A recycling method for rubber asphalt mixture

Abstract

The present invention discloses a method for recycling and reusing a rubber asphalt mixture. Aged or fatigue-degraded rubber asphalt mixture is placed in a microwave apparatus for microwave heating and stirring to achieve recycling and reusing the rubber asphalt mixture. The heating temperature T1 is first set to 150-160°C, and the heating time t1 is 1-15 minutes. The heating temperature T2 is then adjusted to 170-180°C, and the heating time t2 is 1-10 minutes. The rubber asphalt mixture is prepared by blending rubber powder, a microwave activator, a composite additive, an accelerator, and a light oil component to produce a rubber particle mixture; fusing the rubber particle mixture with matrix asphalt to produce rubber asphalt; and mixing the rubber asphalt with graded aggregate to form a rubber asphalt mixture. Recycling the rubber asphalt mixture not only forms a stable interconnected network structure, improving the rubber asphalt mixture's crack resistance and mechanical stability, but also significantly improving the rubber asphalt mixture's adhesion and resistance to water damage.

Description

Technical Field

[0001] The invention belongs to the technical field of modified asphalt in road engineering, and particularly relates to a recycling and reusing method for a rubber asphalt mixture. Background Art

[0002] Asphalt is a polymer composite material. During pavement use, it is easily affected by external factors such as light, heat, oxygen, moisture, and traffic loads. Asphalt undergoes a series of changes, such as volatilization, oxidation, decomposition, polymerization, and other physical and chemical reactions of asphalt components. These reactions will cause changes in the internal structure and chemical composition of the asphalt, resulting in a decrease in the road performance of the asphalt, which is called asphalt aging. When rubber asphalt ages, the low-temperature crack resistance and fatigue resistance of its mixture will be significantly reduced. Due to the high viscosity of rubber asphalt, its thermal regeneration process is relatively complex, and it is difficult to restore the performance of the rubber asphalt mixture simply through physical reactions such as heating and softening. Therefore, how to prepare a rubber asphalt mixture with self-recovering performance has become an important key technology that needs to be urgently solved.

[0003] Rubber particles have both physical and chemical effects on asphalt, significantly impacting its high-temperature and low-temperature properties, as well as its elastic recovery. The complex reaction mechanism between rubber particles and asphalt, coupled with ongoing physical and chemical reactions during the preparation of rubber asphalt, leads to moderate oxidative depolymerization of the rubber's spatial network macromolecules under high temperatures, transforming them into a large number of small network fragments and a small amount of chain-like structures. This imparts some plasticity and viscosity, but also results in a loss of some of the rubber's original elasticity. Existing research indicates that to address the aging resistance of rubber asphalt mixtures, domestic and international researchers have primarily optimized the properties of rubber asphalt by adding various modifiers, achieving improved aging resistance and road performance. For example, additives such as anti-aging agents, montmorillonite, layered silicates, and inorganic nanoparticles have been added to asphalt to significantly improve its resistance to thermal oxidative aging and UV oxidation. While these modifiers can extend the service life of rubber asphalt mixtures, they do not fundamentally address the technical challenges of their efficient recycling and reuse. Therefore, the development of a recycling process for rubber asphalt mixtures is crucial. Summary of the Invention

[0004] In order to improve the performance of aged rubber asphalt mixture during use, the present invention provides a method for recycling and reusing rubber asphalt mixture. This method can form a strong chemical connection between the rubber molecular structure and asphalt in the aged rubber asphalt mixture, form a three-dimensional network reinforcement structure inside the rubber particle modified asphalt, and at the same time improve the mechanical properties of the aged rubber asphalt mixture.

[0005] In order to solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for recycling and reusing a rubber asphalt mixture, characterized in that the specific steps are: placing the aged or fatigue-reduced rubber asphalt mixture in a microwave apparatus for microwave heating and stirring treatment to achieve recycling and reusing the rubber asphalt mixture; first, setting the heating temperature T1 in the microwave apparatus to 150-160° C. and the heating time t1 to 1-15 minutes to fully soften, plasticize and desulfurize the rubber particles; then adjusting the heating temperature T2 of the microwave apparatus to 170-180° C. and the heating time t2 to 1-10 minutes, thereby finally achieving recycling and reusing the aged or fatigue-reduced rubber asphalt mixture;

