Gypsum plastering mortar with cohesive strength enhanced by gradient aggregate and preparation method of gypsum plastering mortar

Abstract

The invention discloses gypsum plastering mortar with gradient aggregate enhanced cohesion strength and a preparation method thereof.The gypsum plastering mortar is prepared from anhydrite, modified glass beads, modified quartz sand, ash calcium, modified heavy calcium carbonate, cellulose, starch ether, an air entraining agent, a retarder and a thixotropic lubricant, and the preparation method comprises the steps of S1, preparing the modified glass beads, S2, preparing the modified heavy calcium carbonate, S3, preparing the modified quartz sand, S5, preparing the modified quartz sand, S6, preparing the modified quartz sand, and S6, preparing the gypsum plastering mortar. S4, all the components in the formula are mixed, through gradient particle size design of the modified glass beads, the modified quartz sand, the modified heavy calcium carbonate and the ash calcium, a close packing structure is formed, the compactness of the mortar is improved, and therefore the structural strength of the gypsum plastering mortar is effectively improved; and the interface bonding force with a gypsum matrix can be enhanced, a three-dimensional network is formed with cellulose and starch ether, and the cohesion strength of the gypsum plastering mortar is effectively improved, so that the structural strength of the gypsum plastering mortar is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of plastering mortar, and particularly relates to a gypsum plastering mortar with gradient aggregate enhancing cohesive strength and a preparation method thereof. Background Art

[0002] Gypsum plastering mortar is made of hemihydrate gypsum as the base material, and then inorganic fillers, additives and other components are added and dry-mixed. Gypsum plastering mortar abandons the traditional way of using cement-based as the gelling material, which not only simplifies the construction process but also has the characteristics of environmental protection and energy conservation. Traditional gypsum plastering mortar has certain deficiencies in terms of strength and crack resistance. Especially when facing complex and changeable construction environments and requirements, such as the joints of different walls, grooving and repair areas, etc., its performance often fails to meet the needs. Quality problems such as cracking and hollowing are likely to occur in these parts.

[0003] Based on the above situation, in the prior art, the patent with the patent number CN201811082049.0 discloses an improved gypsum plastering mortar and a preparation method thereof, which is applicable to the base plastering gypsum for leveling the base layer. The method includes steps such as dissolving welan gum and retarder in water and stirring until uniformly dispersed to make an additive solution; mixing gypsum and quartz sand evenly and adding the additive solution and stirring evenly, etc. The above gypsum plastering mortar solves the problems in the prior art that the environmental adaptability of cellulose is poor and the strength of gypsum plastering mortar will be reduced under different dosages. The prepared gypsum plastering mortar has good stability, workability, fluidity and water retention capacity, and its initial setting time, final setting time, flexural strength, compressive strength, and tensile bond strength.

[0004] Although the above gypsum plastering mortar has good flexural strength and compressive strength by dissolving welan gum and retarder in water and stirring until uniformly dispersed to make an additive solution, and then adding gypsum and quartz sand and mixing evenly, the above gypsum plastering mortar still has deficiencies. Specifically, the filler in the composition formula of the above gypsum plastering mortar is quartz sand with a uniform particle size, which makes the gypsum plastering mortar lack gradient filling of the filler in the structure, resulting in insufficient flexural and compressive strengths when the above gypsum plastering mortar is actually used. Summary of the Invention

[0005] Aiming at the technical defects in the background art, the present invention proposes a gypsum plastering mortar with gradient aggregate enhancing cohesive strength and a preparation method thereof, which solves the above technical problems and meets the actual needs. The specific technical solutions are as follows: A gypsum plaster mortar with gradient aggregate enhanced cohesive strength comprises the following raw materials, measured in parts by weight: 400-500 parts of anhydrous gypsum, 50-100 parts of modified glass beads, 80-150 parts of modified quartz sand, 15-30 parts of lime, 200-250 parts of modified heavy calcium, 5-10 parts of cellulose, 0.5-1 part of starch ether, 0.5-1 part of air entraining agent, 1-5 parts of retarder, and 0.5-1 part of thixotropic lubricant. The modified quartz sand is obtained by modifying quartz sand with a mercaptosilane coupling agent, and the modified heavy calcium is obtained by modifying heavy calcium powder with polyvinyl pyrrolidone. The particle size ratio of the modified glass bead powder, (modified quartz sand / lime calcium), and modified heavy calcium is 1:0.414:(0.171-0.225).

[0006] As a further technical solution of the present invention, the particle size of the modified glass bead powder is 0.1-0.5 mm, the particle size of the modified quartz sand is 41-207 μm, the particle size of the lime is 41-207 μm, and the particle size of the modified heavy calcium is 17-86 μm.

