A plant-mixed hot recycled asphalt surface layer RAP content determination method based on multiple performance thresholds

Abstract

The application discloses a plant-mixed hot recycling asphalt surface RAP mixing amount determination method based on multiple performance thresholds and belongs to the field of road engineering materials. The method collects RAP recycling samples and pre-processes, carries out gradation composition, aggregate performance (refinement rate, firmness, acicular flakiness), asphalt aging degree (complex shear modulus ratio, phase angle difference) test, and simultaneously prepares typical mixing amount Marshall test pieces to verify the mixture performance; the traditional weighted calculation method is abandoned, a "aggregate-asphalt-gradation" three-dimensional performance grade system is established, each dimension is determined as "excellent", "medium" and "poor" through preset thresholds; then, the comprehensive evaluation grade is determined according to the three-dimensional grade combination, and finally, the RAP maximum mixing amount range corresponding to different comprehensive grades is given. The method can effectively solve the "over-mixing" or "under-mixing" problem of the traditional experience method, realize the balance between the recycling material utilization rate and the pavement performance, and is simple in operation, strong in repeatability and suitable for engineering practice.

Description

Technical Field

[0001] This invention belongs to the field of road engineering materials, and specifically relates to a method for determining the RAP (Rich Acid Asphalt) content in plant-mixed hot recycled asphalt pavement based on multiple performance thresholds. Background Technology

[0002] In road construction, RAP (recycled asphalt pavement material) is an important recycled resource, and its rational utilization is of great significance for saving resources, protecting the environment, and reducing costs. However, the existing analysis and evaluation of recycled RAP materials have the following shortcomings:

[0003] Evaluation methods rely on weighted calculations: Traditional methods often construct a comprehensive index by setting weight coefficients. The weight values ​​depend on empirical judgment, which can easily lead to subjective evaluation results and fail to truly reflect the impact of each performance dimension of RAP on the doping amount.

[0004] The performance correlation is not intuitive: the correspondence between the weighted comprehensive index and the actual RAP dosage is ambiguous. Engineers cannot quickly determine the dosage range using a single index and need to repeatedly adjust the weights for verification, which is complicated.

[0005] Threshold determination is missing: Some methods only focus on the binary determination of "meeting / not meeting" performance parameters, without refining the performance level, and cannot distinguish the gradient impact of RAP performance differences on doping amount, resulting in insufficient doping amount control accuracy.

[0006] Therefore, there is an urgent need for a weightless method for determining RAP doping based on performance level thresholds to improve the objectivity of evaluation and the accuracy of doping control. Summary of the Invention

[0007] The purpose of this invention is to provide a method for determining the RAP content of plant-mixed hot recycled asphalt surface courses based on multi-dimensional performance thresholds, which solves the problems of subjective weighted calculation, unintuitive performance correlation, and low precision of content control in the prior art, and achieves objective and accurate determination of RAP content.

[0008] Technical solution

[0009] Step 1, Sample Collection and Preprocessing

[0010] Step 2, Multi-dimensional performance testing

[0011] Step 3, Multi-dimensional performance level determination

[0012] Step 4: Comprehensive Grade Determination and Dosage Determination

[0013] Beneficial effects

[0014] Compared with the prior art, the present invention has at least the following beneficial effects:

[0015] More objective evaluation: Abandoning the traditional weighted calculation method, the level is determined by preset performance thresholds, avoiding errors caused by subjective setting of weight coefficients. The level determination of each performance dimension is based on clear test data, and the results are more in line with the actual performance of RAP.

[0016] The correlation between admixture dosage is more intuitive: the three-dimensional grades of "aggregate-asphalt-gradation" are directly combined into a comprehensive grade, which corresponds to a clear admixture dosage range. Engineers do not need complicated calculations and can quickly match the admixture dosage, reducing the difficulty of operation.

[0017] Higher control precision: By refining the performance level into three levels of "excellent-medium-poor", the dosage can be controlled in a gradient manner, avoiding the "one-size-fits-all" problem caused by the traditional binary judgment, and taking into account both the utilization rate of recycled materials and the pavement performance.

