Magnesite-based cement and green building material and method for preparing the same

Abstract

This invention provides a magnesite-based cement and a green building material, as well as a method for preparing the same, belonging to the field of building materials technology. The magnesite-based cement comprises low-grade magnesite powder, a binder, and optionally, additives. The binder is used at 4wt%-6wt% of the mass of the low-grade magnesite powder, and the additives are used at 0-1wt% of the mass of the low-grade magnesite powder. The low-grade magnesite powder has a particle size of 100-200 mesh. The binder is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additives are a compound of ferrous sulfate and sodium lignosulfonate. The magnesite-based cement is efficient, environmentally friendly, and fully utilizes low-grade magnesite resources. The prepared magnesite-based cement has good water resistance, and the green building material prepared from it has a short curing cycle, meeting the needs of large-scale, high-efficiency modern building materials production.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a magnesium oxide-based cement and green building materials and their preparation method. Background Technology

[0002] Magnesite is a key raw material for magnesium cementitious materials and plays an important role in the building materials industry. Although my country has abundant magnesite resources, the reserves of high-grade magnesite (magnesium oxide content ≥45wt%) are relatively limited. Meanwhile, a large amount of low-grade magnesite (magnesium oxide content ≤40wt%) has not been fully and effectively utilized for a long time due to its high impurity content and poor reactivity, resulting in a waste of resources.

[0003] In the traditional preparation process of magnesium cementitious materials, magnesite usually requires a complex pretreatment process, such as the common acid leaching pretreatment. This process consumes a large amount of strong acids, such as sulfuric acid and hydrochloric acid. The use of large amounts of strong acids not only brings high costs, but more seriously, it generates high-concentration acidic wastewater. If this acidic wastewater is discharged directly without proper treatment, it will cause great damage to the ecological environment such as soil and water bodies. Moreover, the solution after acid leaching needs to undergo a multi-stage purification process, which undoubtedly further increases energy consumption and production costs, and also exacerbates the risk of environmental pollution.

[0004] From the perspective of cementitious system performance, traditional magnesium cementitious materials, such as magnesium oxychloride cement, mainly rely on magnesium chloride as raw material. However, this type of cementitious material has obvious performance defects. Its water resistance is poor, and it is prone to efflorescence in humid environments. This greatly limits its widespread application in the construction field. In addition, in order to control its performance, a large amount of admixtures are often required, which not only increases production costs but may also have potential environmental impacts.

[0005] Furthermore, there are also problems in the curing process of preparing green building materials from traditional magnesium cementitious materials. The existing process generally requires 14 days or even longer of curing before the product can reach the design strength. Such a long curing cycle seriously affects production efficiency and makes it difficult to meet the needs of large-scale, high-efficiency modern building material production. This hinders the expansion of the company's production scale and the timeliness of market supply.

[0006] In summary, developing a new green building material preparation process that is efficient, environmentally friendly, can fully utilize low-grade magnesite resources, and can improve product performance and shorten the production cycle compared to similar products is of great practical significance and urgency. This invention is based on this background and is committed to breaking through existing technological bottlenecks to achieve efficient utilization of low-grade magnesite in the field of green building material preparation. Summary of the Invention

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a magnesite-based cement and a green building material, as well as a method for preparing the same. The method for preparing the magnesite-based cement is efficient, environmentally friendly, and makes full use of low-grade magnesite resources. The resulting magnesite-based cement exhibits good water resistance, while the green building material prepared from the magnesite-based cement has a short curing cycle, meeting the needs of large-scale, high-efficiency modern building material production.

[0008] In a first aspect, embodiments of the present invention provide a magnesite-based cement, comprising low-grade magnesite powder, a binder, and optionally an additive, wherein the amount of the binder is 4wt%-6wt% of the mass of the low-grade magnesite powder, the amount of the additive is 0-1wt% of the mass of the low-grade magnesite powder, the particle size of the low-grade magnesite powder is 100-200 mesh, the binder is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignosulfonate.

[0009] The advantages and technical effects of the magnesium-based cement in this invention are as follows:

[0010] (1) The magnesite-based cement of the present invention uses low-grade magnesite powder directly as raw material, without the need for complex beneficiation and enrichment or blending with high-grade ore, which greatly improves the utilization rate of low-grade magnesite, reduces resource waste, and makes full use of a large amount of low-grade magnesite that was originally shelved, thus broadening the scope of resource utilization and helping to alleviate the shortage of high-grade magnesite resources.

[0011] (2) The magnesium-based cement of this invention includes a cementitious agent and optional additives. The cementitious agent is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignosulfonate. By optimizing the formulation of the cementitious agent and additives, the novel magnesium cementitious material prepared has better early strength and water resistance, effectively solving the problems of poor water resistance and easy efflorescence of traditional magnesium cementitious materials (such as magnesium oxychloride cement), expanding the application range of the product in the construction field, and improving product quality and market competitiveness.

