A controllable activation preparation method for rubber asphalt

Abstract

The present invention discloses a method for preparing rubber asphalt with controllable activation. The specific process is as follows: a microwave activator, rubber powder, base asphalt, additives, and accelerator are rapidly sheared at 160-170°C for 10-20 minutes to fully mix and obtain rubber asphalt S1; the rubber asphalt S1 is stirred in a microwave chemical synthesizer for a stirring time t1 of 10-50 minutes and a stirring temperature T1 of 140-170°C to fully desulfurize the rubber particles to obtain rubber asphalt S2; the stirring temperature T2 of the microwave chemical synthesizer is then adjusted to 180-190°C and the stirring time t2 is 5-10 minutes to finally obtain the rubber asphalt. The rubber asphalt can not only form a stable network interconnected structure, improve the rubber asphalt's crack resistance and enhance the stability of its mechanical properties, but also significantly improve the rubber asphalt's adhesion and enhance its resistance to water damage.

Description

Technical Field

[0001] The invention belongs to the technical field of modified asphalt for road engineering, and particularly relates to a method for preparing rubber asphalt with controllable activation. Background Art

[0002] Driven by the concept of building a resource-saving society, the application of rubber asphalt has rapidly expanded in China. However, the actual production of rubber asphalt still faces the challenge of difficult reaction process control, which poses a risk to the stability of the final product quality. Therefore, the development of rubber asphalt with controllable and stable properties has become a key technology that urgently needs to be addressed.

[0003] Rubber particles have both physical and chemical effects on asphalt, significantly affecting the high-temperature performance, low-temperature performance, and elastic recovery properties of asphalt. The reaction mechanism between rubber particles and asphalt is relatively complex, and the physical and chemical reactions between rubber particles and asphalt are always present during the preparation of rubber asphalt. Under high temperature conditions, the spatial network macromolecular structure of rubber undergoes moderate oxidation and depolymerization, turning into a large number of small network structure fragments and a small amount of chain-like substances, thereby gaining some plasticity and viscosity, but also losing some of the original rubber elasticity. As the rubber particles in the hot asphalt desulfurize and degrade, the mechanical properties of the rubber asphalt gradually decrease, making it difficult to control the stability of its quality. For example, US standards require that rubber asphalt be used within four hours of processing. When the temperature is below 190°C, only two heating cycles are allowed, and the rubber asphalt is required to meet all indicators after reheating. If it does not meet the requirements, a small amount of rubber powder needs to be added and reacted for another 45 minutes.

[0004] Existing research shows that the performance indicators of rubber asphalt continue to change with the increase of reaction time and have not reached a stable and unchanging state. In addition, long-term heating of rubber asphalt will cause the asphalt to age and reduce its performance. Therefore, rubber asphalt generally needs to be used immediately after production and does not require long-term storage. However, in the actual construction process, due to the connection of construction processes and the influence of some factors, short-term storage is inevitable, which is bound to increase the difficulty of its quality control, thereby affecting the road performance of rubber asphalt mixtures and causing frequent early road diseases. In summary, the control of rubber asphalt quality stability needs to be further improved. Therefore, it is very necessary to research and develop a material and process technology that can make the performance of rubber asphalt controllable. Summary of the Invention

[0005] In order to improve the performance stability of rubber asphalt during use, the present invention provides a method for preparing rubber asphalt with controllable activation. The rubber asphalt prepared by this method can form a strong chemical connection between the rubber molecular structure and the asphalt, so that a three-dimensional network reinforcement structure is formed inside the rubber particle-modified asphalt, while improving the mechanical properties and stability of the rubber asphalt.

