Aragonite fibers and methods for making same, cementitious materials, cementitious articles

Abstract

The application relates to the technical field of inorganic non-metallic materials, in particular to aragonite fibers, a preparation method thereof, a cement-based material and a cement product. The preparation method comprises the following steps: preparing raw materials including calcium ions, urease and urea into a mixed solution to perform a precipitation reaction, so as to obtain aragonite fibers; wherein the mixed solution further comprises at least one of amylose, magnesium ions and sulfate ions, and the temperature of the mixed solution is less than or equal to 50 DEG C. The catalyst promotes the hydrolysis of urea to generate carbonate ions, and then the calcium ions and the carbonate ions generate calcium carbonate precipitation. The amylose, the magnesium ions and the sulfate ions can induce the calcium ions and the carbonate ions to generate aragonite crystals, and inhibit the generation of other polymorphs; on the other hand, the amylose, the magnesium ions and the sulfate ions can induce the aragonite crystals to precipitate in the form of microfibers, promote the generation of rod-shaped fibers, and inhibit the generation of other micro-morphology particles. The prepared aragonite fibers have good microfiber morphology and are not prone to agglomeration, and can be used for reinforcing a cement-based material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic non-metallic materials, and in particular to aragonite fibers, a preparation method thereof, a cement-based material and a cement product. BACKGROUND

[0002] Traditional cement-based materials often face problems such as insufficient durability and poor crack resistance during use, which limits their service life and application range. Existing research has found that adding microfibers can enhance cement-based materials, with good reinforcing effect and low cost. For example, physical mixing method, polypropylene fibers, steel fibers and glass fibers and other microfibers are physically mixed with cement-based materials, but there are problems such as uneven distribution of fibers and insufficient bonding force between fibers and matrix. For example, chemical synthesis method, introducing polymer monomers into cement-based materials for in-situ polymerization reaction to form reinforcing phase, but the reaction conditions are harsh, the process is complex, and the cost is high. For example, microbial mineralization technology, through the induction of calcium carbonate mineral crystallization by urease-positive bacteria and other microorganisms, the performance of cement-based materials can be improved.

[0003] During the microbial mineralization process, the morphology and size of the mineral crystals are difficult to accurately control, which will affect the mechanical properties and durability of the cement-based material. Because calcium carbonate crystals have multiple polymorphs, such as vaterite, aragonite and calcite. Among them, vaterite is very unstable and easily converts into calcite when heated, and calcite is the most stable, but its common micro-morphology is mainly in the form of flaky, blocky aggregates, and vaterite is mainly in the form of spherical aggregates, which cannot be used as microfibers in cement-based materials.

[0004] Although aragonite has the best compatibility with cement-based materials and is slightly more stable than vaterite, it is also in a metastable state and can easily convert into stable calcite, so the existing preparation method is prone to generate a large amount of calcite when preparing aragonite, which reduces the yield of aragonite. Moreover, aragonite also has multiple micro-morphologies, such as rod-shaped (needle-shaped, fibrous), radial, stalactitic, and bean-shaped, and the existing preparation method is difficult to control the generation of aragonite microfibers, which reduces the yield of aragonite fibers. SUMMARY

[0005] The purpose of the present application is to provide aragonite fibers and a preparation method thereof, aiming to solve the technical problem that the existing preparation method is difficult to prepare aragonite fibers.

[0006] Another purpose of the present application is to provide a cement-based material and a cement product, aiming to solve the technical problem that the existing microfibers do not ideally improve the performance of cement-based materials.

[0007] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0008] In a first aspect, the present application provides a preparation method of aragonite fibers, comprising the following steps:

[0009] precipitating the mixed solution to obtain aragonite fibers.

[0010] The mixed solution further comprises at least one of amylose, magnesium ions, and sulfate ions.

[0011] The preparation method of the present application promotes the hydrolysis of urea to generate carbonate ions in the mixed solution through the catalyst, and then the calcium ions generate calcium carbonate precipitates. In addition, at least one of amylose, magnesium ions, and sulfate ions in the mixed solution can induce the formation of aragonite crystals from calcium ions and carbonate ions, and inhibit the formation of other polymorphs such as vaterite and calcite crystals. On the other hand, it can induce the precipitation of aragonite crystals in the form of microfibers, promote the generation of rod-shaped fibers, and inhibit the generation of particles with radial and bean-shaped micro-morphologies, thereby improving the yield of aragonite fibers. At the same time, the temperature of the mixed solution is controlled to reduce the conversion of aragonite crystals to calcite crystals and improve the yield of aragonite fibers. Therefore, the preparation method of the present application is controllable, the yield of aragonite fibers prepared is high, has a good microfiber morphology, has a large aspect ratio and a small specific surface area, and has a small internal stress. Therefore, the prepared aragonite fibers are not easy to agglomerate and can be used to reinforce cement-based materials.

