Preparation process of low-temperature calcined gypsum powder

Abstract

The invention relates to the technical field of preparation of building materials, and particularly discloses a preparation process of low-temperature calcined gypsum powder. A preparation process of low-temperature calcined gypsum powder comprises the following steps: uniformly mixing 100 parts by mass of primary gypsum powder, 5-15 parts by mass of composite aggregate, 0.5-2.0 parts by mass of silanized fiber, 0.2-0.4 part by mass of hydroxypropyl methyl cellulose ether and 0.05-0.15 part by mass of a protein retarder to obtain the low-temperature calcined gypsum powder. The low-temperature calcined gypsum powder prepared by the invention has good initial setting time and excellent mechanical strength.

Description

Technical Field

[0001] This application relates to the technical field of building material preparation, and more specifically, it relates to a preparation process for low-temperature calcined gypsum powder. Background Technology

[0002] Building gypsum (mainly composed of β-type hemihydrate gypsum, CaSO4·0.5H2O) is a long-established air-hardening cementitious material. Due to its excellent properties such as light weight, fire resistance, thermal insulation, sound absorption, humidity regulation, and ease of construction, it is widely used in the preparation of interior building products such as plastering gypsum, jointing gypsum, and gypsum putty. With the transformation of my country's construction industry towards green, energy-saving, and industrialized directions, higher requirements are being placed on the performance and quality stability of gypsum-based materials.

[0003] Traditional building gypsum powder often employs high-temperature, rapid calcination processes such as air-sweeped mills and woks. This rapid dehydration of the gypsum easily leads to over-burning (generating a large amount of type II anhydrous gypsum) or under-burning (leaving a significant amount of dihydrate gypsum residue). This unstable phase composition directly results in high water requirements for the product's standard consistency, extremely short setting time, low final strength, and significant batch-to-batch performance variations.

[0004] Patent application CN114276107A discloses a rapidly calcined lightweight plastering gypsum, which is made from raw materials comprising the following components in parts by weight: 85-95 parts modified gypsum powder; 6-12 parts vitrified microspheres; 0.5-5 parts heavy calcium carbonate; 0.2-0.5 parts retarder; 0.2-0.3 parts hydroxypropyl methylcellulose ether; 0-0.2 parts starch ether; 0-0.5 parts thickener; and 0.5-1 parts bentonite. 0.02~0.5 parts of air-entraining agent; the modified gypsum powder is obtained by the following method: cooling, homogenizing and aging high-temperature rapid calcined gypsum powder to obtain modified gypsum powder; the high-temperature rapid calcined gypsum powder is obtained by the following method: passing wet gypsum containing attached water at room temperature through hot flue gas / air at 590~650℃ within 2~15s to complete drying and calcination, removing all attached water and some crystal water to obtain high-temperature rapid calcined gypsum powder.

[0005] In this technical solution, from the perspective of the calcination process, although the high-temperature rapid calcination at 590~650℃ shortens the time, the high-temperature heat source acts instantly on the surface of the gypsum particles, creating a huge temperature gradient between the surface and the interior of the wet gypsum particles. This leads to severe dehydration or even over-burning of the surface, while the interior of the particles suffers from severe under-burning due to slow heat conduction. The phase composition is complex and unstable, resulting in insufficient effective cementitious activity of hemihydrate gypsum in the modified gypsum powder, which directly causes a lack of mechanical strength in the product. Summary of the Invention

[0006] To address the problem of insufficient mechanical strength in products produced by traditional processes, this application provides a preparation process for low-temperature calcined gypsum powder.

[0007] This application provides a process for preparing low-temperature calcined gypsum powder, using the following technical solution: A process for preparing low-temperature calcined gypsum powder includes the following steps: Mix 100 parts by weight of primary gypsum powder, 5-15 parts by weight of composite aggregate, 0.5-2.0 parts by weight of silanized fiber, 0.2-0.4 parts by weight of hydroxypropyl methylcellulose ether, and 0.05-0.15 parts by weight of protein retarder evenly to obtain low-temperature calcined gypsum powder. The primary gypsum powder is prepared by the following steps: S1: After mixing the raw material gypsum powder, modified steel slag powder, sodium tripolyphosphate and polycarboxylate superplasticizer evenly, raw meal is obtained; S2: The raw material is first calcined at 255~265℃ for 25~35min, then calcined at 240~250℃ for 7~10min, cooled, and aged to obtain primary gypsum powder; The modified steel slag powder is specifically prepared by wet modification of steel slag powder with sodium silicate solution or a mixed solution of sodium silicate and aluminum sulfate; the composite aggregate includes closed-cell perlite and ceramsite.

[0008] In this technical solution, the dual dispersion effect of sodium tripolyphosphate and polycarboxylate superplasticizer, along with the micro-heat conduction network constructed from modified steel slag powder, ensures uniform dispersion of raw materials and efficient heat transfer during the calcination process from the source. The core two-stage low-temperature calcination process achieves a stable and complete conversion of dihydrate gypsum to hemihydrate gypsum through precise temperature control, effectively preventing excessive dehydration, thereby obtaining a high-content and phase-composite stable hemihydrate gypsum matrix.

