Rapidly forming geopolymer repair material in low-cold climate and preparation method thereof

Abstract

The present invention discloses a geopolymer repair material that can be quickly formed in a low-cold climate and a preparation method thereof. The raw materials of the geopolymer repair material that can be quickly formed in a low-cold climate include: coal slag and a compound activator; wherein, the compound activator is composed of the following components by weight percentage: 30% to 60% calcium oxide, 20% to 50% calcium hydroxide, and 5% to 30% aluminum phosphate. The present invention chemically activates the coal slag. In a multi-calcium system, calcium oxide and calcium hydroxide act as initiating factors for the chemical reaction, which can provide a favorable environment for the chemical reaction. By using aluminum phosphate and calcium hydroxide as regulating agents, the heat release rate of the slurry can be effectively controlled to prevent premature hardening, swelling, and cracking due to instantaneous heat release. The repair material prepared by the present invention can adapt to engineering applications in low-cold climate areas, has high early compressive strength, and good frost resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of repair materials, and in particular to a geopolymer repair material capable of rapid molding in cold climates and a preparation method thereof. Background Art

[0002] Geopolymers are amorphous, three-dimensional aluminosilicate cementitious materials primarily composed of Si-O and Al-O tetrahedra. They are synthesized by obtaining aluminosilicates from materials such as industrial waste, calcined clay, and natural minerals, and then activating them with an alkaline activator. Compared to traditional cement, geopolymers are considered one of the best alternatives to cement due to their lower CO2 emissions and energy consumption, as well as their sustainable raw material sourcing. However, most geopolymers require a certain temperature for curing. Formation and performance are difficult in low-temperature environments, significantly limiting their application. Current geopolymer preparation techniques typically utilize high-temperature and room-temperature curing to ensure rapid early strength gains. For example, Chinese Patent CN202211698448.6 requires a curing temperature of 55-65°C, while Chinese Patent CN202310527147.5 requires room-temperature curing. The lack of sufficient temperatures significantly limits the strength gains of geopolymers in cold environments.

[0003] Coal ash refers to the waste residue left after coal is burned in industrial coal-fired boilers. The resource utilization of coal ash has become a hot topic of research in recent years. Coal ash contains significant amounts of silicon and aluminum components, which react with alkali to form cementitious materials. However, the silicon and aluminum components in coal ash are primarily present in the lattice structure of quartz, mullite, and other materials. These stable components result in extremely low reactivity, resulting in poor strength of the resulting geopolymers. This significantly limits the large-scale utilization of coal ash in the building materials industry. In order to improve the strength of geopolymer cementitious materials based on coal slag, Chinese patents CN202110974024.7 and CN202110974810.7 both use a compound alkali activator system composed of sodium hydroxide, calcium oxide, sodium carbonate and / or sodium bicarbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, and sodium silicate, and combine it with high-temperature roasting at 450-650°C. However, the alkali activators used in these two patents have complex compositions and high energy consumption, and are not suitable for cold environments; Chinese patent CN202210737429.3 uses a compound activator composed of calcium oxide and phosphoric acid. Although the activator composition is simplified, this patent requires curing at a temperature of 40-80°C and is not suitable for the preparation of geopolymers in low-cold climates.

[0004] As infrastructure construction continues, some buildings and water conservancy projects are located in cold mountainous or plateau areas, where seasonal and diurnal temperature differences are significant. Therefore, it is of great significance to systematically conduct research on the application of geopolymers in low-cold areas. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and propose a geopolymer repair material that can be quickly formed in a low-cold climate and a preparation method thereof, so as to solve the technical problem in the prior art that the strength improvement of geopolymers in low-cold environments is greatly limited due to the lack of sufficient temperature.

[0006] In a first aspect, the present invention provides a geopolymer repair material that can be quickly formed in a low-cold climate. The raw materials thereof include: coal slag and a compound activator; wherein, the compound activator is composed of the following components by weight percentage: 30% to 60% calcium oxide, 20% to 50% calcium hydroxide, and 5% to 30% aluminum phosphate.

