Environment-friendly concrete containing tunnel hole slag aggregate and preparation method thereof

Abstract

The present application relates to the technical field of concrete, and discloses an environment-friendly concrete containing tunnel hole slag aggregate and a preparation method thereof.The environment-friendly concrete comprises the following raw materials in parts by weight: cement 500-600 parts, fly ash 120-140 parts, slag powder 100-130 parts, modified polypropylene fiber 55-85 parts, hole slag aggregate 350-450 parts, sand 300-400 parts, water reducing agent 2.5-5.5 parts, and water 180-250 parts; the raw materials are blended, and then casted, shaped and maintained to obtain the environment-friendly concrete; and the addition of the modified polypropylene fiber in the concrete can improve the defects of the concrete caused by the hole slag aggregate, such as the decrease of the strength, the increase of the water absorption rate and the decrease of the durability.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to an environmentally friendly concrete containing tunnel slag aggregate and its preparation method. Background Technology

[0002] Tunnel construction generates a large amount of tunnel debris, which has traditionally been disposed of as solid waste through landfill or stockpiling. This not only occupies valuable land resources but also puts significant pressure on the surrounding ecological environment. With the increasing adoption of green building and sustainable development concepts, using tunnel debris as coarse and fine aggregates in concrete after crushing and screening has become an important way to achieve resource utilization.

[0003] However, tunnel muck aggregate exhibits significant performance differences compared to natural aggregates. On the one hand, tunnel muck is prone to developing numerous internal microcracks and surface defects during blasting, excavation, and crushing, resulting in high porosity and water absorption. On the other hand, the lithology of different tunnel surrounding rocks is complex and varied, leading to some tunnel muck aggregates having low strength and poor particle shape. These inherent defects directly affect the workability, mechanical properties, and durability of concrete. Therefore, how to fully utilize tunnel muck resources while effectively overcoming the performance degradation issues caused by its use as aggregate has become a pressing technical challenge in this field. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an environmentally friendly concrete containing tunnel slag aggregate and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions: An environmentally friendly concrete containing tunnel slag aggregate comprises the following raw materials in parts by weight: 500-600 parts cement, 120-140 parts fly ash, 100-130 parts slag powder, 55-85 parts modified polypropylene fiber, 350-450 parts tunnel slag aggregate, 300-400 parts sand, 2.5-5.5 parts water-reducing agent, and 180-250 parts water. The slag aggregate is rock fragments generated during tunnel excavation, which are then crushed and screened to obtain a particle size of 2.5-4.5mm. The modified polypropylene fiber is prepared by the following steps: Step A1: Add 1-(2-hydroxyethyl)imidazolium and 4-vinylphenylboronic acid to a flask containing toluene, heat to 110°C, and reflux at a constant temperature for 8-10 hours. After the reaction is complete, remove the water and toluene produced during the esterification process from the azeotrope, and distill off the remaining solvent to obtain the modifier. Further, in step A1, the molar ratio of 1-(2-hydroxyethyl)imidazole to 4-vinylphenylboronic acid is 2-2.03:1; Step A2: Mix anhydrous ethanol and deionized water, add silane coupling agent KH570 and stir for 20 minutes, then add polypropylene fiber and stir to react for 2-4 hours. Wash and dry to obtain grafted modified polypropylene fiber. Furthermore, in step A2, the mass ratio of polypropylene fiber, silane coupling agent KH570, anhydrous ethanol, and deionized water is 10:5-8:85:2-4. Furthermore, the length of the polypropylene fiber in step A2 is 10mm-12mm; Step A3: Add methacrylic acid, allyl polyethylene glycol (molecular weight 500-700) and modifier to toluene and stir thoroughly. Then add grafted modified polypropylene fiber and ultrasonically disperse for 10 min, stir vigorously for 30 min, then add azobisisobutyronitrile and stir thoroughly. Then stir and react under argon at 65℃ for 24 h. Wash and dry to obtain modified polypropylene fiber. Furthermore, in step A3, the ratio of methacrylic acid, allyl polyethylene glycol, modifier, toluene, grafted modified polypropylene fiber, and azobisisobutyronitrile is 0.8-1.2g:1-3g:0.2-0.6g:100mL:1g:0.2-0.4g.

