Geopolymer precursor powders for easy on-site construction, along with their preparation and construction methods.

Abstract

This invention discloses a geopolymer precursor powder suitable for on-site construction, along with its preparation and application methods. The preparation method for this geopolymer precursor powder includes the following steps: uniformly mixing granite powder, fly ash, and solid alkali, followed by high-temperature calcination to obtain activated powder; uniformly mixing the activated powder with blast furnace slag to obtain the geopolymer precursor powder suitable for on-site construction. This invention enhances the reactivity of granite powder through thermo-chemical activation, enabling it to participate in the geopolymerization reaction. Then, in conjunction with fly ash and blast furnace slag, a "cement-like" geopolymer cementitious material is prepared. During use, only water needs to be added to the geopolymer precursor powder to prepare a geopolymer cementitious material with high early strength at room temperature. This technology solves the problems of low granite powder utilization, slow room-temperature curing, and difficulties in on-site geopolymer construction found in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, specifically to a geopolymer precursor powder that is easy to use for on-site construction, as well as its preparation and construction methods. Background Technology

[0002] Granite powder refers to the powdery waste generated during the cutting and polishing of stone. Statistics show that approximately 0.6 tons of granite powder are produced for every ton of granite slabs produced. Generally, this waste is either landfilled or directly dumped into the ecosystem. This improper disposal method poses a significant environmental hazard. When granite powder mixes with water, it forms colloidal waste, leading to soil compaction and groundwater pollution. Furthermore, granite powder typically consists of numerous fine particles; long-term inhalation can cause respiratory illnesses such as bronchitis and asthma. Fly ash is one of the solid residues composed of fine particles discharged from boilers in coal-fired power plants along with flue gas. Based on its calcium oxide content, fly ash can be classified into Class C fly ash and Class F fly ash. Class F fly ash has a lower calcium content, with the total content of SiO2, Al2O3, and Fe2O3 exceeding 70 wt%. In addition to Si, Al, Fe, and Ca, fly ash also contains many heavy metal elements, including lead, cadmium, mercury, and chromium. Therefore, fly ash is considered a hazardous substance; improper handling not only increases land occupation but also deteriorates the environment and ecology. Blast furnace slag is a byproduct of iron and steel smelting, mainly composed of CaO, SiO2, Al2O3, and MgO. Blast furnace slag contains heavy metals and harmful substances such as lead, cadmium, and chromium; large-scale stockpiling of it not only excessively occupies land resources but also pollutes the environment.

[0003] Geopolymers are inorganic cementitious materials with a three-dimensional network structure formed by bridging silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. Compared with binders made from silicate cement, geopolymer cementitious materials can be designed with superior properties, namely better acid resistance, sulfate resistance, heat resistance, lower drying shrinkage and creep, and higher strength. Therefore, they are considered an ideal alternative to silicate cement and have broad application prospects. In addition, geopolymers have excellent heavy metal sealing properties and can effectively seal heavy metal ions in fly ash and blast furnace slag. Although granite powder is rich in silicon and aluminum components and is a potential raw material for preparing geopolymers, its silicon and aluminum components are mainly present in highly crystalline inert mineral phases such as quartz and feldspar, making it difficult for them to participate in the geopolymerization process. In cementitious materials, they are usually added as fine aggregates, generally accounting for only 10% to 20% of the cementitious material, which greatly limits the large-scale disposal and utilization of granite powder. Furthermore, geopolymers are typically prepared by mixing aluminosilicate raw materials with strong alkaline solutions, which presents numerous problems during on-site construction. For example, the corrosive and viscous strong alkaline solutions used are difficult to handle and store, posing a serious threat to operator and environmental safety. Operators also need to precisely control the raw material ratios and alkali content to avoid "blooming" in the geopolymer. In addition, geopolymers typically cure slowly at room temperature, and achieving high early strength often requires a high-temperature pre-curing process, limiting their application scenarios. Therefore, researchers have attempted to add chemical agents such as CaO or Ca(OH)2 during geopolymer preparation to improve early strength. However, these analytical-grade chemicals release a large amount of heat when dissolved in water, leading to excessively rapid slurry solidification and the formation of numerous undesirable pores within the geopolymer, severely restricting further improvement in strength. These drawbacks limit the large-scale industrial application of geopolymer cementitious materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and to propose a geopolymer precursor powder, preparation method and construction method that are easy to construct on site, thereby solving the technical problems of low utilization rate of granite powder, slow room temperature curing and difficult on-site construction in the preparation of geopolymers in the prior art.

