A metakaolin modified magnesium silicate hydrate cementitious material, preparation and use thereof

Abstract

The application discloses a metakaolin modified hydrated magnesium silicate cementing material and a preparation and application thereof, the cementing material is prepared from active magnesium oxide, metakaolin, silica ash and water, the active magnesium oxide content is 35% to 50% according to the total mass of the cementing material, the metakaolin content is 1% to 10%, the silica ash content is the balance, the Mg / Si molar ratio is 1.0 to 1.3, and the water-binder ratio is 0.4 to 0.6. The application further discloses a preparation method of the cementing material and application of the cementing material in resisting corrosion of erosive ions such as sulfate ions and / or chloride ions. The metakaolin is introduced as an auxiliary silicon source and aluminum source, and is reacted with the active magnesium oxide to generate M-S-H and M-A-S-H composite gel, so that the compressive strength and the erosion resistance of the material are significantly improved, and the material is suitable for erosive environments such as marine engineering and saline soil areas.

Description

Technical Field

[0001] This invention relates to the field of green building materials technology, specifically to a hydrated magnesium silicate (MSH) cementitious material prepared from metakaolin and magnesium oxide as the main raw materials, its preparation method, and the application of the material in a corrosive ionic environment. Background Technology

[0002] MSH cementitious material is a novel low-carbon building material, formed by the hydration reaction of active magnesium oxide and siliceous raw materials (such as silica fume) to create hydrated magnesium silicate gel. This material possesses advantages such as excellent mechanical properties, low carbon emissions, low heat of hydration, and the ability to solidify heavy metals, making it promising for applications in building structures, nuclear waste encapsulation, and heavy metal pollution remediation.

[0003] Silica fume, as a key silicon source in magnesium silicate cementitious materials, possesses extremely high pozzolanic activity. However, the extremely fine particles and high surface energy of silica fume make it prone to agglomeration during use, leading to uneven dispersion in the cementitious system. This, in turn, affects the uniform formation of hydrated magnesium silicate gel, ultimately reducing the material's mechanical properties and durability. Furthermore, the uneven distribution and high price of silica fume resources also limit its large-scale application in magnesium silicate cementitious materials.

[0004] Metakaolin is an amorphous mixture of silica and aluminum oxides produced by calcining kaolin at 600–900℃, exhibiting excellent pozzolanic activity. Compared to silica fume, metakaolin is more widely available and less expensive, and its chemical composition contains active Al₂O₃, which can participate in the reaction during hydration to form hydrated magnesium aluminosilicate (MASH). Existing research shows that introducing metakaolin into hydrated magnesium silicate cement can significantly improve its mechanical properties. For example, one study introduced metakaolin into hydrated magnesium silicate cement and measured its compressive strength. The results showed that when the metakaolin content was less than 10%, it could improve the 28-day compressive strength of hydrated magnesium silicate cement. Specifically, when the metakaolin content was 8%, the 28-day compressive strength of hydrated magnesium silicate cement increased by 60.9%. Other studies have shown that metakaolin exhibits a very strong early strength-enhancing effect, with its 3-day and 7-day compressive strength showing a strong positive correlation with the content. Microscopic analysis showed that Al2O3 in metakaolin participated in the reaction, leading to an increased degree of hydration in the system.

[0005] However, current research on the durability of metakaolin-modified hydrated magnesium silicate cement in corrosive environments is insufficient. In existing technologies, there is a lack of systematic research and data support regarding the strength retention of magnesium silicate cement under sulfate and chloride corrosion environments. This is especially true in marine engineering and saline soil areas rich in SO4. 2⁻In harsh environments containing Cl⁻ ions, the corrosion resistance of cementitious materials is a key indicator determining their service life in engineering applications. Studies have shown that metakaolin's ability to resist composite salt erosion in concrete exhibits an initial strengthening followed by a weakening pattern, with the strongest resistance observed at a metakaolin content of 5%, where the erosion products are mainly gypsum, ettringite, and Friedel salt. Other studies have indicated that under the coupled effects of brine-wet-dry cycles, nano-metakaolin exceeding 2% can significantly reduce the compressive strength loss rate of concrete. However, these studies primarily focus on silicate cement concrete systems, and may not be relevant for metakaolin-magnesium oxide-based hydrated magnesium silicate cementitious materials in SO₄²⁻ environments. 2⁻ Systematic research on Cl⁻ erosion environments is still lacking.

