Preparation method of cement-based composite material with multistage bionic toughening structure

Abstract

The invention discloses a preparation method of a cement-based composite material with a multistage bionic toughening structure, which comprises the following steps: mixing and stirring a water-based polymer diluent, cement, a thickening agent and deionized water to obtain a water-based polymer modified cement paste, and carrying out bidirectional freezing by using an ice template method to promote the uniform distribution of a water-based polymer in a cement layer, so as to obtain the water-based composite material with the multistage bionic toughening structure. The preparation method comprises the following steps: preparing a modified cement blank with directional pores and a layered structure, de-molding and curing, terminating hydration of the blank, drying and curing polymer particles to form a pomelo peel-like porous structure, immersing in an oily epoxy resin solution, and fully filling interlayer pores with the oily epoxy resin solution by adopting a vacuum negative pressure method to obtain the pomelo peel-like modified cement. And after the resin is cured, a pearl layer brick-mud structure is formed. The pearl layer brick-mud structure and the pomelo peel porous structure are fused, the composite material has low density (about 1.56 g / cm < 3 >) and high mechanical property through the multi-stage bionic structure, the bending strength reaches 35.2 MPa, the bending toughness is improved by 2576% compared with cement paste, and the compressive strength is improved by 82%.

Description

Technical Field

[0001] This invention relates to a method for preparing a cement-based composite material, and more particularly to a method for preparing a cement-based composite material with a multi-level biomimetic toughening structure. Background Technology

[0002] Optimizing the mechanical properties of cement-based composites has always been a core challenge in materials science, especially for applications requiring structural toughness. Traditional cement-based systems, due to their disordered pore structure and uneven distribution of hydration products, have inherent limitations, such as limited tensile strength, low fracture energy, and insufficient impact resistance. These microstructural defects severely weaken the structural stability and service reliability of cement-based composites under complex stress conditions, thus limiting their application in high-stress conditions and dynamic load scenarios. Furthermore, cement-based composites inherently suffer from high bulk density (the density of ordinary concrete can reach 2400 kg / m³). 3 This further exacerbates the limitations of engineering applications. In high-rise buildings and long-span systems, excessive self-weight not only intensifies the foundation's load-bearing requirements but also contradicts the specific strength advantage of lightweight, high-strength materials. Therefore, the development of low-density, high-strength cement-based composite materials has become crucial for their widespread application.

[0003] To improve the mechanical properties of cement-based materials, existing research mainly falls into two categories: First, adding external materials (such as epoxy resin and fibers). However, the compatibility issues between epoxy resin and cement hydration can easily lead to insufficient early strength, while fiber toughening suffers from uneven dispersion and high cost. Second, altering the internal structure by preparing biomimetic layered structures using methods such as ice templates. In these structures, the hard phase cement layer primarily provides support and reinforcement, while the soft phase polymer buffers stress and dissipates energy. When external forces are applied, cracks first form in the hard phase. Under the influence of the soft phase, the cracks deflect or propagate, effectively hindering rapid crack propagation and delaying structural failure. However, the overall strength of such structures is still limited by the brittleness and low ductility of the hard phase, resulting in insufficient damage resistance. Furthermore, traditional research often focuses on altering the soft phase material to assess its impact on mechanical properties, neglecting the primary role of the hard phase cement layer. Single-structure design cannot effectively solve the brittle fracture problem, leading to the mechanical properties of cement-based composites mimicking "brick-and-mortar" structures failing to reach ideal levels.

[0004] Therefore, in order to overcome the brittleness problem of hard phase cement layers, it is necessary to optimize the material composition through modification processes. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for preparing a cement-based composite material with a multi-level biomimetic toughening structure that combines low density and high mechanical properties.

[0006] Technical solution: The preparation method of the cement-based composite material with multi-level biomimetic toughening structure of the present invention includes the following steps:

[0007] (1) Dilute the aqueous polymer emulsion with water to obtain an aqueous polymer diluent, add the aqueous polymer diluent to a mixture of cement, thickener and water, stir evenly, and obtain an aqueous polymer modified cement paste.

[0008] (2) The water-based polymer modified cement slurry is poured into an ice template mold and frozen to form a layered ice surface. The bidirectional freezing gradient causes the slurry to solidify in the horizontal and vertical directions. Then, it is thawed at low temperature to obtain a modified cement blank with directional pores and a layered structure.

