A highly active calcium-magnesium composite crack-resistant agent and its preparation method using microwave-induced assisted heating.

Abstract

This invention discloses a highly active calcium-magnesium composite crack-resistant agent and its preparation method using microwave-induced assisted heating. The raw materials include dolomite powder, serpentine powder, and a complexing agent. The mass ratio of dolomite powder to serpentine powder is 2-3:1. The molecular weight ratio of the complexing agent is 1-2:1 for the total number of Mg²⁺ and Ca²⁺ ions in the dolomite powder and serpentine powder, respectively. The dolomite powder is obtained by high-temperature calcination, digestion, and acidification followed by grinding. The serpentine powder is obtained by grinding serpentine. The complexing agent is one or a combination of several of the following: citric acid, lecithin, starch, and urea. This invention utilizes abundant and inexpensive dolomite and serpentine. Through grinding, digestion, dissolution, and acidification processes, and by adding a complexing agent, a precursor is prepared. The precursor is then treated using microwave-assisted heating. Compared to traditional calcination methods, this significantly reduces calcination temperature and time, lowers energy consumption, and reduces waste emissions, while also resulting in superior product performance.

Description

Technical Field

[0001] This invention relates to the field of building materials technology. More specifically, this invention relates to a highly active calcium-magnesium composite crack-resistant agent and its preparation method using microwave-induced assisted heating. Background Technology

[0002] Shrinkage cracks are a common problem in large-volume concrete structures such as bridge abutments, tower bases, and tower columns, severely impacting the quality of bridge projects. Early shrinkage cracks in large-volume concrete are primarily caused by the self-generated shrinkage deformation of the concrete and shrinkage deformation induced by temperature stress. A common crack control method for addressing the self-generated shrinkage deformation of concrete is to use crack-resistant agents to compensate for shrinkage and reduce shrinkage stress, thereby lowering the risk of cracking. Expansion sources for crack-resistant agents include calcium oxide, calcium sulfoaluminate, and magnesium oxide. Among these, calcium oxide exhibits strong temperature sensitivity during hydration expansion, primarily expanding in the early stages of hydration; the hydration expansion of sulfoaluminate expansive agents also mainly occurs during the temperature rise stage, with limited shrinkage compensation during the temperature drop stage. Highly active magnesium oxide possesses strong expansion properties; concrete incorporating magnesium oxide crack-resistant agents shows slow early expansion development, but its expansion performance continues to develop in the later stages, achieving shrinkage compensation during the temperature drop stage. Therefore, in recent years, calcium-magnesium composite crack-resistant agents have been developed, generating micro-expansion throughout the entire concrete hydration process, achieving controllable expansion history. This approach has been widely adopted in water conservancy and bridge engineering projects.

[0003] The hydration activity of magnesium oxide is the most significant factor affecting its expansion performance, and its hydration activity is related to its degree of sintering (crystal integrity). Re-burned (dead-burned) magnesium oxide and sintered magnesium oxide lose their activity due to their complete crystal structure. Therefore, magnesium oxide used in crack-resistant agents should have high activity, small particle size, and incomplete crystal structure, and should be combined with calcium oxide-based expansion sources to prepare calcium-magnesium composite crack-resistant agents. The common method for preparing calcium-magnesium composite crack-resistant agents is high-temperature calcination, including one-step and two-step calcination methods, using equipment such as rotary kilns, fluidized bed furnaces, and vertical kilns. However, high-temperature calcination consumes large amounts of coal or fuel oil, generating significant amounts of harmful gases and solid waste emissions. Furthermore, traditional calcination methods cannot effectively penetrate the mineral's interior, gradually transferring heat from the surface to the interior, resulting in high energy consumption, uneven product distribution, and environmental damage.

