Evaluation method for dispersibility of graphene nanomaterial in asphalt matrix

Abstract

The invention discloses a method for evaluating the dispersity of a graphene nano material in an asphalt matrix. The method comprises the following steps: step 1, preparing a graphene asphalt composite material; step 2, testing three indexes; 3, dynamic rheological property testing; step 4, testing apparent viscosity; and step 5, comprehensive evaluation. According to the evaluation method, the comprehensive dispersity index is calculated by combining the three indexes, the dynamic rheological property and the apparent viscosity, the dispersity of the graphene nano-material in the asphalt matrix is accurately and quantitatively evaluated, a complex microscopic test process is avoided, dispersion information of the nano-material in the asphalt matrix under large-scale production is rapidly provided, and the method is suitable for large-scale production. The method provides theoretical guidance for design, construction and management of the nano-modified asphalt mixture, and is suitable for the technical field of physical property evaluation of modified asphalt.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of physical performance evaluation of modified asphalt, and particularly relates to a method for evaluating dispersibility of graphene nanomaterial in an asphalt matrix. BACKGROUND

[0002] With the vigorous development of the transportation industry and the increase in traffic volume, asphalt pavements are facing more and more challenges, including extreme weather, heavy traffic conditions and the like, which cause a large number of rutting, cracking, loosening and other diseases of asphalt pavements. In order to solve the above problems, modifying asphalt materials to improve their performance is a relatively common method at present.

[0003] Nanomaterials can fundamentally improve the performance of asphalt due to their new properties different from those of macro-sized particles and single atoms, molecules and other micro-particles. Among them, graphene, as a new nanomaterial, is widely used in various engineering fields due to its unique structure and excellent physical properties and stable chemical structure. Uniform dispersion of nanomaterials is a prerequisite for their mechanical strengthening and functional transmission, but due to their high specific surface area and van der Waals force, they are prone to agglomeration when mixed with asphalt, which not only makes it difficult to exert their performance advantages, but also leads to large performance dispersion of asphalt-based composite materials, thereby affecting the performance of modified asphalt. Therefore, it is particularly important to detect whether the nanomaterials are uniformly dispersed in the asphalt matrix.

[0004] At present, the characterization method of the dispersion degree of graphene nanomaterials in asphalt mainly uses modern imaging observation techniques such as atomic force microscopy (AFM), scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction (XRD) for qualitative analysis, and there is no specific characterization parameter for quantitative analysis. These observations have the following disadvantages: (1) not suitable for large quantities of materials on an industrial scale; (2) limited to a small surface area of asphalt and cannot fully characterize the dispersion degree of graphene nanosheets in a large amount of asphalt matrix; (3) the preparation process of modified asphalt samples for SEM or OM observation is relatively complicated, and the observation process requires high professional skills of the test personnel; (4) in addition to generating reflected electrons, the local surface of asphalt may be sputtered due to high temperature under the action of high-energy electron beam, which affects the micro-topography and even contaminates the SEM detection equipment.

[0005] Therefore, it is necessary to propose a dispersion evaluation method for the characteristics of graphene nanomaterials. SUMMARY

[0006] The present application aims to overcome the deficiencies in the prior art, and provides a method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix. The method combines three indicators, dynamic rheological properties, and apparent viscosity calculations to comprehensively evaluate the dispersibility of graphene nanomaterials in an asphalt matrix, solving the problem of qualitative analysis of dispersibility through microscopic detection in the prior art, which cannot be applied to industrial-scale detection.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present application is: a method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix, characterized by comprising the following steps: Step one, preparing graphene asphalt composite material: adding graphene to the asphalt matrix, stirring uniformly and eliminating air bubbles, then pouring into a container, and sealing the container, sequentially standing at 163℃±5℃ for 48h±1h and standing at-2℃ or below for 4h or more, obtaining consolidated asphalt, then dividing the consolidated asphalt into upper, middle and lower parts according to the horizontal height, and melting the upper, middle and lower parts at 163℃±5℃, respectively, to obtain upper, middle and lower graphene asphalt composite materials; Step two, testing three indicators: testing the penetration, softening point and ductility of the upper, middle and lower graphene asphalt composite materials obtained in step one, and calculating the variation coefficients of the penetration, softening point and ductility; Step three, testing dynamic rheological properties: using a DSR dynamic shear rheometer to perform temperature scanning on the upper, middle and lower graphene asphalt composite materials obtained in step one, taking the logarithm of the measured complex shear modulus G* value, and linearly fitting the temperature value in the temperature scanning process, and defining the slope k of the fitted straight line as the temperature sensitivity index, and calculating the variation coefficient of the temperature sensitivity index k; Step four, testing apparent viscosity: using a rotary viscometer to perform 135℃ rotary viscosity testing on the upper, middle and lower graphene asphalt composite materials obtained in step one, and calculating the variation coefficient of the apparent viscosity value; Step five, comprehensive evaluation: setting the weights of the three indicators, dynamic rheological properties, and apparent viscosity tested in steps two to four, combining the variation coefficients calculated from each indicator, obtaining a comprehensive dispersibility index S, and evaluating the dispersibility of graphene nanomaterials in an asphalt matrix.