[0007] In a second aspect, the present invention provides a method for preparing a geopolymer repair material that can be rapidly formed in a cold climate, comprising the following steps:

[0008] Preparation of chemical agents: Mix calcium oxide, calcium hydroxide and aluminum phosphate in proportion to obtain a compound activator;

[0009] Mixing raw materials: Evenly mix the coal slag and the compound activator to obtain a mixture;

[0010] Mechanical activation: Grind the mixture to obtain precursor powder;

[0011] Prepare slurry: Mix the precursor powder and water evenly to obtain slurry;

[0012] Molding and curing: The clean slurry is shaped and cured to obtain a solidified geopolymer repair material.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention chemically excites the coal slag. In a multi-calcium system, calcium oxide and calcium hydroxide serve as initiators of the chemical reaction and provide a favorable environment for the chemical reaction. The use of aluminum phosphate and calcium hydroxide as regulating agents can effectively control the heat release rate of the slurry and prevent premature hardening, swelling and cracking due to instantaneous heat release. Both aluminum phosphate and calcium hydroxide can inhibit the exothermic reaction of calcium oxide to generate calcium hydroxide, and the added calcium hydroxide can also act as an exciter to promote the geopolymerization reaction in the early stage, preventing the hydration reaction of calcium oxide from being restricted and affecting the geopolymerization reaction. This synergistic excitation of multiple components enriches the number and types of gel phases, inhibits the negative effects of calcification, and ensures a continuous supply of reaction heat. The present invention has the characteristics of simplicity, safety, low cost, low energy consumption, high solid waste utilization rate, environmental friendliness and strong adaptability; the repair material prepared by the present invention can adapt to engineering applications in low-cold climate areas, has high early compressive strength and good frost resistance. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0016] Those skilled in the art know that calcium oxide or sodium hydroxide can release a large amount of heat when in contact with water. However, during the experiment, the inventors found that the heat of the geopolymer reaction stimulated by traditional sodium hydroxide cannot be regulated, and long-term reaction in a low-cold environment cannot be achieved, and it does not have the potential for application in low-cold areas; at the same time, if only calcium oxide or sodium hydroxide is used as an activator, the heat will be released in large quantities in an instant, causing negative effects such as swelling and cracking, and it is impossible to prepare geopolymers with excellent performance in a low-cold climate. It can be seen that the necessary condition for using low-activity solid waste as the raw material of geopolymers and enabling the useful active silicon-aluminum components to dissolve in a low-cold environment is to provide continuous and sufficient reaction heat, but a large amount of heat release will lead to problems such as uncontrolled early hydration rate and cracking, making the selection of the activator a key difficulty.

[0017] Aluminum phosphate has a retarding effect, but this comes at the expense of inhibiting the rate of geopolymerization. This means that the retarding effect of aluminum phosphate will indiscriminately affect the entire geopolymerization reaction. This contradicts the design principle of the present invention, which is to slow down the exothermic reaction and accelerate the geopolymerization reaction. The present invention not only strengthens the inhibition of calcium oxide hydration through the combined inhibition of aluminum phosphate and calcium hydroxide, allowing for a slow release of heat, but also, through the auxiliary stimulation effect of calcium hydroxide, allows calcium oxide to provide calcium ions and an alkaline environment to ensure the progress of the geopolymerization reaction, even under the premise of being jointly inhibited by calcium hydroxide and aluminum phosphate, thus minimizing its negative impact on the geopolymerization reaction.

[0018] Based on this, the present invention is proposed.

[0019] In a first aspect, the present invention provides a geopolymer repair material that can be quickly formed in a low-cold climate. The raw materials thereof include: coal slag and a compound activator A; wherein, by weight percentage, the compound activator A is composed of the following components: 30% to 60% calcium oxide, 20% to 50% calcium hydroxide, and 5% to 30% aluminum phosphate.

[0020] The functions of the components of the chemical agent used in the present invention in the system are as follows:

[0021] Calcium oxide: Calcium oxide releases heat during the geopolymer hydration process. This heat not only promotes the reaction but also ensures the supply of reaction heat required in cold climates. At the same time, calcium hydroxide formed by the reaction of calcium oxide with water makes the aqueous solution alkaline when dissolved, which can accelerate the dissolution of active silicon and aluminum components in coal slag. Calcium hydroxide also has certain gelling properties, adding more useful chemical components and structural components to improve the overall strength. The introduction of calcium ions can generate hydration products (CSH or C-(A)-SH gel), which rapidly increases the early strength. At the same time, calcium ions provide nucleation sites for the formation of geopolymer reaction products with higher polymerization degree (NASH gel), which further improves the early strength, frost resistance, water absorption, corrosion resistance and other properties of the geopolymer.

