Aluminate cement clinker and preparation process thereof

Abstract

The present application relates to the technical field of cement preparation, and specifically discloses an aluminate cement clinker and its preparation process. The aluminate cement clinker comprises raw materials including 50-60 parts of bauxite; 20-25 parts of limestone; 10-15 parts of dolomite; 5-8 parts of zircon sand; 2-4 parts of magnesia borax; 5-8 parts of modified silicon carbide whiskers; 20-25 parts of rare earth metal-doped calcium aluminate; 1-3 parts of nano-titanium dioxide; modified silicon carbide whiskers obtained by grafting polyethylene glycol onto the surface of the silicon carbide whiskers; and rare earth metal-doped calcium aluminate obtained by mixing a rare earth metal salt solution with calcium aluminate powder, atomizing, drying, and calcining. The aluminate cement clinker of the present application can effectively reduce the hydration heat release rate and heat release of the aluminate cement clinker, thereby effectively improving the crack resistance of concrete.

Description

Technical Field

[0001] The present application relates to the technical field of cement preparation, and more specifically, to an aluminate cement clinker and a preparation process thereof. Background Art

[0002] Aluminate cement clinker is a type of cement clinker primarily composed of calcium aluminate. Its typical components include calcium monoaluminate (CA) and calcium dialuminate (CA2), with small amounts of other mineral phases added depending on specific performance requirements. Aluminate cement clinker possesses many unique characteristics. It develops extremely quickly at early ages, achieving high strength within a short period of time after construction, meeting the demands of projects with tight deadlines. It also exhibits excellent high-temperature resistance, maintaining structural stability and strength even in high-temperature environments and resisting heat-related performance degradation. Furthermore, aluminate cement clinker exhibits excellent corrosion resistance, showing strong resistance to a variety of acids, alkalis, and salts, effectively protecting its internal structure from erosion. Based on these excellent properties, aluminate cement clinker is used in a variety of special engineering scenarios. For example, in emergency repair and construction projects, it can quickly form a structure with a certain strength to ensure that the project is put into use as soon as possible; in the field of refractory materials, as an important binder, it can firmly bond refractory aggregates and powders together to make refractory products with excellent performance; in marine engineering, due to its corrosion resistance, it can be used to build the foundation of marine platforms, docks and other facilities to resist the erosion of seawater.

[0003] In existing technology, the main raw materials for aluminate cement clinker include high-alumina bauxite, limestone, and appropriate amounts of auxiliary raw materials. High-alumina bauxite provides a rich source of aluminum oxide, a key component in the formation of calcium aluminate minerals; limestone, as a calcareous raw material, provides calcium (CaO) for the formation of calcium aluminate. By precisely controlling the ratio of high-alumina bauxite to limestone and adding appropriate amounts of auxiliary raw materials, the content of each oxide in the clinker can be adjusted to meet specific performance requirements. During the production process, these raw materials are mixed in appropriate proportions and calcined in a high-temperature kiln, causing the raw materials to undergo a series of complex physical and chemical changes, ultimately forming aluminate cement clinker with calcium aluminate as the primary mineral phase. This component design can, to a certain extent, produce aluminate cement clinker that meets basic performance requirements and has been applied in various engineering fields.

[0004] However, existing aluminate cement clinker presents several pressing challenges in practical applications. The most prominent of these is the adverse effects of its hydration properties. Aluminate cement clinker hydrates extremely rapidly, releasing over 80% of its total heat within 24 hours, and its heat release per unit mass is 2-3 times that of Portland cement. In concrete construction, this rapid and massive heat release causes a sharp rise in the concrete's internal temperature, while the concrete surface dissipates heat relatively quickly, resulting in a large temperature difference between the concrete's interior and surface. Due to the varying degrees of thermal expansion and contraction of various concrete components, this temperature difference can generate significant thermal stress within the concrete. When thermal stress exceeds the concrete's tensile strength, cracks develop in the concrete. These cracks not only affect the exterior quality of the concrete structure but, more importantly, reduce its durability and load-bearing capacity, posing a serious safety hazard and limiting the application of aluminate cement clinker in projects requiring high structural integrity. Therefore, improving the hydration properties of aluminate cement clinker and reducing its hydration heat release rate and heat release have become key challenges that need to be addressed in the current research and preparation of aluminate cement clinker. Summary of the Invention

[0005] In order to reduce the hydration heat release rate and heat release of aluminate cement clinker, thereby improving the crack resistance of concrete, the present application provides an aluminate cement clinker and a preparation process thereof.