[0006] A method for preparing environmentally friendly concrete containing tunnel slag aggregate includes the following steps: Step S1: Weigh the raw materials according to the weight parts, add cement, fly ash, slag powder, blast furnace aggregate and sand into the mixer and mix evenly to obtain the premix; Step S2: Mix water and water-reducing agent, add to premix and stir evenly, then add modified polypropylene fiber and mix evenly, pour into shape and cure to obtain environmentally friendly concrete containing tunnel muck aggregate.

[0007] The beneficial effects of this invention are: The environmentally friendly concrete of this invention uses tunnel slag as aggregate, and adds cement, fly ash, slag powder, sand, water-reducing agent, water and modified polypropylene fiber, and then pours and cures it. The addition of modified polypropylene fiber in this concrete can improve the shortcomings of concrete caused by using tunnel slag as aggregate, such as reduced strength, increased water absorption and reduced durability.

[0008] The modified polypropylene fiber introduced in this invention differs from traditional fiber materials. Traditional fiber materials, when directly added, exhibit uneven dispersion in concrete, resulting in limited strength improvement. However, the addition of modified polypropylene fiber enhances the overall performance of concrete. The modifier grafted onto the fiber surface contains imidazole structures with lone pairs of electrons, enabling them to interact with Ca in cement hydration products. 2+ Al 3+When metal ions undergo strong coordination complexation reactions, these coordination bonds are much stronger than ordinary hydrogen bonds or van der Waals forces. They can form a "chemical anchoring layer" between the fiber and the cement paste. Even under stress, this chemical bond can effectively transfer the load, significantly improving flexural strength and splitting tensile strength, and compensating for the mechanical shortcomings caused by aggregate defects. The borate ester structure in the modifier remains stable in the alkaline cement environment. However, when local microcracks are generated, stress changes and moisture intrusion at the cracks can trigger the reversible hydrolysis of the borate ester. The borate groups exposed after hydrolysis can reform covalent bonds or hydrogen bonds with hydroxyl groups (-OH) in cement hydration products or on polymer chains. This gives the interface a dynamic self-healing ability. When microcracks in concrete just begin to emerge, the borate ester on the fiber surface can consume the energy of crack propagation through dynamic covalent bond recombination and "repair" the microcracks, thereby inhibiting crack development and improving the ultimate strength and toughness of concrete.

[0009] Allyl polyethylene glycol is grafted onto the fiber surface to form a fluffy "brush" structure. These flexible long chains fill the tiny gaps between the aggregate and the slurry, and play an internal curing role (slow-release water) during the cement hydration process. By optimizing the pore structure of the interface transition zone, the interconnected macropores are transformed into non-interconnected micropores, thereby reducing the total porosity and water absorption rate.

[0010] Due to the numerous sharp edges and rapid water absorption of slag aggregate, concrete is prone to rapid slump loss and segregation. The methacrylic acid copolymerized on the surface of modified polypropylene fibers ionizes into negatively charged carboxylate ions in an alkaline environment, generating electrostatic repulsion. Simultaneously, the long chains of allyl polyethylene glycol extend in solution, creating a steric hindrance effect. These two effects work together to not only prevent fiber agglomeration (solving the problem of easy clumping in ordinary PP fibers) but also to act as a dispersant, similar to polycarboxylate superplasticizers, helping to disperse cement particles and release trapped free water, thereby improving the initial fluidity and slump retention of concrete. Furthermore, the imidazole ring has a certain pH buffering capacity. In the highly alkaline environment of cement hydration, the imidazole groups can fine-tune the thickness of the interfacial double layer through protonation / deprotonation balance. This adjustment can alleviate the drastic fluctuations in the local water-cement ratio caused by the rapid water absorption of slag aggregate, maintaining a more uniform rheological state in the paste and reducing bleeding and segregation. Detailed Implementation

