Magnesite-based cement, green building material and preparation method of magnesite-based cement

Abstract

The invention provides magnesite-based cement, a green building material and a preparation method of the magnesite-based cement and the green building material, and belongs to the technical field of building materials. The magnesite-based cement comprises low-grade magnesite powder, a gelling agent and an optional additive, the use amount of the gelling agent is 4-6 wt% of the mass of the low-grade magnesite powder, the use amount of the additive is 0-1 wt% of the mass of the low-grade magnesite powder, the granularity of the low-grade magnesite powder is 100-200 meshes, and the granularity of the low-grade magnesite powder is 0-10 meshes. The gelling agent is a compound of monopotassium phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignin sulfonate. The magnesite-based cement can efficiently and fully utilize low-grade magnesite resources in an environment-friendly mode, the prepared magnesite-based cement is good in water resistance, and green building materials prepared from the magnesite-based cement are short in maintenance period and can meet the large-scale and high-efficiency modern building material production requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a magnesia-based cement and a green building material and a preparation method thereof. Background Art

[0002] Magnesite, as a key raw material for magnesium cementitious materials, plays an important role in the field of building materials. Although my country has abundant magnesite resources, the reserves of high-grade magnesite (magnesium oxide content ≥45wt%) are relatively limited. 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 impurities and poor reaction activity, resulting in waste of resources.

[0003] In the traditional preparation process of magnesium cementitious materials, magnesite usually needs to undergo a complex pretreatment process. For example, the common acid leaching pretreatment method requires the consumption of a large amount of strong acid, such as sulfuric acid and hydrochloric acid. The use of a large amount of strong acid not only brings high cost problems, but more seriously, it will produce high-concentration acidic wastewater. If these acidic wastewaters are directly discharged without proper treatment, they 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 impurity removal and purification process, which undoubtedly further increases energy consumption and production costs, and also aggravates 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 cementitious material has obvious performance defects. It has poor water resistance and is prone to frosting in humid environments, which greatly limits its wide application in the construction field. In addition, in order to regulate its performance, a large amount of admixtures are often required, which not only increases production costs but also may have potential impacts on the environment.

[0005] Furthermore, in the process of preparing green building materials from traditional magnesium cementitious materials, there are also problems in the maintenance link. The existing process generally requires 14 days or even longer maintenance during the relevant testing and preparation process before the product reaches the designed strength. Such a long maintenance cycle seriously affects production efficiency and is difficult to meet the needs of large-scale, high-efficiency modern building materials production. This has become an obstacle to the expansion of the company's production scale and the timeliness of market supply.

[0006] To sum up, it is of great practical significance and urgency to develop a new green building material preparation process that is efficient, environmentally friendly, can fully utilize low-grade dolomite resources, and can improve product performance and shorten the production cycle compared with similar products. The present invention is based on this background and is committed to breaking through the bottleneck of existing technologies and realizing the efficient utilization of low-grade dolomite in the field of green building material preparation. Summary of the Invention

[0007] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, embodiments of the present invention provide a magnesia-based cement and a green building material and a method for preparing the same. The method for preparing the magnesia-based cement is efficient, environmentally friendly, and fully utilizes low-grade magnesia ore resources. The prepared magnesia-based cement has good water resistance, and the green building material prepared from the magnesia-based cement has a short maintenance period, which can meet the needs of large-scale, high-efficiency modern building material production.

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

[0009] The advantages and technical effects of the magnesia-based cement of the embodiment of the present invention are as follows: (1) The magnesite-based cement of the embodiment of the present invention directly uses low-grade magnesite powder as raw material, without the need for complex mineral processing and enrichment or blending with high-grade ores, which greatly improves the utilization rate of low-grade magnesite and reduces resource waste. It enables a large amount of low-grade magnesite that was originally shelved to be fully utilized, broadens the scope of resource utilization, and helps to alleviate the shortage of high-grade magnesite resources.

[0010] (2) The magnesia-based cement of the embodiment of the present invention includes a gelling agent and optional additives. The gelling agent is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignin sulfonate. By optimizing the gelling agent and additive formula, the new magnesia-based cementing material prepared has better early strength and water resistance, effectively solving the problems of poor water resistance and easy blooming of traditional magnesia-based cementing materials (such as magnesium oxychloride cement), expanding the application range of the product in the construction field, and improving product quality and market competitiveness.

[0011] In some embodiments, the magnesium oxide content in the low-grade magnesite powder is 20 wt%-40 wt%.

[0012] In some embodiments, the mass ratio of potassium dihydrogen phosphate to magnesium sulfate in the gelling agent is 1:2-1:1.