[0009] (3) After demolding the modified cement billet, cure it, and then terminate the hydration of the billet and dry it;

[0010] (4) The dried blank is immersed in an oily epoxy resin solution, and the oily epoxy resin solution is fully filled into the interlayer pores by vacuum negative pressure filling method. After impregnation for a period of time, a cement-based composite material with a multi-level biomimetic toughening structure is obtained.

[0011] In step (1), the cement material is selected as PO 52.5 ordinary Portland cement; the thickener is selected as hydroxypropyl methylcellulose with a viscosity of 200000 mPa·s.

[0012] In step (1), the waterborne polymer is at least one of waterborne carboxylated styrene-butadiene rubber, waterborne epoxy resin, and waterborne polyurethane emulsion. The carboxylated styrene-butadiene rubber emulsion has a solid content of 65% and a moisture content of 35%; the waterborne epoxy resin has a solid content of 60% and a moisture content of 40%; and the waterborne polyurethane has a solid content of 48% and a moisture content of 52%. The waterborne polymer is used at 5%, 10%, and 15% of the cement mass, respectively.

[0013] In step (1), considering the water content in the aqueous polymer emulsion, the amount of water used to dilute the aqueous polymer emulsion needs to be deducted from the total water volume in step (1). This dilution water volume accounts for 30% of the water volume after deduction.

[0014] In step (1), the aqueous polymer emulsion accounts for 5% to 15% of the cement mass, and the water-cement ratio is 0.6 to 1.0, preferably 0.6, 0.8, or 1.0, more preferably 0.6. The thickener content is increased according to the water-cement ratio, accounting for 0.15% to 0.35% of the cement mass, preferably 0.15%, 0.25%, or 0.35%, more preferably 0.15%.

[0015] In step (1), the slurry is mixed mechanically. First, 30% of the water (minus the water content in the waterborne polymer emulsion) is added to the waterborne polymer emulsion, and the mixture is stirred at low speed for 2 minutes to improve fluidity and facilitate uniform mixing with the cement slurry. Then, the remaining materials are mixed and stirred at low speed for 2 minutes to uniformly disperse the cement materials and obtain the initial slurry. Finally, waterborne polymer diluent is added and the mixture is stirred at low speed for another 2 minutes to obtain the waterborne polymer-modified cement slurry.

[0016] The freezing process in step (2) is as follows: the modified cement slurry is poured into an ice template mold, and the mold is placed in an environment containing liquid nitrogen to cool it, so as to promote the freezing and molding of the modified cement slurry; the freezing temperature is -196~-30℃, and the freezing time is 10~15h.

[0017] The low-temperature thawing method described in step (2) is as follows: the modified cement blank formed by liquid nitrogen freezing is placed together with the mold in an environment of about 5°C. The ice layer gradually melts to obtain the modified cement blank with directional pores and an ordered layered structure. The thawing process lasts for 2 days.

[0018] In step (2), the modified cement blank with a directional interconnected layered pore structure has an average pore diameter of 50-150 micrometers and a pore shape of directional layered structure.

[0019] The maintenance method described in step (3) is as follows: the environment is maintained at a temperature of 20℃~25℃ and a relative humidity of 95%~100% for 7 days and 28 days respectively.

[0020] The process of terminating hydration and drying in step (3) is as follows: the modified cement blank after curing is immersed in isopropanol solution for 7 days to ensure the termination of hydration; after immersion, it is dried in a vacuum drying oven at 60℃ for 3 to 5 days, and when the quality of the blank no longer changes, it is filled with oily epoxy resin solution.

[0021] In step (3), after drying, the cured polymer particles form a porous structure similar to grapefruit peel.

[0022] In step (4), the specific steps of the vacuum negative pressure filling method are as follows: the dried modified cement blank is immersed in an oily epoxy resin solution, the cement blank and the solution are placed in a vacuum dryer and vacuumed, and then vacuum negative pressure is applied for 5-7 days. After complete curing, a multi-level biomimetic toughened cement-based composite material is obtained.