[0006] The specific preparation process of the rubber asphalt mixture is as follows: 10 to 25 parts by weight of rubber powder, 1 to 4 parts by weight of microwave activator, 0.2 to 3 parts by weight of composite additive, 0.08 to 2 parts by weight of accelerator and 1 to 3 parts by weight of light oil are placed in a stirrer with a rotation speed of 200 r / min, maintained at a constant temperature of 60 to 80° C. and stirred for 1 hour, then the stirred mixture is continuously shaken at a constant temperature of 60 to 80° C. in an ultrasonic cleaner for 1 hour, and then placed in a vacuum apparatus for vacuuming for 5 to 30 minutes to obtain a uniform rubber particle mixture S; 15 to 25 parts by weight of the rubber particle mixture S and 75 to 85 parts by weight of base asphalt are placed in a shearing apparatus, and rapidly sheared at 175 to 185° C. for 10 to 30 minutes to fully fuse the rubber asphalt to obtain rubber asphalt S1; and the rubber asphalt S1 is uniformly mixed with graded aggregate to obtain the rubber asphalt mixture;

[0007] The microwave activator is compounded from diphenyl disulfide, tetramethylthiuram disulfide and bismaleimide, the composite auxiliary agent is compounded from maleic anhydride and potassium persulfate, and the accelerator is octadecanoic acid.

[0008] It is further defined that the microwave frequency of the microwave instrument is 2450 MHz ± 50 Hz, and the microwave power is 100 to 900 W.

[0009] It is further defined that the microwave activator mainly refers to a microwave activator that reacts with the sulfur cross-linking bonds in the rubber particles when the microwave environment reaches a certain temperature condition, thereby achieving controllable desulfurization of the rubber asphalt in the mixture; when the microwave environment reaches a certain high temperature condition, the microwave activator can further promote the vulcanization between the rubber particles, thereby achieving controllable staged implementation of desulfurization and vulcanization of the rubber asphalt in the mixture. The microwave activator is a composite component, preferably composed of 0.1 to 0.8 parts by weight of diphenyl disulfide, 0.5 to 2 parts by weight of tetramethylthiuram disulfide and 0.2 to 2 parts by weight of bismaleimide. Under the action of microwaves, when the temperature reaches 150-160°C, diphenyl disulfide and tetramethylthiuram disulfide will react with the sulfur cross-linking bonds in the cross-linked rubber through a free radical mechanism. After the cross-linking bonds are broken by microwave action and mechanical shearing, they are grafted onto the rubber main chain, promoting the rapid desulfurization and depolymerization of the rubber asphalt, thereby achieving the release of light oil inside the rubber particles, which can partially replenish the oil lost by aging rubber asphalt; after the process is completed, the microwave energy is immediately increased to 170-180°C. Under this high temperature condition, the vulcanization activity of bismaleimide can be effectively stimulated, thereby reducing the apparent activation energy of the vulcanization reaction, increasing the reaction rate constant, and increasing the network structure parameters of the vulcanized rubber, which is beneficial to improving the mechanical properties of the rubber asphalt. Its mechanism of action lies in the fact that as the reaction time of rubber asphalt increases, the number of macromolecular free radicals generated by the breakage of rubber molecular chains increases. However, the amount of desulfurization radicals generated by diphenyl disulfide and tetramethylthiuram disulfide is insufficient to terminate the binding of all rubber molecular free radicals. At this time, when the vulcanization temperature is high enough, bismaleimide can react with the rubber without the need for a free radical source, thereby promoting the coupling of rubber macromolecular free radicals and generating a chain extension reaction. The bifunctional bismaleimide not only increases the crosslinking speed and crosslink density during the vulcanization process, but also inhibits polymer disproportionation and chain scission, thereby improving the overall performance of the rubber asphalt mixture.

[0010] Further specified, the composite additive is formed by compounding a polar solubilizer and an initiator. This composite additive can promote a grafting reaction on the surface of rubber particles, improving the compatibility of the rubber particles and enhancing the polarity of the rubber particles, thereby improving the efficiency of microwave treatment. Preferably, it is compounded from maleic anhydride and potassium persulfate, wherein the mass fraction of potassium persulfate is 0.01% to 0.5%. First, the maleic anhydride monomer initiates grafting on the surface of the rubber particles and simultaneously polymerizes with the monomer swollen within the rubber particles, changing the properties of the rubber particles and improving the compatibility of the two-phase interface. Second, the evenly distributed polar maleic anhydride can improve the uniformity of microwave energy transfer under the action of microwaves, thereby improving the heat transfer effect during the rubber asphalt preparation process.