[0006] The present invention adopts the following technical solution to solve the above technical problems, a method for preparing rubber asphalt with controllable activation, characterized by the following specific steps:

[0007] Step S1: 1 to 4 parts by weight of a microwave activator, 5 to 25 parts by weight of rubber powder, 72 to 92 parts by weight of base asphalt, 0.5 to 3 parts by weight of a composite additive, and 0.05 to 2 parts by weight of an accelerator are rapidly sheared at 160 to 170° C. for 10 to 20 minutes to fully mix and obtain rubber asphalt S1, wherein the microwave activator is a compound of diphenyl disulfide, tetramethylthiuram disulfide, and bismaleimide, the composite additive is a compound of maleic anhydride and potassium persulfate, and the accelerator is octadecanoic acid;

[0008] Step S2: placing the rubber asphalt S1 in a microwave chemical synthesizer and stirring, first adjusting the heating temperature T1 of the microwave chemical synthesizer to 140-170°C and the heating time t1 to 10-50 minutes to fully desulfurize the rubber particles to obtain the rubber asphalt S2, then adjusting the heating temperature T2 of the microwave chemical synthesizer to 180-190°C and the heating time t2 to 5-15 minutes, and realizing controllable adjustment of the performance of the rubber asphalt by adjusting the heating temperatures T1, T2 and the heating times t1, t2.

[0009] It is further defined that the microwave frequency of the microwave chemical synthesizer is 2450 MHz ± 50 Hz, and the microwave power is 100 to 900 W.

[0010] 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; 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 implementation of the desulfurization and vulcanization of the rubber asphalt in stages. 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 microwave irradiation, when the temperature reaches 140-170°C, diphenyl disulfide and tetramethylthiuram disulfide react with the sulfur crosslinks in the crosslinked rubber through a free radical mechanism. Microwave irradiation and mechanical shearing break the crosslinks and graft them onto the rubber backbone, achieving rapid desulfurization of the rubber asphalt. After this process, the microwave energy is increased to 180-190°C. Under these high temperatures, the vulcanization activity of bismaleimide is effectively stimulated, thereby reducing the apparent activation energy of the vulcanization reaction, increasing the reaction rate constant, and enhancing the network structure parameters of the vulcanized rubber, which is beneficial for improving the mechanical properties of the rubber asphalt. The mechanism of action is that as the reaction time of the 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 all the rubber molecular free radicals. At this time, when the vulcanization temperature is high enough, bismaleimide reacts with the rubber without the need for a free radical source, promoting the coupling of rubber macromolecular free radicals and generating a chain extension reaction. At the same time, the bifunctional bismaleimide can not only increase the cross-linking speed of the vulcanization process and increase the cross-linking density, but also inhibit the disproportionation and chain scission of the polymer, thereby improving the comprehensive performance of rubber asphalt.

[0011] Further specified, the composite additive is a compound of 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. It can also enhance the polarity of the rubber particles, thereby improving the efficiency of microwave treatment. Preferably, it is a compound of 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.

[0012] It is further defined that the accelerator mainly promotes the bonding of sulfur-sulfur bonds and carbon-sulfur bonds in the rubber asphalt, thereby improving the vulcanization efficiency of the rubber asphalt. It can also improve the acid value of the rubber asphalt and enhance the adhesion of the asphalt. The accelerator is preferably octadecanoic acid.

[0013] It is further specified that the controllable activation process is achieved by controlling the heating time and heating temperature of the rubber asphalt in a microwave chemical synthesizer. When the rubber asphalt requires better high-temperature deformation resistance, 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 rubber asphalt requires better low-temperature crack resistance, 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 controllable regulation of the performance of the rubber asphalt and an important parameter for optimizing the performance of the rubber asphalt. The length of the heating time t1 can control the amount of rubber-breaking free radicals, thereby affecting further crosslinking between rubber molecules. The height of the heating temperature T2 is a key parameter affecting the activity of bismaleimide.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0015] 1. The present invention adopts a continuous preparation process to organically combine microwave desulfurization and microwave vulcanization, realizing the integrated implementation of rubber asphalt desulfurization and vulcanization processes, which can significantly reduce the frequent setting of process flows and the addition of additives in the preparation process, simplify the complex preparation process of existing microwave desulfurization and microwave vulcanization implemented in stages, and form an efficient and stable rubber asphalt preparation method.

