Desulfurized gypsum self-leveling mortar, preparation method and application thereof

Abstract

The application provides a desulfurization gypsum self-leveling mortar and a preparation method and application thereof, and the desulfurization gypsum self-leveling mortar comprises the following raw materials in parts by weight: modified desulfurization gypsum 80-98 parts, cement 1-50 parts, water reducing agent 0.05-0.2 parts, retarder 0.05-0.2 parts, defoaming agent 0.05-0.2 parts, and nano-cellulose / silicon nitride aerogel 0.05-0.5 parts; the water consumption of the gypsum self-leveling mortar is 40-60% of the total mass of the powder. The nano-cellulose / silicon nitride aerogel is obtained by adopting a sol-gel preparation process. In the process of preparing the nano-cellulose aerogel by adopting the sol-gel process, nano-silicon nitride is introduced, the nano-cellulose / silicon nitride aerogel is prepared, the content of N / Si and C elements on the surface is improved after the nano-cellulose / silicon nitride aerogel is added into the gypsum self-leveling mortar, and the wear resistance of the material surface is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a desulfurized gypsum self-leveling mortar and a preparation method and application thereof. Background Art

[0002] During construction, the ground may be uneven, bumpy, or defective. However, as people's requirements for the ground become increasingly higher, they hope that the ground can appear flat, smooth, and beautiful. Gypsum self-leveling mortar has good fluidity and self-leveling properties, and can be spread quickly and evenly, reducing the workload and construction time of construction workers. Compared with traditional ground repair materials, gypsum self-leveling mortar can provide higher construction efficiency and convenience. In addition, gypsum self-leveling mortar is usually made of power plant desulfurization gypsum as the main raw material, supplemented by green functional additives. It does not contain harmful volatile organic compounds (VOCs) and is friendly to the indoor environment. Overall, due to its high flatness, convenient construction, and good decorative properties, gypsum self-leveling mortar is widely used in construction and decoration.

[0003] Patent CN 116283185 A discloses a mortar specifically designed for floor heating and its preparation method. The mortar comprises the following raw materials in percentage by weight: gypsum powder, Portland cement, metal waste, carbon nanoparticles, latex powder, a defoamer, a retarder, a water reducer, and water. The carbon nanoparticles are obtained by carbonizing humic acid and have a hollow tube structure. This mortar exhibits excellent fluidity, wear resistance, compressive and flexural strength, and thermal conductivity, contributing to improved overall performance of the mortar.

[0004] Patent CN 115745548 A discloses a phosphogypsum-based self-leveling material for floor heating backfill and its preparation method. By adding a high-thermal-conductivity phase-change energy storage component, controlling the performance parameters of building gypsum, and coordinating with other components, the material's water requirement is reduced and its thermal conductivity is increased while maintaining fluidity and mechanical properties. SEM images show that a network of fibrous dihydrate gypsum crystals generated by hydration surrounds granular waste rock powder, while a large number of dihydrate gypsum crystals are distributed around flaky expanded graphite powder. The resulting microstructure is very dense, effectively ensuring the mechanical strength and heat transfer performance of the phosphogypsum-based self-leveling floor material for floor heating backfill.

[0005] Patent CN 113372079 A A kind of high wear-resistant gypsum-based self-leveling mortar and its preparation method, using the product of industrial by-product gypsum such as desulfurization gypsum after calcination treatment desulfurization building gypsum as cementing material, due to the fineness of desulfurization building gypsum, reduce water-binder ratio, greatly improve the resource utilization rate of industrial by-product gypsum such as desulfurization gypsum, it is beneficial to the solid waste treatment and resource recycling of industrial by-product gypsum, protect the environment;In the present application, industrial solid waste steel slag is used instead of quartz sand as aggregate, so that the hardness and wear resistance of the prepared gypsum-based self-leveling mortar are correspondingly improved;By adding glue powder as additive, prevent self-leveling mortar segregation, bleeding, reduce sedimentation, improve the apparent effect of hardened self-leveling mortar, improve its wear resistance.

