A freezing-thawing resistant type repair material for hydraulic engineering tunnel structures and a preparation method thereof

Abstract

This invention relates to the field of repair mortar technology, specifically to a freeze-thaw resistant repair material for hydraulic engineering tunnel structures and its preparation method, comprising the following raw materials in parts by weight: 300-350 parts magnesium phosphate cement, 1100-1200 parts aggregate, 40-50 parts fly ash, 40-50 parts additive powder, 4-5 parts polycarboxylate superplasticizer, 3-5 parts polypropylene fiber (from the field of repair mortar technology), and 180-200 parts water. The C-S-H gel generated by the reaction of calcined eggshell powder and fly ash effectively fills the internal pores of the material, reducing the space for water retention. The modified material transforms the eggshell powder from hydrophilic to hydrophobic, further preventing water intrusion. The spheroidized aggregate eliminates stress concentration at the corners. These effects work together to resist the damage to the material structure caused by ice crystal expansion during freeze-thaw cycles, significantly improving the material's freeze-thaw resistance and enabling it to adapt to the complex environment of low-temperature freeze-thaw cycles and humidity in tunnels for a long time.

Description

Technical Field

[0001] This invention relates to the field of repair mortar technology, specifically to a freeze-thaw resistant repair material for water conservancy engineering tunnel structures and its preparation method. Background Technology

[0002] Repair materials for water conservancy engineering tunnel structures are high-performance materials specifically designed to address problems such as tunnel leakage, cracks, and structural deterioration. They possess high impermeability, high strength, and durability, effectively restoring the integrity and waterproofing function of the structure and ensuring the long-term safe operation of water conservancy facilities. Common types include high impermeability cement-based composite materials, epoxy resin grouting liquid, and polymer-modified mortar, suitable for repair and reinforcement needs under different working conditions.

[0003] Existing common cement-based repair materials and conventional modified mortars used in water conservancy engineering tunnels generally suffer from problems such as insufficient filling of internal pores leading to easy water retention, hydrophilic filling components that easily absorb environmental moisture, aggregates prone to stress concentration due to lack of morphological optimization, and insufficient interfacial bond strength between aggregates and cementitious matrix. In the long-term low-temperature freeze-thaw and humid environment of tunnels, these materials are prone to structural cracking and spalling due to repeated expansion of internal ice crystals, exhibiting significantly insufficient freeze-thaw resistance and difficulty in maintaining the structural stability of repaired tunnels over the long term. Therefore, this invention provides a freeze-thaw resistant repair material for water conservancy engineering tunnel structures and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a freeze-thaw resistant repair material for water conservancy engineering tunnel structures and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a freeze-thaw resistant repair material for water conservancy engineering tunnel structures, comprising the following raw materials in parts by weight: 300-350 parts magnesium phosphate cement, 1100-1200 parts aggregate, 40-50 parts fly ash, 40-50 parts additive powder, 4-5 parts polycarboxylate superplasticizer, 3-5 parts polypropylene fiber, and 180-200 parts water;

[0006] The preparation method of the additive powder includes the following steps:

[0007] Step 1: Take waste eggshells, wash them, dry them at 75-85℃ for 4-5 hours, and then calcine them at 700℃ for 3-4 hours. Crush and grind the resulting product to a particle size of 750-850 mesh to obtain the first powder.

[0008] Step 2: Take the modified material, crush and grind it to a particle size of 750-850 mesh to obtain the second powder;

[0009] Step 3: Weigh the first powder and the second powder at a mass ratio of 100:(2-3) and add them to the kneader. Set the kneader to 50-100 rpm and 85-90℃ and process for 30-40 minutes to obtain the additive powder.

[0010] Preferably, the fly ash has a particle size of 750-800 mesh.

[0011] Preferably, the polypropylene fiber is 4-6 mm in length.

