Preparation method of LDPE / EVA / SBS composite modified asphalt mixture by dry method

Abstract

The invention discloses a preparation method of a dry-process LDPE / EVA / SBS composite modified asphalt mixture, and the preparation method comprises the following steps: S1, weighing LDPE, EVA and SBS, and drying to obtain a dried polymer; s2, adding a cross-linking agent, a dispersing agent, an antioxidant, a fluxing agent and a coupling agent into the dried polymer, and stirring and mixing to obtain a premix; s3, shearing and screening the premix to obtain composite modified primary powder; s4, drying the composite modified primary powder, and screening again to obtain composite modified powder; and S5, mixing the composite modified powder with matrix asphalt and mineral aggregate to obtain the dry-process LDPE / EVA / SBS composite modified asphalt mixture. The problems of high energy consumption, easy segregation and poor storage stability of existing wet modified asphalt are solved, the technical bottlenecks of non-uniform dispersion and poor compatibility with asphalt of a traditional dry modifier are broken through, and efficient resource utilization of waste plastics is realized.

Description

Technical Field

[0001] This invention belongs to the field of road engineering materials technology, and in particular relates to a method for preparing dry-process LDPE / EVA / SBS composite modified asphalt mixture. Background Technology

[0002] In the field of road engineering, improving the performance of asphalt mixtures mainly involves polymer modification, among which wet-process SBS modified asphalt is widely used. However, it has significant drawbacks: the preparation process requires high-temperature shearing at 180℃ for more than 30 minutes, resulting in extremely high energy consumption. Furthermore, modified asphalt is prone to segregation and thermal aging during storage and transportation. Meanwhile, my country's annual output of waste plastics exceeds 60 million tons, with a recycling rate of only about 30.65%. A large amount of LDPE / EVA waste plastics are difficult to utilize effectively due to their properties not matching the requirements of traditional road modification, and are thus largely landfilled or incinerated, causing white pollution and resource waste.

[0003] Existing dry modification technologies attempt to address the problems of wet processes and utilize waste plastics, but still face challenges:

[0004] While a single dry process (such as directly adding waste LDPE) can reduce costs by about 15%, the particle agglomeration rate is as high as 30% or more when mixing at 190°C, resulting in uneven dispersion and limited improvement in high-temperature performance.

[0005] Although composite dry processes (such as simple mechanical compounding of LDPE / SBS) simplify the process, they have poor compatibility, with a segregation rate of ≥5% in the mixture. Under a fluorescence microscope, they exhibit obvious "island-like" distribution and cannot form an effective reinforcing structure.

[0006] The above situation fully illustrates the prominent contradiction in balancing high performance, low cost, and environmental benefits. There is an urgent need for a modified asphalt that can overcome the limitations of high energy consumption and easy aging in wet processes, while also solving the problems of insufficient dispersibility and compatibility of dry process modifiers and enabling the large-scale utilization of waste LDPE / EVA plastics. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing dry-process LDPE / EVA / SBS composite modified asphalt mixture, which solves the problems of long high-temperature shearing time, high energy consumption, and easy aging and segregation of modified asphalt in traditional wet-process modification. At the same time, it solves the defects of existing dry-process technology, such as easy agglomeration of modifier particles, "island-like" distribution in the mixture, and inability to form an effective reinforcing structure, and realizes the resource utilization of waste LDPE / EVA plastics.

[0008] To solve the above-mentioned technical problems, the technical solution adopted in this invention is a method for preparing dry-process LDPE / EVA / SBS composite modified asphalt mixture, the preparation steps of which include:

[0009] Step S1: Weigh LDPE, EVA, and SBS by mass percentage, and dry them to obtain a dried polymer.

[0010] Step S2: Add crosslinking agent, dispersant, antioxidant, flux, and coupling agent to the dried polymer, and stir to obtain a premix with uniform composition.

[0011] Step S3: The premix is ​​sheared and sieved to obtain composite modified primary powder;

[0012] Step S4: After drying the primary composite modified powder, it is sieved again to obtain the composite modified powder.

[0013] Step S5: The composite modified powder is mixed with the base asphalt and aggregate to obtain the finished dry-process LDPE / EVA / SBS composite modified asphalt mixture.

[0014] Furthermore, in S1, LDPE accounts for 25% to 35% of the total mass, EVA accounts for 25% to 35% of the total mass, and SBS accounts for 30% to 50% of the total mass.

[0015] Furthermore, in step S1, the drying temperature is 75–85°C, and the drying time is 3–5 hours.

[0016] Furthermore, in step S2, the amount of crosslinking agent is 1.5-2.5 wt% of the dry polymer, the amount of dispersant is 2.5-3.5 wt% of the dry polymer, the amount of antioxidant is 1.5-2.5 wt% of the dry polymer, the amount of flux is 4-6 wt% of the dry polymer, the amount of coupling agent is 2.5-3.5 wt% of the dry polymer, the stirring speed is 800-1500 r / min, and the stirring time is 4-8 min.

[0017] Furthermore, the crosslinking agent is selected as dicumyl peroxide, the dispersant is selected as soybean oil, the antioxidant is selected as hindered phenolic antioxidant pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), the flux is selected as alumina powder, and the coupling agent is selected as titanate coupling agent.

