the curve, determine the corresponding temperature as the glass transition temperature T of the thin film specimen. g ,like Figure 3As shown; the DMA test adopts the strain control mode, the applied strain is 25με, the loading frequency is 10Hz, the scanning temperature range is set to -20℃ to 80℃, each test is repeated three times, and the average value of the three results is taken as the final data; T of thin-film specimens at different positions of group A and group B g The test results are summarized in Table 1.

[0031] Table 1 Glass transition temperature results of group A and group B sheets at different positions

[0032] Step 6: Set the glass transition temperature T of the thin slice specimens of group A and group B. g The water damage gradient coefficient at the same position is obtained by comparing the values. The calculation of the water damage gradient coefficient K is shown in formula (1). The results of the water damage gradient coefficient K in this implementation are shown in Table 2.

[0033] (1).

[0034] Table 2 Gradient water damage coefficients of slices in groups A and B at different locations

[0035] The present invention adopts the glass transition temperature T before and after water damage g The ratio of K to K represents the degree of water damage to the asphalt mixture, referred to herein as the water loss coefficient K. The smaller the K value, the greater the degree of water damage to the asphalt mixture. According to the "Technical Specifications for Highway Asphalt Pavement Construction" (JTG F40-2004), the water damage resistance of asphalt mixtures after immersion in water must not be less than 0.8 of the original performance. Furthermore, when the K value is less than 0.8, the mechanical properties of the water-damaged asphalt mixture significantly degrade, requiring maintenance and recycling. Based on this, the present invention sets the critical value of K to 0.8. When the K value at a certain location in the asphalt pavement structure layer is less than 0.8, it can be determined that the asphalt mixture at that thickness requires milling and recycling. According to the water damage gradient results of the specimens in Table 2, in this embodiment, the water loss coefficient K of the thin slices in layers 1, 2, and 3 is less than 0.8. The critical location for the water loss coefficient K of 0.8 is between layers 3 and 4. Therefore, at least 56.381 mm of the road surface needs to be milled away. In practice, to be on the safe side, the road surface milling thickness is 6 cm. If the number of slices can be increased, the layer position closer to the critical value of 0.8 can be obtained, and the thickness of the road surface removed can be reduced.

[0036] Preferably, the asphalt mixture water damage gradient characterization method based on DMA test further includes step seven, constructing a statistical model of water damage gradient K and different depths h, such as Figure 4The model is used to characterize the gradient water damage behavior of asphalt mixture at different depths in an asphalt pavement structure. By inputting the known thickness of the asphalt pavement structure into the model, the water damage gradient at that location can be obtained. Figure 4 In the case of K=-2.2202E-5h 2 +0.0071h+0.5001, where E represents an exponential with base 10, and 2.2202E-5 is a number expressed in scientific notation, representing 0.000022202; the coefficient of determination of this statistical relationship model is R 2 The value of 0.9818 indicates that the model has a very good fit. This model can be used to quantitatively describe the gradient salt damage behavior of asphalt mixtures at different depths within an asphalt pavement structure. By inputting the thickness of a known asphalt pavement structure into the model, the salt damage gradient at that location can be obtained. Alternatively, the formula can be reversed to determine the slice height when the water damage gradient is 0.8. Substituting K = 0.8 into the above formula yields a solution for h of 50.1 mm, indicating that at least 51 mm of road surface must be milled away.

[0037] Furthermore, in step 2, in addition to applying waterproof glue for waterproofing, waterproofing can also be performed by covering with plastic bags, wrapping with plastic wrap, etc., as long as the purpose of waterproofing can be achieved.

[0038] Furthermore, in step 4, 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 between the water damage gradient and the height curve constructed in step 7, and the more accurate the thickness of the road surface finally milled out. However, the more slices there are, the longer it takes. Considering the time efficiency and model accuracy, the preferred number of slices in each group of the present invention is 9.

[0039] 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 sheet is less than 2 mm, it is difficult to cut. Therefore, the sheet size is designed to be 30 mm (length) × 10 mm (width) × 2 mm (thickness) to 35 mm (length) × 14 mm (width) × 3 mm (thickness); preferably, the sheet size is 30 mm (length) × 10 mm (width) × 3 mm (thickness).

[0040] This method utilizes waterproofing measures, such as waterproof glue, to limit water contact to the upper surface of the specimen, simulating actual pavement waterlogging and seepage. Furthermore, compared to traditional direct coring monitoring, the present invention produces multiple thin slices along the thickness of the asphalt pavement, enabling accurate and objective assessment of the true extent of damage to the asphalt pavement structure. This method is suitable for characterizing AC-graded asphalt mixtures commonly used in asphalt pavements, facilitating structural analysis and maintenance decision-making for asphalt pavements. It holds significant engineering significance for achieving more accurate pavement structural design and developing optimal maintenance measures.

[0041] 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 water damage 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 waterproof glue to the bottom and sides of the test pieces in Group A, and leave the test pieces in Group B untreated. Step 3: Immerse the specimens of group A in water; 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 water damage gradient coefficient of the asphalt mixture at that position is obtained by the ratio of . The calculation formula of the water 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 asphalt mixture water damage gradient characterization method based on DMA test according to claim 1 is characterized in that: The method further includes step seven, calculating the water damage gradient coefficient of the asphalt mixture at different positions, and constructing a statistical relationship model between the water damage gradient coefficient and the slice height based on these data.

3. The asphalt mixture water damage gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 2, the thickness of the waterproof glue is 1 mm to 2 mm. After the waterproof glue is completely dry, the test pieces of group A are immersed in water.

4. The asphalt mixture water damage gradient characterization method based on DMA test according to claim 1 is characterized in that: In step three, the immersion treatment is to place the specimen vertically in a constant temperature water tank at 50℃~60℃, with the water covering the specimen to a height of no less than 1cm, and the immersion time is 36h~48h.

5. The asphalt mixture water damage 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 water damage gradient characterization method 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 8mm~12mm, and the thickness of the slices was 3mm. The reserved distance from the slice at the top to the upper surface of the specimen was not less than 5mm, and the reserved distance from the slice at the bottom to the bottom surface of the specimen was not less than 5mm.

7. The asphalt mixture water damage 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 water damage gradient characterization method based on DMA test according to claim 1 is characterized in that: In step 5, the DMA scan 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 method for characterizing water damage 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 water damage 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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