Method for preparing asphalt pavement base by doping waste asphalt recycled material into sandstone

Abstract

The invention belongs to the technical field of road engineering, and particularly relates to a method for preparing an asphalt pavement base by doping waste recycled asphalt into sandstone. Aiming at southwest China with scarce high-quality stones and rich sandstone resources, hard sandstone is doped into the asphalt waste recycled material, and a reasonable ratio is determined and optimized by taking the aim of reshaping the high-temperature stability, low-temperature crack resistance and water stability of the asphalt waste recycled material. The method specifically comprises the following steps: selecting sandstone gravel aggregate with hard texture and low weathering degree; detecting the old asphalt content and mineral aggregate gradation in the asphalt waste recycled material, determining the target design gradation of the base asphalt mixture, and calculating the mass of sandstone macadam and new asphalt; and preparing the recycled asphalt mixture and testing the pavement performance of the recycled asphalt mixture so as to determine the optimal asphalt dosage, the reasonable mixing amount of the asphalt waste recycled material and the mixing amount of the anti-stripping agent. According to the method, the overall pavement performance of the recycled asphalt mixture is improved, and the development of a green low-carbon road building solid waste material resource utilization technology is promoted.

Description

Technical Field

[0001] This invention belongs to the field of road engineering technology, specifically relating to a method for incorporating recycled asphalt waste into sandstone as a base course for asphalt pavements. Background Technology

[0002] Currently, my country's highway development has moved from "comprehensive construction" to a new stage of sustainable development characterized by "integrated construction and maintenance." As early-built asphalt pavements gradually enter the maintenance, repair, and reconstruction phase, hundreds of millions of tons of asphalt waste and reclaimed materials are generated annually from milling and resurfacing. How to effectively dispose of these asphalt waste and reclaimed materials has become an urgent problem to be solved.

[0003] Currently, there are two main methods for processing recycled asphalt waste, but both have significant limitations:

[0004] I. Centralized stockpiling or landfill disposal. This method has several problems: 1) The stockpiling and landfilling of large quantities of recycled asphalt waste occupies valuable land resources; 2) Under the influence of rainwater, the aged asphalt in the recycled asphalt waste releases harmful substances such as polycyclic aromatic hydrocarbons. These components seep into the soil and migrate to the groundwater system, posing a long-term and irreversible potential threat to the ecological environment; 3) The transportation and landfill cost of each ton of recycled asphalt waste is as high as 80 to 120 yuan, which becomes a burden on project costs and social public finances; 4) The aggregate portion of recycled asphalt waste includes high-quality aggregates such as hard and wear-resistant basalt and limestone. If these resources cannot be efficiently recycled, large-scale mining and processing of natural stone will be required to build new roads.

[0005] II. Recycling Process to Prepare Recycled Asphalt Mixture. During long-term service, asphalt pavements undergo gradual degradation due to the combined effects of traffic loads and the natural environment. On one hand, the aggregates experience surface peeling, polishing, and even crushing due to repeated wear and impact from wheel loads, leading to degradation of the original gradation and damage to the skeleton structure. On the other hand, the asphalt binder, continuously exposed to oxygen, ultraviolet radiation, moisture, and temperature variations, undergoes oxidation, polymerization, and other chemical reactions, resulting in component imbalance, hardening, embrittlement, and decreased ductility and viscosity. To restore and utilize this type of old material, recycling technology is generally used: by adding a specific proportion of new aggregates that meet gradation requirements and an appropriate amount of unaged new asphalt to the recycled asphalt waste, the gradation defects of the recycled asphalt waste are compensated for, the skeleton structure is reconstructed, components lost in the aged asphalt are replenished, the overall hardness of the aged asphalt is reduced, its ductility and bonding ability are improved, and the overall road performance of the recycled asphalt binder is restored.

[0006] Existing recycling methods face the following problems: 1) To improve the road performance of recycled mixtures, existing technologies often choose to add limestone or basalt crushed stone as new aggregates; however, my country's high-quality limestone and basalt resources are becoming increasingly scarce, and their uneven distribution in various regions means that many highway construction projects must rely on long-distance transportation, which not only significantly increases material costs but also generates a large amount of transportation energy consumption and carbon emissions, weakening the economic and environmental benefits of recycling technology from a life-cycle perspective; 2) Currently, the recycling of asphalt waste materials is mainly concentrated in the asphalt pavement surface layer or specific structural layers, and related research and practice are mostly focused on this; in contrast, there are few systematic application studies and engineering cases of asphalt waste materials in the asphalt pavement base layer, which limits the application scope of asphalt waste materials and fails to form a full-section recycling model that runs through the pavement structural layers, thus restricting its overall resource utilization rate and the full realization of its circular economy value.

