Method for testing compactness of road asphalt surface layer based on dielectric constant

Abstract

The invention discloses a method for testing the compactness of a road asphalt surface layer based on dielectric constants, which relates to the technical field of road engineering, can be applied to the detection work of the compactness of a road asphalt pavement, and comprises the following steps of: testing the relative dielectric constants at all test points in a to-be-tested area of the road asphalt surface layer by adopting a ground penetrating radar; calculating a relative dielectric constant of a mucilage phase in the asphalt surface layer at each measuring point; calculating the volume fraction of a void phase in the asphalt surface layer at each measuring point; calculating the normalized total volume of gaps in the asphalt surface layer at each measuring point; calculating the total density of the asphalt surface layer at each measuring point; and calculating the compaction degree in the asphalt surface layer at each measuring point.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering, and in particular to a method for testing the compactness of a highway asphalt surface layer based on a dielectric constant. Background Art

[0002] Compaction refers to the ratio of the dry density of soil or other road construction materials after compaction to the standard maximum dry density, usually expressed as a percentage. In civil engineering, compaction is a key technical indicator used to measure the compaction quality of structural layers such as roadbeds and pavements. In the construction of highway asphalt pavement, sufficient compaction is the basis for ensuring the bearing capacity of the asphalt pavement structure. In the existing technology, the test is relatively complicated and damages the road surface. It is mainly carried out by coring the test point after compaction is completed, and the density of the core sample is tested indoors. The compaction is calculated by the ratio of the measured density to the standard density. Since the test points are randomly selected and the number is limited, this method has a low coverage rate. And because the core drilling is generally carried out after the construction is completed, the asphalt concrete is basically formed at this time, and there is no way to repair it even if you know there is a problem. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for testing the compactness of a highway asphalt surface layer based on dielectric constant. The testing method comprises the following steps:

[0004] S1. Use ground penetrating radar to test the relative dielectric constant of each measuring point in the test area of ​​the highway asphalt surface layer;

[0005] S2. Calculate the relative dielectric constant of the mortar phase in the asphalt surface layer at each measuring point;

[0006] S3, calculating the volume fraction of the void phase in the asphalt surface layer at each measuring point;

[0007] S4. Calculate the normalized total volume of voids in the asphalt surface layer at each measuring point;

[0008] S5. Calculate the total density of the asphalt surface layer at each measuring point;

[0009] S6. Calculate the degree of compaction in the asphalt surface layer at each measuring point.

[0010] According to the type of asphalt used in the asphalt surface layer, it is divided into base asphalt and SBS modified asphalt. SBS modified asphalt is made of base asphalt, and a certain proportion of SBS (styrene-butadiene-styrene) modifier is added. SBS is evenly dispersed in the asphalt through shearing, stirring and other methods. At the same time, a certain proportion of exclusive stabilizer is added to form an SBS blended material. The oil-stone ratio is the ratio of asphalt to aggregate. During construction, there will be a clear value based on the actual project. Usually, it will fluctuate in the range of 3%-6% according to the different proportions of asphalt. Generally, when designing the pavement, indoor tests will be conducted to design the mix ratio to obtain the mass fraction P of the mineral powder content in the total mass of aggregate and mineral powder, as well as the oil-stone ratio. For specific projects and specific materials, the values ​​will fluctuate slightly. In normal industry construction, these two parameters are predetermined.

[0011] The present invention can continuously measure the dielectric constant of each measuring point of the asphalt surface layer through ground penetrating radar, and use the overall dielectric constant to first calculate the volume fraction of the void phase, and then calculate the total density of the asphalt surface layer, and then calculate the compaction degree of each location, which significantly improves the coverage rate and efficiency. In the calculation, the dielectric correction factor, gradation correction factor, and density correction factor are introduced to further improve the calculation accuracy.