[0012] Preferably, the preparation method of the modified treatment material is as follows: pre-treatment of waste cooking oil to obtain oil material, pouring the oil material into a reaction vessel, adding a sodium hydroxide solution with a mass concentration of 28-32%, setting the temperature to 80-90℃ and the stirring speed to 50-80 rpm for 1.5-2 hours, then adjusting the stirring speed to 20-50 rpm, and simultaneously adding a hydrochloric acid solution with a mass concentration of 10%. The obtained product is stirred and filtered, and the solids are collected. The solids are washed with warm water at 40-45℃ until the filtrate is neutral, then transferred to an oven and dried at 75-85℃ for 4-5 hours to obtain the modified treatment material.

[0013] Preferably, the mass ratio of the oil, sodium hydroxide solution, and hydrochloric acid solution is (4-5):(1-2):10.

[0014] Preferred method for pretreatment of gutter oil is as follows: collect gutter oil, add warm water, and process it with an electromagnetic stirrer at a stirring speed of 100-150 rpm for 15-20 minutes. Add salt and continue stirring for 1-3 minutes, then let it stand for 30-45 minutes. Collect the clear oil from the top layer to obtain the oil material.

[0015] Preferably, the warm water temperature is 50-60℃, the mass of the warm water is 30-35% of the mass of the gutter oil, and the mass of the salt is 1.5-2% of the mass of the gutter oil.

[0016] Preferably, the aggregate preparation method is as follows: select quartz sand with a particle size of 0.6-1.2mm and add it to a spheroidizer. Set the rotation speed to 1000-1500rpm and process for 25min to obtain ellipsoidal aggregate. Heat it to 60-70℃ and coat the surface with the modification liquid through a fluidized bed to obtain aggregate. The mass of the modification liquid is 24-26% of the mass of the ellipsoidal aggregate.

[0017] Preferably, the modified liquid is prepared by premixing water and ethanol at a mass ratio of (18-20):1, adding KH550, stirring at 50-100 rpm for 10-15 min with an electromagnetic stirrer, adding waterborne epoxy resin emulsion and stirring for 5-8 min, adding ultrafine calcium carbonate and stirring for 30-50 min to obtain the modified liquid, wherein the mass ratio of KH550, waterborne epoxy resin emulsion, ultrafine calcium carbonate and ethanol is (2.5-3):(25-30):(35-40):10.

[0018] Preferably, a method for preparing a freeze-thaw resistant repair material for hydraulic engineering tunnel structures includes the following steps:

[0019] S1: Dry material mixing: Add magnesium phosphate cement, fly ash, and additive powder to the mixer, set the speed to 30-50 rpm and mix for 3-5 minutes to obtain the mixture;

[0020] S2: Mixing preparation: Add aggregate, polycarboxylate superplasticizer, polypropylene fiber and water to S1 mixer, adjust the speed to 80-100 rpm and mix evenly to obtain a freeze-thaw resistant repair material for water conservancy engineering tunnel structure.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. In this repair material, the CSH gel generated by the reaction of calcined eggshell powder and fly ash effectively fills the internal pores of the material, reducing the space for water retention. The modified treatment material changes the eggshell powder from hydrophilic to hydrophobic, further preventing water intrusion. The spheroidized aggregate eliminates stress concentration at the corners. The KH550 silane coupling agent and water-based epoxy resin in the modified liquid enhance the interfacial adhesion between the aggregate and the cement matrix. These effects work together to resist the damage to the material structure caused by ice crystal expansion during freeze-thaw cycles, greatly improving the material's freeze-thaw resistance and enabling it to adapt to the complex environment of low-temperature freeze-thaw cycles and humidity in tunnels for a long time.

[0023] 2. In this repair material, magnesium phosphate cement has rapid hardening properties, enabling the material to achieve good compressive strength in a short period of time, quickly sealing tunnel cracks and shortening the repair period. In the later stage, calcined eggshell powder and fly ash continue to undergo a pozzolanic reaction to generate CSH gel, which, combined with the three-dimensional random distribution of polypropylene fibers, inhibits crack propagation, allowing the material to reach a new level of compressive strength after stabilization. In addition, the polycarboxylate superplasticizer reduces the water-cement ratio and porosity while improving the material's flowability, ensuring smooth construction even in the narrow space of the tunnel, further improving the convenience and advantages of this material in the tunnel environment of water conservancy projects. Attached Figure Description

[0024] Figure 1 The flowchart illustrates a freeze-thaw resistant repair material for water conservancy engineering tunnel structures and its preparation method. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0027] It should be noted that the raw materials used in the following embodiments are all commercially available.

