A long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate and its preparation method

Abstract

This invention discloses a long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate and its preparation method. The preparation method includes the following steps: Step 1, glacial acetic acid is fully dissolved in water, and the recycled coarse aggregate after washing away impurities is added and stirred. The mixture is then allowed to stand in a constant-temperature water bath to obtain pretreated recycled coarse aggregate. Step 2, phosphoric acid is added, followed by sodium polyacrylate and polyethylene glycol in sequence. After stirring, the mixture is vacuum impregnated. Step 3, dodecylamine and lecithin are added to anhydrous ethanol, and the mixture is magnetically stirred and allowed to stand at room temperature. The recycled coarse aggregate is then filtered out, immersed in the settled solution, stirred at room temperature, and tetraethyl orthosilicate is added and stirred. The resulting suspension is then vacuum impregnated to form a silicon-calcium mineralized polymer. Step 4, the recycled coarse aggregate is filtered out, surface impurities are washed away, and it is dried. This invention can precisely control the reaction process that generates mineralized crystals, improve the reaction activity, and achieve effective strengthening of recycled coarse aggregate at low TEOS concentrations.

Description

Technical Field

[0001] This invention pertains to coarse aggregates and their preparation methods, specifically a long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate and its preparation method. Background Technology

[0002] In recent years, the rapid development of the construction industry has led to a surge in demand for natural aggregates. To alleviate resource pressure, recycled aggregates have gradually become an important alternative material. However, recycled aggregates in old mortar are often porous and fragile, exhibiting defects such as high porosity, high water absorption, and poor mechanical properties, which significantly limits their application. Silicon reagent strengthening treatment of recycled aggregates utilizes nano-silica polymers to fill the pores and cracks on the mortar surface, strengthening the surface pore structure of the recycled aggregates in old mortar, thereby improving the performance of recycled aggregates. This contributes to the further promotion and application of recycled aggregates and the green disposal of construction waste, and has been widely used in the field of recycled aggregate strengthening.

[0003] Biomineralization is the process by which organisms form inorganic minerals under the mediation of biological macromolecules. This process can form more sophisticated structures and exhibit superior properties even under mild conditions. Therefore, by simulating the biomineralization process, long-chain polyamines, in synergistic action with lecithin, can mediate the mineralization of silica using phosphatidylcholine as crystal nuclei. This can form high-strength silicon-calcium polymers with controllable formation locations, reaction processes, and nanoscale morphology, thereby reinforcing the pore structure and surface of recycled aggregate mortar and effectively improving the performance of recycled aggregates.

[0004] Existing methods for modifying recycled aggregates with silica reagents still have the following problems:

[0005] The chemical synthesis method involves reacting silicon-containing reagents with Ca(OH)₂ in the surface layer of recycled aggregate mortar to generate nano-silica. However, the fine structure of this nano-silica is difficult to control effectively, easily leading to uneven coating of the nano-silica polymer on the surface of the mortar, ineffective accumulation, or premature closure of the pores on the surface of the mortar due to agglomeration, resulting in poor internal strengthening of the mortar and severely affecting the modification effect. Furthermore, the reaction conditions are quite harsh, often requiring high temperature and pressure, and the reaction needs to introduce strong acids and alkalis, leading to the generation of toxic byproducts and causing serious environmental pollution.

[0006] Therefore, in order to solve the above-mentioned technical problems, it is necessary to study a modification method that is efficient, low in toxicity, has mild reaction conditions, and can control the formation location, reaction process and nano-morphology of the strong substances, so as to improve the defects of traditional silicon reagent-modified recycled aggregates and further improve the performance and modification efficiency of recycled aggregates. Summary of the Invention

[0007] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing a highly active, mild reaction condition long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate. Another purpose of this invention is to provide a long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate with controllable nanostructure.

[0008] Technical solution: The present invention provides a method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate, comprising the following steps:

[0009] Step 1: Dissolve glacial acetic acid fully in water, add it to the recycled coarse aggregate after washing away impurities, mix, and then let it stand in a constant temperature water bath to obtain the pretreated recycled coarse aggregate.

[0010] Step 2: Add phosphoric acid to the product obtained in Step 1, then add sodium polyacrylate and polyethylene glycol in sequence, mix and vacuum impregnate to introduce calcium phosphate mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar.

[0011] Step 3: Add dodecylamine and lecithin to anhydrous ethanol, stir magnetically at room temperature and let stand, filter out the recycled coarse aggregate obtained in step 2, soak it in the solution after standing and stir at room temperature, add tetraethyl orthosilicate and stir, vacuum impregnate the stirred suspension to form a silicon-calcium mineralization polymer coating on the surface of the recycled coarse aggregate old mortar.

[0012] Step four: Filter out the recycled coarse aggregate from the product obtained in step three, wash away surface impurities, and dry it to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate.

[0013] Furthermore, the mass ratio of recycled coarse aggregate, water, tetraethyl orthosilicate, anhydrous ethanol, glacial acetic acid, phosphoric acid, dodecylamine, polyethylene glycol, lecithin, and sodium polyacrylate is 800–1100:300–600:110–160:100–200:60–120:70–100:9–13:7–10:6–10:2–5.

[0014] Furthermore, in step one, the mixing time is 80–160 seconds, and the temperature of the constant temperature water bath is 40–80°C for 2–4 hours.