[0006] Therefore, it is necessary to develop a material that combines good mechanical properties with excellent SO4 resistance. 2⁻ Metakaolin-magnesium oxide-based hydrated magnesium silicate cementitious materials with good Cl⁻ corrosion resistance have important engineering application value. Summary of the Invention

[0007] This invention addresses the technical problems of insufficient durability data for existing hydrated magnesium silicate cementitious materials under sulfate and chloride corrosion environments, and the unclear optimal dosage of metakaolin in this system and its influence on corrosion resistance. This invention proposes a technical solution to prepare hydrated magnesium silicate cementitious materials by partially replacing traditional silica fume with metakaolin, while simultaneously using it as an auxiliary silicon and aluminum source, through a hydration reaction with active magnesium oxide. This material significantly improves its resistance to SO42- while maintaining good mechanical strength. 2⁻ Durability in Cl- corrosive environments. To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a metakaolin-modified hydrated magnesium silicate cementitious material, which is prepared from the following raw materials: active magnesium oxide, metakaolin, silica fume and water; Based on the total mass of the cementitious materials, the content of active magnesium oxide is 35%~50%, the content of metakaolin is 1%~10%, and the balance is silica fume; the Mg / Si molar ratio of the cementitious materials is 1.0~1.3, and the water-cement ratio is 0.4~0.6.

[0008] The Mg / Si molar ratio is limited to 1.0~1.3. This ratio range can ensure the formation of stable MSH gel and avoid excessive free MgO and poor system volume stability caused by an excessively high Mg / Si ratio, or insufficient hydration products and slow strength development caused by an excessively low Mg / Si ratio.

[0009] The water-cement ratio is limited to 0.4~0.6. When the water-cement ratio is below 0.4, the viscosity of the slurry is too high and the fluidity is poor, which cannot meet the construction requirements such as pouring. When it is above 0.6, there is too much free water in the system, the porosity increases after hardening, and the mechanical properties and durability of the cementitious material decrease significantly.

[0010] Furthermore, the fineness of the active magnesium oxide is ≤5% on a 200-mesh sieve, and the active MgO content is ≥90%.

[0011] Active magnesium oxide is one of the main sources of strength in the system. Too low a dosage will result in insufficient hydration product formation and slow strength development; too high a dosage will lead to an excess of free MgO, which hydrates to form magnesium hydroxide crystals, causing volume expansion and reducing the system's density. The preferred MgO dosage in this invention is 40%~46.5%.

[0012] Furthermore, metakaolin is obtained by calcining kaolin at 600~900℃, wherein the Al2O3 content is ≥42.89% and the SiO2 content is ≥53.48%.

[0013] This invention uses metakaolin as an auxiliary silicon and aluminum source. The principle is that the active SiO2 and Al2O3 in metakaolin react with magnesium oxide during hydration to generate MSH gel and MASH. The Al in metakaolin... 3+ This can be achieved by replacing the Si in the silicon-oxygen tetrahedron. 4+ Or Mg in magnesium-oxygen octahedron 2+ The inclusion of metakaolin into the MSH structure forms a MASH gel, significantly improving the degree of polymerization and structural density of the product. Simultaneously, the incorporation of metakaolin refines the pore structure of the material, reducing the permeation channels for harmful ions, thereby improving the material's performance in SO42--. 2- and Cl - Durability in corrosive environments.

[0014] Furthermore, the amount of metakaolin added is 5% to 10%.

[0015] Furthermore, the amount of metakaolin added is 8%.

[0016] When the metakaolin content is below 1%, its reinforcing effect of active Al2O3 is not significant, and its improvement effect on mechanical properties and corrosion resistance is not significant. When it exceeds 10%, its dissolution is limited, which not only fails to further improve the strength, but also leads to a loose structure and a significant decrease in workability due to the increase in unreacted metakaolin particles. Therefore, the content is limited to 1%~10%, preferably 5%~10%, and more preferably 8%.

