Pavement aggregate grading design method based on reclaimed material caking grading reconstruction

Abstract

The invention relates to asphalt pavement design, and discloses a pavement aggregate gradation design method based on reclaimed material caking gradation reconstruction, which comprises the following steps of: firstly, determining an initial mass ratio of coarse, medium and fine mixed aggregates according to an initial design gradation curve, and determining an initial mixing amount ratio of reclaimed materials meeting pavement performance requirements in the mixed aggregates; measuring the total mass of the residual mixture and the mass of medium and fine aggregates after the reworked material is subjected to hot mixing reconstruction through a hot mixing test and a screening method, calculating a gradation reconstruction coefficient according to the total mass, and calculating a gradation variation coefficient of the reworked material with each grade of particle size according to a gradation variation rule before and after the reworked material is reconstructed; and calculating to obtain the actual mass ratio of the natural aggregate in the mixed aggregate. According to the method, the gradation reconstruction rule and the gradation variation characteristic of the agglomerated particles of the reclaimed material under the action of temperature and mechanical force in the hot mixing process are considered, so that the actual proportion and the initial proportion of the mixed aggregate are kept consistent after the mixed aggregate is mixed, and the pavement performance of the mixed aggregate doped with the reclaimed material is effectively ensured.

Description

Technical Field

[0001] This invention relates to a method for designing pavement aggregate gradation based on the reconstructed gradation of recycled aggregates, and relates to the field of asphalt pavement aggregate design technology. Background Technology

[0002] Reclaimed asphalt pavement (RAP) is an important way to achieve resource conservation and environmental protection goals in modern road engineering. RAP typically contains agglomerated particles, formed by the repeated traffic loads and long-term environmental impacts on asphalt and aggregates during use. Agglomerated particles differ significantly from ordinary aggregates in particle size distribution, internal structure, and mechanical properties. Furthermore, the proportion of agglomerated particles, internal gradation, and asphalt adhesion strength vary considerably due to factors such as processing technology, material source, and origin. The main characteristic of agglomerated particles is that, under the binding effect of asphalt, smaller aggregate particles combine to form larger aggregate particles. This structural characteristic leads to gradation variations during the production and construction of road recycled materials, making gradation remodeling prone to occur during mixing, stirring, and paving. If gradation remodeling is not considered, the proportion of agglomerated particles in the RAP mix is ​​unknown. During the mixing process of pavement aggregates, the presence of agglomerated particles will change the final mix proportion of the aggregate mixture, resulting in a difference from the initial design mix proportion. The more RAP mix there is, the more agglomerated particles there are, and the greater the impact on the mix proportion of the aggregate mixture, which seriously affects the mechanical properties and durability of the pavement.

[0003] The binder within recycled aggregate agglomerates is aged asphalt, which performs worse than new asphalt. Failing to consider gradation reconstruction means neglecting the process of aggregate dispersion within the agglomerates into the asphalt mixture, leading to a difference between the final produced gradation skeleton and the designed gradation skeleton. Agglomerate reconstruction typically results in larger agglomerates producing more fine aggregates. After filling the voids between the skeleton particles, the excess fine aggregates reduce friction between the skeleton particles, weakening the overall crack resistance and water stability of the asphalt mixture. Considering gradation reconstruction of agglomerates prevents the asphalt mixture skeleton structure from being affected by the increased fine aggregates after gradation reconstruction, ensuring that the final gradation remains consistent with the design gradation.

