High-dosage RAP recycled asphalt mixture as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to a high-dosage RAP recycled asphalt mixture as well as a preparation method and application thereof. The high-dosage RAP recycled asphalt mixture is prepared from a waste asphalt pavement material, a regenerant XT-3, new asphalt, a new aggregate, mineral powder, fibers and a silane coupling agent KH550, the waste asphalt pavement material contains aged asphalt; and the regenerant XT-3 accounts for 16-17 wt% of the mass of the aged asphalt. The pavement performance, especially the low-temperature performance and the water stability, of the recycled asphalt mixture is improved under the condition of high-dosage RAP, meanwhile, the use scene of the RAP is expanded, and the recycled asphalt mixture can be used for subsidiary facilities of highway engineering and middle and upper surface layers.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a high-content RAP recycled asphalt mixture, its preparation method, and its application. Background Technology

[0002] Asphalt pavement is a crucial component of modern transportation systems. With the continuous expansion of asphalt pavement scale and the increasing service life of its components in my country, the amount of reclaimed asphalt pavement (RAP) is increasing year by year. The traditional method is to store it in the open, which not only causes water or soil pollution due to rainwater erosion and ultraviolet radiation, but also occupies a large amount of land resources. Furthermore, RAP storage involves maintenance expenses such as seepage prevention treatment, placing a dual burden on both the ecology and the economy. Reusing RAP can not only save on the input costs of asphalt and aggregates, but also solve environmental pollution problems. Therefore, the rational utilization of RAP has become an important measure to promote environmentally friendly roads.

[0003] In recent years, precast components made from recycled asphalt mixtures have emerged as a new approach to utilizing reclaimed asphalt (RAP) materials. The precast components are formed using plant-mixed hot recycling technology, where recycled asphalt mixture (RAP) undergoes a series of processes including crushing, screening, mixing, and pressing to produce precast components for reuse. See invention patent document CN110964336A, which discloses a recycled asphalt mixture. While this allows for the reuse of RAP, the following problems exist: the proportion of recycled asphalt pavement material (RAP) in the asphalt mixture is low, typically 20%–30% of the new base asphalt. This is because the asphalt in RAP is severely aged, and its addition significantly impacts the pavement's performance. Higher RAP content results in poor low-temperature and water stability, leading to low RAP utilization. Furthermore, most recycled asphalt mixtures formed from existing RAP are used in the lower layers, limiting the application scenarios for RAP. Summary of the Invention

[0004] To address the technical problems of low blending ratio and limited use of existing recycled asphalt pavement (RAP) materials, this invention provides a high-content RAP recycled asphalt mixture, its preparation method, and its application.

[0005] This invention utilizes 40wt% to 60wt% of waste asphalt pavement material (RAP) and shear regeneration with recycling agent XT-3; then new asphalt, new aggregates, fibers and silane coupling agent KH550 are added to form recycled asphalt mixture; the road performance of recycled asphalt mixture is improved with high RAP content, especially low temperature performance and water stability, while expanding the application scenarios of RAP. Recycled asphalt mixture can be used for highway engineering ancillary facilities and intermediate and surface layers.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A high-content RAP recycled asphalt mixture is composed of waste asphalt pavement material, recycling agent XT-3, new asphalt, new aggregate, mineral powder, fiber and silane coupling agent KH550; the waste asphalt pavement material contains aged asphalt.

[0008] The amounts of the above raw materials are as follows: waste asphalt pavement material 40wt%~60wt%, new asphalt 1.24wt%~2.66wt%; new aggregate 34.8wt%~55.7wt%; mineral powder 1.6wt%~4wt%;

[0009] The recycling agent XT-3 is 16wt% to 17wt% of the aged asphalt mass; the fiber content is 0.4wt% of the high-content RAP recycled asphalt mixture mass; and the silane coupling agent KH550 is 0.9wt% of the new asphalt mass.

[0010] Further specifying the performance indicators of regenerant XT-3: saturated content ≤30%, aromatic content >65%.

[0011] Further specifying, the fiber is basalt fiber or polyvinyl alcohol fiber.

[0012] Further specifying, the new aggregate is limestone, and the new asphalt is SBS asphalt.

[0013] A method for preparing the high-content RAP recycled asphalt mixture, the method being as follows:

[0014] S1. Heat the new asphalt to 160±5℃, then add the silane coupling agent KH550 dropwise to the new asphalt, and shear and develop to obtain modified asphalt material.

[0015] S2. After heating the waste asphalt pavement material, first add the recycling agent XT-3 to dry it, then add new aggregate and mix; then add fiber and the modified asphalt material from step S1; then add mineral powder and mix to obtain a high-content RAP recycled asphalt mixture.

[0016] Further specifying, in step S1, the shearing is performed at a rate of 1500 r / min to 3000 r / min for 30 min to 60 min.

[0017] Further specifying that in step S2, the heating is maintained at 160℃~170℃ for 1h~2h; after adding new aggregate, it is stirred at 170℃-180℃ for 90s-100s; after adding mineral powder, it is stirred again for 90s-100s.

