A design method of hot-in-place recycled mixture considering multivariate combination

Abstract

The application provides a normal-temperature recycled mixture design method considering multivariate combination and relates to the technical field of road engineering. The application firstly determines indoor performance requirements of the normal-temperature recycled mixture according to road site information and pavement structure design requirements; then samples and analyzes old asphalt pavement recycled materials, designs the gradation of the normal-temperature recycled mixture and determines the optimal water content; then, taking indoor compaction work, emulsified asphalt dosage and indoor secondary compaction temperature as design variables, the indoor multivariate combination scheme is initially selected with the aid of a performance-design variable nomogram; finally, verification is carried out until the performance standard is met. The application simultaneously considers the multivariate combination design of the normal-temperature recycled mixture performance of "compaction work", "secondary compaction temperature" and "emulsified asphalt dosage". The method more considers actual site information, fully develops the potential value of the normal-temperature recycled mixture, makes the design more scientific and reasonable and significantly improves the performance.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and in particular to a design method for ambient temperature recycled mixtures that considers multiple variable combinations. Background Technology

[0002] The composition of ambient temperature recycled asphalt mixtures includes emulsified (or foamed) asphalt, recycled asphalt, new and recycled aggregates, water, cement, etc. Emulsified asphalt further includes emulsifiers, base asphalt, hydrochloric acid, etc. The indoor ambient temperature recycled asphalt mixture design process involves combining these different materials in a certain proportion, mixing them under specific processes, molding the resulting mixture into indoor specimens, and ensuring it meets performance requirements. Since the application of recycling technology, road workers and researchers both domestically and internationally have proposed many design methods for ambient temperature recycled asphalt mixtures. Because ambient temperature recycled asphalt mixtures combine the characteristics of hot-mix asphalt mixtures and water-stabilized materials, most of these design methods are improvements on existing hot-mix asphalt mixture and semi-rigid base course material designs. A complete ambient temperature recycled asphalt mixture design method includes the following steps:

[0003] ① To evaluate the performance of recycled road materials, it is usually necessary to conduct extraction tests on milled road materials to obtain old asphalt and aggregates, and then conduct performance tests on the old asphalt and aggregates.

[0004] ② The gradation design of ambient temperature recycled aggregate is to determine the appropriate blending ratio of different grades of old materials, new aggregates and cement, so that the recycled materials of the road surface meet the gradation requirements of ambient temperature recycled aggregate.

[0005] ③ Determination of the optimal emulsified (foamed) asphalt content and optimal moisture content: According to certain technical requirements, the optimal asphalt content and optimal moisture content of the ambient temperature recycled mixture are determined.

[0006] ④ Determining the mixing process of ambient temperature recycled materials: Materials with different proportions are mixed according to a certain process. The purpose is to ensure that the mixed ambient temperature recycled materials are evenly coated.

[0007] ⑤ Finally, the indoor specimen molding and performance verification of the room temperature recycled mixture were carried out. The specimens were molded and cured indoors according to certain specimen molding methods, including the Marshall method, static pressing method, rotary compaction method, vertical vibration method, etc., and then the performance of the specimens was verified.

[0008] To date, no country internationally has reached a widely accepted standard for the design of ambient temperature recycled asphalt mixtures. By tracing the development of ambient temperature recycled asphalt mixture design methods, from the earliest modified Marshall design method borrowed from asphalt mixture and semi-rigid base course materials, to the Hveem method using a kneading process, the modified Superpave design method, the VVTM method considering modern construction techniques and heavy traffic conditions, and the indoor specimen molding method considering the "secondary hot compaction" process, it can be seen that the development of ambient temperature recycled asphalt mixture design methods has consistently attempted to simulate or approximate the real conditions of ambient temperature recycled pavements, aiming to make indoor design methods more scientific and rational. However, existing domestic and international ambient temperature recycled asphalt mixture design methods still do not truly achieve a correlation between indoor and on-site actual construction conditions. Previous design methods did not consider the impact of different regional construction conditions, climate temperature variations, and the actual on-site compaction conditions of different layers, resulting in a significant difference between the designed ambient temperature recycled asphalt mixture performance and the actual pavement performance. This may be one of the important reasons why it is difficult to reach a consensus on the selection of ambient temperature recycled asphalt mixture design methods among different countries and even different research institutions. Meanwhile, ambient temperature recycled asphalt mixtures are generally applied at lower levels, often used as road subgrades, base course backfill materials, or low-level or low-grade highways. The main reason is that the performance of ambient temperature recycled asphalt mixtures designed using existing methods is too low, making it difficult to meet the performance requirements of higher-level applications. Although numerous ambient temperature recycled asphalt mixture design methods have been striving to make mixture design more scientific, they haven't truly recognized the objective "cold and hot" compaction processes inherent in ambient temperature recycled layers on-site. The design process relies too heavily on past design experience, primarily through aggregate gradation design, determining the optimal emulsified asphalt content and moisture content, and finally completing the design work through mixture performance tests. This neglects the combined effects of design variables such as compaction work, compaction temperature, and emulsified asphalt content on mixture performance, failing to fully unleash the potential performance value of the recycled material. Consequently, the performance of ambient temperature recycled asphalt mixtures is difficult to improve, limiting their application to lower-level or low-grade roads. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a design method for ambient temperature recycled asphalt mixtures that considers multiple variable combinations. This invention considers the "secondary hot compaction" process of the ambient temperature recycled layer, as well as the construction conditions in different regions, climate and temperature changes, and the on-site compaction conditions of different layers. It also considers the multi-variable combination design of "compaction work", "compaction temperature" and "emulsified asphalt content" to design the performance of ambient temperature recycled asphalt mixtures, and establishes a new design method for high-level ambient temperature recycled asphalt mixtures based on actual site conditions.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] This invention provides a method for designing ambient temperature recycled mixtures that considers multiple variable combinations, comprising the following steps:

[0012] (1) Collect on-site road information and formulate design standards for emulsified asphalt ambient temperature recycled mixture; the on-site road information includes traffic design parameters, environmental design parameters and application layers of ambient temperature recycled layer; the design standards for emulsified asphalt ambient temperature recycled mixture include high temperature performance, low temperature performance, fatigue performance, tensile performance, water stability performance and porosity design standards.

[0013] (2) Sampling and analysis of recycled materials from old asphalt pavement were conducted. Based on experience, the gradation curve of emulsified asphalt ambient temperature recycled mixture was initially selected, and the fractal dimension D of the composite gradation and the fractal dimension D of the coarse aggregate gradation were calculated. C Based on the fractal dimension D of the synthetic gradation and the fractal dimension D of the coarse aggregate gradation C Performance prediction of emulsified asphalt ambient temperature recycled mixture, the performance in the performance prediction includes dry splitting strength R T Freeze-thaw splitting strength ratio (TSR) and dynamic stability (D) S and maximum bending tensile strain B ε If the performance meets the requirements, a dummy aggregate test is performed on the emulsified asphalt ambient temperature recycled mixture. If the requirements are not met, the gradation curve is readjusted until the requirements are met; when the variance D of the gradation change rate before and after extraction in the dummy aggregate test... V ≤85 or the change in gradation value V before and after extraction a When the moisture content is ≤3.6, the gradation curve of the emulsified asphalt ambient temperature recycled mixture is designed and the proportion of different aggregate grades is determined. Based on the determined proportion of different aggregate grades, the synthetic aggregate is prepared and the synthetic aggregate is subjected to a compaction test to obtain the optimum moisture content.