[0013] In some embodiments, the mass ratio of ferrous sulfate to sodium lignin sulfonate in the additive is 0.5:1-1.5:1.

[0014] In a second aspect, an embodiment of the present invention provides a method for preparing magnesia-based cement, comprising the following steps: S1. crushing low-grade magnesite ore to a particle size of 100-200 mesh, a passing rate of 90% or more, to obtain the low-grade magnesite powder; S2. mixing the low-grade magnesite powder with a cementing agent, optionally an additive, to obtain the magnesite-based cement of the first aspect.

[0015] The preparation method of the magnesite-based cement of the embodiment of the present application has the following advantages and technical effects: (1) The preparation method of the magnesite-based cement of the embodiment of the present application directly uses low-grade magnesite as raw material, without the need for complex beneficiation enrichment or blending with high-grade ore, greatly improving the utilization rate of low-grade magnesite, reducing resource waste, making full use of a large amount of low-grade magnesite that has been shelved, widening the range of resource utilization, and helping to alleviate the situation of high-grade magnesite resource shortage.

[0016] (2) Compared with the preparation method of the traditional magnesium cementitious material (such as magnesium oxychloride cement) in the prior art, the preparation method of the magnesite-based cement of the embodiment of the present application omits the acid leaching pretreatment step, avoids the use of a large amount of strong acid, eliminates the generation of high-concentration acid wastewater from the source, effectively reduces the pollution risk to the ecological environment such as soil and water, reduces the cost and environmental pressure of subsequent wastewater treatment, reduces the discharge of tailings and other waste due to the absence of the mineral processing process such as magnetic separation and flotation, reduces the secondary pollution to the environment, and conforms to the development concept of green environmental protection.

[0017] (3) Compared with the preparation method of the traditional magnesium cementitious material (such as magnesium oxychloride cement) in the prior art, the preparation method of the magnesite-based cement of the embodiment of the present application simplifies the preparation process, reduces multiple complex and high-cost links such as acid leaching, multi-stage impurity removal and purification, and mineral processing, reduces equipment investment, raw material consumption and labor cost, and does not need to add a large amount of additive to regulate the performance of the cementitious material, further reducing the production cost and improving the economic benefit of the enterprise.

[0018] (4) The preparation method of the magnesite-based cement of the embodiment of the present application optimizes the formulation of the cementing agent (potassium dihydrogen phosphate and magnesium sulfate are compounded in a specific ratio) and the optional additive (ferrous sulfate and sodium lignosulfonate synergistically act), and the new type of magnesium cementitious material prepared has better early strength and water resistance, effectively solving the problems of poor water resistance and easy frosting of the traditional magnesium cementitious material (such as magnesium oxychloride cement), expanding the application range of the product in the building field, and improving the product quality and market competitiveness.

[0019] In some embodiments, in step S2, the mixing method is ultrasonic dispersion treatment, the ultrasonic power of the ultrasonic dispersion treatment is 200-300 W, and the time of the ultrasonic dispersion treatment is 5-10 min.

[0020] In a third aspect, an embodiment of the present invention provides a method for preparing a green building material, comprising the following steps: S3. The magnesite-based cement of the first aspect is mixed with water to obtain a mixture; the mixture is poured into a mold for molding to obtain a molded building material; S4. The molded building material is cured in an environment with a temperature of 18°C-26°C and a humidity of 60%-70% for 7 days to 11 days, and the cured building material is obtained after demoulding; S5. Apply an environmentally friendly waterproof coating on the surface of the cured building material to obtain a green building material.

[0021] The advantages and technical effects of the preparation method of the green building material of the embodiment of the present invention are as follows: Due to the use of the magnesite-based cement described in the first aspect and the optimization of process parameters such as curing temperature and humidity, the building materials obtained by the preparation method of the green building materials in the embodiment of the present invention can achieve the design strength of traditional magnesia cementitious materials (such as magnesium oxychloride cement) within a shorter curing time, which takes 14 days or even longer to achieve. 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 to the market quickly and increase market share.

[0022] In some embodiments, the water-cement ratio of the mixture is 0.35:1-0.40:1, the temperature of the molding process is 30°C-35°C, and the time of the molding process is 1.5h-2h.

[0023] In a fourth aspect, an embodiment of the present invention provides a green building material obtained by the preparation method described in the third aspect.

[0024] The advantages and technical effects of the green building materials of the embodiments of the present invention are as follows: Due to the adoption of the preparation method of the green building material of the third aspect, the green building material of the embodiment of the present invention has higher early strength and water resistance.

