CN112726331B - Two-stage design method for target mix proportion of asphalt mixture - Google Patents

Abstract

A two-stage design method for target mix proportion of asphalt mixture relates to a design method for target mix proportion of asphalt mixture. Designing a target mix proportion in a first stage: the method comprises the following steps: selecting raw materials; step two: monitoring and controlling the quality of raw materials; step three: guiding the preparation of materials according to the median mixing ratio of the aggregates; designing the target mix proportion at the second stage: the method comprises the following steps: screening and monitoring the material preparation process; step two: calculating the blending proportion of the synthetic graded mineral aggregate by a trial-matching method; step three: analyzing the volatility of the blending ratio; step four: determining the optimal asphalt dosage and the final target mixing ratio; step five: testing the performance of the mixture; step six: and correcting the proportion and the quantity of subsequent stock preparation. By reducing the fluctuation of the mineral aggregate ratio, the target mixing ratio result can represent the average characteristic of the field material, the waste of the material is reduced, and the performance and the quality of the material are ensured.

Description

A two-stage design method for target mix ratio of asphalt mixture

technical field

The invention relates to a method for designing a target mix ratio of an asphalt mixture, in particular to a two-stage design method for a target mix ratio of an asphalt mixture, and belongs to the technical field of asphalt pavement engineering.

Background technique

Asphalt mixture target mix ratio design is an important link in the process of asphalt pavement construction. Its essence is the design of the internal material composition ratio and structure of the asphalt mixture. The relevant performance requirements are used to guide the construction, and the proportion and quantity of materials to be prepared are determined, which is an important basis for construction quality control.

In the traditional asphalt pavement design and construction process, the target mix ratio design is generally carried out only once, mainly in two cases: one is to use the materials processed by the gravel yard for the mix ratio design, and the other is to use the materials at the initial stage of material preparation for the mix ratio design. design. The materials in these two cases are in different construction processes and spatial positions, which can only represent the actual situation of the respective material source sites or the initial stage of material preparation, and cannot represent the entire process of material preparation, nor the average state of all materials entering the site.

When designing the target mix ratio, the proportion and quantity of the prepared materials need to be preliminarily determined according to the mix ratio, and the results of the mix ratio design also need to represent the average composition characteristics of all materials on site. The above two situations may cause a large deviation from the average composition of all materials on site, resulting in the failure of the target mix design, resulting in the design of the asphalt mixture structure and composition can not well meet the expected effect, the proportion of the preparation cannot be scientifically determined It is easy to cause excess or waste of materials, and at the same time, it cannot ensure that the quality of the material source meets the requirements, which may cause the design result of the mix ratio to not meet the requirements of the specification.

Therefore, it is urgent to provide an asphalt mixture target mix design method that can avoid the defects of the traditional target mix ratio design, meet the expected requirements, and ensure that the mix ratio can be realized in the project.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a two-stage design method for the target mix ratio of asphalt mixture, which can ensure that the target mix ratio result can represent the average characteristics of the field materials by reducing the fluctuation of the mineral mix ratio, reduce the waste of materials, and ensure that the Material properties and quality.

In order to achieve the above purpose, the present invention adopts the following technical scheme: a two-stage design method for the target mix ratio of asphalt mixture, comprising the following steps:

The first stage target mix design:

Step 1: Select raw materials, including coarse aggregate, fine aggregate, asphalt and mineral powder, among which the coarse aggregate and fine aggregate are processed according to the requirements of 4.8.3 of "Technical Specification for Construction of Asphalt Pavement for Highway Engineering" (JTG F40-2004) 4.8.3 into a variety of specifications;

Step 2: Raw material quality monitoring and control, segregation monitoring is carried out on the piles of coarse and fine aggregates transported to the site, and the upper, middle and lower layers of the ore piles are respectively taken for screening tests, and the pass rate curve is drawn to monitor the ore materials. If the segregation and pollution of the material are unqualified, readjust according to the above step 1, until the maximum difference between the pass rate curves of the upper, middle and lower layers of the stockpile does not exceed 20%;

