A polyurethane-modified asphalt, its preparation method and application

Abstract

This invention belongs to the field of road engineering paving technology, specifically relating to a polyurethane-modified asphalt, its preparation method, and its application. The polyurethane-modified asphalt is composed of the following parts by weight: 51-70 parts base asphalt, 30-48 parts polyurethane prepolymer, 0.02-0.05 parts chain extender, and 0.02-0.05 parts solubilizer. The polyurethane prepolymer is an isocyanate prepolymer containing a dynamic covalent bond structure; the dynamic covalent bond structure in the isocyanate prepolymer contains furan-maleimide bonds and phenolic hydroxy-carbamate bonds. This invention introduces a dynamic covalent network structure of D-A bonds and phenolic hydroxy-carbamate bonds into the polyurethane-modified asphalt, solving the problem of non-recyclability of traditional thermosetting materials. These two dynamic bonds balance the strength and toughness of the material, and further optimize the construction retention time through bond energy response regulation, ultimately endowing the asphalt pavement with self-healing, recyclable, and long-life characteristics.

Description

Technical Field

[0001] This invention belongs to the field of road engineering paving technology, specifically relating to a polyurethane modified asphalt, its preparation method, and its application. Background Technology

[0002] Asphalt pavement, as the main form of road construction, still has shortcomings in terms of long-term durability, construction energy consumption control, and high and low temperature stability, making it difficult to meet the comprehensive requirements of green road construction and long-term service performance. Currently, thermoplastic asphalt modified with styrene-butadiene-styrene block copolymer (SBS) and rubber powder can improve the performance and life of asphalt pavement to a certain extent, but it still suffers from high temperature sensitivity. Polyurethane, as a polymer containing repeating urethane structures, has isocyanate groups (–NCO) in its molecules that can chemically react with active groups such as hydroxyl and amine groups in asphalt to generate strongly bonded structures such as urethane and urea groups, thus achieving good compatibility at the component level. In existing technologies, by optimizing the type of polyurethane, the ratio and dosage of curing agent, and process parameters, thermosetting composite materials with a three-dimensional cross-linked network of polyurethane as the continuous phase and asphalt as the dispersed phase can be formed, effectively improving the high-temperature stability and mechanical properties of the asphalt system.

[0003] Although thermosetting polyurethane-modified asphalt possesses advantages such as low construction temperature, excellent temperature stability, and outstanding fatigue resistance, its highly cross-linked network structure makes effective recycling difficult after its service life, increasing maintenance costs and environmental burden. Currently, thermosetting polyurethane-modified asphalt based on reversible covalent bonds such as disulfide bonds, Diels-Alder (DA) reactions, and phenolic hydroxyl-carbamate bonds shows potential in terms of recyclability, but it is difficult to achieve synergistic optimization in key properties such as recyclability, mechanical toughness, asphalt compatibility, and construction residence time. This is because high strength and high toughness require high cross-linking density and a stable network structure, while good recyclability requires moderate bond energy and rapid reversibility under mild conditions. Simultaneously, the reaction rate of dynamic bonds (such as the temperature trigger window of the DA reaction) is difficult to precisely match with the residence time of asphalt construction; excessively rapid reversibility leads to insufficient stability during construction, while excessively slow reversibility affects recycling efficiency. Furthermore, the introduction of polar dynamic bonds (such as disulfide bonds) may weaken its compatibility with complex asphalt components, inducing phase separation. These interrelationships make it difficult for modified systems relying on a single dynamic bond to break through the balance of multidimensional properties. Summary of the Invention

[0004] The purpose of this invention is to provide a polyurethane-modified asphalt, its preparation method, and its application, thereby overcoming the shortcomings of the prior art. It uses a diol containing DA bonds as the source of dynamic bonds and polyphenolic compounds as the source of phenol-carbamate bonds, combined with chain extenders, solubilizers, etc., to endow polyurethane-modified asphalt with renewable functions and good mechanical properties.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a polyurethane-modified asphalt, which is composed of the following components in parts by weight: The matrix bitumen is 51-70 parts, the polyurethane prepolymer is 30-48 parts, the chain extender is 0.02-0.05 parts, and the solubilizer is 0.02-0.05 parts; the polyurethane prepolymer is an isocyanate prepolymer containing a dynamic covalent bond structure; the dynamic covalent bond structure in the isocyanate prepolymer contains furan-maleimide bonds (DA bonds) and phenolic hydroxy-carbamate bonds.

