A high modulus asphalt mixture and a method of designing the same

Abstract

The application discloses a kind of high modulus asphalt mixture and its design method, belong to road engineering test field.The mixture, 25 DEG C penetration of asphalt cement is required 15-30 (0.1mm), 60 DEG C dynamic shear complex modulus G*≥12.0kPa, mortar film thickness DA*≥21 μm, asphalt film thickness DA is 5 μm-12 μm, the asphalt cement is new addition asphalt or new and old composite asphalt, the new and old composite asphalt is composed of aging asphalt of milling material and new addition asphalt.Compared with prior art, the high modulus asphalt mixture of the application balanced road performance, high, low temperature, water stability and anti-fatigue and other excellent performance, maximum can realize milling material 100% application of dosage, can greatly improve the utilization efficiency of recycled asphalt mixture, with the characteristics such as simple process, strong practicability, with very high popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of road engineering, specifically providing a high-modulus asphalt mixture and its design method. Background Technology

[0002] High-modulus asphalt mixture refers to asphalt mixture with a dynamic compression modulus of 13,000 MPa at 20℃. Compared with traditional asphalt mixtures, high-modulus asphalt mixture has properties such as high modulus and resistance to rutting. According to the design theory of layered elastic system of asphalt pavement, high-modulus asphalt mixture has the characteristic of reducing the thickness of asphalt pavement. High-modulus asphalt mixture can significantly reduce the mining of resources such as stone, reduce the damage to the natural environment, and significantly improve the service level of pavement, resulting in significant social and economic benefits.

[0003] I. Traditional high-modulus asphalt mixture preparation lacks theoretical guidance, and the scientific nature of key material technical indicators and design control indicators is insufficient. As a result, although a wide range of materials are selected for design and application, the actual application effect is poor, the difficulty is high, and the application reproducibility is poor.

[0004] II. Preparation of high-modulus asphalt mixtures using milled materials

[0005] Currently, my country has built the world's largest road transport network. As of 2022, the total length of highways in operation exceeded 5.3 million kilometers, with over 80% of the road surface being asphalt pavement. Statistics show that tens of millions of tons of waste milling material are generated annually from major and medium-scale repairs and reconstruction projects of asphalt pavements, and this figure is expected to grow at a rate of 10% to 15%. Recycling and reusing asphalt milling material can not only restore pavement to meet usage requirements, reduce project costs, and conserve resources, but also prevent pollution of the natural environment from road waste, achieve green development in the industry, and promote ecological civilization. Therefore, the recycling and reuse of milling material has significant social and economic benefits. Currently, there are many application channels for asphalt pavement milling material, mainly conventional hot recycling and cold recycling. However, in practice, these methods are low-quality, low-value applications that do not fully utilize the characteristics of asphalt milling material.

[0006] Studies have found that under the combined effects of pavement loads and environmental factors during the service life of asphalt pavements, milled asphalt exhibits significant hardening characteristics, which are similar to the hard asphalt required for high-modulus asphalt mixtures. Therefore, high-modulus asphalt mixtures can be prepared using milled asphalt pavement materials, combining the inherent characteristics of milled materials with those of high-modulus mixtures to achieve high-quality, high-value applications of asphalt milled materials.

[0007] In fact, numerous research institutions and universities both domestically and internationally have conducted studies on the preparation of high-modulus asphalt mixtures using milled aggregate, resulting in several patents and other intellectual property rights. Traditional research suggests that, based on extraction and sieving results, milled aggregate for asphalt pavement exhibits significant downgrading, meaning its actual gradation is noticeably finer. Furthermore, it is believed that with high admixture dosages, the 0.075mm sieve passing rate is often too high, significantly reducing the mixture's low-temperature and water-stability performance. Therefore, the admixture dosage of milled aggregate should be strictly controlled to prevent excessively high 0.075mm sieve passing rates and high powder-to-binder ratio (Fb), which would negatively impact mixing and pavement performance. Additionally, to prevent further aging of the milled aggregate, its heating temperature is typically between 90℃ and 120℃, leveraging the overall temperature of the new aggregate to raise the overall mixture temperature. However, in practical applications, several shortcomings still exist:

[0008] 1. Lack of theoretical guidance and unclear key control indicators lead to poor reproducibility in application. Many methods emphasize the proportion of material composition, but different milled materials vary greatly. Preparing high-modulus asphalt mixtures according to composition design methods often fails to achieve the expected results.