[0007] As a further technical solution of the present invention, the modified glass beads are composed of glass microbeads and a composite chitosan shell layer coated on the surface of the glass microbeads. The composite chitosan shell layer is filled with modified activated carbon, and the modified activated carbon is obtained by impregnating activated carbon powder in a soluble cobalt salt and then drying it.

[0008] As a further technical solution of the present invention, the anhydrous gypsum is obtained by high-temperature calcination of phosphogypsum, the cellulose is selected from any one of hydroxypropyl methylcellulose and hydroxyethyl methylcellulose, the molecular weight of the cellulose is 7000-10000, and the starch ether is modified potato starch ether.

[0009] As a further technical solution of the present invention, the air entraining agent is any one of rosin-based air entraining agent, sodium alkyl sulfonate, and sodium alkylbenzene sulfonate; the retarder is selected from any one of protein-based retarder, modified amino acid salt retarder, boric acid retarder, citric acid retarder, and tartaric acid retarder; and the thixotropic lubricant is any one of organic bentonite and magnesium aluminum silicate natural mineral salt.

[0010] A method for preparing gypsum plaster mortar with gradient aggregate to enhance cohesive strength comprises the following steps: S1. Prepare modified glass beads: dissolve chitosan in 2% acetic acid solution, then add modified activated carbon and glass beads in sequence, stir for 30-60 minutes to complete the coating, centrifuge the glass beads, and dry to obtain modified glass beads; S2. Prepare modified heavy calcium carbonate. Dissolve polyvinylpyrrolidone in deionized water, add sodium hydroxide solution dropwise to adjust the pH of the solution to 10, then add heavy calcium carbonate powder, and then heat up and stir for a period of time. Filter and dry to obtain modified heavy calcium carbonate; S3. Prepare modified quartz sand. Stir and dissolve mercapto silane coupling agent in ethanol solution, then add quartz sand, and react for a period of time under stirring. Filter and separate, and dry to obtain modified quartz sand; S4. Add anhydrous gypsum, modified glass beads, modified quartz sand, hydrated lime, modified heavy calcium carbonate, cellulose, starch ether, air-entraining agent, setting retarder, thixotropic lubricant into a stirrer and stir evenly to obtain dry mortar powder. Then add an appropriate amount of water and continue to stir evenly to obtain gypsum plastering mortar.

[0011] As a further technical solution of the present invention, in step S1, the preparation method of the modified activated carbon is: prepare a cobalt salt solution with a concentration of 1.0 mol / L from soluble cobalt salt, then add activated carbon powder and cobalt salt solution into a stirrer, and impregnate for 4 - 5 h under stirring. Filter the solid and dry to obtain modified activated carbon. The mass ratio of the activated carbon powder to the cobalt salt solution is 1:10. The soluble cobalt salt is any one of cobalt nitrate and cobalt chloride. The particle size of the activated carbon powder is 10 - 50 μm.

[0012] As a further technical solution of the present invention, in step S1, weigh 8 g of chitosan, add it to 1 L of 2% acetic acid solution, and slowly stir for half an hour to dissolve. Then weigh 1 g of modified activated carbon and 3 g of glass microspheres, mix evenly, and then add 1 L of 0.5% sodium tripolyphosphate, stir for 60 min to complete coating, centrifuge, and dry the precipitate to obtain modified glass beads.

[0013] As a further technical solution of the present invention, in step S2, add 1 g of polyvinylpyrrolidone to 500 mL of deionized water, stir magnetically at room temperature for 3 h to dissolve completely, add sodium hydroxide solution dropwise to adjust the pH of the solution to 11.5, then add 100 mg of heavy calcium carbonate powder, heat up to 60 °C in an oil bath and stir for 4 h, filter the solid, and dry to obtain modified heavy calcium carbonate powder.

[0014] As a further technical solution of the present invention, in step S3, put a certain amount of quartz sand and 3 - mercaptopropyltriethoxysilane - ethanol solution into a stirrer respectively, react for 20 min under stirring, then filter the solid and dry to obtain modified quartz sand. The mass ratio of the quartz sand to the 3 - mercaptopropyltriethoxysilane - ethanol solution is 1:100. The mass percentage of 3 - mercaptopropyltriethoxysilane and ethanol solution in the 3 - mercaptopropyltriethoxysilane - ethanol solution is 5:95. The ethanol solution is 90% ethanol aqueous solution.