[0025] In some embodiments, the green building material is artificial marble, fireproof board or floor tile. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0027] In a first aspect, the embodiments of the present application provide a magnesite-based cement, which comprises low-grade magnesite powder, a cementing agent and optionally an additive, the cementing agent accounts for 4wt%-6wt% of the mass of the low-grade magnesite powder, the additive accounts for 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 cementing agent is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignosulfonate.

[0028] The magnesite-based cement of the embodiments of the present application directly uses low-grade magnesite powder as raw material, without the need for complex beneficiation or blending with high-grade ore, greatly improving the utilization rate of low-grade magnesite, reducing resource waste, fully utilizing a large amount of low-grade magnesite that has been shelved, widening the range of resource utilization, and helping to alleviate the situation of high-grade magnesite resource shortage.

[0029] The magnesite-based cement of the embodiments of the present application comprises a cementing agent and optionally an additive, the cementing 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 formula of the cementing agent and the additive, the prepared new magnesium-based cementing material has better early strength and water resistance, effectively solving the problems of poor water resistance and easy efflorescence of traditional magnesium-based cementing materials (such as magnesium oxychloride cement), expanding the application range of the product in the building field, and improving the product quality and market competitiveness.

[0030] In the magnesite-based cement of the embodiments of the present application, the particle size of the low-grade magnesite powder is 100-200 mesh, for example, 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 the full contact reaction of the cementing 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 cementing 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 preparation principle, the cementing process of the magnesite-based cement depends on the chemical reaction of magnesium oxide in the low-grade magnesite powder with the cementing agent and the additive. If the particle size of the low-grade magnesite powder is too small, the particle size is relatively small, and the specific surface area is too large, it may cause the cementing agent to be unable to fully wrap or penetrate into the interior of the powder particles, hindering the reaction efficiency. If the particle size of the low-grade magnesite powder is too large, the particle size is relatively large, and the cementing agent is difficult to uniformly disperse into the gap between the powder particles, which may cause local reaction to be insufficient, affecting the formation and structural compactness of the hydration product, and further affecting the improvement of the early strength and water resistance of the building material.

[0031] In some embodiments, the content of magnesium oxide in the low-grade magnesite powder is 20wt%-40wt%. When the content of magnesium oxide in the low-grade magnesite powder is too small, it is not conducive to improving the early strength and water resistance of the building material.

[0032] In the magnesite-based cement of the embodiment of the present invention, the amount of the gelling 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% and the like. In the subsequent process of gelling and forming after adding water to the magnesite-based cement, the main component of the low-grade magnesite powder, magnesium oxide, reacts with water to form magnesium hydroxide, which then reacts with the gelling agent in a series of complex reactions to gradually form a gel with strength. When the amount of the gelling agent is too little, it is not conducive to sufficient hydration reaction, thereby being not conducive to improving the early strength and water resistance of building materials. When the amount of the gelling agent is too much, the improvement of the above effects is not obvious, but the production cost of the magnesite-based cement will be increased.

[0033] In some embodiments, the mass ratio of potassium dihydrogen phosphate to magnesium sulfate in the gelling agent is 1:2-1:1, for example, 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 material. When the mass ratio of potassium dihydrogen phosphate to magnesium sulfate is too large, it is not conducive to the full reaction of the gelling agent with low-grade magnesite powder, which may lead to increased costs and insignificant effects on improving early strength and water resistance. The magnesium ions provided by magnesium sulfate are the key components for forming hydration products such as basic magnesium sulfate. If the ratio is too low, it may affect the crystal growth efficiency, delay the hydration reaction process, and lead to insufficient improvement in early strength. Excessive use of potassium dihydrogen phosphate will directly increase the cost of the gelling agent.

[0034] In the magnesite-based cement of the embodiment of the present invention, the amount of the additive is 0-1wt% of the mass of the low-grade magnesite powder, for example, 0, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, etc. In the subsequent process of gelling and forming after adding water to the magnesite-based cement, the main component of the low-grade magnesite powder, magnesium oxide, reacts with water to form magnesium hydroxide, which then reacts with the additive to produce a series of complex reactions, gradually forming a gel with strength, further improving the early strength and water resistance of the building material. When the amount of the additive is too little, it is not conducive to improving the early strength and water resistance of the building material. When the amount of the additive is too much, the improvement of the above effects is not obvious, but the production cost of the magnesite-based cement will increase.

