Polyurethane modified asphalt regenerated mixture and preparation method thereof

Abstract

The invention relates to the technical field of road materials, in particular to a polyurethane modified asphalt regenerated mixture and a preparation method thereof. The modified asphalt comprises the following raw material components: a recycled SBS modified asphalt reclaimed material, polyurethane prepolymer modified asphalt and surface modified nano silicon dioxide. The SBS modified asphalt reclaimed material is used for replacing natural aggregate, so that the consumption of natural resources can be remarkably reduced, the carbon emission is reduced, the cyclic utilization of building wastes is realized, and the environment-friendly and economic benefits are realized. The low-temperature crack resistance of the regenerated mixture is effectively improved, the durability and the performance stability of the regenerated mixture in a cold environment are improved, meanwhile, a compact inorganic-organic hybrid network is formed, the binding force of asphalt and aged asphalt in the regenerated mixture and the adhesion performance of the asphalt and aggregate in the regenerated mixture are enhanced, and the service life of the regenerated mixture is prolonged. The water damage resistance of the recycled asphalt mixture is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of road materials, and particularly relates to a polyurethane-modified asphalt recycled mixture and a preparation method thereof. Background Art

[0002] With the continuous increase in traffic volume, asphalt pavements are accelerating in damage, and more and more expressways are entering the stage of renovation and reconstruction because they can no longer meet the pavement performance requirements. A large amount of recycled asphalt mixture is generated in this process. In recycled asphalt mixtures with a high content of recycled materials, the aged old asphalt will reduce the flexibility of the mixture, and the compatibility between the new and old asphalt is poor. This not only affects the low-temperature crack resistance of the recycled asphalt mixture but also reduces the water damage resistance of the recycled asphalt mixture.

[0003] When using a polyurethane prepolymer as a modifier to modify asphalt, on the one hand, the flexibility of asphalt can be enhanced by introducing soft segments, enabling it to remain elastic even in low-temperature environments; on the other hand, a cross-linked network structure is formed through chemical reactions (such as the reaction between -NCO groups and -OH groups in asphalt), thereby improving the viscoelasticity of asphalt. The polyurethane prepolymer-modified asphalt can improve the low-temperature performance of asphalt recycled materials by virtue of the introduced soft segments. For example, a literature ("Performance and modification mechanism investigation of polyurethane prepolymer system modified bitumen for 100 % reclaimed asphalt pavement (RAP) application", "Construction and Building Materials", 2025) mentions that introducing a polyurethane prepolymer system into asphalt and using it in recycled asphalt mixtures improves the permanent deformation resistance and low-temperature crack resistance of the recycled asphalt mixtures. Another patent (CN 115477852 A) points out that doping polyurethane-glycerol ether into recycled SBS-modified asphalt materials can effectively restore the low-temperature performance of the recycled SBS-modified asphalt. In addition to the low-temperature performance, the biggest problem faced by recycled asphalt mixtures is the poor water damage resistance. At present, there is no invention technology that can synergistically improve the low-temperature performance and water damage resistance of recycled asphalt mixtures.

[0004] Therefore, there is an urgent need to develop a polyurethane-modified asphalt recycled mixture that has both low-temperature crack resistance and water damage resistance. Summary of the Invention

[0005] To achieve the above object, the present invention provides a polyurethane-modified asphalt recycled mixture and a preparation method thereof, and the obtained product has excellent low-temperature crack resistance and water damage resistance.

[0006] The technical solution of the present invention is realized as follows: In a first aspect, the present invention provides a polyurethane-modified asphalt recycled mixture, and its raw material components include recycled SBS-modified asphalt recycled material, polyurethane prepolymer-modified asphalt, and surface-modified nano-silica.

[0007] Preferably, the preparation method of the surface-modified nano-silica includes the following steps: S1. Stir the silane coupling agent and nano-silica at 60 - 80 °C for 2 - 4 h to obtain surface-modified nano-silica.

[0008] More preferably, the weight ratio of the silane coupling agent to nano-silica is (1 - 2):1.

