A rapid hardening geopolymer based on low temperature crystallization and a method of making the same

Abstract

The application relates to a rapid hardening geopolymer based on low-temperature crystallization and a preparation method thereof. The technical scheme is as follows: a mixed solution is obtained by mixing sodium metasilicate and water in a molar ratio of 1:(11-13); the mixed solution is stirred until it is clear, and then the clear mixed solution is cooled to 5-15 DEG C to obtain an alkali activator. A geopolymer gel mixture is obtained by mixing the alkali activator and metakaolin in a mass ratio of sodium metasilicate to metakaolin of 1:(1.80-2.32) and stirring for 1-2 min. The geopolymer gel mixture is placed in a mold, and final setting, demolding and initial product are carried out, and then the initial product is cured at 5-30 DEG C for 2-7 days to obtain the rapid hardening geopolymer based on low-temperature crystallization. The application has the characteristics of rapid forming, early compressive strength and conservation of curing cost, can realize rapid and continuous production, and has a good application prospect in the production of geopolymer prefabricated parts and 3D printing of geopolymer.

Description

Technical Field

[0001] This invention belongs to the field of geopolymer technology. Specifically, it relates to a rapidly curing geopolymer based on low-temperature crystallization and its preparation method. Background Technology

[0002] Geopolymers are three-dimensional network polymeric gels formed by the alkaline activation of silicon-aluminum-rich raw materials, followed by "depolymerization, recombination, condensation, and hardening," resulting in silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra linked by bridging oxygen. They possess excellent properties such as simple processing, high durability, good acid resistance, and high-temperature resistance. Therefore, the development and research of geopolymers have attracted the attention of those skilled in the art.

[0003] The patented technology "A rapidly hardening geopolymer at room temperature and its preparation method" (CN105621911A) uses an alkaline activator consisting of a mixture of sodium hydroxide, water glass, and water. Metakaolin is added to the alkaline activator in steps and mixed and stirred to obtain the geopolymer. The preparation process of this technology involves multiple additions and a long stirring time.

[0004] The patented technology "A rapid-hardening high-strength fly ash geopolymer material and its preparation method" (CN113416025A) involves mixing fly ash with blast furnace slag, then mixing and stirring with an alkali activator, a nano-reinforcing agent, and water to obtain a geopolymer slurry. The preparation process requires shaking for 2-5 minutes, standing for 30-60 minutes, drying in a curing chamber at 60-75℃ for 24-48 hours, and then continuing standard curing. The process requires step-by-step mixing and stirring, high-temperature curing, and a long molding time.

[0005] Wu Hao (Wu Hao. Microstructure and Properties of Geopolymers Based on Metakaolin [D]. Harbin: Northeast Forestry University, 2023.) Alkaolin activated by alkali was thoroughly mixed and stirred to obtain a geopolymer gel. After molding, the gel was placed in a 60℃ oven for 6 hours, then cured at 25℃ for 3 days before demolding. After another 7 days of standard curing, the compressive strength was 22.79 MPa. This process involved slow hardening of the geopolymer gel, requiring high-temperature curing and a long demolding time.

[0006] In summary, geopolymers cannot be rapidly hardened and molded in their gel state, with molding times typically exceeding 6 hours. They also lack early mechanical properties and require methods such as high-temperature autoclaving for curing. Summary of the Invention

[0007] The present invention aims to overcome the defects of the prior art and provides a method for preparing a rapid curing geopolymer based on low-temperature crystallization. This method can cure rapidly, has a short molding time, and low maintenance cost. The prepared rapid curing geopolymer based on low-temperature crystallization has early compressive strength.

[0008] To achieve the above objectives, the specific steps of the technical solution adopted by the present invention are as follows:

[0009] Step 1: Mix sodium metasilicate and water at a molar ratio of 1:(11-13) to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 5-15°C to obtain an alkali activator.

[0010] Step 2: Mix the alkali activator and the metakaolin in a ratio of sodium metasilicate to metakaolin of 1:(1.80-2.32) to obtain a mixture; stir the mixture for 1-2 minutes to obtain a geopolymer gel mixture.

[0011] Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold, and obtain the initial product. Then, cure the initial product at 5-30°C to obtain a rapidly curing geopolymer based on low-temperature crystallization.

[0012] The sodium metasilicate contains 44–47 wt% SiO2.

[0013] The cooling rate is 0.5–3.0 °C / min.

[0014] The metakaolin clay has a SiO2 content of 45–60 wt% and an Al2O3 content of 30–50 wt%.

