Polyurethane modified asphalt recycled mixture and preparation method thereof

Abstract

The present invention relates to the technical field of road materials, and in particular to a polyurethane modified asphalt recycled mixture and a preparation method thereof. Its raw material components include recycled SBS modified asphalt recycled material, polyurethane prepolymer modified asphalt and surface-modified nano-silica. The present invention uses SBS modified asphalt recycled material instead of natural aggregate to significantly reduce natural resource consumption, reduce carbon emissions, and achieve the recycling of construction waste, with both environmental protection and economic benefits. The present invention effectively improves the low-temperature crack resistance of the recycled mixture, improves its durability and performance stability in cold environments, and at the same time forms a dense inorganic-organic hybrid network, enhances the bonding force between asphalt and aged asphalt in the recycled material, and the adhesion performance with aggregates in the recycled material, thereby improving the water damage resistance of the recycled asphalt mixture.

Description

Technical Field

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

[0002] As traffic continues to increase, asphalt pavement deteriorates at an accelerated rate. More and more highways are undergoing reconstruction and renovation due to difficulties meeting pavement performance requirements. This process generates a large amount of recycled asphalt mixtures. In recycled asphalt mixtures with a high recycled content, aging of the old asphalt reduces the mixture's flexibility and poor compatibility between the new and old asphalt. This not only affects the recycled asphalt mixture's low-temperature crack resistance but also reduces its resistance to water damage.

[0003] When polyurethane prepolymers are used as modifiers to modify asphalt, they can enhance its flexibility by introducing soft segments, allowing it to maintain elasticity even at low temperatures. Furthermore, chemical reactions (such as the reaction of -NCO groups with -OH groups in asphalt) form a cross-linked network, further enhancing the asphalt's viscoelasticity. Polyurethane prepolymer-modified asphalt, thanks to the soft segments introduced, can improve the low-temperature performance of recycled asphalt. For example, a paper ("Performance and modification mechanism investigation of polyurethane prepolymer system modified bitumen for 100% reclaimed asphalt pavement (RAP) application," Construction and Building Materials, 2025) reports that the introduction of a polyurethane prepolymer system into asphalt and its use in recycled asphalt mixtures improved the mixture's permanent deformation resistance and low-temperature crack resistance. Another patent (CN 115477852 A) indicates that the addition of polyurethane-glycerol ether to recycled SBS-modified asphalt effectively restores its low-temperature performance. In addition to low-temperature performance, the biggest problem facing recycled asphalt mixtures is their poor resistance to water damage. Currently, there is no invented 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-mentioned purpose, 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 achieved as follows:

[0007] In a first aspect, the present invention provides a polyurethane modified asphalt regeneration mixture, the raw material components of which include recycled SBS modified asphalt regeneration material, polyurethane prepolymer modified asphalt and surface-modified nano-silica.

[0008] Preferably, the preparation method of the surface-modified nano-silica comprises the following steps:

[0009] S1. Stirring the silane coupling agent and nano-silica at 60-80° C. for 2-4 hours to obtain surface-modified nano-silica.

[0010] Further preferably, the weight ratio of the silane coupling agent to the nano-silica is (1-2):1.

[0011] More preferably, the silane coupling agent includes KH-550 aminosilane.

[0012] More preferably, the specific surface area of ​​the nano-silicon dioxide is 180-520m 2 / g, particle size is 20-40nm.

[0013] Further preferably, nano-silica with a specific surface area and particle size within this range can provide sufficient active sites to enhance the chemical bonding ability with the polyurethane prepolymer. At the same time, it can form a uniform dispersion system with the asphalt in the recycled material through surface modification, thereby reducing the risk of sedimentation. It avoids the problem of particle agglomeration caused by an excessively high specific surface area, a too low specific surface area leads to a reduction in active sites, excessively large particles will lose the nanoscale surface effect and cannot effectively provide reaction sites for the polyurethane prepolymer, and excessively small particles are prone to form stress concentration points in the polyurethane hard segment-rich area, resulting in an increased risk of low-temperature brittle fracture.

[0014] Preferably, the weight ratio of the recycled SBS modified asphalt regeneration material, the polyurethane prepolymer modified asphalt and the surface-modified nano-silica is 1000: (30-50): (3-6).

