Waste rubber powder modified asphalt and preparation method thereof

Abstract

The invention discloses waste rubber powder modified asphalt and a preparation method thereof, and belongs to the technical field of modified asphalt. According to the invention, the high-dosage waste rubber powder is added into the asphalt for modification, and the molecular composition, existing functional groups and the change condition of the functional groups of the modified asphalt are analyzed by means of an infrared spectrometer; a thermogravimetric analyzer is used for measuring the relation between the mass of the substance and the temperature; the surface of a sample is scanned by electron beams of an SEM scanning electron microscope, so that the surface microstructure of the rubber powder and the rubber powder modified asphalt is obtained, and the swelling mechanism, the microstructure and the interfacial effect of the high-mixing-amount rubber powder modified asphalt are obtained. The method has important guiding values for revealing the mixing state of the aggregate and the rubber powder modified asphalt, optimizing the design method of the high-mixing-amount rubber powder modified asphalt mixture, constructing the design indexes of the high-mixing-amount rubber powder modified asphalt mixture and the like. And meanwhile, the method has a great engineering value for preparing the high-volume waste rubber modified asphalt mixture which is excellent in preparation performance and easy to construct.

Description

Technical Field

[0001] The present invention relates to the technical field of modified asphalt, in particular to waste rubber powder modified asphalt and a preparation method thereof. Background Art

[0002] Rubber powder and asphalt have a natural affinity and can interact with each other. Performance analysis of rubber-asphalt mixtures demonstrates excellent road performance. Grinding scrap tires into rubber powder for use in road projects both domestically and internationally not only achieves harmless waste disposal but also improves road quality, demonstrating excellent road performance. Experimental testing has revealed that the primary chemical components of rubber powder are natural rubber, synthetic rubber, carbon black, silicon oxide, and iron oxide, all of which can be used to modify asphalt. Processing rubber powder and asphalt into rubber asphalt for use in concrete can thin new pavements, extend the lifespan of asphalt pavements, and reduce noise. For the reconstruction and overlaying of existing asphalt pavements, it can also mitigate reflective cracking in the original pavement, further improving the quality of highway construction. Rubber powder from scrap tires is a highly elastic material. The enhanced resilience of asphalt mixtures containing rubber powder can reduce residual deformation under load and minimize road damage.

[0003] Secondly, when asphalt contacts the aggregate interface, in addition to wetting, adsorption also occurs at the solid-liquid interface. The fundamental reason for adsorption at the solid-liquid interface is the inherent tendency of solid interfacial energy to decrease. When a liquid contacts a solid surface, because the force exerted by the solid's surface molecules (or atoms, ions) on the liquid molecules is greater than the force between the liquid molecules, the liquid molecules will concentrate at the solid-liquid interface, simultaneously reducing the solid-liquid interfacial energy. This concentration is called adsorption, and adsorption at the solid-liquid interface is widely used. However, due to the complexity of liquid-phase adsorption and the numerous influencing factors, the mechanism is still under investigation. Studying the bonding state between high-content waste rubber powder-modified asphalt and granular materials from the perspective of the interfacial effect mechanism between asphalt and granular materials has important guiding value for asphalt mixture design.

[0004] However, the design of asphalt mixture gradation composition is mainly based on traditional dense gradation, which has a high content of fine aggregate, a large amount of asphalt, poor high-temperature stability, and is prone to defects such as rutting and lumps. It can be seen that traditional asphalt pavements can no longer meet the above-mentioned high standards. However, there are few literature reports on high-content waste rubber powder modified asphalt and production processes. In the process of preparing high-content rubber asphalt mixtures, there are still technical difficulties in adding high-content waste rubber powder to asphalt for modification and evaluating whether the high-content waste rubber powder reacts completely with asphalt. In view of this, the study of the swelling mechanism, microstructure and interface effect of rubber powder modified asphalt has great engineering value in guiding how to prepare high-content waste rubber asphalt mixtures with excellent performance and easy construction in road paving projects. Summary of the Invention

[0005] The purpose of the present invention is to provide a waste rubber powder modified asphalt and a preparation method thereof, so as to solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides a method for preparing waste rubber powder modified asphalt, wherein the waste rubber powder modified asphalt comprises, by mass percentage, 25%-40% waste rubber powder, 57-73% base asphalt, and 0.2-3% admixture; the admixture is a mixture of coumarone resin and sulfur;

[0007] The preparation method comprises the following steps:

[0008] Step 1: Preparation of waste rubber powder

[0009] The waste tires are crushed, sheared in a rotating impeller, and ground in a grinder. Finally, the metal and fiber in the rubber powder are separated and sieved to obtain the waste rubber powder.

