Desulfurized gypsum self-leveling mortar as well as preparation method and application thereof

Abstract

The invention provides desulfurized gypsum self-leveling mortar as well as a preparation method and application thereof. The desulfurized gypsum self-leveling mortar is prepared from the following raw materials in parts by weight: 80 to 98 parts of modified desulfurized gypsum, 1 to 50 parts of cement, 0.05 to 0.2 part of a water reducing agent, 0.05 to 0.2 part of a retarder, 0.05 to 0.2 part of a de-foaming agent and 0.05 to 0.5 part of nano cellulose / silicon nitride aerogel, 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. By adopting a sol-gel process, in the process of preparing the nano-cellulose aerogel, nano-silicon nitride is introduced, the nano-cellulose / silicon nitride aerogel is prepared, and after the nano-cellulose / silicon nitride aerogel is added in gypsum self-leveling, the content of N / Si and C elements on the surface is improved, and the wear resistance of the material surface is obviously improved.

Description

Technical Field

[0001] The 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 the construction process, the ground may be uneven, bumpy or defective, but as people's requirements for the ground are getting higher and higher, they hope that the ground can be 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, does not contain harmful volatile organic compounds (VOCs), and is friendly to the indoor environment. In general, due to the characteristics of high flatness, convenient construction, and good decorativeness, gypsum self-leveling mortar is widely used in construction and decoration.

[0003] Patent CN 116283185 A A special mortar for floor heating and its preparation method, comprising the following raw materials in weight percentage: gypsum powder, silicate cement, metal waste, carbon nanoparticles, latex powder, defoamer, retarder, water reducer, water; wherein the carbon nanoparticles are obtained by carbonization of humic acid and have a hollow tube structure. The special mortar for floor heating has good fluidity, wear resistance, compressive and flexural strength and thermal conductivity, which helps to improve the overall performance of the special mortar for floor heating.

[0004] Patent CN 115745548 A A kind of phosphogypsum-based self-leveling material for floor heating backfill and its preparation method, by adding high thermal conductivity phase change energy storage components, controlling the performance parameters of building gypsum, and coordinating other components, under the premise of ensuring the fluidity and mechanical properties of the material, the water demand of the material is reduced and the thermal conductivity of the material is increased. It can be seen from the SEM image that the fibrous dihydrate gypsum crystal network generated by hydration wraps around the granular waste stone powder, and a large number of dihydrate gypsum crystals are distributed around the flaky expanded graphite powder. The microstructure is very dense, which can well ensure the mechanical strength and heat transfer performance of the phosphogypsum-based self-leveling floor material for floor heating backfill.

[0005] Patent CN 113372079 A discloses a highly wear-resistant gypsum-based self-leveling mortar and a preparation method thereof. Desulfurized building gypsum, which is a product of calcined desulfurized building gypsum and other industrial by-product gypsum, is used as a cementitious material. Since the desulfurized building gypsum has a small fineness, the water-cement ratio is reduced, and the resource utilization rate of industrial by-product gypsum such as desulfurized building gypsum is greatly improved, which is beneficial to the solid waste treatment and resource recycling of industrial by-product gypsum and protects the environment. In the present invention, 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 an admixture, the self-leveling mortar is prevented from segregating and bleeding, sedimentation is reduced, the surface effect of the hardened self-leveling mortar is improved, and its wear resistance is improved.

[0006] Gypsum self-leveling mortar is often used for floor leveling in general residences, and then floor or tile adhesive is applied after leveling. The requirements for the surface wear resistance of gypsum self-leveling mortar are relatively small. However, some structural surface layers, such as public buildings, have higher requirements for the wear resistance of the ground leveling layer, and the surface performance of gypsum self-leveling needs to be further improved. Summary of the invention

[0007] Aiming at the above-mentioned series of problems such as poor wear resistance of gypsum-based self-leveling mortar in the prior art, the present application proposes a desulfurized gypsum self-leveling mortar and a preparation method and application thereof, so as to improve the surface wear resistance of the gypsum self-leveling mortar.

[0008] A 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 water reducing agent, 0.05-0.2 parts of retarder, 0.05-0.2 parts of defoaming agent, and 0.05-0.5 parts of nanocellulose / silicon nitride aerogel; the water consumption of the gypsum self-leveling mortar is 40-60% of the total weight of the powder.

