Grading design method of drainage asphalt mixture based on single particle size main skeleton concept

Abstract

The application relates to a drainage asphalt mixture grading design method based on a single particle size main skeleton concept, which comprises the following steps: selecting raw materials; adding 6mm, 8mm and 11mm screen meshes to finely divide coarse aggregate particle size subintervals; designing coarse aggregate grading, selecting single particle size coarse aggregates with different particle size subinterval proportions to construct a coarse aggregate main skeleton structure; proposing a particle size distribution index, calculating the particle size distribution index corresponding to the single particle size coarse aggregates with different particle size subinterval proportions; designing fine aggregate grading; adopting a coarse aggregate void filling method to determine asphalt content and coarse and fine aggregate ratios; forming test pieces to conduct mechanical property verification tests and drainage performance evaluation tests; and taking the particle size distribution index value to guide coarse aggregate grading design. The coarse aggregate main skeleton structure has good embedding and extruding capacity and internal friction resistance, the mixture prepared by optimizing grading has the characteristics of good skid resistance and strong drainage performance, and the rain environment high-speed driving safety can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of road engineering material design technology, specifically to a drainage asphalt mixture gradation design method based on the concept of a single particle size main skeleton. Background Technology

[0002] To meet the ever-increasing traffic demand, improve traffic capacity, and enhance the travel experience, many provinces have begun upgrading and expanding trunk highways. These upgraded roads often feature ultra-wide cross-sections, primarily eight or ten lanes in each direction, which significantly increases the road surface drainage path. In rainy weather, if rainwater is not drained from the road surface in time, it will form a water film, reducing the contact area between tires and the road surface, causing tire slippage and increasing the risk of traffic accidents. Therefore, improving road surface drainage capacity and promptly removing rainwater from the road surface is crucial for increasing the effective contact area between vehicle tires and the road surface, ensuring safe high-speed driving in rainy conditions.

[0003] To address the drainage challenges posed by widened cross-sections, in addition to relying on the elevation difference between transverse and longitudinal slopes to guide drainage, internal pavement drainage can also be considered an important technical strategy to improve drainage efficiency. Drainage asphalt pavement is an open-graded asphalt mixture with a typical skeleton-void structure, mainly composed of single-size crushed stone formed according to the interlocking mechanism. After compaction, its porosity is above 18%. Due to its multi-void structure, rainwater infiltrates into the pavement and drains laterally under rainfall conditions, which can quickly and effectively eliminate rainwater runoff from the pavement and improve driving safety in rainy weather. It is one of the important means to solve highway drainage problems.

[0004] Existing methods for designing the gradation of drainage asphalt mixtures rely on values ​​within a specified range, adjusting the passing rate of key sieves to achieve the target void ratio. This is an empirical design approach. Professor Zhang Xiaoning proposed a coarse aggregate void-filling method (CAVF method), which uses void ratio as a benchmark for controlling the coarse and fine aggregates. This method effectively controls the void ratio of drainage asphalt mixtures and reduces reliance on engineering experience. Researchers using the CAVF method to design drainage asphalt mixtures have found that the gradation design of coarse aggregates in the aggregate determines the void ratio.

[0005] However, traditional drainage asphalt mixture design typically employs a multi-grade coarse aggregate structure to construct the main framework. The CAVF method can only obtain the ratio of coarse to fine aggregates, not the ratio between different grades of coarse aggregates. Even if the coarse aggregate main framework has the same porosity, different coarse aggregate particle size distributions can lead to significant differences in the internal composition of the main framework structure, thus affecting the mixture's performance. Furthermore, the random packing and interlocking of multiple grades of coarse aggregates can adversely affect the structure and performance of drainage asphalt mixtures designed to emphasize drainage functionality. First, the complex arrangement of multi-size coarse aggregates easily leads to uneven void distribution and poor connectivity. Second, the uneven development of pore channels results in a complex pore network with poor straightness. Finally, large fluctuations in pore size make small local pores prone to blockage, reducing durability. Therefore, it is necessary to design a drainage asphalt mixture gradation design method based on a single-size main framework concept to improve the drainage performance of drainage asphalt pavements. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a gradation design method for drainage asphalt mixtures based on the concept of a single particle size main skeleton, which enables uniform distribution of voids and uniform development of pore channels in the mixture, effectively improving the drainage performance, durability, and drainage uniformity of drainage asphalt pavements.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for gradation design of drainage asphalt mixtures based on the concept of a single particle size main skeleton includes the following steps:

[0009] S1. Select raw materials, which include coarse aggregate, fine aggregate, filler and asphalt;

[0010] S2. Based on the conventional three-stage crushing process, special specification materials are used, and an improved fine processing production line is used to add 6mm, 8mm and 11mm screens to the conventional coarse aggregate screen sizes of 2.36mm, 4.75mm, 9.5mm, 13.2mm and 16mm, so as to finely divide the sub-ranges of coarse aggregate particle size, thereby optimizing the particle size distribution and particle shape of coarse aggregate.

[0011] S3. Design the coarse aggregate gradation and select single-size coarse aggregates with different proportions of particle size sub-ranges to construct the main skeleton structure of coarse aggregates;

[0012] S4. Propose a particle size distribution index, calculate the particle size distribution index corresponding to single-size coarse aggregate with different particle size sub-interval proportions, and evaluate the control of particle size distribution of coarse aggregate main skeleton structure.

[0013] S5. Design the fine aggregate gradation, mix the fine aggregate, filler and asphalt to form asphalt mortar, and wrap the coarse aggregate main skeleton structure;

[0014] S6. Based on the target porosity and maximum oil film thickness, the coarse aggregate void filling method is used to determine the asphalt content and the ratio of coarse to fine aggregates;

[0015] S7. Using the asphalt content determined in step S6, form specimens and conduct mechanical property verification tests and drainage performance evaluation tests to determine the range of particle size distribution index values ​​that meet the mechanical property requirements and have excellent drainage performance, thereby guiding the coarse aggregate gradation design.

[0016] Furthermore, in step S3, the raw materials are finely processed and the passing rate of key sieve holes is controlled to form three grades of single-size crushed stone: 8~14mm, 6~11mm, and 5~8mm.

[0017] The key sieve aperture sizes for crushed stone with a single particle size of 8-14mm are 13.2mm and 8mm, for crushed stone with a single particle size of 6-11mm are 9.5mm and 6mm, and for crushed stone with a single particle size of 5-8mm are 8mm and 4.75mm.

[0018] Three grades of single-size crushed stone were used to construct the main coarse aggregate skeleton structure of drainage asphalt mixture with nominal maximum particle sizes of 13.2mm, 9.5mm, and 8mm, respectively.

[0019] Furthermore, the passing rate of key sieve openings for the three grades of single-size crushed stone was controlled to construct a main skeleton structure with uniform void distribution and good interlocking, thereby reducing gradation deviation and enhancing process stability. Specifically, the passing rates of key sieve openings for the three grades of single-size crushed stone are shown in Table 1:

[0020] Table 1. Key sieve aperture passing rate requirements for three grades of single-size crushed stone.

[0021]

[0022] Specifically, by using three specially made 6mm, 8mm, and 11mm sieves, coarse aggregates with a particle size of less than 16mm can be divided into seven particle size sub-ranges: 2.36~4.75mm, 4.75~6mm, 6~8mm, 8~9.5mm, 9.5~11mm, 11~13.2mm, and 13.2~16mm. Taking a drainage asphalt mixture with a nominal maximum particle size of 13.2 mm as an example, conventionally graded coarse aggregate gradation generally has aggregate distribution in all 7 particle size sub-ranges. However, open-graded asphalt mixtures based on the concept of single-size coarse aggregate main skeleton directly use 8~14 mm single-size crushed stone to construct the main skeleton structure. According to the key sieve passing rate requirements of single-size crushed stone in Table 1, the 8~14 mm single-size material has three main particle size sub-ranges: 8~9.5 mm, 9.5~11 mm, and 11~13.2 mm. The 13.2~16 mm and 6~8 mm particle size sub-ranges account for a very small proportion and mainly play a role in controlling the processing quality.

[0023] Furthermore, in step S4, the particle size distribution evaluation index includes the weighted average particle size and the skewness index.

[0024] Furthermore, the formula for calculating the weighted average particle size is:

[0025] ;

[0026] Wherein, WMD is the weighted average particle size; the larger the value, the more the distribution is biased towards larger particle sizes; the smaller the value, the more the distribution is biased towards smaller particle sizes. The mass percentage of the i-th particle size sub-interval; Let be the median particle size of the i-th particle size sub-interval.

