Preparation method of cementing material system based on calcium carboaluminate and hydrated calcium aluminosilicate

Abstract

The invention discloses a preparation method of a cementing material system based on calcium carboaluminate and hydrated calcium aluminosilicate, and belongs to the field of building materials. The method comprises the following steps: heating refractory clay to 500 DEG C within 30 minutes, heating to 750 DEG C at a heating rate of 2 DEG C / min, and keeping the temperature for 3 hours, so that a kaolin crystal structure is destroyed, and amorphous metakaolin with interlayer pore channels is formed; grinding the fly ash in a ball mill; mixing the light-burned refractory clay with quick lime, and grinding; limestone with the CaO content higher than 50% is ground till the specific surface area ranges from 600 m < 2 > / kg to 650 m < 2 > / kg; grinding the cement clinker and the desulfurized gypsum until the specific surface area is 350-400m < 2 > / kg; and mixing the superfine fly ash, the light-burned refractory clay, the quick lime, the limestone powder, the cement clinker and the desulfurized gypsum to generate the cementing material system based on the calcium carboaluminate and the hydrated calcium aluminosilicate. By using the cementing material system, the content of the clinker in the cement is greatly reduced, and the use amount of the cement clinker is only 1 / 3 of that of ordinary cement.

Description

Technical Field

[0001] This invention relates to building materials, and more particularly to a method for preparing a cementitious material system based on calcium aluminate carbide and hydrated calcium aluminosilicate. Background Technology

[0002] Calcium aluminate is a key metastable hydration product in cement chemistry. Its general chemical formula is usually expressed as 3CaO·Al2O3·CaCO3·nH2O (n is usually 11, and the most common form is C3A·CaCO3·11H2O). It has three core functions: retarding setting, contributing to strength and improving durability.

[0003] In ordinary Portland cement systems, calcium aluminate, as a cementitious hydration product, has interwoven needle-like or platy crystals that contribute to mechanical strength and directly improve the early strength of the cement paste. In marine engineering or de-icing salt environments, it reduces the amount of aluminate phases that react with chloride ions, thus significantly improving the concrete's resistance to chloride ion attack. During production, ordinary Portland cement typically incorporates about 5% limestone powder as an admixture. This provides a calcium source and nuclei for the early hydration of tricalcium silicate (C3S). A small amount of limestone also reacts with aluminates to form calcium aluminate, which has a structure similar to ettringite. This plays a role in regulating setting time and improving early strength, but due to its extremely low formation rate, the overall effect is very limited. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing a cementitious material system based on calcium aluminate carbide and hydrated calcium aluminosilicate, which aims to solve the problems of high energy consumption and high CO2 emissions in the traditional cement production process.

[0005] Technical solution: A method for preparing a cementitious material system based on calcium aluminate carbide and hydrated calcium aluminosilicate, comprising the following steps: S1. The refractory clay is heated to 500℃ within 30 minutes, and then heated to 750℃ at a heating rate of 2℃ / min and held at the temperature for 3 hours. The crystal structure of the kaolin is destroyed, forming amorphous metakaolin with interlayer pores. S2. Grind the fly ash in a ball mill until the specific surface area is 600-650 m². 2 / kg; S3. Mix the lightly calcined refractory clay with quicklime and grind it in a mill until the specific surface area is 700-750 m². 2 / kg; S4. Grind limestone with a CaO content higher than 50% to a specific surface area of ​​600-650 m². 2 / kg; S5. Grind cement clinker and desulfurized gypsum to a specific surface area of ​​350-400 m². 2 / kg; S6. Mix ultrafine fly ash, lightly calcined refractory clay, quicklime, limestone powder, cement clinker, and desulfurized gypsum to generate a cementitious material system based on calcium aluminate and hydrated calcium aluminosilicate.

[0006] Preferably, in step S3, the mass ratio of lightly calcined refractory clay to quicklime is 1:9.

[0007] Preferably, in step S5, the mass ratio of cement clinker to desulfurized gypsum is 96:4.

[0008] Preferably, in step S6, ultrafine fly ash, lightly calcined refractory clay, quicklime, limestone powder, cement clinker, and desulfurized gypsum are mixed in proportions of 20%, 36%, 4%, 15%, 24%, and 1% by mass.

