Preparation method of nano silicon dioxide modified asphalt recycled fine aggregate plant-mixed hot recycled high-performance mixture

Abstract

The invention discloses a preparation method of a nano silicon dioxide modified asphalt recycled fine aggregate plant-mixed hot recycled high-performance mixture, and belongs to the field of road engineering materials. The method specifically comprises the following steps: firstly, crushing and screening the waste asphalt mixture to obtain regenerated fine aggregate with the particle size of less than or equal to 2.36 mm, and activating the regenerated fine aggregate with a silane coupling agent KH-560; secondly, nano SiO2 with the particle size of 20-50 nm is subjected to ultrasonic dispersion and then modified with a silane coupling agent KH-570; mixing the aged asphalt and new asphalt according to a certain proportion, adding a proper amount of regenerant and modified nano SiO2, and carrying out shear modification treatment; and finally, mixing the modified recycled fine aggregate, the new coarse aggregate and the new mineral powder according to the target gradation, and fully mixing with the nano-modified recycled asphalt to obtain the mixture. The interface bonding performance of the recycled fine aggregate and asphalt is remarkably improved through dual modification, the problems that a traditional recycled mixture is poor in durability and insufficient in high-temperature stability are solved, and the high-performance mixture is prepared.

Description

Technical Field

[0001] This invention relates to the field of asphalt mixture preparation, specifically to a method for preparing a high-performance plant-mixed recycled fine aggregate asphalt modified with nano-silica. Background Technology

[0002] With the rapid development of highway construction and the increasing service life of asphalt pavements, a large amount of waste asphalt mixtures need to be processed and reused. The recycling of asphalt pavement materials not only reduces the consumption of new materials and lowers project costs, but also reduces waste emissions, protects the environment, and aligns with the sustainable development strategy. Currently, plant-mixed hot recycling technology has become the main method for recycling waste asphalt mixtures due to its high controllability and stable performance of recycled mixtures.

[0003] In the hot recycling process of asphalt mixtures, the treatment and utilization of recycled fine aggregates is a key issue. Recycled fine aggregates (≤2.36mm) have a large specific surface area, are deeply aged, and suffer severe asphalt film loss, resulting in poor adhesion to virgin materials. This leads to problems such as poor water stability and insufficient high-temperature stability in recycled mixtures. To address these issues, scholars both domestically and internationally have conducted extensive research.

[0004] CN113698139B discloses a high-content RAP plant-mixed hot recycled modified asphalt mixture and its preparation method. This method achieves a RAP content of 40%–70% by adding asphalt recycling agents and modifiers, and reduces the preheating temperature of the RAP. While this technology improves the utilization rate of RAP, it does not specifically address the characteristics of recycled fine aggregates, resulting in room for improvement in the interfacial properties of the recycled mixture.

[0005] CN117466563B proposes a process for producing recyclable asphalt mixtures by adding waste rubber. This involves treating waste asphalt milling material through pyrolysis, desulfurizing and coupling-modifying waste rubber powder, and modifying the rubber powder surface with graphene to improve the high and low temperature performance of the mixture. However, this method is complex, energy-intensive, and does not solve the problem of activating recycled fine aggregates.

[0006] CN113511840A discloses a water-resistant recycled asphalt mix and its preparation method. By adding functional materials such as mordenite molecular sieves, nano-silicon carbide, and hydrogels, the water resistance of the recycled asphalt mix is ​​improved. While this method improves the durability of the recycled mix, it does not modify the surface properties of the recycled fine aggregate, making it difficult to fundamentally solve the interfacial bonding problem between the recycled fine aggregate and the new asphalt.

[0007] CN120247462A proposes an in-situ thermally recycled asphalt mixture and its construction method. This method introduces a recycling agent to restore the properties of aged asphalt and combines it with functional materials such as styrene-butadiene rubber modifiers, basalt fibers, and nano-silica to improve the mixture's high-temperature rutting resistance, low-temperature crack resistance, and fatigue resistance. Although this method uses nano-silica, it does not undergo surface modification treatment, resulting in poor dispersion of the nanomaterials in the asphalt.