[0009] Based on this, the gypsum mortar system was optimized in multiple dimensions through the combination of lightweight and high-strength composite aggregates, the three-dimensional toughening of silanized fibers, the water retention of hydroxypropyl methylcellulose ether, and the mild setting regulation of protein retarder. Ultimately, the product achieved excellent mechanical strength and durability while ensuring workability.

[0010] Preferably, the polycarboxylate superplasticizer is an ether-based polycarboxylate superplasticizer.

[0011] Preferably, the mass ratio of the raw material gypsum powder, modified steel slag powder, sodium tripolyphosphate and polycarboxylate superplasticizer is 100:(1~3):(0.1~0.3):(0.1~0.3).

[0012] Preferably, in step S2, the calcination is carried out in a two-stage fluidized bed furnace system; the crystal water content of the output from the first-stage fluidized bed furnace is controlled to be 6%~7%, and the crystal water content of the output from the second-stage fluidized bed furnace is controlled to be 4.5%~5.5%.

[0013] Preferably, in step S2, the heat source used during calcination is natural gas.

[0014] Preferably, the preparation method of the modified steel slag powder includes the following steps: Steel slag powder with a mass ratio of 1:(1.5~2.5) is mixed evenly with a modifier, dried, and dispersed to obtain modified steel slag powder; the modifier is sodium silicate solution or a mixed solution of sodium silicate and aluminum sulfate.

[0015] Preferably, the sodium silicate solution has a mass fraction of 1.5% to 2.5%.

[0016] Preferably, when a mixed solution is used, the mass fraction of sodium silicate is 1.5% to 2.5%, and the mass fraction of aluminum sulfate is 2% to 4%.

[0017] In this technical solution, sodium silicate is used alone or in combination with aluminum sulfate to construct a strong active coating layer on the surface of micro powder particles. On the one hand, the film-forming properties and charge regulation ability of sodium silicate can effectively improve the powder dispersibility and prevent it from agglomerating in the gypsum matrix. On the other hand, sodium silicate and aluminum sulfate (if used) jointly participate in the interfacial reaction, which can significantly enhance the interfacial chemical bonding between the modified steel slag micro powder and the gypsum hydration products, thereby improving the overall performance of the composite material.

[0018] Preferably, in step S1, after the polycarboxylate superplasticizer, the step further includes adding citric acid and aluminum sulfate, wherein the total amount of citric acid and aluminum sulfate is 0.06% to 0.08% of the mass of the raw gypsum powder.

[0019] In this technical solution, citric acid purifies and homogenizes the surface of gypsum particles by complexing impurities during the mixing stage; while pre-adsorbed aluminum sulfate regulates the phase change process during the calcination stage. The two work synergistically to optimize the initial state of the raw materials and the reaction pathway, jointly promoting the formation of hemihydrate gypsum with more complete crystallization and fewer defects.

[0020] Preferably, the ceramsite is clay ceramsite with a particle size of 0.5~1.5mm.

[0021] Preferably, the composite aggregate undergoes a slurry coating pretreatment before use: Mix the composite aggregate with silicate cement, silica fume and water in a mass ratio of 100:(5~10):(1~3):(20~30) until uniform, and dry for later use.

[0022] In this technical solution, closed-cell perlite provides excellent lightweight and thermal insulation properties, while calcined ceramsite, with its higher strength, serves as a supporting framework. The combination of the two achieves a balance between lightweight and high strength. The slurry coating pretreatment of the composite aggregate significantly improves the interfacial adhesion between the aggregate and the gypsum matrix. This dense coating layer effectively blocks the rapid migration of moisture at the aggregate-gypsum interface, ensuring sufficient hydration of the gypsum in the interfacial area, while reducing the local water-cement ratio imbalance caused by the instantaneous water absorption of high-porosity aggregates such as closed-cell perlite.

[0023] Preferably, the silanized fiber comprises polypropylene fiber and wood fiber.

[0024] Preferably, the method for preparing the silanized fiber includes the following steps: After the polypropylene fiber and wood fiber are mixed evenly, they are immersed in the pre-hydrolysis solution of silane coupling agent and mixed for 1-2 hours. After solid-liquid separation, washing and drying, sodium methylsilicate of 1%-3% of the total mass of polypropylene fiber and wood fiber is added and mixed evenly to obtain pretreated fiber.

[0025] Preferably, the method for preparing the pre-hydrolyzed solution of the silane coupling agent includes the following steps: Add a 3%~5% (w / w) aqueous solution of silane coupling agent in ethanol to the reactor, adjust the pH to 5~5.5, raise the temperature to 60~80℃, and hydrolyze for 120~180 min to obtain a pre-hydrolyzed solution of silane coupling agent.

