Preparation method of a coagulant for castable, coagulant prepared by the method and application of the coagulant

Abstract

The application belongs to the technical field of new building materials, and particularly relates to a preparation method of a setting accelerator for castable. The steps of the preparation method are as follows: (1) adding cement and melamine into water, stirring and reacting to obtain a mixed slurry; (2) performing low-speed centrifugation on the mixed slurry, and collecting the upper suspension after the low-speed centrifugation is completed; (3) performing centrifugation on the suspension to collect solid precipitate; performing freezing and drying on the solid precipitate under vacuum conditions in sequence to obtain a powder; and performing powder grinding on the powder after the powder is uniformly mixed with a grinding aid to obtain the setting accelerator for castable. The setting accelerator prepared by the application can not only shorten the setting time of calcium aluminate cement combined castable, but also improve the demolding strength and dry strength of the cement combined castable, greatly improves the production efficiency and economic benefits of the cement combined castable prefabricated part, and has great commercial application value.

Description

Technical Field

[0001] This invention relates to the field of new building materials technology, specifically to a method for preparing a setting accelerator for castables, the prepared setting accelerator, and its application. Background Technology

[0002] Calcium aluminate cement (CAC), a commonly used binder in castables, is favored for its rapid setting and hardening speed, excellent corrosion resistance, and high wear resistance. In the construction of castables, the curing process after casting is crucial. The curing process involves storing the castable at a specific temperature for a period of time to promote the hydration reaction of the CAC binder, thereby providing the necessary early strength. This step is particularly critical for ensuring the integrity of the demolding strength of the castable upon demolding. To improve production efficiency and economic benefits, especially in the production of large CAC-bonded castable precast components, shortening the demolding time is essential. Therefore, accelerators can be added to accelerate the cement hydration process, effectively improving the demolding strength and the strength after drying. This method has significant application value in actual production.

[0003] The hydration process of calcium aluminate cement (CAC) is a chemical reaction in which it reacts with water to produce hydration products. This process mainly consists of three stages: dissolution, nucleation, and precipitation. When CAC is mixed with water, Ca2+ rapidly dissolves. 2+ and [Al(OH)4] - , forming Ca 2+ and [Al(OH)4] - The aqueous solution quickly becomes saturated, and the hydration products then form crystal nuclei and grow. When the crystal nuclei grow to a certain critical size, the hydration products begin to crystallize out of the solution. In these three stages, dissolution and nucleation are the key steps, determining the rate of the hydration reaction and the formation of the final products. To accelerate this process, setting accelerators are commonly added. Setting accelerators promote the dissolution and nucleation of CAC by altering the ion concentration in the solution, thereby accelerating the hydration reaction. These setting accelerators are typically substances that can react with the ions in CAC; they lower the energy barrier during dissolution, accelerate crystal nucleus formation, and ultimately achieve the effect of accelerated setting. In this way, the early strength of the castable can be significantly improved, the construction cycle shortened, and production efficiency increased.

[0004] For example, studies have shown that lithium salts such as LiOH, Li₂CO₃, and LiCl can strongly accelerate the hydration process of CAC because Li + [Al(OH)4] dissolved from CAC -The insoluble hydroxide LiAl(OH)4 is formed, making [Al(OH)4] present in the system. - The concentration decreases, thus promoting further dissolution of CAC and accelerating its hydration process. However, the amount of this accelerator added is difficult to control during construction. When its content is high, it may cause "flash setting" of the castable, which is not conducive to the construction of the castable. Moreover, because the solubility of this accelerator is greatly affected by temperature during the dissolution process, the accelerating effect at low contents is not obvious at lower temperatures.

[0005] Therefore, it is of great significance to find a hydration promoter that has a good hydration effect and does not reduce the effectiveness of CAC. Summary of the Invention

[0006] In view of the problems and shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing a setting accelerator for castables, as well as the prepared setting accelerator and its application.

[0007] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0008] The first aspect of this invention provides a method for preparing a setting accelerator for castables, comprising the following steps:

[0009] (1) Add cement and melamine to water, stir and react to obtain a mixed slurry;

[0010] (2) Centrifuge the mixed slurry prepared in step (1) at low speed, and collect the upper suspension after the low speed centrifugation is completed;

[0011] (3) Centrifuge the suspension obtained in step (2) and collect the solid precipitate; freeze and dry the solid precipitate under vacuum conditions to obtain powder; mix the powder with the grinding aid and grind it to obtain a coagulant for casting refractory.

[0012] The castable is a castable prepared using cement as a binder.