[0006] Gypsum self-leveling mortar is often used for general residential floor leveling, and then floor or tile glue is laid, which has relatively small requirement on the surface wear resistance of gypsum self-leveling mortar. Some structural surface layers, such as public buildings, have higher requirements on the wear resistance of floor leveling layer, and the surface performance of gypsum self-leveling needs to be further improved. SUMMARY

[0007] In view of the above series of problems such as poor wear resistance of gypsum-based self-leveling mortar in the prior art. The present application proposes a desulfurization gypsum self-leveling mortar, its preparation method and application, which improves the surface wear resistance of gypsum self-leveling mortar.

[0008] A desulfurization gypsum self-leveling mortar, which comprises the following raw materials in parts by weight: modified desulfurization gypsum 80-98 parts, cement 1-50 parts, water reducing agent 0.05-0.2 parts, retarder 0.05-0.2 parts, defoaming agent 0.05-0.2 parts, and nano-cellulose / silicon nitride aerogel 0.05-0.5 parts. The water consumption of the gypsum self-leveling mortar is 40-60% of the total mass of the powder.

[0009] The modified desulfurization gypsum is prepared by the following steps: first, the desulfurization gypsum is subjected to low-temperature treatment at 150-160℃ and then ball-milled for 5-8min for preliminary modification, and then the preliminarily modified desulfurization gypsum is uniformly mixed with graphene powder to obtain the modified desulfurization gypsum. The fineness of graphene is selected to be 200-800 mesh.

[0010] The particle size D50 of the modified desulfurization gypsum is 20-35μm. The amount of graphene is 0.05%-0.1% of the amount of gypsum.

[0011] The above nano-cellulose / silicon nitride aerogel is obtained by using sol-gel preparation process.

[0012] The preparation process is specifically as follows: a 5.0% by mass nanocellulose solution (5.0% NCC) is prepared with deionized water, nanometer Si3N4 is added into the solution, the mass ratio of 5.0% NCC to nanometer Si3N4 is (15-25):1, and the homogeneous nanometer Si3N4 / NCC solution is obtained by magnetic stirring at room temperature for 8-9 hours; methyltrimethoxysilane is added into the nanometer Si3N4 / NCC solution, the mass ratio of nanometer Si3N4 / NCC solution to methyltrimethoxysilane is (45-50):1, and the nanometer Si3N4 / NCC aerogel is obtained by magnetic stirring at room temperature for 2-3 hours and vacuum freeze drying for 24-30 hours.

[0013] The cement is PO425 cement. The water reducing agent is polycarboxylic acid water reducing agent. The defoaming agent is any one of mineral oil, silicone, polyether, and polyether modified polysiloxane defoaming agent. The retarder is any one of citric acid, sodium citrate, lignin sulfonate, sodium carboxymethyl cellulose, phosphoric acid, protein-based retarder, and amino acid-based retarder.

[0014] A preparation method of a desulfurization gypsum self-leveling mortar, comprising the following steps: weighing each raw material according to the proportion, adding water, and stirring and mixing uniformly in a cement mortar mixer to obtain the desulfurization gypsum self-leveling mortar. The water amount of the gypsum self-leveling mortar is 40-60% of the total mass of the powder.

[0015] The desulfurization gypsum self-leveling mortar can be applied to automatic leveling of floor surface and backfill system of floor heating of residential or public building floor surface with high requirements of wear resistance and strength.