[0015] Furthermore, in step two, phosphoric acid is added in 2–5 batches with continuous stirring, and the stirring time is 80–160 seconds. The vacuum impregnation time is 90–150 minutes, the negative pressure during vacuum impregnation is 0.05–0.15 MPa, and the vacuum impregnation temperature is 30°C–60°C. The mass fraction of the phosphoric acid solution is 10–20 wt%.

[0016] Furthermore, in step three, the magnetic stirring time is 5–10 min, the rotor stirring speed is 800–1200 r / min, and the settling time is 3–5 days. The mixing time at room temperature is 80–160 s, and the mixing time after adding tetraethyl orthosilicate is 5–10 min. The vacuum impregnation time is 6–10 h, the negative pressure is 0.4–0.6 MPa, and the temperature is 20℃–40℃.

[0017] Furthermore, in step four, the drying temperature is 40–70°C, and the drying time is 36–60 hours.

[0018] The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to the present invention yields long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate with a particle size of 9.5 mm to 26.5 mm.

[0019] Preparation Principle: Current cell biology and molecular biology research indicates that the mineralized cell wall structure of diatoms is an organic-inorganic complex. Organic matter from several diatom organisms participates in the mineralization process, and these natural organic molecules possess unique physicochemical characteristics. Among them, organic amines are widely present in diatom cell walls and can induce the precipitation of spherical silica particles, providing the basic conditions for silica deposition activity under physiological conditions. On the other hand, within diatoms, the entire silica polymerization process occurs in vesicles called SDVs. These vesicles, composed of a phospholipid bilayer, adhere closely to the biosilicic structure within the diatom, ultimately becoming part of the silica cell wall structure. Therefore, both long-chain organic amines and phospholipid molecules have a significant impact on the biomineralization process within diatoms. By mimicking the formation process of mineral cell walls in diatoms through the synergistic effect of long-chain organic amines and lecithin molecules, the nanoscopic morphology of mineralization products can be effectively controlled, generating long-particle silica polymers. Compared with the spherical silica polymers generated by modifying recycled coarse aggregates with traditional silicon reagents, these polymers have certain micropores, allowing the small-molecule effective components in the modifying reagents to continue to penetrate the deep structure of the recycled coarse aggregate old mortar, filling the pores and cracks. This makes the old mortar more compact overall, better improving the strength and density of the recycled coarse aggregate old mortar portion, and further improving its macroscopic properties.

[0020] Mollusc shells are typically composed of calcium carbonate encased in an organic matrix. Before mineralization, nucleation sites for crystal formation are required, and organic matter can form liposomes centered around these nuclei to mediate mineralization. Therefore, by providing mineralization nuclei, the spatial expansion of crystals can be effectively limited, and the distribution of mineralized crystals can be controlled, resulting in a more uniform distribution of strength materials and more thorough regulation of the pore structure. This invention utilizes a phosphoric acid and acetic acid solution for vacuum impregnation of recycled coarse aggregate, causing it to react with Ca(OH)₂ on the surface, pores, and cracks of the recycled coarse aggregate old mortar, generating CaHPO₄ particles. These particles initially fill the pores and cracks of the recycled coarse aggregate old mortar and serve as mineralization nuclei. Under the action of lecithin surfactants, dodecylamine is used for coating, mimicking the liposomes and long-chain polyamines in the diatom cell wall structure. Lecithin can coat the surface of CaHPO4 particles to form bilayer liposomes through dipole-dipole interactions between hydrophilic head groups and van der Waals interactions between alkyl tails. Dodecylamine molecules form positively charged hydrophilic head groups by binding hydrogen ions, and these molecules also have hydrophobic alkyl tails, thus enabling them to interact with lecithin molecules. Due to the electrostatic attraction of lecithin molecules, negatively charged SiO2 particles are attracted to aggregate onto the hydrophilic head groups of lecithin and dodecylamine, depositing and assembling into columnar particles. This forms a high-strength silicon-calcium mineralized polymer coating on the surface of the recycled aggregate mortar layer and modulates its internal structure, thereby further improving the performance of recycled coarse aggregate.

[0021] In this system, tetraethyl orthosilicate serves as the silicon source, while water and ethanol act as solvents. Polyethylene glycol, acting as a dispersant, adsorbs onto the surface of solid particles and utilizes the steric hindrance effect between dispersant molecules to prevent particle aggregation, thereby reducing the viscosity of the slurry and creating a stable dispersion system. Sodium polyacrylate acts as a stabilizer, increasing the suspension stability of the slurry and reducing the settling velocity of particles, allowing for a more complete reaction between the effective components in the slurry and the recycled coarse aggregate surface mortar. Dodecylamine mimics the long-chain polyamines in diatom cell walls, serving as an organic molecular assembly; lecithin mimics the liposomes in diatom cell walls, acting as a surfactant. Phosphoric acid and glacial acetic acid react with Ca(OH)₂ in the recycled coarse aggregate mortar to generate CaHPO₄ particles, which act as mineralization nuclei. Phosphating provides nucleation sites, and long-chain polyamines mediate the formation of silicon-calcium mineralization polymers, thereby controlling the formation location, reaction process, and nanoscale morphology of strength substances to improve the defects of traditional silicon-modified recycled aggregates.

[0022] The equations involved in the core reaction are as follows:

[0023] Ca(OH)2+2CH3COOH=(CH3COO)2Ca+2H2O

[0024] (CH3COO)2Ca+H3PO4=2CH3COOH+CaHPO4

[0025] (C2H5O)4Si+2H2O=4C2H5OH+SiO2

[0026] SiO2=(SiO2) n .

