Design method of mix proportion of skeleton dense type plant-mixed hot recycled asphalt mixture

Abstract

The application discloses a kind of skeleton dense type plant mixing hot regeneration asphalt mixture mix design method, it is related to road engineering technical field, including: selecting raw material;Raw material includes new additional aggregate and RAP, the performance detection is carried out to new additional aggregate, and extraction screening test is carried out to RAP;Mixture uses SAC skeleton dense type gradation, when mix design, raw material is divided into skeleton aggregate and filler, and the volume ratio of skeleton aggregate and filler is 70:30, then according to SAC skeleton aggregate gradation key screen hole passing rate calculation method and new additional aggregate screening result, RAP screening result carries out 4.75mm above coarse aggregate blending ratio calculation, when calculation, the blending ratio of RAP in raw material is consistent with the grading ratio of coarse and fine aggregate in RAP;Plant mixing hot regeneration asphalt mixture is subjected to Marshall test, and the adjustment of filler is carried out according to the size of measured porosity.The application can realize the uniform distribution of asphalt mortar in RAP, and improve the high-temperature rutting resistance of mixture.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, specifically a mix design method for a dense-skeleton plant-mixed hot recycled asphalt mixture. Background Technology

[0002] Plant-mixed hot recycled asphalt mixture technology is a relatively mature road recycling technology. Hot recycled asphalt mixture has significantly improved high-temperature performance compared to ordinary asphalt mixture, and its low-temperature performance and water damage resistance can meet the technical requirements of the specifications.

[0003] However, in the production and application of hot recycled asphalt mixtures (RAP) in China, the variability and instability of RAP materials often affect their dosage. The RAP dosage in China is generally 20%–30%, and high-dosage hot recycled asphalt mixtures exceeding 30%–40% are rarely used on large areas of road surfaces, mainly limited to test sections. This significantly restricts the effective recycling rate of RAP. In the mix design of high-dosage hot recycled asphalt mixtures, it is assumed that RAP will fully dissolve and disperse after mixing with new aggregates. However, research has shown that a 60-second mixing time is insufficient to achieve complete dissolution and dispersion; therefore, some RAP asphalt binder remains dispersed in clumps within the mixture. Hot recycled asphalt mixtures are typically used in the middle and lower layers of road surfaces, employing an AC continuous gradation, and are classified as suspended dense type. Suspended dense mixtures have a poor effect on the extrusion and redistribution of RAP asphalt binder during the rolling process, resulting in poor gradation stability of high-dosage plant-mixed hot recycled asphalt mixtures. During the testing process, this manifests as low stability, high flow value, and large rutting deformation within 45 minutes of rutting test. Suspended dense gradation is not suitable for high-dosage recycled asphalt mixtures. Summary of the Invention

[0004] This invention addresses the shortcomings of current high-content plant-mixed hot recycled asphalt mixture gradation design and the development needs of low-carbon and environmentally friendly asphalt pavements by providing a mix design method for dense-skeleton plant-mixed hot recycled asphalt mixtures.

[0005] The present invention provides a mix design method for a skeleton-dense plant-mixed hot recycled asphalt mixture, and the technical solution adopted to solve the above-mentioned technical problems is as follows:

[0006] A mix design method for a skeleton-dense plant-mixed hot recycled asphalt mixture includes the following steps:

[0007] S1. Select the raw materials for plant-mixed hot recycled asphalt mixture, including newly added aggregates and RAP; conduct performance testing on the newly added aggregates to determine if they meet the requirements of current specifications; conduct extraction and sieve analysis tests on RAP to determine the asphalt content, particle size distribution, proportion of coarse aggregates larger than 4.75mm, and apparent density of the aggregates in the RAP.

[0008] S2, plant-mixed hot recycled asphalt mixture adopts SAC skeleton dense gradation. In the SAC mix design, the raw materials are divided into skeleton aggregate and filler, and the volume ratio of skeleton aggregate to filler is 70:30. Then, based on the calculation method of the key sieve passing rate of SAC skeleton aggregate gradation and the sieving results of newly added aggregate and RAP, the blending ratio of coarse aggregate above 4.75mm is calculated. When calculating, the blending ratio of RAP in the raw materials is consistent with the grading ratio of coarse and fine aggregate in RAP.

