A method of determining a high modulus fatigue resistant hot recycled asphalt mixture formulation

Abstract

The present disclosure provides a method for determining a high modulus fatigue resistant hot recycled asphalt mixture formula, comprising: S10 determining the proportion of old asphalt and PG high temperature grade in RAP divided into n grades; S20 selecting new asphalt; S30 setting the proportion of each grade of RAP in the recycled material; S40 according to the proportion of each grade of RAP, the gradation design of new aggregate, new filler and mineral aggregate in each grade of RAP is carried out, it is judged whether it can meet the requirements, if it can, step S50 is executed, if it cannot, steps S30-S40 are repeated; S40 according to the proportion of each grade of RAP and the designed gradation, at least three groups of recycled material test pieces are prepared, so that the proportion of asphalt in the recycled material corresponding to each group is different, and is in the range of 5.2wt%-6.5wt%; S50 determining the void ratio of the test piece, calculating the average void ratio of each group, selecting the group with the average void ratio of 1.5%-4%; and S60 substituting the parameters corresponding to the selected group into the formula, judging whether it meets the formula. When it is satisfied, the formula of the selected group is determined as the recycled material formula, and when it is not satisfied, steps S20-S70 are repeated.

Description

Technical Field

[0001] This disclosure belongs to the field of asphalt mixture technology, and mainly relates to a method for determining the formulation of high-modulus fatigue-resistant hot recycled asphalt mixture. Background Technology

[0002] Asphalt pavements deteriorate in performance after a certain period of service. When they affect normal traffic, they are usually milled and repaved. Recycled asphalt mixture (RAP) obtained from milled waste asphalt pavements can be completely recycled. It is usually prepared by adding new aggregates, new fillers, new asphalt, and hot recycling agents to produce hot recycled asphalt mixture (referred to as recycled material in this article).

[0003] The properties of reclaimed asphalt (RAP) vary greatly due to factors such as the aging degree, original composition, and milling method of the asphalt mixture on the road surface. Recycled asphalt is also affected by the different sources and particle size distributions of RAP. Therefore, if the old asphalt content, properties, aggregate gradation, and quality in the RAP are not considered during the formulation design of recycled asphalt, the performance stability of the recycled asphalt mixture will be affected. To obtain a stable recycled asphalt, multiple sets of experiments are required to determine the composition of the recycled asphalt, which increases the difficulty and complexity of RAP recycling. This is especially true for high-modulus fatigue-resistant asphalt mixtures, which have high performance requirements. If performance cannot be effectively controlled, it is easy to produce substandard products or increase costs.

[0004] Furthermore, in determining the formulation of high-modulus, fatigue-resistant hot recycled asphalt mixtures, it is necessary to conduct tests to verify the high and low temperature performance, modulus, and fatigue performance of the mixture according to the following methods in JTGE20-2011: T0719-2011 Rutting Test, T0715 Bending Test, T0738 Uniaxial Compression Dynamic Modulus Test, and T0739 Four-Point Bending Fatigue Test. These modulus, fatigue performance, and high and low temperature performance tests typically take more than one month and are costly.

[0005] Therefore, it is necessary to provide an improved method for determining the formulation of high-modulus fatigue-resistant hot recycled asphalt mixtures to ensure that the performance of the recycled material does not fluctuate significantly with changes in RAP. Summary of the Invention

[0006] In view of this, the main objective of the present invention is to provide a method for determining the formulation of high-modulus fatigue-resistant hot recycled asphalt mixtures, which is simple in steps, low in cost, and ensures that the performance of the product is within the allowable range.

[0007] This invention provides a method for determining a high-modulus, fatigue-resistant hot recycled asphalt mixture formulation, wherein the hot recycled asphalt mixture includes recycled asphalt mixture (RAP), new asphalt, new aggregates, and new fillers. The RAP includes old asphalt and mineral aggregates. The asphalt in the hot recycled asphalt mixture is composed of the old asphalt and the new asphalt. The RAP has been crushed and screened. The RAP includes n grades divided according to particle size, where n is an integer greater than or equal to 1. The method includes the following operations.

[0008] S10 determines the mass percentage P of the old asphalt in each grade of RAP. i(RAP) and PG high temperature rating T i(RAP) , where i is an integer from 1 to n.

[0009] S20 selects the type of new asphalt, wherein the selected new asphalt has a PG high-temperature grade T 新 .

[0010] S30 sets the mass percentage M of each grade of RAP in the hot recycled asphalt mixture. i(RAP) .

[0011] S40 according to the set M i(RAP) For each grade of RAP, the mineral material, the new aggregate and the new filler are graded and designed to determine whether the passing rate of the key sieve of the synthetic gradation can meet the requirements. If the requirements can be met, step S50 is executed. If the requirements cannot be met, steps S30 to S40 are repeated.

[0012] S50 according to the M i(RAP) Prepare at least three sets of hot recycled asphalt mixture specimens based on the designed gradation, and adjust the mass fraction of the new asphalt in the hot recycled asphalt mixtures so that the mass percentage P of the asphalt in each set of specimens is such that... 总 They differ, and all fall within the range of 5.2wt%-6.5wt%.

[0013] S60 determines the porosity of the specimen, calculates the average porosity of each group of specimens, and selects the group of specimens with an average porosity of 1.5%-4%.

[0014] S70 substitutes the parameters corresponding to the selected group of test specimens into the following formula (I) to determine whether the formula (I) is satisfied.

[0015]

[0016] When formula (I) is satisfied, the formulation of the selected group of specimens is determined as the formulation of the hot recycled asphalt mixture.

[0017] If formula (I) is not satisfied, repeat steps S20 to S70.

[0018] According to one embodiment of the present invention, in step S60, a specimen with an average porosity of 1.5%-3% is selected.

[0019] According to one embodiment of the present invention, in step S60, a specimen with an average porosity of 2%-3% is selected.

[0020] According to one embodiment of the present invention, the gradation design performed in step S40 results in a pass rate of 66%-84%, 42%-64%, 27%-42%, and 6%-8% through sieves with apertures of 9.5mm, 4.75mm, 2.36mm, and 0.075mm, respectively.

