A kind of magnesium phosphate inorganic glue and its preparation method and application

Abstract

The present invention belongs to the technical field of phosphate binders and discloses a magnesium phosphate inorganic glue, its preparation method, and application. The magnesium phosphate inorganic glue is composed of the following components, measured by mass: 100 parts of dead-burned magnesium oxide, 45-80 parts of potassium dihydrogen phosphate, 1-5 parts of an organic acid metal chelating agent, 1-5 parts of potassium hydroxide, 1-4 parts of borax, 0.7-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 20-32 parts of water. The magnesium phosphate inorganic glue is modified based on raw material selection and mix ratio design, thereby significantly improving the setting time and fluidity of the magnesium phosphate inorganic glue. This solves the problems of conventional magnesium phosphate inorganic glue, such as short setting time, poor fluidity, and inability to meet the construction requirements of the adhesive for fully impregnating and spreading carbon fiber cloth. This ensures the construction and workability of the magnesium phosphate inorganic glue as an adhesive for reinforcing carbon fiber cloth, and can be applied to the field of reinforcement and repair of large-scale concrete structures.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphate binders and relates to a magnesium phosphate inorganic glue and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Existing buildings face reduced safety or failure to meet operational requirements due to factors such as material degradation, approaching or exceeding their design service life, substandard original design standards, and poor maintenance and management. Therefore, reinforcing and renovating existing buildings to improve their safety and functionality is a crucial measure to maximize resource utilization and minimize environmental pollution. Carbon fiber sheet reinforcement uses an adhesive to adhere carbon fiber sheet to the surface of the reinforced component, creating a new composite component that synergizes with the original component to achieve the desired reinforcement.

[0004] The adhesive used in conjunction with the carbon fiber cloth reinforcement method is usually an epoxy organic adhesive, which has problems such as poor durability, poor high performance resistance, and toxic and allergenic curing agents.

[0005] Magnesium phosphate inorganic adhesive is a new inorganic cementitious material. Using it as an adhesive instead of traditional epoxy-based organic adhesives offers an opportunity to improve the fire safety and long-term durability of CFRP sheet reinforced concrete structures. On the one hand, magnesium phosphate inorganic adhesive is an inorganic non-metallic material, which makes it more durable than epoxy-based organic adhesives. On the other hand, magnesium phosphate inorganic adhesive has a similar microstructure to ceramics, so it outperforms epoxy-based organic adhesives in terms of high-temperature resistance. Furthermore, magnesium phosphate inorganic adhesive offers advantages such as rapid hardening and early strength, low shrinkage, good adhesion to the concrete matrix, and strong environmental adaptability, thus holding it in a promising field for concrete structure reinforcement.

[0006] The core issue currently limiting the use of magnesium phosphate inorganic glue as an adhesive for carbon fiber sheet reinforcement is its rapid setting rate. This is due to the fact that the main components of magnesium phosphate inorganic glue include dead-burned magnesium oxide, ammonium dihydrogen phosphate, or potassium dihydrogen phosphate. Ammonium dihydrogen phosphate or potassium dihydrogen phosphate are acidic phosphates, while magnesium oxide is an alkaline oxide. When mixed in water, these two react rapidly and violently, releasing a large amount of heat of hydration. This results in a very short setting time for the magnesium phosphate inorganic glue. Without the addition of a retarder, the setting time of magnesium phosphate inorganic glue is approximately 2 minutes. However, for carbon fiber sheet reinforcement projects, a setting time of at least 30 minutes is required to ensure sufficient wetting and spreading of the adhesive on the carbon fiber sheet. Furthermore, the large particulate matter in magnesium phosphate inorganic glue results in poor slurry flowability, which also hinders its application on the carbon fiber sheet. Given these issues, traditional magnesium phosphate inorganic adhesives are unsuitable for the large-scale and widespread application of concrete structure reinforcement. Summary of the Invention

[0007] The purpose of the present invention is to provide a magnesium phosphate inorganic glue and its preparation method and application. The magnesium phosphate inorganic glue is modified based on raw material selection and mix ratio design, thereby greatly improving the setting time and fluidity of the magnesium phosphate inorganic glue, so as to solve the problems of short setting time, poor fluidity and inability to meet the construction requirements of sufficient wetting and spreading of the adhesive on the carbon fiber cloth of the traditional magnesium phosphate inorganic glue. The construction and workability of the magnesium phosphate inorganic glue as an adhesive for reinforcing the carbon fiber cloth are guaranteed, and it can be applied to the field of reinforcement and repair of concrete structures with large quantities and wide coverage.

[0008] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0009] In a first aspect, the present invention provides a magnesium phosphate inorganic glue, which is composed of the following components, calculated by mass: 100 parts of dead-burned magnesium oxide, 45-80 parts of potassium dihydrogen phosphate, 1-5 parts of an organic acid metal chelating agent, 1-5 parts of potassium hydroxide, 1-4 parts of borax, 0.7-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 20-32 parts of water.