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0028] 1. By inducing silica deposition through organic molecular assemblies with mineralized crystal nuclei as nucleation points, the reaction process for generating mineralized crystals can be precisely controlled, thereby enhancing the reactivity and achieving effective strengthening of recycled coarse aggregates at low TEOS concentrations. This is beneficial for resource conservation and cost control in industrial production.

[0029] 2. Using CaHPO4 particles as nucleation sites can control the growth position of mineralized crystals, allowing the strength material to uniformly coat the surface of the recycled aggregate old mortar and fully fill its internal pores. By controlling the morphological characteristics of silicon-calcium polymers through organic molecular assemblies, the silica polymer structure formed by interwoven columnar particles has a certain degree of microporosity, allowing the effective components in the modifying agent to continue to penetrate the deep structure of the recycled coarse aggregate old mortar, filling the pores and cracks, thereby making the old mortar more compact overall. Compared with traditional silicon reagent modification methods, it can better improve the macroscopic properties of recycled coarse aggregate.

[0030] 3. The method for modifying recycled aggregates with silica reagents can be achieved under low-toxicity and mild reaction conditions, which is beneficial to environmental protection and energy conservation and emission reduction;

[0031] 4. By employing vacuum impregnation to allow the modifying reagent to fully penetrate the pores and cracks of the recycled coarse aggregate surface mortar, and by rationally blending various dispersants, stabilizers and other auxiliary materials, the modification effect, rate and reaction stability are further improved, which helps to improve the modification efficiency and its practical application in industrial production. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the surface of the old mortar with recycled coarse aggregate before reinforcement according to the present invention;

[0033] Figure 2 This is a scanning electron microscope image of the surface of the old mortar with recycled coarse aggregate after the present invention. Detailed Implementation

[0034] Unless otherwise specified, the experimental methods described in the examples are conventional methods; reagents and materials, unless otherwise specified, are commercially available. In the following examples, the purity of tetraethyl orthosilicate is analytical grade. The average molecular weight of sodium polyacrylate is 4 million to 5 million, and the average molecular weight of polyethylene glycol is 200. Long-chain polyamine refers to dodecylamine, with the molecular formula CH3(CH2). 11 NH2.

[0035] Example 1

[0036] A method for preparing long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate includes the following steps:

[0037] (1) Pretreatment of recycled coarse aggregate: Wash away mud and other impurities from the surface of 950 parts of recycled coarse aggregate with an average particle size of 16mm. Dissolve 90 parts of glacial acetic acid in 450 parts of water, add the washed recycled coarse aggregate and mix for 120s. Let stand in a 60℃ constant temperature water bath for 3h to obtain the pretreated recycled coarse aggregate.

[0038] (2) Phosphating treatment of recycled coarse aggregate surface: Keep the temperature of the constant temperature water bath at 60℃, slowly add 85 parts of phosphoric acid to the product obtained in step (1) in 3 portions while stirring continuously, then add 4 parts of sodium polyacrylate and 9 parts of polyethylene glycol in sequence, and stir for 120s. Transfer the mixed suspension and the recycled coarse aggregate soaked in it to a vacuum high-pressure impregnation tank for vacuum impregnation for 120min, with a negative pressure of 0.1MPa and a temperature of 45℃, to introduce phosphate calcium stone mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar.

[0039] (3) Long-chain polyamine-mediated modification treatment: 11 parts dodecylamine and 8 parts lecithin were added to 150 parts anhydrous ethanol and magnetically stirred for 7 min at room temperature. The stirring speed of the rotor was 1000 r / min. The mixture was then allowed to stand at room temperature for 4 days. The recycled coarse aggregate after negative pressure impregnation was filtered out and immersed in the solution after standing. It was stirred at room temperature for 120 s. 135 parts tetraethyl orthosilicate were added and stirred for 7 min. The suspension and the recycled coarse aggregate soaked in it were transferred to a vacuum high-pressure impregnation tank for vacuum impregnation for 8 h at a negative pressure of 0.5 MPa and a temperature of 30 °C to form a silicon-calcium mineralized polymer, which was used to regulate the old mortar of recycled coarse aggregate.

[0040] (4) Washing and drying: Filter out the recycled coarse aggregate obtained in step (3), wash away surface impurities, put it in a drying oven and dry for 48 hours at a temperature of 55°C to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate.

[0041] To determine the specific composition of the surface strength material of the reinforced recycled coarse aggregate, this invention uses X-ray fluorescence spectrometry (XRF) to test the main elemental components and their contents before and after reinforcement. The results are shown in Table 1.

[0042] Table 1 Comparison of the main elemental composition of recycled coarse aggregate before and after modification

[0043] Aggregate type Ca / % Si / % Fe / % Al / ％ K / ％ P / ％ After modification 41.63 14.26 4.65 1.97 1.02 0.63 Before modification 41.34 11.87 6.2 2.29 1.37 0

[0044] Table 1 shows that after biomimetic modification mediated by long-chain polyamine, 0.63% phosphorus was added to the main elemental components of the recycled coarse aggregate. This indicates that during the modification process, the phosphating treatment of the recycled coarse aggregate generated a large number of CaHPO4 particles, which initially filled the pores on the surface of the recycled coarse aggregate mortar as nucleation sites. The silicon content increased by 20.13%, indicating that after the long-chain polyamine-mediated modification, a large number of high-strength silicon-calcium modified polymers were formed to coat the surface of the recycled aggregate mortar and regulate its internal structure. The calcium content remained basically unchanged, while the contents of iron, aluminum, and potassium decreased, indicating that no excess substances were generated on the surface of the recycled coarse aggregate. This suggests that the modification process and the resulting strength material were generally controllable. Based on relative molecular mass, the molar ratio of the effective component CaHPO4 to SiO2 in the silicon-calcium modified polymer, a strength material generated by the long-chain polyamine-mediated biomimetic modification, is 1:8.54.