[0012] Furthermore, in step S1, the relative dielectric constant at each measuring point in the test area of ​​the highway asphalt surface layer is tested by using a ground penetrating radar and a two-way travel time method. In the test, if the two-way travel time of the electromagnetic wave emitted by the ground penetrating radar at a certain measuring point between the top and the bottom of the asphalt surface layer is recorded as t, the thickness of the asphalt surface layer is recorded as h, and the electromagnetic wave speed in vacuum is recorded as c, then the relative dielectric constant ε at this measuring point is calculated by formula (1).

[0013]

[0014] Furthermore, the step S2 specifically includes the following steps:

[0015] S2.1. Calculate the first dielectric correction factor K using formula (2) 1 In the formula, ε 矿粉 and ε 沥青 are the relative dielectric constants of mineral powder and asphalt used in the measured asphalt surface layer, and different formulas are used to calculate the first dielectric correction factor K. 1 ;

[0016]

[0017] S2.2. Calculate the second dielectric correction factor K using formula (3) 2 According to the type of asphalt used in the asphalt surface layer, it is divided into two categories: base asphalt and SBS modified asphalt. Different formulas are used to calculate the second dielectric correction factor K. 2 ;

[0018]

[0019] S2.3. Calculate the relative dielectric constant ε of the mortar phase in the asphalt surface layer at each measuring point using formula (4): 胶浆 , where P is the mass fraction of the mineral powder content in the asphalt surface grading curve to the total mass of aggregate and mineral powder, ρ 沥青 and ρ 矿粉 are the gross volume densities of asphalt and mineral powder in the asphalt surface layer respectively, and R is the oil-stone ratio of the asphalt surface layer.

[0020]

[0021] Furthermore, the step S3 specifically includes the following steps:

[0022] S3.1. Calculate the gradation correction coefficient K according to formula (5) 3 ;

[0023]

[0024] S3.2. According to formula (6), calculate the volume fraction C of the void phase in the asphalt surface layer at each measuring point. 空隙 , where ε 集料 is the relative dielectric constant of aggregate in the asphalt pavement.

[0025]

[0026] Furthermore, in step S4, the normalized total volume V of the voids in the asphalt surface layer at each measuring point is calculated by formula (7): 空隙 , where ρ 集料 It is the gross volume density of aggregate in the asphalt pavement.

[0027]

[0028] Furthermore, the step S5 specifically includes the following steps:

[0029] S5.1. Calculate the density correction factor K according to formula (8): 4 ;

[0030]

[0031] S5.2. Calculate the total density ρ of the asphalt surface layer at each measuring point using formula (9).

[0032]

[0033] Furthermore, in step S6, the compaction degree K at each measuring point of the asphalt surface layer is calculated by formula (10), where ρ 标 It is the standard density of asphalt pavement.

[0034]

[0035] Beneficial effects: The present invention provides a method for testing the compaction of highway asphalt pavement based on dielectric constant. The dielectric constant of each measuring point can be continuously measured by ground penetrating radar, and the compaction degree of each location can be calculated accordingly. Our method is to perform non-destructive testing on the road surface. The distance between adjacent measuring points can be reduced to less than 1 meter, and any point on the road surface can be measured. The coverage rate and efficiency are significantly improved, and real-time detection can be performed during the construction process. If problems are found, the plan can be revised immediately, such as re-compacting, to maximize the quality of pavement compaction. In addition, dielectric correction coefficients, gradation correction coefficients, and density correction coefficients are introduced, and different calculation formulas are provided for the base asphalt and SBS modified asphalt commonly used in asphalt pavement to further improve the calculation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0037] The following is combined with Figure 1 The illustrated process and specific implementation methods provide further detailed description of the present invention, and the above and other advantages of the present invention will become more apparent.

[0038] The invention discloses a method for testing the compactness of a highway asphalt surface layer based on dielectric constant, comprising the following steps:

[0039] S1. Use ground penetrating radar to test the relative dielectric constant of each measuring point in the test area of ​​the highway asphalt surface layer;

[0040] S2. Calculate the relative dielectric constant of the mortar phase in the asphalt surface layer at each measuring point;

[0041] S3, calculating the volume fraction of the void phase in the asphalt surface layer at each measuring point;

[0042] S4. Calculate the normalized total volume of voids in the asphalt surface layer at each measuring point;

[0043] S5. Calculate the total density of the asphalt surface layer at each measuring point;

[0044] S6. Calculate the degree of compaction in the asphalt surface layer at each measuring point.