[0005] In a first aspect, the present invention provides a method for preparing geopolymer precursor powder that is convenient for on-site construction, comprising the following steps:

[0006] Thermo-chemical activation: Granite powder, fly ash and solid alkali are mixed evenly and then calcined at high temperature to obtain activated powder;

[0007] Preparation of geopolymer precursor powder: The activated powder and blast furnace slag are mixed evenly to obtain geopolymer precursor powder that is easy to construct on site.

[0008] Secondly, the present invention provides a geopolymer precursor powder that is easy to apply in the field, which is obtained by the preparation method of the geopolymer precursor powder that is easy to apply in the field mentioned in the first aspect of the present invention.

[0009] Thirdly, the present invention provides a method for constructing geopolymer precursor powder that is convenient for on-site construction, comprising the following steps:

[0010] The above-mentioned geopolymer precursor powder was mixed with water to obtain a slurry;

[0011] The slurry is injected into the mold, and after molding, it is pre-cured at room temperature and then demolded. It is then cured at room temperature until the specified age.

[0012] Fourthly, the present invention provides a geopolymer cementitious material that is easy to construct on-site, which is obtained by the construction method of geopolymer precursor powder that is easy to construct on-site provided in the third aspect of the present invention.

[0013] Compared with the prior art, the beneficial effects of the present invention include:

[0014] This invention enhances the reactivity of granite powder through thermo-chemical activation, enabling it to participate in geopolymerization. Then, in conjunction with fly ash and blast furnace slag, a "cement-like" geopolymer cementitious material is prepared. During use, only water needs to be added to the geopolymer precursor powder to prepare a geopolymer cementitious material with high early strength at room temperature. This technology solves the problems of low granite powder utilization, slow room temperature curing, and difficulties in on-site geopolymer construction found in existing technologies. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] In a first aspect, the present invention provides a method for preparing geopolymer precursor powder that is convenient for on-site construction, comprising the following steps:

[0017] Thermo-chemical activation: Granite powder, fly ash and solid alkali are mixed evenly and then calcined at high temperature to obtain activated powder;

[0018] Preparation of geopolymer precursor powder: The activated powder and blast furnace slag are mixed evenly to obtain geopolymer precursor powder that is easy to construct on site.

[0019] In this invention, the purpose of thermo-chemical activation of granite powder and fly ash is to enhance the reactivity of the raw materials. Although granite powder is rich in silicon and aluminum, these components mostly exist in the form of mineral phases such as quartz, albite, and orthoclase. These mineral phases are well-crystallized, have stable crystal structures, and react slowly with alkaline solutions, thus exhibiting extremely low reactivity. Granite powder is usually added as fine aggregate in cementitious materials, but the amount added is extremely low, which severely limits its large-scale use in cementitious materials. Granite powder is a "high-silicon, low-aluminum" industrial solid waste. During geopolymerization, a suitable Si / Al ratio can enable the geopolymer to form a more stable three-dimensional network gel. Fly ash, as an auxiliary cementitious material, can not only provide aluminum components and adjust the silicon-aluminum ratio in the precursor powder to a suitable range, enabling the geopolymer to form a stable three-dimensional network structure, but also exert a "water-reducing effect," reducing the liquid-solid ratio of the slurry, making the microstructure of the geopolymer more compact, thereby enhancing the mechanical properties of the geopolymer. Thermochemical activation refers to the high-temperature roasting of granite powder, fly ash, and solid alkali together. At high temperatures, the highly crystalline mineral phases such as quartz, feldspar, and mullite in the granite powder and fly ash react with sodium hydroxide particles to form a large amount of soluble silicates, thereby enhancing the reactivity of the raw materials. Traditional geopolymers are prepared by mixing silica-alumina raw materials with an alkaline solution, requiring on-site preparation of a strongly alkaline solution, which is inconvenient for operators. Thermochemical activation not only enhances the reactivity of the raw materials but also enables the integrated preparation of geopolymer precursor powders. During use, only an appropriate amount of water needs to be added to the precursor powder to prepare the geopolymer, greatly facilitating on-site construction. The reaction mechanism of geopolymers can be attributed to the dissolution of soluble silicates in the precursor powder in water, releasing a large amount of active silicon, aluminum components, and OH-. - Then, under alkaline conditions, silicon and aluminum monomers undergo polymerization and condensation reactions to form a three-dimensional network gel.