[0013] According to the above preparation method, preferably, in step (1), the temperature of the stirring reaction is 5-60°C and the time is 2-48 hours. More preferably, the temperature of the stirring reaction is 10-60°C and the time is 3-48 hours. Most preferably, the temperature of the stirring reaction is 25°C and the time is 24 hours.

[0014] According to the above preparation method, preferably, in step (1), the mass ratio of cement to melamine is (20-80):1; the mass ratio of cement to water is 1:(4-8). More preferably, the mass ratio of cement to melamine is (25-75):1. Most preferably, the mass ratio of melamine to cement is 50:1; the mass ratio of cement to water is 1:5.

[0015] According to the above preparation method, preferably, in step (2), the conditions for low-speed centrifugation are: centrifugation speed of 500-2000 r / min and centrifugation time of 1-6 min; more preferably, in step (2), the conditions for low-speed centrifugation are: centrifugation speed of 1500 r / min and centrifugation time of 3 min.

[0016] According to the above preparation method, preferably, in step (3), the centrifugation conditions are: centrifugation speed of 10000-20000 r / min and centrifugation time of 10-30 min; more preferably, the centrifugation conditions are: centrifugation speed of 10000-15000 r / min and centrifugation time of 10-30 min; most preferably, in step (3), the centrifugation conditions are: centrifugation speed of 12000 r / min and centrifugation time of 20 min.

[0017] According to the above preparation method, preferably, in step (3), the freezing temperature is -20℃ to -40℃ and the freezing time is 30 to 120 min; more preferably, the freezing temperature is -30℃ and the freezing time is 60 min.

[0018] According to the above preparation method, preferably, the drying temperature is 40℃~100℃ and the drying time is 6~12h; more preferably, the drying temperature is 50℃ and the drying time is 10h.

[0019] According to the above preparation method, preferably, in step (3), the particle size of the coagulant used in the castable after grinding is 0.95 to 9.56 μm.

[0020] According to the above preparation method, preferably, in step (3), the grinding aid is any one of polymeric polyol, polymeric alkanolamine, triethanolamine, ethylene glycol, propylene glycol, and glycerol; more preferably, the grinding aid is polymeric polyol; most preferably, the grinding aid is polymeric polyol HE-a (purchased from Luoyang Hongen New Building Materials Co., Ltd., product model HE-a), which has good grinding aid effect and early strength increase effect.

[0021] According to the above preparation method, preferably, the mass ratio of the grinding aid to the powder is (0-1):200. More preferably, the mass ratio of the grinding aid to the powder is 0.25:200.

[0022] According to the above preparation method, preferably, the grinding method in step (3) is ball milling, the ball milling time is 0.5 to 6 hours, the ball milling speed is 50 to 400 r / min, and the ball-to-material ratio during the ball milling process is 1 to 4:1.

[0023] According to the above preparation method, preferably, in step (3), the vacuum degree of the vacuum condition is 10 to 30 Pa; more preferably, the vacuum degree is 10 Pa.

[0024] According to the above preparation method, preferably, the cement is aluminate cement; more preferably, the cement is calcium aluminate cement; even more preferably, the alumina content in the cement is 50% to 80%; most preferably, the cement is at least one of CA50, CA60, CA70, and CA80 (as specified in national standard GB / T201-2015).

[0025] According to the above preparation method, preferably, in step (1), the stirring speed is 500-2000 r / min; more preferably, the stirring speed is 1000 r / min.

[0026] According to the above preparation method, preferably, in step (1), the reaction vessel needs to be sealed during the stirring reaction. The purpose of sealing is to prevent CO2 in the air from dissolving in the water and reacting with cement particles to form a carbohydrate product 3CaO·Al2O3·CaCO3·11H2O, which is not conducive to the formation of AH3 gel.

[0027] A second aspect of the present invention provides a coagulant product prepared using the preparation method described in the first aspect above.

[0028] The third aspect of the present invention provides the application of the accelerator product described in the second aspect above in cement-bound castables.

[0029] A fourth aspect of the present invention provides a cement-bonded castable containing the accelerator product described in the second aspect above.