[0007] Sandstone is widely distributed and abundant in southwestern my country. However, due to its inherent physical properties—relatively lower strength, higher water absorption, and poorer adhesion to asphalt compared to basalt and limestone—sandstone aggregate faces significant technical and application bottlenecks in asphalt road construction. Most sandstone excavated during highway construction is disposed of as waste, resulting in substantial environmental and economic pressures. It is worth noting that sandstone with a low degree of weathering possesses advantages such as density, high strength, and durability. Its poor adhesion to asphalt can be compensated for by adding anti-stripping agents, making it a promising candidate for use in asphalt roads. Summary of the Invention

[0008] To overcome the problems of low utilization rates of recycled asphalt and sandstone aggregates in existing technologies, this invention provides a method for incorporating recycled asphalt aggregates into sandstone for use as an asphalt pavement base course. Based on the principle of matching pavement structure layers with material properties, this method uses sandstone aggregates as new aggregates and mixes them with a certain proportion of recycled asphalt aggregates to form a recycled asphalt mixture for application in the asphalt pavement base course, successfully achieving on-site utilization of sandstone and improving the utilization rate of recycled asphalt aggregates.

[0009] One of the objectives of this invention is to provide a method for incorporating recycled asphalt waste into sandstone for use as an asphalt pavement base course.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for incorporating recycled asphalt waste into sandstone for use as an asphalt pavement base course includes the following steps:

[0012] S1: Select hard, low-weathered sandstone aggregate that meets the specifications, and test the old asphalt content and aggregate gradation in the recycled asphalt waste material.

[0013] S2: Determine the target design gradation of the base course asphalt mixture, and calculate the mass of sandstone aggregate and new asphalt based on the preset blending ratio of recycled asphalt and sandstone.

[0014] S3: Prepare recycled asphalt mixture by mixing waste asphalt, sandstone, and new asphalt in the designed ratio, and test its road performance.

[0015] S4: Combine the test results of S2 and S3 to determine the optimal asphalt dosage, reasonable dosage of recycled asphalt material, and dosage of anti-stripping agent.

[0016] Preferably, in S1, the sandstone aggregate is crushed, screened, and then graded according to particle size, and tested according to the current aggregate testing procedures. Its technical indicators must meet the quality requirements for base course aggregates in the current asphalt pavement construction technical specifications.

[0017] Preferably, in S1, the sandstone aggregate is selected from unweathered or slightly weathered quartz sandstone with a quartz content of not less than 80% and a uniaxial compressive strength of not less than 80 MPa.

[0018] In some specific cases, the sandstone is unweathered quartz sandstone, containing 81.5% quartz, 5% potassium feldspar, 2% plagioclase, 2% muscovite, 2.5% biotite, 1.5% rock fragments, 1.5% heavy minerals, and 4% interstitial material.

[0019] Preferably, in step S1, the sandstone is crushed and screened, and divided into coarse aggregate and fine aggregate according to particle size. The particle size between 0.075mm and 2.36mm is fine aggregate, and the particle size greater than 2.36mm is coarse aggregate. The fine aggregate and coarse aggregate are tested for various aggregate indicators such as crushing value and soundness according to the current highway engineering aggregate test specifications. Sandstone crushed stone whose test results meet the technical requirements for base course aggregate quality in the current highway asphalt pavement construction technical specifications is selected.

[0020] Preferably, in S1, the old asphalt content in the recycled asphalt waste is separated and determined by centrifugal extraction, and the remaining aggregate is then screened to determine the aggregate gradation.

[0021] Preferably, in S2, the formula for calculating the mass of sandstone aggregate and new asphalt based on the blending ratio of recycled asphalt material and sandstone is as follows:

[0022]

[0023] In the formula: G represents the total mass of the asphalt mixture, kg;

[0024] G R This indicates the mass of recycled asphalt waste, expressed in kg.

[0025] GA This indicates the mass of newly added asphalt, expressed in kg.

[0026] G S This indicates the total mass of sandstone gravel, expressed in kg.

[0027] α represents the proportion of recycled asphalt material added, %

[0028] β represents the asphalt content in the target graded asphalt mixture, % .

[0029] β R This indicates the asphalt content in recycled asphalt waste, in percentages (%).

[0030] G Ri This indicates the mass (kg) of the recycled asphalt waste material in the i-th size category.