[0018] More comprehensive verification: Add performance testing of Marshall specimens with typical admixture dosages as a supplementary verification basis for admixture dosage, further ensuring that the determined admixture dosage meets the engineering construction requirements and reducing pavement quality risks. Attached Figure Description

[0019] Figure 1 The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 2 This is a schematic diagram of the gradation curve design for plant-mixed hot recycled asphalt mixture according to one or more embodiments of the present invention. Detailed Implementation

[0021] Taking the RAP recycled material collected in the maintenance project of Lianyungang-Xuzhou Expressway as an example, we will conduct analysis and evaluation: Step 1, sample collection and pretreatment;

[0022] Step 2, Multi-dimensional performance testing

[0023] Step 3, Multi-dimensional performance level determination

[0024] Step 4: Comprehensive Grade Determination and Dosage Determination

[0025] The method for analyzing and evaluating RAP recycled materials according to the present invention specifically includes the following steps:

[0026] S1. Sample collection and pretreatment

[0027] 50 kg of RAP recycled material was randomly collected at the construction site. After crushing and screening, particles larger than 20 mm were removed to obtain the test sample.

[0028] S2, Multi-performance testing

[0029] Gradation composition test: First, the test sample was subjected to a sieve test, and the passing rate of each sieve aperture was obtained as shown in the table below. Figure 1 As shown:

[0030] Table 1. Passing rate of each sieve aperture in the test samples

[0031]

[0032] Table 2. Limitations of SUP-20 Design Grading Restriction Zone

[0033]

[0034] Table 3. Limits of SUP-20 Design Grading Control Points

[0035]

[0036] Grading deviation is calculated by summing the area differences between adjacent sieve holes in the entire sieve range of the actual gradation curve and the target gradation curve of the RAP material, which intuitively reflects the overall dispersion of the two.

[0037] Aggregate performance test: Select an appropriate amount of sample to test its strength loss, refinement rate and content of needle-shaped and flaky particles.

[0038] Fineness ratio (FPCR) is the percentage of the mass of particles that pass through a specific sieve opening (e.g., 2.36 mm) in RAP (Reclaimed Aggregate) out of the total aggregate mass. This indicator directly reflects the relative content of fine particles in the reclaimed aggregate, thus demonstrating the degree of fineness of the aggregate.

[0039] Refinement rate (FPCR):

[0040]

[0041] Where: m 2.36 This indicates the mass of particles in the RAP material that pass through a specific sieve opening (e.g., 2.36 mm); m total This indicates the total mass of the RAP material.

[0042] Loss of robustness:

[0043]

[0044] In the formula: Q i This represents the percentage of mass loss (%) for each particle size fraction; m i This indicates the dried mass (g) of each particle size sample before testing; m′ i The value represents the dried mass (g) of the particles remaining on the sieve for each particle size after the sodium sulfate solution method test.

[0045]

[0046] Where: Q represents the percentage of total sample mass loss (%); m i Q represents the fractional mass (g) of each particle size in the sample; i This indicates the percentage of mass loss (%) for each particle size.

[0047] Content of needle-like and flaky particles:

[0048]

[0049] In the formula: Q e m0 represents the content of needle-like and flaky particles (%); m0 represents the total mass of aggregate used in the test (g); m1 represents the mass of needle-like and flaky particles (g).

[0050] Asphalt aging test: After recycling the asphalt, the complex shear modulus and phase angle of the aged asphalt and the complex shear modulus and phase angle of the unaged asphalt were obtained by DSR test.

[0051] S3, Multi-performance level determination

[0052] Aggregate performance: FPCR=18.26%≤20%, Q=6.2%≤8%, Q e =7.8% ≤ 10%, equivalent to "excellent";

[0053] Asphalt aging performance: complex shear modulus ratio ≈ 1.39 ≤ 1.5, phase angle difference = 2.3° ≤ 5°, grade "excellent";

[0054] Grade matching performance: Deviation of 87.56 ≤ 100, grade "Excellent"

[0055] S4. Comprehensive Grade Determination and Dosage Determination

[0056] The aggregate, asphalt, and gradation are all rated "excellent", and the overall grade is "excellent". The dosage is determined as follows: corresponding to the overall grade of "excellent", the maximum RAP dosage is controlled at 30%-40%. Based on the Marshall specimen performance (stability of 8.5kN at 30% dosage), the final RAP dosage for the asphalt pavement in this project is determined to be 35%.