[0011] It is further defined that the accelerator mainly promotes the combination of sulfur-sulfur bonds and carbon-sulfur bonds in rubber asphalt, improves the vulcanization efficiency of rubber asphalt, and also improves the acid value of rubber asphalt and improves the adhesion ability of asphalt to aggregate. The accelerator is preferably octadecanoic acid.

[0012] It is further defined that the density of the light oil is between 0.7 and 0.9 g / cm 3 The viscosity is between 1 and 10 cSt, and it has good fluidity and easy volatility. The light oil is preferably one or more of naphtha, paraffin oil or aromatic oil.

[0013] The graded aggregate is further defined as a mixture of steel slag particles of varying particle sizes or a combination of steel slag particles and mineral particles. Steel slag is a microwave-absorbing material, which gives it excellent heating properties under microwaves. Steel slag can significantly enhance the heating and healing properties of rubber asphalt mixtures under microwave heating. When microwaves pass through the microwave-absorbing material, the lost microwave energy is converted into heat, causing the rubber particles adhered to the aggregate to generate relatively high local temperatures. This achieves targeted heating, increases microwave efficiency, promotes the desulfurization and vulcanization of the microwave activator, and thus improves the performance of the rubber asphalt mixture.

[0014] It is further specified that the performance recovery process of the rubber asphalt mixture is determined by heating the rubber asphalt mixture in a microwave apparatus for a certain time and temperature. When the fatigue cracking resistance of the rubber asphalt mixture is significantly reduced, the heating time t1 should be low, the heating time t2 should be high, the heating temperature T1 should be low, and the heating temperature T2 should be high. When the fatigue cracking resistance of the rubber asphalt mixture is slightly reduced, the heating time t1 should be high, the heating time t2 should be low, the heating temperature T1 should be high, and the heating temperature T2 should be low. Controlling the heating time t1 and the heating temperature T2 is a key technical point in achieving the recycling and reuse of the rubber asphalt mixture and an important parameter for optimizing the performance of the rubber asphalt mixture. This is because the length of the heating time t1 can control the amount of rubber-breaking free radicals, thereby affecting further cross-linking between rubber molecules; the heating temperature T2 is a key parameter affecting the activity of bismaleimide.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] 1. The present invention adopts a continuous activation regeneration preparation process, organically combines microwave desulfurization with microwave vulcanization, and realizes the integrated implementation of the desulfurization and vulcanization processes of the aged rubber asphalt mixture, so that the aged rubber asphalt is first desulfurized and viscosity-reduced, followed by vulcanization to restore performance, which can reduce the difficulty of the rubber asphalt mixture regeneration process, and can significantly reduce the frequent setting of process flow and addition of additives in the thermal regeneration process of the rubber asphalt mixture, simplifying the complex thermal regeneration preparation process.

[0017] To restore the performance of aged rubber asphalt mixtures, this invention innovatively proposes a microwave activator based on microwave effects to control the phased desulfurization and vulcanization of rubber particles, achieving secondary crosslinking of the rubber particles within the rubber asphalt mixture. First, a pre-coated rubber particle mixture is prepared, allowing additives such as light oil and microwave activator to fully penetrate the rubber particles, preparing them for later reuse in the rubber asphalt mixture. When the performance of rubber asphalt mixture deteriorates, it is subjected to microwave regeneration treatment. Under the action of microwaves, when the temperature first reaches 150-160°C, diphenyl disulfide and tetramethylthiuram disulfide will react with the sulfur cross-links in the cross-linked rubber through a free radical mechanism. After the cross-links are broken by microwave action and mechanical shearing, they are grafted onto the rubber main chain, promoting the rapid desulfurization and depolymerization of the rubber asphalt, thereby achieving the release of light oil inside the rubber particles, which can replenish the light oil lost in the aged rubber asphalt mixture, improve the ductility of the rubber asphalt, and reduce its viscosity. After the process is completed, the microwave energy is immediately increased to 170-180°C. Under these high temperature conditions, the vulcanization activity of bismaleimide can be effectively stimulated, thereby reducing the apparent activation energy of the vulcanization reaction, increasing the reaction rate constant, and increasing the network structure parameters of the vulcanized rubber, which is beneficial to improving the mechanical properties of the rubber asphalt. In addition, since some vulcanized rubber is non-polar rubber, microwave desulfurization only has a good thermal effect on vulcanized polar rubber, which limits the selection of rubber types in rubber asphalt. The microwave desulfurization of the rubber asphalt mixture of the present invention can significantly reduce the dependence on the selection of rubber types. First, by using graded aggregates with wave-absorbing properties, when microwaves pass through the graded materials with wave-absorbing properties, molecular vibrations occur inside them, and the lost microwave energy is converted into heat energy, causing the rubber particles to locally generate relatively high temperatures, so as to achieve the effect of targeted fixed-point heating, improve the efficiency of microwave action, and promote the desulfurization and vulcanization effects of microwave activators. Secondly, maleic anhydride can also significantly modify the compatibility of rubber particles with asphalt, helping to improve the high-temperature stability of rubber asphalt mixtures. At the same time, the maleic anhydride, potassium persulfate, and octadecanoic acid selected by the present invention can further improve the acid value of rubber asphalt, optimize the adhesion of rubber asphalt to graded aggregate, on the one hand strengthen the absorbing effect of graded aggregate on the promotion of rubber asphalt desulfurization and vulcanization reactions, and on the other hand improve the water damage resistance of rubber asphalt mixtures.