[0045] According to the type of asphalt used in the asphalt surface layer, it is divided into two categories: base asphalt and SBS modified asphalt. The main components of the asphalt mixture used for paving the asphalt surface layer of highways are asphalt, mineral powder and aggregate.

[0046] In step S1, the relative dielectric constant at each measuring point in the test area of ​​the highway asphalt surface layer is tested by using a ground penetrating radar and a two-way travel time method. The relative dielectric constant ε at the measuring point is calculated as follows:

[0047]

[0048] Where t is the two-way travel time of the electromagnetic wave emitted by the ground penetrating radar between the top and bottom of the asphalt surface layer at the measuring point, h is the thickness of the asphalt surface layer, and c is the electromagnetic wave speed in vacuum.

[0049] The relative dielectric constant calculation formula of the mortar phase in the asphalt surface layer in step S2 is as follows:

[0050]

[0051] Where P is the mass fraction of the mineral powder content in the asphalt surface grading curve to the total mass of aggregate and mineral powder, ρ 沥青 and ρ 矿粉 are the gross volume densities of asphalt and mineral powder in the asphalt surface layer, R is the oil-to-stone ratio of the asphalt surface layer, K 1 is the first dielectric correction factor, K 2 is the second dielectric correction factor, ε 矿粉 and ε 沥青 They are the relative dielectric constants of mineral powder and asphalt used in the measured asphalt pavement, respectively.

[0052] The first dielectric correction factor K 1 The calculation formula is as follows:

[0053]

[0054] The second dielectric correction factor K 2 The calculation formula is as follows:

[0055]

[0056] Gradation correction factor K 3 The calculation formula is as follows:

[0057]

[0058] Density correction factor K 4 The calculation formula is as follows:

[0059]

[0060] The volume fraction C of the void phase in the asphalt surface layer in step S3 空隙 The calculation formula is as follows:

[0061]

[0062] In the formula, ε 胶浆 Relative dielectric constant of the mortar phase in the asphalt surface layer, K 3 is the grading correction coefficient, and ε is the relative dielectric constant at the measuring point.

[0063] In step S4, the normalized total volume V of the voids in the asphalt surface layer at the measuring point 空隙 The calculation formula is as follows:

[0064]

[0065] In the formula, C 空隙 is the volume fraction of the void phase in the asphalt pavement at the measuring point.

[0066] The total density ρ of the asphalt surface layer at the measuring point in step S5 is calculated as follows:

[0067]

[0068] In step S6, the compaction degree K at each measuring point of the asphalt surface layer is calculated and expressed as follows:

[0069]

[0070] In the formula, ρ 标 is the standard density of the asphalt surface layer, and ρ is the total density of the asphalt surface layer at the measuring point.

[0071] Compactness is an important control index in the construction of highway asphalt pavement. Currently, it is mainly done by selecting representative locations for core sampling after compaction is completed. Generally, a core sample is taken at intervals of about 20 meters. The density of the core sample is tested indoors, and the compaction degree is obtained based on the ratio of the measured density to the standard density. Obviously, due to the limited intervals and number of sampling, the coverage rate of this method is low. Sampling after completion is difficult to repair afterwards. Each embodiment in this embodiment reflects the overcoming and solution of the shortcomings of the prior art.

[0072] Example 1: In Example 1 of the present invention, the measured road section uses AC20 asphalt surface layer, the asphalt used is base asphalt, the mass fraction P of the mineral powder content in the asphalt surface layer gradation curve is 5.4% of the total mass of aggregate and mineral powder, and the asphalt-stone ratio R of the asphalt surface layer is 4.5%. According to the "Technical Specifications for Highway Asphalt Pavement Construction" (JTG·F40-2017), the core sampling was carried out at the measuring point, and the test result was 98.23%. The method for compaction measurement in this application includes the following steps:

[0073] Step 1: According to the two-way travel time method, the relative dielectric constant ε of the mineral powder used in the asphalt surface layer can be calculated by formula (1): 矿粉 is 7, the relative dielectric constant of asphalt ε 沥青 is 5, the relative dielectric constant ε of the aggregate 集料The relative dielectric constant at the measuring point is 8 and 7.25.

