An evaluation method for the conductivity of a conductive asphalt mixture

Abstract

An evaluation method for the conductivity of conductive asphalt mixture, which belongs to the field of technical evaluation of road engineering materials, and specifically relates to an evaluation method for the conductivity of conductive asphalt mixture. The purpose of the present invention is to solve the problems that it is difficult to measure the regional resistance of the current conductive asphalt mixture, the measurement method for evaluating the uniformity of the conductive network structure is complex, the subjectivity is too large, and it is difficult to unify the standards. Method: Step 1, evaluate the conductivity effect of the Marshall specimen of the conductive asphalt mixture with resistivity ρ; Step 2, form a rutting plate specimen of the conductive asphalt mixture; Step 3, calculate the F value of the temperature measurement area; Step 4, evaluate the conductive uniformity distribution of the conductive asphalt mixture with the non-uniformity index. The present invention can determine the actual conductivity effect of the conductive asphalt mixture and promote the popularization and application of conductive road surfaces; the present invention provides guidance for the preliminary design and application evaluation of conductive asphalt mixture, reduces the actual construction cost, and is suitable for popularization.

Description

Technical Field

[0001] The present invention belongs to the technical evaluation field of road engineering materials, and particularly relates to a method for evaluating the conductivity of conductive asphalt mixture. Background Art

[0002] As a widely used material, conductive asphalt mixture can be used for road snow and ice removal, health monitoring, etc. It is an important part of future intelligent roads and has good development prospects. At present, the conductive phase materials of conductive asphalt mixture mainly include graphite, steel fiber, carbon fiber, etc. Agglomeration, uneven dispersion and other phenomena are likely to occur, resulting in too large local resistance and inability to play a role, with poor actual effect, and it is difficult to promote conductive road surfaces on a large scale. Therefore, the evaluation of the conductivity network uniformity has important guiding significance for the practical application of conductive asphalt mixture.

[0003] The current evaluation methods for conductive asphalt mixture mostly use overall resistance evaluation, ignoring the analysis of the conductivity network uniformity. The existing evaluation methods for conductivity network uniformity use methods such as cutting specimens to measure resistance, which are too costly, complex in operation and damage the specimens. The actual resistance also increases due to cutting the specimens, reducing the accuracy. For a simple comparison of the magnitudes of regional resistances, there is no quantitative standard for the evaluation results, and there are certain limitations in application. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating the conductivity of conductive asphalt mixture to solve the problems that it is difficult to measure the regional resistance of current conductive asphalt mixture, the measurement methods for evaluating the uniformity of the conductivity network structure are complex, subjective, and difficult to unify the standards.

[0005] A method for evaluating the conductivity of conductive asphalt mixture includes the following steps:

[0006] Step 1: Sprinkle graphite powder on the contact interface between the Marshall specimen of conductive asphalt mixture and the electrode, and use the two-electrode method to test the resistance value, and evaluate the conductivity effect of the Marshall specimen of conductive asphalt mixture with resistivity ρ; the evaluation criteria are:

[0007] ① If the resistivity ρ > 80 Ω·m, the conductivity performance is unqualified and it is prohibited to use;

[0008] ② If the resistivity ρ ≤ 80 Ω·m, the conductivity performance is qualified and proceed to further evaluation in Step 2;

[0009] The calculation formula for the resistivity ρ in Step 1 is as follows:

[0010]

[0011] In the formula: ρ - resistivity of the specimen (Ω·m);

[0012] R—the resistance of the test piece (Ω);

[0013] S—the cross-sectional area of the test piece (m 2 );

[0014] L—the length of the test piece (m);

[0015] Step 2: Re-form a rutting plate test piece of the electrically conductive asphalt mixture using the same raw materials as the Marshall test piece of the electrically conductive asphalt mixture with qualified electrical conductivity in Step 1; during the forming process of the rutting plate test piece of the electrically conductive asphalt mixture, two copper mesh electrodes are built in, and an indoor heating test is carried out on the rutting plate test piece of the electrically conductive asphalt mixture with two built-in copper mesh electrodes.

[0016] Step 3: Divide the rutting plate test piece of the electrically conductive asphalt mixture into 9 temperature measurement areas to measure the temperature. The 9 temperature measurement areas are arranged in 3 rows and 3 columns. The temperature is measured 5 times in each area. The analysis of variance method is adopted to calculate the F value of the temperature measurement area, and the calculated F value of the temperature measurement area is then compared with the corresponding value in the F value table in the analysis of variance method.

