Preparation method and application of hot-mixed RAP recycled asphalt mixture

Abstract

The invention provides a preparation method and application of a hot-mixed RAP recycled asphalt mixture. The preparation method comprises the following steps: (1) crushing and recycling RAP materials, screening to obtain two grades of RAP materials, namely an RAP coarse material and an RAP fine material, and then respectively detecting the RAP coarse material and the RAP fine material; (2) determining the technical indexes of the asphalt, the aggregate and the mineral powder, and mixing the raw materials; and (3) respectively preheating the asphalt, the RAP material, the mineral powder and the aggregate, preliminarily stirring and mixing the RAP material, the aggregate and the mineral powder, adding the asphalt, and stirring and mixing again to obtain the hot-mixed RAP recycled asphalt mixture. According to the method, the recycled RAP material under the municipal road complex material source condition can be comprehensively and accurately evaluated, it is guaranteed that when the mixing amount of the RAP material in the hot-mixed RAP recycled asphalt mixture reaches 30% or even 40%, stable performance can be achieved, and additives such as a regenerant and a warm mixing agent do not need to be additionally used; and the stable high mixing amount of the RAP material of the recycled asphalt mixture product under the municipal complex material source is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt pavement materials, and in particular to a preparation method of a hot-mix RAP recycled asphalt mixture and application thereof. Background Art

[0002] As the urban roads and highways built in the early stage gradually enter the maintenance period, the task of road maintenance and repair increases, which brings two problems: First, the road maintenance and repair process requires raw materials such as stone and asphalt, especially a large amount of funds are needed every year to purchase asphalt, and the demand for stone requires quarrying, which has an adverse impact on the environment. Second, a large amount of waste asphalt pavement materials (Reclaimed Asphalt Pavement, RAP) are generated during the maintenance and repair of roads. If these RAP materials cannot be handled in time and are simply discarded and piled up, they will not only occupy land resources and affect the ecological environment, but also if these RAP materials cannot be used in the process of road maintenance and renovation and expansion, the stone and asphalt in the RAP materials will be wasted, increasing the cost of road maintenance and construction, which is also a great waste of increasingly depleted natural resources.

[0003] Therefore, the research on how to use a certain proportion of RAP materials in fresh asphalt mixtures and use RAP materials to reduce road maintenance and construction costs, save resources, reduce environmental pollution and land occupation, and asphalt pavement recycling technology has become one of the hot research directions of scientific and technological workers. The recycling of RAP materials can also effectively alleviate the pressure and crisis of the increasing shortage of natural resources such as stone and petroleum asphalt, and has significant economic, social and environmental benefits.

[0004] Factory-mixed hot recycling technology is a relatively early and relatively mature method for regenerating old pavements. It is also the most widely used recycling technology in urban road asphalt pavements in my country and can be used for various grades of asphalt pavements. Factory-mixed hot recycling refers to the recycling of old asphalt pavement materials through milling and other devices, and transporting them to the asphalt mixture mixing plant. After pre-treatment such as crushing and screening, they are mixed with new coarse and fine aggregates, new asphalt, added regeneration agents (if necessary), mineral powder, etc. according to a certain RAP material blending ratio to produce hot recycled asphalt mixture that meets the requirements, and then paved on the asphalt pavement.

[0005] RAP recycled from highways mainly comes from major or medium-sized repairs or renovation and expansion projects of high-grade highways such as expressways, national and provincial trunk roads. Due to the large recycling volume, stable performance indicators, and the fact that highway requirements are generally higher than municipal roads, RAP has better quality and greater recycling value; municipal road RAP mostly comes from maintenance projects of urban roads (such as main roads and secondary roads). Due to the complexity of municipal roads, the differences in mixture types are large, and the single batch recycling volume is small, it is easy to cause RAP performance indicators to have large variability and be difficult to control. Domestically, the amount of RAP is usually controlled between 20% and 45%, but due to the large differences in RAP performance, additives are usually required to ensure stable performance, especially under the complex material source conditions of municipal roads. This problem is more prominent. Construction authorities in some regions require that the amount of RAP be reduced as much as possible or even prohibit the use of RAP. Summary of the invention

[0006] In view of this, the present invention proposes a preparation method and application of hot-mix RAP recycled asphalt mixture. The present invention aims at the complex material source conditions of municipal roads. By controlling various technical indicators of RAP materials and adopting appropriate recycled asphalt mixture raw material ratios, the dosage of RAP materials in densely mixed asphalt mixtures can be effectively increased without the need for additives such as regeneration agents, which is also beneficial to the overall quality control of pavement engineering and ensures that the recycled asphalt mixture meets the road performance requirements after being used in municipal roads.

