Method for determining amount of asphalt in cold recycled mixture by considering comprehensive action of environment temperature

Abstract

The invention provides a method for determining the asphalt consumption of a cold-recycled mixture by considering the comprehensive action of environment temperature, and relates to the technical field of cold recycling of road engineering, which comprises the following steps of: preliminarily determining grading design; drying the recycled asphalt pavement material RAP, screening and grading, and designing the composition of each grade according to the grading upper and lower limits to form the mixture grading meeting the requirements; determining the optimal water content OWC based on a heavy compaction test; forming five groups of cold-recycled mixtures with different emulsified asphalt mixing amounts, preparing the cold-recycled mixtures into Marshall test pieces, rut plates and trabecular test pieces, and curing the Marshall test pieces, the rut plates and the trabecular test pieces; carrying out a high-temperature rutting test, a medium-temperature fatigue bending test and a low-temperature small beam cracking test, and determining the optimal emulsified asphalt dosage OEC by considering the comprehensive action of the environment temperature; and verifying the water stability of the cold-recycled mixture under OEC. The method for determining the asphalt consumption of the cold-recycled mixture considering the comprehensive action of the environment temperature is used for regions with large temperature variation amplitude and extreme temperature, and the pavement performance of the cold-recycled mixture can be improved.

Description

Technical Field

[0001] The invention relates to the field of cold regeneration of road engineering, and in particular to a method for determining the amount of asphalt in a cold regeneration mixture taking into account the comprehensive effect of ambient temperature. Background Art

[0002] Cold recycled mixtures are increasingly used in the field of road infrastructure construction and maintenance. Cold recycling technology based on road recycled asphalt material (RAP) is gradually becoming an important means to promote the development of road projects in a green and sustainable direction. Cold recycled mixtures not only effectively utilize waste materials and reduce the demand for new resources, but also reduce construction costs and environmental impact.

[0003] At present, there are certain limitations in the design methods of cold recycled mixtures in China. Cold recycled mixtures are mainly affected by factors such as temperature and precipitation. In the existing specification design, the influence of temperature is mainly evaluated through the 15°C splitting test, but this method is difficult to accurately distinguish the impact of different temperature conditions on cold recycled mixtures, and is insufficient to support the refined needs of specific pavement structure design and performance regulation. As for the impact of precipitation, a 24-hour immersion splitting strength test is usually used for evaluation, but the existing specification evaluation sets this standard relatively low, and almost all mixtures can meet the requirements, which weakens the screening and differentiation function of this indicator to a certain extent. Therefore, scientifically and rationally evaluating the comprehensive impact of the service environment, especially temperature and moisture, on the performance of cold recycled mixtures is a difficult problem that needs to be solved urgently in current research.

[0004] Taking into account that the impact of rain is smaller in some areas and the temperature factor occupies a greater weight in the mixture performance, a method for determining the amount of asphalt in cold raw mixture based on the comprehensive effect of ambient temperature is developed, especially for areas where temperature weight is dominant. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the amount of asphalt in a cold recycled mixture taking into account the comprehensive effect of ambient temperature, so as to more accurately evaluate and optimize the performance characteristics of the cold recycled mixture under different temperature conditions, thereby improving the durability and reliability of road engineering.

[0006] To achieve the above object, the present invention provides a method for determining the amount of asphalt in a cold recycled mixture taking into account the comprehensive effect of ambient temperature, comprising the following steps: S1. Obtaining recycled asphalt material RAP, drying the RAP, screening it, and classifying it according to particle size; S2. Compounding the RAP materials of each grade, combining the upper and lower limits of the recycled asphalt mixture gradation, to obtain the mixture gradation; S3, determine the optimum moisture content OWC of the cold recycled mixture; S4. Based on the composition of cold recycled mixture, the optimal water content OWC and actual experience, the range of emulsified asphalt is preliminarily determined, cold recycled mixtures with different emulsified asphalt dosages are formed, test pieces are prepared, and curing is performed; S5, testing the test piece formed in step S4 and obtaining the test result; S6. Process the test results; based on the road performance requirements of the application area, determine the importance of the intersection of the test results in the performance balance test, and determine the optimal recommended amount of emulsified asphalt under the effect of ambient temperature based on the degree of importance; S7. Prepare Marshall specimens and cure them according to the determined mixture gradation, OWC and OEC to verify the water stability of the cold recycled mixture and determine the rationality of OEC. If it is inappropriate, return to S4 for design.

