Water-resistant anti-cracking phosphogypsum-based plastering mortar and preparation method thereof

Abstract

The invention relates to the technical field of building materials, in particular to water-resistant anti-cracking phosphogypsum-based plastering mortar and a preparation method thereof. Comprising an aggregate and an additive, the aggregate comprises the following raw materials in percentage by weight: 30-50% of phosphogypsum, 10-20% of Portland cement, 5-8% of quick lime, 8-12% of fly ash and 25-35% of quartz sand, and the additive comprises polypropylene fiber, a polycarboxylic acid water reducer, a silane waterproof agent, starch ether, a silane coupling agent and water; the mass ratio of the aggregate to the polypropylene fiber to the polycarboxylate superplasticizer to the silane waterproofing agent to the starch ether to the silane coupling agent to the water is 1: (0.2-0.5): (0.08-0.15): (0.1-0.2): (0.02-0.05): (0.03-0.07): (16-20); the problems that in the prior art, common plastering mortar is high in cost, not environmentally friendly, poor in water resistance and poor in crack resistance are effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, in particular to a water-resistant and crack-resistant phosphogypsum-based plaster mortar and a preparation method thereof. Background Art

[0002] Performance requirements for building materials are becoming increasingly stringent. Plaster mortar, a key material for building wall decoration and protection, has a direct impact on a building's durability, aesthetics, and living comfort. Traditional plaster mortar typically uses cement as the primary binder, but cement production is associated with high energy consumption and significant carbon dioxide emissions, which is inconsistent with current trends toward green, environmentally friendly, and sustainable development.

[0003] Phosphogypsum is a major byproduct of my country's phosphate fertilizer industry, with annual emissions exceeding 120 million tons. However, its comprehensive utilization rate is less than 20%. Large-scale stockpiling has led to land occupation, dust pollution, and groundwater acidification. Driven by the "dual carbon" goals, its potential as a cement substitute has attracted considerable attention, but its industrial application still faces the following key bottlenecks: 1. Phosphogypsum-based materials generally have a water absorption rate greater than 20% and a water-resistance rating less than P6, resulting in insufficient water resistance; drying shrinkage is greater than 0.2%, making it prone to cracking and shedding; 2. Natural phosphogypsum contains impurities (P2O5, organic matter), resulting in abnormal setting time, requiring lime adjustment, but the expansion of free lime causes cracking later; 3. The phosphogypsum dosage is typically less than 20%, preventing large-scale cement replacement and fundamentally addressing carbon emissions.

[0004] In addition, cracks not only destroy the integrity of the wall and reduce its mechanical properties, but also provide channels for water vapor penetration, further aggravating the durability problems of the wall, such as causing mold on the wall and rust of steel bars, shortening the service life of the building.

[0005] Patent document with application number CN202311310201.7 discloses "a crack-resistant and water-resistant phosphogypsum road base material and its preparation method", including base material and additives, wherein the base material is composed of the following raw materials in weight percentage: 15-25% calcined phosphogypsum, 43-47% natural coarse aggregate, 28-32% natural fine aggregate, 3-8% Portland cement; the additive is a composition of modifier, EVA emulsion, PU emulsion and water, wherein the mass ratio of base material, modifier, EVA emulsion, PU emulsion and water is 100:1.1-2.6:0.25-2:0.25-2:4-11; the main components of the base material of the application are as follows: The main raw materials are natural coarse aggregate and natural fine aggregate, and the content of phosphogypsum is relatively low. Although it can reduce carbon emissions and costs, the reduction is not obvious. In addition, the present application adopts modifiers, EVA emulsions, PU emulsions and water to mix with the base material to reduce its early self-shrinkage deformation, thereby reducing its cracking problem. This method has a certain effect within a certain period of time after construction, but its effect is greatly discounted over time, and cracking and other situations are inevitable. In addition, when microcracks appear, it does not have the function of inhibiting the growth of microcracks; it also leads to the problem of poor water resistance; therefore, there is an urgent need for a water-resistant and crack-resistant phosphogypsum-based plaster mortar and a preparation method thereof to solve the current problem. Summary of the Invention

[0006] The purpose of the present invention is to provide a water-resistant and crack-resistant phosphogypsum-based plastering mortar and a preparation method thereof, in response to the problems that the existing plastering mortar has poor water resistance and is easy to crack, thereby effectively solving the problems of high cost, environmental pollution, poor water resistance and poor crack resistance of ordinary plastering mortar in the prior art.

