Super-early-strength high-anti-crack cement-based composite material and preparation method thereof

Abstract

The application discloses an ultra-early-strength high-anti-cracking cement-based composite material and a preparation method thereof, and belongs to the technical field of building materials. The cement-based composite material comprises cement, aggregate, fiber, water reducing agent, early-strength agent, composite expansion agent, admixture and retarder. The composite expansion agent comprises expansion agent A and coated expansion agent B. The tensile strength of the coating layer of the coated expansion agent B is 1.5-2.0 MPa, and the elongation at break is 5-10%. The cement-based composite material effectively solves the problem of early cracking of ultra-early-strength cement and has high anti-cracking performance.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology and relates to an ultra-early strength high crack resistance cement-based composite material and its preparation method. Background Technology

[0002] Ultra-early strength cement, with its ability to rapidly increase strength, is widely used in projects with stringent time constraints, such as road repairs and winter construction. However, this type of cement has a significant problem in practical use: it is extremely prone to cracking, especially during the early hydration stage when the cement volume changes drastically. Once cracking occurs in cement products, it not only severely damages their appearance but also significantly reduces the durability and load-bearing capacity of the structure, posing a potential threat to the safety of the building. Summary of the Invention

[0003] The issues to be addressed This application aims to at least address the technical problems existing in the prior art. To this end, this application proposes an ultra-early strength, high crack-resistant cement-based composite material and its preparation method to solve the problem of early cracking in ultra-early strength cement.

[0004] [Methods for Solving the Problem] In related technologies, the industry commonly uses admixtures to address the cracking problem of ultra-early strength cement. Among these, expansive agents are frequently used. Expansive agents can generate appropriate expansion during cement hydration, compensating for shrinkage during cement hardening, thereby effectively reducing crack formation. However, controlling the amount of expansive agent used is extremely difficult. Excessive addition will cause excessive expansion of the cement-based materials, leading to harmful cracks and weakening the overall structural performance; insufficient addition will fail to fully compensate for shrinkage, leaving the cracking problem unresolved.

[0005] To address the aforementioned challenges, the inventors conducted repeated and in-depth research and realized that a single expansive agent is insufficient for precisely controlling the expansion amount throughout the entire hydration cycle of ultra-early strength cement. Through extensive experimentation and analysis, they creatively discovered that combining expansive agents with different properties and employing a special encapsulation treatment on one of the expansive agents can effectively solve this problem. By designing an encapsulation layer with specific tensile strength and elongation at break, the encapsulation layer is torn open when the cement undergoes early hydration and internal stress reaches a certain level, rapidly releasing the expansive agent and compensating for the large volume changes in the early stages of ultra-early strength cement. Simultaneously, an unencapsulated expansive agent that slowly releases its expansion energy is selected, allowing it to continue functioning in the later stages of cement hardening to compensate for later shrinkage, thereby effectively solving the problem of early cracking in ultra-early strength cement. This invention thus completes the creation of this invention.

[0006] This application provides an ultra-early strength, high crack resistance cement-based composite material, comprising cement, aggregate, fiber, water-reducing agent, early strength agent, composite expansion agent, admixture and retarder; The composite expanding agent comprises expanding agent A and encapsulated expanding agent B. The tensile strength of the encapsulation layer of expanding agent B is 1.5-2.0 MPa, and the elongation at break of the encapsulation layer of expanding agent B is 5-10%. In any embodiment, the encapsulating swelling agent B is coated with a cellulose film.

[0007] In any embodiment, the preparation method of the encapsulating swelling agent B is as follows: S1. Natural fibers are pretreated with cellulase to obtain a cellulose dispersion; S2. Cellulose films are prepared by solution casting or papermaking processes; S3. The expansion agent B particles are wrapped with a cellulose membrane by hot pressing or mechanical compression to obtain the wrapped expansion agent B.

[0008] In any embodiment, the thickness of the cellulose film in step S2 is 0.005-0.01 mm.

[0009] In any embodiment, after obtaining the cellulose film by solution casting in step S2, the cellulose film is then immersed in a ZnCl2 solution to regenerate it, forming a dense regenerated cellulose film.

[0010] In any embodiment, the concentration of the ZnCl2 solution is 1-2 mol / L, and the soaking time is 5-10 min.