[0012] In some embodiments, the magnesium oxide content in the low-grade magnesite powder is 20wt%-40wt%.

[0013] In some embodiments, the mass ratio of potassium dihydrogen phosphate to magnesium sulfate in the gelling agent is 1:2 to 1:1.

[0014] In some embodiments, the mass ratio of ferrous sulfate to sodium lignosulfonate in the additive is 0.5:1 to 1.5:1.

[0015] Secondly, embodiments of the present invention provide a method for preparing magnesium oxychloride-based cement, comprising the following steps:

[0016] S1. Crush the low-grade magnesite ore to a particle size of 100-200 mesh with a throughput of ≥90% to obtain the low-grade magnesite powder;

[0017] S2. The low-grade magnesite powder is mixed with a binder and optionally additives to obtain the magnesite-based cement described in the first aspect.

[0018] The advantages and technical effects of the preparation method of magnesium-based cement in this invention are as follows:

[0019] (1) The method for preparing magnesite-based cement in this embodiment of the invention directly uses low-grade magnesite as raw material, without the need for complex beneficiation and enrichment or blending with high-grade ore, which greatly improves the utilization rate of low-grade magnesite, reduces resource waste, and enables a large amount of low-grade magnesite that was originally shelved to be fully utilized, thus broadening the scope of resource utilization and helping to alleviate the shortage of high-grade magnesite resources.

[0020] (2) Compared with the traditional magnesium cementitious materials (such as magnesium oxychloride cement) preparation methods in the prior art, the preparation method of magnesite-based cement in the present invention omits the acid leaching pretreatment step, avoids the use of a large amount of strong acid, eliminates the generation of high-concentration acidic wastewater from the source, effectively reduces the risk of pollution to the ecological environment such as soil and water, reduces the cost and environmental pressure of subsequent wastewater treatment, and reduces the discharge of tailings and other wastes since it does not involve mineral processing such as magnetic separation and flotation, thus reducing secondary pollution to the environment and conforming to the green and environmentally friendly development concept.

[0021] (3) Compared with the traditional magnesium cementitious materials (such as magnesium oxychloride cement) preparation methods in the prior art, the preparation method of magnesia-based cement in the present invention simplifies the preparation process, reduces multiple complex and costly steps such as acid leaching, multi-stage purification and mineral processing, reduces equipment investment, raw material consumption and manpower costs, and does not require the addition of a large amount of admixtures to regulate the performance of cementitious materials, further reducing production costs and improving the economic benefits of enterprises.

[0022] (4) The method for preparing magnesium-based cement in the embodiments of the present invention optimizes the formulation of the cementitious agent (potassium dihydrogen phosphate and magnesium sulfate in a specific ratio) and optional additives (ferrous sulfate and sodium lignosulfonate working synergistically), and the resulting novel magnesium cementitious material has better early strength and water resistance. It effectively solves the problems of poor water resistance and easy efflorescence of traditional magnesium cementitious materials (such as magnesium oxychloride cement), expands the application range of the product in the construction field, and improves the product quality and market competitiveness.

[0023] In some embodiments, in step S2, the material is mixed by ultrasonic dispersion, the ultrasonic power of which is 200W-300W and the ultrasonic dispersion time is 5min-10min.

[0024] Thirdly, embodiments of the present invention provide a method for preparing green building materials, comprising the following steps:

[0025] S3. The magnesium-based cement described in the first aspect is mixed with water to obtain a mixture; the mixture is poured into a mold for molding to obtain the molded building material;

[0026] S4. The molded building material is cured in an environment with a temperature of 18℃-26℃ and a humidity of 60%-70% for 7-11 days, and the cured building material is obtained after demolding.

[0027] S5. Apply an environmentally friendly waterproof coating to the surface of the cured building materials to obtain green building materials.

[0028] The advantages and technical effects of the green building material preparation method of this invention are as follows:

[0029] Because of the use of the magnesium-based cement described in the first aspect, and the optimization of process parameters such as curing temperature and humidity, the building materials prepared by the green building materials method of this invention can achieve the design strength that traditional magnesium cementitious materials (such as magnesium oxychloride cement) take 14 days or even longer to achieve in a shorter curing time. This greatly improves the production efficiency of building materials, meets the needs of large-scale, high-efficiency modern building materials production, and helps enterprises respond quickly to the market and increase market share.

[0030] In some embodiments, the water-cement ratio in the mixture is 0.35:1-0.40:1, the molding temperature is 30℃-35℃, and the molding time is 1.5h-2h.

[0031] Fourthly, embodiments of the present invention provide a green building material obtained by the preparation method described in the third aspect.