[0018] Furthermore, in step S3, the shearing temperature is 15-30℃, the shearing speed is 1000-2000 r / min, the shearing time is 5-15 min, and the particle size of the composite modified primary powder is 1-6 mm.

[0019] Furthermore, in step S4, the drying temperature is 70~80℃, the drying time is 2~4h, the particle size of the composite modified powder is 1~6 mm, and the storage temperature is 20~30℃.

[0020] Furthermore, in S5, the amount of base asphalt used is 4.5-5.5% of the mass of the aggregate, the amount of composite modified powder is 6-10% of the mass of the base asphalt, and the mineral powder accounts for 5-10% of the total mass of the aggregate.

[0021] Furthermore, the specific steps of mixing in S5 are as follows:

[0022] S51, pretreatment of aggregates and mineral powder: place coarse and fine aggregates in a heating chamber and heat to 190-210℃, heat mineral powder to 160-180℃, and heat base asphalt to 160-180℃;

[0023] S52, the heated aggregate and composite modified powder are put into a mixing pot and dry-mixed at 40-60 r / min for 0.5-1.5 min at 180-200℃.

[0024] S53, add preheated base asphalt to the dry-mixed aggregate-composite modified powder mixture and continue mixing for 2-3 minutes;

[0025] S54. Preheated mineral powder is added to a mixing pot and stirred for 2-3 minutes at 165-175℃ to obtain the finished dry-process LDPE / EVA / SBS composite modified asphalt mixture.

[0026] The beneficial effects of this invention are:

[0027] 1. In this invention, the composite particles form a dense and uniform elastic network structure in the asphalt. The interface between the asphalt and the composite modified particles is tightly bonded, and the structures are interlocked with each other without obvious phase separation.

[0028] 2. EVA effectively improves the compatibility of SBS with asphalt and LDPE. The synergistic effect of the SBS elastic network and LDPE / EVA improves the flexibility and stress relaxation ability of the mixture. The flexural tensile strength and maximum flexural tensile strain reach 95% and 90% of those of SBS modified asphalt mixture, respectively.

[0029] 3. After the composite particles melt, they preferentially coat the surface of the aggregate, forming an interfacial transition layer. The polar groups of EVA enhance the adhesion between asphalt and aggregate. The freeze-thaw splitting strength ratio is as high as 92.3%, which is better than SBS modified asphalt mixture (86.4%) and matrix asphalt mixture (72%). The strength loss rate after freeze-thaw is only 7.7%.

[0030] 4. It has outstanding fatigue resistance, and the "rigid-elastic" composite interface structure significantly delays crack propagation.

[0031] 5. Excellent anti-skid performance: After the modified particles melt, they stabilize the aggregate skeleton, maintaining good macrostructure and microtexture. The average texture depth (MTD) reaches 0.793 mm, and the pendulum value (BPN) reaches 61.5, which is superior to base asphalt mixtures and SBS modified asphalt mixtures.

[0032] 6. The composite modified powder of this invention achieves rapid melting, eliminating the need for the high-temperature, high-shear process that takes 30-60 minutes in traditional wet processes. Based on the power consumption of conventional shearing equipment in the industry, each ton of modified asphalt can save more than 120 kWh of energy. This eliminates the high energy consumption (approximately 120-150 kWh / t), long shearing time, dedicated storage and transportation equipment, and segregation risk associated with premixed modified asphalt in wet modification processes. The composite modified granules can be bagged for transportation, are stable during storage, and can be used immediately after mixing. Furthermore, it does not use large amounts of organic solvents, reducing pollution and lowering the environmental burden from landfilling and incinerating waste plastics. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The results are the dry mixing and dispersibility test results of the composite modified powder, where (a) is the test result of LDPE:EVA:SBS=1:1:1, (b) is the test result of LDPE:EVA:SBS=1:1:2, and (c) is the test result of LDPE:EVA:SBS=1:1:3.

[0035] Figure 2 The results are asphalt fluorescence microscopy test results. (a) is a fluorescence micrograph of pure matrix asphalt, (b) is a fluorescence micrograph of traditional wet-process SBS modified asphalt, (c) is a fluorescence micrograph of composite modified asphalt prepared with the preferred ratio of the present invention (LDPE:EVA:SBS=1:1:1), (d) is a fluorescence micrograph of composite modified asphalt with increased SBS content (ratio 1:1:2), and (e) is a fluorescence micrograph of composite modified asphalt with excessively high SBS content (ratio 1:1:3).

[0036] Figure 3 This is a comparison chart of the dynamic stability of different asphalt mixtures.

[0037] Figure 4 This is a comparison chart of the freeze-thaw splitting strength of different asphalt mixtures.

[0038] Figure 5This is a comparison chart of fatigue life of different asphalt mixtures. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] This invention provides a method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture, the preparation steps of which include:

[0041] Step S1: Weigh 25%–35% of waste low-density polyethylene (LDPE), 25%–35% of waste ethylene-vinyl acetate copolymer (EVA), and 30%–50% of styrene-butadiene-styrene block copolymer (SBS) by mass percentage and place them in a drying oven. Dry them continuously at 75–85°C for 3–5 hours to remove moisture from the surface of the raw materials and prevent material agglomeration due to moisture during subsequent mixing and melting, thereby obtaining a dried polymer.