[0015] The beneficial effects of the present invention are as follows: Through the gradient particle size design of modified glass beads, modified quartz sand, modified heavy calcium carbonate, and hydrated lime, a closely packed structure is formed, reducing the porosity and enhancing the density of the mortar, thereby effectively improving the structural strength of the gypsum plastering mortar. The quartz sand modified by silane coupling agent and the heavy calcium carbonate coated with polyvinylpyrrolidone can enhance the interfacial bonding force with the gypsum matrix and reduce the generation of microcracks. The chitosan on the surface of the modified glass beads and the gradient aggregate form a multi-scale reinforcement network, and form a three-dimensional network with cellulose and starch ether, effectively improving the cohesive strength of the gypsum plastering mortar, and further improving the structural strength of the gypsum plastering mortar. Specific embodiments

[0016] The following describes the embodiments of the present invention in conjunction with relevant examples. The embodiments of the present invention are not limited to the following examples, and the relevant necessary components involved in the present invention should be regarded as well-known technologies in the technical field, which can be known and mastered by those skilled in the technical field.

[0017] A gypsum plastering mortar with gradient aggregate enhancing cohesive strength, by weight, includes the following raw materials: 400-500 parts of anhydrous gypsum, 50-100 parts of modified glass beads, 80-150 parts of modified quartz sand, 15-30 parts of hydrated lime, 200-250 parts of modified heavy calcium carbonate, 5-10 parts of cellulose, 0.5-1 part of starch ether, 0.5-1 part of air-entraining agent, 1-5 parts of retarder, 0.5-1 part of thixotropic lubricant. The modified quartz sand is obtained by modifying quartz sand with mercapto silane coupling agent, the modified heavy calcium carbonate is obtained by modifying heavy calcium carbonate powder with polyvinylpyrrolidone, and the particle size ratio of the modified glass bead powder, (modified quartz sand / hydrated lime), and modified heavy calcium carbonate is 1:0.414:(0.171-0.225).

[0018] Further, in the above solution, the anhydrous gypsum is obtained by high-temperature calcination of phosphogypsum. The modified glass beads are composed of glass microspheres and a composite chitosan shell layer coated on the surface of the glass microspheres. The composite chitosan shell layer is filled with modified activated carbon, and the modified activated carbon is obtained by impregnating activated carbon powder in soluble cobalt salt and then drying.

[0019] Further, in the above solution, the particle size of the modified glass bead powder is 0.1-0.5 mm, the particle size of the modified quartz sand is 41–207 μm, the particle size of the hydrated lime is 41–207 μm, and the particle size of the modified heavy calcium carbonate is 17–86 μm.

[0020] The gypsum plastering mortar of the present invention forms a gradient particle size through modified glass beads powder, modified quartz sand, hydrated lime, and modified heavy calcium carbonate, enabling each component to be closely packed in the mortar, reducing the porosity, thereby enhancing the density of the mortar and effectively strengthening the structural strength of the gypsum plastering mortar. The modified glass beads are composed of glass microspheres and a composite chitosan shell layer coated on the surface of the glass microspheres. The composite chitosan shell layer is filled with modified activated carbon. The chitosan forms a multi-scale reinforcement network with the gradient aggregate and simultaneously forms a three-dimensional network with cellulose and starch ether, effectively enhancing the cohesive strength of the gypsum plastering mortar and further enhancing its structural strength.

[0021] The modified quartz sand is obtained by modifying quartz sand with a mercapto silane coupling agent. The quartz sand modified by the silane coupling agent can enhance the interfacial bonding force with the gypsum matrix, reduce the generation of microcracks, thereby improving the overall performance of the gypsum plastering mortar and making its structure more stable. The modified heavy calcium carbonate is obtained by modifying heavy calcium carbonate powder with polyvinylpyrrolidone. The heavy calcium carbonate coated with polyvinylpyrrolidone can also enhance the interfacial bonding force with the gypsum matrix and reduce the generation of microcracks, contributing to the improvement of the structural strength and stability of the gypsum plastering mortar.

[0022] As one of the preferred embodiments of the present invention, the cellulose is selected from any one of hydroxypropyl methyl cellulose or hydroxyethyl methyl cellulose, the molecular weight of the cellulose is 7000 - 10000, and the starch ether is a modified potato starch ether.