[0015] Further preferably, the preparation method of the polyurethane prepolymer modified asphalt comprises the following steps:

[0016] S1. Under inert gas protection, the polyol and isocyanate from which adsorbed water has been removed are mixed and stirred at 60-80° C. for 2-6 hours to obtain a polyurethane prepolymer;

[0017] S2. The polyurethane prepolymer and the matrix asphalt were sheared at a high speed of 3000 rpm at 120° C. for 2 h to obtain a polyurethane prepolymer modified asphalt.

[0018] Preferably, the recycled SBS modified asphalt regeneration material (RAP) is taken from the milling material after crushing and screening in the mixing station near the road section.

[0019] Further preferably, in order to clearly determine the content of SBS modified asphalt in the recycled material, the RAP is first dried at 60°C to constant weight to remove moisture therein, and then a certain amount of RAP is preheated at 100°C for 0.5h to improve the extraction efficiency; the treated RAP is then placed in an extractor, and a certain amount of trichloroethylene solvent is added to carry out the extraction process; the asphalt mortar obtained after the extraction is completed is centrifuged in a centrifuge at 4000r / min for 5min 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 the SBS modified asphalt is 3-6% of the mass of the SBS modified asphalt RAP material.

[0020] Further preferably, in order to clarify the SBS content in SBS modified asphalt, the extracted SBS modified asphalt sample is heated to a boiling state, and n-heptane is added and continuously dissolved for 0.5h-1h to obtain insoluble matter (asphaltene + SBS) and soluble matter (soft component); the insoluble matter (asphaltene + SBS) is reflux-extracted with boiling n-heptane to obtain a dissolving solution (SBS + soft component) and pure asphaltene; the soluble matter (soft component) and the dissolving solution (SBS + soft component) are combined, and n-hexane is added to obtain a soluble matter (soft component) and an insoluble matter (soft component + SBS); the insoluble matter (soft component + SBS) is treated with ether to obtain an insoluble matter (soft component) and a soluble matter (SBS); finally, pure SBS is obtained by rotary evaporation, and the SBS content is 3-5% of the mass of the SBS modified asphalt.

[0021] In a second aspect, the present invention provides a method for preparing the polyurethane-modified asphalt recycled mixture, comprising the following steps:

[0022] S1. Activate the recycled SBS modified asphalt at 130-160°C for 20-30 minutes;

[0023] S2. Mixing the activated recycled SBS modified asphalt regeneration material with the surface-modified nano-silica at 130-165° C. for 40-60 minutes to obtain a uniformly mixed asphalt regeneration material;

[0024] S3. Heat the polyurethane prepolymer modified asphalt at 120-150° C., mix and stir with the evenly mixed asphalt recycled material at 90-120° C., and place at 90-120° C. for 1-2 hours to obtain the polyurethane modified asphalt recycled mixture.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] (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, thereby improving the bonding strength between the new and old asphalt. The surface-modified nano-silica introduced has amino groups on its surface that can form hydrogen bonds with the aged SBS, making it uniformly dispersed in the old asphalt, acting as a rigid cross-linking center with ultra-high functionality. At the same time, it provides more active sites for the polyurethane prepolymer, thereby forming a dense PU-SiO2-SBS multi-cross-linking system, further improving the bonding strength between the new and old asphalt.

[0027] (2) The dense PU-SiO2-SBS multi-crosslinked network contains a large number of polar groups, which enhances the adhesion between asphalt and recycled aggregate. The high bonding between the new and old asphalt and the high adhesion between asphalt and aggregate synergistically improve the recycled asphalt mixture's resistance to water damage and low-temperature cracking. DETAILED DESCRIPTION

[0028] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0029] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0030] In this document, the terms “contain”, “include” or “include” are open expressions, that is, they include the contents specified in the present invention but do not exclude other contents.

[0031] As used herein, the terms "optionally," "optional," or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0032] The nano-silica of this invention possesses properties such as high specific surface area, surface activity, and chemical stability. Its physical-chemical synergy in polyurethane-modified asphalt significantly enhances asphalt performance. The nano-silica's high specific surface area and surface-modified amino groups (-NH2) form hydrogen bonds with aged SBS, allowing it to be evenly dispersed in the old asphalt, acting as ultra-high-functionality rigid crosslinking centers. This, in turn, provides more active sites for the polyurethane prepolymer, forming a dense PU-SiO2-SBS multi-crosslink system.