Claims

1. This invention provides a method for determining the RAP (Recycled Asphalt) content in plant-mixed hot recycled asphalt surface courses based on multiple performance thresholds, characterized in that, Includes the following steps: Step 1: Collect RAP recycled material samples, pre-treat the samples to obtain test samples; Step 2: Perform multiple performance tests on the test samples to obtain performance parameters. The performance parameters include at least the gradation composition, aggregate properties, and asphalt aging degree. Based on the multi-dimensional performance thresholds of different RAP materials, three typical dosages (such as 10%, 20%, and 30%) need to be selected. Mix the RAP recycled material with new aggregates and new asphalt in a certain proportion to prepare Marshall specimens. Test the stability, flow value, porosity, and other indicators of the mixture to serve as the verification basis for the RAP dosage. Step 3: Based on the performance parameters, establish a comprehensive evaluation system for the RAP dosage determination method. The evaluation system includes three independent dimensions: aggregate performance grade, asphalt aging performance grade, and gradation matching performance grade. Each dimension is judged as "excellent", "medium", or "poor" through a preset threshold. Step 4: Determine the comprehensive evaluation level of RAP recycled material based on the combination of performance levels of the three dimensions, and then determine the maximum dosage range of RAP for different comprehensive levels.

2. The method for determining the RAP (Rich Acrylic Acid) content in plant-mixed hot recycled asphalt surface courses based on multiple performance thresholds according to claim 1, characterized in that, The aggregate performance test in step 2 includes tests for aggregate refinement rate, soundness loss, and content of needle-like and flaky particles; the asphalt aging degree test uses a dynamic shear rheometer (DSR) to test the complex shear modulus and phase angle of the asphalt; the gradation composition test uses sieved sample gradation to calculate the gradation deviation.

3. The method for determining the RAP (Recycled Asphalt) content in plant-mixed hot recycled asphalt surface courses based on multi-dimensional performance thresholds according to claim 1, characterized in that, The criteria for determining the performance level of each dimension in step 3 are as follows: Aggregate performance grades: "Excellent" if all three criteria are met: refining rate ≤ 20%, soundness loss ≤ 8%, and needle-like / flaky particle content ≤ 10%; "Medium" if all three criteria are met: 20% < refining rate ≤ 25%, 8% < soundness loss ≤ 12%, and 10% < needle-like / flaky particle content ≤ 15%; "Poor" if all three criteria are met or only one criterion exceeds the "Excellent" threshold but not the "Poor" threshold; "Poor" if the refining rate is ≥ 25%, the needle-like / flaky particle content is ≥ 15%, or the soundness loss is ≥ 12%. Asphalt aging performance grade: Complex shear modulus ratio ≤ 1.5, phase angle difference ≤ 5°, both of which are met to be rated as "excellent"; If both conditions are met (1.5 < complex shear modulus ratio ≤ 3.0 and 5° < phase angle difference ≤ 10°), the rating is "Medium"; if either condition exceeds 3.0 (complex shear modulus ratio) or 10° (phase angle difference), the rating is "Poor". Performance rating of gradation matching: "Excellent" if deviation ≤ 100; "Medium" if deviation ≤ 150 if deviation < 100; "Poor" if deviation > 150.

4. The method for determining the RAP (Recycled Asphalt) content in plant-mixed hot recycled asphalt surface courses based on multi-dimensional performance thresholds according to claim 1, characterized in that, The comprehensive evaluation level and corresponding dosage standard mentioned in step 4 are as follows: Overall rating "Excellent": All three dimensions of aggregate, asphalt, and gradation are "Excellent", with the maximum admixture controlled at 30%-40%; The overall grade is "Excellent-Medium": two of the three dimensions of aggregate, asphalt, and gradation are "Excellent" and one is "Medium", with the maximum admixture controlled at 25%-35%; Overall grade "Medium": All three dimensions of aggregate, asphalt, and gradation are "Medium", or one is "Excellent" and two are "Medium", with the maximum admixture controlled at 20%-30%; Overall grade "poor": Any one of the three dimensions of aggregate, asphalt, and gradation is "poor", and the maximum admixture content is controlled at 10%-20%.

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