Sodium citrate retarding alkali-activated slag geopolymer, preparation method and application thereof

Abstract

This invention discloses a sodium citrate-retarded alkali-activated slag geopolymer, its preparation method, and its application. The preparation includes the following raw materials: 926-1153 parts of cementitious material, 416-448 parts of alkali activator, 280-306 parts of water, and 8-16 parts of sodium citrate. The cementitious material is obtained by mixing and modifying slag and wollastonite in a mass ratio of (7-9):1. The alkali-activated slag geopolymer prepared in this application not only effectively prolongs the setting time but also improves the strength, effectively balancing workability and mechanical properties, thus breaking through the technical bottleneck in the application of alkali-activated slag geopolymers in high-performance building materials. The obtained sodium citrate-retarded alkali-activated slag geopolymer has a setting time of over 15 minutes and a 7-day compressive strength ≥90 MPa. The preparation process is simple, has good application prospects, and can be applied to high-performance building materials.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and more specifically, to a sodium citrate retarder alkali-activated slag geopolymer, its preparation method, and its application. Background Technology

[0002] Alkali-activated geopolymers (Geopolymers) are widely researched and promoted as alternatives to ordinary silicate cement. Materials rich in calcium, silicon, and aluminum can all serve as raw materials (precursors) for preparing geopolymers. Therefore, alkali-activated geopolymers can absorb large amounts of solid waste, exhibiting excellent low-carbon and cost-effectiveness, making them a novel green inorganic cementitious material. Blast furnace slag is a typical high-calcium precursor. In an alkaline silicate-activated system (a mixture of NaOH and Na₂O·nSiO₂), it forms a dense CASH gel with excellent mechanical strength. Furthermore, to meet engineering requirements, the water-cement ratio is often reduced to further enhance the strength of alkali-activated slag geopolymers, enabling them to meet the strength requirements for high-performance building materials (such as the substrate for alkali-activated ultra-high-performance concrete). However, although alkali-activated slag geopolymers have excellent strength, they suffer from rapid setting limitations, which significantly restricts their promotion and application in practical engineering. This problem becomes particularly prominent after reducing the water-cement ratio. Existing technologies use compatible chemical retarders to alleviate the problem of rapid setting, such as lignin-based, sugar-based, and phosphate-based retarders. However, these chemical retarders are generally used in traditional silicate cements and are not very effective in geopolymers. There are even potential heavy metal pollution issues. Furthermore, conventional methods of delaying setting time with retarders are based on consuming calcium ions into other phases, rather than achieving CASH gelation. The use of this type of retarder can negatively impact strength. Finding a balance between workability and mechanical properties in delaying the setting of alkali-activated slag geopolymers is key to promoting the application of this new type of material. Summary of the Invention

[0003] The purpose of this invention is to provide a sodium citrate-retarded alkali-activated slag geopolymer, its preparation method, and its application, in order to solve the problem that the alkali-activated slag geopolymers prepared in the prior art cannot balance the delay in solidification and mechanical properties.

[0004] To achieve the above objectives, the present invention provides a sodium citrate retarded alkali-activated slag geopolymer, which, by weight, comprises the following raw materials: 926 to 1153 parts of cementitious material, 416 to 448 parts of alkali activator, 280 to 306 parts of water, and 8 to 16 parts of sodium citrate.

[0005] The cementitious material is obtained by mixing and modifying slag and wollastonite in a mass ratio of (7-9):1.

[0006] The alkaline activator is Na2O·nSiO2, where the modulus n is the molar ratio of SiO2 to Na2O in the solution, and the modulus n is conventionally selected from 1 to 1.75.

[0007] Furthermore, the amount of sodium citrate used is 0.1% to 2.5% of the mass of the cementitious material.

[0008] Further, the modification process involves: adding slag and wollastonite into a magnetic stirrer, stirring and heating, adding a composite modifier and stirring continuously, filtering, and drying.

[0009] Furthermore, the composite modifier is obtained by mixing sodium stearate and zinc stearate in a mass ratio of (1-5):(1-7).