[0006] During their research, the inventors discovered that the thermally reversible covalent bonds (DA bonds) formed by the cycloaddition reaction of furan and maleimide groups (Diels-Alder reaction, or DA reaction for short) can not only act as "crosslinking agents" to improve the chemical resistance, high strength and other properties of materials, but also, through the formation / breaking of DA bonds, can be used in synergy with various covalent bonds such as phenolic hydroxy-carbamate bonds and multiple hydrogen bonds to give materials unique self-healing properties and recyclability.

[0007] This invention uses furanylpropionamide polyethylene glycol maleimide containing DA bonds as the source of dynamic bonds and polyphenolic compounds as the source of phenol-urethane bonds to ensure the synthesis of polyurethane prepolymers. The main reactions that occur during the synthesis process are as follows: ① Diisocyanates react with polyols to form carbamates. Simultaneously, during the reaction, carbamates continue to react with diisocyanates. The specific reaction mechanism is as follows: R-NCO+HO-R'-OH→R-NH-CO-O-R'-OH; R-NH-CO-O-R'-OH+R-NCO→R-NH-CO-O-R'-O-CO-NH-R.

[0008] In the above reaction, the diisocyanate is one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), or dicyclohexylmethane diisocyanate (H12MDI); specifically, the isocyanate is diphenylmethane diisocyanate (MDI). The polyol is polyether polyol PPG.

[0009] ② Catalysts (such as organotin compounds or amines) accelerate the reaction between isocyanates and hydroxyl groups. The specific reaction mechanism is as follows: R-NCO+HO-R''+catalyst→R-NH-CO-O-R''; nR-NCO+nHO-R'-OH→[R-NH-CO-O-R'-O-CO-NH-] n .

[0010] ③ Furan propionamide polyethylene glycol maleimide reacts with diisocyanate through the amino group (-NH2) at the end of the molecule, and the complete functional module with furan and maleimide is chemically anchored to the end of the polyurethane prepolymer chain or as a side chain through urea bond.

[0011] R'-NH2+ R-NCO → R' -NH-CO-NH-R Fu-PEG-MAL (fu-propionamide polyethylene glycol maleimide) combines three functional groups: furanylpropionamide, polyethylene glycol (PEG), and maleimide (Mal). Its molecular weight ranges from 400 to 10,000, specifically 400, 600, 1,000, 2,000, 3,400, 5,000, and 10,000, preferably 1,000. Its molecular formula is as follows: .

[0012] ④ The unreacted -NCO group continues to react with the polyphenolic compound, achieving partial end-capping of the isocyanate with the phenolic hydroxyl group. The specific reaction mechanism is as follows: RN=C=O + HO-C6H4-OH → R-NH-CO-O-C6H4-OH R-NH-CO-O-C6H4-OH + O=C=NR' → R-NH-CO-O-C6H4-O-CO-NH-R' In the above reaction, the polyphenolic compound is one of catechol, resorcinol, hydroquinone, and propyl gallate; preferably catechol.

[0013] When the road surface temperature exceeds 130°C, the following reverse reaction will occur between isocyanate and polyphenolic compounds and between DA bonds, thereby making polyurethane modified asphalt materials recyclable. This property makes thermosetting polyurethane asphalt suitable for current asphalt pavement warm recycling technology.

[0014]

[0015] In some other embodiments, the polyurethane prepolymer is composed of the following components by weight: 30-40 parts of polyether polyol, 5-20 parts of furanylpropionamide polyethylene glycol maleimide, 5-15 parts of polyphenol compound, and 40-50 parts of diisocyanate.

[0016] In some other embodiments, the polyether polyol is one or more of polypropylene glycol (PPG) and polytetrahydrofuran ether glycol (PTMEG / PTMG).

[0017] The polyphenolic compound is one of catechol, resorcinol, hydroquinone, and propyl gallate; preferably catechol.

