A mix proportion design method for hot-in-situ recycled asphalt mixture

Abstract

The present invention discloses a method for designing a mix ratio for hot-in-situ regeneration asphalt. The method divides a hot-in-situ regeneration construction section into different construction units based on differences in pavement material and structure, maintenance history, and pavement disease distribution. Samples of recycled asphalt mixture from the original pavement are taken from each construction unit to test the performance indicators of the recycled asphalt mixture. The recycled asphalt mixture gradation and the calculated proportion of added new asphalt mixture are used to design the recycled asphalt mixture gradation and the added new asphalt mixture gradation. The recycled asphalt mixture gradation and the added new asphalt mixture gradation are then used to design the recycled asphalt mixture mix ratio according to the designed proportions, determining the recycled asphalt mixture gradation, asphalt content, regeneration agent dosage, and the added new asphalt mixture gradation and asphalt content. This method meticulously designs the material composition during the hot-in-situ regeneration construction process to ensure the quality of the hot-in-situ regeneration construction.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal regeneration of asphalt pavement materials, and in particular relates to a method for designing a mix ratio of an in-situ hot-regenerated asphalt mixture. Background Art

[0002] With rapid economic development and increasing traffic demand, the highway industry is gradually transitioning from a construction-focused approach to a maintenance-focused approach. According to surveys, asphalt pavements are the primary material for high-grade roads, accounting for over 90%. Asphalt pavements are often affected by factors such as traffic load, atmospheric temperature, and humidity, leading to degradation of their performance. Consequently, asphalt pavement maintenance techniques are required to ensure optimal performance and ensure the comfort and safety of drivers and passengers during their service life.

[0003] Due to the tightening of energy conservation and emission reduction policies, energy consumption and carbon emission control in the transportation sector, especially in highway construction and maintenance, are receiving attention. Therefore, in order to fully achieve the development goals of "carbon peak" and "carbon neutrality", it is necessary to fully utilize the waste generated by traditional construction and maintenance technologies in the field of highway construction and maintenance. Generally, recycled asphalt mixture (RAP) is often generated during the maintenance of asphalt pavement. RAP generated by traditional milling and resurfacing maintenance technology is usually discarded and piled up, which seriously occupies land resources and pollutes water resources, resulting in the waste of residual asphalt and mineral resources in RAP.

[0004] According to the existing literature 1 (Yang Jiangang, Yao Yuquan, Sun Chen. Influence of different working conditions on the performance of in-situ hot-regenerated asphalt mixture [J]. Journal of Highway and Transportation Research and Development, 2019, 36(10): 14-24.), the in-situ hot-regeneration technology of asphalt pavement can 100% utilize the original pavement RAP and effectively repair the surface functional performance defects of the asphalt pavement. It has the advantages of fast construction speed, small traffic impact, and high economic benefits. However, when the in-situ hot-regeneration technology is used for long-distance construction, the original pavement RAP is affected by the differences in the composition of the original construction section materials, traffic load, traffic volume, environmental conditions, etc., resulting in a large variability in the original pavement RAP. Therefore, in the process of designing the mix ratio of in-situ hot-regenerated asphalt mixture, it is necessary to consider the variability of the original pavement RAP in different construction sections and whether the mix ratio of the recycled asphalt mixture obtained by on-site remixing meets the control requirements in JTG / T 5521-2019 "Technical Specifications for Highway Asphalt Pavement Regeneration" and the performance requirements of asphalt mixture in JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction".

[0005] Currently, regarding the design process for hot-in-situ regeneration mixes, the recommended industry standard of the People's Republic of China, JTG / T 5521-2019, "Technical Specifications for Highway Asphalt Pavement Regeneration," covers the steps of evaluating the original pavement, sampling and evaluating the old asphalt mixture, designing the hot-in-situ regeneration scheme, including asphalt regeneration and grading of the recycled asphalt mixture, determining the optimal asphalt dosage for the recycled asphalt mixture, testing the performance of the recycled asphalt mixture, and paving a test section. The patent "Method for Determining the Mix Proportion for Hot-in-situ Regeneration" (CN 110261587 A) reports on collecting old asphalt mixture samples, testing the performance of the old asphalt mixture, determining the optimal regeneration agent ratio and target mix ratio, and then using the test samples to mix the recycled asphalt mixture to determine the ratio of new asphalt to new aggregate in the remixed recycled asphalt mixture and the optimal ratio of new asphalt mixture to old pavement. The patent "A Mix Design Method for Hot-in-Situ Recycled Asphalt Mixture" (CN 111916158 A) collects recycled asphalt from construction pavement. The mix ratio of the recycled asphalt mixture is determined by determining the regeneration agent ratio, the new aggregate ratio, and the recycled asphalt ratio, the optimal asphalt dosage for the recycled asphalt mixture, and the optimal new asphalt dosage. However, existing reports have not yet developed a complete method for hot-in-situ recycled asphalt mixture mix design that considers the RAP distribution and material composition variability of the maintained road section.

[0006] Therefore, in order to ensure the performance stability of recycled asphalt mixture during the hot-in-situ recycling construction process and to ensure that the mix design of recycled asphalt mixture meets the requirements of JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction", it is necessary to develop a mix design method for hot-in-situ recycled asphalt mixture. Summary of the Invention

[0007] In response to the problems existing in the prior art, the present invention provides a method for designing the mix ratio of asphalt mixture for hot-in-situ regeneration. During the design stage, the problem of variability in the composition of original pavement materials that may be encountered during the hot-in-situ regeneration construction process is fully considered. From the perspective of ensuring the construction quality of the hot-in-situ regenerated asphalt mixture, a method for designing the mix ratio of asphalt mixture for hot-in-situ regeneration is proposed, and the material composition in the hot-in-situ regeneration construction process is refined to ensure the construction quality of the hot-in-situ regeneration.

[0008] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0009] A method for designing a mix ratio of hot-in-situ recycled asphalt mixture, comprising:

[0010] Evaluate the basic conditions of the original pavement, including the original pavement structure and material conditions, the original pavement maintenance history, and the distribution of rutting defects in the original pavement sections;

[0011] Evaluate the RAP performance of the original pavement on different road sections, including the aggregate gradation, the aged asphalt content, and the aged asphalt penetration in the original pavement RAP;

[0012] Using the evaluation results of the aged asphalt content and the aged asphalt penetration in the original pavement RAP, it is determined whether the original pavement RAP can be constructed using the in-situ hot regeneration technology;

[0013] If the original pavement RAP can be constructed using in-situ thermal regeneration technology, the maintenance section construction units are divided according to the original pavement structure and material conditions, the original pavement maintenance history, and the distribution of the original pavement rutting disease sections;

[0014] According to the penetration index of the aged asphalt in the original road surface RAP, the amount of regeneration agent is determined by whether the penetration index of the aged asphalt is restored to the new asphalt standard;

[0015] Determine the ratio of the new asphalt mixture to the original pavement RAP in the designed recycled asphalt mixture based on the evaluation results of the cross-sectional distribution of the original pavement rutting disease;

[0016] Based on the ratio of the added new asphalt mixture to the original pavement RAP and the RAP aggregate gradation, the fluctuation range of the recycled asphalt mixture aggregate gradation is preliminarily calculated and compared with the allowable fluctuation range of the designed recycled asphalt mixture aggregate gradation. Based on the comparison results, it is analyzed whether the deviation of the pass rate of different sieve holes meets the requirements;

[0017] If the requirements are met, determine the designed recycled asphalt mixture aggregate quantity and designed aggregate gradation;

[0018] If the requirements are not met, the RAP aggregate gradation is classified, and the Fréchet similarity is used to quantitatively represent the aggregate gradation of the original pavement RAP in different sections. The cluster analysis method is used to cluster the aggregate gradation of the original pavement RAP into two or more categories. After classification, it is tested whether the fluctuation range of the RAP aggregate gradation of different categories meets the requirements of different sieve hole pass rate deviations, and the design quantity of the aggregate gradation of the recycled asphalt mixture is determined;