[0010] The main function of introducing a small amount of potassium hydroxide is to react with the organic acid metal chelating agent to generate some water-soluble potassium salts, which can enhance the retarding effect.

[0011] Calcium chloride hexahydrate uses water of crystallization to absorb reaction heat. The water of crystallization in barium hydroxide octahydrate has the same effect as that of calcium chloride hexahydrate. The synergistic effect of calcium chloride hexahydrate and barium hydroxide octahydrate effectively prevents excessive chloride ion corrosion on reinforced concrete. Furthermore, barium, calcium, and magnesium ions are all +2 valent ions, which compete with magnesium ions to slow the formation of KMgPO4.

[0012] In some embodiments, the magnesium phosphate inorganic glue is composed of the following components, by mass: 100 parts of dead-burned magnesium oxide, 45-60 parts of potassium dihydrogen phosphate, 1-3 parts of organic acid metal chelating agent, 1-3 parts of potassium hydroxide, 1-3 parts of borax, 0.7-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 25-32 parts of water.

[0013] Preferably, the magnesium phosphate inorganic glue is composed of the following components, by mass: 100 parts of dead-burned magnesium oxide, 45-50 parts of potassium dihydrogen phosphate, 1-2 parts of organic acid metal chelating agent, 1-2 parts of potassium hydroxide, 1.5-2.5 parts of borax, 0.9-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 28-32 parts of water.

[0014] In some embodiments, the mass fraction of MgO in the dead-burned magnesium oxide is 92% to 97%, and the particle size of the dead-burned magnesium oxide is 250 mesh to 425 mesh.

[0015] In some embodiments, the potassium dihydrogen phosphate has a purity of more than 95% and a particle size of 32 mesh to 40 mesh.

[0016] In some embodiments, the organic acid metal chelating agent has an analytical grade purity of more than 99%, including but not limited to one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, octanoylhydroxamic acid, diethylenetriaminepentaacetic acid, and methylglycine diacetic acid, but does not include phosphonic acid metal chelating agents. This is because phosphonic acid metal chelating agents contain phosphate groups, which can replace part of the phosphate and react with dead-burned magnesium oxide, resulting in poor retarding effect.

[0017] In some embodiments, the borax is of analytical grade purity with a purity of more than 99%.

[0018] In some embodiments, the potassium hydroxide, barium hydroxide octahydrate, and calcium chloride hexahydrate are chemically pure, with a purity of more than 98%.

[0019] In a second aspect, the present invention provides a method for preparing the magnesium phosphate inorganic glue, comprising the following steps:

[0020] S1. Mix weighed calcium chloride hexahydrate, potassium hydroxide, and an organic acid metal chelating agent, and pour into weighed water to obtain a mixed solution;

[0021] S2. Pour the mixed solution described in S1, dead-burned magnesium oxide, borax, and barium hydroxide octahydrate into a mixing bucket and mix and stir for 2-5 minutes. This step is to ensure that the retarding component is evenly distributed in the mixture to fully exert the retarding effect of the retarder;

[0022] S3. Potassium dihydrogen phosphate is added to the mixture obtained in S2, and stirred for 2 to 5 minutes until the slurry is uniform, thereby obtaining the magnesium phosphate inorganic glue of the present invention.

[0023] In a third aspect, the present invention provides applications of the magnesium phosphate inorganic glue, including but not limited to: application in reinforcing large-volume concrete structures with carbon fiber cloth, or application in reinforcing special concrete structures with long process connection time, or application in reinforcing concrete structures with carbon fiber cloth in hot environments.

[0024] The beneficial effects of the present invention are:

[0025] (1) The magnesium phosphate inorganic gel of the present invention has a longer setting time. The setting time of magnesium phosphate inorganic gel without any retarding material is only about 2 minutes, and the setting time of traditional magnesium phosphate inorganic gel with borax as retarder is only 15-20 minutes. However, the setting time of the magnesium phosphate inorganic gel of the present invention is as long as 60 minutes, which is more than 200% longer than the setting time of traditional magnesium phosphate inorganic gel with borax as retarder.

[0026] This invention modifies traditional magnesium phosphate inorganic adhesive using an organic acid metal chelating agent (MCA), borax, and an inorganic phase change material (PCM). The mechanism by which these three agents exert their retarding effect is as follows:

[0027] MCA and Mg 2+ It has a good chelating effect, thereby inhibiting the formation of inorganic hydration products of magnesium phosphate (mainly potassium magnesium phosphate hexahydrate).

[0028] In addition, MCA is slightly soluble in water, so introducing a small amount of potassium hydroxide to react with it to form potassium salt that is easily soluble in water can enhance the above-mentioned chelating effect.

[0029] Borax can adhere to the surface of dead-burned magnesium oxide, preventing it from undergoing acid-base neutralization reaction with potassium dihydrogen phosphate, thereby reducing the intensity of the reaction and reducing the release of hydration heat.