[0020] Although thermo-chemical activation significantly increases the content of soluble silicon and aluminum components in granite powder and fly ash, the main gel phase of geopolymer cementitious materials prepared from these two solid wastes is NASH gel, which cures slowly at room temperature. Therefore, geopolymers typically require a high-temperature pre-curing process, which severely limits their application range. Researchers have found that incorporating chemical agents such as CaO or Ca(OH)2 during geopolymer preparation can significantly improve the early strength of geopolymers. Ca in the geopolymer reaction... 2+The incorporation of these reagents induces the formation of calcium-rich hydration products, which exhibit rapid precipitation rates and provide nucleation sites for the precipitation of other hydration products, thus accelerating the solidification rate of the slurry and achieving room-temperature curing of the geopolymer. However, these analytically pure reagents rapidly absorb water and release a large amount of heat during use, leading to excessively rapid solidification of the slurry and the formation of more undesirable pores, severely limiting further improvement in the strength of the geopolymer. Furthermore, the large-scale incorporation of these reagents can disrupt the three-dimensional network structure of the geopolymer gel (NASH gel) because Ca... 2+ Than Na + and K + It is more reactive and will preferentially react with Si-O-Si or [SiO4]. 4- The reaction forms CSH gel. Blast furnace slag, as another auxiliary cementitious material, has the following advantages: First, the calcium in blast furnace slag exists in the form of compounds, which, when dissolved in water with analytical grade CaO and Ca(OH)2, rapidly release heat and simultaneously ionize to produce Ca... 2+ Unlike other materials, high-alumina slag contains Ca. 2+ The release of calcium is a process of slow dissolution of calcium-containing compounds in an alkaline environment, with low heat of hydration. Furthermore, blast furnace slag contains a high content of Al2O3, which plays a crucial role in the polymerization reaction. 3+ It will replace some of the Si in CSH gel 4+ The formation of C-(A)-SH gel is induced, thereby delaying the formation rate of CSH gel and avoiding the destruction of the three-dimensional structure of NASH gel by the excessive formation of CSH gel. Secondly, blast furnace slag contains a high concentration of Mg, which is crucial for the polymerization process. 2+ Will be like Al 3+ Same as replacing Si 4+ To promote the formation of the NA(M)-SH gel phase, the interweaving of multiple gel phases makes the microstructure of the geopolymer more compact, which macroscopically manifests as a significant enhancement of the mechanical properties of the geopolymer.

[0021] In this invention, the main chemical components of the granite powder are as follows (by mass percentage): SiO2 50%–75%, Al2O3 10%–20%, Fe2O3 0.5%–3%, and CaO 0%–3%; furthermore, the median particle size of the granite powder is 5–20 μm.

[0022] In this invention, the fly ash is Class F fly ash, and the main chemical components by mass percentage are: SiO2 30%–55%, Al2O3 20%–30%, Fe2O3 3%–6%, CaO 3%–6%, SO3 0.5%–3%; furthermore, the median particle size of the fly ash is 5–20 μm.

[0023] In this invention, the main chemical components of blast furnace slag by mass percentage are: CaO 35%–40%, Al2O3 15%–20%, and MgO 8%–15%; furthermore, the median particle size of the blast furnace slag is 5–20 μm.

[0024] In this invention, the mass ratio of granite powder to fly ash in the activated powder is (1.5-4):1, more preferably (2-3):1, and even more preferably (2-2.5):1; the solid alkali accounts for 15%-35% of the total mass of fly ash and granite powder, more preferably 20%-30%, and even more preferably 25%-30%.

[0025] In this invention, the mass ratio of activated powder to blast furnace slag in the geopolymer precursor powder is (0.5-9):1, further (1-3):1, and even further 1.5:1.

[0026] In some specific embodiments of the present invention, the solid alkali is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0027] In this invention, a muffle furnace is used for high-temperature calcination, with a calcination temperature of 550–750°C, further 650–750°C, and even further 700°C; and a calcination time of 0.5–2 hours, further 1–1.5 hours, and even further 1.5 hours.