[0008] CN113683897B describes an environmentally friendly modified asphalt and its preparation method, which uses an antioxidant with nano-silica as a carrier to improve the anti-aging properties of asphalt by grafting imino groups. This technology utilizes the spatial network structure of nano-silica to enhance the strength of asphalt, but it does not solve the problem of nanomaterial dispersion in asphalt, nor does it specifically address the issue of recycled fine aggregates.

[0009] In summary, existing technologies have the following problems in the preparation of recycled asphalt mixtures:

[0010] 1. Due to severe aging, recycled fine aggregate has low surface energy and poor adhesion to new asphalt and aggregates, which makes recycled mixtures prone to water damage, high-temperature rutting, and decreased anti-aging properties.

[0011] 2. Although nanomaterials can improve the performance of recycled mixtures, their high specific surface area makes them prone to agglomeration and difficult to disperse evenly in asphalt mastic, thus failing to effectively exert their interfacial reinforcement effect.

[0012] 3. Existing technologies only involve simple screening for the pretreatment of recycled fine aggregates, without any activation modification to address their aging characteristics. This results in the fine aggregates not being activated, limiting their dosage in practical applications and causing resource waste.

[0013] Therefore, there is an urgent need to develop a preparation method that can effectively activate recycled fine aggregates, improve the dispersibility of nanomaterials, and enhance the overall performance of recycled mixtures.

[0014] Patent content

[0015] To address the technical problems of insufficient performance of recycled fine aggregates, uneven dispersion of nanomaterials, and low utilization rate of recycled fine aggregates, and to achieve the technical effects of efficient activation of recycled fine aggregates, uniform dispersion of nanomaterials, comprehensive improvement of mixture performance, and high utilization of recycled fine aggregates, this invention provides a method for preparing plant-mixed hot recycled high-performance mixtures of asphalt recycled fine aggregates modified with nano-silica.

[0016] The technical solution adopted by this invention to solve its technical problem is: to provide a method for preparing high-performance recycled asphalt fine aggregate plant-mixed hot-mixed aggregate modified with nano-silica, comprising the following steps:

[0017] (1) Pretreatment and activation of recycled fine aggregate: The waste asphalt mixture is crushed and screened to obtain recycled fine aggregate with a diameter of ≤2.36mm. After drying, 1% to 3% silane coupling agent (KH-560) is added and stirred at high speed at 80 to 100℃ for 15 to 20 minutes.

[0018] (2) Modification of nano-silica: 20-50 nm nano-SiO2 is dispersed in anhydrous ethanol, ultrasonically dispersed, and then 3%-5% silane coupling agent (KH-570) is added. The mixture is refluxed at 60-80℃ for 2-3 h, filtered and dried.

[0019] (3) Compounding and modification of recycled asphalt: Mix aged asphalt and new asphalt at a ratio of 1:1 to 1:2, add 3% to 8% recycling agent and stir, then add 2% to 5% modified nano-SiO2, and shear with a colloid mill for 5 to 10 minutes.

[0020] (4) Gradation design and mixing of the mixture: Weigh modified recycled fine aggregate (30% to 50%), new coarse aggregate (30% to 50%), and new mineral powder (5% to 10%) according to the target gradation, heat them and then forcibly mix them with nano-modified recycled asphalt (4.5% to 5.5%). First, dry mix for 90 to 120 seconds, and then wet mix for 180 to 240 seconds.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. High-efficiency activation of recycled fine aggregate: Through surface treatment with silane coupling agent, the hydroxyl groups (-OH) on the surface of recycled fine aggregate condense with the silicon-oxygen bonds (-Si-OH) after silane hydrolysis to form an organic-inorganic interface layer, which significantly improves its adhesion to asphalt and increases the pull-out strength by 30% to 50%, solving the problems of asphalt film peeling and low surface energy caused by aging of traditional recycled fine aggregate;