[0021] According to one embodiment of the present invention, the RAP may be from the same or different sources, and when the RAP sources are different, the crushed RAP is screened according to the different sources.

[0022] According to one embodiment of the present invention, when the RAP sources are different, the n-grade RAP is selected from different road sections or different pavement layers from the same road section, and the sieve particle size of each grade is the same or different.

[0023] According to one embodiment of the present invention, the mass percentage M of each RAP is... i(RAP) The sum ranges from 10% to 60%.

[0024] According to one embodiment of the present invention, the new asphalt is selected from one or more of natural asphalt, modified asphalt, and petroleum asphalt with a grade not exceeding 30.

[0025] According to one embodiment of the present invention, the new asphalt has a PG high temperature rating T. 新 Selected from 82, 88, and 94.

[0026] According to one embodiment of the present invention, the hot recycled asphalt mixture has a uniaxial compression dynamic modulus of not less than 15,000 MPa at 20°C and 10 Hz, and a fatigue life of not less than 1 million cycles at 15°C, 10 Hz and 230 με.

[0027] This disclosure measures the percentage (P) of used asphalt in each grade of RAP by mass determination. i(RAP) PG high temperature grade T of old asphalt i(RAP) The required mass percentage P of asphalt in the recycled material was obtained by measuring the porosity of the specimens. 总Formula (I) can be used to quickly assess whether the formulation meets the performance requirements of having a uniaxial compression dynamic modulus of not less than 15,000 MPa at 20℃ and 10Hz, and a fatigue life of not less than 1 million cycles at 15℃, 10Hz and 230με, achieving the following significant progress.

[0028] (1) The method disclosed herein takes into account the performance of old asphalt in RAP, the blending ratio of different grades of RAP and the possible impact of different sources, and can more accurately assess whether the formulation meets the above performance requirements.

[0029] (2) The method disclosed herein can reduce the number of tests required in determining the high and low temperature performance, modulus and fatigue performance during the formulation process, thereby saving the time and economic costs involved in these tests. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a method for determining a high-modulus, fatigue-resistant hot recycled asphalt mixture formulation according to an embodiment of this disclosure. Detailed Implementation

[0031] The technical solutions of this disclosure will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] Asphalt aging refers to the process during the service life of asphalt pavements where small molecules (aromatic and saturated components) in the asphalt decrease due to continuous volatilization or aggregation into larger molecules, while asphaltene increases, causing the asphalt to gradually harden. Aging asphalt exhibits reduced penetration, increased softening point, decreased ductility, and reduced flexibility. Waste asphalt pavement is removed and recycled to obtain RAP (Rich Asphalt Powder). Then, recycled asphalt is prepared according to a designed and tested formula. Typically, the recycled asphalt is required to meet the relevant technical indicators of high-modulus fatigue-resistant asphalt mixtures as specified in the national industry standard GB / T 36143-2018 "High Modulus Fatigue-Resistant Asphalt Mixtures for Roads". Specifically, if the asphalt mixture meets the gradation requirements (passing rates through 16mm, 13.2mm, 9.5mm, 4.75mm, 2.36mm, and 0.075mm sieves of 100%, 80-100%, 66%-82%, 41%-64%, 28%-43%, and 6%-8% respectively), asphalt-aggregate ratio ≥ 5.2%, and porosity ≤ 4%, the performance of the asphalt mixture needs to achieve the following: dynamic stability at 60℃ ≥ 4000 cycles / mm, dynamic modulus ≥ 4000MPa, fatigue life ≥ 1 million cycles, and low-temperature bending failure strain at -10℃ ≥ 2000με. For heavy-load highways, higher-performance asphalt mixtures are preferred.

[0033] Traditional thermal recycling theory suggests adding softer thermal recycling agents containing aromatic and saturated components to RAP (asphalt aggregate) to compensate for the lack of "flexibility" in the mixture due to asphalt aging. However, applying RAP to high-modulus asphalt mixtures does not adhere to this theory. Without adding thermal recycling agents, when the old asphalt in the RAP is harder, adding harder new asphalt can achieve the performance of a high-modulus fatigue-resistant asphalt mixture. This approach preserves the "hardness" of the old asphalt in the RAP, leveraging its excellent high-temperature stability, while also utilizing the high asphalt-aggregate ratio and low porosity of high-modulus asphalt mixtures to avoid the poor fatigue resistance of thermally recycled asphalt mixtures.

[0034] However, in the actual process of determining the formulation of recycled materials, it is necessary to consider that the performance of recycled materials is affected by a complex number of factors, including the properties and content of old asphalt in the RAP, the amount of RAP incorporated into the recycled material, the properties of new asphalt, and the mass percentage P of asphalt (composed of old and new asphalt) in the recycled material. 总Furthermore, asphalt performance includes multiple indicators such as penetration, softening point, ductility, and PG grade. In addition, RAP in the same recycled material can originate from the same source or different sources; for example, one type may come from road section A, another from road section B, or from different pavement layers within the same road section. Each type of RAP is typically crushed and screened, then divided into different grades according to particle size (e.g., coarse and fine grades) to facilitate gradation design. All these factors increase the complexity of the formulation design process, requiring extensive experimental verification. These tests ultimately rely on multiple performance tests for judgment, and these performance tests are both time-consuming and costly.

[0035] Therefore, this disclosure provides a method for determining the formulation of high-modulus, fatigue-resistant hot recycled asphalt mixtures. See also Figure 1 The method includes the following steps.

[0036] S10, determine the mass percentage P of old asphalt in each grade of RAP. i(RAP) and PG high temperature rating T i(RAP) , where i is an integer from 1 to n.

[0037] S20, select the type of new asphalt, wherein the selected new asphalt has a PG high temperature rating (T). 新 .

[0038] S30, setting the mass percentage of each grade of RAP in the hot recycled asphalt mixture. i(RAP) .