[0009] 2. Some methods result in low asphalt milling aggregate content, often below 60%, which severely restricts the application efficiency and value of asphalt milling aggregate. In order to achieve high modulus of milling aggregate, the newly added asphalt is mostly hard asphalt, which makes mixing and compaction extremely difficult, making it practically impossible to achieve high content application. Alternatively, the proportion of milling aggregate added is too small, making it impossible to utilize the milling aggregate efficiently.

[0010] 3. Some methods involve high asphalt milling aggregate content, but the application of milling aggregate is complex, requiring asphalt-aggregate separation technology or multi-stage mixing technology. The above methods have high equipment requirements, require new supporting equipment, and are expensive, which greatly increases the application cost of milling aggregate and is not conducive to its popularization in actual engineering. In addition, a large amount of unnecessary energy consumption is generated during the process, which is not environmentally friendly. Summary of the Invention

[0011] This invention addresses the shortcomings of the prior art by providing a design method for high-modulus asphalt mixtures.

[0012] A further technical objective of this invention is to provide a high-modulus asphalt mixture.

[0013] The technical solution adopted by the present invention to solve its technical problem is: a high modulus asphalt mixture, wherein the asphalt binder in the mixture has a penetration requirement of 15-30 (0.1mm) at 25℃, a dynamic shear complex modulus G*≥12.0kPa at 60℃, a binder film thickness DA*≥21μm, and an asphalt film thickness DA of 5μm-12μm. The asphalt binder is newly added asphalt or a composite asphalt of new and old materials, wherein the composite asphalt of new and old materials is composed of aged asphalt from milled material and newly added asphalt.

[0014] Preferably, the high-modulus asphalt mixture of the present invention can be prepared from new aggregates and newly added asphalt as the main raw materials. The newly added asphalt can be any type of asphalt binder suitable for high-modulus asphalt mixtures, such as low-grade petroleum asphalt, modified asphalt, or asphalt material with added high-modulus modifiers, as long as it meets the requirements of a penetration of 15-30 (0.1 mm) at 25°C and a dynamic shear complex modulus G* ≥ 12.0 kPa at 60°C. In this case, the mixture design method includes:

[0015] S1. Preset the composition ratio of each raw material, wherein the raw materials include new mineral materials and newly added asphalt, and the new mineral materials are new aggregates and / or fillers;

[0016] S2. Conduct a 25°C penetration test and a 60°C dynamic shear test on the newly added asphalt; at the same time, calculate the asphalt film thickness and the mastic film thickness of the mixture.

[0017] S3. If the penetration at 25℃, complex modulus at 60℃, asphalt film thickness, and adhesive film thickness do not meet the requirements, return to step S1 and redesign; if they meet the requirements, verify the performance of the mixture according to the determined material composition.

[0018] S4. Determine whether the test parameters of each performance of the mixture meet the requirements. If a certain performance does not meet the requirements, return to step S1, change the amount of newly added asphalt, and retest, or return to step S1 to redesign the gradation and retest. If all the performance of the mixture meets the test requirements, the mixture design process is completed.

