A high-elasticity modifier for recycling asphalt mortar and a method for preparing the same

Abstract

The application discloses a high-elastic modifier for regenerating asphalt mortar, which comprises the following components in parts by weight: modified waste EPDM plastic track granules 20-30 parts, modified crosslinking agent 10-15 parts, penetrating agent 5-10 parts, plasticizer 3-10 parts, solubilizer 20-40 parts, sulfur granules 5-10 parts and surfactant 5-10 parts. The waste EPDM plastic track granules and the crosslinking agent are modified respectively, the modified EPDM can further react with anhydride groups of LDPE to form an imide structure, a chemical bond is established between the EPDM and the LDPE, the interface bonding force is significantly enhanced, a crosslinking network is generated, and the elasticity and fatigue performance of the regenerated asphalt mortar are improved.

Description

Technical Field

[0001] This invention belongs to the field of recycled asphalt preparation technology, specifically relating to a high-elasticity modifier for recycled asphalt mortar and its preparation method. Background Technology

[0002] Traditional recycled asphalt mortar faces key technical bottlenecks in road repair and construction projects, including insufficient elastic recovery and poor fatigue resistance. These bottlenecks primarily stem from the inherent defects of weak interfacial compatibility between conventional rubber modifiers and the asphalt matrix, making it difficult to form effective chemical bonds through physical blending. While existing technologies have attempted to use waste tire rubber powder or unmodified EPDM particles as elastic components, their surface inertness leads to low bonding strength with asphalt, resulting in easy softening at high temperatures and brittleness at low temperatures. Furthermore, the crosslinking systems often rely on a single sulfur curing mechanism, resulting in insufficient crosslinking density and network stability, leading to stress relaxation and structural deterioration after long-term use. In addition, traditional solubilizers have limited effectiveness in modifying the significantly polar rubber-asphalt interface, failing to synergistically improve the material's dynamic mechanical properties and environmental durability. The efficient recycling of waste EPDM plastic track granules remains constrained by the lack of surface activation technology and functional modification methods, resulting in resource waste and environmental pressure. Therefore, there is an urgent need to develop a high-performance recycled asphalt modifier based on interfacial chemical bond reconstruction and multi-scale synergistic enhancement, so as to realize the high-value utilization of waste rubber resources and break through the technical limitations of existing recycled asphalt materials. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a high-elasticity modifier for recycled asphalt mortar and its preparation method. By modifying waste EPDM plastic track particles and crosslinking agents respectively, the modified EPDM can further react with the anhydride groups of LDPE to form an imide structure, establishing chemical bonds between EPDM and LDPE, significantly enhancing interfacial bonding, generating a crosslinking network, and improving the elasticity and fatigue performance of recycled asphalt mortar.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A high-elasticity modifier for recycled asphalt mortar comprises the following components in parts by weight: 20-30 parts modified waste EPDM plastic track granules, 10-15 parts modified crosslinking agent, 5-10 parts penetrant, 3-10 parts plasticizer, 20-40 parts solubilizer, 5-10 parts sulfur granules, and 5-10 parts surfactant.

[0006] Preferably, the preparation method of the aforementioned modified waste EPDM plastic track granules is as follows:

[0007] (1) The pretreated waste EPDM plastic track granules are subjected to plasma treatment;

[0008] (2) The treated waste EPDM plastic track granules are mixed with hexamethylene diisocyanate under an inert atmosphere, a catalyst is added, and the mixture is allowed to react fully to obtain modified waste EPDM plastic track granules.

[0009] Preferably, in step (1) above, the oxygen flow rate during plasma treatment is 15-25 sccm, the treatment time is 5-10 min, the temperature is 25-30℃, and the power is 100-200W.

[0010] Preferably, in step (1) above, the waste EPDM plastic track granules are oil-extended EPDM rubber containing EPDM rubber, wherein the ethylene content is 65%, the Mooney viscosity is 60, and the third monomer ENB is 4. The pretreatment method is to mechanically crush the waste EPDM plastic track granules and screen them to 80-100 mesh.

[0011] Preferably, in step (2) above, the mass ratio of modified waste EPDM plastic track granules, hexamethylene diisocyanate and catalyst is 100:3~5:0.1~0.5, the reaction temperature is 80~100℃, the reaction time is 20~30min, and the catalyst is dibutyltin dilaurate.

