A Reinforcing Glass Fiber for All-Solid Waste Concrete, Its Modification Method and Application

Abstract

This invention discloses a special reinforcing glass fiber for ultra-high performance concrete made entirely from solid waste, its modification method, and its application. The reinforcing glass fiber is prepared using recycled glass fiber from wind turbine blades as the substrate, through pyrolysis pretreatment, surface activation treatment, and ettringite / hydrated calcium silicate deposition modification process. After modification, the epoxy resin residue on the glass fiber surface is less than 5%, and the fiber length of 6-15mm accounts for more than 80%, forming a stable mineral bond interface with the solid waste concrete matrix. The suitable solid waste concrete system consists of granulated blast furnace slag powder, industrial by-product gypsum, alkaline industrial by-products, and iron tailings sand. After adding 1-2% of this modified glass fiber, the 28-day compressive strength increase rate of the concrete is ≥10%, and the flexural strength increase rate is ≥100%. This invention achieves high-value utilization of solid waste resources, combining environmental protection and economy, and is suitable for high-end construction engineering.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and building materials technology, specifically relating to a special reinforcing glass fiber for ultra-high performance concrete made entirely from solid waste, its modification method and application, and particularly to a modification process based on glass fiber recycled from wind turbine blades and an adapted all-solid waste concrete system. Background Technology

[0002] With the rapid development of the wind power industry, the large amount of glass fiber composite materials generated from retired wind turbine blades has become a pressing solid waste problem. Traditional landfill or incineration methods not only waste resources but also cause serious environmental pollution. While existing technologies have attempted to use recycled glass fibers for concrete reinforcement, two major problems exist: first, the residual epoxy resin on the surface of the recycled glass fibers (typically exceeding 10%) severely reduces the interfacial bonding performance between the fibers and the concrete matrix; second, the uneven fiber length distribution and the excessively high proportion of short fibers limit the reinforcement effect.

[0003] To address these issues, existing technologies employ high-temperature calcination (>600℃) or strong acid etching to remove surface resin, but this easily leads to deterioration of fiber mechanical properties, with strength loss exceeding 40%. Mechanical crushing processes result in less than 50% of usable fibers being 6-15mm in length. Furthermore, while conventional silane coupling agent treatment can improve fiber hydrophilicity in the short term, it is prone to hydrolytic failure in highly alkaline concrete environments, causing interfacial bond strength to decrease significantly with age, with a reduction of over 50% after 28 days.

[0004] On the other hand, traditional ultra-high performance concrete (UHPC) relies heavily on high-carbon emission raw materials such as silicate cement and silica fume, and is reinforced with virgin glass fiber or synthetic fiber. This not only results in high costs, but also poor chemical compatibility with solid waste-based hydration products. The interfacial porosity is as high as 25%, which becomes a weak link for stress concentration and microcrack propagation, making it difficult to meet the comprehensive requirements of green buildings for environmental protection, low cost and high performance.

[0005] To address the aforementioned technical deficiencies, this invention proposes a multi-stage modification process that controls resin residue through pyrolysis-mechanical exfoliation, combines surface activation and in-situ deposition modification to construct a stable interface, and designs a complete solid waste concrete system to achieve the dual goals of solid waste resource utilization and concrete performance improvement. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as poor modification effect of recycled glass fiber, high carbon emissions of concrete system, and high cost, and to provide a special reinforcing glass fiber for ultra-high performance concrete made entirely from solid waste, as well as its modification method and application, so as to realize the high-value utilization of solid waste resources and improve the strength and toughness of concrete.

[0007] To achieve the above objectives, the present invention provides a method for modifying reinforcing glass fibers specifically for solid waste concrete, comprising the following steps: (1) Fiber pretreatment: The recycled glass fibers of the wind turbine blades are placed in an industrial electric furnace for pyrolysis, and then the epoxy resin on the surface is removed by ball milling, so that the epoxy resin content is less than 5% and the recycled glass fibers with a length of 6-15mm account for ≥80%; (2) Surface activation: The pretreated fibers are treated with hydrofluoric acid, modified with silane coupling agent and treated with hydrogen peroxide, cleaned and dried to constant weight; (3) Chemical deposition modification: The activated fiber is added to a reaction system containing specific chemical reagents, the pH is controlled at 11.5-12.5, and the reaction is carried out at 40℃ for 6-8 hours to generate ettringite / hydrated calcium silicate coating layer. The fiber is then washed with ethanol and vacuum dried to obtain reinforced glass fiber.