[0042] Step S2: Transfer the dried polymer to a high-speed mixer, add 1.5-2.5 wt% of crosslinking agent, 2.5-3.5 wt% of dispersant, 1.5-2.5 wt% of antioxidant, 4-6 wt% of flux, and 2.5-3.5 wt% of coupling agent to the dried polymer, close the machine cover, start the high-speed mixer, and mix at a speed of 800-1500 r / min for 4-8 min to obtain a premix with uniform composition.

[0043] The crosslinking agent can be an environmentally friendly organic peroxide, preferably dicumyl peroxide; the dispersant is soybean oil, which helps the polymer spread more evenly; the antioxidant is the hindered phenolic antioxidant pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate); the flux is alumina powder; and the coupling agent is a titanate coupling agent.

[0044] Step S3: All the premixed material is put into a room temperature crushing device and subjected to impact and shearing at a speed of 1000-2000 r / min for 5-15 minutes at 15-30℃. The purpose is to break and refine the polymer clumps and further mix the additives attached to them with the polymer. Then, the crushed particles are sieved to select particles with a particle size of 1-6 mm as the primary powder for composite modification.

[0045] Step S4: Spread the composite modified primary powder evenly in a shallow dish and dry it at a low temperature of 70-80℃ for 2-4 hours in a forced-air drying oven to completely remove moisture. Then, sieve it again to accurately select and retain particles with a particle size of 1-6 mm as composite modified powder. Then, pack it into a sealed and moisture-proof packaging bag and store it in a dry and light-proof environment at a temperature of 20-30℃.

[0046] Step S5: Mix the composite modified powder with 70# base asphalt and aggregate. The base asphalt is 70# road petroleum asphalt, and its dosage is 4.5~5% of the aggregate mass. The dosage of the composite modified powder is 6~10% of the base asphalt mass. The aggregate gradation adopts the median or design gradation of AC-13 type dense gradation specified in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40). Among them, mineral powder accounts for 5~10% of the total aggregate mass, and the remainder is coarse and fine aggregate. The specific mixing process is as follows:

[0047] S51, Pretreatment of aggregates and mineral powder: Place coarse and fine aggregates in a heating chamber and heat to 190-210°C to ensure that the aggregate surface is dry and reaches the high temperature required for subsequent mixing. Heat the mineral powder in a separate container to 160-180°C and heat the base asphalt to 160-180°C to give it good fluidity.

[0048] S52, the heated aggregate and composite modified powder are put into a forced mixing pot and dry-mixed at 180-200℃ and a speed of 40-60 r / min for 0.5-1.5 min. During this stage, the high-temperature aggregate acts as a heat source, rapidly heating the surface of the composite modified powder to a molten or semi-molten state. Under the collision and friction of the aggregate, the powder adheres evenly to the aggregate surface, forming a preliminary plastic coating layer.

[0049] S53. Add preheated base asphalt to the dry-mixed aggregate-composite modified powder mixture and continue mixing for 2-3 minutes. At this time, the molten composite modified powder and liquid asphalt permeate and fuse with each other under shear force, forming a continuous and uniform composite modified asphalt mortar coating layer on the aggregate surface and in the asphalt matrix.

[0050] S54. Preheated mineral powder is added to the mixing pot and stirred for 2-3 minutes at 165-175℃ to obtain the finished dry-process LDPE / EVA / SBS composite modified asphalt mixture. During this process, the addition of mineral powder further stabilizes the mixture system, fills the voids, and interacts with the composite modified asphalt mastic. Throughout the mixing process, the mixture has a uniform color and no obvious clumping of modifiers or asphalt leakage.

[0051] Example 1

[0052] Step S1: Weigh LDPE, EVA, and SBS in a mass ratio of 1:1:1, place them in a drying oven, and dry them continuously at 80°C for 4 hours to obtain the dried polymer.

[0053] In step S2, the dried polymer is transferred to a high-speed mixer, and 2 wt% of peroxide, 3 wt% of soybean oil, 2 wt% of antioxidant, 5 wt% of alumina powder, and 3 wt% of titanate coupling agent are added. After closing the machine cover, the high-speed mixer is started and mixed at 1200 r / min for 6 min to obtain a premix with uniform composition.

[0054] Step S3: All the premixed material is put into a room temperature crushing device and subjected to impact and shearing at a speed of 1500 r / min for 10 minutes at 20℃. Then the crushed particles are screened to obtain composite modified primary powder with a particle size of 3 mm.

[0055] Step S4: Spread the composite modified primary powder evenly in a shallow dish, place it in a forced-air drying oven at 75°C for 3 hours, sieve it again, accurately select and retain particles with a diameter of 3 mm as composite modified powder, pack it into a sealed moisture-proof packaging bag, and store it in a dry and light-proof environment at 25°C.

[0056] Step S5: Mix the composite modified powder with 70# base asphalt and aggregate. The base asphalt is 70# road petroleum asphalt, and its dosage is 4.8% of the aggregate mass. The composite modified powder dosage is 8% of the base asphalt mass. The aggregate gradation adopts the median or design gradation of AC-13 type dense gradation specified in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40). Among them, mineral powder accounts for 8% of the total aggregate mass, and the remainder is coarse and fine aggregate. The specific mixing process is as follows:

[0057] S51, coarse and fine aggregates are placed in heating chambers and heated to 200°C, mineral powder is heated to 170°C, and base asphalt is heated to 170°C.