[0027] Furthermore, the formula for calculating the skewness index is:

[0028] ;

[0029] Skewness is the skewness index; a Skewness greater than 0 indicates a right-skewed distribution of particle size with a large proportion of large particles; a Skewness less than 0 indicates a left-skewed distribution of particle size with a large proportion of small particles; a Skewness equal to 0 indicates a symmetrical distribution of particle size across the range. The standard deviation of the particle size distribution reflects the degree of dispersion in the gradation. This represents the mass percentage of this particle size range.

[0030] To distinguish it from traditional permeable asphalt mixtures (PA) designed with multiple grades of coarse aggregates, this invention names its open-graded asphalt mixture (SOGA) based on the concept of single-size stone crushed stone, emphasizing the design concept of using single-size coarse aggregates to construct the main skeleton structure. Specifically, based on engineering environment and road performance requirements, three types of SOGA mixtures—SOGA-13, SOGA-10, and SOGA-8—are designed.

[0031] SOGA-13, with a nominal maximum particle size of 13.2mm, is suitable for the upper layer of single-layer drainage asphalt pavement and the lower layer of double-layer drainage asphalt pavement. Rainwater can be quickly discharged from the pavement system, effectively reducing surface water film, water mist and splashing, and improving driving safety in rainy weather.

[0032] SOGA-10, with a nominal maximum particle size of 9.5mm, is suitable for the surface layer paving of double-layer drainage asphalt pavements, further improving drainage and noise reduction performance.

[0033] SOGA-8, with a nominal maximum particle size of 8mm, can be used as an ultra-thin overlay in preventive maintenance projects to restore the anti-skid performance of the road surface, improve drainage and noise reduction performance, and extend the service life of the road surface.

[0034] To investigate the distribution of single coarse aggregate across different particle size ranges, SOGA mixtures exhibit excellent drainage performance and meet mechanical performance requirements; coarse aggregate design was carried out using fine screening and manual distribution methods.

[0035] SOGA-13 uses 8-14mm single-size coarse aggregates that meet the key sieve aperture passing rate requirements in Table 1 to construct the main skeleton structure; by artificially controlling the proportion of particle size sub-ranges, coarse aggregate gradations with different WMD and Skewness values ​​are designed.

[0036] SOGA-10 uses 6-11mm single-size coarse aggregates that meet the key sieve aperture passing rate requirements in Table 1 to construct the main skeleton structure; by artificially controlling the proportion of particle size sub-ranges, coarse aggregate gradations with different WMD and Skewness values ​​are designed.

[0037] SOGA-8 uses 5-8mm single-size coarse aggregates that meet the key sieve aperture passing rate requirements in Table 1 to construct the main skeleton structure; by artificially controlling the proportion of particle size sub-ranges, coarse aggregate gradations with different WMD and Skewness values ​​are designed.

[0038] Furthermore, in step S4, the bulk relative density of coarse aggregates of each single particle size is tested. Apparent relative density Water absorption rate ; Measure the compacted density of the preferred coarse aggregate gradation Calculate the gap ratio of coarse aggregate skeleton Coarse aggregate skeleton gap ratio The calculation formula is:

[0039] .

[0040] Furthermore, in step S5, the passing rate of the key sieve openings of the fine aggregate is controlled to avoid interference between the fine aggregate and the main skeleton structure of the coarse aggregate. The passing rate of the key sieve openings of the fine aggregate is shown in Table 2. Specifically, the fine aggregate is 0~3mm manufactured sand.

[0041] Table 2 Requirements for the Passing Rate of Key Screen Sizes in Fine Aggregates

[0042]

[0043] like Figure 1 As shown, when all aggregate particles are spherical, the ratio of the secondary aggregate particle size to the nominal maximum particle size to achieve the interlocking state is 0.154; Figure 2 As shown, when all aggregate particles are square, the ratio of the secondary aggregate particle size to the nominal maximum particle size that achieves the interlocking state is 0.289; Figure 3 As shown, when the ratio of the secondary aggregate particle size to the nominal maximum particle size is greater than 0.289, it will interfere with the main skeleton structure formed by the nominal maximum particle size, making the void distribution complex and difficult to control. Since the aggregate particles cannot all be round or square, the average of the two, 0.22, is taken as the basis for controlling the particle size of the fine aggregate. At this time, the fine aggregate does not interfere with the main skeleton structure of the coarse aggregate.