[0039] S40, according to the set M i(RAP) Perform gradation design for the minerals, new aggregates and new fillers in each grade of RAP, and determine whether the passing rate of the key sieve of the synthetic gradation can meet the requirements. If the requirements can be met, proceed to step S50. If the requirements cannot be met, repeat steps S30 to S40.

[0040] S50, according to M i(RAP) Prepare at least three sets of hot recycled asphalt mixture specimens based on the designed gradation, and adjust the mass fraction of new asphalt in the hot recycled asphalt mixtures so that the mass percentage P of asphalt for each set of specimens is equal to the desired result. 总 They differ, and all fall within the range of 5.2%-6.5%.

[0041] S60, determine the porosity of the specimen, calculate the average porosity of each group of specimens, and select the group of specimens with an average porosity of 1.5%-4%.

[0042] S70, substitute the parameters corresponding to the selected test specimen group into the following formula (I) to determine whether formula (I) is satisfied.

[0043]

[0044] When formula (I) is satisfied, the formulation of the selected specimen group is determined as the formulation of the hot recycled asphalt mixture; when formula (I) is not satisfied, steps S20 to S70 are repeated.

[0045] When designing high-modulus fatigue-resistant hot recycled asphalt mixture formulations, the final formulation is determined based on the available RAP, new aggregates, and new fillers.

[0046] RAP has been crushed and sieved into several grades according to the particle size, such as grades 1, 2, 3, and 4. Typically, RAP is sieved into two grades: a low-size grade (e.g., less than 10mm) and a high-size grade (e.g., 10-20mm). The particle size range and the number of grades can be determined based on actual conditions and needs.

[0047] According to the embodiments of this disclosure, the RAPs from different sources may be the same or different. Ideally, RAPs from the same source may refer to the same pavement layer from the same road segment, exhibiting relatively consistent aging. Conversely, RAPs from different sources may refer to different pavement layers from the same road segment, such as when the upper, middle, and lower layers are recycled separately. In actual engineering projects, all pavement layers are often milled together and recycled together. In this case, RAPs from the same source may refer to RAPs from the same road segment, while RAPs from different sources may refer to RAPs from different road segments.

[0048] When RAP comes from different sources, the crushed RAP is screened separately according to its source. The properties and content of old bitumen in RAP from different sources are usually different. However, even within RAP from the same source, different particle size grades, while having the same old bitumen properties, will have different old bitumen contents. According to the inventors' experience, the old bitumen content is generally lower in coarser (larger particle size) grades than in finer (smaller particle size) grades.

[0049] First, proceed to step S10, determining the mass percentage P of the old asphalt in each grade of RAP. i(RAP) and PG high temperature rating T i(RAP) Where i is used to distinguish RAPs from different sources / grades, and its value is an integer from 1 to n. According to this disclosure, n can be 1, meaning that only one grade of material screened from a certain source of RAP is recycled. n can also be 2, 3, 4, etc. Taking n as 2 as an example, it means that the RAPs involved in the formulation design can be two grades of RAPs from the same source, or RAPs of the same grade or different grades from two different sources. As mentioned above, the RAPs involved in the design can be determined based on the availability of RAPs.

[0050] In step S10, the mass percentage P of old asphalt in RAP i(RAP)It can be determined by the extraction method (T0727) or the combustion method (T0735) in JTG E20 "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering".

[0051] Determining the high-temperature PG grade (T) of old asphalt i(RAP) First, the old asphalt needs to be separated from the sampled RAP. Any separation method can be used, and this disclosure does not impose any particular limitation. For example, each grade of RAP sample is first extracted with an organic solvent (such as trichloroethylene) to obtain solutions of aggregate and old asphalt respectively. Then, a small amount of solid impurities in the old asphalt solution is removed by high-speed centrifugation. Finally, the organic solvent in the old asphalt solution is removed by rotary evaporation to obtain the old asphalt. The high-temperature grade (PG) of asphalt can be determined using the dynamic shear rheometer method for asphalt as described in T0628-2022. Specifically, a virgin asphalt sample and the asphalt aged after RTFOT aging are subjected to DSR tests at different temperatures on a dynamic shear rheometer to determine the lowest temperature corresponding to a G* / sinδ value of not less than 1 kPa for the virgin asphalt sample and the lowest temperature corresponding to a G* / sinδ value of not less than 2.2 kPa for the aged asphalt after RTFOT aging. The lowest of these two temperatures is used as the PG high-temperature grade of the asphalt. The PG high-temperature grade is divided in 6°C increments. The PG high-temperature rating of old asphalt in RAP is typically 64, 70, or 76, but is not limited to these values.

[0052] Step S20: Select the type of new asphalt. The selected new asphalt has a PG high-temperature rating (T). 新 The new asphalt is selected from one or more of natural asphalt, modified asphalt, and petroleum asphalt with a grade not exceeding 30. Optional natural asphalt and modified asphalt include, for example, HMB-II and HMB-III. Optional petroleum asphalt includes, for example, 30# petroleum asphalt and 20# petroleum asphalt.

[0053] The selection of new asphalt needs to consider factors such as raw material availability and cost, with its PG high-temperature grade being the most important. High-modulus fatigue-resistant asphalt mixtures use hard asphalt as the binder. Although the penetration of old asphalt in RAP (Rich Asphalt Compound) is usually relatively low, around 20-40, old asphalt may not meet the requirements of high-modulus fatigue-resistant asphalt mixtures for hard asphalt. Therefore, harder new asphalt is often needed for adjustment. Preferably, the new asphalt has a PG high-temperature grade T... 新 Choose from one of 82, 88, and 94. If T 新 If the RAP content is too low, it may be impossible to meet formula (I) no matter how the RAP content is adjusted, thus failing to meet the performance requirements of high-modulus fatigue-resistant asphalt mixtures; if T 新 If the asphalt content is too high, the cost of asphalt will increase, and the construction difficulty will also increase.