[0009] More preferably, the silane coupling agent includes KH-550 amino silane.

[0010] More preferably, the specific surface area of the nano-silica is 180 - 520 m 2 / g, and the particle size is 20 - 40 nm.

[0011] More preferably, the nano-silica with such a specific surface area and particle size range can provide sufficient active sites, enhance the chemical bonding ability with the polyurethane prepolymer, and at the same time can form a uniform dispersion system with the asphalt in the recycled material through surface modification, reducing the risk of sedimentation; avoiding the problem of particle agglomeration caused by too high specific surface area, reducing the active sites caused by too low specific surface area, too large particles will lose the nano-scale surface effect and cannot effectively provide reaction sites for the polyurethane prepolymer, and too small particles are prone to form stress concentration points in the polyurethane hard segment enrichment area, resulting in an increased risk of low-temperature brittle fracture.

[0012] Preferably, the weight ratio of the recycled SBS-modified asphalt recycled material, polyurethane prepolymer-modified asphalt, and surface-modified nano-silica is 1000:(30 - 50):(3 - 6).

[0013] More preferably, the preparation method of the polyurethane prepolymer-modified asphalt includes the following steps: S1. Under the protection of inert gas, mix and stir the polyol with adsorbed water removed and isocyanate at 60 - 80 °C for 2 - 6 h to obtain a polyurethane prepolymer; S2. High-speed shear the polyurethane prepolymer and matrix asphalt at 120 °C at 3000 rpm for 2 h to obtain polyurethane prepolymer-modified asphalt.

[0014] Preferably, the recycled SBS-modified asphalt recycled material (RAP) is taken from the milled material after crushing and screening in the mixing plant near the road section.

[0015] Further preferably, to clarify the content of SBS modified asphalt in the recycled material, first dry the RAP at 60 °C until constant weight to remove the moisture therein, and then it is necessary to preheat a certain amount of RAP at 100 °C for 0.5 h to improve the extraction efficiency; then place the treated RAP in an extractor, and add a certain amount of trichloroethylene solvent to carry out the extraction process; after the extraction is completed, the asphalt mortar obtained is centrifuged at 4000 r / min for 5 min in a centrifuge to remove the mineral powder to obtain a solution of asphalt and trichloroethylene; finally, the trichloroethylene solvent is recovered by a rotary evaporator to obtain the SBS asphalt in the RAP, and the content of SBS modified asphalt is 3-6% of the mass of the SBS modified asphalt RAP material.

[0016] Further preferably, to clarify the content of SBS in the SBS modified asphalt, heat the extracted SBS modified asphalt sample to the boiling state, add n-heptane and continuously dissolve it for 0.5 h - 1 h to obtain insoluble matter (asphaltene + SBS) and soluble matter (soft components); reflux extract the insoluble matter (asphaltene + SBS) with boiling n-heptane to obtain a solution (SBS + soft components) and pure asphaltene; combine the soluble matter (soft components) and the solution (SBS + soft components), add n-hexane to obtain soluble matter (soft components) and insoluble matter (soft components + SBS); treat the insoluble matter (soft components + SBS) with ether to obtain insoluble matter (soft components) and soluble matter (SBS); finally, obtain pure SBS through a rotary evaporator, and the SBS content is 3-5% of the mass of the SBS modified asphalt.

[0017] In a second aspect, the present invention provides a method for preparing the polyurethane modified asphalt recycled mixture, comprising the following steps: S1. Activate the recycled SBS modified asphalt material at 130-160 °C for 20-30 min; S2. Mix and stir the activated recycled SBS modified asphalt material with surface-modified nano-silica at 130-165 °C for 40-60 min to obtain a uniformly mixed asphalt recycled material; S3. Heat the polyurethane prepolymer modified asphalt at 120-150 °C and then mix and stir it with the uniformly mixed asphalt recycled material at 90-120 °C, and place it at 90-120 °C for 1-2 h to prepare the polyurethane modified asphalt recycled mixture.

