A method for evaluating the workability of asphalt mixture for recycling technology based on uniformity of aggregate distribution

Abstract

A kind of based on aggregate distribution uniformity of recycling technology asphalt mixture and workability evaluation method, comprising the following steps: weighing total weight 12kg of asphalt, mineral aggregate and old aggregate (4.6:50:50) are placed in mixing kettle and are mixed;The mixed mixture is divided into four by crosswise equal division method, and four portions of mixture are respectively burned using calcining furnace until the surface of mixture is gray;Screening is carried out by standard screen, the weights of aggregate of different particle sizes are weighed, and aggregate dispersion degree evaluation index (DDA) is proposed;For the aggregate distribution of four portions of asphalt mixture, comprehensive index: aggregate distribution uniformity evaluation index (HA) is proposed to evaluate the workability of recycled asphalt mixture in a mixing kettle.The technical effects achieved are: by the present application, the problem that engineering experience or mixing current test during mixing process cannot accurately reflect the workability of recycled asphalt mixture for recycling technology is avoided, and the evaluation of workability of recycled asphalt mixture is more scientific.

Description

Technical Field

[0001] This invention relates to the field of highway asphalt pavement recycling technology, specifically to a method for evaluating the workability of asphalt mixtures used in recycling technology based on the uniformity of aggregate distribution. Background Technology

[0002] Using recycled asphalt mixtures allows for the recycling of asphalt pavement waste, offering advantages such as energy conservation, environmental protection, and reduced project costs. The workability of recycled asphalt mixtures is a crucial construction characteristic indicator for ensuring project quality. It directly reflects the paving and compaction performance of asphalt pavements and is directly related to the smoothness and compaction degree of the asphalt pavement. Workability of recycled asphalt mixtures characterizes the ease of construction operations during paving and compaction. Road industry standards indirectly reflect workability through viscosity indicators such as asphalt binder viscosity, i.e., apparent viscosity. However, indicators characterizing the workability of recycled asphalt mixtures are not directly specified. Initially, using viscosity to indirectly reflect asphalt mixture workability was feasible, but with the promotion of new technologies and processes, this method has many limitations. By testing the uniformity of aggregate distribution of each particle size after mixing the recycled asphalt mixture and measuring the mass loss of asphalt before and after combustion, an evaluation index for aggregate distribution uniformity is proposed to evaluate the workability of the mixture in different parts of the same mixing pot. This workability evaluation method can intuitively characterize the workability of recycled asphalt mixtures during the mixing process, which is of great significance for quality control during construction. Summary of the Invention

[0003] Technical problem to be solved: In view of the problems existing in the prior art, the present invention proposes a workability evaluation method for recycled asphalt mixtures based on aggregate distribution uniformity. The aggregate distribution uniformity evaluation index HA is used to evaluate the difference in aggregate distribution in an asphalt mixture in a mixing pot, so as to solve the problem that the existing engineering technology is not accurate enough in evaluating the workability of recycled asphalt mixtures based on engineering experience or viscosity.

[0004] Technical solution:

[0005] A method for evaluating the workability of recycled asphalt mixtures based on aggregate distribution uniformity includes the following steps:

[0006] Step 1. Weigh out 12 kg of asphalt, mineral aggregate and old aggregate and put them into the mixing pot for mixing. The ratio of asphalt, mineral aggregate and old aggregate is 4.6:50:50.

[0007] Step 2. Divide the recycled asphalt mixture in the mixing pot into four portions using the cross-division method, and burn each portion of the recycled asphalt mixture in a calcining furnace until the asphalt surface turns gray.

[0008] Step 3. Cool the burned recycled asphalt mixture, sieve it through a standard sieve, weigh the aggregates of different particle sizes, and test the mass loss of the recycled asphalt mixture before and after combustion.

[0009] Step 4. Compare and analyze the content of different particle sizes in the sieved aggregate with the aggregate content in the production gradation, and obtain the aggregate dispersion evaluation index DDA based on the standard deviation formula.