[0007] The technical solution of the present invention is achieved in this way: A method for preparing a hot mix RAP recycled asphalt mixture comprises the following steps: (1) The RAP material is crushed and recovered, and after recovery, it is sieved through a sieve to obtain two grades of RAP material, namely, RAP coarse material and RAP fine material. The two grades of RAP material are tested respectively to determine the technical index requirements of the two grades of RAP material and the coefficient of variation index requirements of the corresponding technical indicators; (2) Determine the technical indicators of asphalt, aggregate and mineral powder, and prepare the raw materials; (3) Preheat the asphalt to 150°C; preheat the RAP material to 140°C; preheat the mineral powder and aggregate to 190°C respectively, then preliminarily stir and mix the RAP material, aggregate and mineral powder for 15 to 20 seconds, then add the asphalt and stir and mix again for 40 to 60 seconds to obtain a hot-mix RAP recycled asphalt mixture.

[0008] Furthermore, when the RAP material is recycled, single-layer recycling is performed, that is, only the upper layer or the middle layer is recycled, or both the upper and middle layers are recycled.

[0009] Furthermore, the objects of technical indicator testing of the two grades of RAP materials are RAP materials, RAP recycled asphalt and RAP aggregates; among them, the technical indicators of RAP materials are asphalt content, moisture content, nominal maximum particle size, and impurity content; the technical indicators of RAP recycled asphalt are 25°C needle penetration and asphalt softening point; the technical indicators of RAP aggregates are relative apparent density, bulk relative density, water absorption, adhesion, crushing value, needle-like shape, and mud content.

[0010] Furthermore, the technical indicators of the two grades of RAP materials are tested as follows:

[0011] Furthermore, among the technical indicators of the two grades of RAP materials, asphalt content and asphalt softening point are the core indicators, and the coefficient of variation of asphalt content and asphalt softening point are required to be ≤5%; moisture content, needle penetration at 25℃, needle-like shape, and crushing value are the main indicators, and the coefficient of variation of moisture content, needle penetration at 25℃, and needle-like shape are required to be ≤10%, and the coefficient of variation of crushing value is required to be ≤8%; mud content and debris content are the secondary indicators, and the coefficient of variation of mud content and debris content is required to be controlled at 14%~16%.

[0012] Furthermore, the sampling requirements for RAP materials used for testing are as follows: the recycled RAP materials are recycled and piled according to different particle size specifications of coarse aggregate, medium aggregate and fine aggregate. Different material sources or batches need to be sampled separately. The number of test samples is not less than 5 times. When sampling, the unrepresentative layer of 15~25cm on the surface of the recycled RAP material pile with different particle sizes is removed separately. Samples are taken from at least 9 points in different directions at the top, middle and bottom of the pile. More than 10kg of samples are sampled at each point. After being mixed evenly, they are used as test samples for testing.

[0013] Furthermore, the aggregate is divided into five grades: 16-22mm aggregate, 11-16mm aggregate, 6-11mm aggregate, 3-6mm aggregate, and 0-3mm aggregate. It is mainly used to form medium-grained densely mixed asphalt mixture, that is, conventional asphalt mixture for upper and middle surface layer construction.

[0014] Furthermore, with an aperture of 4.75 mm as the key sieve aperture, the passing rate of the RAP coarse material > 4.75 mm is > 60%; the passing rate of the RAP fine material ≤ 4.75 mm is > 60%.

[0015] Furthermore, the asphalt preheating temperature is 150-170°C; the RAP material preheating temperature is 140-160°C; the mineral powder preheating temperature is 180-190°C; and the aggregate preheating temperature is 180-190°C.

[0016] Furthermore, the time for the initial stirring and mixing is 15 to 20 seconds, and the time for the secondary stirring and mixing is 40 to 60 seconds.

[0017] Furthermore, the mineral raw materials, calculated by weight percentage, include 0% to 40% RAP coarse material, 0% to 40% RAP fine material, 40% to 85% aggregate, 1% to 4% mineral powder, and all mineral raw materials total 100%; the blending mass of the asphalt is 3% to 5% of the mass of the mineral raw materials.

[0018] Furthermore, the aggregate, calculated by weight percentage of the mineral raw materials, includes 5% to 30% aggregate with a particle size of 0-3mm, 5% to 20% aggregate with a particle size of 3-6mm, 8% to 20% aggregate with a particle size of 6-11mm, 10% to 30% aggregate with a particle size of 11-16mm, and 0% to 20% aggregate with a particle size of 16-22mm.

[0019] Application of the hot-mix RAP recycled asphalt mixture prepared by the preparation method of the present invention in road construction.

[0020] Furthermore, the asphalt is 70# asphalt; and the aggregate is limestone.

[0021] Furthermore, the RAP of the present invention refers to waste asphalt pavement material.