[0044] This invention uses the nominal maximum particle size of the smallest single-size coarse aggregate for control. The nominal maximum particle size of the 5-8mm single-size crushed stone is 8mm, which is 8 × 0.22 = 1.76mm. Therefore, the study assumes that after intermittently processing 2.36-4.75mm particle size aggregate, the remaining fine aggregate and asphalt binder have virtually no interference with the skeleton. Fine aggregate that meets the key sieve passing rate is selected, along with fillers and asphalt binders, to form asphalt mortar, which coats the main skeleton structure of the coarse aggregate.

[0045] Furthermore, set a target porosity. The mass fraction of mineral powder is Cement mass fraction is oilstone ratio ;

[0046] Preferably, based on the actual engineering conditions, the target void ratio is 21%, the mineral powder mass fraction is 3%, the cement mass fraction is 1%, and the asphalt content is estimated according to Article 6.3.2 of the "Technical Specification for Design and Construction of Drainage Asphalt Pavement" based on the asphalt film thickness and aggregate surface area.

[0047] Furthermore, in step S6, the formula for calculating the amount of asphalt used is:

[0048] Asphalt usage = aggregate surface area × asphalt film thickness.

[0049] Aggregate surface area = (0.41a + 0.41b + 0.82c + 1.64d + 2.87e + 6.14f + 12.29g + 32.77h) / 10^3;

[0050] Where a is the pass rate of a 19mm sieve aperture; b is the pass rate of a 4.75mm sieve aperture; c is the pass rate of a 2.36mm sieve aperture; d is the pass rate of a 1.18mm sieve aperture; e is the pass rate of a 0.6mm sieve aperture; f is the pass rate of a 0.3mm sieve aperture; g is the pass rate of a 0.15mm sieve aperture; and h is the pass rate of a 0.075mm sieve aperture.

[0051] Furthermore, in step S6, after calculating the amount of asphalt, the apparent relative density of the fine aggregate is measured. Apparent relative density of mineral powder apparent relative density of cement Relative density of asphalt .

[0052] Furthermore, in step S6, the calculation formula for the coarse aggregate void filling method is:

[0053] ;

[0054] ;

[0055] in, This represents the mass percentage of coarse aggregate. This represents the mass percentage of fine aggregate. This represents the mass percentage of mineral powder. The ratio of oil to stone; The gap ratio of coarse aggregate skeleton under dry compaction state; To design the target porosity of the mixture; This refers to the compaction density of coarse aggregate; The apparent relative density of fine aggregate; The apparent relative density of the mineral powder; This represents the relative density of asphalt.

[0056] Furthermore, in step S6, based on the volume loss of asphalt caused by the adsorption of asphalt by aggregates, the calculation formula for the coarse aggregate void filling method is modified. The modified formula for the coarse aggregate void filling method is as follows:

[0057] ;

[0058] in, This represents the effective asphalt volume.

[0059] First, the effective asphalt volume range is determined using the conventional coarse aggregate void filling method. Then, a suitable effective asphalt volume is selected and substituted into the above-mentioned coarse aggregate void filling method correction formula as a correction, and the coarse and fine aggregate ratio is re-determined.

[0060] Preferably, the optimal amount of coarse aggregate is determined. The mass fraction of coarse aggregate with a single particle size was used in the test group. Form the main framework structure; determine the optimal amount of fine aggregate. The mass fraction of fine aggregate in the test group was [missing information]. It forms asphalt mortar with fillers and asphalt.

[0061] After adopting the above-mentioned single-size coarse aggregate gradation design and fine aggregate gradation design, the preferred lignin fiber content in the mixture is 0.15% by mass.

[0062] Furthermore, after adjusting the coarseness ratio, the asphalt film thickness was again set at 14 based on the maximum oil film thickness. Continue to calculate the asphalt-aggregate ratio according to the formula for calculating asphalt content, mold Marshall specimens, and determine whether the porosity and mechanical properties of the specimens meet the requirements. If they meet the requirements, it is the optimal asphalt content; otherwise, the asphalt content needs to be adjusted and the coarse-fine ratio needs to be re-determined.