[0016] Compared with the prior art, the application has the following advantages:

[0017] (1) The modified desulfurization gypsum has a particle size D50 of 20-35 μm after ball milling, and the modified desulfurization gypsum can effectively control the bleeding and stratification of the gypsum self-leveling mortar and improve the flow performance of the system;

[0018] (2) Silicon nitride has high wear resistance, but in the gypsum self-leveling system, the density of silicon nitride is higher than the wet density of the gypsum self-leveling, and the silicon nitride is completely settled at the bottom in the gypsum self-leveling system, and cannot play a role in surface wear resistance. In the application, nanometer silicon nitride is introduced in the process of preparing nanometer cellulose aerogel by using a sol-gel process, and nanometer cellulose / silicon nitride aerogel is prepared. After the nanometer cellulose / silicon nitride aerogel is added into the gypsum self-leveling, the content of N / Si elements on the surface is improved by XRF detection, and the wear resistance of the material surface is obviously improved. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions 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 creative efforts are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the raw materials and reagents used in the following examples and comparative examples are all commercially available products. The polycarboxylate superplasticizer is Huaxuan High-Tech PC-3008; the retarder is SG-12; and the defoamer is A306, all manufactured by Suzhou Xingbang.

[0021] Example 1

[0022] The desulfurized gypsum self-leveling mortar includes the following raw materials in parts by weight: 85 parts of modified desulfurized gypsum, 14 parts of cement, 0.15 parts of water reducer, 0.15 parts of retarder, 0.15 parts of defoamer, and 0.05 parts of nanocellulose / silicon nitride aerogel. The water content accounts for 43% of the total mass of the powder.

[0023] The modified desulfurized gypsum was prepared by subjecting the desulfurized gypsum to a low-temperature treatment at 160°C for 2 minutes, ball milling for 5 minutes, and then uniformly mixing the preliminarily modified desulfurized gypsum with 0.05% graphene powder to obtain the modified desulfurized gypsum. The D50 value was 20 μm.

[0024] The specific preparation process of nanocellulose / silicon nitride aerogel is as follows: a nanocellulose solution with a mass fraction of 5.0% (5.0% NCC) is prepared with deionized water, nano-Si3N4 is added to the solution, the mass ratio of 5.0% NCC to nano-Si3N4 is 15:1, and magnetic stirring is performed at room temperature for 8 hours to obtain a homogeneous nano-Si3N4 / NCC solution; methyltrimethoxysilane is added to the nano-Si3N4 / NCC solution, the mass ratio of nano-Si3N4 / NCC solution to methyltrimethoxysilane is 50:1, magnetic stirring is performed at room temperature for 3 hours, and nano-Si3N4 / NCC aerogel is obtained after vacuum freeze drying for 25 hours.

[0025] Example 2

[0026] The desulfurized gypsum self-leveling mortar includes the following raw materials in parts by weight: 85 parts of modified desulfurized gypsum, 14 parts of cement, 0.15 parts of water reducer, 0.15 parts of retarder, 0.15 parts of defoamer, and 0.25 parts of nanocellulose / silicon nitride aerogel. The water content accounts for 43% of the total mass of the powder.

[0027] The modified desulfurized gypsum was prepared by subjecting the desulfurized gypsum to a low-temperature treatment at 150°C for 2 minutes, ball milling for 7 minutes, and then uniformly mixing the preliminarily modified desulfurized gypsum with 0.07% graphene powder to obtain the modified desulfurized gypsum. The D50 value was 35 μm.

[0028] The specific preparation process of nanocellulose / silicon nitride aerogel is as follows: a nanocellulose solution with a mass fraction of 5.0% (5.0% NCC) is prepared with deionized water, nano-Si3N4 is added to the solution, the mass ratio of 5.0% NCC to nano-Si3N4 is 20:1, and magnetic stirring is performed at room temperature for 8 hours to obtain a homogeneous nano-Si3N4 / NCC solution; methyltrimethoxysilane is added to the nano-Si3N4 / NCC solution, the mass ratio of nano-Si3N4 / NCC solution to methyltrimethoxysilane is 50:1, magnetic stirring is performed at room temperature for 3 hours, and nano-Si3N4 / NCC aerogel is obtained after vacuum freeze drying for 25 hours.