[0028] In this invention, a vibratory grinder is used to grind the raw materials to make them uniform.

[0029] In some specific embodiments of the present invention, the rotation speed of the vibratory grinder is 600 to 1500 rpm, and the grinding time is 0.5 to 6 minutes.

[0030] In some more specific embodiments of the invention, the rotational speed of the vibratory grinder is 800 revolutions per minute.

[0031] Secondly, the present invention provides a geopolymer precursor powder that is easy to apply in the field, which is obtained by the preparation method of the geopolymer precursor powder that is easy to apply in the field mentioned in the first aspect of the present invention.

[0032] Thirdly, the present invention provides a method for constructing geopolymer precursor powder that is convenient for on-site construction, comprising the following steps:

[0033] The above-mentioned geopolymer precursor powder was mixed with water to obtain a slurry;

[0034] The slurry is injected into the mold, and after molding, it is pre-cured at room temperature and then demolded. It is then cured at room temperature until the specified age.

[0035] It should be noted that the curing temperature of this invention includes, but is not limited to, room temperature. Those skilled in the art can appropriately increase the curing temperature during the geopolymer curing process. The advantage of this invention over other existing precursor powders is that it can obtain geopolymer cementitious materials with high early strength and high late strength even when cured at room temperature.

[0036] In this invention, the liquid-to-solid ratio of the slurry is (0.25-0.35) mL / g, and more specifically 0.275 mL / g.

[0037] In this invention, the sealing and pre-curing time at room temperature is 12 to 36 hours, and more specifically 24 hours.

[0038] This invention does not limit the curing time; those skilled in the art can choose according to the actual situation, such as 3 days, 7 days, 28 days, etc.

[0039] Fourthly, the present invention provides a geopolymer cementitious material that is easy to construct on-site, which is obtained by the construction method of geopolymer precursor powder that is easy to construct on-site provided in the third aspect of the present invention.

[0040] To avoid redundancy, some of the raw materials used in the following embodiments and comparative examples of this invention are summarized as follows:

[0041] The median particle size of the granite powder is 10.51 μm, and the main chemical components by mass percentage are: SiO2 70.01%, Al2O3 16.32%, Fe2O3 1.78%, and CaO 1.27%.

[0042] The fly ash is classified as Class F fly ash, with a median particle size of 15.83 μm. Its main chemical components by mass percentage are: SiO2 50.47%, Al2O3 27.54%, Fe2O3 4.83%, CaO 3.45%, and SO3 0.65%.

[0043] The median particle size of blast furnace slag is 11.49 μm, and the main chemical components by mass percentage are: CaO 39.06%, Al2O3 16.22%, and MgO 9.08%.

[0044] Example 1

[0045] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 15 parts sodium hydroxide.

[0046] (2) Preparation of geopolymer precursor powder: The activated powder and blast furnace slag were ground in a vibrating mill for 30 seconds to obtain the precursor powder. The components of the precursor powder were proportioned by weight (total 100 parts): 70 parts of activated powder and 30 parts of blast furnace slag.

[0047] (3) Molding and curing: The above precursor powder is mixed with water to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration molding is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0048] In this embodiment, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days are 12.20 MPa and 24.45 MPa, respectively.

[0049] Example 2

[0050] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 20 parts sodium hydroxide.

[0051] (2) Preparation of geopolymer precursor powder: The activated powder and blast furnace slag were ground in a vibrating mill for 30 seconds to obtain the precursor powder. The components of the precursor powder were proportioned by weight (total 100 parts): 70 parts of activated powder and 30 parts of blast furnace slag.

[0052] (3) Molding and curing: The above precursor powder is mixed with water to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration molding is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0053] In this embodiment, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days are 29.95 MPa and 49.25 MPa, respectively.

[0054] Example 3

[0055] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 30 parts sodium hydroxide.

[0056] (2) Preparation of geopolymer precursor powder: The activated powder and blast furnace slag were ground in a vibrating mill for 30 seconds to obtain the precursor powder. The components of the precursor powder were proportioned by weight (total 100 parts): 70 parts of activated powder and 30 parts of blast furnace slag.

[0057] (3) Molding and curing: The above precursor powder is mixed with water to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration molding is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0058] In this embodiment, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days are 45.40 MPa and 53.10 MPa, respectively.