[0004] Therefore, in view of the high energy consumption and high pollution in the current production process of calcium-magnesium composite crack-resistant agents, the problem of "cold center" can be solved by using inexpensive dolomite and serpentine tailings and microwave radiation-induced auxiliary heating. This allows for the preparation of highly active and homogeneous calcium-magnesium composite products at lower temperatures and in a shorter time, thereby reducing the production cost of crack-resistant agents. This has positive significance for energy conservation, emission reduction, and the promotion and application of green environmental protection. Summary of the Invention

[0005] The purpose of this invention is to provide a highly active calcium-magnesium composite crack-resistant agent and its preparation method using microwave-induced assisted heating. The method uses dolomite and serpentine, which are abundant and inexpensive, and prepares precursors through grinding, digestion, dissolution, acidification, and the addition of complexing agents. The precursors are then treated by microwave-assisted heating. Compared with traditional calcination methods, this method can significantly reduce calcination temperature and time, reduce energy consumption, reduce waste emissions, and improve product performance.

[0006] The technical solution adopted by the present invention to solve this technical problem is: to provide a highly active calcium-magnesium composite crack-resistant agent, the raw materials of which include: dolomite powder, serpentine powder and complexing agent, wherein the mass ratio of dolomite powder to serpentine powder is 2~3:1, and the molecular number of the complexing agent is: the total number of Mg²⁺ and Ca²⁺ ions in dolomite powder and serpentine powder is 1~2:1;

[0007] The dolomite powder is obtained by grinding dolomite after high-temperature calcination, digestion and acidification treatment. The serpentine powder is obtained by grinding serpentine. The complexing agent is one or a combination of citric acid, lecithin, starch and urea.

[0008] Preferably, in the highly active calcium-magnesium composite crack-resistant agent, the dolomite is high-purity dolomite, wherein the calcium-magnesium content is 1:1, the silicon content is ≤2%, the aluminum content is ≤0.5%, the iron content is ≤0.2%, and the titanium content is ≤0.2%.

[0009] Preferably, in the highly active calcium-magnesium composite crack-resistant agent, the serpentine contains ≥36% magnesium, ≥36% silicon, ≤2.5% calcium, and ≤1% iron.

[0010] Preferably, in the highly active calcium-magnesium composite anti-cracking agent, the citric acid is a 10% (w / w) citric acid solution made by mixing white crystalline citric acid powder with water, wherein the purity of the white crystalline citric acid powder is not less than 99%.

[0011] Preferably, in the highly active calcium-magnesium composite anti-cracking agent, the ovogloss is composed of phosphatidylcholine, cephalin, inositol phospholipid and sphingomyelin, wherein the content of phosphatidylcholine is ≥22%.

[0012] This invention also provides a microwave-induced assisted heating preparation method using the above-mentioned highly active calcium-magnesium composite anti-cracking agent, comprising the following steps:

[0013] S1: Prepare the raw materials according to any one of claims 1 to 5 for the high-activity calcium-magnesium composite anti-cracking agent. After screening the dolomite mineral, calcine it at 800-900℃, cool it, grind it into 10-40μm particles, add deionized water, stir evenly, and dry, cool, crush and filter it after no precipitate is generated. Grind the remaining material after filtration into 10-40μm particles, add dilute nitric acid solution to fully dissolve it, and dry it to obtain dolomite powder. Grind serpentine into 10-40μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 2-3:1, add a complexing agent according to the proportion, mix and add to the ball mill, grind at room temperature for 30 minutes to obtain a microwave-assisted heating precursor.

[0014] S2: A microwave-induced auxiliary heating device is used, which uses ceramic or carbon fiber as the heat-absorbing carrier and corundum crucible as the sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 2~3GHz and a power of 4000~8000W and microwaved for 10~30 minutes. The precursor is processed by industrial microwave-assisted heating.

[0015] S3: The precursor treated as described above is calcined at 400℃~600℃ and held at that temperature for 1-2 hours to obtain the final product.

[0016] Preferably, in the microwave-induced assisted heating preparation method, in step S1, the concentration of the dilute nitric acid solution is 1 mol / L.

[0017] Preferably, in the microwave-induced assisted heating preparation method, in step S1, the step of adding dilute nitric acid solution to fully dissolve the product involves:

[0018] The molar ratio of the dilute nitric acid solution to the deionized dolomite is 1:2~3.

[0019] Preferably, in the microwave-induced assisted heating preparation method, in step S2, the ceramic is selected from one or more of SiC, TiO2, and ZrO2 ceramics.