[0011] In any embodiment, the composite expanding agent is formed by mixing expanding agent A and encapsulating expanding agent B, and the composite expanding agent passes through a 100-150 mesh sieve.

[0012] In any embodiment, the expanding agent A is UEA, the encapsulating expanding agent B is encapsulated calcium oxide, and the mass ratio of the expanding agent A to the encapsulating expanding agent B is (1):(2-3).

[0013] This application also provides a method for preparing the ultra-early strength, high crack resistance cement-based composite material as described above, the steps of which are as follows: Z1. Mix cement, aggregate, fiber, water-reducing agent, early strength agent, admixture and retarder evenly; Z2. Add the composite expanding agent and stir evenly at a speed of <800 rpm; Z3. Add water and stir evenly to obtain ultra-early strength and high crack resistance cement-based composite material.

[0014] In any embodiment, in step Z2, the composite expanding agent is added in stages, and the composite expanding agent is added in stages 3-5 times until the composite expanding agent is completely added.

[0015] [Invention Effects] The ultra-early strength and high crack resistance cement-based composite material provided by this invention effectively solves the problem of early cracking of early strength cement and has high crack resistance. Detailed Implementation

[0016] The embodiments of this application are disclosed in detail below as appropriate. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims. The "scope" disclosed in this application is defined in the form of a lower limit and an upper limit, whereby a given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular scope. Scopes defined in this way may include or exclude end values ​​and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope. For example, if a scope of 60-120 and 80-110 is listed for a specific parameter, it is expected that the scopes of 60-110 and 80-120 are also included. Furthermore, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are listed, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range “ab” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range “0-5” means that all real numbers between “0-5” have been listed herein, and “0-5” is merely a shortened representation of these numerical combinations. Additionally, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0017] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0018] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0019] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0020] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0021] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0022] Cement-based composite materials As described in this article, the term "cement-based composite material" refers to a multiphase material made by combining cement as a matrix with one or more reinforcing materials, functional materials, and other auxiliary materials through a certain process.

[0023] The ultra-early strength and high crack resistance cement-based composite material disclosed herein includes cement, aggregate, fiber, water-reducing agent, early strength agent, composite expansion agent, admixture and retarder.

[0024] The cement, aggregate, fiber, water-reducing agent, early-strength agent, composite expansion agent, admixture and retarder used in this application may be materials applicable to ultra-early-strength high-crack-resistant cement-based composite materials.

[0025] This section details the types and dosages of cement, aggregates, fibers, water-reducing agents, early-strength agents, composite expansive agents, admixtures, and retarders used in ultra-early-strength, high-crack-resistant cement-based composite materials widely known in this field. These materials can be listed as follows: a. Cement, used to provide the basic strength of materials and to dominate the hydration process. Rapid-hardening sulfoaluminate cement is a representative example.

[0026] b. Aggregates, used to form the material skeleton and improve the material's volume stability and strength, are divided into coarse and fine aggregates. River sand is a representative example of fine aggregates.

[0027] c. Fibers, used to effectively prevent the propagation of microcracks and enhance the toughness and crack resistance of materials, with polypropylene fibers as the representative.

[0028] d. Water-reducing agents are used to reduce the water-cement ratio and improve the strength and durability of concrete while maintaining its workability. Polycarboxylate-based high-performance water-reducing agents are the most representative.

[0029] e. Accelerating agents are used to accelerate the hydration process of cement and significantly improve early strength, with sodium sulfate as a representative example.

[0030] f. Admixtures, used to improve the workability of concrete, reduce the heat of hydration, and enhance durability, with Grade I fly ash as the representative.

[0031] g. Retarder, used to slow down the hydration rate of cement, prolong the setting time of concrete, and facilitate construction operations, with sodium gluconate as the representative.

[0032] h. Composite expansive agents are used to solve the problem of cracking in ultra-early strength cement. They are admixtures composed of various expansive components with different functions and auxiliary additives in a certain proportion. Expansive agents are represented by calcium oxide and calcium sulfoaluminate.