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a method for preparing a polyurethane-modified asphalt recycled mixture, comprising the following steps:

[0036] (1) Surface modification of nano-silica: 100 g of nano-silica (purchased from Ningbo Bohuasi Nanotechnology Co., Ltd.) was added to 100 g of KH-550 aminosilane (purchased from Hubei Jianghan New Materials Co., Ltd.) and stirred at 80 °C for 4 h. The specific surface area of ​​nano-silica was selected to be 180 m 2 / g, particle size is 20nm;

[0037] (2) Preparation of polyurethane prepolymer modified asphalt:

[0038] ① Dehydrate polytetramethylene ether glycol (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) under vacuum at 120°C for 2 hours to remove moisture. Add 50g of the dehydrated polytetramethylene ether glycol and 10g of diphenylmethane diisocyanate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) into the reactor. After the raw materials are added and mixed evenly, react the entire system at 80°C under a nitrogen atmosphere for 2 hours to obtain a polyurethane prepolymer.

[0039] ② Heat the base asphalt to 120°C, add 3g of polyurethane prepolymer to 100g of base asphalt, and high-speed shear at 3000rpm at 120°C for 2h to obtain polyurethane prepolymer modified asphalt.

[0040] (3) Preparation of polyurethane modified asphalt recycled mixture:

[0041] ① Activate the recycled SBS modified asphalt (taken from the middle and upper layers of the G50 Hanshi section of the Wuhuang Expressway in China) at 150°C for 30 minutes to obtain the activated recycled SBS modified asphalt;

[0042] ② 1000g of activated recycled SBS modified asphalt regeneration material and 3g of surface-modified nano-silica were mixed and stirred at 155°C for 60min to obtain a uniformly mixed asphalt regeneration material;

[0043] ③ After heating 30g of polyurethane prepolymer modified asphalt at 150℃ for 20min, mix and stir with the evenly mixed asphalt recycled material at 120℃, and place it at 120℃ for 2h to obtain the polyurethane modified asphalt recycled mixture.

[0044] Example 2

[0045] This embodiment provides a method for preparing a polyurethane-modified asphalt recycled mixture, comprising the following steps:

[0046] (1) Surface modification of nano-silica: 100 g of nano-silica (purchased from Ningbo Bohuasi Nanotechnology Co., Ltd.) was added to 100 g of KH-550 aminosilane (purchased from Hubei Jianghan New Materials Co., Ltd.) and stirred at 60 °C for 4 h. The specific surface area of ​​nano-silica was 520 m 2 / g, particle size is 40nm;

[0047] (2) Preparation of polyurethane prepolymer modified asphalt:

[0048] ① Dehydrate polytetramethylene ether glycol (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) under vacuum at 120°C for 2 hours to remove moisture. Add 50g of the dehydrated polytetramethylene ether glycol and 10g of diphenylmethane diisocyanate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) into the reactor. After the raw materials are added and mixed evenly, react the entire system at 80°C under a nitrogen atmosphere for 2 hours to obtain a polyurethane prepolymer.

[0049] ② Heat the base asphalt to 120°C, add 3g of polyurethane prepolymer to 100g of base asphalt, and high-speed shear at 3000rpm at 120°C for 2h to obtain polyurethane prepolymer modified asphalt.

[0050] (3) Preparation of polyurethane modified asphalt recycled mixture:

[0051] ① Activate the recycled SBS modified asphalt (taken from the middle and upper layers of the G50 Hanshi section of the Wuhuang Expressway in China) at 150°C for 30 minutes to obtain the activated recycled SBS modified asphalt;

[0052] ② 1000 g of activated recycled SBS modified asphalt regeneration 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 regeneration material;

[0053] ③ After heating 50g of polyurethane prepolymer modified asphalt at 150℃ for 20min, mix and stir with the evenly mixed asphalt recycled material at 120℃, and place it at 120℃ for 2h to obtain the polyurethane modified asphalt recycled mixture.

[0054] Example 3

[0055] This embodiment provides a method for preparing a polyurethane-modified asphalt recycled mixture, comprising the following steps:

[0056] (1) Surface modification of nano-silica: 100 g of nano-silica (purchased from Ningbo Bohuasi Nanotechnology Co., Ltd.) was added to 200 g of KH-550 aminosilane (purchased from Hubei Jianghan New Materials Co., Ltd.) and stirred at 60 °C for 4 h. The specific surface area of ​​nano-silica was 320 m 2 / g, particle size is 30nm;

[0057] (2) Preparation of polyurethane prepolymer modified asphalt:

[0058] ① Dehydrate polytetramethylene ether glycol (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) under vacuum at 120°C for 2 hours to remove moisture. Add 50g of the dehydrated polytetramethylene ether glycol and 10g of diphenylmethane diisocyanate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) into the reactor. After the raw materials are added and mixed evenly, react the entire system at 80°C under a nitrogen atmosphere for 2 hours to obtain a polyurethane prepolymer.