[0018] Compared with the prior art, the advantages of the present invention are: (1) The isocyanate groups in the polyurethane prepolymer modified asphalt of the present invention can chemically react with the aged SBS in the recycled material to improve the bonding strength between the new and old asphalt. The introduced surface-modified nano-silica can form hydrogen bonds between the amino groups on its surface and the aged SBS, enabling it to be uniformly dispersed in the old asphalt, acting as a rigid crosslinking center with ultra-high functionality, and at the same time providing more active sites for the polyurethane prepolymer, thereby forming a dense PU-SiO2-SBS multi-crosslinking system and further enhancing the bonding strength between the new and old asphalt.

[0019] (2) The dense PU-SiO2-SBS multi-crosslinking network contains a large number of polar groups, enhancing the adhesion between the asphalt and the old aggregates in the recycled material. The synergistic effect of the high bonding property between the new and old asphalt and the high adhesion between the asphalt and the aggregates improves the water damage resistance and low-temperature cracking resistance of the recycled asphalt mixture as a whole. Specific Embodiments

[0020] The embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0021] It should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0022] In this article, the terms "containing", "comprising" or "including" are open expressions, that is, including the content specified by the present invention, but not excluding other aspects.

[0023] In this article, the terms "optionally", "optional" or "option" generally mean that the subsequent events or conditions may or may not occur, and this description includes the cases where such events or conditions occur and the cases where such events or conditions do not occur.

[0024] The nano-silica of the present invention has properties such as high specific surface area, surface activity and chemical stability. Through physical-chemical synergistic effects in the polyurethane modified asphalt, it can significantly improve the asphalt properties. On the one hand, the high specific surface area of the nano-silica and the amino groups (-NH2) after surface modification can form hydrogen bonds with the aged SBS, enabling it to be uniformly dispersed in the old asphalt, acting as a rigid crosslinking center with ultra-high functionality, and at the same time providing more active sites for the polyurethane prepolymer to form a dense PU-SiO2-SBS multi-crosslinking system.

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] Example 1 This embodiment provides a preparation method of a polyurethane-modified asphalt recycled mixture, including the following steps: (1) Surface modification of nano-silica: Add 100 g of nano-silica (purchased from Ningbo Bohuasi Nano Technology Co., Ltd.) to 100 g of KH-550 amino-silane (purchased from Hubei Jianghan New Materials Co., Ltd.), stir at 80 °C for 4 h, and select the specific surface area of the nano-silica to be 180 m 2 / g, and the particle size is 20 nm; (2) Preparation of polyurethane prepolymer modified asphalt: ① Vacuum dehydrate polytetrahydrofuran ether glycol (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) at 120 °C for 2 h to remove moisture. Add 50 g of dehydrated polytetrahydrofuran ether glycol and 10 g of diphenylmethane diisocyanate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) to the reaction kettle. After the raw materials are added and mixed evenly, make the whole system react at 80 °C under a nitrogen atmosphere for 2 h to obtain a polyurethane prepolymer.

[0027] ② Heat the base asphalt to 120 °C, add 3 g of polyurethane prepolymer to 100 g of base asphalt, and perform high-speed shearing at 120 °C at 3000 rpm for 2 h to obtain polyurethane prepolymer modified asphalt.

[0028] (3) Preparation of polyurethane-modified asphalt recycled mixture: ① Activate the recycled SBS-modified asphalt recycled material (taken from the middle and upper surface layers of the G50 Hanshi section of the Wuhuang Expressway in China) at 150 °C for 30 min to obtain the activated recycled SBS-modified asphalt recycled material; ② Mix 1000 g of the activated recycled SBS-modified asphalt recycled material with 3 g of surface-modified nano-silica at 155 °C and stir for 60 min to obtain a uniformly mixed asphalt recycled material; ③ Heat 30 g of polyurethane prepolymer modified asphalt at 150 °C for 20 min, then mix and stir it with the uniformly mixed asphalt recycled material at 120 °C, and let it stand at 120 °C for 2 h to obtain the polyurethane-modified asphalt recycled mixture.