[0023] 2. Uniform dispersion of nanomaterials: The double bonds (-C=C-) on the surface of modified nano-SiO2 undergo a conjugated reaction with the aromatics in the new asphalt, forming an "anchoring effect" that prevents agglomeration. This allows the nanoparticles to be uniformly distributed in the asphalt mastic, refining the particle size distribution of the asphalt mastic (average particle size ≤1μm), improving the temperature sensitivity and shear resistance of the mastic, and overcoming the defect of easy agglomeration of nanomaterials in traditional processes.

[0024] 3. Comprehensive improvement in mixture performance: The synergistic effect of modified recycled fine aggregate and nano-asphalt mastic makes the high-temperature dynamic stability (60℃) of the mixture ≥6000 times / mm, which is more than 50% higher than that of traditional recycled mixtures; the freeze-thaw splitting residual strength ratio ≥85%, which is more than 20% higher than that of traditional recycled mixtures; and the mass loss after aging in a rotating film oven ≤0.8%, which is 30% lower than that of traditional recycled mixtures, effectively solving the problems of water damage, high-temperature rutting, and decreased anti-aging performance of recycled mixtures.

[0025] 4. High utilization of recycled fine aggregate: Through the technical solution of this invention, the content of recycled fine aggregate can reach 30% to 50%, which is far higher than the traditional process limit of less than 20%, significantly reducing the amount of new aggregate and new asphalt used, saving 20% ​​to 30% of costs, meeting the needs of resource recycling and low-carbon development, and solving the problem of low utilization rate of recycled fine aggregate in traditional processes. Attached Figure Description

[0026] Figure 1 This is a key process flow diagram of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Example 1

[0029] Pretreatment and activation of recycled fine aggregate: Crushed and screened recycled fine aggregate ≤2.36mm, dried at 105℃ to a moisture content of 0.3%, add 2% (by mass of recycled fine aggregate) of KH-560, stir at 90℃ for 18min, and set aside.

[0030] Nano SiO2 modification: 30nm nano SiO2 was dispersed in anhydrous ethanol and ultrasonically dispersed for 30min. Then, 4% (by mass of nano SiO2) KH-570 was added, and the mixture was refluxed at 70℃ for 2.5h. After filtration, the mixture was dried at 80℃ for later use.

[0031] Recycled asphalt compounding and modification: aged asphalt: new asphalt = 1:1.5, add 5% (by mass of mixed asphalt) recycling agent and stir for 10 min, then add 3.5% (by mass of mixed asphalt) modified nano SiO2, and shear in a colloid mill (3000 r / min) for 8 min to obtain nano-modified recycled asphalt;

[0032] Mixing: Weigh the following according to the target gradation: 40% modified recycled fine aggregate, 45% new coarse aggregate, and 5% new mineral powder, and heat to 175℃; add 5.0% nano-modified recycled asphalt and heat to 165℃; dry mix for 100s, then wet mix for 210s to obtain the mixture.

[0033] Example 2 (Low Parameter Group)

[0034] Activation of recycled fine aggregate: with a moisture content of 0.4%, add 1% KH-560 and stir at 80℃ for 15 minutes;

[0035] Nano-SiO2 modification: Add 3% KH-570 and reflux at 60℃ for 2 hours;

[0036] Recycled asphalt compound: aged asphalt: new asphalt = 1:2, add 3% recycling agent, add 2% modified nano-SiO2, and shear in colloid mill for 5 min;

[0037] Mixing of aggregates: 30% modified recycled fine aggregate, 55% new coarse aggregate, 5% new mineral powder, graded AC-16; aggregate temperature 170℃, asphalt temperature 160℃; dry mixing 90s, wet mixing 180s.