[0014] (3) Using emulsified asphalt dosage, indoor secondary compaction temperature and number of secondary compactions as indoor design variables, by changing different combinations of indoor design variables, the performance of the mixture made according to the proportion of different aggregates and the optimum moisture content determined in step (2) reaches the design standard of emulsified asphalt ambient temperature recycled mixture in step (1), and the preliminary design variable combination scheme is obtained.

[0015] (4) The performance of the initial design variable combination scheme in (3) is verified. If all the performances meet the design standards of emulsified asphalt ambient temperature recycled mixture in step (1), then the design variable combination scheme is determined to be a feasible scheme.

[0016] Preferably, the traffic design parameters in step (1) include traffic volume, axle load spectrum and tire ground pressure, and the environmental design parameters include groundwater level, annual precipitation, annual temperature, historical extreme high temperature, historical extreme low temperature and atmospheric conditions during construction.

[0017] Preferably, the sampling analysis in step (2) refers to the "Specifications for Testing Aggregates in Highway Engineering".

[0018] Preferably, the performance prediction of the fractal dimension room temperature recycled mixture in step (2) is performed using the fractal dimension room temperature recycled mixture performance prediction equation, which is as follows:

[0019] R T =3.03 - 0.1098D - 0.7559D C

[0020] TSR = -92.58 + 60.96D + 9.483D C

[0021] D S =(6.865e+04)-(1.976e+04)D-6056D C

[0022] B ε =(-1.926e+04)+(1.017e+04)D-1149D C ,

[0023] Among them, R T The unit is MPa; the unit of TSR is %; D S The unit is times·mm -1 B ε The unit is με.

[0024] Preferably, in step (2), when D V and V a D is not satisfied V ≤85 or V a When the requirement is ≤3.6, adjust the gradation curve of the emulsified asphalt ambient temperature recycled mixture closer to the lower limit, or adjust the gradation by using 15-25mm grade crushed stone, and then re-evaluate the performance and test the dummy aggregate until the requirement is met.

[0025] Preferably, the combination of different indoor design variables in step (3) includes: when the amount of emulsified asphalt is fixed, changing the indoor secondary compaction temperature and the number of secondary compactions; when the number of indoor secondary compactions is fixed, changing the indoor secondary compaction temperature and the amount of emulsified asphalt.

[0026] Preferably, in step (4), if some performance aspects of the initially proposed design variable combination scheme cannot meet the design standards of the emulsified asphalt ambient temperature recycled mixture, the indoor secondary compaction times and the amount of emulsified asphalt are adjusted to improve the performance. If the adjustment still cannot meet the design standards of the emulsified asphalt ambient temperature recycled mixture, the gradation design is carried out again by replacing the raw materials, or the road performance of the ambient temperature recycled mixture is improved by changing the type of emulsified asphalt or adding admixtures, or the road structure is redesigned.

[0027] Preferably, when there are multiple feasible options in step (4), the option is further selected based on the specific construction conditions during actual construction.

[0028] This invention provides a design method for ambient temperature recycled asphalt mixtures considering multiple variable combinations. First, based on road site information and pavement structure design requirements, the indoor performance requirements of the ambient temperature recycled asphalt mixture are determined. Then, samples of recycled asphalt pavement material (RMAP) are taken and analyzed to design the gradation of the ambient temperature recycled asphalt mixture and determine the optimum moisture content. Next, using emulsified asphalt content, indoor secondary compaction temperature, and the number of secondary compactions (representing indoor compaction work) as indoor design variables, a preliminary indoor multivariate combination scheme is selected using a "performance-design variable" nomograph. Finally, the performance of the ambient temperature recycled asphalt mixture under the selected scheme is verified until the performance standards are met. This invention considers the "secondary hot compaction" process of the ambient temperature recycled layer, as well as the construction conditions, climate and temperature variations in different regions, and the on-site compaction conditions of different layers. It also considers the multi-variable combination design of "compaction work," "compaction temperature," and "emulsified asphalt content" to design the performance of ambient temperature recycled mixtures. This establishes a new design method for high-level ambient temperature recycled mixtures based on actual site conditions. This design method takes into greater consideration actual site information, adding indoor "secondary compaction temperature" and "compaction work" as means to adjust the performance of ambient temperature recycled mixtures, fully leveraging the potential value of ambient temperature recycled mixtures, and providing more options for indoor design. This invention is designed with pavement performance in mind, taking into account more actual site information, thus setting indoor performance design goals. These goals are used as key criteria for the success of indoor design, making the design of ambient temperature recycled mixtures more scientific and reasonable, and significantly improving their performance. The design method proposed in this invention solves the problems of low pavement performance of ambient temperature recycled mixtures, low application layer in pavement structures, and mismatch between indoor design and actual on-site construction. Attached Figure Description

[0029] Figure 1 The flowchart of the room temperature recycled mixture design method considering multiple variable combinations is shown below.

[0030] Figure 2 This is a flowchart of the gradation design for the emulsified asphalt ambient temperature recycled mixture of the present invention;

[0031] Figure 3 This invention provides a design combination scheme for recycled intermediate layer emulsified asphalt at room temperature in an embodiment of the invention (fixing the amount of emulsified asphalt, varying the indoor secondary compaction temperature and the number of indoor secondary compaction cycles). Figure 3 (a) is a design combination scheme that satisfies high-temperature performance, (b) is a design combination scheme that satisfies low-temperature performance, (c) is a design combination scheme that satisfies tensile performance, (d) is a design combination scheme that satisfies fatigue performance, (e) is a design combination scheme that satisfies water stability performance, and (f) is a feasible scheme.

[0032] Figure 4 This invention presents a design combination scheme for recycled intermediate layer emulsified asphalt ambient temperature recycled mixture (fixing the number of indoor secondary compaction cycles, varying the indoor secondary compaction temperature and emulsified asphalt dosage). Figure 4 (a) is a design combination scheme that satisfies high-temperature performance, (b) is a design combination scheme that satisfies low-temperature performance, (c) is a design combination scheme that satisfies tensile performance, (d) is a design combination scheme that satisfies fatigue performance, (e) is a design combination scheme that satisfies water stability performance, and (f) is a feasible scheme.