[0015] The stirring speed in step one is 150-600 r / min; the stirring speed in step two is 1600-2200 r / min.

[0016] The final setting time is 4–15 minutes.

[0017] The curing period is 2 to 7 days.

[0018] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0019] 1. This invention uses low-temperature cooling of the alkali activator to suppress the rapid initial reaction between the alkali activator and the raw materials. After mixing with metakaolin, the low-temperature environment and the crystallization tendency provided by metakaolin facilitate the rapid formation of hydrated crystals (such as Na2SiO3·9H2O, Na2SiO3·8H2O) that encapsulate the metakaolin. The hydrated crystals spontaneously engulf each other and grow rapidly, migrating close to the grain boundaries, reducing interfacial energy and ultimately forming a stable morphology. This achieves rapid hardening of the initial product and provides a certain early compressive strength. According to GB / T 50081 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", the compressive strength of the initial product is 1.76~3.21MPa, and no high-temperature or autoclaving is required.

[0020] 2. The final setting time of this invention is 4–15 min, which significantly shortens the initial setting time of the rapid-curing geopolymer based on low-temperature crystallization compared to conventionally prepared geopolymers. Under the same conditions of metakaolin and alkali activator dosage, tests were conducted according to GB / T 1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". The final setting time of the rapid-curing geopolymer based on low-temperature crystallization was 15 min, which is 335 min shorter than the test results of conventionally prepared geopolymers.

[0021] 3. In this invention, the alkali activator and metakaolin are well dispersed during the stirring process, and the crystallized sodium silicate can continue to undergo geopolymerization with metakaolin at room temperature. The initial product is cured at 5-30℃ for 2-7 days to obtain geopolymer. According to GB / T50081 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", its compressive strength after curing is 18.49-39.08 MPa. The compressive strength results, phase and chemical structure are basically consistent with those of the rapid hardening geopolymer based on low-temperature crystallization prepared under the same proportion and different curing conditions for 2-7 days in the prior art.

[0022] Therefore, this invention features rapid molding, early compressive strength, and cost-saving maintenance, enabling rapid continuous production and showing promising application prospects in the production of geopolymer preforms and geopolymer 3D printing. Attached Figure Description

[0023] Figure 1 This is a graph showing the initial product solidification time test results of a rapidly curing geopolymer based on low-temperature crystallization according to the present invention.

[0024] Figure 2 yes Figure 1 The image shown is a photograph of an early product of a rapidly curing geopolymer based on low-temperature crystallization. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but this is not intended to limit the scope of protection thereof:

[0026] A rapidly curing geopolymer based on low-temperature crystallization and its preparation method. The preparation method of this specific embodiment is as follows:

[0027] Step 1: Mix sodium metasilicate and water at a molar ratio of 1:(11-13) to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 5-15°C to obtain an alkali activator.

[0028] Step 2: Mix the alkali activator and the metakaolin in a ratio of sodium metasilicate to metakaolin of 1:(1.80-2.32) to obtain a mixture; stir the mixture for 1-2 minutes to obtain a geopolymer gel mixture.

[0029] Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold, and obtain the initial product. Then, cure the initial product at 5-30°C to obtain a rapidly curing geopolymer based on low-temperature crystallization.

[0030] The sodium metasilicate contains 44–47 wt% SiO2.

[0031] The cooling rate is 0.5–3.0 °C / min.

[0032] The metakaolin clay has a SiO2 content of 45–60 wt% and an Al2O3 content of 30–50 wt%.

[0033] The stirring speed in step one is 150-600 r / min; the stirring speed in step two is 1600-2200 r / min.

[0034] The final setting time is 4–15 minutes.

[0035] The curing period is 2 to 7 days.

[0036] Example 1

[0037] A rapidly curing geopolymer based on low-temperature crystallization and its preparation method. The specific steps of the method described in this embodiment are as follows:

[0038] Step 1: Mix sodium metasilicate and water at a molar ratio of 1:11 to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 5°C to obtain an alkali activator.

[0039] Step 2: Mix the alkali activator and the metakaolin in a mass ratio of sodium metasilicate to metakaolin of 1:1.80 to obtain a mixture; stir the mixture for 2 minutes to obtain a geopolymer gel mixture.

[0040] Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold it to obtain an initial product, and then cure the initial product at 25°C to obtain a rapidly curing geopolymer based on low-temperature crystallization.

[0041] The sodium metasilicate contains 47 wt% SiO2.