[0006] The aluminate cement clinker provided in this application adopts the following technical solution:

[0007] An aluminate cement clinker comprises the following raw materials in parts by weight:

[0008] 50-60 parts of bauxite;

[0009] 20-25 parts of limestone;

[0010] 10-15 parts of dolomite;

[0011] 5-8 parts of zircon sand;

[0012] 2-4 parts of boraxite;

[0013] 5-8 parts of modified silicon carbide whiskers;

[0014] 20-25 parts of rare earth metal-doped calcium aluminate;

[0015] 1-3 parts of nano titanium dioxide;

[0016] The modified silicon carbide whiskers are obtained by grafting polyethylene glycol onto the surface of the silicon carbide whiskers;

[0017] The rare earth metal-doped calcium aluminate is obtained by mixing a rare earth metal salt solution with calcium aluminate powder, followed by atomization drying and calcination.

[0018] Through the above technical solution, bauxite and limestone serve as the basic raw materials for calcium aluminate, maintaining the high early strength, high-temperature resistance, and corrosion resistance of aluminate cement. Dolomite is added to introduce magnesium oxide and calcium carbonate, producing magnesia-aluminate spinel and periclase. Magnesia-aluminate spinel has a lower coefficient of linear expansion than calcium carbonate, thereby reducing cracking caused by thermal stress. Magnesium oxide exists as a stable compound, preventing the volume expansion caused by the hydration of free magnesium oxide to magnesium hydroxide, thereby reducing the risk of cement cracking. Zircon sand is calcined in the system to form calcium zirconate. Needle-shaped calcium zirconate crystals are interspersed in the matrix, creating a "micro-reinforcement" effect that inhibits crack propagation. Calcium zirconate also remains stable at high temperatures, enhancing its suitability for corrosive environments such as marine engineering. Magnesium oxide is introduced into boraxite to form magnesium borate and magnesia-aluminate spinel. Boron oxide adsorbs on the surface of the calcium aluminate, slowing the hydration reaction and reducing the early exotherm. Boron oxide also synergizes with the magnesium oxide in the dolomite, reducing the harmful effects of free magnesium oxide and improving volume stability.

[0019] Modified silicon carbide whiskers achieve multi-scale stress regulation by grafting polyethylene glycol on the surface, and the silane coupling agent layer improves the bonding strength between the whiskers and the matrix interface, avoiding debonding cracks. Grafted polyethylene glycol can swell and fill micropores, generate pre-compressive stress, offset the shrinkage tensile stress caused by temperature difference, and thus improve crack resistance. Rare earth metal-doped calcium aluminate enters the CA2 lattice through the doping of rare earth metal elements to form a "dislocation solid solution". The spin-orbit coupling of the electron layer of the solid solution effectively improves the activation energy of the hydration reaction of calcium aluminate, thereby reducing the hydration rate of calcium aluminate, and then reducing the hydration heat release rate and heat release, thereby solving the problem of concentrated heat release. Therefore, the aluminate cement clinker of the present application can effectively reduce the hydration heat release rate and heat release of the aluminate cement clinker through the coordinated action of the above-mentioned components, thereby helping to improve the crack resistance of concrete, so that the aluminate cement clinker provided by the present application can be used in some projects with high requirements for structural integrity.

[0020] Optionally, the modified silicon carbide whiskers are prepared by the following method:

[0021] A. Pre-treating silicon carbide whiskers;

[0022] B. Add the pretreated silicon carbide whiskers to an ethanol solution of a silane coupling agent, stir at 60-70°C for 2-3 hours, filter, and dry. Then, disperse the dried silicon carbide whiskers in an amino-terminated polyethylene glycol solution, ultrasonically treat at 80-90°C for 1-2 hours, filter, and dry to obtain modified silicon carbide whiskers.

[0023] By adopting the above technical solution, the silicon carbide whiskers are first pretreated and then surface-modified using a silane coupling agent and an amino-terminated polyethylene glycol solution. This orderly preparation process ensures that the silane coupling agent layer and the grafted polyethylene glycol layer are evenly formed on the whisker surface, effectively achieving multi-scale stress regulation, improving the interfacial bonding strength between the whisker and the substrate, and preventing the occurrence of debonding cracks. At the same time, the swelling effect of the polyethylene glycol filling the micropores generates pre-compressive stress, which improves the crack resistance.

[0024] Optionally, the method for pretreating the silicon carbide whiskers in step A is as follows:

[0025] The silicon carbide whiskers are placed in a vacuum tube furnace, a mixed gas of silane and methane is introduced, and the temperature is kept at 1200-1300°C for 4-6 hours.