[0022] Calcium hydroxide: During the calcium activation process, calcium hydroxide is a major hydration product, which promotes the early strength development of geopolymers. It is also the primary product of the exothermic reaction of calcium oxide. Adding calcium hydroxide can inhibit the exothermic reaction. Furthermore, calcium hydroxide combines with active silica and aluminum components during the geopolymerization reaction, gradually consuming it. This allows the exothermic reaction to continue, replenishing new calcium hydroxide and heat, ensuring stable geopolymerization in cold climates. This ensures a continuous heat flow, rather than instantaneous heat loss. Furthermore, calcium hydroxide can replace calcium oxide depending on ambient temperature, preventing negative effects such as expansion and cracking in geopolymers caused by excessive heat. Calcium hydroxide is a strong alkaline substance, which promotes the reactions of other minerals, affecting their chemical properties and performance, and accelerating the early strength development of geopolymers. During the early stages of geopolymer hardening, calcium hydroxide chemically reacts with minerals and water to form hardening products, enhancing the strength of geopolymer mortars. An appropriate pH value can also influence the activity of other additives and components in the mortar.

[0023] Aluminum phosphate: The introduction of a large amount of calcium source significantly reduces the workability of the slurry, leading to uncontrolled hydration rate of the CSH gel and the formation of numerous inclusions that hinder the subsequent geopolymerization reaction. Aluminum phosphate acts as a regulator of the geopolymerization reaction, slowing the solidification rate and preventing premature hardening, swelling, and cracking. Furthermore, aluminum phosphate effectively mitigates rapid heat loss in low-temperature environments, ensuring a continuous supply of heat required for the geopolymerization reaction. This is primarily due to aluminum phosphate inhibiting the formation of calcium hydroxide, allowing the exothermic reaction of calcium oxide to continue. The hydrolysis of aluminum phosphate renders the solution alkaline, creating a favorable environment for the dissolution of soluble silicon and aluminum components. Under the action of aluminum phosphate, the aluminosilicate precursor can also be polymerized to form a Si-Al-P gel, which can also polymerize with the calcium source in the components to form a more complex gel phase. Aluminum phosphate can be used as a regulator of the water absorption properties of geopolymers, adjusting their absorption rate, amount, and water retention. This further improves the rate of heat release from calcium oxide's absorption, preventing the drawbacks of localized overheating and rapid heat generation and loss to the environment. Furthermore, the addition of aluminum phosphate enhances the stability and durability of geopolymer gels. Aluminum phosphate interacts with the polymer chains in the geopolymer, forming a cross-linked structure that strengthens the gel's structural stability and prevents dehydration or decomposition. The introduction of phosphate groups gives geopolymers a smoother, denser gel structure, low blooming, and low dielectric loss, significantly improving the application performance of the cementitious material.

[0024] In some specific embodiments of the present invention, the main chemical components of the coal slag are: CO2 loss on ignition of 4wt% to 10wt%, SiO2 content of 43wt% to 64wt%, Al2O3 content of 20wt% to 40wt%, Fe2O3 content of 2wt% to 6wt%, and CaO content of 1wt% to 3wt%; the initial particle size of the coal slag is 5 mesh or less.

[0025] In the present invention, the mass ratio of calcium oxide to calcium hydroxide in the compound activator A is 1:(0.4-1.5). In this process, the mass ratio of calcium oxide to calcium hydroxide can be adjusted to adapt to cold climates of different temperatures, and the proportion of calcium oxide increases as the ambient temperature decreases.

[0026] In some specific embodiments of the present invention, in the composite activator A, the mass ratio of calcium oxide to calcium hydroxide is 1:(0.6-1).

[0027] In some more specific embodiments of the present invention, the composite activator A is composed of the following components by weight: 40% to 50% calcium oxide, 30% to 40% calcium hydroxide, and 10% to 20% aluminum phosphate.

[0028] In the present invention, the mass ratio of the coal slag to the compound activator A is (2.5-4.5):1.

[0029] In some specific embodiments of the present invention, the mass ratio of the coal ash to the compound activator A is (3-4):1.