[0063] In summary, this invention has the following advantages: It employs a single-size coarse aggregate main skeleton structure. Fine aggregate, filler, and asphalt form asphalt mortar, which fills and coats the coarse aggregate main skeleton structure. The coarse aggregate main skeleton has a single, uniform aggregate size, possessing good interlocking ability and internal friction resistance, greatly avoiding the interference between aggregates and uneven distribution of void spaces that occur when the main skeleton is composed of multi-stage aggregates. This results in a skeleton void structure with uniform void space distribution, high pore connectivity, and uniformly developed interconnected pore channels, while also exhibiting good construction uniformity. The mixture prepared according to the optimized gradation has good anti-skid performance, strong drainage performance, and high stiffness modulus, which helps reduce the impact of rain and fog in rainy weather and improves the safety of high-speed driving in rainy environments. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the skeleton gap interference when all aggregate particles are spherical.

[0065] Figure 2 This is a schematic diagram of the skeleton gap interference when all aggregate particles are square.

[0066] Figure 3 This is a schematic diagram of the skeleton gap interference when the ratio of the secondary aggregate particle size to the nominal maximum particle size is greater than 0.289.

[0067] Figure 4 This is a schematic diagram showing the permeability coefficient and dynamic stability of the four SOGA mixtures in the example.

[0068] Figure 5 This is a schematic diagram illustrating the stability of the four SOGA mixtures in the example. Detailed Implementation

[0069] The present invention will be described in detail below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited to the following embodiments.

[0070] This embodiment provides a design method for SOGA-10 asphalt mixtures, which is carried out according to the following steps:

[0071] S1. Selection and testing of raw materials:

[0072] In this embodiment, high-viscosity modified asphalt is used; mineral powder and cement are selected as fillers; and fiber is used as a plasticizing and stabilizing material. The test results of its main technical properties are shown in Tables 3 to 7.

[0073] Table 3 Test results of high-viscosity modified asphalt performance

[0074]

[0075] The coarse aggregate is made from basalt with a single particle size of 6-11mm, and the passing rate of the key sieve holes must meet the requirements of Table 1.

[0076] Table 4. Test Results for Coarse Aggregate Performance Evaluation

[0077]

[0078] Fine aggregates are made of 0-3mm manufactured sand, and the passing rate of key sieves meets the requirements of Table 2.

[0079] Table 5. Results of Fine Aggregate Performance Evaluation Tests

[0080]

[0081] The mineral powder is made from finely ground limestone, and is dry, clean, unweathered, and free of impurities.

[0082] Table 6 Results of mineral powder performance tests

[0083]

[0084] Table 7 Cement Test Results

[0085]

[0086] After testing, all technical indicators of the raw materials met the technical requirements of the "Technical Specification for Design and Construction of Drainage Asphalt Pavement" (JTG / T3350-03—2020).

[0087] S2. Based on the conventional coarse aggregate screen sizes of 2.36mm, 4.75mm, 9.5mm, 13.2mm and 16mm, screens of 6mm, 8mm and 11mm are added to more finely divide the coarse aggregate particle size sub-ranges.

[0088] S3. Design the coarse aggregate gradation and select single-size coarse aggregates with different proportions of particle size sub-ranges to construct the main skeleton structure of coarse aggregates;

[0089] In this embodiment, crushed stone with a single particle size of 6~11mm is used to construct the main skeleton structure of coarse aggregate.

[0090] S4. Propose a particle size distribution index, calculate the particle size distribution index corresponding to coarse aggregates of different particle size sub-intervals, and evaluate the control of particle size distribution in the main skeleton structure of coarse aggregates.

[0091] This embodiment designed four groups of single-size coarse aggregates with different weighted average particle size (WMD) and skewness index (Skewness). PA-10, which adopts the median value of the gradation recommended in the "Technical Specification for Design and Construction of Drainage Asphalt Pavement" (JTG / T 3350-03—2020), was set as a control group. The proportion of particle size sub-intervals of different gradations is shown in Table 8.