[0018] The application of the high-content RAP recycled asphalt mixture in highway engineering ancillary facilities and intermediate and surface layers.

[0019] Further defining, highway engineering ancillary facilities include curbs, drainage channels, or drainage ditches.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention comprises a high-content RAP recycled asphalt mixture composed of waste asphalt pavement material, recycling agent XT-3, new asphalt, new aggregate, mineral powder, fiber, and silane coupling agent KH550. The waste asphalt pavement material (RAP) is recycled using recycling agent XT-3, which improves the road performance of the high-content RAP recycled asphalt mixture, especially its low-temperature performance and water stability. At the same time, it expands the application scenarios of RAP, and the recycled asphalt mixture can be used for highway engineering ancillary facilities and intermediate and surface layers.

[0022] 2. The present invention provides a regenerator XT-3, which has a saturated content of ≤30% and an aromatic content of greater than 65%. It can effectively regenerate aged asphalt in waste asphalt pavement materials (RAP), improve the performance of RAP, and enable the performance of recycled asphalt mixtures with high RAP content to meet road use requirements. It also improves the utilization rate of RAP and realizes the effective utilization of solid waste resources.

[0023] 3. By adding fibers and silane coupling agents, this invention further significantly enhances the low-temperature performance and water stability of recycled asphalt mixtures with a large amount of RAP and a low content of new asphalt.

[0024] 4. In this invention, the content of recycled asphalt pavement material (RAP) is as high as 60%. Through the action of the recycling agent, the performance of aged asphalt in RAP is improved, so that the content of new asphalt is only 1.24wt% to 2.66wt%. This greatly reduces the demand for non-renewable virgin materials such as new asphalt, protects natural resources, and avoids most carbon emissions, thus achieving the goal of carbon neutrality and carbon emission reduction. Attached Figure Description

[0025] Figure 1 This is a macroscopic morphology diagram of the regenerant XT-3;

[0026] Figure 2 The penetration of recycled bitumen in RAP under different amounts of XT-3 recycling agent;

[0027] Figure 3 Ductility of recycled bitumen in RAP under different amounts of XT-3 recycling agent;

[0028] Figure 4 The softening point of recycled bitumen in RAP under different amounts of XT-3 recycling agent;

[0029] Figure 5 Initial and water-immersion pull-out strength;

[0030] Figure 6 For drawing loss rate;

[0031] Figure 7 Dynamic stability of recycled asphalt mixtures with different RAP content;

[0032] Figure 8 Stability of recycled asphalt mixtures with different RAP content;

[0033] Figure 9 The specimen is a semi-circular bending specimen;

[0034] Figure 10 The results show the effect of silane coupling agents on the water stability of recycled asphalt mixtures.

[0035] Figure 11 Water stability of basalt fiber recycled asphalt mixture without added silane coupling agent;

[0036] Figure 12 This is a schematic diagram of the contact angle measurement process;

[0037] Figure 13 Comparison of surface energies of different materials;

[0038] Figure 14 The results show the comparison of adhesion work and peeling work of different materials. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto. Other methods for preparing the compounds of the present invention, with some conventional modifications to the reaction conditions according to the present invention, are considered to be within the scope of the present invention.

[0040] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0041] It should be noted that, unless otherwise specified, the chemicals and reagents used in the following embodiments are all commercially available products commonly used in the field.

[0042] It should be noted that, unless otherwise specified, the operations used in the following embodiments are all conventional operations; for example, the operating temperature is always at room temperature unless otherwise specified. The test methods are all existing standard test methods in the art unless otherwise specified.

[0043] The present invention uses the recycling agent XT-3 to regenerate waste asphalt pavement materials, and then forms a recycled asphalt mixture with new asphalt, silane coupling agent, new aggregate, mineral aggregate and fiber. Under high dosage (referring to the dosage of waste asphalt pavement materials of 40wt% to 60wt%), it improves the low temperature performance and water stability of waste asphalt pavement materials and increases the utilization rate of waste asphalt pavement materials.

[0044] The materials used in this invention are as follows.

[0045] 1. In this invention, the recycling agent XT-3 produced by Changzhou Xintuo Road Modification Materials Co., Ltd. is viscous, and its macroscopic morphology is as follows: Figure 1 As shown in Table 1, its main technical specifications are as follows.

[0046] Table 1 XT-3 Technical Specifications

[0047]

[0048]

[0049] In this invention, the performance indicators of the regenerator XT-3 need to meet the technical requirements. Within the limited technical requirements, it can regenerate the aged asphalt in the asphalt mixture recycled material (denoted as RAP) and improve its performance. Thus, adding a small amount of new asphalt to high-content RAP can improve the road performance of the recycled asphalt mixture.

[0050] 2. In this invention, the asphalt mixture recycled material (denoted as RAP) is taken from the surface layer of a national highway in Xinjiang Uygur Autonomous Region. The various indicators of RAP are shown in Tables 2 to 4.