[0012] In a second aspect, the present application provides aragonite fibers prepared by the preparation method of the present application.

[0013] The aragonite fibers of the present application are aragonite crystals, have good compatibility with cement-based materials, and are in the form of microfibers, have a high aspect ratio and a small specific surface area in size, have a small cohesive force, and are well dispersed and not easy to agglomerate into large particles. When used in cement-based materials, the aragonite fibers of the present application can significantly play the modification effect of microfibers and improve the crack resistance. At the same time, the chemical composition of the aragonite fibers is mainly calcium carbonate, which can improve the workability and strength as an admixture. In summary, the aragonite fibers of the present application can improve the mechanical strength, toughness, and durability of cement-based materials.

[0014] In a third aspect, the present application provides a cement-based material comprising a cement material and aragonite fibers prepared by the preparation method of the present application or aragonite fibers of the present application.

[0015] The aragonite fibers in the cement-based material of the present application have good compatibility with the cement material, and the rod-shaped aragonite fibers are not easy to be adsorbed and aggregated into large particles, and have good dispersibility, and can be uniformly distributed in the cement material. Therefore, the cement-based material can fully exert the modification effect of the fibers on the cement material, and improve the crack resistance. At the same time, the chemical composition of the aragonite fiber is mainly calcium carbonate, which can improve the workability and strength as an admixture. In summary, the cement-based material of the present application has high mechanical strength, crack resistance and durability.

[0016] In a fourth aspect, the present application provides a cement product, which is prepared by hydrating the cement-based material of the present application.

[0017] The cement product of the present application is prepared by hydrating the cement-based material described above. The aragonite fibers act as nucleation sites for the hydration products of cement, which can accelerate the hydration of cement and promote the formation of cement hydration products, thereby improving the mechanical properties thereof. After the cement material hardens, the aragonite fibers are uniformly filled and combined in the cement product. When the cement product is subjected to external tensile force, pressure and bending force, these aragonite fibers can cooperate with the solidified cement to absorb and migrate stress, thereby further improving the mechanical strength of the cement product, especially the tensile, compressive and bending properties. Moreover, these aragonite fibers form a three-dimensional network distribution in the cement product, which can effectively reduce the generation of microcracks in the cement product. When the cement product is subjected to a large stress to generate fine cracks, the aragonite fibers are bridged at the crack sites to prevent the crack from further growing and propagating, thereby further improving the toughness and crack resistance of the cement product. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 is a 2000 times magnification SEM image of the aragonite fiber of Example A1 of the present application;

[0020] Figure 2 is a 10000 times magnification SEM image of the aragonite fiber of Example A1 of the present application;

[0021] Figure 3 is a 2000 times magnification SEM image of calcite of Comparative Example A1 of the present application;

[0022] Figure 4 is a 10000 times magnification SEM image of calcite of Comparative Example A1 of the present application;

[0023] Figure 5is a 2000 times magnification SEM image of the ball vaterite of Comparative Example A1 of the present application;

[0024] Figure 6 is a 10000 times magnification SEM image of the ball vaterite of Comparative Example A1 of the present application. DETAILED DESCRIPTION

[0025] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application more clearly understood, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application.

[0026] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent the following three cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects.

[0027] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one" or similar expressions mean any combination of these items, including any combination of single item or multiple items.

[0028] It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence. The execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0029] The weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass in the specification of the embodiments of the present application can be μg, mg, g, kg and other mass units commonly known in the chemical field.

[0030] The terms "first", "second", etc. are only used for descriptive purposes and are used to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features limited by "first" and "second" can explicitly or implicitly include one or more of the features.

[0031] The concentration in the present application is mass concentration, for example, the calcium ion concentration of 3% represents that the mass of calcium ion accounts for 3% of the mass of the whole solution.

[0032] The first aspect of the embodiment of the present application provides a preparation method of aragonite fibers, comprising the following steps S10:

[0033] S10. Preparing a mixed solution by mixing raw materials including calcium ions, urea and a catalyst, and performing a precipitation reaction to obtain aragonite fibers;

[0034] In the mixed solution, at least one of amylose, magnesium ions and sulfate ions is further included, and the temperature of the mixed solution is ≤50°C.