[0018] 3. In order to improve the crack resistance and high-temperature stability of aged rubber asphalt mixture, the present invention further adopts a preparation method of microwave-vulcanized rubber asphalt. Under the action of microwave activator and accelerator, the composite additive can, on the one hand, enhance the network structure connection between rubber molecules, and on the other hand, promote the chemical bonding between rubber molecules and asphalt molecules, forming a more solid macromolecular network three-dimensional interpenetrating structure, thereby improving the interfacial cross-linking ability of aged rubber asphalt, and thus improving the crack resistance and high-temperature stability of aged rubber asphalt mixture.

[0019] In summary, the present invention realizes a process of synchronously implementing desulfurization and vulcanization of aged rubber asphalt mixture in stages by organically combining microwave desulfurization and microwave vulcanization, forming a preparation method for recycling and utilizing rubber asphalt mixture with high efficiency and stability, improving the application efficiency of aged rubber asphalt mixture, and restoring its performance by more than 80%, with significant economic and social benefits. DETAILED DESCRIPTION

[0020] The technical solutions in the specific implementation process of the present invention will be clearly and completely explained below.

[0021] The test used Karamay 90# asphalt as the base asphalt, and the experimental ratio of the rubber particle mixture is shown in Table 1. According to previous research and experimental experience, the pre-treated rubber particle mixture was first prepared, and then the base asphalt was heated to about 180℃, and then the pre-treated rubber particle mixture was added and the mixture was heated at 4500r·min. -1 Rubber asphalt was obtained by high-speed shearing for 30 minutes.

[0022] An AC-13 gradation was selected, and the steel slag aggregate mix was designed according to this gradation standard to produce a rubber asphalt mixture. The rubber asphalt mixture was subjected to cyclic wheel load testing and then thermal aging. Finally, the aged specimens were placed in a microwave apparatus for microwave stirring. The microwave apparatus's heating temperature (T1) was adjusted to 160°C and the heating time (t1) was adjusted to 5 minutes. The heating temperature (T2) was then adjusted to 175°C and the heating time (t2) was adjusted to 6 minutes. The resulting recycled rubber asphalt mixture was then subjected to performance testing. The results are shown in Table 2.

[0023] Table 1 Experimental mix design

[0024]

[0025] Table 2 Test results of specimens

[0026]

[0027] As can be seen from Table 2, the low-temperature crack resistance of the rubber asphalt mixture in Example 3 is improved by 26% and the high-temperature deformation resistance is improved by 29% compared to Comparative Example 1. Furthermore, compared to the unaged rubber asphalt mixture, the performance change is less than 18%, indicating that the performance recovery rate of the rubber asphalt mixture can reach 82%. Table 2 also shows that the low-temperature crack resistance of the rubber asphalt mixture gradually increases with the gradual increase of bismaleimide. Compared with Comparative Example 1, the rubber asphalt mixture in Example 3 exhibits better low-temperature crack resistance, indicating that the degree of vulcanization and crosslinking of the rubber particles is significant. This also further improves the water damage resistance of the rubber asphalt mixture. This demonstrates that the present invention, by organically combining microwave desulfurization and microwave vulcanization, fully utilizes the synergistic effect of the composite process, significantly improves the crosslinking ability of aged rubber asphalt, promotes the formation of a rubber-asphalt composite interpenetrating network structure, and thus improves the mechanical properties of the mixture.