[0030] PCMs such as calcium chloride hexahydrate and barium hydroxide octahydrate can effectively absorb the hydration heat generated during the reaction, thereby delaying the temperature increase of the magnesium phosphate inorganic slurry. At the same time, barium hydroxide octahydrate can also supplement calcium chloride hexahydrate to prevent Cl - Excessive use will cause corrosion to concrete structures.

[0031] In addition, Ba 2+ , Ca 2+ With Mg 2+ All of them belong to +2 valent metal ions, Ba 2+ , Ca 2+Can be used with Mg 2+ The competition delays the formation of potassium magnesium phosphate hexahydrate (the main hydration product of magnesium phosphate inorganic adhesive), thereby enhancing the retarding effect. Through the synergistic effect of three retarding components—metal chelating agent, borax, and inorganic phase change material—the setting time of magnesium phosphate inorganic adhesive can be extended to 60 minutes. This solves the problem of traditional magnesium phosphate inorganic adhesive having too short a setting time, which prevents the adhesive from fully impregnating and spreading the carbon fiber cloth. This meets the construction time requirements of carbon fiber cloth reinforcement projects. It can be used in carbon fiber cloth reinforcement of large-volume concrete structures, or in the reinforcement of special concrete structures with long process connection times.

[0032] (2) The magnesium phosphate inorganic glue of the present invention has good fluidity. The fluidity of traditional magnesium phosphate inorganic glue is 120mm-130mm, while the fluidity of the magnesium phosphate inorganic glue of the present invention can reach about 150mm. It has good fluidity, can achieve self-leveling, and can omit the manual paving process, significantly improving the efficiency of reinforcement construction. It can be used in carbon fiber cloth reinforcement of concrete structures in hot environments.

[0033] (3) The magnesium phosphate inorganic adhesive of the present invention has high strength. The 28-day flexural strength of conventional magnesium phosphate inorganic adhesive is 7.2 MPa, and the 28-day compressive strength is 54 MPa. The magnesium phosphate inorganic adhesive of the present invention has a 28-day flexural strength of up to 8.2 MPa, which is 13.8% higher than that of conventional magnesium phosphate inorganic adhesive; and a 28-day compressive strength of up to 61.8 MPa, which is 14.4% higher than that of conventional magnesium phosphate inorganic adhesive. This broadens the application range of magnesium phosphate inorganic adhesive as an adhesive for reinforcing carbon fiber cloth.

[0034] (4) The bonding performance of the magnesium phosphate inorganic adhesive at room temperature is close to that of epoxy organic adhesive, but the durability of the magnesium phosphate inorganic adhesive is better than that of epoxy organic adhesive, which solves the problem of poor durability of epoxy organic adhesive and the need for frequent periodic inspections, and effectively reduces the maintenance cost of the reinforced structure.

[0035] At the same time, the high-temperature resistance of the magnesium phosphate inorganic glue of the present invention is stronger than that of the epoxy organic glue, which ensures the bonding reliability between the carbon fiber cloth and the concrete structure at high temperatures, solves the problem that the epoxy organic glue loses its bonding strength after reaching the glass temperature, thereby causing reinforcement failure, and improves the fire safety of the reinforced concrete structure.

[0036] The above two points have broadened the application scope of carbon fiber cloth reinforcement technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0038] Figure 1 This is a flow chart for preparing the magnesium phosphate inorganic glue in Example 1 of the present invention.

[0039] Figure 2 Diagram of the equipment for measuring the coagulation time of magnesium phosphate inorganic gel.

[0040] Figure 3 Diagram of the equipment for measuring the fluidity of magnesium phosphate inorganic glue.

[0041] Figure 4 Schematic diagram of the preparation of test blocks for mechanical properties testing of magnesium phosphate inorganic glue.

[0042] Figure 5 The figure is a comparison chart of the flexural strength of magnesium phosphate inorganic glue of different embodiments and comparative examples.

[0043] Figure 6 The figure is a comparison chart of the compressive strength of magnesium phosphate inorganic glue of different embodiments and comparative examples.

[0044] Figure 7 Schematic diagram of double shear specimen based on carbon fiber cloth bonded with magnesium phosphate inorganic adhesive.

[0045] Figure 8 Figure 2 is a flow chart for bonding carbon fiber cloth to double shear specimens based on magnesium phosphate inorganic adhesive; (a) the area of ​​the concrete specimen to be bonded with carbon fiber cloth is roughened, (b) magnesium phosphate inorganic adhesive is applied to the roughened area of ​​the concrete specimen, and (c) magnesium phosphate inorganic adhesive is applied to the carbon fiber cloth.

[0046] Figure 9 Schematic diagram of the loading equipment for the interface bonding test.

[0047] Figure 10 The figure is a comparison chart of the in-plane shear strength of magnesium phosphate inorganic glue of different embodiments and comparative examples.