[0023] In step (4), the oily epoxy resin solution is free of water and includes liquids A and B. Liquid A is the main component of the epoxy resin, and liquid B is an amine curing agent. Liquid A uses Nanya 128 epoxy resin and adds solvents such as acetone and methyl ethyl ketone to improve the permeability of the epoxy resin. The epoxy resin has a solid content of 74%. Liquid B is an amine curing agent. The mass ratio of liquid A to liquid B is 3:1, and the initial viscosity of the mixture of liquid A and liquid B is 14 mPa·s.

[0024] In step (4), the resin cures to form a pearl layer “brick-mud” structure.

[0025] Invention Principle: The core innovation of this invention lies in its multi-level biomimetic design that integrates the "brick-and-mortar" structure of nacre with the porous structure of grapefruit peel. Through an improved ice template preparation process and polymer coupling effect, synergistic performance optimization is achieved. The main principles are as follows:

[0026] (1) The co-mixing and co-freezing process of waterborne polymer emulsion and cement paste promotes the formation of a uniform granular distribution effect of waterborne polymer emulsion in cement slab, thereby constructing a porous elastic skeleton. Figure 1 This is a three-dimensional porous structure distribution diagram of carboxylated styrene-butadiene rubber particles, which plays a dual role: the dehydration of waterborne carboxylated styrene-butadiene rubber promotes the hydration reaction of surrounding cement particles, generating needle-like ettringite, which promotes the early strength development of the cement layer. Figure 2 Simultaneously, a transition zone is formed at the interface between the cement layer and the epoxy resin layer. Partial carboxylated styrene-butadiene rubber particles were observed at this interface, and these particles simultaneously crosslinked with the oily epoxy resin sheets. The mechanism follows the principle of carboxylic acid-catalyzed ring-opening reaction of epoxides described in relevant literature; the molecular-level bonds formed at the interface significantly enhance the interfacial compatibility of the heterogeneous materials. Figure 3 ).

[0027] (2) The pores between the modified cement layers contain a large amount of plate-like Ca(OH)2, forming a strongly alkaline microenvironment. When oil-based epoxy resin is filled in, the alkaline environment promotes the nucleophilic attack of the epoxy groups by the polyamine curing agent, ultimately forming a continuous epoxy resin layered structure. This organic layered structure achieves mechanical interlocking with the plate-like Ca(OH)2 through a dual mechanism of physical encapsulation and chemical anchoring. Figure 4 This further enhances the structural integrity and toughness of the composite material.

[0028] (3) By optimizing the ice template preparation process, the compatibility problem between aqueous polymer and oily polymer systems was effectively solved, and a stable multiphase interfacial interaction mechanism was successfully constructed. The complex multiphase physicochemical interactions in this composite material system significantly enhance the interfacial bonding strength between the inorganic phase (cement matrix) and the organic phase (aqueous polymer and oily epoxy resin) and the organic phase (aqueous polymer) and the organic phase (oily epoxy resin) at the microscale, thereby significantly improving the comprehensive mechanical properties of the composite material.

[0029] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0030] (1) This invention utilizes the compatibility of aqueous polymer emulsion with cement and its air-entraining properties during stirring to form a porous structure resembling grapefruit peel in the layered cement body through co-stirring and co-freezing. This effectively improves the energy absorption characteristics of the hard phase cement layer. Subsequently, a highly permeable epoxy resin solution is filled into the interlayer pores, and after curing, a pearl layer "brick-mud" structure is formed. This invention integrates the pearl layer "brick-mud" structure with the porous structure of grapefruit peel. Through a multi-level biomimetic structure, the composite material possesses both low density (≈1.56 g / cm³) and high permeability. 3 It has high mechanical properties, with a flexural strength of 35.2 MPa, which is 590% higher than that of ordinary cement, a flexural toughness that is 2576% higher than that of cement paste, and a compressive strength that is 82% higher. Its low density and high strength characteristics have important engineering application value. (2) The low density advantage is prominent: the material density is only 1.56 g / cm³. 3 The specific flexural strength reaches 22.6 N·m / g, which is significantly higher than that of single biomimetic systems and some fiber-reinforced concrete, meeting the requirements of lightweight and high-strength engineering; (3) Simple preparation process: Based on the improved ice template method, no complex equipment is required, the raw material cost is controllable, and it can be mass-produced; (4) Short curing period: Excellent mechanical properties can be achieved in 7 days of curing age, which greatly shortens the curing time compared with traditional cement-based materials and improves the efficiency of engineering construction; (5) Wide range of applications: It is suitable for tall structures, large-span systems, extreme environments and other scenarios with strict requirements for material mechanical properties and density, and has broad engineering application prospects. (6) Through a simple improvement strategy, this invention can effectively integrate multiple complex microstructure features and make up for the limitation that the ice template method can only prepare a single biomimetic structure. Attached Figure Description

[0031] Figure 1 The effect diagram shows the uniformly distributed three-dimensional porous structure formed by co-freezing carboxylated styrene-butadiene rubber latex and cement slurry.