[0033] Regarding the specific composition of cement, aggregates, fibers, water-reducing agents, early-strength agents, composite expansive agents, admixtures, and retarders, some implementation forms applicable to the above-mentioned cement-based composite materials of this application can be demonstrated as follows: Cement-based composite material 1, specifically as follows: 450-550 parts of sulfoaluminate cement and 600-750 parts of river sand 1.2-1.8 parts polypropylene fiber, 5-7 parts sodium polycarboxylate. 5-7 parts sodium sulfate, 100-150 parts grade I fly ash Sodium gluconate 0.6-0.9 parts, compound expanding agent 24-36 parts Among them, Grade I fly ash conforms to the standard GB / T 1596-2017.

[0034]

Packaging Expander B

[0035] A suitable but non-limiting implementation is provided, wherein the tensile strength of the coating layer of the encapsulating expanding agent B is 1.5-2.0 MPa, and exemplary values ​​are 1.52-2.0 MPa, 1.55-2.0 MPa, 1.6-2.0 MPa, 1.65-2.0 MPa, 1.7-2.0 MPa, 1.75-2.0 MPa, 1.8-2.0 MPa, 1.85-2.0 MPa, 1.9-2.0 MPa, 1.95-2.0 MPa, 1.5-1.98 MPa, 1.5-1.95 MPa, 1.5-1.9 MPa, 1.5-1.85 MPa, 1.5-1.8 MPa, 1.5-1.75 MPa, 1.5-1.7 MPa, 1.5-1.65 MPa, 1.5-1.6 MPa, and 1.5-1.55 MPa. The elongation at break of the encapsulation layer of the expanding agent B is 5-10%, and can be exemplified as 5.2-10%, 5.5-10%, 6-10%, 6.5-10%, 7-10%, 7.5-10%, 8-10%, 8.5-10%, 9-10%, 9.5-10%, 5-9.8%, 5-9.5%, 5-9%, 5-8.5%, 5-8%, 5-7.5%, 5-7%, 5-6.5%, 5-6%, and 5-5.5%.

[0036] If the tensile strength and elongation at break of the coating layer containing expansive agent B exceed or fall below this range, the coating layer will be unable to accurately release expansive agent B at the predetermined cement hydration stage. If the tensile strength is too low, the coating layer may crack prematurely in the early stage of cement hydration, causing expansive agent B to be released early. This, combined with the expansion effect of expansive agent A, will lead to excessive early expansion, which will exacerbate internal stress concentration and induce harmful cracks. If the tensile strength is too high, the coating layer may not crack in the critical early hydration stage, resulting in delayed release of expansive agent B. This will fail to compensate for the volume shrinkage caused by rapid hydration of ultra-early strength cement, increasing the risk of early cracking. Similarly, if the elongation at break is too low, the coating layer will lack ductility and may directly fracture under stress, leading to uneven release of expansive agent B and fluctuations in the shrinkage compensation effect. If the elongation at break is too high, excessive stretching of the coating layer will reduce its sealing performance, potentially causing premature breakage during mixing or transportation, which will also disrupt the timing of expansive agent release.

[0037] The specific preparation method of the encapsulating expansion agent B is as follows: S1. Natural fibers are pretreated with cellulase to obtain a cellulose dispersion; S2. Cellulose films are prepared by solution casting or papermaking processes; S3. The expansion agent B particles are wrapped with a cellulose membrane by hot pressing or mechanical compression to obtain the wrapped expansion agent B.

[0038] As is well known to those skilled in the art, natural fibers are widely available, inexpensive, and possess excellent biodegradability and renewability; examples include cotton fibers and wood pulp fibers. Cellulase, as a highly efficient biocatalyst, can specifically act on the cellulose component in natural fibers, degrading it into smaller molecular fragments. Regarding the specific composition of the natural fibers and cellulase, some implementations applicable to the aforementioned cement-based composite materials of this application can be demonstrated as follows: the natural fiber used is cotton fiber, which has a high cellulose content and long, fine fibers, facilitating the formation of a uniform and stable cellulose dispersion; the cellulase used is β-glucosidase.

[0039] The above casting method specifically involves: spreading a cellulose dispersion evenly on a smooth substrate surface, controlling conditions such as the thickness of the dispersion and the solvent evaporation rate to form a continuous film on the substrate, and then peeling the film off the substrate to obtain a cellulose film.

[0040] The papermaking process described above is as follows: similar to the traditional papermaking process, a cellulose dispersion is suspended in water and filtered through a filter screen, allowing the cellulose fibers to interweave and deposit on the filter screen to form a film with a certain thickness and strength, which is then dried to obtain the cellulose film.