[0032] The advantages and technical effects of the green building materials in this invention are as follows:

[0033] Due to the adoption of the green building material preparation method of the third aspect, the green building material of the present invention has high early strength and water resistance.

[0034] In some embodiments, the green building material is artificial marble, fireproof board, or floor tile. Detailed Implementation

[0035] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] In a first aspect, embodiments of the present invention provide a magnesite-based cement, comprising low-grade magnesite powder, a binder, and optionally an additive, wherein the amount of the binder is 4wt%-6wt% of the mass of the low-grade magnesite powder, the amount of the additive is 0-1wt% of the mass of the low-grade magnesite powder, the particle size of the low-grade magnesite powder is 100-200 mesh, the binder is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignosulfonate.

[0037] The magnesite-based cement of this invention uses low-grade magnesite powder directly as raw material, without the need for complex beneficiation and enrichment or blending with high-grade ore. This greatly improves the utilization rate of low-grade magnesite, reduces resource waste, and allows a large amount of previously unused low-grade magnesite to be fully utilized, thus broadening the scope of resource utilization and helping to alleviate the shortage of high-grade magnesite resources.

[0038] The magnesium-based cement of this invention includes a cementitious agent and optional additives. The cementitious agent is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignosulfonate. By optimizing the formulation of the cementitious agent and additives, the prepared novel magnesium cementitious material has better early strength and water resistance, effectively solving the problems of poor water resistance and easy efflorescence of traditional magnesium cementitious materials (such as magnesium oxychloride cement), expanding the application range of the product in the construction field, and improving product quality and market competitiveness.

[0039] In the magnesite-based cement of this invention, the low-grade magnesite powder has a particle size of 100-200 mesh, such as 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, 200 mesh, etc. When the particle size of the low-grade magnesite powder is too small, it is not conducive to sufficient contact and reaction between the cementitious agent and the low-grade magnesite powder. When the particle size of the low-grade magnesite powder is too large, it is not conducive to the uniform dispersion of the cementitious agent in the low-grade magnesite powder, affecting the full progress of the hydration reaction and the strength and stability of the building material. From the perspective of preparation principle, the cementitious process of magnesite-based cement depends on the chemical reaction between magnesium oxide in low-grade magnesite powder and cementitious agents and additives. If the particle size of low-grade magnesite powder is too small, the particle size is small, and the specific surface area of ​​the particles is too large, it may cause the cementitious agent to be unable to fully coat or penetrate into the interior of the mineral powder particles, thus hindering the reaction efficiency. If the particle size of low-grade magnesite powder is too large, the particle size is large, and the cementitious agent is difficult to disperse evenly in the gaps between the mineral powder particles, which may cause insufficient local reaction, affecting the formation of hydration products and the density of the structure, and thus is not conducive to improving the early strength and water resistance of building materials.

[0040] In some embodiments, the magnesium oxide content in the low-grade magnesite powder is 20wt%-40wt%. When the magnesium oxide content in the low-grade magnesite powder is too low, it is not conducive to improving the early strength and water resistance of building materials.

[0041] In the magnesite-based cement of this invention, the amount of the cementitious agent is 4wt%-6wt% of the mass of the low-grade magnesite powder, for example, 4wt%, 4.2wt%, 4.4wt%, 4.6wt%, 4.8wt%, 5wt%, 5.2wt%, 5.4wt%, 5.6wt%, 5.8wt%, 6wt%, etc. During the subsequent cementitious cement gelation process after adding water, the main component of the low-grade magnesite powder, magnesium oxide, reacts with water to generate magnesium hydroxide. Magnesium hydroxide then undergoes a series of complex reactions with the cementitious agent, gradually forming a strong gel. When the amount of cementitious agent is too small, it is not conducive to a complete hydration reaction, thus hindering the improvement of the early strength and water resistance of the building material. When the amount of cementitious agent is too large, the improvement on the above effects is not significant; instead, it increases the production cost of the magnesite-based cement.

[0042] In some embodiments, the mass ratio of potassium dihydrogen phosphate to magnesium sulfate in the gelling agent is 1:2 to 1:1, such as 1:2, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, etc. When the mass ratio of potassium dihydrogen phosphate to magnesium sulfate is too small, it is not conducive to improving the early strength and water resistance of the building materials. When the mass ratio of potassium dihydrogen phosphate to magnesium sulfate is too large, it is not conducive to the full reaction between the gelling agent and low-grade magnesite powder, which may lead to increased costs and insignificant improvement in early strength and water resistance. Magnesium ions provided by magnesium sulfate are key components in the formation of hydration products such as basic magnesium sulfate; a low proportion may affect crystal growth efficiency, delay the hydration reaction process, and result in insufficient improvement in early strength. Excessive use of potassium dihydrogen phosphate directly increases the cost of the gelling agent.