[0038] Example 3 (High Parameter Group)

[0039] Activation of recycled fine aggregate: with a moisture content of 0.2%, add 3% KH-560 and stir at 100℃ for 20 minutes;

[0040] Nano-SiO2 modification: Add 5% KH-570 and reflux at 80℃ for 3 hours;

[0041] Recycled asphalt compound: aged asphalt: new asphalt = 1:1, add 8% recycling agent, add 5% modified nano-SiO2, and shear in colloid mill for 10 min;

[0042] Mixing of aggregates: 50% modified recycled fine aggregate, 40% new coarse aggregate, and 10% new mineral powder; aggregate temperature 180℃, asphalt temperature 170℃; dry mixing for 120s, wet mixing for 240s.

[0043] Comparative Example 1 (Missing "Activation of recycled fine aggregate KH-560")

[0044] Differences: The recycled fine aggregate was only dried (moisture content 0.3%) and not activated with KH-560. Other steps and parameters were completely consistent with those in Example 1.

[0045] Comparative Example 2 (Missing "Nano SiO2 KH-570 Modification")

[0046] Differences: Nano-SiO2 was only ultrasonically dispersed (without KH-570 reflux modification) and directly added to asphalt. Other steps and parameters were the same as in Example 1.

[0047] Comparative Example 3 (using "unmodified nano-SiO2 instead of modified nano-SiO2")

[0048] Differences: Raw nano-SiO2 without ultrasonication or KH-570 modification was directly added; other steps and parameters were the same as in Example 1.

[0049] Comparative Example 4 (low content of recycled fine aggregate, not within the scope of innovation)

[0050] Differences: The amount of recycled fine aggregate is 20% (traditional process level), and other steps and parameters are the same as in Example 1.

[0051] Comparative Example 5 (Traditional recycling process, with no innovation)

[0052] Differences: Recycled fine aggregate was not activated, nano-SiO2 was not modified, recycled asphalt was only added with recycling agent (without nano-modification), and the content of recycled fine aggregate was 20%; other steps and parameters were the same as in Example 1.

[0053] The specific data of the performance test results of each embodiment and comparative example are shown in Table 1.

[0054] Table 1 Performance Test Data

[0055]

[0056]

[0057] Data comparison and analysis:

[0058] (1) The overall high-temperature dynamic stability of the embodiments was in the range of 6200 to 7500 cycles / mm, with Embodiment 3 (high parameter group) showing the best performance at 7500 cycles / mm. In contrast, the comparative examples, corresponding to the traditional process, only achieved 2800 cycles / mm, which is lower than the minimum requirement of ≥3000 cycles / mm in the general specification. The comparative example 3, which lacked nano-SiO2 modification, achieved only 3200 cycles / mm, all of which failed to meet the basic engineering requirements. In terms of the improvement, the embodiments improved by 121.4% to 167.9% compared to the traditional process (calculated based on 6200 cycles / mm in Embodiment 2, (6200-2800) / 2800≈121.4%; calculated based on 7500 cycles / mm in Embodiment 3, (7500-2800) / 2800≈167.9%), and 100% met the patent's high-performance target of ≥6000 cycles / mm.

[0059] (2) Comparative Example 1 lacked only the KH-560 activation step; all other parameters were the same as in Example 1. The results showed a significant decrease in all four core properties: high-temperature dynamic stability decreased from 6800 cycles / mm to 4200 cycles / mm (a decrease of 38.2%), freeze-thaw splitting residual strength ratio decreased from 88% to 65% (a decrease of 26.1%), mass loss after aging increased from 0.65% to 1.2% (an increase of 84.6%), and pull-out strength decreased from 1.8 MPa to 1.1 MPa (a decrease of 38.9%). This indicates that KH-560, through "silicon-oxygen bond condensation with hydroxyl groups on the surface of recycled fine aggregates," can repair the defects of porous and low-activity surfaces of recycled fine aggregates. Without this step, interfacial bonding directly fails, and subsequent nano-modification cannot function effectively.

