A method for gradation design of drainage asphalt mixtures based on target porosity

Abstract

This invention discloses a method for gradation design of drainage asphalt mixtures based on a target void ratio, relating to the field of road engineering technology. The method includes: determining the target void ratio; initially proposing a skeleton-void type gradation curve and determining the passing rate of the boundary sieve; obtaining gradation parameters, including coarse aggregate void ratio, coarse aggregate compacted density, fine aggregate compacted density, and asphalt density; calculating the fine aggregate content at the target void ratio based on the gradation parameters; adjusting the fine aggregate content according to the difference between the fine aggregate content and the passing rate of the boundary sieve; testing the void ratio of the drainage asphalt mixture; and completing the gradation design when the void ratio is within the allowable error range of the target void ratio. This invention calculates the fine aggregate content using a theoretical formula based on the target void ratio, allowing the void ratio to directly participate in the gradation design process, ensuring that the designed drainage asphalt mixture achieves the preset target void ratio; it can quickly achieve drainage asphalt mixtures meeting the target void ratio, reducing experimental workload and improving gradation design efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road engineering, and particularly relates to a drainage asphalt mixture gradation design method based on a target void ratio and a mixture. BACKGROUND

[0002] Porous asphalt mixture (PA) is a typical skeleton void structure, and the void ratio after compaction is above 18%. Due to its unique large-pore structure, the porous asphalt pavement has the functions of drainage, noise reduction, anti-skid and the like, and becomes an ecological pavement with good road performance. Studies have shown that the void ratio of the porous asphalt mixture is positively correlated with the permeability coefficient, and is negatively correlated with the anti-leakage, anti-dispersion and water stability of the mixture. Therefore, the void ratio is a key index for the design of the porous asphalt mixture.

[0003] However, in the gradation design method of the porous asphalt mixture at present, the void ratio is only a verification index after the product test after the gradation design, and is not directly involved in the gradation design process; when the tested void ratio does not meet the target void ratio requirement, the gradation design must be re-performed until the requirement is met. Although the Technical Specification for Design and Construction of Porous Asphalt Pavement (JTG / T 3350-03-2020) gives the recommended range of the passing rate of each sieve size of the porous asphalt mixture gradation design, it does not propose a method for determining the passing rate of the key sieve (the coarse-fine aggregate dividing sieve) according to the target void ratio. In addition, the main skeleton void type gradation design methods proposed in China are based on the CAVF design method and the mineral aggregate interstitial void ratio model, and these methods do not design the mineral aggregate gradation according to the target void ratio. The United States, Japan and other countries have issued the gradation design methods of the porous asphalt mixture suitable for the local climate environment. The Federal Highway Administration of the United States adopts the volume filling principle for the gradation design, and the Technical Guidelines for Drainage Pavement (Japan) proposes the gradation design range of the porous asphalt mixture suitable for the natural conditions of the country, and neither of them proposes a gradation design method based on the target void ratio. Patent CN111892335A discloses a porous asphalt mixture gradation design method based on the main skeleton theory, and although the method can ensure the skeleton stability and high-temperature performance of the porous asphalt mixture, it does not consider the influence of the void ratio on the drainage performance and road performance of the mixture. Patent CN101244911A also discloses a porous asphalt mixture gradation design method, and the method also regards the void ratio as a verification index.

[0004] In summary, in the gradation design method of the existing drainage asphalt mixture, the void ratio is measured by preparing Marshall test pieces after the gradation is determined, and the void ratio is unknown during the design process. Therefore, the value of the key sieve pass rate during the gradation design process mainly depends on the engineering experience of the designer, which brings certain randomness to the entire gradation design process, and the test workload is large, the design period is long, and the efficiency is low. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a drainage asphalt mixture gradation design method based on target void ratio, which calculates the amount of fine materials under the target void ratio by the established theoretical formula, so that the void ratio directly participates in the gradation design process, and ensures that the designed drainage asphalt mixture reaches the preset target void ratio. The present application can quickly realize that the drainage asphalt mixture meets the target void ratio requirement, reduces the test workload, and improves the gradation design efficiency.