[0023] Specifically, the cellulose is selected as hydroxyethyl methyl cellulose with a molecular weight of 10000. This type of cellulose ether can dissolve in water and form a solution with a certain viscosity. In the gypsum plastering mortar, it can increase the viscosity of the mortar, enabling the mortar to better adhere to substrates such as walls during construction and not easily flow, ensuring the smooth progress of construction. For example, when applying the mortar on a vertical wall, the appropriate viscosity can make the mortar evenly adhere to the wall without sagging. At the same time, hydrophilic groups such as hydroxyl groups on the cellulose molecular chain can adsorb and retain water. During the hardening process of the gypsum plastering mortar, cellulose can slow down the evaporation rate of water, allowing sufficient water inside the mortar for the hydration reaction. This is crucial for the hydration of the gypsum matrix because the hydration of gypsum requires certain water conditions. The water retention effect can ensure the full hydration of gypsum, forming strong hydration products, thereby improving the strength and durability of the mortar.

[0024] Modified potato starch ether can improve the anti-sagging performance of gypsum plastering mortar. When constructing on vertical walls or inclined surfaces, it can prevent the mortar from sagging due to its own weight and keep the shape and thickness of the mortar uniform. The modified potato starch ether and cellulose act synergistically to jointly improve the performance of gypsum plastering mortar. Cellulose mainly plays a role in thickening and water retention, while starch ether focuses on improving the construction performance and anti-sagging property. The two cooperate with each other to enable the mortar to have good construction performance while ensuring the strength and durability after hardening.

[0025] As one of the preferred embodiments of the present invention, the air-entraining agent is any one of rosin-based air-entraining agents, alkyl sulfonates, and alkyl benzene sulfonates; the retarder is selected from any one of protein-based retarders, modified amino acid salt-based retarders, boric acid-based retarders, citric acid-based retarders, and tartaric acid-based retarders; the thixotropic lubricant is any one of organic bentonite and magnesium aluminum silicate natural mineral salts.

[0026] Specifically, the rosin-based air-entraining agent is selected as the air-entraining agent, the protein-based retarder is selected as the retarder, and the magnesium aluminum silicate natural mineral salt is selected as the thixotropic lubricant.

[0027] The rosin-based air-entraining agent can introduce tiny and stable air bubbles into the gypsum plastering mortar. The air bubbles are evenly distributed in the mortar system, which reduces the friction between the internal particles of the mortar. Moreover, the presence of air bubbles changes the pore structure of the mortar, making the pores inside the mortar smaller, more uniform, and closed. During the mixing and construction process, the mortar can flow more smoothly, thus significantly improving the workability of the mortar and making the construction operation easier and more efficient.

[0028] The protein-based retarder can delay the setting speed of the gypsum plastering mortar. During the actual construction process, it can provide more sufficient time for construction workers to perform operations such as mixing, transportation, and spreading. And an appropriate setting time helps the mortar to hydrate fully, forming a more uniform and dense hardened structure. The protein-based retarder can make the water in the gypsum plastering mortar more evenly distributed during the slow setting process, and the hydration reaction is more sufficient, thereby improving the strength and durability of the mortar and ensuring the construction quality.

[0029] The magnesium aluminum silicate natural mineral salt makes the gypsum plastering mortar thixotropic. In the static state, the mortar has a high viscosity, can maintain its shape, and is not easy to flow. During the mixing or construction process, the viscosity of the mortar decreases, making it easy to spread and form.

[0030] A preparation method of a gypsum plastering mortar with gradient aggregate to enhance cohesive strength includes the following steps: S1. Prepare modified glass beads. Dissolve chitosan in 2% acetic acid solution, then sequentially add modified activated carbon and glass microspheres, stir for 30 - 60 min to complete coating, centrifuge and separate the glass microspheres, and dry to obtain modified glass beads; S2. Prepare modified heavy calcium carbonate. Dissolve polyvinylpyrrolidone in deionized water, add sodium hydroxide solution dropwise to adjust the pH of the solution to 10, then add heavy calcium carbonate powder, then heat up and stir for a period of time, filter, and dry to obtain modified heavy calcium carbonate; S3. Prepare modified quartz sand. Stir and dissolve mercapto silane coupling agent in ethanol solution, then add quartz sand, react for a period of time under stirring, filter and separate, and dry to obtain modified quartz sand; S4. Add anhydrous gypsum, modified glass beads, modified quartz sand, hydrated lime, modified heavy calcium carbonate, cellulose, starch ether, air-entraining agent, setting retarder, thixotropic lubricant into a stirrer and stir evenly to obtain dry mortar powder, then add appropriate amount of water and continue to stir evenly to obtain gypsum plastering mortar.