[0007] To achieve the above objectives, the present invention proposes the following technical solutions:

[0008] The first object of the present invention is to provide a water-resistant and crack-resistant phosphogypsum-based plaster mortar, comprising aggregate and admixtures. The aggregate is composed of raw materials in percentage by weight, including 30-50% of phosphogypsum, 10-20% of Portland cement, 5-8% of quicklime, 8-12% of fly ash, and 25-35% of quartz sand. The admixtures include polypropylene fiber, polycarboxylate water-reducing agent, silane waterproofing agent, starch ether, silane coupling agent, and water. The mass ratio of the aggregate to the polypropylene fiber, polycarboxylate water-reducing agent, silane waterproofing agent, starch ether, silane coupling agent, and water is 1: 0.2-0.5%: 0.08-0.15%: 0.1-0.2%: 0.02-0.05%: 0.03-0.07%: 16-20%.

[0009] Furthermore: the fly ash is grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (45μm square hole sieve residue) is not more than 25%, and the water demand ratio of the fly ash is not more than 105%.

[0010] Furthermore: the quartz sand is 20-70 mesh quartz sand.

[0011] Furthermore: the length of the polypropylene fiber is 5-10 mm.

[0012] Furthermore: the starch ether is glutinous rice starch ether.

[0013] The second object of the present invention is to provide a method for preparing the above-mentioned water-resistant and crack-resistant phosphogypsum-based plaster mortar, comprising the following steps:

[0014] S1: Modification of phosphogypsum: wash the phosphogypsum with water and calcine it at 140±5℃ for 2-3 hours, then cool the calcined phosphogypsum.

[0015] S2: crush the cooled phosphogypsum into 120 mesh, with a specific surface area of ​​≥300m 2 / kg;

[0016] S3: drying the quartz sand until the moisture content is ≤3%;

[0017] S4: Activate the coupling agent. Dilute the silane coupling agent five times and spray it on the aggregate surface. Let it stand for 3 minutes for adsorption.

[0018] S5: dry mixing, adding polypropylene fiber to the mixer, stirring the polypropylene fiber at high speed (60 rpm) for 2 minutes, and then adding aggregate; finally, adding polycarboxylate water reducer, silane water repellent and starch ether.

[0019] S6: Wet mixing: add water to the mixer and stir for 10-20 minutes until there is no water seepage.

[0020] Furthermore: in step S1, the cooled phosphogypsum is subjected to XRD detection, and its β hemihydrate phase content is ≥90%.

[0021] Furthermore: in step S5, the mixer is a horizontal forced mixer with a rotation speed of ≥30 rpm.

[0022] Furthermore: in step S6, the rotation speed during wet mixing is ≥40 rpm.

[0023] Compared with the prior art, the present invention has the following gain effects:

[0024] 1. Breakthrough in water resistance: Through the synergistic effect of the silane hydrophobic layer and nano-SiO2, the silane modified layer reduces the water absorption rate to ≤8%, so that the mortar anti-seepage grade reaches P10 (0.8MPa water pressure for 24 hours without seepage), and the compressive strength retention rate after 28 days of immersion in water is greater than 90% (traditional materials <60%), making its water resistance effect significant.

[0025] 2. Significantly improved crack resistance: The synergistic effect of silane coupling agent and starch ether, as well as high-speed stirring (60rpm) of polypropylene fiber for 2 minutes, can disperse the fibers, prevent them from "clumping", and solve the problem of fiber "floating", thereby increasing their bonding strength by 25%. The fiber-matrix interface bonding strength is greater than 1.5MPa. Combined with the gradient dense structure, the 28-day flexural strength is ≥6.5MPa, the shrinkage rate is ≤0.1%, and the crack rate is <2% (traditional materials are >15%), which significantly improves the crack resistance of the mortar compared to traditional mortar.