Step 3: Guide the preparation of materials according to the median mix ratio of the aggregates, determine the synthesis ratio of various minerals according to the gradation range corresponding to the type of asphalt mixture, and use the Try to formulate the required synthetic gradation curve close to the median value, and obtain the composition ratio of various ore materials under the gradation curve, and use the blending ratio as the ratio of various ore materials to prepare;

The second stage target mix design:

Step 1: Screening and monitoring during the material preparation process. During the material preparation process, a screening monitoring test is performed on each prepared mineral material to obtain the screening test data of each material preparation;

Step 2: Calculate the blending ratio of synthetic graded ore by the trial blending method, design the blending ratio when the prepared material reaches 60-70%, and according to the trial blending method, the prepared aggregates are trial-blended to be close to the upper limit and close to the middle as required by the specification documents. The three synthetic gradation curves that are close to the lower limit are obtained, and then the proportion of mineral material blending corresponding to the grading curves of each level is obtained respectively;

Step 3: Analysis of the fluctuation of the blending ratio, using the blending ratios of the above three groups of ore materials of each specification that are close to the upper limit, close to the median value, and close to the lower limit, combined with all the screening test data obtained from quality control monitoring, use the test algorithm to classify Combined, get three groups of grades to form a curve set, calculate the coefficient of variation of the sieve hole pass rate of each grade of aggregate synthesis grading, calculate the average coefficient of variation of the sieve holes, and analyze the volatility of the three groups of grades to form a curve set to the target curve;

Step 4: Determination of the optimum asphalt dosage and final target mix ratio. For the three groups of blending ratios, the OAC method is used to determine the optimum asphalt dosage, and the average values of OAC ₁ and OAC ₂ , and OAC ₁ and OAC ₂ are calculated as the optimum Asphalt consumption, the final target mixing ratio and the optimal asphalt consumption are determined by considering the asphalt consumption, construction and mixture characteristics and the fluctuation of each mixing ratio;

Step 5: Check the performance of the mixture, check the high temperature stability, water stability and low temperature crack resistance of the mixture, if all meet the specification requirements, the target mix design is qualified, otherwise go back to step 2 of the second stage and repeat;

Step 6: Correct the proportion and quantity of subsequent material preparation, and correct the proportion and quantity of material preparation according to the final determined mixing ratio of mineral material for the ore material that needs to be prepared subsequently.

Compared with the prior art, the beneficial effects of the present invention are: the present invention considers the fluctuation of the material blending ratio, effectively ensures that the synthetic blending ratio of the material can represent the average level of the prepared materials, and improves the mixing ratio design. Realizability and effectiveness of the method, according to the first-stage design method, the blending ratio of various minerals close to the gradation median value is used as the material preparation ratio, which improves the efficiency of material preparation, reduces the waste of materials, and combines the quality Control, in the first-stage design method, the performance and quality of the field materials are guaranteed, and the segregation monitoring of the stockpile is carried out, which effectively reduces the problem that the material performance test of the target mix design does not meet the requirements.

Description of drawings

Fig. 1 is the flow chart of the two-stage design method of the asphalt mixture target mix ratio of the present invention;

Fig. 2 is the data graph of the pile segregation monitoring of fine aggregate and coarse aggregate in the embodiment;

Fig. 3 is the data graph of the gradation formation curve set close to the gradation median in the embodiment;

FIG. 4 is a data graph of the coefficient of variation of each sieve opening rate of synthetic gradation near the median value in the Examples.

Detailed ways

The technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments, based on the present invention The embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work, fall within the protection scope of the present invention.

The target mix ratio of the asphalt mixture is the basis for determining the composition of the mixture. Its mix ratio design results need to meet the actual conditions of the site materials, represent the average characteristics of the site materials, and are also the basis for construction quality control. The results can be used to guide the construction. This requires a set of reasonable and effective mixing ratio design methods to ensure that the designed target mixing ratio meets the above requirements. The present invention designs the target mixing ratio in two stages, combined with The quality control technology of on-site materials ensures the quality control of incoming materials, and guides the material preparation process, taking into account the fluctuation of synthetic gradation, so that the designed target mix ratio can effectively represent the actual situation of on-site materials, and finally can be mixed A mixture with a target mix ratio design is produced, so that the composition, structure and performance of the asphalt mixture meet the expected results, thereby ensuring durability and service life.