[0018] In some other embodiments, the chain extender is one of 1,4-butanediol (BDO), ethylene glycol (EG), and diethylene glycol (DEG); preferably, the chain extender is diethylene glycol (DEG).

[0019] In some other embodiments, the solubilizer is an aromatic diamine and hydroxyl-terminated polybutadiene or γ-aminopropyltriethoxysilane; preferably, the solubilizer is γ-aminopropyltriethoxysilane.

[0020] In a second aspect, the present invention provides a method for preparing the polyurethane-modified asphalt described in the first aspect, comprising the following steps: After dehydrating the base asphalt, stir and heat it. Then add the polyurethane prepolymer and continue stirring and heating. Finally, add the chain extender and solubilizer, stir and heat again to mix evenly.

[0021] In some other embodiments, the stirring and heating time is 1-15 min, the stirring rate is 450-550 rpm, and the heating temperature is 120-130°C.

[0022] Specifically, after dehydrating the base asphalt, stir for 1-3 minutes at a stirring speed of 500 rpm and control the temperature at 120-130℃; slowly add polyurethane prepolymer, stir for 10-15 minutes at a stirring speed of 500 rpm and control the temperature at 120-130℃; add chain extender and solubilizer, stir for 2-5 minutes at a stirring speed of 500 rpm and control the temperature at 120-130℃.

[0023] In some other embodiments, the polyurethane prepolymer is prepared as follows: Polyether polyol, furanylpropionamide polyethylene glycol maleimide and polyphenol compounds are mixed and stirred and dehydrated under vacuum to obtain a dehydrated mixture; under a protective atmosphere, diisocyanate and catalyst are added to carry out a polymerization reaction, and the polyurethane prepolymer is obtained by vacuum degassing.

[0024] In some other embodiments, the catalyst is one of an organometallic catalyst or a tertiary amine catalyst. Specifically, the organometallic catalyst is bismuth isooctanoate and bismuth laurate; the tertiary amine catalyst is triethylenediamine.

[0025] In some other embodiments, the vacuum degree of the stirring dehydration is < -0.095 MPa, the temperature is 110-120°C, and the time is 1.5-2.5 h.

[0026] In some other embodiments, the polymerization reaction is carried out at a temperature of 75-85°C for 3-5 hours.

[0027] Thirdly, the present invention provides the application of the polyurethane modified asphalt described in the first aspect in road engineering paving and recycled asphalt materials.

[0028] Specifically, the recycled asphalt material includes recycled asphalt pavement material (RAP), aggregates, and new asphalt, wherein the mass ratio of recycled asphalt pavement material (RAP), aggregates, and new asphalt is (46-25):(52-72):(2-3), and the recycled asphalt pavement material is polyurethane modified asphalt.

[0029] The beneficial effects of this invention are: (1) A dynamic covalent network of furan-maleimide DA bonds and phenolic hydroxy-carbamate bonds is introduced into polyurethane modified bitumen. Through the thermal reversibility of DA bonds, microcracks can be repaired autonomously, significantly improving fatigue resistance and durability. The topological rearrangement ability of phenolic hydroxy-carbamate bonds enables the material to reshape and regenerate the network structure under high temperature shear, completely breaking through the bottleneck of traditional thermosetting materials being non-recyclable.

[0030] (2) The thermosetting polyurethane modified asphalt prepared by the present invention using two different modifier dosages (large and small) can be applied to the warm recycling technology route under different RAP dosage conditions. Among them, the recycled mixture prepared by the large dosage of polyurethane modified asphalt has significantly better road performance than SBS modified asphalt and base asphalt recycled mixture; while the small dosage of polyurethane modified asphalt recycled mixture has comparable performance to SBS modified asphalt recycled mixture, while the construction temperature is significantly reduced, realizing the efficient recycling of thermosetting polyurethane modified asphalt materials under the condition of balancing high performance and low energy consumption. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 The infrared spectra of polyurethane-modified asphalt in Example 1 and Comparative Example 4 of this invention are shown below. Figure 2The images shown are atomic force micrographs of polyurethane modified asphalt in Examples 1 and 4 of the present invention, where a represents 0 wt% of the chain extender in the polyurethane modified asphalt, b represents 3 wt% of the chain extender in the polyurethane modified asphalt, and c represents 6 wt% of the chain extender in the polyurethane modified asphalt. Detailed Implementation

[0033] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0034] Example 1 This embodiment provides a polyurethane-modified asphalt and its preparation method, as detailed below: (1) The composition of the polyurethane prepolymer by weight is shown in Table 1.