[0045] To determine the changes in the microstructure of the reinforced product and the surface of the recycled coarse aggregate old mortar after reinforcement, this invention uses an S-4800Ⅱ field emission scanning electron microscope to observe the surface of the recycled coarse aggregate old mortar before and after reinforcement. The obtained images are shown below. Figure 1 , Figure 2 As shown, the magnification is 500x.

[0046] from Figure 1 As can be seen, the surface of the unmodified recycled coarse aggregate old mortar is characterized by high roughness, numerous pores and cracks, and uneven texture. From Figure 2 As can be seen, after long-chain polyamine-mediated biomimetic modification, a silicon-calcium modified polymer coating layer is formed on the surface of the recycled coarse aggregate mortar, which significantly improves its surface smoothness, effectively fills pores and cracks, and greatly improves its texture uniformity. This indicates that the long-chain polyamine-mediated biomimetic modification method proposed in this invention can effectively improve the performance of recycled coarse aggregate by generating silicon-calcium modified polymers to fill the pores on the surface of recycled coarse aggregate mortar and improve its surface properties. Referring to the "Specifications for Testing Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the recycled coarse aggregate before reinforcement (referred to as Comparative Example 1) is 2453 kg / m³. 3 The water absorption rate was 6.67%, and the crushing value was 28.35%. The apparent density of the reinforced recycled coarse aggregate increased by 6.81% compared to before reinforcement, the water absorption rate decreased by 42.28%, and the crushing value decreased by 33.47%.

[0047] Example 2

[0048] A method for preparing long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate includes the following steps:

[0049] (1) Pretreatment of recycled coarse aggregate: Wash away mud and other impurities from the surface of 800 parts of recycled coarse aggregate with an average particle size of 9.5 mm. Dissolve 60 parts of glacial acetic acid in 300 parts of water, add the washed recycled coarse aggregate and mix for 80 seconds. Let it stand in a constant temperature water bath at 40℃ for 4 hours to obtain the pretreated recycled coarse aggregate.

[0050] (2) Phosphating treatment of recycled coarse aggregate surface: Keep the temperature of the constant temperature water bath at 40℃, slowly add 70 parts of phosphoric acid in two portions to the product obtained in step (1) while stirring continuously, then add 2 parts of sodium polyacrylate and 7 parts of polyethylene glycol in sequence, and stir for 80s. Transfer the mixed suspension and the recycled coarse aggregate soaked in it to a vacuum high-pressure impregnation tank for vacuum impregnation for 90min, with a negative pressure of 0.05MPa and a temperature of 30℃, to introduce phosphate calcium stone mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar.

[0051] (3) Long-chain polyamine-mediated modification: 9 parts dodecylamine and 6 parts lecithin were added to 100 parts anhydrous ethanol and magnetically stirred for 5 min at room temperature with a rotor stirring speed of 800 r / min. The mixture was then allowed to stand at room temperature for 3 days. The recycled coarse aggregate after negative pressure impregnation was filtered out and immersed in the solution after standing. It was stirred at room temperature for 80 s, and 110 parts tetraethyl orthosilicate were added and stirred for 5 min. The suspension and the recycled coarse aggregate soaked in it were transferred to a vacuum high-pressure impregnation tank for vacuum impregnation for 6 h at a negative pressure of 0.4 MPa and a temperature of 20 °C to form a silicon-calcium mineralized polymer, which was used to regulate the recycled coarse aggregate old mortar.

[0052] (4) Washing and drying: Filter out the recycled coarse aggregate obtained in step (3), wash away surface impurities, put it in a drying oven and dry for 36 hours at a temperature of 40°C to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate.

[0053] According to the "Specifications for Testing Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the recycled coarse aggregate before reinforcement was 2453 kg / m³. 3 The water absorption rate was 6.67%, and the crushing value was 28.35%. The apparent density of the reinforced recycled aggregate increased by 5.42% compared to before reinforcement, the water absorption rate decreased by 36.58%, and the crushing value decreased by 28.82%.

[0054] Example 3

[0055] A method for preparing long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate includes the following steps:

[0056] (1) Pretreatment of recycled coarse aggregate: Wash away mud and other impurities from the surface of 1100 parts of recycled coarse aggregate with an average particle size of 26.5 mm. Dissolve 120 parts of glacial acetic acid in 600 parts of water, add the washed recycled coarse aggregate and mix for 160 s. Let stand in an 80℃ constant temperature water bath for 4 h to obtain pretreated recycled coarse aggregate.

[0057] (2) Phosphating treatment of recycled coarse aggregate surface: Keep the temperature of the constant temperature water bath at 80℃, slowly add 100 parts of phosphoric acid to the product obtained in step (1) in 5 portions while stirring continuously, then add 5 parts of sodium polyacrylate and 10 parts of polyethylene glycol in sequence, and stir for 160s. Transfer the mixed suspension and the recycled coarse aggregate soaked in it to a vacuum high-pressure impregnation tank for vacuum impregnation for 150min, with a negative pressure of 0.15MPa and a temperature of 60℃, to introduce phosphate calcium stone mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar.