[0051] Table 2 Moisture content of RAP material

[0052] Particle size / mm 0～5 5～10 10～15 15～30 Moisture content / % 1.7 0.8 2.2 1.6

[0053] Table 3 Technical Specifications of RAP Material

[0054] Testing items Crushing value / % needle-like and flaky particle content / % Oilstone ratio % numerical values 12.4 7.2 5.4

[0055] Table 4. RAP screening results

[0056]

[0057] 3. In this invention, the new asphalt used is SBS modified asphalt, and the new aggregate is limestone; the mineral powder is prepared by grinding limestone. The basic performance indicators of the new asphalt, new aggregate, and mineral powder are shown in Tables 5-8.

[0058] Table 5. Test results of performance indicators of new asphalt

[0059]

[0060]

[0061] Table 6 Technical Specifications for New Aggregates

[0062] Testing items Crushing value / % needle-like and flaky particle content / % Moisture content % numerical values 25.9 7.43 0.8

[0063] Table 7 Technical Specifications for New Aggregates (II)

[0064] Aggregate particle size / mm Apparent relative density Surface relative density relative density of hair volume 10～20 2.848 2.803 2.778 5～10 2.872 2.806 2.772 2.36～5 2.841 2.738 2.682 0～2.36 2.94 2.666 2.523

[0065] Table 8 Technical Specifications of Mineral Powder

[0066] type <![CDATA[Density / (g·cm -3 )]]> relative density Mineral powder 2.68 2.686

[0067] Preferred Example 1

[0068] First, the optimal dosage of regenerant XT-3 was selected.

[0069] Specifically, aged asphalt recovered from RAP is mixed with the rejuvenator XT-3 to obtain RAP recycled asphalt. The optimal dosage of rejuvenator XT-3 is determined by testing the penetration, ductility, and softening point of RAP recycled asphalt with different XT-3 dosages.

[0070] The method for recovering aged asphalt in RAP is as follows: Based on the centrifugal separation method (JTG E20 T0722) and the rotary evaporator method (JTG E20 T0727), aged asphalt is recovered from the recycled asphalt pavement material (RAP) using the DLC-3 type centrifugal rapid extraction instrument for asphalt mixture produced by Beijing Schenker Experimental Instrument Factory and the R-205 rotary evaporator produced by Swiss Buqi. The technical indicators of the aged asphalt are shown in Table 9.

[0071] Table 9 Technical Indicators of Aging Asphalt

[0072]

[0073]

[0074] The tested RAP showed an aged asphalt content of 3.7 wt%. Different amounts of the recycling agent XT-3 were then added to the aged asphalt to obtain recycled RAP asphalt. The mass of XT-3 added was 12%, 14%, 16%, 16.5%, 17%, 17.5%, and 18% of the aged asphalt. The basic properties of the resulting recycled RAP asphalt showed the following trends: Figures 2-4 As shown in Table 10.

[0075] Table 10 Performance Indicators of RAP Recycled Asphalt

[0076] Dosage Needle penetration / 0.1mm Softening point / °C Ductility / cm 12% XT-3 143 1000 -25.77 14% XT-3 146.3 1313.33 -25.77 16% XT-3 234.23 2920 -33.08 16.5% XT-3 243.62 3953.33 -33.72 17% XT-3 184.56 2593.33 -32.95 17.5% XT-3 228.86 2526.67 -33.08 18% XT-3 177.85 1773.33 -30.13

[0077] From Table 10, Figure 2 , Figure 3 and Figure 4 It can be seen that with the increase of the XT-3 recycling agent dosage, the penetration and ductility of the high-dosage RAP recycled asphalt mixture first increase and then decrease with the increase of dosage; the penetration and ductility of the high-dosage RAP recycled asphalt mixture reach the maximum value when the dosage is 16.5%; the softening point is the smallest when the dosage is 16.5%.

[0078] Preferred Example 2

[0079] Adhesion is improved by using silane coupling agents.

[0080] Silane coupling agents contain two groups with different properties. One end is a polymer chain (R) that can physically entangle or chemically bond with organic molecular chains, and the other end is a siloxane group that can undergo hydrolysis and inorganic interface reaction. Its general molecular formula is RSiX3. It can be used to improve the adhesion performance of asphalt and acid aggregates. For ease of research, this invention selects silane coupling agent KH550 (3-aminopropyltrimethoxysilane), and its properties are shown in Table 11.

[0081] Table 11 Physical properties of silane coupling agent KH550

[0082] index molecular weight Density (25℃) Melting point (°C) Boiling point (°C) Flash point (°C) Refractive index Solubility KH-550 221.37 0.949 -70 217 96 1.42 Water, organic matter

[0083] The specific operation is as follows: Take the aged asphalt recovered from RAP, add the recycling agent XT-3 to it at a dosage of 16.5 wt% of the aged asphalt, and then add the silane coupling agent to obtain the mixture.