[0010] Step 2: Activation of waste rubber powder

[0011] The waste rubber powder obtained in step 1 is processed using a twin-screw extrusion process, and the waste rubber powder is desulfurized by the shearing action of the screw;

[0012] Step 3: Preparation of modified asphalt

[0013] The matrix asphalt is heated to a fluid state, the activated waste rubber powder obtained in step 2 is added and stirred, and then the admixture is added and stirred continuously to obtain a modified asphalt material with a stable network structure.

[0014] Preferably, the particle size of the waste rubber powder is 40-80 mesh.

[0015] Preferably, the matrix asphalt is 70# asphalt or 90# asphalt.

[0016] Preferably, in step 1, the rotation speed of the rotating impeller is 100-1200 rpm.

[0017] Preferably, in step 2, the extrusion temperature of the twin-screw is 190-280°C.

[0018] Preferably, in step three, the heating temperature of the matrix asphalt is 150-180°C.

[0019] The present invention also provides a waste rubber powder modified asphalt prepared by the above preparation method.

[0020] The present invention produces a waste rubber powder modified asphalt. The molecular composition, existing functional groups, and changes in functional groups of the modified asphalt are analyzed using an infrared spectrometer; the relationship between mass and temperature is measured using a thermogravimetric analyzer; and the surface structure of the waste rubber powder and the rubber powder modified asphalt is obtained by scanning the sample surface with an electron beam of a scanning electron microscope (SEM). The microscopic characteristics of the waste rubber powder and the modified asphalt are explored and analyzed. The test and analysis yield the following main research conclusions:

[0021] ① Thermogravimetric analysis of waste rubber powder shows that the mass percentage of rubber in waste tire rubber powder is about 53.2%, carbon black is 31.2%, water and small molecule additives are 6.1%, and inorganic additives are 9.5%. Thermogravimetric analysis of the four components of 70# asphalt shows that at 180°C, among the four components of 70# asphalt, the saturated component is the most unstable (starting to lose weight at 130°C) and is easy to volatilize during the production process, followed by aromatic phenol, but its volatility is very low, while the colloid and asphalt are basically non-volatile and are completely stable during the production process. 70# asphalt loses 15% of its weight after 1 day, 17.4% after 2 days, 19.2% after 3 days, and about 20% after 4 days. The volatilization of saturated fractions and dehydration are the main reasons for the weight loss of the sample. Thermogravimetric analysis test of rubber powder modified asphalt shows that the surface is smooth after 1 day of heat treatment, and sharp cracks and fragments are formed after stress, which is related to the volatilization of liquid saturated fractions. When treated at high temperature for 1 day to 4 days, the volatilization of saturated fractions is mainly limited to the surface of the material.

[0022] ② The infrared spectrum of rubber powder shows that the cracking oil contains isoprene (natural rubber monomer), indicating that the rubber is mainly natural rubber. After heating at 180℃ for 1h or 2h, the rubber powder loses all its moisture, undergoes oxidative decomposition, and changes its chemical structure. The infrared spectrum of 70# asphalt waste rubber powder shows that the wavenumber of the infrared spectrum is between 2500 and 3000cm -1 Range, the absorption peak is cycloalkanes and alkanes -CH (alkanes: -CH stretching vibration 2850 ~ 3000cm -1 ) stretching vibration, the absorption peak of -CH2 is the largest. The wave number range is 1450~1600cm -1 The absorption peak is caused by conjugated double bonds (benzene ring skeleton vibration); the wave number range is 1340~1450cm -1 The absorption peak is caused by -CH bending vibration; the wave number is between 1000 and 1300 cm -1 The absorption peak is the result of CO stretching vibration; the wave number range is 680~880cm -1The absorption peak is the result of the out-of-plane bending vibration of -CH. The infrared spectrum characteristic diagram of rubber powder modified asphalt shows that when the rubber powder content is 25%, 1d-2d shows an increase in carbonyl content (oxidation); 3d-4d show characteristic peaks of acid anhydride, indicating dehydration condensation between carboxyl groups; when the rubber powder content is 30%, 1d-2d shows an increase in carbonyl content (oxidation); 3d-4d shows a decrease in carbonyl content (oxidative decomposition, gasification); when the rubber powder content is 35%, 1d shows an increase in carbonyl content (oxidation); 2d shows a decrease in carbonyl content (oxidative decomposition, gasification); 3d-4d shows an increase in carbonyl content (oxidation). When the rubber powder content is 40%, 1d-4d shows an increase in carbonyl content (oxidation).