Referring to Figure 1, the present invention discloses a two-stage design method for the target mix ratio of asphalt mixture, comprising the following steps:

The first stage target mix design:

Step 1: Select raw materials, including coarse aggregate, fine aggregate, asphalt and mineral powder, among which the coarse aggregate and fine aggregate are processed according to the requirements of 4.8.3 of "Technical Specification for Construction of Asphalt Pavement for Highway Engineering" (JTG F40-2004) 4.8.3 into a variety of specifications;

Step 2: Raw material quality monitoring and control, the above-mentioned coarse aggregate, fine aggregate, mineral powder and asphalt are selected as raw materials, all of which meet the requirements of "Technical Specification for Construction of Asphalt Pavement for Highway Engineering" (JTG F40-2004), and are transported to the site. The segregation monitoring is carried out on the piles of coarse and fine aggregates, and the upper, middle and lower layers of the pile are respectively taken for screening tests, and the pass rate curve is drawn to monitor the segregation and pollution of the ore. Adjust until the maximum difference between the pass rate curves of the upper, middle and lower layers of the pile does not exceed 20%;

Step 3: Guide the preparation of materials according to the median mix ratio of the aggregates, determine the synthesis ratio of various minerals according to the gradation range corresponding to the type of asphalt mixture, and use the The required synthetic gradation curve close to the median value is obtained by trial method, and the composition ratio of various minerals under the gradation curve is obtained. The blending ratio is used as the ratio of various mineral materials to prepare materials, and the materials are prepared according to this ratio. ;

The second stage target mix design:

Step 1: Screening and monitoring during the material preparation process, prepare materials according to the material preparation ratio obtained in the first stage, in the process of material preparation, carry out a screening monitoring test for each prepared mineral material, and obtain the screening test data of each material preparation;

Step 2: Calculate the blending ratio of synthetic graded ore by the trial blending method, design the blending ratio when the prepared material reaches 60-70%, and according to the trial blending method, the prepared aggregates are trial-blended to be close to the upper limit and close to the middle as required by the specification documents. The three synthetic gradation curves that are close to the lower limit are obtained, and then the proportion of mineral material blending corresponding to the grading curves of each level is obtained respectively;

Step 3: Analysis of the fluctuation of the blending ratio, using the blending ratios of the above three groups of ore materials of each specification that are close to the upper limit, close to the median value, and close to the lower limit, combined with all the screening test data obtained from quality control monitoring, use the test algorithm to classify Combined, get three groups of grades to form a curve set, calculate the coefficient of variation of the sieve hole pass rate of each grade of aggregate synthesis grading, calculate the average coefficient of variation of the sieve holes, and analyze the volatility of the three groups of grades to form a curve set to the target curve;

Step 4: Determination of the optimum asphalt dosage and final target mix ratio. For the three groups of blending ratios, the OAC method is used to determine the optimum asphalt dosage, and the average values of OAC ₁ and OAC ₂ , and OAC ₁ and OAC ₂ are calculated as the optimum Asphalt consumption, the final target mixing ratio and the optimal asphalt consumption are determined by considering the asphalt consumption, construction and mixture characteristics and the fluctuation of each mixing ratio;

Step 5: Check the performance of the mixture, check the high temperature stability, water stability and low temperature crack resistance of the mixture, if all meet the specification requirements, the target mix design is qualified, otherwise go back to step 2 of the second stage and repeat;

Step 6: Correct the proportion and quantity of subsequent material preparation, and correct the proportion and quantity of material preparation according to the final determined mixing ratio of mineral material for the ore material that needs to be prepared subsequently.