[0030] The setting accelerator mechanism of the cement-bonded castable accelerator prepared in this invention is as follows:

[0031] When calcium aluminate cement is mixed with the dispersant melamine and water, and stirred at a certain temperature for a period of time, the calcium aluminate cement will hydrate to produce different hydration products, such as CAH. 10The hydration products were C2AH8(2CaO·Al2O3·10H2O), C3AH6(3CaO·Al2O3·6H2O), and AH3(Al2O3·3H2O). Due to the presence of melamine as a dispersant, the AH3 crystal nuclei, a hydration product, were uniformly dispersed in the mixed slurry in the form of a gel. After stirring, the mixture was first centrifuged at a low speed to separate the AH3 gel from the cement particles and other hydration products in the slurry, resulting in a suspension containing the AH3 gel. Then, the suspension was centrifuged at a higher speed to precipitate the AH3 gel, which was then collected. The collected AH3 is vacuum freeze-dried and ground to obtain AH3 nuclei solids with smaller particle size (i.e., accelerator). During the hydration process of cement in castables, the introduced AH3 nuclei solids with smaller particle size can serve as nuclei during the nucleation period of hydration products, promoting the rapid nucleation of hydration products and their precipitation. Moreover, since the core component of the accelerator of this invention, AH3, is a common product of the hydration reaction of CAC at different temperatures and has a higher specific surface area, this product can more effectively promote the setting of castables and improve their strength.

[0032] Compared with the prior art, the positive and beneficial effects achieved by the present invention are as follows:

[0033] (1) The accelerator of the present invention can effectively promote the solidification of calcium aluminate cement-bonded castables. Compared with cement-bonded castables without accelerator, the initial setting time of cement-bonded castables after adding the accelerator of the present invention is shortened from 7h-8h to 2-3h, and the final setting time is shortened from about 19h to about 5h. At the same time, the accelerator of the present invention can effectively improve the demolding strength and drying strength of cement-bonded castables. Compared with cement-bonded castables without accelerator, after adding the accelerator of the present invention, the flexural strength and compressive strength of cement-bonded castables after demolding after 24h curing are increased by 62.5% and 84.6%, respectively. Moreover, the flexural strength and compressive strength of cement-bonded castables after curing and drying are increased by 50.5% and 35.8%, respectively. Therefore, the accelerator prepared by this invention can not only shorten the setting time of calcium aluminate cement-bonded castables, but also improve the demolding strength and drying strength of cement-bonded castables, which greatly improves the production efficiency and economic benefits of cement-bonded castable precast parts and has great commercial application value.

[0034] (2) The coagulant prepared by the present invention has small particle size, good stability, and can significantly improve the demolding strength of calcium aluminate cement-bonded castables and shorten the curing time of calcium aluminate cement-bonded castables, and has a good application prospect.

[0035] (3) The coagulant prepared by the present invention has readily available raw materials, low cost, and convenient construction, which is conducive to large-scale production and promotion. Attached Figure Description

[0036] Figure 1 for Figure 1 The image shows the particle size distribution of the accelerator for castables prepared in Example 1-1 of this invention. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0038] The following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, components, and / or combinations thereof. Experimental methods in the following embodiments that do not specify specific conditions employ conventional techniques in the art or follow the conditions recommended by the manufacturer; reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0039] Example 1: Discussion on the temperature of the stirred reaction

[0040] To investigate the effect of stirring reaction temperature on the performance of the coagulant during its preparation, experiments were conducted in Examples 1-1 to 1-4. The specific details of Examples 1-1 to 1-4 are as follows:

[0041] Example 1-1:

[0042] A method for preparing a setting accelerator for castables, wherein the castable is a castable prepared using cement as a binder, and the specific steps are as follows:

[0043] (1) Cement, melamine and water are added to a reaction vessel and the mixture is sealed and stirred for 24 hours at a reaction temperature of 25°C to obtain a mixed slurry. The mass ratio of cement to melamine is 50:1, the mass ratio of cement to water is 1:5, the stirring speed is 1000r / min, and the calcium aluminate cement is Secar71 calcium aluminate cement.

[0044] (2) The mixed slurry prepared in step (1) is centrifuged at low speed, and the upper suspension is collected after the low speed centrifugation is completed; wherein, the centrifugation speed of the low speed centrifugation is 1500 r / min and the centrifugation time is 3 min.

[0045] (3) The suspension obtained in step (2) is centrifuged at 12000 r / min for 20 min and the lower solid precipitate is collected. The solid precipitate is frozen and dried under vacuum to obtain powder. The powder is mixed with grinding aid and then ball-milled to obtain a coagulant for casting. The freezing temperature is -30℃ and the freezing time is 60 min. The drying temperature is 50℃ and the drying time is 10 h. The grinding aid is a polymeric polyol HE-a (purchased from Luoyang Hongen New Building Materials Co., Ltd., product model HE-a). The mass ratio of grinding aid to powder is 0.25:200. The ball milling time is 2 h and the ball milling speed is 100 r / min. The ball-to-powder ratio during the ball milling process is 2:1.