[0059] ② Heat the base asphalt to 120°C, add 3g of polyurethane prepolymer to 100g of base asphalt, and high-speed shear at 3000rpm at 120°C for 2h to obtain polyurethane prepolymer modified asphalt.

[0060] (3) Preparation of polyurethane modified asphalt recycled mixture:

[0061] ① Activate the recycled SBS modified asphalt (taken from the middle and upper layers of the G50 Hanshi section of the Wuhuang Expressway in China) at 150°C for 30 minutes to obtain the activated recycled SBS modified asphalt;

[0062] ② 1000g of activated recycled SBS modified asphalt regeneration material and 5g of surface-modified nano-silica were mixed and stirred at 155°C for 60min to obtain a uniformly mixed asphalt regeneration material;

[0063] ③ After heating 50g of polyurethane prepolymer modified asphalt at 150℃ for 20min, mix and stir with the evenly mixed asphalt recycled material at 120℃, and place it at 120℃ for 2h to obtain the polyurethane modified asphalt recycled mixture.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a conventional SBS modified asphalt recycled mixture, comprising the following steps:

[0066] (1) Take 3g SBS and 100g base asphalt, heat the base asphalt to 150℃, add SBS, turn on the high-speed shear instrument to 3000rpm, and shear at 150℃ for 2h to obtain SBS modified asphalt;

[0067] (2) Take 30g of SBS modified asphalt and 1000g of SBS modified asphalt recycled material. Activate the recycled SBS modified asphalt recycled material at 150℃ for 30min and then mix and stir with the SBS modified asphalt recycled material at 150℃ for 20min to obtain ordinary SBS modified asphalt recycled mixture.

[0068] Comparative Example 2

[0069] This comparative example provides a method for preparing a common polyurethane-modified SBS asphalt recycled mixture, which differs from Example 1 in that nano-silica is not added, and the rest is the same.

[0070] Comparative Example 3

[0071] This comparative example provides a method for preparing a polyurethane-modified asphalt recycled mixture, which differs from Example 1 in that the added nano-silica is not surface-modified, and the rest is the same.

[0072] Comparative Example 4

[0073] This comparative example provides a method for preparing a polyurethane-modified asphalt recycled mixture, which differs from Example 1 in that the amount of surface-modified nano-silica used is 1 g, and the rest is the same.

[0074] The inventors found that when the dosage of the surface-modified nano-silica is 1 g, too low a dosage of nano-silica will reduce the cross-linking network density of the recycled mixture, thereby reducing the low-temperature crack resistance and water damage resistance.

[0075] Comparative Example 5

[0076] This comparative example provides a method for preparing a polyurethane-modified asphalt recycled mixture. The difference from Example 1 is that the amount of surface-modified nano-silica used is 8 g, and the rest is the same.

[0077] The inventors found that when the amount of surface-modified nano-silica was 8 g, excessive nano-silica particle dosage would hinder the movement of polyurethane chain segments, resulting in an increase in the elastic modulus of the recycled mixture but a decrease in low-temperature ductility.

[0078] To verify the performance advantages of the polyurethane-modified asphalt recycled mixture described in this invention, comparative tests were conducted on low-temperature crack resistance and interfacial adhesion using comparative examples with different modification conditions. The following test data and analysis are based on the "Testing Procedures for Asphalt and Asphalt Mixtures for Highway Engineering" (JTG E20-2011). First, rutting plate specimens were prepared using the asphalt recycled mixtures obtained in the above examples and comparative examples. These specimens were then cut using a large-scale cutting machine to produce small beams with a notched bottom. The beams measured 100 mm × 45 mm × 50 mm, with a notch of 10 mm × 4 mm. The beams were then subjected to three-point bending fracture tests using a universal mechanical testing machine at -10°C to measure their low-temperature crack resistance. Similarly, standard Marshall specimens were formed using the asphalt recycled mixtures obtained in the above examples and comparative examples, and freeze-thaw splitting tests were performed to measure their interfacial adhesion. The test results are shown in Table 1.