[0029] Example 3

[0030] The desulfurized gypsum self-leveling mortar includes the following raw materials in parts by weight: 85 parts of modified desulfurized gypsum, 14 parts of cement, 0.15 parts of water reducer, 0.15 parts of retarder, 0.15 parts of defoamer, and 0.5 parts of nanocellulose / silicon nitride aerogel. The water content accounts for 43% of the total mass of the powder.

[0031] The modified desulfurized gypsum was prepared by subjecting the desulfurized gypsum to a low-temperature treatment at 155°C for 3 minutes, ball milling for 6 minutes, and then uniformly mixing the preliminarily modified desulfurized gypsum with 0.06% graphene powder to obtain the modified desulfurized gypsum. The D50 value was 30 μm.

[0032] The specific preparation process of nanocellulose / silicon nitride aerogel is as follows: a nanocellulose solution with a mass fraction of 5.0% (5.0% NCC) is prepared with deionized water, nano-Si3N4 is added to the solution, the mass ratio of 5.0% NCC to nano-Si3N4 is 25:1, and magnetic stirring is performed at room temperature for 8 hours to obtain a homogeneous nano-Si3N4 / NCC solution; methyltrimethoxysilane is added to the nano-Si3N4 / NCC solution, the mass ratio of nano-Si3N4 / NCC solution to methyltrimethoxysilane is 45:1, magnetic stirring is performed at room temperature for 3 hours, and nano-Si3N4 / NCC aerogel is obtained after vacuum freeze drying for 25 hours.

[0033] Example 4

[0034] The desulfurized gypsum self-leveling mortar includes the following raw materials in parts by weight: 80 parts of modified desulfurized gypsum, 19 parts of cement, 0.15 parts of water reducer, 0.15 parts of retarder, 0.15 parts of defoamer, and 0.25 parts of nanocellulose / silicon nitride aerogel, and the water content accounts for 40% of the total mass of the powder.

[0035] The modified desulfurized gypsum was prepared by subjecting the desulfurized gypsum to a low-temperature treatment at 160°C for 3 minutes, ball milling for 8 minutes, and then uniformly mixing the preliminarily modified desulfurized gypsum with 0.1% graphene powder to obtain the modified desulfurized gypsum. The D50 value was 20 μm.

[0036] The specific preparation process of nanocellulose / silicon nitride aerogel is as follows: a nanocellulose solution with a mass fraction of 5.0% (5.0% NCC) is prepared with deionized water, nano-Si3N4 is added to the solution, the mass ratio of 5.0% NCC to nano-Si3N4 is 20:1, and magnetic stirring is performed at room temperature for 8 hours to obtain a homogeneous nano-Si3N4 / NCC solution; methyltrimethoxysilane is added to the nano-Si3N4 / NCC solution, the mass ratio of nano-Si3N4 / NCC solution to methyltrimethoxysilane is 45:1, magnetic stirring is performed at room temperature for 3 hours, and nano-Si3N4 / NCC aerogel is obtained after vacuum freeze drying for 25 hours.

[0037] Example 5

[0038] The desulfurized gypsum self-leveling mortar includes the following raw materials in parts by weight: 98 parts of modified desulfurized gypsum, 1 part of cement, 0.15 parts of water reducer, 0.15 parts of retarder, 0.15 parts of defoamer, and 0.25 parts of nanocellulose / silicon nitride aerogel. The water content accounts for 48% of the total mass of the powder.

[0039] The modified desulfurized gypsum was prepared by subjecting the desulfurized gypsum to a low-temperature treatment at 150°C for 2 minutes, ball milling for 8 minutes, and then uniformly mixing the preliminarily modified desulfurized gypsum with 0.08% graphene powder to obtain the modified desulfurized gypsum. The D50 value was 35 μm.