[0031] In the preparation scheme of the present invention, anhydrous gypsum, modified glass beads, modified quartz sand, hydrated lime, modified heavy calcium carbonate, cellulose, starch ether, air-entraining agent, setting retarder, thixotropic lubricant are added into a stirrer and stirred evenly. Since the modified glass beads, modified quartz sand, modified heavy calcium carbonate and hydrated lime have gradient particle size design, a closely packed structure can be formed during the stirring process, which can reduce the porosity inside the mortar and improve the density of the mortar, thereby effectively improving the structural strength of the gypsum plastering mortar.

[0032] Each component synergistically acts during the stirring process. Cellulose and starch ether form a three-dimensional network, which cooperates with the multi-scale reinforcement network formed by chitosan on the surface of the modified glass beads, further improving the cohesive strength of the mortar. At the same time, the addition of the air-entraining agent, setting retarder and thixotropic lubricant respectively improves the workability, setting time and construction performance of the mortar, making the gypsum plastering mortar have high strength while also having good construction operability and service performance.

[0033] As a further technical solution of the present invention, in step S1, weigh 8 g of chitosan, add it to 1 L of 2% acetic acid solution, slowly stir for half an hour to dissolve, then weigh 1 g of modified activated carbon and 3 g of glass microspheres, mix evenly, then add 1 L of sodium tripolyphosphate with a concentration of 0.5%, stir for 60 min to complete coating, centrifuge, and dry the precipitate to obtain the prepared modified glass beads.

[0034] Further, in the above step S1, the preparation method of the modified activated carbon is as follows: Prepare a cobalt salt solution with a concentration of 1.0 mol / L from a soluble cobalt salt, then add activated carbon powder and the cobalt salt solution into a stirrer, impregnate for 4 - 5 h under stirring, filter the solid, and dry to obtain the modified activated carbon. The mass ratio of the activated carbon powder to the cobalt salt solution is 1:10. The soluble cobalt salt is any one of cobalt nitrate and cobalt chloride, and the particle size of the activated carbon powder is 10 - 50 μm.

[0035] The modified activated carbon is obtained by impregnating activated carbon powder in a soluble cobalt salt and then drying it. It adsorbs cobalt ions inside. When the modified glass beads are added to the gypsum plaster mortar, the modified activated carbon component in the composite chitosan shell layer will release cobalt ions. The cobalt ions can undergo complexation reactions with polyvinylpyrrolidone on the surface of the modified heavy calcium and mercapto groups on the surface of the modified quartz. Through the complexation reaction, relatively stable chemical connections are formed between different components, tightly binding the originally relatively independent components together, thereby enhancing the structure and cohesive strength of the mortar. In addition, hydrogen bond - connected cross - linked structures can be formed between polyvinylpyrrolidone on the surface of the modified glass beads, mercapto groups on the surface of the modified quartz, and chitosan on the surface of the modified glass beads, further strengthening the connection between each component inside the mortar, making the structure of the mortar more compact and the cohesive strength improved.

[0036] Chitosan on the surface of the modified glass beads forms a multi - scale reinforcement network with the gradient aggregate, and at the same time, it synergistically acts with the three - dimensional network formed by cellulose and starch ether. The formed multi - scale network structure can enhance the mortar from different levels and scales. When the modified activated carbon releases cobalt particles to trigger complexation reactions and hydrogen bond connections are formed between components, these new connection points further integrate into and strengthen the original multi - scale reinforcement network. The networks are intertwined and supported by each other, enabling the mortar to better disperse stress when subjected to external forces, thereby improving the structural strength and cohesive strength of the mortar.

[0037] As a further technical solution of the present invention, in step S2, add 1 g of polyvinylpyrrolidone to 500 mL of deionized water, stir magnetically at room temperature for 3 h to fully dissolve, add sodium hydroxide solution to adjust the pH of the solution to 11.5, then add 100 mg of heavy calcium powder, heat up to 60 °C in an oil bath and stir for 4 h, filter the solid, and dry to obtain the modified heavy calcium powder.

[0038] Polyvinylpyrrolidone contains polar pyrrolidone rings (containing carbonyl groups) in its molecular chain. After dissolution, polyvinylpyrrolidone molecules adsorb on the surface of CaCO3 particles through hydrogen bonds or van der Waals forces to form a physical coating layer. Under alkaline conditions, it may hydroxylate the surface of CaCO3 (-OH groups increase), enhancing its interaction with PVP. In addition, the molecular chain of PVP stretches more fully in an alkaline medium, which is beneficial to uniformly coating the particles.