[0092] Table 8. Proportion of particle size sub-ranges in different gradations of the mixture

[0093]

[0094] The compaction density of five single-size coarse aggregates was further tested using the tamping method. And calculate the gap ratio of the coarse aggregate skeleton. The particle size distribution and interstitial gap ratio of the five gradations are shown in Table 9.

[0095] Table 9. Statistics on particle size distribution index and skeleton porosity of mixtures with different gradations

[0096]

[0097] S5. Design the fine aggregate gradation and mix the fine aggregate, filler and asphalt to form asphalt mortar to cover the coarse aggregate main skeleton structure.

[0098] S6. Based on the target porosity and maximum oil film thickness, the asphalt content and coarse-fine aggregate ratio are determined using the coarse aggregate void filling method.

[0099] SOGA-10-1 was selected as the preliminary test gradation, and its skeleton porosity was determined using the tamping method. The design porosity is 41.20%; The asphalt film thickness is set at 14, representing 21%. The initial coarse-to-fine aggregate ratio was set at 86%:10%, and the initial asphalt-aggregate ratio was calculated to be 5.1% based on the asphalt dosage formula. Using the coarse aggregate void-filling method, the optimal coarse-to-fine aggregate ratio was calculated to be 84.8%:11.2%. After readjustment, the asphalt-aggregate ratio was determined to be 5.3%, with mineral powder dosage at 3%, cement dosage at 1%, and fiber dosage at 0.15%. Volumetric parameters of the molded Marshall specimens were measured, revealing a porosity of 21.7%, which was higher than the target porosity. The effective asphalt volume was 9.37%. Therefore, this invention presupposes an effective asphalt volume of 9.3% and employs the modified CAVF method, considering the influence of aggregate absorption of asphalt, for design research.

[0100] After revised calculations, the final coarse-to-fine ratio and asphalt dosage are shown in Table 10.

[0101] Table 10. Revised coarseness ratio and asphalt dosage

[0102]

[0103] After determining the coarseness ratio, the final pass rate of each sieve aperture for each gradation is shown in Table 11.

[0104] Table 11 Passing rate of each sieve aperture for the test gradation

[0105]

[0106] S7. Using the asphalt content determined in step S6, mold specimens and conduct mechanical property verification tests and drainage performance evaluation tests to determine the range of particle size distribution index values ​​that meet the mechanical property requirements and have excellent drainage performance, thereby guiding the coarse aggregate gradation design.

[0107] The results of the Marshall volume index are summarized in Table 12.

[0108] Table 12 Results of the Marshall Test

[0109]

[0110] Due to its porous nature, drainage asphalt mixtures are easily affected by a combination of factors, including sunlight, water, and temperature. This invention verifies the road performance of the mixture through Kentucky divergence tests, Schellenberg segregation tests, water stability tests, high-temperature stability tests, and permeability tests.

[0111] Table 13 Results of Road Performance Tests for Mixed Asphalt

[0112]

[0113] As shown in Tables 12 and 13, overall, SOGA mixtures using single-size coarse aggregates to construct the main skeleton structure have significantly improved drainage capacity compared to conventional gradations. SOGA-10-2 mixtures with a weighted average particle size (WMD) of 8.31 mm and a skewness index of 1.155 not only meet the various technical requirements of drainage asphalt mixtures, but also have a permeability coefficient that is 13.14% higher than that of PA-10 designed using the median gradation, thus being selected as the preferred gradation.

[0114] While SOGA-10-4 mixture, which has a larger WMD and coarser gradation, also has excellent drainage performance, its Marshall stability does not meet the requirements because its coarse aggregate distribution is too uniform. The aggregate is neatly and evenly arranged but lacks interlocking filling, resulting in insufficient skeleton strength.

[0115] Although the SOGA-10-3 mixture with coarse aggregates distributed to the left (fine gradation) can meet the mechanical properties and other road performance requirements, its drainage performance is not significantly improved compared to conventional gradation.

[0116] Although the drainage performance of SOGA-10-1 mixture with symmetrical coarse aggregate gradation is somewhat improved, its high-temperature performance does not meet the technical requirements due to insufficient skeleton interlocking caused by the symmetrical distribution of aggregates.