[0008] Furthermore, the pyrolysis temperature in step (1) is 400-500℃ and the pyrolysis time is 1-2h.

[0009] Furthermore, the working parameters of the ball mill in step (1) are: ball-to-material ratio 2-4:1, rotation speed 200-400 rpm.

[0010] Further, in step (2), the mass fraction of hydrofluoric acid is 5-15%, and the treatment time is 1-15 min; the silane coupling agent is any one or a combination of two of 3-aminopropyltriethoxysilane (APTES) and mercaptopropyltrimethoxysilane (MPTMS), with a concentration of 1-3 g / L. A hydrofluoric acid-oxidized silane coupling agent directional modification technique is used to construct an alkali-resistant covalent network. The amino (-NH2) and mercapto (-SH) groups of the silane coupling agent are oxidized by H2O2 to nitro (-NO2) and sulfonic acid (-SO3H), respectively. These strongly polar groups can preferentially adsorb Ca in the solution. 2+ With SiO3 2- Ions induce the directional nucleation and growth of ettringite and hydrated calcium silicate along the fiber surface. Further, through in-situ deposition of ettringite / hydrated calcium silicate, a hydration product layer homogeneous with the matrix is ​​formed on the fiber surface, reducing the interfacial porosity to below 8% and inducing the directional growth of matrix minerals along the fiber axis, achieving a flexural strength increase of over 100%.

[0011] Furthermore, in step (2), the mass fraction of the hydrogen peroxide solution is 20-40%, the reaction temperature is 50-70℃, and the reaction time is 4-6h; the silane coupling agent modification is performed by ultrasonic dispersion, the ultrasonic dispersion frequency is 40kHz, the reaction temperature is 30-40℃, and the reaction time is 2-3h.

[0012] Furthermore, the specific chemical reagents mentioned in step (3) include: 0.05 mol / L Al2(SO4)3·18H2O solution, 0.3 mol / L Ca(OH)2 solution, 0.2 mol / L Ca(NO3)2·4H2O solution, 0.2 mol / L Na2SiO3·9H2O solution and 10 mol / L NaOH solution.