[0058] S52, the heated aggregate and composite modified powder are put into a forced mixing pot and dry-mixed at 50 r / min for 1 min at 190℃, so that the composite modified powder is evenly adhered to the surface of the aggregate to form a preliminary plastic coating layer.

[0059] S53, add preheated base asphalt to the dry-mixed aggregate-composite modified powder mixture, and continue mixing for 2.5 minutes to form a continuous and uniform composite modified asphalt mortar coating layer on the aggregate surface and in the asphalt matrix.

[0060] S54. Preheated mineral powder is added to the mixing pot and stirred for 2.5 minutes at 170°C to obtain LDPE / EVA / SBS composite modified asphalt mixture.

[0061] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0062] Composite modified powder: melt index is 4.28 g / 10min. Dry mixing and dispersion test shows that the powder is completely melted, the aggregate surface is uniformly coated, and there is no residue visible to the naked eye.

[0063] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4171 cycles / mm, low-temperature flexural strain at -10℃ is 5283 µε, freeze-thaw splitting strength ratio (TSR) is 92.3%, fatigue life (0.6 stress ratio) is 674 cycles, pendulum value (BPN) is 61.5, and mean texture depth (MTD) is 0.793 mm.

[0064] The aforementioned excellent performance results are attributed to the good processing and dispersion characteristics of the composite modified particles. The dry-mixing dispersion test results of the composite modified particles in this embodiment are as follows: Figure 1 As shown in (a), the dry-mixing dispersion test shows that the composite modified powder prepared in this embodiment can completely melt and uniformly coat the surface of high-temperature aggregates without any visible residue, laying the foundation for the formation of homogeneous modified asphalt mastic. In this invention, the fluorescence micrograph of the modified asphalt is shown in the figure. Figure 2 As shown, where Figure 2 (a) is a fluorescence micrograph of pure matrix bitumen. Figure 2 (b) is a fluorescence micrograph of conventional wet-process SBS modified bitumen. Figure 2 (c) is a fluorescence micrograph of the modified asphalt in this embodiment. Under the fluorescence microscope, the LDPE / EVA / SBS ternary system forms a dense, continuous, and uniform composite network structure in the asphalt, with no obvious phase separation. This is the fundamental reason for its superior comprehensive performance. In this embodiment, the dynamic stability, freeze-thaw splitting strength, and fatigue life of the mixture are as follows: Figures 3-5 As shown.

[0065] Example 2

[0066] Step S1: Weigh 25% of waste low-density polyethylene (LDPE), 35% of waste ethylene-vinyl acetate copolymer (EVA), and 40% of styrene-butadiene-styrene block copolymer (SBS) by mass percentage and place them in a drying oven. Dry them continuously at 75°C for 3 hours to remove moisture from the surface of the raw materials and prevent material agglomeration due to moisture during subsequent mixing and melting, thereby obtaining a dried polymer.

[0067] In step S2, the dried polymer is transferred to a high-speed mixer, and 1.5 wt% of peroxide, 2.5 wt% of soybean oil, 1.5 wt% of antioxidant, 4 wt% of alumina powder, and 2.5 wt% of titanate coupling agent are added. After closing the machine cover, the high-speed mixer is started and mixed at 800 r / min for 3 minutes to obtain a premix with uniform composition.

[0068] Step S3: All premixed materials are put into a room temperature crushing device and subjected to impact and shearing at 1000 r / min for 5 minutes at 15℃ to break and refine the polymer clumps and further mix the adhering additives with the polymer. Then, the crushed particles are sieved to obtain composite modified primary powder with a particle size of 1 mm.

[0069] Step S4: Spread the composite modified primary powder evenly in a shallow dish, place it in a forced-air drying oven at 70°C for 2 hours, sieve it again, accurately select and retain particles with a diameter of 1 mm as composite modified powder, pack it into a sealed moisture-proof packaging bag, and store it in a dry and light-proof environment at 20°C.

[0070] Step S5: Mix the composite modified powder with 70# base asphalt and aggregate. The base asphalt is 70# road petroleum asphalt, and its dosage is 4.5% of the aggregate mass. The composite modified powder dosage is 6% of the base asphalt mass. The aggregate gradation adopts the median or design gradation of AC-13 type dense gradation specified in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40). Among them, mineral powder accounts for 5% of the total aggregate mass, and the remainder is coarse and fine aggregate. The specific mixing process is as follows:

[0071] S51, coarse and fine aggregates are placed in a heating chamber and heated to 190°C, mineral powder is heated to 160°C in a separate container, and base asphalt is heated to 160°C.

[0072] S52, the heated aggregate and composite modified powder are put into a forced mixing pot and dry-mixed at 180°C and a speed of 40 r / min for 0.5 min, so that the composite modified powder is evenly adhered to the surface of the aggregate to form a preliminary plastic coating layer.

[0073] S53, add preheated base asphalt to the dry-mixed aggregate-composite modified powder mixture, and continue mixing for 2 minutes to form a continuous and uniform composite modified asphalt mortar coating layer on the aggregate surface and in the asphalt matrix.

[0074] S54. Preheated mineral powder is added to a mixing pot and stirred for 2 minutes at 165°C to obtain the finished dry-process LDPE / EVA / SBS composite modified asphalt mixture.