[0022] Compared with the prior art, the present invention has the following beneficial effects: The present invention selects RAP material, RAP recycled asphalt and RAP aggregate as detection objects for the recycled RAP material, and correspondingly detects technical indicators such as asphalt content, moisture content, 25°C needle penetration, asphalt softening point, crushing value, needle-like shape, mud content, etc., as well as the variation coefficient requirements for controlling the corresponding technical indicators. The present invention can make a relatively comprehensive and accurate evaluation of the RAP material recycled under the conditions of complex material sources for municipal roads, and ensure that the RAP material content in the hot-mix RAP recycled asphalt mixture reaches 30% or even 40%. It can have a relatively stable performance, and there is no need to additionally use additives such as regeneration agents and warm mix agents, so as to effectively improve the stable high content of RAP material in the recycled asphalt mixture products under the conditions of complex municipal material sources.

[0023] The present invention selects suitable asphalt, RAP coarse material, RAP fine material, mineral powder and aggregate for use and controls the particle sizes of the RAP coarse material, RAP fine material, mineral powder and aggregate, so that the various raw materials can be more fully integrated and the bonding force between the raw material components can be improved, thereby effectively improving the various performances of the hot-mix RAP recycled asphalt mixture used in road construction and effectively improving the recycling and reuse of RAP materials.

[0024] The hot-mix RAP recycled asphalt mixture prepared by the present invention has good overall construction performance in the test process without adding a regeneration agent, the temperature during the paving process is appropriate, and the road surface is flat and has no obvious defects after paving. Its technical indicators such as compaction degree, friction coefficient, water permeability coefficient, structural depth and flatness all meet the requirements of the specifications, and no appearance defects and diseases are found, and the use effect is good. DETAILED DESCRIPTION

[0025] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0026] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0027] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0028] The raw material information of the present invention is as follows:

[0029] The aggregate is limestone.

[0030] The corresponding index tests of the RAP coarse material and the RAP fine material of the present invention are carried out in accordance with the "Technical Specifications for Highway Asphalt Pavement Regeneration" (JTG / T 5521-2019).

[0031] Example 1 A method for preparing a hot mix RAP recycled asphalt mixture comprises the following steps: (1) RAP materials are crushed and recycled, and then sieved through a sieve to obtain two grades of RAP materials, namely, RAP coarse material and RAP fine material. The two grades of RAP materials are tested for technical indicators respectively to determine the technical indicator requirements of the two grades of RAP materials and the coefficient of variation indicator requirements of the corresponding technical indicators, which serve as the basis for evaluating the feasibility of RAP recycling; The sampling requirements for RAP materials used for testing are as follows: the recycled RAP materials shall be recycled and piled according to different particle sizes of coarse aggregate, medium aggregate and fine aggregate. Different material sources or batches shall be sampled separately. The number of test samples shall be no less than 5 times. When sampling, the non-representative layer of 15~25cm on the surface of the pile of recycled RAP materials with different particle sizes shall be removed respectively. Samples shall be taken from at least 9 points in different directions at the top, middle and bottom of the pile. Each point shall be sampled with more than 10kg. After being mixed evenly, they shall be used as test samples for testing. Among them, the test objects, technical indicators, test methods, technical indicator requirements, coefficient of variation requirements and test standards of the two grades of recycled RAP materials are shown in the following table: Table 1 RAP material testing performance requirements

[0032] (2) Determine the technical indicators of asphalt, aggregate, and mineral powder, and prepare the raw materials according to the technical indicator test results of the RAP material in step (1); Among them, the technical indicators of asphalt are shown in the following table: Table 2 Asphalt technical indicators

[0033] The technical indicators of aggregate and mineral powder are shown in the following table: Table 3 Technical indicators of aggregate and mineral powder

[0034] Take 4.75mm aperture as the key sieve hole; the passing rate of RAP coarse material>4.75mm is>60%; the passing rate of RAP fine material ≤4.75mm is>60%; the particle size distribution of the mineral material is shown in the following table: Table 4 Particle size distribution of ore materials

[0035] The technical indicators and coefficient of variation of the RAP coarse material and RAP fine material all meet the requirements of Table 1, among which, the asphalt content is 4.1%, the impurity content is 0.41%, the needle penetration is 46.66 (0.1mm), the softening point is 59.19℃, the moisture content is 1.43%, the crushing value is 13.15%, and the needle-like shape is 7.93%; the mineral raw materials are calculated by weight percentage, including: the proportion of aggregates with a particle size of 0-3mm is 11%, the proportion of aggregates with a particle size of 3-6mm is 7%, the proportion of aggregates with a particle size of 6-11mm is 15%, the proportion of aggregates with a particle size of 11-16mm is 17%, the proportion of aggregates with a particle size of 16-22mm is 18%, the proportion of RAP coarse material is 15%, the proportion of RAP fine material is 15%, and the proportion of mineral powder is 2%; the amount of asphalt is 4.05% of the mass of the mineral raw materials; (3) Preheat the asphalt to 150°C, the RAP material to 140°C, the mineral powder and aggregate to 190°C respectively, then preliminarily stir and mix the RAP material, aggregate and mineral powder for 15 seconds, then add the asphalt and stir and mix again for 50 seconds to obtain a hot-mix RAP recycled asphalt mixture.