[0032] Figure 2 This is a scan image showing the distribution of carboxylated styrene-butadiene rubber particles in a cement layer.

[0033] Figure 3 This diagram illustrates the coupling effect between the carboxylated styrene-butadiene rubber latex and the epoxy resin at the interface.

[0034] Figure 4 This diagram illustrates the mechanical interlocking effect between layered epoxy resin and the hydration product Ca(OH)2.

[0035] Figure 5 The diagram shows the disordered pore structure and hydration product distribution of cement paste in Comparative Example 1.

[0036] Figure 6 This is a diagram showing the ordered layered distribution of the multi-level biomimetic toughened cement-based composite material in Example 1;

[0037] Figure 7 The diagram shows the pore structure and hydration product distribution of the polymer directly stirred and molded in Comparative Example 2. Detailed Implementation

[0038] The present invention will now be described in further detail.

[0039] Comparative Example 1

[0040] According to the proportions in Table 1, PO 52.5 ordinary Portland cement, deionized water, and thickener were mixed and stirred at low speed for 2 minutes to prepare a blank control group of cement paste. The microstructure diagram is shown below. Figure 5 As shown, the disordered pore structure and uneven hydration products of the pure cement matrix can be observed. The raw materials used include: ordinary Portland cement (PO 52.5); deionized water; and thickener. The specific preparation process is as follows:

[0041] (1) Weigh 1000g of PO 52.5 ordinary Portland cement, 1.5g of thickener, and 600g of deionized water. First, add the cement and thickener to a 5L mixer for mechanical mixing. Mix at low speed for 1 minute to ensure that the cement and thickener are evenly mixed, which is beneficial for subsequent mixing with water. Continue mixing at low speed for 4 minutes, and slowly add the weighed water during the mixing process.

[0042] (2) Pour the well-stirred cement slurry into the mold and let it stand in a laboratory environment at 22℃ for one day to cure. After curing, demold and place it in an environment with a temperature range of 20℃~25℃ and a relative humidity of 95%~100% for 7 days.

[0043] (3) After curing, immerse the cement billet in isopropanol solution, changing the isopropanol solution every 24 hours and keeping it soaked for 7 days. Then place the soaked cement billet in a vacuum drying oven to dry, maintaining the oven temperature at 60℃ for more than 3 days, and remove it when the quality of the cement billet no longer changes. Finally, perform strength tests on the dried cement billet, measuring at least 3 test blocks for each strength test and taking the average value.

[0044] Example 1

[0045] Weigh out PO 52.5 ordinary Portland cement, deionized water, thickener, and carboxylated styrene-butadiene rubber latex according to the proportions in Table 1. Stir thoroughly, then freeze-mold. After thawing, curing, and drying, fill with an oil-based epoxy resin solution to prepare a multi-level biomimetic structure cement-based composite material. The microstructure diagram is shown below. Figure 6 As shown, a biomimetic cement matrix with an orderly distribution of cement layers and pore layers was prepared using the ice template process. The raw materials used include: ordinary Portland cement (PO 52.5); deionized water; carboxylated styrene-butadiene rubber latex; thickener; and a highly permeable oily epoxy resin solution. This oily epoxy resin solution does not contain water and includes solutions A and B; solution A is the epoxy resin matrix, and solution B is an amine curing agent. Specifically, solution A uses Nan Ya 128 epoxy resin, with an epoxy resin solid content of 74%; solution B is an amine curing agent, and the mass ratio of solution A to solution B is 3:1. The initial viscosity of the mixture of solutions A and B is 14 mPa·s.