[0012] Preferably, the preparation method of the aforementioned modified crosslinking agent is as follows: low-density polyethylene (LDPE), maleic anhydride (MAH) and dicumyl peroxide are premixed and ground, melt grafted at high temperature, and extruded and granulated after the reaction is completed to obtain the modified crosslinking agent.

[0013] Preferably, the mass ratio of the aforementioned low-density polyethylene, maleic anhydride, and dicumyl peroxide is 100:(1.5-3):(0.25-0.5); the melt grafting reaction is carried out in a twin-screw extruder at a reaction temperature of 160-190°C, a screw speed of 200-250 RPM, and a reaction time of 8-12 min.

[0014] Preferably, the aforementioned penetrant is isooctyl alcohol polyoxyethylene ether or isooctyl alcohol polyoxyethylene ether phosphate, the plasticizer is one or a mixture of dioctyl phthalate or dibutyl phthalate, the solubilizer is a compound oil of atmospheric distillate oil and desalinated oil in a compound ratio of 2:1, and the surfactant is a fluorocarbon surfactant.

[0015] A method for preparing a high-elasticity modifier for recycled asphalt mortar includes the following specific steps:

[0016] S1. Add the modified waste EPDM plastic track granules, modified crosslinking agent and solubilizer into the internal mixer according to the ratio, and heat for premixing;

[0017] S2. Transfer the premix to a twin-screw extruder, add plasticizer, penetrant and surfactant, mix, and ensure that all components are completely dissolved;

[0018] S3. Add sulfur granules, cool and extrude to obtain granular high-elasticity modifier.

[0019] Preferably, the temperature of the aforementioned internal mixer is 95–105°C, the air pressure is 7–8 bar, and the mixing time is 8–15 min; the temperature of the twin-screw extruder is 220–250°C.

[0020] The advantages of this invention are:

[0021] (1) The modified crosslinking agent of the present invention itself grafts the polar anhydride groups of maleic anhydride onto the LDPE molecular chain through free radical reaction, forming a polarized modified material of LDPE main chain + MAH side chain. The anhydride groups (-CO-O-CO-) of MAH form hydrogen bonds or chemical bonds with the gum and asphaltenes in asphalt, which significantly improves the compatibility with asphalt. The grafted LDPE has both flexibility and polarity, which can enhance the elastic recovery ability and fatigue resistance of recycled mortar. On the other hand, sulfur reacts with the double bonds of EPDM molecular chain to form a polysulfide crosslinking network.

[0022] (2) The modified EPDM introduces highly reactive isocyanate groups on its molecular chain, which can further react with the anhydride groups of LDPE to form an imide structure (-CO-NH-CO-), thereby establishing chemical bond (covalent bond) between EPDM and LDPE, significantly enhancing the interfacial bonding force, generating a cross-linked network, and improving the elasticity and fatigue performance of recycled asphalt mortar. Detailed Implementation

[0023] The present invention will be described in detail below with reference to specific embodiments.

[0024] Example 1

[0025] A method for preparing a high-elasticity modifier for recycled asphalt mortar includes the following steps:

[0026] Step 1: Preparation of modified waste EPDM plastic track granules:

[0027] (1) The waste EPDM plastic track granules are mechanically crushed and screened to 80-100 mesh. The pretreated waste EPDM powder is then subjected to plasma treatment using a low-temperature oxygen plasma treatment instrument. The oxygen flow rate during plasma treatment is 20 sccm, the treatment time is 10 min, the temperature is 25℃, and the power is 100W.

[0028] (2) 100 parts of treated waste EPDM plastic track granules and 3 parts of hexamethylene diisocyanate were mixed in an inert atmosphere, and 0.2 parts of dibutyltin dilaurate catalyst were added. The mixture was allowed to react fully at a temperature of 80°C for 20 minutes to obtain modified waste EPDM plastic track granules.

[0029] Step 2: Preparation of modified crosslinking agent:

[0030] 100 parts of low-density polyethylene (LDPE), 3 parts of maleic anhydride (MAH) and 0.4 parts of dicumyl peroxide were premixed and ground, and then added to a twin-screw extruder. Melt grafting was carried out at 160-190°C, with a screw speed of 200-250 RPM and a reaction time of 8-12 min. After the reaction was completed, the mixture was extruded and granulated to obtain the modified crosslinking agent.