[0036] The hot mix RAP recycled asphalt mixture prepared in this embodiment was tested for performance according to the corresponding test methods of JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction" and JTG E20-2011 "Test Procedures for Asphalt-Based Asphalt Mixtures for Highway Engineering", and the results are shown in the following table.

[0037] Table 5 Performance measurement of hot mix RAP recycled asphalt mixture in Example 1

[0038] The above results show that, through the reasonable proportion of various raw materials and the preparation method in this embodiment, various performance test results of the prepared hot mix RAP recycled asphalt mixture can meet the specification requirements.

[0039] Example 2 A method for preparing a hot mix RAP recycled asphalt mixture comprises the following steps: (1) The RAP material is crushed and recycled, and after recycling, it is sieved through a sieve to obtain two grades of RAP material, namely, RAP coarse material and RAP fine material. The technical index requirements of the two grades of RAP material and the coefficient of variation index requirements of the corresponding technical indicators are determined as the basis for evaluating the feasibility of RAP recycling; The sampling requirements for RAP materials used for testing are as follows: the recycled RAP materials shall be recycled and piled according to different particle sizes of coarse aggregate, medium aggregate and fine aggregate. Different material sources or batches shall be sampled separately. The number of test samples shall be no less than 5 times. When sampling, the non-representative layer of 15~25cm on the surface of the pile of recycled RAP materials with different particle sizes shall be removed respectively. Samples shall be taken from at least 9 points in different directions at the top, middle and bottom of the pile. Each point shall be sampled with more than 10kg. After being mixed evenly, they shall be used as test samples for testing. Among them, the detection objects, technical indicators, detection methods, technical indicator requirements, coefficient of variation requirements and detection standards of the two grades of RAP materials recovered are the same as those in Table 1 of Example 1; (2) Determine the technical indicators of asphalt, aggregate, and mineral powder, and prepare the raw materials according to the technical indicator test results of the RAP material in step (1); Among them, the technical indicators of asphalt, aggregate, and mineral powder are the same as those in Table 2 and Table 3 of Example 1, respectively, with a 4.75 mm aperture as the key sieve aperture; the passing rate of the RAP coarse material>4.75 mm is>60%; the passing rate of the RAP fine material ≤4.75 mm is>60%; the particle size distribution of the mineral material is the same as that in Table 4 of Example 1; The technical indicators and coefficient of variation of the RAP coarse material and RAP fine material all meet the requirements of Table 1 of Example 1, wherein the asphalt content is 4.1%, the impurity content is 0.41%, the needle penetration is 46.66 (0.1mm), the softening point is 59.19°C, the moisture content is 1.43%, the crushing value is 13.15%, and the needle-like shape is 7.93%; the mineral raw materials, by weight percentage, include: the proportion of aggregates with a particle size of 0-3mm is 7%, the proportion of aggregates with a particle size of 3-6mm is 5%, the proportion of aggregates with a particle size of 6-11mm is 14%, the proportion of aggregates with a particle size of 11-16mm is 15%, the proportion of aggregates with a particle size of 16-22mm is 18%, the proportion of RAP coarse material is 20%, the proportion of RAP fine material is 20%, and the proportion of mineral powder is 1%; the amount of asphalt used is 4.13% of the mass of the mineral raw materials; (3) Preheat the asphalt to 160°C, the RAP material to 150°C, the mineral powder and aggregate to 180°C respectively, then preliminarily stir and mix the RAP material, aggregate and mineral powder for 20 seconds, then add the asphalt and stir and mix again for 45 seconds to obtain a hot-mix RAP recycled asphalt mixture.

[0040] The hot mix RAP recycled asphalt mixture prepared in this embodiment was tested for performance according to the corresponding test methods of JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction" and JTG E20-2011 "Test Procedures for Asphalt-Based Asphalt Mixtures for Highway Engineering", and the results are shown in the following table.

[0041] Table 6 Performance measurement of hot mix RAP recycled asphalt mixture in Example 2

[0042] The above results show that, through the reasonable proportion of various raw materials and the preparation method in this embodiment, various performance test results of the prepared hot mix RAP recycled asphalt mixture can meet the specification requirements.