[0084] The pull-out test, derived from the Pneumatic Adhesion Tension Test (PATTI), is now widely used to evaluate the bond strength of asphalt and aggregate systems under dry and immersion conditions. The Posi Test AT-A automatic tensile testing instrument is used to test the bond strength at the gneiss-asphalt interface. The pull-out strength loss rate α between asphalt and aggregate under immersion conditions is then measured. i As an evaluation indicator, α i The higher the value, the worse the adhesion between asphalt and aggregate. i The calculation is shown in equation (1), and the result is as follows: Figure 5 and Figure 6 As shown.

[0085]

[0086] In the formula, α i - Pull-out strength loss rate, %; P - Initial pull-out strength, MPa; P i -

[0087] Pull-out strength (MPa) after immersion in water for a specific time.

[0088] Depend on Figure 5 and Figure 6 It can be seen that after adding silane coupling agent KH550, the strength loss rate decreased from 37% to 19%, indicating that silane coupling agent KH550 increased the cohesion and adhesion of aged asphalt to a certain extent and reduced adhesion loss.

[0089] Preferred Example 3

[0090] 1. Gradation design of high-content RAP recycled asphalt mixture

[0091] Based on the experimentally determined scheme, the upper, middle, and lower limits of the AC-13 gradation pass rate were used as constraints. The gradations of three recycled asphalt mixtures with RAP content of 40wt%, 50wt%, and 60wt% were calculated by the programming solution method, as shown in Table 12.

[0092] Table 12 Gradation composition of recycled asphalt mixtures with different RAP contents.

[0093]

[0094] 2. Determining the optimal amount of asphalt

[0095] Based on the mixture gradation in Table 12, the optimal asphalt-aggregate ratio was determined using the Marshall test method, thereby screening the dosages of new asphalt (SBS), new aggregate, and mineral powder. This was mainly based on the following formulas, where the mineral powder dosage could be calculated using the mix proportions:

[0096] M 新集料 =(1-α) 沥青含量 )×M 再生沥青混合料 -M RAP ×(1-β 老化沥青含量 (1)

[0097] M 新沥青 =α 沥青含量 ×M 再生沥青混合料 -M RAP ×β 老化沥青含量 (2)

[0098] Where: M 新集料 This refers to the amount of new aggregate used; α 沥青含量 M represents the asphalt content in recycled asphalt mixtures. 再生沥青混合料 For the quality of recycled asphalt mixtures, M RAP For the total mass of RAP; β 老化沥青含量 M represents the bitumen content in RAP. 新沥青 This refers to the amount of new asphalt used.

[0099] The dosage of recycling agent XT-3 was calculated as 16.5 wt% of the aged asphalt mass, and the aged asphalt content in RAP was 3.7 wt%. Then, waste asphalt pavement material (RAP), new asphalt (SBS), new aggregate (limestone), and mineral powder were mixed to obtain asphalt mixture. The RAP dosages were 40%, 50%, and 60%, respectively; corresponding amounts of new asphalt (SBS) and new aggregate (limestone) were added. The optimal asphalt content for the high-dosage RAP recycled asphalt mixture was determined according to the Marshall test in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG 3410-2025), and the specific results are shown in Table 13.

[0100] Table 13 Optimal Asphalt-Aggregate Ratio and Performance of Recycled Asphalt Mixtures with Different RAP Contents

[0101]

[0102]

[0103] It should be noted that in Table 13, "oil" refers to the oil material in asphalt mixtures, including new asphalt and aged asphalt in RAP; "stone" refers to the stone material in asphalt mixtures, including new aggregates, mineral powder, and old aggregates in RAP.

[0104] As shown in the table above, stability and flow value increase with increasing RAP content. Compared to 40% RAP content, the stability of recycled asphalt mixtures with 50% and 60% RAP content increases by 45.11% and 92.27%, respectively, and the flow value increases by 1.7% and 33.79%, respectively. At the corresponding asphalt-aggregate ratios, all three meet the requirements of the JTG F40 specification. This demonstrates the feasibility and rationality of the preferred scheme of this invention, and the resulting recycled asphalt mixture exhibits superior performance.

[0105] The optimal asphalt-aggregate ratio was determined using the Marshall test method, and the optimal amounts of new asphalt (SBS), new aggregate, and mineral powder were then selected—a well-known and conventional technique in the field. Ultimately, the optimal asphalt-aggregate ratio was determined to be 1.24wt%–2.66wt% for 40wt%–60wt% RAP content, 34.8wt%–55.7wt% for new aggregate, and 1.6wt%–4wt% for mineral powder.

[0106] The following examples use the above-preferred proportions to form high-content RAP recycled asphalt mixtures, and their performance is tested through experiments.

[0107] Examples 1 to 8

[0108] This embodiment provides a high-content RAP recycled asphalt mixture composed of the following raw materials:

[0109] The materials consist of recycled asphalt pavement (RAP), new asphalt (SBS modified asphalt), new aggregate (limestone), mineral powder (fine limestone), fiber, silane coupling agent KH550, and recycling agent XT-3.