[0043] In the magnesite-based cement of this invention, the amount of additive is 0-1 wt% of the mass of the low-grade magnesite powder, for example, 0, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, etc. During the subsequent gelation process after adding water to the magnesite-based cement, the main component of the low-grade magnesite powder, magnesium oxide, reacts with water to generate magnesium hydroxide. Magnesium hydroxide then undergoes a series of complex reactions with the additive, gradually forming a strong gel, further improving the early strength and water resistance of the building material. When the amount of additive is too small, it is not conducive to improving the early strength and water resistance of the building material. When the amount of additive is too large, the improvement on the above effects is not significant, but rather increases the production cost of the magnesite-based cement.

[0044] In some embodiments, the mass ratio of ferrous sulfate to sodium lignosulfonate in the additive is 0.5:1-1.5:1, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc. When the mass ratio of ferrous sulfate to sodium lignosulfonate is too small, it is not conducive to improving the compressive strength and water resistance of building materials. When the mass ratio of ferrous sulfate to sodium lignosulfonate is too high, it is not conducive to further improving the compressive strength and water resistance of building materials, and may increase production costs. Sodium lignosulfonate, as a dispersant, needs to form an appropriate ratio with ferrous sulfate to promote uniform dispersion of the gelation system. If there is too much ferrous sulfate, it may destroy the dispersion effect, resulting in a loose structure of hydration products, affecting strength and water resistance. On the other hand, an excessively high proportion of ferrous sulfate will directly increase the cost of raw materials, but it cannot significantly improve performance through ratio optimization, which is not in line with the concept of green production. At the same time, the role of ferrous sulfate is to promote gel formation through ionic reaction, but its excess may exceed the reaction capacity of the system, and the excess components cannot participate in the reaction, resulting in resource waste and no additional benefit.

[0045] Secondly, embodiments of the present invention provide a method for preparing magnesium oxychloride-based cement, comprising the following steps:

[0046] S1. Crush the low-grade magnesite ore to a particle size of 100-200 mesh with a throughput of ≥90% to obtain the low-grade magnesite powder;

[0047] S2. The low-grade magnesite powder is mixed with a binder and optionally additives to obtain the magnesite-based cement described in the first aspect.

[0048] The method for preparing magnesite-based cement in this invention uses low-grade magnesite ore directly as raw material, without the need for complex beneficiation and enrichment or blending with high-grade ore. This greatly improves the utilization rate of low-grade magnesite ore, reduces resource waste, and allows a large amount of previously unused low-grade magnesite ore to be fully utilized, thus broadening the scope of resource utilization and helping to alleviate the shortage of high-grade magnesite ore resources.

[0049] Compared to the traditional preparation methods of magnesium-based cementitious materials (such as magnesium oxychloride cement) in the prior art, the preparation method of magnesite-based cement in this invention omits the acid leaching pretreatment step, avoids the use of large amounts of strong acid, eliminates the generation of high-concentration acidic wastewater from the source, effectively reduces the risk of pollution to the ecological environment such as soil and water bodies, reduces the cost and environmental pressure of subsequent wastewater treatment, and reduces the discharge of tailings and other wastes since it does not involve mineral processing processes such as magnetic separation and flotation, thus reducing secondary pollution to the environment and conforming to the concept of green and environmentally friendly development.

[0050] Compared with the existing methods for preparing traditional magnesium cementitious materials (such as magnesium oxychloride cement), the method for preparing magnesite-based cement in this invention simplifies the preparation process, reduces multiple complex and costly steps such as acid leaching, multi-stage purification and mineral processing, lowers equipment investment, raw material consumption and labor costs, and eliminates the need to add large amounts of admixtures to regulate the performance of cementitious materials, further reducing production costs and improving the economic benefits of enterprises.

[0051] The method for preparing magnesium-based cement according to this invention optimizes the formulation of the cementitious agent (potassium dihydrogen phosphate and magnesium sulfate in a specific ratio) and optional additives (ferrous sulfate and sodium lignosulfonate working synergistically). The resulting novel magnesium cementitious material has better early strength and water resistance, effectively solving the problems of poor water resistance and easy efflorescence of traditional magnesium cementitious materials (such as magnesium oxychloride cement). This expands the application range of the product in the construction field and improves product quality and market competitiveness.

[0052] In some embodiments, in step S2, the material is mixed by ultrasonic dispersion, wherein the ultrasonic power of the ultrasonic dispersion is 200W-300W, and the ultrasonic dispersion time is 5min-10min. Ultrasonic dispersion can enhance the dispersibility of the gelling agent and optionally additives in low-grade magnesite powder.