[0031] Step 3: Preparation of high-elasticity modifier:

[0032] S1. Add 30 parts of modified waste EPDM plastic track granules, 15 parts of modified crosslinking agent and 20 parts of solubilizer (a compound oil of atmospheric distillate oil and reduced-line extraction oil in a compound ratio of 2:1) into a mixer according to the ratio, heat to 100℃ for premixing, wherein the air pressure of the mixer is 8 bar, and the intermediate pressure cap is raised twice, and the mixing is carried out for 10 minutes.

[0033] S2. Transfer the premix to a twin-screw extruder, heat to 230°C for secondary treatment, continue heating for 10 minutes, add 10 parts of dioctyl phthalate, 10 parts of isooctyl alcohol polyoxyethylene ether and 5 parts of fluorocarbon activator, mix, and ensure that all components are completely dissolved.

[0034] S3. Add 10 parts of sulfur granules, cool and extrude to obtain granular high-elasticity modifier.

[0035] Example 2

[0036] The preparation method in this embodiment is the same as that in Example 1, except that the amount of each component is different:

[0037] In step one: 100 parts of modified waste EPDM plastic track granules, 5 parts of hexamethylene diisocyanate, and 0.5 parts of catalyst;

[0038] In step two: 100 parts low-density polyethylene, 3 parts maleic anhydride, and 0.4 parts dicumyl peroxide;

[0039] In step three: 30 parts modified waste EPDM plastic track granules, 10 parts modified crosslinking agent, 10 parts penetrant, 5 parts plasticizer, 40 parts solubilizer, 5 parts sulfur granules, and 5 parts surfactant.

[0040] Example 3

[0041] The preparation method in this embodiment is the same as that in Example 1, except that the amount of each component is different:

[0042] In step one: 100 parts of modified waste EPDM plastic track granules, 4 parts of hexamethylene diisocyanate, and 0.2 parts of catalyst;

[0043] In step two: 100 parts low-density polyethylene, 3 parts maleic anhydride, and 0.4 parts dicumyl peroxide;

[0044] Step 3: 30 parts modified waste EPDM plastic track granules, 10 parts modified crosslinking agent, 10 parts penetrant, 5 parts plasticizer, 35 parts solubilizer, 5 parts sulfur granules, and 10 parts surfactant.

[0045] Comparative Example 1

[0046] The preparation method of this comparative example is the same as that of Example 1, except that no modified crosslinking agent is added.

[0047] Comparative Example 2

[0048] The preparation method of this comparative example is the same as that of Example 1, except that waste tire rubber powder is used instead of modified waste EPDM plastic track granules.

[0049] Comparative Example 3

[0050] The preparation method of this comparative example is the same as that of Example 1, except that the waste EPDM plastic track granules were not modified.

[0051] Comparative Example 4

[0052] The preparation method of this comparative example is the same as that of Example 1, except that sulfur particles are not added.

[0053] Performance testing

[0054] (1) Testing of ductility and fatigue crack resistance of asphalt mortar

[0055] The method for testing the ductility performance of asphalt mortar is as follows: Based on the SMA-13 ​​mix design, the content of oil-rich RAP fine aggregate is 18%. Coarse aggregate (particle size > 3mm) is removed. The ratio of RAP fine aggregate to new asphalt is 4:1. The recycled asphalt mortar, prepared by mixing the base asphalt and oil-rich RAP fine aggregate, is heated to 160℃. Then, 20% by mass of a high-elasticity modifier is added, and the mixture is stirred at a stirring rate of 500R for 20 minutes. The prepared recycled high-elasticity asphalt mortar is placed in a 160℃ oven for 20 minutes for development, and then tested using a ductility tester at a test temperature of 5℃. The method for testing fatigue crack resistance is as follows: According to the SMA-13 ​​mix design, the content of oil-rich RAP fine aggregate is 18%. The above-mentioned recycled asphalt mortar is mixed with coarse aggregate (particle size > 3mm) according to the designed recycled asphalt mixture ratio. According to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), recycled asphalt mixture slab specimens were formed by wheel rolling and cut into small beam specimens with a length of 380±5mm, a thickness of 50±5mm, and a width of 63.5±5mm. Four-point bending tests with strain control (400με) were conducted to determine the fatigue life of the recycled asphalt mixture. Specific results are shown in Table 1.