[0019] Preferably, the high-modulus asphalt mixture of the present invention can also be prepared using new aggregates, milled aggregates, and newly added asphalt as the main raw materials, wherein the newly added asphalt is preferably emulsified asphalt, petroleum asphalt, modified asphalt, or foamed asphalt. In this case, the mixture design method includes:

[0020] S11. Conduct extraction tests on milled asphalt material from the road surface, recover aged asphalt, and obtain the gradation and asphalt content of the milled material;

[0021] S12. Preset the composition ratio of each raw material, wherein the raw materials include milling material, new mineral aggregate and newly added asphalt, wherein the new mineral aggregate is new aggregate and / or filler;

[0022] S2. Prepare the new and old composite asphalt according to the preset composition ratio, and conduct a 25℃ penetration test and a 60℃ dynamic shear test on the new and old composite asphalt; at the same time, calculate the asphalt film thickness and the mastic film thickness of the mixture.

[0023] S3. If the penetration at 25℃, complex modulus at 60℃, asphalt film thickness, and adhesive film thickness do not meet the requirements, return to step S12 and redesign; if the requirements are met, verify the performance of the mixture according to the determined material composition.

[0024] S4. Determine whether the test parameters of each performance of the mixture meet the requirements. If a certain performance does not meet the requirements, return to step S12, change the amount of newly added asphalt, and retest, or return to step S12 to redesign the gradation and conduct the test. If all the performance of the mixture meets the test requirements, the mixture design process is completed.

[0025] As a preferred option, the asphalt binder should have a penetration of 20-30 (0.1 mm) at 25℃, a dynamic shear complex modulus G* ≥ 12 kPa at 60℃, a binder film thickness of 21-30 μm, and an asphalt film thickness of 6 μm-11 μm.

[0026] Preferably, the thickness of the adhesive film is calculated according to the following formula:

[0027] SA=∑(P i ×FA i ) Formula 1

[0028]

[0029]

[0030]

[0031] In Equation 1:

[0032] SA is the specific surface area of ​​the aggregate, in kg / m². 2 ;

[0033] P i The sieve passing rate (%) of aggregates of various particle sizes;

[0034] FA i This refers to the surface area coefficient corresponding to each aggregate size;

[0035] The aggregates include new aggregates and / or aggregates from milled material, excluding aggregates smaller than 0.075mm;

[0036] In Equation 2:

[0037] P fb The percentage of binder in asphalt mixture;

[0038] P b The content of asphalt binder (the asphalt binder is newly added asphalt or a combination of new and old asphalt), %;

[0039] P0.075mm This indicates the pass rate (%) of aggregates with a screen aperture of less than 0.075 mm.

[0040] In Equation 3:

[0041] γ fb This represents the relative density of the adhesive.

[0042] γ f The bulk relative density of the filler;

[0043] γ b The relative density of the asphalt binder (25℃) is the asphalt binder, which is either newly added asphalt or a combination of new and old asphalt.

[0044] In Equation 4:

[0045] DA represents the thickness of the adhesive film, in μm.

[0046] As a preferred method, a dynamic shear modulus at 60℃ was tested using a dynamic shear rheometer, under the following test conditions:

[0047] Test spacing 1000μm; parallel plate diameter Strain control range 5%-12%; sinusoidal loading.

[0048] As a preferred option, when the content of milled material in the mixture reaches 70% or more, the newly added asphalt is preferably emulsified asphalt, and the base asphalt grade of the emulsified asphalt is not higher than 70#.

[0049] As a preferred option, the performance tests of high modulus asphalt mixtures in step S4 mainly include high temperature performance, water stability performance, low temperature performance, and dynamic modulus test.

[0050] Through extensive indoor research and engineering practice, the applicant discovered a strong correlation between the complex modulus of asphalt at 60°C and the high-temperature performance and modulus of asphalt mixtures. The workability, water stability, and low-temperature performance of the mixture are determined by the thickness of the asphalt film and the thickness of the binder film: the asphalt film thickness provides the necessary mixing characteristics, while the thickness of the binder film determines the low-temperature and water stability of the mixture. Based on this, the applicant proposes a high-modulus asphalt mixture obtained by the method designed in this invention.