[0010] Step 5. Based on the aggregate distribution in the four evenly divided asphalt mixtures in the mixing pot, a comprehensive index is proposed as the aggregate distribution uniformity evaluation index HA.

[0011] As an improvement, in step one, the asphalt is Korean SK-70 base asphalt and SBS modified asphalt, the aggregate is limestone, the old aggregate gradation is AC-20, the mixing temperature is 180℃, the mixing time is 3min, and the mixing speed is 80r / min.

[0012] As an improvement, in step two, the weight of each of the four portions of asphalt mixture after mixing is 3 kg, the combustion temperature of the calcining furnace is set to 540℃, and the combustion time is 3.5 h.

[0013] As an improvement, the specific steps of the aggregate dispersion evaluation index DDA mentioned in step four are as follows: the percentage of aggregate passing through the sieve of a single batch is the percentage of aggregate undersize, and the percentage of aggregate synthesis proportion passing through the sieve is the percentage of aggregate undersize.

[0014] (A) Calculation of the percentage of material passing through the screen holes of a single batch: Based on the cumulative amount of material passing through each screen hole, the percentage of material passing through each screen hole is calculated.

[0015] (B) The aggregate dispersion evaluation index (DDA) is obtained based on the mean square error formula.

[0016]

[0017] In the formula:

[0018] DDA—An index for evaluating the dispersion of aggregates;

[0019] H n —Percentage of material passing through the screen openings of a single batch;

[0020] h n —Percentage of aggregate synthesis proportions passing through the sieve openings;

[0021] n—The key sieve aperture sizes in the laboratory are 0.075 mm, 0.15 mm, ... 19 mm.

[0022] As an improvement, the calculation method for the aggregate distribution uniformity evaluation index HA in step five is as follows:

[0023]

[0024] Where: HA—evaluation index for uniformity of aggregate distribution; DDA1, DDA2, DDA3, DDA4—evaluation index for dispersion of aggregate in a single batch.

[0025] Beneficial effects:

[0026] Compared with the prior art, the present invention obtains the aggregate distribution uniformity evaluation index by calculating the dispersion index of single-batch aggregate distribution. The dispersion index of single-batch aggregate distribution is calculated by the screening pass rate of each asphalt aggregate according to the standard deviation formula. Then, the single-batch aggregate is divided into four parts, and the average value is calculated to calculate the aggregate distribution uniformity evaluation index. That is, the workability of single-batch recycled asphalt mixture is evaluated by the aggregate distribution uniformity evaluation index, which is applicable to both ordinary asphalt mixtures and recycled asphalt mixtures. Attached Figure Description

[0027] Figure 1 Schematic diagram of a mixing pot for recycled asphalt mixture;

[0028] Figure 2 A schematic diagram of the cross-shaped distribution of recycled asphalt mixture;

[0029] The components include: 1. belt; 2. variable speed motor; 3. lifting column; 4. main power switch; 5. electrical control board; 6. base platform; 7. base; 8. support; 9. heat transfer oil tank; 10. mixing pot; 11. rotating handle; 12. temperature sensor; 13. stirring paddle; 14. gearbox. Detailed Implementation

[0030] Example 1

[0031] This embodiment uses a workability evaluation method for recycled asphalt mixtures based on aggregate uniformity. First, according to... Figure 1 The components are assembled, and the technical methods not mentioned in the assembly process are all conventional assembly methods in the mechanical field. It is only necessary to achieve the desired effect for each component.

[0032] The specific test methods for evaluating the workability of the above-mentioned recycled asphalt mixture are as follows:

[0033] Step 1: Determine the raw materials

[0034] The asphalt used is Korean SK-70 base asphalt and SBS modified asphalt. The basic performance indicators of the asphalt are shown in Table 1 below. The aggregate is limestone, and its performance indicators meet the requirements of the actual project or comply with the requirements of the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40-2004). The extraction and screening data of the old aggregate are shown in Table 2 below.