[0023] ③ SEM scanning of rubber powder revealed a wide particle size distribution of approximately 10-400 microns, with varying morphologies and features. Each particle contained numerous smaller secondary particles. SEM scanning of rubber powder-modified asphalt revealed uniform distribution of rubber particles, ranging in size from 10-200 microns. Observations also revealed good compatibility between rubber powder and asphalt, with waste rubber powder serving both adsorption and filling functions.

[0024] ④ The overall experimental test shows that after the addition of waste rubber powder to asphalt, both chemical modification and physical dissolution and swelling occur, and the waste rubber powder changes the structure of the asphalt to a certain extent.

[0025] ⑤ The effective content of rubber powder in asphalt was calculated based on the asphaltene content in asphalt (11.8%) and the weight loss of rubber powder after immersion (8.3%).

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the waste rubber powder obtained;

[0028] Figure 2 The thermogravimetric spectrum of the activated waste rubber powder prepared;

[0029] Figure 3 The thermogravimetric spectra of the waste rubber powder treated at 75℃ and 180℃ for different times;

[0030] Figure 4 The infrared spectrum of the pyrolysis oil obtained from the activated waste rubber powder obtained by extraction;

[0031] Figure 5 The infrared spectra of the activated waste rubber powder and the unactivated waste rubber powder after heating at 70℃ for 1h and 2h;

[0032] Figure 6 The infrared spectra of the prepared waste rubber powder and the unactivated waste rubber powder after heating at 180℃ for 1h and 2h;

[0033] Figure 7 This is the SEM image of the activated waste rubber powder prepared;

[0034] Figure 8 This is the SEM image of the pyrolysis oil obtained from the activated waste rubber powder;

[0035] Figure 9 The SEM images of the activated waste rubber powder treated at 75℃ and 180℃ for different time periods are shown;

[0036] Figure 10 Thermogravimetric spectra of rubber-modified asphalt with different rubber powder contents prepared in Examples 1-4 and Comparative Examples 1-2 at 180°C;

[0037] Figure 11 The infrared spectra of the rubber-modified asphalts with different rubber powder contents prepared in Examples 1-4 and Comparative Example 1 after heat treatment at 180°C;

[0038] Figure 12 This is the SEM image of the rubber-modified asphalt prepared in Comparative Example 1;

[0039] Figure 13 This is an SEM image of the rubber-modified asphalt prepared in Example 1;

[0040] Figure 14 This is the SEM image of the rubber-modified asphalt prepared in Example 2;

[0041] Figure 15 This is an SEM image of the rubber-modified asphalt prepared in Example 3;

[0042] Figure 16 This is an SEM image of the rubber-modified asphalt prepared in Example 4;

[0043] Figure 17 This is an SEM image of the rubber-modified asphalt prepared in Example 2 after heat treatment for 1 day;

[0044] Figure 18 This is an SEM image of the rubber-modified asphalt prepared in Example 2 after 2 days of heat treatment;

[0045] Figure 19 This is an SEM image of the rubber-modified asphalt prepared in Example 2 after 4 days of heat treatment;

[0046] Figure 20 This is a SEM image of the rubber powder extract of the rubber-modified asphalt prepared in Comparative Example 1;

[0047] Figure 21This is a SEM image of the rubber powder extract of the rubber-modified asphalt prepared in Example 1;

[0048] Figure 22 This is a SEM image of the rubber powder extract of the rubber-modified asphalt prepared in Example 2;

[0049] Figure 23 This is a SEM image of the rubber powder extract of the rubber-modified asphalt prepared in Example 3;

[0050] Figure 24 This is the SEM image of the rubber powder extract of the rubber-modified asphalt prepared in Example 4. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by means of the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without violating the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the protection scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application and belong to the scope of protection of the present invention.