[0035] In some embodiments, the mass ratio of ferrous sulfate to sodium lignin sulfonate 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 lignin sulfonate is too low, it is not conducive to improving the compressive strength and water resistance of the building material. When the mass ratio of ferrous sulfate to sodium lignin sulfonate 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 lignin sulfonate, as a dispersant, needs to form an appropriate ratio with ferrous sulfate to promote uniform dispersion of the gelling system. If there is too much ferrous sulfate, it may destroy the dispersion effect, resulting in a loose structure of the hydration product, affecting the strength and water resistance. If the proportion of ferrous sulfate is too high, it will directly increase the cost of raw materials, but it will not be able to significantly improve the 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 the formation of gel through ion reaction, but its excessive amount may exceed the reaction capacity of the system, and the excess components cannot participate in the reaction, resulting in waste of resources and no additional gain.

[0036] In a second aspect, an embodiment of the present invention provides a method for preparing magnesia-based cement, comprising the following steps: S1. The low-grade magnesite ore is crushed to a particle size of 100 mesh -200 mesh, with a pass rate of ≥90%, to obtain the low-grade magnesite powder; S2. The low-grade magnesite powder is mixed with a gelling agent and optionally an additive to obtain the magnesite-based cement described in the first aspect.

[0037] The preparation method of magnesite-based cement in the embodiment of the present invention directly uses low-grade magnesite as raw material, without the need for complex mineral processing and enrichment or blending with high-grade ores, which greatly improves the utilization rate of low-grade magnesite and reduces resource waste. It enables a large amount of low-grade magnesite that was originally shelved to be fully utilized, broadens the scope of resource utilization, and helps alleviate the shortage of high-grade magnesite resources.

[0038] Compared with the preparation method of traditional magnesia cementitious materials (such as magnesium oxychloride cement) in the prior art, the preparation method of magnesia-based cement in the embodiment of 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 pollution risk to the ecological environment such as soil and water bodies, reduces the cost and environmental pressure of subsequent wastewater treatment, and since it does not involve mineral processing processes such as magnetic separation and flotation, it reduces the discharge of waste such as tailings, reduces secondary pollution to the environment, and conforms to the development concept of green environmental protection.

[0039] Compared with the preparation method of the traditional magnesia cementitious material (such as magnesium oxychloride cement) in the prior art, the preparation method of the magnesite-based cement in the embodiment of the present application simplifies the preparation process, reduces multiple complex and high-cost links such as acid leaching, multi-stage impurity removal and purification, and mineral processing, reduces equipment investment, raw material consumption and labor cost, and does not need to add a large amount of additive to regulate the performance of the cementitious material, thereby further reducing the production cost and improving the economic benefit of the enterprise.

[0040] The preparation method of the magnesite-based cement in the embodiment of the present application optimizes the formulation of the cementing agent (potassium dihydrogen phosphate and magnesium sulfate are compounded in a specific ratio) and the optional additive (ferrous sulfate and sodium lignosulfonate synergistically act), and the prepared new type of magnesia cementitious material has better early strength and water resistance, effectively solves the problems of poor water resistance and easy efflorescence of the traditional magnesia cementitious material (such as magnesium oxychloride cement), expands the application range of the product in the building field, and improves the product quality and market competitiveness.

[0041] In some embodiments, in step S2, the mixing of the materials is performed by ultrasonic dispersion treatment, the ultrasonic power of the ultrasonic dispersion treatment is 200W-300W, and the time of the ultrasonic dispersion treatment is 5min-10min. The ultrasonic dispersion treatment can enhance the dispersibility of the cementing agent and the optional additive in the low-grade magnesite powder.

[0042] In a third aspect, the embodiment of the present application provides a preparation method of green building materials, comprising the following steps: S3. mixing the magnesite-based cement in the first aspect with water to obtain a mixed material; pouring the mixed material into a mold for forming treatment to obtain a formed building material; S4. curing the formed building material in an environment with a temperature of 18℃-26℃ and a humidity of 60%-70% for 7-11 days to obtain a cured building material after demolding; S5. applying an environmentally-friendly waterproof coating on the surface of the cured building material to obtain a green building material.

[0043] Due to the use of the magnesite-based cement in the first aspect and the optimization of the curing temperature, humidity and other process parameters, the preparation method of the green building material in the embodiment of the present application can make the building material reach the design strength in a shorter curing time than the traditional magnesia cementitious material (such as magnesium oxychloride cement) which needs 14 days or even a longer time, greatly improves the production efficiency of the building material, meets the demand of large-scale and high-efficiency modern building material production, helps the enterprise to quickly respond to the market and improve the market share.