[0009] The modified desulfurized gypsum is prepared by the following steps: firstly, the desulfurized gypsum is subjected to a low temperature treatment at 150-160°C and then ball milled for 5-8 minutes for preliminary modification; then, the preliminarily modified desulfurized gypsum is evenly mixed with graphene powder to obtain the modified desulfurized gypsum; the fineness of the graphene is selected to be 200-800 mesh.

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

[0011] The nanocellulose / silicon nitride aerogel is obtained by adopting a sol-gel preparation process.

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

[0013] The cement is PO425 cement. The water reducer is a polycarboxylate water reducer. The defoamer is any one of mineral oil, organosilicon, polyether and polyether modified polysiloxane defoamers. The retarder is any one of citric acid, sodium citrate, lignin sulfonate, sodium carboxymethyl cellulose, phosphoric acid, protein retarder and amino acid retarder.

[0014] A method for preparing a desulfurized gypsum self-leveling mortar comprises the following steps: weighing various raw materials according to a proportion, adding water, and stirring and mixing in a cement mortar mixer to obtain the mortar. The water consumption of the gypsum self-leveling mortar is 40-60% of the total mass of the powder.

[0015] The desulfurized gypsum self-leveling mortar can be used in automatic leveling and floor heating backfill systems of residential or public buildings that have high requirements on floor surface wear resistance and strength.

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

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

[0018] (2) Silicon nitride itself has high wear resistance, but in the gypsum self-leveling system, because the density of silicon nitride is higher than the wet density of gypsum self-leveling, silicon nitride is completely sunk to the bottom of the gypsum self-leveling system and does not play a role in surface wear resistance. In the process of preparing nanocellulose aerogel by adopting the sol-gel process, nano silicon nitride is introduced to prepare nanocellulose / silicon nitride aerogel. After adding the nanocellulose / silicon nitride aerogel to the gypsum self-leveling, the surface N / Si element content is increased through XRF detection, and the wear resistance of the material surface is significantly improved. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The raw materials and reagents used in the following examples and comparative examples are all common commercially available products unless otherwise specified. The polycarboxylate water reducer is Huaxuan High-tech PC-3008; the retarder is SG-12; and the defoamer is A306, all of which are produced 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, 0.05 parts of nanocellulose / silicon nitride aerogel, and the amount of water used accounts for 43% of the total mass of the powder.

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

[0024] The specific preparation process of nano-cellulose / silicon nitride aerogel is as follows: a nano-cellulose solution (5.0% NCC) with a mass fraction of 5.0% 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 the nano-Si3N4 / NCC solution to methyltrimethoxysilane is 50:1, and magnetic stirring is performed at room temperature for 3 hours. After vacuum freeze-drying for 25 hours, nano-Si3N4 / NCC aerogel is obtained.

[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, 0.25 parts of nanocellulose / silicon nitride aerogel, and the amount of water used accounts for 43% of the total mass of the powder.

[0027] The modified desulfurized gypsum was prepared by the following steps: firstly, the desulfurized gypsum was subjected to a low temperature treatment at 150°C for 2 minutes, and a ball milling treatment was performed for 7 minutes, and then the preliminarily modified desulfurized gypsum was uniformly mixed with 0.07% graphene powder to obtain the modified desulfurized gypsum. The D50 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 the nano-Si3N4 / NCC solution to methyltrimethoxysilane is 50:1, and magnetic stirring is performed at room temperature for 3 hours. After vacuum freeze drying for 25 hours, nano-Si3N4 / NCC aerogel is obtained.

[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, 0.5 parts of nanocellulose / silicon nitride aerogel, and the amount of water used accounts for 43% of the total mass of the powder.

[0031] The modified desulfurized gypsum was prepared by the following steps: firstly, the desulfurized gypsum was subjected to a low temperature treatment at 155°C for 3 minutes, and a ball milling treatment was performed for 6 minutes, and then the preliminarily modified desulfurized gypsum was uniformly mixed with 0.06% graphene powder to obtain the modified desulfurized gypsum. The D50 was 30 μm.

[0032] The specific preparation process of nano-cellulose / silicon nitride aerogel is as follows: a nano-cellulose solution (5.0% NCC) with a mass fraction of 5.0% 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 the nano-Si3N4 / NCC solution to methyltrimethoxysilane is 45:1, and magnetic stirring is performed at room temperature for 3 hours. After vacuum freeze-drying for 25 hours, nano-Si3N4 / NCC aerogel is obtained.