[0013] Further, the order of adding the chemical reagents and the supporting process in step (3) are as follows: The activated recycled glass fiber is added to a Ca(OH)2 solution, with the fiber volume to total solution volume ratio fixed at 1:3-7. Al2(SO4)3·18H2O solution, Ca(NO3)2·4H2O solution, Na2SiO3·9H2O solution, and 0.2%-0.4% polycarboxylate superplasticizer (based on the total solution volume) are added sequentially at a stirring speed of 100-500 rpm. Then, NaOH is added to adjust the pH of the system to 11.5-12.5. The activated fiber surface contains a large number of strongly polar groups, such as Si-OH, -NO2, and -SO3H, derived from the hydrofluoric acid activation and silane oxidation in step 2. These groups have a strong effect on Ca... 2+ It has a strong adsorption capacity. First, immerse the fiber in a Ca(OH)₂ solution, which allows the Ca... 2+ Preferentially adsorbed onto the fiber surface, forming initial nucleation sites to provide anchoring centers for subsequent processes; subsequently, Al2(SO4)3·18H2O, Ca(NO3)2·4H2O, and Na2SiO3·9H2O are added stepwise to regulate the formation of ettringite (AFt) and hydrated calcium silicate, ensuring synergistic composition of the coating layer. The purpose of adding Al2(SO4)3·18H2O in the first step is to provide Al... 3+ and SO4 2- Al 3+ It rapidly transforms into AlO2 under alkaline conditions. - , with Ca pre-adsorbed on the fiber surface 2+ The reaction preferentially generates initial AFt nuclei, which serve as a supporting framework for subsequent calcium silicate hydrate growth, preventing the coating layer from detaching due to a loose structure when CSH is generated alone. The second step, adding Ca(NO3)2·4H2O, aims to supplement the Ca content. 2+ The generation of AFt consumes a large amount of Ca. 2+ If Ca 2+ Insufficient Ca will lead to incomplete formation of AFt; at the same time, it will reserve sufficient Ca for the subsequent formation of hydrated calcium silicate. 2+This avoids uneven composition caused by competition for calcium source between the two products. It ensures the continuous generation of AFt, covering the fiber surface and providing a sufficient calcium source for hydrated calcium silicate, ultimately forming a composite coating layer with AFt as the framework and hydrated calcium silicate filling the gaps, resulting in a denser structure. The third step, adding Na2SiO3·9H2O, aims to provide SiO3. 2- , with the remaining Ca on the fiber surface 2 + and free Ca in solution 2+ The reaction produces hydrated calcium silicate, which fills the voids between AFt crystal nuclei and improves the coating structure. The hydration products of the composite coating layer are completely homogeneous with those of the solid waste concrete matrix, and can form mineral bonds when subsequently bonding with the matrix, significantly reducing interfacial porosity. The core function of polycarboxylate superplasticizer is dispersion, dispersing both the fibers and the reacted ettringite (AFt) and hydrated calcium silicate. If the dosage is <0.2%, the dispersion effect is insufficient, resulting in fiber or crystal agglomeration and uneven coating; if the dosage is >0.4%, excessive superplasticizer will adsorb onto the fiber surface, clogging the active groups and hindering the formation of calcium silicate. 2+ The binding with functional groups leads to a reduction in the thickness of the coating layer.

[0014] This invention also provides a special reinforcing glass fiber for ultra-high performance concrete made entirely from solid waste, prepared using the above-mentioned modification method. The surface epoxy resin residue of the reinforcing glass fiber is ≤5%, the fiber length of 6-15mm accounts for ≥80%, and the surface is coated with an ettringite / hydrated calcium silicate composite layer. On the other hand, the present invention also proposes an all-solid-waste ultra-high performance concrete, which contains the above-mentioned reinforcing glass fiber, and its dosage is 0.5-2% of the total mass of concrete.

[0015] Furthermore, the all-solid-waste ultra-high performance concrete is composed of granulated blast furnace slag powder, industrial by-product gypsum, and alkaline industrial by-products, with iron tailings sand as the aggregate; by mass, it consists of 85-90 parts granulated blast furnace slag powder, 5-15 parts industrial by-product gypsum, 1-5 parts alkaline industrial by-products, and 80-120 parts iron tailings sand.

[0016] The beneficial effects of this invention are: (1) Mild and efficient modification process: The process adopts a pyrolysis combined with ball milling and exfoliation process at 400-500℃, while controlling the epoxy resin residue to 5%. (1) The fiber length retention rate is ≥80% and the strength loss is ≤15%, which is significantly better than the existing high temperature calcination or strong acid etching process; (2) Excellent interface bonding performance: through hydrofluoric acid activation and silane coupling agent oxidation modification, an alkali-resistant covalent bond network is constructed, and then through in-situ deposition of ettringite / hydrated calcium silicate, a composite coating layer homogeneous with the concrete matrix is ​​formed, so that the interface porosity is reduced to below 8%, and the chemical bonding and mechanical anchoring are synergistically enhanced; (3) The concrete performance is greatly improved: after adding 1-2% modified glass fiber, the 28-day compressive strength growth rate of all solid waste concrete is ≥10%, and the flexural strength growth rate is ≥100%, which solves the problem of insufficient toughness of traditional solid waste concrete; (4) Significant environmental and economic value: the present invention realizes the high-value utilization of various solid wastes such as wind turbine blade recycled glass fiber, granulated blast furnace slag, and iron tailings sand, reduces the amount of solid waste landfill per ton of product, reduces carbon emissions compared with traditional processes, and lowers the overall cost. Detailed Implementation

[0017] The following examples illustrate specific implementations of the present invention. However, these examples are merely for illustrative purposes and do not limit the scope of the invention in any way.