[0054] In step S30, the mass percentage M of each grade of RAP in the hot recycled asphalt mixture is set. i(RAP) M i(RAP) It can be selected based on the acceptable cost of the specific project. Although theoretically M i(RAP) The higher the setting, the lower the cost, but correspondingly, the more difficult it is to achieve the formulation under the expected performance constraints. According to embodiments of this disclosure, the mass percentage M of the RAP in each specification... i(RAP) The concentration of RAP1 is preferably in the range of 10wt%-60wt%. For example, two grades of RAP from the same source, one coarse and one fine, can be used: RAP1 with a particle size greater than or equal to 10mm and RAP2 with a particle size less than 10mm. The M of RAP1 is... 1(RAP) It can be set to 10wt%, M of RAP2 2(RAP) It can be set to 10wt%. In this case, the PG ratings of RAP1 and RAP2 are the same, i.e., T. 1(RAP) =T 2(RAP) For example, two RAPs from different sources, both with particle sizes less than 15mm, can be configured, where RAP1 has an M... 1(RAP) It can be set to 10wt%, M of RAP2 2(RAP) It can be set to 20wt%. In this case, the PG ratings of RAP1 and RAP2 are usually different, i.e., T... 1(RAP) ≠T 2(RAP) .

[0055] In steps S20 and S30, the mass percentage M of each grade of RAP in the hot recycled asphalt mixture is set. i(RAP) When choosing a new type of asphalt, one can rely on past experience to reduce the number of repeated trials.

[0056] In step S40, according to M set in S30 i(RAP) The gradation design is performed on the mineral aggregate, new aggregate, and new filler in each grade of RAP to determine whether the passing rate of the key sieve openings of the synthesized gradation meets the requirements. If the requirements are met, step S50 is executed; otherwise, steps S30 to S40 are repeated. This disclosure does not impose any particular limitations on the gradation design method; those skilled in the art can use the M set in step S30 as a guide. i(RAP) The specific particle size distribution of the aggregates, new aggregates, and new fillers in each grade of RAP is determined, and the proportions of the new aggregates and fillers are adjusted to ensure that the composite gradation meets the set passing rates for each sieve aperture. According to some implementation methods, the gradation of hot recycled asphalt mixtures should meet the passing rates of 66%-84%, 42%-64%, 27%-42%, and 6%-8% for 9.5mm, 4.75mm, 2.36mm, and 0.075mm sieve apertures, respectively. If based on M set in S30... i(RAP)If adjusting the proportions of new aggregates and fillers fails to meet the requirements for the pass rate of the key sieve openings in the composite gradation, steps S30 to S40 need to be repeated, i.e., M needs to be reset. i(RAP) Then, based on the new M i(RAP) Redesign the gradation, repeating this process until the critical sieve aperture throughput of the synthesized gradation meets the requirements. Then, the M corresponding to the achieved requirement can be used. i(RAP) And grade it, then proceed with the next steps.

[0057] In step S50, according to M i(RAP) Based on the designed gradation, at least three sets of hot recycled asphalt mixture specimens were prepared. The mass fraction of new asphalt in the hot recycled asphalt mixture was adjusted so that the total mass percentage P of asphalt in each set of specimens was equal to the desired result. 总 The differences are all within the range of 5.2 wt% to 6.5 wt%. This disclosure applies to different P... 总 There is no particular limitation on the number of test specimen groups, but 3-5 groups are preferred, with each group typically including 4-6 specimens. For example, three groups of specimens can be selected, such that their P... 总 The content is relatively uniformly distributed within the above range, for example, it can be 5.2 wt%, 5.7 wt%, and 6.2 wt%, respectively.

[0058] The specimen is a Marshall test specimen or a rotary compaction specimen prepared according to standard methods, such as the compaction method in standard JTG E20 T0702-2011, which is used to prepare a Marshall specimen by compacting it on both sides 75 times.

[0059] In step S60, the porosity of the specimen is determined, the average porosity of each group of specimens is calculated, and the group of specimens with an average porosity of 1.5%-4% is selected. Methods for determining porosity are known, and this disclosure does not impose any particular limitation on them. For example, the bulk relative density of the specimen can be determined according to T0705-2011 in JTG E20-2011, and the theoretical maximum relative density of the mixture can be measured using the vacuum method according to T0711-2011. Porosity = (1 - bulk density of specimen / maximum theoretical density) × 100%.

[0060] According to embodiments of this disclosure, it is only necessary to measure the porosity of the specimens and select a group of specimens with an average porosity in the range of 1.5%-4%, preferably in the range of 1.5%-3%, and more preferably in the range of 2%-3%. The porosity is affected by P. 总The porosity is also affected by gradation design. When the porosity is too high, the performance of recycled materials decreases significantly; when the porosity is too low, it leads to an increase in the amount of new asphalt used, resulting in higher economic costs. For example, taking three groups of specimens, assuming average porosities of 4.2%, 2.9%, and 1.8%, respectively, two of the groups have average porosities in the range of 1.5-4%. Therefore, the group with the optimal average porosity of 2.9% is selected.

[0061] In step S70, the parameters corresponding to the selected specimen group (including T) are set. 新 Each P i(RAP) Each T i(RAP) M i(RAP) P 总 Substitute the following formula (I) into the equation and determine whether it conforms to the formula (I):

[0062]

[0063] When formula (I) is satisfied, the formulation corresponding to the selected group of specimens is determined to be the formulation of the hot recycled asphalt mixture.

[0064] If formula (I) is not satisfied, return to step S20 and replace with T, which has a higher PG high temperature rating. 新 New asphalt, or without replacing the asphalt, but resetting the mass percentage of each grade of RAP in the recycled material. i(RAP) Repeat the above steps until formula (I) is satisfied, thereby determining the formula.

[0065] When the new asphalt in the formulation needs to be fixed to a certain type, the method disclosed herein can quickly screen out the appropriate mass percentage M of each grade of RAP. i(RAP) When the M of each grade of RAP in the formula i(RAP) When fixed, the method disclosed herein can quickly screen suitable new asphalt. Because formula (I) considers the mass percentage M of each grade of RAP... i(RAP) Considering the potential impact of different RAP sources, the method disclosed herein can accurately obtain a high-modulus fatigue-resistant asphalt mixture formula that meets the following requirements: dynamic stability at 60℃ ≥ 5000 cycles / mm, dynamic modulus ≥ 15000 MPa, and fatigue life ≥ 1 million cycles. This saves time and costs associated with repeated testing and performance evaluation, and facilitates the use of RAP materials, resulting in high-performance, high-modulus fatigue-resistant asphalt mixtures at a lower cost. These performance indicators even exceed those specified in the national standard GB / T 36143-2018, ensuring that the asphalt mixture prepared according to the described formula can be effectively used in heavy-duty highways.