[0042] The cooling rate is 0.5℃ / min.

[0043] The metakaolin clay has a SiO2 content of 55 wt% and an Al2O3 content of 35 wt%.

[0044] The stirring speed in step one is 600 r / min; the stirring speed in step two is 2200 r / min.

[0045] The final setting time is 15 minutes.

[0046] The maintenance period is 7 days.

[0047] According to the test results of this embodiment, the initial compressive strength of the product was 2.66 MPa; the compressive strength after curing was 39.08 MPa.

[0048] Example 2

[0049] A rapidly curing geopolymer based on low-temperature crystallization and its preparation method. The specific steps of the method described in this embodiment are as follows:

[0050] Step 1: Mix sodium metasilicate and water at a molar ratio of 1:11.8 to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 12°C to obtain an alkali activator.

[0051] Step 2: Mix the alkali activator and the metakaolin in a ratio of sodium metasilicate to metakaolin of 1:1.98 to obtain a mixture; stir the mixture for 1.7 min to obtain a geopolymer gel mixture.

[0052] Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold, and obtain the initial product. Then, cure the initial product at 30°C to obtain a rapidly hardening geopolymer based on low-temperature crystallization.

[0053] The sodium metasilicate contains 46 wt% SiO2.

[0054] The cooling rate is 3.0℃ / min.

[0055] The metakaolin clay has a SiO2 content of 60 wt% and an Al2O3 content of 30 wt%.

[0056] The stirring speed in step one is 450 r / min; the stirring speed in step two is 2000 r / min.

[0057] The final setting time is 12 minutes.

[0058] The maintenance period is 5 days.

[0059] According to the test results of this embodiment, the initial compressive strength of the product was 3.12 MPa; the compressive strength after curing was 31.46 MPa.

[0060] Example 3

[0061] A rapidly curing geopolymer based on low-temperature crystallization and its preparation method. The specific steps of the method described in this embodiment are as follows:

[0062] Step 1: Mix sodium metasilicate and water at a molar ratio of 1:12.5 to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 8°C to obtain an alkali activator.

[0063] Step 2: Mix the alkali activator and the metakaolin in a ratio of sodium metasilicate to metakaolin of 1:2.15 to obtain a mixture; stir the mixture for 1.4 min to obtain a geopolymer gel mixture.

[0064] Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold, and obtain the initial product. Then, cure the initial product at 15°C to obtain a rapidly curing geopolymer based on low-temperature crystallization.

[0065] The sodium metasilicate contains 45 wt% SiO2.

[0066] The cooling rate is 1.0℃ / min.

[0067] The metakaolin clay has a SiO2 content of 50 wt% and an Al2O3 content of 40 wt%.

[0068] The stirring speed in step one is 300 r / min; the stirring speed in step two is 1800 r / min.

[0069] The final setting time is 8 minutes.

[0070] The maintenance period is 3 days.

[0071] In this embodiment, the initial compressive strength of the product was tested to be 2.15 MPa; the compressive strength after curing was 25.23 MPa.

[0072] Example 4

[0073] A rapidly curing geopolymer based on low-temperature crystallization and its preparation method. The specific steps of the method described in this embodiment are as follows:

[0074] Step 1: Mix sodium metasilicate and water at a molar ratio of 1:13 to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 15°C to obtain an alkali activator.

[0075] Step 2: Mix the alkali activator and the metakaolin in a mass ratio of sodium metasilicate to metakaolin of 1:2.32 to obtain a mixture; stir the mixture for 1 minute to obtain a geopolymer gel mixture.

[0076] Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold, and obtain the initial product. Then, cure the initial product at 5°C to obtain a rapidly curing geopolymer based on low-temperature crystallization.

[0077] The sodium metasilicate contains 44 wt% SiO2.

[0078] The cooling rate is 2.0℃ / min.

[0079] The metakaolin clay has a SiO2 content of 45 wt% and an Al2O3 content of 50 wt%.

[0080] The stirring speed in step one is 150 r / min; the stirring speed in step two is 1600 r / min.

[0081] The final setting time is 4 minutes.

[0082] The maintenance period is 2 days.

[0083] According to the test results of this embodiment, the compressive strength of the initial product was 1.76 MPa; the compressive strength after curing was 18.49 MPa.