[0035] The preparation method of the embodiment of the present application promotes the hydrolysis of urea to generate carbonate ions in the mixed solution by the catalyst, and then the calcium ions and the carbonate ions generate calcium carbonate precipitates. At least one of amylose, magnesium ions and sulfate ions included in the mixed solution can induce the generation of aragonite crystals from calcium ions and carbonate ions, and inhibit the generation of other polymorphs such as vaterite and calcite crystals. On the other hand, it can induce the precipitation of aragonite crystals in the form of microfibers, promote the generation of rod-shaped fibers, and inhibit the generation of particles in the form of radial and bean-shaped microstructures, thereby improving the yield of aragonite fibers. At the same time, the temperature of the mixed solution is controlled to reduce the conversion of aragonite crystals to calcite crystals and improve the yield of aragonite fibers. Therefore, the preparation method of the embodiment of the present application is controllable, the yield of aragonite fibers prepared is high, has a good microfiber morphology, has a large aspect ratio, a small specific surface area and internal stress, and therefore, the prepared aragonite fibers are not easy to agglomerate and can be used to reinforce cement-based materials.

[0036] Regarding calcium ions:

[0037] The concentration of calcium ions in the mixed solution directly affects the nucleation and growth rate of calcium carbonate aragonite crystals. In some embodiments, the concentration of calcium ions in the mixed solution is 0.5 mol / L-2.0 mol / L, which can include but is not limited to any value or range between any two values of 0.5 mol / L, 1.0 mol / L, 1.5 mol / L and 2.0 mol / L. The above-mentioned concentration of calcium ions is conducive to inducing the formation of microfibers and improving the yield of aragonite fibers. If the concentration of calcium ions is too low, it may promote the generation of small nanoscale calcium carbonate particles and reduce the yield of aragonite fibers, and if the concentration is too high, it may lead to the formation of larger size crystal particles and reduce the yield of aragonite fibers in the form of microfibers.

[0038] The source of calcium ions can be a common soluble calcium salt, such as calcium chloride, etc. dissolved in the mixed solution, or extracted from common industrial solid waste, such as extracted from waste concrete with hydrochloric acid, or extracted from industrial solid waste such as phosphogypsum, steel slag, and recycled micro powder, etc. with water, hydrochloric acid, sodium hydroxide solution, ammonium chloride solution, etc. as solvent or extraction solution for secondary extraction treatment. During extraction, the solid-liquid mass ratio of industrial solid waste to extraction solution can be 1:(1-10). The extraction can be carried out at room temperature. After mixing the solid-liquid, stirring for 6-12 hours, and then filtering to retain the upper clear liquid, a solution containing calcium ions is obtained.

[0039] Regarding urea:

[0040] Urea can undergo hydrolysis reaction under the action of a catalyst to generate ammonia and carbon dioxide, and obtain carbonate ions in the solution, which further react with calcium ions to promote the nucleation and growth of calcium carbonate crystals and further generate precipitates. In some embodiments, the concentration of urea in the mixed solution is 0.5 mol / L-2.0 mol / L, which can include but is not limited to 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, or any range between any two of the values. The above concentration of urea is beneficial to induce the formation of microfibers and improve the yield of aragonite fibers. If the concentration of urea is too low, too little precipitate is generated, and if the concentration is too high, amorphous calcium carbonate may be generated, which is unstable in nature and reduces the yield of aragonite crystals.

[0041] Regarding catalyst:

[0042] The catalyst can cause urea to undergo hydrolysis reaction in the solution to obtain carbonate ions, and further generate calcium carbonate precipitates. The catalyst can include urease, which has high specificity and can catalyze the hydrolysis of urea into ammonia and carbonate ions. The urease can be microbial urease, which is provided by microorganisms such as Bacillus pasteurii and Bacillus subtilis. The urease can also be extracted from animals and plants, and can be extracted from plants such as jack beans and soybeans for first extraction treatment. The first extraction treatment method can use water to extract by centrifugation. Specifically, the soybeans can be weighed and dried at room temperature, crushed using a crushing device, and the crushed soybean powder can be sieved. The sieved soybean powder can be mixed with deionized water and stirred thoroughly to obtain a soybean powder solution. The solution can be centrifuged using a centrifuge at a temperature of 20°C and a speed of 4000 r / min. The bottom sediment after centrifugation can be discarded, and the filtered upper clear liquid can be retained to obtain a solution containing soybean urease.

