Functionalized fiber material with concrete chlorine fixation and crack resistance, preparation method and application thereof

Abstract

The present invention discloses a functionalized fiber material with concrete chlorine fixation and crack resistance, and a preparation method and application thereof, which relates to the field of concrete technology. The functionalized fiber material includes carbon fiber, and a functional material coating located on the surface of the carbon fiber, wherein the functional material coating includes magnesium oxide and / or aluminum oxide. In the present invention, magnesium oxide and / or aluminum oxide are introduced to the surface of the carbon fiber, which can effectively improve the interfacial adhesion between the carbon fiber and the cement mortar, thereby improving the crack resistance of the concrete. When the functional material coating includes aluminum oxide, the functionalized fiber material is added to the cement mortar to not only improve its mechanical properties, but also improve the cement mortar's ability to bind chloride ions, thereby effectively improving the durability of the concrete in a coastal environment.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and in particular to a functionalized fiber material with concrete chlorine fixation and crack resistance performance, and a preparation method and application thereof. Background Art

[0002] Reinforced concrete components often face severe durability challenges due to chloride ion corrosion during service in coastal environments. Chloride ions have strong penetration ability and can easily penetrate into the concrete, then react chemically with the steel bars, causing steel bar corrosion and accelerating the destruction of the concrete structure. In addition, microcracks in the concrete components themselves further aggravate the degree of steel bar corrosion.

[0003] In recent years, some achievements have been made in improving the performance of reinforced concrete structures by adding fiber-reinforced materials to cement mortar. Carbon fiber (CF), as a high-strength, high-modulus fiber material, is widely used in the crack-resistant reinforcement of concrete structures. Its excellent mechanical properties enable carbon fiber to effectively resist cracking and deformation of concrete structures, improving their durability and seismic performance. However, the interfacial bonding between carbon fiber and cement mortar is poor, resulting in the unsatisfactory crack resistance of concrete prepared by cement mortar with carbon fiber.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] Based on the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a functional fiber material with concrete chlorine fixing and crack resistance performance and a preparation method and application thereof, aiming to solve the problem that the crack resistance of concrete prepared by the existing cement mortar mixed with carbon fiber needs to be further improved.

[0006] The technical solution of the present invention is as follows:

[0007] According to a first aspect of the present invention, a functionalized fiber material is provided, wherein the functionalized fiber material comprises carbon fibers and a functional material coating on the surface of the carbon fibers, wherein the functional material coating comprises magnesium oxide and / or aluminum oxide.

[0008] In the present invention, magnesium oxide and / or aluminum oxide are introduced to the surface of carbon fiber, which can effectively improve the interfacial adhesion between carbon fiber and cement mortar, thereby improving the crack resistance of concrete. When the functional material coating includes aluminum oxide, the functionalized fiber material is added to the cement mortar to not only improve its mechanical properties, but also improve the cement mortar's ability to bind chloride ions, thereby effectively improving the durability of concrete in a coastal environment. At the same time, compared to the direct addition of nanoparticles to cement mortar, magnesium oxide and / or aluminum oxide are attached to the surface of carbon fiber in the form of a coating and then added to the cement mortar, which can effectively avoid the problem of nanoparticles being easily agglomerated and affecting the performance of cement mortar.

[0009] In one embodiment, the length of the carbon fiber is 3 to 12 mm. For example, it can be 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 mm. When the carbon fiber is within this range, the mechanical properties (compressive strength, tensile strength, flexural strength, etc.) and shrinkage resistance of the cement mortar containing the functionalized fiber material are much better than those of the cement mortar containing pure carbon fiber.

[0010] The second aspect of the present invention provides a method for preparing the functionalized fiber material as described above, comprising the following steps:

[0011] S1. Provide carbon fiber;

[0012] S2. Forming a functional material coating on the surface of the carbon fiber by a sol-gel method to obtain the functionalized fiber material.