[0017] ① If the F value of the temperature measurement area ≥ the corresponding value in the F value table, the distribution of the conductive network is affected by the position, the distribution of the conductive network is uneven, and the electrical conductivity is unqualified, and it is prohibited from being used.

[0018] ② If the F value of the temperature measurement area < the corresponding value in the F value table, the distribution of the conductive network has no significant influence on the temperature, the distribution of the conductive network is uniform, and the electrical conductivity is qualified, and it enters Step 4 for further evaluation.

[0019] The calculation formula for the F value of the temperature measurement area described in Step 3 is as follows:

[0020]

[0021]

[0022] df b = k - 1;

[0023] df e = p - k;

[0024]

[0025]

[0026]

[0027]

[0028] In the formula: k is the number of temperature measurement areas; r is the number of temperatures measured in a certain temperature measurement area; p—the total number of temperatures measured.

[0029] SS k — Sum of squares of temperature deviations in a certain temperature measurement area; SS b is the sum of squares of temperature deviations between temperature measurement areas, SS e is the sum of squares of temperature deviations within the temperature measurement area, df b is the degree of freedom between temperature measurement areas, df e is the degree of freedom within the temperature measurement area; i is the i-th temperature measurement in a certain temperature measurement area; s is the total number of temperature measurement areas;

[0030] Step Four: Evaluate the conductive uniformity distribution of the conductive asphalt mixture with the non-uniformity index. The smaller the non-uniformity index, the better the network distribution of the conductive asphalt mixture;

[0031] ①. If 0 < H ≤ 0.05, the conductive network distribution uniformity level of the conductive asphalt mixture is excellent and it is recommended for use;

[0032] ②. If 0.05 < H ≤ 0.1, the conductive network distribution uniformity level of the conductive asphalt mixture is good and it can be used without special requirements;

[0033] ③. If 0.1 < H ≤ 0.2, the conductive network distribution uniformity level of the conductive asphalt mixture is qualified and its use should be restricted;

[0034] ④. If H > 0.2, the conductive network distribution uniformity level is unqualified and its use is prohibited;

[0035] The calculation formula for the non-uniformity index described in Step Four is as follows:

[0036]

[0037] In the formula: H is the non-uniformity index, g j,i is the average temperature of the temperature measurement area in the j-th row and i-th column in Step Three, m is the number of rows of the temperature measurement area, and n is the number of columns of the temperature measurement area.

[0038] Compared with the existing methods for evaluating the conductivity of conductive asphalt mixtures, the present invention has the following advantages:

[0039] 1. The invention takes the conductivity network uniformity as the decisive index for evaluating the conductivity of conductive asphalt mixture, which meets the actual application requirements. Sprinkling graphite powder at the contact interface between the conductive asphalt mixture Marshall specimen and the electrode fills the gap between the specimen surface and the electrode, enabling a better contact state between the electrode and the specimen surface, and ensuring that the measured resistance value is close enough to the true resistance of the specimen. Based on the electrothermal effect, using temperature to reflect resistance is simple to operate without additional treatment means, effectively solving the problem of difficult measurement of regional resistance. Introducing variance analysis determines the degree of position influence, providing a prerequisite for analyzing the conductivity network uniformity. Proposing the non-uniformity index improves the reliability of the measurement results, quantitatively evaluates the degree of conductivity network uniformity, and effectively solves the problem of excessive subjectivity and difficulty in unifying standards in the current evaluation of the conductivity network structure uniformity of conductive asphalt mixture, providing data support for determining the actual conductivity application effect evaluation of conductive asphalt mixture.

[0040] 2. The invention can determine the actual conductivity effect of conductive asphalt mixture and promote the popularization and application of conductive pavement.

[0041] 3. The invention provides guidance for the preliminary design application evaluation of conductive asphalt mixture, reduces the actual construction cost, and is suitable for popularization. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of sprinkling graphite powder on the surface of the conductive asphalt mixture Marshall specimen in Step 1 of Example 1 and measuring the resistance value of the specimen using the two-electrode method.