[0044] In some embodiments, the water-cement ratio in the mixture is 0.35:1-0.40:1, the temperature of the molding process is 30°C-35°C, and the molding time is 1.5h-2h. From the perspective of chemical reaction kinetics, during the molding process of building materials, the chemical reaction between magnesium oxide in low-grade magnesia ore powder and water, gelling agent, and optional additives requires an appropriate temperature to promote. A temperature of 30°C-35°C can moderate the reaction rate, ensuring that the reaction proceeds fully without causing local overheating or stress defects due to excessive reaction. For example, at 30°C-35°C, the hydration reaction of magnesia-based cement can proceed well, which is conducive to the formation of 5·1·8 crystal phase, thereby improving the strength and stability of the building material. From the perspective of water evaporation and solidification balance, this temperature range helps to maintain a suitable evaporation rate of water inside the building material and achieve a good balance between water evaporation and material solidification. If the temperature is too low and the water evaporates too slowly, it will prolong the molding time and reduce production efficiency. It may also cause problems such as pores and reduced strength of the building material due to excessive water during the solidification process. Excessively high temperatures and rapid evaporation of moisture can cause the surface of building materials to dry out prematurely, forming a hard crust that hinders internal moisture evaporation and chemical reactions, and can easily lead to defects such as cracking and delamination. Therefore, at 30°C-35°C, the moisture evaporation rate can both ensure rapid curing of building materials and avoid the occurrence of the aforementioned undesirable phenomena. From the perspective of material plasticity and formability, within this temperature range, the mixture has good plasticity and fluidity, facilitating molding operations and enabling better filling of building materials in molds, resulting in products with complete shapes and high dimensional accuracy. It also helps reduce defects such as pores, missing edges and corners caused by poor material fluidity during the molding process.

[0045] In some embodiments, the mold is made of reusable stainless steel, and the mold surface is polished, which facilitates subsequent demoulding.

[0046] During the curing step, the curing temperature is 18-26°C. The gelling process involves a complex series of reactions between the magnesium oxide in the low-grade magnesite powder and the gelling agent and, optionally, additives, to form a gelled product with a certain strength. A temperature of 18-26°C is ideal for these chemical reactions, neither slowing down the reaction rate due to low temperatures, which would extend the production cycle, nor accelerating the reaction due to high temperatures, which would produce undesirable reaction products and affect the performance of the building material. From the perspective of moisture evaporation, a curing temperature of 18-26°C achieves a moderate evaporation rate. If the curing temperature is too high, rapid evaporation can lead to uneven moisture distribution within the building material, resulting in defects such as cracking. On the other hand, if the curing temperature is too low, evaporation can be too slow, leaving the building material damp for an extended period of time, affecting the hardening process of the cementitious material and reducing its early strength. Based on industry standards and experience, 18-26°C is a relatively reasonable temperature range for curing building materials.

[0047] In the curing process, the curing time is set to 7-11 days for the following reasons: (1) The strength of magnesite building materials depends on the hydration reaction of the magnesite-based cement of the present invention. Magnesium oxide, the main component of low-grade magnesite powder, reacts with water to form magnesium hydroxide. The magnesium hydroxide then undergoes a series of complex reactions with the gelling agent and optional additives to gradually form a strong gel. Generally speaking, this reaction process is relatively fast in the first few days and then gradually slows down. The main hydration reaction is basically completed within 7-11 days, allowing the building material to obtain relatively stable strength.

[0048] (2) Referring to the curing standards for similar magnesia cementitious materials in the construction industry, such as some magnesia fireproof boards and magnesia 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 meet certain strength requirements without excessively extending the production cycle. This curing time is consistent with such standards.

[0049] (3) Actual performance test results: Through a large number of actual production and performance tests, it was found that low-grade magnesite green building materials can achieve the design requirements of compressive strength, flexural strength and other performance indicators by curing for 7 to 11 days at a curing temperature of 18°C ​​to 26°C. If the curing time is further extended, the strength growth rate will gradually decrease. From the perspective of economic benefits and production efficiency, 7 to 11 days is a more appropriate curing time.

[0050] (4) Adaptability to environmental factors: In actual production environments, a temperature of 18°C-26°C and a curing time of 7 days-11 days can better adapt to environmental changes in different seasons and regions. It will not lead to incomplete hydration reaction and slow strength growth of building materials due to too short curing time when the ambient temperature is low or the humidity is high, nor will it lead to excessive drying of building materials and cracks when the ambient temperature is high due to too long curing time.

[0051] In summary, a curing temperature of 18-26°C 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 products.