[0048] Among them, 1-Vicat instrument pointer; 2-Vicat instrument pointer knob; 3-Vicat instrument panel; 4-Vicat initial setting needle knob; 5-Vicat instrument base; 6-Vicat initial setting needle; 7-glass bottom plate; 8-magnesium phosphate inorganic glue; 9-truncated cone circular mold; 10-ruler; 11-concrete test block; 12-carbon fiber cloth; 13-semicircular pad; 14-hydraulic jack; 15-pressure sensor; 16-square pad; 17-digital display; 18-oil pump. DETAILED DESCRIPTION

[0049] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0051] A magnesium phosphate inorganic glue consists of the following components, measured by mass: 100 parts of dead-burned magnesium oxide, 45-80 parts of potassium dihydrogen phosphate, 1-5 parts of an organic acid metal chelating agent, 1-5 parts of potassium hydroxide, 1-4 parts of borax, 0.7-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 20-32 parts of water.

[0052] The present invention will be further described below with reference to the embodiments.

[0053] In the following examples, the mass fraction of MgO in the dead-burned magnesia is 95%, and the particle size of the dead-burned magnesia is 425 mesh, which is purchased from Haicheng Yuchen Refractory Manufacturing Co., Ltd.

[0054] Potassium dihydrogen phosphate with a purity of more than 95% and a particle size of 40 mesh was purchased from Lianyungang Geli Chemical Co., Ltd.

[0055] Borax was of analytical grade with a purity of more than 99% and was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0056] The metal chelating agent was of analytical grade with a purity of more than 99% and was purchased from Shijiazhuang Jack Chemical Co., Ltd.

[0057] Potassium hydroxide, barium hydroxide octahydrate, and calcium chloride hexahydrate were of chemically pure grade with a purity of more than 98% and were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0058] Example 1:

[0059] A magnesium phosphate inorganic glue is composed of the following components: dead-burned magnesium oxide, potassium dihydrogen phosphate, nitrilotriacetic acid, potassium hydroxide, borax, calcium chloride hexahydrate, barium hydroxide octahydrate and water.

[0060] The preparation method of magnesium phosphate inorganic glue, such as Figure 1 As shown, the following steps are included:

[0061] S1. Weigh 34.6 g of calcium chloride hexahydrate, 34.6 g of potassium hydroxide, and 34.6 g of nitrilotriacetic acid, respectively, mix the three, and pour into 1027.2 g of water to obtain a mixed solution;

[0062] S2. Pour the mixed solution described in S1, 3456 g of dead-burned magnesium oxide, 69.2 g of borax, and 17.3 g of barium hydroxide octahydrate into a mixing bucket and mix and stir for 3 minutes. This step is to ensure that the retarding component can be evenly distributed in the mixture to fully exert the retarding effect of the retarder;

[0063] S3. Add 1680 g of potassium dihydrogen phosphate to the mixture obtained in S2, and stir for 3 minutes until the slurry is uniform, thereby obtaining the magnesium phosphate inorganic glue of the present invention.

[0064] Example 2:

[0065] The difference from Example 1 is that nitrilotriacetic acid is replaced by ethylenediaminetetraacetic acid, and the rest is the same as Example 1. Specifically:

[0066] A magnesium phosphate inorganic glue is composed of the following components: 3456g of dead-burned magnesium oxide, 1680g of potassium dihydrogen phosphate, 34.6g of ethylenediaminetetraacetic acid, 34.6g of potassium hydroxide, 69.2g of borax, 34.6g of calcium chloride hexahydrate, 17.3g of barium hydroxide octahydrate, and 1027.2g of water.

[0067] Example 3:

[0068] The difference from Example 1 is that nitrilotriacetic acid is replaced by octanoylhydroxamic acid, and the rest is the same as Example 1. Specifically:

[0069] A magnesium phosphate inorganic glue is composed of the following components: 3456g of dead-burned magnesium oxide, 1680g of potassium dihydrogen phosphate, 34.6g of octanoylhydroxamic acid, 34.6g of potassium hydroxide, 69.2g of borax, 34.6g of calcium chloride hexahydrate, 17.3g of barium hydroxide octahydrate, and 1027.2g of water.

[0070] Example 4:

[0071] The difference from Example 1 is that nitrilotriacetic acid is replaced by diethylenetriaminepentaacetic acid, and the rest is the same as Example 1. Specifically:

[0072] A magnesium phosphate inorganic glue is composed of the following components: 3456g of dead-burned magnesium oxide, 1680g of potassium dihydrogen phosphate, 34.6g of diethylenetriaminepentaacetic acid, 34.6g of potassium hydroxide, 69.2g of borax, 34.6g of calcium chloride hexahydrate, 17.3g of barium hydroxide octahydrate, and 1027.2g of water.