[0035] Table 1: Basic Performance Indicators of Asphalt

[0036]

[0037] Table 2: Data from extraction and screening of old aggregates

[0038]

[0039] Step 2: Mixing test of recycled asphalt mixture

[0040] This experiment first involved weighing a total of 12 kg of asphalt, aggregate, and recycled aggregate (mass ratio 4.6:50:50). The asphalt was required to meet the specifications for basic properties, and the aggregate was required to have sharp edges and a clean surface. The asphalt and aggregate were preheated to 180℃, and the mixing pot was also preheated to 180℃. Once the temperature stabilized, the aggregate, asphalt, and recycled aggregate were added to the mixing pot sequentially according to the specifications. The mixing time was set to 3 minutes and the mixing speed to 80 r / min. The mixing head was lowered, the mixing pot was started, and the mixing process was allowed to complete.

[0041] Step 3: Calcination of recycled asphalt mixture

[0042] After the recycled asphalt mixture is mixed, each batch of asphalt mixture is divided into 4 equal parts using the cross-division method, with each part weighing 3 kg. Each part of the asphalt mixture is then taken out and burned separately in a calcining furnace. The calcining furnace is set to a combustion temperature of 540℃ and a combustion time of 3.5 hours until the asphalt surface turns gray, indicating that the asphalt on the aggregate surface has been completely burned.

[0043] Step 4: Sieve test of calcined recycled asphalt mixture

[0044] Each batch of aggregate after complete combustion was placed in a standard sieve and sieved according to the specifications. The maximum aperture of the standard sieve was 19 mm and the minimum aperture was 0.075 mm. After sieving, the weight of the aggregates of different particle sizes was weighed, and the mass loss of the recycled asphalt mixture before and after combustion was tested.

[0045] Step 5: Calculate the Dispersion Index (DDA) of aggregates in a single batch.

[0046] The percentage of aggregates passing through the sieve after weighing different particle sizes was calculated. The percentage of aggregates passing through the sieve for each grade was obtained. Based on the proposed formula for calculating the dispersion index (DDA) of aggregates in a single batch of recycled asphalt mixture, the square difference was used to calculate the index of the four aggregates in a single batch of recycled asphalt mixture. Some data and formulas are shown in Table 3 below:

[0047] Table 3: Evaluation Index of Aggregate Dispersion in Single-Batch Recycled Asphalt Mixture (DDA)

[0048]

[0049] Where: DDA—an evaluation index for the dispersion of aggregates;

[0050] H n —Percentage of material passing through the screen aperture of a single batch (m) n / M,m n For each sieve opening, calculate the cumulative undersize mass (M is the total sieve mass). Based on the cumulative undersize mass of the ore in each sieve opening, calculate the percentage of ore passing through each sieve opening.

[0051] h n —Percentage of aggregate composition sieves passing through (M n / M,M n The cumulative sieve mass in the composite mix for each sieve opening (M is the total sieve mass) is calculated. Based on the cumulative sieve mass in the composite mix, the percentage of aggregate passing through the sieve openings in the composite mix is ​​calculated.

[0052] n—Key sieve aperture sizes in the laboratory, namely 0.075mm, 0.15mm, ..., 19mm, etc.;

[0053] Step 6: Calculate the aggregate distribution uniformity evaluation index (HA).

[0054] The uniformity of aggregate distribution in single-batch recycled asphalt mixtures was calculated by averaging the four aggregate dispersion evaluation indices (DDA1, DDA2, DDA3, and DDA4). The data are shown in Table 4.

[0055]

[0056] Where: HA—evaluation index for uniformity of aggregate distribution;

[0057] DDA1, DDA2, DDA3, DDA4 — Evaluation indexes of the dispersion of aggregates in a single pot.