[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, 0.25 parts of nanocellulose / silicon nitride aerogel, and the amount of water used accounts for 40% of the total mass of the powder.

[0035] The modified desulfurized gypsum was prepared by the following steps: firstly, the desulfurized gypsum was subjected to a low temperature treatment at 160°C for 3 minutes, and a ball milling treatment was performed for 8 minutes, and then the preliminarily modified desulfurized gypsum was uniformly mixed with 0.1% graphene powder to obtain the modified desulfurized gypsum. The D50 was 20 μm.

[0036] The specific preparation process of nano-cellulose / silicon nitride aerogel is as follows: a nano-cellulose solution (5.0% NCC) with a mass fraction of 5.0% 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 the nano-Si3N4 / NCC solution to methyltrimethoxysilane is 45:1, and magnetic stirring is performed at room temperature for 3 hours. After vacuum freeze-drying for 25 hours, nano-Si3N4 / NCC aerogel is obtained.

[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, 0.25 parts of nanocellulose / silicon nitride aerogel, and the amount of water used accounts for 48% of the total mass of the powder.

[0039] The modified desulfurized gypsum was prepared by the following steps: firstly, the desulfurized gypsum was subjected to a low temperature treatment at 150°C for 2 minutes, and a ball milling treatment was performed for 8 minutes, and then the preliminarily modified desulfurized gypsum was uniformly mixed with 0.08% graphene powder to obtain the modified desulfurized gypsum. The D50 was 35 μm.

[0040] The specific preparation process of nano-cellulose / silicon nitride aerogel is as follows: a nano-cellulose solution (5.0% NCC) with a mass fraction of 5.0% 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 the nano-Si3N4 / NCC solution to methyltrimethoxysilane is 50:1, and magnetic stirring is performed at room temperature for 3 hours. After vacuum freeze-drying for 25 hours, nano-Si3N4 / NCC aerogel is obtained.

[0041] Comparative Example 1

[0042] The difference between Comparative Example 1 and Example 2 is that: Comparative Example 1 uses desulfurized gypsum with D50=14 μm to replace the modified desulfurized gypsum.

[0043] Comparative Example 2

[0044] Compared with Example 2, Comparative Example 2 differs in that: Comparative Example 1 uses desulfurized gypsum with D50=55 μm 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 0.238 parts, and the amount of silicon nitride 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 to replace nanocellulose / silicon nitride aerogel.

[0051] Comparative Example 6

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

[0053] Comparative Example 7

[0054] Compared with Example 2, Comparative Example 7 differs 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 desulfurized gypsum is prepared by the following steps: first, the desulfurized gypsum is subjected to a low-temperature treatment at 150°C for 2 minutes and a ball milling treatment for 7 minutes; then, the preliminarily modified desulfurized gypsum is evenly mixed with 0.2% graphene powder to obtain the modified desulfurized gypsum.

[0057] Comparative Example 9

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

[0059] Comparative Example 10

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

[0061] Test Example 1: Element Content Determination

[0062] The surface gypsum self-leveling mortar samples of the embodiments and comparative examples were taken from the surface of the absolute dry compressive strength test block, and the surface of the test block was polished with 360 mesh sandpaper. The polished surface thickness was about 1 mm, and 5 g of the polished powder was taken for XRF analysis. The data in Table 1 lists the main element contents, and 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 examples and comparative examples

[0064]

[0065]

[0066] It can be seen from Table 1 that 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, while 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 embodiments can be effectively enriched on the surface of the gypsum self-leveling mortar.

[0067] Test Example 2: Performance Test

[0068] Mixing method of gypsum self-leveling: After pouring appropriate water into the mixer, pour the powder into the mixer at a uniform speed within 30 seconds, and mix at a low speed for 60 seconds; stop stirring, and use a scraper to scrape off the uneven mixture on the stirring blade and the wall of the material pot within 30 seconds; stir at high speed for 60 seconds, stop for 60 seconds, and continue to stir at high speed for 15 seconds to obtain a uniformly mixed gypsum self-leveling mortar. The appropriate amount of water refers to the amount of water used when the fluidity is between 140-150mm through the fluidity test.