[0035] (2) The preparation method of polyurethane prepolymer is as follows: Polypropylene glycol (PPG), furanylpropionamide polyethylene glycol maleimide (molecular weight 1000) and catechol were heated to 110°C under vacuum (vacuum degree below -0.095 MPa), stirred for 1.5 h, dehydrated, and then cooled to 50°C. Under nitrogen protection, diphenylmethane diisocyanate was slowly added dropwise, followed by bismuth isooctanoate catalyst. The mixture was heated to 80°C and reacted for 3 h. After degassing under vacuum for 15 min, the product was obtained.

[0036] Table 1. Composition of polyurethane prepolymer

[0037] (3) Polyurethane modified bitumen, the composition by weight is shown in Table 2.

[0038] (4) The preparation method of polyurethane modified asphalt is as follows: After dehydrating the base asphalt, stir for 2 minutes at a stirring speed of 500 rpm and a temperature of 120 ℃; slowly add polyurethane prepolymer, stir for 10 minutes at a stirring speed of 500 rpm and a temperature of 120 ℃; add chain extender diethylene glycol and solubilizer γ-aminopropyltriethoxysilane, stir for 5 minutes at a stirring speed of 500 rpm and a temperature of 120 ℃ to obtain the final product.

[0039] Table 2. Component composition of polyurethane-modified asphalt

[0040] (5) Performance testing Polyurethane modified asphalt mixtures were prepared according to the AC-13 gradation specified in the "Technical Specification for Construction of Asphalt Pavement on Highways" (JTG F40-2004), where AC is an abbreviation for asphalt concrete and 13 represents the maximum nominal particle size of the aggregates used is 13 mm. The optimal asphalt content was 5.0%. The road performance indicators of the polyurethane modified asphalt mixture were tested and compared with the performance test results of 70# base asphalt and SBS modified asphalt AC-13 mixtures. The test results are shown in Table 3. The test methods for splitting tensile strength, dynamic stability, low-temperature flexural strain, and freeze-thaw splitting strength ratio were based on standards T0716-2011, T0719-2011, T0715-2011, and T0729-2000, respectively.

[0041] Table 3 Performance Indicators of AC-13 Asphalt Mixture

[0042] Table 3 shows that the splitting tensile strength of AC-13 graded polyurethane modified asphalt mixture reached 1.7 and 1.4 times that of 70# base asphalt and SBS modified asphalt mixture, respectively; its dynamic stability reached 5.3 and 1.9 times, respectively; and its low-temperature flexural strain at -10℃ reached 2.5 and 2.0 times, respectively, indicating that polyurethane modified asphalt mixture possesses excellent high and low temperature stability. The splitting tensile strength ratio of AC-13 graded polyurethane modified asphalt mixture is higher than that of base asphalt mixture and comparable to that of SBS modified asphalt mixture, indicating that polyurethane modified asphalt mixture has good water stability.

[0043] After preparation, Marshall specimens of the asphalt mixture were molded and subjected to simulated long-term aging tests. The simulated aging test procedure was as follows: The oven was preheated to 85℃ ± 1℃; the specimens were placed vertically on the specimen rack, ensuring good air circulation around each specimen. The spacing between specimens was at least 20 mm. The specimen rack containing the specimens was placed in the preheated 85℃ oven. The temperature was maintained at 85℃ for 120 hours (5 days). After the specified aging time was reached, the oven was closed, and the door was slightly opened to allow the specimens to cool slowly to room temperature inside the oven (usually requiring several hours).