[0058] Table 4: Evaluation Index of Aggregate Distribution Uniformity (HA) in Single-Batch Recycled Asphalt Mixtures

[0059]

[0060] The workability evaluation of recycled asphalt mixtures in a mixing pot using the aggregate distribution uniformity (HA) index is applicable not only to recycled asphalt mixtures but also to ordinary asphalt mixtures. For recycled asphalt mixtures, the HA index calculated by averaging the single-pot aggregate dispersion (DDA) index proposed in this invention is consistent with the actual workability of the recycled asphalt mixture after mixing. A higher HA value indicates poorer distribution uniformity and workability of the corresponding recycled asphalt mixture. Therefore, the workability evaluation method for recycled asphalt mixtures based on aggregate distribution uniformity proposed in this invention is reasonable and feasible.

[0061] In summary, this invention calculates the passing rates of different asphalt aggregates and the passing rates of the synthetic mix after weighing, mixing, sieving, and combustion in a single batch of recycled asphalt mixture. Then, it calculates the aggregate distribution uniformity evaluation index (HA) for a single batch using the root mean square error formula. The average of the four aggregate distribution uniformity evaluation indices (HA) for each batch is used to obtain the aggregate distribution uniformity evaluation index (HA). The workability of the recycled asphalt mixture is evaluated using the aggregate distribution uniformity evaluation index (HA). This provides a new method for evaluating the workability of recycled asphalt mixtures during construction, thereby ensuring good construction quality and providing certain guidance.

[0062] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A method for evaluating the workability of asphalt mixtures for recycling technology based on aggregate distribution uniformity, characterized in that, Includes the following steps: Step 1. Weigh out 12 kg of asphalt, mineral aggregate and old aggregate and put them into the mixing pot for mixing. The mass ratio of asphalt, mineral aggregate and old aggregate is 4.6:50:

50. Step 2. Divide the recycled asphalt mixture in the mixing pot into four portions using the cross-division method, and burn each portion of the recycled asphalt mixture in a calcining furnace until the asphalt surface turns gray. Step 3. Cool the burned recycled asphalt mixture, sieve it through a standard sieve, weigh the aggregates of different particle sizes, and test the mass loss of the recycled asphalt mixture before and after combustion. Step 4. Compare and analyze the content of different particle sizes in the sieved aggregate with the content of aggregate in the production gradation, and propose the aggregate dispersion evaluation index DDA. The specific steps are as follows: the percentage of aggregate passing through the sieve of a single batch is the percentage of undersize aggregate, and the percentage of aggregate passing through the sieve of the aggregate synthesis ratio is the percentage of undersize aggregate. The percentage of material passing through each screen hole in a single batch is calculated based on the cumulative amount of material passing through each screen hole. An evaluation index for aggregate dispersion (DDA) is proposed; ； In the formula: DDA—An index for evaluating the dispersion of aggregates; H n —Percentage of material passing through the screen openings of a single batch; h n —Percentage of aggregate synthesis proportions passing through the sieve apertures; n—The key sieve aperture sizes in the laboratory are 0.075 mm, 0.15 mm, ... 19 mm, respectively; Step 5. Based on the aggregate distribution in the four evenly divided asphalt mixtures in the mixing tank, an aggregate distribution uniformity evaluation index HA is proposed; the calculation method for the aggregate distribution uniformity evaluation index HA is as follows: ， Where: HA—evaluation index for uniformity of aggregate distribution; DDA1, DDA2, DDA3, DDA4—evaluation index for dispersion of aggregate in a single batch.

2. The workability evaluation method for asphalt mixtures in recycling technology based on aggregate distribution uniformity according to claim 1, characterized in that, In step one, the asphalt is Korean SK-70 base asphalt and SBS modified asphalt, the aggregate is limestone, the old aggregate gradation is AC-20, the mixing temperature is 180℃, the mixing time is 3min, and the mixing speed is 80r / min.

3. The workability evaluation method for asphalt mixtures in recycling technology based on aggregate distribution uniformity according to claim 1, characterized in that, In step two, the weight of each of the four portions of asphalt mixture after mixing is 3 kg, the combustion temperature of the calcining furnace is set to 540℃, and the combustion time is 3.5 h.

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