[0073] Example 5:

[0074] The difference from Example 1 is that nitrilotriacetic acid is replaced by methylglycine diacetic acid, and the rest is the same as Example 1. Specifically:

[0075] A magnesium phosphate inorganic glue is composed of the following components: 3456g of dead-burned magnesium oxide, 1680g of potassium dihydrogen phosphate, 34.6g of methylglycine diacetic acid, 34.6g of potassium hydroxide, 69.2g of borax, 34.6g of calcium chloride hexahydrate, 17.3g of barium hydroxide octahydrate, and 1027.2g of water.

[0076] Example 6:

[0077] The difference from Example 1 is that a single type of organic acid metal chelating agent is replaced by a dual type of organic acid metal chelating agent, the total weight of the organic acid metal chelating agent remains unchanged, and the rest are the same as Example 1.

[0078] A magnesium phosphate inorganic glue is composed of the following components: 3456g of dead-burned magnesium oxide, 1680g of potassium dihydrogen phosphate, 17.3g of nitrilotriacetic acid, 17.3g of diethylenetriaminepentaacetic acid, 34.6g of potassium hydroxide, 69.2g of borax, 34.6g of calcium chloride hexahydrate, 17.3g of barium hydroxide octahydrate, and 1027.2g of water.

[0079] Comparative Example 1:

[0080] Conventional magnesium phosphate inorganic glue is composed of the following components: 3456g dead-burned magnesium oxide, 1680g potassium dihydrogen phosphate, 69.2g borax, and 1027.2g water.

[0081] The conventional method for preparing magnesium phosphate inorganic glue comprises the following steps:

[0082] S1. Weigh 1680 g of potassium dihydrogen phosphate and 69.2 g of borax respectively, pour into a mixing bucket and mix for 1 min;

[0083] S2. Add 1027.2 g of water to the mixture obtained in S1 and stir for 2 min;

[0084] S3. Weigh 3456 g of dead-burned magnesium oxide, add it to the mixture obtained in S2, and continue stirring for 3 minutes to obtain the conventional magnesium phosphate inorganic glue.

[0085] Comparative Example 2:

[0086] The difference from Example 1 is that barium hydroxide octahydrate is replaced by calcium chloride hexahydrate of equal mass, and the rest is the same as Example 1.

[0087] Comparative Example 3:

[0088] The difference from Example 1 is that calcium chloride hexahydrate is replaced by barium hydroxide octahydrate of equal mass, and the rest is the same as Example 1.

[0089] Comparative Example 4:

[0090] The difference from Example 1 is that potassium hydroxide is omitted, and the rest is the same as Example 1.

[0091] Example Retarding Effect Verification

[0092] According to the provisions of "Test Methods for Standard Water Consumption, Setting Time and Stability of Cement" (GB / T 1346-2011), the setting time of the magnesium phosphate inorganic glue prepared in the example was measured. The setting time of the magnesium phosphate inorganic glue was measured using a Vicat apparatus and a truncated cone mold. Figure 2 As shown. As the fluidity of magnesium phosphate inorganic glue decreases over time, it will solidify and harden when it reaches final setting, completely losing its fluidity and adhesion. Therefore, the initial setting time is used as the setting time of magnesium phosphate inorganic glue. The specific measurement steps are as follows:

[0093] S1. Place the glass bottom plate 7 on the Vicat instrument base 5 and adjust the Vicat instrument initial setting needle knob 4 so that the Vicat instrument initial setting needle 6 contacts the glass bottom plate 7. Adjust the Vicat instrument pointer knob 2 so that the Vicat instrument pointer 1 is aligned with the Vicat instrument panel 3 at zero.

[0094] S2, take out the glass bottom plate 7 from the Vicat instrument base 5, wipe the glass bottom plate 7 with an alcohol cotton pad and place the truncated cone circular mold 9 at the center of the glass bottom plate 7, pour the prepared magnesium phosphate inorganic glue 8 into the truncated cone circular mold 9 and vibrate it gently, and use a scraper to scrape off excess magnesium phosphate inorganic glue 8, then place the smoothed truncated cone circular mold 9 and the glass bottom plate 7 together on the Vicat instrument base 5, and make the Vicat instrument initial setting needle 6 contact the surface of the magnesium phosphate inorganic glue 8;

[0095] S3. When the Vicat instrument pointer 1 shows 4 mm ± 1 mm, the magnesium phosphate inorganic glue is determined to have reached its setting time. The setting time is measured every 10 minutes for the first 40 minutes and every 5 minutes thereafter. The setting time measurement results are shown in Table 1.

[0096] Verification of retarding effect of comparative example:

[0097] The procedure for measuring the setting time of the magnesium phosphate inorganic gel prepared in the comparative example is the same as that in the embodiment, except that the setting time is measured every 5 minutes in S3.

[0098] Example flow effect verification:

[0099] According to the provisions of "Test Method for Homogeneity of Concrete Admixtures" (GB / T 8077-2012), the fluidity of the magnesium phosphate inorganic glue prepared in the example was measured. The fluidity of the magnesium phosphate inorganic glue was measured using a ruler, a glass bottom plate and a truncated cone mold. Figure 3 The specific measurement steps are as follows:

[0100] S1. Place the glass bottom plate 7 on a horizontal table and wipe it with an alcohol pad to clean its surface. Then place the truncated cone mold 9 at the center of the glass bottom plate 7.