Example (AC-20 as an example)

The first stage target mix design:

Step 1: Choose raw materials

In this example, the construction project of the A2 section of Beigu Expressway is taken as an example. AC-20C is used for the middle surface layer of asphalt concrete, and limestone is used for coarse and fine aggregates to be processed into four specifications. -25]mm, 2# material [10-15)mm, 3# material [5-10)mm and fine aggregate: 4# material (0-5)mm, the specification of asphalt selected is 90#A, mineral powder Mineral powder processed from limestone;

Step 2: Raw material quality monitoring and control

The above-mentioned coarse aggregate, fine aggregate, mineral powder and asphalt are selected as raw materials, which all meet the requirements of "Technical Specification for Construction of Asphalt Pavement for Highway Engineering" (JTG F40-2004). Specifications (JTG F40-2004), the required index value is called the required value, and the index value of the material selected in the experiment is called the experimental value. in,

The required value and experimental value of coarse aggregate are shown in the following table:

The required value and experimental value of fine aggregate are shown in the following table:

The required value and experimental value of mineral powder are shown in the following table:

The required and experimental values of asphalt are shown in the following table:

Monitor and control the quality of raw materials, and monitor the segregation of the piles of coarse and fine aggregates delivered to the site. Referring to Figure 2, take the upper, middle and lower layers of the pile for screening tests, and draw the pass rate. curve to monitor the segregation and contamination of the ore material. The stockpile in Figure 2 has been segregated and is unqualified. It should be readjusted according to the above steps and then the segregation monitoring should be carried out until the maximum difference between the pass rate curves of the upper, middle and lower layers of the stockpile does not meet the requirements. After more than 20%, go to step three;

Step 3: Prepare materials according to the median mix ratio of aggregates

Determine the synthesis ratio of various minerals (including coarse and fine aggregates and slag powder) according to the gradation range corresponding to the type of asphalt mixture. The required synthetic gradation curve close to the median value is obtained, and the composition ratio of various ore materials under the gradation curve is obtained. Referring to Table 1 below, the blending ratio is used as the ratio of various ore materials to be prepared. According to this Proportion to prepare.

Table 1 Mineral composition ratio

The second stage target mix design:

Step 1: Screening monitoring during material preparation

Prepare materials according to the material preparation ratio obtained in the first stage. During the material preparation process, carry out a screening monitoring test for each prepared mineral material, and obtain the screening test data of each material preparation, as shown in Table 2 below.

Table 2 The results of each screening test in the material preparation process

Step 2: Calculate the blending ratio of synthetic graded minerals by trial blending method

When the prepared material reaches 60-70%, the mix proportion design is carried out. According to the trial algorithm, the prepared aggregates are tested to produce three synthetic gradation curves that are close to the upper limit, close to the median value, and close to the lower limit according to the requirements of the specification document, and then obtain respectively. The proportion of mineral material blending corresponding to each level of distribution curve is shown in Table 3 below.

Table 3. The composition of all levels and the corresponding proportion of mineral materials

Step 3: Analysis of the volatility of the blending ratio

Using the blending ratios of the three groups of ore materials of various specifications that are close to the upper limit, close to the median value, and close to the lower limit, combined with all the screening test data obtained from the previous quality control monitoring, the trial algorithm is used for graded compounding, and three groups of graded compounding compounds are obtained. The curve set, taking the curve set close to the median value as an example, refer to Figure 3, and calculate the coefficient of variation of the sieve hole passing rate of each grade of aggregate synthesis grading, as shown in Figure 4, calculate the average coefficient of variation of the sieve hole, and analyze the three groups The volatility of the graded composition curve set to the target curve,

The formula for calculating the coefficient of variation:

where σ: sample standard deviation

μ: sample mean

Average coefficient of variation of sieve openings:

The area method can be used to analyze the volatility. By calculating the area formed by each of the three sets of curves, the overall volatility of each group of gradations is evaluated. The smaller the area, the smaller the overall volatility. The corresponding coefficient of variation of the pass rate of synthetic grading sieve holes of each grade is shown in Figure 4, and it is required that the maximum pass rate coefficient of variation of each sieve hole should not exceed 20%, and then calculate the average coefficient of variation of the sieve holes, and finally comprehensively evaluate the three groups of blends. The volatility of the proportioning ratio is shown in Table 4 below.