[0066] Furthermore, the preferred formulation obtained according to the method of this disclosure, i.e., when natural asphalt modified asphalt is selected as the new asphalt, can achieve resistance to low-temperature cracking, with a flexural failure strain ≥2800με at -10℃. According to the national industry standard JTGF40-2004 "Technical Specification for Construction of Highway Asphalt Pavement," the flexural failure strain of modified asphalt mixtures in cold winter regions should not be less than 2800με at -10℃. Therefore, the preparation of hot recycled asphalt mixtures using the preferred formulation obtained according to the method of this disclosure is also suitable for road construction in cold regions, such as the vast western regions of my country.

[0067] The present disclosure will be further described below with reference to specific embodiments.

[0068] raw material:

[0069] The new asphalt used below includes SBS ID modified asphalt, 50# petroleum asphalt, 20# petroleum asphalt, natural asphalt modified asphalt HMB-II and HMB-III, some of which have performance indicators shown in Table 1.

[0070] Table 1. Technical Specifications of New Asphalt

[0071]

[0072] The new aggregates are all made of limestone, and the new fillers are all made of mineral powder.

[0073] RAP from source A was crushed and sieved into two grades: 0-10mm and 10-20mm. The old asphalt in the RAP was extracted with trichloroethylene, yielding both aggregate and a trichloroethylene solution containing old asphalt. The trichloroethylene solution was then centrifuged to remove trace amounts of solid impurities, and a rotary evaporator was used to fully recover the trichloroethylene solvent, yielding the old asphalt from the RAP. The old asphalt content in the two grades of RAP was measured to be 5.3% and 3.8%, respectively, and the PG high-temperature rating of the old asphalt was 76.

[0074] RAP from source B was crushed and screened into two grades: 0-10mm and 10-20mm. Using the above method, the old asphalt content in the two grades of RAP was measured to be 5.7% and 4.0%, respectively. The PG high temperature grade of the old asphalt was 70.

[0075] Example 1. Determine the formulation using RAP from source A.

[0076] Formula A1

[0077] Choose to use the 0-10mm and 10-20mm RAP settings from source A, i.e., T 1(RAP) =T 2(RAP) =76, P 1(RAP) =5.3%, P2(RAP) =3.8%. 50# petroleum asphalt was selected as the new asphalt, i.e., T 新 =70. Relative to the sum of new aggregates, new fillers, and minerals in the recycled material, the minerals in these two RAP grades are set to account for 10% by weight respectively. Using these two RAP grades of minerals, new aggregates, and new fillers, a gradation design is performed to achieve passing rates of 66%-84%, 42%-64%, 27%-42%, and 6%-8% through 9.5mm, 4.75mm, 2.36mm, and 0.075mm sieves, respectively. The proportions of new aggregates and new fillers at different particle size grades are shown in Table 2.

[0078] Table 2. Gradation design of formulation A1

[0079]

[0080] Three groups of Marshall specimens were prepared according to the following steps. Since total bitumen accounts for only about 5-6% of the recycled material, and the proportion of RAP aggregate (relative to the sum of new aggregate, new filler, and aggregate in the recycled material) is close to the proportion of RAP in the recycled material, it is possible to set two levels where RAP also accounts for 10% in the recycled material, i.e., M... 1(RAP) =10%, M 2(RAP) =10%, then the old asphalt content in the recycled material of the three groups of specimens is 10% × 5.3% + 10% × 3.8% = 0.91%. Let the new asphalt content in the recycled material of the three groups of specimens be set to 4.0%, 4.5%, and 5.0%, respectively. The corresponding asphalt content P in the recycled material of the three groups of specimens is... 总 The proportions were 4.9%, 5.4%, and 5.9%, respectively. Based on the proportions of each grade of new aggregate, new filler, and two grades of RAP obtained from the above gradation design, the content of each grade of new aggregate and new filler in the recycled material was calculated, resulting in three sets of specimen formulations. The RAP was heated at 120℃ for 2 hours, the new asphalt was heated to 180℃, and the new aggregate was heated to 200℃. The mixing pot temperature was set to 185℃. The new aggregate was poured into the mixing pot and stirred for 30 seconds, then the RAP was added and stirred for 90 seconds. The new asphalt was added and stirred for another 90 seconds. Finally, room-temperature mineral powder was added and stirred for 90 seconds to obtain the recycled material. Three types of recycled materials were prepared using the formulations of the three sets of specimens described above. Three sets of five Marshall specimens were prepared according to the JTG E20-2011 T0702-2011 standard, with each side impacted 75 times. After standing for 24 hours, the specimens were demolded.

[0081] According to T0705-2011 in JTG E20-2011, the bulk relative density of the above three groups of Marshall specimens was determined, and the theoretical maximum relative density of the mixture was measured by vacuum method according to T0711-2011. The porosity of the three groups of Marshall specimens was calculated, and the average value was taken. The results are shown in Table 3 below.

[0082] Table 3. Average void fraction of Marshall specimens with different asphalt contents

[0083]

[0084] Based on the average porosity results shown in Table 3, the asphalt content P of the recycled material in formulation A1 was selected. 总 It is 5.4%. The above T 新 P 1(RAP) P 2(RAP) T 1(RAP) T 2(RAP) M 1(RAP) M 2(RAP) P 总 Substituting this into the left side of formula (I), the value is 71.01, which is less than 80, and therefore does not satisfy formula (I).