[0043] In some embodiments, the concentration of the catalyst in the mixed solution is 20 g / L to 50 g / L. Any value or range between any two values can be included, such as 20 g / L, 30 g / L, 40 g / L, 50 g / L. The above concentration of the catalyst is conducive to catalyzing the generation of carbonate ions with a suitable concentration of urea, improving the nucleation rate and growth rate of calcium carbonate crystals, inducing the generation of microfibers, and improving the yield of aragonite fibers. If the concentration of the catalyst is too low, too little precipitation is generated, and if the concentration is too high, amorphous calcium carbonate may be generated, which is unstable in nature and reduces the yield of aragonite crystals.

[0044] Compared with the uncontrollability of direct precipitation with calcium ions and carbonate ions, the preparation method of the present application induces the generation of calcium carbonate crystals through precipitation reactions of calcium ions, urea, and catalysts, which belongs to mineralization reactions. The reaction conditions can be better controlled to regulate the generation of aragonite fibers. Since the concentrations of the above-mentioned calcium ions, urea, and catalysts all affect the nucleation rate and growth rate of calcium carbonate crystals and the generation of aragonite fibers, the ratio of the three can be controlled to improve the effect of the reaction. In some embodiments, the mass ratio of calcium ions, urea, and catalysts in the mixed solution is 1:(0.5-2):(1-5). In exemplary embodiments, any ratio or range between any two ratios can be included, such as 1:(0.5 or 1 or 2):(1 or 2 or 3 or 5). These ratios of raw materials are conducive to improving the yield of aragonite fibers.

[0045] In some embodiments, in order to uniformly mix the solutes in the mixed solution for precipitation reaction, the solutes can be optionally prepared into solutions and then mixed into a mixed solution. The concentration of the calcium ion solution can be 0.5 mol / L to 2.0 mol / L, the concentration of the catalyst solution can be 20 g / L to 50 g / L, and the concentration of the urea solution can be 0.5 mol / L to 2.0 mol / L. Then, the calcium ion solution, the catalyst solution, and the urea solution are mixed in a volume ratio of 1:(0.5-2):(1-5) for precipitation reaction.

[0046] Regarding amylose, magnesium ions, and sulfate ions:

[0047] At least one of the three components can act as a crystal form stabilizer in the precipitation reaction, which is conducive to inducing the generation of aragonite crystals from calcium ions and carbonate ions during the precipitation reaction and inhibiting the generation of other polymorphs such as vaterite and calcite crystals; it is also conducive to inducing the precipitation of aragonite crystals in the form of microfibers and promoting the generation of rod-shaped fibers to improve the yield of aragonite fibers. If the above-mentioned crystal form stabilizer is absent, a large amount of vaterite and calcite crystals may be generated, and the generated aragonite crystals are also prone to generating various shapes such as radial, stalactite, and bean-shaped, thereby reducing the yield of aragonite fibers in the form of microfibers.

[0048] The components can be added to the mixed solution together with raw materials such as calcium ions during the mixing process, and one of amylose, magnesium ions, sulfate ions, or any two or all of them can be added.

[0049] In some embodiments, when the mixed solution contains amylose, the concentration of amylose is 2% to 5%, which is a mass ratio concentration. Amylose can be extracted from plants such as corn and beans. The extraction method can refer to the method of extracting urease from soybeans in the above description. When extracting from soybeans, not only urease but also amylose can be extracted, which can promote the formation of aragonite fibers in the precipitation reaction and improve the yield.

[0050] In some embodiments, when the mixed solution contains magnesium ions, the concentration of magnesium ions is 0.01 mol / L to 0.1 mol / L, and magnesium ions can be provided by adding soluble magnesium salts such as magnesium chloride and magnesium sulfate to the mixed solution. In some embodiments, when the mixed solution contains sulfate ions, the concentration of sulfate ions is 0.01 mol / L to 0.1 mol / L, and sulfate ions can be provided by adding soluble sulfate salts to the mixed solution. In addition, the method of extracting from phosphogypsum described above can be used to extract calcium ions and sulfate ions from phosphogypsum.