[0026] Optionally, the volume ratio of silane to methane in the mixed gas is (2.8-3.0):1; and the gas flow rate of the mixed gas is 60-80 mL / min.

[0027] By adopting the above technical solution and the above pretreatment, silicon atoms will gradually diffuse into the interior of the whiskers during vapor deposition. Since the diffusion rate of silicon is relatively slow, a region with a relatively high carbon content will form inside the whiskers, resulting in a relatively high C / Si ratio in the core. In the surface layer of the whiskers, the concentration of silicon atoms produced by the decomposition of silane is high, while the concentration of carbon atoms produced by the decomposition of methane is relatively low. Therefore, a region with a high silicon content will form on the surface. The silicon carbide whiskers with the above structure give the whiskers themselves a gradient thermal expansion coefficient, thereby offsetting the thermal stress of the cement paste through their own deformation. This in turn helps to enhance the crack resistance of concrete.

[0028] Optionally, in step B, the mass concentration of the silane coupling agent ethanol solution is 5%-8%; the mass concentration of the amino-terminated polyethylene glycol solution is 10%-15%, and the mass ratio of the dried silicon carbide whiskers to the amino-terminated polyethylene glycol solution is 1:(8-10).

[0029] Optionally, the rare earth metal-doped calcium aluminate is prepared by the following method:

[0030] (1) Calcium aluminate powder is added to a rare earth metal salt solution, stirred at 30-40°C for 1-2 hours to obtain a suspension, and then the suspension is dried and atomized by a spray dryer to obtain nanoparticles;

[0031] (2) The nanoparticles are placed in a muffle furnace, heated to 800-900°C at a heating rate of 5-8°C / min in an air atmosphere, kept at this temperature for 2-3 hours, and cooled to obtain rare earth metal-doped calcium aluminate.

[0032] By adopting the above technical solution, calcium aluminate powder is first added to a rare earth metal salt solution and stirred to obtain a suspension. This is then dried and atomized in a spray dryer to obtain nanoparticles. Finally, the nanoparticles are calcined and cooled in a muffle furnace to produce rare earth metal-doped calcium aluminate. Spray drying allows the calcium aluminate powder and rare earth metal salt solution to be thoroughly mixed and form uniform nanoparticles, creating favorable conditions for the uniform doping of rare earth metal elements into the CA2 lattice. The calcination process promotes a chemical reaction between the rare earth metal elements and the calcium aluminate, forming a "dislocated solid solution." This effectively increases the activation energy of the calcium aluminate hydration reaction, reduces the hydration rate and heat release, and solves the problem of concentrated heat release, thereby enhancing the crack resistance of the cement paste.

[0033] Optionally, the rare earth metal salt solution is a mixture of a neodymium nitrate solution and a dysprosium nitrate solution.

[0034] The difference in radius between the neodymium and dysprosium ions in the rare earth salt solution creates periodic "stress traps" in the crystal lattice. When thermal expansion stress is transmitted to these traps, it is absorbed by the localized distortion energy within the traps, thereby enhancing the cement paste's crack resistance. The paramagnetic nature of dysprosium causes the hydration products to form a directional, fibrous CAH gel under magnetic field curing. The entanglement between the fibers increases the cement paste's toughness and forcibly distorts the crack propagation path, thereby enhancing the cement paste's crack resistance.

[0035] Optionally, the mass ratio of the neodymium nitrate solution to the dysprosium nitrate solution in the rare earth metal salt solution is (2-3):1; the mass concentration of the neodymium nitrate is 12%-15%; the mass concentration of the dysprosium nitrate solution is 8%-10%; and the mass ratio of the calcium aluminate powder to the rare earth metal salt solution is 1:(6-8).

[0036] Optionally, the particle size of the nano titanium dioxide is 30-50 nm.

[0037] By adopting this technical solution, nano-anatase TiO2 dissolves into the calcium aluminate lattice, catalyzing the polymerization of the CAH gel, which then forms a three-dimensional network structure. This reduces porosity by over 40%, significantly improving impermeability and toughness. Furthermore, nano-TiO2 helps degrade organic pollutants on the concrete surface, extending its service life in corrosive environments such as marine engineering.