[0029] Example 2 This embodiment provides a preparation method of a polyurethane-modified asphalt recycled mixture, including the following steps: (1)Surface modification of nano-silica: 100 g of nano-silica (purchased from Ningbo Bohuasi Nano-Technology Co., Ltd.) was added to 100 g of KH-550 amino-silane (purchased from Hubei Jianghan New Materials Co., Ltd.), and the mixture was stirred at 60 °C for 4 h. The specific surface area of the nano-silica was 520 m 2 / g, and the particle size was 40 nm; (2)Preparation of polyurethane prepolymer modified asphalt: ① Poly(tetramethylene ether) glycol (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was dehydrated under vacuum at 120 °C for 2 h to remove moisture. 50 g of dehydrated poly(tetramethylene ether) glycol and 10 g of diphenylmethane diisocyanate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) were added to a reaction kettle. After the raw materials were added and mixed evenly, the whole system was reacted at 80 °C under a nitrogen atmosphere for 2 h to obtain a polyurethane prepolymer.

[0030] ② The matrix asphalt was heated to 120 °C, and 3 g of the polyurethane prepolymer was added to 100 g of the matrix asphalt. The mixture was sheared at a high speed of 3000 rpm at 120 °C for 2 h to obtain the polyurethane prepolymer modified asphalt.

[0031] (3)Preparation of polyurethane modified asphalt recycled mixture: ① The recycled SBS modified asphalt recycled material (from the middle and upper layers of the Wuhuang Expressway G50 Hanshi Section in China) was activated at 150 °C for 30 min to obtain the activated recycled SBS modified asphalt recycled material; ② 1000 g of the activated recycled SBS modified asphalt recycled material and 6 g of surface-modified nano-silica were mixed and stirred at 155 °C for 60 min to obtain a uniformly mixed asphalt recycled material; ③ 50 g of the polyurethane prepolymer modified asphalt was heated at 150 °C for 20 min, and then mixed and stirred with the uniformly mixed asphalt recycled material at 120 °C. After being placed at 120 °C for 2 h, the polyurethane modified asphalt recycled mixture was obtained.

[0032] Example 3 This example provides a method for preparing a polyurethane modified asphalt recycled mixture, including the following steps: (1)Surface modification of nano-silica: 100 g of nano-silica (purchased from Ningbo Bohuasi Nano-Technology Co., Ltd.) was added to 200 g of KH-550 amino-silane (purchased from Hubei Jianghan New Materials Co., Ltd.), and the mixture was stirred at 60 °C for 4 h. The specific surface area of the nano-silica was 320 m 2 / g, and the particle size was 30 nm; (2)Preparation of polyurethane prepolymer modified asphalt: ① Tetrahydrofuran polyether glycol (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was dehydrated under vacuum at 120 °C for 2 h to remove moisture. 50 g of dehydrated tetrahydrofuran polyether glycol and 10 g of diphenylmethane diisocyanate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) were added to the reaction kettle. After the raw materials were added and mixed evenly, the whole system was reacted at 80 °C under a nitrogen atmosphere for 2 h to obtain a polyurethane prepolymer.

[0033] ② The matrix asphalt was heated to 120 °C, and 3 g of the polyurethane prepolymer was added to 100 g of the matrix asphalt. It was sheared at high speed at 3000 rpm at 120 °C for 2 h to obtain a polyurethane prepolymer modified asphalt.

[0034] (3) Preparation of polyurethane modified asphalt recycled mixture: ① The recycled SBS modified asphalt recycled material (from the middle and upper layers of the Wuhuang Expressway G50 Hanshi section in China) was activated at 150 °C for 30 min to obtain the activated recycled SBS modified asphalt recycled material; ② 1000 g of the activated recycled SBS modified asphalt recycled material and 5 g of surface-modified nano-silica were mixed and stirred at 155 °C for 60 min to obtain a uniformly mixed asphalt recycled material; ③ 50 g of the polyurethane prepolymer modified asphalt was heated at 150 °C for 20 min, then mixed and stirred with the uniformly mixed asphalt recycled material at 120 °C, and left at 120 °C for 2 h to obtain the polyurethane modified asphalt recycled mixture.