[0101] S2, pour the prepared magnesium phosphate inorganic glue 8 into the truncated cone mold 9 and smooth it with a scraper;

[0102] S3, lift the truncated cone mold 9 vertically upward to allow the magnesium phosphate inorganic glue 8 to flow freely on the glass bottom plate 7 for 30 seconds;

[0103] S4. Use a ruler 10 to measure the maximum diameters of the magnesium phosphate inorganic glue 8 in two mutually perpendicular directions, and take the average value as the fluidity of the magnesium phosphate inorganic glue. The fluidity measurement results are shown in Table 1.

[0104] Verification of proportional flow effect:

[0105] The procedure for determining the fluidity of the magnesium phosphate inorganic glue prepared in the comparative example is the same as that in the embodiment.

[0106] Table 1 Results of setting time and fluidity of magnesium phosphate inorganic gel

[0107]

[0108] Note: wt % indicates the mass fraction of this material component in dead-burned magnesia.

[0109] Compared with the conventional magnesium phosphate inorganic glue of Comparative Example 1, the modified magnesium phosphate inorganic glue of Examples 1 to 6 and Comparative Example 2 of the present invention is modified by adding an organic acid metal chelating agent, borax and an inorganic phase change material to the magnesium phosphate inorganic glue. The modified magnesium phosphate inorganic glue has a longer setting time, which can reach 60 minutes, while the setting time of the magnesium phosphate inorganic glue without any retarding material is only about 2 minutes. Comparative Example 1 is a traditional magnesium phosphate inorganic glue with borax as a retarder, and its setting time is only 15-20 minutes. Compared with the unmodified magnesium phosphate inorganic glue, the setting time of the modified magnesium phosphate inorganic glue is extended by 300%.

[0110] MCA and Mg added in the embodiment 2+ It has good chelation effect and can form stable hydration products, thereby reducing the Mg content in magnesium phosphate inorganic colloid. 2+ The concentration is low, and the potassium salt generated by the reaction of a small amount of potassium hydroxide with the metal chelating agent is easily soluble in water and can enhance the chelating effect.

[0111] Borax can cover the surface of MgO to prevent the acid-base neutralization reaction between dead-burned magnesium oxide and potassium dihydrogen phosphate; inorganic phase change materials such as calcium chloride hexahydrate and barium hydroxide octahydrate can effectively absorb the hydration heat generated during the reaction, slowing down the temperature increase rate of the magnesium phosphate inorganic adhesive, and in the endothermic process, the inorganic phase change material can release crystal water by absorbing heat, thereby increasing the fluidity of the magnesium phosphate inorganic adhesive by 28%, achieving self-leveling, reducing manual paving, and facilitating the application of the magnesium phosphate inorganic adhesive on carbon fiber cloth.

[0112] It solves the problems of traditional magnesium phosphate inorganic adhesive, such as short setting time and poor fluidity, which does not allow sufficient impregnation of carbon fiber cloth and spreading of adhesive, and is not suitable for reinforcement of large-scale and wide-area concrete structures. It meets the requirements of carbon fiber cloth reinforcement projects for construction process time.

[0113] Mechanical performance verification:

[0114] According to the provisions of "Test method for strength of cement mortar (ISO method)" (GB / T 17671-2021), if Figure 4 As shown, the magnesium phosphate inorganic adhesive prepared based on Examples 1-6 and Comparative Examples 1-4 was poured into a 40mm×40mm×160mm triple mold, vibrated and compacted, and covered with a plastic film. After indoor curing for 24 hours, the mold was removed and cured in an environment with a relative humidity of 50±5% and a temperature of 23±2°C to the target age. The flexural strength and compressive strength tests were performed on ten groups of magnesium phosphate inorganic adhesive test blocks of Examples 1-6 and Comparative Examples 1-4. The mechanical properties test results of magnesium phosphate inorganic adhesive are shown in Tables 2, 3 and Figure 5 、 Figure 6 shown.

[0115] Table 2 Test results of flexural strength of magnesium phosphate inorganic glue

[0116]

[0117] Table 3 Compressive strength test results of magnesium phosphate inorganic glue

[0118]

[0119] Mechanical test results show that the mechanical strength of the magnesium phosphate inorganic glue with the composite retarder is generally superior to that of the traditional magnesium phosphate inorganic glue in Comparative Example 1; the magnesium phosphate inorganic glue of the embodiment of the present invention has high mechanical strength. The traditional magnesium phosphate inorganic glue has a 28-day flexural strength of 7.2 MPa and a 28-day compressive strength of 54 MPa, while the magnesium phosphate inorganic glue of the present invention has a 28-day flexural strength of 8.2 MPa, a 13.8% increase compared to the traditional magnesium phosphate inorganic glue; the 28-day compressive strength can reach 61.8 MPa, a 14.4% increase compared to the traditional magnesium phosphate inorganic glue. The modified magnesium phosphate inorganic glue of the present invention not only extends the setting time but also improves its mechanical strength, thereby broadening the application range of magnesium phosphate inorganic glue as an adhesive for reinforcing carbon fiber cloth.