[0006] In order to achieve the above purpose, the present application is realized by the following technical solutions:

[0007] In a first aspect, the embodiments of the present application provide a drainage asphalt mixture gradation design method based on target void ratio, comprising:

[0008] determining the target void ratio;

[0009] preliminarily determining the skeleton void type gradation curve, and determining the boundary sieve pass rate x;

[0010] obtaining the gradation parameters, the gradation parameters including the coarse aggregate gap ratio VCA, the coarse aggregate vibrating density p, the fine material tight packing density p' and the asphalt density p b , the oil-stone ratio P a ;

[0011] based on the gradation parameters, calculating the amount of fine materials x0 under the target void ratio;

[0012] adjusting the amount of fine materials according to the difference between the amount of fine materials and the boundary sieve pass rate;

[0013] testing the void ratio of the drainage asphalt mixture, and when the void ratio is within the allowable error range of the target void ratio, completing the gradation design.

[0014] As a further implementation manner, based on the skeleton void structure composition principle of the drainage asphalt mixture and the function of each material component therein, a fine material amount calculation formula based on the target void ratio is established.

[0015] As a further implementation manner, the fine material amount calculation formula is expressed as:

[0016]

[0017] Wherein, VV represents target air void.

[0018] As a further implementation, coarse aggregate is used to constitute a skeleton, and the gap volume of the skeleton is equal to the sum of the fine aggregate volume, the asphalt volume and the air void volume.

[0019] As a further implementation, the following equation is established according to the quantity relationship of the coarse aggregate gap ratio VCA, the target air void VV and the skeleton gap volume:

[0020]

[0021] Wherein, V represents the total volume of the coarse aggregate skeleton;

[0022] The total mass of the coarse aggregate and the fine aggregate is set to a set value, and the volume V of the coarse aggregate skeleton is obtained.

[0023] As a further implementation, when the fine aggregate amount x0 is close to the cut-off sieve pass rate x, the gradation does not need to be adjusted.

[0024] As a further implementation, when the fine aggregate amount x0 is different from the cut-off sieve pass rate x, under the premise that the internal ratio of the coarse aggregate and the fine aggregate is unchanged, the ratio of each grade aggregate is recalculated according to the ratio of x0 to x and the amount of each grade aggregate in the preliminary gradation, and the fine aggregate amount is adjusted to x0.

[0025] As a further implementation, when the air void is not within the allowable error range of the target air void, the fine aggregate amount is continuously adjusted under the premise that the internal ratio of the coarse aggregate and the fine aggregate is unchanged.

[0026] As a further implementation, the fine aggregate amount is adjusted by 1% to 3% on the basis of the original amount.

[0027] As a further implementation, when the measured air void is large, 1% to 3% of fine aggregate is added, and when the measured air void is small, 1% to 3% of fine aggregate is reduced.

[0028] In a second aspect, the embodiments of the present application also provide a drainage asphalt mixture prepared by using the gradation design method.

[0029] The beneficial effects of the present application are as follows:

[0030] (1) The present application calculates the amount of fine material based on the theoretical formula of target porosity, so that the porosity directly participates in the grading design process, ensures that the designed drainage asphalt mixture reaches the preset target porosity, and realizes the functions of drainage, noise reduction and anti-skid of the drainage asphalt mixture; using the method can quickly realize that the drainage asphalt mixture meets the target porosity, realize the prior control of porosity, effectively avoid the drawbacks of rework due to the fact that the porosity does not meet the requirements afterwards, reduce the test workload, and improve the grading design efficiency.

[0031] (2) The present application establishes a fine material amount calculation formula based on target porosity based on the skeleton void structure composition principle of drainage asphalt mixture and the function of each material component therein, and provides a theoretical basis for grading design based on target porosity. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings accompanying the specification of the present application form part of the present application and serve to further understand the present application, the illustrative embodiments of the present application and the description thereof serve to explain the present application and do not constitute an improper limitation of the present application.