Table 4 Synthetic gradation volatility analysis

Gradation type composite gradation curve set area Maximum Variation Coefficient of Sieve Size Average coefficient of variation of sieve openings close to the upper limit Big 20.91 11.45 close to the median Small 10.37 5.62 close to the lower limit middle 14.82 8.21

Based on the above, it can be seen that the proportionate volatility of the grade close to the median value is the smallest, which can be given priority. The proportion of the grade close to the upper limit is the largest, and the maximum coefficient of variation of the sieve hole exceeds 20%, this ratio should be abandoned;

Step 4: Determination of the optimal asphalt dosage and final target mix ratio (take close to median grading as an example)

First of all, according to the requirements of the specification and the properties of the asphalt used, the optimal asphalt content is preliminarily estimated to be 4.9%, and the estimated asphalt content is ±5% and ±10%, respectively. The amount of asphalt in the formed Marshall specimens was measured for four volume parameters: gross bulk density, calculated porosity, slag gap ratio, and effective asphalt saturation, and the Marshall stability and flow value were measured. Relationship lines.

According to the relationship curve, the corresponding asphalt content a ₁ = 5.12% corresponding to the maximum density, the asphalt content a ₂ = 4.87% corresponding to the maximum stability, the asphalt content a ₃ = 4.60% corresponding to the target porosity, and the asphalt saturation The amount of asphalt corresponding to the median degree of asphalt a ₄ =4.79%, according to the formula:

OAC ₁ =(a ₁ +a ₂ +a ₃ +a ₄ )/4=4.85%

Taking the range of asphalt dosage that the density, stability, flow value, target porosity, and asphalt saturation all meet the requirements, OAC _min =4.52%, OAC _max =5.03%, and the value is taken as OAC ₂ :

OAC ₂ =(OAC _min +OAC _max )/2=4.78%

Calculate the optimum bitumen usage OAC as the median of OAC ₁ and OAC ₂ :

OAC=(OAC ₁ +OAC ₂ )/2=4.8%

After obtaining the mixing ratios close to the upper limit, the median value and the lower limit according to the above method, Marshall specimens with different asphalt dosages are formed, and the final target is determined by taking into account the fluctuation of the asphalt dosage, construction and mixture characteristics and the fluctuation of each blending ratio. The mix ratio and optimum asphalt dosage are shown in Table 5 below.

Table 5 Comparison of standards for determining the amount of asphalt at all levels

Gradation type Asphalt consumption Construction and Mixture Properties Blending Ratio Volatility close to the upper limit Big A lot of coarse aggregate, easy to segregate Failed close to the median middle better better close to the lower limit Small There are many fine aggregates, and the peristalsis is poor generally

Therefore, the mixture ratio that is close to the median value of the gradation is finally selected, that is, 1# material: 2# material: 3# material: 4# material: mineral powder = 24%: 17%: 18%: 35%: 6%, The optimum asphalt dosage is 4.8%;

Step 5: Mixture performance inspection

The performance of the mixture is tested, and the high temperature stability test is carried out according to the methods and test conditions specified in the "Highway Engineering Asphalt and Asphalt Mixture Test Regulations" T0719, and the standard rutting test is carried out to determine the dynamic stability index for testing, water stability and low temperature. The crack resistance test is carried out according to the methods and test conditions specified in T0709 and T0729 of "Asphalt and Asphalt Mixture Test Regulations for Highway Engineering", and the residual stability and freeze-thaw splitting test are carried out, and the ratio of residual stability to residual strength is measured. As shown in Table 6, if all of the above meet the requirements of the specification, the target mix design is qualified; otherwise, go back to step 2 of the second stage and repeat.

Table 6 Freeze-thaw split test and rutting test results

Step 6: Correct the proportion and quantity of subsequent preparations

For the ore materials that need to be prepared successively in the future, according to the final determined ore material mixing ratio (ie 1# material: 2# material: 3# material: 4# material: ore powder = 24%: 17%: 18%: 35 %: 6%) to correct the proportion and quantity of materials, and through the above process, all the work of the target mix design is completed.

It will be apparent to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, but that the present invention may be implemented in other packaging forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments are to be regarded in all respects as illustrative and not restrictive, and the scope of the invention is to be defined by the appended claims rather than the foregoing description, which are therefore intended to fall within the scope of the claims. All changes within the meaning and range of the equivalents of , are embraced within the invention. Any reference signs in the claims shall not be construed as limiting the involved claim.