[0120] Bonding performance verification:

[0121] The bonding performance of the magnesium phosphate inorganic adhesive of the present invention was obtained through an interfacial bonding test of double shear specimens. A total of 33 double shear specimens were prepared and divided into 11 groups. The specific groups are as follows:

[0122] Group 1: 3 double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Example 1 to bond carbon fiber cloth;

[0123] The second group: three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Example 2 to bond carbon fiber cloth;

[0124] The third group: 3 double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Example 3 to bond carbon fiber cloth;

[0125] Group 4: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Example 4 to bond carbon fiber cloth;

[0126] Group 5: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Example 5 to bond carbon fiber cloth;

[0127] Group 6: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Example 6 to bond carbon fiber cloth;

[0128] Group 7: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Comparative Example 1 to bond carbon fiber cloth;

[0129] Group 8: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Comparative Example 2 to bond carbon fiber cloth;

[0130] Group 9: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Comparative Example 3 to bond carbon fiber cloth;

[0131] Group 10: The three double shear specimens were identical, all using the magnesium phosphate inorganic adhesive of Comparative Example 4 to bond carbon fiber cloth;

[0132] Group 11: The three double shear specimens are identical, all using epoxy resin organic glue to bond carbon fiber cloth.

[0133] Double shear specimen based on magnesium phosphate inorganic adhesive bonded carbon fiber cloth Figure 7 As shown, the double shear specimen consists of a concrete specimen 11, a carbon fiber cloth 12, and a magnesium phosphate inorganic adhesive 8. The concrete specimen 11 measures 120 mm × 120 mm × 450 mm, and the concrete strength grade is C30. According to the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T 50081-2019), the measured concrete compressive strength is 30.3 MPa. Carbon fiber cloth 12 is attached to two opposing sides of the concrete specimen 11 using magnesium phosphate inorganic adhesive 8. The bonded length of the carbon fiber cloth 12 on the concrete specimen 11 is 100 mm, and the bonded width is 70 mm. The free lengths of the carbon fiber cloth 12 at both ends of the concrete specimen 11 are 80 mm and 50 mm, respectively.

[0134] The steps for bonding carbon fiber cloth based on magnesium phosphate inorganic adhesive on double shear specimens are as follows:

[0135] Step 1: Use an angle grinder to roughen the area on the surface of the concrete test block where the carbon fiber cloth is to be pasted. Figure 8 As shown in (a), a blower is used to remove impurities in the chiseled area;

[0136] Step 2: Moisten the roughened area of ​​the concrete test block to prevent the moisture in the magnesium phosphate inorganic glue from being absorbed by the dry concrete surface and affecting its bonding performance;

[0137] Step 3: Apply the magnesium phosphate inorganic slurry evenly on the roughened area of ​​the concrete test block surface with a thickness of 2 mm. Figure 8 As shown in (b);

[0138] Step 4: Wetting the cut strips of carbon fiber cloth and pasting them on the magnesium phosphate inorganic glue prepared in step 3, and repeatedly scraping along the pasting direction with a scraper to allow the magnesium phosphate inorganic glue to fully soak the carbon fiber cloth;

[0139] Specifically, the carbon fiber cloth used is RLS-I-300 CFRP cloth produced by Shanghai Zhinuo Decoration Materials Co., Ltd., with a thickness of 0.167 mm and a density of 300 g / m 2 , tensile strength is 3668MPa, elastic modulus is 240GPa, and elongation is 1.74%;

[0140] Step 5: Apply a layer of magnesium phosphate inorganic adhesive evenly on the surface of the carbon fiber cloth with a thickness of 3mm, and use a scraper to repeatedly scrape and smooth it along the pasting direction. Figure 8 As shown in (c);

[0141] Step 6: After the magnesium phosphate inorganic gel is solidified, it is naturally cured in an environment with a temperature of 23±2°C for 14 days.

[0142] The preparation steps for double-shear specimens using epoxy resin organic adhesive and carbon fiber cloth were similar to those for magnesium phosphate inorganic adhesive, except that the magnesium phosphate inorganic adhesive was replaced with epoxy resin organic adhesive. The epoxy resin organic adhesive was purchased from Beijing Jinhong Century Technology Co., Ltd. and has the following mechanical properties: tensile strength of 48.8 MPa, flexural strength of 93.8 MPa, and compressive strength of 97.2 MPa.