[0038] The present application also provides a process for preparing aluminate cement clinker, which adopts the following technical solution:

[0039] A process for preparing aluminate cement clinker comprises the following steps:

[0040] S1. Bauxite, limestone, dolomite, zircon sand, and magnesia borax are crushed to ≤5 mm, mixed, and pre-calcined at 750-800° C. for 2-3 hours to obtain a pre-calcined material. The pre-calcined material is fed into a plasma arc furnace and calcined at 1750-1800° C. for 30-40 minutes, and then rapidly cooled to room temperature at a rate of 90-100° C. / min to obtain a calcined clinker matrix;

[0041] S2. Stir and mix the modified silicon carbide whiskers, rare earth metal-doped calcium aluminate, and nano-titanium dioxide for 30-40 minutes to obtain a functional premix, and put the calcined clinker matrix and the functional premix into a twin-screw mixer and mix for 1-2 hours to obtain aluminate cement clinker.

[0042] By adopting the above-mentioned technical solution, the crushing process can increase the specific surface area of ​​the raw materials, promote the reaction between the various raw materials during the pre-burning process, and achieve initial decomposition and uniform mixing of the raw materials, providing favorable conditions for the subsequent calcination reaction, ensuring that the various components can fully react to form the desired mineral phases, and improving the quality and performance stability of the cement clinker. The high-temperature calcination in the plasma arc furnace can fully calcine the various raw materials to form a uniform aluminate cement clinker mineral composition. The functional premix prepared by mixing modified silicon carbide whiskers, rare earth metal-doped calcium aluminate, and nano-titanium dioxide can prevent high-temperature damage to the structure and composition of the modified silicon carbide whiskers, thereby improving the crack resistance of the cement paste.

[0043] In summary, this application has the following beneficial effects:

[0044] 1. This application uses a carefully matched combination of raw materials and a unique process to significantly improve the performance of aluminate cement clinker. In terms of raw materials, bauxite and limestone lay the foundation, and dolomite is introduced to reduce the hazards of temperature difference stress cracking and free magnesium oxide; zircon sand forms calcium zirconate, which produces a "micro-reinforcement" effect and enhances corrosion resistance; boron magnesium stone delays the hydration reaction and improves volume stability; rare earth metal doped calcium aluminate reduces the hydration rate and heat release; nano-titanium dioxide reduces porosity, improves impermeability and toughness, and can also degrade pollutants. Overall, the cement clinker combination and process of this application effectively reduces the hydration heat release rate and heat release of cement clinker, greatly improves the crack resistance of concrete, and expands its application in high-demand projects.

[0045] 2. This application prefers a specific method for preparing rare earth metal-doped calcium aluminate. First, calcium aluminate powder is mixed with a rare earth metal salt solution to form a suspension, which is then spray-dried to form uniform nanoparticles. This process creates conditions for the uniform doping of rare earth metals into the CA2 lattice. The nanoparticles are then calcined, prompting the rare earth metals to react with the calcium aluminate to form a "dislocated solid solution," which increases the activation energy of the calcium aluminate hydration reaction, reduces the hydration rate and heat release, and solves the problem of concentrated heat release. A mixed solution of neodymium nitrate and dysprosium nitrate is used. The difference in ionic radius between neodymium and dysprosium forms a "stress trap," which absorbs thermal expansion stress and enhances crack resistance. The paramagnetism of dysprosium causes the hydration products to form a fibrous CAH gel under magnetic field curing. The fiber entanglement improves the toughness of the cement paste and distorts the crack propagation path. This method improves the performance of cement clinker at the microstructural level, effectively enhancing the crack resistance of concrete and meeting the stringent material performance requirements of special projects.

[0046] 3. This application prepares modified silicon carbide whiskers through a specific process. The whiskers are first pretreated, and a mixed gas is introduced under specific conditions to diffuse silicon atoms to form a gradient thermal expansion coefficient structure. The whiskers can deform themselves to offset the thermal stress of the cement stone. Surface modification is then performed, and the pretreated whiskers are sequentially added with a silane coupling agent ethanol solution and an amino-terminated polyethylene glycol solution. After stirring, ultrasonic treatment, and other operations, a silane coupling agent layer and a grafted polyethylene glycol layer are uniformly formed on the whisker surface. The silane coupling agent layer enhances the bonding strength between the whiskers and the matrix interface, avoiding debonding cracks; the grafted polyethylene glycol swells and fills the micropores, generating pre-compressive stress to offset the temperature difference shrinkage tensile stress. The modified silicon carbide whiskers improve the crack resistance of cement stone from multiple angles, effectively improve the performance of aluminate cement clinker, and provide a strong guarantee for the stable use of concrete in complex environments. DETAILED DESCRIPTION

[0047] The present application is further described in detail below with reference to the embodiments.