[0075] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0076] Composite modified powder: melt index is 3.12 g / 10min. Dry mixing and dispersion test shows that the powder has melted and the aggregate surface is relatively uniformly coated, with occasional slight agglomeration.

[0077] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 3852 cycles / mm, low-temperature flexural strain at -10℃ is 4985 µε, freeze-thaw splitting strength ratio (TSR) is 88.7%, fatigue life (0.6 stress ratio) is 612 cycles, pendulum value (BPN) is 59.8, and mean texture depth (MTD) is 0.756 mm.

[0078] Example 3

[0079] Step S1: Weigh 35% of waste low-density polyethylene (LDPE), 25% of waste ethylene-vinyl acetate copolymer (EVA), and 40% of styrene-butadiene-styrene block copolymer (SBS) by mass percentage and place them in a drying oven. Dry them continuously at 85°C for 5 hours to obtain the dried polymer.

[0080] In step S2, the dried polymer is transferred to a high-speed mixer, and 2.5 wt% of peroxide, 3.5 wt% of soybean oil, 2.5 wt% of antioxidant, 6 wt% of alumina powder, and 3.5 wt% of titanate coupling agent are added. After closing the machine cover, the high-speed mixer is started and mixed at 1500 r / min for 8 minutes to obtain a premix with uniform composition.

[0081] Step S3: All premixed materials are put into a room temperature crushing device and subjected to impact and shearing at 2000 r / min for 15 minutes at 30℃ to break and refine the polymer clumps and further mix the adhering additives with the polymer. Then, the crushed particles are sieved to obtain composite modified primary powder with a particle size of 6 mm.

[0082] Step S4: Spread the composite modified primary powder evenly in a shallow dish, place it in a forced-air drying oven at 80°C for 4 hours, sieve it again, accurately select and retain particles with a particle size of 6 mm as composite modified powder, pack it into a sealed moisture-proof packaging bag, and store it in a dry and light-proof environment at 30°C.

[0083] Step S5: Mix the composite modified powder with 70# base asphalt and aggregate. The base asphalt is 70# road petroleum asphalt, and its dosage is 5.5% of the aggregate mass. The composite modified powder dosage is 10% of the base asphalt mass. The aggregate gradation adopts the median or design gradation of AC-13 type dense gradation specified in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40). Among them, mineral powder accounts for 10% of the total aggregate mass, and the remainder is coarse and fine aggregate. The specific mixing process is as follows:

[0084] S51, Pretreatment of aggregates and mineral powder: Place coarse and fine aggregates in a heating chamber and heat to 210°C to ensure that the aggregate surface is dry and reaches the high temperature required for subsequent mixing. Heat the mineral powder in a separate container to 180°C and heat the base asphalt to 180°C to give it good fluidity.

[0085] S52, the heated aggregate and composite modified powder are put into a forced mixing pot and dry-mixed at 60 r / min for 1.5 min at 200℃, so that the composite modified powder is evenly adhered to the surface of the aggregate to form a preliminary plastic coating layer.

[0086] S53, add preheated base asphalt to the dry-mixed aggregate-composite modified powder mixture, and continue mixing for 3 minutes to form a continuous and uniform composite modified asphalt mortar coating layer on the aggregate surface and in the asphalt matrix.

[0087] S54. Preheated mineral powder is added to a mixing pot and stirred for 3 minutes at 175°C to obtain the finished dry-process LDPE / EVA / SBS composite modified asphalt mixture.

[0088] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0089] Composite modified powder: melt index is 4.75 g / 10min. Dry mixing and dispersion test shows that the powder melts rapidly, the aggregate surface is uniformly coated, and there is no obvious agglomeration.

[0090] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4023 cycles / mm, low-temperature flexural strain at -10℃ is 5120 µε, freeze-thaw splitting strength ratio (TSR) is 90.5%, fatigue life (0.6 stress ratio) is 645 cycles, pendulum value (BPN) is 60.9, and mean texture depth (MTD) is 0.781 mm.

[0091] Example 4

[0092] The difference from Example 1 is that in S1, 25% LDPE, 25% EVA, and 50% SBS are weighed by mass percentage, that is, LDPE:EVA:SBS is 1:1:2.

[0093] Everything else is the same as in Example 1.

[0094] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0095] Composite modified powder: melt index is 2.86 g / 10min. Dry mixing and dispersion test shows that most of the powder can be melted and dispersed, but there is slight agglomeration in some areas.

[0096] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability is 3981 cycles / mm, low temperature flexural strain is 4605µε, and freeze-thaw splitting strength ratio is 81.3%.

[0097] The results of the dry-mixing dispersibility test of the composite modified particles in this implementation are as follows: Figure 1 As shown in (b), the microstructure of the composite modified asphalt under this mix proportion is as follows: Figure 2 As shown in (d), compared with Example 1, the uniformity of the modifier phase decreased, and the dynamic stability, freeze-thaw splitting strength, and fatigue life of the corresponding mixture are as follows: Figures 3-5 As shown.

[0098] Example 5

[0099] The only differences from Example 1 are: in S51, the aggregate is heated to 190°C and the base asphalt is heated to 160°C; in S52, the dry mixing temperature is 180°C; and in S54, the mixing temperature is 165°C.