[0039] The polyvinylpyrrolidone coating layer on the surface of the modified heavy calcium powder prepared by the above steps can enhance the interfacial bonding force with the gypsum matrix and reduce the generation of microcracks, which helps to improve the structural stability and durability of the gypsum plaster mortar, enabling it to better resist external force damage and environmental erosion during use. At the same time, the modified heavy calcium powder and other components (such as modified glass beads, modified quartz sand, etc.) act synergistically to form a closely packed structure through gradient particle size design, further enhancing the structural strength and cohesive strength of the gypsum plaster mortar.

[0040] As a further technical solution of the present invention, in step S3, a certain amount of quartz sand and 3-mercaptopropyltriethoxysilane-ethanol solution are respectively put into the stirrer, reacted for 20 min under stirring, and then the solid is filtered and dried to obtain modified quartz sand. The mass ratio of the quartz sand to the 3-mercaptopropyltriethoxysilane-ethanol solution is 1:100. The mass percentage of 3-mercaptopropyltriethoxysilane and ethanol solution in the 3-mercaptopropyltriethoxysilane-ethanol solution is 5:95, and the ethanol solution is a 90% ethanol aqueous solution.

[0041] The molecular structure of 3-mercaptopropyltriethoxysilane contains two different types of groups. One end is a mercapto group (-SH), and the other end is a triethoxysilyl group (-Si(OC2H5)3). This group can react under hydrolysis conditions. When 3-mercaptopropyltriethoxysilane is dissolved in an ethanol solution and contacts the quartz sand, the triethoxysilyl group will undergo a hydrolysis reaction under the action of water (a certain amount of water is contained in the ethanol solution) to generate silanol groups (-Si-OH). The silanol groups will undergo a condensation reaction to form siloxane-silicon bonds (-Si-O-Si-), thereby forming an organic-inorganic hybrid network structure on the surface of the quartz sand. The surface of the quartz sand usually has certain active groups such as hydroxyl groups (-OH). The silanol groups generated by the hydrolysis of the silane coupling agent can interact with the hydroxyl groups on the surface of the quartz sand through hydrogen bonds or chemical bonds and adsorb on the surface of the quartz sand. As the reaction proceeds, the siloxane-silicon bonds formed by the condensation of the silanol groups further enhance the bonding force between the silane coupling agent and the surface of the quartz sand, making the silane coupling agent firmly adhere to the surface of the quartz sand.

[0042] As the other functional group of the silane coupling agent at the other end, the mercapto group is introduced to the surface of the quartz sand during the modification process. The mercapto group has high chemical activity and can crosslink with other components in the gypsum plaster mortar (such as polyvinylpyrrolidone on the surface of the modified heavy calcium, chitosan on the surface of the modified glass beads, etc.), which helps to enhance the interfacial bonding force between the quartz sand and the gypsum matrix and other modified components and improve the overall performance of the mortar.

[0043] Example 1

[0044] Preparation method of gypsum plaster mortar with gradient aggregate enhancing cohesive strength, preparation steps: S1. Preparation of modified glass beads: 8 g of chitosan is dissolved in 1 L of 2% acetic acid solution and stirred for 30 minutes; 1 g of modified activated carbon (impregnated with cobalt nitrate) and 3 g of glass microspheres are added, 1 L of 0.5% sodium tripolyphosphate is added dropwise, and stirred for 60 minutes; centrifuged and dried to obtain modified glass beads.

[0045] S2. Preparation of modified heavy calcium carbonate: 1 g of polyvinylpyrrolidone is dissolved in 500 mL of deionized water, and the pH is adjusted to 11.5; 100 g of heavy calcium carbonate powder is added, and stirred in an oil bath at 60 °C for 4 hours, filtered and dried.

[0046] S3. Preparation of modified quartz sand: Mix 5% 3-mercaptopropyltriethoxysilane ethanol solution with quartz sand at a ratio of 1:100; stir for 20 minutes, filter and dry.

[0047] S4. Mortar mixing: 450 parts of anhydrous gypsum (calcined phosphogypsum), 75 parts of modified glass beads (particle size 0.3 mm), 120 parts of modified quartz sand (particle size 100 μm), 20 parts of hydrated lime (particle size 100 μm), 225 parts of modified heavy calcium carbonate (particle size 50 μm), 8 parts of hydroxyethyl methyl cellulose (molecular weight 10000), 0.8 part of modified potato starch ether, 0.7 part of rosin-based air-entraining agent, 3 parts of protein-based setting retarder, 0.8 part of magnesium aluminum silicate thixotropic lubricant are added to the mixer in sequence and mixed evenly to obtain mortar dry powder, and then an appropriate amount of water is added, and the weight ratio of water to mortar dry powder is 0.6:1. Continue to stir evenly to obtain gypsum plaster mortar. Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the particle sizes of the modified glass beads, modified quartz sand, hydrated lime, and modified heavy calcium carbonate are 100 μm, and the rest are the same as in Example 1.