[0041] A suitable, but non-limiting, implementation method is that the thickness of the cellulose film in step S2 is 0.005-0.01 mm, and exemplary values ​​are 0.006-0.01 mm, 0.007-0.01 mm, 0.008-0.01 mm, 0.009-0.01 mm, 0.001-0.009 mm, 0.001-0.008 mm, 0.001-0.007 mm, 0.001-0.006 mm, 0.001-0.005 mm, 0.001-0.004 mm, 0.001-0.003 mm, and 0.001-0.002 mm. When the film thickness is within this range, it can ensure that the coating layer has sufficient strength to avoid premature cracking during cement mixing, and also ensure that the coating layer can be easily torn apart when the cement hydrates in the early stage and the internal stress reaches a certain level, so as to release the expansion agent B in time. If the film is too thick, the coating strength is too high, and the release of the expansive agent B is delayed, failing to effectively compensate for the early volume change of the ultra-early strength cement; if the film is too thin, the coating strength is insufficient, and the expansive agent B may be released prematurely, leading to uncontrolled early expansion.

[0042] A suitable, but not limiting, implementation method is provided, wherein the concentration of the ZnCl2 solution is 1-2 mol / L, and examples include 1.2-2 mol / L, 1.4-2 mol / L, 1.6-2 mol / L, 1.8-2 mol / L, 1-1.8 mol / L, 1-1.6 mol / L, 1-1.4 mol / L, and 1-1.2 mol / L. The soaking time is 5-10 min, and examples include 6-10 min, 7-10 min, 8-10 min, 9-10 min, 5-9 min, 5-8 min, 5-7 min, and 5-6 min. When the ZnCl2 solution concentration is 1-2 mol / L, the rate and extent of its complexation reaction with cellulose molecules are relatively moderate. If the concentration is too low, the hydrogen bonds between cellulose molecules cannot be sufficiently broken, resulting in poor regeneration and limited improvement in film performance; if the concentration is too high, it may lead to excessive degradation of cellulose, reducing film strength. The soaking time is 5-10 minutes, which ensures that ZnCl2 and cellulose react fully to achieve effective film regeneration, while avoiding damage to the film structure due to excessive soaking time. If the soaking time is too short, the regeneration reaction will be insufficient; if the soaking time is too long, the film may dissolve or become over-crosslinked, affecting its performance.

[0043]

Compound Expanding Agent

[0044] As is well known to those skilled in the art, expansion agents include calcium oxide-based and calcium sulfoaluminate-based agents (such as UEA). Calcium oxide-based expansion agents react with water to form calcium hydroxide, resulting in a significant increase in solid volume and thus expansion. Calcium sulfoaluminate-based expansion agents react with gypsum and other components in cement during hydration to form ettringite crystals, which also cause volume expansion. The expansion effect produced by these expansion agents through the aforementioned mechanisms compensates for the shrinkage of cement during the hardening process.

[0045] Calcium oxide-based expansive agents compensate for cement shrinkage relatively quickly. Their reaction with water is extremely rapid; typically, calcium hydroxide is rapidly generated within hours of cement being mixed with water, completing most of the expansion in a short time and significantly compensating for shrinkage during early cement hardening. In contrast, calcium sulfoaluminate-based expansive agents exhibit a phased approach to compensating for cement shrinkage. In the early stages of cement hydration, they react slowly with components such as gypsum to form ettringite crystals, resulting in a more gradual rate of shrinkage compensation. As the hydration reaction progresses, the amount of ettringite formed gradually increases, continuously compensating for shrinkage during the cement hardening process.

[0046] A suitable but non-limiting implementation is that the composite expanding agent includes expanding agent A and encapsulating expanding agent B.

[0047] A suitable, but non-limiting, implementation method is provided, wherein the expansive agent A is UEA, the encapsulating expansive agent B is encapsulated calcium oxide, and the mass ratio of the expansive agent A to the encapsulated expansive agent B is 1:(2-3), which can be exemplified as 1:(2.2-3), 1:(2.5-3), 1:(2.8-4), 1:(2-2.8), 1:(2-2.5), or 1:(2-2.2). When the mass ratio of expansive agent A to encapsulated expansive agent B is within the range of 1:(2-3), the concrete can achieve a relatively ideal expansion effect. The synergistic effect of UEA and calcium oxide during the hydration reaction allows the early expansion characteristics of calcium oxide to be utilized, while also leveraging the sustained expansion performance of UEA in the later stages. This ensures that the material has appropriate expansion at different stages, effectively compensating for shrinkage and improving crack resistance.