[0110] The mass fraction of each raw material and the type of fiber in Examples 1 to 8 are shown in Table 14 below.

[0111] Table 14. Mass fraction of raw materials (unit: wt%)

[0112] RAP regenerator New asphalt new aggregate Mineral powder fiber Silane coupling agents Example 1 40％ 16％ 2.66％ 57.34％ 4.0％ 0.4% basalt fiber 0.9％ Example 2 40％ 16.5％ 2.63％ 57.34％ 4.0％ 0.4% basalt fiber 0.9％ Example 3 40％ 17.5％ 2.60％ 57.34％ 4％ 0.4% basalt fiber 0.9％ Example 4 50％ 16.5％ 1.55％ 48.45％ 3.7％ 0.4% basalt fiber 0.9％ Example 5 60％ 16.5％ 1.24％ 38.76％ 1.6％ 0.4% basalt fiber 0.9％ Example 6 40％ 16.5％ 1.24％ 38.76％ 4％ 0.4% Polyvinyl alcohol fiber 0.9％ Example 7 50％ 16.5％ 1.55％ 48.45％ 3.7％ 0.4% Polyvinyl alcohol fiber 0.9％ Example 8 60％ 16.5％ 1.24％ 38.76％ 1.6％ 0.4% Polyvinyl alcohol fiber 0.9％

[0113] It should be noted that the waste asphalt pavement material (RAP) contains aged asphalt, and the aged asphalt content is 3.7 wt%. The performance indicators are shown in Table 9.

[0114] The mass fraction of recycling agent XT-3 refers to the mass fraction of aged asphalt in which the amount of recycling agent XT-3 is used; the mass fraction of fiber refers to the mass fraction of high-content RAP recycled asphalt mixture in which the amount of fiber is used; the mass fraction of silane coupling agent KH550 refers to the mass fraction of silane coupling agent KH550 in new asphalt.

[0115] The preparation method of high-content RAP recycled asphalt mixture provided in this embodiment is as follows:

[0116] S1. Heat the new asphalt to 160±5℃, then add the silane coupling agent KH550 dropwise to the new asphalt, and shear it at 1500r / min for 30min to develop it, thus obtaining the modified asphalt material.

[0117] S2. Take waste asphalt pavement material and heat it at 160℃ for 2 hours. First, add recycling agent XT-3 to dry it, then add new aggregate and mix at 170℃ for 90 seconds. Next, add fiber, modified asphalt material and mineral powder from step S1, and mix for another 90 seconds to obtain high-content RAP recycled asphalt mixture.

[0118] It should be noted that the new aggregate in the above embodiments can also be basalt or other aggregates that meet the road construction specifications; the new asphalt can also be replaced with base asphalt.

[0119] It should be noted that during the preparation process, the shearing speed can be arbitrarily selected within the range of 1500 r / min to 3000 r / min, and the shearing time can be arbitrarily selected within the range of 30 min to 60 min; the heating temperature of the waste asphalt pavement material can be arbitrarily selected within the range of 160℃ to 170℃, and the heating time can be arbitrarily selected within the range of 1 h to 2 h; the temperature after adding new aggregate can be arbitrarily selected within the range of 170℃ to 180℃, and the mixing time can be arbitrarily selected within the range of 90 s to 100 s.

[0120] The performance of the high-content RAP recycled asphalt mixtures prepared in Examples 1 to 8 above was verified. Meanwhile, to highlight the technical advantages of this invention, the following comparative examples were designed.

[0121] Comparative Example 1

[0122] This comparative example provides a high-content RAP recycled asphalt mixture composed of the following raw materials: waste asphalt pavement material (RAP), new asphalt (SBS asphalt), new aggregate (limestone), mineral aggregate, silane coupling agent KH550, and recycling agent XT-3.

[0123] The RAP content is 40 wt%, the aged asphalt content in the RAP is 3.7 wt%, the amount of recycling agent XT-3 is 16.5 wt% of the aged asphalt, the new asphalt is 2.63 wt%, the mineral powder is 4 wt%, the new aggregate is 57.34 wt%, and the silane coupling agent KH550 is 0.9%.

[0124] Comparative Example 2

[0125] This comparative example provides a high-content RAP recycled asphalt mixture composed of the following raw materials: waste asphalt pavement material (RAP), new asphalt (SBS asphalt), new aggregate (limestone), mineral aggregate, silane coupling agent KH550, and recycling agent XT-3.

[0126] The RAP content is 40 wt%, the aged asphalt content in the RAP is 3.7 wt%, the amount of recycling agent XT-3 is 16.5 wt% of the aged asphalt, the amount of new asphalt is 1.55 wt%, the amount of mineral powder is 4 wt%, the amount of new aggregate is 48.45 wt%, and the amount of silane coupling agent KH550 is 0.9 wt%.