[0004] Therefore, it is necessary to provide a pavement aggregate gradation design method based on the reconstructed gradation of recycled aggregates. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that existing mix design methods for RAP-containing asphalt mixtures fail to fully consider the gradation reconstruction caused by the segregation of fine particles from RAP agglomerates during the mixing and construction process, which in turn affects the performance of the mixture. This invention proposes a pavement aggregate gradation design method based on the gradation reconstruction of recycled aggregate agglomerates, which can improve the gradation variation and performance of RAP-containing agglomerate asphalt mixtures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for designing pavement aggregate gradation based on reconstructed aggregate gradation of recycled materials includes the following steps: Step 1: Obtain the initial design gradation curve of the road aggregate mixture, divide it into three grades (coarse, medium, and fine) according to the particle size range, and record the initial mass percentage (A) of the aggregate mixture in each grade. i ;i represents the three grades of mixed aggregate: coarse, medium, and fine; Step 2: Based on the asphalt mixture road performance test, determine the initial admixture ratio R of each particle size of recycled asphalt mixture that meets the road performance requirements in the corresponding grade of aggregate mixture. i ; Step 3: Weigh the initial mass of each grade of recycled asphalt mixture as M. i Hot-mix tests were conducted on recycled asphalt mixtures of each particle size. After cooling, the remaining mixture was obtained. The mass M of the remaining mixture after sieving under a grade j sieve was measured using the sieve method. i-j j represents the medium and fine grades of the remaining mixture; according to M i and M i-j The gradation reconstruction coefficient C of recycled asphalt mixtures of various particle sizes during the mixing process was calculated. i-j Repeat the hot-mixing experiment multiple times and calculate C. i-j The average value; Step 4: Define the difference in mass percentage of each particle size of recycled asphalt mixture before and after hot-mix reconstitution as the coefficient of variation Ki; based on the gradation change law of each particle size of recycled asphalt mixture before and after reconstitution and the obtained C i-j Calculate the coefficient of variation K for each particle size of the recycled asphalt mixture based on the average value. i ; Step 5: Based on A obtained in Step 1 i The R obtained in step two i K obtained in step four i The actual mass proportion q of recycled asphalt mixture in the aggregate after gradation reconstruction was calculated. i and the adjusted mass percentage p of natural aggregates i .

[0007] It should be noted that in step one, when dividing the particle size range of the mixed aggregate, the division is based on the 1 / 3 and 2 / 3 positions of the maximum particle size of the design gradation, and then the corresponding particle size range is determined according to the sieve size.

[0008] It should be noted that in step three, the gradation reconstruction coefficient C of recycled asphalt mixtures of different particle sizes during the mixing process... i-j Determine according to formula (3.1): (3.1); In the formula: C i-j M is the gradation reconstruction coefficient; i M represents the initial mass of recycled asphalt mixtures of various particle sizes; i-j The mass of the recycled mixture after hot mixing and reconstruction is the mass of the residue on a grade j screen.

[0009] It should be noted that in step four, the coefficient of variation K for each particle size of the recycled asphalt mixture is... i Determine according to formulas (4.1) to (4.3): (4.1); (4.2); (4.3); Where: K 粗 K 中 K 细 These are the gradation variation coefficients of recycled asphalt mixtures with coarse, medium, and fine particle sizes, respectively.

[0010] It should be noted that in step five, the actual mass percentage q of the recycled asphalt mixture after gradation reconstruction is... i Determine according to formulas (5.1) to (5.3): (5.1); (5.2); (5.3); In the formula: q 粗 q 中 q 细 These represent the actual mass percentages of recycled asphalt mixtures with coarse, medium, and fine particle sizes after gradation reconstruction.

[0011] It should be noted that in step five, the adjusted mass percentage (p) of natural aggregate in the aggregate mixture after adding recycled asphalt mixture... i Determine according to formulas (5.4) to (5.6): (5.4); (5.5); (5.6); In the formula: p 粗 p 中 p 细 These represent the adjusted mass percentages of natural aggregates in three particle sizes: coarse, medium, and fine.

[0012] It should be noted that when applying the above method, the adjusted mass percentage (p) of natural aggregates of each particle size should be considered. i Initial mass ratio A of recycled asphalt mixture i R i , to carry out road aggregate mixing construction.