[0052] The green building material preparation method according to the embodiment of the present invention can achieve the design strength of the building material within a shorter curing time (7-11 days), which is 14 days or even longer for building materials made from traditional magnesia cementitious materials (such as magnesium oxychloride cement). This may be due to the following reasons: (1) The phosphate ions and potassium ions provided by potassium dihydrogen phosphate, and the magnesium ions and sulfate ions provided by magnesium sulfate, can synergize with other components in the system to promote the hydration reaction of the magnesia cement. For example, the phosphate ions can combine with the magnesium ions to form some intermediate products that facilitate the formation of hydration products, accelerating the hydration process and thus shortening the curing period of the building material. At the same time, the potassium ions can increase the ionic strength of the solution, promoting ion exchange and chemical reactions.

[0053] (2) The components in the compound of potassium dihydrogen phosphate and magnesium sulfate can provide favorable conditions for the crystal growth of the hydration products of the magnesia cement. For example, the magnesium ions in magnesium sulfate are the key ions for the formation of hydrated products such as basic magnesium sulfate, and their presence helps the rapid formation and growth of these crystals. Potassium dihydrogen phosphate can also adjust the growth environment of the crystals by affecting the pH and ion concentration of the solution, allowing the crystals to grow to a sufficient size in a relatively short time, thereby increasing the early strength of the magnesia-based cement of the embodiments of the present application and shortening the curing period of the building material.

[0054] (3) The addition of potassium dihydrogen phosphate and magnesium sulfate can lower the surface tension of the system, making the distribution of water on the surface of the magnesia-based cement particles of the embodiments of the present application more uniform, facilitating the full contact between water and the magnesia-based cement of the embodiments of the present application and accelerating the hydration reaction. At the same time, the lower surface tension also helps the uniform deposition and growth of the hydration products on the particle surface, improving the structural density of the building material and thus shortening the curing time of the building material.

[0055] (4) The compound of potassium dihydrogen phosphate and magnesium sulfate can generate some fine crystals or gel-like substances during the hydration process, which can fill the pores inside the building material, reduce the porosity, and improve the density of the building material. On the one hand, this helps to improve the early strength of the building material, allowing it 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 magnesia-based cement of the embodiments of the present application, thereby shortening the curing period of the building material.

[0056] 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 ester waterproof coating. The presence of the waterproof coating can further improve the water resistance of the green building material.

[0057] In a fourth aspect, the embodiments of the present application provide a green building material obtained by the method for preparing a green building material of the third aspect.

[0058] Due to the adoption of the preparation method of the green building material of the third aspect, the green building material of the embodiment of the present invention has higher early strength and water resistance.

[0059] In some embodiments, the green building material is artificial marble, fireproof board or floor tile.

[0060] The present invention is described in detail below with reference to the embodiments.

[0061] Example 1 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 120 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0062] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a mass ratio of 1:1). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 40 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which is adapted to the subsequent performance testing standards. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0063] Curing treatment: the formed building materials are placed in an environment with a temperature of 20° C. and a humidity of 65 wt % for curing for 9 days, and the cured building materials are obtained after demoulding.

[0064] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0065] Example 2 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 35wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0066] Gelling molding: 10 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a 2:3 mass ratio) and 2 kg of additives (ferrous sulfate to sodium lignin sulfonate in a 1:1 mass ratio) were added to 200 kg of low-grade magnesite ore powder. The mixture was ultrasonically dispersed at 260 W for 8 minutes to produce magnesite-based cement. 85 kg of water was then added to the magnesite-based cement and stirred at 33°C to obtain a mixture. The mixture was poured into a polished stainless steel mold, the mold size of which was adapted to the subsequent performance testing standards. During the pouring process, the mold was gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasted 1.8 hours.

[0067] Curing treatment: The formed building materials are placed in an environment with a temperature of 22° C. and a humidity of 70 wt % for curing for 9 days, and the cured building materials are obtained after demoulding.

[0068] Post-processing: Apply a 0.2mm thick acrylic waterproof coating on the surface of the cured building materials to obtain green building materials.

[0069] Example 3 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 38wt% is crushed to a particle size of 180 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0070] Gelling molding: Add 7.5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a 2:3 mass ratio) and 1.5 kg of additives (ferrous sulfate to sodium lignin sulfonate in a 1:1 mass ratio) to 150 kg of low-grade magnesite ore powder. Ultrasonic dispersion is then performed at 260 W for 8 minutes to produce magnesite-based cement. 60 kg of water is then added to the magnesite-based cement and stirred at 30°C to obtain a mixture. The mixture is then poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts for 2 hours.