[0008] The above-mentioned method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix is characterized in that the particle size of the graphene in step one is 100nm-1μm.

[0009] The above-mentioned method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix is characterized in that the height of the container in step one is not less than 100mm.

[0010] The method for evaluating dispersibility of the graphene nanomaterial in the asphalt base body, characterized in that the specific process of the weight setting in step five is: Step 501: The group weight of the three indexes, dynamic rheological property and apparent viscosity is determined by using the analytic hierarchy process, and consistency test is performed; Step 502: The group weight of the three indexes in step two is calculated by using the inverse variance weighting method: , wherein i=1, 2, 3, σ1 is the penetration standard deviation, w1 is the penetration group weight; σ2 is the softening point standard deviation, w2 is the softening point group weight; σ3 is the ductility standard deviation, w3 is the ductility group weight; Step 503: The comprehensive dispersibility index S is calculated according to the group weight and the group weight determined in steps 501 and 502 according to the following formula: ; ; , wherein S is the comprehensive dispersibility index; W A is the group weight of the three indexes; CV A is the coefficient of variation of the three indexes; W B is the group weight of the dynamic rheological property; CV B is the coefficient of variation of the temperature sensitivity index k in the dynamic rheological property; W C is the group weight of the apparent viscosity; CV C is the coefficient of variation of the apparent viscosity value in the apparent viscosity; w1 is the group weight of the penetration; CV1 is the coefficient of variation of the penetration; w2 is the group weight of the softening point; CV2 is the coefficient of variation of the softening point; w3 is the group weight of the ductility; CV3 is the coefficient of variation of the ductility; Step 504: The dispersibility is evaluated according to the comprehensive dispersibility index S calculated in step 503, and the evaluation rules are as follows: S≤3.0, A level, uniform dispersion; 3.0<S≤4.0, B level, good dispersibility, a small amount of agglomeration; 4.0<S≤5.0, C level, general dispersibility, obvious agglomeration exists; S>5.0, D level, poor dispersibility, serious agglomeration; And when any coefficient of variation value is >8%, it is directly evaluated as D level; when any coefficient of variation value is >5% and the level evaluation is A level or B level, it is reduced by one level.

[0011] The application adopts the analytic hierarchy process (AHP) to determine the group weight of the three indexes, dynamic rheological performance and apparent viscosity, forms a judgment matrix by pairing the three indexes, dynamic rheological performance and apparent viscosity with each other to judge the importance (such as 1-9 scale method), deduces the weight, and then performs consistency check to ensure that the consistency ratio CR<0.1, so as to meet the consistency requirement of the analytic hierarchy process, and further ensure that the group weight division is reasonable.

[0012] Compared with the prior art, the application has the following advantages: 1. The uniform dispersion of graphene in the asphalt matrix is the premise for exerting the mechanical strengthening and functional transmission effect, but the existing dispersion characterization means can only characterize the interaction between the nanomaterial and the asphalt matrix at the laboratory scale, cannot be applied to the large amount of materials at the industrial scale, and the characterization is limited to the surface area of the asphalt, and the dispersion in the internal matrix cannot be fully characterized. The evaluation method of the application combines the three indexes, apparent viscosity and complex shear modulus G* to quantitatively evaluate the dispersion characteristics of graphene, avoids the complex microscopic test process, and quickly provides the dispersion information of the nanomaterial in the asphalt matrix at the scale production, which provides theoretical guidance for the design, construction and management of the nanomodified asphalt mixture, and has very important significance.

[0013] 2. The evaluation method of the application uses macroscopic indexes that are more convenient to test to characterize uniformity, effectively reduces the cumbersome microscopic test process, reduces the test cost, avoids the generation of reflected electrons under the action of high-energy electron beam bombardment of the asphalt surface, and the local sputtering due to high temperature, which affects the microscopic morphology and even pollutes the SEM detection equipment.