[0046] The particle size of the accelerator for the castable prepared in Example 1-1 was tested, and the test results are as follows: Figure 1 As shown.

[0047] Depend on Figure 1 It can be seen that the accelerator prepared in Example 1-1 of the present invention has a D10 particle size of 0.95μm, a D50 particle size of 3.78μm, and a D90 particle size of 9.56μm. The particle size is small and has reached the target level, so it can be used in cement-bonded castables.

[0048] The contents of Examples 1-2 to 1-4 are basically the same as those of Example 1-1, except that the reaction temperature of the stirring reaction in step (1) is different; the stirring reaction temperatures in step (1) of Examples 1-2 to 1-4 are 10℃, 40℃ and 60℃ respectively.

[0049] To test the setting-accelerating effect of the accelerators prepared in Examples 1-1 to 1-4 on castables, the accelerators prepared in Examples 1-1 to 1-4 were added to the castables respectively, resulting in five castables, named castables S1, S2, S3, and S4; a castable without added accelerator was also prepared and named S0. The five castables prepared above were poured into 40mm×40mm×160mm molds and placed on a GZ-85 type vibrating table for vibration molding. The samples were then placed in a constant temperature and humidity curing chamber at 25℃ for 24 hours, and their initial setting time and final setting time were measured according to standard GB / T1346-2011.

[0050] The raw materials for the castable are: aggregate (tabular corundum with different particle size distributions, 0-0.5mm, 0.5-1mm, 1-3mm, 3-6mm, Al2O3≥99%, Shandong Hengjia Co., Ltd.), tabular corundum fine powder (≤0.045mm, Shandong Hengjia Co., Ltd.), α-Al2O3 micro powder (CL370, Anmai Aluminum (Qingdao) Co., Ltd.), calcium aluminate cement Secar71 (Tianjin Kainuos), and water-reducing agents (ADW1 and ADS3, Anmai Aluminum (Qingdao) Co., Ltd.). The formulation of the cement-bonded castable is shown in Table 1.

[0051] The preparation method of the castable is as follows: weigh each raw material according to the raw material composition in the castable formula, add the raw materials except water to the mortar mixer and dry mix for 60 seconds, then add water and mix for 180 seconds to obtain the castable.

[0052] Table 1 Formulations of castable samples S0 to S4

[0053]

[0054] The initial setting time and final setting time test results of castable samples S0, S1, S2, S3 and S4 are shown in Table 2.

[0055] Table 2 Test results of castable samples S0 to S4

[0056] S0 / 7.1 19.0 S1 25 2.3 5.1 S2 10 3.4 6.1 S3 40 4.3 9.0 S4 60 6.5 14.7

[0057] As shown in Table 2, compared with cement-bonded castables without accelerators, the initial and final setting times of the castables were significantly shortened after adding 1% of the accelerators prepared in Examples 1-1 to 1-4 of this invention. Furthermore, the initial and final setting times of the castables first decreased and then increased with increasing stirring temperature during the reaction. The shortest initial and final setting times were reached at a stirring temperature of 25°C, at 2.3 h and 5.1 h, respectively. This is because the degree of cement hydration and the size and crystallinity of the AH3 crystal nuclei differed under different stirring temperatures during the preparation of the accelerator. At stirring temperatures of 10°C and 25°C, due to the lower reaction temperature, the AH3 generated by cement hydration was an amorphous gel, resulting in smaller particle size and a larger specific surface area. When introduced into the castable, it effectively provided crystal nuclei for CAC hydration during cement hydration, thus promoting cement hydration and shortening the setting time of the castable. However, at lower mixing temperatures (10℃), the degree of cement hydration is lower, resulting in lower production efficiency, increased costs, and hindering the promotion of accelerators. At higher mixing temperatures (40℃, 60℃), although the degree of cement hydration is higher, the resulting AH3 crystals are already well-developed and larger in size. Compared to the smaller amorphous AH3, the larger AH3 crystals have a lower effect on promoting cement hydration. Therefore, accelerators produced at higher temperatures have a less effective setting effect than those produced at lower mixing temperatures.

[0058] The above results show that the accelerator prepared by this invention can effectively promote the solidification of cement-bonded castables, shorten the solidification time of cement castables, and greatly improve the production efficiency of cement-bonded castable precast components. Furthermore, the preferred temperature during stirring is 10–60°C, and most preferably 25°C.