[0046] The specific preparation process is as follows:

[0047] (1) Weigh 1000g of PO 52.5 ordinary Portland cement, 1.5g of thickener, 100g of carboxylated styrene-butadiene rubber latex, and 565g of deionized water; wherein the water content in the carboxylated styrene-butadiene rubber latex is 35g.

[0048] (2) Add 169.5g of deionized water to the carboxylated styrene-butadiene rubber emulsion and stir at low speed for 2 minutes to improve the fluidity of the emulsion, so as to facilitate uniform mixing with cement paste later. Mix cement, thickener and remaining deionized water and stir at low speed for 2 minutes, then add carboxylated styrene-butadiene rubber diluent and continue stirring at low speed for 2 minutes to obtain carboxylated styrene-butadiene rubber modified cement paste;

[0049] (3) The modified cement slurry was poured into an ice mold and frozen to form a shape. Then it was placed in a 5°C cold storage room to thaw for 2 days to obtain a modified cement blank with directional pores and a layered structure.

[0050] (4) After demolding the obtained green body, place it in an environment with a temperature range of 20℃~25℃ and a relative humidity of 95%~100% for 7 days. After curing, immerse the green body in isopropanol solution to stop hydration. Place the green body immersed in isopropanol in a vacuum drying oven to dry for at least 3 days until the quality no longer changes.

[0051] (5) The dried preform was immersed in an oily epoxy resin solution, and the oily epoxy resin solution was fully filled into the interlayer pores using a vacuum negative pressure filling method. After immersion for 7 days, a fully cured multi-level biomimetic toughened cement-based composite material was obtained. The strength of the finally cured cement-based composite material was tested, and at least 3 specimens were measured for each strength test and the average value was taken. The mass change of the cured sample was calculated. The mass of epoxy resin was 200g, which is used as a guide for comparative example 2.

[0052] Example 2

[0053] Based on Example 1, the difference from Example 1 is that the curing period in step (4) is 28 days. The finally cured cement-based composite material is subjected to strength tests, and at least 3 test blocks are measured for each strength test and the average value is taken.

[0054] Example 3

[0055] Based on Example 1, the difference from Example 1 is that in step (1), a 5% mass ratio of carboxylated styrene-butadiene rubber latex is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 50g of carboxylated styrene-butadiene rubber latex with a water content of 17.5g, and 582.5g of deionized water are weighed.

[0056] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0057] Example 4

[0058] Based on Example 1, the difference from Example 1 is that in step (1), a 15% mass ratio of carboxylated styrene-butadiene rubber latex is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 150g of carboxylated styrene-butadiene rubber latex with a water content of 52.5g, and 547.5g of deionized water are weighed.

[0059] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0060] Example 5

[0061] Based on Example 1, the difference from Example 1 is that in step (1), a 5% waterborne epoxy resin emulsion by mass is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 50g of waterborne epoxy resin emulsion with a water content of 20g, and 580g of deionized water are weighed.

[0062] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0063] Example 6

[0064] Based on Example 5, the difference from Example 5 is that in step (1), a 10% waterborne epoxy resin emulsion by mass is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 100g of waterborne epoxy resin emulsion with a water content of 40g and 560g of deionized water are weighed.

[0065] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0066] Example 7

[0067] Based on Example 5, the difference from Example 5 is that in step (1), a 15% waterborne epoxy resin emulsion by mass is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 150g of waterborne epoxy resin emulsion with a water content of 60g and 540g of deionized water are weighed.

[0068] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0069] Example 8

[0070] Based on Example 1, the difference from Example 1 is that in step (1), a 5% waterborne polyurethane emulsion by mass is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 50g of waterborne polyurethane emulsion with a water content of 26g and 574g of deionized water are weighed.

[0071] The cement-based composite material was finally cured and its strength was tested. For each strength test, at least three specimens were measured and the average value was taken.

[0072] Example 9

[0073] Based on Example 8, the difference from Example 8 is that in step (1), a 10% waterborne polyurethane emulsion by mass is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 100g of waterborne polyurethane emulsion with a water content of 52g and 548g of deionized water are weighed.

[0074] The cement-based composite material was finally cured and its strength was tested. For each strength test, at least three specimens were measured and the average value was taken.

[0075] Example 10

[0076] Based on Example 8, the difference from Example 8 is that in step (1), a waterborne polyurethane emulsion with a mass ratio of 15% is used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 150g of waterborne polyurethane emulsion with a water content of 78g and 522g of deionized water are weighed.

