Road engineering fiber recycled asphalt mixture mix proportion design method

Abstract

The invention discloses a road engineering fiber regenerated asphalt mixture mix proportion design method in the technical field of thermal regeneration road engineering material optimization, which comprises the following steps: acquiring a function taking fiber length, diameter and mixing amount as independent variables and an optimal asphalt-aggregate ratio as a dependent variable and a response surface diagram through a pre-experiment, and analyzing the influence of each factor on the optimal asphalt-aggregate ratio; obtaining the optimal asphalt-aggregate ratio of the recycled asphalt mixture, carrying out pavement performance test, and inputting the test result into the response surface method model to obtain a function relational expression which takes the fiber length, diameter and mixing amount as independent variables and takes each performance index as dependent variable; and drawing a three-dimensional curved surface diagram which takes a single pavement performance index as a z axis and two parameters in the fiber as an x axis and a y axis, and preferably selecting a proper fiber parameter range according to the quality of different pavement performance indexes. According to the design method, material consumption is low, consumed time is short, the requirement for a short-term engineering period is met, the design cost is only about half of the cost of an existing scheme, and cost is greatly saved.

Description

Technical Field

[0001] The present invention relates to the technical field of optimization of hot recycling road engineering materials, and particularly relates to a method for designing the mix proportion of fiber recycled asphalt mixture for road engineering, so as to optimize the mix proportion design of fiber recycled asphalt mixture and improve the road performance of fiber recycled asphalt. Background Art

[0002] Recycled asphalt mixture avoids land occupation and environmental pollution caused by the accumulation of waste mixture through the secondary utilization of old asphalt mixture. By adding adulterated fibers, rejuvenators and other admixtures, the performance of aged asphalt can be repaired, and the service life of recycled asphalt pavement can be extended.

[0003] Fiber asphalt mixture is a new type of road material in which fiber materials are added in equal proportion to the original mix proportion. Fibers can improve the road performance of asphalt mixture and extend the service life of asphalt pavement. At present, it has been widely used in the field of road engineering.

[0004] The current mix proportion design method of fiber asphalt mixture still follows the Marshall design method. However, the Marshall design method takes the trial-and-error method as the guiding core, which is time-consuming and consumes a lot of materials, and it is difficult to meet the current high-efficiency and low-carbon production requirements. In addition, in different application scenarios, road engineering has different performance requirements for recycled asphalt mixture, and there are also mutual constraints among various performances. Therefore, providing a mix proportion of asphalt mixture with corresponding emphasis for the required project plays an important role in the long-term and scientific development of road engineering.

[0005] According to research, the incorporation of fibers can significantly improve the various performances of fiber asphalt mixture, but there are mutual constraints among the performances. The design scheme of the traditional mixture mix proportion takes a long time and cannot meet the needs of short-term project cycles. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects in the prior art and provide a method for designing the mix proportion of fiber recycled asphalt mixture for road engineering, which can quickly obtain the mix proportion of fiber asphalt mixture through the response surface method, improve the resource utilization rate, reduce the engineering cost and shorten the engineering construction period.

[0007] The purpose of the present invention is achieved as follows: A method for designing the mix proportion of fiber recycled asphalt mixture for road engineering includes the following steps:

[0008] Select fibers, old asphalt and old aggregate types suitable for the corresponding project, determine the gradation type of the old asphalt mixture through engineering data, prepare a suitable gradation curve of the recycled asphalt mixture through the Marshall design method, and calculate the optimum asphalt-aggregate ratio without fibers;

[0009] Based on engineering experience and pre-test results, initially determine the reasonable range of fiber length, diameter, and dosage.

[0010] Taking fiber length, diameter, and dosage as input values and the optimum asphalt-aggregate ratio as the output value, use the Box-Behnken method in the response surface method to design the test plan, and on this basis, conduct tests to determine the optimum asphalt-aggregate ratio for each plan point.

[0011] Input the test results into the response surface method model to obtain a multiple linear function with fiber length, diameter, and dosage as independent variables and the optimum asphalt-aggregate ratio as the dependent variable, as well as a response surface graph, and analyze the influence of each factor on the optimum asphalt-aggregate ratio. The multiple linear function is shown in formula (1):

[0012] OAC = a1 + a2A + a3B + a4C Formula (1),

[0013] where OAC is the optimum asphalt-aggregate ratio; A, B, and C are fiber length, diameter, and dosage respectively; a1, a2, a3, and a4 are fitting constants.