[0044] Asphalt mixtures simulating long-term aging were subjected to low-RAP (RAP is an abbreviation for Recycled Asphalt Pavement Material) temperature recycling. The heating temperature of both old and new aggregates was 130℃. The new asphalt used for recycling was the same type of asphalt as that in the old mixture, and the proportions of various materials were as follows: aged asphalt mixture: aggregate: new asphalt = 25:72:3. Given the high temperature requirements for recycling base asphalt and SBS modified asphalt, the recycling process was adopted for mixture preparation and performance testing in accordance with the relevant provisions of the "Technical Specification for Recycling Asphalt Pavement of Highways" (JTG / T 5521-2019). The performance test results of the three recycled mixtures are shown in Table 4.

[0045] Table 4 Performance Indicators of Low-Dosage Warm Recycled Asphalt Mixtures

[0046] As shown in Table 4, the splitting strength, Marshall stability, dynamic stability, and low-temperature flexural strain of the polyurethane modified asphalt mixture recycled at 130℃ are higher than those of the recycled matrix asphalt mixture and SBS modified asphalt mixture, indicating that the polyurethane modified asphalt mixture has excellent high and low temperature stability. The dynamic modulus of the recycled polyurethane modified asphalt mixture is higher than 14000 MPa, indicating its excellent mechanical properties. The recycled polyurethane modified asphalt mixture has the lowest Kentucky scattering loss and the highest freeze-thaw splitting strength ratio, indicating that the recycled polyurethane modified asphalt mixture has excellent water stability.

[0047] Example 2 Unlike Example 1, the RAP content in the simulated aging test of three AC-13 graded asphalt mixtures was studied. The composition, preparation method and testing method of other polyurethane prepolymers and polyurethane modified asphalts were the same as in Example 1.

[0048] Specifically, asphalt mixtures simulating long-term aging were recycled with high RAP content. The proportions of various materials during the warm recycling process were as follows: aged asphalt mixture: aggregate: new asphalt = 46:52:2. The performance test results of the three recycled mixtures are shown in Table 5.

[0049] Table 5 Performance Indicators of High RAP Content Warm Recycled Asphalt Mixture

[0050] Table 5 shows that the high-temperature performance, low-temperature performance, and water stability of the polyurethane-modified asphalt warm-recycled mixture with high RAP content are superior to those of the recycled base asphalt and SBS-modified asphalt mixtures. Polyurethane-modified asphalt is suitable for high-volume warm-recycled processes. Comparison with the data in Table 4 shows that increasing the RAP content reduces the performance of the polyurethane-modified asphalt recycled mixture to some extent.

[0051] Example 3 Unlike Example 1, the composition of the polyurethane modified bitumen is shown in Table 6. The composition and preparation method of the polyurethane prepolymer are the same as those of the polyurethane modified bitumen in Example 1.

[0052] Table 6. Composition of thermosetting polyurethane-modified asphalt with minor modifier dosage

[0053] Asphalt mixtures that had undergone simulated long-term aging were subjected to low-RAP-dosage temperature recycling. The heating temperature for both the old and new aggregates was 130℃. The new asphalt used for recycling was the same type of asphalt as that in the old mixture, and the proportions of various materials were as follows: aged asphalt mixture: aggregate: new asphalt = 25:72:3. The performance test results of the three recycled mixtures are shown in Table 7.

[0054] Table 7 Performance Indicators of Low-RAP Content Warm Recycled Asphalt Mixture

[0055] As shown in Table 7, reducing the amount of polyurethane prepolymer in polyurethane modified asphalt will reduce the performance indicators of polyurethane modified asphalt warm recycled mixture to a certain extent. However, when the amount of polyurethane prepolymer is 30%, the polyurethane modified asphalt mixture after low-dosage warm recycling still has excellent high and low temperature stability and water stability, and its mechanical properties are comparable to those of SBS modified asphalt hot recycled mixture.

[0056] Example 4 Unlike Example 3, the RAP content in the simulated aging test of three AC-13 graded asphalt mixtures was studied. The polyurethane prepolymer, the polyurethane modified asphalt preparation scheme, and the simulated aging of the polyurethane modified asphalt mixture were consistent with those in Example 3.