[0059] Example 4

[0060] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 30 parts sodium hydroxide.

[0061] (2) Preparation of geopolymer precursor powder: The activated powder and blast furnace slag were ground in a vibrating mill for 30 seconds to obtain the precursor powder. The components of the precursor powder were proportioned by weight (total 100 parts): 60 parts of activated powder and 40 parts of blast furnace slag.

[0062] (3) Molding and curing: The above precursor powder is mixed with water to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration molding is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0063] In this embodiment, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days are 53.45 MPa and 68.50 MPa, respectively.

[0064] As shown in Examples 1-3, the mechanical properties of the geopolymer significantly improved with the increase of alkali dosage from 15% to 30%, with a 3-day compressive strength increase of 33.20 MPa and a 28-day compressive strength increase of 28.65 MPa. During the thermo-chemical activation process, increasing the alkali dosage accelerates the dissolution of inert mineral phases such as quartz, feldspar, and mullite in granite powder and fly ash, increasing the content of active silicon and aluminum components in the activated powder. This allows for the formation of more gel products during the geopolymerization reaction, enhancing the mechanical properties of the geopolymer. Furthermore, as shown in Examples 3-4, the compressive strength of the geopolymer significantly improved with the increase of blast furnace slag dosage from 30 parts to 40 parts. After incorporating blast furnace slag, various calcium-rich hydration products, such as CASH gel and CSH gel, are formed in the geopolymer. These calcium-rich hydration products have a fast precipitation rate and can provide nucleation sites for other hydration products, accelerating the hardening of the slurry. At this point, the main gel phase of the geopolymer is a C(N)-ASH gel formed by the interweaving of calcium-rich hydration products and NASH gel. Therefore, after incorporating blast furnace slag, it can be observed that the curing time of the slurry is shortened and the microstructure of the geopolymer is more compact, which is beneficial to enhancing the mechanical properties of the geopolymer.

[0065] Comparative Example 1

[0066] In Comparative Example 1, the geopolymer precursor powder did not contain blast furnace slag, and all other conditions were the same as in Example 1, including the following steps:

[0067] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 15 parts sodium hydroxide.

[0068] (2) Preparation of geopolymer precursor powder: The activated powder was further ground in a vibratory mill for 30 seconds to obtain the precursor powder;

[0069] (3) Molding and curing: The above precursor powder is mixed with water to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration molding is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0070] In this comparative example, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days were 0.50 MPa and 11.45 MPa, respectively.

[0071] As shown in Comparative Example 1, the geopolymer prepared from the precursor powder without blast furnace slag exhibits extremely poor mechanical properties. Because it lacks blast furnace slag, the geopolymer's strength is solely provided by the NASH gel. However, NASH gel cures slowly at room temperature, making it difficult to provide high early strength to the geopolymer without increasing the curing temperature during the early curing stage. Furthermore, due to the absence of blast furnace slag in the precursor powder, the system has an excessively high alkali content, leading to excess Na+ during the geopolymer curing process. + It will gradually migrate to the surface of the geopolymer and react with CO2 in the air to form Na2CO3, thus deteriorating the microstructure of the geopolymer.

[0072] Comparative Example 2

[0073] In Comparative Example 2, the granite powder and fly ash were not thermally-chemically activated, and all other conditions were the same as in Example 2, including the following steps:

[0074] (1) Preparation of geopolymer precursor powder: Granite powder, fly ash and blast furnace slag were ground in a vibratory mill for 180 seconds to obtain precursor powder. The precursor powder components were proportioned by weight (100 parts in total): 46.224 parts granite powder, 19.812 parts fly ash and 33.964 parts blast furnace slag.

[0075] (2) Preparation of alkaline activator: Sodium hydroxide particles are dissolved in water to prepare an alkaline activator, wherein the mass ratio of sodium hydroxide particles to precursor powder is 0.132;

[0076] (3) Molding and curing: The above precursor powder and alkali activator are stirred evenly to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0077] In this comparative example, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days were 9.70 MPa and 22.45 MPa, respectively.