[0048] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the modified glass beads are replaced with ordinary glass microspheres; untreated quartz sand and heavy calcium carbonate are used, and the rest are the same as in Example 1.

[0049] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the modified glass beads are only glass microspheres (without chitosan coating and modified activated carbon filling), and the rest are the same as in Example 1.

[0050] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that ordinary activated carbon is used inside the chitosan coating layer of the modified glass beads, and the activated carbon is not loaded with cobalt salt, and the rest are the same as in Example 1.

[0051] The performance of the above-mentioned Example 1 and Comparative Examples 1-4 was detected. The test method was in accordance with GB / T 28627-2023, and the test results are shown in the following table:

[0052] In Example 1, the modified glass beads, modified quartz sand, hydrated lime, and modified heavy calcium carbonate were designed with gradient particle sizes. The 28-day compressive strength, flexural strength, and bond strength were all higher than those of Comparative Example 1 (the particle size of each component was 100 μm). This indicates that the gradient particle size design can enable the components to be closely packed in the mortar, reduce the porosity, and improve the density, thereby effectively enhancing the structural strength and cohesive strength of the gypsum plastering mortar.

[0053] Example 1 used modified glass beads (chitosan-coated + cobalt-modified activated carbon), mercapto-modified quartz sand, and PVP-modified heavy calcium carbonate. Its flexural strength (5.2 MPa) and tensile bond strength (0.85 MPa) were both superior to those of unmodified Comparative Example 2 (9.8 MPa, 0.41 MPa), indicating that the improved interfacial bonding force effectively reduced microcracks, demonstrating that the cohesive strength of the gypsum plastering mortar can be enhanced through the synergistic effect of the above-mentioned modified aggregate components.

[0054] The compressive strengths of Comparative Example 3 (without chitosan coating and activated carbon) and Comparative Example 4 (ordinary activated carbon) (14.2 MPa, 15.7 MPa) were lower than that of Example 1 (18.5 MPa), indicating that the complexation reaction induced by the chitosan network and cobalt ions strengthened the multi-scale network and further improved the cohesive strength of the gypsum plastering mortar. In Comparative Example 4, ordinary activated carbon (not loaded with cobalt salt) was used inside the chitosan coating layer of the modified glass beads, and all performance indicators were lower than those of Example 1. This shows that after the modified activated carbon was loaded with cobalt salt, the released cobalt ions could react with the polyvinylpyrrolidone on the surface of the modified heavy calcium carbonate and the mercapto group on the surface of the modified quartz to form a relatively stable chemical bond, enhancing the structure and cohesive strength of the gypsum plastering mortar.

[0055] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A gypsum plastering mortar with enhanced cohesive strength by gradient aggregate, characterized in that, Comprising the following raw materials by weight parts: 400 - 500 parts of anhydrous gypsum, 50 - 100 parts of modified glass beads, 80 - 150 parts of modified quartz sand, 15 - 30 parts of hydrated lime, 200 - 250 parts of modified heavy calcium carbonate, 5 - 10 parts of cellulose, 0.5 - 1 part of starch ether, 0.5 - 1 part of air-entraining agent, 1 - 5 parts of setting retarder, 0.5 - 1 part of thixotropic lubricant. The modified quartz sand is obtained by modifying quartz sand with mercapto silane coupling agent. The modified heavy calcium carbonate is obtained by modifying heavy calcium carbonate powder with polyvinylpyrrolidone. The particle size ratio of the modified glass bead powder, (modified quartz sand / hydrated lime), and modified heavy calcium carbonate is 1:0.414:(0.171 - 0.225).

2. The gypsum plastering mortar for enhancing cohesive strength with gradient aggregate according to claim 1, wherein, The particle size of the modified glass bead powder is 0.1 - 0.5 mm, the particle size of the modified quartz sand is 41–207 μm, the particle size of the hydrated lime is 41–207 μm, and the particle size of the modified heavy calcium carbonate is 17–86 μm.

3. A gypsum plaster mortar for enhancing cohesive strength with gradient aggregates according to claim 1, wherein, The modified glass bead is composed of a glass microsphere and a composite chitosan shell layer coated on the surface of the glass microsphere. The composite chitosan shell layer is filled with modified activated carbon. The modified activated carbon is obtained by impregnating activated carbon powder in soluble cobalt salt and then drying.