[0010] Furthermore, the stirring speed is 50 r / min to 150 r / min, the time is 45 min to 60 min, and the temperature is 72℃ to 78℃.

[0011] Furthermore, the continuous stirring time is 20 min to 30 min, and the temperature is 70℃ to 80℃.

[0012] Furthermore, the amount of the composite modifier added is 0.5% to 3% of the mass of the cementitious material.

[0013] In addition, the present invention also provides a method for preparing sodium citrate retarding alkali-activated slag geopolymer, the preparation method comprising the following steps:

[0014] S1. Mix the gelling material and sodium citrate thoroughly and stir evenly for 120s to 180s to obtain a powder mixture;

[0015] S2. Mix the alkaline activator with water and stir thoroughly for 30 to 60 seconds to obtain a clear and transparent solution;

[0016] S3. Pour the transparent and clear solution into the powder mixture and stir thoroughly for 2 to 3 minutes to obtain the sodium citrate retarder alkali-activated slag geopolymer.

[0017] This application also provides an application of sodium citrate retarder alkali-activated slag geopolymer, wherein the application is the use of sodium citrate retarder alkali-activated slag geopolymer as a building material in the construction field, wherein the building material is a raw material and / or a semi-finished material and / or a finished material.

[0018] Compared with existing technologies, its beneficial effects include: modifying slag and wollastonite with sodium stearate and zinc stearate forms coordination bonds on the surface of slag and wollastonite, exhibiting better compatibility and helping to improve the compressive strength of alkali-activated slag geopolymers. The alkali-activated slag geopolymers prepared in this application not only effectively prolong the setting time but also improve the strength of alkali-activated slag geopolymers, effectively balancing workability and mechanical properties, and breaking through the technical bottleneck of the application of alkali-activated slag geopolymers in high-performance building materials. The obtained sodium citrate retarded alkali-activated slag geopolymer has a setting time of more than 15 minutes and a 7-day compressive strength ≥90 MPa. The preparation process is simple, has good application prospects, and can be applied to high-performance building materials. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0022] An embodiment of the present invention provides a sodium citrate retarded alkali-activated slag geopolymer, comprising the following raw materials by weight: 926 to 1153 parts of cementitious material, 416 to 448 parts of alkali activator, 280 to 306 parts of water, and 8 to 16 parts of sodium citrate.

[0023] The cementitious material is obtained by mixing and modifying slag and wollastonite in a mass ratio of (7-9):1. Sodium stearate and zinc stearate are combined to modify slag and wollastonite, forming coordination bonds on the surface of slag and wollastonite, exhibiting better compatibility and helping to improve the compressive strength of alkali-activated slag geopolymer.

[0024] The alkaline activator is Na2O·nSiO2, where the modulus n is the molar ratio of SiO2 to Na2O in the solution, and the modulus n is conventionally selected from 1 to 1.75.

[0025] In one embodiment, the modulus n of the alkali activator is 1.5.

[0026] This application utilizes modified industrial by-products slag and silica fume as the main cementing materials. In an alkaline silicate-activated system (a mixture of NaOH and Na₂O·nSiO₂), the modified slag dissolves to form Ca. 2+ Si 4+ And Al 3+ Sodium citrate can provide three negatively charged carboxylate ions (-C=OO) to the reaction system. - Positively charged substances (such as locally released Ca) 2+ Mg 2+ ) and the carboxyl group of sodium citrate (-C=OO) - The electrostatic interaction between these groups allows for their adsorption on the surface of the modified slag. Carboxylate (-C=OO) groups... - The adsorption of ) will form a molecular film, which can prevent the alkaline silicate-activated modified slag, delay the initial dissolution of the modified slag, and achieve the purpose of slowing down the coagulation of the alkali-activated modified slag.