[0014] 3. The application divides the consolidated asphalt into layers according to the horizontal height, tests the indexes of the samples at different horizontal heights, and quantitatively evaluates the dispersion characteristics of graphene by using the variation coefficients of the indexes of the samples at different heights, which eliminates the dispersion difference of graphene at different heights in the asphalt matrix; in addition, combined with the rating regulation of abnormal variation coefficient, the dispersion of graphene can be more accurately evaluated.

[0015] The technical solutions of the application will be further described in detail through the following examples. DETAILED DESCRIPTION

[0016] Example 1 The evaluation method of this example includes the following steps: Step one, preparation of graphene asphalt composite material: add graphene with particle size of 100 nm~1 μm into 70# base asphalt matrix, use high-speed shearing emulsification homogenizer to stir at 5000 rpm for 30 min at 150℃ and 170℃ respectively, then use glass rod to stir slowly for 10 min to eliminate bubbles, obtain graphene asphalt mixture; the mass of graphene is 0.5% of the mass of 70# base asphalt; Put 50 g of graphene asphalt mixture into an upright aluminum tube (diameter 25 mm, height 140 mm) with one end open, the height of the injection container is not less than 100 mm, then pinch the open end of the aluminum tube into a thin sheet, fold it twice, and clamp it tightly with a clamp, sequentially place it vertically in an oven at 163℃±5℃ for 48 h, and in a refrigerator below-2℃ for 4 h, obtain the solidified asphalt, then divide the solidified asphalt into upper, middle and lower parts according to the horizontal height, melt them at 163℃±5℃ respectively, obtain the upper, middle and lower graphene asphalt composite materials; Step two, three major index tests: according to "Highway Engineering Asphalt and Asphalt Mixture Test Regulations" (JTG E20-2011), test the penetration, softening point and ductility of the upper, middle and lower graphene asphalt composite materials obtained in step one, and calculate the variation coefficients of penetration, softening point and ductility, see Table 1; the penetration test temperature is 25℃, and the ductility test temperature is 10℃; Step three, dynamic rheological property test: according to "Standard Test Method for Determining the Rheological Properties of Asphalt Binder Using the Dynamic Shear Rheometer (DSR)" (AASHTO T 315), use DSR dynamic shear rheometer to perform temperature scanning on the upper, middle and lower graphene asphalt composite materials obtained in step one, take the logarithm of the measured complex shear modulus G* value and linearly fit it with the temperature value in the temperature scanning process, and define the slope k of the fitted straight line as the temperature sensitivity index, calculate the variation coefficient of the temperature sensitivity index k, see Table 2; the temperature scanning temperature is 46℃~82℃, the controlled strain is 0.25%, and the loading frequency is 10 rad / s; Step four, apparent viscosity test: according to "Standard Test Method for Determining the Viscosity of Asphalt Binders Using a Rotational Viscometer" (AASHTO T 316), use a rotational viscometer (Brookfield Viscometer DV-Ⅱ+ Pro) to perform 135℃ rotational viscosity test on the upper, middle and lower graphene asphalt composite materials obtained in step one, and calculate the variation coefficient of the apparent viscosity value, see Table 3; Step five, comprehensive evaluation: set the weights of the three major indexes, dynamic rheological properties and apparent viscosity in steps two to four, and combine the variation coefficients calculated from each index to obtain the comprehensive dispersion index S: Step 501: Use the analytic hierarchy process (AHP) to determine the between-group weights of the three major indicators, dynamic rheological properties, and apparent viscosity. Pair the three major indicators (denoted as A), dynamic rheological properties (denoted as B), and apparent viscosity (denoted as C) and determine their importance: A / B = 1 / 3, A / C = 1 / 2, B / C = 3. Construct a judgment matrix and perform a consistency check to obtain the normalized between-group weights: W A =0.157, W B =0.594, W C =0.249, the largest eigenvalue λmax is 3.0536, the consistency index CI=(λmax-n) / (n-1)=0.0268, the random consistency index RI(n=3)=0.58RI(n!=3)=0.58, the consistency ratio CR=CI / RI=0.046<0.1, which meets the consistency requirements of the analytic hierarchy process; Step 502: Calculate the in-group weights of the three major indicators in Step 2 using the inverse variance weighting method. According to the data in Table 1, the in-group weights of penetration, softening point, and ductility are 0.098, 0.885, and 0.016, respectively. Step 503: Calculate the comprehensive dispersion index S based on the weights determined in steps 501 and 502. =0.7965%; =0.99%; Since S≤3.0, it is grade A, and the coefficient of variation of each item is ≤5%, the final dispersion grade is grade A.