[0127] Comparative Example 3

[0128] This comparative example provides a high-content RAP recycled asphalt mixture composed of the following raw materials: waste asphalt pavement material (RAP), new asphalt (SBS asphalt), new aggregate (limestone), mineral aggregate, silane coupling agent KH550, and recycling agent XT-3.

[0129] The RAP content is 60 wt%, the aged asphalt content in the RAP is 3.7 wt%, the amount of recycling agent XT-3 is 16.5 wt% of the aged asphalt, the new asphalt content is 1.24 wt%, the mineral powder content is 1.6 wt%, the new aggregate content is 38.76 wt%, and the silane coupling agent KH550 content is 0.9 wt%.

[0130] Furthermore, the performance verification of the embodiments and comparative examples is as follows.

[0131] Verification 1: High Temperature Performance

[0132] High temperature stability refers to the performance of asphalt mixture under high temperature conditions, where the pavement material can withstand repeated vehicle loads without significant permanent deformation, still maintain a certain level of flatness, and not affect the normal use of the road surface. There are usually two test methods to measure the high temperature performance of asphalt mixture: Marshall stability test and high temperature rutting test. The Marshall stability test reflects the high temperature stability of asphalt mixture by measuring the stability of Marshall specimens, but this test cannot reflect the permanent deformation formed by vehicle loads acting on the asphalt mixture pavement in actual situations; it is necessary to further combine the rutting test to jointly evaluate the high temperature stability of asphalt mixture.

[0133] Test samples: Take the high-dose RAP recycled asphalt mixtures prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 2, Example 4, Example 5, Example 6, Example 7 and Example 8, and label them as 4, 5, 6, 4 + Xuan, 5 + Xuan, 6 + Xuan, 4 + Gao, 5 + Gao and 6 + Gao in sequence, where: 4, 5, 6 represent that the RAP dosages are 40%, 50% and 60% in sequence; Xuan represents basalt fiber, and Gao represents polyvinyl alcohol fiber.

[0134] High temperature performance test method: Prepare rutting specimens according to "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20 - 2011), and use a rutting tester to conduct dynamic stability tests on them according to the rutting test method (T 0719). Also, test its stability through the Marshall stability test. The dynamic stability and stability of recycled asphalt mixtures with different RAP dosages are as Figure 7 and Figure 8 shown.

[0135] It can be seen from the above two technical indicators that as the RAP dosage increases, both the dynamic stability and stability increase. This is because although the proportion of aged asphalt increases with the increase of RAP dosage, the stiffness of the blended asphalt increases, resulting in an increase in the stiffness of the recycled asphalt mixture, and the proportion of elastic strain in the total strain increases. Therefore, the dynamic stability and stability increase with the increase of RAP dosage. And after adding fibers, the dynamic stability and stability of the recycled asphalt mixture are both improved, indicating that the recycled asphalt mixture of the present invention has significant high temperature performance. At the same time, when the RAP dosage is not more than 50%, the high temperature performance of the polyvinyl alcohol fiber recycled asphalt mixture is better than that of the basalt fiber recycled asphalt mixture. When the RAP dosage is 60%, the dynamic stability of the basalt fiber recycled asphalt mixture is much greater than that of the polyvinyl alcohol fiber recycled asphalt mixture; under the stability index, the basalt fiber recycled asphalt mixture is greater than the polyvinyl alcohol fiber recycled asphalt mixture. Preferably, the fiber is basalt fiber.

[0136] Verification 2. Low temperature performance

[0137] Test samples: High-content RAP recycled asphalt mixtures prepared according to Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 2, Example 4, Example 5, Example 6, Example 7 and Example 8.

[0138] Test Method: The low-temperature performance of recycled asphalt mixtures was evaluated using the semicircular bending test (SCB) at -10℃. Standard Marshall specimens were prepared according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20-2011). Following the requirements of the SCB test, the Marshall specimens were cut into semicircular pieces with a diameter of 101.6 ± 0.2 mm and a thickness of 30 mm using a cutting machine. A crack with a depth of 10 mm and a width of 1.5 mm was cut at the center of the bottom of the specimen to simulate the low-temperature fracture of existing cracked asphalt pavements. The semicircular bending specimens and test procedure are as follows. Figure 9 As shown.

[0139] Fracture energy is defined as the work required to resist crack initiation, propagation, and eventual fracture of a specimen (with an applied load ≤ 0.1 kN), and can be represented by the area enclosed by the load-displacement curve. A higher fracture energy indicates better crack resistance of the asphalt mixture at the test temperature. Its relevant technical indicators are shown in Table 15.