[0052] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0053] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0054] Unless otherwise specified in the present invention, the reagents, instruments, and equipment used are those commonly used by those skilled in the art.

[0055] Example 1

[0056] This embodiment provides a method for preparing waste rubber powder modified asphalt, comprising the following steps:

[0057] Step 1: Preparation of waste rubber powder

[0058] At room temperature or under certain conditions, the entire tire is crushed into fragments of approximately 50 mesh. The rubber fragments are sheared in a high-speed rotating impeller (one end is fixed, the other end rotates around the fixed end) at a speed of 800 rpm. The rubber powder is further ground in a grinder. Metals are removed from the rubber powder using a magnetic separator, and then the rubber powder is sent to an air gravity separation table for fiber removal. The coarsely ground rubber powder is then placed in a grinder for a second metal removal, then sieved and the coarser particles are re-ground to obtain waste rubber powder with a particle size of 40 mesh.

[0059] Step 2: Activation of waste rubber powder

[0060] The waste rubber powder obtained in step 1 is processed by a twin-screw extrusion process at 220° C., and the waste rubber powder is desulfurized by the shearing action of the screw;

[0061] Step 3: Preparation of modified asphalt

[0062] According to the mass percentage, take 74.4% of 70# matrix asphalt and 25% of the activated waste rubber powder obtained in step 2, heat the 70# matrix asphalt to 180°C, add the activated waste rubber powder and stir, then add 0.3% coumarone resin and 0.3% sulfur as cross-linking stabilizers, and finally continue stirring to obtain a modified asphalt material with a stable network structure.

[0063] Example 2

[0064] This embodiment provides a method for preparing waste rubber powder modified asphalt, comprising the following steps:

[0065] Step 1 and step 2 are exactly the same as those in Example 1 and will not be repeated here.

[0066] Step 3: Preparation of modified asphalt

[0067] According to the mass percentage, 68.4% of 70# matrix asphalt and 30% of the activated waste rubber powder obtained in step 2 are taken, the 70# matrix asphalt is heated to 180°C, the activated waste rubber powder is added and stirred, and then 0.8% coumarone resin and 0.8% sulfur are added as cross-linking stabilizers, and finally stirred to obtain a modified asphalt material with a stable network structure.

[0068] Example 3

[0069] This embodiment provides a method for preparing waste rubber powder modified asphalt, comprising the following steps:

[0070] Step 1 and step 2 are exactly the same as those in Example 1 and will not be repeated here.

[0071] Step 3: Preparation of modified asphalt

[0072] According to the mass percentage, take 63% of 70# matrix asphalt and 35% of the activated waste rubber powder obtained in step 2, heat the 70# matrix asphalt to 180°C, add the activated waste rubber powder and stir, then add 1% coumarone resin and 1% sulfur as cross-linking stabilizers, and finally continue stirring to obtain a modified asphalt material with a stable network structure.

[0073] Example 4

[0074] This embodiment provides a method for preparing waste rubber powder modified asphalt, comprising the following steps:

[0075] Step 1 and step 2 are exactly the same as those in Example 1 and will not be repeated here.

[0076] Step 3: Preparation of modified asphalt

[0077] According to the mass percentage, take 57% of 70# matrix asphalt and 40% of the activated waste rubber powder obtained in step 2, heat the 70# matrix asphalt to 180°C, add the activated waste rubber powder obtained in step 2 and stir, then add 1.5% coumarone resin and 1.5% sulfur as cross-linking stabilizers, and finally continue stirring to obtain a modified asphalt material with a stable network structure.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing asphalt modified with low-content waste rubber powder, comprising the following steps:

[0080] Step 1 and step 2 are exactly the same as those in Example 1 and will not be repeated here.

[0081] Step 3: Preparation of modified asphalt

[0082] According to the mass percentage, take 79.8% of 70# matrix asphalt and 20% of the activated waste rubber powder obtained in step 2, heat the 70# matrix asphalt to 180°C, add the activated waste rubber powder obtained in step 2 and stir, then add 0.1% coumarone resin and 0.1% sulfur as cross-linking stabilizers, and finally continue stirring to obtain a modified asphalt material with a stable network structure.

[0083] Comparative Example 2

[0084] This comparative example uses unmodified 70# pure asphalt.