[0058] (3) Long-chain polyamine-mediated modification: 13 parts dodecylamine and 10 parts lecithin were added to 200 parts anhydrous ethanol and magnetically stirred for 10 min at room temperature. The stirring speed of the rotor was 1200 r / min. The mixture was then allowed to stand at room temperature for 5 days. The recycled coarse aggregate after negative pressure impregnation was filtered out and immersed in the solution after standing. It was stirred at room temperature for 160 s. 160 parts tetraethyl orthosilicate were added and stirred for 10 min. The suspension and the recycled coarse aggregate soaked in it were transferred to a vacuum high-pressure impregnation tank and vacuum impregnated for 10 h at a negative pressure of 0.6 MPa and a temperature of 40 °C to form a silicon-calcium mineralized polymer, which was used to regulate the old mortar of recycled coarse aggregate.

[0059] (4) Washing and drying: Filter out the recycled coarse aggregate obtained in step (3), wash away surface impurities, put it in a drying oven and dry for 60 hours at a temperature of 70°C to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate.

[0060] According to the "Specifications for Testing Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the recycled coarse aggregate before reinforcement was 2453 kg / m³. 3 The water absorption rate was 6.67%, and the crushing value was 28.35%. The apparent density of the reinforced recycled aggregate increased by 8.97% compared to the unreinforced aggregate. The water absorption rate of the reinforced recycled aggregate decreased by 37.48% compared to the unreinforced aggregate. The crushing value of the reinforced recycled aggregate decreased by 31.32% compared to the unreinforced aggregate.

[0061] Example 4

[0062] A method for preparing long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate includes the following steps:

[0063] (1) Pretreatment of recycled coarse aggregate: Wash away mud and other impurities from the surface of 850 parts of recycled coarse aggregate with an average particle size of 13.2 mm. Dissolve 80 parts of glacial acetic acid in 400 parts of water, add the washed recycled coarse aggregate and mix for 100 seconds. Let it stand in a 50℃ constant temperature water bath for 2 hours to obtain the pretreated recycled coarse aggregate.

[0064] (2) Phosphating treatment of recycled coarse aggregate surface: Keep the temperature of the constant temperature water bath at 50℃, slowly add 80 parts of phosphoric acid to the product obtained in step (1) in 4 portions while stirring continuously, then add 3 parts of sodium polyacrylate and 8 parts of polyethylene glycol in sequence, and stir for 100s. Transfer the stirred suspension and the recycled coarse aggregate soaked in it to a vacuum high-pressure impregnation tank for vacuum impregnation for 100min, with a negative pressure of 0.08MPa and a temperature of 40℃, to introduce phosphate calcium stone mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar.

[0065] (3) Long-chain polyamine-mediated modification: 10 parts dodecylamine and 7 parts lecithin were added to 120 parts anhydrous ethanol and magnetically stirred for 6 minutes at room temperature with a rotor stirring speed of 900 r / min. The mixture was then allowed to stand at room temperature for 4 days. The recycled coarse aggregate after negative pressure impregnation was filtered out and immersed in the solution after standing. It was stirred at room temperature for 90 seconds, and 150 parts tetraethyl orthosilicate were added and stirred for 6 minutes. The suspension and the recycled coarse aggregate soaked in it were transferred to a vacuum high-pressure impregnation tank for vacuum impregnation for 7 hours at a negative pressure of 0.5 MPa and a temperature of 25°C to form a silicon-calcium mineralized polymer, which was used to regulate the old mortar of recycled coarse aggregate.

[0066] (4) Washing and drying: Filter out the recycled coarse aggregate obtained in step (3), wash away surface impurities, put it in a drying oven and dry for 50 hours at a temperature of 60°C to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate.

[0067] According to the "Specifications for Testing Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the recycled coarse aggregate before reinforcement was 2453 kg / m³. 3 The water absorption rate was 6.67%, and the crushing value was 28.35%. The apparent density of the reinforced recycled aggregate increased by 5.63% compared with that before reinforcement, the water absorption rate decreased by 41.08%, and the crushing value decreased by 31.99%.

[0068] Example 5

[0069] A method for preparing long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate includes the following steps:

[0070] (1) Pretreatment of recycled coarse aggregate: Wash away mud and other impurities from the surface of 1000 parts of recycled coarse aggregate with an average particle size of 19mm. Dissolve 100 parts of glacial acetic acid in 500 parts of water, add the washed recycled coarse aggregate and mix for 140s. Let it stand in a 70℃ constant temperature water bath for 2h to obtain the pretreated recycled coarse aggregate.

[0071] (2) Phosphating treatment of recycled coarse aggregate surface: Keep the temperature of the constant temperature water bath at 70℃, slowly add 70 parts of phosphoric acid in two portions to the product obtained in step (1) while stirring continuously, then add 4 parts of sodium polyacrylate and 8 parts of polyethylene glycol in sequence, and stir for 140s. Transfer the mixed suspension and the recycled coarse aggregate soaked in it to a vacuum high-pressure impregnation tank for vacuum impregnation for 140min, with a negative pressure of 0.12MPa and a temperature of 50℃, to introduce phosphate calcium stone mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar.