[0056] Table 1 Performance Tests of High-Elasticity Modifiers

[0057] Specimen type Ductility(mm) Fatigue life (times) Example 1 58.1 85112 Example 2 53.6 83227 Example 3 55.9 82876 Comparative Example 1 23.1 61334 Comparative Example 2 35.9 63113 Comparative Example 3 32.5 62118 Comparative Example 4 24.3 64137 No high-elasticity modifier added 10.2 50112

[0058] As shown in Table 1, the recycled asphalt mortars prepared with the high-elasticity modifiers in Examples 1-3 exhibit excellent ductility and fatigue life. A comparison between Example 1 and Comparative Example 1 reveals that without the addition of the modified crosslinking agent, both ductility and fatigue crack resistance significantly decrease. This is because the modified crosslinking agent itself grafts the polar anhydride groups of maleic anhydride onto the LDPE molecular chain via a free radical reaction, forming a polarized modified material with the LDPE main chain and MAH side chains. The anhydride groups (-CO-O-CO-) of MAH form hydrogen bonds or chemical bonds with the asphalt resins and asphaltenes, significantly improving compatibility with asphalt. The grafted LDPE possesses both flexibility and polarity, enhancing the elastic recovery and fatigue resistance of the recycled mortar.

[0059] Comparisons of Example 1, Comparative Example 2, and Comparative Example 3 show that using waste tire rubber powder to replace modified waste EPDM plastic track granules or directly using unmodified waste EPDM plastic track granules are not ideal. This is because after plasma treatment, a small amount of hydroxyl (-OH) or amino (-NH2) groups are generated on the surface of EPDM. After adding hexamethylene diisocyanate (HDI), its isocyanate groups (-NCO) can react with the hydroxyl or amino groups on the surface of EPDM to generate urethane bonds (-NH-CO-O-), thereby introducing highly reactive isocyanate groups into the EPDM molecular chain. The modified LDPE main chain carries the anhydride groups (-CO-O-CO-) of the MAH side chain. The -NCO groups remaining on EPDM by HDI can further react with the anhydride groups of LDPE to form an imide structure (-CO-NH-CO-), thereby establishing a chemical bond between EPDM and LDPE, significantly enhancing the interfacial bonding force, and improving the elasticity and fatigue performance of recycled asphalt mortar.

[0060] A comparison of Example 1 and Comparative Example 4 shows that without the addition of sulfur particles, the ductility and fatigue crack resistance both decreased significantly. This is because the reaction between sulfur and the double bonds of the EPDM molecular chain can form a polysulfide cross-linking network, which further enhances the elasticity and fatigue resistance of the material.

[0061] (2) Elastic recovery performance test

[0062] Recycled asphalt mortar specimens (size: 50×50×5mm) were prepared according to the method in Example 1. A strain of 50% (at a rate of 5mm / min) was applied using a universal testing machine, held for 10 seconds, and then unloaded. The residual deformation of the specimens after unloading was recorded. The specific results are shown in Table 2.

[0063] Table 2 Elastic recovery performance test of high-elasticity modifier

[0064] Specimen type elastic recovery rate Example 1 89％ Comparative Example 1 (without added crosslinking agent) 47％ Comparative Example 3 (without modified EPDM) 55％

[0065] As shown in Table 2, the elastic recovery rate of Example 1 is much higher than that of Comparative Example 1 and Comparative Example 3. This indicates that the chemical bond connection between the modified crosslinking agent and EPDM can significantly improve the elastic recovery ability of recycled asphalt mortar, verifying the strengthening effect of interfacial bonding.

[0066] (3) Long-term aging performance test

[0067] Recycled asphalt mortar specimens were prepared according to the method in Example 1. They were then subjected to UV aging in a QUV ultraviolet aging chamber (UVB-313 lamp, 60℃) for 500 hours. The ductility and fatigue life of the specimens after aging were tested. The specific results are shown in Table 3.