[0027] During the dissolution process of the modified slag, the modified slag particles act as nucleation sites, and the alkali-activated products mainly form on the surface of the modified slag. However, the product layer acts as a diffusion barrier, inhibiting OH-. - The diffusion into the undissolved modified slag actually inhibits the formation of reaction products. After the addition of sodium citrate, the large amount of citric acid provides a large amount of carboxylate ions (-C=OO). - The modified slag can be attracted by electrostatic forces near or potentially far from its surface, leading to the formation of positively charged dissolved substances (such as Ca) within the modified slag. 2+ Mg 2+ The redistribution of slag particles creates more nucleation sites (not just on the slag surface), effectively filling the pores between the modified slag particles and enhancing the strength of alkali-activated slag geopolymers.

[0028] This invention utilizes the combined effects of sodium citrate's retarding and activating properties, along with modification treatment, to effectively extend the setting time of alkali-activated slag geopolymers and significantly improve their strength, achieving a balance between workability and mechanical properties. This breakthrough overcomes the technical bottleneck in the application of alkali-activated slag geopolymers in high-performance building materials.

[0029] In one embodiment, the amount of sodium citrate used is 0.1% to 2.5% of the mass of the cementitious material. The sodium citrate-retarded alkali-activated slag geopolymer of the present invention requires control of the content of each component. When the content of sodium citrate is moderate, sodium citrate can effectively delay the setting time of the alkali-activated slag geopolymer and effectively improve its compressive strength. When there is too much sodium citrate, although it can significantly prolong the setting time, it has a significant negative impact on the strength of the alkali-activated slag geopolymer.

[0030] In one embodiment, the modification process is as follows: slag and wollastonite are added to a magnetic stirrer, stirred and heated, a composite modifier is added and stirred continuously, filtered, and dried.

[0031] In one embodiment, the sodium citrate retarded alkali-activated slag geopolymer comprises the following raw materials by weight: 1030-1153 parts of cementitious material, 420-448 parts of alkali activator, 285-300 parts of water, and 9-16 parts of sodium citrate.

[0032] In one embodiment, the composite modifier is a mixture of sodium stearate and zinc stearate in a mass ratio of (1-5):(1-7).

[0033] In one embodiment, the stirring speed is 50 r / min to 150 r / min, the time is 45 min to 60 min, and the temperature is 72°C to 78°C.

[0034] In one embodiment, the continuous stirring time is 20 min to 30 min, and the temperature is 70°C to 80°C.

[0035] In one embodiment, the amount of the composite modifier added is 0.5% to 3% of the mass of the cementitious material.

[0036] In one embodiment, the composite modifier is added to an appropriate amount of anhydrous ethanol solvent before being added to a magnetic stirrer.

[0037] In addition, the present invention also provides a method for preparing sodium citrate retarding alkali-activated slag geopolymer, the preparation method comprising the following steps:

[0038] S1. Mix the gelling material and sodium citrate thoroughly and stir evenly for 120s to 180s to obtain a powder mixture;

[0039] S2. Mix the alkaline activator with water and stir thoroughly for 30 to 60 seconds to obtain a clear and transparent solution;

[0040] S3. Pour the transparent and clear solution into the powder mixture and stir thoroughly for 2 to 3 minutes to obtain the sodium citrate retarder alkali-activated slag geopolymer.

[0041] The preparation process of sodium citrate retarder alkali-activated slag geopolymer described in this invention is easy to operate and implement.

[0042] This application also provides an application of sodium citrate retarder alkali-activated slag geopolymer, wherein the application is the use of sodium citrate retarder alkali-activated slag geopolymer as a building material in the construction field, wherein the building material is a raw material and / or a semi-finished material and / or a finished material.

[0043] The alkali-activated slag geopolymer prepared in this application not only effectively prolongs the setting time but also improves the strength of the alkali-activated slag geopolymer, effectively balancing workability and mechanical properties, and breaking through the technical bottleneck of the application of alkali-activated slag geopolymer in high-performance building materials. The obtained sodium citrate retarded alkali-activated slag geopolymer has a setting time of more than 15 minutes and a 7-day compressive strength ≥90 MPa. The preparation process is simple, and it has good application prospects and can be applied to high-performance building materials.

[0044] To further explain this application, the following specific embodiments are provided.