[0100] Everything else is the same as in Example 1.

[0101] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0102] Composite modified powder: Same as in Example 1.

[0103] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4010 cycles / mm, low-temperature flexural strain at -10℃ is 5150 µε, and freeze-thaw splitting strength ratio (TSR) is 89.8%. During the mixing process, the melting rate of the modified powder is slightly slower than that in Example 1, but the final mixture is uniform.

[0104] Conclusion: Even when operating at the lower limit of the process temperature range, the effective melting and dispersion of the composite modified powder and its good comprehensive performance can still be guaranteed, proving that the process of the present invention has a wide temperature operating window and good construction tolerance.

[0105] Example 6

[0106] The only difference from Example 1 is that in S3 and S4, the final composite modified powder with a particle size of 1 mm was screened and retained.

[0107] Everything else is the same as in Example 1.

[0108] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0109] Composite modified powder: melt index 4.35 g / 10min;

[0110] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4105 cycles / mm, and low-temperature flexural strain at -10℃ is 5200 µε. Powder dust increased slightly during mixing, but dispersion and melting speeds were faster.

[0111] Conclusion: Small-particle-size powder has a large specific surface area, melts and reacts faster, which is conducive to the formation of a denser modified network, and its performance is comparable to that of the preferred particle size (3 mm).

[0112] Example 7

[0113] The only difference from Example 1 is that in S3 and S4, the final composite modified powder with a particle size of 2 mm was screened and retained.

[0114] Everything else is the same as in Example 1.

[0115] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0116] Composite modified powder: melt flow index is 4.31 g / 10 min;

[0117] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4135 cycles / mm, low-temperature flexural strain at -10℃ is 5230με, freeze-thaw splitting strength ratio (TSR) is 92.0%, and fatigue life (0.6 stress ratio) is 670 cycles.

[0118] Example 8

[0119] The only difference from Example 1 is that in S3 and S4, the final composite modified powder with a particle size of 5 mm was screened and retained.

[0120] Everything else is the same as in Example 1.

[0121] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0122] Composite modified powder: melt flow index is 4.15 g / 10 min;

[0123] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4080 cycles / mm, low-temperature flexural strain at -10℃ is 5100με, freeze-thaw splitting strength ratio (TSR) is 90.5%, and fatigue life (0.6 stress ratio) is 645 cycles.

[0124] Example 9

[0125] The only difference from Example 1 is that in S1, 35% LDPE, 35% EVA, and 30% SBS are weighed by mass percentage respectively.

[0126] Everything else is the same as in Example 1.

[0127] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0128] Composite modified powder: melt flow index is 4.82 g / 10 min;

[0129] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 3920 cycles / mm, low-temperature flexural strain at -10℃ is 4850με, freeze-thaw splitting strength ratio (TSR) is 88.5%, and fatigue life (0.6 stress ratio) is 590 cycles.

[0130] Example 10

[0131] The only difference from Example 1 is that S2 contains 1.8 wt% of a dry polymer peroxide, 2.8 wt% of soybean oil, 1.7 wt% of an antioxidant, 4.5 wt% of alumina powder, and 2.8 wt% of a titanate coupling agent.

[0132] Everything else is the same as in Example 1.

[0133] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0134] Composite modified powder: melt index 4.22 g / 10 min;

[0135] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4110 cycles / mm, low-temperature flexural strain at -10℃ is 5180με, freeze-thaw splitting strength ratio (TSR) is 91.2%, and fatigue life (0.6 stress ratio) is 655 cycles.

[0136] Example 11

[0137] The only difference from Example 1 is that S2 contains 2.3 wt% of a dry polymer peroxide, 3.3 wt% of soybean oil, 2.2 wt% of an antioxidant, 5.5 wt% of alumina powder, and 3.2 wt% of a titanate coupling agent.

[0138] Everything else is the same as in Example 1.

[0139] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment were tested, and the results are as follows:

[0140] Composite modified powder: melt flow index is 4.45 g / 10 min;

[0141] LDPE / EVA / SBS composite modified asphalt mixture: dynamic stability at 60℃ is 4160 cycles / mm, low-temperature flexural strain at -10℃ is 5240με, freeze-thaw splitting strength ratio (TSR) is 91.8%, and fatigue life (0.6 stress ratio) is 672 cycles.

[0142] Example 12

[0143] The only difference from Example 1 is that in S5, the amount of base asphalt is 4.3% of the mass of the aggregate, the amount of composite modified powder is 7% of the mass of the base asphalt, and the mineral powder accounts for 6% of the total mass of the aggregate.

[0144] Everything else is the same as in Example 1.

[0145] The performance of the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment was tested, and the results are as follows:

[0146] The dynamic stability at 60℃ is 4350 cycles / mm (due to the low oilstone ratio, the high temperature stability is improved), the low temperature bending strain at -10℃ is 4620με, the freeze-thaw splitting strength ratio (TSR) is 89.2%, and the fatigue life (0.6 stress ratio) is 565 cycles.

[0147] Example 13

[0148] The only difference from Example 1 is that in S5, the amount of base bitumen is 5.2% of the mass of the aggregate, the amount of composite modified powder is 9% of the mass of the base bitumen, and the mineral powder accounts for 9% of the total mass of the aggregate.