[0026] Preferably, the polypropylene fibers have a length distribution of 3-6 mm, and the wood fibers have a length distribution of 2-3 mm.

[0027] In this technical solution, polypropylene fibers, with their high tensile strength, effectively bridge and suppress macroscopic cracks after the mortar hardens; wood fibers, as micro-toughening units, with their unique capillary structure and flexibility, can improve the thixotropy of the mortar, reduce plastic shrinkage, and disperse micro-stress. The combination of the two achieves full-cycle, multi-dimensional crack resistance from construction to hardening.

[0028] Preferably, the protein-based retarder is a composite of anhydride-modified gelatin and sodium alginate.

[0029] Preferably, the preparation method of the protein-based retarder includes the following steps: S11: Disperse gelatin evenly in deionized water, adjust the pH to 7.5~8.0, add succinic anhydride at 6%~8% of the gelatin mass, heat to 50~60℃, mix for 120~180min, cool, add anhydrous ethanol to precipitate, separate solid and liquid, wash, dry, and obtain anhydride modified gelatin. S12: Mix anhydride-modified gelatin and sodium alginate at a mass ratio of (3~5):1, disperse in deionized water, and spray dry to obtain a protein retarder.

[0030] In this technical solution, more carboxyl groups are introduced into the gelatin molecular chain modified with acid anhydride. These carboxyl groups react with the Ca released during the hydration of gypsum. 2+ Controlled complexation adsorption occurs, forming a temporary, dynamic protective film on the surface of gypsum crystals. This physically blocks the contact and ion exchange of water molecules, thus achieving slow setting. This modification makes the adsorption process smoother and more reversible, avoiding the excessive inhibition of crystal nucleation and growth caused by strong adsorption or steric hindrance in unmodified gelatin. Therefore, while effectively regulating the setting time, it minimizes the negative impact on the structure and gel strength of the final gypsum hydration products.

[0031] In summary, this application has the following beneficial effects: This application fundamentally ensures the high purity and high cementitious activity of the gypsum matrix through pre-processing of raw material homogenization and two-stage low-temperature calcination. Then, by strengthening the aggregate interface, multi-scale crack resistance of fibers, and introducing water-retaining components, the mortar structure is optimized from three dimensions: reinforcement, toughening, and ensuring sufficient hydration. This allows the product to successfully balance excellent workability with mechanical strength, crack resistance, and durability. Detailed Implementation

[0032] The present application will be further described in detail below with reference to the embodiments.

[0033] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0034] The low-temperature calcined gypsum powder prepared in this application is very suitable for use as plastering gypsum.

[0035] In the following embodiments: The desulfurized gypsum contains 32.5% CaO, 45.6% SO3, 0.91% Al2O3, 0.24% MgO, 0.45% Fe2O3, and 2.10% SiO2. The remainder is mainly water of crystallization and small amounts of alkali metal oxides such as K2O and Na2O. Before use, the desulfurized gypsum is ground and selected to control its fineness to ≤12% residue on an 80μm square-hole sieve. The preparation of steel slag powder is as follows: steel slag is magnetically separated by a strong magnetic separator, then piled up in the open air for 7 days. 1 kg of the aged steel slag is taken and heated to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere, calcined for 2 hours, naturally cooled to room temperature, and then ground until the particle size distribution D50 is 20μm. The final steel slag powder contained 50.20% CaO, 12.83% SiO2, 22.11% Fe2O3, 3.26% Al2O3, and 7.59% MgO, with the remainder being trace elements such as MnO and loss on ignition. Because this process uses a nitrogen atmosphere for calcination, the iron element actually exists mainly in the form of ferrous oxide in the physical phase, and also contains iron(III) oxide. The ether-based polycarboxylate superplasticizer is an isopentenyl alcohol polyoxyethylene ether type polycarboxylate superplasticizer with a solid content of 40% and a pH of approximately 6.5. The length distribution of polypropylene fibers is 3~6mm, and the length distribution of wood fibers is 2~3mm; the particle size distribution of clay ceramsite is 0.5mm~1.5mm, and the particle size distribution of closed-cell perlite is 0.5mm~1.2mm.

[0036] Preparation Examples 1-3: Protein Retarder Preparation Example 1 The preparation method of the protein retarder in this example includes the following steps: S11: Add 5g of gelatin to 50mL of deionized water, stir and mix evenly, adjust the pH to 7.5 with 5% ammonia water, add 0.3g of succinic anhydride, stir and mix evenly, heat to 50℃, stir and mix for 120min, cool to room temperature, add 300mL of anhydrous ethanol and stir until no precipitate forms, filter, wash 3 times with anhydrous ethanol, dry at 50℃ to constant weight, and obtain anhydride modified gelatin; S12: Mix 5g of anhydride-modified gelatin and 1.67g of sodium alginate evenly, add 60mL of deionized water, stir and mix for 20min, transfer to a spray dryer, atomize and dry under nitrogen atmosphere, set the inlet temperature to 120℃ and the outlet temperature to 60℃, dry at 50℃ for 2h to obtain a powdered product, pass through a 100-mesh standard sieve to obtain a protein retarder.