[0009] S3. Conduct Marshall tests on the plant-mixed hot recycled asphalt mixture and adjust the filler according to the measured porosity.

[0010] Optionally, the newly added aggregates involved include coarse aggregates, fine aggregates, mineral powder, and asphalt;

[0011] The newly added aggregates include four specifications: 10-20mm, 10-15mm, 5-10mm, and 0-3mm. Among them, aggregates larger than 4.75mm are coarse aggregates, and those smaller than 4.75mm are fine aggregates. The performance of the coarse and fine aggregates in the newly added aggregates was tested, and all test indicators met the technical requirements in JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement". Then, the coarse and fine aggregates in the newly added aggregates were screened.

[0012] The asphalt used in the newly added aggregates is SBS modified asphalt. The SBS modified asphalt was tested, and all the test indicators met the technical requirements in JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement".

[0013] The mineral powder in the newly added aggregate was tested, and all the test results met the technical requirements of JTG F40-2004 "Technical Specification for Construction of Asphalt Pavement of Highway".

[0014] Further optional, the RAP involved includes coarse aggregate, fine aggregate, mineral powder, and bitumen;

[0015] RAP (Raw Aggregate Extraction) is milled and impact crushed into two sizes: 0-10mm and 10-20mm. Extraction sieve analysis is performed on the RAP to determine its asphalt content. The old aggregate after extraction sieve analysis is then categorized into coarse and fine aggregate grades, with aggregates larger than 4.75mm classified as coarse and smaller than 4.75mm as fine. The apparent relative density, water absorption rate, and proportion of the 0-4.75mm, 4.75-9.5mm, and 9.5-19mm old aggregates are determined by testing.

[0016] Further optionally, the skeleton aggregates involved include coarse aggregates in the newly added aggregates and coarse aggregates in the RAP, and the fillers include fine aggregates and mineral powders in the newly added aggregates and fine aggregates and mineral powders in the RAP;

[0017] Calculate the critical sieve aperture passing rate P of SAC skeleton aggregate gradation di The formula is as follows:

[0018] P di =A(d) i / D max ) B ,

[0019] In the formula: P di D represents the throughput (in %) of the sieve aperture size di. max denoted as the maximum particle size of the mineral, in mm; di is the size of a certain sieve aperture, in mm; A and B are coefficients, respectively.

[0020] Based on the calculation results of the key sieve aperture passing rate of SAC skeleton aggregate gradation, as well as the sieving results of newly added aggregates and RAP, the blending ratio of coarse aggregates larger than 4.75mm was calculated. During the calculation, the blending ratio of RAP in the raw materials was synthesized according to the graded ratio of coarse and fine RAP aggregates under two specifications: RAP 0-10mm and RAP 10-20mm.

[0021] Alternatively, considering the different densities of RAP aggregate and new aggregate, the RAP blending ratio can be converted into a volume ratio, and the asphalt content can be determined based on past engineering experience.

[0022] The formula for calculating the equal volume replacement of aggregates in RAP is as follows:

[0023]

[0024] Where: m RAP The percentage of total RAP content, %; m RAPsi To match the specifications of s i The percentage of old aggregate by mass, %; ρ asi For specification s i The apparent density of the newly added aggregate (g / cm³)3 ;ρ aRAPsi Specifications in RAP i Apparent density of old aggregate (g / cm³) 3 ;ω RAPsi Specifications in RAP i Percentage of old aggregates, %.

[0025] The formula for calculating the mass ratio of the mixture after equal volume replacement is as follows:

[0026]

[0027]

[0028] Where: m tsi For specification s i The percentage of newly added aggregates after quality replacement, %; m RAPsi Specifications in RAP i Quality percentage, %; m si To convert to 100% specification s i The percentage of newly added aggregate by mass, %; m′ RAPsi To calculate the percentage of old aggregate mass of specification si in RAP after conversion to 100%, %; m k This represents the percentage of mineral powder by weight, in percentages.