[0053] Thirdly, embodiments of the present invention provide a method for preparing green building materials, comprising the following steps:

[0054] S3. The magnesium-based cement described in the first aspect is mixed with water to obtain a mixture; the mixture is poured into a mold for molding to obtain the molded building material;

[0055] S4. The molded building material is cured in an environment with a temperature of 18℃-26℃ and a humidity of 60%-70% for 7-11 days, and the cured building material is obtained after demolding.

[0056] S5. Apply an environmentally friendly waterproof coating to the surface of the cured building materials to obtain green building materials.

[0057] Because of the use of the magnesium-based cement described in the first aspect, and the optimization of process parameters such as curing temperature and humidity, the building materials prepared by the green building materials method of this invention can achieve the design strength that traditional magnesium cementitious materials (such as magnesium oxychloride cement) take 14 days or even longer to achieve in a shorter curing time. This greatly improves the production efficiency of building materials, meets the needs of large-scale, high-efficiency modern building materials production, and helps enterprises respond quickly to the market and increase market share.

[0058] In some embodiments, the water-cement ratio in the mixture is 0.35:1-0.40:1, the molding temperature is 30℃-35℃, and the molding time is 1.5h-2h. From a chemical reaction kinetics perspective, during the molding process of building materials, the chemical reaction between magnesium oxide in low-grade magnesite powder and water, binders, and optionally additives requires a suitable temperature to drive it. A temperature of 30℃-35℃ allows for a moderate reaction rate, ensuring sufficient reaction without causing local overheating or stress defects due to excessively rapid reaction. For example, at 30℃-35℃, the hydration reaction of magnesite-based cement can proceed well, which is conducive to the formation of the 5·1·8 crystal phase, thereby improving the strength and stability of the building materials. From the perspective of moisture evaporation and curing balance, this temperature range helps maintain a suitable evaporation rate of moisture inside the building materials, achieving a good balance between moisture evaporation and material curing. If the temperature is too low, moisture evaporation will be too slow, which will prolong the molding time, reduce production efficiency, and may also cause problems such as porosity and reduced strength in the building materials during the curing process due to excessive moisture. Excessive temperature causes rapid evaporation of moisture, leading to premature drying of building materials and the formation of a hard shell. This hinders internal moisture evaporation and the continuation of chemical reactions, easily resulting in defects such as cracking and delamination. Therefore, at 30℃-35℃, the moisture evaporation rate ensures rapid curing of building materials while avoiding the aforementioned adverse phenomena. From the perspective of material plasticity and formability, within this temperature range, the mixture exhibits good plasticity and fluidity, facilitating molding operations. This allows the building materials to fill the mold better, resulting in products with complete shapes and high dimensional accuracy. It also helps reduce defects such as air pockets and chipped edges caused by poor material fluidity during the molding process.

[0059] In some embodiments, the mold is made of reusable stainless steel and its surface is polished. This facilitates subsequent demolding.

[0060] In the curing process, the curing temperature is 18-26℃. During the gelation process, a series of complex reactions occur between magnesium oxide in low-grade magnesite powder and the gelling agent and optional additives, resulting in a gelled product with a certain strength. A temperature of 18-26℃ is suitable for these chemical reactions; it avoids both excessively low temperatures that slow down the reaction rate and prolong the production cycle, and excessively high temperatures that cause the reaction to be too rapid, producing undesirable reaction products and affecting the performance of the building materials. From the perspective of moisture evaporation: at a curing temperature of 18-26℃, the rate of moisture evaporation is moderate. If the curing temperature is too high, the moisture evaporates rapidly, leading to uneven moisture distribution within the building materials and defects such as cracking; conversely, if the curing temperature is too low, the moisture evaporates too slowly, leaving the building materials in a damp state for an extended period, affecting the hardening process of the gelling material and reducing the early strength of the building materials. From the perspective of industry standards and experience: 18-26℃ is also a relatively reasonable temperature range for the curing of building materials.

[0061] The maintenance period is set at 7-11 days for the following reasons:

[0062] (1) The strength formation of magnesite building materials depends on the hydration reaction of the magnesite-based cement in the embodiments of the present invention. The main component of low-grade magnesite powder, magnesium oxide, reacts with water to generate magnesium hydroxide. The magnesium hydroxide then undergoes a series of complex reactions with the cementitious agent and optional additives to gradually form a gel with strength. Generally speaking, this reaction process is faster in the first few days, and then gradually slows down. The main hydration reaction can be basically completed in 7-11 days, allowing the building materials to obtain relatively stable strength.

[0063] (2) Referring to the curing standards of similar magnesium cementitious materials in the construction industry, such as some magnesium fireproof boards and magnesium oxychloride concrete products, the curing time is usually 7-14 days. 7-11 days is within this reasonable range, which can ensure that the building materials reach a certain strength requirement without excessively prolonging the production cycle. This curing time is in line with such standards.