[0026] 3. Process stability optimization: Standardized processes for phosphogypsum pretreatment (calcination at 140±5℃ for 2-3 hours and crushing to 120 mesh) and aggregate silane activation (diluting the silane coupling agent five times and spraying it on the aggregate surface, allowing it to stand for 3 minutes for adsorption) ensure batch-to-batch strength fluctuations of less than 5%.

[0027] 4. Balance between economy and environmental protection: the content of phosphogypsum is ≥30%, and the fly ash is ≥8%; the comprehensive utilization rate of solid waste reaches 85%, carbon emissions are reduced by 42% compared with traditional C30 mortar, and the overall cost is reduced by 20%-25%. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0029] A water-resistant and crack-resistant phosphogypsum-based plaster mortar comprises aggregate and admixtures. The aggregate is composed of 30-50% phosphogypsum, 10-20% Portland cement, 5-8% quicklime, 8-12% fly ash, and 25-35% quartz sand in weight percentage. The admixtures comprise polypropylene fiber, polycarboxylate water-reducing agent, silane waterproofing agent, starch ether, silane coupling agent, and water. The mass ratio of the aggregate to the polypropylene fiber, polycarboxylate water-reducing agent, silane waterproofing agent, starch ether, silane coupling agent, and water is 1: 0.2-0.5%: 0.08-0.15%: 0.1-0.2%: 0.02-0.05%: 0.03-0.07%: 16-20%.

[0030] In this application, the aggregates are phosphogypsum, Portland cement, quicklime, fly ash and quartz sand. The phosphogypsum is used as the main cementitious material and needs to be pretreated. It needs to be calcined at 140±5℃ for 2-3 hours. After cooling, the XRD test shows that its β semi-aqueous phase content is ≥90%. At the same time, it is crushed to 120 mesh with a specific surface area of ​​≥300m 2 / kg; Portland cement provides early strength and impermeability, reduces the water demand of phosphogypsum, quicklime can stimulate the coagulation of phosphogypsum, regulate the coagulation time, and reduce the damage of free lime; thus avoiding the late cracking problem caused by free lime; fly ash improves workability, reduces hydration heat, and realizes solid waste utilization.

[0031] Quartz sand serves as the aggregate skeleton, controlling shrinkage stress and preventing cracking caused by excessive shrinkage. Polypropylene fiber has crack resistance and can also inhibit the propagation of microcracks. Through the optimization of aggregate grading, the coordinated ratio of phosphogypsum cementitious system and polypropylene fiber, a "dense-flexible" composite structure is constructed, and the drying shrinkage rate is controlled at 0.08%-0.12%. The effect of polycarboxylate superplasticizer can reduce the water content of mortar by ≥25% while optimizing its fluidity. Polycarboxylate superplasticizer optimizes fiber dispersion and prevents agglomeration. The synergistic effect of polypropylene fiber and polycarboxylate superplasticizer can inhibit cracks, while the superplasticizer optimizes fluidity. The flexural strength can reach 7.5MPa (30% higher than traditional mortar). Silane waterproofing agent will form a hydrophobic layer. Silane waterproofing agent forms a hydrophobic network on the substrate surface, increasing the contact angle to 110°. Combined with silicate cement to fill the pores, the bonding strength is increased to 2.0MPa (200% higher than traditional materials). ), while the silane waterproofing layer reduces the water absorption rate to ≤8%, thereby greatly improving the water resistance of the mortar. The silane coupling agent activates the aggregate surface and combines with the phosphogypsum particles through chemical bonds, increasing the interfacial shear strength by 25%. The addition of starch ether inhibits water evaporation and reduces plastic cracking. The fiber bridges the cracks and the silicate cement inhibits the expansion of microcracks, thereby constructing a dense-flexible composite structure and inhibiting shrinkage cracking. According to the data results, the mortar has a 28-day flexural strength of ≥6.5MPa, a shrinkage rate of ≤0.1%, and a crack rate of <2% (traditional materials>15%). At the same time, the silane modified layer reduces the water absorption rate to ≤8%, the impermeability grade reaches P10 (0.8MPa water pressure for 24 hours without seepage), and the compressive strength retention rate after immersion in water for 28 days is>90% (traditional materials<60%). Therefore, the phosphogypsum anti-cracking plaster mortar has a better ability to bond to the wall and will not crack or fall off after long-term use.