[0014] Conduct road performance tests on the recycled asphalt mixture at the optimum asphalt-aggregate ratio obtained by the response surface method, input the test results into the response surface method model, and obtain a functional relationship with fiber length, diameter, and dosage as independent variables and dynamic stability, fracture energy, and immersion residual stability as dependent variables, as shown in formula (2):

[0015] Y = b1 + b2A + b3B + b4C + b5AB + b6AC + b7BC + b8A 2 + b9B 2 + b 10 C 2 Formula (2),

[0016] where Y is the test result of dynamic stability, fracture energy, and immersion residual stability; b1 to b 10 are fitting constants.

[0017] Draw a three-dimensional surface graph with a single road performance index as the z-axis and two parameters in the fiber as the x and y axes, and optimize the appropriate range of fiber parameters according to the quality of different road performance indexes.

[0018] Comprehensively consider engineering workability, durability, and cost, and finally determine the mix ratio of the recycled fiber asphalt mixture within the range of fiber optimization parameters obtained by the response surface method.

[0019] Furthermore, the pretest results include conducting Marshall tests on the marginal values of the fiber parameter ranges to measure five conventional indicators of the fiber asphalt mixture under each fiber parameter, namely the flow value, stability, void ratio, voids in mineral aggregate (VMA), and asphalt saturation. Among them, the flow value parameter range is 1.5 - 4.5 mm, the stability value should be ≥ 8 kN, the calculation formula for the void ratio is as shown in formula (3), and the test calculation range for the void ratio is 3 - 6%. The calculation formula for the VMA is as shown in formula (4), and the test calculation range for the VMA is 14 - 18%. The calculation formula for the asphalt saturation is as shown in formula (5), and the test calculation range for the asphalt saturation is 65 - 75%. Eliminate the fiber parameter groups that do not meet the specification requirements according to the results;

[0020]

[0021]

[0022] Furthermore, the reasonable level ranges of the length, diameter, and dosage of the fibers are 3 - 15 mm in length, 5 - 25 μm in diameter, and 0.1 - 0.6 wt% of the fiber asphalt mixture by mass, respectively.

[0023] Furthermore, the Box - Behnken method in the response surface method includes taking three factors: fiber length, diameter, and dosage, with each factor taking three levels and being coded as -1, 0, 1, thereby listing the experimental design scheme.

[0024] Furthermore, the road - using performance tests of the recycled asphalt mixture include high - temperature rutting tests, low - temperature beam tests, and water stability tests, and the service performance of the fiber - recycled asphalt mixture under different traffic environments is reflected through the performance tests.

[0025] Furthermore, the three - dimensional surface diagrams are three surface diagrams with fiber parameters as independent variables drawn for a single road - using performance index, and the optimal fiber parameter range is extruded through the method of number sets.

[0026] Furthermore, the single road - using performance indexes include the dynamic stability for indicating the high - temperature rutting test, the fracture energy for indicating the low - temperature beam test, and the immersion residual stability for indicating the water stability test.

[0027] When the present invention works, the length, diameter and dosage of the incorporated fibers are used as input values, and the optimal asphalt-aggregate ratio is used as the output value. The Box-Behnken method in the response surface method is adopted to design the test scheme, and on this basis, the test for determining the optimal asphalt-aggregate ratio is carried out for each scheme point; the test results are input into the response surface method model to obtain a function with the fiber length, diameter and dosage as independent variables and the optimal asphalt-aggregate ratio as the dependent variable, as well as the response surface diagram, analyze the influence of each factor on the optimal asphalt-aggregate ratio, so as to obtain the optimal asphalt-aggregate ratio of the recycled asphalt mixture, and conduct road performance tests, and then input the test results into the response surface method model to obtain a functional relationship with the fiber length, diameter and dosage as independent variables and each performance index as the dependent variable; draw a three-dimensional surface diagram with a single road performance index as the z-axis and two parameters in the fiber as the x and y axes, and select a suitable fiber parameter range according to the quality of different road performance indexes. Compared with the Marshall design method that simply takes the trial-and-error method as the guiding core in the prior art, the material consumption is less, the design scheme time of the mixture ratio is short, which meets the requirements of the short-term project cycle, and the recycled asphalt mixture obtained by the design method of the present invention can meet the requirements of service performance under different traffic environments through testing, and the design cost is only nearly half of the existing scheme, greatly saving costs. Brief Description of the Drawings

[0028] Figure 1 It is a schematic flow chart of the mixture ratio design method of the fiber recycled asphalt mixture of the present invention.

[0029] Figure 2 It is the contour line and response surface diagram of the influencing factors of the dynamic stability in the performance test of the recycled asphalt mixture obtained by the mixture ratio design method of the fiber recycled asphalt mixture of the present invention.

[0030] Figure 3 It is the contour line and response surface diagram of the influencing factors of the fracture energy in the performance test of the recycled asphalt mixture obtained by the mixture ratio design method of the fiber recycled asphalt mixture of the present invention.