[0009] Preferably, the method further includes preparing nano-sized calcium aluminate as seed crystals for the hydration reaction of the calcium aluminate cementitious material system; the preparation method of nano-sized calcium aluminate is as follows: (1) Sol-gel transition stage Raw material preparation and mixing: Take calcium oxalate solution and aluminum citrate solution with a concentration of 1 mol / L respectively, and mix them in a precise molar ratio of 4:1. Mix the two solutions thoroughly by mechanical stirring to form a homogeneous mixture system. Phase transition control: The above mixture is heated to 60°C, and the solvent (mainly water) is slowly evaporated under continuous stirring. As the solvent decreases, the mixture gradually undergoes a sol-gel transition, eventually forming a viscous gel, which lays a uniform material basis for subsequent reactions. (2) Freeze-drying stage Freeze-freeze: The viscous gel formed by the sol-gel transformation is rapidly frozen to -40°C, so that the water contained in the gel is directly converted into solid ice, avoiding the collapse of the gel structure during the water loss process; Vacuum sublimation: The frozen solid gel is placed in a high vacuum environment with a pressure of <100Pa, and the solid ice is directly converted into water vapor and removed from the system by the principle of sublimation. This process can preserve the porous structure of the gel to the greatest extent, and finally obtain a porous precursor, in which the calcium source and aluminum source are still uniformly distributed. (3) High-temperature synthesis stage Reaction environment and temperature control: The porous precursor was placed in a small boiling furnace, nitrogen was introduced to create a non-oxidizing atmosphere, and the temperature was raised to 1200℃ at a uniform rate of 5℃ / min and held for 1-2 hours to carry out the high-temperature synthesis reaction. Product formation and particle size control: Under a high-temperature nitrogen atmosphere, the calcium and aluminum sources in the precursor react to form nano-sized calcium aluminate carbonitrate. Simultaneously, the organic functional groups undergo partial carbonization at high temperature, providing physical isolation for the in-situ generated calcium aluminate carbonitrate particles. Furthermore, the nitrogen flow further promotes particle dispersion, preventing agglomeration. In addition, the shorter duration of high temperature effectively inhibits excessive grain growth, ultimately ensuring precise control of the particle size of the generated nano-sized calcium aluminate carbonitrate particles within the range of 40-60 nm.

[0010] Preferably, the prepared nano-aluminate calcium carbon is dispersed in an ether solvent with a boiling point of 34.6℃: the nano-aluminate calcium carbon is uniformly dispersed in the ether by means of mechanical stirring or ultrasonic dispersion, and the mass percentage concentration of the dispersion system is finally controlled at 5% to obtain a stable nano-aluminate calcium carbon ether dispersion system.

[0011] Beneficial Effects: This invention focuses on increasing the aluminate content in hydration products, constructing a novel material system. Limestone powder serves as the primary calcium and carbon source, while ultrafine fly ash and lightly calcined refractory clay (mainly metakaolin) act as the core aluminum source. A portion of cement clinker supplements the aluminum source and provides early strength, while a small amount of quicklime powder supplements the calcium source. Simultaneously, the heat of hydration from the quicklime powder's reaction with water accelerates the early hydration process. Furthermore, the CASH gel formed by the reaction of metakaolin in the lightly calcined refractory clay with calcium hydroxide further enhances the overall strength of the material system due to its strong covalent bonds. Using this cementitious material system significantly reduces the clinker content in cement, requiring only one-third the amount of clinker used in ordinary cement, effectively alleviating the problems of high energy consumption and high CO2 emissions in cement production. It also improves the comprehensive utilization rate of industrial solid waste, fly ash.