[0037] Preparation Example 2 The preparation method of the protein retarder in this example includes the following steps: S11: Add 5g of gelatin to 50mL of deionized water, stir and mix evenly, adjust the pH to 7.5 with 5% ammonia water, add 0.35g of succinic anhydride, stir and mix evenly, heat to 55℃, stir and mix for 150min, cool to room temperature, add 300mL of anhydrous ethanol and stir until no precipitate forms, filter, wash 3 times with anhydrous ethanol, dry at 50℃ to constant weight, and obtain anhydride modified gelatin; S12: Mix 5g of anhydride-modified gelatin and 1.25g of sodium alginate evenly, add 60mL of deionized water, stir and mix for 20min, transfer to a spray dryer, atomize and dry under nitrogen atmosphere, set the inlet temperature to 120℃ and the outlet temperature to 60℃, dry at 50℃ for 2h to obtain a powdered product, pass through a 100-mesh standard sieve to obtain a protein retarder.

[0038] Preparation Example 3 The preparation method of the protein retarder in this example includes the following steps: S11: Add 5g of gelatin to 50mL of deionized water, stir and mix evenly, adjust the pH to 8.0 with 5% ammonia water, add 0.4g of succinic anhydride, stir and mix evenly, heat to 60℃, stir and mix for 180min, cool to room temperature, add 300mL of anhydrous ethanol and stir until no precipitate forms, filter, wash 3 times with anhydrous ethanol, dry at 50℃ to constant weight, and obtain anhydride modified gelatin; S12: Mix 5g of anhydride-modified gelatin and 1g of sodium alginate evenly, add to 60mL of deionized water, stir and mix for 20min, transfer to a spray dryer, atomize and dry under nitrogen atmosphere, set the inlet temperature to 120℃ and the outlet temperature to 60℃, dry at 50℃ for 2h to obtain a powdered product, pass through a 100-mesh standard sieve to obtain a protein retarder.

[0039] Example 1 The preparation process of low-temperature calcined gypsum powder in this embodiment includes the following steps: Add 1000g of primary gypsum powder, 50g of composite aggregate, 5g of silanized fiber, 2g of hydroxypropyl methylcellulose ether, and 0.5g of protein retarder to a mixer and mix at 800rpm for 15min to obtain low-temperature calcined gypsum powder.

[0040] The composite aggregate consisted of 35g of closed-cell perlite and 15g of clay ceramsite; the protein-based retarder was derived from Preparation Example 1.

[0041] Primary gypsum powder is prepared by the following steps: S1: Add 1500g of desulfurized gypsum powder, 15g of modified steel slag powder, 1.5g of sodium tripolyphosphate and 1.5g of ether polycarboxylate superplasticizer into a mixer and mix at 800rpm for 30min to obtain raw material; S2: The raw material is fed into a two-stage series fluidized bed furnace system with an effective volume ratio of 3.5:1. First, in the first-stage fluidized bed furnace, the temperature is raised to 255℃ at a rate of 1℃ / min and calcined for 25 minutes. The crystal water content of the output is monitored and controlled at about 7.0% by an online moisture meter. Then, the material is automatically conveyed to the second-stage fluidized bed furnace, the temperature is adjusted to 245℃, and calcined for 7 minutes. The crystal water content of the output is controlled at about 5.5%. The calcined material is collected by a cyclone separator and immediately enters a forced air cooling system with an air temperature of 25℃, an air speed of 8m / s, and a cooling time of 10 minutes. The material temperature drops to below 50℃. Then, it is placed in a constant temperature and humidity chamber with an ambient temperature of 25℃ and a relative humidity of 70% for aging for 48 hours to obtain primary gypsum powder.

[0042] The preparation method of modified steel slag powder includes the following steps: 15g of steel slag powder was placed in a small mixer, the mixer was turned on, the mixing speed was set to 200rpm, and 22.5g of sodium silicate solution with a mass fraction of 1.5% was evenly sprayed in at a constant flow rate of 5mL / min using a peristaltic pump. After the spraying was completed, the mixture was stirred and mixed for 10min. The mixture was then dried at 100℃ to constant weight. The dried block material was dispersed to obtain modified steel slag powder.

[0043] The preparation method of silanized fibers includes the following steps: After mixing 3g of polypropylene fiber and 2g of wood fiber evenly, the mixture was immersed in a pre-hydrolyzed solution of silane coupling agent, stirred and mixed for 1 hour, filtered, washed twice with anhydrous ethanol, dried at 50°C to constant weight, and then a sodium methylsilicate ethanol dispersion (0.05g sodium methylsilicate and 2mL anhydrous ethanol were stirred and mixed evenly) was added. The mixture was stirred and mixed for 30 minutes to obtain pretreated fiber.