[0140] Table 15 Fracture Energy of High-RAP Recycled Asphalt Mixture

[0141] type <![CDATA[Fracture energy (J / m 2 )]]> 40% RAP (Comparative Example 1) 921 50% RAP (Comparative Example 2) 2463 60% RAP (Comparative Example 3) 2262 40% RAP + Basalt Fiber (Example 2) 1709 50% RAP + Basalt Fiber (Example 4) 3916 60% RAP + Basalt Fiber (Example 5) 8253 40% RAP + Polyvinyl Alcohol Fiber (Example 6) 990 50% RAP + Polyvinyl Alcohol Fiber (Example 7) 3090 60% RAP + Polyvinyl Alcohol Fiber (Example 8) 3964

[0142] Based on fracture energy data, it can be found that at -10℃, the addition of two types of fibers improves the low-temperature performance of recycled asphalt mixtures with different RAP dosages. The best low-temperature performance is achieved with 60% RAP recycled asphalt mixture containing basalt fiber. Comparison shows that after adding fibers, the low-temperature performance of the recycled asphalt mixture improved by 85%, 59%, 264%, 7.5%, 25.6%, and 75% respectively. It can be seen that the low-temperature performance of the 60% RAP recycled asphalt mixture without fiber decreased, mainly because the increased RAP dosage led to a higher proportion of unactivated asphalt in the aged asphalt, resulting in poorer integration with the recycling agent and new asphalt, thus reducing the recycling effect and deteriorating low-temperature performance. However, the addition of basalt fiber significantly improved its low-temperature performance; especially at a RAP dosage of 60%, the fracture energy of the basalt fiber recycled asphalt mixture was much higher than that of the other two types of recycled asphalt mixtures. Preferably, basalt fiber is used.

[0143] Verification 3: Water stability

[0144] Water damage can affect the service life and performance of asphalt pavements, impacting driving safety. Therefore, the water stability of the high-content RAP recycled asphalt mixture prepared in this invention was investigated.

[0145] Test samples: High-content RAP recycled asphalt mixtures prepared by Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 2, Example 4, Example 5, Example 6, Example 7 and Example 8 were taken and successively labeled as 40% RAP, 50% RAP, 60% RAP, 40% RAP + basalt fiber, 50% RAP + basalt fiber, 60% RAP + basalt fiber, 40% RAP + polyvinyl alcohol fiber, 50% RAP + polyvinyl alcohol fiber and 60% RAP + polyvinyl alcohol fiber.

[0146] Test Method: Standard Marshall specimens were prepared according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20-2011), and water stability tests were conducted according to the immersion stability test method (T 0709). Residual stability was used to characterize the water stability of the recycled asphalt mixture in the test. Results are shown in [reference needed]. Figure 10 .

[0147] according to Figure 10 It can be seen that the addition of fibers reduces the water stability of recycled asphalt mixtures to some extent. However, except for the 60% RAP+polyvinyl alcohol fiber recycled asphalt mixture, the water temperature stability of the other recycled asphalt mixtures meets the relevant requirements of JTG F40.

[0148] In addition, to investigate the effect of silane coupling agent KH550 on the water stability of recycled asphalt mixtures, the water stability of basalt fiber recycled asphalt mixtures with and without the addition of silane coupling agent KH550 was compared.

[0149] The test samples were: high-content RAP recycled asphalt mixtures prepared in Examples 2, 4, and 5, 40% + basalt fiber + silane coupling agent, 50% + basalt fiber + silane coupling agent, and 60% + basalt fiber + silane coupling agent; a control without silane coupling agent KH550 was used, and the samples were labeled as 40% + basalt fiber, 50% + basalt fiber, and 60% + basalt fiber, respectively. Wherein: basalt fiber represents basalt fiber, and silane coupling agent represents silane coupling agent.

[0150] The water stability was examined using the method described above, and the results are as follows: Figure 11 As shown.

[0151] See Figure 11 The test results show that with the addition of silane coupling agent KH550, the water stability of recycled asphalt mixtures increased by 14.0%, 5.8%, and 12.1%, respectively, resulting in a significant improvement in water stability. Preferably, the water stability performance is optimal when the RAP content is 60% and basalt fiber is 0.4 wt%.

[0152] Verification 4

[0153] In this experiment, the lying-drop method was chosen to measure the contact angle of asphalt. The contact angle is the angle between the solid-liquid tangent and the droplet tangent at the intersection of the gas, liquid, and solid phases. The test principle is described in [link to test principle]. Figure 12 (a)

[0154] Test samples: The modified asphalt material prepared in step S1 of Example 5 was taken as the experimental group, denoted as S-KH, and the control group without the addition of silane coupling agent KH550 was set as SBS.

[0155] This experiment used a contact angle meter from Shanghai Zhongchen Digital Technology Equipment Co., Ltd., and the ambient temperature was controlled at 22±1℃. The titrants were distilled water and ethylene glycol, both characterized by poor solubility in asphalt, slow evaporation, and easy differentiation. The distilled water was prepared in the laboratory; the ethylene glycol was analytical grade from Tianjin Fuyu Fine Chemical Co., Ltd. The surface energy and contact angle parameters of the test liquids are shown in Tables 16 and 17.