[0031] ω Ri This indicates the passing rate of recycled asphalt waste through the sieve of the i-th size.

[0032] G Si This indicates the mass of sandstone crushed stone in the i-th size category, in kg;

[0033] ω i This represents the passing rate of the target graded asphalt mixture through the sieve of size i.

[0034] Preferably, in S2, the preset blending ratio of the recycled asphalt material and sandstone must be determined by setting multiple gradient blending amounts.

[0035] Preferably, in S3, the road performance test includes tests for high temperature stability, low temperature crack resistance, water stability, and mechanical performance indicators.

[0036] Preferably, in S3, the road performance test includes road performance tests such as high temperature rutting test, low temperature bending test, water stability test and dynamic modulus test.

[0037] Preferably, in S3, the recycled asphalt mixture is subjected to road performance testing in accordance with the current design specifications for asphalt and asphalt mixtures in highway engineering.

[0038] Preferably, in S4, the optimal asphalt content, the reasonable blending ratio of recycled asphalt material, and the amount of anti-stripping agent are comprehensively determined based on the road performance test results of the recycled asphalt mixture meeting the technical requirements of the current highway asphalt pavement design specifications.

[0039] Preferably, S4 specifically includes:

[0040] 1) The dynamic stability and failure strain of the mixture under different asphalt contents were obtained by high-temperature rutting test and low-temperature bending test.

[0041] 2) Based on the technical requirements for dynamic stability and failure strain in the current highway asphalt pavement design specifications, determine the feasible range of asphalt content that meets the specifications;

[0042] 3) Taking into account the climate conditions and common road surface distress types of the project site, and with the goal of improving the targeted resistance to damage, select the optimal asphalt dosage from the feasible range obtained in step 2).

[0043] 4) Conduct water stability tests, including immersion Marshall and freeze-thaw splitting tests, after determining the optimal asphalt content. The results of the immersion Marshall and freeze-thaw splitting tests must meet the specific requirements of the current highway asphalt pavement design specifications for the ratio of immersion residual stability to freeze-thaw splitting residual strength.

[0044] 5) Under the optimal asphalt content and the determined anti-stripping agent content, a dynamic modulus test was conducted to obtain the dynamic modulus values ​​under different asphalt waste recycling material blending ratios, different temperatures, and different loading frequencies.

[0045] 6) Based on the dynamic modulus test results, using the Sigmoid function and WLF equation, the master curve of the dynamic modulus of recycled asphalt mixtures with different asphalt waste recycling ratios at the reference temperature is obtained using the time-temperature equivalence principle; then, according to the reference frequency specified in the current highway asphalt pavement design specifications, the dynamic modulus values ​​corresponding to recycled asphalt mixtures with different asphalt waste recycling ratios are calculated; finally, the asphalt waste recycling ratio with a modulus value falling within the recommended range of the current specifications is selected as the reasonable blending ratio.

[0046] Preferably, the formal expression of the Sigmoid function is:

[0047]

[0048] In the formula: E * For dynamic modulus, MPa; f r To reduce the frequency, Hz; δ, β, γ and α are fitting parameters for the Sigmoid function.

[0049] Preferably, the WLF equation is expressed as follows:

[0050]

[0051]

[0052] In the formula: T i T0 is the test temperature; C1 and C2 are the material parameters in the WLF equation.

[0053] Preferably, in step 4), if the results of the immersion Marshall test and freeze-thaw splitting test do not meet the requirements, an anti-stripping agent is added and verified until the indicators are qualified, thereby determining the minimum effective dosage of the anti-stripping agent.

[0054] The second objective of this invention is to provide a recycled asphalt mixture suitable for road construction in the Southwest region.

[0055] To achieve the above objectives, the present invention adopts the following technical solution:

[0056] A recycled asphalt mixture comprises the following components in parts by weight: 10-20 parts recycled asphalt waste, 70-90 parts crushed sandstone, 3-5 parts new asphalt, 2-4 parts mineral powder, and 1-3 parts anti-stripping agent.

[0057] Preferably, the sandstone crushed stone is selected from unweathered or slightly weathered quartz sandstone with a quartz content ≥80% and a uniaxial compressive strength ≥80MPa.

[0058] Preferably, the asphalt content in the recycled asphalt waste is 3-5%, more preferably 3.66%.

[0059] Preferably, the anti-stripping agent comprises silicate cement.

[0060] Preferably, the recycled asphalt mixture comprises the following components in parts by weight: 10 parts recycled asphalt waste, 81.52 parts crushed sandstone, 3.48 parts new asphalt, 3.57 parts mineral powder, and 1.43 parts anti-stripping agent.