[0043] Figure 2 It is a schematic diagram of the heating test and temperature measurement area division of the conductive asphalt mixture rutting plate with two copper mesh electrodes built in in Step 2 of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0044] DETAILED DESCRIPTION OF THE INVENTION 1: A method for evaluating the conductivity of conductive asphalt mixture includes the following steps:

[0045] Step 1: Sprinkle graphite powder on the contact interface between the conductive asphalt mixture Marshall specimen and the electrode, and use the two-electrode method to measure the resistance value, and evaluate the conductivity effect of the conductive asphalt mixture Marshall specimen with resistivity ρ. The evaluation criteria are as follows:

[0046] ①. If the resistivity ρ > 80 Ω·m, the conductivity performance is unqualified and it is prohibited to use.

[0047] ②. If the resistivity ρ ≤ 80 Ω·m, the conductivity performance is qualified and proceed to Step 2 for further evaluation.

[0048] The calculation formula for the resistivity ρ in Step 1 is as follows:

[0049]

[0050] Where: ρ—the resistivity of the test piece (Ω·m);

[0051] R—the resistance of the test piece (Ω);

[0052] S—the cross-sectional area of the test piece (m 2 );

[0053] L—the length of the test piece (m);

[0054] Step 2: Re-form a rutting plate test piece of the electrically conductive asphalt mixture using the same raw materials as the Marshall test piece of the electrically conductive asphalt mixture with qualified electrical conductivity in Step 1; during the forming process of the rutting plate test piece of the electrically conductive asphalt mixture, two copper mesh electrodes are built in, and an indoor heating test is carried out on the rutting plate test piece of the electrically conductive asphalt mixture with two built-in copper mesh electrodes;

[0055] Step 3: Divide the rutting plate test piece of the electrically conductive asphalt mixture into 9 temperature measurement areas to measure the temperature. The 9 temperature measurement areas are arranged in 3 rows and 3 columns. The temperature is measured 5 times in each area. The variance analysis method is adopted to calculate the F value of the temperature measurement area, and the calculated F value of the temperature measurement area is then compared with the corresponding value in the F value table in the variance analysis method;

[0056] ① If the F value of the temperature measurement area ≥ the corresponding value in the F value table, the distribution of the conductive network is affected by the position, the distribution of the conductive network is uneven, and the electrical conductivity is unqualified, and it is prohibited from being used;

[0057] ② If the F value of the temperature measurement area < the corresponding value in the F value table, the distribution of the conductive network has no significant influence on the temperature, the distribution of the conductive network is uniform, and the electrical conductivity is qualified, and it enters the further evaluation in Step 4;

[0058] The calculation formula for the F value of the temperature measurement area described in Step 3 is as follows:

[0059]

[0060]

[0061] df b = k - 1;

[0062] df e = p - k;

[0063]

[0064]

[0065]

[0066]

[0067] Where: k is the number of temperature measurement regions; r is the number of temperatures measured in a certain temperature measurement region; p is the total number of temperatures measured;

[0068] SS k — The sum of squares of temperature deviations in a certain temperature measurement region; SS b is the sum of squares of temperature deviations between temperature measurement regions, SS e is the sum of squares of temperature deviations within the temperature measurement region, df b is the degree of freedom between temperature measurement regions, df e is the degree of freedom within the temperature measurement region; i is the i-th temperature measurement in a certain temperature measurement region; s is the total number of temperature measurement regions;

[0069] Step Four: Evaluate the conductive uniformity distribution of the conductive asphalt mixture with the non-uniformity index. The smaller the non-uniformity index, the better the network distribution of the conductive asphalt mixture;

[0070] ①. If 0 < H ≤ 0.05, the conductive network distribution uniformity level of the conductive asphalt mixture is excellent, and it is recommended to use;

[0071] ②. If 0.05 < H ≤ 0.1, the conductive network distribution uniformity level of the conductive asphalt mixture is good, and it can be used without special requirements;

[0072] ③. If 0.1 < H ≤ 0.2, the conductive network distribution uniformity level of the conductive asphalt mixture is qualified, and its use should be restricted;

[0073] ④. If H > 0.2, the conductive network distribution uniformity level is unqualified, and it is prohibited to use;

[0074] The calculation formula of the non-uniformity index described in Step Four is as follows:

[0075]

[0076] Where: H is the non-uniformity index, g j,i is the average temperature of the temperature measurement region in the j-th row and i-th column in Step Three, m is the number of rows of the temperature measurement region, and n is the number of columns of the temperature measurement region.

[0077] In this embodiment, graphite powder is spread on the contact interface between the specimen and the electrode to fill the gap between the surface of the specimen and the electrode, so that the electrode and the surface of the specimen reach a better contact state, thereby ensuring that the measured resistance value is close enough to the true resistance of the specimen.