[0007] Preferably, in S3, in S3, different masses of water are added according to the mixture gradation determined in S2 to form cold recycled mixtures with different moisture contents; The dry density of cold recycled mixtures with different moisture contents was measured experimentally, and the optimal moisture content OWC of cold recycled mixtures was determined.

[0008] Preferably, in S3, the optimal moisture content is the moisture content corresponding to the maximum dry density.

[0009] Preferably, in S4, the test specimens include rutting plates, Marshall test specimens and beam test specimens.

[0010] Preferably, in S5, the tests include a high temperature stability test (rutting test), a medium temperature fatigue bending test (IEADL CT test) and a low temperature cracking resistance test (three-point bending beam test).

[0011] Preferably, in S5, the test results include, The test result obtained from the high temperature stability test is the dynamic stability DS, DS ≥ 2000 times; (1); Where, DS is the dynamic stability of asphalt mixture (times / mm); d 1 corresponds to the deformation at time t1 (mm); d 2 corresponds to time t 2. Deformation (mm); C 1 is the test machine type coefficient, and the crank-connecting rod drives the loading wheel to run back and forth, which is 1.0; C 2 is the specimen coefficient, and the specimen with a width of 300 mm prepared in the laboratory is 1.0; N The reciprocating rolling speed of the test wheel is usually 42 times / min.

[0012] The test result of the medium temperature fatigue bending test is the crack resistance index CT index (2); Where: is the fracture energy (J·m-2); D is the specimen diameter (mm); t is the specimen thickness (mm); is the displacement at 75% peak force (mm); m 75 is the slope of the load-displacement curve at 75% peak force (N·m -1 ).

[0013] The test result of low temperature crack resistance is the ultimate bending tensile strain με (3); Where: ε B is the bending-tensile strain at the bottom of the specimen beam (µε); h is the height of the test piece across the interruption (mm); L is the span of the specimen (mm); d is the mid-span deflection of the specimen that changes with time during loading (mm).

[0014] Preferably, in S6, processing the test results includes The dynamic stability DS, crack resistance index CT index and ultimate bending strain µε are normalized.

[0015] Preferably, in S6, based on the road performance requirements of the application area, the importance of the intersection of the test results in the performance balance test is determined, and the optimal recommended amount of emulsified asphalt under the effect of ambient temperature OEC is determined in combination with the importance, including The emulsified asphalt content corresponding to the intersection of DS and CT index is taken as OEC1 in high temperature areas; the emulsified asphalt content corresponding to the intersection of DS and µε is taken as OEC2 in cold areas.

[0016] Preferably, in S7, a freeze-thaw splitting TSR test is used to verify the water stability of the cold recycled mixture.

[0017] (4); Where: TSR is the freeze-thaw splitting test strength ratio (%); R T1 is the average splitting tensile strength of effective specimens after freeze-thaw cycles (MPa); R T2 is the average splitting tensile strength of valid specimens without freeze-thaw cycles (MPa).

[0018] Therefore, the present invention adopts the above-mentioned method for determining the amount of asphalt in cold recycled mixture considering the comprehensive effect of ambient temperature, and the technical effects are as follows: (1) The present invention comprehensively considers the effects of high, medium and low temperatures on asphalt pavement, in order to preliminarily determine the optimal emulsified asphalt dosage OEC by balancing the high, medium and low temperature performance of the cold recycled pavement, and then conducts water stability verification to finally determine the OEC of the cold recycled mixture.

[0019] (2) The cold recycled mixture mix design method determined by the present invention is more suitable for areas with large temperature changes and extreme temperatures. It can ensure the road performance of the cold recycled mixture and reduce the risk of later pavement diseases. It is a highly innovative method for determining the cold recycled mixture mix design method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of the method for determining the amount of asphalt for cold raw mixture considering the comprehensive effect of ambient temperature of the present invention; Figure 2 is a gradation curve diagram of the cold recycled mixture in an embodiment of the present invention; Figure 3 This is a curve diagram of the optimum moisture content of the cold recycled mixture in the embodiment of the present invention; Figure 4 This is a relationship diagram between the dynamic stability DS of the cold recycled mixture and the asphalt-stone ratio in an embodiment of the present invention; Figure 5 This is a relationship diagram between the CT index and the asphalt-stone ratio of the cold recycled mixture in the embodiment of the present invention; Figure 6 : is a relationship diagram between the ultimate bending tensile strain µε and the asphalt-stone ratio of the cold recycled mixture in the embodiment of the present invention; Figure 7 The OEC diagram of cold recycled mixture determined based on the comprehensive effect of ambient temperature in the embodiment of the present invention; Figure 8 The OEC diagram of the cold recycled mixture is determined based on the existing standard design method in the comparative example of the present invention. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0022] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0023] Embodiment 1 like Figure 1 As shown, the method for determining the amount of asphalt used in the cold raw mixture considering the comprehensive effect of ambient temperature is as follows: Step 1: Preliminary completion of gradation design The target gradation of this embodiment is AC-20, and full dosage RAP is used, cement and mineral powder are added, and the gradation design is shown in Table 1 and Figure 2 shown.