[0072] (3) Long-chain polyamine-mediated modification: 12 parts dodecylamine and 9 parts lecithin were added to 180 parts anhydrous ethanol and magnetically stirred for 9 min at room temperature. The stirring speed of the rotor was 1100 r / min. The mixture was then allowed to stand at room temperature for 4 days. The recycled coarse aggregate after negative pressure impregnation was filtered out and immersed in the solution after standing. It was stirred at room temperature for 140 s, and 120 parts tetraethyl orthosilicate were added and stirred for 8 min. The suspension and the recycled coarse aggregate soaked in it were transferred to a vacuum high-pressure impregnation tank for vacuum impregnation for 9 h at a negative pressure of 0.5 MPa and a temperature of 35 °C to form a silicon-calcium mineralized polymer, which was used to regulate the old mortar of recycled coarse aggregate.

[0073] (4) Washing and drying: Filter out the recycled coarse aggregate obtained in step (3), wash away surface impurities, put it in a drying oven and dry for 40 hours at a temperature of 65°C to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate.

[0074] According to the "Specifications for Testing Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the recycled coarse aggregate before reinforcement was 2453 kg / m³. 3 The water absorption rate was 6.67%, and the crushing value was 28.35%. The apparent density of the reinforced recycled aggregate increased by 7.42% compared to before reinforcement, the water absorption rate decreased by 45.13%, and the crushing value decreased by 33.72%.

[0075] Comparative Example 1

[0076] The unreinforced recycled coarse aggregate in Example 1 has an apparent density of 2453 kg / m³. 3 The water absorption rate is 6.67%, and the crushing value is 28.35%.

[0077] Comparative Example 2

[0078] A method for modifying recycled coarse aggregate with conventional silicon reagents includes the following steps:

[0079] (1) 135 parts of tetraethyl orthosilicate, 150 parts of anhydrous ethanol, 450 parts of water and 0.7 parts of hydrochloric acid were mixed evenly to obtain a tetraethyl orthosilicate (TEOS) modifier.

[0080] (2) Wash 950 parts of recycled coarse aggregate with a particle size of 16mm to remove surface mud and sand and other impurities, add it to the above TEOS modifier and mix for 120s, and let it stand in a 30℃ constant temperature water bath for 8h.

[0081] (3) The soaked recycled coarse aggregate is filtered out to remove surface impurities and placed in a drying oven to dry for 48 hours at a temperature of 55°C to obtain traditional silicon reagent modified recycled coarse aggregate.

[0082] The apparent density of the reinforced recycled aggregate obtained in this embodiment was tested according to the "Test Procedures for Aggregates in Highway Engineering" (JTG E42-2005), and it increased by 1.51% compared with that before reinforcement. The water absorption rate of the reinforced recycled aggregate decreased by 39.73% compared with that before reinforcement. The crushing value of the reinforced recycled aggregate decreased by 18.73% compared with that before reinforcement.

[0083] Comparative Example 3

[0084] The raw materials and other steps of this comparative example are the same as those of Example 1. The only difference is that in step (1), the surface of the recycled coarse aggregate is washed away with mud and sand and other impurities. Glacial acetic acid is fully dissolved in water, added to the washed recycled coarse aggregate and mixed for 70 seconds. The aggregate is then left to stand in a 35°C constant temperature water bath for 2 hours.

[0085] According to the "Test Procedure for Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the reinforced recycled aggregate obtained in this comparative example increased by 0.9% compared with that before reinforcement, the water absorption decreased by 11.24% compared with that before reinforcement, and the crushing value decreased by 7.65% compared with that before reinforcement.

[0086] Comparative Example 4

[0087] The raw materials and other steps of this comparative example are the same as those of Example 2. The only difference is that in step (1), the surface of the recycled coarse aggregate is washed away with mud and sand and other impurities. Glacial acetic acid is fully dissolved in water, added to the washed recycled coarse aggregate and stirred for 170 seconds. The aggregate is then left to stand in a 90°C constant temperature water bath for 4 hours.

[0088] The apparent density of the reinforced recycled aggregate obtained in this comparative example was tested according to the "Test Procedure for Aggregates in Highway Engineering" (JTG E42-2005). It was 6.85% higher than that before reinforcement, the water absorption rate was 37.18% lower than that before reinforcement, and the crushing value was 29.28% lower than that before reinforcement.

[0089] Comparative Example 5

[0090] The raw materials and other steps of this comparative example are the same as those of Example 3, except that: in step (2), the mixed suspension and the recycled coarse aggregate soaked in it are transferred to a vacuum high-pressure impregnation tank for vacuum impregnation for 160 min, the negative pressure is 0.2 MPa and the temperature is 70℃; in step (3), dodecylamine and lecithin are added to anhydrous ethanol and magnetically stirred at room temperature for 3 min, the rotor stirring speed is 700 r / min; the recycled coarse aggregate is transferred to a vacuum high-pressure impregnation tank for vacuum impregnation for 12 h, the negative pressure is 0.7 MPa and the temperature is 50℃.

[0091] The apparent density of the reinforced recycled aggregate obtained in this comparative example was tested according to the "Test Procedure for Aggregates in Highway Engineering" (JTG E42-2005). It was 2.61% higher than that before reinforcement, the water absorption rate was 28.64% lower than that before reinforcement, and the crushing value was 18.31% lower than that before reinforcement.

[0092] Comparative Example 6

[0093] The steps of this comparative example are the same as those of Example 2, except that the raw materials are different. By weight, the raw materials in Comparative Example 6 include: 800 parts recycled coarse aggregate, 700 parts water, 170 parts tetraethyl orthosilicate, 220 parts anhydrous ethanol, 50 parts glacial acetic acid, 60 parts phosphoric acid, 8 parts dodecylamine, 6 parts polyethylene glycol, 5 parts lecithin, and 1 part sodium polyacrylate.