[0117] Further regression analysis of particle size distribution index and drainage performance revealed a strong correlation between the permeability coefficient K and the weighted average particle size (WMD) and skewness index (Skewness). The fitted equations showed an R² value above 0.95, as shown below:

[0118] K=654.65755×WMD+17.50909×Skewness+1352.21097;

[0119] like Figure 4 As shown, combining the permeability coefficient and dynamic stability of the four SOGA mixtures, and as... Figure 5As shown, based on the stability results of the four SOGA mixtures, linear interpolation revealed that when the Skewness value of the single-size coarse aggregate is between 0.42 and 1.58, and the weighted average particle size (WMD) is between 8.04 and 8.38, the drainage performance is excellent and the mechanical performance requirements are met. That is, when 6-11mm single-size crushed stone is processed according to the proportion of this particle size sub-range, the SOGA-10 mixture can not only meet basic road performance requirements but also effectively improve drainage performance.

[0120] The drainage asphalt mixture gradation design method based on the single-size coarse aggregate main skeleton structure concept of this invention can not only obtain a good skeleton structure by setting a reasonable weighted average particle size (WMD) and skewness index (Skewness), i.e., a reasonable distribution of particle size sub-intervals, thus ensuring the interlocking capacity and internal friction resistance between aggregates, and ensuring the mechanical properties of the mixture by designing based on the maximum oil film thickness and target porosity; but also significantly improve the drainage performance of the mixture by constructing a skeleton structure with a single particle size, thereby significantly improving the proportion of large-size voids and the uniformity of void distribution.

[0121] Drainage asphalt mixtures based on the single-size coarse aggregate main skeleton structure not only meet the requirements of good high-temperature performance and water damage resistance, but also have excellent design ease and construction uniformity.

[0122] The main functions of this invention are as follows: This invention employs a single-size coarse aggregate main skeleton structure. Fine aggregate, filler, and asphalt form asphalt mortar, which fills and coats the coarse aggregate main skeleton structure. The coarse aggregate main skeleton has a single, uniform aggregate size, possessing good interlocking ability and internal friction resistance, greatly avoiding the interference between aggregates and uneven distribution of void spaces that occur when the main skeleton is composed of multi-grade aggregates. This results in a skeleton void structure with uniform void space distribution, high pore connectivity, and uniform development of connected pore channels, while also exhibiting good construction uniformity. The mixture prepared according to the optimized gradation has characteristics such as good anti-skid performance, strong drainage performance, and high stiffness modulus, which helps to reduce the impact of rain and fog in rainy weather and improve the safety of high-speed driving in rainy environments. This invention links the coarse aggregate particle size distribution with the drainage performance of asphalt mixtures through the particle size distribution index. Combining the relationship between the mechanical properties and drainage performance of the mixture, a suitable range of particle size distribution index values ​​is determined, thereby guiding the coarse aggregate gradation design.

[0123] This invention is simple to operate and effectively improves the drainage performance of drainage asphalt mixtures, reducing the blind spots in the design of drainage asphalt mixtures. The three types of drainage asphalt mixtures designed in this invention can be flexibly applied to different alignments, structural types, and environments with different skid resistance and noise reduction functions, which is conducive to improving the application level of drainage asphalt mixtures.

[0124] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for gradation design of drainage asphalt mixtures based on the concept of a single particle size main skeleton, characterized in that: Includes the following steps: S1. Select raw materials, which include coarse aggregate, fine aggregate, filler and asphalt; S2. Based on the conventional coarse aggregate screen sizes of 2.36mm, 4.75mm, 9.5mm, 13.2mm and 16mm, screens of 6mm, 8mm and 11mm are added to more finely divide the coarse aggregate particle size sub-ranges; S3. Design the coarse aggregate gradation and select single-size coarse aggregates with different proportions of particle size sub-ranges to construct the main skeleton structure of coarse aggregates; S4. Propose a particle size distribution index, calculate the particle size distribution index corresponding to single-size coarse aggregate with different particle size sub-interval proportions, and evaluate the control of particle size distribution of coarse aggregate main skeleton structure. In step S4, the particle size distribution evaluation index includes the weighted average particle size and the skewness index; The formula for calculating the weighted average particle size is: ； Wherein, WMD is the weighted average particle size; the larger the value, the more the distribution is biased towards the larger particle size range; the smaller the value, the more the distribution is biased towards the smaller particle size range. The mass percentage of the i-th particle size range; Let be the median particle size of the i-th particle size interval; The formula for calculating the skewness index is: ； Skewness is the skewness index; when Skewness is greater than 0, the particle size range is right-skewed, with the distribution biased towards larger particles; when Skewness is less than 0, the particle size range is left-skewed, with the distribution biased towards smaller particles; when Skewness is equal to 0, the particle size range is symmetrically distributed. The standard deviation of the particle size distribution reflects the degree of dispersion in the gradation. This represents the mass percentage of this particle size range; S5. Design the fine aggregate gradation and mix the fine aggregate, filler and asphalt to form asphalt mortar to cover the coarse aggregate main skeleton structure; S6. Based on the target porosity and maximum oil film thickness, the coarse aggregate void filling method is used to determine the asphalt content and the ratio of coarse to fine aggregates; S7. Using the asphalt content determined in step S6, form specimens and conduct mechanical property verification tests and drainage performance evaluation tests to determine the range of particle size distribution index values ​​that meet the mechanical property requirements and have excellent drainage performance, thereby guiding the coarse aggregate gradation design.