[0033] Figure 5 This is a design combination scheme for the recycled lower layer emulsified asphalt ambient temperature recycled mixture in an embodiment of the present invention. Figure 5 (a) is a feasible scheme with a fixed amount of emulsified asphalt and varying the indoor secondary compaction temperature and the number of indoor secondary compaction cycles, and (b) is a feasible scheme with a fixed number of indoor secondary compaction cycles and varying the indoor secondary compaction temperature and the amount of emulsified asphalt.

[0034] Figure 6 This is a schematic diagram illustrating the calculation of the coefficient of variation (Va) in this invention. Detailed Implementation

[0035] This invention provides a method for designing ambient temperature recycled mixtures that considers multiple variable combinations, comprising the following steps:

[0036] (1) Collect on-site road information and formulate design standards for emulsified asphalt ambient temperature recycled mixture; the on-site road information to be built includes traffic design parameters, environmental design parameters and application layer of ambient temperature recycled layer; the design standards for emulsified asphalt ambient temperature recycled mixture include high temperature performance, low temperature performance, fatigue performance, tensile performance, water stability performance and porosity design standards.

[0037] (2) Sampling and analysis of recycled materials from old asphalt pavement were conducted. Based on experience, the gradation curve of emulsified asphalt ambient temperature recycled mixture was initially selected, and the fractal dimension D of the composite gradation and the fractal dimension D of the coarse aggregate gradation were calculated. C Based on the fractal dimension D of the synthetic gradation and the fractal dimension D of the coarse aggregate gradationC Performance prediction of emulsified asphalt ambient temperature recycled mixture, the performance in the performance prediction includes dry splitting strength R T Freeze-thaw splitting strength ratio (TSR) and dynamic stability (D) S and maximum bending tensile strain B ε If the performance meets the requirements, a dummy aggregate test is performed on the emulsified asphalt ambient temperature recycled mixture. If the requirements are not met, the gradation curve is readjusted until the requirements are met; when the variance D of the gradation change rate before and after extraction in the dummy aggregate test... V ≤85 or the change in gradation value V before and after extraction a When the moisture content is ≤3.6, the gradation curve of the emulsified asphalt ambient temperature recycled mixture is designed and the proportion of different aggregate grades is determined. Based on the determined proportion of different aggregate grades, the synthetic aggregate is prepared and the synthetic aggregate is subjected to a compaction test to obtain the optimum moisture content.

[0038] (3) Using emulsified asphalt dosage, indoor secondary compaction temperature and number of secondary compactions as indoor design variables, by changing different combinations of indoor design variables, the performance of the mixture made according to the proportion of different aggregates and the optimum moisture content determined in step (2) reaches the design standard of emulsified asphalt ambient temperature recycled mixture in (1), and the initial design variable combination scheme is obtained.

[0039] (4) The performance of the initial design variable combination scheme in (3) is verified. If all the performances meet the design standards of emulsified asphalt ambient temperature recycled mixture in step (1), then the design variable combination scheme is determined to be a feasible scheme.

[0040] The flowchart of the design method for ambient temperature recycled mixture considering multiple variable combinations in this invention is as follows: Figure 1 As shown below. A detailed explanation follows.

[0041] This invention collects on-site road information and formulates design standards for emulsified asphalt ambient temperature recycled mixtures.

[0042] In this invention, the road site information includes traffic design parameters, environmental design parameters, and the application layer of the ambient temperature recycled layer. The traffic design parameters preferably include traffic volume, axle load spectrum, and tire ground pressure. The environmental design parameters preferably include groundwater level, historical precipitation, historical temperature, historical extreme high temperatures, historical extreme low temperatures, and atmospheric conditions during construction. In this invention, the design standards for the ambient temperature recycled asphalt mixture include high-temperature performance, low-temperature performance, fatigue performance, and tensile strength design standards (i.e., including road performance and volumetric parameter design requirements). These design standards serve as the basis for judging the success of the indoor design of the ambient temperature recycled mixture.

[0043] This invention takes into account the actual working conditions of ambient temperature recycling projects, including construction conditions in different regions, climate and temperature changes, and actual compaction conditions of different layers, which can better ensure the construction quality of ambient temperature recycled pavement.

[0044] In this invention, the method for formulating indoor ambient temperature recycled mixture design standards based on road site information is as follows:

[0045] (a) Determination of high-temperature performance design standards:

[0046] Referring to the shear strength model for evaluating the high-temperature performance of asphalt mixtures proposed in the "Specifications for Design of Highway Asphalt Pavement" (JTG D50-2017), the indoor shear strength requirements of recycled asphalt mixtures at normal temperature can be obtained through calculation. This model comprehensively considers information such as the climate environment, design traffic volume, and structural layer position in different regions. Among them, when the base course uses semi-rigid materials, the shear strength model is shown in Equations 1 and 2.

[0047]

[0048]

[0049] In equations 1 and 2, R ts The comprehensive shear strength of asphalt mixture (MPa); N e The cumulative number of times the equivalent design axle load of the design lane is applied within the design service life or from the opening to the first rut maintenance; [R] a [T] represents the allowable permanent deformation of the asphalt mixture layer (mm); d Design temperature (°C); h is the pavement structure coefficient. a h represents the thickness of the asphalt surface layer (mm). b Thickness (mm) when it is a cement concrete layer or an inorganic binder layer; E b It is the modulus (MPa) of the cement concrete layer or inorganic binder layer.

[0050] According to the above formula, the calculated shear strength is the comprehensive shear strength standard for the entire surface layer. In actual design, it is sufficient as long as the weighted average of the shear strength of each asphalt layer meets the comprehensive shear strength requirement. However, the calculated result that meets the condition is not unique. Therefore, in practical applications, it is also necessary to determine the minimum shear strength required for each of the upper, middle, and lower surface layers. The relevant calculation formula is shown in Equation 3.

[0051]

[0052] In Equation 3, R ti The shear strength (MPa) of the i-th asphalt mixture layer; w isis the weight of the i-th asphalt mixture layer. For a 3-layer body, the weights of the upper, middle, and lower layers can be 0.35, 0.42, and 0.23, respectively; n is the number of asphalt mixture layers.

[0053] (b) Determination of fatigue performance standards

[0054] The purpose of indoor fatigue testing is to simulate the actual fatigue damage process of real pavement. However, the actual service environment of pavement is quite complex, with the magnitude of the load, the duration of application, the interval between applications, and factors such as temperature and humidity constantly changing. In reality, the actual fatigue life of pavement is often much longer than that obtained from indoor tests. To address this issue, and considering both the flexural strain of the asphalt layer and the flexural stress on the bottom surface of the integral material, Harvey et al. proposed an indoor fatigue life analysis model for surface asphalt mixtures in the 1990s. This model can calculate the design fatigue life requirements for indoor asphalt mixtures, as shown in Equations 4 and 5. This model fully considers factors such as regional climate, design traffic volume, asphalt layer application location, and reliability level.