[0059] Example 2: An Experiment Exploring the Effect of Stirring Reaction Time

[0060] To investigate the effect of stirring reaction time on the performance of the coagulant during its preparation, experiments were conducted in Examples 2-1 to 2-3. The specific details of Examples 2-1 to 2-3 are as follows:

[0061] Example 2-1:

[0062] A method for preparing a setting accelerator for castables, wherein the castable is a castable prepared using cement as a binder, and the specific steps are as follows:

[0063] (1) Add cement, melamine and water into a reaction vessel, and under the condition of reaction temperature of 25℃, seal and stir for 3h to obtain a mixed slurry; wherein, the mass ratio of cement to melamine is 50:1, the mass ratio of cement to water is 1:5, the stirring speed of the stirring reaction is 1000r / min, and the calcium aluminate cement is calcium aluminate cement Secar71.

[0064] (2) The mixed slurry prepared in step (1) is centrifuged at low speed, and the upper suspension is collected after the low speed centrifugation is completed; wherein, the centrifugation speed of the low speed centrifugation is 1500 r / min and the centrifugation time is 3 min.

[0065] (3) The suspension obtained in step (2) is centrifuged at 12000 r / min for 20 min and the lower solid precipitate is collected. The solid precipitate is frozen and dried under vacuum to obtain powder. The powder is mixed with grinding aid and then ball-milled to obtain a coagulant for casting. The freezing temperature is -30℃ and the freezing time is 60 min. The drying temperature is 50℃ and the drying time is 10 h. The grinding aid is a polymeric polyol HE-a (purchased from Luoyang Hongen New Building Materials Co., Ltd., product model HE-a). The mass ratio of grinding aid to powder is 0.25:200. The ball milling time is 2 h and the ball milling speed is 100 r / min. The ball-to-powder ratio during the ball milling process is 2:1.

[0066] The contents of Examples 2-2 to 2-3 are basically the same as those of Example 2-1, except that the stirring reaction time in step (1) is 12h and 48h respectively.

[0067] To test the setting-accelerating effect of the accelerators prepared in Examples 2-1 to 2-3 on castables, the accelerators prepared in Examples 2-1 to 2-3 were added to the castables respectively, resulting in three types of cement castables, named castables S5, S6, and S7. The three types of castables prepared above were poured into 40mm×40mm×160mm molds and placed on a GZ-85 vibrating table for vibration molding. The samples were then placed in a constant temperature and humidity curing chamber at 25℃ for 24 hours. The initial setting time and final setting time were measured according to standard GB / T1346-2011.

[0068] The raw materials of the castable are the same as those in Example 1, the formula of the castable is shown in Table 3, and the preparation method of the castable is the same as that in Example 1.

[0069] Table 3 Formulations of castable samples S5-S7

[0070]

[0071] The initial setting time and final setting time test results of castable samples S0, S5, S6 and S7 are shown in Table 4.

[0072] Table 4. Test results of castable samples S5-S7

[0073]

[0074]

[0075] As shown in Table 4, compared with cement-bonded castables without accelerators, the initial and final setting times of the castables were significantly shortened after adding 1% of the accelerators prepared in Examples 2-1 to 2-3 of this invention. Furthermore, with increasing mixing time, both the initial and final setting times of the castables first decreased and then increased, reaching their shortest values ​​of 2.3 hours and 5.1 hours when the mixing time was 24 hours. This is because, during the preparation of the accelerator, a longer mixing time (48 hours) resulted in a longer cement hydration reaction time, leading to larger AH3 particles. Therefore, the larger AH3 particles had a lower effect on promoting cement hydration after being introduced into the castable. Conversely, shorter mixing times (3 hours and 12 hours) resulted in a shorter cement hydration reaction time and a lower degree of cement hydration, leading to fewer AH3 particles. Consequently, the production efficiency of the accelerator product was lower, increasing costs and hindering its widespread adoption. When the stirring reaction time is 24 hours, the generated AH3 crystal nuclei are smaller in size. When introduced into the castable, they more effectively provide crystal nuclei for CAC hydration, thus promoting cement hydration and shortening the setting time of the castable. Furthermore, this stirring time allows for greater cement hydration, resulting in a higher amount of AH3 hydration product and higher production efficiency of the accelerator. These results demonstrate that the accelerator prepared in this invention can effectively promote the setting of cement-bonded castables, shorten their setting time, and significantly improve the production efficiency of cement-bonded castable precast components. Moreover, the stirring time is preferably 3–48 hours, with 24 hours being the most preferred.