[0017] Example 2 The evaluation method in this embodiment includes the following steps: Step 1: Preparation of graphene-modified asphalt composite material: Graphene with a particle size of 100 nm to 1 μm was added to the SBS modified asphalt matrix. The mixture was continuously stirred at 5000 rpm for 30 min at 150 °C and 170 °C respectively using a high-speed shear emulsification homogenizer. Then, the mixture was slowly stirred with a glass rod for 10 min to eliminate air bubbles, resulting in a graphene-modified asphalt mixture. The mass of the graphene was 0.5% of the mass of the SBS modified asphalt. 50g of graphene asphalt mixture was injected into a vertical aluminum tube (25mm in diameter and 140mm in height) with one end open. The height of the injection into the container was not less than 100mm. Then, the open end of the aluminum tube was pinched into a thin sheet, folded twice, and clamped tightly. The tube was then placed vertically in an oven at 163℃±5℃ for 48 hours and in a refrigerator at -2℃ or below for 4 hours to obtain solidified asphalt. The solidified asphalt was then divided into three equal parts according to the horizontal height: upper, middle, and lower. Each part was melted at 163℃±5℃ to obtain the upper, middle, and lower graphene asphalt composite materials. Step two, three major indicators test: according to the 'highway engineering asphalt and asphalt mixture test regulation' (JTG E20-2011) to the upper, middle, lower three graphene asphalt composite obtained in step one is tested respectively, softening point and ductility, and the variation coefficient of penetration, softening point and ductility is calculated, see table 1; the penetration test temperature is 25℃, the ductility test temperature is 5℃; Step three, dynamic rheological property test: according to'standard test method for determining the rheological properties of asphalt binder using a dynamic shear rheometer (DSR)' (AASHTO T 315), the DSR dynamic shear rheometer is used to scan the temperature of the upper, middle, lower three graphene asphalt composite obtained in step one, the logarithm of the measured composite shear modulus G* value is taken, and the temperature value in the temperature scanning process is linearly fitted, and the slope k of the fitted straight line is defined as the temperature sensitivity index, the variation coefficient of temperature sensitivity index k is calculated, see table 2; the temperature scanning temperature is 46℃~82℃, the control strain is 0.25%, and the loading frequency is 10 rad / s; Step four, apparent viscosity test: according to'standard test method for determining the viscosity of asphalt binders using a rotary viscometer' (AASHTO T 316), the rotary viscometer (Brookfield Viscometer DV-Ⅱ+ Pro) is used to test the 135℃ rotary viscosity of the upper, middle, lower three graphene asphalt composite obtained in step one, and the variation coefficient of apparent viscosity value is calculated, see table 3; Step five, comprehensive evaluation: the three major indicators, dynamic rheological property and apparent viscosity in step two to step four are set weight, and the variation coefficient calculated by each index is obtained to get the comprehensive dispersion index S: Step 501, the intergroup weight of three major indicators, dynamic rheological property and apparent viscosity is judged by using the analytic hierarchy process, the three major indicators (denoted as A), dynamic rheological property (denoted as B) and apparent viscosity (denoted as C) are paired twice to judge the importance: A / B = 1 / 3, A / C = 1 / 2, B / C = 3, the judgment matrix is constructed and the consistency is checked, and the normalized intergroup weight is obtained: W A =0.157, W B =0.594, W C =0.249, the maximum eigenvalue λmax is 3.0536, the consistency index CI=(λmax-n) / (n-1)=0.0268, the random consistency index RI(n=3)=0.58RI(n\!=\!3)=0.58, the consistency ratio CR=CI / RI=0.046<0.1, which meets the consistency requirement of analytic hierarchy process; Step 502, the weight in group of three indexes in step two is calculated by inverse variance weighting method, and the weight in group of penetration, softening point and ductility is 0.288, 0.593 and 0.018 respectively according to the data in table 1; Step 503, according to the weight determined in step 501 and step 502, the comprehensive dispersion index S is calculated: =2.0678%; =1.94%; Since S≤3.0, A level, wherein the coefficient of variation of ductility is greater than 5%, according to the evaluation rules: when any coefficient of variation value is greater than 5% and the grade evaluation is A level or B level, then reduce one level; the final dispersion level is B level.