[0019] According to the classified mineral aggregate gradation of the original pavement RAP of different groups, the average value of the mineral aggregate gradation passing rate of the original pavement RAP of different groups is calculated, and the mineral aggregate gradation of the recycled asphalt mixture is determined by using the average value of the ratio of the added new asphalt mixture to the original pavement RAP of different groups;

[0020] Determine the mineral gradation of different groups of added new asphalt mixtures according to the mineral gradation of the recycled asphalt mixture, the mineral gradation of the original road surface RAP of different groups, and the ratio of the added new asphalt mixture of different groups to the original road surface RAP;

[0021] According to the aggregate gradation of the added new asphalt mixture in different groups, the average passing rate of the aggregate gradation of all the added new asphalt mixtures in different groups is calculated, and the aggregate gradation of all the recycled asphalt mixtures in different groups is calculated in combination with the aggregate gradation of the original pavement RAP in different groups and the ratio of the added new asphalt mixture in different groups to the original pavement RAP;

[0022] Compare the aggregate gradations of all recycled asphalt mixtures in different groups with the designed aggregate gradations of recycled asphalt mixtures, and analyze whether the deviations of the pass rates of different sieve holes meet the requirements based on the comparison results;

[0023] If the requirements are met, determine the aggregate gradation of the new asphalt mixture. The aggregate gradation of the new asphalt mixture is mainly used to make up for the insufficient sieve pass rate ratio in the aggregate gradation of the original road surface RAP. The designed aggregate gradation of the new asphalt mixture may not meet the upper and lower limit requirements of the characteristic gradation in JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction";

[0024] If the requirements are not met, all the mineral gradations of the new asphalt mixtures added in different groups are classified, and the Fréchet similarity is used to quantitatively represent the mineral gradations of all the new asphalt mixtures added in different groups. The high cluster analysis method is used to cluster all the mineral gradations of the new asphalt mixtures added in different groups into two or more categories. The average value of the mineral gradation pass rate is calculated based on the clustered mineral gradations of the new asphalt mixtures added in different groups, and the mineral grade of the recycled asphalt mixture is calculated using the ratio of the new asphalt mixtures added in different groups to the original pavement RAP;

[0025] Compare the aggregate gradation of all recycled asphalt mixtures in different groups after clustering with the designed aggregate gradation of recycled asphalt mixtures, and analyze whether the deviation of the pass rate of different sieve holes meets the requirements based on the comparison results;

[0026] If the requirements are met, determine the mineral aggregate gradation of the new asphalt mixture;

[0027] If the requirements are not met, increase the number of cluster groups and recalculate until the sieve pass rate deviation calculation result meets the requirements;

[0028] Determine the estimated asphalt-to-stone ratio of the recycled asphalt mixture based on the aggregate gradation of the recycled asphalt mixture, the average value of the RAP asphalt content of the original pavement in different groups or the average value of the RAP asphalt content of the original pavement in different groups after clustering, the average value of the ratio of the added new asphalt mixture to the original pavement RAP in different groups or the average value of the ratio of the added new asphalt mixture to the original pavement RAP in different groups after clustering, and the aggregate gradation of the added new asphalt mixture;

[0029] According to the estimated asphalt-to-stone ratio of the recycled asphalt mixture, Marshall specimens of the recycled asphalt mixture with different asphalt-to-stone ratios are prepared, and the gross volume density, void ratio, mineral gap ratio, effective asphalt saturation, stability and flow value index of the Marshall specimens are tested to determine the optimal asphalt-to-stone ratio of the recycled asphalt mixture;

[0030] According to the optimal asphalt-stone ratio of recycled asphalt mixture, the road performance of recycled asphalt mixture was analyzed by rutting test, low temperature bending test and freeze-thaw splitting test.

[0031] Based on the road performance test results of the recycled asphalt mixture, determine whether it meets the preset performance requirements; if it meets the performance requirements, it means that the designed recycled asphalt mixture gradation and optimal asphalt content are feasible; otherwise, the recycled asphalt mixture gradation is re-determined and the additional new asphalt mixture gradation is re-determined accordingly;

[0032] Determine the maximum usable mass of the added new asphalt and its mass ratio to the new mineral aggregate in the new asphalt mixture based on the optimal asphalt-to-stone ratio of the recycled asphalt mixture that meets the road performance requirements, the average value of the ratio of the added new asphalt mixture to the original road surface RAP in different groups, or the average value of the ratio of the added new asphalt mixture to the original road surface RAP in different groups after clustering;

[0033] Based on the maximum usable mass of the added new asphalt and its mass ratio to the new mineral aggregate in the new asphalt mixture, a leakage test is used to determine the optimal mass ratio of the new asphalt to the new mineral aggregate in the added new asphalt mixture, and the mass ratio is less than the maximum mass ratio of the added new asphalt to the new mineral aggregate;

[0034] The mass of the new asphalt added during the construction process is calculated based on the optimal mass ratio of the new asphalt to the new mineral material in the added new asphalt mixture, the optimal oil-stone ratio of the regenerated asphalt mixture, and the optimal addition ratio of the regeneration agent;

[0035] Based on the optimal mass ratio of new asphalt to new mineral aggregate in the added new asphalt mixture, the optimal oil-to-stone ratio of the recycled asphalt mixture, and the quality of the added new asphalt, a test section is paved to test the technical indicators, Marshall stability, gradation and gradation deviation, high-temperature stability, low-temperature crack resistance, and water stability of the recycled asphalt to determine whether it meets the design requirements;

[0036] Determine the design mix ratio of the recycled asphalt mixture based on whether the on-site index test results meet the design requirements, mainly including the gradation of the recycled asphalt mixture, the optimal asphalt content, the amount of regeneration agent, the gradation of the added new asphalt mixture and the optimal asphalt-to-stone ratio, and the quality of the new asphalt added on-site;

[0037] If the design requirements are not met, the aggregate gradation of the recycled asphalt mixture shall be adjusted accordingly, and the aggregate gradation of the new asphalt mixture and its optimal oil-stone ratio, as well as the quality of the new asphalt added on site, shall be re-determined.

[0038] Furthermore, the amount of regeneration agent is determined based on whether the penetration index of the aged asphalt is restored to the new asphalt standard, as follows:

[0039] Using regeneration agents with different mass ratios of aged asphalt, different amounts of regeneration agents were added to the aged asphalt and mixed evenly. The penetration of the aged asphalt containing the regeneration agent after mixing was tested, and the amount of regeneration agent was determined with the penetration at 25°C restored to the original asphalt standard as the control target.

[0040] Furthermore, the Fréchet similarity is used to quantitatively represent the mineral aggregate gradation of the original road surface RAP of different sections, specifically including:

[0041] Step 1: Construct the distance matrix D between any two points on L and L′;

[0042] Wherein, the curve L={L(1),L(2),...,L(n),...,L(N)}, L(n)=(x n ,y n ), x n Indicates the aggregate particle size passing through the nth sieve hole, mm; y n represents the percentage of aggregate passing through the nth sieve hole, %; gradation curve L′={L′(1),L′(2),...,L′(m),...,L′(M)}, L′(m)=(x′ m ,y′ m ), x′ m Indicates the aggregate particle size passing through the nth sieve hole, mm; y′ m Indicates the percentage of aggregate passing through the nth sieve hole, %;

[0043]

[0044] Where: It represents the distance between the mth point on the grading curve L′ and the nth point on the curve L; 1≤n≤N, 1≤m≤M, N and M represent the total number of screens used in the process of screening ore materials with different grading curves;

[0045] Step 2: Initialize the target distance f;

[0046] Calculate the longest distance d in matrix D max =max(D) and the shortest distance d min =min(D), and use d min Represents the target distance f after initialization;

[0047] Step 3: Binarization of matrix D;

[0048] Binarize the matrix D to obtain D′;

[0049]

[0050] Where:

[0051] Step 4: Calculate Fréchet similarity;

[0052] Find a path R in the binary matrix D′ whose elements satisfy the constituent element d′ 11 With element d′ MN The continuous straight line or curve between them, and the elements on the path R are all 1, calculate the Fréchet distance F, and the Fréchet similarity S = 1 / F; In addition, when the path R does not meet the screening conditions, initialize the target distance f′ = f + r, and use f′ to calculate steps 3 and 4 until a path that meets the conditions is found

[0053]

[0054] Furthermore, the ratio of the added new asphalt mixture to the original pavement RAP is determined based on the evaluation results of the cross-sectional distribution of the original pavement rutting disease, specifically using the following formula:

[0055] A=0.0335m 2 +4.35+2.5h

[0056] Where: m is the rutting depth, mm; h is the road elevation increase, mm, generally 2 mm.