[0044] Preferably, the method for preparing the pre-hydrolyzed solution of the silane coupling agent includes the following steps: A 3% (w / w) aqueous solution of silane coupling agent in ethanol was added to the reactor, the pH was adjusted to 5.5 with 5% (w / w) acetic acid, the temperature was raised to 60℃, and hydrolysis was carried out for 120 min to obtain a pre-hydrolyzed solution of silane coupling agent.

[0045] Example 2 The preparation process of low-temperature calcined gypsum powder in this embodiment includes the following steps: Add 1000g of primary gypsum powder, 150g of composite aggregate, 20g of silanized fiber, 4g of hydroxypropyl methylcellulose ether, and 1.5g of protein retarder to a mixer and mix at 800rpm for 25min to obtain low-temperature calcined gypsum powder.

[0046] The composite aggregate consisted of 100g of closed-cell perlite and 50g of clay ceramsite; the protein-based retarder came from Preparation Example 2.

[0047] Primary gypsum powder is prepared by the following steps: S1: Add 1500g of desulfurized gypsum powder, 45g of modified steel slag powder, 4.5g of sodium tripolyphosphate and 4.5g of ether polycarboxylate superplasticizer into a mixer and mix at 800rpm for 40min to obtain raw material; S2: The raw material is fed into a two-stage series fluidized bed furnace system with an effective volume ratio of 3.5:1. First, in the first-stage fluidized bed furnace, the temperature is raised to 265℃ at a rate of 1℃ / min and calcined for 35 minutes. The crystal water content of the output is monitored and controlled at about 6.0% by an online moisture meter. Then, the material is automatically conveyed to the second-stage fluidized bed furnace, the temperature is adjusted to 250℃, and calcined for 10 minutes. The crystal water content of the output is controlled at about 4.5%. The calcined material is collected by a cyclone separator and immediately enters a forced air cooling system with an air temperature of 25℃, an air speed of 8m / s, and a cooling time of 10 minutes. The material temperature drops to below 50℃. Then, it is placed in a constant temperature and humidity chamber with an ambient temperature of 25℃ and a relative humidity of 75% for 72 hours to obtain primary gypsum powder.

[0048] The preparation method of modified steel slag powder includes the following steps: 45g of steel slag powder was placed in a small mixer, the mixer was turned on, the mixing speed was set to 200rpm, and 112.5g of sodium silicate solution with a mass fraction of 2.5% was evenly sprayed in at a constant flow rate of 5mL / min using a peristaltic pump. After the spraying was completed, the mixture was stirred and mixed for 20min. The mixture was then dried at 100℃ to constant weight. The dried block material was dispersed to obtain modified steel slag powder.

[0049] The preparation method of silanized fibers includes the following steps: After mixing 12g of polypropylene fiber and 8g of wood fiber evenly, the mixture was immersed in a pre-hydrolyzed solution of silane coupling agent and stirred for 2 hours. The mixture was then filtered, washed twice with anhydrous ethanol, dried at 50°C to constant weight, and then a sodium methylsilicate ethanol dispersion (0.54g of sodium methylsilicate and 10mL of anhydrous ethanol were stirred and mixed evenly) was added. The mixture was stirred for 30 minutes to obtain the pretreated fiber.

[0050] Preferably, the method for preparing the pre-hydrolyzed solution of the silane coupling agent includes the following steps: A 5% (w / w) aqueous solution of silane coupling agent in ethanol was added to the reactor, the pH was adjusted to 5 with 5% (w / w) acetic acid, the temperature was raised to 80℃, and hydrolysis was carried out for 180 min to obtain a pre-hydrolyzed solution of silane coupling agent.

[0051] Example 3 The preparation process of low-temperature calcined gypsum powder in this embodiment includes the following steps: Add 1000g of primary gypsum powder, 100g of composite aggregate, 12g of silanized fiber, 3g of hydroxypropyl methylcellulose ether, and 1g of protein retarder to a mixer and mix at 800rpm for 20min to obtain low-temperature calcined gypsum powder.

[0052] The composite aggregate consisted of 70g of closed-cell perlite and 30g of clay ceramsite; the protein-based retarder came from Preparation Example 3.

[0053] Primary gypsum powder is prepared by the following steps: S1: Add 1500g of desulfurized gypsum powder, 25g of modified steel slag powder, 3g of sodium tripolyphosphate and 3g of ether polycarboxylate superplasticizer into a mixer and mix at 800rpm for 40min to obtain raw material; S2: The raw material is fed into a two-stage series fluidized bed furnace system with an effective volume ratio of 3.5:1. First, in the first-stage fluidized bed furnace, the temperature is raised to 260℃ at a rate of 1℃ / min and calcined for 30 minutes. The crystal water content of the output is monitored and controlled at about 6.3% by an online moisture meter. Then, the material is automatically conveyed to the second-stage fluidized bed furnace, the temperature is adjusted to 245℃, and calcined for 9 minutes. The crystal water content of the output is controlled at about 5.0%. The calcined material is collected by a cyclone separator and immediately enters a forced air cooling system with an air temperature of 25℃, an air speed of 8m / s, and a cooling time of 10 minutes. The material temperature drops to below 50℃. Then, it is placed in a constant temperature and humidity chamber with an ambient temperature of 25℃ and a relative humidity of 75% for 60 hours to obtain primary gypsum powder.