[0149] Everything else is the same as in Example 1.

[0150] The performance of the LDPE / EVA / SBS composite modified asphalt mixture obtained in this embodiment was tested, and the results are as follows:

[0151] The dynamic stability at 60℃ is 3950 cycles / mm, the low-temperature bending strain at -10℃ is 5450με (due to the high content of modifier, the toughness is significantly improved), the freeze-thaw splitting strength ratio (TSR) is 93.8%, and the fatigue life (0.6 stress ratio) is 720 cycles.

[0152] Comparative Example 1

[0153] The difference from Example 1 is that in S1, 20 wt% of LDPE, 20% of EVA, and 60 wt% of SBS are weighed by mass percentage, that is, LDPE:EVA:SBS is 1:1:3.

[0154] Everything else is the same as in Example 1.

[0155] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this comparative example were tested, and the results are as follows:

[0156] Composite modified powder: The powder melt index is only 1.53 g / 10min. After dry mixing, a large amount of unmelted powder agglomerates into hard lumps, and the dispersion is extremely uneven, making it impossible to carry out effective modification.

[0157] LDPE / EVA / SBS composite modified asphalt mixture: performance deterioration, dynamic stability <2800 cycles / mm.

[0158] In this comparative example, the dry-mixing dispersibility test results of the composite modified particles are as follows: Figure 1 As shown in (c), the fluorescence micrograph of the modified bitumen is as follows: Figure 2 As shown in (e), the figure exhibits obvious uneven dispersion and "island-like" structure. The corresponding dynamic stability, freeze-thaw splitting strength, and fatigue life of the mixture are as follows: Figures 3-5 As shown, the extremely low melt index and deteriorated mixture properties corroborate the fact that mismatched proportions disrupt an effective polymer network. This comparative example clearly demonstrates the negative impact of excessive SBS content.

[0159] Comparative Example 2

[0160] The difference from Example 1 is that in S1, EVA is not added, and 50wt% of LDPE and 50wt% of SBS are weighed out by mass percentage.

[0161] Everything else is the same as in Example 1.

[0162] In this comparative example, dry-mixing dispersion was acceptable, but due to the lack of bridging and compatibility effects of EVA, fluorescence microscopy showed severe separation between the SBS and LDPE / asphalt phases, forming an "island" structure, such as... Figure 2 (b) and Figure 2 As shown in the comparison of (c), the SBS and LDPE / asphalt phases are severely separated, forming an "island" structure similar to but more severe than that of traditional wet-process SBS modified asphalt, rather than the uniform ternary network of this invention, resulting in an improvement of less than 5% in low-temperature performance and fatigue performance.

[0163] Comparative Example 3

[0164] The difference from Example 1 is that S2 is omitted and no functional additives are added.

[0165] Everything else is the same as in Example 1.

[0166] In this comparative example, the crushing process generated a lot of dust, the composite modified powder had poor flowability, the melting lag was severe during dry mixing, the powder residue rate was >30%, and the dispersibility was poor, resulting in the various properties of the LDPE / EVA / SBS composite modified asphalt mixture being significantly lower than those of Example 1.

[0167] Comparative Example 4

[0168] The difference from Example 1 is that the following scheme replaces the process of preparing the composite modified powder in Example 1, namely S1~4, specifically:

[0169] Waste tire rubber powder sieved through an 80-mesh sieve was desulfurized by microwave (800W power, 10min time) to remove the surface vulcanization layer and improve its activity.

[0170] Weigh out LDPE, EVA, SBS, and 20wt% of pretreated waste tire rubber powder according to the ratio of LDPE:EVA:SBS=1:1:1. Add 2wt% of crosslinking agent, 3wt% of dispersant, 2wt% of antioxidant, 5wt% of alumina powder, and 3wt% of titanate coupling agent according to the total polymer mass. Dry at 75℃ for 3h to obtain composite powder.

[0171] Everything else is the same as in Example 1.

[0172] In this comparative example, the melt flow index decreased significantly (from 4.28 to 2.76) due to the addition of waste tire rubber powder. The low surface activity of the rubber powder resulted in poor compatibility with the ternary system, hindering melt flow. The agglomeration rate increased with increasing rubber powder content, indicating that the rubber powder could not integrate into the synergistic network of LDPE / EVA / SBS, forming "island-like" dispersions. The overall performance of the mixture deteriorated. Its dynamic stability at 60°C was only 3350 cycles / mm (approximately 80% of Example 1), its low-temperature bending strain at -10°C was 3950 µε (approximately 75% of Example 1), its freeze-thaw splitting strength ratio (TSR) decreased to 75.6% (significantly lower than 92.3% of Example 1), and its fatigue life (0.6 stress ratio) decreased drastically to 380 cycles (approximately 56% of Example 1). All performance characteristics were significantly inferior to Example 1. The insufficient synergy between the rigidity of the rubber powder and the elasticity of SBS disrupted the "rigid-elastic-flexible" three-dimensional network.

[0173] Comparative Example 5

[0174] The only difference from Example 1 is that in S3 and S4, the final composite modified powder with a particle size of 10 mm was screened and retained.

[0175] Everything else is the same as in Example 1.