[0013] Compared with the prior art, the advantages of the present invention are: 1) The method of the present invention can effectively improve the road performance of the aggregate of asphalt mixture with recycled material: considering that the reconstructed particle size distribution can effectively improve the uniform dispersion of the overall skeleton and interface weaknesses of the mixture during the construction and mixing process, the road performance of the asphalt mixture can be further improved. 2) The method of this invention is reasonable and has a wide range of applications: The method of this invention proposes a gradation reconstruction coefficient for RAP materials, which can directly reflect the variation characteristics of the gradation within the agglomerated particles of RAP under the action of temperature and mechanical force during high-temperature mixing. It can be used for RAP materials with different agglomeration rates and different sources. The gradation reconstruction coefficient can effectively adjust RAP materials with different sources and agglomeration rates, solving the problem that the mix design of recycled asphalt mixtures with RAP admixtures in traditional methods does not consider the gradation reconstruction within the agglomerated particles of RAP. The method of this invention is applicable to RAP materials from different sources. 3) This invention is simple to operate and highly feasible: For RAP materials with different sources and agglomeration rates, the mixing test in this method is used to determine the gradation reconstruction coefficient of the RAP material, which can quickly obtain the gradation variation characteristics of the RAP material in the asphalt mixture. For the same batch of RAP material, the gradation variation can be quickly obtained, and the mix design of the RAP material can be adjusted accordingly. This method is applicable to RAP materials with different sources and agglomeration rates. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the design process of the method of the present invention; Figure 2 This is a schematic diagram of the gradation composition of natural aggregates and RAP materials in the mixed aggregates of the present invention; Figure 3 This is a schematic diagram showing the unreconstructed particle size distribution of RAP material agglomeration during the mixing process in this invention. Figure 4 This is a schematic diagram of the reorganization of RAP material agglomeration particle size distribution and adjustment of natural aggregate ratio during the mixing process in this invention; Figure 5 This is a schematic diagram of the coefficient of variation of the gradation in this invention. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0016] Example 1; Please see Figure 1 This embodiment implements the method based on SMA-13 ​​gradation design. The specific process of this embodiment of a pavement aggregate gradation design method based on recycled material agglomeration gradation reconstruction is as follows: Step 1: Obtain the initial design gradation curve of the road aggregate mixture. Divide it into three grades: coarse, medium, and fine, according to the particle size range. The maximum particle size of SMA-13 ​​is 16.16mm. Divide the particle size grades according to the 1 / 3 and 2 / 3 positions of the maximum particle size in the design gradation. 16.16 / 3 = 5.33, 16.16 × (2 / 3) = 10.67. Combined with the commonly used sieve size, determine the particle size grades. The coarse, medium, and fine particle sizes are 9.5-15mm, 4.75-9.5mm, and 0-4.75mm, respectively. Record the mass proportion of the three particle sizes in the design gradation: coarse aggregate (9.5-15mm) proportion A 粗 Medium aggregate (4.75-9.5mm) accounts for A 中 Fine aggregate (0-4.75mm) percentage A 细 ; Step 2: Determine the percentage of RAP material with different particle size ranges in the corresponding grade of mixed aggregate through road performance tests. i (Where i = coarse, medium, fine); Step 3: Weigh 2 kg of each grade of RAP agglomerated granules (M) separately. i The mixture was stirred in a mixing pot at 130℃ (i.e., hot mixing test). After cooling, the remaining aggregate was obtained and then sieved through a sieve with aperture sizes of 9.5mm (corresponding to j=medium) and 4.75mm (corresponding to j=fine). The mass M of the remaining aggregate after sieving through the j-grade sieve was obtained. i-j According to M i and M i-j The gradation reconstruction coefficient C of RAP agglomerates of various particle sizes during the mixing process was calculated. i-j Where j = medium and fine, corresponding to 4.75-9.5mm and 0-4.75mm respectively; C i-j Includes: C 粗-中 C 粗-细 and C 中-细 Repeat the hot-mixing experiment multiple times and calculate C. i-j The average value; among them, fine-grained RAP agglomerated particles do not require hot mixing test; Step 4: Based on the changes in the recycled asphalt mixture before and after reconstruction for each particle size, and in conjunction with the RAP mixing gradation reconstruction coefficient C... i-j Calculate the coefficient of variation K of the gradation of RAP material based on the average value. i ;K i Including K 粗 K 中 K 细 ; Step 5: Based on the initial mass percentage A of each batch of mixed aggregates i The initial dosage ratio of RAP material R i With the coefficient of variation of gradation K i The actual mass proportion q of recycled asphalt mixture in the aggregate after gradation reconstruction was calculated. i and the adjusted mass percentage p of natural aggregates i .