[0057] Specifically, simulated long-term aged asphalt mixtures were subjected to high-RAP-dosage high-temperature recycling. The heating temperature for both the old and new aggregates was 130℃. The new asphalt used for recycling was the same type of asphalt as that in the old mixture, and the proportions of various materials were as follows: aged asphalt mixture: aggregate: new asphalt = 46:52:2. The performance test results of the three recycled mixtures are shown in Table 8.

[0058] Table 8 Performance of High-Dosage Warm Recycled Asphalt Mixtures

[0059] As shown in Table 8, reducing the amount of polyurethane prepolymer in polyurethane-modified asphalt will, to some extent, reduce the performance indicators of high-volume polyurethane-modified asphalt warm-recycled mixtures. However, all technical indicators still meet the technical requirements for hot-mix modified asphalt mixtures in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40-2004). High-volume polyurethane-modified asphalt mixtures after warm recycling still exhibit excellent high and low temperature stability and water stability, and their mechanical properties are comparable to those of SBS-modified asphalt hot-recycled mixtures.

[0060] Comparative Example 1 The polyurethane prepolymer is a polyurethane prepolymer containing only a single furan-maleimide bond. Its specific composition (as shown in Table 9), preparation method, and the polyurethane-modified asphalt and its preparation method are as follows: Polypropylene glycol (PPG) and furanylpropionamide polyethylene glycol maleimide were heated to 100°C under vacuum and dried for 1 hour to remove water. The dehydrated polypropylene glycol (PPG) and furanylpropionamide polyethylene glycol maleimide were added to a reaction vessel, and the temperature was controlled at 50°C. Diphenylmethane diisocyanate was slowly added dropwise, followed by the addition of bismuth isooctanoate catalyst. The mixture was then heated to 80°C and reacted for 3 hours to obtain the final product.

[0061] Table 9 Composition of Polyurethane Prepolymer

[0062] Polyurethane-modified asphalt and a low-dosage polyurethane-modified asphalt warm recycled mixture (PU45-25-1) were prepared according to the method and material ratio in Example 1. A high-dosage polyurethane-modified asphalt warm recycled mixture (PU45-46-1) was prepared according to the method and material ratio in Example 2. Polyurethane-modified asphalt and a low-dosage polyurethane-modified asphalt warm recycled mixture (PU30-25-1) were prepared according to the method and material ratio in Example 3. A high-dosage polyurethane-modified asphalt warm recycled mixture (PU30-46-1) was prepared according to the method and material ratio in Example 4. The performance indicators of the polyurethane-modified asphalt mixture in Example 4 are shown in Table 10.

[0063] Table 10 Properties of Polyurethane Modified Asphalt Warm Recycled Mixture with Single DA Covalent Bonds

[0064] As shown in Table 10, the performance of recycled asphalt mixture modified with single DA covalent bonds is worse than that of polyurethane-modified asphalt mixture after dual covalent bond synergistic recycling. Specifically, the splitting strength, Marshall stability, dynamic stability, and low-temperature flexural strain of the DA covalent bond polyurethane-modified asphalt mixture are comparable to those of the thermally recycled SBS-modified asphalt mixture, meaning that the high and low temperature technical indicators meet the specifications. However, its freeze-thaw splitting strength ratio and Kentucky spillage loss, among other water stability indicators, are lower than those of the thermally recycled matrix asphalt mixture and the SBS-modified asphalt mixture, and do not meet the technical requirements of the specifications.

[0065] Comparative Example 2 The polyurethane prepolymer is a polyurethane prepolymer containing only a single phenolic hydroxyl-urethane bond. Its specific composition (as shown in Table 11), preparation method, and the polyurethane-modified asphalt and its preparation method are as follows: Catechol and polypropylene glycol (PPG) were heated to 100°C under vacuum and dried for 1 hour to remove water. The dehydrated cadmium and PPG were added to a reaction vessel, and the temperature was controlled at 50°C. Diphenylmethane diisocyanate was slowly added dropwise, followed by the addition of bismuth isooctanoate catalyst. The mixture was then heated to 80°C and reacted for 3 hours to obtain the final product.