[0074] Step 2: Based on the general objective value of the material used, the bulk density ρ of the mineral powder used 矿粉 2.70g / cm 3 , the bulk density of asphalt ρ 沥青 1.05g / cm 3 , the bulk density of aggregate ρ 集料 2.90g / cm 3 , standard density of asphalt pavement ρ 标 2.581g / cm 3 .

[0075] Step 3: Calculate the first dielectric correction factor K according to formulas (3), (4), (5), and (6): 1 , the second dielectric correction factor K 2 , Gradation correction coefficient K 3 , Density correction factor K 4 The values ​​are 1, 1.019, 1.013, and 1.020.

[0076] Step 4: Calculate the volume fraction C of the void phase according to formula (7): 空隙 is 4.884%, and the total volume of the voids V is normalized by formula (8): 空隙 is 2.022.

[0077] Step 5: Calculate the relative dielectric constant ε of the cement phase in the asphalt pavement according to formula (2): 胶浆 It is 5.637.

[0078] Step 6: According to formula (9), the total density ρ of the asphalt surface layer at the measuring point is 2.558 g / cm 3 .

[0079] Step 7: According to formula (10), the compaction degree is 99.11%, and the error is less than 1% compared with the result measured in the above standard.

[0080] Example 2: In Example 2 of the present invention, the measured road section uses SMA13 asphalt surface layer, the asphalt used is SBS modified asphalt, the mass fraction P of the mineral powder content in the asphalt surface layer gradation curve is 6.2% of the total mass of aggregate and mineral powder, and the asphalt-stone ratio R of the asphalt surface layer is 10.3%. According to the "Technical Specifications for Highway Asphalt Pavement Construction" (JTG·F40-2017), the core sampling was carried out at the measuring point, and the test result was 96.51%. .

[0081] Step 1: According to the two-way travel time method, the relative dielectric constant ε of the mineral powder used in the asphalt surface layer can be calculated by formula (1): 矿粉is 7, the relative dielectric constant of asphalt ε 沥青 is 5, the relative dielectric constant ε of the aggregate 集料 The relative dielectric constant measured at a certain measuring point is 8 and is 6.98.

[0082] Step 2: Based on the general objective value of the material used, the bulk density ρ of the mineral powder used 矿粉 2.70g / cm 3 , the bulk density of asphalt ρ 沥青 1.05g / cm 3 , the bulk density of aggregate ρ 集料 2.90g / cm 3 , standard density of asphalt pavement ρ 标 2.463g / cm 3 .

[0083] Step 3: Calculate the first dielectric correction factor K according to formulas (3), (4), (5), and (6): 1 , the second dielectric correction factor K 2 , Gradation correction coefficient K 3 , Density correction factor K 4 The values ​​are 1.048, 1.022, 1.006, and 1.010.

[0084] Step 4: Calculate the volume fraction C of the void phase according to formula (7): 空隙 The normalized total volume V of the voids is calculated by formula (8): 空隙 It is 2.244.

[0085] Step 5: Calculate the relative dielectric constant ε of the cement phase in the asphalt pavement according to formula (2): 胶浆 It is 5.779.

[0086] Step 6: According to formula (9), the total density ρ of the asphalt surface layer at the measuring point is 2.365 g / cm 3 .

[0087] Step 7. According to formula (10), the compaction degree is 96.05%, and the error is less than 5‰ compared with the result measured in the above standard.