[0030] In the present invention, the raw materials of the geopolymer repair material that can be quickly formed in cold climates further include: water.

[0031] In some specific embodiments of the present invention, the liquid-to-solid ratio of water to the total mass of the coal ash and the composite activator A is 0.28-0.41 mL:1 g, preferably 0.30-0.35 mL:1 g.

[0032] In the present invention, the low-cold climate referred to includes not only the ambient temperature, but also the temperature of the medium in the environment, that is, it is also applicable to the corresponding low-temperature water medium.

[0033] In some specific embodiments of the present invention, the water medium and the curing temperature are not lower than 0°C to avoid water solidification, more specifically 5-15°C.

[0034] In a second aspect, the present invention provides a method for preparing a geopolymer repair material that can be rapidly formed in a cold climate, comprising the following steps:

[0035] S1. Prepare chemical agents: Mix calcium oxide, calcium hydroxide, and aluminum phosphate in proportion to obtain compound activator A;

[0036] S2, mixed raw materials: the coal slag and the compound activator A are mixed evenly to obtain a mixture B;

[0037] S3, mechanical activation: grinding the mixture B to obtain a precursor powder;

[0038] S4. Prepare slurry: Mix the precursor powder and water evenly to obtain slurry;

[0039] S5. Forming and curing: The clean slurry is formed and cured to obtain a solidified geopolymer repair material.

[0040] In the present invention, the D90 particle size of the precursor powder is 260 mesh or less.

[0041] In some specific embodiments of the present invention, the grinding time is 4 to 6 minutes.

[0042] In the present invention, the molding method is: pouring the slurry into a mold and vibrating the mold.

[0043] In the present invention, the curing method is: sealing the mold containing the vibration-molded sample, curing for 18 to 24 hours, and then demoulding, and then continuing to seal and cure to a specified age to obtain a solidified geopolymer repair material.

[0044] In some preferred embodiments of the present invention, the prescribed age is 7 to 28 days.

[0045] To avoid redundancy, some of the raw materials involved in the following examples and comparative examples of the present invention are described as follows:

[0046] Coal slag refers to the waste residue left after coal is burned in a coal-fired boiler in the industrial coal-fired boiler industry. Its main chemical components are: CO2 loss on ignition is 6.684wt%, SiO2 content is 53.976wt%, Al2O3 content is 30.310wt%, Fe2O3 content is 4.204wt%, and CaO content is 1.769wt%.

[0047] Example 1

[0048] Example 1 provides a method for preparing a geopolymer repair material that can be rapidly formed in a cold climate, comprising the following steps:

[0049] (1) Preparation of chemical agents: Calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 are mixed evenly at a ratio of m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate) = 3:2:1 to prepare a compound activator A;

[0050] (2) Mixing raw materials: Place coal slag (with an initial particle size of less than 5 mesh) in an oven and bake until the mass no longer changes. After cooling to room temperature, mix the mixture at a ratio of m (coal slag): m (compound activator A) = 3.4:1 to obtain mixed material B;

[0051] (3) Mechanical activation: Mixture B was placed in a vibration mill and ground for 4 min until the D90 particle size was less than 260 mesh to obtain a precursor powder;

[0052] (4) Preparation of slurry: Add 5°C water to the precursor powder and stir evenly to obtain a slurry; wherein the ratio of the volume (mL) of water to the mass (g) of the precursor powder is 0.30;

[0053] (5) Molding and curing: The above-mentioned slurry is poured into a mold and vibrated to obtain a sample. The sample after vibration molding is then sealed with a ziplock bag and cured at a temperature of 5°C for 24 hours before demolding. After demolding, it is continued to be sealed and cured at an ambient temperature of 5°C until the 28th day to obtain a solidified geopolymer repair material.