[0048] Preparation example of modified silicon carbide whiskers

[0049] Preparation Example 1

[0050] Modified silicon carbide whiskers are prepared by the following method:

[0051] A. Place the silicon carbide whiskers in a vacuum tube furnace and introduce a mixed gas of silane and methane at a volume ratio of 2.8:1; the mixed gas is introduced at a gas flow rate of 60 mL / min, and then the mixture is kept at 1200°C for 4 hours to complete the pretreatment of the silicon carbide whiskers;

[0052] B. Add 1 kg of pretreated silicon carbide whiskers to 6 kg of a 5% silane coupling agent ethanol solution, stir at 60°C for 2 hours, then filter and dry. Then, take 1 kg of the dried silicon carbide whiskers and disperse them in 8 kg of a 10% amino-terminated polyethylene glycol solution. Ultrasonicate at 80°C with a power of 500 W for 1 hour, then filter and vacuum dry at 60°C for 5 hours to obtain modified silicon carbide whiskers.

[0053] Preparation Example 2

[0054] Modified silicon carbide whiskers are prepared by the following method:

[0055] A. Place the silicon carbide whiskers in a vacuum tube furnace and introduce a mixed gas of silane and methane with a volume ratio of 3.0:1; the gas flow rate of the mixed gas is 70 mL / min, and then keep the temperature at 1250°C for 5 hours to complete the pretreatment of the silicon carbide whiskers;

[0056] B. Add 1 kg of pretreated silicon carbide whiskers to 6 kg of a 6% silane coupling agent ethanol solution, stir at 65°C for 2.5 hours, then filter and dry. Then, take 1 kg of the dried silicon carbide whiskers and disperse them in 9 kg of a 12% amino-terminated polyethylene glycol solution. Ultrasonicate at 85°C with a power of 500 W for 1.5 hours, then filter and vacuum dry at 60°C for 5 hours to obtain modified silicon carbide whiskers.

[0057] Preparation Example 3

[0058] Modified silicon carbide whiskers are prepared by the following method:

[0059] A. Place the silicon carbide whiskers in a vacuum tube furnace and introduce a mixed gas of silane and methane at a volume ratio of 3.2:1 at a flow rate of 80 mL / min. Then, keep the temperature at 1300°C for 6 hours to complete the pretreatment of the silicon carbide whiskers.

[0060] B. Add 1 kg of pretreated silicon carbide whiskers to 5 kg of 8% silane coupling agent ethanol solution, stir at 70°C for 3 hours, then filter and dry, then take 1 kg of dried silicon carbide whiskers and disperse them in 10 kg of 15% amino-terminated polyethylene glycol solution, ultrasonically treat at 90°C with a power of 500 W for 2 hours, then filter and vacuum dry at 60°C for 5 hours to obtain modified silicon carbide whiskers.

[0061] Preparation Example 4

[0062] Modified silicon carbide whiskers are prepared by the following method:

[0063] 1 kg of silicon carbide whiskers was added to 5 kg of an 8% silane coupling agent ethanol solution, stirred at 70°C for 3 hours, then filtered and dried. Then, 1 kg of the dried silicon carbide whiskers was dispersed in 10 kg of a 15% amino-terminated polyethylene glycol solution, ultrasonically treated at 90°C with a power of 500 W for 2 hours, then filtered and vacuum dried at 60°C for 5 hours to obtain modified silicon carbide whiskers.

[0064] Preparation Example of Rare Earth Metal Doped Calcium Aluminate

[0065] Preparation Example 5

[0066] Rare earth metal-doped calcium aluminate is prepared by the following method:

[0067] (1) 4 kg of 12% neodymium nitrate solution and 2 kg of 8% dysprosium nitrate solution were mixed to obtain 6 kg of rare earth metal salt solution, 1 kg of calcium aluminate powder was added to the 6 kg of rare earth metal salt solution, and the mixture was stirred at 30°C for 1 hour to obtain a suspension, which was then dried and atomized by a spray dryer to obtain nanoparticles at an atomization pressure of 0.5 MPa.

[0068] (2) The nanoparticles were placed in a muffle furnace, heated to 800°C at a heating rate of 5°C / min in an air atmosphere, kept at this temperature for 2 h, and cooled to obtain rare earth metal-doped calcium aluminate.