[0061] Preferably, the number of new asphalt parts = 3.85 parts - the number of recycled asphalt waste parts × 3.66%, and the number of recycled asphalt waste parts + the number of sandstone crushed stone parts + the number of new asphalt parts + the number of mineral powder parts + the number of anti-stripping agent parts = 100 parts.

[0062] The recycled asphalt mixture is prepared using the following method:

[0063] (1) Heat the sandstone crushed stone at 170~180℃ for 3-5 hours;

[0064] (2) Heat the recycled asphalt waste at 120-130℃ for 1-3 hours;

[0065] (3) Melt the new asphalt at 130~150℃;

[0066] (4) Dry mix the preheated sandstone crushed stone for 60-120s, add the preheated recycled asphalt waste and dry mix for 60-120s, then add the heated and melted new asphalt and mix for 60-120s, and finally add the mineral powder and anti-stripping agent (such as silicate cement) and mix for 60-120s to obtain recycled asphalt mixture.

[0067] Preferably, the heating temperature of recycled asphalt waste should be controlled at 120-130℃ and the heating time should be controlled at 2 hours; the heating temperature of sandstone crushed stone should be controlled at 170-180℃ and the heating time should be controlled at 4 hours; and the heating temperature of new asphalt should be controlled at 135℃.

[0068] Preferably, the mixing temperature is controlled at 150~160℃.

[0069] Preferably, step (4) is as follows: dry-mix the preheated sandstone crushed stone for 90s, add the preheated recycled asphalt waste material and dry-mix for 90s, then add the heated and melted new asphalt and stir for 90s, and finally add the mineral powder and anti-stripping agent (such as silicate cement) and stir for 90s to obtain recycled asphalt mixture.

[0070] Preferably, when preparing recycled asphalt mixtures by mixing waste asphalt, sandstone, and new asphalt, attention should be paid to whether the old and new materials are completely integrated.

[0071] Preferably, after mixing, the mixture should have a uniform color, without obvious asphalt lumps or white aggregate not coated with asphalt, and the old aggregate in the recycled asphalt material should be evenly dispersed throughout the mixture without obvious aggregation.

[0072] Preferably, the recycled asphalt mixture is used for road construction in the southwest region. This region belongs to the hot summer and mild winter zone (zones 1-4).

[0073] The beneficial effects of this invention are as follows:

[0074] 1. In view of the reality of highway construction in Southwest my country, where high-quality stone materials such as basalt and limestone are scarce but sandstone resources are abundant, this invention is based on the principle of matching pavement structure layers with material properties. Hard sandstone crushed stone is used as new aggregate, and a certain proportion of recycled asphalt waste is mixed to form recycled asphalt mixture, which is applied to the base layer of asphalt pavement. By optimizing the mix ratio, the overall road performance of the recycled asphalt mixture is improved. Thus, on the basis of enriching the available resources for road construction, it promotes the development of green and low-carbon road construction solid waste material resource utilization technology.

[0075] 2. Based on the fact that the technical requirements for aggregate quality in asphalt pavement base courses are relatively lower than those in surface courses, this invention innovatively uses local sandstone aggregate as a new aggregate for the base course. This method is particularly suitable for areas rich in sandstone resources, significantly reducing sandstone waste and transportation costs, enriching the selection of road construction materials, reducing reliance on traditional high-quality stone, and conforming to the economic principle of on-site resource utilization.

[0076] 3. This invention enhances and reshapes the high-temperature stability, low-temperature crack resistance, and water stability of recycled asphalt waste material through sandstone, effectively expanding the application scenarios of recycled asphalt waste material from the surface layer to the base layer. It breaks through the bottleneck that the recycling of recycled asphalt waste material has long been limited to the surface layer, significantly improves the overall resource utilization rate of recycled asphalt waste material, provides technical support for the construction of full-section recycled asphalt pavement, and promotes the green and low-carbon development of road engineering.

[0077] 4. This method provides a reasonable mixture design approach and technical measures. By optimizing key parameters through performance verification, it effectively avoids the performance degradation of the mixture caused by improper asphalt content or unreasonable blending ratio of recycled asphalt, thereby ensuring that the recycled asphalt mixture has excellent high-temperature stability, water stability and fatigue resistance, and extending the service life of the pavement. Attached Figure Description

[0078] Figure 1 This is a schematic diagram of raw materials, where A is a schematic diagram of hard sandstone and B is a schematic diagram of recycled asphalt waste material for the lower layer of the highway.