[0085] Formula A1 is as follows. Two grades of RAP (0-10mm and 10-20mm) from source A each account for 10% of the recycled material. 50# petroleum asphalt, as new asphalt, accounts for 4.5% of the recycled material. The ratio of new aggregates (16-22mm, 11-16mm, 7-11mm, 4-7mm, and 0-4mm) and mineral powder is 6:9:20:10:32:3, and their combined mass accounts for 75.5% of the recycled material.

[0086] The RAP content should be reset or a new asphalt with a higher PG grade should be selected to adjust the formula to meet formula (I).

[0087] Formula A2

[0088] The proportions of the two grades of RAP in the recycled material are set to be the same as in formulation A1, so the gradation design is also the same as in formulation A1. However, 20# petroleum asphalt with a higher PG high-temperature grade is used as the new asphalt, T 新 =82. Three groups of Marshall specimens with different asphalt contents were prepared, and the average void ratio of each group was measured and calculated, as shown in Table 4.

[0089] Table 4. Average void fraction of Marshall specimens with different asphalt contents

[0090]

[0091] Based on the porosity results, the asphalt content P of formulation A2 was selected. 总 It is 5.4%. The above T 新 P 1(RAP) P 2(RAP) T 1(RAP) T 2(RAP) M 1(RAP) M 2(RAP) P 总Substituting this into the left side of formula (I), the value is 80.97, which is greater than 80, thus satisfying formula (I).

[0092] The final formulation A2 is as follows: Both the 0-10mm and 10-20mm grades of RAP from source A account for 10% of the recycled material. 20# petroleum asphalt, as new asphalt, accounts for 4.5% of the recycled material. The ratio of new aggregates (16-22mm, 11-16mm, 7-11mm, 4-7mm, and 0-4mm) and mineral powder is 6:9:20:10:32:3, and their combined mass accounts for 75.5% of the recycled material.

[0093] Replacing new asphalt with modified natural asphalt could reduce costs and improve performance.

[0094] Formula A3

[0095] The proportions of the two RAP grades in the recycled material are set to be consistent with formulations A1 and A2, so the gradation design is also consistent with formulations A1 and A2. However, PG high-temperature grade T is used. 新 =82 HMB-II as new asphalt, T 新 The method is the same as that for #20 petroleum asphalt in formulation A2. Three groups of Marshall specimens with different asphalt contents were prepared, and the average void ratio of each group was measured and calculated. The results are shown in Table 5.

[0096] Table 5. Average void fraction of Marshall specimens with different asphalt contents

[0097]

[0098] Based on the average porosity results shown in Table 5, the asphalt content P of formulation A3 was selected. 总 It is 5.9%. The above T 新 P 1(RAP) P 2(RAP) T 1(RAP) T 2(RAP) M 1(RAP) M 2(RAP) P 总 Substituting this into the left side of formula (I), the value is 81.06, which is greater than 80, thus satisfying formula (I).

[0099] The final formulation A3 is as follows: Both the 0-10mm and 10-20mm grades of RAP from source A account for 10% of the recycled material. HMB-II, as new asphalt, accounts for 5% of the recycled material. The ratio of new aggregates (16-22mm, 11-16mm, 7-11mm, 4-7mm, and 0-4mm) and mineral powder is 6:9:20:10:32:3, and their combined mass accounts for 75% of the recycled material.

[0100] Further increasing the RAP incorporation could be considered to obtain a lower-cost formulation.

[0101] Formula B

[0102] Use new asphalt identical to formulation A3, but set the proportions of 0-10mm and 10-20mm RAP in the recycled material to be M respectively. 1(RAP) =20%, M 2(RAP) =10%, that is, increasing the total RAP content to 30%. Relative to the sum of new aggregates, new fillers, and minerals in the recycled material, the minerals in these two RAP grades are also set to account for 20% and 10% by weight, respectively. The gradation design is performed, and the results are shown in Table 6.

[0103] Table 6. Gradation Design of Formula B

[0104]

[0105] Three groups of Marshall specimens with different asphalt contents were prepared, and the average void ratio of each group was measured and calculated. The results are shown in Table 7.

[0106] Table 7. Average void fraction of Marshall specimens with different asphalt contents

[0107]

[0108] Based on the average porosity results shown in Table 7, the asphalt content P of the recycled material in formulation B was selected. 总 It is 5.9%. The above T 新 P 1(RAP) P 2(RAP) T 1(RAP) T 2(RAP) M 1(RAP) M 2(RAP) P 总 Substituting this into the left side of formula (I), the value is 80.54, which is greater than 80, thus satisfying formula (I).

[0109] The final formulation B is as follows. The 0-10mm and 10-20mm grades of RAP from source A account for 20% and 10% of the recycled material, respectively. HMB-II, as new asphalt, accounts for 4.5% of the recycled material. The ratio of new aggregates (16-22mm, 11-16mm, 7-11mm, 4-7mm, and 0-4mm) and mineral powder is 8:10:12:10:28:2, and their total mass accounts for 65.5% of the recycled material.

[0110] The high and low temperature performance, modulus and fatigue performance of recycled materials prepared according to formulas A1, A2, A3 and B were tested according to the T0719-2011 rutting test method, T0715 bending test, T0738 uniaxial compression dynamic modulus test method and T0739 four-point bending fatigue test in JTG E20-2011. The results are shown in Table 8.

[0111] Table 8. Performance of recycled materials from formulations A1, A2, A3, and B

[0112]

[0113] The four performance requirements for the recycled material specified in this invention are shown in Table 8. The requirement for dynamic modulus is significantly higher than that stipulated in the national industry standard GB / T 36143-2018, which requires a minimum of 15000 MPa. Formula A1 does not meet formula (I), and the four performance indicators of the recycled material prepared according to formula A1 are all low, with the dynamic stability at 60℃, dynamic modulus, and fatigue life being far below the corresponding performance requirements. Formula A2, by improving the PG high-temperature grade of the new asphalt, meets formula (I), and the four performance indicators of the recycled material prepared according to formula A2 all meet the corresponding performance requirements. Formula A3, by using natural asphalt to modify the asphalt, satisfies Formula (I). The four properties of the recycled material prepared according to Formula A3 are all improved compared to Formula A2, and the low-temperature flexural failure strain at -10℃ reaches as high as 3100με, even meeting the requirement of the national industry standard JTG F40-2004 "Technical Specification for Construction of Highway Asphalt Pavement" that the low-temperature flexural failure strain of modified asphalt mixtures in cold winter regions should not be less than 2800με at -10℃. Formula B, by further increasing the total RAP content, can still just meet Formula (I). Although its four properties are lower than those of Formula A3, they still far meet the corresponding performance requirements.