[0045] Examples 1-5:

[0046] Examples 1-5 describe sodium citrate retarder-activated alkali-activated slag geopolymers, comprising the preparation raw materials as described in Table 1;

[0047] A method for preparing sodium citrate-retarded alkali-activated slag geopolymers according to Examples 1-5 includes the following steps:

[0048] S1. Sodium stearate and zinc stearate in a mass ratio of 3:5 are mixed and dissolved in an appropriate amount of anhydrous ethanol to obtain a composite modifier; slag and wollastonite are added to a magnetic stirrer and stirred for 50 minutes at a stirring speed of 80 r / min and a temperature of 72℃; the composite modifier is added and stirred continuously for 30 minutes at 75℃; the mixture is then filtered and dried to obtain a cementitious material.

[0049] S2. Mix the gelling material and sodium citrate thoroughly and stir evenly for 180 seconds to obtain a powder mixture;

[0050] S3. Mix the alkaline activator with water and stir thoroughly for 60 seconds to obtain a transparent and clear solution;

[0051] S4. Pour the transparent and clear solution into the powder mixture and stir thoroughly for 3 minutes to obtain sodium citrate retarder alkali-activated slag geopolymer.

[0052] Table 1: Raw materials (parts by weight) for the preparation of Examples 1-5

[0053]

[0054] Comparative Example 1:

[0055] The difference between Comparative Example 1 and Example 5 is that sodium citrate was not added in Comparative Example 1, that is, the mass ratio of sodium citrate to cementitious material was 0%, while the rest was the same as in Example 5.

[0056] Comparative Examples 2-4:

[0057] The difference between Comparative Examples 2-4 and Example 5 is that the weight ratio of the raw materials used in Comparative Examples 2-4 is different, as shown in Table 2. The other aspects are the same as in Example 5.

[0058] Table 2: Raw materials (parts by weight) for Comparative Examples 2-4

[0059]

[0060] Comparative Examples 5-6:

[0061] The difference between Comparative Examples 5 and 6 and Example 5 lies in the different raw materials used in their preparation, as shown in Table 3. Otherwise, they are the same as Example 5.

[0062] Table 3: Raw materials (parts by weight) for the preparation of Comparative Examples 5-6

[0063]

[0064] Comparative Example 7:

[0065] The difference between Comparative Example 7 and Example 5 is that the slag and wollastonite in Comparative Example 7 were used directly after being mixed without modification treatment, while the rest was the same as in Example 5.

[0066] Comparative Example 8:

[0067] The difference between Comparative Example 8 and Example 5 is that the slag and wollastonite in Comparative Example 8 were mixed and then modified with sodium stearate alone; otherwise, they were the same as in Example 5.

[0068] Comparative Example 9:

[0069] The difference between Comparative Example 9 and Example 5 is that the slag and wollastonite in Comparative Example 8 were mixed and then modified with a single zinc stearate, while the rest was the same as in Example 5.

[0070] The samples obtained in Examples 1 to 5 and the samples obtained in Comparative Examples 1 to 9 were subjected to performance tests. The methods for testing setting time and compressive strength were in accordance with JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar". The test results are shown in Table 4.

[0071] Table 4: Performance Test Results

[0072] sample Initial setting time (min) 7-day compressive strength (MPa) Example 1 15 92.1 Example 2 16 94.2 Example 3 18 96.7 Example 4 20 102.7 Example 5 21 93.1 Comparative Example 1 12 91.8 Comparative Example 2 13 91.5 Comparative Example 3 23 81.5 Comparative Example 4 25 52.6 Comparative Example 5 21 85.4 Comparative Example 6 25 79.9 Comparative Example 7 10 83.6 Comparative Example 8 12 86.4 Comparative Example 9 13 81.9