[0017] The second aspect of this invention provides a method for preparing the above-mentioned metakaolin-modified hydrated magnesium silicate cementitious material, comprising the following steps: Metakaolin is calcined at 600-900℃ for 2-4 hours, cooled, ground and sieved to obtain metakaolin. Weigh out the active magnesium oxide, silica fume and metakaolin according to the ratio, mix and stir evenly to obtain a dry powder mixture; Add water to the dry powder mixture and stir well to obtain a cementitious material slurry; The slurry is poured into a mold and cured under conditions of 20±2℃ and relative humidity ≥95%.

[0018] Furthermore, the mixing process is carried out using a planetary mixer at a speed of 40-60 r / min for 3-5 minutes; after adding water, the mixture is first stirred at a low speed of 140±5 r / min for 30-60 seconds, and then stirred at a high speed of 285±10 r / min for 2 minutes.

[0019] Furthermore, the curing process includes: curing in the mold for 24 hours, then removing the mold, and continuing to cure in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% until the specified age, keeping the surface of the specimen moist during the curing period.

[0020] A third aspect of the present invention provides the application of the above-mentioned metakaolin-modified hydrated magnesium silicate cementitious material, which is used to resist the corrosion of building materials by corrosive ions.

[0021] Furthermore, the corrosive ions include sulfate ions and / or chloride ions.

[0022] Compared with the prior art, the present invention has the following beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: 1. Excellent corrosion resistance: The metakaolin-modified hydrated magnesium silicate cementitious material prepared in this invention exhibits excellent corrosion resistance in SO42-. 2- and Cl - After immersion in the solution, the strength retention coefficients can reach over 0.90 and 0.85 respectively, demonstrating excellent resistance to sulfate and chloride corrosion. The mechanism is as follows: Al2O3 in metakaolin participates in the reaction to form MASH gel, which improves the degree of polymerization and structural compactness of the product; at the same time, the incorporation of metakaolin refines the pore structure of the material and reduces the penetration channels of harmful ions.

[0023] 2. High mechanical strength: The 28-day compressive strength of the material of this invention can reach more than 62.4 MPa. Under the optimized formula (8% metakaolin content, Mg / Si=1.0, water-cement ratio 0.5), the 28-day compressive strength is about 38.5% higher than the control sample without metakaolin. At the same time, metakaolin exhibits a very strong early strength enhancement effect.

[0024] 3. Green and low-carbon: Made from metakaolin and magnesium oxide, it avoids the high carbon emissions of traditional silicate cement and is a green and low-carbon building material.

[0025] 4. Wide range of raw material sources: Metakaolin can be obtained by calcining kaolin, and magnesium oxide can be obtained from resources such as magnesite. The raw material sources are abundant and the cost is low, which overcomes the limitations of uneven distribution and high price of silica fume resources. Detailed Implementation

[0026] 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. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] The raw materials involved in the following embodiments and comparative examples of the present invention are as follows: Metakaolin: Used as an auxiliary silicon and aluminum source, it is produced by calcining kaolin at 750℃ for 2 hours, with a specific surface area ≥15m². 2 / g, Al2O3 content ≥42.89%, SiO2 content ≥53.48%.

[0028] Activated magnesium oxide: As a magnesium source, commercially available lightly calcined magnesium oxide powder has a fineness of ≤5% residue on a 200-mesh sieve and an active MgO content of ≥90%.

[0029] Silica Fume: As the main silicon source, commercially available silica fume has a SiO2 content of ≥90%.

[0030] Water: Deionized water is used as the reaction medium to avoid interference from impurity ions in the hydration system.

[0031] In the following embodiments and comparative examples of the present invention, the cementitious material reference system is set as follows: The cementitious material is composed of active magnesium oxide, metakaolin and silica fume. The total mass of the cementitious material is 1000g. The dosage of each component is calculated as a percentage of the total mass of the cementitious material, and the silica fume dosage is the balance. The Mg / Si molar ratio is 1.0~1.3 and the water-cement ratio is 0.4~0.6.

[0032] In the following embodiments and comparative examples of the present invention, the performance testing methods are as follows: Compressive strength test: The test was conducted in accordance with GB / T 17671 "Test method for strength of cement mortar (ISO method)" and the specimen size was 40mm×40mm×40mm.

[0033] Corrosion resistance test: The specimens cured for 28 days were immersed in the following corrosive solutions: 5% Na2SO4 solution and 5% NaCl solution, for immersion periods of 28 days, 56 days and 90 days respectively.