[0068] Table 3. Long-term aging performance test of high-elasticity modifiers

[0069] Specimen type Ductility retention rate Fatigue life retention rate Example 1 87％ 91％ Comparative Example 4 (without added sulfur particles) 52％ 43％

[0070] As shown in Table 3, the ductility retention rate and fatigue life retention rate of Example 1 are much higher than those of Comparative Example 4. This indicates that sulfur particles and stable chemical structures in the high-elasticity modifier can delay the aging and degradation of recycled asphalt mortar.

[0071] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A high-elasticity modifier for recycled asphalt mortar, characterized in that, It includes the following components by weight: 20-30 parts modified waste EPDM plastic track granules, 10-15 parts modified crosslinking agent, 5-10 parts penetrant, 3-10 parts plasticizer, 20-40 parts solubilizer, 5-10 parts sulfur granules, and 5-10 parts surfactant. The preparation method of the modified waste EPDM plastic track granules is as follows: (1) The pretreated waste EPDM plastic track granules are subjected to plasma treatment; (2) The treated waste EPDM plastic track granules are mixed with hexamethylene diisocyanate under an inert atmosphere, a catalyst is added, and the mixture is allowed to react fully to obtain modified waste EPDM plastic track granules. The preparation method of the modified crosslinking agent is as follows: Low-density polyethylene, maleic anhydride, and dicumyl peroxide were premixed and ground, then melt-grafted at high temperature. After the reaction was completed, the mixture was extruded and granulated to obtain a modified crosslinking agent.

2. The high-elasticity modifier for recycled asphalt mortar according to claim 1, characterized in that, In step (1), the oxygen flow rate during plasma treatment is 15-25 sccm, the treatment time is 5-10 min, the temperature is 25-30 ℃, and the power is 100-200 W.

3. The high-elasticity modifier for recycled asphalt mortar according to claim 1, characterized in that, In step (1), the waste EPDM plastic track granules are oil-extended EPDM rubber containing EPDM rubber, wherein the ethylene content is 65%, the Mooney viscosity is 60, and the content of the third monomer ethylidene norbornene is 4 wt%. The pretreatment method is to mechanically crush the waste EPDM plastic track granules and screen them to 80~100 mesh.

4. The high-elasticity modifier for recycled asphalt mortar according to claim 1, characterized in that, In step (2), the mass ratio of modified waste EPDM plastic track granules, hexamethylene diisocyanate and catalyst is 100:3~5:0.1~0.5, the reaction temperature is 80~100 ℃, the reaction time is 20~30 min, and the catalyst is dibutyltin dilaurate.

5. The high-elasticity modifier for recycled asphalt mortar according to claim 1, characterized in that, The mass ratio of the low-density polyethylene, maleic anhydride, and dicumyl peroxide is 100:(1.5~3):(0.25~0.5); the melt grafting reaction is carried out in a twin-screw extruder at a reaction temperature of 160~190 ℃, a screw speed of 200~250 RPM, and a reaction time of 8~12 min.

6. The high-elasticity modifier for recycled asphalt mortar according to claim 1, characterized in that, The penetrant is isooctyl alcohol polyoxyethylene ether or isooctyl alcohol polyoxyethylene ether phosphate, the plasticizer is one or a mixture of dioctyl phthalate or dibutyl phthalate, the solubilizer is a compound oil of atmospheric distillate oil and desalinated oil in a compound ratio of 2:1, and the surfactant is a fluorocarbon surfactant.

7. The method for preparing a high-elasticity modifier for recycled asphalt mortar according to claim 1, characterized in that, The specific steps include the following: S1. Add the modified waste EPDM plastic track granules, modified crosslinking agent and solubilizer into the internal mixer according to the ratio, and heat for premixing; S2. Transfer the premix to a twin-screw extruder, add plasticizer, penetrant and surfactant, mix, and ensure that all components are completely dissolved; S3. Add sulfur granules, cool and extrude to obtain granular high-elasticity modifier.

8. The preparation method according to claim 7, characterized in that, The internal mixer has a temperature of 95~105 ℃, a gas pressure of 7~8 bar, and a mixing time of 8~15 min; the twin-screw extruder has a temperature of 220~250 ℃.