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0012] Example 1: Modified polypropylene fiber was prepared by the following steps: Step A1: Add 1-(2-hydroxyethyl)imidazole and 4-vinylphenylboronic acid to a flask containing toluene, heat to 110°C, and reflux for 8 hours. After the reaction is complete, remove the water and toluene produced during the esterification process from the azeotrope, and remove the remaining solvent by distillation to obtain the modifier. The molar ratio of 1-(2-hydroxyethyl)imidazole to 4-vinylphenylboronic acid is 2.01:1. Step A2: After mixing anhydrous ethanol and deionized water, add silane coupling agent KH570 and stir for 20 minutes. Then add polypropylene fiber and stir for 2 hours. Wash and dry to obtain grafted modified polypropylene fiber. The mass ratio of polypropylene fiber, silane coupling agent KH570, anhydrous ethanol and deionized water is 10:5:85:2. The length of polypropylene fiber is 10mm-12mm. Step A3: Add methacrylic acid, allyl polyethylene glycol (molecular weight 500-700) and modifier to toluene and stir thoroughly. Then add grafted modified polypropylene fiber and ultrasonically disperse for 10 min, stir vigorously for 30 min, then add azobisisobutyronitrile and stir thoroughly. Subsequently, stir and react under argon at 65℃ for 24 h. Wash and dry to obtain modified polypropylene fiber. The ratio of methacrylic acid, allyl polyethylene glycol, modifier, toluene, grafted modified polypropylene fiber and azobisisobutyronitrile is 0.8g:1g:0.2g:100mL:1g:0.2g.

[0013] Example 2: Modified polypropylene fiber was prepared by the following steps: Step A1: Add 1-(2-hydroxyethyl)imidazolium and 4-vinylphenylboronic acid to a flask containing toluene, heat to 110°C, and reflux at a constant temperature for 9 hours. After the reaction is complete, remove the water and toluene produced during the esterification process from the azeotrope, and remove the remaining solvent by distillation to obtain the modifier. The molar ratio of 1-(2-hydroxyethyl)imidazolium to 4-vinylphenylboronic acid is 2.02:1. Step A2: After mixing anhydrous ethanol and deionized water, add silane coupling agent KH570 and stir for 20 minutes. Then add polypropylene fiber and stir to react for 3 hours. Wash and dry to obtain grafted modified polypropylene fiber. The mass ratio of polypropylene fiber, silane coupling agent KH570, anhydrous ethanol and deionized water is 10:6.5:85:3. The length of polypropylene fiber is 10mm-12mm. Step A3: Add methacrylic acid, allyl polyethylene glycol (molecular weight 500-700) and modifier to toluene and stir thoroughly. Then add grafted modified polypropylene fiber and ultrasonically disperse for 10 min, stir vigorously for 30 min, then add azobisisobutyronitrile and stir thoroughly. Subsequently, stir and react under argon at 65℃ for 24 h. Wash and dry to obtain modified polypropylene fiber. The ratio of methacrylic acid, allyl polyethylene glycol, modifier, toluene, grafted modified polypropylene fiber and azobisisobutyronitrile is 1g:2g:0.4g:100mL:1g:0.3g.

[0014] Example 3: Modified polypropylene fiber was prepared by the following steps: Step A1: Add 1-(2-hydroxyethyl)imidazolium and 4-vinylphenylboronic acid to a flask containing toluene, heat to 110°C, and reflux for 10 hours. After the reaction is complete, remove the water and toluene produced during the esterification process from the azeotrope, and remove the remaining solvent by distillation to obtain the modifier. The molar ratio of 1-(2-hydroxyethyl)imidazolium to 4-vinylphenylboronic acid is 2.03:1. Step A2: After mixing anhydrous ethanol and deionized water, add silane coupling agent KH570 and stir for 20 min. Then add polypropylene fiber and stir for 4 h. Wash and dry to obtain grafted modified polypropylene fiber. The mass ratio of polypropylene fiber, silane coupling agent KH570, anhydrous ethanol and deionized water is 10:8:85:4. The length of polypropylene fiber is 10 mm-12 mm. Step A3: Add methacrylic acid, allyl polyethylene glycol (molecular weight 500-700) and modifier to toluene and stir thoroughly. Then add grafted modified polypropylene fiber and ultrasonically disperse for 10 min, stir vigorously for 30 min, then add azobisisobutyronitrile and stir thoroughly. Subsequently, stir and react under argon at 65℃ for 24 h. Wash and dry to obtain modified polypropylene fiber. The ratio of methacrylic acid, allyl polyethylene glycol, modifier, toluene, grafted modified polypropylene fiber and azobisisobutyronitrile is 1.2g:3g:0.6g:100mL:1g:0.4g.