[0051] The high-modulus asphalt mixture of this invention can meet the pavement design requirements specified in various existing road engineering specifications. However, if it is necessary to further improve certain aspects of the pavement performance of the mixture, certain road engineering additives, such as warm mix additives and high-modulus additives, can be added.

[0052] Compared with existing technologies, the high-modulus asphalt mixture and its design method of the present invention have the following outstanding advantages:

[0053] (i) For the first time, the thickness of the asphalt film is proposed as the design standard for preparing high modulus asphalt mixtures. This is simpler and more practical than existing design methods. The designed mixtures have balanced road performance and excellent high and low temperature, water stability and fatigue resistance.

[0054] (II) The high-modulus asphalt mixture obtained by the design method of this invention: ① There is no specific limitation on the amount of milled material, and 100% recycled material can be achieved, which effectively improves the utilization rate of milled material; ② The resulting mixture can be directly used for the pavement surface layer, which improves the utilization effect of pavement milled material; ③ The high-value utilization of asphalt milled material can be achieved using existing equipment, which is of great significance for promotion and popularization. Attached Figure Description

[0055] Appendix Figure 1 The flowchart of the mixture design method (including milled material) is shown in the example.

[0056] Appendix Figure 2 The flowchart of the mixture design method for the example is shown (excluding milled materials);

[0057] Appendix Figure 3 The flowchart of the mixture preparation method (including milled material) is shown in the example.

[0058] Appendix Figure 4 This is a flowchart of the mixture preparation method for an example (excluding milled materials). Detailed Implementation

[0059] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the present invention.

[0060] Example

[0061] High-modulus asphalt mixtures are prepared using new mineral materials (new aggregates, mineral powder), milled material, and newly added asphalt as the main raw materials.

[0062] As attached Figure 1 , 2 As shown, the design method for high-modulus asphalt mixtures includes:

[0063] 1. Determine the composition of raw materials.

[0064] 1.1 When milled material is present, an extraction test is conducted on the milled material to obtain the aged asphalt content and aggregate sieve data of the milled material; at the same time, a rotary evaporator is used to recover the aged asphalt; a large amount of trichloroethylene is still present in the recovered aged asphalt. Under ventilated conditions, the mixture of trichloroethylene and aged asphalt is heated at a temperature controlled at 110℃-120℃ until the trichloroethylene is completely volatilized.

[0065] 1.2 Based on the project requirements and the characteristics of the raw materials, the composition ratio of milling material, new mineral material, and newly added asphalt is preset (see Table 1 and Table 2 for details);

[0066] Table 1 Material Composition

[0067]

[0068] Table 2 shows the gradation composition of each example.

[0069]

[0070] 2. Indicator Verification

[0071] 2.1 Asphalt binder configuration

[0072] The composition of the asphalt binder is shown in Table 3.

[0073] Table 3 shows the pre-set ratio of new and old asphalt according to the gradation composition.

[0074]

[0075] 2.2 Membrane thickness calculation and verification

[0076] The thickness of the asphalt film and the thickness of the adhesive film were determined according to the raw material ratios in Tables 1, 2 and 3.

[0077] a. The asphalt film thickness was calculated according to the method described in the "Technical Specification for Construction of Asphalt Pavement of Highway" (JTGF40), and the calculation results are shown in Table 4.

[0078] b. The thickness of the adhesive film is calculated according to the following formula steps, and the calculation results are shown in Table 4:

[0079] SA=∑(P i ×FA i ) Formula 1

[0080]

[0081]

[0082]

[0083] In Equation 1:

[0084] SA is the specific surface area of ​​the aggregate, in kg / m². 2 ;

[0085] P i The sieve passing rate (%) of aggregates of various particle sizes;

[0086] FA i This refers to the surface area coefficient corresponding to each aggregate size;

[0087] The aggregates referred to are new aggregates and / or aggregates from milling materials; aggregates smaller than 0.075mm are not included.