[0057] Furthermore, according to the estimated asphalt-to-stone ratio of the recycled asphalt mixture, Marshall specimens of recycled asphalt mixture with different asphalt-to-stone ratios are prepared, as follows:

[0058] Taking the estimated oil-stone ratio of the recycled asphalt mixture as the median value, 5 groups of recycled asphalt mixture oil-stone ratios were designed with 0.5% as the equal interval. Recycled asphalt mixtures were prepared and Marshall specimens were formed according to the ratio of the added new asphalt mixture to the original pavement RAP.

[0059] Furthermore, the bulk density, void ratio, mineral gap ratio, effective asphalt saturation, stability and flow value of the Marshall test specimen are tested to determine the optimal asphalt-to-stone ratio of the recycled asphalt mixture, as follows:

[0060] Based on the test results of Marshall specimens of recycled asphalt mixtures with different oil-to-stone ratios, the oil-to-stone ratio corresponding to the maximum gross volume density of the Marshall specimens of recycled asphalt mixtures with different oil-to-stone ratios is determined as the first asphalt dosage, the oil-to-stone ratio corresponding to the maximum stability is determined as the second asphalt dosage, the oil-to-stone ratio corresponding to the void ratio is determined as the third asphalt dosage, and the oil-to-stone ratio corresponding to the median value of the effective asphalt saturation is determined as the fourth asphalt dosage. All indicators meet the maximum and minimum values ​​of the oil-to-stone ratio in the technical standards. The above indicators do not include the mineral aggregate void ratio.

[0061] The optimal asphalt-to-stone ratio of the recycled asphalt mixture is determined according to the first asphalt dosage, the second asphalt dosage, the third asphalt dosage, the fourth asphalt dosage and the maximum and minimum values ​​of the asphalt-to-stone ratio.

[0062] Furthermore, during the preparation of the recycled asphalt mixture, the following conditions are met:

[0063] The preheating temperature of the added new aggregate is 190-210°C, and the preheating time is 2-2.5 hours; the preheating temperature of the original pavement RAP is 130°C, and the preheating time does not exceed 2 hours; the preheating temperature of the new asphalt is 150-170°C, and the preheating time does not exceed 3 hours; the mixing temperature is 150-170°C.

[0064] Furthermore, the aged asphalt content in the original road surface RAP is obtained by extraction or combustion;

[0065] The mineral gradation in the RAP is tested by washing and screening the extracted or burned RAP mineral particles; the penetration of the aged asphalt in the original road surface RAP is tested by extracting the aged asphalt solution, separating the solvent from the aged asphalt in the aged asphalt solution by rotary evaporation or Absen method, and testing the penetration of the aged asphalt using a fully automatic asphalt penetrometer;

[0066] The indicators of the original pavement RAP performance evaluation were all tested in parallel, and the average value of the test results was used to represent the final test result;

[0067] The standard sieves used in the mineral gradation test in the original pavement RAP have a sieve aperture distribution of 0.075 mm, 0.15 mm, 0.3 mm, 0.6 mm, 1.18 mm, 2.36 mm, 4.75 mm, 9.5 mm, 13.2 mm, 16.0 mm and 19.0 mm.

[0068] Furthermore, the original pavement structure and material conditions are determined using original pavement design data; the original pavement maintenance history is determined by querying maintenance data after the road section is completed and opened to traffic; and the cross-sectional distribution of the original pavement rutting defects is determined using a multi-functional road inspection vehicle.

[0069] Furthermore, the cluster analysis method is a K-Means clustering method.

[0070] Compared with the prior art, the present invention has at least the following beneficial effects:

[0071] The present invention fully considers the problem of variability in the composition of recycled asphalt mixture materials of original pavement on different pavements during the in-situ hot regeneration construction process, involving the gradation of recycled asphalt mixture materials, asphalt content, and degree of asphalt aging. It proposes an in-situ hot regeneration asphalt mixture mix ratio design method and a specific implementation process based on the variability in the composition of the original pavement asphalt mixture materials. First, the original pavement materials and structures, maintenance history, and distribution of pavement rutting defects were investigated and divided into construction units. Second, the original pavement asphalt mixture was sampled using the core sampling method, and the gradation of the recycled material, asphalt content, and asphalt aging degree (needle penetration) of the original pavement asphalt mixture were tested to evaluate whether the original pavement asphalt mixture could be used to design the in-situ hot recycled asphalt mixture. Then, based on the variation range of the gradation of the recycled material in the asphalt mixture and the proportion of the added new asphalt mixture, it was determined whether it exceeded the design requirement of the gradation range. If the requirements were not met, the Frechet similarity was used based on the shape algorithm to represent the gradation of the recycled material in the asphalt mixture, and the cluster analysis method was used to classify the gradation of the asphalt mixture until the requirements were met. Then, based on the design value of the gradation of the recycled material in the asphalt mixture, the gradation of the recycled material in the asphalt mixture was calculated. The mineral gradation of the added new asphalt mixture is determined, and the Frechet similarity and cluster analysis methods are used to classify the mineral gradation of the added new asphalt mixture. On this basis, the calculated values ​​of the mineral gradation of the recycled asphalt mixture in different construction units are obtained. The differences between the calculated values ​​and the designed values ​​are compared in combination with the specifications to complete the mineral gradation design of the recycled asphalt mixture and the added new asphalt mixture; then, the amount of regeneration agent in the recycled asphalt mixture is determined, and the Marshall test is used to determine the optimal asphalt amount of the recycled asphalt mixture. The recycled asphalt mixture with the optimal asphalt amount is subjected to high-temperature stability, low-temperature crack resistance, water stability, and fatigue performance tests of the recycled asphalt mixture to determine whether the performance of the designed recycled asphalt mixture meets the requirements of the specifications; finally, according to the results of the recycled asphalt mixture performance test, the design results of the in-situ hot recycled asphalt mixture mix ratio are determined. During the design phase, this method fully considers the problem of variability in the composition of original pavement materials that may be encountered during the in-situ hot regeneration construction process, and proposes an in-situ hot regeneration asphalt mixture mix ratio design method from the perspective of ensuring the construction quality of the in-situ hot regeneration asphalt mixture, and refines the design of the material composition during the in-situ hot regeneration construction process to ensure the construction quality of the in-situ hot regeneration.

[0072] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the specific embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0074] Figure 1 This is an overall flow chart of a mix ratio design method for hot-in-situ recycled asphalt mixture according to the present invention;

[0075] Figure 2 This is a flow chart of the K-means clustering calculation steps in a method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to the present invention;

[0076] Figure 3 The results of the RAP ore gradation test in the examples are as follows;

[0077] Figure 4 The test results of RAP asphalt content and aged asphalt index in the examples;

[0078] Figure 5 The calculation results of RAP ore gradation deviation in the embodiment;

[0079] Figure 6 is the design value of the mineral gradation of the recycled asphalt mixture in the embodiment;

[0080] Figure 7 This is the new asphalt mixture aggregate gradation in the embodiment. DETAILED DESCRIPTION

[0081] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0082] As a specific embodiment of the present invention, Figure 1 As shown in FIG, a method for designing a mix ratio of hot-in-situ recycled asphalt mixture specifically includes:

[0083] S1. Evaluate the basic conditions of the original pavement, including the original pavement structure and material conditions, the original pavement maintenance history, and the cross-sectional distribution of the original pavement rutting defects.

[0084] Specifically, the original pavement structure and material conditions are determined using the original pavement design data; the original pavement maintenance history is determined by querying the maintenance data after the road section is completed and opened to traffic; and the cross-sectional distribution of the original pavement rutting defects is determined using a multi-functional road inspection vehicle.