[0064] (3) Actual performance test results: Through a large number of actual production and performance tests, it was found that the compressive strength, flexural strength and other performance indicators of low-grade magnesite green building materials can reach the design requirements after curing at a curing temperature of 18℃-26℃ for 7-11 days. If the curing time is extended further, the strength increase gradually decreases. From the perspective of economic benefits and production efficiency, 7-11 days is a more suitable curing time.

[0065] (4) Environmental adaptability: In actual production environment, the temperature of 18℃-26℃ and the curing time of 7-11 days can adapt well to the environmental changes of different seasons and regions. It will not cause incomplete hydration reaction and slow strength growth of building materials due to the curing time being too short when the ambient temperature is low or the humidity is high, nor will it cause excessive drying and cracks in building materials due to the curing time being too long when the ambient temperature is high.

[0066] In conclusion, a curing temperature of 18-26℃ and a curing time of 7-11 days are reasonable for the curing treatment of low-grade magnesite green building materials, which is conducive to ensuring the quality and performance of building materials.

[0067] The green building material preparation method of this invention can achieve the design strength of building materials made of traditional magnesium cementitious materials (such as magnesium oxychloride cement) in a shorter curing time (7-11 days), which would take 14 days or even longer. This may be due to the following reasons:

[0068] (1) The phosphate and potassium ions provided by potassium dihydrogen phosphate, and the magnesium and sulfate ions provided by magnesium sulfate, may synergistically interact with other components in the system to promote the hydration reaction of magnesium-based cementitious materials. For example, phosphate ions may combine with magnesium ions to form intermediate products that facilitate the formation of hydration products, thereby accelerating the hydration process and shortening the curing cycle of building materials. At the same time, potassium ions can increase the ionic strength of the solution and promote ion exchange and chemical reactions.

[0069] (2) The components in the compound of potassium dihydrogen phosphate and magnesium sulfate may provide favorable conditions for the crystal growth of hydration products of magnesium cementitious materials. For example, magnesium ions in magnesium sulfate are key ions for the formation of hydration products such as basic magnesium sulfate, and their presence helps these crystals to form and grow rapidly. Potassium dihydrogen phosphate may also regulate the crystal growth environment by affecting the pH and ion concentration of the solution, enabling the crystals to grow to a sufficient size in a shorter time, thereby improving the early strength of the magnesium-based cement in the embodiments of the present invention and shortening the curing cycle of the building materials.

[0070] (3) The addition of potassium dihydrogen phosphate and magnesium sulfate may reduce the surface tension of the system, making the distribution of water on the surface of the magnesium-based cement particles in this embodiment of the invention more uniform, which is conducive to the full contact between water and the magnesium-based cement in this embodiment of the invention, and accelerates the hydration reaction. At the same time, the lower surface tension also helps the hydration products to be uniformly deposited and grown on the particle surface, improving the structural density of the building materials, and thus shortening the curing time of the building materials.

[0071] (4) The compound of potassium dihydrogen phosphate and magnesium sulfate may generate some fine crystals or gel-like substances during the hydration process. These substances can fill the pores inside the building materials, reduce the porosity, and increase the density of the building materials. On the one hand, this helps to improve the early strength of the building materials, enabling them to reach the required performance indicators in a shorter time; on the other hand, the dense structure also helps to prevent external moisture and air from entering, reducing the further hydration and reaction of the magnesium-based cement in the embodiments of the present invention, thereby shortening the curing cycle of the building materials.

[0072] In some embodiments, the thickness of the waterproof coating is 0.2mm-0.3mm, such as 0.2mm, 0.22mm, 0.24mm, 0.26mm, 0.28mm, 0.3mm, etc., and the material of the waterproof coating is an acrylic waterproof coating. The presence of the waterproof coating can further improve the water resistance of green building materials.

[0073] Fourthly, embodiments of the present invention provide a green building material, obtained by the preparation method of the green building material in the third aspect.

[0074] Due to the adoption of the green building material preparation method of the third aspect, the green building material of the present invention has high early strength and water resistance.

[0075] In some embodiments, the green building material is artificial marble, fireproof board, or floor tile.

[0076] The present invention will now be described in detail with reference to the embodiments.

[0077] Example 1

[0078] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 120 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0079] Cementitious molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 40 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold, the mold size of which is adapted to subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0080] Curing treatment: The molded building materials are placed in an environment with a temperature of 20℃ and a humidity of 65wt% for 9 days to cure. After demolding, the cured building materials are obtained.

[0081] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0082] Example 2

[0083] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 35wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0084] Cementing and Molding: Add 10 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 2 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) to 200 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 85 kg of water to the magnesite-based cement and stir thoroughly at 33°C to obtain a mixture. Pour the mixture into a polished stainless steel mold, the mold size of which is adapted to subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.8 hours.