[0020] Preferably, in the microwave-induced assisted heating preparation method, the microwave-induced assisted heating device further includes glass fiber cotton wrapped around the corundum crucible.

[0021] The present invention has at least the following beneficial effects:

[0022] 1. Acid-treated digested dolomite is mixed with milled serpentine to form a molecular-level solid-solid interface. The addition of citric acid has three main functions: (1) as a coordination complexing agent for the solid-solid reaction; (2) as fuel to obtain the energy required for the synthesis of magnesium oxide and calcium oxide during the heat treatment process, making it easier to form the composite crack-resistant agent; (3) the combustion of citric acid produces a large amount of gas, which expands and loosens the reaction system, hinders the bonding and growth of MgO crystals, and improves the activity of MgO. Other organic complexing agents are added to promote the formation of products. The above material types and ratios ensure the synthesis of highly active calcium-magnesium composite crack-resistant agents at lower temperatures, greatly reducing the calcination temperature and calcination time for the synthesis of magnesium oxide, reducing the production difficulty, and improving product quality.

[0023] 2. Microwave-assisted heating of precursors. Since magnesium nitrate and calcium nitrate are good microwave heat absorbers, the paste obtained by grinding can be directly microwave-heated to obtain powdered precursors, or SiC can be used as a heat absorber, and a corundum crucible can be used as a sagger to wrap the powdered precursors and process them by microwave-assisted heating. Microwave-assisted heating technology has some advantages that microwave direct heat treatment does not have: (1) Microwave-assisted heating heats both inside and outside at the same time, thus avoiding the formation of excessively high temperature gradients and making the product heating more uniform; (2) Microwave-assisted heating is easier to reach ultra-high temperatures than simple microwave heating, thus allowing for rapid product acquisition and avoiding high energy consumption; (3) Since microwave-assisted heating uses special heat-insulating materials or structures to better prevent heat loss, the temperature required for materials that require high temperatures for general microwave sintering or traditional sintering is much lower than that for traditional sintering methods under microwave-assisted heating conditions, and energy can be saved more effectively.

[0024] 3. After microwave treatment for 3-5 minutes, a molecularly mixed precursor is formed. Extending the treatment time promotes the mixing of water and NO in the precursor. X The rapid evaporation of the gas and the resulting adhesion, with magnesium nitrate and calcium nitrate as the absorption medium, make this substance a good microwave heat absorber. Its penetration depth is much greater than the thickness of the precursor itself. Therefore, the substance is completely penetrated and heated uniformly from the inside out, and reacts completely in a short time, thus obtaining a more homogeneous product.

[0025] 4. A calcium-magnesium composite crack-resistant agent can be prepared using microwave-induced assisted heating. Compared to traditional calcination methods, this method significantly reduces calcination temperature and time, lowers energy consumption and waste emissions, and produces a product with superior performance. The calcium-magnesium composite material prepared by this method is a molecular-level, highly homogeneous, and highly active composite expansive crack-resistant agent with incomplete crystal development. Furthermore, the expansion performance can be adjusted by modifying the calcium-magnesium ratio, microwave-assisted heating power, and the type and dosage of the complexing agent. This makes it suitable for concrete with different structural components and performance requirements, and thus more suitable for large-scale application.

[0026] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0027] Figure 1 This is a structural diagram of the microwave-induced auxiliary heating device in the microwave-induced assisted heating preparation method of the present invention;

[0028] Reference numerals: 1. Precursor, 2. Corundum crucible, 3. Ceramic / carbon fiber, 4. Glass fiber wool. Detailed Implementation

[0029] The present invention will now be described in detail and completely with reference to the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention with reference to the accompanying drawings, it should be particularly noted that the technical solutions and features provided in various parts of the present invention, including the following description, can be combined with each other without conflict.

[0030] Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, and the specific implementation process is as follows:

[0032] This invention provides a highly active calcium-magnesium composite crack-resistant agent, the raw materials of which include: dolomite powder, serpentine powder and complexing agent, wherein the mass ratio of dolomite powder to serpentine powder is 2~3:1, and the molecular number of the complexing agent is: the total number of Mg²⁺ and Ca²⁺ ions in dolomite powder and serpentine powder is 1~2:1.