[0079] Table 1 Comparison of low-temperature crack resistance and interface bonding performance data of different modified asphalt samples

[0080]

[0081] The results show that compared with Comparative Example 1 (ordinary SBS modification), the bending strain of the mixture in the embodiment of the present invention is increased by 22%-26%, indicating that the present invention can effectively enhance the low-temperature crack resistance of the recycled mixture and improve its durability and performance stability in cold environments.

[0082] The performance improvement of Comparative Example 3 (containing unmodified nanosilica) is less than that of the present invention. This indicates that the unmodified nanosilica has a higher surface hydroxyl (-OH) content. 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 with aged SBS molecules and polar components in asphalt, to a certain extent improving the low-temperature crack resistance and interfacial bonding of the recycled mixture, the unmodified nanosilica tends to agglomerate in asphalt to form micron-sized particles. This agglomeration hinders the flexible movement of the polyurethane molecular chains and increases the brittleness of the asphalt. In addition, the hydrophilic surface of the unmodified nanosilica has poor compatibility with the hydrophobic asphalt and polyurethane matrix, resulting in micropores and weakly bonded areas at the interface between the particles and the matrix, which may partially weaken the recycled mixture's resistance to water damage.

[0083] Modification with a silane coupling agent (such as KH-550) forms a hydrophobic layer on the surface of the nano-silica, reducing aggregation and allowing it to be evenly dispersed in the asphalt. Furthermore, the amino groups (-NH2) formed after modification react with the isocyanate groups (-NCO) of the polyurethane to form a denser three-dimensional cross-linked network, giving the asphalt elastic recovery capabilities and improving low-temperature crack resistance and resistance to water damage. Secondly, the freeze-thaw splitting strength of the mixture of the present invention is increased by 8%-10% compared to 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 the nano-silica effectively improves the chemical adhesion between the new and old asphalt and inhibits interfacial debonding caused by water damage.

[0084] The above description is only a 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polyurethane modified asphalt recycled mixture, characterized in that: The following steps are involved: S1. Activate the recycled SBS modified asphalt by heating at 130-160℃; S2. Mixing the activated recycled SBS modified asphalt regeneration material with the surface-modified nano-silica to obtain a uniformly mixed asphalt regeneration material; S3, heating the polyurethane prepolymer modified asphalt at 120-150° C. and mixing with the uniformly mixed asphalt recycled material at 90-120° C., and placing at 90-120° C. for 1-2 hours to obtain the polyurethane modified asphalt recycled mixture; in, The preparation method of the surface-modified nano-silica comprises the following steps: S2-1, stirring a silane coupling agent and nano-silica at 60-80° C. to obtain surface-modified nano-silica; the silane coupling agent is KH-550 aminosilane; In the steps S1 to S3, the weight ratio of the recovered SBS modified asphalt recycled material, the polyurethane prepolymer modified asphalt and the surface-modified nano-silica is 1000: (30-50): (3-6).

2. The method for preparing polyurethane modified asphalt recycled mixture according to claim 1, characterized in that: The weight ratio of the silane coupling agent to the nano-silica is (1-2):

1.

3. The method for preparing polyurethane modified asphalt recycled mixture according to claim 1, characterized in that: The specific surface area of ​​the nano-silicon dioxide is 180-520m 2 / g, particle size is 20-40nm.

4. The method for preparing a polyurethane modified asphalt recycled mixture according to claim 1, characterized in that: The preparation method of the polyurethane prepolymer modified asphalt in step S3 comprises the following steps: S3-1. Under the protection of an inert gas, the polyol from which adsorbed water has been removed and the isocyanate are mixed and stirred to react to obtain a polyurethane prepolymer; S3-2. Shear the polyurethane prepolymer and the matrix asphalt to obtain polyurethane prepolymer modified asphalt.

5. The method for preparing polyurethane modified asphalt recycled mixture according to claim 1, characterized in that: The recycled SBS modified asphalt regeneration material is taken from the milling material after crushing and screening in the mixing station near the road section.

6. The method for preparing polyurethane modified asphalt recycled mixture according to claim 1, characterized in that: In the recycled SBS modified asphalt regeneration material, the mass of SBS modified asphalt accounts for 3-6% of the recycled SBS modified asphalt regeneration material; in the SBS modified asphalt, the mass of SBS accounts for 3-5% of the SBS modified asphalt.

7. A polyurethane modified asphalt recycled mixture obtained by the preparation method according to any one of claims 1 to 6.

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