[0076] Example 3: Discussion on the centrifugation speed of mixed slurry

[0077] To investigate the effect of centrifugation speed of the mixed slurry on the performance of the coagulant during its preparation, experiments were conducted in Examples 3-1 to 3-3. The specific details of Examples 3-1 to 3-3 are as follows:

[0078] Example 3-1:

[0079] A method for preparing a setting accelerator for castables, wherein the castable is a castable prepared using cement as a binder, and the specific steps are as follows:

[0080] (1) Cement, melamine and water are added to a reaction vessel and the mixture is sealed and stirred for 24 hours at a reaction temperature of 25°C to obtain a mixed slurry. The mass ratio of cement to melamine is 50:1, the mass ratio of cement to water is 1:5, the stirring speed is 1000r / min, and the calcium aluminate cement is Secar71 calcium aluminate cement.

[0081] (2) The mixed slurry prepared in step (1) is centrifuged at low speed, and the upper suspension is collected after the low speed centrifugation is completed; wherein, the centrifugation speed is 500 r / min and the centrifugation time is 3 min.

[0082] (3) The suspension obtained in step (2) is centrifuged at 12000 r / min for 20 min and the lower solid precipitate is collected. The solid precipitate is frozen and dried under vacuum to obtain powder. The powder is mixed with grinding aid and then ball-milled to obtain a coagulant for casting. The freezing temperature is -30℃ and the freezing time is 60 min. The drying temperature is 50℃ and the drying time is 10 h. The grinding aid is a polymeric polyol HE-a (purchased from Luoyang Hongen New Building Materials Co., Ltd., product model HE-a). The mass ratio of grinding aid to powder is 0.25:200. The ball milling time is 2 h and the ball milling speed is 100 r / min. The ball-to-powder ratio during the ball milling process is 2:1.

[0083] The contents of Examples 3-2 to 3-3 are basically the same as those of Example 3-1. The difference is that the centrifugation speed in step (2) is different. The centrifugation speeds in step (2) of Examples 3-2 to 3-3 are 1000 r / min and 2000 r / min, respectively.

[0084] To test the setting accelerators prepared in Examples 3-1 to 3-3 on the castings, the accelerators prepared in Examples 3-1 to 3-3 were added to the castings respectively, resulting in three castings, named castings S8, S9, and S10. The three castings were poured into 40mm×40mm×160mm molds and vibrated on a GZ-85 type vibration table. The samples were then placed in a constant temperature and humidity curing chamber at 25℃ for 24 hours. The initial setting time and final setting time were measured according to standard GB / T1346-2011.

[0085] The raw materials of the castable are the same as those in Example 1, the formula of the castable is shown in Table 5, and the preparation method of the castable is the same as that in Example 1.

[0086] Table 5. Formulations of castable samples S8, S9, and S10

[0087]

[0088] The initial setting time and final setting time test results of castable samples S8, S9 and S10 are shown in Table 6.

[0089] Table 6. Test results of castable samples S8, S9, and S10

[0090]

[0091]

[0092] As shown in Table 6, compared with cement-bonded castables without accelerator, the initial and final setting times of the castables were significantly shortened after adding 1% of the accelerator prepared in Examples 3-1 to 3-3 of this invention. Furthermore, with the increase of centrifugation speed during centrifugation of the mixed slurry, both the initial and final setting times of the castables first decreased and then stabilized. The accelerating effect was most significant at a centrifugation speed of 1500 r / min, with the shortest initial and final setting times of 2.3 h and 5.1 h, respectively. This is because the purpose of centrifuging the mixed slurry during accelerator preparation is to separate the AH3 crystal nuclei, hydration products suspended in the mixing liquid, from the cement particles and other hydration products. When the centrifugation speed is low (500 r / min, 1000 r / min), other hydration products generated during hydration and some cement particles are also retained in the suspension, resulting in the prepared accelerator containing not only AH3 crystal nuclei but also some other hydration products and cement particles. At high centrifugation rates (2000 r / min), although smaller AH3 crystal nuclei remain in the suspension, some are easily removed due to the high centrifugation rate, resulting in a relatively low AH3 crystal nuclei content. This leads to a smaller yield of the accelerator, lower production efficiency, increased costs, and hinders the widespread adoption of the accelerator. At a centrifugation rate of 1500 r / min, most of the AH3 crystal nuclei remaining in the suspension after centrifugation are smaller, and the content of hydration products and cement particles is lower, resulting in a higher AH3 crystal nuclei content in the prepared accelerator. Since AH3 crystal nuclei have a larger surface area than other hydration products, a higher content of fully crystalline AH3 crystal nuclei in the accelerator allows for more effective provision of crystal nuclei for CAC hydration after introduction into castables, thus promoting cement hydration and shortening the setting time of the castable.