[0033] The dolomite powder is obtained by grinding dolomite after high-temperature calcination, digestion and acidification treatment. The serpentine powder is obtained by grinding serpentine. The complexing agent is one or a combination of citric acid, lecithin, starch and urea.

[0034] Furthermore, in the highly active calcium-magnesium composite anti-cracking agent, the dolomite is high-purity dolomite, wherein the calcium-magnesium content is 1:1, the silicon content is ≤2%, the aluminum content is ≤0.5%, the iron content is ≤0.2%, and the titanium content is ≤0.2%.

[0035] In the above technical solution, the high-purity dolomite refers to dolomite ore with a CaO content of not less than 30% and an MgO content of not less than 19%.

[0036] Furthermore, in the highly active calcium-magnesium composite crack-resistant agent, the serpentine contains ≥36% magnesium, ≥36% silicon, ≤2.5% calcium, and ≤1% iron.

[0037] Furthermore, in the highly active calcium-magnesium composite anti-cracking agent, the citric acid is a 10% (w / w) citric acid solution obtained by mixing white crystalline citric acid powder with water, wherein the purity of the white crystalline citric acid powder is not less than 99%.

[0038] Furthermore, in the highly active calcium-magnesium composite anti-cracking agent, the ovogloss is composed of phosphatidylcholine, cephalin, inositol phospholipids and sphingomyelin, wherein the content of phosphatidylcholine is ≥22%.

[0039] This invention also provides a microwave-induced assisted heating preparation method using the above-mentioned highly active calcium-magnesium composite anti-cracking agent, comprising the following steps:

[0040] S1: Prepare the raw materials according to any one of claims 1 to 5 for the high-activity calcium-magnesium composite anti-cracking agent. After screening the dolomite mineral, calcine it at 800-900℃, cool it, grind it into 10-40μm particles, add deionized water, stir evenly, and dry, cool, crush and filter it after no precipitate is generated. Grind the remaining material after filtration into 10-40μm particles, add dilute nitric acid solution to fully dissolve it, and dry it to obtain dolomite powder. Grind serpentine into 10-40μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 2-3:1, add a complexing agent according to the proportion, mix and add to the ball mill, grind at room temperature for 30 minutes to obtain a microwave-assisted heating precursor.

[0041] S2: Using a microwave-induced auxiliary heating device with ceramic or carbon fiber 3 as the heat-absorbing carrier and corundum crucible 2 as the sagger to wrap the precursor 1, the precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 2~3GHz and a power of 4000~8000W and microwaved for 10~30 minutes. The precursor is treated by industrial microwave-assisted heating.

[0042] S3: The precursor treated as described above is calcined at 400℃~600℃ and held at that temperature for 1-2 hours to obtain the final product.

[0043] This invention utilizes abundant and inexpensive minerals such as dolomite and serpentine. Through grinding, digestion, dissolution, and acidification processes, and by adding a complexing agent, a microwave-assisted heating precursor is prepared. After treating the precursor with microwave-assisted heating, a mixture of MgO and 2CaO·SiO2 is obtained by calcination at a specific temperature. MgO is an excellent concrete expansion material, while dicalcium silicate is a major component in cement clinker that provides hydration and enhances strength. It is also volume-stable and its reaction is easier to control than that of CaO, effectively improving concrete strength. The composite of MgO and 2CaO·SiO2 is a superior calcium-magnesium composite crack-resistant agent, avoiding the inhomogeneity, high energy consumption, and environmental pollution problems caused by long-term high-temperature calcination. This represents a new method for preparing low-cost, low-carbon, and green crack-resistant agents.

[0044] Furthermore, in the microwave-induced assisted heating preparation method, in step S1, the concentration of the dilute nitric acid solution is 1 mol / L.

[0045] Furthermore, in the microwave-induced assisted heating preparation method, in step S1, the step of adding dilute nitric acid solution to fully dissolve the substance involves:

[0046] The molar ratio of the dilute nitric acid solution to the deionized dolomite is 1:2~3.