[0085] Based on the original pavement structure and material conditions, the original pavement maintenance history, and the cross-sectional distribution of the original pavement rutting disease, the variability of the original pavement RAP material properties was preliminarily determined. Based on the distribution of the maintenance sections, the construction units were divided and the original pavement RAP sampling plan was determined.

[0086] S2. Evaluate the RAP performance of the original pavement in different road sections. The RAP performance of the original pavement includes the mineral aggregate gradation in the original pavement RAP, the aged asphalt content in the original pavement RAP, and the aged asphalt penetration in the original pavement RAP.

[0087] In the present invention, the needle penetration of the aged asphalt in the original road surface RAP is the needle penetration of the aged asphalt in the original road surface RAP at 25°C.

[0088] The sampling of recycled asphalt mixture from the original pavement in different maintenance sections adopts the core sampling method, with the core sample diameter of 100-150mm. The core sampling locations of different maintenance sections are distributed in the wheel track strips on both sides and the center of the lane, and the number of cross-section cores is 3. For different maintenance sections, cross-sections are randomly selected for core sampling in each maintenance section. For longer maintenance sections, the core sampling is carried out according to the 5000m 2 / times to carry out cross-section coring.

[0089] The aggregate gradation, aged asphalt content, and penetration of aged asphalt in the original pavement RAP of different maintenance sections were determined by collecting core samples. Based on the core samples from different maintenance sections, the upper RAP layer of the asphalt pavement was separated by heating and cutting at a temperature of 60-80°C to soften the interlayer bonding asphalt. When cut with a tool, the softened interlayer bonding asphalt reduces its viscosity, thus separating the upper layer of the asphalt pavement from the other surface layers. The original pavement RAP core samples were subjected to a heat exfoliation method to obtain dispersed original pavement RAP particles at a heating temperature of 110-130°C.

[0090] Specifically:

[0091] The aged asphalt content in the original pavement RAP is obtained by extraction or combustion method;

[0092] The aggregate gradation in RAP is tested by washing and screening after extraction or combustion. The penetration of aged asphalt in the original road surface RAP is tested by extracting the aged asphalt solution, separating the solvent from the aged asphalt solution by rotary evaporation or the Absen method, and testing the penetration of the aged asphalt at 25°C using a fully automatic asphalt penetrometer.

[0093] All indicators of the original pavement RAP performance evaluation were tested in parallel, and the average value of the test results was used to represent the final test results;

[0094] The standard sieves used in the mineral aggregate gradation test in the original pavement RAP have a sieve aperture distribution of 0.075 mm, 0.15 mm, 0.3 mm, 0.6 mm, 1.18 mm, 2.36 mm, 4.75 mm, 9.5 mm, 13.2 mm, 16.0 mm, and 19.0 mm, which are taken from the sieve aperture requirements for the mineral aggregate gradation curve in JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction".

[0095] S3. Using the assessment results of the aged asphalt content and penetration of the aged asphalt in the original pavement RAP, combined with the requirements for the aged asphalt content in RAP and the penetration of the aged asphalt in RAP at 25°C in JTG / T 5521-2019 "Technical Specifications for Regeneration of Highway Asphalt Pavements," which are ≥3.8% and ≥2 mm, respectively, determine whether the original pavement RAP can be constructed using in-situ hot regeneration technology;

[0096] If the original pavement RAP can be constructed using in-situ hot regeneration technology, the amount of regeneration agent will be determined based on whether the penetration index of the aged asphalt has been restored to the new asphalt standard, using the aged asphalt mass percentage table.

[0097] Specifically, different amounts of regeneration agents with different mass ratios of aged asphalt are added to the aged asphalt and mixed evenly. The penetration of the aged asphalt containing the regeneration agent after mixing is tested, and the amount of regeneration agent is determined with the penetration at 25°C restored to the original asphalt standard as the control target.

[0098] S4. Based on the evaluation results of the cross-sectional distribution of the original pavement rutting disease, determine the ratio of the added new asphalt mixture to the original pavement RAP. Specifically, the following formula is used:

[0099] A=0.0335m 2 +4.35+2.5h

[0100] Where: m is the rutting depth, mm; h is the road elevation increase, mm, generally 2 mm.

[0101] S5. According to the ratio of the added new asphalt mixture to the original pavement RAP, determine whether the RAP aggregate gradation fluctuation range meets the requirements of the recycled asphalt mixture aggregate gradation fluctuation range when calculating the ratio of the added new asphalt mixture to the original pavement RAP.

[0102] The fluctuation range of mineral aggregate gradation of recycled asphalt mixture complies with the requirements of mineral aggregate gradation fluctuation range in JTG T5521-2019 "Technical Specifications for Regeneration of Highway Asphalt Pavement". Specifically, the allowable deviation of sieve hole of 0.075mm is ±2, the allowable deviation of sieve hole ≤2.36mm is ±5 (expressways, first-class highways) and ±6 (other grades of highways), and the allowable deviation of sieve hole ≥4.75mm is ±6 (expressways, first-class highways) and ±7 (other grades of highways).

[0103] If the requirements are met, the average value of the mineral gradation pass rate of different groups of original pavement RAP is calculated based on the mineral gradation of different groups of original pavement RAP after classification, and the average value of the ratio of different groups of added new asphalt mixture to original pavement RAP is used to determine the mineral gradation of the recycled asphalt mixture.

[0104] The mineral aggregate gradation of the recycled asphalt mixture complies with the upper and lower limit requirements of the gradation design in JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction".

[0105] If the requirements are not met, the mineral gradations of different groups of RAP are grouped, and the Fréchet similarity is used to quantitatively represent the mineral gradations of the original pavement RAP of different sections. The cluster analysis method is used to cluster the mineral gradations of the original pavement RAP into two or more categories. According to the mineral gradations of the original pavement RAP of different groups after clustering, the fluctuation range of the passing rate of the mineral gradation of different groups of RAP after classification is calculated, and the number of RAP mineral gradation groups and the mineral gradation of recycled asphalt mixture are determined based on whether the fluctuation range meets the design or specification requirements.

[0106] Preferably, the cluster analysis method is the K-Means clustering method, for details refer to Figure 2 shown.

[0107] Specifically, the Fréchet similarity is used to quantitatively represent the aggregate gradation of the original pavement RAP of different sections, including:

[0108] S501, constructing a distance matrix D between any two points on L and L′;

[0109] Wherein, the curve L={L(1),L(2),...,L(n),...,L(N)}, L(n)=(x n ,y n ), x n Indicates the aggregate particle size passing through the nth sieve hole, mm; yn represents the percentage of aggregate passing through the nth sieve hole, %; gradation curve L′={L′(1),L′(2),...,L′(m),...,L′(M)}, L′(m)=(x′ m ,y′ m ), x′ m Indicates the aggregate particle size passing through the nth sieve hole, mm; y′ m Indicates the percentage of aggregate passing through the nth sieve hole, %;

[0110]

[0111] Where: It represents the distance between the mth point on the grading curve L′ and the nth point on the curve L; 1≤n≤N, 1≤m≤M, N and M represent the total number of screens used in the process of screening ore materials with different grading curves;

[0112] S502, initializing the target distance f;

[0113] Calculate the longest distance d in matrix D max =max(D) and the shortest distance d min =min(D), and use d min Represents the target distance f after initialization;

[0114] S503, matrix D is binarized;

[0115] Binarize the matrix D to obtain D′;

[0116]

[0117] Where:

[0118] S504, calculating Fréchet similarity;

[0119] Find a path R in the binary matrix D′ whose elements satisfy the constituent element d′ 11 With element d′ MN The continuous straight line or curve between them, and the elements on the path R are all 1, calculate the Fréchet distance F, and the Fréchet similarity S = 1 / F; In addition, when the path R does not meet the screening conditions, initialize the target distance f′ = f + r, and use f′ to calculate steps 3 and 4 until a path that meets the conditions is found

[0120]

[0121] S6. Calculate the aggregate gradation of different groups of added new asphalt mixtures based on the aggregate gradation of recycled asphalt mixture, the aggregate gradation of different groups of original pavement RAP, and the ratio of the added new asphalt mixture to the original pavement RAP.