[0018] Table 1, test results of three indexes of graphene asphalt composite material

[0019] Table 2, test results of dynamic rheological properties of graphene asphalt composite material

[0020] Table 3, test results of apparent viscosity of graphene asphalt composite material

[0021] The above is only the preferred embodiment of the present application, not any limitation on the present application, any simple modification, change and equivalent structure transformation according to the technical essence of the present application to the above embodiment, still belongs to the protection scope of the technical scheme of the present application.

Claims

1. A method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix, characterized in that, It includes the following steps: Step 1. Prepare graphene asphalt composite material: Add graphene into the asphalt matrix, stir evenly to eliminate air bubbles, then inject it into a container, seal the container, and let it stand at 163°C ± 5°C for 48h ± 1h and then at a temperature below -2°C for more than 4h to obtain consolidated asphalt. Then divide the consolidated asphalt into three equal parts, upper, middle, and lower, according to the horizontal height, and melt them at a temperature of 163°C ± 5°C respectively to obtain three parts of graphene asphalt composite material, namely the upper, middle, and lower parts; Step 2. Test of three major indicators: Test the penetration, softening point, and ductility of the upper, middle, and lower parts of the graphene asphalt composite material obtained in Step 1 respectively, and calculate the coefficient of variation of the penetration, softening point, and ductility; Step 3. Test of dynamic rheological properties: Use a DSR dynamic shear rheometer to perform a temperature sweep on the upper, middle, and lower parts of the graphene asphalt composite material obtained in Step 1. Take the logarithm of the measured complex shear modulus G* value and perform a linear fit with the temperature value during the temperature sweep. Define the slope k of the fitted straight line as the temperature sensitivity index, and calculate the coefficient of variation of the temperature sensitivity index k; Step 4. Apparent viscosity test: Use a rotational viscometer to perform a 135°C rotational viscosity test on the upper, middle, and lower parts of the graphene asphalt composite material obtained in Step 1, and calculate the coefficient of variation of the apparent viscosity value; Step 5. Comprehensive evaluation: Set weights for the three major indicators, dynamic rheological properties, and apparent viscosity tested in Steps 2 to 4. Combine the coefficients of variation calculated for each indicator to obtain the comprehensive dispersion index S, and evaluate the dispersion of the graphene nanomaterial in the asphalt matrix.

2. The method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix according to claim 1, characterized in that, The particle size of the graphene described in Step 1 is 100nm - 1μm.

3. The method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix according to claim 1, characterized in that, The height of the injection container described in Step 1 is not less than 100mm.

4. The method for evaluating the dispersibility of graphene nanomaterials in an asphalt matrix according to claim 1, characterized in that, The specific process of the weight setting described in Step 5 is as follows: Step 501. Use the analytic hierarchy process to determine the inter-group weights of the three major indicators, dynamic rheological properties, and apparent viscosity, and conduct a consistency test; Step 502: Calculate the within-group weights of the three major indicators from Step 2 using the inverse variance weighting method: Where i = 1, 2, 3, σ1 is the standard deviation of penetration, w1 is the weight within the penetration group; σ2 is the standard deviation of softening point, w2 is the weight within the softening point group; σ3 is the standard deviation of ductility, w3 is the weight within the ductility group. Step 503. According to the inter-group weights and intra-group weights determined in Step 501 and Step 502, calculate the comprehensive dispersion index S according to the following formula: ； ； Where S is the comprehensive dispersion index; W A The inter-group weights of the three major indicators; CV A The coefficient of variation for the three major indicators; W B Between-group weights for dynamic rheological properties; CV B W is the coefficient of variation of the temperature sensitivity index k in dynamic rheological properties. C The between-group weights for apparent viscosity; CV C 1 is the coefficient of variation of apparent viscosity; w1 is the within-group weight of penetration; CV1 is the coefficient of variation of penetration; w2 is the within-group weight of softening point; CV2 is the coefficient of variation of softening point; w3 is the within-group weight of ductility; CV3 is the coefficient of variation of ductility. Step 504. Evaluate the dispersion according to the comprehensive dispersion index S calculated in Step 503. The evaluation rules are as follows: S ≤ 3.0, Grade A, evenly dispersed; 3.0 < S ≤ 4.0, Grade B, good dispersion, with a small amount of agglomeration; 4.0 < S ≤ 5.0, Grade C, general dispersion, with obvious agglomeration; S > 5.0, Grade D, poor dispersion, with serious agglomeration; And when any coefficient of variation value > 8%, it is directly evaluated as Grade D; when any coefficient of variation value > 5% and the grade evaluation is Grade A or B, it is downgraded by one level.

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