[0084] This specific implementation method has the following advantages compared with the prior art:

[0085] 1. In this specific embodiment, the alkali activator is cooled at low temperature, which inhibits the rapid initial reaction between the alkali activator and the raw materials. After mixing with metakaolin, due to the low temperature environment and the crystallization tendency provided by metakaolin, the alkali activator is conducive to the rapid generation of hydrated crystals (such as Na2SiO3·9H2O, Na2SiO3·8H2O) that encapsulate metakaolin. The hydrated crystals spontaneously engulf each other and grow rapidly, migrating close to the grain boundaries, which reduces the interfacial energy and eventually forms a stable morphology, achieving rapid hardening of the initial product and giving it a certain early compressive strength. According to GB / T 50081 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", the compressive strength of the initial product is 1.76~3.21MPa, and no high temperature or autoclaving is required.

[0086] 2. The initial product of the rapid curing geopolymer based on low-temperature crystallization prepared in this specific embodiment is shown in the attached figure: Figure 1 The graph shows the initial product solidification time test results of the rapid curing geopolymer based on low-temperature crystallization prepared in Example 1. Figure 2 yes Figure 1 The image shows a photograph of the initial product obtained after demolding at the shown final setting time. From Figure 1 It can be seen that the geopolymer gel mixture had already solidified and formed within 15 minutes of being placed in the mold; from Figure 2 It can be seen that when the final setting time is 15 minutes, the initial product obtained after demolding has hardened and formed. Under the same conditions of metakaolin and alkali activator dosage, according to GB / T 1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", the final setting time of the rapid curing geopolymer based on low-temperature crystallization is 15 minutes, which is 335 minutes shorter than the test results of conventionally prepared geopolymers.

[0087] 3. In this specific embodiment, the alkali activator and metakaolin are well dispersed during the stirring process, and the crystallized sodium silicate can continue to undergo geopolymerization with metakaolin at room temperature. The initial product is cured at 5-30℃ for 2-7 days to obtain geopolymer. According to GB / T50081 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", its compressive strength after curing is 18.49-39.08 MPa. The compressive strength results and phase and chemical structure are basically consistent with those of the rapid hardening geopolymer based on low-temperature crystallization prepared under the same proportion and different curing conditions for 2-7 days in the prior art.

[0088] Therefore, this specific embodiment features rapid molding, early compressive strength, and cost-saving maintenance, enabling rapid continuous production and showing promising application prospects in the production of geopolymer preforms and geopolymer 3D printing.

Claims

1. A method for preparing a rapidly curing geopolymer based on low-temperature crystallization, characterized in that... The specific steps of the preparation method are as follows: Step 1: Mix sodium metasilicate and water at a molar ratio of 1:(11-13) to obtain a mixture; stir the mixture until it becomes clear, and then cool the clear mixture to 5-15°C to obtain an alkali activator. Step 2: Mix the alkali activator and the metakaolin in a ratio of sodium metasilicate to metakaolin of 1:(1.80-2.32) to obtain a mixture; stir the mixture for 1-2 minutes to obtain a geopolymer gel mixture. Step 3: Place the geopolymer gel mixture into a mold, allow it to solidify, demold, and obtain the initial product. Then, cure the initial product at 5-30°C to obtain a rapidly curing geopolymer based on low-temperature crystallization.

2. The method for preparing a rapidly curing geopolymer based on low-temperature crystallization according to claim 1, characterized in that... The sodium metasilicate contains 44–47 wt% SiO2.

3. The method for preparing a rapidly curing geopolymer based on low-temperature crystallization according to claim 1, characterized in that... The cooling rate is 0.5–3.0 °C / min.

4. The method for preparing a rapidly curing geopolymer based on low-temperature crystallization according to claim 1, characterized in that... The metakaolin clay has a SiO2 content of 45–60 wt% and an Al2O3 content of 30–50 wt%.

5. The method for preparing a rapidly curing geopolymer based on low-temperature crystallization according to claim 1, characterized in that... The stirring speed in step one is 150-600 r / min; the stirring speed in step two is 1600-2200 r / min.

6. The method for preparing a rapidly curing geopolymer based on low-temperature crystallization according to claim 1, characterized in that... The final setting time is 4–15 minutes.

7. The method for preparing a rapidly curing geopolymer based on low-temperature crystallization according to claim 1, characterized in that... The curing period is 2 to 7 days.

8. A rapidly curing geopolymer based on low-temperature crystallization, characterized in that... The rapid curing geopolymer based on low-temperature crystallization is a rapid curing geopolymer based on low-temperature crystallization prepared by the preparation method of the rapid curing geopolymer based on low-temperature crystallization according to any one of claims 1 to 7.

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