[0071] Curing treatment: The formed building materials are placed in an environment with a temperature of 25° C. and a humidity of 60 wt % for curing for 9 days, and the cured building materials are obtained after demoulding.

[0072] Post-processing: Apply a 0.3mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0073] Example 4 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0074] Gelling molding: To 100 kg of low-grade magnesite powder, add 4 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a mass ratio of 1:1). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 38 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, a small vibration device is used to gently vibrate the mold to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0075] Curing treatment: The formed building materials are placed in an environment with a temperature of 22° C. and a humidity of 65 wt % for curing for 9 days, and the cured building materials are obtained after demoulding.

[0076] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0077] Example 5 Low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0078] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a 1:2 mass ratio) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a 1:1 mass ratio). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 39 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0079] Curing treatment: The formed building materials are placed in an environment with a temperature of 22° C. and a humidity of 65 wt % for curing for 9 days, and the cured building materials are obtained after demoulding.

[0080] Post-processing: Apply a 0.25mm thick acrylic waterproof coating to the surface of the cured building materials to obtain green building materials.

[0081] Example 6 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0082] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a 1:1 mass ratio) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a 1:1 mass ratio). Ultrasonic dispersion is then applied to the mixture at 260 W for 8 minutes to produce magnesite-based cement. 38 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is then poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles from the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0083] Curing treatment: The formed building materials are placed in an environment with a temperature of 22° C. and a humidity of 65 wt % for curing for 9 days, and the cured building materials are obtained after demoulding.

[0084] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0085] Example 7 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0086] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 0.5 kg of additive (ferrous sulfate to sodium lignin sulfonate in a mass ratio of 1:1). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 37 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, a small vibration device is used to gently vibrate the mold to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0087] Curing treatment: The formed building materials are placed in an environment with a temperature of 22°C and a humidity of 65% for curing for 9 days, and the cured building materials are obtained after demoulding.

[0088] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0089] Example 8 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0090] Gelling molding: Add 5 kg of gelling agent (potassium dihydrogen phosphate: magnesium sulfate in a mass ratio of 2:3) to 100 kg of low-grade magnesite ore powder. Without adding any additives, ultrasonically disperse the mixture at 260 W for 8 minutes to produce 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, the mold size adapted to the subsequent performance testing standards. During the pouring process, use a small vibration device to gently vibrate the mold to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0091] Curing treatment: The formed building materials are placed in an environment with a temperature of 22°C and a humidity of 65% for curing for 9 days, and the cured building materials are obtained after demoulding.

[0092] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0093] Example 9 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0094] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a mass ratio of 0.5:1). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 38 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0095] Curing treatment: The formed building materials are placed in an environment with a temperature of 22°C and a humidity of 65% for curing for 9 days, and the cured building materials are obtained after demoulding.

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

[0097] Example 10 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0098] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a mass ratio of 1.5:1). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 38 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0099] Curing treatment: The formed building materials are placed in an environment with a temperature of 22°C and a humidity of 65% for curing for 9 days, and the cured building materials are obtained after demoulding.

[0100] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0101] Example 11 Crushing treatment: low-grade magnesite ore with a magnesium oxide content of 32wt% is crushed to a particle size of 150 mesh with a pass rate of ≥90% to obtain low-grade magnesite ore powder.

[0102] Gelling molding: To 100 kg of low-grade magnesite powder, add 5 kg of gelling agent (potassium dihydrogen phosphate to magnesium sulfate in a mass ratio of 2:3) and 1 kg of additive (ferrous sulfate to sodium lignin sulfonate in a mass ratio of 1:1). Ultrasonic dispersion of the mixture is performed at 260 W for 8 minutes to produce magnesite-based cement. 38 kg of water is then added to the magnesite-based cement and stirred at 32°C to obtain a mixture. The mixture is poured into a polished stainless steel mold, the mold size of which meets the standards for subsequent performance testing. During the pouring process, the mold is gently vibrated using a small vibration device to remove bubbles in the mixture and ensure molding quality. The entire molding process lasts 1.5 hours.

[0103] Curing treatment: The formed building materials are placed in an environment with a temperature of 22°C and a humidity of 65% for curing for 9 days, and the cured building materials are obtained after demoulding.

[0104] Post-processing is omitted, so the building materials after curing in this embodiment are the green building materials finally obtained.

[0105] Comparative Example 1 Raw material selection and proportioning: Conventional commercially available magnesium oxychloride cement is selected, whose main components are light-burned magnesia (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 properties of cement. The active magnesium oxide content of the light-burned magnesia in the magnesium oxychloride cement is 80wt%.