4. A gypsum plaster mortar with enhanced cohesive strength by gradient aggregates according to claim 1, characterized in that, The anhydrous gypsum is obtained by high-temperature calcination of phosphogypsum. The cellulose is selected from any one of hydroxypropyl methylcellulose or hydroxyethyl methylcellulose. The molecular weight of the cellulose is 7000 - 10000. The starch ether is selected as modified potato starch ether.

5. The gypsum plastering mortar for enhancing the cohesive strength with gradient aggregate according to claim 1, wherein The air-entraining agent is any one of rosin-based air-entraining agents, sodium alkyl sulfonate, and sodium alkyl benzene sulfonate. The setting retarder is selected from any one of protein-based setting retarders, modified amino acid salt-based setting retarders, boric acid-based setting retarders, citric acid-based setting retarders, and tartaric acid-based setting retarders. The thixotropic lubricant is any one of organic bentonite and magnesium aluminum silicate natural mineral salt.

6. The preparation method of a gypsum plastering mortar for enhancing the cohesive strength with gradient aggregates as claimed in any one of claims 1 to 5, characterized in that, Comprising the following steps: S1. Prepare modified glass beads. Dissolve chitosan in 2% acetic acid solution, then sequentially add modified activated carbon and glass microspheres, stir for 30 - 60 min to complete coating, centrifuge and separate the glass microspheres, and dry to obtain modified glass beads; S2. Prepare modified heavy calcium carbonate. Dissolve polyvinylpyrrolidone in deionized water, add sodium hydroxide solution to adjust the pH of the solution to 10, then add heavy calcium carbonate powder, then heat up and stir to react for a period of time, filter, and dry to obtain modified heavy calcium carbonate; S3. Prepare modified quartz sand. Stir and dissolve mercapto silane coupling agent in ethanol solution, then add quartz sand, react for a period of time under stirring, filter and separate, and dry to obtain modified quartz sand; S4. Add anhydrous gypsum, modified glass beads, modified quartz sand, hydrated lime, modified heavy calcium carbonate, cellulose, starch ether, air-entraining agent, setting retarder, and thixotropic lubricant into a stirrer and stir evenly to obtain a mortar dry powder, then add an appropriate amount of water and continue to stir evenly to obtain a gypsum plaster mortar.

7. The preparation method of a gypsum plastering mortar with enhanced cohesive strength by gradient aggregates according to claim 6, characterized in that, In step S1, the preparation method of the modified activated carbon is as follows: Prepare a cobalt salt solution with a concentration of 1.0 mol / L from a soluble cobalt salt, then add activated carbon powder and the cobalt salt solution into a stirrer, impregnate for 4 - 5 h under stirring, filter the solid, and dry to obtain the modified activated carbon. The mass ratio of the activated carbon powder to the cobalt salt solution is 1:

10. The soluble cobalt salt is any one of cobalt nitrate and cobalt chloride. The particle size of the activated carbon powder is 10 - 50 μm.

8. The preparation method of a gypsum plastering mortar for enhancing cohesive strength with gradient aggregate according to claim 6, characterized in that, In step S1, weigh 8 g of chitosan, add it to 1 L of 2% acetic acid solution, slowly stir for half an hour to dissolve, then weigh 1 g of modified activated carbon and 3 g of glass microspheres, mix evenly, then add 1 L of sodium tripolyphosphate with a concentration of 0.5%, stir for 60 min to complete the coating, centrifuge, and dry the precipitate to obtain the prepared modified glass beads.

9. The preparation method of a gypsum plastering mortar for enhancing cohesive strength with gradient aggregates according to claim 6, characterized in that In step S2, add 1 g of polyvinylpyrrolidone to 500 mL of deionized water, magnetically stir at room temperature for 3 h to fully dissolve, add sodium hydroxide solution to adjust the pH of the solution to 11.5, then add 100 mg of heavy calcium powder, heat to 60 °C in an oil bath and stir for 4 h, filter the solid, and dry to obtain the modified heavy calcium powder.

10. The preparation method of a gypsum plastering mortar for enhancing cohesive strength with gradient aggregate according to claim 6, characterized in that, In step S3, put a certain amount of quartz sand and 3 - mercaptopropyltriethoxysilane - ethanol solution into a stirrer respectively, react for 20 min under stirring, then filter the solid, and dry to obtain the modified quartz sand. The mass ratio of the quartz sand to the 3 - mercaptopropyltriethoxysilane - ethanol solution is 1:

100. The mass percentage of 3 - mercaptopropyltriethoxysilane and ethanol solution in the 3 - mercaptopropyltriethoxysilane - ethanol solution is 5:

95. The ethanol solution is a 90% ethanol aqueous solution.

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