[0073] The test results above show that the sodium citrate-activated slag geopolymers described in Examples 1-5 have a setting time of over 15 minutes and a compressive strength ≥90 MPa, exhibiting superior performance and potential for application in building materials, making them a potential base material for high-performance building materials. The test results of Example 5 and Comparative Example 1 show that the additional addition of sodium citrate to the alkali-activated slag geopolymer effectively prolongs the setting time and simultaneously improves its strength. The test results of Example 5 and Comparative Examples 2-4 show that when the amount of sodium citrate added is too small, it cannot effectively exert its retarding effect and enhance its compressive strength. Excessive sodium citrate negatively impacts the strength of the alkali-activated slag geopolymer. Sodium citrate can only exert its retarding effect and improve the strength of the alkali-activated slag geopolymer when used in appropriate amounts. Comparing the test results of Example 5 and Comparative Examples 5-6 shows that the addition of barium chloride prolongs the setting time of the alkali-activated slag, negatively affecting its strength. Furthermore, the use of barium chloride poses a potential heavy metal pollution problem and cannot balance the initial setting time and strength. Comparing the test results of Example 5 with those of Comparative Examples 7-9, it can be seen that modifying the slag and wollastonite helps to balance the initial setting time and strength. This invention provides a feasible method for the engineering application of alkali-activated slag in building materials. The combined effect of sodium citrate's retarding and activating properties, along with the modification treatment, effectively extends the setting time of the alkali-activated slag geopolymer and improves its strength, achieving a balance between workability and mechanical properties. This breaks through the technical bottleneck in the application of alkali-activated slag geopolymers in high-performance building materials. The method for preparing sodium citrate-retarded alkali-activated slag geopolymers described in this invention is simple, has good application prospects, and can be applied to building materials.

[0074] The above embodiments should be understood as illustrative only and not as limiting the scope of protection of the present invention. After reading the description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A sodium citrate-retarring alkali-activated slag geopolymer, characterized in that, According to the weight parts, the following raw materials are included: 926 to 1153 parts of cementitious material, 416 to 448 parts of alkali activator, 280 to 306 parts of water, and 8 to 16 parts of sodium citrate. The cementitious material is obtained by mixing and modifying slag and wollastonite in a mass ratio of (7~9):

1. The modification process involves adding slag and wollastonite to a magnetic stirrer, stirring and heating, adding a composite modifier and stirring continuously, filtering, and drying. The composite modifier is obtained by mixing sodium stearate and zinc stearate in a mass ratio of (1~5):(1~7). The amount of the composite modifier added is 0.5%~3% of the mass of the cementitious material. The alkaline activator is Na2O·nSiO2, where the modulus n is the molar ratio of SiO2 to Na2O in the solution, and the modulus n is conventionally selected to be 1~1.

75.

2. The sodium citrate retarder-activated slag geopolymer according to claim 1, characterized in that, The amount of sodium citrate used is 0.1% to 2.5% of the mass of the cementitious material.

3. The sodium citrate retarder-activated alkali-activated slag geopolymer according to claim 2, characterized in that, The stirring speed is 50 r / min to 150 r / min, the time is 45 min to 60 min, and the temperature is 72℃ to 78℃.

4. The sodium citrate retarder-activated slag geopolymer according to claim 2, characterized in that, The continuous stirring time is 20-30 minutes, and the temperature is 70-80℃.

5. A method for preparing sodium citrate-retarded alkali-activated slag geopolymer, characterized in that, The preparation method is used to prepare the sodium citrate retarder-activated slag geopolymer as described in any one of claims 1 to 4, and the preparation method includes the following steps: S1. Mix the gelling material and sodium citrate thoroughly and stir evenly for 120s~180s to obtain a powder mixture; S2. Mix the alkaline activator with water and stir thoroughly for 30-60 seconds to obtain a clear and transparent solution; S3. Pour the transparent and clear solution into the powder mixture and stir thoroughly for 2 to 3 minutes to obtain the sodium citrate retarder alkali-activated slag geopolymer.

6. An application of sodium citrate retarder-activated alkali-activated slag geopolymer, characterized in that, The application is the use of the sodium citrate retarder alkaline activated slag geopolymer as described in claim 1 as a building material in the construction field, wherein the building material is a raw material and / or a semi-finished material and / or a finished material.

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