[0085] The microscopic characteristic structures of waste rubber powder and modified asphalt were analyzed and measured.

[0086] Specifically, an infrared spectrometer (IR) is used to analyze the molecular composition of asphalt and modified asphalt, the functional groups present, and the changes in functional groups; a thermogravimetric analyzer is used to measure the relationship between the mass of the substance and temperature; and a scanning electron microscope (SEM) is used to scan the sample surface with an electron beam to obtain a high-resolution image of the sample surface, which is used to identify the surface structure of the sample.

[0087] The present invention mainly uses the above three experimental methods to test and analyze the microstructure of waste rubber powder, matrix asphalt and waste rubber powder modified asphalt, and uses this to explore and analyze the microscopic characteristics of waste rubber powder and modified asphalt.

[0088] The scanning electron microscope image of the waste rubber powder obtained by the room temperature method in step 1 is as follows Figure 1 As shown. Figure 1 It can be seen that the surface of waste rubber powder is rough and irregular in shape, and rubber powder particles with rough surface react better with asphalt.

[0089] The activated waste rubber powder obtained in step 2 was subjected to thermogravimetric analysis at 350°C. The results are as follows: Figure 2 As shown. Figure 2 As can be seen, the weight loss in the first stage is approximately 6.1%, the second stage is 53.2%, and the third stage is 31.2%, leaving a residual ash content of 9.5%. Regarding the composition of the rubber powder, it can be seen that the first stage is primarily the decomposition of small organic molecules and oligomers, the second stage is the decomposition of rubber, and the third stage is the oxidation of carbon black. The ash content is generally composed of inorganic additives. Therefore, based on these results, the mass percentage of rubber in waste tire rubber powder is approximately 53.2%, carbon black is 31.2%, water and small molecule additives are 6.1%, and inorganic additives are 9.5%.

[0090] Thermogravimetric analysis of the waste rubber powder obtained in step 1 was performed at 75°C and 180°C. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that after treatment at 75°C for 1h and 2h, the sample lost about 0.5-0.6% of its weight (mainly due to water volatilization), and after treatment at 180°C for 1h and 2h, the sample lost about 1.9-2.6% of its weight (including water volatilization, volatilization of small molecule additives, and partial oxidation decomposition reaction).

[0091] The analysis and identification of the molecules of activated waste rubber powder were carried out by infrared spectroscopy. The analysis and determination were carried out by potassium bromide tablet method. 300 mg of potassium bromide and 2 mg of solid sample were ground into um-grade fine powder and then placed in a mold with a diameter of 5 to 10 × 10 7 After being pressed into a transparent sheet by a hydraulic press with a pressure of Pa, it is placed under the light path for analysis. Potassium bromide is used as an analytical reagent. It is dried in an oven at 150-200℃ for 6 hours to remove the moisture in the potassium bromide, and then placed in a desiccator to cool.

[0092] The waste rubber powder was activated by cracking and extraction at high temperature, and the obtained cracking oil was subjected to infrared spectroscopy. The results are as follows Figure 4 As shown. Figure 4 It can be seen that the waste rubber powder has a wave number of 2600-3000cm -1 In the range of 2000-2500 nm, the infrared spectrum of waste rubber powder showed strong absorption peaks, among which -CH2 had the largest absorption. These absorption peaks were caused by cycloalkanes and alkanes -CH (alkanes: -CH stretching vibration 2850-3000 cm -1 ) stretching vibration results. 1600cm -1 The peaks near the fingerprint region are partly caused by the conjugated double bond C=C (benzene ring skeleton vibration) and partly by C=O absorption. -1 The absorption peaks that appear in the wavenumber range are caused by the out-of-plane swing vibration of the -CH on the benzene ring. From these absorption peaks, it can be judged that the cracking oil contains isoprene (natural rubber monomer).

[0093] Figure 5 The infrared spectra of the activated waste rubber powder obtained in step 2 after heating at 70℃ for 1h and 2h are shown in Figure 2. Figure 5 It can be seen that the infrared spectra of the samples remained essentially unchanged after heating for 1 and 2 hours, indicating that the structure of the rubber powder is stable in air at 70°C. Combined with the results shown in the figure, this indicates that some moisture was lost at 70°C.