[0088] The present invention provides a method for testing the compaction of a highway asphalt surface layer based on dielectric constant. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for testing the compaction of highway asphalt surface layer based on dielectric constant, characterized in that: The following steps are involved: S1. Use ground penetrating radar to test the relative dielectric constant of each measuring point in the test area of ​​the highway asphalt surface layer; S2. Calculate the relative dielectric constant of the mortar phase in the asphalt surface layer at each measuring point; S3, calculating the volume fraction of the void phase in the asphalt surface layer at each measuring point; S4. Calculate the normalized total volume of voids in the asphalt surface layer at each measuring point; S5. Calculate the total density of the asphalt surface layer at each measuring point; S6. Calculate the degree of compaction in the asphalt surface layer at each measuring point.

2. A method for testing the compaction of a highway asphalt surface layer based on dielectric constant according to claim 1, characterized in that: According to the type of asphalt used in the asphalt surface layer, it is divided into two categories: base asphalt and SBS modified asphalt. The main components of the asphalt mixture used for paving the asphalt surface layer of highways are asphalt, mineral powder and aggregate.

3. A method for testing the compaction of a highway asphalt surface layer based on dielectric constant according to claim 2, characterized in that: In step S1, ground penetrating radar is used to test the relative dielectric constant of each measuring point in the test area of ​​the highway asphalt surface layer using the two-way travel time method. The relative dielectric constant ε at the measuring point is calculated as follows: Where t is the two-way travel time of the electromagnetic wave emitted by the ground penetrating radar between the top and bottom of the asphalt surface layer at the measuring point, h is the thickness of the asphalt surface layer, and c is the electromagnetic wave speed in vacuum.

4. A method for testing the compaction of a highway asphalt surface layer based on dielectric constant according to claim 3, characterized in that: The relative dielectric constant calculation formula of the mortar phase in the asphalt surface layer in step S2 is as follows: Where P is the mass fraction of the mineral powder content in the asphalt surface grading curve to the total mass of aggregate and mineral powder, ρ 沥青 and ρ 矿粉 are the bulk density of asphalt and mineral powder in the asphalt surface layer, R is the oil-stone ratio of the asphalt surface layer, K1 is the first dielectric correction factor, K2 is the second dielectric correction factor, ε 矿粉 and ε 沥青 They are the relative dielectric constants of mineral powder and asphalt used in the measured asphalt pavement, respectively.

5. A method for testing the compaction of highway asphalt surface layer based on dielectric constant according to claim 4, characterized in that: The calculation formula of the first dielectric correction factor K1 is as follows:

6. A method for testing the compaction of highway asphalt surface layer based on dielectric constant according to claim 5, characterized in that: The calculation formula of the second dielectric correction factor K2 is as follows: The calculation formula of gradation correction coefficient K3 is as follows: The calculation formula of density correction factor K4 is as follows:

7. A method for testing the compaction of a highway asphalt surface layer based on dielectric constant according to claim 6, characterized in that: The volume fraction C of the void phase in the asphalt surface layer in step S3 is 空隙 The calculation formula is as follows: In the formula, ε 胶浆 The relative dielectric constant of the mortar phase in the asphalt surface layer, K3 is the gradation correction coefficient, and ε is the relative dielectric constant at the measuring point.

8. A method for testing the compaction of highway asphalt surface layer based on dielectric constant according to claim 7, characterized in that: In step S4, the normalized total volume V of the voids in the asphalt surface layer at the measuring point 空隙 The calculation formula is as follows: In the formula, C 空隙 is the volume fraction of the void phase in the asphalt pavement at the measuring point.

9. A method for testing the compaction of highway asphalt surface layer based on dielectric constant according to claim 8, characterized in that: The total density ρ of the asphalt surface layer at the measuring point in step S5 is calculated as follows: Where K4 is the density correction factor, V 空隙 is the normalized total volume of voids in the asphalt pavement.

10. A method for testing the compaction of highway asphalt surface layer based on dielectric constant according to claim 9, characterized in that: In step S6, the compaction degree K at each measuring point of the asphalt surface layer is calculated and expressed as follows: In the formula, ρ 标 is the standard density of the asphalt surface layer, and ρ is the total density of the asphalt surface layer at the measuring point.

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