[0051] In some embodiments, the temperature of the mixed solution is ≤50℃, to prevent the aragonite crystals from converting to stable calcite crystals due to high temperature. Further, the temperature of the mixed solution is 20 to 50℃, which can be any one of 20℃, 30℃, 40℃, 50℃, or a range between any two of them. Limiting the temperature of the mixed solution to the above range can promote the activity of the catalyst, improve the nucleation rate and growth rate of the calcium carbonate crystals, and improve the stability of the aragonite fibers generated in the precipitation reaction. If the temperature is too high, it may promote the conversion of aragonite crystals to stable calcite, reducing the yield of aragonite fibers.

[0052] In some embodiments, the precipitation reaction time is 1 to 3 hours, which can be any one of 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or a range between any two of them. The above reaction time is conducive to inducing the nucleation and growth of calcium carbonate, and improving the yield of aragonite fibers. If the reaction time is too long, it may promote the formation of larger calcium carbonate crystal structures, and also promote the conversion of aragonite crystals to stable calcite crystals.

[0053] After the above precipitation reaction is completed, the aragonite fibers can be obtained by solid-liquid separation. The aragonite fibers prepared by the above method have a needle-like rod-shaped microfiber structure, a high aspect ratio, and a small specific surface area, and are well dispersed and not easily agglomerated. When used in cement-based materials, it can significantly improve the mechanical properties of the cement-based materials.

[0054] The second aspect of the embodiment of the present application provides aragonite fibers, which are prepared by the preparation method of the embodiment of the present application.

[0055] The aragonite fibers of the embodiment of the present application are aragonite crystals, which have good compatibility with cement-based materials and are in the form of microfibers, have a high aspect ratio and a small specific surface area in size, and thus have small cohesion and good dispersibility and are not easy to be aggregated into large particles. When used in cement-based materials, the aragonite fibers can significantly play the modification effect of microfibers and improve the crack resistance. Meanwhile, the aragonite fibers mainly contain calcium carbonate, which can improve the working performance and strength as an admixture. In summary, the aragonite fibers of the embodiment of the present application can improve the mechanical strength, toughness and durability of cement-based materials.

[0056] As an embodiment of the present application, the SEM image of the aragonite fibers amplified by 2000 times is shown in FIG. 2, and the SEM image amplified by 10000 times is shown in FIG. 3. Figure 1 Figure 2 As can be seen from FIG. 2 and FIG. 3, the aragonite fibers are in the form of rod-shaped microfibers, have clear shapes and almost no aggregation and entanglement. Figure 1 Figure 2 As can be seen from FIG. 2 and FIG. 3, the aragonite fibers are in the form of rod-shaped microfibers, have clear shapes and almost no aggregation and entanglement.

[0057] The aragonite fibers have an aspect ratio of (3-6):1, which can include but is not limited to any one of 3:1, 4:1, 5:1, 6:1 or a range between any two of them, and form the shape of rod-shaped microfibers. Compared with shapes with a smaller aspect ratio, the rod-shaped microfibers are more likely to be aggregated into secondary particles. The rod-shaped microfibers with the aspect ratio are more likely to be uniformly dispersed and not easy to be aggregated, which is beneficial to the uniform dispersion in the cement matrix. The length of the aragonite fibers can be 7-15 μm, which can include but is not limited to any one of 7 μm, 8 μm, 10 μm, 15 μm or a range between any two of them.

[0058] In some embodiments, the specific surface area of the aragonite fibers is 0.3-0.5 m 2 / g, which can include but is not limited to any one of 0.3 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g or a range between any two of them. Compared with micro shapes such as spherical and flaky shapes with a high specific surface area, the rod-shaped aragonite with a relatively small specific surface area has a weak surface adsorption force and is not easy to be adsorbed and aggregated together. Therefore, the rod-shaped aragonite is more likely to be dispersed when applied in cement-based materials.

[0059] The third aspect of the embodiment of the present application provides a cement-based material, which comprises a cement material and aragonite fibers prepared by the preparation method of the embodiment of the present application or the aragonite fibers of the embodiment of the present application.

[0060] ​​The aragonite fibers in the cement-based material of the embodiments of the present application have good compatibility with the cement material, and the rod-shaped aragonite fibers are not prone to be adsorbed and aggregated into large particles, and have good dispersibility, and can be uniformly distributed in the cement material. Therefore, the cement-based material can fully exert the modification effect of the fibers on the cement material, and improve the crack resistance. Meanwhile, the chemical composition of the aragonite fibers is mainly calcium carbonate, and as an admixture, the aragonite fibers can improve the workability and improve the strength. In summary, the cement-based material of the embodiments of the present application has high mechanical strength, crack resistance and durability.