[0094] Figure 6 The infrared spectra of the waste rubber powder obtained in step 1 after heating at 180℃ for 1h and 2h are shown in Figure 2. Figure 6 It can be seen that after heating for 1h and 2h, the infrared spectrum of the sample changes greatly, and the water peak (3413cm -1 ) basically disappeared, and some of the absorption peaks attributed to rubber became weaker (2922 -1 、2853 -1 、1418cm -1 ), even disappear after 2 hours of heating (1607cm -1 ), and a new absorption peak (1697cm -1 , which belongs to the carbonyl group formed after the oxidation of CH). Combined with the weight loss results shown in the figure, it shows that at 180°C, the rubber powder will lose all its moisture, undergo oxidative decomposition reaction, and change its chemical structure, but the thermal impact is small and the weight loss is small. The total weight loss in 2h is 2.6%.

[0095] The microscopic morphology of the activated waste rubber powder obtained in step 2 was observed using scanning electron microscopy. Figure 7 As shown. Figure 7It can be seen that the particle size of the rubber powder is about 10-400 microns, the particle size distribution is relatively wide, the morphological characteristics are different, and each particle has many smaller secondary particles.

[0096] The SEM image of the waste rubber powder is shown below: Figure 8 As shown. Figure 8 It can be seen that the morphology of the rubber powder has not changed before extraction.

[0097] Figure 9 The infrared spectra of the activated waste rubber powder obtained in step 2 after heating at 70℃ and 180℃ for 1h and 2h. Figure 9 It can be seen that no morphological changes were observed after heating at 70°C for 1-2 hours; after heating at 180°C for 1-2 hours, the surface of the rubber particles became slightly smoother and no other changes were observed, indicating that after heating at 180°C, the sample shrank to a certain extent and the surface became denser, which may be related to the volatilization of small molecules in the rubber powder and the oxidation of the surface rubber powder.

[0098] The rubber-modified asphalts with different rubber powder contents prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to thermogravimetric testing at 180°C. The results are as follows: Figure 10 As shown, by Figure 10 As shown, after heat treatment at 180°C for 2 hours, the asphalt loses approximately 6.1% weight. The rubber-modified asphalt containing 20% rubber powder loses approximately 4.8%, while the rubber-modified asphalt containing 25-40% rubber powder loses between 3.2% and 3.6%. Combined with the asphalt analysis results, this weight loss is primarily due to the volatilization of saturated components in the asphalt. The rubber-modified asphalt containing 25% rubber powder exhibits relatively high thermal stability.

[0099] The rubber-modified asphalts with different rubber powder contents obtained in Examples 1-4 and Comparative Example 1 were analyzed and identified by infrared spectroscopy after heat treatment at 180°C. Figure 11 As shown. Figure 11 It can be seen that at wave numbers 2500-3000 cm -1 A strong absorption peak appeared in the range, and the position of the absorption peak was very similar to that of the matrix asphalt, with a slight change in intensity. This was caused by the addition of waste rubber powder. In addition, it is well known in the art that the infrared spectrum of 70# asphalt has a wavelength of 750cm -1 The absorption peaks around Figure 11 The peak disappeared in the matrix asphalt, while the waste rubber powder had an absorption peak at the corresponding position. It can be inferred that a chemical reaction occurred between the functional groups of the matrix asphalt and the active substances in the waste rubber powder.

[0100] Depend on Figure 11 At the same time, it can be seen that when 20% of rubber-modified asphalt is added and untreated (0d), the infrared spectrum is mainly CH and bound water (1630cm -1) absorption vibration peak; after heat treatment for 1d, the spectrum is at 1500-1900cm -1 There are multiple absorption vibration peaks, 1600cm -1 Represents the vibration peak of the benzene ring skeleton, 1600-1900cm -1 These peaks represent the absorption vibrations of carbonyl groups, indicating that the carbon in the asphalt or rubber powder has been oxidized after heat treatment. When heat treated for 2-4 days, the infrared spectrum is similar to that of treatment for 1 day, except that the peak at 1700 cm -1 , 1200cm -1 The peak intensities around 1 and 2 increase after 2 days and decrease after 3-4 days, indicating that when the heat treatment time is 1-2 days, the chemical composition changes of the rubber-modified asphalt are mainly due to the oxidation of weak bonds (mainly unsaturated double bonds in the rubber powder). When the heat treatment time is 3-4 days, the main changes are due to decarbonylation and decomposition reactions between carbonyl groups or ester groups.