[0143] Schematic diagram of the interface bonding test loading equipment Figure 9 As shown, a square pad 16, a pressure sensor 15, a hydraulic jack 14, and a semicircular pad 13 are sequentially placed on top of the double shear specimen. The carbon fiber cloth 12 of the double shear specimen is passed around the semicircular pad 13. The height of the hydraulic jack 14 and the pressure sensor 15 are adjusted so that the carbon fiber cloth 12 is vertically straightened on both sides of the double shear specimen. An oil pump 18 drives the hydraulic jack 14 to apply an upward load P to the semicircular pad 13, causing the carbon fiber cloth on both sides of the double shear specimen to bear a tensile force of P / 2. This tensile force, in turn, causes the adhesive to withstand shear force in the bonding area until the adhesive fails. The applied load value during the loading process is collected by the pressure sensor 15 and displayed on the digital display 17.

[0144] The test results of the bonding performance of magnesium phosphate inorganic glue and epoxy resin organic glue are shown in Table 6 and Figure 10 As shown in the shear strength test results, it can be seen that the bonding performance of the magnesium phosphate inorganic adhesives of Examples 1, 3, and 5 of the present invention is better than that of the traditional magnesium phosphate inorganic adhesive of Comparative Example 1 at room temperature, and slightly lower than that of the epoxy organic adhesive. The magnesium phosphate inorganic adhesive of the present invention needs to be coated with a top coat and a base coat when pasting. Figure 8 , which reinforces and protects the carbon fiber cloth, solving the problem of poor durability and frequent periodic inspection required by epoxy-based organic adhesives, effectively reducing the maintenance cost of the reinforced structure; and the magnesium phosphate inorganic adhesive of the present invention has excellent high-temperature resistance, ensuring the bond reliability between the carbon fiber cloth and the concrete structure at high temperatures, solving the problem of epoxy-based organic adhesives losing bond strength after reaching the glass transition temperature, which leads to reinforcement failure, and improving the fire safety of reinforced concrete structures. Both of the above points broaden the application scope of carbon fiber cloth reinforcement technology.

[0145] Table 6 Test results of bonding performance of magnesium phosphate inorganic glue and epoxy resin organic glue

[0146]

[0147] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A magnesium phosphate inorganic glue, characterized in that: The invention is composed of the following components by mass: 100 parts of dead-burned magnesium oxide, 45-80 parts of potassium dihydrogen phosphate, 1-5 parts of an organic acid metal chelating agent, 1-5 parts of potassium hydroxide, 1-4 parts of borax, 0.7-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 20-32 parts of water; The organic acid metal chelating agent includes one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, octanoylhydroxamic acid, diethylenetriaminepentaacetic acid, and methylglycinediacetic acid, but does not include phosphonic acid metal chelating agents.

2. The magnesium phosphate inorganic glue according to claim 1, wherein: The invention is composed of the following components in parts by mass: 100 parts of dead-burned magnesium oxide, 45-60 parts of potassium dihydrogen phosphate, 1-3 parts of organic acid metal chelating agent, 1-3 parts of potassium hydroxide, 1-3 parts of borax, 0.7-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 25-32 parts of water.

3. The magnesium phosphate inorganic glue according to claim 2, comprising the following components in parts by mass: 100 parts of dead-burned magnesium oxide, 45-50 parts of potassium dihydrogen phosphate, 1-2 parts of organic acid metal chelating agent, 1-2 parts of potassium hydroxide, 1.5-2.5 parts of borax, 0.9-1.5 parts of calcium chloride hexahydrate, 0.4-0.6 parts of barium hydroxide octahydrate, and 28-32 parts of water.

4. The magnesium phosphate inorganic glue according to any one of claims 1 to 3, characterized in that: The mass fraction of MgO in the dead-burned magnesia is 92% to 97%, and the particle size of the dead-burned magnesia is 250 meshes to 425 meshes.

5. The magnesium phosphate inorganic glue according to any one of claims 1 to 3, characterized in that: The potassium dihydrogen phosphate has a purity of more than 95% and a particle size of 32-40 meshes.

6. The magnesium phosphate inorganic glue according to any one of claims 1 to 3, characterized in that: The purity of the borax is analytical grade, with a purity of more than 99%.

7. The magnesium phosphate inorganic glue according to claim 1, characterized in that: The potassium hydroxide, barium hydroxide octahydrate and calcium chloride hexahydrate are of chemically pure grade, with a purity of more than 98%.

8. The method for preparing the magnesium phosphate inorganic glue according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Mix weighed calcium chloride hexahydrate, potassium hydroxide, and an organic acid metal chelating agent, and pour into weighed water to obtain a mixed solution; S2. Pour the mixed solution described in S1, dead-burned magnesium oxide, borax, and barium hydroxide octahydrate into a stirring bucket and mix and stir for 2-5 minutes; S3. Add potassium dihydrogen phosphate to the mixture obtained in S2, and stir for 2 to 5 minutes until the slurry is uniform, thereby obtaining magnesium phosphate inorganic glue.

9. Use of the magnesium phosphate inorganic adhesive according to any one of claims 1 to 7 in reinforcing concrete structures with carbon fiber cloth or in reinforcing concrete structures with long process connection time.

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