[0094] According to the "Test Procedure for Aggregates in Highway Engineering" (JTG E42-2005), the apparent density of the reinforced recycled aggregate obtained in this comparative example was increased by 0.57% compared with that before reinforcement, the water absorption rate decreased by 20.24% compared with that before reinforcement, and the crushing value decreased by 5.22% compared with that before reinforcement.

[0095] Comparative Example 7

[0096] The steps of this comparative example are the same as those of Example 3, except that the raw materials are different. By weight, the raw materials in Comparative Example 7 include: 1100 parts recycled coarse aggregate, 250 parts water, 100 parts tetraethyl orthosilicate, 90 parts anhydrous ethanol, 130 parts glacial acetic acid, 110 parts phosphoric acid, 14 parts dodecylamine, 12 parts polyethylene glycol, 12 parts lecithin, and 7 parts sodium polyacrylate.

[0097] The apparent density of the reinforced recycled aggregate obtained in this comparative example was tested according to the "Test Procedure for Aggregates in Highway Engineering" (JTG E42-2005). It was 1.35% higher than that before reinforcement, the water absorption rate was 26.69% lower than that before reinforcement, and the crushing value was 9.03% lower than that before reinforcement.

[0098] The apparent density, water absorption rate, and crushing value of the recycled coarse aggregate samples before and after modification in Examples 1-3 and Comparative Examples 1-7 are shown in Table 2.

[0099] Table 2 Comparison of the properties of recycled coarse aggregate before and after strengthening

[0100]

[0101] As shown in Examples 1-3 and Comparative Example 1 in Table 2, the reinforced recycled aggregate prepared by this invention exhibits an increased apparent density and a significantly reduced crushing value compared to the original aggregate. This is because glacial acetic acid reacts with Ca(OH)₂ in the old mortar on the surface of the recycled aggregate to generate calcium acetate, which is uniformly distributed in the surface, pores, and cracks of the recycled aggregate. This calcium acetate then undergoes a series of reactions with phosphoric acid, sodium polyacrylate, and polyethylene glycol to generate microparticle calcium phosphate, which fills the pores and microcracks of the old mortar on the surface as crystal nuclei. Under the action of the lecithin surfactant, dodecylamine is used for coating, mimicking the liposomes and long-chain polyamines in the diatom cell wall structure. Lecithin coats the surface of the microparticle calcium phosphate through dipole-dipole interactions between hydrophilic head groups and van der Waals forces between alkyl tails, forming bilayer liposomes. Dodecylamine molecules form positively charged hydrophilic head groups by binding hydrogen ions, and these molecules also possess hydrophobic alkyl tails, thus enabling them to interact with lecithin molecules. Due to the electrostatic attraction of lecithin molecules, negatively charged silica particles are attracted to aggregate onto the hydrophilic head groups of lecithin and dodecylamine, depositing and assembling into columnar particles. This forms a high-strength silicon-calcium modified polymer that coats the surface of the recycled aggregate mortar layer and regulates its internal structure, thereby further improving the performance of the recycled coarse aggregate.

[0102] As shown in Example 1 and Comparative Example 2 in Table 2, compared with the traditional method of modifying recycled aggregates with silicon reagents, the recycled aggregates of the present invention show a significant improvement in apparent density and a significant reduction in crushing value and water absorption. This is because traditional silicon reagent modification methods often struggle to control the formation of a fine structure of nano-silica on the surface of recycled aggregates, easily leading to uneven coating of nano-silica polymers on the surface of old mortar, ineffective accumulation, or premature closure of surface pores due to agglomeration effects, resulting in poor internal strengthening of the mortar and severely affecting the modification effect. In contrast, the present invention, based on biomimetic principles, mediates the formation of silicon-calcium polymers with controllable generation location, reaction process, and nano-morphology through organic molecular assemblies, effectively improving the above-mentioned defects of traditional silicon reagent-modified recycled aggregates and further enhancing the performance of recycled aggregates.

[0103] As can be seen from Example 1 and Comparative Example 3 in Table 2, in the pretreatment step of the recycled coarse aggregate of the present invention, if the mixing time of glacial acetic acid and the washed recycled coarse aggregate is less than the range provided by the present invention, or if the temperature of the constant temperature water bath in the pretreatment step is less than the range provided by the present invention, the strengthening effect is poor. This is because the reaction rate is slow due to the short mixing time and low temperature, making it difficult for the glacial acetic acid solution to fully react with the calcium hydroxide in the recycled aggregate old mortar, and the modifier fails to penetrate the internal pore structure of the recycled aggregate old mortar, affecting the modification effect of subsequent steps.

[0104] As shown in Table 2, Example 2 and Comparative Example 4, in the pretreatment step of the recycled coarse aggregate of this invention, if the mixing time of glacial acetic acid with the washed recycled coarse aggregate exceeds the range provided by this invention, or if the temperature of the constant temperature water bath in the pretreatment step exceeds the range provided by this invention, the strengthening effect will not be significantly improved. This is because within the temperature and mixing time range provided by this invention, acetic acid has already fully reacted with calcium hydroxide in the recycled aggregate old mortar. Even if the temperature is increased or the mixing time is extended, it is difficult to further improve the modification effect. In addition, excessively high temperatures also cause the reaction between the glacial acetic acid solution and the aggregate surface to be too violent, causing certain corrosion or microscopic damage to the aggregate surface. Excessively long mixing times will also cause certain mechanical damage to the surface of the recycled aggregate.