[0015] Example 4: A method for preparing environmentally friendly concrete containing tunnel slag aggregate includes the following steps: 500 parts cement, 120 parts fly ash, 100 parts slag powder, 55 parts modified polypropylene fiber prepared in Example 1, 350 parts slag aggregate, 300 parts sand, 2.5 parts water-reducing agent, and 180 parts water. Preferably, the excavated material is rock fragments generated during tunnel excavation, which are then crushed and screened to obtain a particle size of 2.5-4.5 mm. Preferably, the water-reducing agent is a polycarboxylate water-reducing agent; Step S1: Weigh the raw materials according to the weight parts, add cement, fly ash, slag powder, blast furnace aggregate and sand into the mixer and mix evenly to obtain the premix; Step S2: After mixing water and water-reducing agent, add it to the premix and stir evenly. Then add the modified polypropylene fiber prepared in Example 1, mix evenly, pour into molds, and cure to obtain environmentally friendly concrete containing tunnel slag aggregate.

[0016] Example 5: A method for preparing environmentally friendly concrete containing tunnel slag aggregate includes the following steps: 550 parts cement, 130 parts fly ash, 130 parts slag powder, 70 parts modified polypropylene fiber prepared in Example 2, 400 parts slag aggregate, 350 parts sand, 4 parts water-reducing agent, and 220 parts water. Preferably, the excavated material is rock fragments generated during tunnel excavation, which are then crushed and screened to obtain a particle size of 2.5-4.5 mm. Preferably, the water-reducing agent is a polycarboxylate water-reducing agent; Step S1: Weigh the raw materials according to the weight parts, add cement, fly ash, slag powder, blast furnace aggregate and sand into the mixer and mix evenly to obtain the premix; Step S2: After mixing water and water-reducing agent, add it to the premix and stir evenly. Then add the modified polypropylene fiber prepared in Example 2, mix evenly, pour into molds, and cure to obtain environmentally friendly concrete containing tunnel slag aggregate.

[0017] Example 6: A method for preparing environmentally friendly concrete containing tunnel slag aggregate includes the following steps: 600 parts cement, 140 parts fly ash, 130 parts slag powder, 85 parts modified polypropylene fiber prepared in Example 3, 450 parts slag aggregate, 400 parts sand, 5.5 parts water-reducing agent, and 250 parts water. Preferably, the excavated material is rock fragments generated during tunnel excavation, which are then crushed and screened to obtain a particle size of 2.5-4.5 mm. Preferably, the water-reducing agent is a polycarboxylate water-reducing agent; Step S1: Weigh the raw materials according to the weight parts, add cement, fly ash, slag powder, blast furnace aggregate and sand into the mixer and mix evenly to obtain the premix; Step S2: After mixing water and water-reducing agent, add it to the premix and stir evenly. Then add the modified polypropylene fiber prepared in Example 3, mix evenly, pour into molds, and cure to obtain environmentally friendly concrete containing tunnel slag aggregate.

[0018] Comparative Example 1: This comparative example is an environmentally friendly concrete. The difference between this example and Example 6 is that polypropylene fibers are used instead of the modified polypropylene fibers prepared in Example 3. All other aspects are the same.

[0019] Comparative Example 2: This comparative example is an environmentally friendly concrete. The difference between this example and Example 6 is that the grafted modified polypropylene fiber prepared in Example 3 is used instead of the modified polypropylene fiber prepared in Example 3. All other aspects are the same.

[0020] Comparative Example 3: This comparative example is an environmentally friendly concrete, which differs from Example 6 in that silica fume is used instead of slag powder.