[0122] S7. Calculate the average value of the mineral gradation of different groups of added new asphalt mixtures, and calculate the calculated value of the mineral gradation of the recycled asphalt mixture based on the mineral gradation of different groups of original pavement RAP and the ratio of different groups of added new asphalt mixtures to original pavement RAP.

[0123] S8. Compare the mineral gradation of all recycled asphalt mixtures in different groups with the mineral gradation of the designed recycled asphalt mixture, and analyze whether the deviation of the pass rate of different sieve holes meets the requirements based on the comparison results.

[0124] If the requirements are met, determine the mineral aggregate gradation of the new asphalt mixture;

[0125] If the requirements are not met, the proportion of the added new asphalt mixture and the original pavement RAP that does not meet the requirements of the deviation calculation results will be grouped, and the Fréchet similarity will be used to quantitatively represent the mineral gradation of the original pavement RAP in different sections. The cluster analysis method will be used to cluster the mineral gradation of the added new asphalt mixture into two or more categories, and the calculated values ​​of the mineral gradation of the recycled asphalt mixture in different groups will be calculated.

[0126] S9. Compare the aggregate gradations of all recycled asphalt mixtures in different groups after clustering with the designed aggregate gradations of recycled asphalt mixtures, and analyze whether the deviations of the pass rates of different sieve holes meet the requirements based on the comparison results;

[0127] If the requirements are met, determine the mineral aggregate gradation of the new asphalt mixture;

[0128] If the requirements are not met, increase the number of cluster groups and recalculate until the sieve pass rate deviation calculation result meets the requirements.

[0129] S10. Determine the estimated asphalt-to-stone ratio of the recycled asphalt mixture based on the mineral gradation of the recycled asphalt mixture, the average RAP asphalt content of the original pavement in different groups or the average RAP asphalt content of the original pavement in different groups after clustering, the average ratio of the added new asphalt mixture to the original pavement RAP in different groups or the average ratio of the added new asphalt mixture to the original pavement RAP in different groups after clustering, and the mineral gradation of the added new asphalt mixture.

[0130] S11. Based on the estimated oil-to-stone ratio of the recycled asphalt mixture, Marshall specimens of the recycled asphalt mixture with different oil-to-stone ratios are prepared respectively, and the gross volume density, void ratio, mineral gap ratio, effective asphalt saturation, stability and flow value index of the Marshall specimens are tested to determine the optimal oil-to-stone ratio of the recycled asphalt mixture.

[0131] Specifically, the estimated oil-stone ratio of the recycled asphalt mixture was taken as the median value, and 0.5% was used as the equal interval to design five groups of oil-stone ratios of the recycled asphalt mixture. Based on the ratio of the added new asphalt mixture to the original pavement RAP, the recycled asphalt mixture was prepared and Marshall specimens were formed.

[0132] Based on the test results of Marshall specimens of recycled asphalt mixtures with different oil-to-stone ratios, the oil-to-stone ratio corresponding to the maximum gross volume density of the Marshall specimens of recycled asphalt mixtures with different oil-to-stone ratios was determined as the first asphalt dosage, the oil-to-stone ratio corresponding to the maximum stability was determined as the second asphalt dosage, the oil-to-stone ratio corresponding to the void ratio was determined as the third asphalt dosage, and the oil-to-stone ratio corresponding to the median effective asphalt saturation was determined as the fourth asphalt dosage. All indicators met the maximum and minimum values ​​of the oil-to-stone ratio in accordance with the technical standards, and all indicators did not include the mineral aggregate void ratio.

[0133] The optimal asphalt-stone ratio of the recycled asphalt mixture is determined according to the first asphalt dosage, the second asphalt dosage, the third asphalt dosage, the fourth asphalt dosage and the maximum and minimum values ​​of the asphalt-stone ratio.

[0134] S12. Based on the optimal asphalt-stone ratio of the recycled asphalt mixture, the road performance of the recycled asphalt mixture was analyzed using rutting test, low-temperature bending test, and freeze-thaw splitting test.

[0135] S13. Based on the road performance test results of the recycled asphalt mixture, determine whether it meets the preset performance requirements; if it meets the performance requirements, it means that the designed recycled asphalt mixture gradation and optimal asphalt content are feasible; otherwise, redetermine the recycled asphalt mixture gradation and the additional new asphalt mixture gradation accordingly.

[0136] S14. Determine the maximum usable mass of the added new asphalt and its mass ratio to the new mineral aggregate in the new asphalt mixture based on the optimal oil-to-stone ratio of the recycled asphalt mixture that meets the requirements of the specifications, the average value of the ratio of the added new asphalt mixture to the original pavement RAP in different groups, or the average value of the ratio of the added new asphalt mixture to the original pavement RAP in different groups after clustering.

[0137] S15. Based on the maximum usage mass of the added new asphalt and its mass ratio to the new mineral aggregate in the new asphalt mixture, a leakage test is used to determine the optimal mass ratio of the new asphalt to the new mineral aggregate in the added new asphalt mixture, and the mass ratio is less than the maximum mass ratio of the added new asphalt to the new mineral aggregate.

[0138] S16. Calculate the mass of new asphalt added during construction based on the optimal mass ratio of new asphalt to new mineral aggregate in the new asphalt mixture, the optimal oil-stone ratio in the recycled asphalt mixture, and the optimal addition ratio of the regeneration agent.

[0139] S17. Based on the optimal mass ratio of new asphalt to new mineral aggregate in the added new asphalt mixture, the optimal oil-stone ratio of the recycled asphalt mixture, and the quality of the added new asphalt, a test section is paved to test the technical indicators, Marshall stability, gradation and gradation deviation, high-temperature stability, low-temperature crack resistance, and water stability of the on-site recycled asphalt to determine whether it meets the design requirements.

[0140] S18. Determine the design mix ratio of the recycled asphalt mixture based on whether the on-site index test results meet the design requirements, which mainly includes the gradation of the recycled asphalt mixture, the optimal asphalt content, the amount of regeneration agent, the gradation of the added new asphalt mixture and the optimal oil-stone ratio, as well as the quality of the new asphalt added on site.

[0141] S19. If the design requirements are not met, the gradation of the mineral aggregate of the recycled asphalt mixture shall be adjusted accordingly, and the gradation of the mineral aggregate of the added new asphalt mixture and its optimal oil-stone ratio, as well as the quality of the new asphalt added on site, shall be re-determined.

[0142] In the present invention, during the preparation of the recycled asphalt mixture, the following conditions are met:

[0143] The preheating temperature for added new aggregate is 190-210°C for 2-2.5 hours. The preheating temperature for the original pavement RAP is 130°C for no more than 2 hours. The preheating temperature for the new asphalt is 150-170°C for no more than 3 hours. The mixing temperature is 150-170°C. Based on the different preheating times and temperatures of the recycled asphalt mixture components, the laboratory mixing process for the recycled asphalt mixture is to mix the RAP and regeneration agent for 60-90 seconds, then add the new aggregate and new asphalt and mix for 60-90 seconds. The mixed recycled asphalt mixture is then oven-heated at 120°C, 130°C, and 140°C. Marshall specimens are then formed and cured indoors for 24 hours before testing Marshall performance indicators. Three temperatures, 120°C, 130°C, and 140°C, are used during the Marshall forming process. These temperatures are determined based on the temperature deviation range that the recycled asphalt mixture will experience during in-situ hot recycling.

[0144] The present invention will be described in more detail below with reference to specific embodiments.

[0145] 3.1 Project Overview

[0146] The reliability of this mix design method was demonstrated during the major asphalt pavement renovation project on the Dechang Expressway in Jiangxi Province. The project employed in-situ hot recycling technology to regenerate 4cm SMA-13 ​​on the roadway.

[0147] 3.2 Original pavement evaluation

[0148] An investigation of the original pavement's structural composition, maintenance history, and distribution of pavement defects revealed a 4cm SMA-13 ​​top layer. The original pavement had not undergone major or medium-sized repairs since opening to traffic in 2011, with routine maintenance being the primary treatment. The primary asphalt pavement defects were surface spalling and minor rutting.