[0029] Alternatively, after determining the gradation, a Marshall test can be conducted based on engineering experience.

[0030] When the test results of graded porosity, stability and flow value meet the relevant requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement", the high temperature performance, low temperature performance and water damage resistance of the plant-mixed hot recycled asphalt mixture shall be evaluated.

[0031] When the test results of the gradation porosity exceed the relevant requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement", the gradation of the mixture can be adjusted by increasing or decreasing the proportion of mineral powder, fine aggregate or asphalt in the filler, while ensuring that the volume ratio of skeleton aggregate to filler remains unchanged at 70:30. Alternatively, the optimal asphalt content of the mixture can be determined by fluctuating the initial asphalt content by ±0.3%.

[0032] Optionally, the amount of RAP in the raw materials shall not be less than 30%.

[0033] The mix design method for a skeleton-dense plant-mixed hot recycled asphalt mixture of the present invention has the following advantages compared with the prior art:

[0034] (1) The present invention can achieve uniform distribution of asphalt mortar in RAP, making the mixture more stable and improving the high temperature rutting resistance of the mixture.

[0035] (2) This invention is applicable to the gradation design of mixtures composed of aggregates of different regions and different specifications. It improves the rationality and pertinence of the mix design of high-content hot recycled asphalt mixtures. Compared with the traditional asphalt mixture mix design method, it can improve the RAP content and gradation control, and has significant social benefits and market promotion value. Attached Figure Description

[0036] Appendix Figure 1 This is a gradation curve of the mix proportion after SAC-20 is replaced by an equal volume in Embodiment 1 of the present invention;

[0037] Appendix Figure 2 This is a longitudinal section view of the SAC-20 specimen in Embodiment 1 of the present invention. Detailed Implementation

[0038] To make the technical solution, the technical problem solved, and the technical effect of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments.

[0039] Example 1:

[0040] This embodiment proposes a mix design method for a skeleton-dense plant-mixed hot recycled asphalt mixture, which includes the following steps:

[0041] S1. Select the raw materials for plant-mixed hot recycled asphalt mixture. The raw materials include new aggregates and RAP. The new aggregates include coarse aggregates, fine aggregates, mineral powder, and asphalt. The RAP includes coarse aggregates, fine aggregates, mineral powder, and asphalt.

[0042] Taking a 40% RAP content in raw materials as an example.

[0043] In this embodiment, the newly added coarse and fine aggregates are typical limestone from Yishui area, Shandong Province, including four specifications: 10-20mm, 10-15mm, 5-10mm and 0-3mm. Among them, the aggregates above 4.75mm are coarse aggregates and the aggregates below 4.75mm are fine aggregates. The performance of the newly added coarse and fine aggregates was tested, and the test results are shown in Table 1 below.

[0044] Table 1. Performance test results of coarse and fine aggregates in the newly added aggregates.

[0045]

[0046] As shown in Table 1, all the tested indicators meet the technical requirements of JTG F40-2004 "Technical Specification for Construction of Asphalt Pavement on Highways".

[0047] The coarse and fine aggregates in the newly added aggregates were then screened, and the screening results are shown in Table 2 below.

[0048] Table 2 Screening results of coarse and fine aggregates in the newly added aggregates

[0049] sieve holes 26.5 19 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075 Coarse aggregate 10-20mm 100 89.8 2.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Coarse aggregate 10-15mm 100 100 96.3 60.2 1.2 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Coarse aggregate 5-10mm 100 100 100 100 93.4 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Fine aggregate 0-3mm 100 100 100 100 100 100 67.8 46.1 25.2 11.5 5.6 3.2

[0050] The newly added asphalt was SBS modified asphalt produced by Shandong Expressway Materials. The SBS modified asphalt was tested, and the test results are shown in Table 3.

[0051] Table 3. Test results of SBS modified asphalt

[0052]

[0053] As shown in Table 3, all the tested indicators meet the technical requirements of JTG F40-2004 "Technical Specification for Construction of Asphalt Pavement on Highways".