[0031] Figure 4 It is the contour line and response surface diagram of the influencing factors of the immersion residual stability in the performance test of the recycled asphalt mixture obtained by the mixture ratio design method of the fiber recycled asphalt mixture of the present invention. Detailed Embodiment

[0032] In order to verify and illustrate the technical effects adopted in this method, in this embodiment, a traditional technical scheme and this method are selected for comparative testing, and the test results are compared by means of scientific demonstration to verify the real effects of this method.

[0033] First, design the fiber characteristic parameters. The three factors, three levels and the coding of the test groups are shown in Tables 1-2.

[0034] Table 1 Correspondence Table of Factors and Encodings

[0035]

[0036] Table 2 Test Scheme

[0037]

[0038] According to the design scheme, three performance tests, namely the high-temperature rutting test, the low-temperature beam test, and the water stability test, are carried out. All three performance tests are selected from JTG E20 - 2011 "Test Procedures for Bitumen and Bituminous Mixtures in Highway Engineering". The reference test number for the high-temperature rutting test is T0719 - 2011, the reference number for the low-temperature beam test is T 0715 - 2011, and the reference number for the water stability test is T 0709 - 2011. The obtained results are shown in Table 3.

[0039] Table 3 Performance Test Results

[0040]

[0041] Response surface calculation and model establishment are carried out on the test results of the three tests. The response surface of the dynamic stability is as Figure 2 shown. The model equation is as shown in formula (6), and the analysis of variance results are shown in Table 4. The p-value of the model < 0.0001, indicating that the model is highly significant. The difference between the adjusted R 2 and the predicted R 2 as well as the Adequate Precision of the model all meet the requirements, indicating that this model can be used to predict the dynamic stability. In this model, B (fiber length), C (fiber diameter), A2 (quadratic term of fiber content), B2 (quadratic term of fiber length), and C2 (quadratic term of fiber diameter) are significant model terms.

[0042] Formula (6) is as follows:

[0043] DS = 2602.98971 + 18051.78241A + 206.30704B + 63.99633C + 31.81667AB - 23.53241AC - 1.96574BC - 19960.90278A 2 - 14.78179B 2 - 2.19742C 2 .

[0044] Table 4 Analysis of Variance of the Dynamic Stability Model

[0045]

[0046] The response surface of the fracture energy is shown in Figure 3, the model equation is as shown in Equation (7), and the results of its analysis of variance are shown in Table 5.

[0047] Equation (7) is:

[0048] G f = 10400.99136 + 32720.54630A + 881.38889B - 18.0405C - 66.11111AB - 17.96296AC + 14.42593BC - 37921.11111A 2 - 67.51358B 2 - 3.59753C 2 .

[0049] Analysis of Variance of the Fracture Energy Model

[0050]

[0051] The response surface of the residual stability after immersion is shown in Figure 4 , the model equation is as shown in Equation (8), and the results of its analysis of variance are shown in Table 6.

[0052] Equation (8) is:

[0053] MS0 = 93.96272 + 9.84954A + 0.096235B - 0.465941C - 0.020370AB + 0.012963AC + 0.002654BC - 11.33333A 2 - 0.013704B 2 + 0.009198C 2 .

[0054] Analysis of Variance of the Residual Stability Model after Immersion

[0055]

[0056] By analyzing and comparing the parameter ranges under various performances, the mix ratio of the final fiber-reclaimed asphalt mixture within the optimized fiber parameter range is obtained. The optimal fiber parameters and the measured performance values under the optimal parameters are shown in Table 7.

[0057] Table 7 Global Optimal Solution and Its Measured Values

[0058]

[0059] Traditional technical solutions generally use the orthogonal experimental design method to design the mix ratio of fiber content, length, and diameter. In the case of three factors and three levels, a total of 27 groups of mix ratio designs are required. Assuming that the labor cost plus material cost for one group of mix ratio is 1 constant, then 27 groups require 27 constants. In contrast, the response surface method only requires a cost of 17 constants.

[0060] The costs under the two mix ratio design methods are calculated respectively using the traditional technical solution and this method, and the fiber mass error and mass loss degree obtained from the calculation are shown in Table 8 below.

[0061] Table 8 Scheme Selection and Cost Comparison

[0062]

[0063] As can be seen from Table 8, the cost required by this method is only nearly half of that of the traditional scheme, and the orthogonal experiment can only obtain the optimal mix ratio under the number of groups done and cannot achieve prediction. It is difficult to capture the actual optimal fiber parameters.