[0093] The above results show that the accelerator prepared by this invention can effectively promote the solidification of cement-bonded castables, shorten the solidification time of cement castables, and greatly improve the production efficiency of cement-bonded castable precast components. Moreover, when centrifuging the mixed slurry, the centrifugation speed is preferably 500-2000 r / min, and most preferably 1500 r / min.

[0094] Example 4: Discussion on the mass ratio of cement to melamine

[0095] To investigate the effect of the mass ratio of cement to melamine on the performance of the accelerator in its preparation method, experiments were conducted in Examples 4-1 and 4-2. The specific details of Examples 4-1 and 4-2 are as follows:

[0096] Example 4-1:

[0097] A method for preparing a setting accelerator for castables, wherein the castable is a castable prepared using cement as a binder, and the specific steps are as follows:

[0098] (1) Cement, melamine and water are added to a reaction vessel and the mixture is sealed and stirred for 24 hours at a reaction temperature of 25°C to obtain a mixed slurry. The mass ratio of cement to melamine is 25:1, the mass ratio of cement to water is 1:5, the stirring speed is 1000r / min, and the calcium aluminate cement is Secar71 calcium aluminate cement.

[0099] (2) The mixed slurry prepared in step (1) is centrifuged at low speed, and the upper suspension is collected after the low speed centrifugation is completed; wherein, the centrifugation speed of the low speed centrifugation is 1500 r / min and the centrifugation time is 3 min.

[0100] (3) The suspension obtained in step (2) is centrifuged at 12000 r / min for 20 min and the lower solid precipitate is collected. The solid precipitate is frozen and dried under vacuum to obtain powder. The powder is mixed with grinding aid and then ball-milled to obtain a coagulant for casting. The freezing temperature is -30℃ and the freezing time is 60 min. The drying temperature is 50℃ and the drying time is 10 h. The grinding aid is a polymeric polyol HE-a (purchased from Luoyang Hongen New Building Materials Co., Ltd., product model HE-a). The mass ratio of grinding aid to powder is 0.25:200. The ball milling time is 2 h and the ball milling speed is 100 r / min. The ball-to-powder ratio during the ball milling process is 2:1.

[0101] The content of Example 4-2 is basically the same as that of Example 4-1, except that the mass ratio of cement to melamine in step (1) is 75:1.

[0102] To test the setting accelerators prepared in Examples 4-1 and 4-2 on the castings, the accelerators prepared in Examples 4-1 and 4-2 were added to the castings respectively, resulting in two castings, named castings S11 and S12. The two castings were poured into 40mm×40mm×160mm molds and placed on a GZ-85 vibrating table for vibration molding. The samples were then placed in a constant temperature and humidity curing chamber at 25℃ for 24 hours. The initial setting time and final setting time were measured according to standard GB / T1346-2011.

[0103] The raw materials of the castable are the same as those in Example 1, the formula of the castable is shown in Table 7, and the preparation method of the castable is the same as that in Example 1.

[0104] Table 7 Formulations of castable samples S11 and S12

[0105]

[0106] The initial setting time and final setting time test results of castable samples S11 and S12 are shown in Table 8.