In addition, it should be understood that although this specification is described in terms of embodiments, not each embodiment only includes an independent technical solution, and this description in the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (2)

1. a two-stage design method for an asphalt mixture target mix ratio, is characterized in that: comprise the following steps: The first stage target mix design: Step 1: Select raw materials, including coarse aggregate, fine aggregate, asphalt and mineral powder, among which the coarse aggregate and fine aggregate are processed according to the requirements of 4.8.3 of "Technical Specification for Construction of Asphalt Pavement for Highway Engineering" (JTG F40-2004) 4.8.3 into a variety of specifications; Step 2: Raw material quality monitoring and control, segregation monitoring is carried out on the piles of coarse and fine aggregates transported to the site, and the upper, middle and lower layers of the ore piles are respectively taken for screening tests, and the pass rate curve is drawn to monitor the ore materials. If the segregation and pollution of the material are unqualified, readjust according to the above step 1, until the maximum difference between the pass rate curves of the upper, middle and lower layers of the stockpile does not exceed 20%; Step 3: Guide the preparation of materials according to the median mix ratio of the aggregates, determine the synthesis ratio of various minerals according to the gradation range corresponding to the type of asphalt mixture, and use the Try to formulate the required synthetic gradation curve close to the median value, and obtain the composition ratio of various ore materials under the gradation curve, and use the blending ratio as the ratio of various ore materials to prepare; The second stage target mix design: Step 1: Screening and monitoring during the material preparation process. During the material preparation process, a screening monitoring test is performed on each prepared mineral material to obtain the screening test data of each material preparation; Step 2: Calculate the blending ratio of synthetic graded ore by the trial blending method, design the blending ratio when the prepared material reaches 60-70%, and according to the trial blending method, the prepared aggregates are trial-blended to be close to the upper limit and close to the middle as required by the specification documents. The three synthetic gradation curves that are close to the lower limit are obtained, and then the proportion of mineral material blending corresponding to the grading curves of each level is obtained respectively; Step 3: Analysis of the fluctuation of the blending ratio, using the blending ratios of the above three groups of ore materials of each specification that are close to the upper limit, close to the median value, and close to the lower limit, combined with all the screening test data obtained from quality control monitoring, use the test algorithm to classify Combined, get three groups of grades to form a curve set, calculate the coefficient of variation of the sieve hole pass rate of each grade of aggregate synthesis grading, calculate the average coefficient of variation of the sieve holes, and analyze the volatility of the three groups of grades to form a curve set to the target curve; Step 4: Determination of the optimum asphalt dosage and final target mix ratio. For the three groups of blending ratios, the OAC method is used to determine the optimum asphalt dosage, and the average values of OAC ₁ and OAC ₂ , and OAC ₁ and OAC ₂ are calculated as the optimum Asphalt consumption, the final target mixing ratio and the optimal asphalt consumption are determined by considering the asphalt consumption, construction and mixture characteristics and the fluctuation of each mixing ratio; Step 5: Check the performance of the mixture, check the high temperature stability, water stability and low temperature crack resistance of the mixture, if all meet the specification requirements, the target mix design is qualified, otherwise go back to step 2 of the second stage and repeat; Step 6: Correct the proportion and quantity of subsequent material preparation, and correct the proportion and quantity of material preparation according to the final determined mixing ratio of mineral material for the ore material that needs to be prepared subsequently. 2. the two-stage design method of a kind of asphalt mixture target mix ratio according to claim 1, is characterized in that: in the step 3 of described second-stage target mix ratio design, the area method is used to analyze the volatility, and by calculating three The area formed by each group of curve sets is used to evaluate the overall volatility of the gradation in each group. The smaller the area, the smaller the overall volatility. Then calculate the pass rate of the synthetic gradation sieve hole of each grade corresponding to the three groups of blending ratios. The coefficient of variation of the maximum pass rate of each sieve hole should not exceed 20%, and then the average coefficient of variation of the sieve hole was calculated, and finally the fluctuation of the blending ratio of the three groups was comprehensively evaluated.

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