[0040] The specific preparation process of nanocellulose / silicon nitride aerogel is as follows: a nanocellulose solution with a mass fraction of 5.0% (5.0% NCC) is prepared with deionized water, nano-Si3N4 is added to the solution, the mass ratio of 5.0% NCC to nano-Si3N4 is 25:1, and magnetic stirring is performed at room temperature for 8 hours to obtain a homogeneous nano-Si3N4 / NCC solution; methyltrimethoxysilane is added to the nano-Si3N4 / NCC solution, the mass ratio of nano-Si3N4 / NCC solution to methyltrimethoxysilane is 50:1, magnetic stirring is performed at room temperature for 3 hours, and nano-Si3N4 / NCC aerogel is obtained after vacuum freeze drying for 25 hours.

[0041] Comparative Example 1

[0042] Comparative Example 1 is compared with Example 2, except that: Comparative Example 1 uses desulfurized gypsum with D50=14 μm to replace the modified desulfurized gypsum.

[0043] Comparative Example 2

[0044] Comparative Example 2 is compared with Example 2, except that: in Comparative Example 1, desulfurized gypsum with D50=55 μm is used to replace the modified desulfurized gypsum.

[0045] Comparative Example 3

[0046] Compared with Example 2, Comparative Example 3 differs in that: Comparative Example 3 uses nanocellulose and silicon nitride to replace the nanocellulose / silicon nitride aerogel, the amount of nanocellulose solution with a mass fraction of 5.0% is added in an amount of 0.238 parts, and the amount of silicon nitride added is 0.119 parts (consistent with the content of nanocellulose and silicon nitride in nano-Si3N4 / NCC aerogel).

[0047] Comparative Example 4

[0048] Compared with Example 2, Comparative Example 4 is different in that: No nanocellulose / silicon nitride aerogel is added in Comparative Example 4.

[0049] Comparative Example 5

[0050] Compared with Example 2, Comparative Example 5 differs in that: Comparative Example 5 uses cellulose / silicon dioxide aerogel instead of nanocellulose / silicon nitride aerogel.

[0051] Comparative Example 6

[0052] Compared with Example 2, Comparative Example 6 differs in that: Comparative Example 6 uses cellulose / carbonized silicon aerogel instead of nanocellulose / silicon nitride aerogel.

[0053] Comparative Example 7

[0054] Comparative Example 7 is different from Example 2 in that the modified desulfurized gypsum is prepared by the following steps: the desulfurized gypsum is subjected to a low-temperature treatment at 150° C. for 2 minutes and ball-milled for 7 minutes to obtain the modified desulfurized gypsum.

[0055] Comparative Example 8

[0056] Compared with Example 2, Comparative Example 8 differs in that the modified desulfurization gypsum is prepared by the following steps: first, the desulfurization gypsum is subjected to a low-temperature treatment at 150°C for 2 minutes and a ball milling treatment for 7 minutes, and then the preliminarily modified desulfurization gypsum is uniformly mixed with 0.2% graphene powder to obtain the modified desulfurization gypsum.

[0057] Comparative Example 9

[0058] Comparative Example 9 is different from Example 2 in that the modified desulfurization gypsum is prepared by the following steps: desulfurization gypsum is uniformly mixed with 0.07% graphene powder to obtain the modified desulfurization gypsum.

[0059] Comparative Example 10

[0060] Comparative Example 10 is different from Example 2 in that the modified desulfurization gypsum is prepared by the following steps: the desulfurization gypsum is ball-milled for 7 minutes, and then uniformly mixed with 0.07% graphene powder to obtain the modified desulfurization gypsum.

[0061] Test Example 1: Element Content Determination

[0062] The surface gypsum self-leveling mortar samples of the embodiment and the comparative example were taken from the surface of the absolute dry compressive strength test block. The surface of the test block was polished with 360-grit sandpaper to a surface thickness of about 1 mm. 5 g of the polished powder was taken for XRF analysis. The data in Table 1 lists the main element contents. Other very small amounts of Zr, Cl, Mn, Zn, Na, and Ni elements are not reflected in the table.