[0043] Example 3 A method for preparing a hot mix RAP recycled asphalt mixture comprises the following steps: (1) The RAP material is crushed and recycled, and after recycling, it is sieved through a sieve to obtain two grades of RAP material, namely, RAP coarse material and RAP fine material. The technical index requirements of the two grades of RAP material and the coefficient of variation index requirements of the corresponding technical indicators are determined as the basis for evaluating the feasibility of RAP recycling; (2) The sampling requirements for RAP materials used for testing are as follows: the recycled RAP materials shall be recycled and piled according to different particle sizes of coarse aggregate, medium aggregate and fine aggregate. Different material sources or batches shall be sampled separately. The number of test samples shall be no less than 5 times. When sampling, the non-representative layer of 15~25cm on the surface of the pile of recycled RAP materials with different particle sizes shall be removed respectively. Samples shall be taken from at least 9 points in different directions at the top, middle and bottom of the pile. Each point shall be sampled with more than 10kg. After being mixed evenly, they shall be used as test samples for testing; Among them, the detection objects, technical indicators, detection methods, technical indicator requirements, coefficient of variation requirements and detection standards of the two grades of RAP materials recovered are shown in Table 1 of Example 1; (2) Determine the technical indicators of asphalt, aggregate, and mineral powder, and prepare the raw materials according to the technical indicator test results of the RAP material in step (1); Among them, the technical indicators of asphalt are shown in the following table: Table 7 Asphalt technical indicators

[0044] The technical indicators of aggregate and mineral powder are shown in the following table: Table 8 Technical indicators of aggregate and mineral powder

[0045] Take 4.75mm aperture as the key sieve hole; the passing rate of RAP coarse material>4.75mm is>60%; the passing rate of RAP fine material ≤4.75mm is>60%; the particle size distribution of the mineral material is shown in the following table: Table 9 Particle gradation of ore materials

[0046] The technical indicators and coefficient of variation of the RAP coarse material and RAP fine material meet the requirements of Table 1, among which the asphalt content is 4.1%, the debris content is 0.60%, the needle penetration is 48.19 (0.1mm), the softening point is 53.12℃, the moisture content is 1.07%, the crushing value is 12.08%, and the needle-like shape is 8.59%. The mineral raw materials are calculated by weight percentage, including: 21% of the aggregate with a particle size of 0-3mm, 9% of the aggregate with a particle size of 3-6mm, and 6-11 The proportion of mm aggregate is 15%, the proportion of 11-16mm aggregate is 23%, the proportion of RAP fine material is 30%, and the proportion of mineral powder is 2%; the amount of asphalt is 4.90% of the mass of the mineral raw material; the asphalt is preheated to 170℃, the RAP material is preheated to 150℃, the mineral powder and aggregate are preheated to 180℃ respectively, and then the RAP material, aggregate and mineral powder are preliminarily stirred and mixed for 15s, and then the asphalt is added and stirred and mixed again for 50s to obtain a hot-mixed RAP recycled asphalt mixture.

[0047] The hot mix RAP recycled asphalt mixture prepared in this embodiment was tested for performance according to the corresponding test methods of JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction" and JTG E20-2011 "Test Procedures for Asphalt-Based Asphalt Mixtures for Highway Engineering", and the results are shown in the following table.

[0048] Table 10 Performance measurement of hot mix RAP recycled asphalt mixture in Example 3

[0049] The above results show that, through the reasonable proportion of each raw material and the preparation method in this embodiment, the various performance test results of the prepared hot mix RAP recycled asphalt mixture also meet the specification requirements.

[0050] Example 4 A method for preparing a hot mix RAP recycled asphalt mixture comprises the following steps: (1) The RAP material is crushed and recycled, and after recycling, it is sieved through a sieve to obtain two grades of RAP material, namely, RAP coarse material and RAP fine material. The technical index requirements of the two grades of RAP material and the coefficient of variation index requirements of the corresponding technical indicators are determined as the basis for evaluating the feasibility of RAP recycling; The sampling requirements for RAP materials used for testing are as follows: the recycled RAP materials shall be recycled and piled according to different particle sizes of coarse aggregate, medium aggregate and fine aggregate. Different material sources or batches shall be sampled separately. The number of test samples shall be no less than 5 times. When sampling, the non-representative layer of 15~25cm on the surface of the pile of recycled RAP materials with different particle sizes shall be removed respectively. Samples shall be taken from at least 9 points in different directions at the top, middle and bottom of the pile. Each point shall be sampled with more than 10kg. After being mixed evenly, they shall be used as test samples for testing. Among them, the detection objects, technical indicators, detection methods, technical indicator requirements, coefficient of variation requirements and detection standards of the two grades of RAP materials recovered are the same as those in Table 1 of Example 1; (2) Determine the technical indicators of asphalt, aggregate, and mineral powder and prepare the raw materials according to the technical indicator test results of the RAP material in step (1); Among them, the technical indicators of asphalt, aggregate, and mineral powder are the same as those in Table 7 and Table 8 of Example 3, respectively, with a 4.75 mm aperture as the key sieve aperture; the partial pass rate of RAP coarse material>4.75 mm>60%; the partial pass rate of RAP fine material ≤4.75 mm>60%; the particle size distribution of the mineral material is the same as that in Table 9 of Example 3; The technical indicators and coefficient of variation of the RAP coarse material and RAP fine material all meet the requirements of Table 1 of Example 1, wherein the asphalt content is 4.1%, the debris content is 0.60%, the needle penetration is 48.19 (0.1mm), the softening point is 53.12°C, the moisture content is 1.07%, the crushing value is 12.08%, and the needle-like shape is 8.59%; the mineral raw materials, calculated by weight percentage, include: the proportion of aggregate with a particle size of 0-3mm is 26%, the proportion of aggregate with a particle size of 3-6mm is 17%, and the proportion of aggregate with a particle size of 6 -11mm aggregate proportion is 10%, 11-16mm aggregate proportion is 25%, RAP fine material proportion is 20%, mineral powder proportion is 2%; the asphalt dosage is 4.93% of the mineral raw material mass; the asphalt is preheated to 160℃, the RAP material is preheated to 160℃, the mineral powder and aggregate are preheated to 190℃ respectively, and then the RAP material, aggregate and mineral powder are preliminarily stirred and mixed for 15s, and then the asphalt is added and stirred and mixed again for 60s to obtain a hot-mixed RAP recycled asphalt mixture.