[0078] This embodiment is based on the electrothermal reaction, and the conductive network distribution is characterized by temperature.

[0079] Embodiment 2: The difference between this embodiment and Embodiment 1 is that: the size of the conductive asphalt mixture rutting plate specimen described in step 2 is 300 mm × 300 mm × 50 mm. Other steps are the same as those in Embodiment 1.

[0080] Embodiment 3: The difference between this embodiment and either Embodiment 1 or 2 is that: the two copper mesh electrodes described in step 2 are respectively parallel to the plane of the conductive asphalt mixture rutting plate specimen, and the distance between the two copper mesh electrodes is 30 mm. Other steps are the same as those in Embodiment 1 or 2.

[0081] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that: the structure of the conductive asphalt mixture rutting plate specimen described in step 2 from top to bottom is successively a 10-mm conductive asphalt mixture layer, a copper mesh electrode, a 30-mm conductive asphalt mixture layer, a copper mesh electrode, and a 10-mm conductive asphalt mixture layer. Other steps are the same as those in Embodiments 1 to 3.

[0082] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that: the indoor heating test described in step 2 is as follows: apply a voltage of 30 V to the two copper mesh electrodes, and the initial input power is 366 W / m 2 , and the power-on time is 60 min. Other steps are the same as those in Embodiments 1 to 4.

[0083] The following examples are used to verify the beneficial effects of the present invention:

[0084] Example 1: A method for evaluating the conductivity of a conductive asphalt mixture, comprising the following steps:

[0085] Step 1. Prepare a Marshall specimen of conductive asphalt mixture:

[0086] Use the AC-13 median gradation in the suspension-dense structure as the target gradation. The gradation composition is shown in Table 1, and the asphalt-aggregate ratio is 5%.

[0087] Table 1 Target gradation composition

[0088]

[0089] The asphalt is 90# base asphalt, and the material properties are shown in Table 2:

[0090] Table 2 Asphalt material properties

[0091]

[0092] The aggregate and mineral powder are limestone.

[0093] Heat both the coarse aggregate and the fine aggregate to 140°C, then simultaneously put them into a mixing pot at 160°C and stir for more than 90 seconds until a uniformly mixed solid mixture is obtained. Add the flowing No. 90 asphalt and mix until there is no unmixed asphalt; finally, add mineral powder and stir until it is fully uniform, and obtain Marshall specimens of conductive asphalt mixture according to the indoor compaction molding method.

[0094] Demold after cooling for more than 24 hours;

[0095] Step 2: Sprinkle graphite powder on the contact interface between the Marshall specimen of conductive asphalt mixture and the electrode, and use the two-electrode method to test the resistance value, and evaluate the conductivity of the Marshall specimen of conductive asphalt mixture with resistivity ρ; the evaluation criteria are:

[0096] ①. If the resistivity ρ > 80 Ω·m, the conductivity is unqualified;

[0097] ②. If the resistivity ρ ≤ 80 Ω·m, the conductivity is qualified and enter the further evaluation in Step 2;

[0098] The calculation formula for the resistivity ρ described in Step 1 is as follows:

[0099]

[0100] In the formula: ρ—resistivity of the specimen (Ω·m);

[0101] R—resistance of the specimen (Ω);

[0102] S—cross-sectional area of the specimen (m 2 )

[0103] L—length of the specimen (m);

[0104] The detection method in Step 2 is as Figure 1 shown, and the test result is: the resistance value shows that it exceeds the range of the multimeter, it does not have conductivity, it is unqualified, and it is prohibited from being used.

[0105] Example 2: A method for evaluating the conductivity of a conductive asphalt mixture, comprising the following steps:

[0106] Step 1: Prepare a Marshall specimen of carbon fiber conductive asphalt mixture:

[0107] Adopt the AC-13 median gradation in the suspension-dense structure as the target gradation, add 0.3% carbon fiber, and the gradation composition is shown in Table 3, and the asphalt-aggregate ratio is 5.2%.

[0108] Table 3 Target gradation composition

[0109]

[0110] The asphalt is 90# matrix asphalt, and its material properties are shown in Table 4:

[0111] Table 4 Asphalt Material Properties

[0112]

[0113] The aggregate and mineral powder are limestone.

[0114] The carbon fiber uses 6mm long polyacrylonitrile (PAN) based chopped carbon fiber. The basic parameters of the carbon fiber are shown in Table 5.