[0013] The specific surface area of ​​carbon fiber is relatively large, which means that there are more atoms or molecules exposed on its surface, thereby increasing the possibility of interaction with the external environment. These atoms or molecules exposed to the outside often have electronic structures and chemical properties different from those inside the material, so they are more likely to become active centers of reactions, i.e., active sites. In addition, the chemical composition of the surface of carbon fiber is diverse, including elements such as C, H, and O. The presence of these elements makes the surface of carbon fiber have abundant functional groups, such as hydroxyl, carboxyl, etc. These functional groups can react chemically with other substances, providing a reaction site for the growth of nanoparticles. In addition, the microstructure of the surface of carbon fiber also provides a large number of active sites for it. There may be structures such as micropores and grooves on the surface of carbon fiber. These structures not only increase the roughness of the surface, but also provide attachment points for the growth of nanoparticles. In these microstructures, nanoparticles can grow stably and connect to each other to form a uniform nanolayer. Therefore, the present invention utilizes the properties of carbon fiber and adopts a sol-gel method to form a functional material coating containing magnesium oxide and / or aluminum oxide on the surface of the carbon fiber.

[0014] In one embodiment, in step S1, the carbon fiber may be pretreated by heating it in a muffle furnace at 350° C. for 2.5 hours to remove the resin on the surface of the carbon fiber before proceeding to the subsequent steps.

[0015] In one embodiment, in step S2, when the functional material coating comprises magnesium oxide, the method for preparing the functionalized fiber material comprises the following steps:

[0016] S21, mixing a magnesium source, acetic acid and a first organic solvent to obtain a magnesium oxide precursor solution;

[0017] S22, immersing the carbon fiber in the magnesium oxide precursor solution, drying it, and then heating it at a first preset temperature for a first preset time to obtain the functionalized fiber material (the functionalized fiber material includes carbon fiber and a magnesium oxide coating on the surface of the carbon fiber).

[0018] In one embodiment, in step S21, the molar ratio of the magnesium source, acetic acid and the first organic solvent is 1: (1-9): 29, the magnesium source includes magnesium acetate hydrate, the first organic solvent includes ethanol, the first preset temperature is 300-500°C (for example, 300°C, 350°C, 400°C, 450°C or 500°C), and the first preset time is 1 hour. The heating temperature, i.e., the first preset temperature, has a significant effect on the crystallization of magnesium oxide, and this temperature range can ensure the formation of magnesium oxide.

[0019] In one embodiment, in step S2, when the functional material coating comprises aluminum oxide, the method for preparing the functionalized fiber material comprises the following steps:

[0020] Step A, providing AlOOH solution and carbon fiber;

[0021] Step B, soaking the carbon fiber in the AlOOH solution for a preset time and drying it;

[0022] Step C, soaking the dried product again in the AlOOH solution for a preset time, and then drying it again;

[0023] Step D, after repeating step C several times (the number of times can be set according to actual needs, such as 1 time, 2 times, 3 times, 4 times or 5 times, etc.), a functionalized fiber material precursor is obtained;

[0024] Step E: heating the functionalized fiber material precursor at a second preset temperature for a second preset time to obtain the functionalized fiber material (the functionalized fiber material includes carbon fibers and an aluminum oxide coating on the surface of the carbon fibers).

[0025] In some embodiments, in step A, the method for preparing the AlOOH solution comprises the following steps:

[0026] Aluminum sec-butoxide and sec-butanol are mixed in a volume ratio of (0.5-2.5):1, and then deionized water (the ratio of its volume to the sum of the volumes of aluminum sec-butoxide and sec-butanol is 1:(2-5)) is added, and stirred at 85° C. for 2 hours to obtain a mixed solution; then 1.0-2.5 mol / L nitric acid solution (the volume ratio of the nitric acid solution to the mixed solution is (0.01-0.025):1) is added to the mixed solution, and stirring is continued at 85° C. for 4 hours, and the obtained solution is refluxed overnight to obtain an AlOOH solution.

[0027] In some embodiments, in step B and step C, the preset time is 3 to 11 minutes (for example, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes or 11 minutes, etc.); in step E, the second preset temperature is 550 to 750°C (for example, 550°C, 600°C, 650°C, 700°C or 750°C, etc.), and the second preset time is 2.5 hours. During the heating process, AlOOH dehydrates to form Al 2 O 3 At this temperature, a good quality aluminum oxide coating can be formed.

[0028] The third aspect of the present invention provides use of the functionalized fiber material as described above in cement mortar or concrete.