[0156] Table 16 Surface energy parameters at 22℃ (mJ·m -2 )

[0157] reagents Molecular formula <![CDATA[γ L ]]> <![CDATA[γ d ]]> <![CDATA[γ p ]]> <![CDATA[γ + ]]> <![CDATA[γ - ]]> distilled water <![CDATA[H2O]]> 72.8 21.8 51.0 25.5 25.5 Ethylene glycol <![CDATA[(CH2OH)2]]> 48.0 29.0 19.0 3.0 30.1

[0158] Table 17 shows the contact angles between two test liquids and asphalt tested using the lying drop method.

[0159]

[0160] The surface energy components of each modified asphalt material were calculated based on the contact angle data and the surface energy parameters of the tested liquid, as shown in the following figures. Figure 13 As shown.

[0161] Depend on Figure 13 It can be seen that the surface energy increased by 17.1% after the addition of silane coupling agent KH550, indicating that silane coupling agent KH550 has a certain degree of effect on improving the surface energy of asphalt.

[0162] Subsequently, its adhesion work, peeling work, and compatibility were analyzed, such as... Figure 14 As shown.

[0163] The greater the adhesion work between asphalt and aggregate, the more stable the interfacial system. Conversely, the greater the stripping work, the easier it is for water molecules to replace the asphalt film on the aggregate surface, resulting in poorer interfacial stability. After incorporating KH550, the adhesion work of asphalt in the modified asphalt mixture increased by 8.0%. This is mainly because KH550, as a high-molecular-weight coupling agent, possesses siloxane groups and organic macromolecular chains. The siloxane groups react with the hydroxyl groups on the aggregate surface to form chemical bonds, while the organic macromolecular chains physically entangle or chemically bond with the organic molecular chains of asphalt, thus "coupling" the two materials with different surface chemical properties and enhancing the adhesion between asphalt and aggregate. The compatibility of asphalt and aggregate characterizes the process of asphalt wetting and adhering to the aggregate surface. After incorporating KH550, the compatibility ER value increased by 8.2%. The higher the ER value, the better the compatibility of the asphalt-aggregate system and the superior its resistance to water damage.

[0164] The above are several preferred embodiments of the preparation method of the present invention, but they should not be regarded as limitations on the technical solutions protected by the present invention. Any simple modifications, changes and equivalent changes made based on the technical concept of the present invention, and all alternative solutions obtained by those skilled in the art without creative labor, should fall within the protection scope of the present invention.

Claims

1. A high RAP content asphalt recycling mixture, characterized in that, The high-mixing RAP recycled asphalt mixture is composed of waste asphalt pavement material, recycling agent XT-3, new asphalt, new aggregate, mineral powder, fiber and silane coupling agent KH550; the waste asphalt pavement material contains aged asphalt; The above raw materials are used in the following amounts: waste asphalt pavement material 40wt%-60wt%, new asphalt 1.24wt%-2.66wt%, new aggregate 34.8wt%-55.7wt%, and mineral powder 1.6wt%-4wt%. The recycling agent XT-3 is 16wt%-17wt% of the mass of aged asphalt; the amount of fiber is 0.4wt% of the mass of the high-mixing RAP recycled asphalt mixture; and the mass of silane coupling agent KH550 is 0.9wt% of the mass of new asphalt.

2. The high RAP content asphalt recycling mixture according to claim 1, wherein, The performance index of recycling agent XT-3 is: saturated component content ≤30%, and aromatic component content >65%.

3. The high RAP content asphalt recycling mixture of claim 1, wherein, The fiber is basalt fiber or polyvinyl alcohol fiber.

4. The high RAP content asphalt recycling mixture of claim 1, wherein, The new aggregate is limestone or basalt, and the new asphalt is base asphalt or SBS modified asphalt.

5. A process for the preparation of high RAP content asphalt recycling mixture as claimed in claim 1, wherein, The preparation method is as follows: S1, heat the new asphalt to 160±5℃, then add the silane coupling agent KH550 drop by drop into the new asphalt, shear and develop to obtain modified asphalt material; S2, after heating the waste asphalt pavement material, first add the recycling agent XT-3 and dry, then add the new aggregate and mix; then add the fiber and the modified asphalt material of step S1; and then add the mineral powder and mix to obtain the high-mixing RAP recycled asphalt mixture.

6. The method of claim 5, wherein the high RAP content asphalt mixture is prepared by the steps of: In the step S1, the shearing is at a rate of 1500r / min-3000r / min for 30min-60min.

7. The method of claim 5, wherein the high RAP content asphalt mixture is prepared by mixing the RAP, the virgin asphalt, the filler, and the additive in the mixing chamber of the hot mix asphalt plant. In the step S2, the heating is at 160℃-170℃ for 1h-2h; after adding the new aggregate, mix at 170℃-180℃ for 90s-100s; and after adding the mineral powder, mix for another 90s-100s.

8. Application of the high-mixing RAP recycled asphalt mixture of claim 1 in highway engineering auxiliary facilities and middle-upper surface layers.

9. Use according to claim 8, characterized in that, The highway engineering auxiliary facilities include kerb, water drain or drainage ditch.

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