[0114] Example 2. The formulation was determined using RAP from source B.

[0115] Use the 0-10mm and 10-20mm RAP settings from source B, i.e., T 1(RAP) =T 2(RAP) =70, P 1(RAP) =5.7%, P 2(RAP)=4.0%. Since the price of each ton of new asphalt is typically more than 50 times that of each ton of RAP, and the price of each ton of new aggregate or filler is 1-2 times that of each ton of RAP, increasing the total RAP content can reduce the amount of new asphalt, new aggregate, or new filler incorporated, thus significantly reducing the cost of recycled materials. In this embodiment, the total RAP content in the formulation is gradually increased from 20% to 60%, with different PG grades of new asphalt selected. The adjustment process involves formulations C1, C2, D1, D2, E1, E2, F1, F2, G1, and G2, to illustrate the relationship between the RAP content design and formula (I) and the performance of the asphalt mixture corresponding to the final formulation.

[0116] Formula C1 has a total RAP content of 20%, using SBS ID modified asphalt as the new asphalt, T 新 =76. The total RAP content in formulation C2 remains at 20%, and the proportion of the two RAP grades in the recycled material is set to be the same as in formulation C1, so the gradation design is also the same as in formulation C2, but T is used instead. 新 HMB-II with a gradation of 82 was used as the new asphalt, thus improving the high-temperature PG rating of the new asphalt. Formulation D1 increased the total RAP content to 30%.

[0117] Formula D2 maintains a total RAP content of 30%, but further improves the PG high-temperature grade of the new asphalt, i.e., using HMB-III as the new asphalt, T 新 =88. Formula E1 increases the total RAP content to 40%. Formula E2 uses the same RAP content, gradation design, and new asphalt as Formula E1, but reduces the proportion of new asphalt and allows a void ratio of more than 4% to reduce costs.

[0118] The total RAP content of formulations F1 and F2 is 50%, and the total RAP content of formulations G1 and G2 is 60%. For these two formulations, the proportion of 0-10mm and 10-20mm RAP in the recycled material has been adjusted.

[0119] When determining each formulation, the proportion of RAP aggregate (relative to the sum of new aggregate, new filler, and aggregate in the recycled material) and the proportion of RAP in the recycled material were first set, and both were set to the same value. EME20 gradation design was performed for these formulations to obtain the proportions of new aggregate and new filler at different particle size ranges, as shown in Table 9. For two formulations with the same total RAP content, the proportions of new aggregate and new filler at different particle size ranges were also similar after gradation design. The key sieve passing rates of the synthetic gradations of each formulation were basically similar, as shown in Table 10.

[0120] Table 9. Gradation design results of formulations C1, C2, D1, D2, E1, E2, F1, F2, G1, and G2

[0121]

[0122] Table 10. Sieve passing rates of gradation designs for formulations C1, C2, D1, D2, E1, E2, F1, F2, G1, and G2

[0123]

[0124] When determining formulations C1, C2, D1, D2, E1, F1, F2, G1, and G2, three groups of Marshall specimens were prepared following the steps in Example 1, and the average porosity of each group was measured to determine the asphalt content P of each formulation. 总 However, in recipe E2, P is preset. 总 It is 5.0%.

[0125] Substitute the relevant values ​​of each formulation into the left side of formula (I) for calculation, and then conduct performance tests on the mixture of each formulation. The results are shown in Table 11.

[0126] Table 11. Properties of recycled materials from formulations C1, C2, D1, D2, E1, E2, F1, F2, G1, and G2

[0127]

[0128] Formula C1 has a left-hand side value of 75.0, which is significantly lower than 80. The recycled material prepared according to Formula C1 fails to meet the performance requirements for dynamic modulus and fatigue life, and the deviation is substantial. Based on Formula C1, Formula C2 only increases the PG high-temperature grade of the new asphalt from 76 to 82, while keeping other aspects (including the proportions of new asphalt, various grades of RAP, various grades of new aggregate, and mineral powder) unchanged. The left-hand side value of Formula C2 reaches 80.1, and the recycled material prepared according to Formula C2 shows a significant improvement in dynamic modulus and fatigue life, both meeting the corresponding performance requirements. Compared to Formulas C1 and C2, where the total RAP content is 20%, Formula D1 increases it to 30%, resulting in a left-hand side value of 79.0, slightly lower than 80. The recycled material prepared according to Formula D1 shows a slight decrease in all four performance indicators compared to Formula C2, and the dynamic modulus no longer meets the requirements. Based on formulation D1, formulation D2 further increases the PG high temperature grade of the new asphalt from 82 to 88. The proportions of each grade of RAP, each grade of new aggregate and mineral powder remain unchanged, while the proportion of new asphalt is reduced by 0.1%. The value on the left side of formula (I) reaches 83.4. The four properties of the recycled material prepared according to formulation D2 meet the corresponding performance requirements.

[0129] To further increase the total RAP content and reduce the cost of recycled materials, formulations E1, E2, F1, F2, G1, and G2 continue to use new asphalt with a PG high-temperature grade of 88. The total RAP content in formulation E1 is further increased to 40%, and the value on the left side of formula (I) reaches 82.0. The four properties of the prepared recycled material all meet the corresponding requirements, especially the dynamic modulus, which reaches 17558 MPa. Compared to formulation E1, formulation E2 reduces the proportion of new asphalt in the recycled material by 0.8%, resulting in a void ratio of 4.2%, exceeding 4%. Although the value on the left side of formula (I) remains above 80, the four properties of the recycled material decrease significantly, no longer meeting the corresponding performance requirements, especially the dynamic modulus, which drops to 11039 MPa. Formula (I) is only effective within a void ratio range of 1.5%-4%. Void ratio has a significant impact on the performance of recycled materials, and the attempt by formulation E2 to reduce costs by decreasing the incorporation of new asphalt has failed.