[0029] A fourth aspect of the present invention provides a cement mortar, wherein the cement mortar comprises a first component and a second component;

[0030] In parts by mass, the first component includes 1 part of cement, 0.01-0.2 parts of silica fume, 0.5-2 parts of quartz sand, and 0.35-0.55 parts of water;

[0031] The mass of the second component accounts for 0.5%-8% of the mass of the cement;

[0032] The second component comprises at least one functionalized fiber material as described above in the present invention.

[0033] Of course, the cement mortar may also be added with a water reducing agent, such as a polycarboxylic acid high-efficiency water reducing agent, according to actual needs.

[0034] In the present invention, the second component may include carbon fiber containing magnesium oxide coating, may include carbon fiber containing aluminum oxide coating, may include carbon fiber containing magnesium oxide coating and carbon fiber containing aluminum oxide, and may include carbon fiber containing functional material coating (the functional material coating contains magnesium oxide and aluminum oxide).

[0035] The concrete obtained after curing the cement mortar provided by the invention has good crack resistance and chloride ion binding capacity, and has good durability in a seaside environment.

[0036] A fifth aspect of the present invention provides concrete, wherein the concrete is prepared from the cement mortar described above in the present invention.

[0037] A fifth aspect of the present invention provides a reinforced concrete component, wherein the reinforced concrete component comprises the concrete of the present invention as described above and steel bars located in the concrete.

[0038] Beneficial effects: In the present invention, magnesium oxide and / or aluminum oxide are introduced to the surface of carbon fiber, which can effectively improve the interfacial adhesion between carbon fiber and cement mortar, thereby improving the crack resistance of concrete. When the functional material coating includes aluminum oxide, the functionalized fiber material is added to the cement mortar to not only improve its mechanical properties, but also improve the cement mortar's ability to bind chloride ions, thereby effectively improving the durability of concrete in coastal environments. At the same time, compared to adding nanoparticles directly to cement mortar, magnesium oxide and / or aluminum oxide are attached to the surface of carbon fiber in the form of a coating and then added to cement mortar, which can effectively avoid the problem of nanoparticles being easily agglomerated and affecting the performance of cement mortar. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the XRD diagram of the functionalized fiber material prepared under different heating temperature conditions in Example 1.

[0040] Figure 2 These are SEM images of pure carbon fiber and functionalized fiber materials prepared under different heating temperature conditions in Example 1, where (a) is pure carbon fiber; (b) is 300°C; (c) is 400°C; and (d) is 500°C.

[0041] Figure 3 This is the XRD diagram of the functional fiber material prepared under different molar ratios of magnesium acetate hydrate, acetic acid and anhydrous ethanol in Example 2.

[0042] Figure 4 These are the SEM and EDS images of the functionalized fiber materials prepared under different molar ratios of magnesium acetate hydrate, acetic acid, and anhydrous ethanol in Example 2, wherein (a) is 1:1:29, SEM image; (b) is 1:3:29, SEM image; (c) is 1:6:29, SEM image; (d) is 1:9:29, SEM image; (e) is 1:1:29, EDS image; (f) is 1:3:29, EDS image; (g) is 1:6:29, EDS result image; (h) is 1:9:29, EDS result image.

[0043] Figure 5 The TG test and analysis results of the functionalized fiber material prepared under different molar ratios of magnesium acetate hydrate, acetic acid and anhydrous ethanol in Example 2 are shown in FIG. 1 , wherein (a) is a curve showing weight change with temperature; and (b) is the percentage of the remaining substance, i.e., MgO, after the TG test.

[0044] Figure 6 This is the XRD diagram of the functionalized fiber material prepared under different heating temperature conditions in Example 3.

[0045] Figure 7 These are SEM images of the functionalized fiber materials prepared under different heating temperature conditions in Example 3, where (a) is unheated; (b) is heated at 550°C; (c) is heated at 650°C; and (d) is heated at 750°C.

[0046] Figure 8 These are SEM images of the functionalized fiber materials prepared under different immersion time conditions in Example 4, where (a) is 5 min; (b) is 7 min; (c) is 9 min; and (d) is 11 min.

[0047] Fig. 9 The Al content in the functionalized fiber material prepared under different immersion time conditions in Example 4 is 2 O 3 Coating thickness distribution diagram, where (a) is 5 min; (b) is 7 min; (c) is 9 min; (d) is 11 min; (e) is 13 min.

[0048] Fig.10 These are the tensile strength test results of different cement mortars in Example 5.