[0047] Furthermore, in the microwave-induced assisted heating preparation method, in step S2, the ceramic is selected from one or more of SiC, TiO2, and ZrO2 ceramics.

[0048] Furthermore, the microwave-induced assisted heating preparation method, such as... Figure 1 As shown: The microwave-induced auxiliary heating device also includes glass fiber cotton 4 wrapped around the corundum crucible 2.

[0049] The technical solution of the present invention will be demonstrated below with reference to specific embodiments.

[0050] Example 1:

[0051] Formula: 1200 parts dolomite (chemical formula CaMg(CO3)2), serpentine (chemical formula Mg6[Si4O3]2) 10 ](OH)8) 500 parts, using citric acid and lecithin as complexing agents, citric acid at n(citric acid):n(Mg²⁺+ Ca²⁺)=1:1, lecithin 10 parts, deionized water as needed;

[0052] n (dilute nitric acid): n (dolomite after deionization treatment) = 1:2, with SiC ceramic as the heat absorber.

[0053] Process: S1: Prepare the raw materials according to the above formula. After screening the dolomite mineral, calcine it at 850℃, cool it, grind it into 10μm particles, add deionized water, stir evenly, and dry, cool, crush and filter it after no precipitate is formed. Grind the remaining material after filtration into 30μm particles, add dilute nitric acid solution to fully dissolve it, and dry it to obtain dolomite powder. Use a small ball mill to grind serpentine into 30μm particles of serpentine powder. Mix the dolomite powder and serpentine powder at a mass ratio of 5:2, add citric acid and lecithin, mix and add to the ball mill, grind at room temperature for 30 minutes to obtain microwave-assisted heating precursor.

[0054] S2: A microwave-induced auxiliary heating device is used, which uses SiC ceramic as a heat-absorbing carrier and corundum crucible as a sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 3GHz and a power of 6000W and microwaved for 20 minutes. The precursor is processed by industrial microwave-assisted heating.

[0055] S3: The precursor treated as described above is calcined at 500°C and held at that temperature for 1 hour to obtain the final product.

[0056] Example 2:

[0057] The difference from Example 1 is that high-silicon serpentine with a silicon content of ≥40% is used, which is conducive to the formation of C2S. The proportion of dolomite is reduced, eliminating the role of citric acid in the complex. The powder is ground finely to promote solid-phase reaction. At the same time, the calcination temperature, microwave treatment power and time are reduced to avoid product sintering and reduced activity.

[0058] Formula: 1200 parts dolomite (chemical formula CaMg(CO3)2), high-silica serpentine (chemical formula Mg6[Si4O3]2) 10 700 parts of (OH)8, with urea as the complexing agent, 100 parts of urea, and a certain amount of deionized water;

[0059] n (dilute nitric acid): n (dolomite after deionization treatment) = 1:2, with ZrO2 ceramic as the heat-absorbing carrier.

[0060] Process: S1: Prepare materials according to the above raw material formula. After screening the dolomite mineral, calcine it completely at 800℃. After cooling, grind it into 10μm particles and add deionized water. Stir evenly and dry, cool, crush and filter after no precipitate is formed. Grind the remaining material after filtration into 10μm particles, add dilute nitric acid solution to fully dissolve and dry to obtain dolomite powder. Grind high-silica serpentine into 10μm particles of serpentine powder using a small ball mill. Mix dolomite powder and serpentine powder at a mass ratio of 2:1, add urea, mix and add to the ball mill, grind at room temperature for 10 minutes to obtain microwave-assisted heating precursor.

[0061] S2: A microwave-induced auxiliary heating device is used, which uses ZrO2 ceramic as a heat-absorbing carrier and corundum crucible as a sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 2GHz and a power of 4500W and microwaved for 10 minutes. The precursor is treated by industrial microwave-assisted heating.

[0062] S3: The precursor treated as described above is calcined at 400°C and held at that temperature for 1 hour to obtain the final product.

[0063] Example 3:

[0064] The difference from Example 1 is that the mixture is made according to the theoretical molecular weight values ​​of dolomite and serpentine, reducing other components in the product, and using carbon fiber as a heat-absorbing carrier to improve the heat absorption rate and uniformity, ensuring product homogeneity.