[0034] Calculation of strength retention coefficient: Strength retention coefficient = compressive strength after immersion in erosion solution / compressive strength under standard curing at the same age.

[0035] Example 1: The preparation of the metakaolin-modified hydrated magnesium silicate cementitious material in this example is as follows: Kaolin was calcined at 750℃ for 2 hours, cooled, and then ground through a 200-mesh sieve to obtain metakaolin. With a total mass of 1000g of cementitious materials, 40% active magnesium oxide, 8% metakaolin, and the remainder silica fume, and a Mg / Si molar ratio of 1.0, weigh out 400g of active magnesium oxide, 80g of metakaolin, and 520g of silica fume, add them to a planetary mixer, and dry mix at 40r / min for 3 minutes to obtain a uniform dry powder mixture. Based on a water-cement ratio of 0.5, the water dosage is 500g. Add the water to the dry powder mixture, stir at a low speed of 140±5r / min for 30 seconds, and then stir at a high speed of 285±10r / min for 2 minutes to obtain a uniform cementitious material slurry. The grout was poured into a 40mm×40mm×40mm triple mold and vibrated on a vibrating table for 60 seconds until compacted. The mold was then placed in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 24 hours before demolding. After demolding, the specimens continued to be cured in the standard curing room for 3 days, 7 days, and 28 days. During the curing period, the surface of the specimens was kept moist.

[0036] Example 2 differs from Example 1 only in that the active magnesium oxide content is 40%, the metakaolin content is 2%, and the silica fume content is 58%. The remaining raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0037] Example 3 differs from Example 1 only in that the active magnesium oxide content is 40%, the metakaolin content is 5%, and the silica fume content is 55%. The remaining raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0038] Example 4 differs from Example 1 only in that the active magnesium oxide content is 40%, the metakaolin content is 10%, and the silica fume content is 50%. The remaining raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0039] Example 5 differs from Example 1 only in that the active magnesium oxide content is 46.5%, the silica fume content is 45.5%, the Mg / Si molar ratio is 1.3, and the metakaolin content remains at 8%. All other raw materials, preparation processes, and curing conditions are completely consistent with Example 1.

[0040] Example 6 differs from Example 1 only in that the water-to-gel ratio is 0.4 (i.e., 400g of water). All other raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0041] Example 7 differs from Example 1 only in that the water-to-gel ratio is 0.6 (i.e., 600g of water). All other raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0042] Comparative Example 1: This comparative example does not add metakaolin. It only uses active magnesium oxide and silica fume to prepare hydrated magnesium silicate cementitious material (i.e., pure silica fume system). The active magnesium oxide content is 40%, the silica fume content is 60%, the Mg / Si molar ratio is 1.0, and the water-cement ratio is 0.5. The rest of the preparation process and curing conditions are completely consistent with those of Example 1. Comparative Example 2 differs from Example 1 only in that the active magnesium oxide content is 40%, the metakaolin content is 15%, and the silica fume content is 45%. The remaining raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0043] Comparative Example 3 differs from Example 1 only in that: the active magnesium oxide content is 40%, the metakaolin content is 20%, and the silica fume content is 40%. The remaining raw materials, preparation process, and curing conditions are completely consistent with Example 1.

[0044] For the test examples, the basic mechanical properties of the cementitious material specimens prepared in each embodiment and comparative example were tested. The test method was in accordance with GB / T 17671 "Test Method for Strength of Cement Mortar (ISO Method)". The specimen size was 40mm×40mm×40mm. The test results are shown in Table 1.

[0045] The specimens of each embodiment and the comparative example, after being cured for 28 days, were immersed in 5% Na2SO4 solution and 5% NaCl solution, respectively, for immersion periods of 28 days, 56 days, and 90 days. Their corrosion resistance was evaluated by the strength retention coefficient, which is calculated as: strength retention coefficient = compressive strength after immersion in the corrosion solution / compressive strength after standard curing at the same age. The test results are shown in Table 2.

[0046] Table 1 Summary of basic performance test results for each embodiment and comparative example

[0047] Table 2 Summary of corrosion resistance test results for each embodiment and comparative example

[0048] 1. Performance Analysis: (1) Effect of metakaolin content on performance: As shown in Tables 1 and 2, under the conditions of fixed active magnesium oxide content of 40%, Mg / Si molar ratio of 1.0 and water-cement ratio of 0.5, the mechanical properties and corrosion resistance of the cementitious material showed a trend of first increasing and then decreasing with the increase of metakaolin content.