[0149] 3.3RAP sampling and evaluation

[0150] According to the evaluation results of the original pavement, it can be considered that the composition of the original pavement materials is basically the same. However, according to the bidding documents, the maintenance section involves different construction sections during the construction period and is completed by different construction units. Therefore, RAP sampling is carried out considering different construction sections, and 12 sampling locations are designed according to the differences in the division of construction sections, as shown in Table 1. The sampling positions are designed according to Table 1, and the sampling scheme in Table 1 is adopted. The original pavement RAP is obtained by core sampling. The mineral gradation of RAP at different sampling positions is tested by extraction method. The results are as follows Figure 3 As shown in the following table. The test results of asphalt content in RAP and 25℃ needle penetration index of aged asphalt are shown in the table. Figure 4 shown.

[0151] Table 1 Designed sampling locations

[0152]

[0153] Depend on Figure 3 As can be seen, the pass rates at the 0.075mm to 4.75mm sieve apertures at sections K257+500, K261+100, K263+100, and K277+600 exceed the upper limit of the SMA-13 ​​asphalt mixture, while the aggregate gradation at K286+100 approaches the lower limit of the SMA-13 ​​asphalt mixture gradation. Overall, the aggregate gradation of these 12 sections is above the median of the SMA-13 ​​gradation, with a relatively fine aggregate composition, and significant differences are observed among the 12 sections.

[0154] Depend on Figure 4 As can be seen, the RAP asphalt content of the test sections ranged from 4.98% to 5.63%, with an average of 5.31%, a standard deviation of 0.20%, and a range of 0.65%. The 25°C penetration of the aged asphalt in the RAP ranged from 3.6 to 4.5 mm, with an average of 3.9 mm, a standard deviation of 0.27 mm, and a range of 0.9 mm. Overall, the asphalt content and penetration values ​​of the 12 sections were relatively close, with low dispersion.

[0155] 3.4 Mineral gradation design

[0156] This study divided the construction sections into 12 units using the designed sampling locations (construction sections) shown in Table 1. The average rutting depth for each of the 12 units was calculated, and the proportion of added new asphalt mixture was calculated based on a 2mm pavement elevation increase. The results are shown in Table 2. Table 2 shows that the proportion of added new asphalt mixture ranged from 10% to 12% for each construction unit.

[0157] Table 2 Construction unit rutting depth and proportion of added new asphalt mixture

[0158]

[0159] Note: The meanings of the numbers in Table 2 are the same as those in Table 1.

[0160] According to the test results of RAP ore gradation in different construction units, the extreme difference distribution of RAP ore gradation with different sieve holes is as follows: Figure 5 As shown. According to the design requirements, the difference between the on-site construction mineral gradation of the highway and the design gradation at 0.075mm, ≤2.36mm, ≥4.75mm sieve holes should be controlled within ±2%, ±5%, ±6%, and the range should be controlled within 4%, 10%, and 12%. Therefore, according to the amount of RAP mineral gradation in the recycled asphalt mixture and the addition ratio of 10% new asphalt mixture, the range of the pass rate of different sieve holes of RAP mineral gradation in different construction units is calculated respectively. However, Figure 5 Calculation results show that the extreme differences in RAP aggregate gradation for different construction units, at 0.075mm and 2.36-9.5mm sieve openings, do not meet design requirements. Therefore, prioritizing the classification of recycled asphalt mixture aggregate gradations for different construction units and determining the aggregate gradation for recycled asphalt mixtures, should be considered before designing the aggregate gradation for recycled asphalt mixtures.

[0161] The Fréchet similarity method was used to calculate the Fréchet similarity of the RAP aggregate gradations of the 12 construction units, taking the median value of the SMA-13 ​​aggregate gradation as the reference aggregate gradation. The calculation results were divided into four categories, as shown in Table 3.

[0162] Table 3 Fréchet similarity calculation and classification results

[0163]

[0164] Note: The meanings of the numbers in Table 3 are the same as those in Table 1.

[0165] According to the classification results, the gradation range of RAP aggregates under different classification conditions was calculated, and the results are shown in Table 4. As can be seen from Table 4, the gradation ranges of the four types of RAP aggregates after classification basically meet the design requirements.

[0166] Table 4 RAP aggregate grading range after classification

[0167]

[0168] According to the classification results, 4 types of recycled asphalt mixture aggregate gradations are designed as follows: Figure 6 As shown. Figure 6 It can be seen that the design gradations of recycled asphalt mixtures corresponding to the four types of RAP aggregate gradations differ significantly. Specifically, the design value of the Class A aggregate gradation does not meet the upper limit of the specification at the 4.75mm sieve aperture. This is primarily because the RAP aggregate gradation's pass rate at the 4.75mm sieve aperture exceeds the design upper limit, and the 90% RAP aggregate addition cannot reduce the 4.75mm aggregate pass rate to within the design upper limit. As a result, the designed recycled asphalt mixture's 4.75mm pass rate does not meet the SMA-13 ​​requirements. Therefore, for complex working conditions where the RAP aggregate gradation exceeds the design requirements, the design should be adjusted based on the proportion of new asphalt mixture added. This study does not consider the limitations of designing recycled asphalt mixtures exceeding the SMA-13 ​​upper limit; it only demonstrates the feasibility of the proposed design method.

[0169] According to the design of mineral aggregate gradation of recycled asphalt mixture, combined with the calculation results of the proportion of new asphalt mixture in different construction units, the mineral aggregate gradation of the new asphalt mixture is calculated respectively, and the mineral aggregate gradation that does not meet the gradation change trend after calculation is adjusted to obtain the mineral aggregate gradation of the new asphalt mixture. Figure 7 As shown. Figure 7 It can be seen that the aggregate gradation of the added new asphalt mixture has a high degree of discreteness. In engineering, the aggregate gradation of the added new asphalt mixture can be designed accordingly for different construction units to accurately control the aggregate gradation during the construction of the recycled asphalt mixture. However, when the number of construction units is large, the large number of new asphalt mixture aggregate gradation designs will increase the burden of gradation adjustment when the asphalt mixing plant produces new asphalt mixture, which may cause production inconvenience and overflow in the mixing plant.

[0170] To reduce the types of aggregate gradations in the new asphalt mixture, the Fréchet similarity method was used. The median of the SMA-13 ​​aggregate gradation was used as the reference aggregate gradation. The Fréchet similarity of the aggregate gradations of the 11 construction units plus the new asphalt mixture was calculated. A preliminary classification was proposed into four categories. The results are shown in Table 5.

[0171] Table 5 Fréchet similarity calculation and classification results

[0172]

[0173] Note: The meanings of the numbers in Table 5 are the same as those in Table 1.

[0174] Based on the classification results, the average values ​​of the aggregate gradations of the new asphalt mixtures for each classification were calculated. Based on this, the calculated values ​​of the aggregate gradations of the recycled asphalt mixtures for each construction unit were calculated, and the differences between the designed and calculated values ​​were compared. The results are shown in Table 6. As can be seen from Table 6, the pass rate difference between the calculated and designed values ​​of the aggregate gradations of the recycled asphalt mixtures basically meets the design requirements.

[0175] Table 6 Comparison of design and calculated values ​​of aggregate gradation for recycled asphalt mixture

[0176]

[0177] In summary, it is necessary to design 4 types of recycled asphalt mixture aggregate gradations and additional new asphalt mixture aggregate gradations to make the recycled asphalt mixture aggregate gradations meet the design change requirements under this complex working condition. The recycled asphalt mixture aggregate gradations are designed as follows: Figure 6 As shown in Table 7, the new asphalt mixture aggregate gradation is shown in Table 7, and the design gradation of different construction units and the new asphalt mixture aggregate gradation are shown in Table 3 and Table 5 respectively.