[0115] Table 5 Basic Parameters of Carbon Fiber

[0116]

[0117] Heat both the coarse aggregate and the fine aggregate to 140°C, then simultaneously put them into a mixing pot at 160°C and stir well for more than 90 seconds until a uniformly mixed solid mixture is obtained. Add 90# asphalt in a flowing state and mix until there is no white and gray material; after the asphalt and aggregate are evenly mixed, add 6mm polyacrylonitrile (PAN) based chopped carbon fiber in an external admixture form and stir for 60 seconds to prevent fiber agglomeration; finally, add mineral powder and stir until fully uniform, and obtain the conductive asphalt mixture according to the indoor forming method. Obtain the Marshall specimens of the conductive asphalt mixture according to the indoor compaction forming method. Demold after cooling for more than 24 hours;

[0118] Step 2: Sprinkle graphite powder on the contact interface between the Marshall specimen of the carbon fiber conductive asphalt mixture and the electrode, and use the two-electrode method to measure the resistance value, and evaluate the conductive effect of the Marshall specimen of the carbon fiber conductive asphalt mixture with resistivity ρ; the evaluation criteria are:

[0119] ①. If the resistivity ρ > 80 Ω·m, the conductivity is unqualified;

[0120] ②. If the resistivity ρ ≤ 80 Ω·m, the conductivity is qualified and enter the further evaluation in Step 2;

[0121] The calculation formula of the resistivity ρ described in Step 1 is as follows:

[0122]

[0123] In the formula: ρ—resistivity of the specimen (Ω·m);

[0124] R—resistance of the specimen (Ω);

[0125] S—cross-sectional area of the specimen (m 2 )

[0126] L—length of the specimen (m);

[0127] The test result shows that the resistivity of the Marshall specimen of carbon fiber conductive asphalt mixture is 25.1 Ω·m, and its conductivity is qualified, then it enters the further evaluation in Step 3;

[0128] Step 3: Remold the rutting plate specimen of conductive asphalt mixture with the same raw materials as the Marshall specimen of conductive asphalt mixture with qualified conductivity in Step 2; During the molding process of the rutting plate specimen of conductive asphalt mixture, two copper mesh electrodes are built in, and an indoor heating test is carried out on the rutting plate specimen of conductive asphalt mixture with two built-in copper mesh electrodes;

[0129] The size of the rutting plate specimen of conductive asphalt mixture described in Step 3 is 300 mm×300 mm×50 mm;

[0130] The two copper mesh electrodes described in Step 3 are respectively parallel to the plane of the rutting plate specimen of conductive asphalt mixture, and the distance between the two copper mesh electrodes is 30 mm;

[0131] The structure of the rutting plate specimen of conductive asphalt mixture described in Step 3 from top to bottom is successively a 10-mm conductive asphalt mixture layer, a copper mesh electrode, a 30-mm conductive asphalt mixture layer, a copper mesh electrode, and a 10-mm conductive asphalt mixture layer;

[0132] The indoor heating test described in Step 3 is as follows: Input a voltage of 30 V to the two copper mesh electrodes, the initial input power is 366 W / m 2 , the power-on time is 60 min, and the schematic diagram is shown in Figure 2 as follows;

[0133] Step 4: Divide the rutting plate specimen of conductive asphalt mixture into 9 temperature measurement regions to measure the temperature, measure the temperature 5 times in each region, adopt the analysis of variance method, calculate the F value of the temperature measurement region, and then compare the calculated F value of the temperature measurement region with the corresponding value in the F value table in the analysis of variance method;

[0134] ①. If the F value of the temperature measurement region ≥ the corresponding value in the F value table, it means that the distribution of the conductive network is affected by the position, the distribution of the conductive network is uneven, and the conductivity is unqualified;

[0135] ②. If the F value of the temperature measurement region < the corresponding value in the F value table, it means that the distribution of the conductive network has no significant influence on the temperature, the distribution of the conductive network is uniform, the conductivity is qualified, and it enters the further evaluation in Step 5;

[0136] The calculation formula of the F value of the temperature measurement region described in Step 4 is as follows:

[0137]

[0138]

[0139] df b= k - 1;

[0140] df e = p - k;

[0141]

[0142]

[0143]

[0144]

[0145] Where: k is the number of temperature measurement regions; r is the number of temperatures measured in a certain temperature measurement region; p—the total number of measured temperatures;