[0054] The preparation method of modified steel slag powder includes the following steps: 25g of steel slag powder was placed in a small mixer, and the mixer was turned on. The mixing speed was set to 200rpm. A peristaltic pump was used to uniformly spray 50g of a mixed solution of sodium silicate and aluminum sulfate at a constant flow rate of 5mL / min. The mass fraction of sodium silicate in the mixed solution was 2%, and the mass fraction of aluminum sulfate was 2%. After the spraying was completed, the mixture was stirred for 15min. The mixture was dried at 100℃ to constant weight. The dried block material was dispersed to obtain modified steel slag powder.

[0055] The preparation method of silanized fibers includes the following steps: After mixing 6g of polypropylene fiber and 6g of wood fiber evenly, the mixture was immersed in a pre-hydrolyzed solution of silane coupling agent and stirred for 1.5h. After filtration, the mixture was washed twice with anhydrous ethanol and dried at 50℃ to constant weight. A sodium methylsilicate ethanol dispersion (0.24g sodium methylsilicate and 6mL anhydrous ethanol were stirred and mixed evenly) was added and stirred for 30min to obtain pretreated fiber.

[0056] Preferably, the method for preparing the pre-hydrolyzed solution of the silane coupling agent includes the following steps: A 4% (w / w) aqueous solution of silane coupling agent in ethanol was added to the reactor, the pH was adjusted to 5 with 5% (w / w) acetic acid, the temperature was raised to 70°C, and hydrolysis was carried out for 150 min to obtain a pre-hydrolyzed solution of silane coupling agent.

[0057] Example 4 The difference between this embodiment and embodiment 3 is as follows: Primary gypsum powder is prepared by the following steps: S1: Add 1500g of desulfurized gypsum powder, 25g of modified steel slag powder, 3g of sodium tripolyphosphate, 3g of ether polycarboxylate superplasticizer, 0.5g of citric acid and 0.4g of aluminum sulfate into a mixer and mix at 800rpm for 40min to obtain raw material; Everything else is the same as in Example 3.

[0058] Example 5 The difference between this embodiment and embodiment 4 is that: Primary gypsum powder is prepared by the following steps: S1: Add 1500g of desulfurized gypsum powder, 25g of modified steel slag powder, 3g of sodium tripolyphosphate, 3g of ether polycarboxylate superplasticizer, 0.6g of citric acid and 0.6g of aluminum sulfate into a mixer and mix at 800rpm for 40min to obtain raw material; The preparation method of modified steel slag powder includes the following steps: 25g of steel slag powder was placed in a small mixer, and the mixer was turned on. The mixing speed was set to 200rpm. A peristaltic pump was used to uniformly spray 50g of a mixed solution of sodium silicate and aluminum sulfate at a constant flow rate of 5mL / min. The mass fraction of sodium silicate in the mixed solution was 2%, and the mass fraction of aluminum sulfate was 4%. After the spraying was completed, the mixture was stirred for 15min. The mixture was then dried at 100℃ to constant weight. The dried block material was dispersed to obtain modified steel slag powder.

[0059] The rest is the same as in Example 4.

[0060] Example 6 The difference between this embodiment and embodiment 5 is as follows: Before use, the composite aggregate undergoes a slurry coating pretreatment: Add 70g of closed-cell perlite, 30g of clay ceramsite, 5g of silicate cement, 1g of silica fume and 20g of deionized water to a mixer and mix at 200rpm for 20min. Dry at 100℃ to constant weight. The dried block material is then dispersed and set aside for later use.

[0061] The rest is the same as in Example 5.

[0062] Example 7 The difference between this embodiment and embodiment 6 is that: Before use, the composite aggregate undergoes a slurry coating pretreatment: Add 70g of closed-cell perlite, 30g of clay ceramsite, 10g of silicate cement, 3g of silica fume and 30g of deionized water to a mixer and mix at 200rpm for 20min. Dry at 100℃ to constant weight. The dried block material is then dispersed and set aside for later use.

[0063] The rest is the same as in Example 6.

[0064] Comparative Example 1 The difference between this comparative example and Example 3 is as follows: Primary gypsum powder is prepared by the following steps: S1: Add 1500g of desulfurized gypsum powder, 25g of modified steel slag powder, 3g of sodium tripolyphosphate and 3g of ether polycarboxylate superplasticizer into a mixer and mix at 800rpm for 40min to obtain raw material; S2: The raw material is calcined in a single fluidized bed furnace at 260℃ for 39 minutes, and the crystal water content of the output is controlled at about 5.0%. The calcined material is collected by a cyclone separator and immediately enters a forced air cooling system at 25℃ and 8m / s for 10 minutes. The material temperature drops to below 50℃, and then it is placed in a constant temperature and humidity chamber at 25℃ and 75% relative humidity for 60 hours to obtain primary gypsum powder.