[0028] The waterborne epoxy resin emulsion was purchased from Baoji Didu Pharmaceutical Chemical Co., Ltd., and the ultrafine calcium carbonate was purchased from Dongzheng Chemical Co., Ltd. in Shangnan County, Shaanxi Province.

[0029] Example 1:

[0030] A freeze-thaw resistant repair material for water conservancy engineering tunnel structures comprises the following raw materials in parts by weight: 300 parts magnesium phosphate cement, 1100 parts aggregate, 40 parts fly ash, 40 parts additive powder, 4 parts polycarboxylate superplasticizer, 3 parts polypropylene fiber, and 180 parts water.

[0031] The preparation method of the additive powder includes the following steps:

[0032] Step 1: Take waste eggshells, wash them, dry them at 75℃ for 4 hours, and then calcine them at 700℃ for 3 hours. Crush and grind the resulting product to a particle size of 750 mesh to obtain the first powder.

[0033] Step 2: Take the modified material, crush and grind it to a particle size of 750 mesh to obtain the second powder;

[0034] Step 3: Weigh the first powder and the second powder at a mass ratio of 100:2 and add them to the kneader. Set the kneader to 50 rpm and 85 ℃ and process for 30 minutes to obtain the additive powder.

[0035] The fly ash has a particle size of 750 mesh.

[0036] The polypropylene fiber is 4 mm in length.

[0037] The preparation method of the modified treatment material is as follows: the waste cooking oil is pretreated to obtain oil material, the oil material is poured into the reaction vessel, a 28% sodium hydroxide solution is added, and the mixture is stirred at 80℃ and 50rpm for 1.5h. Then the stirring speed is adjusted to 20rpm, and a 10% hydrochloric acid solution is added dropwise. The obtained product is stirred and filtered, and the solids are collected. The solids are washed with 40℃ warm water until the filtrate is neutral, and then transferred to an oven and dried at 75℃ for 4h to obtain the modified treatment material.

[0038] The mass ratio of the oil, sodium hydroxide solution, and hydrochloric acid solution is 4:1:10.

[0039] The pretreatment method for waste cooking oil is as follows: collect waste cooking oil, add warm water, process it with an electromagnetic stirrer at a stirring speed of 100 rpm for 15 minutes, add salt and continue stirring for 1 minute, let it stand for 30 minutes, collect the clear oil from the top layer, and obtain the oil material.

[0040] The water temperature was 50℃, the water weight was 30% of the gutter oil weight, and the salt weight was 1.5% of the gutter oil weight.

[0041] The method for preparing aggregate is as follows: select 0.6 mm quartz sand and add it to a spheroidizer, set the rotation speed to 1000 rpm and process for 25 min to obtain ellipsoidal aggregate, heat it to 60℃, and coat the surface with the modification liquid through a fluidized bed to obtain aggregate. The mass of the modification liquid is 24-26% of the mass of the ellipsoidal aggregate.

[0042] The modified liquid is prepared as follows: water and ethanol are premixed at a mass ratio of 18:1, KH550 is added, and the mixture is stirred at 50 rpm for 10 min using an electromagnetic stirrer. Then, waterborne epoxy resin emulsion is added and the mixture is stirred for another 5 min. Finally, ultrafine calcium carbonate is added and the mixture is stirred for another 30 min to obtain the modified liquid. The mass ratio of KH550, waterborne epoxy resin emulsion, ultrafine calcium carbonate, and ethanol is 2.5:25:35:10.