[0055]

[0056] TCF = aLn(d) + b (Equation 5);

[0057] In Equations 4 and 5, N is the fatigue life (times) of indoor asphalt mixture under the same loading level; ESALs is the equivalent cumulative number of axle loads (times); TCF is the temperature conversion coefficient; M is the reliability coefficient; SF is the indoor-outdoor fatigue life conversion coefficient; d is the asphalt mixture surface layer thickness (cm); and a and b are the regression coefficients related to the environment.

[0058] Among these studies, there are numerous researches on the conversion factor between indoor and outdoor fatigue life of hot-mix asphalt mixtures. Representative examples include: SF Brown et al. found that the fatigue crack propagation rate of field asphalt pavements, supported by a base course or subgrade, was significantly lower than that of indoor asphalt mixture specimens, resulting in a difference of over 20 times between the fatigue life of field asphalt pavements and indoor fatigue test results; Mateos et al., based on CEDEX loop test data and using 20% ​​crack area of ​​the asphalt pavement as the fatigue failure standard, established a conversion factor of 41.7 based on a four-point bending beam fatigue test; Craus et al., through analysis of fatigue cracking in field test roads and indoor fatigue testing machine data, ultimately determined the indoor-outdoor fatigue life conversion factor to be 11. Finn et al., based on AASHTO test road data and considering the actual damage conditions of asphalt mixture pavements with a surface layer thickness greater than 100 mm, concluded that the indoor-outdoor fatigue life conversion factors for asphalt mixtures were 13.4 and 18.45 when the pavement damage rate was 10% and 45%, respectively. The American Asphalt Institute ultimately recommended 18.4 as the conversion factor for indoor-outdoor fatigue life. However, current research on the fatigue life conversion coefficient of ambient temperature recycled pavement materials is relatively lacking both domestically and internationally. In 2017, the inventors of this invention analyzed the fatigue life of in-service emulsified asphalt ambient temperature recycled mixtures, combined with indoor splitting fatigue test data, and considered the actual stress-strain state of the ambient temperature recycled layer under standard axle load, and derived an indoor-outdoor splitting fatigue life conversion coefficient of 124.4 for ambient temperature recycled mixtures. In subsequent example analyses of this invention, this research result will continue to be used, with 124.4 adopted as the indoor-outdoor fatigue life conversion coefficient for ambient temperature recycled mixtures.

[0059] (c) Determination of tensile performance design parameters

[0060] Emulsified asphalt ambient temperature recycled mixtures are generally used in the base course of high-grade pavement structures and the surface course or base course of ordinary highways. This location is precisely where tensile strain is significant, therefore, requirements must be placed on the tensile properties of the mixture. Tests for the tensile properties of asphalt mixtures generally include direct tensile testing, indirect tensile testing, and beam bending testing. Direct tensile testing is rarely used due to the difficulty in controlling test conditions; beam bending testing best reflects the bending and tensile stress characteristics of the mixture, but is mostly used for fatigue performance studies; indirect tensile testing is widely used due to its simple test conditions and low data variability. Therefore, using splitting tensile strength as a design parameter for the mixture is more reasonable. In recent years, with the increasing demand for high-efficiency utilization of waste pavement materials, ambient temperature recycled mixtures have also begun to be gradually used in the surface course structure of high-grade roads. With the increasing layer level of the ambient temperature recycled layer structure, higher requirements should be placed on the splitting tensile strength.

[0061] The inventors of this invention believe that the design standards for ambient temperature recycled asphalt mixtures should be formulated according to the road grade and the structural layer in which the ambient temperature recycled material is located. This invention references the Changjiu Ambient Temperature Recycling Project (heavy traffic section) paved in 2007, and core samples were taken from the ambient temperature recycled layer in 2013 and 2018. The results showed that the longitudinal cracks below the wheel track were shear-induced top-down cracks, not bottom-up cracks caused by flexural fatigue. The ambient temperature recycled layer also did not experience fatigue damage. Furthermore, in the initial design, the average splitting tensile strength of the ambient temperature recycled asphalt mixture at 15°C was approximately 0.80 MPa, indicating that this splitting tensile strength meets the flexural tensile performance requirements of high-grade heavy traffic roads for ambient temperature recycled asphalt mixtures. This invention also consulted the Wirtgen Recycling Design Guidelines, South African recycling standards, and relevant domestic literature, and further refined the design principles. The research findings of Dr. Jiang Tao, Dr. Yang Jin, and Dr. Xu Yan were summarized. Through the design of different types of recycled materials, it was found that there were significant differences in the old asphalt content, penetration index, 4.75mm sieve passing rate after mineral extraction, and gradation change rate before and after extraction among different recycled materials, which are highly representative. The study found that when the minimum emulsified asphalt content is 1%, the splitting tensile strength of the ambient temperature recycled mixture designed by different types of recycled materials still reaches above 0.58MPa, which is close to the design requirements of my country's standard for surface layers of heavy and above traffic load level (≥0.6MPa), and exceeds the design requirement of 0.5MPa for ambient temperature recycled subbase in the recycling standard.

[0062] Based on the above-mentioned references and the research results of the research group on ambient temperature recycled mixtures, and combined with the results of the indoor 15℃ splitting tensile strength test of this invention, it is recommended to divide the ambient temperature recycled layer into four levels: middle and lower layers with heavy and above traffic load ratings; base layers and below with heavy and above traffic load ratings; surface layers with other traffic load ratings; and base layers and below with other traffic load ratings. The reference values ​​for splitting tensile strength are shown in Table 1.

[0063] Table 1 Technical Requirements for Splitting Strength Design of Recycled Aggregates at 15℃

[0064]

[0065] (4) Determination of water stability and porosity design parameters

[0066] Room-temperature recycled asphalt mixtures are characterized by high porosity and low bonding performance. Through reviewing relevant literature and examining numerous practical projects, it was found that the porosity is generally between 5% and 15%, with 7% to 13% being the most common. Therefore, this invention recommends a design porosity range of 7% to 13% for room-temperature recycled asphalt mixtures. High-porosity mixtures are susceptible to water damage as moisture easily penetrates the mixture under vehicle loads. Furthermore, after the emulsified asphalt in the mixture hardens, the remaining pure asphalt adheres to the aggregate in an incompletely continuous "spot weld" pattern, resulting in poor bonding performance and susceptibility to erosion and damage from high-pressure water. Therefore, the water stability of room-temperature recycled asphalt mixtures should be a key concern.