[0051] The hot mix RAP recycled asphalt mixture prepared in this embodiment was tested for performance according to the corresponding test methods of JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction" and JTG E20-2011 "Test Procedures for Asphalt-Based Asphalt Mixtures for Highway Engineering", and the results are shown in the following table.

[0052] Table 11 Performance measurement of hot mix RAP recycled asphalt mixture in Example 4

[0053] The above results show that, through the reasonable proportion of each raw material and the preparation method in this embodiment, the various performance test results of the prepared hot mix RAP recycled asphalt mixture still meet the specification requirements.

[0054] Application Example 1 The hot-mix RAP recycled asphalt mixture of the present invention is a 19 mm maximum nominal particle size asphalt mixture, which is mainly used for the lower layer construction. The hot-mix RAP recycled asphalt mixture prepared in the above-mentioned examples 1 and 2 is used for the lower pavement experiment to verify the performance and use effect of the hot-mix RAP recycled asphalt mixture. The lower layer test section is selected from a city road in Hangzhou with a total length of 605 m and a total surface area of ​​12,000 m 2 The hot mix RAP recycled asphalt mixture test section prepared in Example 1 was applied to the lower layer of the northern half of the road from K0+000 to K0+200, and the hot mix RAP recycled asphalt mixture test section prepared in Example 2 was applied to the lower layer of the southern half of the road from K0+200 to K0+400. The length of both test sections was 200m, and the designed thickness of the lower layer of the test section was 60mm.

[0055] The construction equipment is as follows: 2 pavers, 2 double steel wheel rollers, 1 rubber wheel roller, and 1 small steel wheel roller. Before formal paving, the penetration oil is sprayed in advance and the synchronous crushed stone seal is spread; then the two pavers work in parallel, strictly controlling the elevation, and a dedicated person handles the paving of the asphalt mixture at the joints, manhole covers, and the side of the curb; the rolling work is divided into three processes: initial compaction, re-compacting, and final compaction. During the paving construction process, the overall appearance of the mixture is good and the temperature meets the specification requirements (the paving temperature is about 156.7℃, the initial compaction temperature is about 147.6℃, and the final compaction end temperature is about 73℃).

[0056] After the paving of the lower test section was completed, a three-month quality tracking observation was carried out, and the compaction, water permeability coefficient and flatness performance were measured on the 7th day, 1st month and 3rd month. The results are shown in the following table.

[0057] Table 12 Quality tracking observation of hot mix RAP recycled asphalt mixture in Example 1

[0058] Table 13 Quality tracking observation of hot mix RAP recycled asphalt mixture in Example 2

[0059] It can be seen from Tables 12 and 13 that the performance of the hot-mix RAP recycled asphalt mixtures prepared in Example 1 and Example 2 meets the relevant standards, and no obvious defects were found in the surface layer during the follow-up observation process, indicating that the hot-mix RAP recycled asphalt mixtures prepared in Example 1 and Example 2 are of reliable quality and the construction process is feasible.