[0064] The present invention is not limited to the above embodiments. Based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations to some of the technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A design method for the mix proportion of a road engineering fiber-recycled asphalt mixture, characterized in that, It includes the following steps: Select the types of fibers, old asphalt and old aggregates suitable for the corresponding project, determine the gradation type of the old asphalt mixture through engineering data, formulate a suitable gradation curve of the recycled asphalt mixture through the Marshall design method, and calculate the optimum asphalt-aggregate ratio without fibers; According to engineering experience and the results of preliminary tests, initially determine the reasonable level ranges of the fiber length, diameter and dosage; Taking the fiber length, diameter and dosage as input values and the optimum asphalt-aggregate ratio as the output value, design the test plan using the Box-Behnken method in the response surface method, and based on this, conduct tests to determine the optimum asphalt-aggregate ratio for each plan point; Input the test results into the response surface method model to obtain a multiple linear function and a response surface diagram with the fiber length, diameter and dosage as independent variables and the optimum asphalt-aggregate ratio as the dependent variable, and analyze the influence of each factor on the optimum asphalt-aggregate ratio. The multiple linear function is shown in formula (1): OAC = a1 + a2A + a3B + a4C Formula (1), where, OAC: optimum asphalt-aggregate ratio; A, B, C are the fiber length, diameter and dosage respectively; a1, a2, a3, a4 are fitting constants; Conduct road performance tests on the recycled asphalt mixture at the optimum asphalt-aggregate ratio obtained by the response surface method, input the test results into the response surface method model, and obtain a functional relationship with the fiber length, diameter and dosage as independent variables and the dynamic stability, fracture energy and immersion residual stability as dependent variables, as shown in formula (2): Y = b1 + b2A + b3B + b4C + b5AB + b6AC + b7BC + b8A 2 + b9B 2 + b 10 C 2 Formula (2), Among them, Y is the test result of dynamic stability, fracture energy and immersion residual stability; b1 to b 10 are fitting constants; Draw a three-dimensional surface diagram with a single road performance index as the z-axis and two parameters of the fiber as the x and y axes, and optimize the appropriate fiber parameter range according to the quality of different road performance indicators; Comprehensively consider the workability, durability and cost of the project, and finally determine the mix ratio of the recycled fiber asphalt mixture within the range of fiber optimization parameters extruded by the response surface method.

2. The mix proportion design method of a road engineering fiber recycled asphalt mixture according to claim 1, characterized in that: The results of the preliminary tests include conducting Marshall tests on the marginal values of the fiber parameter range, testing five conventional indicators of the fiber asphalt mixture under each fiber parameter, namely the flow value, stability, void ratio, mineral aggregate void ratio, and asphalt saturation. Among them, the flow value parameter range is 1.5 - 4.5 mm, the stability value should be ≥ 8 kN, the calculation formula of the void ratio is shown in formula (3), the test calculation range of the void ratio is 3 - 6%, the calculation formula of the mineral aggregate void ratio is shown in formula (4), the test calculation range of the mineral aggregate void ratio is 14 - 18%, the calculation formula of the asphalt saturation is shown in formula (5), the test calculation range of the asphalt saturation is 65 - 75%, and eliminate the fiber parameter groups that do not meet the specification requirements according to the results; 3. A design method for the mix proportion of a road engineering fiber-recycled asphalt mixture according to claim 1, characterized in that: The reasonable level ranges of the fiber length, diameter and dosage are 3 - 15 mm in length, 5 - 25 μm in diameter, and 0.1 - 0.6 wt% of the fiber asphalt mixture by mass respectively.

4. A design method for the mix proportion of a road engineering fiber-recycled asphalt mixture according to claim 1, characterized in that: The Box-Behnken method in the response surface method includes taking three factors of fiber length, diameter and dosage, each factor taking three levels, and coding with -1, 0, 1, thus listing the test design plan.

5. A method for designing the mix proportion of a road engineering fiber-recycled asphalt mixture according to claim 1, characterized in that: The road performance tests of the recycled asphalt mixture include high-temperature rutting test, low-temperature beam test and water stability test, and the service performance of the fiber recycled asphalt mixture under different traffic environments is reflected through the performance tests.

6. A method for designing the mix proportion of a road engineering fiber-recycled asphalt mixture according to claim 1, characterized in that: The three-dimensional surface diagram is three surface diagrams drawn with fiber parameters as independent variables for a single road performance index, and the range of fiber parameters with the best performance is obtained by the method of number set.

7. A method for designing the mix proportion of a road engineering fiber-recycled asphalt mixture according to claim 6, characterized in that: The single road performance index includes dynamic stability for indicating the high-temperature rutting test, fracture energy for indicating the low-temperature beam test, and immersion residual stability for indicating the water stability test.

Images