[0061] In some embodiments, the mass ratio of the cement material to the aragonite fibers is (2-4):1, which can include but is not limited to any one of 2:1, 2.5:1, 3:1, 4:1 or a range between any two of them. In addition, the cement-based material can also include aggregate, auxiliary cementitious material, water reducing agent and other components, which are mixed in a reasonable ratio. The raw materials can also contain magnesium ions and sulfate ions, which can further inhibit the conversion of aragonite fibers to calcite. When the cement-based material is mixed with water to prepare a slurry, the water-cement ratio can be (2-4):1. Since the aragonite fibers have a rod-shaped structure, they have better fluidity in the cement slurry, which further facilitates the uniform dispersion of the aragonite fibers in the cement slurry.

[0062] The fourth aspect of the embodiments of the present application provides a cement product, which is prepared by hydrating the cement-based material of the above embodiments of the present application.

[0063] The cement product of the embodiments of the present application is prepared by hydrating the cement-based material described above. The aragonite fibers act as nucleation sites for the hydration products of cement, which can accelerate the hydration of cement and promote the formation of cement hydration products, thereby improving the mechanical properties thereof. After the cement material hardens, the aragonite fibers are uniformly filled and combined in the cement product. When the cement product is subjected to external tensile force, pressure or bending force, these aragonite fibers can cooperate with the solidified cement to absorb and migrate the stress, thereby further improving the mechanical strength of the cement product, especially the tensile, compressive and bending properties. Furthermore, the aragonite fibers form a three-dimensional network distribution in the cement product, which can effectively reduce the generation of microcracks in the cement product. When the cement product is subjected to a large stress and generates small cracks, the aragonite fibers bridge across the cracks to prevent the cracks from further growing and propagating, thereby further improving the toughness and crack resistance of the cement product.

[0064] Under normal cement hydration exothermic conditions, the calcium carbonate crystal form will not be greatly affected, but in order to reduce the conversion of aragonite fibers to calcite and better avoid the possible influence of cement hydration exothermic, mineral admixtures such as fly ash, silica fume or slag can be introduced, which can effectively reduce the hydration heat and improve the long-term strength and durability of the concrete. Or wet curing can be used to effectively reduce temperature fluctuations and make the hydration reaction of the cement more stable.

[0065] In some embodiments, the cement-based material described above can be cast into a mold, cured in a standard curing room for 28 days, and the curing environment temperature is controlled at 10-25℃ during the curing process to prevent the heat released by the hydration reaction from converting the aragonite fibers into calcite, ensuring that the aragonite fibers continue to play a modifying role of microfibers and improve the crack resistance of the cement product. The 7d flexural strength can reach 9.6MPa.

[0066] The following will be described in conjunction with specific embodiments.

[0067] Embodiment A1

[0068] This embodiment provides aragonite fibers and a preparation method thereof, comprising the following steps:

[0069] S1. Extraction of calcium ions and sulfate ions:

[0070] Phosphogypsum and water are mixed according to a solid-liquid mass ratio of 1:4, and left to stand at room temperature for 1h. After filtration, the supernatant is reserved to obtain a calcium ion solution, and the concentration of calcium ions is measured to be 1.5mol / L, which also contains a small amount of sulfate ions.

[0071] S2. Extraction of biological urease and amylose:

[0072] 30g of soybeans are weighed and dried at room temperature, and an electric pulverizer is used to pulverize the soybeans. After pulverization, the soybean powder is passed through a 100-mesh sieve. The filtered soybean powder is mixed with 1L of deionized water, and a magnetic stirrer is used to fully stir for 15min. The stirred soybean powder solution is centrifuged for 30min using a centrifuge, with the temperature of the centrifuge controlled at 20℃ and the rotation speed at 4000r / min. The bottom precipitate after centrifugation is discarded, and the supernatant is filtered to obtain a soybean urease solution, i.e., a biological urease solution, which has a soybean urease concentration of 30g / L and also contains amylose.

[0073] S3. Preparation of aragonite fibers through precipitation reaction:

[0074] A urea solution with a concentration of 0.5mol / L is provided, and the calcium ion solution obtained in step S1, the biological urease solution obtained in step S2, and the urea solution are mixed according to a volume ratio of 1:1:2 to obtain a mixed solution. The mixed solution is subjected to a precipitation reaction at room temperature for 2h, and after being filtered again, the generated precipitate is rod-shaped aragonite.