[0066] Table 11 Composition of Polyurethane Prepolymer

[0067] Polyurethane-modified asphalt and a low-dosage polyurethane-modified asphalt warm recycled mixture (PU45-25-2) were prepared according to the method and material ratio in Example 1. A high-dosage polyurethane-modified asphalt warm recycled mixture (PU45-46-2) was prepared according to the method and material ratio in Example 2. Polyurethane-modified asphalt and a low-dosage polyurethane-modified asphalt warm recycled mixture (PU30-25-2) were prepared according to the method and material ratio in Example 3. A high-dosage polyurethane-modified asphalt warm recycled mixture (PU30-46-2) was prepared according to the method and material ratio in Example 4. The performance indicators of the polyurethane-modified asphalt mixtures are shown in Table 12.

[0068] Table 12 Properties of Polyurethane Modified Asphalt Recycled Mixture with Single Phenolic Hydroxyl-Carbamate Bonds

[0069] Table 12 shows that the performance of the polyurethane-modified asphalt mixture modified with single phenolic hydroxyl-carbamate bonds in warm recycling is worse than that of the polyurethane-modified asphalt mixture after bivalent bond synergistic recycling. Specifically, the splitting strength, Marshall stability, dynamic stability, and low-temperature flexural strain of the DA covalent bond polyurethane-modified asphalt mixture are comparable to those of the hot-recycled SBS-modified asphalt mixture, meaning that the high and low temperature technical indicators meet the specifications. However, its freeze-thaw splitting strength ratio and Kentucky spillage loss, among other water stability indicators, are lower than those of the hot-recycled base asphalt mixture and the SBS-modified asphalt mixture, and do not meet the specifications. Furthermore, the experiment revealed that the cohesiveness of the old polyurethane-modified asphalt mixture is relatively high at a recycling temperature of 130℃, leading to insufficient mixing between the RAP and the new aggregate, affecting the uniformity of the recycled mixture, which may be the reason for the poor water stability of the polyurethane-modified asphalt recycled mixture.

[0070] Comparative Example 4 Unlike Example 1, the content of polyurethane prepolymer was kept constant at 48 wt%, and the amount of chain extender was adjusted to 0 wt% and 6 wt% of the polyurethane modified asphalt, respectively, to obtain polyurethane modified asphalts, labeled as polyurethane asphalt-48%-0% and polyurethane asphalt-48%-6%. In Example 1, the polyurethane modified asphalt (labeled as polyurethane asphalt-48%-3%) contained 48 wt% polyurethane prepolymer and 3 wt% chain extender.

[0071] Three types of polyurethane-modified asphalt were characterized using infrared spectroscopy. Figure 1 It can be seen that the three polyurethane-modified asphalts at 3302 cm⁻¹- ¹The presence of NH stretching vibration peaks near the 1780 cm⁻¹ indicates that polyurethane was successfully introduced into the bitumen system, with peaks observed at 1780 cm⁻¹. -1 The appearance of characteristic peaks and their reversible thermal response, combined with 1535 cm⁻¹ -1 The presence of characteristic urethane peaks strongly demonstrates, at the FTIR level, the successful introduction of a dynamic covalent network based on furan-maleimide DA bonds and phenolic hydroxyl-urethane bonds into polyurethane-modified asphalt. A peak at 1720 cm⁻¹ was observed in the polyurethane-modified asphalt. -1 With 1538 cm -1 The C=O stretching vibration peak at 1620 cm⁻¹ indicates that isocyanate can undergo carbamate esterification with the active hydrogen groups of pitch. -1 The NH stretching vibration of the urea group represents the urethane group, which can react with isocyanate to form a urethane group.

[0072] Three polyurethane-modified asphalts were characterized using atomic force microscopy, and the results are as follows: Figure 2 As shown. By Figure 2 As shown in 'a', without the addition of chain extender, due to the slow curing reaction, most of the polyurethane phase is distributed in the asphalt matrix as isolated particles, resulting in a clearly visible phase interface and relatively dispersed protrusions on the sample surface. When the chain extender is increased to 3% ( Figure 2 In step b), the protrusions become denser and more orderly, the phase interface becomes blurred, and the number of protrusions increases, but some isolated protrusions still exist, indicating that the addition of the chain extender promotes the formation of a local cross-linked network. As the chain extender increases to 6% (…),… Figure 2 (c) The surface morphology exhibits a fine and uniform distribution of protrusions, with isolated protrusions completely disappearing, indicating that the curing reaction has reached completion and a spatially continuous three-dimensional network structure has been successfully constructed. When the chain extender dosage is 0%, 3%, and 6%, the average roughness is 13.6 mm, 15 mm, and 19.5 mm, respectively, and the root mean square roughness is 16.8 nm, 20 nm, and 29.1 nm, respectively.