[0146] SS k —The sum of squares of temperature deviations in a certain temperature measurement region; SS b is the sum of squares of temperature deviations between temperature measurement regions, SS e is the sum of squares of temperature deviations within the temperature measurement region, df b is the degree of freedom between temperature measurement regions, df e is the degree of freedom within the temperature measurement region; i is the i-th temperature measurement in a certain temperature measurement region; s is the total number of temperature measurement regions;

[0147] The F value of the temperature measurement region is shown in Table 6;

[0148] Table 6

[0149]

[0150] Result: Refer to the F value table, F 0.05 (8, 36) = 2.28. Within the 95% confidence interval, the resistance is not affected by the position and the conductivity is qualified. Proceed to the further evaluation in Step Five;

[0151] Step Five: Evaluate the conductive uniformity distribution of the conductive asphalt mixture with the non-uniformity index. The smaller the non-uniformity index, the better the network distribution of the conductive asphalt mixture;

[0152] The calculation formula for the non-uniformity index described in Step Five is as follows:

[0153]

[0154] Where: H is the non-uniformity index, g j,i is the average temperature of the temperature measurement region in the j-th row and i-th column, m is the number of rows of the temperature measurement region, and n is the number of columns of the temperature measurement region;

[0155] The inhomogeneity index H is calculated to be 0.14267, that is, 0.1 < H ≤ 0.2. Then, the conductivity network distribution uniformity level of the conductive asphalt mixture is qualified, and its use should be restricted.

[0156] Example 3: A method for evaluating the conductivity of a conductive asphalt mixture, comprising the following steps:

[0157] Step 1: Prepare Marshall specimens of graphite tailings conductive asphalt mixture:

[0158] Use the AC-13 median gradation in the suspension-dense structure as the target gradation. The graphite tailings completely replace the fine aggregate, with a proportion of 12%, the carbon fiber content is 0.3%, the asphalt-aggregate ratio is 5.2%, and the gradation composition is shown in Table 7.

[0159] Table 7 Target gradation composition

[0160]

[0161] The asphalt is 90# base asphalt, and the material properties are shown in Table 8:

[0162] Table 8 Asphalt material properties

[0163]

[0164] The aggregate and mineral powder are limestone.

[0165] The carbon fiber uses 6mm long polyacrylonitrile (PAN)-based chopped carbon fiber. The basic parameters of the carbon fiber are shown in Table 5.

[0166] Table 9 Basic parameters of carbon fiber

[0167]

[0168] The graphite tailings are from a certain graphite tailings in Luobei. The mineral composition of the tailings is shown in Table 10; the gradation composition of the tailings is shown in Table 11.

[0169] Table 10 Mineral composition of tailings

[0170]

[0171] Table 11 Screening results of a certain graphite tailings in Luobei

[0172]

[0173] Replace the fine aggregate with graphite tailings. Without special treatment, heat and mix it completely according to the treatment method of the fine aggregate in the asphalt mixture forming process. Heat the coarse aggregate and graphite tailings to 140 °C, and then put them into the mixing pot at 160 °C and stir well for more than 90 seconds until a uniformly mixed solid mixture is obtained.

[0174] Add 90# asphalt in a flowing state to the mixture of graphite tailings and coarse aggregate and mix until no white and flower-like materials are produced; after the asphalt and aggregate are evenly mixed, add polyacrylonitrile (PAN)-based short carbon fibers accounting for 0.3% of the specific gravity of the asphalt mixture in an external addition form and stir for 60 seconds. The lengths of the carbon fibers are 6 mm respectively to prevent fiber agglomeration; finally, add mineral powder and stir until fully uniform, and obtain Marshall specimens of graphite tailings conductive asphalt mixture according to the indoor forming method;

[0175] Step 2: Sprinkle graphite powder on the contact interface between the Marshall specimen of graphite tailings conductive asphalt mixture and the electrode, and use the two-electrode method to measure the resistance value, and evaluate the conductivity of the Marshall specimen of conductive asphalt mixture with resistivity ρ; The evaluation criteria are:

[0176] ① If the resistivity ρ > 80 Ω·m, the conductivity is unqualified;

[0177] ② If the resistivity ρ ≤ 80 Ω·m, the conductivity is qualified and enter the further evaluation in Step 2;

[0178] The calculation formula for the resistivity ρ described in Step 1 is as follows:

[0179]

[0180] In the formula: ρ—resistivity of the specimen (Ω·m);

[0181] R—resistance of the specimen (Ω);