2. The drainage asphalt mixture gradation design method based on the single-size main skeleton concept according to claim 1, characterized in that: In step S3, the raw materials are finely processed and the passing rate of key sieve holes is controlled to form three grades of single-size crushed stone: 8~14mm, 6~11mm, and 5~8mm. The key sieve aperture sizes for crushed stone with a single particle size of 8-14mm are 13.2mm and 8mm, for crushed stone with a single particle size of 6-11mm are 9.5mm and 6mm, and for crushed stone with a single particle size of 5-8mm are 8mm and 4.75mm. Three grades of single-size crushed stone were used to construct the main coarse aggregate skeleton structure of drainage asphalt mixture with nominal maximum particle sizes of 13.2mm, 9.5mm, and 8mm, respectively.

3. The drainage asphalt mixture gradation design method based on the single-size main skeleton concept according to claim 1, characterized in that: In step S4, the bulk relative density of coarse aggregates of each single particle size is tested. Apparent relative density Water absorption rate ; Measure the compacted density of the preferred coarse aggregate gradation Calculate the gap ratio of coarse aggregate skeleton Coarse aggregate skeleton gap ratio The calculation formula is: 。 4. The drainage asphalt mixture gradation design method based on the single-size main skeleton concept according to claim 1, characterized in that: In step S6, the formula for calculating the amount of asphalt used is: Asphalt usage = aggregate surface area × asphalt film thickness; Aggregate surface area = (0.41a + 0.41b + 0.82c + 1.64d + 2.87e + 6.14f + 12.29g + 32.77h) / 10^3; Where a is the pass rate of a 19mm sieve aperture; b is the pass rate of a 4.75mm sieve aperture; c is the pass rate of a 2.36mm sieve aperture; d is the pass rate of a 1.18mm sieve aperture; e is the pass rate of a 0.6mm sieve aperture; f is the pass rate of a 0.3mm sieve aperture; g is the pass rate of a 0.15mm sieve aperture; and h is the pass rate of a 0.075mm sieve aperture.

5. The drainage asphalt mixture gradation design method based on the single-size main skeleton concept according to claim 4, characterized in that: In step S6, after calculating the asphalt content, the apparent relative density of the fine aggregate is measured. Apparent relative density of mineral powder apparent relative density of cement Relative density of asphalt .

6. The drainage asphalt mixture gradation design method based on the single-size main skeleton concept according to claim 5, characterized in that: In step S6, the calculation formula for the coarse aggregate void filling method is: ； ； in, This represents the mass percentage of coarse aggregate. This represents the mass percentage of fine aggregate. This represents the mass percentage of mineral powder. The ratio of oil to stone; The gap ratio of coarse aggregate skeleton under dry compaction state; To design the target porosity of the mixture; This refers to the compaction density of coarse aggregate; The apparent relative density of fine aggregate; The apparent relative density of the mineral powder; This represents the relative density of asphalt.

7. The drainage asphalt mixture gradation design method based on the single-size main skeleton concept according to claim 6, characterized in that: In step S6, based on the volume loss of asphalt caused by the adsorption of asphalt by aggregates, the calculation formula for the coarse aggregate void filling method is modified. The modified formula for the coarse aggregate void filling method is as follows: ； in, This represents the effective asphalt volume.

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