[0176] The properties of the composite modified powder and the LDPE / EVA / SBS composite modified asphalt mixture obtained in this comparative example were tested, and the results are as follows:

[0177] Composite modified powder: melt flow index is 4.28 g / 10 min;

[0178] LDPE / EVA / SBS composite modified asphalt mixture: Due to the excessively large particle size, the center of the particles cannot be completely melted during the dry mixing process, and obvious residues are visible on the surface of the aggregate, resulting in a significant deterioration in performance. The dynamic stability drops to 3150 cycles / mm, the low-temperature bending strain is 3720με, the TSR drops to 74.8%, and the fatigue life is only 410 cycles.

[0179] Comparative Example 6

[0180] The only difference from Example 1 is that in S5, the amount of base bitumen is 2% of the mass of the aggregate, the amount of composite modified powder is 3% of the mass of the base bitumen, and the mineral powder accounts for 3% of the total mass of the aggregate.

[0181] Everything else is the same as in Example 1.

[0182] The performance of the composite modified powder and LDPE / EVA / SBS composite modified asphalt mixture obtained in this comparative example was tested. Due to the obvious insufficient aggregate coating rate during the mixing process, the asphalt film on the aggregate surface was discontinuous, with obvious peeling in some areas. The aggregate was not fully coated, and due to the serious lack of adhesion, the dynamic stability was 1050 cycles / mm, the low temperature bending strain was 1850με, the TSR was 52.4%, and the fatigue life was 120 cycles, which were far below the specifications.

[0183] Comparative Example 7

[0184] The only difference from Example 1 is that in S5, the amount of base asphalt is 8% of the mass of the aggregate, the amount of composite modified powder is 15% of the mass of the base asphalt, and the mineral powder accounts for 15% of the total mass of the aggregate.

[0185] Everything else is the same as in Example 1.

[0186] The performance of the LDPE / EVA / SBS composite modified asphalt mixture obtained in this comparative example was tested. Due to severe segregation of the mixture, although the low-temperature flexural strain reached 5850με, the high-temperature rutting resistance deteriorated sharply, the dynamic stability was only 1680 cycles / mm, and the TSR dropped to 80.6% due to the low porosity, with a fatigue life of 530 cycles.

[0187] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0188] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture, characterized in that, The preparation steps include: Step S1: Weigh out LDPE, EVA, and SBS respectively, and dry them to obtain a dried polymer; Step S2: Add crosslinking agent, dispersant, antioxidant, flux, and coupling agent to the dried polymer, and stir to obtain a premix with uniform composition. Step S3: The premix is ​​sheared and sieved to obtain composite modified primary powder; Step S4: After drying the primary composite modified powder, it is sieved again to obtain the composite modified powder. Step S5: The composite modified powder is mixed with the base asphalt and aggregate to obtain a dry LDPE / EVA / SBS composite modified asphalt mixture.

2. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1, characterized in that, In S1, LDPE accounts for 25% to 35% of the total mass, EVA accounts for 25% to 35% of the total mass, and SBS accounts for 30% to 50% of the total mass.

3. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1, characterized in that, In step S1, the drying temperature is 75–85°C and the drying time is 3–5 hours.

4. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1, characterized in that, In step S2, the amount of crosslinking agent is 1.5-2.5 wt% of the dry polymer, the amount of dispersant is 2.5-3.5 wt% of the dry polymer, the amount of antioxidant is 1.5-2.5 wt% of the dry polymer, the amount of flux is 4-6 wt% of the dry polymer, the amount of coupling agent is 2.5-3.5 wt% of the dry polymer, the stirring speed is 800-1500 r / min, and the stirring time is 4-8 min.

5. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 4, characterized in that, The crosslinking agent is selected from dicumyl peroxide, the dispersant is selected from soybean oil, the antioxidant is selected from hindered phenolic antioxidant pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, the flux is selected from alumina powder, and the coupling agent is selected from titanate coupling agents.

6. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1, characterized in that, In step S3, the shearing temperature is 15-30℃, the shearing speed is 1000-2000 r / min, the shearing time is 5-15 min, and the particle size of the composite modified primary powder is 1-6 mm.

7. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1, characterized in that, In step S4, the drying temperature is 70~80℃, the drying time is 2~4h, the particle size of the composite modified powder is 1~6 mm, and the storage temperature is 20~30℃.

8. The method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1, characterized in that, In S5, the amount of base asphalt used is 4.5-5.5% of the mass of the aggregate, the amount of composite modified powder is 6-10% of the mass of the base asphalt, and the mineral powder accounts for 5-10% of the total mass of the aggregate.

9. A method for preparing a dry-process LDPE / EVA / SBS composite modified asphalt mixture according to claim 1 or 8, characterized in that, The specific steps of mixing in S5 are as follows: S51, Pretreatment of aggregates and mineral powder: Place coarse and fine aggregates in a heating chamber and heat to 190-210℃, heat mineral powder to 160-180℃, and heat base asphalt to 160-180℃; S52, the heated aggregate and composite modified powder are put into a mixing pot and dry-mixed at 40-60 r / min for 0.5-1.5 min at 180-200℃. S53, add preheated base asphalt to the dry-mixed aggregate-composite modified powder mixture and continue mixing for 2-3 minutes; S54. Preheated mineral powder is added to a mixing pot and stirred for 2-3 minutes at 165-175℃ to obtain dry-process LDPE / EVA / SBS composite modified asphalt mixture.

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