[0079] Figure 2 This is a gradation curve for recycled mineral materials.

[0080] Figure 3 Design a gradation curve for the target.

[0081] Figure 4 The figure shows the test results of different proportions of recycled material under the optimal asphalt content.

[0082] Figure 5 This is a graph showing the relationship between water immersion residual stability and cement dosage.

[0083] Figure 6 This is a graph showing the relationship between the freeze-thaw splitting strength ratio and the cement dosage.

[0084] Figure 7 The main curves of dynamic modulus of ATB-25 with different dosages are shown. Detailed Implementation

[0085] The technical solution of the present invention will be described more clearly and completely below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0086] In this embodiment of the invention, the sandstone aggregate is selected from unweathered or slightly weathered quartz sandstone with a quartz content of not less than 80% and a uniaxial compressive strength of not less than 80 MPa.

[0087] In this embodiment of the invention, the formula for calculating the mass of sandstone aggregate and new asphalt based on the blending ratio of recycled asphalt waste to sandstone is as follows:

[0088]

[0089] In the formula: G represents the total mass of the asphalt mixture, kg;

[0090] G R This indicates the mass of recycled asphalt waste, expressed in kg.

[0091] G A This indicates the mass of newly added asphalt, expressed in kg.

[0092] G S This indicates the total mass of sandstone gravel, expressed in kg.

[0093] α represents the proportion of recycled asphalt material added, %

[0094] β represents the asphalt content in the target graded asphalt mixture, % .

[0095] β R This indicates the asphalt content in recycled asphalt waste, in percentages (%).

[0096] G Ri This indicates the mass (kg) of the recycled asphalt waste material in the i-th size category.

[0097] ω Ri This indicates the passing rate of recycled asphalt waste through the sieve of the i-th size.

[0098] G Si This indicates the mass of sandstone crushed stone in the i-th size category, in kg;

[0099] ω i This represents the passing rate of the target graded asphalt mixture through the sieve of size i.

[0100] In this embodiment of the invention,

[0101] 1) The dynamic stability and failure strain of the mixture under different asphalt contents were obtained by high-temperature rutting test and low-temperature bending test.

[0102] 2) Based on the technical requirements for dynamic stability and failure strain in the current highway asphalt pavement design specifications, determine the feasible range of asphalt content that meets the specifications;

[0103] 3) Taking into account the climate conditions and common road surface distress types of the project site, and with the goal of improving the targeted resistance to damage, select the optimal asphalt dosage from the feasible range obtained in step 2).

[0104] 4) Conduct water stability tests, including immersion Marshall and freeze-thaw splitting tests, after determining the optimal asphalt content. The results of the immersion Marshall and freeze-thaw splitting tests must meet the specific requirements of the current highway asphalt pavement design specifications for the ratio of immersion residual stability to freeze-thaw splitting residual strength. If they do not meet the requirements, add an anti-stripping agent and verify it until the indicators are qualified, thereby determining the minimum effective dosage of the anti-stripping agent.

[0105] 5) Under the optimal asphalt content and the determined anti-stripping agent content, a dynamic modulus test was conducted to obtain the dynamic modulus values ​​under different asphalt waste recycling material blending ratios, different temperatures, and different loading frequencies.

[0106] 6) Based on the dynamic modulus test results, using the Sigmoid function and WLF equation, the master curve of the dynamic modulus of recycled asphalt mixtures with different asphalt waste recycling ratios at the reference temperature is obtained using the time-temperature equivalence principle; then, according to the reference frequency specified in the current highway asphalt pavement design specifications, the dynamic modulus values ​​corresponding to recycled asphalt mixtures with different asphalt waste recycling ratios are calculated; finally, the asphalt waste recycling ratio with a modulus value falling within the recommended range of the current specifications is selected as the reasonable blending ratio.

[0107] In this embodiment of the invention, the formal expression of the Sigmoid function is:

[0108]

[0109] In the formula: E * For dynamic modulus, MPa; f r To reduce the frequency, Hz; δ, β, γ and α are fitting parameters for the Sigmoid function.

[0110] In this embodiment of the invention, the WLF equation is expressed as follows:

[0111]

[0112]

[0113] In the formula: T i T0 is the test temperature; C1 and C2 are the material parameters in the WLF equation.

[0114] Example 1

[0115] 1. Raw materials

[0116] Hard sandstone, recycled asphalt waste material for the highway lower layer, and 70# base asphalt.

[0117] Among them, hard sandstone, such as Figure 1 As shown in Figure A, the recycled asphalt waste material for the lower layer of the highway is as follows: Figure 1 As shown in B.