[0085] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 70wt% for 9 days to cure. After demolding, the cured building materials are obtained.

[0086] Post-treatment: Apply a 0.2mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0087] Example 3

[0088] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 38wt% is crushed to a particle size of 180 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0089] Cementing and Molding: 7.5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1.5 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) were added to 150 kg of low-grade magnesite powder. The mixture was then ultrasonically dispersed at a power of 260 W for 8 minutes to obtain magnesite-based cement. Next, 60 kg of water was added to the magnesite-based cement, and the mixture was stirred evenly at 30°C to obtain a binder. The binder was poured into a polished stainless steel mold, the mold size of which was adapted to subsequent performance testing standards. During the pouring process, a small vibrator was used to gently vibrate the mold to remove air bubbles in the binder and ensure molding quality. The entire molding process lasted 2 hours.

[0090] Curing treatment: The molded building materials are placed in an environment with a temperature of 25℃ and a humidity of 60wt% for 9 days to cure. After demolding, the cured building materials are obtained.

[0091] Post-treatment: Apply a 0.3mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0092] Example 4

[0093] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0094] Cementing and Molding: Add 4 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 38 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0095] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65wt% for 9 days to cure. After demolding, the cured building materials are obtained.

[0096] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0097] Example 5

[0098] Low-grade magnesite ore with a magnesium oxide content of 32wt% was crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0099] Cementitious molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 1:2) and 1 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 39 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0100] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65wt% for 9 days to cure. After demolding, the cured building materials are obtained.

[0101] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building materials to obtain green building materials.

[0102] Example 6

[0103] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0104] Cementing and Molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate and magnesium sulfate in a 1:1 mass ratio) and 1 kg of additive (ferrous sulfate and sodium lignosulfonate in a 1:1 mass ratio) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 38 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0105] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65wt% for 9 days to cure. After demolding, the cured building materials are obtained.

[0106] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0107] Example 7

[0108] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0109] Cementing and Molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 0.5 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 37 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0110] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65% for 9 days to cure. After demolding, the cured building materials are obtained.

[0111] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0112] Example 8

[0113] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0114] Cementitious molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) to 100 kg of low-grade magnesite powder. No additives are added. The mixture is ultrasonically dispersed at a power of 260 W for 8 minutes to obtain magnesite-based cement. Then, add 36 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions adapted to subsequent performance testing standards. During the pouring process, a small vibrator is used to gently vibrate the mold to remove air bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0115] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65% for 9 days to cure. After demolding, the cured building materials are obtained.

[0116] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0117] Example 9

[0118] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0119] Cementing and Molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 0.5:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at 260 W for 8 minutes to obtain magnesite-based cement. Then add 38 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0120] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65% for 9 days to cure. After demolding, the cured building materials are obtained.

[0121] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0122] Example 10

[0123] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0124] Cementing and Molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1.5:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at a power of 260 W for 8 minutes to obtain magnesite-based cement. Then add 38 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0125] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65% for 9 days to cure. After demolding, the cured building materials are obtained.

[0126] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0127] Example 11

[0128] Crushing process: Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a passing rate of ≥90% to obtain low-grade magnesite powder.

[0129] Cementing and Molding: Add 5 kg of cementitious agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignosulfonate in a mass ratio of 1:1) to 100 kg of low-grade magnesite powder. Disperse the mixture using ultrasound at a power of 260 W for 8 minutes to obtain magnesite-based cement. Then add 38 kg of water to the magnesite-based cement and stir evenly at 32°C to obtain a mixture. Pour the mixture into a polished stainless steel mold with dimensions suitable for subsequent performance testing standards. During pouring, use a small vibrator to gently vibrate the mold to remove air bubbles and ensure molding quality. The entire molding process lasts 1.5 hours.

[0130] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65% for 9 days to cure. After demolding, the cured building materials are obtained.

[0131] Since post-processing is omitted, the building materials cured in this embodiment are the final green building materials.

[0132] Comparative Example 1

[0133] Raw material selection and proportion: Commercially available magnesium oxychloride cement is selected. Its main components are light-burned magnesium oxide (MgO) and magnesium chloride hexahydrate (MgCl2•6H2O). The two form a ternary reaction system of MgO-MgCl2-H2O in the system, which is the key component that determines the basic performance of cement. The active magnesium oxide content of light-burned magnesium oxide in this magnesium oxychloride cement is 80wt%.

[0134] Cementitious molding: 38 kg of water is added to 106 kg of magnesium oxychloride cement and stirred evenly at 32°C to obtain a mixture. During the stirring process, the lightly calcined magnesium oxide in the cement gradually undergoes a hydration reaction with water and magnesium chloride hexahydrate, and begins to form a preliminary cementitious structure. Subsequently, the mixture is quickly poured into a polished stainless steel mold. The mold size is adapted to the subsequent performance testing standards. During the pouring process, a small vibration device is used to slightly vibrate the mold to remove air bubbles in the mixture and ensure molding quality. The entire molding process lasts for 1.5 hours.