[0033] Figure 1 is a drainage asphalt mixture composition diagram according to one or more embodiments of the present application;

[0034] Figure 2 is a design method flowchart according to one or more embodiments of the present application;

[0035] Figure 3 is a preliminary skeleton void type grading curve diagram according to one or more embodiments of the present application;

[0036] Figure 4 is an adjusted grading curve diagram according to one or more embodiments of the present application.

[0037] Wherein, 1, coarse aggregate, 2, asphalt, 3, fine material. DETAILED DESCRIPTION

[0038] Example one:

[0039] In a typical embodiment of the present application, as shown in Figure 2 , a drainage asphalt mixture grading design method based on target porosity is given.

[0040] Since the current grading design method does not consider the target porosity in the design process, it mainly relies on experience to design the grading, and the porosity is determined after the preparation of test pieces; if the measured porosity is greatly different from the target porosity, rework is needed, and the grading design and test piece testing need to be performed again, which causes large design and test workload and long design cycle.

[0041] Based on this, the embodiment provides a drainage asphalt mixture grading design method based on target air voids, comprising:

[0042] determining target air voids;

[0043] preliminarily determining a skeleton air void type grading curve and determining a boundary screen passing rate x;

[0044] obtaining grading parameters, the grading parameters including coarse aggregate air voids VCA, coarse aggregate vibrating density p, fine aggregate tight packing density p' and asphalt density p b , oil-stone ratio P a ;

[0045] based on the grading parameters, calculating the amount of fine aggregate x0 under the target air voids;

[0046] adjusting the amount of fine aggregate according to the difference between the amount of fine aggregate and the boundary screen passing rate;

[0047] testing the air voids of the drainage asphalt mixture, and completing the grading design when the air voids are within the target air voids error range.

[0048] Specifically, the method comprises the following steps:

[0049] Step 1: determining target air voids VV according to local hydro-meteorological data and functional requirements of the drainage asphalt pavement.

[0050] Step 2: preliminarily determining a skeleton air void type grading curve within the grading range specified in the “Drainage Asphalt Pavement Design and Construction Technical Specification” (JTGT 3350-03-2020) and determining a boundary screen passing rate x.

[0051] Step 3: determining the coarse aggregate air voids VCA, the vibrating density p of the coarse aggregate and the tight packing density p' of the fine aggregate according to the method in the “Highway Engineering Aggregate Test Specification” (JTG E42-2005), testing the asphalt density p b according to the “Highway Engineering Asphalt and Asphalt Mixture Test Specification” (JTG E20-2011) T 0603-2011, and estimating the oil-stone ratio P a according to the asphalt film thickness required by the “Drainage Asphalt Pavement Design and Construction Technical Specification” (JTGT 3350-03-2020).

[0052] Step 4: calculating the key screen passing rate under the target air voids, i.e. the amount of fine aggregate x0.

[0053] According to the skeleton air void structure composition principle of the drainage asphalt mixture and the functions of each material component therein, a fine aggregate amount calculation formula based on target air voids is established, which provides theoretical guidance for the grading design based on target air voids.

[0054] As Figure 1 shown, the function of coarse aggregate 1 (particle size ≥ 4.75 mm) in the drainage asphalt mixture is to form a skeleton, and the total volume of the skeleton (including the gap volume V C between the coarse aggregate 1 particles) is set to V; the function of fine aggregate 3 (composed of fine aggregate with a particle size < 4.75 mm and mineral powder) and asphalt 2 is to fill the gap volume (V C ) formed by the skeleton, and the volume remaining after filling is the volume of the target void (V O ).

[0055] Since the drainage asphalt mixture belongs to a skeleton pore structure, the skeleton structure formed by the coarse aggregate 1 will not be expanded by the filling of the fine aggregate 3, so the gap volume of the skeleton is equal to the sum of the volume of the fine aggregate 3, the volume of the asphalt 2, and the volume of the void.

[0056] According to the existing VCA, VV definitions in the specification and the above quantity relationship, an equation is established, as shown in equation (1):

[0057]

[0058] In equation (1), VCA is the coarse aggregate skeleton gap rate; V is the total volume of the coarse aggregate skeleton; x0 is the mass fraction of the fine aggregate; ρ' is the tight packing density of the fine aggregate; VV is the target void ratio; P a is the oil-stone ratio; and ρ b is the asphalt density.