[0067] The commonly used method for testing the water stability of room-temperature recycled aggregates both domestically and internationally is the immersion test. Chinese recycling standards employ the immersion test to design room-temperature recycled aggregates, while the freeze-thaw splitting test is used to verify the aggregate performance. The immersion test compares the performance of aggregate specimens immersed in water for a certain period with those not immersed. Common performance indicators include splitting strength, Marshall stability, and compressive resilient modulus. Jiang Tao, Yang Jin, Chen Guoqiang, Xu Yan, and others, through extensive indoor experimental research, have discovered the phenomenon of "wet splitting without water immersion" in room-temperature recycled aggregates. This means that after immersing room-temperature recycled aggregate specimens formed by single-stage room-temperature compaction in a water bath for 24 hours, some water seeps into the interior of the specimen, while specimens formed by secondary room-temperature compaction do not. In other words, the immersion test cannot cause substantial water damage to the secondary-formed specimens, and therefore cannot be used to determine the quality of water stability of room-temperature recycled aggregates. Meanwhile, Yang Jin, Chen Guoqiang, and others, through repeated indoor experiments, discovered that after immersion in water and vacuuming, water seeped into the interior of the indoor-formed specimens, and there was a significant difference in the splitting tensile strength of the room-temperature recycled mixture specimens before and after vacuuming. In 2013, Xu Yan designed room-temperature recycled mixtures using different types of recycled materials and, under different amounts of emulsified asphalt, further verified the rationality of the freeze-thaw splitting test as an evaluation of the water stability of room-temperature recycled mixtures. The 2016 Shanghai Municipal "Technical Specification for Cold Recycling of Asphalt Pavement" also adopted the freeze-thaw splitting strength ratio (TSR) as an evaluation index for the water stability of room-temperature recycled mixtures. Therefore, this invention recommends using the freeze-thaw splitting test to evaluate the water stability of room-temperature recycled mixtures. The design reference values ​​for porosity and freeze-thaw splitting strength ratio (TSR) of this invention are shown in Table 2.

[0068] Table 2. Porosity and Freeze-Thaw Splitting Strength Ratio of Ambient Temperature Recycled Mixtures (TSR) Design Technical Requirements

[0069]

[0070] (5) Determination of low-temperature performance design parameters

[0071] For the low-temperature performance of emulsified asphalt recycled mixtures at room temperature, this invention uses the IDT (Indirect Tensile Strength Test Method) fracture work test to evaluate it, and the evaluation criteria are shown in Table 3.

[0072] Table 3. Low-Temperature Crack Resistance Requirements of Recycled Aggregates under IDT Test at Room Temperature

[0073]

[0074] After establishing the design standard for room-temperature recycled emulsified asphalt mixtures, this invention samples and analyzes recycled materials from old asphalt pavements, initially selects the gradation curve of room-temperature recycled emulsified asphalt mixtures based on experience, and calculates the fractal dimension D of the composite gradation and the fractal dimension D of the coarse aggregate gradation. C Based on the fractal dimension D of the synthetic gradation and the fractal dimension D of the coarse aggregate gradation C Performance prediction of emulsified asphalt ambient temperature recycled mixture, the performance in the performance prediction includes dry splitting strength R T Freeze-thaw splitting strength ratio (TSR) and dynamic stability (D) S and maximum bending tensile strain B ε If the performance meets the requirements, a dummy aggregate test is performed on the emulsified asphalt ambient temperature recycled mixture. If the requirements are not met, the gradation curve is readjusted until the requirements are met; the variance D of the gradation change rate before extraction... V ≤85 or the change in gradation value V before and after extraction a When the moisture content is ≤3.6, the gradation curve of the emulsified asphalt ambient temperature recycled mixture is designed and the proportion of different aggregate grades is determined. Based on the determined proportion of different aggregate grades, the synthetic aggregate is prepared and the synthetic aggregate is subjected to a compaction test to obtain the optimal moisture content.

[0075] In this invention, the sampling and analysis are preferably carried out in accordance with the "Specifications for Testing Aggregates in Highway Engineering", including sand equivalent testing, old material screening, old material extraction testing, etc. Before sampling the recycled old asphalt pavement, a portion of the surface within a depth range of 150 to 250 mm should be removed.

[0076] In this invention, the formula for calculating the fractal dimension D of the synthetic gradation is shown in Equation 6:

[0077] P(x) = m / M = (d / d max ) 3-D Formula 6;

[0078] In Equation 6: P(x) is the mass distribution function; m is the total mass of aggregates not greater than particle size d; M is the maximum nominal particle size d. max The mass of the aggregate. Taking the logarithm of both sides of equation 6, we get:

[0079] ln(m / M)=(3-D)ln(d)+a Formula 7;

[0080] Let 3-D equal b. According to Equation 7, the least squares method is used to perform the best curve fitting on the cold recycled mixture. The parameters b and a are then obtained, and the fractal dimension D of the gradation can be solved.

[0081] In this invention, the fractal dimension D of the coarse aggregate gradation is... C The calculation of the fractal dimension D of the composite gradation is the same as that of the composite gradation, except that the particle size is different. D is the overall gradation. C It is a coarse aggregate gradation.

[0082] In this invention, the prediction is preferably performed using a fractal dimension room-temperature recycled mixture performance prediction equation, which is as follows:

[0083] R T =3.03 - 0.1098D - 0.7559D C

[0084] TSR = -92.58 + 60.96D + 9.483D C

[0085] D S =(6.865e+04)-(1.976e+04)D-6056D C

[0086] B ε =(-1.926e+04)+(1.017e+04)D-1149D C .

[0087] The present invention does not have any special requirements for the method of testing the dummy aggregate; any method known to those skilled in the art can be used.

[0088] In this invention, the V a The calculation formulas are shown in Equations 8 and 9 (e.g.) Figure 6 As shown):

[0089]

[0090] Va = S1 + S2 (Equation 9);

[0091] In Equations 8 and 9, y1 is the best-fit line for the pre-extraction gradation; y2 is the best-fit line for the post-extraction gradation; the horizontal and vertical coordinates (ln(d), ln(m / M)) refer to Equation 7; a1 and a2 are fixed intervals for the horizontal coordinates, which are taken as [-2, 2] in this invention; S1 and S2 are the areas of the regions enclosed by the two lines.

[0092] In this invention, the D V The calculation formula is shown in Equation 10:

[0093] D V =VAR(g 13.2or9.5 g 4.75 g 2.36 g 0.3 g 0.075 Formula 10;

[0094] In Equation 10, D V To extract the equation for the rate of change of gradation before and after extraction, VAR(x) is a function for calculating the variance, and g 13.2or9.5 This indicates the difference in passing rate before and after sampling at a 13.2mm (for coarse-grained gradations) or 9.5mm (for medium-grained gradations) sieve opening, expressed in % (g). 4.75 g 2.36 g 0.3 g 0.075 Similar.

[0095] In this invention, when D V and V a D is not satisfied V ≤85 or V a When the aggregate density is ≤3.6, adjust the gradation curve of the emulsified asphalt ambient temperature recycled mixture closer to the lower limit, or adjust the gradation by using 15-25mm grade crushed stone. Then, re-evaluate the mixture performance and conduct dummy aggregate testing until the D requirement is met. V ≤85 or V a Until the requirement of ≤3.6 is met.

[0096] Figure 2 This is a flowchart illustrating the gradation design process for the ambient temperature recycled emulsified asphalt mixture of the present invention.

[0097] In this invention, the compaction test is preferably performed in accordance with the method of the current "Specifications for Testing Aggregates in Highway Engineering" (JTG E40) T0131.