[0054] Example 2

[0055] Example 2 provides a method for preparing a geopolymer repair material that can be rapidly formed in a cold climate, comprising the following steps:

[0056] (1) Preparation of chemical agents: Calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 are mixed evenly at a ratio of m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate) = 3:2:1 to prepare a compound activator A;

[0057] (2) Mixing raw materials: Place coal slag (with an initial particle size of less than 5 mesh) in an oven and bake until the mass no longer changes. After cooling to room temperature, mix the mixture at a ratio of m (coal slag): m (compound activator A) = 3.6:1 to obtain mixed material B;

[0058] (3) Mechanical activation: Mixture B was placed in a vibration mill and ground for 4 min until the D90 particle size was less than 260 mesh to obtain a precursor powder;

[0059] (4) Preparation of slurry: Add 5°C water to the precursor powder and stir evenly to obtain a slurry; wherein the ratio of the volume (mL) of water to the mass (g) of the precursor powder is 0.34;

[0060] (5) Molding and curing: The above-mentioned slurry is poured into a mold and vibrated to obtain a sample. The sample after vibration molding is then sealed with a ziplock bag and cured at a temperature of 5°C for 24 hours before demolding. After demolding, it is continued to be sealed and cured at an ambient temperature of 5°C until the 28th day to obtain a solidified geopolymer repair material.

[0061] Example 3

[0062] Example 3 provides a method for preparing a geopolymer repair material that can be rapidly formed in a cold climate, comprising the following steps:

[0063] (1) Preparation of chemical agents: Calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 are mixed uniformly at a ratio of m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate) = 2:2:1 to prepare a compound activator A;

[0064] (2) Mixing raw materials: Place coal slag (with an initial particle size of less than 5 mesh) in an oven and bake until the mass no longer changes. After cooling to room temperature, mix the mixture at a ratio of m (coal slag): m (compound activator A) = 3.4:1 to obtain mixed material B;

[0065] (3) Mechanical activation: Mixture B was placed in a vibration mill and ground for 4 min until the D90 particle size was less than 260 mesh to obtain a precursor powder;

[0066] (4) Preparation of slurry: Add 15°C water to the precursor powder and stir evenly to obtain a slurry; wherein the ratio of the volume (mL) of water to the mass (g) of the precursor powder is 0.32;

[0067] (5) Molding and curing: The above-mentioned slurry is poured into a mold and vibrated to obtain a sample. The sample after vibration molding is then sealed with a ziplock bag and cured at a temperature of 15°C for 24 hours before demolding. After demolding, it is further sealed and cured at an ambient temperature of 15°C until the 28th day to obtain a solidified geopolymer repair material.

[0068] Comparative Example 1

[0069] Compared with Example 1, Comparative Example 1 differs only in that the contents of the components in the compound stimulator A are inconsistent, as follows:

[0070] Preparation of chemical agents: Mix calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 at a ratio of m (calcium oxide): m (calcium hydroxide): m (aluminum phosphate) = 0:2:1 to prepare a compound activator A.

[0071] Comparative Example 2

[0072] Compared with Example 1, Comparative Example 2 differs only in that the contents of the components in the compound stimulator A are inconsistent, as follows:

[0073] Preparation of chemical agents: Mix calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 at a ratio of m (calcium oxide): m (calcium hydroxide): m (aluminum phosphate) = 10:2:1 to prepare compound activator A.

[0074] Comparative Example 3

[0075] Compared with Example 1, Comparative Example 3 differs only in that the contents of the components in the compound stimulator A are inconsistent, as follows:

[0076] Preparation of chemical agents: Mix calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 at a ratio of m (calcium oxide): m (calcium hydroxide): m (aluminum phosphate) = 3:0:1 to prepare a compound activator A.

[0077] Comparative Example 4

[0078] Compared with Example 1, Comparative Example 4 differs only in that the contents of the components in the compound stimulator A are inconsistent, as follows:

[0079] Preparation of chemical agents: Mix calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 at a ratio of m (calcium oxide): m (calcium hydroxide): m (aluminum phosphate) = 3:10:1 to prepare a compound activator A.

[0080] Comparative Example 5

[0081] Compared with Example 1, Comparative Example 5 differs only in that the contents of the components in the compound stimulator A are inconsistent, as follows:

[0082] Preparation of chemical agents: Mix calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 in a ratio of m (calcium oxide): m (calcium hydroxide): m (aluminum phosphate) = 3:2:0 to prepare a compound activator A.

[0083] Comparative Example 6

[0084] Compared with Example 1, Comparative Example 6 differs only in that the contents of the components in the compound stimulator A are inconsistent, as follows:

[0085] Preparation of chemical agents: Mix calcium oxide K1, calcium hydroxide K2, and aluminum phosphate K3 at a ratio of m (calcium oxide): m (calcium hydroxide): m (aluminum phosphate) = 3:2:10 to prepare a compound activator A.