[0017] The above mix design method can be expressed in Table 1 as follows: .

[0018] Figure 2 This is a schematic diagram of the gradation composition of natural aggregates and RAP materials in mixed aggregates. Natural aggregates and RAP materials of different particle sizes have different dosage ranges, but aggregates of the same particle size must be consistent with the initial proportion. Figure 3 This is a schematic diagram of the RAP material before particle size distribution is reconstructed during the mixing process. 粗-中 C 粗-细 These respectively reflect the amount of gradation remodeling that will occur in coarse-grained RAP materials, C 中-细 This reflects the amount of gradation remodeling that will occur in medium-sized RAP materials. Figure 4 The diagrams illustrate the particle size distribution reconstruction of RAP aggregate during the mixing process and the adjustment of the natural aggregate proportion. After the gradation reconstruction, the coarse-sized RAP aggregate reduces the corresponding C. 粗-中 C 粗-细 To maintain the initial mix proportions of the mixed aggregates, the amount of natural aggregates needs to be increased by the corresponding amount of C. 粗-中 C 粗-细 The amount; after gradation reconstruction, the medium-sized RAP material reduced the corresponding C 中-细 The amount increased, which in turn increased the corresponding C. 粗-细 To maintain the initial mix proportions of the mixed aggregates, the amount of natural aggregates needs to be increased by the corresponding C. 中-细 The amount, reduce the corresponding C 粗-细 The amount; after gradation reconstruction, the fine-particle-size RAP material increased the corresponding C 中-细 C 粗-细 To maintain the initial mix proportions of the mixed aggregates, the amount of natural aggregates needs to be reduced by the corresponding C. 中-细C 粗-细 The amount. Figure 5 This is a schematic diagram of the coefficient of variation of the gradation of the present invention, illustrating the variation process of the RAP material.

[0019] In traditional design methods, RAP (recycled asphalt mixture) aggregates are added to natural aggregates as individual particles, forming part of the aggregate mix. However, because these aggregates contain old aggregates of varying sizes, they undergo gradation remodeling after hot mixing, severely impacting the final mix design and road performance. RAP aggregates consist of multiple old aggregate particles and old asphalt cement adhering to their surfaces. During the hot mixing process with new asphalt, the old asphalt softens due to heat, causing some of the bonded old aggregate particles to detach from the aggregate aggregates, forming new aggregate particles. These new particles shift the original designed aggregate gradation, increasing fine aggregate and decreasing coarse aggregate – this is known as gradation remodeling. After some aggregate particles loosen and peel off, the remaining mixture remains agglomerated. The fact that these agglomerated particles remain agglomerated even after heating and mixing indicates that the aggregate-asphalt bonded particles are almost unaffected by heating and mixing. Upon cooling, they continue to recover to the strength of RAP particles and are considered as single aggregate particles. Therefore, in the method of this invention, a hot-mix test is conducted to fully melt the old asphalt in the RAP mix. This melted old asphalt adheres to a very small number or even a single old aggregate particle before cooling to obtain the remaining mixture (i.e., very small agglomerated particles). The remaining mixture is then sieved, and the mass of the sieve residue is measured. Based on this, the gradation remodeling coefficient of the RAP mix is ​​calculated. This gradation remodeling coefficient fully reflects the gradation remodeling phenomenon of the RAP mix during the hot-mix process and is basically consistent with actual hot-mix construction.