[0078] As shown in Comparative Example 2, when granite powder and fly ash are not thermo-chemically activated, the geopolymer exhibits poor mechanical properties, with compressive strength decreasing by 20.25 MPa and 26.80 MPa at 3 days and 28 days, respectively. Granite powder is mainly composed of inert mineral phases such as quartz, albite, and orthoclase. These mineral phases react slowly with alkali activators, making it difficult for them to participate in the geopolymerization reaction. In cementitious materials, they are only incorporated as fine aggregates. In this case, the strength of the geopolymer is mainly provided by the gel formed by fly ash and blast furnace slag under alkaline conditions, which greatly restricts the mechanical properties of the geopolymer.

[0079] Comparative Example 3

[0080] The activated powder in Comparative Example 3 did not contain fly ash, and all other conditions were the same as in Example 4, including the following steps:

[0081] (1) Thermo-chemical activation: Granite powder and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain mixed powder. Then, the mixed powder is placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratio: 100 parts granite powder and 30 parts sodium hydroxide.

[0082] (2) Preparation of geopolymer precursor powder: The activated powder and blast furnace slag were ground in a vibrating mill for 30 seconds to obtain the precursor powder. The precursor powder components were proportioned by weight (total 100 parts): 60 parts of activated powder and 40 parts of blast furnace slag.

[0083] (3) Molding and curing: The above precursor powder is mixed with water to obtain a slurry with a liquid-to-solid ratio of 0.275 mL / g. The slurry is then injected into a mold and vibrated to form the slurry. The mold after vibration molding is sealed in a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and cured at room temperature until the specified age.

[0084] In this comparative example, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days were 25.80 MPa and 34.50 MPa, respectively.

[0085] Comparative Example 3 shows that when the precursor powder does not contain fly ash, the compressive strength of the geopolymer at 3 days and 28 days decreased by 27.65 MPa and 34.00 MPa, respectively. Granite powder is a "high-silicon, low-alumina" industrial solid waste. Because it lacks fly ash, the precursor powder lacks an active aluminum source. During geopolymerization, the Ca released from the dissolution of blast furnace slag... 2+ It will quickly react with [SiO4] in the system. 4- The formation of a large amount of CSH gel has two main consequences. First, it results in a single type of gel in the cementitious material system. Second, the large amount of CSH formation leads to rapid solidification of the slurry, resulting in many undesirable pores inside the cementitious material.

[0086] Comparative Examples 4-5

[0087] Comparative Examples 4 and 5 only changed the amount of blast furnace slag in the precursor powder; all other conditions were the same as in Examples 1 and 4, respectively.

[0088] Comparative Example 4

[0089] In Comparative Example 4, the components of the precursor powder were proportioned by weight (total 100 parts): 50 parts activated powder, 50 parts blast furnace slag, and the remaining conditions were the same as in Example 1.

[0090] In this comparative example, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days were 11.05 MPa and 20.30 MPa, respectively.

[0091] Comparative Example 5

[0092] In Comparative Example 5, the components of the precursor powder were proportioned by weight (total 100 parts): 50 parts activated powder, 50 parts blast furnace slag, and the remaining conditions were the same as in Example 4.

[0093] In this comparative example, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days were 57.10 MPa and 58.05 MPa, respectively.

[0094] Comparative Examples 4 and 5 show that adding excessive blast furnace slag deteriorates the mechanical properties of the geopolymer. In the geopolymerization reaction, silicon and aluminum monomers undergo polymerization and condensation reactions to form a three-dimensional gel. Due to the presence of Ca... 2+ Than Na + and K + More reactive, it will preferentially interact with [SiO4]. 4- and [AlO4] 5- The combination forms CSH or CASH gels, thus introducing excess Ca into the polymer. 2+ Excessive blast furnace slag will hinder the formation of NASH gel. NASH gel typically possesses superior properties; therefore, when the blast furnace slag content is too high, the main gel phase in the geopolymer will transform into CSH gel, which is detrimental to improving its compressive strength. On the other hand, the excessive formation of CSH gel will lead to excessively rapid solidification of the cementitious material, resulting in numerous undesirable pores within. Therefore, adding excessive blast furnace slag will reduce the compressive strength of the geopolymer.

[0095] Comparative Examples 6-7

[0096] In Comparative Examples 6 and 7, analytically pure calcium oxide with the same calcium content as in Examples 1 and 4 was used to replace blast furnace slag to prepare geopolymer precursor powders.

[0097] Comparative Example 6

[0098] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 15 parts sodium hydroxide.