[0060] Application Example 2 The hot-mixed RAP recycled asphalt mixtures of the present invention are asphalt mixtures with a maximum nominal particle size of 13.2 mm, which are mainly used for upper layer construction. The hot-mixed RAP recycled asphalt mixtures prepared in the above-mentioned Examples 3 and 4 are used in upper pavement experiments to verify the performance and use effect of the hot-mixed RAP recycled asphalt mixtures. The upper layer test section was selected on a road in Hangzhou City, with a total area of ​​20290m 2 The construction scale is 678m. The hot-mix RAP recycled asphalt mixture of Example 3 is used in the northern half of the test section 1 K0+200~K0+400, and the hot-mix RAP recycled asphalt mixture of Example 4 is used in the southern half of the test section 2 K0+0~K+200. The designed thickness of the upper layer is 40mm.

[0061] The on-site construction equipment for this test section includes 2 pavers, 2 double steel wheel rollers, 2 rubber wheel rollers and 1 small steel wheel roller. Before formal paving, the tack coat is sprayed in advance; then the two pavers work in parallel, strictly controlling the elevation, and a dedicated person handles the asphalt paving at the joints, manhole covers and the side of the curb; the rolling work is divided into three processes: initial compaction, re-compacting and final compaction. During the paving construction process, the overall appearance of the mixture is good and the temperature meets the requirements of the specification (paving temperature is about 165.1℃, initial compaction temperature is about 130℃, and final compaction end temperature is about 75℃). After the paving of the upper layer test section is completed, a 6-month quality tracking observation is carried out, and the compaction degree, friction coefficient, water permeability coefficient, structural depth, and flatness performance are measured. The results are shown in the following table.

[0062] Table 14 Quality tracking observation of hot mix RAP recycled asphalt mixture in Example 3

[0063] Table 15 Quality tracking observation of hot mix RAP recycled asphalt mixture in Example 4

[0064] The above results show that the hot-mix RAP recycled asphalt mixture of Example 3 and Example 4 of the present invention has good performance and reliable quality within 6 months after being used for paving the upper pavement, and the upper pavement is uniform and dense without any disease. The hot-mix RAP recycled asphalt mixture has good construction performance.

[0065] Comparative test Comparative Examples 1-4 adopt the same raw material mix ratio design scheme as Example 1, including the same asphalt, aggregate, and preparation method, except that: Comparative Example 1: Use ungraded RAP mixture, directly use original RAP material (crushed and screened), do not distinguish between coarse and fine materials, ignore the 4.75mm key sieve hole, add asphalt according to empirical values, and do not consider the actual asphalt content of the RAP material.

[0066] Comparative Example 2: RAP material without controlling the variability of the softening point of the old asphalt. RAP with different aging degrees was mixed and used, with a softening point range of 45~60℃ and a coefficient of variation of 15%, and no regeneration agent was used to adjust the asphalt properties.

[0067] Comparative Example 3: RAP material without controlling the variability of the crushing value was used, and weak particles were not removed. The fluctuation range of the crushing value detection was between 20% and 35%, and the coefficient of variation was 25%.

[0068] Comparative Example 4: RAP without controlling the variability of needle-like particles. The RAP material was not subjected to secondary crushing, and the fluctuation range of needle-like particles was between 10% and 30%, with a coefficient of variation of 40%.

[0069] The performance of the hot-mix RAP recycled asphalt mixtures prepared in Comparative Examples 1-4 was measured according to the corresponding test methods of JTG F40-2004 "Technical Specifications for Highway Asphalt Pavement Construction" and JTG E20-2011 "Test Procedures for Asphalt-Based Asphalt Mixtures for Highway Engineering", and the results are shown in the following table.

[0070] Table 16 Performance measurement of hot mix RAP recycled asphalt mixture of comparative examples 1-4

[0071] From the test results of comparative example 1, it can be seen that the use of ungraded RAP mixture resulted in a relatively low relative density and a small flow value due to the concentration of coarse materials in the specimens; the uneven grading weakened the interlocking effect between aggregates and the unsatisfactory stability; the bonding performance between asphalt and aggregates was poor, and the residual stability was significantly reduced under the action of water. In addition, due to the instability of grading, the depth of the rutting specimens at different locations was significantly different.

[0072] From the test results of comparative example 2, due to the failure to control the variability of the softening point of the old asphalt, the technical indicators of the various mixtures are not ideal, among which the stability and rutting test index data are significantly improved, but the residual stability index is poor, and the Kentaburg scattering loss increases. It can be basically judged that due to the failure to control the coefficient of variation of the asphalt softening point, the softening point of the RAP sample is larger than the test result, and the compatibility of the new and old asphalt is poor, resulting in the unsatisfactory performance of the asphalt mixture.

[0073] From the test results of comparative example 3, since the weak particles in RAP were not controlled, the stability was obviously weak, the Kentburg scattering loss increased significantly, the residual stability was lower than the technical requirements, and the flow value was greater than the relevant technical requirements. It can be basically judged that in the RAP samples that formed the mixture test pieces, the proportion of weak particles was greater than the test results, the coefficient of variation was not ideal, the weak particles destroyed the aggregate embedding structure, the stability decreased significantly, and the durability also showed obvious changes, which was reflected in the high risk of exceeding the residual stability and scattering loss.