[0107] Table 8 Test results of castable samples S11 and S12

[0108] S0 / 7.1 19.0 S11 25:1 4.3 9.1 S1 50:1 2.3 5.1 S12 75:1 2.3 5.2

[0109] As shown in Table 8, compared with cement-bonded castables without accelerators, the initial and final setting times of the castables were significantly shortened after adding 1% of the accelerators prepared in Examples 4-1 to 4-2 of this invention. The accelerator effect was most pronounced when the mass ratio of cement to melamine was 50:1, with the shortest initial and final setting times of 2.3 h and 5.1 h, respectively. This is because the purpose of introducing melamine dispersant during accelerator preparation is to better suspend and disperse AH3 crystal nuclei in the mixed slurry, facilitating subsequent centrifugation to obtain AH3 crystal nuclei. When the mass ratio of cement to melamine is small (25:1), the melamine content is high, and melamine promotes cement hydration, resulting in larger AH3 particles. Therefore, after introducing the prepared accelerator into the castable, the larger AH3 particles have a lower effect on promoting cement hydration. When the mass ratio of cement to melamine is high (75:1), the melamine content is low, and the dispersion effect is not obvious. This results in a low content of AH3 crystal nuclei dispersed in the upper suspension after low-speed centrifugation. Therefore, the production efficiency of the accelerator product is low, which easily increases costs and is not conducive to the promotion of the accelerator. Only when the mass ratio of cement to melamine is 50:1, the generated AH3 crystal nuclei are smaller. After being introduced into the castable, they can more effectively provide crystal nuclei for CAC hydration, which is more conducive to promoting cement hydration and shortening the setting time of the castable. Moreover, at this mass ratio of cement to melamine, more AH3 crystal nuclei can be better suspended and dispersed in the mixed slurry, resulting in a higher production efficiency of the accelerator product. The above results show that the accelerator prepared by the present invention can effectively promote the setting of cement-bonded castables, shorten the setting time of cement castables, and greatly improve the production efficiency of cement-bonded castable precast components. Moreover, the preferred mass ratio of cement to melamine is 25-75:1, and the most preferred is 50:1.

[0110] 1. The effect of the accelerator of this invention on the strength of calcium aluminate cement-bonded castables

[0111] Taking the castable sample S1 prepared in Example 1 as an example, the effect of the coagulant of the present invention on the strength of the castable was studied, while the castable sample S0 was used as a blank control.

[0112] Cement-bonded castable samples S1 and S0 were poured into a 40mm×40mm×160mm mold and placed on a GZ-85 vibrating table for vibration molding. The samples were then placed in a constant temperature and humidity curing chamber at 25℃ for 24 hours. The initial setting time and final setting time were measured according to standard GB / T1346-2011. After curing, the castable was demolded and placed in an oven (110℃) for drying for 24 hours. The room temperature flexural strength and room temperature compressive strength of the samples after curing and drying were then tested. The test results are shown in Table 9.

[0113] Table 9 Performance test results of castable samples S1 and S0

[0114] Initial setting time / h 7.1 2.3 Final setting time / h 19.0 5.1 Flexural strength after demolding after 24 hours of curing / MPa 7.2 11.7 Compressive strength after demolding after 24 hours of curing / MPa 40.3 74.4 Flexural strength after drying / MPa 19.2 28.9 Pressure resistance after drying / MPa 138 187.4

[0115] As shown in Table 9, after the accelerator prepared in Example 1-1 was introduced into the castable, the demolding strength and drying strength of the castable increased significantly. This indicates that the accelerator not only has the effect of accelerating setting, but also helps to promote the further hydration of calcium aluminate cement during the curing process, thereby improving the strength of the castable.

[0116] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may use the above technical content as inspiration to make changes or modifications. These are equivalent embodiments with variations. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical concept of the present invention still fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a setting accelerator for castables, characterized in that, Includes the following steps: (1) Add cement and melamine to water, stir and react to obtain a mixed slurry. The mass ratio of cement to melamine is (20-80):1; the mass ratio of cement to water is 1:(4-8); the temperature of the stirring reaction is 5-60℃ and the time is 2-48h. (2) The mixed slurry prepared in step (1) is centrifuged at low speed. After the low speed centrifugation is completed, the upper suspension is collected. The conditions for the low speed centrifugation are: centrifugation speed of 500 to 2000 r / min and centrifugation time of 1 to 6 min. (3) The suspension obtained in step (2) is centrifuged to collect solid precipitate; the solid precipitate is frozen and dried under vacuum to obtain powder; the powder is mixed with grinding aid and then ground to obtain coagulant for casting; the centrifugation conditions are: centrifugation speed of 10000-25000 r / min and centrifugation time of 10-30 min; The castable is a castable prepared using cement as a binder.

2. The preparation method according to claim 1, characterized in that, In step (3), the freezing temperature is -20℃ to -40℃ and the freezing time is 30 to 120 min; the drying temperature is 40℃ to 100℃ and the drying time is 6 to 12 h.

3. The preparation method according to claim 2, characterized in that, The particle size of the accelerator used in the castable is 0.95-9.56 μm; the grinding aid is any one of polymeric polyol, polymeric alcohol amine, triethanolamine, ethylene glycol, propylene glycol, and glycerol; the mass ratio of the grinding aid to the powder is (0-1):

200.

4. The preparation method according to claim 3, characterized in that, The cement is aluminate cement.

5. A coagulant product prepared by any one of the preparation methods described in claims 1 to 4.

6. The application of the accelerator product according to claim 5 in cement-bound castables.

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