[0012] The nano-calcium aluminate diethyl ether dispersion system can serve as a highly efficient seed crystal for the hydration of calcium aluminate cementitious materials. The specific mechanism and application conditions are as follows: Mechanism of action: During the hydration process of the cementitious material system, the addition of the nano-calcium aluminate diethyl ether dispersion system allows the heat of hydration released from the quicklime hydration to rapidly and fully volatilize the diethyl ether (boiling point 34.6℃), avoiding interference from solvent residues on the hydration reaction. After the diethyl ether volatilizes, the nano-calcium aluminate particles remain in the system as seed crystals, effectively inducing further formation of calcium aluminate and significantly accelerating its formation rate, thus improving the hydration efficiency and performance of the cementitious material. Optimal dosage: Experiments show that when the dosage of the nano-calcium aluminate diethyl ether dispersion system is 0.1-0.3% of the total mass of the cementitious material system, the ideal seed crystal induction effect can be achieved, improving hydration efficiency without negatively impacting other mechanical properties or stability of the cementitious material. Attached Figure Description

[0013] Figure 1This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0014] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] Example like Figure 1 As shown, a method for preparing a cementitious material system based on calcium aluminate carbide and hydrated calcium aluminosilicate includes: (1) The refractory clay is heated to 500℃ within 30 minutes, and then heated to 750℃ at a heating rate of 2℃ / min and kept at the temperature for 3 hours. The crystal structure of the kaolin is destroyed, forming amorphous metakaolin with interlayer pores, and its hydration activity is greatly improved.

[0016] (2) Grind the fly ash in a ball mill until the specific surface area is 625 m². 2 / kg, the particle size of fly ash is greatly reduced, which makes the alumina in fly ash more reactive and provides better kinetic conditions for the formation of aluminocarbonates.

[0017] (3) Mix lightly calcined refractory clay and quicklime in a mass ratio of 1:9 and grind them into a mill until the specific surface area is 730 m². 2 / kg, quicklime and metakaolin have good grindability, and the high specific surface area can provide good kinetic conditions for CASH gel. At the same time, metakaolin also serves as an aluminum source to provide some reaction raw materials for the formation of aluminocarbonate.

[0018] (4) Grind limestone with a CaO content higher than 50% to a specific surface area of ​​625 m². 2 / kg, providing calcium and carbon sources for the formation of aluminocarbonates.

[0019] (5) Grind cement clinker and desulfurized gypsum at a mass ratio of 96:4 until the specific surface area is 370 m². 2 / kg, comparable to traditional cement. First, it generates traditional hydrated calcium silicate gel, ensuring a certain early strength for the cementitious material system of this invention. Second, the particles are larger than other materials, ensuring the preferential occurrence of the reaction between aluminate carboxylate and hydrated CASH gel. Third, the hydration of cement clinker provides some calcium and aluminum sources for the production of aluminate carboxylate. Fourth, the hydration of cement clinker provides some calcium sources for CASH gel.

[0020] (6) Ultrafine fly ash, lightly burned refractory clay, quicklime, limestone powder, cement clinker, and desulfurized gypsum are mixed in proportions of 20%, 36%, 4%, 15%, 24%, and 1% by mass to generate a cementitious material system based on calcium aluminate and hydrated calcium aluminosilicate.

[0021] The method also includes preparing nano-sized calcium aluminate as seed crystals for the hydration reaction of the calcium aluminate cementitious material system; the preparation method of nano-sized calcium aluminate is as follows: (1) Sol-gel transition stage Raw material preparation and mixing: Take calcium oxalate solution and aluminum citrate solution with a concentration of 1 mol / L respectively, and mix them in a precise molar ratio of 4:1. Mix the two solutions thoroughly by mechanical stirring to form a homogeneous mixture system. Phase transition control: The above mixture was heated to 60°C and the solvent was slowly evaporated under continuous stirring. As the solvent decreased, the mixture gradually underwent a sol-gel transition, eventually forming a viscous gel, which laid a uniform material basis for subsequent reactions. (2) Freeze-drying stage Freeze-freeze: The viscous gel formed by the sol-gel transition is rapidly frozen to -40°C, so that the water contained in the gel is directly converted into solid ice; Vacuum sublimation: The frozen solid gel is placed in a high vacuum environment with a pressure of <100Pa, and the solid ice is directly converted into water vapor and removed from the system by the principle of sublimation. (3) High-temperature synthesis stage Reaction environment and temperature control: The porous precursor was placed in a small boiling furnace, nitrogen was introduced to create a non-oxidizing atmosphere, and the temperature was raised to 1200℃ at a uniform rate of 5℃ / min and held for 1-2 hours to carry out the high-temperature synthesis reaction. Product formation and particle size control: Under a high-temperature nitrogen atmosphere, the calcium source and aluminum source in the precursor react to generate nano-sized calcium aluminate carbon.