[0098] After determining the proportions and optimum moisture content of different aggregate grades, this invention uses the amount of emulsified asphalt, indoor secondary compaction temperature, and number of secondary compactions as indoor design variables. By changing the combination of different indoor design variables, the performance of the mixture made by mixing different aggregate grades and optimum moisture content according to the above scheme reaches the indoor ambient temperature recycled mixture design standard, thus obtaining the preliminary design variable combination scheme.

[0099] In this invention, the combination of different design variables in the indoor environment includes: when the amount of emulsified asphalt is fixed, changing the indoor secondary compaction temperature and the number of secondary compactions; when the number of secondary compactions in the indoor environment is fixed, changing the indoor secondary compaction temperature and the amount of emulsified asphalt.

[0100] Since it is necessary to simultaneously meet the high-temperature performance, low-temperature performance, and tensile strength requirements of room-temperature recycled mixtures, the selection of indoor design variable combinations may conflict. Therefore, when selecting design variables, it is necessary to take into account and balance various properties of room-temperature recycled mixtures.

[0101] Taking a fixed emulsified asphalt content and varying the number of indoor secondary compaction cycles and the indoor secondary compaction temperature as an example, firstly, a design variable combination scheme is selected based on the shear strength requirements (i.e., the selectable range of indoor compaction work and indoor secondary compaction temperature) to meet the high-temperature performance requirements of the mixture; then, a design variable combination scheme is selected based on the fracture work requirements to meet the low-temperature performance requirements of the mixture; next, a design variable combination scheme is selected based on the fatigue life requirements to meet the fatigue performance requirements of the mixture; finally, a design variable combination scheme is selected based on the dry splitting strength and TSR design target value of the room-temperature recycled mixture to meet the tensile performance and water stability requirements of the mixture. In other words, different properties have their own suitable design variable combination schemes, i.e., their own satisfaction zones. By squeezing these zones together, a zone that satisfies "high-temperature performance, low-temperature performance, fatigue performance, tensile performance, and water stability" can be obtained. Ultimately, a room-temperature recycled mixture design combination scheme that simultaneously satisfies high-temperature performance, low-temperature performance, fatigue performance, tensile performance, and water stability is obtained, which is the feasibility design scheme, also known as the preliminary design variable combination scheme.

[0102] After obtaining the preliminary design variable combination scheme, the present invention performs performance verification on the preliminary design variable combination scheme. If all performances meet the indoor ambient temperature recycled mixture design standards described in the above technical solution, the design variable combination scheme is determined to be a feasible scheme (i.e., suitable aggregate gradation, emulsified asphalt content, secondary compaction temperature and secondary compaction number).

[0103] In this invention, if some performance aspects of the initially proposed design variable combination scheme fail to meet the design standard requirements, it is preferable to adjust the indoor compaction work and the amount of emulsified asphalt to improve the performance. If the adjustment still fails to meet the design standard requirements, the gradation design is carried out again by replacing the raw materials, or the road performance of the ambient temperature recycled mixture is improved by changing the type of emulsified asphalt or adding admixtures (such as recycling agents, fibers, etc.). If the requirements still cannot be met, the redesign of the pavement structure is considered.

[0104] Based on the above steps, this invention can obtain a design scheme that meets road performance requirements. If multiple design combinations exist, further selection can be made according to the specific construction conditions during actual construction to determine the final design combination scheme. Specifically, when the ambient temperature is low during on-site construction (generally during autumn and winter), the ambient temperature recycled layer is difficult to compact and has low performance due to objective natural conditions. On the one hand, the problem of low compaction and low mixture performance can be solved by increasing the on-site compaction work. However, for some construction units, because the tonnage configuration of construction equipment (single and double steel drum rollers, rubber-tired rollers) is low, it is difficult to increase the compaction work even by increasing the number of compaction passes. In this case, it is possible to increase the amount of emulsified asphalt, i.e., the high value of emulsified asphalt content.

[0105] Currently, most design methods for ambient temperature recycled asphalt mixtures are modified from those for hot-mix asphalt mixtures, including the modified Marshall design method, the modified Superpave method, and the vertical vibration test method. The modified Marshall design method is recommended in my country's recycling standards and has been widely used in ambient temperature recycling projects in my country. This method involves molding specimens under given indoor compaction work and curing conditions, and then determining the target gradation, optimum moisture content, and optimum emulsified asphalt content based on the volumetric parameters and mechanical properties of the ambient temperature recycled mixture. The modified Superpave method is an ambient temperature recycled asphalt design method explored by North American road engineers using rotary compaction equipment. It mainly determines the optimum moisture content and optimum emulsified asphalt content of the ambient temperature recycled mixture based on volumetric parameters. The vertical vibration method also involves molding specimens indoors with fixed compaction work, and then determining the optimum moisture content and optimum emulsified asphalt content of the ambient temperature recycled mixture based on volumetric and mechanical properties, ultimately completing the design of the ambient temperature recycled mixture. These existing design methods have the following shortcomings:

[0106] First, the commonly used design methods currently all design the mixture based on indoor volumetric parameters and mechanical performance indicators, without considering the actual road performance requirements on site. For example, the optimal emulsified asphalt content in the Marshall design method is mainly determined based on the peak splitting strength at 15℃. This design mainly considers improving the flexural tensile strength of the ambient temperature recycled mixture. However, with the increase in the application layer and the objective "secondary hot compaction" phenomenon during the construction of ambient temperature recycled mixtures, such a design will easily lead to an excessive amount of emulsified asphalt, resulting in poor economic efficiency and potentially insufficient high-temperature resistance of the ambient temperature recycled mixture. This phenomenon occurred during the ambient temperature recycling technology renovation of the Changjiu Expressway in 2007.

[0107] Secondly, existing indoor ambient temperature recycled asphalt mixture design processes do not consider actual on-site construction conditions, including construction conditions in different regions, climate and temperature variations, and actual compaction conditions at different layers. For example, several commonly used design methods both domestically and internationally do not account for the objectively existing "secondary hot compaction" phenomenon during the construction of ambient temperature recycled asphalt mixtures. This is the main reason for the significant differences in porosity and road performance between on-site ambient temperature recycled asphalt mixtures and those designed indoors. Furthermore, ambient temperature recycled asphalt mixtures constructed under different regions and climatic conditions often exhibit substantial performance differences.

[0108] Finally, the modified Marshall design method, the modified Superpave method, and the vertical vibration test method mainly adjust the performance of ambient temperature recycled mixtures by optimizing aggregate gradation and changing the amount or type of emulsified asphalt, resulting in relatively limited performance adjustment methods. Furthermore, two other important variable factors—compaction energy and secondary compaction temperature—are not involved in the design of ambient temperature recycled mixtures. For compaction energy, it is directly selected based on the expected traffic volume and treated as a prerequisite "fixed value" without participating in the mixture design. Similarly, the secondary compaction temperature of the specimens, selected solely to accelerate curing, is also treated as a prerequisite "fixed value" without participating in the mixture design. As mentioned above, although the current design process for ambient temperature recycled mixtures is simple, it cannot reflect the specific actual construction conditions of ambient temperature recycling projects and also limits the full expression of the performance of ambient temperature recycled mixtures.