[0118] 2. Method of mixing recycled asphalt waste into sandstone for use as asphalt pavement base course.

[0119] (1) Screening of sandstone crushed stone

[0120] Core samples were taken from the sandstone parent rock for composition analysis and uniaxial compressive strength testing. The results showed that the sandstone in this embodiment was unweathered quartz sandstone, containing 81.5% quartz, 5% potassium feldspar, 2% plagioclase, 2% muscovite, 2.5% biotite, 1.5% rock fragments, 1.5% heavy minerals, and 4% interstitial material. Furthermore, the natural uniaxial compressive strength of the sandstone parent rock was greater than 80 MPa. After crushing the sandstone raw material, it was sieved and graded using a standard square-hole sieve. According to the "Specifications for Testing Aggregates in Highway Engineering" (JTG 3432-2024), tests were conducted on coarse aggregates with a particle size greater than 2.36 mm for crushing and abrasion values. Tests were also conducted on fine aggregates with a particle size between 0.075 mm and 2.36 mm for soundness and angularity. The results showed that the sandstone crushed stone in this embodiment met the quality technical requirements of the "Technical Specifications for Construction of Asphalt Pavement of Highways" (JTG F40-2004).

[0121] (2) Detect the content of old asphalt and the aggregate gradation in recycled asphalt waste.

[0122] The asphalt content in recycled asphalt waste was separated and determined using centrifugal extraction. The test results showed that the asphalt content in the recycled material was 3.66%, and its aggregate gradation curve is as follows: Figure 2 As shown.

[0123] (3) Determine the target design gradation of the base course asphalt mixture and calculate the mass of sandstone aggregate and new asphalt.

[0124] The proposed base course mix is ​​ATB-25, and the target design gradation curve is as follows: Figure 3 As shown, the proportions of recycled asphalt material are set at 0%, 10%, 20%, 30%, 40% and 50%. For each preset amount, the amount of each grade of sandstone crushed stone to be added is accurately calculated based on the aggregate gradation of recycled asphalt material obtained in step (2) so that the composite gradation curve meets the target design gradation.

[0125] (4) Recycled asphalt mixtures are prepared by mixing waste asphalt, sandstone, and new asphalt in the designed proportions, and various road performance characteristics are tested. The optimal asphalt content, the reasonable blending ratio of waste asphalt, and the dosage of anti-stripping agent are determined comprehensively.

[0126] 1) Determine the optimal amount of asphalt.

[0127] Referring to the asphalt content in recycled asphalt waste, five levels of total asphalt content were set: 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%. Recycled ATB-25 mixtures were mixed according to these proportions, and recycled ATB-25 rutting specimens and small beam bending specimens were formed. High-temperature rutting tests and low-temperature bending tests were conducted according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG 3410-2025).

[0128] The test site is located in a hot-summer, temperate-winter zone (zones 1-4). According to the "Specifications for Design of Asphalt Pavement on Highways" (JTG D50-2017), the dynamic stability shall not be less than 1000 cycles / mm. -1 The requirement that the flexural failure strain must not be less than 2000 με, combined with the high-temperature climate characteristics of the test area in summer, determines the optimal asphalt dosage to just meet the failure strain requirement. Table 1 shows the optimal asphalt dosage and dynamic stability improvement rate of recycled ATB-25 under different asphalt waste reclaiming amounts; the dynamic stability and flexural strain test results are as follows: Figure 4 As shown in the figure, the dynamic stability is highest when the amount of recycled asphalt is 10%~20%, specifically reaching 2359 cycles / mm. -1 ~ 2389 times·mm -1 While meeting the requirement of low bending strain, it also meets the specification requirement of 1000 cycles / mm. -1 It increased by 135.9% to 138.9%.

[0129] Table 1. Optimal Asphalt Dosage and Dynamic Stability Improvement Rate

[0130]

[0131] 2) Confirm the appropriate amount of recycled asphalt material.

[0132] Under the optimal asphalt content determined in 1), immersion Marshall tests and freeze-thaw splitting tests were conducted on recycled ATB-25 with different amounts of recycled asphalt waste. The test results are shown in Table 2. According to the "Specifications for Design of Highway Asphalt Pavement" (JTGD50-2017), the residual stability of ordinary asphalt mixture after immersion should not be less than 80%, and the freeze-thaw splitting strength ratio should not be less than 75%. The test results show that, without anti-stripping measures, all recycled ATB-25 in this embodiment does not meet the technical requirements of the "Specifications for Design of Highway Asphalt Pavement" (JTG D50-2017).