[0035] Comparative Example 1 This comparative example provides a preparation method of a common SBS modified asphalt recycled mixture, including the following steps: (1) Take 3 g of SBS and 100 g of matrix asphalt. The matrix asphalt was heated to 150 °C, SBS was added, the high-speed shearer was turned on to 3000 rpm, and it was sheared at 150 °C for 2 h to obtain SBS modified asphalt; (2) Take 30 g of SBS modified asphalt and 1000 g of SBS modified asphalt recycled material. The recycled SBS modified asphalt recycled material was activated at 150 °C for 30 min and then mixed and stirred with the SBS modified asphalt recycled material at 150 °C for 20 min to obtain a common SBS modified asphalt recycled mixture.

[0036] Comparative Example 2 This comparative example provides a preparation method of a common polyurethane modified SBS asphalt recycled mixture, which is different from Example 1 in that nano-silica is not added, and the rest is the same.

[0037] Comparative Example 3 This comparative example provides a method for preparing a polyurethane-modified asphalt recycled mixture, which is different from Example 1 in that the added nano-silica is not surface-modified, and the rest is the same.

[0038] Comparative Example 4 This comparative example provides a method for preparing a polyurethane-modified asphalt recycled mixture, which is different from Example 1 in that the dosage of surface-modified nano-silica is 1 g, and the rest is the same.

[0039] The inventors found that when the dosage of surface-modified nano-silica is 1 g, the too low dosage of nano-silica will reduce the crosslinking network density of the recycled mixture, resulting in a decrease in low-temperature crack resistance and water damage resistance.

[0040] Comparative Example 5 This comparative example provides a method for preparing a polyurethane-modified asphalt recycled mixture, which is different from Example 1 in that the dosage of surface-modified nano-silica is 8 g, and the rest is the same.

[0041] The inventors found that when the dosage of surface-modified nano-silica is 8 g, the excessive dosage of nano-silica particles will hinder the movement of polyurethane segments, resulting in an increase in the elastic modulus of the recycled mixture but a decrease in low-temperature ductility performance.

[0042] To verify the performance advantages of the polyurethane-modified asphalt recycled mixture of the present invention, comparative tests were carried out on low-temperature crack resistance and interface bonding strength by setting comparative examples with different modification conditions. The following are the test data and analysis based on the "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). First, the asphalt recycled mixtures obtained from the above examples and comparative examples were used to prepare rutting plate specimens respectively, and were cut by a large cutting machine to make small beams with a notch at the bottom. The size of the small beam is 100 mm × 45 mm × 50 mm, and the notch size is 10 mm × 4 mm. Three-point bending fracture was carried out by a universal mechanical testing machine, the test temperature was set at -10°C, and its low-temperature crack resistance was measured. Similarly, the standard Marshall specimens were formed by the asphalt recycled mixtures obtained from the above examples and comparative examples respectively, and freeze-thaw splitting tests were carried out to measure their interface bonding performance. The test results are shown in Table 1.

[0043] Table 1 Comparison of low-temperature crack resistance and interface bonding performance data of different modified asphalt samples

[0044] The results show that compared with Comparative Example 1 (ordinary SBS modification), the bending strain of the mixture in the examples of the present invention is increased by 22% - 26%, indicating that the present invention can effectively improve the low-temperature crack resistance of the recycled mixture and improve its durability and performance stability in cold environments.

[0045] The performance improvement of Comparative Example 3 (containing unmodified nano-silica) is less than that of the present invention. This shows that due to the relatively high content of surface hydroxyl groups (-OH) in unmodified nano-silica, although the active hydroxyl groups (-OH) can react with the isocyanate groups (-NCO) in the polyurethane prepolymer to form a dense network, and its surface functional groups can bind to the aged SBS molecules and polar components in asphalt, to a certain extent, it can improve the low-temperature cracking resistance and interfacial bonding strength of the recycled mixture. However, unmodified nano-silica is prone to agglomerate into micron-sized particles in asphalt, and this agglomeration will hinder the flexible movement of polyurethane molecular chains and increase the brittleness of asphalt. In addition, unmodified nano-silica is hydrophilic on the surface and has poor compatibility with hydrophobic asphalt and polyurethane matrix, resulting in micropores and weakly bonded regions at the particle-matrix interface, which may weaken the water damage resistance of the recycled mixture to a certain extent.