[0048] The composite expansive agent is prepared by mechanical mixing. Expansive agent A and encapsulated expansive agent B are stirred at 20-40 rpm for 20-40 minutes until they are uniformly mixed. The mixture is then passed through a 100-150 mesh sieve to obtain the composite expansive agent. Examples of suitable sieve sizes for the composite expansive agent include 110-150 mesh, 120-150 mesh, 130-150 mesh, 140-150 mesh, 100-140 mesh, 100-130 mesh, 100-120 mesh, and 100-110 mesh. Screening ensures uniform particle size of the composite encapsulated expansive agent. Uniformly sized composite expansive agents disperse more evenly in cement-based composite materials, ensuring consistent expansion effects across different parts of the material. This effectively avoids localized expansion anomalies caused by uneven agent distribution, thereby improving the overall crack resistance and stability of the cement-based composite material.

[0049] The mixing speed and time of the composite expanding agent are well known to those skilled in the art. The mixing speed of the composite expanding agent is low, which is to prevent the coating layer of expanding agent B from being broken during the stirring process. The stirring time can be appropriately reduced or extended according to the mixing situation to ensure that the composite expanding agent is mixed evenly.

[0050] Preparation method of ultra-early strength and high crack resistance cement-based composite materials The preparation method of ultra-early strength and high crack resistance cement-based composite materials is as follows: Z1. Mix cement, aggregate, fiber, water-reducing agent, early strength agent, admixture and retarder evenly; Z2. Add the composite expanding agent and stir evenly at a speed of <800 rpm; Z3. Add water and stir evenly to obtain ultra-early strength and high crack resistance cement-based composite material.

[0051] The process of obtaining an ultra-early-strength, high-crack-resistant cementitious composite material, using cement-based composite material 1 as an example (which can be demonstrated but is not limited to this example), is as follows: Z1. Mix 450-550 parts of sulfoaluminate cement, 600-750 parts of river sand, 1.2-1.8 parts of polypropylene fiber, 5-7 parts of sodium polycarboxylate, 5-7 parts of sodium sulfate, 100-150 parts of Grade I fly ash and 0.6-0.9 parts of sodium gluconate evenly. Z2. Add 24-36 parts of composite expanding agent and stir evenly at a speed of <800 rpm; Z3. Add 160-180 parts of water and stir evenly to obtain ultra-early strength and high crack resistance cement-based composite material.

[0052] A suitable, but not limiting, implementation method is as follows: in step Z2, the composite expansive agent is added in stages, with 3-5 additions until the composite expansive agent is completely added. Staged addition helps the composite expansive agent to disperse more evenly in the cement-based material. Adding it all at once may result in excessively high concentrations of expansive agent in some areas while insufficient concentrations are found in others, affecting overall performance. Multiple additions and stirring allow the expansive agent to mix better with other components, ensuring uniform distribution throughout the system. This results in a more consistent expansion effect across different parts, effectively improving the overall crack resistance and stability of the cement-based composite material. [Implementation process of the examples and comparative examples] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0053] 1. [Series C: Manufacturing Examples of Expanding Agent B] S1. Add 100g of wood pulp fiber to 1000ml of buffer solution (pH 6.0) containing 1.5g of cellulase, and stir at a constant temperature in a 50℃ water bath for 2 hours to allow the cellulase to fully degrade the cellulose and form a uniform cellulose dispersion. Filter to remove undecomposed fiber residue, collect the dispersion, and set aside for later use. S2. Spread the cellulose dispersion evenly on a polytetrafluoroethylene (PTFE) plate to a thickness of 0.005-0.01 mm. Allow it to air dry at room temperature for 12 hours to form a nascent cellulose film. Immerse the nascent cellulose film in a 1-2 mol / L ZnCl2 solution for 5-10 minutes to allow cellulose molecules to pass through the ZnCl2 solution. 2+ Complexation forms a cross-linked network, which is then regenerated into a dense thin film. S3. 30g of expansion agent B granules (calcium oxide) and a dense film are rolled together at room temperature and pressure of 10MPa using a compressor to completely coat the granules with the film, thus obtaining coated expansion agent B. Finally, the film is passed through a 100-mesh sieve to ensure uniform size.