[0032] In a specific embodiment, the fly ash is grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (residue on a 45 μm square sieve) is not greater than 25%, and the water requirement ratio of the fly ash is not greater than 105%.

[0033] In a specific embodiment, the quartz sand is 20-70 mesh quartz sand.

[0034] In a specific embodiment, the length of the polypropylene fibers is 5-10 mm.

[0035] In a specific embodiment, the starch ether is glutinous rice starch ether.

[0036] In a specific embodiment, the preparation method of the water-resistant and crack-resistant phosphogypsum-based plaster mortar comprises the following steps:

[0037] S1: Modification of phosphogypsum: wash the phosphogypsum with water and calcine it at 140±5℃ for 2-3 hours, then cool the calcined phosphogypsum.

[0038] S2: crush the cooled phosphogypsum into 120 mesh, with a specific surface area of ​​≥300m 2 / kg;

[0039] S3: drying the quartz sand until the moisture content is ≤3%;

[0040] S4: Activate the coupling agent. Dilute the silane coupling agent five times and spray it on the aggregate surface. Let it stand for 3 minutes for adsorption.

[0041] S5: Dry mixing: Add polypropylene fiber to the mixer, stir the polypropylene fiber at high speed (60 rpm) for 2 minutes, then add the activated aggregate; finally, add the polycarboxylate water reducer, silane water repellent and starch ether.

[0042] S6: Wet mixing: add water into the mixer gradually as needed and stir for 10-20 minutes until there is no water seepage in the mortar.

[0043] In a specific embodiment, in step S1, the cooled phosphogypsum is subjected to XRD detection, and the β hemihydrate phase content thereof is ≥90%.

[0044] In a specific embodiment, the mixer in step S5 is a horizontal forced mixer with a rotation speed of ≥30 rpm.

[0045] In a specific embodiment, the rotation speed during wet mixing in step S6 is ≥40 rpm.

[0046] The synergistic effect of silane coupling agent and starch ether, as well as high-speed stirring (60rpm) of polypropylene fiber for 2 minutes, can achieve dispersion of the fibers, prevent them from "clumping", solve the problem of fiber "floating", and increase their bonding strength by 25%. The fiber-matrix interface bonding strength is greater than 1.5MPa. Combined with the gradient dense structure, the 28-day flexural strength is ≥6.5MPa, the shrinkage rate is ≤0.1%, and the crack rate is <2% (traditional materials are >15%), which significantly improves its crack resistance compared to traditional mortar.

[0047] Example 1:

[0048] A water-resistant and crack-resistant phosphogypsum plaster mortar comprises aggregate and admixtures; the aggregate comprises 45% phosphogypsum, 15% Portland cement, 10% fly ash, 25% quartz sand, and 5% quicklime; the admixtures comprise 0.4% polypropylene fiber, 0.12% polycarboxylate water reducer, 0.15% silane waterproofing agent, 0.04% starch ether, 0.05% silane coupling agent, and 18% water; wherein the fly ash is Grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (residue on a 45μm square sieve) is not greater than 25%, and the water requirement ratio of the fly ash is not greater than 105%; and the quartz sand is 20-70 mesh quartz sand.

[0049] In the admixture of this embodiment, the length of the polypropylene fiber is 5-8 mm, and the starch ether is glutinous rice starch ether;

[0050] The preparation method of the water-resistant and crack-resistant phosphogypsum plaster mortar comprises the following steps:

[0051] S1: Modification of phosphogypsum: wash the phosphogypsum with water and calcine it at 140℃ for 2.5 hours, then cool the calcined phosphogypsum.