[0101] The chemical changes in the system during treatment at 180°C with 25%, 30%, 35%, and 40% rubber-modified asphalt were similar to those observed with 20% rubber powder, but with slight variations likely due to the different rubber powder content. The 25% component showed an increase in carbonyl content (oxidation) in 1d-2d, while characteristic anhydride peaks appeared in 3d-4d, indicating dehydration condensation between carboxyl groups, which may be responsible for the highest thermal stability. The 30% component showed an increase in carbonyl content (oxidation) in 1d-2d, while a decrease in carbonyl content (oxidative decomposition and gasification) in 3d-4d. The 35% component showed an increase in carbonyl content (oxidation) in 1d, a decrease in carbonyl content (oxidative decomposition and gasification) in 2d, and an increase in carbonyl content (oxidation) in 3d-4d. The 40% component showed an increase in carbonyl content (oxidation) in 1d-4d.

[0102] The rubber-modified asphalt samples with different rubber powder contents obtained in Examples 1-4 and Comparative Example 1 were frozen and fractured, and then the cross-sections were etched with a solvent and observed under SEM. The results are as follows: Figure 12-16 As shown. Figure 12 It can be seen that the surface of the rubber-modified asphalt containing 20% rubber powder is irregular after etching, and the uneven morphology after dissolution can be seen. After magnification to 510 times, white rubber powder particles can be observed distributed on the surface, and the degree of dispersion is relatively uniform, indicating that there is good compatibility between the rubber powder and asphalt, and that the mixing process can meet the dispersion requirements. In addition, the particle size is small, generally below 40 microns, and varies in size. This is related to the embedding of the asphalt and also related to the fact that some rubber powder particles dissolve into the solvent during the dissolution process. Figure 13 It can be seen that the surface of the rubber-modified asphalt containing 25% rubber powder can be observed to have a denser distribution of particles, with a particle size of approximately less than 30 microns and a very uniform distribution. Figure 14It can be seen that white particles can be observed on the surface of the rubber-modified asphalt containing 30% rubber powder. The particle size is about 30 microns and the distribution is relatively uniform. Figure 15 It can be seen that dense particle distribution can be observed on the surface of rubber-modified asphalt containing 35% rubber powder. The particle size is about 40 microns or less, with different sizes and relatively uniform distribution. Figure 16 It can be seen that a dense distribution of particles can be observed on the magnified surface of the rubber-modified asphalt containing 40% rubber powder. The particle size is approximately below 40 microns, with different sizes and relatively uniform distribution.

[0103] In summary, the SEM images taken at different dosages clearly demonstrate the distribution and development of waste rubber powder in asphalt. Most of the waste rubber powder's surface has been dissolved and swelled by the light components in the asphalt, and a small amount of the light components has penetrated the waste rubber powder. This is because after the waste rubber powder and asphalt are thoroughly mixed at high temperatures, the waste rubber powder particles absorb the light components in the asphalt, dissolving and swelling. Simultaneously, a gel film forms on the surface of the waste rubber powder particles. The volume of the swollen waste rubber powder particles can reach 20%-30% of the binder. The gel film effectively connects the waste rubber powder particles together, forming a semi-solid continuous phase system with high viscosity. The waste rubber powder particles have both an adsorption and filling function.

[0104] The rubber-modified asphalt prepared in Example 2 was heat-treated at 180°C for 1, 2, and 4 days, and the morphological characteristics were observed using SEM. The results are as follows: Figure 17-19 As shown. Figure 17 It can be seen that the surface is smooth after 1 day of heat treatment, but sharp cracks and fragments are formed after being stressed, indicating that the surface is very brittle, which is related to the volatilization of liquid saturated components. Although the surface is very brittle, the bottom layer still maintains the flexibility of the asphalt, indicating that during the high temperature treatment of 1d-4d, the volatilization of saturated components is mainly limited to the surface of the material. Figure 18 It can be seen that after 2 days of heat treatment, some small holes are found on the surface of the sample. These holes should be bubbles formed when saturated components gradually rise from the interior of the asphalt to the surface and volatilize. In addition, it can be seen from the figure that the depth of the brittle fracture layer is about 100 microns. Figure 19 It can be seen that the sample after 4 days of heat treatment also showed the characteristics of surface embrittlement, which is also related to the volatilization of liquid saturated components.