[0054] The particle size of calcium oxide is 50-100 μm.

[0055] Using the above-described operations in “[Example of manufacturing encapsulating expander B]” in this section and in conjunction with the process conditions in Table 1, a series of encapsulating expanders B, C1-C8, were prepared.

[0056] 2. [Example D of the manufacture of composite expanding agents] Mix the expanding agent A and the encapsulated expanding agent B in a mass ratio of 1:(1-2) at 30 r / min for 30 minutes to make the expanding agent A and the encapsulated expanding agent B evenly mixed. Then pass the mixture through a 100-150 mesh sieve to obtain the composite expanding agent.

[0057] Using the above-described operations in “[Example of Manufacturing Composite Expanding Agents]” in this section and in conjunction with the process conditions in Table 2, a series of composite expanding agents, D1-D12, were prepared.

[0058] 3. [Example of manufacturing ultra-early strength, high crack resistance cement-based composite materials] Z1. Mix 500 parts of sulfoaluminate cement, 700 parts of river sand, 1.5 parts of polypropylene fiber, 6 parts of sodium polycarboxylate, 6 parts of sodium sulfate, 120 parts of grade I fly ash and 0.7 parts of sodium gluconate evenly. Z2. Add 30 parts of the composite expansion agent in 5 portions, with an interval of 2 minutes between each addition, and then stir evenly at 600 rpm. Z3. Add 170 parts water and stir evenly to obtain ultra-early strength and high crack resistance cement-based composite material.

[0059] The polypropylene fiber is a monofilament fiber with a length of 9 mm and a diameter of 30 μm.

[0060] Using the above-described operations in this section, “[Examples of Manufacturing Ultra-Early Strength High Crack-Resistant Cement-Based Composite Materials]”, and in conjunction with the process conditions in Table 3, a series of ultra-early strength high crack-resistant cement-based composite materials were prepared, Examples 1-3.

[0061] 4. [Comparative Example of Ultra-early Strength and High Crack-Resistant Cement-Based Composite Materials] Based on the [Example of Manufacturing Ultra-Early Strength High Crack-Resistant Cement-Based Composite Materials], the composite expansion agent is replaced with D4-D12.

[0062] Table 1 Process conditions for encapsulating expanding agent B Table 2 Process conditions for composite expanding agent Table 3. Process conditions for manufacturing examples of ultra-early strength, high crack resistance cement-based composite materials Table 4 Process conditions for comparative examples of ultra-early strength and high crack resistance cement-based composite materials

evaluate

[0063] [Compressive strength] According to GB / T 17671-1999 standard, specimens with dimensions of 40mm×40mm×160mm were prepared. In the compressive strength test, a pressure testing machine was used, and the compression rate was set to 2400N / s. The compressive strength of each embodiment was measured at three key ages: 3h, 24h, and 28d. Flexural strength Referring to GB / T 17671-1999 standard, specimens with dimensions of 40mm×40mm×160mm were prepared. Using a flexural testing machine, the loading rate was set to 50N / s, and the flexural strength of each embodiment was measured at 3h, 24h, and 28d.

[0064] [Expansion Rate] The expansion rate of each embodiment and comparative example was measured over 24 hours. In accordance with GB / T 23439-2017 standard, a concrete restricted expansion rate tester was used to prepare specimens with dimensions of 100mm×100mm×515mm, and the free expansion rate of each embodiment and comparative example was measured after 24 hours.

[0065] [Cracking condition] At three time points—3h, 24h, and 28d—the surface cracking of the specimens in each embodiment and comparative example was visually observed. To ensure the accuracy and consistency of the evaluation, a detailed grading standard for cracking was established: "No cracking" indicates that there are no visible cracks on the surface of the specimen; "Slight cracking" refers to the presence of a small number of fine cracks on the surface of the specimen, with narrow crack widths and minimal impact on the overall performance of the material; "Severe cracking" means that there are many and wide cracks on the surface of the specimen, which may have a significant impact on the structural performance and durability of the material.