[0043] One method for preparing a freeze-thaw resistant repair material for water conservancy engineering tunnel structures includes the following steps:

[0044] S1: Dry material mixing: Add magnesium phosphate cement, fly ash and additive powder to the mixer, set the speed to 30 rpm and mix for 3 minutes to obtain the mixture;

[0045] S2: Mixing preparation: Add aggregate, polycarboxylate superplasticizer, polypropylene fiber and water to S1 mixer, adjust the speed to 80 rpm and mix evenly to obtain a freeze-thaw resistant repair material for water conservancy engineering tunnel structure.

[0046] Example 2:

[0047] A freeze-thaw resistant repair material for water conservancy engineering tunnel structures comprises the following raw materials in parts by weight: 320 parts magnesium phosphate cement, 1150 parts aggregate, 45 parts fly ash, 45 parts additive powder, 4.5 parts polycarboxylate superplasticizer, 4 parts polypropylene fiber, and 190 parts water.

[0048] The preparation method of the additive powder includes the following steps:

[0049] Step 1: Take waste eggshells, wash them, dry them at 80℃ for 4.5 hours, and then calcine them at 700℃ for 3.5 hours. Crush and grind the resulting product to a particle size of 800 mesh to obtain the first powder.

[0050] Step 2: Take the modified material, crush and grind it to a particle size of 800 mesh to obtain the second powder;

[0051] Step 3: Weigh the first powder and the second powder at a mass ratio of 100:2.5 and add them to the kneader. Set the kneader to 80 rpm and 88 ℃ and process for 35 minutes to obtain the additive powder.

[0052] The fly ash has a particle size of 780 mesh.

[0053] The polypropylene fiber is 5 mm in length.

[0054] The preparation method of the modified treatment material is as follows: the waste cooking oil is pretreated to obtain oil material, the oil material is poured into the reaction vessel, a 30% sodium hydroxide solution is added, and the mixture is stirred at 85℃ and 65rpm for 1.8h. Then the stirring speed is adjusted to 35rpm, and a 10% hydrochloric acid solution is added dropwise. The resulting product is stirred and filtered, and the solids are collected. The solids are washed with 43℃ warm water until the filtrate is neutral, and then transferred to an oven and dried at 80℃ for 4.5h to obtain the modified treatment material.

[0055] The mass ratio of the oil, sodium hydroxide solution, and hydrochloric acid solution is 4.5:1.5:10.

[0056] The pretreatment method for gutter oil is as follows: collect gutter oil, add warm water, process it with an electromagnetic stirrer at a stirring speed of 120 rpm for 18 minutes, add salt and continue stirring for 2 minutes, let it stand for 38 minutes, collect the clear oil from the top layer, and obtain the oil material.

[0057] The water temperature was 55℃, the water weight was 32% of the gutter oil weight, and the salt weight was 1.8% of the gutter oil weight.

[0058] The method for preparing aggregate is as follows: 0.9 mm quartz sand is added to a spheroidizer and processed at 1200 rpm for 25 min to obtain ellipsoidal aggregate. The aggregate is heated to 65°C and coated with a modifying liquid through a fluidized bed to obtain aggregate. The mass of the modifying liquid is 25% of the mass of the ellipsoidal aggregate.

[0059] The modified liquid is prepared as follows: water and ethanol are premixed at a mass ratio of 19:1, KH550 is added, and the mixture is stirred at 80 rpm for 12 min using an electromagnetic stirrer. Then, waterborne epoxy resin emulsion is added and the mixture is stirred for another 6.5 min. Finally, ultrafine calcium carbonate is added and the mixture is stirred for another 40 min to obtain the modified liquid. The mass ratio of KH550, waterborne epoxy resin emulsion, ultrafine calcium carbonate, and ethanol is 2.8:28:38:10.

[0060] One method for preparing a freeze-thaw resistant repair material for water conservancy engineering tunnel structures includes the following steps:

[0061] S1: Dry material mixing: Add magnesium phosphate cement, fly ash and additive powder to the mixer, set the speed to 40 rpm and mix for 4 minutes to obtain the mixture;

[0062] S2: Mixing preparation: Add aggregate, polycarboxylate superplasticizer, polypropylene fiber and water to S1 mixer, adjust the speed to 90 rpm and mix evenly to obtain a freeze-thaw resistant repair material for water conservancy engineering tunnel structure.