[0052] S2: crush the cooled phosphogypsum into 120 mesh, with a specific surface area of ​​≥300m 2 / kg;

[0053] S3: drying the quartz sand until the moisture content is ≤3%;

[0054] S4: Activate the coupling agent. Dilute the silane coupling agent five times and spray it on the aggregate surface. Let it stand for 3 minutes for adsorption.

[0055] S5: dry mixing, adding polypropylene fiber to the mixer, stirring the polypropylene fiber at high speed (60 rpm) for 2 minutes, and then adding the adsorbed aggregate; finally, adding the polycarboxylate water reducer, silane water repellent and starch ether.

[0056] S6: Wet mixing: add water to the mixer and stir for 15 minutes until there is no water seepage.

[0057] The amount of water added can be calculated based on the water distribution model formula, which is as follows:

[0058] Wtotal = Wadmixture + Waggregate + 10% × (Wadmixture + Waggregate)

[0059] Where: Wtotal is the total water requirement, Wadmixture is the water requirement of admixture, and Waggregate is the water requirement of aggregate.

[0060] Example 2:

[0061] A water-resistant and crack-resistant phosphogypsum plaster mortar comprises aggregate and admixtures; the aggregate comprises 35% phosphogypsum, 18% Portland cement, 12% fly ash, 28% quartz sand, and 7% quicklime; the admixtures comprise 0.3% polypropylene fiber, 0.12% polycarboxylate water-reducing agent, 0.2% silane waterproofing agent, 0.04% starch ether, 0.05% silane coupling agent, and 17% water; wherein the fly ash is Grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (45μm square hole sieve residue) is not greater than 25%, and the water demand ratio of the fly ash is not greater than 105%; and the quartz sand is 20-70 mesh quartz sand.

[0062] In the admixture of this embodiment, the length of the polypropylene fiber is 5-10 mm, and the starch ether is glutinous rice starch ether;

[0063] The preparation method is the same as that in Example 1.

[0064] Example 3:

[0065] A water-resistant and crack-resistant phosphogypsum plaster mortar comprises aggregate and admixtures; the aggregate comprises 40% phosphogypsum, 15% Portland cement, 10% fly ash, 30% quartz sand, and 5% quicklime; the admixtures comprise 0.5% polypropylene fiber, 0.1% polycarboxylate water-reducing agent, 0.1% silane waterproofing agent, 0.03% starch ether, 0.04% silane coupling agent, and 17% water; wherein the fly ash is Grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (residue on a 45μm square sieve) is not greater than 25%, and the water requirement ratio of the fly ash is not greater than 105%; and the quartz sand is 20-70 mesh quartz sand.

[0066] In the admixture of this embodiment, the length of the polypropylene fiber is 10-15 mm, and the starch ether is glutinous rice starch ether;

[0067] The preparation method is the same as that in Example 1.

[0068] Example 4:

[0069] A water-resistant and crack-resistant phosphogypsum plaster mortar comprises aggregate and admixtures; the aggregate comprises 38% phosphogypsum, 15% Portland cement, 10% fly ash, 32% quartz sand, and 5% quicklime; the admixtures comprise 0.5% polypropylene fiber, 0.15% polycarboxylate water-reducing agent, 0.18% silane waterproofing agent, 0.03% starch ether, 0.05% silane coupling agent, and 19% water; wherein the fly ash is Grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (residue on a 45μm square sieve) is not greater than 25%, and the water requirement ratio of the fly ash is not greater than 105%; and the quartz sand is 20-70 mesh quartz sand.

[0070] In the admixture of this embodiment, the length of the polypropylene fiber is 12-15 mm, and the starch ether is glutinous rice starch ether;

[0071] The preparation method is the same as that in Example 1.