[0049] Regarding mechanical properties, as shown in Table 1, the 28-day compressive strength of Comparative Example 1 (0% metakaolin content) was 45.1 MPa. When the metakaolin content was 2%, 5%, 8%, and 10%, the 28-day strengths were 45.6 MPa, 53.6 MPa, 62.4 MPa, and 47.2 MPa, respectively, with the peak strength reaching 8%, which was 38.5% higher than that of Comparative Example 1. In Comparative Examples 2 and 3 (with metakaolin content increased to 15% and 20%), the 28-day strengths decreased to 42.3 MPa and 38.7 MPa, respectively, with the latter decreasing by 14.2% compared to Comparative Example 1. The 3-day and 7-day strengths followed the same variation pattern.

[0050] Regarding corrosion resistance, as shown in Table 2, the strength retention coefficients of Comparative Example 1 after 90 days of immersion in sulfate and sodium chloride were 0.84 and 0.77, respectively; when the metakaolin content was 8%, the corresponding retention coefficients were 0.92 and 0.88, respectively, which were 9.5% and 14.3% higher than those of Comparative Example 1. In the range of 5% to 10% metakaolin content, the corrosion resistance was better than that of Comparative Example 1. After the content exceeded 10%, it gradually decreased. When the content was 20%, the sulfate retention coefficient dropped to 0.81, which was lower than that of Comparative Example 1.

[0051] (2) Effect of Mg / Si molar ratio on performance: As shown in Table 1, under the conditions of fixed active magnesium oxide content, metakaolin content of 8%, and water-cement ratio of 0.5, when the Mg / Si molar ratio increases from 1.0 to 1.3, the 3-day strength decreases from 37.5 MPa to 34.8 MPa, a decrease of 7.2%; the 7-day strength decreases from 51.2 MPa to 48.5 MPa, a decrease of 5.3%; and the 28-day strength decreases from 62.4 MPa to 58.7 MPa, a decrease of 5.9%.

[0052] (3) Effect of water-cement ratio on performance: As shown in Tables 1 and 2, under the conditions of fixed active magnesium oxide content of 40%, metakaolin content of 8%, and Mg / Si molar ratio of 1.0, the 28-day strengths corresponding to water-cement ratios of 0.4, 0.5, and 0.6 are 66.8 MPa, 62.4 MPa, and 58.3 MPa, respectively. The strength of the water-cement ratio group 0.6 is 12.7% lower than that of the 0.4 group. In terms of corrosion resistance, the retention coefficients of the water-cement ratio group after 90-day immersion in sulfate and sodium chloride are 0.94 and 0.90, respectively, which are better than those of the water-cement ratio groups 0.5 (0.92, 0.88) and 0.6 (0.89, 0.85).

[0053] 2. Mechanism Discussion (1) Mechanism of influence of metakaolin content: The strengthening and corrosion resistance mechanism of appropriate amounts of metakaolin can be attributed to two aspects: First, the active SiO2 and Al2O3 in metakaolin react with MgO hydration products to generate MSH and MASH gels, in which Al... 3+ By replacing Si in silicon-oxygen tetrahedra 4+ Firstly, metakaolin can enter the gel network, increasing the degree of polymerization and structural density of the product. Secondly, ultrafine metakaolin particles can fill the pores of the matrix, exerting a micro-aggregate effect, refining the pore size distribution, and reducing pore connectivity. However, with excessive metakaolin incorporation, there is an excess of active Al2O3 in the system, resulting in an imbalance in the effective Mg / Si ratio. A large number of unreacted metakaolin particles form interface defects and harmful pores in the matrix, which degrades the mechanical properties and provides penetration channels for corrosive ions. Therefore, the reaction exhibits a pattern of initial increase followed by decrease.

[0054] (2) Mechanism of influence of Mg / Si molar ratio: When the Mg / Si molar ratio is 1.0, the ratio of magnesium source to silicon source is optimal, which can generate a dense MSH / MASH gel to the greatest extent. When the Mg / Si ratio is too high (e.g., 1.3), excess MgO hydrates to form magnesium hydroxide crystals. This process consumes mixing water, reduces the effective amount of gel generated, and causes volume expansion due to crystal growth, introducing microcracks into the matrix, reducing density and corrosion resistance. Macroscopically, this manifests as a comprehensive decrease in strength at all ages.