[0049] Fig.11 This is a curve diagram showing the change in tensile strength of cement mortar with carbon fiber length in Example 5.

[0050] Fig.12 These are the test results of drying shrinkage performance of different cement mortars in Example 5.

[0051] Fig.13 This is a curve chart showing the change in flexural strength of cement mortar with carbon fiber length in Example 5.

[0052] Fig.14 This is a curve diagram showing the change of the compressive strength of the cement mortar with the length of the carbon fiber in Example 5.

[0053] Fig.15 These are the flexural strength test results of different cement mortars in Example 7.

[0054] Fig.16These are the compressive strength test results of different cement mortars in Example 7.

[0055] Fig.17 Figure 7 shows the compressive failure morphology of different cement mortars in Example 7, where (a) is ordinary cement mortar; (b) is cement mortar based on CF-3; (c) is cement mortar based on CF-6; (d) is cement mortar based on CF-12; (e) is cement mortar based on Al 2 O 3 @CF-3 cement mortar; (f) is Al-based 2 O 3 @CF-6 cement mortar; (g) is based on Al 2 O 3 @CF-12 cement mortar.

[0056] Fig.18 (a) is a graph showing the flexural strength test results of different cement mortars in Example 8, and (b) is a graph showing the compressive strength test results of different cement mortars.

[0057] Fig.19 These are the compressive failure morphologies of different cement mortars in Example 8, where (a) is ordinary cement mortar; (b) is cement mortar 1; (c) is cement mortar 2; (d) is cement mortar 3; (e) is cement mortar 5; and (f) is cement mortar 5.

[0058] Fig. 20 This is a graph showing the tensile strength test results of different cement mortars in Example 8.

[0059] Fig.21 The figures are the test results of drying shrinkage performance of different cement mortars in Example 8, wherein (a) is the drying shrinkage strain result figure, and (b) is the drying shrinkage performance improvement rate result figure. DETAILED DESCRIPTION

[0060] The present invention provides a functional fiber material with concrete chlorine fixation and crack resistance, a preparation method thereof, cement mortar, concrete and reinforced concrete components. In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0061] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0062] The present invention will be further described below by means of specific examples.

[0063] Unless otherwise specified, the raw materials used in the following examples are all commercially available products. Specifically, the cement used in the following examples is P.O42.5 grade ordinary Portland cement; SiO in silica ash is 2 The content is 94% and the fineness is 1500-2000 mesh.

[0064] The carbon fiber used in the following examples has a diameter of 7 μm and a density of 1.75 g / cm 3 , the tensile strength is 5490MPa.

[0065] Example 1

[0066] This embodiment provides four kinds of functionalized fiber materials, including the following steps:

[0067] The carbon fiber (length 3 mm) was placed in a muffle furnace and heated at 350° C. for 2.5 h for pretreatment to remove the resin on the surface of the carbon fiber so that the coating can be better coated on the carbon fiber to obtain the pretreated carbon fiber.

[0068] Magnesium acetate hydrate, acetic acid and anhydrous ethanol were mixed in a molar ratio of 1:6:29 to obtain a magnesium oxide precursor solution.

[0069] The pretreated carbon fibers were immersed in the above-mentioned magnesium oxide precursor solution for 5 min, then placed in an oven and baked at 85 °C for 24 h, and finally heated in a tubular furnace at vacuum and 300 °C (heating rate of 5 °C / min), vacuum and 400 °C (heating rate of 5 °C / min), and vacuum and 500 °C (heating rate of 5 °C / min) for 1 h to form a MgO coating on the surface of the carbon fibers, and three functionalized fiber materials were obtained, recorded as MgO@CF.

[0070] At the same time, the pretreated carbon fibers were immersed in the above-mentioned magnesium oxide precursor solution for 5 minutes, and then placed in an oven and baked at 85° C. for 24 hours. The obtained materials were recorded as unheated functionalized fiber materials.