[0065] Formula: 1500 parts dolomite (chemical formula CaMg(CO3)2), serpentine (chemical formula Mg6[Si4O3]2) 10 ](OH)8) 500 parts, using citric acid and starch as complexing agents, 500 parts citric acid, 100 parts starch, and a certain amount of deionized water;

[0066] n (dilute nitric acid): n (dolomite after deionization treatment) = 1:2, with carbon fiber as the heat-absorbing carrier.

[0067] Process: S1: Prepare the raw materials according to the above formula. After sieving the dolomite mineral, calcine it completely at 900℃. After cooling, grind it into 10μm particles and add deionized water. Stir evenly and dry, cool, crush and filter after no precipitate is formed. Grind the remaining material after filtration into 20μm particles. Add dilute nitric acid solution to dissolve it completely and dry to obtain dolomite powder. Grind serpentine into 20μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 3:1. Add citric acid and starch and mix them in a ball mill. Grind at room temperature for 20 minutes to obtain the microwave-assisted heating precursor.

[0068] S2: A microwave-induced auxiliary heating device is used, which uses carbon fiber as a heat-absorbing carrier and corundum crucible as a sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 3GHz and a power of 5000W, and microwaved for 15 minutes. The precursor is processed by industrial microwave-assisted heating.

[0069] S3: The precursor treated as described above is calcined at 500°C and held at that temperature for 1 hour to obtain the final product.

[0070] Example 4:

[0071] The difference from Example 1 is that the mixture is made according to the theoretical molecular weight values ​​of dolomite and serpentine, the powder is coarsely ground, urea is used as a complexing agent, and SiC is used as a heat-absorbing carrier. This reduces costs, extends the grinding time of the mixture, increases the microwave-assisted heating power, and raises the calcination temperature, so that the mixture reacts fully.

[0072] Formula: 1500 parts dolomite (chemical formula CaMg(CO3)2), serpentine (chemical formula Mg6[Si4O3]2) 10 ](OH)8) 500 parts, using urea as a complexing agent, 1000 parts urea, and a certain amount of deionized water;

[0073] n (dilute nitric acid): n (dolomite after deionization treatment) = 1:2, with SiC ceramic as the heat absorber.

[0074] Process: S1: Prepare the raw materials according to the above formula. After screening the dolomite mineral, calcine it completely at 900℃. After cooling, grind it into 40μm particles and add deionized water. Stir evenly and dry, cool, crush and filter after no precipitate is formed. Grind the remaining material after filtration into 40μm particles, add dilute nitric acid solution to dissolve it completely, and dry to obtain dolomite powder. Grind serpentine into 40μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 3:1, add urea, mix and add to the ball mill, grind at room temperature for 60 minutes to obtain microwave-assisted heating precursor.

[0075] S2: A microwave-induced auxiliary heating device is used, which uses SiC ceramic as a heat-absorbing carrier and corundum crucible as a sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 3GHz and a power of 8000W and microwaved for 15 minutes. The precursor is processed by industrial microwave-assisted heating.

[0076] S3: The precursor treated as described above is calcined at 600°C and held at that temperature for 2 hours to obtain the final product.

[0077] Comparative Example 1:

[0078] The difference from Example 1 is that it is carried out according to the traditional calcination process, directly mixing dolomite and serpentine according to their theoretical molecular weight values, without acidifying the dolomite, extending the grinding time of the mixture, without using microwave radiation process, and directly calcining to 850°C to ensure the mixture reacts fully.

[0079] Formula: 1500 parts dolomite (chemical formula CaMg(CO3)2), serpentine (chemical formula Mg6[Si4O3]2) 10 ](OH)8)500 portions.

[0080] Process: S1: Prepare the raw materials according to the above formula, grind the dolomite mineral into dolomite powder with 40μm particles, grind the serpentine into serpentine powder with 40μm particles using a small ball mill, mix the dolomite powder and serpentine powder at a mass ratio of 3:1, add them to the ball mill, and grind at room temperature for 60 minutes to obtain the precursor.