[0135] Curing treatment: The molded building materials are placed in an environment with a temperature of 22℃ and a humidity of 65% for 9 days to cure. After demolding, the cured building materials are obtained.

[0136] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building material to obtain green building material.

[0137] Performance testing:

[0138] (1) Compressive strength test (without immersion): According to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the cured building materials are processed into cubic blocks with dimensions of 100mm×100mm×100mm. On a universal testing machine, a loading rate of 0.5MPa per second is applied until the block fails. The failure load value is recorded and the result is calculated according to the formula. Calculate compressive strength;

[0139] in: Compressive strength (MPa);

[0140] F is the failure load value of the test block (N);

[0141] A is the bearing area of ​​the test block (mm²) 2 For a 100mm × 100mm test block, (A = 100 × 100 = 10) 4 mm 2 )).

[0142] (2) Compressive strength test (immersion in water for 7 days): According to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the cured building materials are processed into cubic test blocks with dimensions of 100mm×100mm×100mm. The test blocks are then completely immersed in water for 7 days and then removed. On a universal testing machine, a loading rate of 0.5MPa per second is applied until the test block fails. The failure load value is recorded and calculated according to the formula. Calculate compressive strength;

[0143] in: Compressive strength (MPa);

[0144] F is the failure load value of the test block (N);

[0145] A is the bearing area of ​​the test block (mm²) 2 For a 100mm × 100mm test block, (A = 100 × 100 = 10) 4 mm 2 )).

[0146] (3) Water absorption rate test: Refer to GB / T17657-2013 "Test methods for physical and chemical properties of wood-based panels and decorative wood-based panels", first dry the green building material to constant weight and record its mass m1. Then immerse the test block completely in water and soak it for 48 hours. Take it out, wipe the surface moisture with a damp cloth, and immediately weigh its mass m2. Calculate the water absorption rate according to the formula (m2-m1) / m1×100%.

[0147] Table 1. Composition of building materials in the above embodiments and comparative examples.

[0148]

[0149] Table 2. Compressive strength and water resistance of the building materials in the above embodiments and comparative examples.

[0150]

[0151] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0152] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A magnesium oxychloride-based cement, characterized in that, The mixture includes low-grade magnesite powder, a gelling agent, and additives. The amount of gelling agent is 4wt%-6wt% of the mass of the low-grade magnesite powder, and the amount of additives is 0-1wt% of the mass of the low-grade magnesite powder. The amount of additives is not zero. The particle size of the low-grade magnesite powder is 100-200 mesh. The gelling agent is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the mass ratio of potassium dihydrogen phosphate to magnesium sulfate in the gelling agent is 1:2-1:

1. The additive is a compound of ferrous sulfate and sodium lignosulfonate, and the mass ratio of ferrous sulfate to sodium lignosulfonate in the additive is 0.5:1-1.5:

1.

2. The magnesium oxychloride-based cement according to claim 1, characterized in that, The low-grade magnesite powder contains 20wt%-40wt% magnesium oxide.

3. The method for preparing magnesium-based cement according to claim 1 or 2, characterized in that, Includes the following steps: S1. Crush the low-grade magnesite ore to a particle size of 100-200 mesh with a throughput of ≥90% to obtain the low-grade magnesite powder; S2. The low-grade magnesite powder is mixed with a binder and additives to obtain the magnesite-based cement.

4. The method for preparing magnesium-based cement according to claim 3, characterized in that, In step S2, the material is mixed by ultrasonic dispersion, the ultrasonic power of which is 200W-300W and the ultrasonic dispersion time is 5min-10min.

5. A method for preparing a green building material, characterized in that, Includes the following steps: S3. Mix the magnesium oxide-based cement as described in claim 1 or 2 with water to obtain a mixture; pour the mixture into a mold for molding to obtain the molded building material; S4. The molded building material is cured in an environment with a temperature of 18℃-26℃ and a humidity of 60%-70% for 7-11 days, and the cured building material is obtained after demolding. S5. Apply an environmentally friendly waterproof coating to the surface of the cured building materials to obtain green building materials.

6. The preparation method according to claim 5, characterized in that, The water-cement ratio in the mixture is 0.35:1-0.40:1, the molding temperature is 30℃-35℃, and the molding time is 1.5h-2h.

7. A green building material, characterized in that, Obtained by the preparation method of claim 5 or 6.

8. The green building material according to claim 7, characterized in that, The green building materials mentioned are artificial marble, fireproof boards, or floor tiles.

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