[0105] As can be seen from Examples 1 and 3 and Comparative Example 5 in Table 2, in the long-chain polyamine-mediated modification process of this invention, the stirring time and rotor speed are lower than the range provided by this invention. Even with increased vacuum high-pressure impregnation time, pressure, and temperature, the strengthening effect remains limited. This is because the addition of dodecylamine and lecithin was not sufficiently stirred, preventing them from fully coating the surface of the recycled aggregate and penetrating the pore structure of the old mortar. Even with the action of the lecithin surfactant, dodecylamine cannot form a uniform coating layer on the CaHPO4 particles in the pores and cracks of the recycled coarse aggregate mortar, resulting in poor mediating effect on the deposition and assembly of nano-silica. The surfactant effect of lecithin molecules is also difficult to fully exert, failing to achieve the goal of fully filling the pores and cracks of the recycled coarse aggregate mortar surface with silicon-calcium polymer, thus leading to poor modification effect of the recycled aggregate.

[0106] In general, with the raw materials unchanged, within the scope given by this invention, the temperature of the constant temperature water bath in the pretreatment needs to be reduced, and the mixing time in the pretreatment can be appropriately reduced; alternatively, the vacuum high pressure impregnation time, pressure and temperature can be reduced by appropriately increasing the stirring time and rotor speed in the long-chain polyamine mediated modification treatment step.

[0107] As can be seen from Examples 1, 2, and 3 and Comparative Examples 6 and 7 in Table 2, when the proportions of each raw material used in the long-chain polyamine-mediated biomimetic modification of recycled coarse aggregate according to the present invention are not within the range provided by the present invention, the apparent density of the modified recycled coarse aggregate decreases and the crushing value increases. This is because changes in the proportions of each raw material can lead to an excessively small proportion of one or more components in the long-chain polyamine-mediated biomimetic modification of the recycled coarse aggregate, resulting in insufficient crystal nuclei or uneven coating film formation. In severe cases, this can lead to poor improvement in various performance indicators of the recycled aggregate. For example, in Comparative Example 6, the proportion of glacial acetic acid in the raw material is significantly low, making it difficult to form a sufficient number of CaHPO4 particles as crystal nuclei in the pores, cracks, and surface of the recycled aggregate. This makes it difficult to effectively control the formation location, reaction process, and nanostructure of the high-strength silicon-calcium polymer deposition assembly, resulting in poor modified recycled aggregate performance. At the same time, changes in the proportions of each raw material can lead to insufficient or excessive products in the silanization process, thereby affecting the performance of the modified recycled aggregate.

[0108] Of the above embodiments, the preferred embodiment is Embodiment 5.

Claims

1. A method for preparing long-chain polyamine-mediated biomimetic mineralization-modified recycled coarse aggregate, characterized in that, Includes the following steps: Step 1: Dissolve glacial acetic acid fully in water, add it to the recycled coarse aggregate after washing away impurities, mix, and then let it stand in a constant temperature water bath to obtain the pretreated recycled coarse aggregate. Step 2: Add phosphoric acid to the product obtained in Step 1, then add sodium polyacrylate and polyethylene glycol in sequence, mix and vacuum impregnate to introduce calcium phosphate mineralization nuclei into the surface and pores of the recycled coarse aggregate old mortar. Step 3: Add dodecylamine and lecithin to anhydrous ethanol, stir magnetically at room temperature and let stand, filter out the recycled coarse aggregate obtained in step 2, soak it in the solution after standing and stir at room temperature, add tetraethyl orthosilicate and stir, vacuum impregnate the stirred suspension to form a silicon-calcium mineralization polymer coating on the surface of the recycled coarse aggregate old mortar. Step 4: Filter out the recycled coarse aggregate from the product obtained in Step 3, wash away surface impurities, and dry it to obtain long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate. The mass ratio of the recycled coarse aggregate, water, tetraethyl orthosilicate, anhydrous ethanol, glacial acetic acid, phosphoric acid, dodecylamine, polyethylene glycol, lecithin, and sodium polyacrylate is 800~1100:300~600:110~160:100~200:60~120:70~100:9~13:7~10:6~10:2~5.

2. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step one, the mixing time is 80~160s, and the temperature of the constant temperature water bath is 40~80℃ for 2~4h.

3. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step two, phosphoric acid is added in 2 to 5 batches while continuously stirring, with a stirring time of 80 to 160 seconds.

4. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step two, the vacuum impregnation time is 90~150min, the negative pressure of vacuum impregnation is 0.05~0.15MPa, and the vacuum impregnation temperature is 30℃~60℃.

5. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step three, the magnetic stirring time is 5-10 minutes, the rotor stirring speed is 800-1200 r / min, and the settling time is 3-5 days.

6. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step three, the mixing time at room temperature is 80-160 seconds, and the mixing time after adding tetraethyl orthosilicate is 5-10 minutes.

7. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step three, the vacuum impregnation time is 6~10h, the negative pressure is 0.4~0.6MPa, and the temperature is 20℃~40℃.

8. The method for preparing long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to claim 1, characterized in that: In step four, the drying temperature is 40~70℃ and the time is 36~60h.

9. The long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate obtained by the preparation method of the long-chain polyamine-mediated biomimetic mineralization modified recycled coarse aggregate according to any one of claims 1 to 8, characterized in that: The particle size of the recycled coarse aggregate is 9.5mm to 26.5mm.

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