[0077] The cement-based composite material was finally cured and its strength was tested. For each strength test, at least three specimens were measured and the average value was taken.

[0078] Comparative Example 2

[0079] Based on Example 1, the difference from Example 1 is that a pure stirring process was used to prepare two polymer-modified cement-based composite materials. Furthermore, based on the weight change of the sample after filling in Example 2, it can be seen that the epoxy resin mixture accounted for 20% of the cement material mass. Figure 7 As shown, it can be seen that through a simple mixing process, a large number of large pores and distinct interfaces of oily epoxy resin are formed in the cement matrix.

[0080] The specific preparation process is as follows:

[0081] (1) Weigh 1000g of PO 52.5 ordinary silicate cement, 1.5g of thickener, 100g of carboxylated styrene-butadiene rubber latex with a water content of 35g, 565g of deionized water, and 200g of oily epoxy resin solution as in Example 1.

[0082] (2) Add 169.5g of deionized water to the carboxylated styrene-butadiene rubber emulsion and stir at low speed for 2 minutes to improve the fluidity of the emulsion and facilitate the uniform mixing with cement paste later; mix cement, thickener and remaining deionized water and stir at low speed for 2 minutes, then add carboxylated styrene-butadiene rubber diluent and continue stirring at low speed for 2 minutes to obtain carboxylated styrene-butadiene rubber modified cement paste.

[0083] (3) Add 200g of oily epoxy resin solution to the carboxylated styrene-butadiene rubber modified cement slurry and stir for 2 minutes to promote uniform mixing of the oily epoxy resin solution in the carboxylated styrene-butadiene rubber modified cement slurry.

[0084] (4) Pour the well-stirred cement slurry into the mold and let it stand in a laboratory environment at 22℃ for one day to cure. After curing, demold and place it in an environment with a temperature range of 20℃~25℃ and a relative humidity of 95%~100% for 7 days.

[0085] After curing, the cement billets are immersed in an isopropanol solution, with the solution changed every 24 hours, and the immersion period is maintained for 7 days. The immersed cement billets are then placed in a vacuum drying oven at 60°C for at least 3 days, until the quality of the cement billets no longer changes. Finally, the dried cement billets are subjected to strength tests, with at least three specimens measured for each strength test and the average value taken.

[0086] Example 11

[0087] Based on Example 1, the difference from Example 1 is that in step (1), a water-to-cement ratio of 0.8 and a thickener mass ratio of 0.25% are used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 2.5g of thickener, 100g of carboxylated styrene-butadiene rubber latex with a water content of 35g and 765g of deionized water are weighed.

[0088] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0089] Example 12

[0090] Based on Example 1, the difference from Example 1 is that in step (1), a water-to-cement ratio of 1.0 and a thickener mass ratio of 0.35% are used. That is, in step (1), 1000g of PO 52.5 ordinary silicate cement, 3.5g of thickener, 100g of carboxylated styrene-butadiene rubber latex with a water content of 35g and 965g of deionized water are weighed.

[0091] The final cured cement-based composite material was subjected to strength tests. For each strength test, at least three test blocks were measured and the average value was taken.

[0092] Table 1. Effects of different material ratios on the mechanical properties of cement-based composite materials

[0093]

[0094] As shown in Table 1, comparing the mechanical properties of Example 1 with those of Examples 3-10, Example 1 exhibits the best mechanical properties. This result indicates that a multi-level biomimetic toughened cement-based composite material with 10% by mass of waterborne carboxylated styrene-butadiene rubber can achieve optimal performance.

[0095] Further comparison of the test results of Example 1 and Example 2 shows that the composite material exhibits superior mechanical properties after a 7-day curing period. This is because, with the extension of the curing period, the pore size of the internal pore structure of the composite material gradually decreases, leading to a reduction in the amount of epoxy resin filling, which in turn affects the mechanical properties.

[0096] Comparing Example 1 and Comparative Example 2, the sample prepared using the improved ice template process exhibited significantly better mechanical properties than the sample prepared using the simple stirring process. This is mainly because the poor compatibility between the water-based polymer and the oil-based polymer interferes with the hydration process of the cement-based material, ultimately leading to a deterioration in the material's mechanical properties.