[0046] By modification with a silane coupling agent (such as KH-550), a hydrophobic layer is formed on the surface of nano-silica, reducing agglomeration and uniformly dispersing in asphalt. Moreover, the formed amino groups (-NH2) after modification react with the isocyanate groups (-NCO) of polyurethane to form a denser three-dimensional crosslinked network, endowing asphalt with elastic recovery ability and improving the low-temperature cracking resistance and water damage resistance. Secondly, the freeze-thaw splitting strength ratio of the mixture of the present invention is increased by 8%-10% compared with Comparative Example 1, indicating that the inorganic-organic hybrid network formed by the reaction of the -NCO groups of the polyurethane prepolymer with the amino groups on the surface of nano-silica effectively improves the chemical bonding force between the new and old asphalt and inhibits the interfacial peeling caused by water damage.

[0047] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polyurethane-modified asphalt recycled mixture, characterized in that, Its raw material components include recycled SBS modified asphalt regenerant, polyurethane prepolymer modified asphalt, and surface-modified nano-silica.

2. The polyurethane-modified asphalt recycled mixture according to claim 1, wherein The preparation method of the surface-modified nano-silica includes the following steps: S1. Stir the silane coupling agent and nano-silica at 60 - 80 °C to obtain surface-modified nano-silica.

3. The polyurethane-modified asphalt recycled mixture according to claim 2, wherein The weight ratio of the silane coupling agent to nano-silica is (1 - 2):

1.

4. The polyurethane-modified asphalt recycled mixture according to claim 2, wherein, The silane coupling agent includes KH-550 amino silane.

5. The polyurethane-modified asphalt recycled mixture according to claim 2, characterized in that, The specific surface area of the nano-silica is 180 - 520 m 2 / g, and the particle size is 20 - 40 nm.

6. The polyurethane-modified asphalt recycled mixture according to claim 1, wherein The weight ratio of the recycled SBS modified asphalt regenerant, polyurethane prepolymer modified asphalt, and surface-modified nano-silica is 1000:(30 - 50):(3 - 6).

7. The polyurethane-modified asphalt recycled mixture according to claim 1, wherein The preparation method of the polyurethane prepolymer modified asphalt includes the following steps: S1. Under the protection of inert gas, mix and stir the polyol with adsorbed water removed and isocyanate to react to obtain a polyurethane prepolymer; S2. Shear the polyurethane prepolymer and matrix asphalt to obtain polyurethane prepolymer modified asphalt.

8. The polyurethane-modified asphalt recycled mixture according to claim 1, wherein The recycled SBS modified asphalt regenerant is taken from the milled materials after crushing and screening in the mixing station near the road section.

9. The polyurethane-modified asphalt recycled mixture according to claim 8, characterized in that, In the recycled SBS modified asphalt regenerant, the mass of SBS modified asphalt accounts for 3 - 6% of the recycled SBS modified asphalt regenerant; in the SBS modified asphalt, the mass of SBS accounts for 3 - 5% of the SBS modified asphalt.

10. A method for preparing a polyurethane-modified asphalt recycled mixture as described in any one of claims 1-9, characterized in that, It includes the following steps: S1. Heat and activate the recycled SBS modified asphalt regenerant; S2. Mix and stir the activated recycled SBS modified asphalt regenerant with the surface-modified nano-silica to obtain a uniformly mixed asphalt regenerant; S3. Heat the polyurethane prepolymer modified asphalt and then mix and stir it with the uniformly mixed asphalt regenerant, and let it stand to obtain the polyurethane modified asphalt regenerated mixture.

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