[0018] The pyrolysis-ball milling stripping method is as follows: (1) Place the recycled glass fiber in an industrial electric furnace and pyrolyze it at 400-500℃ for 1-2 hours to remove more than 90% of the epoxy resin on the surface. (2) Place the heat-treated recycled glass fiber in a ball mill jar and peel off the residual resin on the surface of the recycled glass fiber at a ball-to-material ratio of 3:1 by volume and a working condition of 200-400 rpm, so that the epoxy resin content is less than 5% and the proportion of recycled glass fiber with a length of 6-15 mm is more than 80%. The relevant processes and properties of the recycled glass fiber series products (A1-17) after pyrolysis-ball milling are shown in Table 1.

[0019] Table 1. Relevant processes and properties of recycled glass fiber products obtained through pyrolysis-ball milling.

[0020] The surface activation method for recycled glass fiber is as follows: (1) Treat the recycled glass fiber with 10% hydrofluoric acid for 10 min; (2) Immerse the surface-activated recycled glass fiber in a 1-3 g / L mixture of ethanol / water (volume ratio 9:1) of either 3-aminopropyltriethoxysilane (APTES) or mercaptopropyltrimethoxysilane. Use an industrial-grade ultrasonic disperser at a frequency of 40 kHz and a temperature of 30-40℃ for 2-3 h; (3) Immerse the recycled glass fiber modified with silane coupling agent in a 30% H2O2 solution and react at 60℃ for 5 h; (4) Wash with water to remove residual oxidant and dry at 40℃ to constant weight. The specific process parameters (B1-B10) for surface activation of recycled glass fiber are shown in Table 2.

[0021] Table 2. Specific process parameters and performance of surface activation of recycled glass fiber

[0022] The deposition methods of ettringite and hydrated calcium silicate on the surface are as follows: (1) Prepare a certain volume of Al2(SO4)3·18H2O solution with a concentration of 0.05 mol / L, a Ca(OH)2 solution with a concentration of 0.3 mol / L, a Ca(NO3)2·4H2O solution with a concentration of 0.2 mol / L, a Na2SiO3·9H2O solution with a concentration of 0.2 mol / L, and a NaOH solution with a concentration of 10 mol / L; (2) Add the recycled glass fiber to the Ca(OH)2 solution (the fiber volume and the total solution volume are fixed at 1:5), and add a certain volume of Al2(SO4)3·18H2O solution, Ca(NO3)2·4H2O solution, Na2SiO3·9H2O solution, and a polycarboxylate superplasticizer with a total solution volume of 0.3 mol / L in sequence under a stirring speed of 200 rpm. Add NaOH to control the pH of the system to 11.5-12.5. Control the temperature at 40 ℃ and the reaction time at 6-8 h during the reaction. (3) The reaction was terminated by rinsing with ethanol and then dried under vacuum at 60 °C to constant weight. A series of modified recycled glass fiber products (C1-C8) coated with ettringite and hydrated calcium silicate were obtained, as shown in Table 3.

[0023] Table 3. Process parameters of a series of modified recycled glass fiber products coated with ettringite and hydrated calcium silicate.

[0024] Table 4. Process Flow of Examples

[0025] Table 5 Evaluation Table of Examples

[0026] General description of the implementation example: Table 5 presents the mechanical properties of all-solid-waste ultra-high performance concrete and its reinforcing effect relative to the unmodified glass fiber comparison under different embodiment conditions. Each embodiment systematically investigated the influence of interfacial structural characteristics on the macroscopic mechanical properties of concrete by adjusting the pretreatment method of recycled glass fibers (Series A), surface activation process (Series B), and ettringite / hydrated calcium silicate deposition parameters (Series C), thereby changing the ratio of AFt to CSH on the fiber surface and the coating structure.

[0027] Examples 1-3: Effect of pyrolysis strength on reinforcement effect: Examples 1-3 were conducted with the same fiber content of 2%, surface activation process (B10), and deposition process (C6), except for the pyrolysis temperature and resin peeling degree (A1-A3).