[0086] Comparative Example 7

[0087] Comparative Example 7 is compared with Example 1, except that sodium hydroxide is used in the composite stimulator A instead of the calcium oxide in Example 1, as follows:

[0088] Preparation of chemical agents: Sodium hydroxide K4, calcium hydroxide K2, and aluminum phosphate K3 are uniformly mixed at a ratio of m (sodium hydroxide): m (calcium hydroxide): m (aluminum phosphate) = 3:2:1 to prepare a compound activator A.

[0089] Comparative Example 8

[0090] The difference between Comparative Example 8 and Example 1 is that the distribution ratio of each component in Mixture B is different, as follows:

[0091] Mixed raw materials: Place coal slag (with an initial particle size of less than 5 meshes) in an oven and bake until the mass no longer changes. After cooling to room temperature, mix evenly at a ratio of m (coal slag): m (compound activator A) = 5:1 to obtain mixture B.

[0092] Comparative Example 9

[0093] The difference between Comparative Example 9 and Example 1 is that the distribution ratio of each component in Mixture B is different, as follows:

[0094] Mixed raw materials: Place coal slag (with an initial particle size of less than 5 meshes) in an oven and bake until the mass no longer changes. After cooling to room temperature, mix evenly at a ratio of m (coal slag): m (compound activator A) = 2:1 to obtain mixture B.

[0095] Comparative Example 10

[0096] The only difference between Comparative Example 10 and Example 1 is that the water temperature for preparing the slurry and the ambient temperature for forming and curing are different, as follows:

[0097] Prepare a slurry: Add 35°C water to the precursor powder and stir evenly to obtain a slurry; the ratio of the volume (mL) of water to the mass (g) of the precursor powder is 0.32;

[0098] Molding and curing: Pour the above-mentioned slurry into a mold and vibrate to obtain a sample. Then, seal the vibration-formed sample with a ziplock bag and cure it at 35°C for 24 hours before demolding. After demolding, continue to seal and cure it at an ambient temperature of 35°C until the 28th day to obtain a solidified geopolymer repair material.

[0099] experimental group

[0100] The performance of the geopolymer repair materials obtained in Examples 1 to 3 and Comparative Examples 1 to 10 was tested using the test standards specified in GB 175-2007 General Portland Cement and GB 50164-2011 Concrete Quality Control Standard. The results are shown in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] It can be seen from the data in Table 1 that the methods in Examples 1 to 3 of the present invention can all be used to prepare rapidly formed geopolymer repair materials in low-cold climates. The prepared geopolymer repair materials have good compressive strength and can be suitable for use as building repair materials in low-cold climates.

[0105] Compared with Example 1, the compressive strength of the sample in Comparative Example 1 with compound activator A without calcium oxide decreased significantly. This is because calcium oxide is the main component of the activator. Relying solely on the effects of calcium hydroxide and aluminum phosphate, on the one hand, it cannot provide a sufficient alkaline environment to dissolve the silicon and aluminum components in the coal slag. On the other hand, the lack of calcium oxide leads to insufficient heat supply, making it difficult for hydration to occur in the cold climate. The gel structure that provides strength cannot be formed, and the compressive strength of the material is almost completely lost. The compressive strength of the sample in Comparative Example 2 with compound activator A doped with excessive calcium oxide decreased significantly. This is because although excessive addition of calcium oxide can increase the degree of early geopolymerization reaction, the excessively fast reaction rate and excessive local reaction heat lead to a large number of holes and structural defects in the geopolymer repair material, which significantly reduces the strength of the geopolymer. In the later maintenance under the cold climate, it also shows inadaptability, that is, the holes and cracks in the geopolymer repair material further expand, causing the sample to crack easily.