[0063] Example 3:

[0064] A freeze-thaw resistant repair material for water conservancy engineering tunnel structures comprises the following raw materials in parts by weight: 350 parts magnesium phosphate cement, 1200 parts aggregate, 50 parts fly ash, 50 parts additive powder, 5 parts polycarboxylate superplasticizer, 5 parts polypropylene fiber, and 200 parts water.

[0065] The preparation method of the additive powder includes the following steps:

[0066] Step 1: Take waste eggshells, wash them, dry them at 85℃ for 5 hours, and then calcine them at 700℃ for 4 hours. Crush and grind the resulting product to a particle size of 850 mesh to obtain the first powder.

[0067] Step 2: Take the modified material, crush and grind it to a particle size of 850 mesh to obtain the second powder;

[0068] Step 3: Weigh the first powder and the second powder at a mass ratio of 100:3 and add them to the kneader. Set the kneader to 100 rpm and 90℃ and process for 40 minutes to obtain the additive powder.

[0069] The fly ash has a particle size of 800 mesh.

[0070] The polypropylene fiber is 6 mm in length.

[0071] The preparation method of the modified treatment material is as follows: the waste cooking oil is pretreated to obtain oil material, the oil material is poured into the reaction vessel, a 32% sodium hydroxide solution is added, and the mixture is stirred at 90℃ and 80rpm for 2 hours. Then the stirring speed is adjusted to 50rpm, and a 10% hydrochloric acid solution is added dropwise. The resulting product is stirred and filtered, and the solids are collected. The solids are washed with 45℃ warm water until the filtrate is neutral. The solids are then transferred to an oven and dried at 85℃ for 5 hours to obtain the modified treatment material.

[0072] The mass ratio of the oil, sodium hydroxide solution, and hydrochloric acid solution is 5:2:10.

[0073] The pretreatment method for gutter oil is as follows: collect gutter oil, add warm water, process it with an electromagnetic stirrer at a stirring speed of 150 rpm for 20 minutes, add salt and continue stirring for 3 minutes, let it stand for 45 minutes, collect the clear oil from the top layer, and obtain the oil material.

[0074] The water temperature was 60℃, the water weight was 35% of the gutter oil weight, and the salt weight was 2% of the gutter oil weight.

[0075] The method for preparing aggregate is as follows: 1.2 mm quartz sand is added to a spheroidizer and processed at 1500 rpm for 25 min to obtain ellipsoidal aggregate. The aggregate is heated to 70°C and coated with a modifying liquid through a fluidized bed to obtain aggregate. The mass of the modifying liquid is 26% of the mass of the ellipsoidal aggregate.

[0076] The modified liquid is prepared as follows: water and ethanol are premixed at a mass ratio of 20:1, KH550 is added, and the mixture is stirred at 100 rpm for 15 min using an electromagnetic stirrer. Then, waterborne epoxy resin emulsion is added and the mixture is stirred for another 8 min. Finally, ultrafine calcium carbonate is added and the mixture is stirred for another 50 min to obtain the modified liquid. The mass ratio of KH550, waterborne epoxy resin emulsion, ultrafine calcium carbonate, and ethanol is 3:30:40:10.

[0077] One method for preparing a freeze-thaw resistant repair material for water conservancy engineering tunnel structures includes the following steps:

[0078] S1: Dry material mixing: Add magnesium phosphate cement, fly ash and additive powder to the mixer, set the speed to 50 rpm and mix for 5 minutes to obtain the mixture;

[0079] S2: Mixing preparation: Add aggregate, polycarboxylate superplasticizer, polypropylene fiber and water to S1 mixer, adjust the speed to 100 rpm and mix evenly to obtain a freeze-thaw resistant repair material for water conservancy engineering tunnel structure.

[0080] Comparative Example 1: The difference between this comparative example and Example 1 is that this comparative example does not contain any added powder.

[0081] Comparative Example 2 differs from Example 1 in that no modified materials are added during the powder preparation process in this comparative example.