[0028] The results showed that as the pyrolysis temperature increased from 400℃ (A1) to 500℃ (A3), the amount of epoxy resin residue on the glass fiber surface further decreased, but the proportion of effective fiber length decreased, resulting in a gradual weakening of the reinforcing effect. In Example 1, the 28-day compressive strength and flexural strength reached 149.5 MPa and 35.0 MPa, respectively, with growth rates of 30.0% and 169.2%, respectively, the highest among the three. This indicates that moderate resin removal while maintaining high fiber integrity is more beneficial to the reinforcing effect than simply pursuing the lowest possible resin residue. When the pyrolysis conditions are too strong, although resin residue can be further reduced, the fiber length retention rate decreases, weakening fiber bridging and crack passivation effects.

[0029] Examples 4-5: The effect of surface activation method on interfacial mineral composition: Examples 4 and 5 were performed using the same pyrolysis process (A1) and deposition process (C6), but with different silane coupling agent ratios (B1 and B5), and compared with Example 1 (B10). Table 4 shows that under process B1, the fiber surface was dominated by CSH (94%), with extremely low AFt content of only 6%; while under process B10, the AFt to CSH ratio was close (47% : 53%). Correspondingly, in terms of mechanical properties, the 28-day flexural strength growth rate of Example 4 was 104.6%, significantly lower than the 169.2% of Example 1.

[0030] The results show that although single CSH coating can improve the interfacial compactness, its ability to impede crack propagation is limited; the spatial skeleton structure formed by AFt crystals at the fiber interface is beneficial to improving the interfacial roughness and mechanical interlocking effect; when AFt and CSH coexist, the interface has both toughness and load-bearing capacity, which is the key to achieving a significant improvement in flexural strength.

[0031] Examples 6-7: Effect of pH in the deposition system on coating structure and properties: Examples 6 and 7 investigated the effects of changes in coating thickness and mineral composition on concrete performance by adjusting the pH (C1, C3) of the deposition reaction system.

[0032] The results showed that as the reaction pH increased from 11.5 (C1) to 12.5 (C3), the coating thickness increased from 3.2 μm to 4.3 μm, the CSH content on the fiber surface increased slightly, but the AFt content decreased relatively. Correspondingly, the flexural strength growth rate increased from 129.2% (Example 6) to 134.6% (Example 7), but was still lower than that of Example 1 with pH = 12 and a moderate coating thickness. This indicates that: under excessively low pH conditions, the coating layer is insufficiently formed, and the interfacial reinforcement effect is limited; while excessively high pH is beneficial to CSH growth, the AFt content decreases, which is not conducive to the formation of multi-scale bridging structures; within the pH range of 11.5–12.5, especially under the condition of pH ≈ 12, the formation of a dense AFt-CSH synergistic coating layer is most favorable.

[0033] Examples 8-10: The effect of fiber content on reinforcement effect: In Examples 8-10, under the same process flow (Process 1), the modified glass fiber content was reduced from 1.5% to 0.5% in successive steps.

[0034] The results show that the growth rates of both compressive and flexural strength decrease with decreasing fiber content. In Example 8, the flexural strength growth rate still reached 141.5% at a content of 1.5%; however, when the content was reduced to 0.5% (Example 10), the flexural strength growth rate decreased to 93.1%. These results indicate that modified glass fibers can form an effective three-dimensional reinforcing network within the 1-2% content range; when the content is too low, the fiber spacing increases, the probability of crack bridging decreases, and the reinforcing effect is limited; 1.5-2% is the optimal content range that balances performance and economy.

[0035] Comprehensive comparative analysis with the comparative example: Compared with the control group without modified glass fiber, all embodiments showed significant improvements in compressive and flexural strength, especially with flexural strength growth rates generally exceeding 100%. This fully demonstrates that a multi-stage modification process involving pyrolysis, ball milling, surface activation, and mineral deposition can effectively construct a mineral-bonded interface homogeneous with the solid waste concrete matrix; the modified glass fiber not only plays the bridging role of traditional fibers but also significantly improves the toughness and crack propagation resistance of concrete through the interfacial mineral synergistic growth mechanism; this invention achieves high-value utilization of various solid wastes while taking into account mechanical properties, stability, and engineering applicability.