[0069] Preparation Example 6

[0070] Rare earth metal-doped calcium aluminate is prepared by the following method:

[0071] (1) 5 kg of 13% neodymium nitrate solution and 2 kg of 9% dysprosium nitrate solution were mixed to obtain 7 kg of rare earth metal salt solution, 1 kg of calcium aluminate powder was added to the 7 kg of rare earth metal salt solution, and the mixture was stirred at 35 ° C for 1.5 h to obtain a suspension, which was then dried and atomized by a spray dryer to obtain nanoparticles at an atomization pressure of 0.5 MPa;

[0072] (2) The nanoparticles were placed in a muffle furnace and heated to 850°C at a heating rate of 7°C / min in an air atmosphere. The temperature was kept at this temperature for 2.5 h and rare earth metal-doped calcium aluminate was obtained after cooling.

[0073] Preparation Example 7

[0074] Rare earth metal-doped calcium aluminate is prepared by the following method:

[0075] (1) 6 kg of 15% neodymium nitrate solution and 2 kg of 10% dysprosium nitrate solution were mixed to obtain 8 kg of rare earth metal salt solution, 1 kg of calcium aluminate powder was added to the 8 kg of rare earth metal salt solution, and the mixture was stirred at 40 ° C for 2 h to obtain a suspension, which was then dried and atomized by a spray dryer to obtain nanoparticles at an atomization pressure of 0.5 MPa;

[0076] (2) The nanoparticles were placed in a muffle furnace and heated to 900°C at a heating rate of 8°C / min in an air atmosphere. The temperature was kept at this temperature for 3 h and rare earth metal-doped calcium aluminate was obtained after cooling.

[0077] Preparation Example 8

[0078] The difference between the rare earth metal-doped calcium aluminate and Preparation Example 7 is that the mass concentration of the neodymium nitrate solution in this Preparation Example is 5%, and the mass concentration of the dysprosium nitrate solution is 5%.

[0079] Example

[0080] Example 1

[0081] An aluminate cement clinker, whose raw material components and proportions are shown in Table 1, wherein the modified silicon carbide whiskers are selected from the modified silicon carbide whiskers of Preparation Example 1; the rare earth metal-doped calcium aluminate is selected from the rare earth metal-doped calcium aluminate of Preparation Example 5; and the average particle size of nano-titanium dioxide is 30 nm.

[0082] Aluminate cement clinker, its preparation process comprises the following steps:

[0083] S1. Bauxite, limestone, dolomite, zircon sand, and magnesia stone are crushed to ≤5 mm, mixed, and pre-calcined at 750° C. for 3 h to obtain a pre-calcined material. The pre-calcined material is fed into a plasma arc furnace, calcined at 1750° C. for 40 min, and then rapidly cooled to room temperature at a rate of 90° C. / min to obtain a calcined clinker matrix;

[0084] S2. The modified silicon carbide whiskers, rare earth metal-doped calcium aluminate, and nano-titanium dioxide are stirred and mixed for 30 minutes to obtain a functional premix. The calcined clinker matrix and the functional premix are put into a twin-screw mixer and mixed for 1 hour to obtain aluminate cement clinker.

[0085] Example 2

[0086] An aluminate cement clinker, whose raw material components and proportions are shown in Table 1, wherein the modified silicon carbide whiskers are selected from the modified silicon carbide whiskers of Preparation Example 2; the rare earth metal-doped calcium aluminate is selected from the rare earth metal-doped calcium aluminate of Preparation Example 6; and the average particle size of nano-titanium dioxide is 40 nm.

[0087] Aluminate cement clinker, its preparation process comprises the following steps:

[0088] S1. Bauxite, limestone, dolomite, zircon sand, and magnesia stone are crushed to ≤5 mm, mixed, and pre-calcined at 780° C. for 2.5 hours to obtain a pre-calcined material. The pre-calcined material is fed into a plasma arc furnace, calcined at 1780° C. for 35 minutes, and then rapidly cooled to room temperature at a rate of 95° C. / min to obtain a calcined clinker matrix;

[0089] S2. The modified silicon carbide whiskers, rare earth metal-doped calcium aluminate, and nano-titanium dioxide were stirred and mixed for 35 minutes to obtain a functional premix. The calcined clinker matrix and the functional premix were put into a twin-screw mixer and mixed for 1.5 hours to obtain aluminate cement clinker.

[0090] Example 3

[0091] An aluminate cement clinker, whose raw material components and proportions are shown in Table 1, wherein the modified silicon carbide whiskers are selected from the modified silicon carbide whiskers of Preparation Example 3; the rare earth metal-doped calcium aluminate is selected from the rare earth metal-doped calcium aluminate of Preparation Example 7; and the average particle size of nano-titanium dioxide is 50 nm.