[0105] Rubber powder has a stable three-dimensional network system. When reacting with hot asphalt, a part of the rubber powder undergoes a swelling and degradation reaction and dissolves in the asphalt to form a sol, while the other part still exists in the asphalt in the form of a small elastic structure. Studies have shown that this part of rubber particles that have not been completely dissolved, namely the nucleus, is the main body that plays a filling and reinforcing role in asphalt under normal or low temperature conditions. The performance of rubber asphalt is closely related to the size, distribution uniformity and area of the nucleus. The present invention uses SEM electron microscope scanning technology to sample rubber asphalt, and processes the image through Image software to study the microscopic characteristics of the nucleus of rubber asphalt under different process parameters. The characterization indicators include average area, average diameter, etc. The results are shown in Table 1.

[0106] Table 1 Microscopic characteristic values of rubber asphalt with different rubber powder content

[0107]

[0108] The average area and average size represent the size of the rubber nuclei, the total area percentage indicates the proportion of effective rubber particles, and the number and average area of the rubber nuclei reflect, to a certain extent, the degree of dispersion of the rubber nuclei. As shown in Table 1, the higher the rubber powder content, the larger the average area, diameter, and total area percentage of the rubber nuclei. In rubber asphalt with a 40% rubber powder content, the rubber nuclei are too large and too numerous, exceeding the solubility range of the asphalt.

[0109] The rubber-converted asphalt was dissolved in n-heptane, filtered, and the filter cake dried. The resulting filter cake was a mixture of asphaltene and rubber powder. Based on the measured asphaltene content (11.8%) and the weight loss of the rubber powder after immersion (8.3%), the effective content of the rubber powder in the asphalt was calculated. The results are shown in Table 2. Table 2 shows that some of the waste rubber powder loses weight during mixing with the asphalt, while some dissolves in the asphalt.

[0110] Table 2 Percentage of effective rubber powder extracted from different rubber-modified asphalts

[0111]

[0112] The microscopic morphology of the rubber powder extracts of the rubber-modified asphalt prepared in Examples 1-4 and Comparative Example 1 was observed using SEM scanning electron microscopy technology. The results are as follows: Figure 20-24 As shown. Figure 20-24 It can be seen that the effective rubber powder still exists in the rubber powder modified asphalt in the form of rubber phase, making it have some properties of rubber.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing waste rubber powder modified asphalt, characterized in that: The waste rubber powder modified asphalt comprises, by mass percentage, 25%-40% of waste rubber powder, 57-73% of base asphalt, and 0.2-3% of an admixture; the admixture is a mixture of coumarone resin and sulfur; The preparation method comprises the following steps: Step 1: Preparation of waste rubber powder The waste tires are crushed, sheared in a rotating impeller, and ground in a grinder. Finally, the metal and fiber in the rubber powder are separated and sieved to obtain the waste rubber powder. Step 2: Activation of waste rubber powder The waste rubber powder obtained in step 1 is processed using a twin-screw extrusion process, and the waste rubber powder is desulfurized by the shearing action of the screw; Step 3: Preparation of modified asphalt The matrix asphalt is heated to a fluid state, the activated waste rubber powder obtained in step 2 is added and stirred, and then the admixture is added and stirred continuously to obtain a modified asphalt material with a stable network structure.

2. The method for preparing waste rubber powder modified asphalt according to claim 1, wherein: The particle size of the waste rubber powder is 40-80 meshes.

3. The method for preparing waste rubber powder modified asphalt according to claim 1, characterized in that: The matrix asphalt is 70# asphalt or 90# asphalt.

4. The method for preparing waste rubber powder modified asphalt according to claim 1, characterized in that: In step 1, the rotating speed of the impeller is 100-1200 rpm.

5. The method for preparing waste rubber powder modified asphalt according to claim 1, characterized in that: In step 2, the extrusion temperature of the twin screw is 190-280°C.

6. The method for preparing waste rubber powder modified asphalt according to claim 1, characterized in that: In step 3, the heating temperature of the matrix asphalt is 150-180°C.

7. A waste rubber powder modified asphalt, characterized by: The waste rubber powder modified asphalt is prepared by the preparation method according to any one of claims 1 to 6.

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