[0133] Table 2. Results of water stability test

[0134]

[0135] 3) Confirm the dosage of anti-stripping agent

[0136] Using ordinary Portland cement as an anti-stripping agent, and replacing mineral powder with ordinary Portland cement at dosages of 1%, 2%, and 3% of the total aggregate mass, the minimum cement dosage required to meet the water stability index of recycled ATB-25 with different amounts of recycled asphalt waste material is determined through experiments, as shown in Table 3.

[0137] Table 3. Minimum Cement Dosage

[0138]

[0139] The curves showing the relationship between water immersion residual stability, freeze-thaw splitting strength ratio, and cement dosage after adding ordinary Portland cement are as follows: Figure 5 and Figure 6 As shown.

[0140] 4) Dynamic modulus test

[0141] Dynamic modulus tests were conducted on recycled ATB-25 with different asphalt waste reclaiming content under the optimal asphalt content and at a minimum cement dosage not less than that determined in step 3). Based on the test data, the dynamic modulus master curve at the reference temperature was fitted using the time-temperature equivalence principle through the Sigmoid function and the WLF equation. The "Specifications for Design of Highway Asphalt Pavement" (JTG D50-2017) stipulates that the results for ATB-25 should be taken under 5Hz conditions, preferably within the range of greater than 7000 MPa and less than 11000 MPa. The dynamic modulus results of recycled ATB-25 with different asphalt waste reclaiming content are shown in Table 4, and the dynamic modulus master curve is plotted as follows. Figure 7 As shown.

[0142] Table 4. Dynamic modulus results of regenerated ATB-25 at 5Hz

[0143]

[0144] Based on the above test results, the reasonable range of the asphalt waste recycling ratio in this embodiment is 10%~20%. If we consider the modulus range of ATB-25, the optimal mixing ratio is 10%, and the optimal asphalt content of the synthetic mixture is 3.85%, of which the content of new asphalt is 3.48%, the content of sandstone and crushed stone is 81.52%, the content of mineral powder is 3.57%, and the content of anti-stripping agent (i.e., cement) is 1.43%.

[0145] Example 2

[0146] A recycled asphalt mixture comprises the following components in parts by weight: 10 parts recycled asphalt waste, 81.52 parts crushed sandstone, 3.48 parts new asphalt, 3.57 parts mineral powder, and 1.43 parts anti-stripping agent.

[0147] The preparation method of recycled asphalt mixture includes: heating sandstone aggregate at 170-180℃ for 4 hours; heating recycled asphalt material at 120-130℃ for 2 hours; and melting new asphalt at 135℃. The preheated sandstone aggregate is dry-mixed for 90 seconds, then the preheated recycled asphalt material is added and dry-mixed for another 90 seconds. The melted new asphalt is then added and mixed for another 90 seconds. Finally, mineral powder and anti-stripping agent (such as silicate cement) are added and mixed for another 90 seconds. The mixing temperature is controlled at 150-160℃ to obtain the recycled asphalt mixture. After mixing, the mixture should have a uniform color, without obvious asphalt lumps or uncoated "white aggregate." The old aggregate in the recycled asphalt material should be evenly dispersed throughout the mixture without obvious aggregation.

[0148] Further testing was conducted on the road performance of the recycled asphalt mixture obtained under the optimal dosage ratio, and the results are shown in Table 5. The dynamic stability of the recycled asphalt mixture prepared by this invention is 2359 cycles / mm. -1 It exhibits excellent road performance with a flexural failure strain of 2077 με, a water immersion residual stability of 85.33%, a freeze-thaw splitting strength ratio of 76.47%, and a dynamic modulus of 7103 MPa.

[0149] Table 5. Test results of road performance of recycled asphalt mixtures under optimal asphalt content and recycled asphalt admixture.

[0150]

Claims

1. A method for incorporating recycled asphalt waste into sandstone for use as an asphalt pavement base course, characterized in that, The method includes the following steps: S1: Select hard, low-weathered sandstone aggregate that meets the specifications, and test the old asphalt content and aggregate gradation in the recycled asphalt waste material. S2: Determine the target design gradation of the base course asphalt mixture, and calculate the mass of sandstone aggregate and new asphalt based on the preset blending ratio of recycled asphalt and sandstone. S3: Prepare recycled asphalt mixture by mixing waste asphalt, sandstone, and new asphalt in the designed ratio, and test its road performance. S4: Combine the test results of S2 and S3 to determine the optimal asphalt dosage, reasonable dosage of recycled asphalt material, and dosage of anti-stripping agent.