[0059] Assuming that the total mass of the coarse aggregate and the fine aggregate is 1, the volume V of the coarse aggregate skeleton can be represented as:

[0060]

[0061] In equation (2), ρ is the vibrating density of the coarse aggregate.

[0062] After substituting equation (2) into equation (1), we get:

[0063]

[0064] Solving equation (3) gives:

[0065]

[0066] Equation (4) is the calculation formula of the amount of fine aggregate x0 under the target void ratio VV, and determining x0 can guide the gradation design.

[0067] Step five: compare x and x0.

[0068] If x0 is very close to x, the gradation does not need to be adjusted. If x0 is far from x, the proportion of each size of aggregate needs to be recalculated according to the ratio of x0 to x and the amount of each size of aggregate in the initial gradation, while ensuring that the internal proportion of coarse aggregate and fine aggregate remains unchanged, and the amount of fine aggregate is adjusted to x0.

[0069] Step six: Test the air voids of the porous asphalt mixture using Appendix B of the Technical Specification for Design and Construction of Porous Asphalt Pavement (JTGT 3350-03-2020).

[0070] Verify whether the air voids are within the allowable error range of the target air voids. If the requirements are met, the gradation design is complete; if the requirements are not met, continue to adjust the amount of fine aggregate while keeping the internal proportion of coarse aggregate and fine aggregate unchanged, and adjust the passing rate of the key sieve opening by ±(1% to 3%) based on the original basis. If the measured air voids are too large, increase the amount of fine aggregate by 1% to 3%, and vice versa.

[0071] The calculation formula between air voids and the amount of fine aggregate established in this embodiment reveals the physical relationship between the volume indicators of the skeleton void type gradation, providing a theoretical basis for guiding the skeleton void type gradation design. By calculating the amount of fine aggregate based on the theoretical formula of the target air voids, the air voids are directly involved in the gradation design process, ensuring that the designed porous asphalt mixture achieves the preset target air voids, thereby realizing the functions of drainage, noise reduction, and anti-skid of the porous asphalt mixture.

[0072] The gradation design method of this embodiment can reduce the workload of gradation design, improve design efficiency, and reduce the dependence on experience in the gradation design process.

[0073] Example Two

[0074] This embodiment takes PA-13 as an example to specifically describe the implementation process of the porous asphalt mixture gradation design method based on the target air voids:

[0075] First, an initial skeleton void type gradation curve is proposed within the gradation range, as shown in FIG. 1. Figure 3 The passing rate of the boundary sieve x is 21.97%, and the calculated amount of mineral aggregate (the amount of each size of coarse aggregate and fine aggregate) and the oil-stone ratio are shown in Table 1.

[0076] Table 1 Amount of mineral aggregate and oil-stone ratio of the initial gradation

[0077]

[0078] The relevant volume parameters are measured, and the coarse aggregate skeleton void ratio VCA is 43.2%, the compacted density of coarse aggregate ρ is 1.710 g / cm 3 , and the tight packing density of fine aggregate ρ' is 2.107 g / cm 3, oil stone ratio is 5.0%, asphalt density p b 1.030 g / cm 3 .

[0079] According to the local hydrological data and the requirements of the drainage pavement, the target air void is determined to be 22%, and the amount of fine aggregate x0 is calculated to be 12.7% by the formula. Comparing x0 and x, the difference is large, so the proportion of each size aggregate needs to be recalculated to make the amount of fine aggregate 12.7%, that is, the passing rate of the dividing screen aperture needs to be adjusted to 12.7%, and the adjusted grading curve is shown in Figure 4 .

[0080] The amount of each size coarse aggregate and fine aggregate calculated after adjustment is shown in Table 2.

[0081] Table 2 Amount of mineral aggregate of adjusted grading

[0082]

[0083] To verify the effectiveness of the above-mentioned grading design method, the related volume indicators of the grading are calculated, as shown in Table 3. Four groups of Marshall test specimens are prepared to test their air voids, and the test results are shown in Table 4.