[0024] Table 1 Cold recycled mixture gradation design results ;

[0025] Step 2: RAP is dried and screened according to the determined grading design In this embodiment, the milling material of the upper layer of a highway is used, and the original gradation of the old RAP material is ATB-30, which is divided into two grades: coarse RAP (16-30 mm) and fine RAP (0-16 mm). The RAP material is screened according to the target gradation determined in step 1.

[0026] Step 3: Determine the optimal moisture content OWC of cold recycled mixture In this example, a heavy compaction test is used to determine OWC. According to the specification, the recommended cement content is 1.5% and the emulsified asphalt content is 3.5%. The moisture content ranges from 3% to 6%, and the moisture content is changed by 0.5% step to form 7 groups of cold recycled mixtures. The moisture content corresponding to the maximum dry density is the OWC. The optimal moisture content determined in the example is 4.5%. The experimental results are as follows Figure 3 shown.

[0027] Step 4: Determine the optimal amount of emulsified asphalt (OEC) This example considers the comprehensive effect of ambient temperature to determine OEC. The amount of external water is kept unchanged at 4.5%, and the emulsified asphalt dosage is 3%, 3.5%, 4%, 4.5%, and 5% respectively, to form 5 groups of cold recycled mixtures. According to the current specifications, Marshall specimens, rutting plates and beam specimens are prepared and cured, and the 5 groups of specimens are subjected to void ratio, high temperature rutting test, IDEAL-CT test, and low temperature beam cracking test. Based on the determined OWC, Marshall specimens, rutting plates and beam specimens are formed according to the target gradation. The method is as follows: (1) Form at least 5 groups of cold recycled mixtures, and change the emulsified asphalt dosage in steps of 0.5%; (2) Prepare Marshall specimens and cure them in accordance with the Technical Specifications for Regeneration of Highway Asphalt Pavement; and mold rutting plates and beam specimens in accordance with the Test Procedures for Asphalt and Asphalt Mixtures for Highway Engineering; (3) The wax sealing method was used to test the bulk relative density of the specimens, and the vacuum method was used to test the maximum theoretical density of each group of mixtures. The porosity of five groups of recycled mixture specimens with different emulsified asphalt dosages was calculated to ensure that the void ratio was controlled within 8% to 13%.

[0028] Conduct high temperature rutting test and three-point beam bending test according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering", and conduct IDEAL-CT test according to ASTM D8225; The performance test results of the five groups of specimens are shown in Table 2. Based on the results in Table 2, a relationship diagram between the dynamic stability DS of the cold recycled mixture and the asphalt-stone ratio was drawn (see Figure 4 ), the relationship between the cold recycled mixture crack resistance index CT index and the asphalt-stone ratio (see Figure 5 ), the relationship between the ultimate bending strain µε of cold recycled mixture and the asphalt-stone ratio (see Figure 6 ).

[0029] Table 2 Experimental results of various performance indicators of cold recycled mixture under different emulsified asphalt dosages ;

[0030] According to the technical requirements in Table 2, the dynamic stability DS, crack resistance index CT index and ultimate bending strain µε that meet the requirements of the specification are normalized (see Figure 7 ).like Figure 7 As shown in the figure, the amount of emulsified asphalt corresponding to the intersection of dynamic stability DS and crack resistance index CT index is taken as the OEC1 of cold recycled mixture in high temperature areas. At this time, OEC1=4.3%. The cold recycled mixture at this amount has both excellent high-temperature rutting resistance and medium-temperature fatigue cracking resistance; the amount of emulsified asphalt corresponding to the intersection of dynamic stability DS and ultimate bending tensile strain µε is taken as the OEC2 of cold recycled mixture in cold areas. At this time, OEC2=4.5%. This content is the optimal balance point between dynamic stability and ultimate bending tensile strain of cold recycled mixture. Compared with OEC1, a slightly higher asphalt dosage significantly improves the fatigue resistance and low-temperature cracking resistance of cold recycled mixture.

[0031] Step 5: Verification of cold recycled mixture ratio In this embodiment, Marshall was formed and cured according to the determined gradation design, optimal water content OWC and optimal emulsified asphalt dosage OEC, and then a freeze-thaw splitting experiment was carried out to verify the water stability of the cold recycled mixture. The experimental results are shown in Table 3.