[0075] Embodiment A2

[0076] This embodiment provides aragonite fibers and a preparation method thereof, which are different from those of embodiment A1 only in that the solid-liquid mass ratio of phosphogypsum to water in step S1 is changed from 1:4 to 1:10, and the others are the same.

[0077] Embodiment A3

[0078] This embodiment provides aragonite fibers and a preparation method thereof, which is different from that of Example A1 only in that the soybean raw material in step S2 is weighed to be 20 g, and the concentration of the soybean urease solution obtained is 20 g / L, and the others are the same.

[0079] Example A4

[0080] This embodiment provides aragonite fibers and a preparation method thereof, which is different from that of Example A1 only in that the concentration of the urea solution selected in step S3 is changed to 1 mol / L, and the others are the same.

[0081] Example A5

[0082] This embodiment provides aragonite fibers and a preparation method thereof, which is different from that of Example A1 only in that the phosphogypsum extraction in step S1 is not used, but a calcium chloride solution with the same calcium ion concentration is provided instead, and the solution does not contain sulfate ions, and the others are the same.

[0083] Example A6

[0084] This embodiment provides aragonite fibers and a preparation method thereof, which is different from that of Example A1 only in that the phosphogypsum extraction in step S1 is not used, but a pure calcium chloride solution with a concentration of 1.5 mol / L is provided instead, and the solution does not contain sulfate ions.

[0085] In step S2, a commercially available pure biological urease solution is used instead, and the concentration is the same, which is 15 g / L, and the solution does not contain amylose.

[0086] In step S3, when the mixed solution is mixed, a magnesium chloride solution is also added to the mixed solution, so that the concentration of magnesium ions in the final mixed solution is 0.5 mol / L, and the others are the same.

[0087] Comparative Example A1

[0088] This comparative example is different from Example A1 only in that the room temperature in step S3 is changed to 70°C, and the others are the same, and calcite is prepared in the last step S3.

[0089] Comparative Example A2

[0090] This comparative example is different from Example A1 only in that the calcium ion solution in step S1 is not extracted by phosphogypsum, but is directly changed to a pure calcium chloride solution with a concentration of 1.5 mol / L, and in step S2, the soybean urease is changed to a commercially available pure urease, which does not contain amylose, and the others are the same, and in the last step S3, vaterite is prepared.

[0091] Comparative Example A3

[0092] This comparative example is different from Example A6 only in that the magnesium chloride solution added in step S3 is changed to a sodium chloride solution with the same amount and concentration, and the others are the same, and in the last step S3, vaterite is prepared.

[0093] Correlation performance test and result analysis

[0094] The products prepared from the aragonite fibers provided by the above-mentioned Examples A1 to A6 and the products prepared from the Comparative Examples A1 to A3 were respectively analyzed by scanning electron microscopy to obtain SEM images, wherein the 2000 times magnified image of the aragonite fibers of Example A1 is shown in Figure 1 , the 10000 times magnified image is shown in Figure 2 ; the 2000 times magnified image of the vaterite of Comparative Example A1 is shown in Figure 3 , the 10000 times magnified image is shown in Figure 4 ; the 2000 times magnified image of the calcite of Comparative Example A2 is shown in Figure 5 , the 10000 times magnified image is shown in Figure 6 .

[0095] Figure 1 , Figure 2 As can be seen from the above-mentioned SEM images, the aragonite fibers of Example A1 have a rod-like microstructure, a high aspect ratio, and are uniformly distributed without local agglomeration and adsorption into large particles. Figure 3 , Figure 4 As can be seen from the above-mentioned SEM images, the calcite of Comparative Example A1 has a flaky microstructure and is locally agglomerated and adsorbed into secondary particles. Figure 5 , Figure 6 As can be seen from the above-mentioned SEM images, the vaterite of Comparative Example A2 has a spherical microstructure and is locally agglomerated and adsorbed into secondary particles.

[0096] Examples A1 to A4 all have sulfate ions and amylopectin as crystal form stabilizers, Example A5 has only amylopectin as a crystal form stabilizer compared with Example A1, Example A6 has only magnesium ions as a crystal form stabilizer compared with Example A1, and Comparative Example A3 differs from Example A6 only in the absence of magnesium ions and the absence of aragonite fibers, which shows that chloride ions do not have a crystal form stabilizing effect and confirms the role of magnesium ions. It can be seen that sulfate ions, amylopectin, and magnesium ions all contribute to the formation of aragonite fibers.