[0063] Table 1 XRF analysis of element contents in the examples and comparative examples

[0064]

[0065]

[0066] As can be seen from Table 1, in Examples 1-5, the surface samples contain N and C elements, while in the comparative examples, the surface contains very little N and C elements or no N element is detected; in comparative examples 1-10, the Si element comes from gypsum powder and cement, and the Si element content in Examples 1-5 is significantly higher than that in the comparative examples, which means that silicon nitride and graphene in the examples can be effectively enriched on the surface of the gypsum self-leveling mortar.

[0067] Test Example 2: Performance Test

[0068] Mixing method for self-leveling gypsum: After adding an appropriate amount of water to the mixer, pour the powder into the mixer at a uniform speed over 30 seconds. Mix at a low speed for 60 seconds. Stop stirring and use a scraper to scrape off any uneven mixture from the stirring blades and the walls of the pot within 30 seconds. Mix at a high speed for 60 seconds, let it rest for 60 seconds, and then continue stirring at a high speed for 15 seconds to obtain a uniformly mixed gypsum self-leveling mortar. The appropriate water dosage refers to the amount of water used when the fluidity test shows a fluidity between 140-150mm.

[0069] In the present invention, the test block size of the absolute shrinkage rate and the absolute dry compressive strength is 40*40*160mm. The test block is cured for 28 days under the conditions of humidity 65±5% and temperature 23±5℃, and then dried in an oven at 40℃ until it is absolutely dry. The data obtained by measuring the absolute dry tensile bond strength is obtained by using a concrete test block that complies with JC / T547-2017. The outer frame size of the test block molding frame is 70*70mm, the inner frame size is 50*50mm, and the thickness is 5mm. The test block is cured for 28 days under the conditions of humidity 65±5% and temperature 23±5℃, and then dried in an oven at 40℃ until it is absolutely dry. After curing for 28 days at 23±5°C, the mortar was dried in a 40°C oven until absolutely dry, and the tensile bond strength was measured. Absolute shrinkage, absolute compressive strength, and absolute tensile bond strength were tested in accordance with the provisions of the standard JC / T1023-2021 "Gypsum-based Self-leveling Mortar." The 30-minute fluidity loss is the difference between the fluidity measured after the slurry that meets the initial fluidity is allowed to stand in a mixing bowl for 30 minutes and then stirred for 30 seconds. The wear resistance test was conducted in accordance with the provisions of the current standard GB / T 50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete." The test instrument used was the Tianjin Sansi TMS-04 cement mortar wear tester, with specimen dimensions of 150*150*150mm. The test results are shown in Table 2 below:

[0070] Table 2

[0071]

[0072]

[0073] Compared with Comparative Example 4, Examples 1-3 show a decreasing trend in abrasion loss with increasing nanocellulose / silicon nitride aerogel addition, indicating improved surface wear resistance. In Examples 1-5, the gypsum self-leveling mortar prepared using ball-milled desulfurized gypsum exhibited minimal fluidity loss after 30 minutes, exhibited no delamination or water exudation, and exhibited excellent surface wear resistance. Furthermore, the absolute dry shrinkage was reduced, indicating stable volume changes over later stages and reduced the risk of shrinkage cracking. Furthermore, the absolute dry compressive strength and absolute dry tensile bond strength were improved.

[0074] Compared with Example 2, Comparative Examples 1-2 use coarser or finer gypsum powder to prepare gypsum self-leveling mortar, which easily leads to delamination and water seepage problems, and has higher abrasion and poor surface wear resistance.

[0075] Compared with Example 2, Comparative Example 3 uses nanocellulose and silicon nitride to replace the nanocellulose / silicon nitride aerogel. The silicon nitride is not concentrated on the surface, so the wear rate is higher and the surface wear resistance is poor.

[0076] Comparative Examples 5-6 use cellulose / silicon dioxide aerogel and cellulose / carbonized silicon aerogel to replace nanocellulose / silicon nitride aerogel, respectively. Their wear resistance is improved, but due to the problems of delamination and water exudation, their wear resistance is not as good as that of nanocellulose / silicon nitride aerogel.