[0028] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A recycling method for rubber asphalt mixture, characterized in that The specific steps are as follows: placing the aged or fatigue-reduced rubber asphalt mixture in a microwave instrument for microwave heating and stirring treatment to achieve the recycling and reuse of the rubber asphalt mixture; first setting the heating temperature T1 in the microwave instrument to 150-160°C and the heating time t1 to 1-15 minutes to fully soften and plasticize the rubber particles and desulfurize them; then adjusting the heating temperature T2 of the microwave instrument to 170-180°C and the heating time t2 to 1-10 minutes, and finally achieving the recycling and reuse of the aged or fatigue-reduced rubber asphalt mixture; The specific preparation process of the rubber asphalt mixture is as follows: 10-25 parts by weight of rubber powder, 1-4 parts by weight of microwave activator, 0.2-3 parts by weight of composite additive, 0.08-2 parts by weight of accelerator and 1-3 parts by weight of light oil are placed in a stirrer with a rotation speed of 200 r / min, maintained at a constant temperature of 60-80° C. and stirred for 1 hour, then the stirred mixture is continuously shaken in an ultrasonic cleaner at a constant temperature of 60-80° C. for 1 hour, and then placed in a vacuum apparatus and vacuumed for 5-30 minutes to obtain a uniform rubber particle mixture S; 15-25 parts by weight of the rubber particle mixture S and 75-85 parts by weight of base asphalt are placed in a shearing apparatus, and rapidly sheared at 175-185° C. for 10-30 minutes to fully fuse the rubber asphalt to obtain rubber asphalt S1; and the rubber asphalt S1 is uniformly mixed with graded aggregate to obtain the rubber asphalt mixture; The microwave activator is compounded from diphenyl disulfide, tetramethylthiuram disulfide and bismaleimide, the composite auxiliary agent is compounded from maleic anhydride and potassium persulfate, and the accelerator is octadecanoic acid; The microwave frequency of the microwave instrument is 2450 MHz ± 50 Hz, and the microwave power is 100-900 W.

2. The recycling method for rubber asphalt mixture according to claim 1, characterized in that: The microwave activator refers to a microwave activator that reacts with the sulfur cross-linking bonds in the rubber particles when the microwave environment reaches 150-160°C, thereby achieving controllable desulfurization of the rubber asphalt in the mixture; when the microwave environment reaches 170-180°C, the microwave activator can further promote the vulcanization between the rubber particles, thereby achieving controllable staged implementation of the desulfurization and vulcanization of the rubber asphalt in the mixture. The microwave activator is compounded with 0.1-0.8 parts by weight of diphenyl disulfide, 0.5-2 parts by weight of tetramethylthiuram disulfide, and 0.2-2 parts by weight of bismaleimide.

3. The recycling method for rubber asphalt mixture according to claim 1, characterized in that: The composite additive is compounded by a polar solubilizer and an initiator. The composite additive is used to promote a grafting reaction on the surface of rubber particles, improve the compatibility of rubber particles, enhance the polarity of rubber particles, and facilitate improving the efficiency of microwave treatment. The composite additive is compounded by maleic anhydride and potassium persulfate, wherein the mass fraction of potassium persulfate is 0.01% to 0.5%.

4. The recycling method for rubber asphalt mixture according to claim 1, characterized in that: The density of the light oil is 0.7-0.9 g / cm 3 The viscosity is between 1 and 10 cSt, and it has good fluidity and easy volatility. The light oil is divided into one or more of naphtha, paraffin oil or aromatic oil.

5. The recycling method for rubber asphalt mixture according to claim 1, characterized in that: The graded aggregate is a mixture of steel slag particles of different particle sizes or a compound of steel slag particles and mineral particles. When microwaves pass through the graded aggregate, the lost microwave energy is converted into heat energy, causing the rubber particles adhered to the graded aggregate to generate a relatively high local temperature, achieving a targeted point heating effect, improving the efficiency of microwave action, promoting the desulfurization and vulcanization effects of the microwave activator, and thereby improving the performance of the rubber asphalt mixture.

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