[0021] The environmentally friendly concrete prepared in Examples 4-6 and Comparative Examples 1-3 was subjected to performance testing: The mechanical properties of concrete specimens were determined according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The specimens were water-cured in a standard curing room for 28 days (temperature 20±2℃), and the compressive strength was tested. According to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete", a plate-type constrained cracking test device was used. A constant wind speed (usually 3-5 m / s) was applied above the specimen, and the time of crack appearance, crack width, length, and number were recorded. The total cracked area per unit area was calculated. According to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete", a frustum-shaped specimen with a top diameter of 175 mm, a bottom diameter of 185 mm, and a height of 150 mm was used. Water pressure was applied incrementally (starting from 0.1 MPa, increasing by 0.1 MPa every 8 hours), and maintained at the specified pressure for 24 hours. The water seepage height was measured by splitting the specimen to evaluate the impermeability grade. The test results are shown in Table 1: Table 1: Performance Test Results

[0022] As can be seen from Table 1, the environmentally friendly concrete prepared by this invention has excellent compressive strength, crack resistance and impermeability.

[0023] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. An environmentally friendly concrete containing tunnel slag aggregate, characterized in that, The raw materials include the following parts by weight: 500-600 parts cement, 120-140 parts fly ash, 100-130 parts slag powder, 55-85 parts modified polypropylene fiber, 350-450 parts slag aggregate, 300-400 parts sand, 2.5-5.5 parts water-reducing agent, and 180-250 parts water. The slag aggregate is rock fragments generated during tunnel excavation, which are then crushed and screened to obtain a particle size of 2.5-4.5mm. The modified polypropylene fiber is prepared by free radical polymerization on the surface of grafted modified polypropylene fiber after the action of an initiator, using methacrylic acid, allyl polyethylene glycol and a modifier as monomers; the grafted modified polypropylene fiber is polypropylene fiber modified by silane coupling agent KH570; the modifier is prepared by the reaction of 1-(2-hydroxyethyl)imidazolium and 4-vinylphenylboronic acid.

2. The environmentally friendly concrete containing tunnel slag aggregate according to claim 1, characterized in that, The modified polypropylene fiber is prepared by the following steps: Step A1: Add 1-(2-hydroxyethyl)imidazolium and 4-vinylphenylboronic acid to a flask containing toluene, heat to 110°C, and reflux at a constant temperature for 8-10 hours. After the reaction is complete, remove the water and toluene produced during the esterification process from the azeotrope, and distill off the remaining solvent to obtain the modifier. Step A2: Mix anhydrous ethanol and deionized water, add silane coupling agent KH570 and stir for 20 minutes, then add polypropylene fiber and stir to react for 2-4 hours. Wash and dry to obtain grafted modified polypropylene fiber. Step A3: Add methacrylic acid, allyl polyethylene glycol and modifier to toluene and stir thoroughly. Then add grafted modified polypropylene fiber and ultrasonically disperse for 10 min, stir vigorously for 30 min, then add azobisisobutyronitrile and stir thoroughly. Then stir and react under argon at 65℃ for 24 h. Wash and dry to obtain modified polypropylene fiber.

3. The environmentally friendly concrete containing tunnel slag aggregate according to claim 2, characterized in that, In step A1, the molar ratio of 1-(2-hydroxyethyl)imidazole to 4-vinylphenylboronic acid is 2-2.03:

1.

4. The environmentally friendly concrete containing tunnel slag aggregate according to claim 2, characterized in that, In step A2, the mass ratio of polypropylene fiber, silane coupling agent KH570, anhydrous ethanol, and deionized water is 10:5-8:85:2-4.

5. The environmentally friendly concrete containing tunnel slag aggregate according to claim 2, characterized in that, The length of the polypropylene fiber in step A2 is 10mm-12mm.

6. The environmentally friendly concrete containing tunnel slag aggregate according to claim 2, characterized in that, In step A3, the ratio of methacrylic acid, allyl polyethylene glycol, modifier, toluene, grafted modified polypropylene fiber, and azobisisobutyronitrile is 0.8-1.2g:1-3g:0.2-0.6g:100mL:1g:0.2-0.4g.

7. A method for preparing environmentally friendly concrete containing tunnel slag aggregate as described in any one of claims 1-6, characterized in that, Includes the following steps: Step S1: Weigh the raw materials according to the weight parts, add cement, fly ash, slag powder, blast furnace aggregate and sand into the mixer and mix evenly to obtain the premix; Step S2: Mix water and water-reducing agent, add to premix and stir evenly, then add modified polypropylene fiber and mix evenly, pour into shape and cure to obtain environmentally friendly concrete containing tunnel muck aggregate.

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