[0077] In Comparative Example 7, the desulfurized gypsum was subjected to a low-temperature treatment at 150° C. for 2 minutes and ball milling for 7 minutes. The desulfurized gypsum was not treated with graphene, and its wear resistance, absolute dry compressive strength, and absolute dry tensile bond strength were all reduced.

[0078] In Comparative Example 8, the graphene content is too high, the fluidity loss in 30 minutes is large, and the fluidity of the gypsum self-leveling mortar is poor, but it has no adverse effect on the strength and wear resistance.

[0079] In Comparative Examples 9-10, the desulfurized gypsum powder was not subjected to low-temperature ball milling modification, or was only ball milled without low-temperature modification. This can easily lead to delamination and bleeding in the self-leveling gypsum, which in turn affects the wear resistance and strength of the product. The desulfurized gypsum powder after ball milling and low-temperature modification is more homogeneous, improves the hydration activity of the gypsum, and exhibits excellent flow properties, which can solve the delamination and bleeding problems of the slurry material.

[0080] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A desulfurized gypsum self-leveling mortar, characterized in that: The desulfurized gypsum self-leveling mortar comprises the following raw materials in parts by weight: 80-98 parts of modified desulfurized gypsum, 1-50 parts of cement, 0.05-0.2 parts of a water reducer, 0.05-0.2 parts of a retarder, 0.05-0.2 parts of a defoamer, and 0.05-0.5 parts of a nanocellulose / silicon nitride aerogel. The modified desulfurized gypsum is prepared by the following steps: first, subjecting the desulfurized gypsum to a low-temperature treatment at 150-160° C. and then to a ball milling treatment for 5-8 minutes for preliminary modification; and then uniformly mixing the preliminarily modified desulfurized gypsum with graphene powder to obtain the modified desulfurized gypsum. The modified desulfurized gypsum particle size D50 is 20-35 μm; the amount of graphene used is 0.05%-0.1% of the amount of gypsum used; The nanocellulose / silicon nitride aerogel is obtained by adopting a sol-gel preparation process; The preparation process is specifically as follows: preparing a nanocellulose solution (5.0% NCC) with a mass fraction of 5.0% using deionized water, adding nano-Si3N4 to the solution, with the mass ratio of 5.0% NCC to nano-Si3N4 being (15-25):1, and magnetically stirring at room temperature for 8-9 hours to obtain a homogeneous nano-Si3N4 / NCC solution; adding methyltrimethoxysilane to the nano-Si3N4 / NCC solution, with the mass ratio of the nano-Si3N4 / NCC solution to methyltrimethoxysilane being (45-50):1, and magnetically stirring at room temperature for 2-3 hours, and obtaining a nano-Si3N4 / NCC aerogel after vacuum freeze-drying for 24-30 hours.

2. A desulfurized gypsum self-leveling mortar according to claim 1, characterized in that: The cement is PO425 cement; the water reducer is polycarboxylate water reducer.

3. The desulfurized gypsum self-leveling mortar according to claim 1, characterized in that: The defoaming agent is any one of mineral oil, silicone, polyether and polyether-modified polysiloxane defoaming agents.

4. The desulfurized gypsum self-leveling mortar according to claim 1, characterized in that: The retarder is any one of citric acid, sodium citrate, lignin sulfonate, sodium carboxymethyl cellulose, phosphoric acid, protein retarder, and amino acid retarder.

5. The method for preparing a desulfurized gypsum self-leveling mortar according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: weighing raw materials according to a proportion, adding water, and stirring and mixing in a cement mortar mixer until the mixture is evenly mixed; the water content of the gypsum self-leveling mortar is 40-60% of the total mass of the powder.

6. Application of a desulfurized gypsum self-leveling mortar according to any one of claims 1 to 4, characterized in that: The desulfurized gypsum self-leveling mortar can be used in automatic leveling of building floors and floor heating backfill systems.

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