[0099] (2) Preparation of geopolymer precursor powder: The activated powder and calcium oxide were ground in a vibratory mill for 30 seconds to obtain the precursor powder. The precursor powder components were proportioned by weight (100 parts in total): 85.66 parts of activated powder and 14.34 parts of calcium oxide.

[0100] (3) Molding and curing: After the above precursor powder is mixed with water evenly, a slurry is obtained. At the original liquid-to-solid ratio (0.275 mL / g), the slurry solidifies too quickly and is difficult to cast. Therefore, in order to ensure the fluidity of the slurry, the liquid-to-solid ratio is adjusted to 0.35 mL / g. Then, the slurry is injected into the mold and vibrated to form the slurry. After vibration molding, the mold is sealed with a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and sealed at room temperature for curing until the specified age.

[0101] In this embodiment, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days are 11.35 MPa and 16.85 MPa, respectively.

[0102] Comparative Example 7

[0103] (1) Thermo-chemical activation: Granite powder, fly ash and sodium hydroxide particles are ground in a vibratory mill for 30 seconds to obtain a mixed powder. The mixed powder is then placed in a muffle furnace and calcined at 700°C for 1.5 hours to obtain sintered powder. After cooling, the sintered powder is ground in a vibratory mill for 150 seconds to obtain activated powder. The components in the activated powder are in the following weight ratios: 70 parts granite powder, 30 parts fly ash and 30 parts sodium hydroxide.

[0104] (2) Preparation of geopolymer precursor powder: The activated powder and calcium oxide were ground in a vibratory mill for 30 seconds to obtain the precursor powder. The components of the precursor powder were proportioned by weight (100 parts in total): 79.34 parts of activated powder and 20.66 parts of calcium oxide.

[0105] (3) Molding and curing: After the above precursor powder is mixed with water evenly, a slurry is obtained. At the original liquid-solid ratio (0.275mL / g), the slurry solidifies too quickly and is difficult to cast. Therefore, in order to ensure the fluidity of the slurry, the liquid-solid ratio is adjusted to 0.4mL / g. Then, the slurry is injected into the mold and vibrated to form the slurry. After vibration molding, the mold is sealed with a self-sealing sample bag and cured at room temperature for 24 hours. Finally, after demolding, the sample block is placed in a self-sealing bag and sealed at room temperature for curing until the specified age.

[0106] In this embodiment, the compressive strength values ​​of the geopolymer cementitious material at 3 days and 28 days are 32.45 MPa and 44.58 MPa, respectively.

[0107] Comparative Examples 6 and 7 show that when analytical grade calcium oxide with the same calcium content was used to replace blast furnace slag in the preparation of geopolymers, the strength of the geopolymers decreased to varying degrees. This is attributed to the following reasons: First, analytical grade calcium oxide releases a large amount of heat when dissolved in water, causing the slurry to solidify too quickly at the original liquid-to-solid ratio, making it difficult to cast. Therefore, it is often necessary to increase the liquid-to-solid ratio to ensure the fluidity of the slurry. However, at a high liquid-to-solid ratio, a large number of undesirable pores will form inside the geopolymer, which will limit the improvement of the geopolymer's strength. Second, Ca... 2+ Than Na + and K + It is more reactive and will preferentially bind with free [SiO4] in the slurry. 4- The combination forms a large amount of CSH gel, thereby inhibiting the formation of NASH gel; thirdly, blast furnace slag also contains a high content of Al2O3 and MgO, which can induce the formation of hydration products such as C-(A)-SH and hydrotalcite during the geopolymer reaction. Therefore, geopolymers prepared with blast furnace slag as an auxiliary cementing material can obtain higher strength.

[0108] To better demonstrate the effectiveness of this application, the performance of the cementitious materials obtained from the embodiments and comparative examples of this invention is summarized in Table 1.

[0109] Table 1

[0110]

[0111]

[0112] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0113] (1) Granite powder is mainly composed of inert mineral phases such as quartz and feldspar, which have low reactivity and are difficult to participate in geopolymerization reaction. This invention can accelerate the dissolution of inert mineral phases in granite powder through thermo-chemical activation, increase its active silicon and aluminum content, thereby achieving efficient activation of inert solid waste. Moreover, the geopolymer precursor powder prepared by this technology can be hardened by adding water when used, avoiding the need for operators to prepare strong alkaline solutions on site, which greatly facilitates on-site construction.