[0069] In the present invention, the test block size of the absolute shrinkage rate and the absolute dry compressive strength is 40*40*160mm. After the test block is cured for 28 days under the conditions of humidity 65±5% and temperature 23±5°C, it is dried in an oven at 40°C until it is absolutely dry to obtain the data; the measurement of the absolute dry tensile bond strength adopts a concrete test block that conforms to 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 at a humidity of 65±5%, After curing for 28 days at a temperature of 23±5℃, dry in an oven at 40℃ until absolutely dry to measure the tensile bond strength; the tests of absolute dry shrinkage, absolute dry compressive strength, and absolute dry tensile bond strength are carried out 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 by the slurry that meets the initial fluidity and the initial fluidity after standing in the mixing bowl for 30 minutes and then stirring for 30 seconds; the wear resistance test is carried out in accordance with the provisions of the current standard specification GB / T 50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The test instrument uses the TMS-04 cement mortar wear tester of Tianjin Sansi, and the specimen size is 150*150*150mm. The test results are shown in Table 2 below:

[0070] Table 2

[0071]

[0072]

[0073] Compared with Comparative Example 4, in Example 1-3, as the amount of nanocellulose / silicon nitride aerogel added increases, the amount of wear decreases, that is, the wear resistance of the surface is improved; in Example 1-5, the desulfurized gypsum after ball milling is used to prepare the gypsum self-leveling mortar, the fluidity loss is small in 30 minutes, and there is no stratification or water seepage, the surface wear resistance is good, and the absolute shrinkage rate is also reduced, that is, the volume change in the later period is stable, and it is not easy to shrink and crack. In addition, the absolute dry compressive strength and absolute dry tensile bond strength are improved.

[0074] Compared with Example 2, Comparative Examples 1-2 use coarser or finer gypsum powder to prepare gypsum self-leveling mortar, which is very likely to cause 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 nanocellulose / silicon nitride aerogel. Silicon nitride is not concentrated on the surface, so the wear amount is higher and the surface wear resistance is poor.

[0076] Comparative Examples 5-6 respectively use cellulose / silicon dioxide aerogel and cellulose / silicon carbide aerogel to replace nanocellulose / silicon nitride aerogel, and their wear resistance is improved. However, due to the problems of stratification and water seepage, 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 a ball milling treatment for 7 minutes. The desulfurized gypsum was not treated with graphene, and its wear resistance, absolute dry compressive strength and absolute dry tensile bonding 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 was not subjected to low-temperature modification by ball milling, or only subjected to ball milling without low-temperature modification, which easily led to the problems of stratification and water seepage in the self-leveling of the gypsum, thereby affecting the wear resistance and strength of the product. The desulfurized gypsum powder after ball milling and low-temperature modification is more homogeneous, can improve the hydration activity of the gypsum, show excellent flow properties, and can solve the problems of stratification and water seepage in the slurry material.

[0080] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present 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 water reducing agent, 0.05-0.2 parts of retarder, 0.05-0.2 parts of defoaming agent and 0.05-0.5 parts of nano cellulose / silicon nitride aerogel.

2. A desulfurized gypsum self-leveling mortar according to claim 1, characterized in that: The modified desulfurized gypsum is prepared by the following steps: firstly, the desulfurized gypsum is subjected to a low temperature treatment at 150-160° C. and then subjected to a ball milling treatment for 5-8 minutes for preliminary modification, and then the preliminarily modified desulfurized gypsum is uniformly mixed with graphene powder to obtain the modified desulfurized gypsum.

3. A desulfurized gypsum self-leveling mortar according to claim 2, characterized in that: The particle size D50 of the modified desulfurized gypsum is 20-35 μm; the amount of graphene used is 0.05%-0.1% of the amount of gypsum used.

4. A desulfurized gypsum self-leveling mortar according to claim 1, characterized in that: The nanocellulose / silicon nitride aerogel is obtained by adopting a sol-gel preparation process.

5. A desulfurized gypsum self-leveling mortar according to claim 4, characterized in that: The preparation process is specifically as follows: preparing a nanocellulose solution (5.0% NCC) with a mass fraction of 5.0% with deionized water, adding nano-Si3N4 to the solution, 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, 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.

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

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

8. 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.

9. The method for preparing a desulfurized gypsum self-leveling mortar according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: weighing various raw materials according to a proportion, adding water, and stirring and mixing in a cement mortar mixer to obtain the gypsum self-leveling mortar; the water consumption of the gypsum self-leveling mortar is 40-60% of the total weight of the powder.

10. The use of a desulfurized gypsum self-leveling mortar according to any one of claims 1 to 8, 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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