[0092] Aluminate cement clinker, its preparation process comprises the following steps:

[0093] S1. Bauxite, limestone, dolomite, zircon sand, and magnesia stone are crushed to ≤5 mm, mixed, and pre-calcined at 800° C. for 2 h to obtain a pre-calcined material. The pre-calcined material is fed into a plasma arc furnace, calcined at 1800° C. for 30 min, and then rapidly cooled to room temperature at a rate of 100° C. / min to obtain a calcined clinker matrix;

[0094] S2. The modified silicon carbide whiskers, rare earth metal-doped calcium aluminate, and nano-titanium dioxide are stirred and mixed for 40 minutes to obtain a functional premix. The calcined clinker matrix and the functional premix are put into a twin-screw mixer and mixed for 2 hours to obtain aluminate cement clinker.

[0095] Table 1 Raw material components and proportions of watertight clinker in Examples 1-3 (kg)

[0096]

[0097] Example 4

[0098] An aluminate cement clinker is different from Example 1 in that the average particle size of the nano-titanium dioxide in the raw materials of this example is 100 nm.

[0099] Example 5

[0100] An aluminate cement clinker is different from Example 1 in that the modified silicon carbide whiskers in the raw materials of this embodiment are the modified silicon carbide whiskers of Preparation Example 4.

[0101] Example 6

[0102] An aluminate cement clinker is different from Example 1 in that the rare earth metal-doped calcium aluminate in the raw materials of this example is the rare earth metal-doped calcium aluminate prepared in Preparation Example 8.

[0103] Comparative Example

[0104] Comparative Example 1

[0105] Disclosed is an aluminate cement, wherein the raw materials comprise, by mass percentage, 70% aluminate cement, 12% sodium hexametaphosphate, 5% microsilica fume, and 13% slag powder.

[0106] Comparative Example 2

[0107] An aluminate cement clinker is different from Example 1 in that an equal amount of unmodified silicon carbide whiskers is used in the raw materials of this comparative example instead of the modified silicon carbide whiskers.

[0108] Comparative Example 3

[0109] An aluminate cement clinker is different from Example 1 in that an equal amount of calcium aluminate not doped with rare earth metals is used in the raw materials of this comparative example to replace the rare earth metal-doped calcium aluminate.

[0110] Comparative Example 4

[0111] An aluminate cement clinker is different from Example 1 in that nano titanium dioxide is not added to the raw materials of this comparative example, and the difference is supplemented by bauxite.

[0112] Performance testing

[0113] Test sample: The cement clinker prepared in Examples 1-6 and Comparative Examples 2-4 was ball-milled, and then mixed with 3% gypsum powder and 8% fly ash to obtain aluminate cement.

[0114] Test method:

[0115] 1. Heat of hydration and heat release rate

[0116] The hydration heat and average heat release rate of aluminate cement over 24 hours were measured using the direct method specified in GB / T 12959-2008. The results are shown in Table 2.

[0117] 2. Crack resistance

[0118] Using the aforementioned test samples, 1000 mm × 1000 mm × 500 mm concrete specimens were made (mix ratio: aluminate cement: sand: stone: water = 1:2.5:4:1.5). The number of surface cracks in the concrete specimens was observed after 7 days. The results are shown in Table 2.

[0119] Table 2 Test results

[0120]

[0121] As can be seen from Table 2, the 24h heat release of the aluminate cement of Examples 1-3 is 284.9-287.5 kJ / kg, and the heat release rate is 11.87-11.98 kJ / (kg·h), which is 523.4 kJ / kg and 21.80 kJ / (kg·h) of the aluminate cement of Comparative Example 1. The heat release is reduced by more than 45%, indicating that the hydration heat release of the aluminate cement provided in the present application within 24 hours is low, and the heat release rate is also effectively reduced. In addition, the concrete test blocks of Examples 1-3 did not crack during the 7d observation period, which is significantly better than the comparative example, verifying that the aluminate cement of the present application is beneficial to improving the crack resistance of concrete.

[0122] In Example 5, the gradient structure of the silicon carbide whiskers was lost due to the lack of whisker pretreatment, resulting in 12 cracks in the final concrete. In Example 6, the rare earth metal salt solution concentration was insufficient (the concentration of neodymium and dysprosium nitrate was 5%), which weakened the rare earth metal ion doping effect and increased the heat release of the aluminate cement to 386.7 kJ / kg, verifying the positive correlation between the rare earth doping amount and the heat release suppression effect.