[0072] The water-resistant and crack-resistant phosphogypsum mortars obtained in Examples 1-4 were tested for flexural strength, compressive strength, bond strength, shrinkage, impermeability, and water absorption using GB / T 27077-2011, ASTM C157, GB / T 50110-2010, and ISO 4892-2, respectively. The test results are as follows:

[0073]

[0074]

[0075] According to the data in the table, it can be seen that the water-resistant and crack-resistant phosphogypsum plaster mortars prepared in Examples 1-4 of the present application have higher test results of flexural strength, compressive strength, bonding strength, shrinkage, impermeability grade and water absorption rate than traditional cement mortar and existing phosphogypsum mortar; the water-resistant and crack-resistant phosphogypsum plaster mortar in the embodiments of the present application has a synergistic effect of the silane hydrophobic layer and nano-SiO2, and the silane modified layer reduces the water absorption rate to ≤8%, so that the mortar impermeability grade reaches P10 (0.8MPa water pressure for 24 hours without seepage), and the compressive strength retention rate after 28 days of immersion is greater than 90% (traditional materials <60%), making its water resistance effect significant; the combination of polypropylene fiber and aggregate significantly improves its crack resistance, and the setting of each component in the aggregate achieves a balance between economy and environmental protection: the phosphogypsum content is ≥30%, and the fly ash is ≥8%; the comprehensive utilization rate of solid waste reaches 85%, carbon emissions are reduced by 42% compared with traditional C30 mortar, and the comprehensive cost is reduced by 20%-25%.

[0076] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., are used solely to facilitate description and simplify the present invention. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0077] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be internal communication between two components; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Claims

1. A water-resistant and crack-resistant phosphogypsum-based plaster mortar, characterized in that: The invention comprises aggregates and admixtures. The aggregates are composed of raw materials in percentage by weight, including 30-50% of phosphogypsum, 10-20% of Portland cement, 5-8% of quicklime, 8-12% of fly ash and 25-35% of quartz sand. The admixtures comprise polypropylene fiber, polycarboxylic acid water-reducing agent, silane waterproofing agent, starch ether, silane coupling agent and water. The mass ratio of the aggregates to the polypropylene fiber, polycarboxylic acid water-reducing agent, silane waterproofing agent, starch ether, silane coupling agent and water is 1: 0.2-0.5%: 0.08-0.15%: 0.1-0.2%: 0.02-0.05%: 0.03-0.07%: 16-20%.

2. The water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 1, characterized in that: The fly ash is grade II fly ash; the SiO2 content in the fly ash is 40%-50%, the fineness of the fly ash (residue on a 45μm square sieve) is not greater than 25%, and the water requirement ratio of the fly ash is not greater than 105%.

3. The water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 1, characterized in that: The quartz sand is 20-70 mesh quartz sand.

4. The water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 1, characterized in that: The length of the polypropylene fibers is 5-15 mm.

5. The water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 1, characterized in that: The starch ether is glutinous rice starch ether.

6. The method for preparing the water-resistant and crack-resistant phosphogypsum-based plaster mortar according to any one of claims 1 to 5, characterized in that: The steps include: S1: Modification of phosphogypsum: wash the phosphogypsum with water and calcine it at 140±5℃ for 2-3 hours, then cool the calcined phosphogypsum. S2: crush the cooled phosphogypsum into 120 mesh, with a specific surface area of ​​≥300m 2 / kg; S3: drying the quartz sand until the moisture content is ≤3%; S4: Activate the coupling agent. Dilute the silane coupling agent five times and spray it on the aggregate surface. Let it stand for 3 minutes for adsorption. S5: Dry mixing: Add polypropylene fiber to the mixer, stir the polypropylene fiber at high speed (60 rpm) for 2 minutes, then add the activated aggregate; finally, add the polycarboxylate water reducer, silane water repellent and starch ether. S6: Wet mixing: add water into the mixer gradually as needed and stir for 10-20 minutes until there is no water seepage in the mortar.

7. The method for preparing the water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 6, characterized in that: In step S1, the cooled phosphogypsum is subjected to XRD detection, and its β hemihydrate phase content is ≥90%.

8. The method for preparing the water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 6, characterized in that: In step S5, the mixer is a horizontal forced mixer with a rotation speed of ≥30 rpm.

9. The method for preparing the water-resistant and crack-resistant phosphogypsum-based plaster mortar according to claim 6, characterized in that: During wet mixing in step S6, the rotation speed is ≥40 rpm.

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