[0036] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for modifying reinforcing glass fibers specifically for solid waste concrete, characterized in that, Includes the following steps: (1) Fiber pretreatment: The recycled glass fibers of the wind turbine blades are placed in an industrial electric furnace for pyrolysis, and then the epoxy resin on the surface is removed by ball milling, so that the epoxy resin content is less than 5% and the recycled glass fibers with a length of 6-15mm account for ≥80%; (2) Surface activation: The pretreated fibers are treated with hydrofluoric acid, modified with silane coupling agent and treated with hydrogen peroxide, cleaned and dried to constant weight; (3) Chemical deposition modification: The activated fiber is added to a reaction system containing specific chemical reagents, the pH is controlled at 11.5-12.5, and the reaction is carried out at 40℃ for 6-8 hours to generate ettringite / hydrated calcium silicate coating layer. The fiber is then washed with ethanol and vacuum dried to obtain reinforced glass fiber.

2. The modification method according to claim 1, characterized in that, The pyrolysis temperature in step (1) is 400-500℃ and the pyrolysis time is 1-2h.

3. The modification method according to claim 1, characterized in that, The working parameters of the ball mill in step (1) are: ball-to-material ratio 2-4:1, rotation speed 200-400 rpm.

4. The modification method according to claim 1, characterized in that, The hydrofluoric acid in step (2) has a mass fraction of 5-15% and a treatment time of 1-15 min; the silane coupling agent is any one or a combination of two of 3-aminopropyltriethoxysilane (APTES) and mercaptopropyltrimethoxysilane (MPTMS), with a concentration of 1-3 g / L.

5. The modification method according to claim 1, characterized in that, In step (2), the mass fraction of the hydrogen peroxide solution is 20-40%, the reaction temperature is 50-70℃, and the reaction time is 4-6h; the silane coupling agent modification is performed by ultrasonic dispersion at a frequency of 40kHz, a reaction temperature of 30-40℃, and a reaction time of 2-3h.

6. The modification method according to claim 1, characterized in that, The specific chemical reagents mentioned in step (3) include: 0.05 mol / L Al2(SO4)3·18H2O solution, 0.3 mol / L Ca(OH)2 solution, 0.2 mol / L Ca(NO3)2·4H2O solution, 0.2 mol / L Na2SiO3·9H2O solution and 10 mol / L NaOH solution.

7. The modification method according to claim 1, characterized in that, The order of adding chemical reagents and the supporting process in step (3) are as follows: the activated recycled glass fiber is added to Ca (OH)2 solution, the ratio of fiber volume to total solution volume is fixed at 1:3-7, Al2(SO4)3·18H2O solution, Ca (NO3)2·4H2O solution, Na2SiO3·9H2O solution and polycarboxylate superplasticizer accounting for 0.2%-0.4% of the total solution volume are added in sequence under a stirring speed of 100-500 rpm, and then NaOH is added to adjust the pH of the system to 11.5-12.

5.

8. A special reinforcing glass fiber for ultra-high performance concrete made entirely from solid waste, characterized in that, The glass fiber is prepared by any of the modification methods described in claims 1-7, wherein the residual epoxy resin content on the surface of the reinforcing glass fiber is ≤5%, the fiber content of 6-15mm in length is ≥80%, and the surface is coated with an ettringite / hydrated calcium silicate composite layer.

9. A type of ultra-high performance concrete made entirely from solid waste, characterized in that, It contains the reinforcing glass fiber as described in claim 8, wherein the amount of the fiber is 0.5-2% of the total mass of the concrete.

10. The all-solid-waste ultra-high-performance concrete according to claim 9, characterized in that, The cementitious system of the concrete consists of granulated blast furnace slag powder, industrial by-product gypsum, and alkaline industrial by-products, with iron tailings sand as the aggregate; by mass, the granulated blast furnace slag powder is 85-90 parts, the industrial by-product gypsum is 5-15 parts, the alkaline industrial by-products are 1-5 parts, and the iron tailings sand is 80-120 parts.

Images