[0123] Comparative Example 2, which uses unmodified silicon carbide whiskers, exhibits insufficient interfacial bonding strength and 18 cracks, demonstrating the importance of silane coupling agent grafting and gradient composition-designed silicon carbide whiskers in improving the crack resistance of cement paste. Comparative Example 3, which lacks the addition of rare earth metal-doped calcium aluminate, exhibits a heat release of 485.6 kJ / kg and a heat release rate of 20.23 kJ / (kg·h), significantly higher than those of the examples, demonstrating the crucial role of rare earth metal-doped calcium aluminate in reducing the hydration heat and heat release rate of aluminate cement. Comparative Example 4, which lacks the addition of nano-titanium dioxide, exhibits a higher porosity and 15 cracks, demonstrating the significant contribution of nano-titanium dioxide to structural density and crack resistance.

[0124] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An aluminate cement clinker, characterized in that: The raw materials include the following parts by weight: 50-60 parts of bauxite; 20-25 parts of limestone; 10-15 parts of dolomite; 5-8 parts of zircon sand; 2-4 parts of boraxite; 5-8 parts of modified silicon carbide whiskers; 20-25 parts of rare earth metal-doped calcium aluminate; 1-3 parts of nano titanium dioxide; The modified silicon carbide whiskers are prepared by the following method: A. Pre-treating silicon carbide whiskers; B. Adding the pretreated silicon carbide whiskers to an ethanol solution of a silane coupling agent, stirring at 60-70° C. for 2-3 hours, filtering, and drying, then dispersing the dried silicon carbide whiskers in an amino-terminated polyethylene glycol solution, ultrasonically treating at 80-90° C. for 1-2 hours, and then filtering and drying to obtain modified silicon carbide whiskers; Step A: The method for pre-treating silicon carbide whiskers is as follows: Place the silicon carbide whiskers in a vacuum tube furnace, introduce a mixture of silane and methane, and keep the temperature at 1200-1300°C for 4-6 hours; The rare earth metal doped calcium aluminate is obtained by mixing a rare earth metal salt solution with calcium aluminate powder, followed by atomization drying and calcination; The rare earth metal salt solution is a mixture of a neodymium nitrate solution and a dysprosium nitrate solution.

2. The aluminate cement clinker according to claim 1, characterized in that: The volume ratio of silane to methane in the mixed gas is (2.8-3.0):1; the gas flow rate of the mixed gas is 60-80 mL / min.

3. The aluminate cement clinker according to claim 1, characterized in that: In step B, the mass concentration of the silane coupling agent ethanol solution is 5%-8%; the mass concentration of the amino-terminated polyethylene glycol solution is 10%-15%, and the mass ratio of the dried silicon carbide whiskers to the amino-terminated polyethylene glycol solution is 1:(8-10).

4. The aluminate cement clinker according to claim 1, characterized in that: The rare earth metal-doped calcium aluminate is prepared by the following method: (1) Calcium aluminate powder is added to a rare earth metal salt solution, stirred at 30-40°C for 1-2 hours to obtain a suspension, and then the suspension is dried and atomized by a spray dryer to obtain nanoparticles; (2) The nanoparticles are placed in a muffle furnace, heated to 800-900°C at a heating rate of 5-8°C / min in an air atmosphere, kept at this temperature for 2-3 hours, and cooled to obtain rare earth metal-doped calcium aluminate.

5. The aluminate cement clinker according to claim 4, characterized in that: The mass ratio of the neodymium nitrate solution to the dysprosium nitrate solution in the rare earth metal salt solution is (2-3):1; the mass concentration of the neodymium nitrate is 12%-15%; the mass concentration of the dysprosium nitrate solution is 8%-10%; and the mass ratio of the calcium aluminate powder to the rare earth metal salt solution is 1:(6-8).

6. The aluminate cement clinker according to claim 1, characterized in that: The particle size of the nano titanium dioxide is 30-50 nm.

7. A process for preparing aluminate cement clinker according to any one of claims 1 to 6, characterized in that: The steps include: S1. Bauxite, limestone, dolomite, zircon sand, and magnesia borax are crushed to ≤5 mm, mixed, and pre-calcined at 750-800° C. for 2-3 hours to obtain a pre-calcined material. The pre-calcined material is fed into a plasma arc furnace and calcined at 1750-1800° C. for 30-40 minutes, and then rapidly cooled to room temperature at a rate of 90-100° C. / min to obtain a calcined clinker matrix; S2. Stir and mix the modified silicon carbide whiskers, rare earth metal-doped calcium aluminate, and nano-titanium dioxide for 30-40 minutes to obtain a functional premix, and put the calcined clinker matrix and the functional premix into a twin-screw mixer and mix for 1-2 hours to obtain aluminate cement clinker.

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