[0054] The newly added mineral powder is qualified mineral powder processed from typical limestone in Yishui. The test results are shown in Table 4 below.

[0055] Table 4. Mineral Powder Detection Results

[0056]

[0057]

[0058] In this embodiment, an extraction and sieving test was conducted on RAP (old pavement asphalt milling material). The RAP came from the basalt SMA-13 ​​surface layer of a highway overhaul and maintenance project in Qingdao. Considering the stability of the secondary crushing gradation of RAP, the RAP was divided into two specifications: 0-10mm and 10-20mm. An extraction and sieving test was conducted on the RAP, and the specific test results are shown in Table 5 below.

[0059] Table 5. Results of RAP extraction and sieving tests

[0060]

[0061] After the extraction and screening test, the old aggregate was classified into coarse and fine aggregates: those with a diameter of 4.75 mm or more were classified as coarse aggregates, and those with a diameter of less than 4.75 mm were classified as fine aggregates.

[0062] Further testing determined the apparent relative density, water absorption rate, and proportion of old aggregates in the RAP 0-10mm and RAP 10-20mm sizes after grading for the old aggregates 0-4.75mm, 4.75-9.5mm, and 9.5-19mm sizes. The test results are shown in Table 6 below.

[0063] Table 6. Results of aggregate density after RAP extraction and screening.

[0064]

[0065] S2, plant-mixed hot recycled asphalt mixture adopts SAC skeleton dense gradation. In the SAC mix design, the raw materials are divided into skeleton aggregate and filler. The skeleton aggregate includes coarse aggregate in the newly added aggregate and coarse aggregate in RAP. The filler includes fine aggregate and mineral powder in the newly added aggregate and fine aggregate and mineral powder in RAP. The volume ratio of skeleton aggregate to filler is 70:30.

[0066] Calculate the critical sieve aperture passing rate P of SAC skeleton aggregate gradation di The formula is as follows:

[0067] P di =A(d) i / D max ) B ,

[0068] In the formula: P di D represents the throughput (in %) of the sieve aperture size di. max denoted as the maximum particle size of the ore (mm); di is the size of a certain sieve aperture (mm); A and B are coefficients, respectively.

[0069] Referring to Tables 5 and 6, the proportion of coarse aggregates larger than 4.75mm was calculated based on the calculation results of the key sieve aperture passing rate of SAC skeleton aggregate gradation, the sieving results of newly added aggregates, and the sieving results of RAP. During the calculation, the proportion of RAP in the raw materials was 40%, which was synthesized according to the grade ratio of coarse and fine RAP aggregates under two specifications: RAP 0-10mm and RAP 10-20mm.

[0070] Based on the selected coarse aggregate, fine aggregate, RAP, and mineral powder screening results and the coarse and fine RAP blending ratio, the proportions of newly added coarse aggregate, fine aggregate, and mineral powder are adjusted with reference to the key sieve aperture passing rate, so that the synthetic gradation passing rate is as close as possible to the key sieve aperture calculated passing rate.

[0071] In this embodiment, considering the different densities of RAP aggregate and new aggregate, the RAP blending ratio is converted into a volume ratio, and the asphalt content is determined based on previous engineering experience.

[0072] The formula for calculating the equal volume replacement of aggregates in RAP is as follows:

[0073]

[0074] Where: m RAP The percentage of total RAP content, %; m RAPsi To match the specifications of s i The percentage of old aggregate by mass, %; ρ asi For specification s i The apparent density of the newly added aggregate (g / cm³)3 ;ρ aRAPsi Specifications in RAP i Apparent density of old aggregate (g / cm³) 3 ;ω RAPsi Specifications in RAP i Percentage of old aggregates, %.

[0075] The formula for calculating the mass ratio of the mixture after equal volume replacement is as follows:

[0076]

[0077]

[0078] Where: m tsi For specification s i The percentage of newly added aggregates after quality replacement, %; m RAPsi Specifications in RAP i Quality percentage, %; m si To convert to 100% specification s i The percentage of newly added aggregate by mass, %; m′ RAPsi To calculate the percentage of old aggregate mass of specification si in RAP after conversion to 100%, %; m k This represents the percentage of mineral powder by weight, in percentages.