[0097] Cement-based material and cement product examples:

[0098] The products prepared from the aragonite fibers provided by the above-mentioned Examples A1 to A6 and the products prepared from the Comparative Examples A1 to A3 were respectively prepared into cement mortar according to the following mass ratio:

[0099]

[0100]

[0101] Then, casting and molding were performed, and the cement products were obtained after curing in a curing room for 28 days at a temperature of 20℃.

[0102] In the formula, the aragonite fibers of Example A1 are used to prepare the cement product of Example B1, the aragonite fibers of Example A2 are used to prepare the cement product of Example B2, and so on until the calcite of Comparative Example A1 is used to prepare the cement product of Comparative Example B1, the vaterite of Comparative Example A2 is used to prepare the cement product of Comparative Example B2, and the vaterite of Comparative Example A3 is used to prepare the cement product of Comparative Example B3.

[0103] Mechanical strength test

[0104] The cement products of Examples B1 to B6 and Comparative Examples B1 to B3 are subjected to performance tests. The cement products are all test blocks with a size of 40 cm x 40 cm x 160 cm, and in order to reduce errors, 3 test block samples are provided for each example or comparative example, and the average of the test results is taken as the test result of the example or comparative example.

[0105] The cement mortar samples maintained for 7 days are tested on a YYW-300DS cement compression and bending strength integrated machine. The equivalent compressive strength and bending strength tests are carried out under the conditions of a loading rate of 0.6 KN / s and 20 N / s. The test results are recorded in Table 1 below.

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from Table 1, by carrying out a precipitation reaction with a mixed solution containing calcium ions, urea and urease, the amylose, magnesium ions and sulfate ions in the mixed solution are conducive to inducing the formation of aragonite crystals, and in combination with temperature control, the generation of vaterite and calcite is reduced. The generated aragonite crystals are in the form of microfibers, which are conducive to improving the crack resistance of cement-based materials.

[0110] The crack resistance of each test block is evaluated by the above bending strength test. Comparative Example B1 is a test block prepared from calcite, so the compressive strength of the test block is high, but the bending strength is significantly lower than that of all the test blocks prepared from aragonite fibers, and does not have high crack resistance. Comparative Examples B2 and B3 are test blocks prepared from vaterite, and the compressive performance is lower than that of the test blocks prepared from aragonite fibers, and the bending performance is significantly lower, so compared with the performance comparison of Comparative Examples B1 to B3 in which vaterite or calcite is added to cement-based materials, aragonite fibers significantly improve the crack resistance and other mechanical properties of cement-based materials.

[0111] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing aragonite fibers, characterized by, The method comprises the following steps: The raw materials including calcium ions, urea and a catalyst are prepared into a mixed solution to carry out a precipitation reaction, so as to obtain aragonite fibers; The mixed solution further comprises at least one of amylose, magnesium ions and sulfate ions, and the temperature of the mixed solution is ≤50℃; When the mixed solution contains the amylose, the concentration of the amylose is 2%-5%; When the mixed solution contains the magnesium ions, the concentration of the magnesium ions is 0.01 mol / L-0.1 mol / L; When the mixed solution contains the sulfate ions, the concentration of the sulfate ions is 0.01 mol / L-0.1 mol / L; The catalyst comprises urease, and at least one of the urease and the amylose is obtained by a first extraction treatment of soybeans; The first extraction treatment comprises the following steps: crushing the soybeans to obtain soybean powder, mixing the soybean powder with deionized water to obtain a soybean powder solution, centrifuging and filtering to obtain supernatant, and obtaining a solution containing soybean urease; At least one of the calcium ions and the sulfate ions is obtained by a second extraction treatment of phosphogypsum.

2. The method of claim 1, wherein: In the mixed solution, the mass ratio of the calcium ions, the catalyst and the urea is 1:(0.5-2):(1-5); And / or, in the mixed solution, the concentration of the calcium ions is 0.5 mol / L-2.0 mol / L; And / or, in the mixed solution, the concentration of the urea is 0.5 mol / L-2.0 mol / L; And / or, in the mixed solution, the concentration of the catalyst is 20 g / L-50 g / L.

3. The production method according to claim 1 or 2, characterized by: The temperature of the mixed solution is 20-50℃; And / or, the time of the precipitation reaction is 1-3 h.

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