[0106] Cementitious molding: Add 38kg of water to 106kg of magnesium oxychloride cement and stir evenly at 32°C to obtain a mixture. During the stirring process, the lightly burned magnesium oxide in the cement gradually undergoes 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 test standards. During the pouring process, a small vibration device is used to slightly vibrate the mold to eliminate bubbles in the mixture and ensure the molding quality. The entire molding process lasts 1.5 hours.

[0107] Curing treatment: The formed building materials are placed in an environment with a temperature of 22°C and a humidity of 65% for curing for 9 days, and the cured building materials are obtained after demoulding.

[0108] Post-treatment: Apply a 0.25mm thick acrylic waterproof coating on the surface of the cured building material to obtain a green building material.

[0109] Performance testing: (1) Compressive strength test (not immersed in water): 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 a size of 100mm×100mm×100mm. Load them on a universal material testing machine at a loading rate of 0.5MPa per second until the test block is destroyed. The failure load value is recorded and the value is calculated according to the formula Calculate compressive strength; in: is the compressive strength (MPa); F is the failure load value of the specimen (N); A is the bearing area of ​​the test block (mm 2 , for a test block of 100mm×100mm, (A=100X100=10 4 mm 2 )).

[0110] (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 a size of 100mm×100mm×100mm. The test blocks are then completely immersed in water for 7 days and then taken out. On a universal material testing machine, load at a loading rate of 0.5MPa per second until the test blocks are destroyed. The destruction load value is recorded and calculated according to the formula Calculate compressive strength; in: is the compressive strength (MPa); F is the failure load value of the specimen (N); A is the bearing area of ​​the test block (mm 2 , for a test block of 100mm×100mm, (A=100X100=10 4 mm 2 )).

[0111] (3) Water absorption test: Refer to GB / T17657-2013 "Test methods for physical and chemical properties of artificial boards and veneer artificial boards". First, dry the green building materials to constant weight and record its mass m1. Then, immerse the test block completely in water. After soaking for 48 hours, take it out and wipe the surface moisture with a wet cloth. Immediately weigh its mass m2 and calculate the water absorption rate according to the formula (m2-m1) / m1×100%.

[0112] Table 1. Composition of building materials of the above embodiments and comparative examples

[0113] Table 2. Compressive strength and water resistance of the building materials of the above embodiments and comparative examples

[0114] In the present invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0115] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A magnesite-based cement, characterized in that: The invention comprises low-grade magnesite powder, a gelling agent and optional additives, wherein the amount of the gelling agent 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 gelling agent is a compound of potassium dihydrogen phosphate and magnesium sulfate, and the additive is a compound of ferrous sulfate and sodium lignin sulfonate.

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

3. Magnesium-based cement according to claim 1 or 2, characterized in that The mass ratio of potassium dihydrogen phosphate to magnesium sulfate in the gelling agent is 1:2-1:

1.

4. Magnesium-based cement according to claim 1 or 2, characterized in that The mass ratio of ferrous sulfate to sodium lignin sulfonate in the additive is 0.5:1-1.5:

1.

5. The method for preparing magnesia-based cement according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. The low-grade magnesite ore is crushed to a particle size of 100 mesh -200 mesh, with a pass rate of ≥90%, to obtain the low-grade magnesite powder; S2. The low-grade magnesite powder is mixed with a gelling agent and optionally an additive to obtain the magnesite-based cement.

6. The method for preparing magnesia-based cement according to claim 5, characterized in that: In step S2, the material mixing method is ultrasonic dispersion treatment, the ultrasonic power of the ultrasonic dispersion treatment is 200W-300W, and the time of the ultrasonic dispersion treatment is 5min-10min.

7. A method for preparing green building materials, characterized in that: The following steps are involved: S3. The magnesite-based cement according to any one of claims 1 to 4 is mixed with water to obtain a mixture; the mixture is poured into a mold for molding to obtain a molded building material; S4. The molded building material is cured in an environment with a temperature of 18°C-26°C and a humidity of 60%-70% for 7 days to 11 days, and the cured building material is obtained after demoulding; S5. Apply an environmentally friendly waterproof coating on the surface of the cured building material to obtain a green building material.

8. The preparation method according to claim 7, characterized in that The water-cement ratio of the mixture is 0.35:1-0.40:1, the temperature of the molding process is 30° C.-35° C., and the time of the molding process is 1.5 h-2 h.

9. A green building material, characterized in that: Obtained by the preparation method of claim 7 or 8.

10. The green building material according to claim 9, characterized in that: The green building materials are artificial marble, fireproof board or floor tiles.

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