[0088] In Equation 2:

[0089] P fb The percentage of binder in asphalt mixture;

[0090] P b The content of asphalt binder (the asphalt binder is newly added asphalt or a combination of new and old asphalt), %;

[0091] P 0.075mm This indicates the pass rate (%) of aggregates with a screen aperture of less than 0.075 mm.

[0092] In Equation 3:

[0093] γ fb This represents the relative density of the adhesive.

[0094] γ f The bulk relative density of the mineral powder;

[0095] γ b The relative density of the asphalt binder (25℃) is the asphalt binder, which is either newly added asphalt or a combination of new and old asphalt.

[0096] In Equation 4:

[0097] DA represents the thickness of the adhesive film, in μm.

[0098] Table 4 shows the calculated asphalt film thickness and sealant film thickness.

[0099]

[0100] 2.3 Properties of binders

[0101] The asphalt binder was prepared according to Table 3, and its performance was tested. Specific indicators included penetration at 25℃ and complex modulus of asphalt at 60℃.

[0102] The penetration at 25℃ was tested according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20), and the results are shown in Table 5.

[0103] The complex modulus at 60℃ was determined using a dynamic shear rheometer. The test fixture consisted of 25mm circular parallel plates with a spacing of 1000μm. The strain was controlled at 12%, and sinusoidal loading was applied at a frequency of 10rad / s and a scanning time of 10s. The test temperature was 60℃. The test results are shown in Table 5.

[0104] Table 5 Asphalt Performance Indicators

[0105]

[0106] 3. Performance Testing

[0107] According to the raw material ratios in Tables 1, 2, and 3, according to Figure 3 or Figure 4 The following steps were taken to prepare the mixtures from Examples 1 to 7 and to conduct performance tests:

[0108] a) Heat the milled asphalt mix to 140℃-160℃, add it to the mixing pot and premix for 1-1.5 minutes; (omit this step if no milled asphalt mix is ​​added)

[0109] b) Heat the new aggregate to 180℃-190℃, and add it to the mixing pot along with the newly added asphalt, and continue mixing for 1-1.5 minutes;

[0110] c) The specimens were compacted and molded according to the test methods specified in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20) to obtain the specimens.

[0111] d) The prepared asphalt mixture was tested for high temperature performance, water stability, low temperature performance and dynamic modulus according to the relevant test methods of the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20). The test results are shown in Table 6.

[0112] Table 6 Performance Verification Results

[0113]

[0114] As can be seen from the test data in Table 6, the mixtures in Examples 1-7 all meet the requirements of the specifications.

Claims

1. A method of designing a high modulus asphalt mixture, characterized by: The 25℃ penetration of the asphalt binder in the mixture is required to be 15-30, unit 0.1mm, the 60℃ dynamic shear complex modulus G* is ≥12.0kPa, the mortar film thickness DA* is ≥21μm, and the asphalt film thickness DA is 5μm-12μm, The asphalt binder is new added asphalt or new-old composite asphalt, the new-old composite asphalt is composed of aged asphalt of milling material and new added asphalt, The mortar film thickness is calculated according to the following formula: In formula 1: SA is the specific surface area of the aggregate, kg / m 2 ; P i Passing rate of each particle size aggregate through the sieve hole; FA i is a surface area coefficient corresponding to each particle size aggregate; The aggregate includes aggregate in new aggregate and / or milling material, and aggregate below 0.075mm is not counted; In formula 2: P fb To the proportion of asphalt mixture in the paste, P b For bitumen binder content, the bitumen binder is fresh bitumen or fresh- old complex bitumen. P 0.075mm represents the % passing of aggregates through a 0.075 mm sieve; In formula 3: gamma fb Relative density of the cement paste; gamma f Bulk relative density of the filler; gamma b Relative density of the asphalt binder at 25°C, the asphalt binder being fresh or aged asphalt or fresh and aged combined asphalt In formula 4: DA is the mortar film thickness, μm, The design method includes: S1. presetting the composition ratio of each raw material; S2. performing 25℃ penetration test and 60℃ dynamic shear test on new added asphalt or new-old composite asphalt; meanwhile, calculating the asphalt film thickness and the mortar film thickness of the mixture; S3. if the 25℃ penetration, 60℃ complex modulus, asphalt film thickness and mortar film thickness do not meet the requirements, returning to step S1 to redesign; if the requirements are met, performing mixture performance verification according to the determined material composition; S4. judging whether the performance test parameters of the mixture meet the requirements, if a certain performance does not meet the requirements, returning to step S1 to change the amount of new added asphalt and then retesting, or returning to step S1 to redesign and testing; if all the performances of the mixture meet the test requirements, completing the mixture design process.