[0055] (3) Mechanism of influence of water-cement ratio: The water-binder ratio determines the porosity characteristics of the matrix. At a water-binder ratio of 0.4, the system exhibits optimal hydration, lowest porosity, and densest structure, resulting in superior mechanical strength and corrosion resistance. As the water-binder ratio increases to 0.5 or 0.6, the number of interconnected capillaries remaining after the evaporation of free water increases, leading to the formation of SO42-. 2- Corrosive ions such as Cl⁻ provide rapid diffusion channels, accelerating the degradation of matrix properties.

[0056] (4) Overall corrosion resistance mechanism: The superior resistance of this system to sulfate and chloride erosion stems from four key factors. First, the hydration products are primarily MSH and MASH, with no free calcium hydroxide. Under sulfate erosion, no expansion products such as gypsum and ettringite are generated, preventing expansion and cracking. Under chloride erosion, there is no risk of damage to the high-alkali passivation film. Second, Al... 3+Compared to MSH, MASH, which enters the gel network, has a higher degree of cross-linking and stronger chemical inertness, making it difficult for corrosive ions to break its chemical bonds. Third, an appropriate amount of metakaolin refines the pore structure, prolongs the diffusion path of corrosive ions, and reduces the penetration rate. Fourth, no expansive products are generated throughout the entire corrosion process, preventing internal stress cracking and resulting in a gradual decline in long-term performance; therefore, it maintains a high strength retention rate even after 90 days of immersion.

[0057] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A metakaolin-modified hydrated magnesium silicate cementitious material, characterized in that, It is prepared from the following raw materials: activated magnesium oxide, metakaolin, silica fume and water; Based on the total mass of the cementitious materials, the content of active magnesium oxide is 35%~50%, the content of metakaolin is 1%~10%, and the balance is silica fume; the Mg / Si molar ratio of the cementitious materials is 1.0~1.3, and the water-cement ratio is 0.4~0.

6.

2. The metakaolin-modified hydrated magnesium silicate cementitious material according to claim 1, characterized in that, The fineness of active magnesium oxide is ≤5% residue on a 200-mesh sieve, and the active MgO content is ≥90%.

3. The metakaolin-modified hydrated magnesium silicate cementitious material according to claim 1, characterized in that, Metakaolin is obtained by calcining kaolin at 600~900℃, with an Al2O3 content ≥42.89% and a SiO2 content ≥53.48%.

4. The metakaolin-modified hydrated magnesium silicate cementitious material according to claim 1, characterized in that, The amount of metakaolin added is 5% to 10%.

5. The metakaolin-modified hydrated magnesium silicate cementitious material according to claim 4, characterized in that, The amount of metakaolin added is 8%.

6. A method for preparing a metakaolin-modified hydrated magnesium silicate cementitious material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Kaolin is calcined at 600-900℃ for 2-4 hours, cooled, ground and sieved to obtain metakaolin. Weigh out the active magnesium oxide, silica fume and metakaolin according to the ratio, mix and stir evenly to obtain a dry powder mixture; Add water to the dry powder mixture and stir well to obtain a cementitious material slurry; The slurry is poured into a mold and cured under conditions of 20±2℃ and relative humidity ≥95%.

7. The preparation method according to claim 6, characterized in that, The mixing process is carried out using a planetary mixer at a speed of 40-60 r / min for 3-5 minutes. After adding water, the mixture is first stirred at a low speed of 140±5 r / min for 30-60 seconds, and then stirred at a high speed of 285±10 r / min for 2 minutes.

8. The preparation method according to claim 6, characterized in that, Maintenance includes: After curing in the mold for 24 hours, the mold is removed. After removal, the specimens are cured in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% until the specified age is reached. During the curing period, the surface of the specimens is kept moist.

9. An application of the metakaolin-modified hydrated magnesium silicate cementitious material as described in any one of claims 1 to 5, characterized in that, Cementitious materials are used to resist the corrosion of building materials by corrosive ions.

10. The application according to claim 9, characterized in that, Corrosive ions include sulfate ions and / or chloride ions.

Images