[0022] The prepared nano-aluminate calcium carbonate was dispersed in diethyl ether solvent with a boiling point of 34.6℃. The nano-aluminate calcium carbonate was uniformly dispersed in diethyl ether by mechanical stirring or ultrasonic dispersion. The mass percentage concentration of the dispersion system was controlled at 5% to obtain a stable nano-aluminate calcium carbonate diethyl ether dispersion system.

[0023] The strength of the gel material system prepared according to the above steps was tested according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar". The setting time of the cementitious material system was tested according to GB / T 1346-2024 "Test Method for Standard Water Requirement, Setting Time and Soundness of Cement". The test results are shown in the table below.

[0024]

[0025] The hydration products of this cementitious material system are mainly calcium aluminate carbohydrate and hydrated CASH gel. Compared with traditional cement (whose hydration products are mainly ettringite and hydrated CSH gel), calcium aluminate carbohydrate has higher strength than ettringite, and hydrated CASH gel has higher strength than hydrated CSH gel. Therefore, the strength of this cementitious material system is higher than that of traditional cement. Approximately 25% of the components in this material system are identical to those in traditional cement, which effectively ensures the setting time and early strength of the cementitious material system.

[0026] The 28-day compressive strength of conventional cement made from the same cement clinker and desulfurized gypsum was 49.2 MPa. The 28-day compressive strength of this cementitious material system is 69.8 MPa, which is much higher than that of traditional cement.

[0027] The 3-day compressive strength of conventional cement prepared using the same cement clinker and desulfurized gypsum was 29.3 MPa. The 3-day compressive strength of this cementitious material system is 30.2 MPa, which is comparable to that of traditional cement.

[0028] The initial setting time of traditional cement made from the same cement clinker and desulfurized gypsum was 145 minutes, and the final setting time was 195 minutes. The initial setting time of this cementitious material system is 155 minutes, and the final setting time is 200 minutes, which is slightly longer than that of traditional cement, but does not affect construction.

[0029] Compared with the sample of this invention (without seed crystals), the initial setting time was shortened from 155 min to 140-150 min after adding seed crystals, and the final setting time was shortened from 200 min to 185-195 min. Furthermore, the higher the amount of seed crystals added, the shorter the setting time became. The heat released during the hydration of quicklime caused the ether (boiling point 34.6℃) to evaporate rapidly, leaving no solvent residue. The nano-sized calcium aluminate particles, acting as seed crystals, accelerated the formation rate of calcium aluminate and shortened the hydration reaction induction period.

[0030] 3D flexural strength: increased from 4.6 MPa without seeding to 5.8-6.1 MPa, an increase of 26.1%-32.6%; 3D compressive strength: increased from 30.2 MPa without seeding to 36.5-38.5 MPa, an increase of 20.8%-27.4%; When the amount of seed crystals increases from 0.1% to 0.3%, the early strength steadily improves. The increase slows down in the 0.2%-0.3% range. Within this range, the seed crystals can fully induce the formation of calcium aluminate carbohydrate, and the strength improvement will not stagnate due to particle agglomeration.

[0031] 28-day flexural strength increased from 9.7 MPa without seeding to 9.8-10.0 MPa, and 28-day compressive strength increased from 69.8 MPa to 70.5-71.5 MPa, an increase of 0.3%-3.3%. Nano-sized calcium aluminate not only accelerates early hydration but also supplements later strength by inducing the generation of more calcium aluminate, with no decrease in later strength. This proves that seeding only enhances hydration efficiency and does not compromise the long-term stability of the cementitious material.

[0032] Even with the addition of the minimum amount of seed crystals (0.1%), the 28-day flexural strength (9.8 MPa) and 28-day compressive strength (70.5 MPa) of the sample of this invention are still far higher than those of traditional cement (7.6 MPa and 49.2 MPa), and the 3-day flexural strength (5.8 MPa) and 3-day compressive strength (36.5 MPa) are far superior to those of traditional cement (4.1 MPa and 29.3 MPa). Moreover, the amount of cement clinker used is only 1 / 3 of that of traditional cement. It retains the core advantages of low energy consumption and low CO2 emissions, and further compensates for the industry pain point of insufficient early strength of traditional low clinker systems by using seed crystals.