[0073] The above studies show that the thermosetting polyurethane modified asphalt prepared by the present invention with large and small modifier dosages is suitable for warm recycling with large and small RAP dosages. The performance of the warm recycled asphalt mixture with large modifier dosage is significantly better than that of SBS modified asphalt recycled mixture and matrix asphalt recycled mixture (Examples 1 and 2). The performance of the warm recycled asphalt mixture with small modifier dosage is significantly better than that of matrix asphalt recycled mixture and comparable to that of SBS modified asphalt recycled mixture, but the construction temperature is lower than that of SBS modified asphalt recycled mixture, thus realizing the low-energy recycling of thermosetting polyurethane modified asphalt materials.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polyurethane-modified asphalt, characterized in that, It consists of the following components in parts by weight: The matrix bitumen comprises 51-70 parts, the polyurethane prepolymer comprises 30-48 parts, the chain extender comprises 0.02-0.05 parts, and the solubilizer comprises 0.02-0.05 parts; the polyurethane prepolymer is an isocyanate prepolymer containing a dynamic covalent bond structure; The dynamic covalent bond structure in the isocyanate prepolymer contains furan-maleimide bonds and phenolic hydroxy-carbamate bonds.

2. The polyurethane-modified asphalt according to claim 1, characterized in that, The polyurethane prepolymer is composed of the following components by weight: 30-40 parts of polyether polyol, 5-20 parts of furanylpropionamide polyethylene glycol maleimide, 5-15 parts of polyphenol compound, and 40-50 parts of diisocyanate.

3. The polyurethane-modified asphalt according to claim 1, characterized in that, The chain extender is one of 1,4-butanediol, ethylene glycol, and diethylene glycol. The solubilizer is one of aromatic diamine, hydroxyl-terminated polybutadiene, and γ-aminopropyltriethoxysilane.

4. The polyurethane-modified asphalt according to claim 2, characterized in that, The polyether polyol is one of polypropylene glycol and polytetrahydrofuran ether glycol; The polyphenolic compound is one of catechol, resorcinol, hydroquinone, and propyl gallate.

5. The polyurethane-modified asphalt according to claim 2, characterized in that, The diisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

6. A method for preparing polyurethane-modified asphalt according to any one of claims 1-5, characterized in that, Includes the following steps: After dehydrating the base asphalt, stir and heat it. Then add the polyurethane prepolymer and continue stirring and heating. Next, add the chain extender and solubilizer, stir and heat until well mixed to obtain the final product.

7. The method for preparing polyurethane-modified asphalt according to claim 6, characterized in that, The stirring and heating time is 1-15 minutes, the stirring speed is 450-550 rpm, and the heating temperature is 120-130℃.

8. The method for preparing polyurethane-modified asphalt according to claim 6, characterized in that, The preparation method of the polyurethane prepolymer is as follows: polyether polyol, furanylpropionamide polyethylene glycol maleimide and polyphenol compound are mixed and stirred and dehydrated under vacuum to obtain a dehydrated mixture; under a protective atmosphere, diisocyanate and catalyst are added to carry out a polymerization reaction, and the polyurethane prepolymer is obtained by vacuum degassing.

9. The method for preparing polyurethane-modified asphalt according to claim 8, characterized in that, The catalyst is one of the following: organometallic catalyst, tertiary amine catalyst, and acid catalyst; The vacuum degree of the stirring dehydration is < -0.095 MPa, the temperature is 110-120℃, and the time is 1.5-2.5 h; The polymerization reaction is carried out at a temperature of 75-85℃ for 3-5 hours.

10. The application of the polyurethane modified asphalt according to any one of claims 1-5 in road engineering paving and recycled asphalt materials.

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