[0130] Formula F1 further increases the total RAP content to 50%, with the 0-10mm and 10-20mm RAP components at 40% and 10% respectively. Formula F1 does not satisfy formula (I), and the dynamic modulus of the prepared recycled material is 12752 MPa, which is less than 15000 MPa, failing to meet the dynamic modulus requirement of this invention; the fatigue life is 870,000 cycles, failing to meet the fatigue resistance requirement. Formula F2, by adjusting the RAP components of the 0-10mm and 10-20mm components to 30% and 20% respectively, satisfies formula (I) while maintaining a total RAP content of 50%. The recycled material prepared according to formula F2 shows significant improvements in all four aspects of performance, meeting the corresponding performance requirements.

[0131] Formula G1 further increases the total RAP content to 60%, with the 0-10mm and 10-20mm RAP inclusion ratios at 25% and 35%, respectively. Formula G1 does not satisfy formula (I), and its dynamic modulus is 13200 MPa, which is less than 15000 MPa, failing to meet the dynamic modulus requirements of this invention. Formula G2, by adjusting the inclusion ratios of the 0-10mm and 10-20mm RAP to 10% and 50%, respectively, maintains a total RAP content of 60% while satisfying formula (I). The recycled material prepared according to formula G2 shows significant improvements in all four performance aspects, meeting the corresponding performance requirements.

[0132] In summary, formula (I) can accurately determine whether the recycled material corresponding to the formula can meet the performance requirements of having a uniaxial compression dynamic modulus of not less than 15000MPa at 20℃ and 10Hz, and a fatigue life of not less than 1 million cycles at 15℃, 10Hz, and 230με. This is achieved by introducing the mass percentage P of the old asphalt for each grade of RAP. i(RAP)and PG high temperature rating T i(RAP) And the mass percentage (M) of each grade of RAP in the recycled material. i(RAP) This is achieved. In the formulation adjustment process of this embodiment, the performance testing of recycled materials for formulations C1, C2, D1, D2, E1, E2, F1, F2, and G1 can be omitted to save the time and cost required for these tests.

[0133] The above descriptions are merely some specific embodiments of this disclosure, intended to illustrate the present invention, and are not intended to limit the scope of protection claimed in this application. Any modifications or substitutions made based on the inventive concept of this invention and the content of this application's specification and drawings, or direct / indirect applications in other related technical fields, are included within the scope of protection claimed in this application.

Claims

1. A method for determining a high-modulus fatigue-resistant hot recycled asphalt mixture formulation, wherein the hot recycled asphalt mixture comprises recycled asphalt mixture (RAP), new asphalt, new aggregates, and new fillers, wherein the RAP comprises old asphalt and mineral aggregates, the asphalt in the hot recycled asphalt mixture is composed of the old asphalt and the new asphalt, the RAP has been crushed and screened, and the RAP comprises n grades, where n is an integer greater than or equal to 1, the method comprising: S10 determines the mass percentage P of the old asphalt in each grade of RAP. i(RAP) and PG high temperature rating T i(RAP) , where i is an integer from 1 to n; S20 selects the type of new asphalt, wherein the selected new asphalt has a PG high-temperature grade T 新 ; S30 sets the mass percentage M of each grade of RAP in the hot recycled asphalt mixture. i(RAP) ; S40 according to the set M i(RAP) Perform gradation design for minerals, new aggregates and new fillers in each grade of RAP, and determine whether the key sieve passing rate of the synthetic gradation can meet the requirements. If the requirements can be met, proceed to step S50. If the requirements cannot be met, repeat steps S30 to S40. S50 according to the M i(RAP) Prepare at least three sets of hot recycled asphalt mixture specimens based on the designed gradation, and adjust the mass fraction of the new asphalt in the hot recycled asphalt mixtures so that the mass percentage P of the asphalt in each set of specimens is such that... 总 They differ, and all fall within the range of 5.2wt%-6.5wt%. S60 determines the porosity of the specimen, calculates the average porosity of each group of specimens, and selects the group of specimens with an average porosity of 1.5%-4%. and S70 substitutes the parameters corresponding to the selected group of specimens into the following formula (I) to determine whether the formula (I) is satisfied. When formula (I) is satisfied, the formulation of the selected specimen group is determined as the formulation of the hot recycled asphalt mixture. If formula (I) is not satisfied, repeat steps S20 to S70.

2. The method according to claim 1, wherein in step S60, the group of specimens with an average porosity of 1.5%-3% is selected.

3. The method according to claim 2, wherein in step S60, the group of specimens with an average porosity of 2%-3% is selected.

4. The method according to claim 1, wherein the gradation design performed in step S40 results in a pass rate of 66%-84%, 42%-64%, 27%-42%, and 6%-8% through sieves of 9.5mm, 4.75mm, 2.36mm, and 0.075mm, respectively.

5. The method according to claim 1, wherein the RAP sources are the same or different, and when the RAP sources are different, the crushed RAP is screened according to the different sources.

6. The method according to claim 5, wherein when the RAP sources are different, the n-grade RAP is selected from different road sections or different pavement layers of the same road section, and the sieve particle size of each grade is the same or different.

7. The method of claim 6, wherein the mass percentage M of each RAP is... i(RAP) The sum ranges from 10% to 60%.

8. The method according to claim 1, wherein the new asphalt is selected from one or more of natural asphalt, modified asphalt, and petroleum asphalt with a grade not exceeding 30.

9. The method of claim 8, wherein the new asphalt has a PG high-temperature grade T 新 Selected from 82, 88, and 94.

10. The method according to claim 1, wherein the hot recycled asphalt mixture has a uniaxial compression dynamic modulus of not less than 15,000 MPa at 20°C and 10 Hz, and has a fatigue life of not less than 1 million cycles at 15°C, 10 Hz, and 230 με.

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