[0106] Compared with Example 1, the compressive strength of the sample in which the compound stimulator A is not mixed with calcium hydroxide in Comparative Example 3 decreases. Calcium hydroxide itself is a hydration product with certain gelling properties, which can effectively promote the development of the early strength of the geopolymer calcium excitation system. The lack of calcium hydroxide reduces the alkalinity of the reaction environment, reduces the generated hydration products, and thus reduces the compressive strength of the reaction product. At the same time, the lack of calcium hydroxide leads to a weakening of the hydration inhibitory effect of calcium oxide, causing a large amount of heat release and loss. The compressive strength of the sample in which the compound stimulator A is excessively mixed with calcium hydroxide in Comparative Example 4 decreases significantly. Under certain conditions of the introduced calcium ions, excessive addition of calcium hydroxide will cause the relative content of calcium oxide to drop sharply. In the cold climate, there is no continuous heat release of calcium oxide, and various chemical reactions are difficult to proceed, and the performance of the prepared geopolymer is poor.

[0107] Compared with Example 1, the sample of the composite stimulator A in Comparative Example 5 without aluminum phosphate showed obvious cracks during the demolding process, and the results of the strength test also showed that the compressive capacity of the sample was weak. The lack of aluminum phosphate resulted in a lack of regulation of calcium oxide in the early exothermic reaction, and the early hydration reaction was too rapid, resulting in large heat loss. In cold climates, premature hardening easily occurred, causing the geopolymer reaction to terminate prematurely and cracking. At the same time, the lack of aluminum phosphate caused the hydration product to change into CSH gel, lacking a denser gel structure, and its stability was reduced. In Comparative Example 6, the composite stimulator A was excessively mixed with aluminum phosphate, and calcium oxide and calcium hydroxide, as the main stimulating components, were greatly reduced. It was difficult to initiate the geopolymer reaction by relying solely on the salt regulator aluminum phosphate, and thus its compressive strength dropped sharply.

[0108] Compared with Example 1, the composite activator A in Comparative Example 7, which uses sodium hydroxide instead of calcium oxide, exhibits significant frosting. Furthermore, the compressive strength of samples activated by conventional sodium hydroxide in cold climates is significantly insufficient, as the low temperature inhibits the occurrence and continuation of the geopolymerization reaction.

[0109] Compared with Example 1, the ratio of coal slag to compound stimulant A was significantly increased in Comparative Example 8. This resulted in insufficient relative dosage of compound stimulant A, a large amount of coal slag could not be stimulated, the active silica-alumina components could not be dissolved, and the generated gel product was greatly reduced. In Comparative Example 9, the ratio of coal slag to compound stimulant A was significantly reduced. This resulted in a significant reduction in the amount of stimulated coal slag raw material, and the active silica-alumina components that could be formed were significantly insufficient. While the generated gelled product was reduced, the concentration of compound stimulant A was too high, resulting in more defects in the geopolymer, thereby affecting the performance of the geopolymer.

[0110] Compared with Example 1, the water temperature for preparing the slurry and the ambient temperature for molding and curing in Comparative Example 10 were further increased from 5°C to 35°C. The increase in ambient temperature is theoretically more suitable for the geopolymer reaction. However, since the amount of calcium oxide added was not adjusted accordingly, the local temperature was too high, and the sample showed obvious structural defects such as cracking and bulging. As a result, the compressive strength of the prepared geopolymer repair material was significantly reduced.

[0111] Compared with the prior art, the present invention has the following beneficial effects:

[0112] (1) The compound activator A prepared by the present invention can effectively improve the reaction activity, play a complementary role between the components in the geopolymerization reaction, synergistically activate and cooperate with each other, so that the reaction process can be accurately controlled to obtain a more ideal quality and performance of the geopolymer repair material. The alkaline environment after the compound activator A is dissolved is conducive to the dissolution of the active silicon and aluminum components, forming a complex multiphase hydration product. The heat released by the hydration reaction of calcium oxide accelerates the formation of the gel phase in low-cold climates. Aluminum phosphate can prevent the hydration rate from getting out of control, delay heat loss, prevent premature hardening and optimize the gel structure. Calcium hydroxide, while synergistically inhibiting the heat release of calcium oxide hydration with aluminum phosphate, also has the function of providing calcium ions and an alkaline environment, avoiding the geopolymerization reaction being inhibited by aluminum phosphate. At the same time, the optimal compound activator A can be quickly adjusted according to the ambient temperature.