[0065] The rest is the same as in Example 3.

[0066] Comparative Example 2 The difference between this comparative example and Example 3 is as follows: In the preparation of primary gypsum powder, steel slag powder of equal mass is used to replace modified steel slag powder.

[0067] Everything else is the same as in Example 3.

[0068] Comparative Example 3 The difference between this comparative example and Example 3 is that: Sodium tripolyphosphate and ether-based polycarboxylate superplasticizers were not added during the preparation of primary gypsum powder.

[0069] Everything else is the same as in Example 3.

[0070] Comparative Example 4 The difference between this comparative example and Example 3 is that: The preparation process of the low-temperature calcined gypsum powder in this comparative example includes the following steps: Add 1000g of primary gypsum powder, 100g of closed-cell perlite, 12g of silanized fiber, 3g of hydroxypropyl methylcellulose ether, and 1g of protein retarder to a mixer and mix at 800rpm for 20min to obtain low-temperature calcined gypsum powder.

[0071] Everything else is the same as in Example 3.

[0072] Comparative Example 5 The difference between this comparative example and Example 3 is as follows: The preparation method of the protein-based retarder in this comparative example includes the following steps: Mix 5g of gelatin and 1g of sodium alginate evenly, add to 60mL of deionized water, stir and mix for 20min, transfer to a spray dryer, atomize and dry under nitrogen atmosphere, set the inlet temperature to 120℃ and the outlet temperature to 60℃, dry at 50℃ for 2h to obtain a powdered product, pass through a 100-mesh standard sieve to obtain a protein retarder.

[0073] Everything else is the same as in Example 3.

[0074] Performance testing The low-temperature calcined gypsum powders obtained in Examples 1-7 and Comparative Examples 1-5 were mixed with water according to the standard consistency to prepare slurries. Then, following standard construction methods, the slurries were applied to standard wooden frames, leveled, and the top edges were flush. The frames were then placed in an environment of 20℃±2℃ and 60±5% relative humidity for 30 minutes to allow the slurries to initially harden and solidify. Specific tests are as follows: (1) To quickly assess the early strength of gypsum powder, the following custom test was used: After molding for 30 minutes, the mold was removed and the specimen was immediately placed in a forced-air drying oven at 40℃±2℃ for 2 hours. The compressive strength and flexural strength were tested after 2 hours. After drying to constant weight at 40℃±2℃, the oven-dry compressive strength and oven-dry flexural strength were tested. The specific test results are shown in Table 1. (2) Based on GB / T17669.4-1999, pour the mixed slurry into the metal round mold, gently shake to remove air bubbles, scrape the surface with a scraper, and test with a Vicat apparatus. Test once every 5 minutes, and after 3 consecutive tests, test once every 1 minute until initial setting. The specific test results are shown in Table 1. (3) Take the completely dry specimen, gently polish the surface of the specimen with 120-mesh sandpaper to remove loose floating powder, then clean the surface of the specimen with a brush, put it in a desiccator at 25℃ to cool to room temperature, weigh the pretreated specimen with an electronic balance and record it as m1 (accurate to 0.001g), put the specimen into a negative pressure sieve analyzer equipped with a 200-mesh standard sieve, adjust and maintain the negative pressure at 4000Pa, and continue sieving for 3min. After sieving, take out the specimen, put it in a desiccator at 25℃ to cool to room temperature again, weigh the specimen and record it as m2 (accurate to 0.001g), calculate the powder loss rate, and see Table 1 for specific test results.

[0075] Powder shedding rate (%) = 100% × (m1 - m2) / m1 Table 1. Performance test results of the low-temperature calcined gypsum powders prepared in Examples 1-7 and Comparative Examples 1-5

[0076] As can be seen from Table 1, in Examples 1-3 and Comparative Examples 1-5, Comparative Example 1 adopted a single-stage calcination process, which resulted in a short initial setting time and low strength. The excessively short initial setting time indicates that the hydration reaction rate is abnormally accelerated, suggesting that the internal phase composition of the primary gypsum powder is complex and unstable, which may be due to excessive dehydration of hemihydrate gypsum or uneven distribution of crystal water during the calcination process.

[0077] The performance decline in Comparative Examples 2 and 3 indicates that the unmodified steel slag cannot effectively homogenize heat transfer. The lack of sodium tripolyphosphate and ether-based polycarboxylate superplasticizers led to the agglomeration of some gypsum particles, which easily formed calcination dead zones, resulting in decreased strength and loose structure.

[0078] The oven-dry compressive strength of Comparative Example 4, which uses only closed-cell perlite, is much lower than that of Example 3, which uses composite aggregate, and it also exhibits a relatively high dust loss rate. This indicates that without the rigid support provided by clay ceramsite, the surface wear resistance and anti-dustling ability of the material will also decrease significantly.