2. The method of designing high modulus asphalt mixtures of claim 1, wherein, including: S1. presetting the composition ratio of each raw material, the raw material including new mineral aggregate and new added asphalt, the new mineral aggregate being new aggregate and / or filler; S2. performing 25℃ penetration test and 60℃ dynamic shear test on new added asphalt; meanwhile, calculating the asphalt film thickness and the mortar film thickness of the mixture; S3. if the 25℃ penetration, 60℃ complex modulus, asphalt film thickness and mortar film thickness do not meet the requirements, returning to step S1 to redesign; if the requirements are met, performing mixture performance verification according to the determined material composition; S4. judging whether the performance test parameters of the mixture meet the requirements, if a certain performance does not meet the requirements, returning to step S1 to change the amount of new added asphalt and then retesting, or returning to step S1 to redesign and testing; if all the performances of the mixture meet the test requirements, completing the mixture design process.

3. The method of designing high modulus asphalt mixtures of claim 1, wherein, including: S11. performing extraction test on pavement asphalt milling material, recovering aged asphalt, and obtaining the gradation and asphalt content of the milling material; S12. presetting the composition ratio of each raw material, the raw material including milling material, new mineral aggregate and new added asphalt, the new mineral aggregate being new aggregate and / or filler; S2. configuring new-old composite asphalt according to the preset composition ratio, performing 25℃ penetration test and 60℃ dynamic shear test on the new-old composite asphalt; meanwhile, calculating the asphalt film thickness and the mortar film thickness of the mixture; S3. If the penetration at 25℃, the complex modulus at 60℃, the asphalt film thickness and the mortar film thickness do not meet the requirements, return to step S12 to redesign; if the requirements are met, the mixture performance verification is carried out according to the determined material composition; S4. Determine whether the performance test parameters of the mixture meet the requirements, if a certain performance does not meet the requirements, return to step S12, change the amount of newly added asphalt, and then retest, or return to step S12 to redesign the gradation and then test; if all the performances of the mixture meet the test requirements, the mixture design process is completed.

4. The method of designing high modulus asphalt mixtures of claim 1, 2 or 3, characterized in that: The penetration of the asphalt binder at 25℃ is required to be 20-30, the unit is 0.1mm, the complex modulus G* of dynamic shear at 60℃ is greater than or equal to 12kPa, the mortar film thickness of the mixture is 21-30μm, and the asphalt film thickness is 6μm-11μm.

5. The design method of high modulus asphalt mixture according to claim 1, 2 or 3, characterized in that: The dynamic shear rheometer is used to test the dynamic shear modulus at 60℃, and the test conditions are as follows: The test distance is 1000μm, the parallel plate diameter is φ25mm, the control strain range is 5%-12%, and the sine loading is used.

6. The method of designing high modulus asphalt mixtures of claim 1 or 3, wherein: The newly added asphalt is emulsified asphalt, petroleum asphalt, modified asphalt or foamed asphalt.

7. The method of designing high modulus asphalt mixtures of claim 6, wherein: When the milling material content is more than 70%, the newly added asphalt is emulsified asphalt, and the base asphalt grade of the emulsified asphalt is not higher than 70#.

8. The high modulus asphalt mixture obtained by the design method of high modulus asphalt mixture according to any one of claims 1-7.

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