[0084] Table 3 Grading volume parameters

[0085]

[0086] Table 4 Measured values of air voids

[0087] Test No. Specimen bulk density (g / cm 3 ) Porosity / % Test 1 2.08 21.3 Test 2 2.05 22.5 Test 3 2.04 22.9 Test 4 2.06 22.2

[0088] From Table 4, the average air void after grading adjustment is 22.2%, with an error of only 0.2% compared with the target air void of 22%, and the relative error is 1.0%, which is within the allowable range. It shows that the drainage asphalt mixture grading design method based on the target air void has high effectiveness and accuracy, and can provide guidance for grading design.

[0089] Example Three:

[0090] This example also takes the grading shown in Figure 3 as the initial grading, and the target air void is determined to be 18%, and the amount of fine aggregate x0 is calculated to be 19.6%. The amount of each size aggregate is calculated, and Marshall test specimens are prepared to test their air voids. The air voids of 4 groups of Marshall test specimens are tested, and the average is 19.8%, which exceeds the allowable error of the target air void, and the amount of fine aggregate needs to be adjusted. Since the tested air void is larger, the amount of fine aggregate needs to be increased, so the amount of fine aggregate is adjusted to 20.6%. The air void is tested to be 18.4%, which meets the allowable error requirement, and the grading design is completed.

[0091] The above descriptions are only the preferred embodiments of the present application, and are not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for designing the gradation of a drained asphalt mixture based on a target void ratio, characterized in that, Comprising: determining a target air void; Preliminary skeleton gap-type gradation curve, determine the boundary screen hole passing rate x ; obtaining gradation parameters including coarse aggregate interstitial volume VCA, coarse aggregate compacted density , fine aggregate close-packed density , and asphalt density , oil-stone ratio ; Based on the gradation parameters, the amount of fine material under the target void ratio is calculated The formula is expressed as: ； wherein VV represents the target air void; Adjust the fine material dosage based on the difference between the fine material dosage and the passing rate of the dividing screen aperture; fine material dosage With the passing rate of the dividing screen aperture x When there are differences, under the premise that the internal ratio of coarse aggregate to fine aggregate remains unchanged, according to and x Based on the ratio and the amount of each aggregate grade in the initial gradation, the proportion of each aggregate grade is recalculated, and the amount of fine aggregate is adjusted to... ; testing the air void of the drainage asphalt mixture, and when the air void is within the allowable error range of the target air void, completing the gradation design.

2. The target void-based design method for drainage asphalt mix gradation as claimed in claim 1 wherein, Based on the skeleton void structure composition principle of drainage asphalt mixture and the function of each material component therein, a fine material amount calculation formula based on the target air void is established.

3. The target void-based design method for drainage asphalt mix gradation as claimed in claim 2 wherein, Coarse aggregate is used to constitute the skeleton, and the gap volume of the skeleton is equal to the sum of the fine material volume, the asphalt volume and the air void volume.

4. The target void-based design method for drainage asphalt mix gradation as claimed in claim 3 wherein, According to the quantity relationship among the coarse aggregate air void VCA, the target air void VV and the skeleton gap volume, the following equation is established: wherein V represents the total volume of the coarse aggregate skeleton; The total mass of the coarse aggregate and the fine material is set to a set value, and the volume V of the coarse aggregate skeleton is obtained.

5. The target void-based design method for drainage asphalt mix gradation as claimed in claim 1 wherein, Fine aggregate usage Approach to the cut-off sieve pass x In this case, the gradation does not need to be adjusted.

6. The target void-based design method for drainage asphalt mix gradation as claimed in claim 1 wherein, When the air void is not within the allowable error range of the target air void, the fine material amount is continuously adjusted under the premise that the internal proportion of the coarse aggregate and the fine material remains unchanged.

7. The target void-based design method for drainage asphalt mix gradation as claimed in claim 6 wherein, The fine material amount is adjusted by 1%~3% larger or smaller on the basis of the original.

8. The target void-based design method for drainage asphalt mixture gradation as claimed in claim 7 wherein, When the measured air void is too large, the fine material is increased by 1%~3%, and when the measured air void is too small, the fine material is reduced by 1%~3%.

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