[0016] 2. Currently, it is difficult to effectively control the stability of the final product quality during the production and preparation of rubber asphalt, resulting in constant fluctuations in its properties. Furthermore, prolonged heating can age the asphalt and reduce its performance, significantly impacting its paving and compaction process control and its road durability. To address this issue, the present invention creatively proposes a microwave activator based on the microwave effect to control the desulfurization rate of rubber particles in rubber asphalt, achieving a staged, controlled deep desulfurization and vulcanization of the rubber particles in the rubber asphalt. In processes that pre-treat the rubber particles with microwave activation before modification and preparation, the uneven distribution of additives and impurities in the rubber powder during pre-treatment and activation makes it difficult to precisely control the heat transfer effect generated by the microwave energy. Consequently, the rupture of cross-links is accompanied by partial degradation of the main chain, which can easily lead to localized heat accumulation and combustion, or the generation of large amounts of foul-smelling smoke. Adding rubber particles to asphalt for microwave-controlled desulfurization significantly reduces this heat accumulation effect, improves the desulfurization uniformity of the rubber particles, and further significantly increases the deep desulfurization rate of the rubber particles under the action of the microwave activator. At the same time, under high-temperature microwave 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 rubber asphalt. In addition, since some vulcanized rubbers are non-polar rubbers, and microwave desulfurization only has a good thermal effect on vulcanized polar rubbers, this limits the selection of rubber types in rubber asphalt. The microwave desulfurization of rubber asphalt based on the present invention can significantly reduce the selection dependence on rubber type. First, the components in asphalt are complex and contain a large amount of polar and non-polar substances. Through the full mutual solubility of rubber and polar components in asphalt, and under the grafting effect of polar maleic anhydride, the microwave desulfurization effect of different types of rubber can be significantly improved, thereby improving the applicability of the process of the present invention. Secondly, maleic anhydride can also significantly modify the compatibility of rubber particles with asphalt, which helps to improve the high-temperature stability of rubber asphalt. At the same time, the maleic anhydride, potassium persulfate, and octadecanoic acid selected in the present invention can further improve the acid value of the rubber asphalt, optimize the adhesion between the rubber asphalt and the alkaline aggregate, and improve the water damage resistance of the rubber asphalt.

[0017] 3. In order to improve the high-temperature stability of rubber asphalt, the present invention adopts a microwave-vulcanized rubber asphalt preparation process. Under the action of microwave activator and promoter, the composite additive can enhance the network structure connection between rubber molecules, and also promote the chemical bonding between rubber molecules and asphalt molecules to form a more solid macromolecular network three-dimensional interpenetrating structure, thereby improving the interfacial cross-linking ability of rubber asphalt, and thus improving the anti-cracking ability and high-temperature stability of rubber asphalt.

[0018] In summary, this patent realizes the process of simultaneous implementation of rubber asphalt desulfurization and vulcanization in stages by organically combining microwave desulfurization and microwave vulcanization, forming a method for preparing efficient and stable rubber asphalt, improving the production efficiency of rubber asphalt, and increasing the high-temperature stability of rubber asphalt by 40%, with significant economic and social benefits. DETAILED DESCRIPTION

[0019] The technical solutions in the specific implementation process of the present invention will be clearly and completely explained below.

[0020] Table 1 Experimental mix design

[0021]

[0022] The test used Karamay 90# asphalt as the base asphalt, and the test mix ratio is shown in Table 1. Based on previous research and test experience, in the preparation of rubber asphalt S1, the base asphalt was first heated to about 160°C, and then 60 mesh rubber powder, a microwave activator formed by compounding diphenyl disulfide, tetramethylthiuram disulfide and bismaleimide, a composite additive formed by compounding maleic anhydride and potassium persulfate, and an accelerator octadecanoic acid were added. The temperature was kept at about 160°C and the mixture was rotated at 4500 r / min. -1 Rubber asphalt S1 was obtained by high-speed shearing at a rate of 100°C for 20 minutes. In the preparation of rubber asphalt S2, the ambient temperature of the microwave chemical synthesizer was set to 150°C, and rapid stirring was performed for 30 minutes. The ambient temperature of the microwave chemical synthesizer was then set to 190°C, and rapid stirring was performed for 10 minutes, ultimately producing the rubber asphalt. The properties of the rubber asphalt were controllably adjusted by adjusting the temperature and time during the preparation of rubber asphalt S2. Finally, the prepared rubber asphalt was stored in an oven at 165°C for 5 hours. The performance of the rubber asphalt after long-term storage was tested according to the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). The test results are shown in Table 2.