[0081] S2: The precursor treated as described above is calcined at 850°C and held at that temperature for 2 hours to obtain the final product.

[0082] Comparative Example 2:

[0083] The difference from Example 1 lies in that the proportions were not carried out within the range specified in this invention. Dolomite and serpentine were mixed at a mass ratio of 1:1, and SiC was used as the heat-absorbing carrier to improve the heat absorption rate and uniformity, ensuring product homogeneity. This shortened the grinding time of the mixture, eliminated the use of complexing agents, reduced microwave-assisted heating power, lowered the calcination temperature, and improved process efficiency.

[0084] Formula: 1000 parts dolomite (chemical formula CaMg(CO3)2), serpentine (chemical formula Mg6[Si4O3]2) 10 1000 parts of (OH)8, and a certain amount of deionized water;

[0085] n (dilute nitric acid): n (dolomite after deionization treatment) = 1:2, with SiC ceramic as the heat absorber.

[0086] Process: S1: Prepare the raw materials according to the above formula. After screening the dolomite mineral, calcine it completely at 850℃. After cooling, grind it into 10μm particles and add deionized water. Stir evenly and dry, cool, crush and filter after no precipitate is formed. Grind the remaining material after filtration into 30μm particles. Add dilute nitric acid solution to dissolve it completely and dry to obtain dolomite powder. Grind serpentine into 30μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 1:1 and add them to the ball mill. Grind at room temperature for 15 minutes to obtain the microwave-assisted heating precursor.

[0087] S2: A microwave-induced auxiliary heating device is used, which uses SiC ceramic as a heat-absorbing carrier and corundum crucible as a sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 3GHz and a power of 3500W, and microwaved for 20 minutes. The precursor is treated by industrial microwave-assisted heating.

[0088] S3: The precursor treated as described above is calcined at 300°C and held at that temperature for 0.5 hours to obtain the final product.

[0089] Setting time, restricted expansion rate, compressive strength, and concrete volumetric deformation were tested on the products of the above four embodiments and two comparative examples. The setting time, restricted expansion rate, and compressive strength were tested according to the methods in T / CECS 10082-2020 "Calcium-Magnesium Composite Expansive Agent for Concrete". The concrete volumetric deformation was measured using a stress-free meter to determine the free strain of the concrete. The test used C35 concrete mix proportions, as shown in Table 1. The specimen dimensions were 300mm × 100mm × 100mm (length × width × height).

[0090] Table 1. Mix proportions of C35 concrete with calcium-magnesium composite crack-resistant agent

[0091]

[0092] The measurement results are shown in Table 2:

[0093] Table 2. Results of test on setting time, restricted expansion rate, compressive strength, and concrete volumetric deformation in the examples / comparative cases.

[0094]

[0095] As can be seen from Table 2 above, the raw materials and process of the present invention can be used to prepare composite crack-resistant agent products that meet the specifications and have good technical indicators. However, after changing the process or proportion of Comparative Examples 1 and 2, it is impossible to produce a suitable mixture of MgO and 2CaO·SiO2, which will eventually lead to concrete volume shrinkage and fail to achieve the effect of expansion and crack resistance.

[0096] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A highly active calcium-magnesium composite crack-resistant agent, characterized in that, The raw materials include: dolomite powder, serpentine powder, and a complexing agent, wherein the mass ratio of dolomite powder to serpentine powder is 2-3:1, and the molecular weight of the complexing agent is: (1 / 3 of the mass ratio of dolomite powder to serpentine powder) / (1 / 3 of the mass ratio of serpentine powder to ... and The total number of ions is 1~2:1; The dolomite powder is obtained by grinding dolomite after high-temperature calcination, digestion and acidification treatment; the serpentine powder is obtained by grinding serpentine; and the complexing agent is one or a combination of citric acid, lecithin, starch and urea. The microwave-induced assisted heating preparation method of the highly active calcium-magnesium composite crack-resistant agent includes the following steps: S1: Prepare the raw materials according to the high-activity calcium-magnesium composite crack-resistant agent. After screening the dolomite mineral, calcine it at 800-900℃, cool it, grind it into 10-40μm particles, add deionized water, stir evenly, and dry, cool, crush and filter it after no precipitate is generated. Grind the remaining material after filtration into 10-40μm particles, add dilute nitric acid solution to fully dissolve it, and dry it to obtain dolomite powder. Grind serpentine into 10-40μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 2-3:1, add a complexing agent according to the proportion, mix and add to the ball mill, grind at room temperature for 30 minutes to obtain the microwave-assisted heating precursor. S2: A microwave-induced auxiliary heating device is used, which uses ceramic or carbon fiber as the heat-absorbing carrier and corundum crucible as the sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 2~3GHz and a power of 4000~8000W and microwaved for 10~30 minutes. The precursor is processed by industrial microwave-assisted heating. S3: The precursor treated as described above is calcined at 400℃~600℃ and held at that temperature for 1-2 hours to obtain the final product.