[0033] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a cementitious material system based on calcium aluminate carbohydrate and hydrated calcium aluminosilicate, characterized in that, Includes the following steps: S1. The refractory clay is heated to 500℃ within 30 minutes, and then heated to 750℃ at a heating rate of 2℃ / min and held at the temperature for 3 hours. The crystal structure of the kaolin is destroyed, forming amorphous metakaolin with interlayer pores. S2. Grind the fly ash in a ball mill until the specific surface area is 600-650 m². 2 / kg; S3. Mix the lightly calcined refractory clay with quicklime and grind it in a mill until the specific surface area is 700-750 m². 2 / kg; S4. Grind limestone with a CaO content higher than 50% to a specific surface area of ​​600-650 m². 2 / kg; S5. Grind cement clinker and desulfurized gypsum to a specific surface area of ​​350-400 m². 2 / kg; S6. Mix ultrafine fly ash, lightly calcined refractory clay, quicklime, limestone powder, cement clinker, and desulfurized gypsum to generate a cementitious material system based on calcium aluminate and hydrated calcium aluminosilicate.

2. The method for preparing a cementitious material system based on calcium aluminate carbohydrate and hydrated calcium aluminosilicate according to claim 1, characterized in that, In step S3, the mass ratio of lightly calcined refractory clay to quicklime is 1:

9.

3. The method for preparing a cementitious material system based on calcium aluminate carbohydrate and hydrated calcium aluminosilicate according to claim 1, characterized in that, In step S5, the mass ratio of cement clinker to desulfurized gypsum is 96:

4.

4. The method for preparing a cementitious material system based on calcium aluminate carbohydrate and hydrated calcium aluminosilicate according to claim 1, characterized in that, In step S6, ultrafine fly ash, lightly calcined refractory clay, quicklime, limestone powder, cement clinker, and desulfurized gypsum are mixed in proportions of 20%, 36%, 4%, 15%, 24%, and 1% by mass.

5. The method for preparing a cementitious material system based on calcium aluminate carbohydrate and hydrated calcium aluminosilicate according to claim 1, characterized in that, This method also includes preparing nano-sized calcium aluminate as seed crystals for the hydration reaction of the calcium aluminate cementitious material system; the preparation method of nano-sized calcium aluminate is as follows: (1) Sol-gel transition stage Raw material preparation and mixing: Take calcium oxalate solution and aluminum citrate solution with a concentration of 1 mol / L respectively, and mix them in a precise molar ratio of 4:

1. Mix the two solutions thoroughly by mechanical stirring to form a homogeneous mixture system. Phase transition control: The above mixture was heated to 60°C and the solvent was slowly evaporated under continuous stirring. As the solvent decreased, the mixture gradually underwent a sol-gel transition, eventually forming a viscous gel, which laid a uniform material basis for subsequent reactions. (2) Freeze-drying stage Freeze-freeze: The viscous gel formed by the sol-gel transition is rapidly frozen to -40°C, so that the water contained in the gel is directly converted into solid ice; Vacuum sublimation: The frozen solid gel is placed in a high vacuum environment with a pressure of <100Pa, and the solid ice is directly converted into water vapor and removed from the system by the principle of sublimation. (3) High-temperature synthesis stage Reaction environment and temperature control: The porous precursor was placed in a small boiling furnace, nitrogen was introduced to create a non-oxidizing atmosphere, and the temperature was raised to 1200℃ at a uniform rate of 5℃ / min and held for 1-2 hours to carry out the high-temperature synthesis reaction. Product formation and particle size control: Under a high-temperature nitrogen atmosphere, the calcium source and aluminum source in the precursor react to generate nano-sized calcium aluminate carbon.

6. The method for preparing a cementitious material system based on calcium aluminate carbohydrate and hydrated calcium aluminosilicate according to claim 5, characterized in that, The prepared nano-aluminate calcium carbonate was dispersed in diethyl ether solvent with a boiling point of 34.6℃. The nano-aluminate calcium carbonate was uniformly dispersed in diethyl ether by mechanical stirring or ultrasonic dispersion. The mass percentage concentration of the dispersion system was controlled at 5% to obtain a stable nano-aluminate calcium carbonate diethyl ether dispersion system.

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