[0060] (3) The performance comparison between Comparative Example 2 (lacking only KH-570 modification, with nano-SiO2 only ultrasonically dispersed) and Comparative Example 3 (without any modification to nano-SiO2) further verifies the irreplaceability of this innovation: Comparative Example 2, due to the lack of "amphiphilic groups (silicon-oxygen bonds + carbon chains)" in nano-SiO2, has poor compatibility with asphalt and is prone to agglomeration, resulting in a 44.1% decrease in high-temperature dynamic stability and a 69.2% increase in aging loss; Comparative Example 3, due to more severe agglomeration of nanoparticles, forms a "weak point" in the mixture, resulting in the most significant performance degradation, with a high-temperature dynamic stability of only 3200 cycles / mm (a decrease of 53%) and a pull-out strength of 1.0 MPa (a decrease of 44.4%), and even some indicators being inferior to those of traditional processes. It can be seen that KH-570 modification is a prerequisite for nano-SiO2 to achieve "uniform dispersion + interface enhancement," and unmodified nano-SiO2 not only does not provide any benefit but also drags down performance.

[0061] (4) Although Comparative Example 4 (with 20% recycled fine aggregate content, lower than the patent's 30%–50% range) had high-temperature dynamic stability (6500 cycles / mm) and freeze-thaw splitting ratio (86%) close to Example 1, the amount of new aggregate increased by 25%, material costs increased by 25%, and approximately 80 tons of waste mixture were recycled less per kilometer of road surface, failing to achieve the goal of "high-value utilization". This shows that the patent's synergistic design of "high content + activation + nano-modification" is key to balancing environmental protection and economy while ensuring high performance. If only performance is pursued and the content is reduced, the core application value of the patent is lost.

[0062] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance recycled asphalt fine aggregate plant-mixed hot-mixed aggregate modified with nano-silica, characterized in that, Includes the following steps: Step S1: Pretreatment and activation of recycled fine aggregate: The waste asphalt mixture is crushed and screened to obtain recycled fine aggregate ≤2.36mm. After drying, 1% to 3% silane coupling agent (KH-560) is added, and the mixture is stirred at high speed at 80 to 100℃ for 15 to 20 minutes. Step S2: Modification of nano-silica: Disperse 20-50 nm nano-SiO2 in anhydrous ethanol, ultrasonically disperse, add 3%-5% silane coupling agent (KH-570), reflux at 60-80℃ for 2-3 h, filter and dry. Step S3: Compounding and modification of recycled asphalt: Mix aged asphalt and new asphalt at a ratio of 1:1 to 1:2, add 3% to 8% recycling agent and stir, then add 2% to 5% modified nano-SiO2 and shear with a colloid mill for 5 to 10 minutes. Step S4: Gradation design and mixing of the mixture: Weigh modified recycled fine aggregate (30%–50%), new coarse aggregate (30%–50%), and new mineral powder (5%–10%) according to the target gradation, heat them, and then forcibly mix them with nano-modified recycled asphalt (4.5%–5.5%). First, dry mix for 90–120 seconds, and then wet mix for 180–240 seconds.

2. The preparation method according to claim 1, characterized in that: The moisture content of the recycled fine aggregate in step S1 is ≤0.5%, and the amount of silane coupling agent (KH-560) added is 1% to 3% of the mass of the recycled fine aggregate.

3. The preparation method according to claim 1, characterized in that: The nano-SiO2 in step S2 has a particle size of 20-50 nm and a specific surface area of ​​≥200 m² / g. The amount of silane coupling agent (KH-570) added is 3%-5% of the mass of nano-SiO2.

4. The preparation method according to claim 1, characterized in that: The penetration of the aged asphalt in step S3 is ≤40 (0.1 mm), the new asphalt is AH-70 or AH-90, and the recycling agent is furfural extract oil or a special recycling agent.

5. The preparation method according to claim 1, characterized in that: The target gradation mentioned in step S4 is AC-13 or AC-16 type, and the mixing temperature of the mixture is 170-180℃ for aggregate and 160-170℃ for asphalt.

Images