[0066] Table 5 Evaluation Results Table 6 Evaluation Results Table 7 Evaluation Results Tables 5, 6, and 7 show that the tensile strength (1.5-1.8 MPa) and elongation at break (6-8%) of the film in C1-C3 ensure that the expanded agent B is released in a timely manner under the early hydration stress of cement. However, in C4-C8, due to excessive film thickness, abnormal ZnCl2 concentration, or improper soaking time, the strength is too high / too low or the ductility is insufficient, which directly affects the release sequence of the expanded agent, thereby causing cracking or a decrease in strength.

[0067] As shown in Table 6, Examples 1-3 use a mass ratio of UEA (expansion agent A) to calcium oxide (encapsulated expansion agent B) of 1:2~3, combined with 100-150 mesh sieve treatment, so that the early expansion agent B can quickly compensate for hydration shrinkage, and the material has both ultra-early strength and high crack resistance.

[0068] As shown in Table 7, the specimens of Examples 1-3 did not crack at 3h, 24h, and 28d. In contrast, the comparative examples all showed cracks of varying degrees, and their strength was lower than that of the Examples.

[0069] In summary, the ultra-early strength high crack resistance cement-based composite material of the present invention has high crack resistance and effectively solves the problem of early cracking of ultra-early strength cement.

[0070] The above embodiments are merely illustrative of the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A high-early-strength, high-crack-resistant cement-based composite material, characterized in that, This includes cement, aggregates, fibers, water-reducing agents, early-strength agents, composite expansion agents, admixtures, and retarders; The composite expanding agent includes expanding agent A and encapsulated expanding agent B. The tensile strength of the encapsulation layer of the encapsulated expanding agent B is 1.5-2.0 MPa, and the elongation at break of the encapsulation layer of the encapsulated expanding agent B is 5-10%.

2. The ultra-early strength, high crack resistance cementitious composite material according to claim 1, characterized in that: The expanding agent B is coated with a cellulose film.

3. The ultra-early strength, high crack resistance cementitious composite material according to claim 1, characterized in that: The preparation method of the encapsulating expansion agent B is as follows: S1. Natural fibers are pretreated with cellulase to obtain a cellulose dispersion; S2. Cellulose films are prepared by solution casting or papermaking processes; S3. The expansion agent B particles are wrapped with a cellulose membrane by hot pressing or mechanical compression to obtain the wrapped expansion agent B.

4. The ultra-early strength, high crack resistance cement-based composite material according to claim 3, characterized in that: In step S2, the thickness of the cellulose film is 0.005-0.01 mm.

5. The ultra-early strength, high crack resistance cementitious composite material according to claim 3, characterized in that: In step S2, after the cellulose film is prepared by solution casting, the cellulose film is then immersed in ZnCl2 solution to regenerate it, forming a dense regenerated cellulose film.

6. The ultra-early strength, high crack resistance cementitious composite material according to claim 5, characterized in that: The concentration of the ZnCl2 solution is 1-2 mol / L, and the soaking time is 5-10 min.

7. The ultra-early strength, high crack resistance cementitious composite material according to claim 1, characterized in that: The composite expanding agent is formed by mixing expanding agent A and encapsulating expanding agent B, and the composite expanding agent passes through a 100-150 mesh sieve.

8. The ultra-early strength, high crack resistance cement-based composite material according to claim 1, characterized in that: The expanding agent A is UEA, the encapsulating expanding agent B is encapsulated calcium oxide, and the mass ratio of the expanding agent A to the encapsulating expanding agent B is (1):(2-3).

9. The method for preparing the ultra-early strength, high crack resistance cementitious composite material according to any one of claims 1-9, characterized in that, The steps are as follows: Z1. Mix cement, aggregate, fiber, water-reducing agent, early strength agent, admixture and retarder evenly; Z2. Add the composite expanding agent and stir evenly at a speed of <800 rpm; Z3. Add water and stir evenly to obtain ultra-early strength and high crack resistance cement-based composite material.

10. The preparation method of the ultra-early strength high crack-resistant cement-based composite material according to claim 9, characterized in that: In step Z2, the composite expanding agent is added in stages, and the composite expanding agent is added in stages 3-5 times until the composite expanding agent is completely added.

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