[0023] As can be seen from Table 2, the high-temperature storage stability of the rubber asphalt prepared in Example 3 is improved by 76% relative to Comparative Example 2. It can also be seen from Table 2 that after the addition of diphenyl disulfide and tetramethylthiuram disulfide, the needle penetration of the rubber asphalt increases and the softening point decreases, indicating that the degree of depolymerization of the rubber particles in the rubber asphalt is relatively large and the overall performance of the rubber asphalt is relatively soft. As the amount of bismaleimide gradually increases, the softening point and low-temperature ductility of the rubber asphalt gradually increase. Relative to Comparative Example 2, the rubber asphalt prepared in Example 3 exhibits good high-temperature deformation resistance and low-temperature cracking resistance, indicating that the degree of vulcanization crosslinking of the rubber particles is significant. This also further improves the adhesion of the rubber asphalt. This demonstrates that the present invention, by organically combining microwave desulfurization with microwave vulcanization, gives full play to the synergistic effect of its composite process, can significantly improve the crosslinking ability of the rubber asphalt, and is conducive to promoting the formation of a rubber-asphalt composite interpenetrating network structure, thereby improving the mechanical stability of the rubber asphalt.

[0024] Table 2 Test results of specimens

[0025] Needle penetration / 0.1mm Softening point / ℃ 5℃ elongation / mm Storage stability / ℃ Adhesion level Example 1 73 54 120 2.9 4 Example 2 68 58 138 2.3 5 Example 3 62 63 142 1.8 5 Comparative Example 1 74 56 111 3.6 4 Comparative Example 2 72 61 107 7.6 3

[0026] 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 method for preparing rubber asphalt with controlled activation, characterized in that The specific steps are: Step S1: 1-4 parts by weight of a microwave activator, 5-25 parts by weight of rubber powder, 72-92 parts by weight of base asphalt, 0.5-3 parts by weight of a composite additive, and 0.05-2 parts by weight of an accelerator are rapidly sheared at 160-170° C. for 10-20 minutes to fully mix them and obtain rubber asphalt S1, wherein the microwave activator is a compound of diphenyl disulfide, tetramethylthiuram disulfide, and bismaleimide, the composite additive is a compound of maleic anhydride and potassium persulfate, and the accelerator is octadecanoic acid; Step S2: placing the rubber asphalt S1 in a microwave chemical synthesizer and stirring, first adjusting the heating temperature T1 of the microwave chemical synthesizer to 140-170° C. and the heating time t1 to 10-50 min to fully desulfurize the rubber particles to obtain the rubber asphalt S2, then adjusting the heating temperature T2 of the microwave chemical synthesizer to 180-190° C. and the heating time t2 to 5-15 min. By adjusting the heating temperatures T1, T2 and the heating times t1, t2, the properties of the rubber asphalt can be controlled. The microwave frequency of the microwave chemical synthesizer is 2450 MHz ± 50 Hz, and the microwave power is 100-900 W.

2. The method for preparing rubber asphalt with controlled activation according to claim 1, wherein: 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 140-170°C, thereby achieving controllable desulfurization of the rubber asphalt; when the microwave environment reaches 180-190°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. 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 method for preparing rubber asphalt with controlled activation according to claim 1, characterized in that: The composite additive is compounded from a polar solubilizer and an initiator. The composite additive promotes a grafting reaction on the surface of rubber particles, improves the compatibility of the rubber particles, enhances the polarity of the rubber particles, and facilitates improving the efficiency of microwave treatment. The composite additive is compounded from maleic anhydride and potassium persulfate, wherein the mass fraction of the potassium persulfate is 0.01% to 0.5%.

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