[0097] Comparing the performance differences between Example 1 and Examples 11 and 12, it can be concluded that increasing the water-cement ratio has a significant inhibitory effect on the overall mechanical properties of the composite material. Therefore, a water-cement ratio of 0.6 is preferred in this invention.

Claims

1. A method for preparing a cement-based composite material with a multi-level biomimetic toughening structure, characterized in that, Includes the following steps: (1) Dilute the aqueous polymer emulsion with water to obtain an aqueous polymer diluent, add the aqueous polymer diluent to a mixture of cement, thickener and water, stir evenly, and obtain an aqueous polymer modified cement paste. (2) The water-based polymer modified cement slurry is poured into an ice template mold and frozen to form a layered ice surface. The bidirectional freezing gradient causes the slurry to solidify in the horizontal and vertical directions. Then, it is thawed at low temperature to obtain a modified cement blank with directional pores and a layered structure. (3) After demolding the modified cement blank, cure it, and then terminate the hydration of the blank and dry it; (4) The dried blank is immersed in an oily epoxy resin solution, and the oily epoxy resin solution is fully filled into the interlayer pores by vacuum negative pressure filling method. After impregnation for a period of time, a cement-based composite material with a cured multi-level biomimetic toughening structure is obtained.

2. The method for preparing the cement-based composite material with a multi-level biomimetic toughening structure according to claim 1, characterized in that, In step (1), the water-based polymer emulsion accounts for 5% to 15% of the cement mass, the water-cement ratio is 0.6 to 1.0, and the thickener content is increased according to the water-cement ratio, accounting for 0.15% to 0.35% of the cement mass.

3. The method for preparing cement-based composite materials with multi-level biomimetic toughening structures according to claim 1, characterized in that, In step (1), the aqueous polymer is at least one of aqueous carboxylated styrene-butadiene rubber, aqueous epoxy resin, and aqueous polyurethane emulsion.

4. The method for preparing cement-based composite materials with multi-level biomimetic toughening structures according to claim 1, characterized in that, In step (1), the water used to dilute the aqueous polymer emulsion accounts for 30% of the total water used in step (1) minus the water content of the aqueous polymer emulsion.

5. The method for preparing cement-based composite materials with multi-level biomimetic toughening structures according to claim 1, characterized in that, In step (4), the oily epoxy resin solution does not contain water and includes liquids A and B; liquid A is the epoxy resin matrix and liquid B is an amine curing agent.

6. The method for preparing the cement-based composite material with a multi-level biomimetic toughening structure according to claim 1, characterized in that, The freezing process in step (2) is as follows: the modified cement slurry is poured into an ice template mold, and the mold is placed in an environment containing liquid nitrogen to cool it, so as to promote the freezing and molding of the modified cement slurry; the freezing temperature is -196~-30℃, and the freezing time is 10~15h.

7. The method for preparing the cement-based composite material with a multi-level biomimetic toughening structure according to claim 1, characterized in that, The low-temperature thawing method described in step (2) is as follows: the modified cement blank formed by liquid nitrogen freezing is placed together with the mold in a low-temperature environment, and the ice layer gradually melts to obtain a modified cement blank with directional pores and an ordered layered structure.

8. The method for preparing cement-based composite materials with multi-level biomimetic toughening structures according to claim 1, characterized in that, The maintenance method described in step (3) is to place the product in an environment with a temperature of 20℃~25℃ and a relative humidity of 95%~100%.

9. The method for preparing the cement-based composite material with a multi-level biomimetic toughening structure according to claim 1, characterized in that, The process of terminating hydration and drying in step (3) is as follows: the modified cement blank after curing is immersed in isopropanol solution to ensure the termination of hydration; after immersion, it is dried in a vacuum drying oven, and when the quality of the blank no longer changes, it is filled with oily epoxy resin solution.

10. The method for preparing the cement-based composite material with a multi-level biomimetic toughening structure according to claim 1, characterized in that, In step (4), the specific steps of the vacuum negative pressure filling method are as follows: the dried modified cement blank is immersed in an oily epoxy resin solution, the cement blank and the solution are placed in a vacuum dryer and vacuumed, and then vacuum negative pressure is applied for 5d~7d to obtain a fully cured multi-level biomimetic toughened cement-based composite material.

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