[0109] It is evident that traditional design methods for ambient temperature recycled asphalt mixtures primarily involve aggregate gradation design, determining the optimal emulsified asphalt content and moisture content, and finally completing the design work through mixture performance tests. However, these methods do not consider the impact of construction under different regional, seasonal, and layer conditions. During the design process, the selection of compaction work and molding temperature relies excessively on past design experience, thus neglecting the role of these variables in improving mixture performance. This invention weakens the concept of a single optimal emulsified asphalt content. The optimal emulsified asphalt content should be dynamically adjusted according to different seasons, layers, and temperature compaction conditions, and should be included as one of the design variables for ambient temperature recycled asphalt mixtures. This invention proposes a multi-variable design approach for ambient temperature recycled asphalt mixtures, combining compaction work, indoor secondary compaction temperature, and emulsified asphalt content. A "performance-design variable" nomograph for ambient temperature recycled asphalt mixtures is established. By employing a synergistic combination of compaction work, emulsified asphalt content, and indoor secondary molding temperature, the volumetric parameters and various road performance characteristics of ambient temperature recycled asphalt mixtures are comprehensively tested, thereby enabling the design of ambient temperature recycled asphalt mixtures. The design method proposed in this invention solves the problems of low road performance of ambient temperature recycled mixtures, low application pavement structure layers, and mismatch between indoor design and actual on-site construction.

[0110] To further illustrate the present invention, the design method for ambient temperature recycled mixtures considering multiple variable combinations provided by the present invention will be described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0111] Example 1

[0112] To better demonstrate the superiority of the design method proposed in this invention, the design method of emulsified asphalt ambient temperature recycled mixture considering the actual working conditions of a highway in northern China is described and analyzed using the middle and lower layers of the ambient temperature recycled layer as an example.

[0113] (1) Room temperature regeneration of the middle layer

[0114] A highway in northern China is located in a cold region with an average annual temperature of 6°C. The average temperature of the coldest month (January) is -10°C, with an extreme minimum temperature of -22°C. The average temperature of the hottest month (July) is 25°C, with an extreme maximum temperature of 34°C. The road primarily carries trucks and cars. Based on standard axle load calculations, the cumulative traffic volume of the designed lanes reaches 4 × 10⁻⁶ km² within the design life. 6 The allowable rut depth is 15mm, and the vehicle speed is 60km / h. The asphalt pavement structure consists of a 4cm top layer (SMA-13) + a 6cm intermediate layer (normal temperature recycled mixture) + an 8cm bottom layer (AC-25), totaling 18cm. The intermediate layer uses a recycled layer structure. The road base consists of a 40cm thick lime-stabilized crushed stone layer and a 25cm thick graded crushed stone layer. The tested resilient modulus of the lime-stabilized crushed stone layer is 20000MPa. The design process of the emulsified asphalt normal temperature recycled mixture using the design method of this invention is as follows:

[0115] ① Determination of indoor performance targets for ambient temperature recycled mixtures

[0116] Based on the on-site information of the planned highway, including traffic design parameters, environmental design parameters, and asphalt pavement structure layers, the indoor performance design targets were calculated. For high-temperature performance, substituting the known parameters into the shear strength model formulas (Equations 1-2), the comprehensive shear strength requirement for the asphalt layer is 0.349 MPa. For a structure composed of three asphalt layers, the shear strength weights of the upper, middle, and lower layers can be taken as 0.35, 0.42, and 0.23, respectively. Substituting these values ​​into the minimum shear strength formula (Equation 3), the target shear strength values ​​for each of the three layers are 0.421 MPa, 0.505 MPa, and 0.277 MPa, respectively. For fatigue performance, the location of the maximum tensile strain in the middle layer was first calculated to be at the bottom of the layer, in the y-direction of the center of the single circular load, with a strain value of 43.2 με. Then, based on the stress-strain relationship in fatigue testing, the corresponding tensile stress at the center of the specimen was calculated to be 0.550 MPa when the maximum tensile strain of 43.2 με was generated in the indoor fatigue specimen. That is, when using this stress-controlled testing method for fatigue testing, based on the surface fatigue life model (Equations 4-5), the indoor-outdoor fatigue life conversion coefficient, and the fatigue performance relationship between in-service ambient temperature recycled mixture and newly formed indoor specimens, the design target for the fatigue life of the newly formed indoor specimens can be obtained as 3215 cycles. For tensile strength, water stability, and low-temperature performance, according to the corresponding performance index technical requirements, the design target values ​​for dry splitting strength, TSR, and fracture energy are 0.80 MPa, 75%, and 14.0 N·m, respectively.

[0117] ② Multi-factor design of performance-based ambient temperature recycled mixtures

[0118] When the emulsified asphalt content is fixed, and the indoor secondary compaction temperature and the number of indoor secondary compaction cycles are varied, the design variable combination scheme is first selected based on the shear strength of 0.505 MPa to meet the high-temperature performance requirements of the mixture, such as... Figure 3 The upper right half of the dashed line in (a) represents a feasible solution to meet high-temperature performance requirements; subsequently, based on the fracture energy of 14.0 N·m, different combinations of design variables are selected to meet the low-temperature performance requirements of the mixture, such as... Figure 3 The upper right half of the dashed line in (b) represents a feasible solution to meet the low-temperature performance requirements of the mixture; then, a design scheme is selected based on fatigue life to meet the fatigue performance requirements of the mixture, such as... Figure 3 The lower left half of the dashed line in (d) represents a feasible scheme that satisfies the fatigue performance of the mixture; finally, different combinations of design variables are selected based on the design target values ​​of the dry splitting strength (≥0.80MPa) and TSR (≥75%) of the room-temperature recycled mixture, such as... Figure 3 As shown in (c) and (e), the final design combination scheme for ambient temperature recycled mixtures should simultaneously meet the requirements of high-temperature performance, low-temperature performance, fatigue performance, tensile strength, and water stability. Feasible design schemes obtained through mutual combination are shown in...Figure 3 As shown in (f).

[0119] Similarly, when the number of indoor secondary compaction cycles is fixed, but the indoor secondary compaction temperature and the amount of emulsified asphalt are varied, a combination of design variables should be selected, such as... Figure 4 As shown in (a) to (e), the indoor design process for ambient temperature recycled aggregates considering actual on-site working conditions and performance requirements is illustrated. The final variable combination scheme simultaneously satisfies high-temperature performance, low-temperature performance, fatigue performance, tensile strength, and water stability. The feasible design scheme obtained through these combinations is shown in Figure 1. Figure 4 As shown in (f).