[0079] Comparative Example 5, using a simple compound of gelatin and sodium alginate, showed a significantly prolonged initial setting time, and its strength at each stage was lower than that of Example 3, with a higher powdering rate. This indicates that the unmodified gelatin has an excessively strong inhibitory effect on gypsum hydration. Although it can delay setting, it severely interferes with the normal formation of hydration products and intercrystalline bonding, resulting in a loose structure and slow strength development.

[0080] In Examples 4-7, the introduction of citric acid and aluminum sulfate further optimized the matrix structure, resulting in a steady increase in strength; while the final aggregate slurry coating treatment improved the compatibility between the aggregate and the matrix, ultimately reducing the problem of powder shedding while ensuring workability and strength.

[0081] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for preparing low-temperature calcined gypsum powder, characterized in that, Includes the following steps: Mix 100 parts by weight of primary gypsum powder, 5-15 parts by weight of composite aggregate, 0.5-2.0 parts by weight of silanized fiber, 0.2-0.4 parts by weight of hydroxypropyl methylcellulose ether, and 0.05-0.15 parts by weight of protein retarder evenly to obtain low-temperature calcined gypsum powder. The primary gypsum powder is prepared by the following steps: S1: After mixing the raw material gypsum powder, modified steel slag powder, sodium tripolyphosphate and polycarboxylate superplasticizer evenly, raw meal is obtained; S2: The raw material is first calcined at 255~265℃ for 25~35min, then calcined at 240~250℃ for 7~10min, cooled, and aged to obtain primary gypsum powder; The modified steel slag powder is specifically prepared by wet modification of steel slag powder with sodium silicate solution or a mixed solution of sodium silicate and aluminum sulfate; the composite aggregate includes closed-cell perlite and ceramsite.

2. The preparation process of low-temperature calcined gypsum powder according to claim 1, characterized in that, The mass ratio of the raw material gypsum powder, modified steel slag powder, sodium tripolyphosphate and polycarboxylate superplasticizer is 100:(1~3):(0.1~0.3):(0.1~0.3).

3. The preparation process of low-temperature calcined gypsum powder according to claim 1, characterized in that, In step S2, the calcination is carried out in a two-stage fluidized bed furnace system; the crystal water content of the output from the first-stage fluidized bed furnace is controlled to be 6%~7%, and the crystal water content of the output from the second-stage fluidized bed furnace is controlled to be 4.5%~5.5%.

4. The preparation process of low-temperature calcined gypsum powder according to claim 1, characterized in that, The method for preparing the modified steel slag powder includes the following steps: Steel slag powder with a mass ratio of 1:(1.5~2.5) is mixed evenly with a modifier, dried, and dispersed to obtain modified steel slag powder; the modifier is sodium silicate solution or a mixed solution of sodium silicate and aluminum sulfate.

5. The preparation process of low-temperature calcined gypsum powder according to claim 1, characterized in that, The composite aggregate undergoes a slurry coating pretreatment before use: Mix the composite aggregate with silicate cement, silica fume and water in a mass ratio of 100:(5~10):(1~3):(20~30) until uniform, and dry for later use.

6. The preparation process of low-temperature calcined gypsum powder according to claim 1, characterized in that, The silanized fibers include polypropylene fibers and wood fibers.

7. The preparation process of low-temperature calcined gypsum powder according to claim 6, characterized in that, The method for preparing the silanized fiber includes the following steps: After the polypropylene fiber and wood fiber are mixed evenly, they are immersed in the pre-hydrolysis solution of silane coupling agent and mixed for 1-2 hours. After solid-liquid separation, washing and drying, sodium methylsilicate of 1%-3% of the total mass of polypropylene fiber and wood fiber is added and mixed evenly to obtain pretreated fiber.

8. The preparation process of low-temperature calcined gypsum powder according to claim 7, characterized in that, The method for preparing the pre-hydrolyzed solution of the silane coupling agent includes the following steps: Add a 3%~5% (w / w) aqueous solution of silane coupling agent in ethanol to the reactor, adjust the pH to 5~5.5, raise the temperature to 60~80℃, and hydrolyze for 120~180 min to obtain a pre-hydrolyzed solution of silane coupling agent.

9. The preparation process of low-temperature calcined gypsum powder according to claim 1, characterized in that, The protein-based retarder is composed of anhydride-modified gelatin and sodium alginate.

10. The preparation process of low-temperature calcined gypsum powder according to claim 9, characterized in that, The preparation method of the protein-based retarder includes the following steps: S11: Disperse gelatin evenly in deionized water, adjust the pH to 7.5~8.0, add succinic anhydride at 6%~8% of the gelatin mass, heat to 50~60℃, mix for 120~180min, cool, add anhydrous ethanol to precipitate, separate solid and liquid, wash, dry, and obtain anhydride modified gelatin. S12: Mix anhydride-modified gelatin and sodium alginate at a mass ratio of (3~5):1, disperse in deionized water, and spray dry to obtain a protein retarder.

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