2. The method according to claim 1, characterized in that, In S1, the sandstone aggregate is crushed, screened, and then graded according to particle size. It is tested in accordance with the current aggregate testing procedures, and its technical indicators must meet the quality requirements for base course aggregates in the current asphalt pavement construction technical specifications.

3. The method according to claim 1, characterized in that, In S1, the old asphalt content in the recycled asphalt waste is separated and determined by centrifugal extraction, and the remaining aggregate is then screened to determine the aggregate gradation.

4. The method according to claim 1, characterized in that, In S2, the formula for calculating the mass of sandstone aggregate and new asphalt based on the blending ratio of recycled asphalt waste to sandstone is as follows: In the formula: G represents the total mass of the asphalt mixture, kg; G R This indicates the mass of recycled asphalt waste, expressed in kg. G A This indicates the mass of newly added asphalt, expressed in kg. G S This indicates the total mass of sandstone gravel, expressed in kg. α represents the proportion of recycled asphalt material added, % β represents the asphalt content in the target graded asphalt mixture, % . β R This indicates the asphalt content in recycled asphalt waste, in percentages (%). G Ri This indicates the mass (kg) of the recycled asphalt waste material in the i-th size category. ω Ri This indicates the passing rate of recycled asphalt waste through the sieve of the i-th size. G Si This indicates the mass of sandstone crushed stone in the i-th size category, in kg; ω i This represents the passing rate of the target graded asphalt mixture through the sieve of size i.

5. The method according to claim 1, characterized in that, In S3, road performance testing includes high-temperature stability, low-temperature crack resistance, water stability, and mechanical performance index testing.

6. The method according to claim 1, characterized in that, S4 specifically includes: 1) The dynamic stability and failure strain of the mixture under different asphalt contents were obtained by high-temperature rutting test and low-temperature bending test. 2) Based on the technical requirements for dynamic stability and failure strain in the current highway asphalt pavement design specifications, determine the feasible range of asphalt content that meets the specifications; 3) Taking into account the climate conditions and common road surface distress types of the project site, and with the goal of improving the targeted resistance to damage, select the optimal asphalt dosage from the feasible range obtained in step 2). 4) Conduct water stability tests, including immersion Marshall and freeze-thaw splitting tests, after determining the optimal asphalt content. The results of the immersion Marshall and freeze-thaw splitting tests must meet the specific requirements of the current highway asphalt pavement design specifications for the ratio of immersion residual stability to freeze-thaw splitting residual strength. 5) Under the optimal asphalt content and the determined anti-stripping agent content, a dynamic modulus test was conducted to obtain the dynamic modulus values ​​under different asphalt waste recycling material blending ratios, different temperatures, and different loading frequencies. 6) Based on the dynamic modulus test results, using the Sigmoid function and WLF equation, the master curve of the dynamic modulus of recycled asphalt mixtures with different asphalt waste recycling ratios at the reference temperature is obtained using the time-temperature equivalence principle; then, according to the reference frequency specified in the current highway asphalt pavement design specifications, the dynamic modulus values ​​corresponding to recycled asphalt mixtures with different asphalt waste recycling ratios are calculated; finally, the asphalt waste recycling ratio with a modulus value falling within the recommended range of the current specifications is selected as the reasonable blending ratio.

7. A recycled asphalt mixture, characterized in that, It includes the following components by weight: 10-20 parts recycled asphalt, 60-90 parts crushed sandstone, 3-5 parts new asphalt, 2-4 parts mineral powder, and 1-3 parts anti-stripping agent.

8. The recycled asphalt mixture according to claim 7, characterized in that, The sandstone crushed stone is selected from unweathered or slightly weathered quartz sandstone with a quartz content ≥80% and a uniaxial compressive strength ≥80MPa.

9. The recycled asphalt mixture according to claim 7, characterized in that, The anti-stripping agent includes silicate cement.

10. The recycled asphalt mixture according to claim 7, characterized in that, The recycled asphalt mixture is prepared using the following method: (1) Heat the sandstone crushed stone at 170~180℃ for 3-5 hours; (2) Heat the recycled asphalt waste at 120-130℃ for 1-3 hours; (3) Melt the new asphalt at 130~150℃; (4) Dry mix the preheated sandstone crushed stone for 60~120s, add the preheated recycled asphalt waste and dry mix for 60~120s, then add the heated and melted new asphalt and mix for 60~120s, and finally add the mineral powder and anti-stripping agent and mix for 60~120s to obtain recycled asphalt mixture.

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