[0020] When applying the above method, the adjusted mass percentage p of natural aggregates of each particle size should be used. i Initial mass ratio A of recycled asphalt mixture i R i , to carry out road aggregate mixing construction.

[0021] Example 2; The initial SMA-13 ​​gradation was determined to have coarse, medium, and fine particle sizes with mass percentages of 30%, 45%, and 25%, respectively. After initial asphalt mixture performance tests, the mass percentages of recycled asphalt mixtures with each particle size were determined to be 60%, 50%, and 40%, respectively. The known initial gradation parameters are shown in Table 2.

[0022] .

[0023] Hot-mix tests were conducted on coarse and medium-sized aggregates of recycled asphalt mixtures, followed by sieve analysis tests on the coarse-sized aggregates to determine the gradation reconstruction coefficient C. 粗-中 and C粗-细 Screening tests were conducted on medium-sized aggregates to determine the gradation reconstruction coefficient C. 中-细 As shown in Table 3.

[0024] .

[0025] After determining the gradation reconstruction coefficients of the coarse and medium grade recycled materials, calculate the mass of the aggregates with the three particle sizes: The mass percentage of coarse recycled material after mixing = 18% - 18% × 29% - 18% × 25% = 8.28%; The mass percentage of medium-grade recycled material after mixing = 22.5% + 18% × 29% - 22.5% × 42% = 18.27%; The mass percentage of fine recycled material after mixing = 10% + 18% × 25% + 22.5% × 42% = 23.95%; The mass percentage of coarse-grained natural aggregates = 12% + 18% × 29% + 18% × 25% = 21.72%; The proportion of medium-grade natural aggregates by mass = 22.5% - 18% × 29% + 22.5% × 42% = 26.73%; The mass percentage of fine-grained natural aggregates = 15% - 18% × 25% - 22.5% × 42% = 1.05%.

[0026] The adjusted weight ratios of natural aggregates and recycled aggregates are shown in Table 4.

[0027] .

[0028] When mixing recycled asphalt mixtures in subsequent construction, the mass ratio of natural aggregate gradation is p. 粗 =21.72%, p 中 =26.73%, p 细 =1.05%; the mass percentage of recycled asphalt mixture before gradation reconstruction is A 粗 R 粗 =18%, A 中 R 中 =22.5%, A 细 R 细=10%; Natural aggregates and recycled asphalt mixtures are mixed according to the above proportions, and the skeleton gradation that meets the design requirements can be obtained after hot mixing. Without considering gradation reconstruction, the actual mass proportions of coarse, medium, and fine aggregates during hot mixing are 20.28%, 40.77%, and 38.95%, respectively. Compared with the design mass proportions, coarse aggregates decrease by 9.72%, medium aggregates decrease by 4.23%, and fine aggregates increase by 13.95%. Clearly, without considering gradation reconstruction, the actual mix proportion of the aggregate mixture with added RAP after hot mixing differs significantly from the design mix proportion. The increase in fine particles reduces the friction between aggregates, severely weakening the crack resistance and water stability of the asphalt mixture. Conversely, after considering gradation reconstruction, based on the method of this invention, the natural aggregates are changed, and the actual final mix proportion remains consistent with the design mix proportion. The crack resistance and water stability of the asphalt mixture are guaranteed.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A pavement aggregate gradation design method based on recycled material cluster gradation reconstruction, characterized in that, The method comprises the following steps: Step one: Obtain the initial design gradation curve of the pavement mixture aggregate, divide it into three grades of coarse, medium and fine according to the particle size range, and record the initial mass proportion A of each grade of mixture aggregate i ; i represents the coarse, medium and fine three grades of mixture aggregate; Step two: according to the road performance test of the asphalt mixture, the initial mixing amount proportion R of each grade particle size recycled asphalt mixture in the corresponding grade mixed aggregate that meets the road performance requirements is determined i ; Step three: take the initial mass of each size fraction of reclaimed asphalt mixture as M i , and the remaining mixture is obtained after cooling. The mass of the remaining mixture under the jth screen is measured by sieving method i-j , j represents the medium and fine fractions of the remaining mixture; according to M i and M i-j , the gradation reconstruction coefficient C i-j of each size fraction of reclaimed asphalt mixture in the mixing process is calculated; the average value of C i-j is calculated by repeating the hot mixing experiment multiple times; Step four: define the difference between the quality proportion of each size range of the regenerated asphalt mixture in the caking state and the hot mixing and reconstruction as the gradation variation coefficient Ki; according to the gradation change rule of each size range of the regenerated asphalt mixture before and after the reconstruction and the obtained C i-j The average value is calculated, and the gradation variation coefficient K i of each size range of the regenerated asphalt mixture is calculated. Step five: the A obtained in step one i , R obtained in step two i and K obtained in step four i are calculated to obtain the actual mass ratio q of the recycled asphalt mixture in the graded reconstructed recycled asphalt mixture in the mixed aggregate after adding the recycled asphalt mixture i and the adjusted mass ratio p of the natural aggregate i .