[0182] S—cross-sectional area of the specimen (m 2 );

[0183] L—length of the specimen (m);

[0184] Result: The measured result of the resistivity of the Marshall specimen of graphite tailings conductive asphalt mixture is 8.17 Ω·m, and the conductivity is qualified. Proceed to the further evaluation of the uniformity of the conductive network in Step 3;

[0185] Step 3: Re-form a rutting plate specimen of conductive asphalt mixture with the same raw materials as the Marshall specimen of conductive asphalt mixture with qualified conductivity in Step 2; During the forming process of the rutting plate specimen of conductive asphalt mixture, two copper mesh electrodes are built in, and an indoor heating test is carried out on the rutting plate specimen of conductive asphalt mixture with two built-in copper mesh electrodes;

[0186] The size of the rutting plate specimen of conductive asphalt mixture described in Step 3 is 300 mm × 300 mm × 50 mm;

[0187] The two copper mesh electrodes described in Step 3 are respectively parallel to the plane of the rutting plate specimen of conductive asphalt mixture, and the distance between the two copper mesh electrodes is 30 mm;

[0188] In the rutting plate specimen of the conductive asphalt mixture described in Step 3, the structure from top to bottom is successively a 10-mm conductive asphalt mixture layer, a copper mesh electrode, a 30-mm conductive asphalt mixture layer, a copper mesh electrode, and a 10-mm conductive asphalt mixture layer;

[0189] The indoor heating test described in Step 3 is as follows: Input a voltage of 30 V to the two copper mesh electrodes, and the initial input power is 366 W / m 2 , and the power-on time is 60 min;

[0190] Step 4: Divide the rutting plate specimen of the conductive asphalt mixture into 9 temperature measurement areas to measure the temperature. Measure the temperature 5 times in each area. Use the analysis of variance method to evaluate the temperature measurement results. Determine the F value of the temperature measurement area as shown in Table 12. Within the 95% confidence interval, it is considered that the position has no influence on the measured results, the conductive network is evenly distributed, and it can be used. Consult the F value table, F 0.05 (8, 36) = 2.28. Within the 95% confidence interval, the resistance is not affected by the position, the conductivity is qualified, and proceed to further evaluation in Step 5.

[0191] Table 12

[0192]

[0193] The calculation formula for the F value of the temperature measurement area described in Step 4 is as follows:

[0194]

[0195]

[0196] df b = k - 1;

[0197] df e = p - k;

[0198]

[0199]

[0200] .

[0201]

[0202] In the formula: k is the number of temperature measurement areas; r is the number of temperatures measured in a certain temperature measurement area; p is the total number of temperatures measured;

[0203] SS k — The sum of squares of deviations of temperatures in a certain temperature measurement area; SS b is the sum of squares of deviations of temperatures between temperature measurement areas, SSe is the sum of squares of temperature deviations within the temperature measurement area, df b is the degree of freedom between temperature measurement areas, df e is the degree of freedom within the temperature measurement area; i is the i-th temperature measurement of a certain temperature measurement area; s is the total number of temperature measurement areas;

[0204] Step Five: Evaluate the conductive uniformity distribution of the conductive asphalt mixture with the non-uniformity index. The smaller the non-uniformity index, the better the network distribution of the conductive asphalt mixture;

[0205] The calculation formula of the non-uniformity index described in Step Five is as follows:

[0206]

[0207] In the formula: H is the non-uniformity index, g j,i is the average temperature of the temperature measurement area in the j-th row and i-th column, m is the number of rows of the temperature measurement area, and n is the number of columns of the temperature measurement area;

[0208] The non-uniformity index H is calculated to be 0.02843, that is, 0 < H ≤ 0.05, then the conductive network distribution uniformity grade of the conductive asphalt mixture is excellent and it is recommended for use.