[0082] Comparative Example 3 differs from Example 1 in that the quartz sand is not spheroidized during the aggregate preparation process in this comparative example.

[0083] Comparative Example 4 differs from Example 1 in that an equal amount of 1mm diameter quartz sand is used to replace aggregate in this comparative example.

[0084] Performance testing:

[0085] 3d and 28d compressive strength tests: In accordance with GBT17671-2021 standard, 40mm×40mm×160mm specimens were prepared and cured under standard conditions (temperature 20±2℃, relative humidity ≥95%) for 3d and 28d. The compressive strength was determined using a pressure testing machine at a loading rate of 2.4kN / s. The average value of 3 specimens in each group was taken.

[0086] Freeze-thaw resistance test: In accordance with GB / T50082-2024 standard, 100mm×100mm×100mm specimens were prepared. After standard curing for 28 days, they were placed in a rapid freezing test chamber. One cycle was "freezing at -18℃ for 4 hours → thawing at 20℃ for 4 hours". The maximum number of cycles when the mass loss rate was ≤5% was determined. After 500 freeze-thaw cycles, the porosity was determined in accordance with GB / T50081-2019 standard. At the same time, the number of cracks per square millimeter was determined.

[0087] Water absorption test: Prepare 50mm×50mm×50mm specimens according to ASTM C1585-13 standard, dry to constant weight (mass M0), immerse completely in distilled water at 20±2℃ for 24h, remove, wipe off surface moisture and weigh mass M1, calculate according to the formula "water absorption rate = (M1-M0) / M0×100%", take the average value of 3 specimens in each group;

[0088] The performance of the freeze-thaw resistant repair materials for hydraulic engineering tunnel structures prepared in Examples 1-3 and Comparative Examples 1-4 was tested, and the test data are recorded in the table below.

[0089] Table 1:

[0090] Test Project 3D compressive strength (MPa) 28-day compressive strength (MPa) Number of freeze-thaw cycles (times) Volumetric water absorption rate (%) Porosity (%) <![CDATA[Number of cracks (pieces / mm 2 )]]> Example 1 34.5 45.2 340 3.9 1.8 4 Example 2 35.8 47.6 380 3.8 1.5 3 Example 3 38.3 49.1 400 3.5 1.6 2 Comparative Example 1 25.1 36.8 150 6.8 3.5 12 Comparative Example 2 28.7 40.3 200 6.5 3.2 10 Comparative Example 3 26.3 35.2 180 5.9 3.0 11 Comparative Example 4 27.5 38.5 220 5.6 2.8 9

[0091] Comparative analysis of the data in the table shows that the freeze-thaw resistant repair materials for water conservancy engineering tunnel structures prepared in Examples 1-3 are superior to the freeze-thaw resistant repair materials for water conservancy engineering tunnel structures prepared in Comparative Examples 1-4.

[0092] In terms of freeze-thaw resistance testing, Example 3 achieved 400 freeze-thaw cycles, compared to only 150 for Comparative Example 1 and 220 for Comparative Example 4. Furthermore, the porosity and crack count data in the 500 freeze-thaw cycle tests of Examples 1-3 were superior to those of Comparative Examples 1-4. This is because the additives in these examples included calcined eggshell powder and modified waste cooking oil. The calcined eggshell powder decomposes into CaO after calcination, and CaO hydrates to form Ca(OH)2. Ca(OH)2 reacts with the active SiO2 in fly ash to form a dense CSH gel, which fills the internal pores of the material and reduces moisture retention space. Simultaneously, the fatty acid molecules in the modified waste cooking oil react with the CaO on the surface of the eggshell powder through their carboxyl groups. 2+During the reaction, long-chain hydrophobic groups coat the surface of the eggshell powder to form a hydrophobic film, transforming the eggshell powder from hydrophilic to hydrophobic, further preventing water intrusion. Meanwhile, the spheroidization treatment of the aggregate eliminates stress concentration at the corners. Combined with the KH550 silane coupling agent in the modified liquid, which connects the inorganic quartz sand and the organic epoxy resin, the interfacial adhesion between the aggregate and the cement matrix is ​​enhanced, reducing cracks caused by ice crystal expansion at the interface during freeze-thaw cycles. These effects collectively improve the freeze-thaw resistance. However, Comparative Example 1 lacks additive powder, lacks the filling effect of CSH gel and the water-blocking effect of the hydrophobic film, and has high internal porosity. During freeze-thaw cycles, ice crystals easily expand and damage the structure. Comparative Example 4 uses ordinary quartz sand instead of modified aggregate, lacking the interfacial bonding enhancement effect. Cracks easily initiate at the aggregate-matrix interface, resulting in a decrease in the number of freeze-thaw cycles.