[0074] Judging from the test results of Comparative Example 4, the stability of the mixture specimens is significantly reduced, the residual stability and asphalt saturation data are not ideal, and the rutting dynamic stability times are low. Combined with the test variables of this group, it is determined that this is caused by the excessive number of needle-like particles. The needle-like particles are easy to break, have a loose structure, weak embedding effect, insufficient shear strength, poor adhesion between flat particles and asphalt, and the peeling rate increases after water damage, indicating that the control of needle-like indicators is not ideal.

[0075] It can be seen from the above results that, compared with Example 1, the performance of the hot-mix RAP recycled asphalt mixture obtained in Comparative Examples 1-4 is reduced due to unreasonable control of RAP material indicators. This shows that after reasonable technical indicator selection and control of RAP material by the present invention, a more comprehensive and accurate evaluation of RAP material recovered under complex material source conditions of municipal roads can be carried out, ensuring that the RAP material content in the hot-mix RAP recycled asphalt mixture reaches 30% or even 40%. It can have a relatively stable performance, and there is no need to use additional additives such as regeneration agent and warm mix agent, which effectively improves the stable high content of RAP material in the recycled asphalt mixture product under complex municipal material sources.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing hot mix RAP recycled asphalt mixture, characterized in that: The following steps are involved: (1) The RAP material is crushed and recovered, and after recovery, it is sieved through a sieve to obtain two grades of RAP material, namely, RAP coarse material and RAP fine material. The technical index requirements of the two grades of RAP material and the coefficient of variation index requirements of the corresponding technical indicators are determined; (2) Determine the technical indicators of asphalt, aggregate and mineral powder, and prepare the raw materials; (3) Preheat the asphalt, RAP material, mineral powder and aggregate respectively, then stir and mix the RAP material, aggregate and mineral powder preliminarily, then add asphalt and stir and mix again to obtain a hot mix RAP recycled asphalt mixture.

2. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: When the RAP material is recycled, single-layer recycling is performed, that is, only the upper layer or the middle layer is recycled, or both the upper and middle layers are recycled.

3. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: The technical indicators of the two grades of RAP materials are tested for RAP material, RAP recycled asphalt and RAP aggregate; among them, the technical indicators of RAP material are asphalt content, moisture content, nominal maximum particle size, and impurity content; the technical indicators of RAP recycled asphalt are needle penetration at 25°C and asphalt softening point; the technical indicators of RAP aggregate are relative apparent density, bulk relative density, water absorption rate, adhesion, crushing value, needle-like shape, and mud content.

4. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: Among the technical indicators of the two-grade RAP materials, asphalt content and asphalt softening point are the core indicators, and the coefficients of variation of asphalt content and asphalt softening point are both ≤5%; moisture content, needle penetration at 25℃, needle-like shape, and crushing value are the main indicators, and the coefficients of variation of moisture content, needle penetration at 25℃, and needle-like shape are all ≤10%, and the coefficient of variation of crushing value is ≤8%; mud content and debris content are secondary indicators, and the coefficients of variation of mud content and debris content are controlled at 14%~16%.

5. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: The sampling requirements for RAP materials used for testing are as follows: the recycled RAP materials shall be recycled and piled according to different particle size specifications of coarse aggregate, medium aggregate and fine aggregate. Different material sources or batches shall be sampled separately. The number of test samples shall be no less than 5 times. When sampling, the unrepresentative layer of 15~25cm on the surface of the pile of recycled RAP materials with different particle sizes shall be removed separately. Samples shall be taken from at least 9 points in different directions at the top, middle and bottom of the pile. More than 10kg of samples shall be sampled at each point. After being mixed evenly, they shall be used as test samples for testing.

6. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: The aggregate is divided into five grades: 16-22 mm aggregate, 11-16 mm aggregate, 6-11 mm aggregate, 3-6 mm aggregate, and 0-3 mm aggregate.

7. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: The aperture of 4.75mm is taken as the key sieve hole; the passing rate of RAP coarse material>4.75mm is>60%; the passing rate of RAP fine material ≤4.75mm is>60%.

8. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: The asphalt preheating temperature is 150-170°C; the RAP material preheating temperature is 140-160°C; the mineral powder preheating temperature is 180-190°C; and the aggregate preheating temperature is 180-190°C.

9. The method for preparing hot mix RAP recycled asphalt mixture according to claim 1, characterized in that: The time for the initial stirring and mixing is 15 to 20 seconds, and the time for the secondary stirring and mixing is 40 to 60 seconds.

10. Application of the hot mix RAP recycled asphalt mixture prepared by the preparation method according to any one of claims 1 to 9 in road construction.

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