[0113] (2) The present invention can achieve the continuous progress of calcium-stimulated geopolymerization reaction in cold climates by regulating calcium hydroxide and aluminum phosphate as auxiliary activators, effectively delaying heat loss and providing continuous reaction heat, greatly compensating for the difficulty of lack of heat in cold regions and ensuring the progress of chemical reactions. The reaction heat of the compound calcium activator of the present invention lasts for a long time and is more stable. The geopolymer repair material prepared in cold climates also exhibits excellent compressive properties, has a wide range of applications, and is highly controllable.

[0114] (3) The present invention uses coal slag as raw material to prepare geopolymer repair materials, which can effectively and efficiently utilize coal slag as a solid waste on a large scale, reducing waste emissions and dependence on natural resources. It can also reduce the potential harm of coal slag to the environment, solidify harmful substances in the repair material, and reduce the risk of their release to the environment. No calcination or high-temperature curing is required, and environmentally friendly chemical reactions are used instead of traditional physical processes, thereby reducing energy consumption in the preparation process.

[0115] (4) The compressive strength of the repair material prepared by the present invention using coal slag in a low-cold climate reaches the 32.5R grade specified in "GB 175-2007 General Portland Cement", which provides a new idea for the application of geopolymer materials in low-cold climates and broadens the application scenarios of geopolymers as cement substitutes.

[0116] (5) The present invention can be applied to the simple preparation and rapid prototyping of building materials in low-cold climates, and the ratio and dosage of the composite activator can be adjusted according to the ambient temperature to meet industrial requirements, thereby promoting the rapid start-up and continuous progress of the geopolymerization reaction in low-cold climates.

[0117] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A geopolymer repair material that can be quickly formed in cold climates, characterized in that: Ingredients include: Coal slag and a compound activator; wherein, the compound activator is composed of the following components by weight: 30% to 60% calcium oxide, 20% to 50% calcium hydroxide, and 5% to 30% aluminum phosphate; wherein, the mass ratio of the coal slag to the compound activator is (2.5 to 4.5): 1; the curing temperature of the geopolymer repair material is 5 to 15°C.

2. The geopolymer repair material for rapid prototyping in cold climates according to claim 1, characterized in that: The main chemical components of the coal slag are: CO2 loss on ignition of 4wt%~10wt%, SiO2 content of 43wt%~64wt%, Al2O3 content of 20wt%~40wt%, Fe2O3 content of 2wt%~6wt%, and CaO content of 1wt%~3wt%; the initial particle size of the coal slag is 5 mesh or less.

3. The geopolymer repair material for rapid prototyping in cold climates according to claim 1, characterized in that: In the composite activator, the mass ratio of calcium oxide to calcium hydroxide is 1:(0.4-1.5).

4. The geopolymer repair material for rapid prototyping in cold climates according to claim 1, characterized in that: The composite activator is composed of the following components by weight: 40% to 50% calcium oxide, 30% to 40% calcium hydroxide, and 10% to 20% aluminum phosphate.

5. The geopolymer repair material for rapid prototyping in cold climates according to claim 1, characterized in that: The raw materials of the geopolymer repair material that can be quickly formed in a low-cold climate also include: water; and the liquid-to-solid ratio of the water to the total mass of the coal slag and the composite activator is 0.28~0.41 mL: 1 g.

6. The geopolymer repair material for rapid prototyping in cold climates according to claim 5, characterized in that: The temperature of the water is not lower than 0°C.

7. A method for preparing a geopolymer repair material that can be rapidly formed in cold climates as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: Preparation of chemical agents: Mix calcium oxide, calcium hydroxide and aluminum phosphate in proportion to obtain a compound activator; Mixing raw materials: Evenly mix the coal slag and the compound activator to obtain a mixture; Mechanical activation: Grind the mixture to obtain precursor powder; Prepare slurry: Mix the precursor powder and water evenly to obtain slurry; Molding and curing: The clean slurry is shaped and cured to obtain a solidified geopolymer repair material.

8. The method for preparing a geopolymer repair material for rapid prototyping in cold climates according to claim 7, characterized in that: The D90 particle size of the precursor powder is 260 mesh or less.

9. The method for preparing a geopolymer repair material for rapid prototyping in cold climates according to claim 7, wherein: The grinding time is 4 to 6 minutes; the molding method is: pouring the clean slurry into a mold and vibrating the mold; the curing method is: sealing the mold containing the vibration-molded sample, curing it for 18 to 24 hours, then demoulding, and then continuing to seal and cure it to a specified age.

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