[0178] Table 7 New asphalt mixture aggregate gradation

[0179]

[0180] 3.5 Determine the amount of regeneration agent

[0181] The regeneration agent used was RA-102, and the regeneration agent was added in equal proportions of 0%, 2%, 4%, and 6% by mass relative to the aged asphalt. Penetration test results for the regenerated asphalt were measured at the maximum and minimum penetrations of the aged asphalt. The target grade of the regenerated asphalt was Type I-D SBS modified asphalt, with a 25°C penetration control target of 40-60 (0.1 mm). Based on the 25°C penetration test results for the regenerated asphalt at different regeneration agent dosages, a 3% regeneration agent dosage was determined.

[0182] 3.6 Marshall test and determination of optimal asphalt dosage

[0183] Taking construction unit K312+900 (number 5) as an example, the designed recycled asphalt mix proportion was Class C, the added fresh asphalt mix had a Class IV aggregate gradation, the RAP asphalt content was 5.01%, and the fresh asphalt mix addition ratio was 11.2%. Based on the designed material composition, Marshall specimens with asphalt contents of 4.7%, 5.2%, and 5.7% were formed at 150°C using Marshall test specimens. Marshall volume index, stability, and flow index were tested accordingly. The RAP heating temperature was 130°C, the mixing temperature was 150°C, the fresh material heating temperature was 190°C, the fresh asphalt heating temperature was 170°C, and the double-sided compaction number was 75. The test results are shown in Table 8.

[0184] Table 8 Marshall test results

[0185]

[0186] Table 8 shows that the optimal asphalt content of the recycled asphalt mixture is 5.2%. Based on the RAP asphalt content and RAP usage ratio, the added fresh asphalt content is 0.7% (by mass of the recycled asphalt mixture). By further dividing the added fresh asphalt content, the optimal asphalt content of the recycled asphalt mixture is 4.3% (by mass of the new asphalt mixture), the regeneration agent dosage is 3% (by mass of the aged asphalt), and the added fresh asphalt dosage during construction is 0.1% (by mass of the recycled asphalt mixture).

[0187] 3.7 Mix design test

[0188] In view of the hot and rainy climate characteristics of Jiangxi Province, the high-temperature stability, water stability, and water permeability of the designed recycled asphalt mixture were tested, and the test results are shown in Table 9. As shown in Table 9, the performance test results of the designed recycled asphalt mixture meet the design requirements.

[0189] Table 9 Test results of recycled asphalt mixture performance

[0190]

[0191] 3.8 Test section to test the performance of recycled asphalt mixture

[0192] Based on the designed recycled asphalt mixture proportion, the recycled asphalt mixture proportion design was verified at construction unit K312+900 (number 5). Recycled asphalt mixture was collected from the test section and tested for high-temperature stability, water stability, and water permeability. The test results were generally consistent with those in Table 9. Therefore, the designed recycled asphalt mixture gradation met the regulatory requirements.

[0193] Finally, it should be noted that the above-described embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-described embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. Such modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for designing the mix ratio of hot-in-situ recycled asphalt mixture, characterized in that: include: Evaluate the basic conditions of the original pavement, including the original pavement structure and material conditions, the original pavement maintenance history, and the distribution of rutting defects in the original pavement sections; Evaluate the RAP performance of the original pavement on different road sections, including the aggregate gradation, the aged asphalt content, and the aged asphalt penetration in the original pavement RAP; Using the evaluation results of the aged asphalt content and the aged asphalt penetration in the original pavement RAP, it is determined whether the original pavement RAP can be constructed using the in-situ hot regeneration technology; If the original pavement RAP can be constructed using in-situ thermal regeneration technology, the maintenance section construction units are divided according to the original pavement structure and material conditions, the original pavement maintenance history, and the distribution of the original pavement rutting disease sections; The amount of regeneration agent is determined based on the penetration index of the aged asphalt in the original pavement RAP and whether the penetration index of the aged asphalt is restored to the new asphalt standard; Based on the evaluation results of the cross-sectional distribution of the original pavement rutting defects, the ratio of the added new asphalt mixture to the original pavement RAP in the designed recycled asphalt mixture is determined using the following formula: Where: is the rutting depth, mm; h is the road elevation increase, mm, which is 2 mm; Based on the ratio of the added new asphalt mixture to the original pavement RAP and the RAP aggregate gradation, the fluctuation range of the recycled asphalt mixture aggregate gradation is preliminarily calculated and compared with the allowable fluctuation range of the designed recycled asphalt mixture aggregate gradation. Based on the comparison results, it is analyzed whether the deviation of the pass rate of different sieve holes meets the requirements; If the requirements are met, determine the designed recycled asphalt mixture aggregate quantity and designed aggregate gradation; If the requirements are not met, the RAP aggregate gradation is classified, and the Fréchet similarity is used to quantitatively represent the aggregate gradation of the original pavement RAP in different sections. The cluster analysis method is used to cluster the aggregate gradation of the original pavement RAP into two or more categories. After classification, it is tested whether the fluctuation range of the RAP aggregate gradation of different categories meets the requirements of different sieve hole pass rate deviations, and the design quantity of the aggregate gradation of the recycled asphalt mixture is determined; According to the classified mineral aggregate gradation of the original pavement RAP of different groups, the average value of the mineral aggregate gradation passing rate of the original pavement RAP of different groups is calculated, and the mineral aggregate gradation of the recycled asphalt mixture is determined by using the average value of the ratio of the added new asphalt mixture to the original pavement RAP of different groups; Determine the mineral gradation of different groups of added new asphalt mixtures according to the mineral gradation of the recycled asphalt mixture, the mineral gradation of the original road surface RAP of different groups, and the ratio of the added new asphalt mixture of different groups to the original road surface RAP; According to the aggregate gradation of the added new asphalt mixture in different groups, the average passing rate of the aggregate gradation of all the added new asphalt mixtures in different groups is calculated, and the aggregate gradation of all the recycled asphalt mixtures in different groups is calculated in combination with the aggregate gradation of the original pavement RAP in different groups and the ratio of the added new asphalt mixture in different groups to the original pavement RAP; Compare the aggregate gradations of all recycled asphalt mixtures in different groups with the designed aggregate gradations of recycled asphalt mixtures, and analyze whether the deviations of the pass rates of different sieve holes meet the requirements based on the comparison results; If the requirements are met, determine the aggregate gradation of the new asphalt mixture. The aggregate gradation of the new asphalt mixture is mainly used to make up for the insufficient sieve pass rate ratio in the aggregate gradation of the original road surface RAP. The designed aggregate gradation of the new asphalt mixture may not meet the upper and lower limit requirements of the characteristic gradation in JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction"; If the requirements are not met, all the mineral gradations of the new asphalt mixtures added in different groups are classified, and the Fréchet similarity is used to quantitatively represent the mineral gradations of all the new asphalt mixtures added in different groups. The high cluster analysis method is used to cluster all the mineral gradations of the new asphalt mixtures added in different groups into two or more categories. The average value of the mineral gradation pass rate is calculated based on the clustered mineral gradations of the new asphalt mixtures added in different groups, and the mineral grade of the recycled asphalt mixture is calculated using the ratio of the new asphalt mixtures added in different groups to the original pavement RAP; Compare the aggregate gradation of all recycled asphalt mixtures in different groups after clustering with the designed aggregate gradation of recycled asphalt mixtures, and analyze whether the deviation of the pass rate of different sieve holes meets the requirements based on the comparison results; If the requirements are met, determine the mineral aggregate gradation of the new asphalt mixture; If the requirements are not met, increase the number of cluster groups and recalculate until the sieve pass rate deviation calculation result meets the requirements; Determine the estimated asphalt-to-stone ratio of the recycled asphalt mixture based on the aggregate gradation of the recycled asphalt mixture, the average value of the RAP asphalt content of the original pavement in different groups or the average value of the RAP asphalt content of the original pavement in different groups after clustering, the average value of the ratio of the added new asphalt mixture to the original pavement RAP in different groups or the average value of the ratio of the added new asphalt mixture to the original pavement RAP in different groups after clustering, and the aggregate gradation of the added new asphalt mixture; According to the estimated asphalt-to-stone ratio of the recycled asphalt mixture, Marshall specimens of the recycled asphalt mixture with different asphalt-to-stone ratios are prepared, and the gross volume density, void ratio, mineral gap ratio, effective asphalt saturation, stability and flow value index of the Marshall specimens are tested to determine the optimal asphalt-to-stone ratio of the recycled asphalt mixture; According to the optimal asphalt-stone ratio of recycled asphalt mixture, the road performance of recycled asphalt mixture was analyzed by rutting test, low temperature bending test and freeze-thaw splitting test. Based on the road performance test results of the recycled asphalt mixture, determine whether it meets the preset performance requirements; if it meets the performance requirements, it means that the designed recycled asphalt mixture gradation and optimal asphalt content are feasible; otherwise, the recycled asphalt mixture gradation is re-determined and the additional new asphalt mixture gradation is re-determined accordingly; Determine the maximum usable mass of the added new asphalt and its mass ratio to the new mineral aggregate in the new asphalt mixture based on the optimal asphalt-to-stone ratio of the recycled asphalt mixture that meets the road performance requirements, the average value of the ratio of the added new asphalt mixture to the original road surface RAP in different groups, or the average value of the ratio of the added new asphalt mixture to the original road surface RAP in different groups after clustering; Based on the maximum usable mass of the added new asphalt and its mass ratio to the new mineral aggregate in the new asphalt mixture, a leakage test is used to determine the optimal mass ratio of the new asphalt to the new mineral aggregate in the added new asphalt mixture, and the mass ratio is less than the maximum mass ratio of the added new asphalt to the new mineral aggregate; The mass of the new asphalt added during the construction process is calculated based on the optimal mass ratio of the new asphalt to the new mineral material in the added new asphalt mixture, the optimal oil-stone ratio of the regenerated asphalt mixture, and the optimal addition ratio of the regeneration agent; Based on the optimal mass ratio of new asphalt to new mineral aggregate in the added new asphalt mixture, the optimal oil-to-stone ratio of the recycled asphalt mixture, and the quality of the added new asphalt, a test section is paved to test the technical indicators, Marshall stability, gradation and gradation deviation, high-temperature stability, low-temperature crack resistance, and water stability of the recycled asphalt to determine whether it meets the design requirements; Determine the design mix ratio of the recycled asphalt mixture based on whether the technical indicator test results of the on-site recycled asphalt meet the design requirements, mainly including the gradation of the recycled asphalt mixture, the optimal asphalt content, the amount of regeneration agent, the gradation of the added new asphalt mixture and the optimal asphalt-to-stone ratio, and the quality of the on-site added new asphalt; If the design requirements are not met, the aggregate gradation of the recycled asphalt mixture shall be adjusted accordingly, and the aggregate gradation of the new asphalt mixture and its optimal oil-stone ratio, as well as the quality of the new asphalt added on site, shall be re-determined.

2. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, characterized in that: The dosage of the regeneration agent is determined based on whether the penetration index of the aged asphalt is restored to the new asphalt standard, specifically as follows: Using regeneration agents with different mass ratios of aged asphalt, different amounts of regeneration agents were added to the aged asphalt and mixed evenly. The penetration of the aged asphalt containing the regeneration agent after mixing was tested, and the amount of regeneration agent was determined with the penetration at 25°C restored to the original asphalt standard as the control target.

3. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, characterized in that: The Fréchet similarity is used to quantitatively represent the mineral aggregate gradation of the original road surface RAP of different sections, specifically including: Step 1: Build and The distance matrix between any two points on ; Among them, the curve , , Indicates the n The aggregate particle size passing through the sieve hole, mm; Indicates the n Percentage of aggregate passing through the sieve holes, %; gradation curve , , Indicates the n The aggregate particle size passing through the sieve hole, mm; Indicates the n Percentage of aggregate passing through the sieve holes, % Where: , represents the gradation curve Previous m Points and curves Previous n The distance between points; 1≤ n ≤ N , 1≤ m ≤ M , N and M Indicates the total number of screens used in the process of screening ore with different grading curves; Step 2: Initialize target distance f ; Calculate the matrix The longest distance in and the shortest distance , and adopt Indicates the target distance after initialization f ; Step 3: Matrix Binarization processing; The matrix Binarization processing, we get ; Where: , 1≤ n ≤ N , 1≤ m ≤ M ; Step 4: Calculate Fréchet similarity; In the binary matrix Find a path in R , the path R The elements in satisfy the constituent elements With elements Continuous straight lines or curves between, and the path R The elements on the graph all have the value 1, and the Fréchet distance is calculated. F , and Fréchet similarity ; In addition, when the path R When the filtering conditions are not met, initialize the target distance , and adopt Perform steps 3 and 4 until a path that meets the conditions is found. 。 4. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, wherein: According to the estimated asphalt-stone ratio of the recycled asphalt mixture, Marshall specimens of recycled asphalt mixture with different asphalt-stone ratios are prepared, as follows: Taking the estimated oil-stone ratio of the recycled asphalt mixture as the median value, 5 groups of recycled asphalt mixture oil-stone ratios were designed with an equal interval of 0.5%. Recycled asphalt mixtures were prepared and Marshall specimens were formed according to the ratio of the added new asphalt mixture to the original pavement RAP.

5. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, wherein: The bulk density, void ratio, mineral gap ratio, effective asphalt saturation, stability and flow value of the Marshall test specimens are tested to determine the optimal asphalt-to-stone ratio of the recycled asphalt mixture, as follows: Based on the test results of Marshall specimens of recycled asphalt mixtures with different oil-to-stone ratios, the oil-to-stone ratio corresponding to the maximum gross volume density of the Marshall specimens of recycled asphalt mixtures with different oil-to-stone ratios is determined as the first asphalt dosage, the oil-to-stone ratio corresponding to the maximum stability is determined as the second asphalt dosage, the oil-to-stone ratio corresponding to the void ratio is determined as the third asphalt dosage, and the oil-to-stone ratio corresponding to the median value of the effective asphalt saturation is determined as the fourth asphalt dosage. All indicators meet the maximum and minimum values ​​of the oil-to-stone ratio in the technical standards. The above indicators do not include the mineral aggregate void ratio. The optimal asphalt-to-stone ratio of the recycled asphalt mixture is determined according to the first asphalt dosage, the second asphalt dosage, the third asphalt dosage, the fourth asphalt dosage and the maximum and minimum values ​​of the asphalt-to-stone ratio.

6. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, characterized in that: During the preparation of the recycled asphalt mixture, the following conditions are met: The preheating temperature of the added new aggregate is 190~210℃, and the preheating time is 2~2.5h; the preheating temperature of the original pavement RAP is 130℃, and the preheating time does not exceed 2h; the preheating temperature of the new asphalt is 150~170℃, and the preheating time does not exceed 3h; the mixing temperature is 150~170℃.

7. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, characterized in that: The aged asphalt content in the original road surface RAP is obtained by extraction or combustion; The mineral gradation in the RAP is tested by washing and screening the extracted or burned RAP mineral particles; the penetration of the aged asphalt in the original road surface RAP is tested by extracting the aged asphalt solution, separating the solvent from the aged asphalt in the aged asphalt solution by rotary evaporation or Absen method, and testing the penetration of the aged asphalt using a fully automatic asphalt penetrometer; The indicators of the original pavement RAP performance evaluation were all tested in parallel, and the average value of the test results was used to represent the final test result; The standard sieves used in the mineral gradation test in the original pavement RAP have a sieve aperture distribution of 0.075 mm, 0.15 mm, 0.3 mm, 0.6 mm, 1.18 mm, 2.36 mm, 4.75 mm, 9.5 mm, 13.2 mm, 16.0 mm and 19.0 mm.

8. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, characterized in that: The original pavement structure and material conditions are determined using the original pavement design data; the original pavement maintenance history is determined by querying the maintenance data after the road section is completed and opened to traffic; the cross-sectional distribution of the original pavement rutting disease is determined using a multi-functional road inspection vehicle.

9. The method for designing a mix ratio of hot-in-situ recycled asphalt mixture according to claim 1, wherein: The cluster analysis method is the K-Means clustering method.

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