Claims

1. A method for evaluating the conductivity of a conductive asphalt mixture, characterized in that The evaluation method includes the following steps: Step 1: Sprinkle graphite powder on the contact interface between the Marshall specimen of conductive asphalt mixture and the electrode, and use the two-electrode method to measure the resistance value. Evaluate the conductivity effect of the Marshall specimen of conductive asphalt mixture with the resistivity ρ of the specimen. The evaluation criteria are as follows: ① If the resistivity ρ of the specimen > 80 Ω·m, the conductivity is unqualified and it is prohibited to use; ② If the resistivity ρ of the specimen ≤ 80 Ω·m, the conductivity is qualified and proceed to the further evaluation in Step 2; The calculation formula for the resistivity ρ of the specimen described in Step 1 is as follows: In the formula: ρ—the resistivity of the specimen, unit is Ω·m; R—the resistance of the specimen, unit is Ω; S—the cross-sectional area of the specimen, unit: m 2 ; L—the length of the specimen, unit is m; Step 2: Re-form a rutting plate specimen of conductive asphalt mixture with the same raw materials as the Marshall specimen of conductive asphalt mixture with qualified conductivity in Step 1. During the forming process of the rutting plate specimen of conductive asphalt mixture, two copper mesh electrodes are built in, and an indoor heating test is carried out on the rutting plate specimen of conductive asphalt mixture with two built-in copper mesh electrodes; Step 3: Divide the rutting plate specimen of conductive asphalt mixture into 9 temperature measurement areas to measure the temperature. The 9 temperature measurement areas are arranged in 3 rows and 3 columns. Measure the temperature 5 times in each area. Adopt the analysis of variance method to calculate the F value of the temperature measurement area, and then compare the calculated F value of the temperature measurement area with the corresponding value in the F value table in the analysis of variance method; ① If the F value of the temperature measurement area ≥ the corresponding value in the F value table, the distribution of the conductive network is affected by the position, the distribution of the conductive network is uneven, and the conductivity is unqualified and it is prohibited to use; ② If the F value of the temperature measurement area < the corresponding value in the F value table, the distribution of the conductive network has no significant influence on the temperature, the distribution of the conductive network is uniform, and the conductivity is qualified and proceed to the further evaluation in Step 4; The calculation formula for the F value of the temperature measurement area described in Step 3 is as follows: df b = k - 1; df e = p - k; Where: k is the number of temperature measurement regions; r is the number of temperatures measured in a certain temperature measurement region; p is the total number of measured temperatures; SS k — The sum of squares of temperature deviations in a certain temperature measurement region; SS b is the sum of squares of temperature deviations between temperature measurement regions, SS e is the sum of squares of temperature deviations within a temperature measurement region, df b is the degree of freedom between temperature measurement regions, df e is the degree of freedom within a temperature measurement region; i is the i-th temperature measurement in a certain temperature measurement region; s is the total number of temperature measurement regions; Step 4: Evaluate the conductive uniformity distribution of the conductive asphalt mixture with the non-uniformity index. The smaller the non-uniformity index, the better the network distribution of the conductive asphalt mixture; ① If 0 < H ≤ 0.05, the conductive network distribution uniformity level of the conductive asphalt mixture is excellent and it is recommended to use; ② If 0.05 < H ≤ 0.1, the conductive network distribution uniformity level of the conductive asphalt mixture is good and it can be used without special requirements; ③ If 0.1 < H ≤ 0.2, the conductive network distribution uniformity level of the conductive asphalt mixture is qualified and its use should be restricted; ④ If H > 0.2, the conductive network distribution uniformity level is unqualified and it is prohibited to use; The calculation formula for the non-uniformity index described in Step 4 is as follows: Where: H is the inhomogeneity index, and g j,i is the average temperature of the temperature measurement area in the j-th row and the i-th column in the third step, m is the number of rows of the temperature measurement area, and n is the number of columns of the temperature measurement area.

2. The evaluation method for the conductivity of a conductive asphalt mixture according to claim 1, characterized in that The size of the rutting plate specimen of conductive asphalt mixture described in Step 2 is 300 mm × 300 mm × 50 mm.

3. The evaluation method for the conductivity of a conductive asphalt mixture according to claim 1, characterized in that The two copper mesh electrodes described in Step 2 are respectively parallel to the plane of the rutting plate specimen of conductive asphalt mixture, and the distance between the two copper mesh electrodes is 30 mm.

4. The evaluation method for the conductivity of a conductive asphalt mixture according to claim 1, characterized in that The structure of the rutting plate specimen of conductive asphalt mixture described in Step 2 from top to bottom is successively a 10-mm conductive asphalt mixture layer, a copper mesh electrode, a 30-mm conductive asphalt mixture layer, a copper mesh electrode, and a 10-mm conductive asphalt mixture layer.

5. The evaluation method for the conductivity of a conductive asphalt mixture according to claim 1, wherein The indoor temperature increase test described in Step 2 is as follows: Apply a voltage of 30V to two copper mesh electrodes, with an initial input power of 366W / m 2 , and the power-on time is 60 minutes.

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