[0079] Taking SAC gradation type as an example, the proportions of the raw materials before the addition of new aggregates and RAP by equal volume replacement are shown in Table 7 below.

[0080] Table 7. Mixing proportions before SAC-20 equal-volume replacement

[0081]

[0082] The above gradation assumption is based on the premise that the density difference between the new and old aggregates is small, and the mass ratio is approximately equal to the volume ratio. Since the apparent relative density of the aggregates in RAP is relatively high, it is necessary to calculate the mass ratio of each material after equal volume replacement. The calculated mass ratios after equal volume replacement are shown in Table 8 below.

[0083] Table 8. Mixing proportions after SAC-20 equal volume replacement

[0084]

[0085] S3. Conduct Marshall tests on the plant-mixed hot recycled asphalt mixture and adjust the filler according to the measured porosity.

[0086] When conducting the Marshall experiment,

[0087] (i) When the test results of gradation porosity, stability and flow value meet the relevant requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement", as shown in Table 9, the high temperature performance, low temperature performance and water damage resistance of the plant-mixed hot recycled asphalt mixture are evaluated.

[0088] Table 9 Performance Results of SAC-20 Asphalt Mixture

[0089]

[0090]

[0091] (ii) When the test results of the gradation porosity exceed the relevant requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement", under the premise of keeping the volume ratio of skeleton aggregate to filler unchanged at 70:30, the proportion of mineral powder, fine aggregate or asphalt in the filler can be increased or decreased to adjust the gradation of the mixture, or the initial asphalt content can be fluctuated by ±0.3% to determine the optimal asphalt content of the mixture.

[0092] In summary, the mix design method for a skeleton-dense plant-mixed hot recycled asphalt mixture of the present invention can achieve uniform distribution of asphalt binder in RAP, resulting in higher stability of the mixture and improved high-temperature rutting resistance.

[0093] The above specific examples illustrate the principles and implementation methods of the present invention in detail. These embodiments are merely for the purpose of helping to understand the core technical content of the present invention. Based on the above specific embodiments of the present invention, any improvements and modifications made to the present invention by those skilled in the art without departing from the principles of the present invention should fall within the patent protection scope of the present invention.

Claims

1. A mix design method for a skeleton-dense plant-mixed hot recycled asphalt mixture, characterized in that, Includes the following steps: S1. Select the raw materials for plant-mixed hot recycled asphalt mixture, including newly added aggregates and RAP; conduct performance testing on the newly added aggregates to determine if they meet current specifications; perform extraction sieve analysis on the RAP to determine the asphalt content, particle size distribution, proportion of coarse aggregates larger than 4.75mm, and apparent density of the aggregates; in this step: The newly added aggregates include coarse aggregates, fine aggregates, mineral powder, and asphalt. The newly added aggregates come in four sizes: 10-20mm, 10-15mm, 5-10mm, and 0-3mm. Aggregates larger than 4.75mm are considered coarse aggregates, and those smaller than 4.75mm are considered fine aggregates. Performance testing was conducted on the coarse and fine aggregates in the newly added aggregates, and all test indicators met the technical requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement". The coarse and fine aggregates were then screened. SBS modified asphalt was used in the newly added aggregates, and testing was conducted on the SBS modified asphalt, with all test indicators meeting the technical requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement". The mineral powder in the newly added aggregates was also tested, and all test indicators met the technical requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement". RAP (Raw Aggregate Extraction) comprises coarse aggregate, fine aggregate, mineral powder, and asphalt. RAP is milled and impact crushed to create two sizes: 0-10mm and 10-20mm. An extraction sieve test is performed on the RAP to determine its asphalt content. The old aggregate after the extraction sieve test is then categorized into coarse and fine aggregate grades. Aggregates larger than 4.75mm are classified as coarse aggregate, and those smaller than 4.75mm as fine aggregate. The apparent relative density, water absorption rate, and proportion of the categorized old aggregate (0-4.75mm, 4.75-9.5mm, and 9.5-19mm) within the RAP 0-10mm and 10-20mm grades are determined by testing. S2, plant-mixed hot recycled asphalt mixture adopts SAC skeleton dense gradation. In the SAC mix design, the raw materials are divided into skeleton aggregates and fillers, with a volume ratio of skeleton aggregates to fillers of 70:

30. Subsequently, based on the calculation method for the passing rate of key sieve openings in the SAC skeleton aggregate gradation, the sieving results of newly added aggregates, and the sieving results of RAP, the proportion of coarse aggregates larger than 4.75mm is calculated. During the calculation, the proportion of RAP in the raw materials is consistent with the gradation ratio of coarse and fine aggregates in the RAP. In this step: The skeleton aggregate includes coarse aggregate in the newly added aggregate and coarse aggregate in the RAP; the filler includes fine aggregate and mineral powder in the newly added aggregate and fine aggregate and mineral powder in the RAP; calculate the key sieve passing rate P of the SAC skeleton aggregate gradation. di The formula is as follows: ， In the formula: P di D represents the throughput (in %) of the sieve aperture size di. max denoted as the maximum particle size of the mineral, in mm; di is the size of a certain sieve aperture, in mm; A and B are coefficients, respectively. Based on the calculation results of the key sieve aperture passing rate of SAC skeleton aggregate gradation, as well as the sieving results of newly added aggregates and RAP sieving results, the blending ratio of coarse aggregates larger than 4.75mm was calculated. During the calculation, the blending ratio of RAP in the raw materials was synthesized according to the graded ratio of coarse and fine RAP aggregates under two specifications: RAP 0-10mm and RAP 10-20mm. S3. Conduct Marshall tests on the plant-mixed hot recycled asphalt mixture and adjust the filler according to the measured porosity.

2. The mix design method for skeleton-dense plant-mixed hot recycled asphalt mixture according to claim 1, characterized in that, Considering the different densities of RAP aggregate and new aggregate, the RAP blending ratio was converted to a volume ratio, and the asphalt content was determined based on previous engineering experience. The formula for calculating the equal volume replacement of aggregates in RAP is as follows: ， Where: m RAP The percentage of total RAP content, %; m RAPsi To match the specifications of s i The percentage of old aggregate by mass, %; ρ asi For specification s i The apparent density of the newly added aggregate (g / cm³) 3 ; ρ aRAPsi Specifications in RAP i Apparent density of old aggregate (g / cm³) 3 ;ω RAPsi Specifications in RAP i The percentage of old aggregates: % The formula for calculating the mass ratio of the mixture after equal volume replacement is as follows: ， ， Where: m tsi For specification s i The percentage of newly added aggregates after quality replacement, %; m RAPsi Specifications in RAP i The percentage of quality, %; m si To convert to 100% specification s i The percentage of newly added aggregate by weight, %; m' RAPsi To calculate the percentage of old aggregate mass of specification si in RAP after conversion to 100%, %; m k The percentage of mineral powder by mass is %.

3. The mix design method for skeleton-dense plant-mixed hot recycled asphalt mixture according to claim 1, characterized in that, After determining the gradation, a Marshall test is conducted based on engineering experience. When the test results of graded porosity, stability and flow value meet the relevant requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement", the high temperature performance, low temperature performance and water damage resistance of the plant-mixed hot recycled asphalt mixture shall be evaluated. When the test results of the gradation porosity exceed the relevant requirements of JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement", under the premise of keeping the volume ratio of skeleton aggregate to filler unchanged at 70:30, the proportion of mineral powder, fine aggregate or asphalt in the filler can be increased or decreased to adjust the gradation of the mixture, or the initial asphalt content can be fluctuated by ±0.3% to determine the optimal asphalt content of the mixture.

4. The mix design method for skeleton-dense plant-mixed hot recycled asphalt mixture according to claim 1, characterized in that, The content of RAP in the raw materials shall not be less than 30%.

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