[0093] Regarding compressive strength, the 28-day compressive strength of Example 3 was 49.1 MPa, while that of Comparative Example 1 was 36.8 MPa and that of Comparative Example 3 was 35.2 MPa. This is because the added powder in the examples filled the pores with CSH gel, making the material structure more compact. The spheroidized aggregate avoided stress concentration, and the modified liquid improved the interfacial adhesion. Under external force, the stress could be uniformly transmitted, reducing damage caused by excessive local stress. In contrast, Comparative Example 1 did not have added powder, and its internal pores were numerous and its structure was loose. Under stress, cracks were easily generated at the pores. The aggregate in Comparative Example 3 was not spheroidized, and the stress concentration at the edges was obvious. Cracks were easy to propagate rapidly, resulting in a significant decrease in compressive strength.

[0094] Regarding water absorption, the water absorption rate of Example 3 was 3.5%, while that of Comparative Example 1 was 6.8% and that of Comparative Example 4 was 5.6%. This is because the calcined eggshell powder particles in the added powder are small and can fill the tiny pores in the cement matrix, reducing the water penetration channels. The hydrophobic groups of the waste cooking oil modifier form hydrophobic regions inside the material, hindering the adsorption and penetration of water. The dense interface of the modified aggregate can also reduce the entry of water. However, Comparative Example 1 did not add any powder, so it has many internal pores and no hydrophobic effect, making it easy for water to penetrate. The ordinary quartz sand in Comparative Example 4 has weak interfacial bonding, and water can easily seep in from the interfacial gaps, resulting in an increased water absorption rate.

[0095] This demonstrates that in this repair material, the CSH gel generated by the reaction of calcined eggshell powder and fly ash effectively fills the internal pores of the material, reducing the space for water retention. The modified material transforms the eggshell powder from hydrophilic to hydrophobic, further preventing water intrusion. The spheroidized aggregate eliminates stress concentration at the corners. The KH550 silane coupling agent and water-based epoxy resin in the modified liquid enhance the interfacial adhesion between the aggregate and the cement matrix. These effects work together to resist the damage to the material structure caused by ice crystal expansion during freeze-thaw cycles, significantly improving the material's freeze-thaw resistance and enabling it to adapt to the complex environment of low-temperature freeze-thaw cycles and humidity in tunnels for a long time.

[0096] Meanwhile, the magnesium phosphate cement in this repair material has rapid hardening properties, enabling the material to achieve good compressive strength in a short period of time, quickly sealing tunnel cracks and shortening the repair period. In the later stage, the calcined eggshell powder and fly ash continue to undergo a pozzolanic reaction to generate CSH gel, which, combined with the three-dimensional random distribution of polypropylene fibers, inhibits crack propagation, allowing the material to reach a new level of compressive strength after stabilization. Furthermore, the polycarboxylate superplasticizer reduces the water-cement ratio and porosity while improving material flowability, ensuring smooth construction even in the narrow space of the tunnel. This further enhances the convenience and advantages of this material in the tunnel environment of water conservancy projects.