[0120] (2) Room temperature regeneration of the lower layer

[0121] A highway in northern China is located in a cold region with an average annual temperature of 6°C. The average temperature of the coldest month (January) is -10°C, with an extreme minimum temperature of -22°C. The average temperature of the hottest month (July) is 25°C, with an extreme maximum temperature of 34°C. The road primarily carries trucks and cars. Based on standard axle load calculations, the cumulative traffic volume of the designed lanes reaches 4 × 10⁻⁶ km² within the design life. 6 The permissible rut depth is 15mm, and the vehicle speed is 60km / h. The asphalt pavement structure consists of a 4cm top layer (SMA-13) + a 6cm intermediate layer (AC-16) + an 8cm bottom layer (emulsified asphalt ambient temperature recycled mixture), totaling 18cm. The bottom layer uses a recycled layer structure. The road base consists of a 40cm thick layer of lime-stabilized crushed stone and a 25cm thick layer of graded crushed stone. The tested resilient modulus of the lime-stabilized crushed stone layer is 20000MPa.

[0122] Based on the site information of the planned highway, the indoor performance design targets were calculated as follows: For high-temperature performance, the comprehensive shear strength requirement for the asphalt layer is 0.326 MPa. For a structure composed of three asphalt layers, the shear strength weights for the upper, middle, and lower layers can be taken as 0.35, 0.42, and 0.23, respectively. Substituting these values ​​into the minimum shear strength formula, the target shear strength values ​​for each of the three layers are 0.406 MPa, 0.489 MPa, and 0.247 MPa, respectively. For fatigue performance, the location of the maximum tensile strain in the lower layer was first calculated as the bottom of the layer, in the y-direction of the center of the single circular load, with a strain value of 60.8 με. Then, based on the stress-strain relationship in fatigue testing, the corresponding tensile stress at the center of the specimen when the maximum tensile strain of 60.8 με is generated in the indoor fatigue specimen is calculated to be 0.453 MPa. That is, when using this stress-controlled test method for fatigue testing, the indoor-outdoor fatigue life conversion coefficient and the fatigue performance relationship between in-service room-temperature recycled mixture and indoor newly formed specimens can be used to obtain the fatigue life design target of 3215 cycles for the indoor newly formed specimens. For tensile properties, water stability properties, and low-temperature properties, the design target values ​​for dry splitting strength, TSR, and fracture energy are 0.80 MPa, 75%, and 14.0 N·m, respectively.

[0123] Based on the aforementioned performance design targets, the final design combination scheme for ambient temperature recycled mixtures should simultaneously meet the requirements of high-temperature performance, low-temperature performance, fatigue performance, tensile strength, and water stability. The feasible design scheme obtained through these combinations is as follows: Figure 5 As shown.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for designing ambient temperature recycled mixtures considering multiple variable combinations, characterized in that, Includes the following steps: (1) Collect on-site road information and formulate design standards for emulsified asphalt ambient temperature recycled mixture; the on-site road information includes traffic design parameters, environmental design parameters and application layer of ambient temperature recycled layer; the design standards for emulsified asphalt ambient temperature recycled mixture include high temperature performance, low temperature performance, fatigue performance, tensile performance, water stability performance and porosity design standards. (2) Sampling and analysis of recycled materials from old asphalt pavement were conducted. Based on experience, the gradation curve of emulsified asphalt ambient temperature recycled mixture was initially selected, and the fractal dimension D of the composite gradation and the fractal dimension D of the coarse aggregate gradation were calculated. C Based on the fractal dimension D of the synthetic gradation and the fractal dimension D of the coarse aggregate gradation C Performance prediction of emulsified asphalt ambient temperature recycled mixture, the performance in the performance prediction includes dry splitting strength R T Freeze-thaw splitting strength ratio (TSR) and dynamic stability (D) S and maximum bending tensile strain B ε If the performance meets the requirements, a dummy aggregate test is performed on the emulsified asphalt ambient temperature recycled mixture. If the requirements are not met, the gradation curve is readjusted until the requirements are met; when the variance D of the gradation change rate before and after extraction in the dummy aggregate test... V ≤85 or the change in gradation value V before and after extraction a When the moisture content is ≤3.6, the gradation curve of the emulsified asphalt ambient temperature recycled mixture is designed and the proportion of different aggregate grades is determined. Based on the determined proportion of different aggregate grades, the synthetic aggregate is prepared and the synthetic aggregate is subjected to a compaction test to obtain the optimum moisture content. (3) Using emulsified asphalt dosage, indoor secondary compaction temperature and number of secondary compactions as indoor design variables, by changing different combinations of indoor design variables, the performance of the mixture made according to the proportion of different aggregates and the optimum moisture content determined in step (2) reaches the design standard of emulsified asphalt ambient temperature recycled mixture in step (1), and the preliminary design variable combination scheme is obtained. (4) The performance of the initial design variable combination scheme in (3) is verified. If all the performances meet the design standards of emulsified asphalt ambient temperature recycled mixture in step (1), then the design variable combination scheme is determined to be a feasible scheme.

2. The method according to claim 1, characterized in that, The traffic design parameters in step (1) include traffic volume, axle load spectrum and tire ground pressure, and the environmental design parameters include groundwater level, annual precipitation, annual temperature, historical extreme high temperature, historical extreme low temperature and atmospheric conditions during construction.

3. The method according to claim 1, characterized in that, In step (2), the performance prediction of the room temperature recycled mixture is performed using the fractal dimension equation, which is as follows: ， Among them, R T The unit is MPa; the unit of TSR is %; D S The unit is times·mm -1 B ε The unit is με.

4. The method according to claim 1 or 3, characterized in that, In step (2), when D V and V a D is not satisfied V ≤85 or V a When the requirement is ≤3.6, adjust the gradation curve of the emulsified asphalt ambient temperature recycled mixture closer to the lower limit, or adjust the gradation by using 15~25mm grade crushed stone, and then re-evaluate the performance and test the dummy aggregate until the requirement is met.

5. The method according to claim 1, characterized in that, The steps (3) include changing different combinations of indoor design variables: when the amount of emulsified asphalt is fixed, changing the indoor secondary compaction temperature and the number of secondary compactions; when the number of secondary compactions is fixed, changing the indoor secondary compaction temperature and the amount of emulsified asphalt.

6. The method according to claim 1, characterized in that, If, in step (4), some of the performance of the initially proposed design variable combination scheme fails to meet the design standard of the emulsified asphalt ambient temperature recycled mixture, the number of indoor secondary compaction times and the amount of emulsified asphalt are adjusted to improve the performance. If the adjustment still fails to meet the design standard of the emulsified asphalt ambient temperature recycled mixture, the gradation design is carried out again by replacing the raw materials, or the road performance of the ambient temperature recycled mixture is improved by changing the type of emulsified asphalt or adding admixtures, or the road structure is redesigned.

7. The method according to claim 1, characterized in that, When there are multiple feasible options in step (4), further selection is made based on the specific construction conditions during actual construction.

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