[0114] (2) The present invention selects fly ash and blast furnace slag as auxiliary cementing materials to achieve efficient synergistic utilization of the three solid wastes:

[0115] Fly ash: Fly ash contains a large amount of active aluminum components, while granite powder is a high-silicon, low-alumina industrial solid waste. By adding fly ash, the silicon-aluminum ratio of the precursor powder can be adjusted to a suitable range, allowing the geopolymer to form a more stable three-dimensional network gel (NASH). In addition, fly ash contains a large amount of glass microspheres, which, when added as an admixture, can improve the fluidity of the slurry, reduce the liquid-solid ratio of the cementitious material, and thus densify the microstructure of the geopolymer.

[0116] Blast furnace slag: Blast furnace slag contains abundant amorphous calcium compounds. Under alkaline conditions, these calcium compounds gradually dissolve and release Ca. 2+ Subsequently Ca 2+ It can provide nucleation sites for hydration products, thereby accelerating slurry hardening to achieve room temperature curing of cementitious materials, and Ca 2+ It will react with [SiO4] in the system. 4- and [AlO4] 5- The combination of these elements forms CSH or C-(A)-SH gels, thus enriching the gel phase of the geopolymer. Furthermore, blast furnace slag contains a high concentration of Mg, which contributes to the geopolymerization process. 2+ Will be like Al 3+ Same as replacing Si 4+ To promote the formation of the NA(M)-SH gel phase, the interweaving of multiple gel phases is beneficial to enhancing the strength of the geopolymer.

[0117] (3) The geopolymer cementitious material prepared by the present invention can be cured at room temperature and has the advantage of high early strength. Under optimal conditions, the compressive strength of the geopolymer prepared can reach the standard of 62.5R silicate cement in GB 175-2007 "General Silicate Cement". It can be applied to the emergency repair and maintenance of roads and airports and the construction of water conservancy projects.

[0118] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing geopolymer precursor powder that is convenient for on-site construction, characterized in that, Includes the following steps: Thermo-chemical activation: Granite powder, fly ash and solid alkali are mixed evenly and then calcined at high temperature to obtain activated powder; Preparation of geopolymer precursor powder: The activated powder and blast furnace slag are mixed evenly to obtain geopolymer precursor powder that is easy to carry out on site; In the activated powder, the mass ratio of granite powder to fly ash is (2~3):1, and the solid alkali accounts for 20%~30% of the total mass of fly ash and granite powder; in the geopolymer precursor powder, the mass ratio of activated powder to blast furnace slag is (1~3):

1. The solid alkali is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. The main chemical components of the granite powder, by mass percentage, are: SiO2 50%~75%, Al2O3 10%~20%, Fe2O3 0.5%~3%, CaO 0%~3%; the fly ash is Class F fly ash, with the main chemical components by mass percentage: SiO2 30%~55%, Al2O3 20%~30%, Fe2O3 3%~6%, CaO 3%~6%, SO3 0.5%~3%; the blast furnace slag, by mass percentage, has the main chemical components by mass percentage: CaO 35%~40%, Al2O3 15%~20%, MgO 8%~15%. The high-temperature calcination temperature is 550~750°C, and the high-temperature calcination time is 0.5~2 hours; The raw materials are mixed evenly by using a vibratory grinder; the speed of the vibratory grinder is 600~1500 rpm, and the grinding time is 0.5~6 minutes.

2. A geopolymer precursor powder that is easy to apply on-site, characterized in that, The geopolymer precursor powder that is easy to apply in the field is obtained by the preparation method of the geopolymer precursor powder that is easy to apply in the field as described in claim 1.

3. A construction method for geopolymer precursor powder as described in claim 2, characterized in that, Includes the following steps: The geopolymer precursor powder was mixed evenly with water to obtain a slurry; The slurry is injected into a mold, and after molding, it is pre-cured at room temperature in a sealed environment before demolding. It is then further cured at room temperature in a sealed environment until the specified age is reached. The liquid-to-solid ratio of the slurry is (0.25~0.35) mL / g.

4. A geopolymer cementitious material that is easy to apply on-site, characterized in that, The geopolymer cementitious material is obtained by the construction method of geopolymer precursor powder that facilitates on-site construction as described in claim 3.

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