2. The method for pavement aggregate gradation design based on recycled material cluster gradation reconstruction according to claim 1, characterized in that, In step one, when dividing the particle size range of the mixed aggregate, 1 / 3 and 2 / 3 of the maximum particle size of the design gradation are divided, and then the corresponding particle size range is determined according to the sieve size.

3. The method for pavement aggregate gradation design based on recycled material cluster gradation reconstruction according to claim 1, characterized in that, In step three, the gradation reconstruction coefficient C of each grade of reclaimed asphalt mixture in the mixing process i-j is determined according to formula (3.1): (3.1)； In the formula: C i-j is the gradation reconstruction coefficient; M i is the initial mass of each grade particle size reclaimed asphalt mixture; M i-j is the mass of the mixture remaining under the jth screen after hot mixing and reconstruction.

4. The method for pavement aggregate gradation design based on recycled material cluster gradation reconstruction according to claim 1, characterized in that, The gradation variation coefficient K of the reclaimed asphalt mixture for each size range in step four i Determined according to formulas (4.1)-(4.3): (4.1)； (4.2)； (4.3)； In the formula: K 粗 , K 中 , K 细 are the gradation variation coefficients of coarse, medium and fine three-grade particle size reclaimed asphalt mixtures, respectively.

5. The method for pavement aggregate gradation design based on recycled material cluster gradation reconstruction according to claim 1, characterized in that, The actual mass proportion q of the reclaimed asphalt mixture after gradation reconstruction in step five i Determined according to formula (5.1)-(5.3): (5.1)； (5.2)； (5.3)； In the formula: q 粗 , q 中 , q 细 are the actual mass proportions of coarse, medium and fine three-grade particle size reclaimed asphalt mixture after gradation reconstruction.

6. The method for pavement aggregate gradation design based on recycled material cluster gradation reconstruction according to claim 1, characterized in that, In step five, the adjusted mass ratio p of the natural aggregate in the mixed aggregate after adding the reclaimed asphalt mixture i Determined according to formula (5.4)-(5.6): (5.4)； (5.5)； (5.6)； In the formula, p 粗 , p 中 , p 细 are the adjusted mass proportions of coarse, medium, and fine natural aggregate particle sizes, respectively.

7. The method for reconstructing the pavement aggregate gradation based on the recycled material cluster gradation according to any one of claims 1-6, characterized in that, In application, according to the adjusted mass proportion p of each grade particle size natural aggregate i The initial mass proportion A of the reclaimed asphalt mixture i R i , and the pavement aggregate mixing construction is carried out.

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