2. The highly active calcium-magnesium composite crack-resistant agent as described in claim 1, characterized in that, The dolomite is high-purity dolomite, with a calcium-to-magnesium ratio of 1:1, silicon content ≤2%, aluminum content ≤0.5%, iron content ≤0.2%, and titanium content ≤0.2%.

3. The highly active calcium-magnesium composite crack-resistant agent as described in claim 1, characterized in that, The serpentine contains ≥36% magnesium, ≥36% silicon, ≤2.5% calcium, and ≤1% iron.

4. The highly active calcium-magnesium composite crack-resistant agent as described in claim 1, characterized in that, The citric acid is a 10% (w / w) citric acid solution obtained by mixing white crystalline citric acid powder with water, wherein the purity of the white crystalline citric acid powder is not less than 99%.

5. The highly active calcium-magnesium composite crack-resistant agent as described in claim 1, characterized in that, The lecithin is composed of phosphatidylcholine, cephalin, inositol phospholipids and sphingomyelin, wherein the content of phosphatidylcholine is ≥22%.

6. A method for preparing a highly active calcium-magnesium composite anti-cracking agent using microwave-induced assisted heating as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Prepare the raw materials for the high-activity calcium-magnesium composite crack-resistant agent as described in any one of claims 1 to 5. After screening the dolomite mineral, calcine it at 800-900℃, cool it, grind it into 10-40μm particles, add deionized water, stir evenly, and dry, cool, crush and filter it after no precipitate is generated. Grind the remaining material after filtration into 10-40μm particles, add dilute nitric acid solution to fully dissolve it, and dry it to obtain dolomite powder. Grind serpentine into 10-40μm particles using a small ball mill. Mix the dolomite powder and serpentine powder at a mass ratio of 2-3:1, add a complexing agent according to the proportion, mix and add to the ball mill, grind at room temperature for 30 minutes to obtain a microwave-assisted heating precursor. S2: A microwave-induced auxiliary heating device is used, which uses ceramic or carbon fiber as the heat-absorbing carrier and corundum crucible as the sagger to wrap the precursor. The precursor is placed in a microwave oven with a voltage of 380V, a microwave frequency of 2~3GHz and a power of 4000~8000W and microwaved for 10~30 minutes. The precursor is processed by industrial microwave-assisted heating. S3: The precursor treated as described above is calcined at 400℃~600℃ and held at that temperature for 1-2 hours to obtain the final product.

7. The microwave-induced assisted heating preparation method as described in claim 6, characterized in that, In step S1, the concentration of the dilute nitric acid solution is 1 mol / L.

8. The microwave-induced assisted heating preparation method as described in claim 6, characterized in that, In step S1, the step involves adding dilute nitric acid solution to fully dissolve the substance. The molar ratio of the dilute nitric acid solution to the dolomite treated with deionized water is 2~3:

1.

9. The microwave-induced assisted heating preparation method as described in claim 6, characterized in that, In step S2, the ceramic is selected from one or more of SiC, TiO2, and ZrO2 ceramics.

10. The microwave-induced assisted heating preparation method as described in claim 6, characterized in that, The microwave-induced auxiliary heating device also includes glass fiber wool wrapped around the corundum crucible.

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