[0032] Table 3 Test results of freeze-thaw splitting TSR of cold recycled mixture in Example ;

[0033] Comparative Example The RAP material with the same raw material source as in the example was used, the same mix ratio and construction standard were maintained, and the same emulsified asphalt was used. The cold recycled mixture mix ratio was designed according to the Technical Specifications for Highway Asphalt Pavement Regeneration, and the optimal moisture content OWC was determined to be 4.5%, and the optimal emulsified asphalt dosage OEC was determined to be 4%. The experimental results are shown in Figure 8In addition, the OWC and OEC obtained according to the examples and comparative examples were tested for high temperature stability, medium temperature fatigue resistance, low temperature crack resistance and water stability. The results are shown in Table 4.

[0034] Table 4 Experimental results of various performance indicators of cold recycled mixtures of the embodiments and comparative examples ;

[0035] As shown in Table 4, the design method of the embodiment is better than the comparative example in medium temperature fatigue cracking resistance, low temperature cracking and water stability. At the same time, although the anti-rutting performance of the embodiment is lower than that of the comparative example, it is much higher than the specification (DS ≥ 2000 times / mm) requirements and can meet the high temperature stability of the asphalt pavement. The method for determining the amount of asphalt in the cold raw mixture considering the comprehensive effect of the ambient temperature in the embodiment has the advantages of small experimental operation variability, and at the same time comprehensively considers the impact of temperature changes on the pavement, reducing the risk of late pavement disease.

[0036] Therefore, the present invention adopts the above-mentioned method for determining the amount of asphalt in cold recycled mixture taking into account the comprehensive effect of ambient temperature, which is used in areas with large temperature changes and extreme temperatures, and helps to improve the road performance of cold recycled mixture.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for determining the amount of asphalt in cold recycled mixture considering the comprehensive effect of ambient temperature, characterized in that: The following steps are involved: S1. Obtaining recycled asphalt material RAP, drying the RAP, screening it, and classifying it according to particle size; S2. Compounding the RAP materials of each grade, combining the upper and lower limits of the recycled asphalt mixture gradation, to obtain the mixture gradation; S3, determine the optimum moisture content OWC of the cold recycled mixture; S4. Based on the composition of cold recycled mixture, the optimal water content OWC and actual experience, the range of emulsified asphalt is preliminarily determined, cold recycled mixtures with different emulsified asphalt dosages are formed, test pieces are prepared, and curing is performed; S5, testing the test piece formed in step S4 and obtaining the test result; S6. Process the test results; Based on the road performance requirements of the application area, determine the importance of the intersection of the test results in the performance balance test, and combine the importance to determine the optimal recommended amount of emulsified asphalt under the effect of ambient temperature OEC, including The emulsified asphalt content corresponding to the intersection of DS and CT index is taken as OEC1 in high temperature areas; the emulsified asphalt content corresponding to the intersection of DS and µε is taken as OEC2 in cold areas; S7. Prepare Marshall specimens and cure them according to the determined mixture gradation, OWC and OEC to verify the water stability of the cold recycled mixture and determine the rationality of OEC. If it is inappropriate, return to S4 for design.

2. The method for determining the amount of asphalt in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S3, according to the mixture gradation determined in S2, different masses of water are added to form cold recycled mixtures with different moisture contents; The dry density of cold recycled mixtures with different moisture contents was measured experimentally, and the optimal moisture content OWC of cold recycled mixtures was determined.

3. The method for determining the amount of asphalt in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S3, the optimum moisture content is the moisture content corresponding to the maximum dry density.

4. The method for determining the amount of asphalt in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S4, the specimens include rutting plates, Marshall specimens and beam specimens.

5. The method for determining the amount of asphalt used in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S5, the tests include high temperature stability test, medium temperature fatigue bending test and low temperature cracking resistance test.

6. The method for determining the amount of asphalt used in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S5, the test results include: the test result obtained from the high temperature stability test is the dynamic stability DS; The test result obtained from the medium temperature fatigue bending test is the crack resistance index CT index; The test result of low temperature crack resistance is the ultimate bending tensile strain με.

7. The method for determining the amount of asphalt used in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S6, the processing test results include The dynamic stability DS, crack resistance index CT index and ultimate bending strain µε are normalized.

8. The method for determining the amount of asphalt used in cold recycled mixture considering the comprehensive effect of ambient temperature according to claim 1 is characterized in that: In S7, freeze-thaw splitting TSR test was used to verify the water stability of cold recycled mixture.

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