[0097] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0098] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A freeze-thaw resistant repair material for water conservancy engineering tunnel structures, characterized in that, The raw materials include the following parts by weight: 300-350 parts magnesium phosphate cement, 1100-1200 parts aggregate, 40-50 parts fly ash, 40-50 parts additive powder, 4-5 parts polycarboxylate superplasticizer, 3-5 parts polypropylene fiber, and 180-200 parts water. The preparation method of the additive powder includes the following steps: Step 1: Take waste eggshells, wash them, dry them at 75-85℃ for 4-5 hours, and then calcine them at 700℃ for 3-4 hours. Crush and grind the resulting product to a particle size of 750-850 mesh to obtain the first powder. Step 2: Take the modified material, crush and grind it to a particle size of 750-850 mesh to obtain the second powder; Step 3: Weigh the first powder and the second powder at a mass ratio of 100:(2-3) and add them to the kneader. Set the kneader to 50-100 rpm and 85-90℃ and process for 30-40 minutes to obtain the additive powder. The preparation method of the modified treatment material is as follows: the waste cooking oil is pretreated to obtain oil material, the oil material is poured into the reaction vessel, a sodium hydroxide solution with a mass concentration of 28-32% is added, the mixture is stirred at 80-90℃ and 50-80rpm for 1.5-2h, the stirring speed is then adjusted to 20-50rpm, and a hydrochloric acid solution with a mass concentration of 10% is added dropwise. The obtained product is stirred and filtered, and the solids are collected. The solids are washed with warm water at 40-45℃ until the filtrate is neutral, and then transferred to an oven and dried at 75-85℃ for 4-5h to obtain the modified treatment material. The mass ratio of the oil material, sodium hydroxide solution and hydrochloric acid solution is (4-5):(1-2):

10. The aggregate preparation method is as follows: Select quartz sand with a particle size of 0.6-1.2mm and add it to a spheroidizer. Set the rotation speed to 1000-1500rpm and process for 25min to obtain ellipsoidal aggregate. Heat the aggregate to 60-70℃ and coat the surface with a modification liquid through a fluidized bed to obtain aggregate. The mass of the modification liquid is 24-26% of the mass of the ellipsoidal aggregate. The modified liquid is prepared as follows: water and ethanol are premixed at a mass ratio of (18-20):1, KH550 is added, and the mixture is stirred at 50-100 rpm for 10-15 min using an electromagnetic stirrer. Then, waterborne epoxy resin emulsion is added and the mixture is stirred for another 5-8 min. Finally, ultrafine calcium carbonate is added and the mixture is stirred for another 30-50 min to obtain the modified liquid. The mass ratio of KH550, waterborne epoxy resin emulsion, ultrafine calcium carbonate, and ethanol is (2.5-3):(25-30):(35-40):

10.

2. The freeze-thaw resistant repair material for water conservancy engineering tunnel structures according to claim 1, characterized in that, The fly ash has a particle size of 750-800 mesh.

3. The freeze-thaw resistant repair material for water conservancy engineering tunnel structures according to claim 1, characterized in that, The polypropylene fiber is 4-6 mm in length.

4. The freeze-thaw resistant repair material for water conservancy engineering tunnel structures according to claim 1, characterized in that, The pretreatment method for gutter oil is as follows: collect gutter oil, add warm water, and process it with an electromagnetic stirrer at a stirring speed of 100-150 rpm for 15-20 minutes. Add salt and continue stirring for 1-3 minutes, then let it stand for 30-45 minutes. Collect the clear oil from the top layer to obtain the oil material.

5. The freeze-thaw resistant repair material for water conservancy engineering tunnel structures according to claim 4, characterized in that, The temperature of the warm water is 50-60℃, the weight of the warm water is 30-35% of the weight of the gutter oil, and the weight of the salt is 1.5-2% of the weight of the gutter oil.

6. A method for preparing a freeze-thaw resistant repair material for hydraulic engineering tunnel structures according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Dry material mixing: Add magnesium phosphate cement, fly ash, and additive powder to the mixer, set the speed to 30-50 rpm and mix for 3-5 minutes to obtain the mixture; S2: Mixing preparation: Add aggregate, polycarboxylate superplasticizer, polypropylene fiber and water to S1 mixer, adjust the speed to 80-100 rpm and mix evenly to obtain a freeze-thaw resistant repair material for water conservancy engineering tunnel structure.

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