[0071] The following tests were performed on the above three functionalized fiber materials and the unheated functionalized fiber material:

[0072] 1. Perform X-ray diffraction (XRD) test, the results are as follows Figure 1As shown in the figure, the results show that the heating temperature has a significant effect on the crystallization of MgO, reflecting the crystallization process of the MgO coating. The MgO coating in the unheated functionalized fiber material is in an amorphous state. When the temperature is heated to 300°C, magnesium acetate crystals appear. When the heating temperature is 400°C, MgO crystals appear. When the temperature continues to increase to 500°C, the crystallization is the same as at 400°C. The acetate group can promote the crystallization of MgO at low temperatures. A heating temperature of 400°C can transform the sol into stable MgO crystals. It can be seen that the formation process of MgO crystals is: as the temperature increases, the gel synthesized by the magnesium acetate hydrate / acetic acid / anhydrous ethanol composition system dehydrates into magnesium acetate and then decomposes into MgO. It can be considered that the last step of the reaction in the MgO precursor gel is the crystallization process of MgO.

[0073] 2. Perform a scanning electron microscope (SEM) test, and the results are as follows: Figure 2 shown. Figure 2 (a) shows that the surface of the original carbon fiber contains many grooves, which are conducive to the adhesion of the sol solution. Figure 2 (b), (c), and (d) show that many white fine particles are arranged along the carbon fiber axis, and the coating is in the form of nanocrystalline particles. The average diameter of these particles is about 130nm, that is, MgO is attached to the carbon fiber surface in the form of white particles. At the same time, elemental analysis was performed on the white particles and non-white particles. Oxygen and magnesium only exist in the white particles, while only carbon exists in the non-white particles, proving that the product is MgO.

[0074] The heating temperature not only affects the formation process of MgO crystals (as shown by the XRD results), but also affects the morphology of the MgO coating on the carbon fiber surface (as shown by the SEM results). When the heating temperature is 300°C, the white fine particles on the carbon fiber surface are relatively sparse, while when the heating temperature is 400°C, the white fine particles on the carbon fiber surface are dense and uniform. When the heating temperature is 500°C, the distribution of white fine particles begins to become uneven, and there are obvious accumulation areas and blank areas on the carbon fiber surface. Based on the analysis of the MgO crystal formation process and the carbon fiber surface coating morphology, the optimal heating temperature is 400°C.

[0075] Example 2

[0076] This embodiment provides four methods for preparing functionalized fiber materials, comprising the following steps:

[0077] The carbon fiber (length 3 mm) was placed in a muffle furnace and heated at 350°C for 2.5 h for pretreatment to obtain pretreated carbon fiber;

[0078] Magnesium acetate hydrate, acetic acid and anhydrous ethanol were mixed in molar ratios of 1:1:29, 1:3:29, 1:6:29 and 1:9:29, respectively, to obtain four magnesium oxide precursor solutions;

[0079] The pretreated carbon fibers were immersed in the above four magnesium oxide precursor solutions for 5 min respectively, then placed in an oven at 85 °C for 24 h, and finally heated in a tubular furnace under vacuum and 400 °C (heating rate of 5 °C / min) for 1 h to obtain four functionalized fiber materials.

[0080] The following tests were conducted on the four functionalized fiber materials:

[0081] 1. Carry out XRD test, the results are as follows Figure 3 As shown, it can be seen that the molar content of acetic acid has little effect on the crystallization transformation of MgO, and the magnesium oxide precursor solutions with different molar contents of acetic acid can all form MgO on the surface of carbon fiber.

[0082] 2. Perform SEM and EDS tests, the results are as follows: Figure 4 As shown in the figure, with the increase of the molar content of acetic acid, the magnesium content on the surface of the carbon fiber also increases. When the molar ratio of magnesium acetate hydrate, acetic acid and anhydrous ethanol is 1:1:29, 1:3:29, 1:6:29 and 1:9:29 respectively, the MgO content in the obtained functionalized fiber material is 3%, 12%, 29% and 29% respectively. At the same time, the results show that the molar content of acetic acid has a direct and significant effect on the quality of MgO coating. When the molar content of acetic acid in the sol is low, the MgO nanoparticles in the coating are locally distributed, resulting in poor coating coverage, while the molar content of acetic acid in the sol is high, which will cause the MgO nanoparticles to agglomerate and the carbon fiber surface coating to be uneven.

[0083] The specific reason is that when acetic acid is added to the sol, the free Mg in the precursor liquid 2+ The ions are reduced by forming a soluble magnesium acetate complex. After removing the solvent and decomposing the magnesium acetate, MgO nanoparticles are obtained. By adjusting the amount of acetic acid added, the hydrolysis reaction and polycondensation complexation process of magnesium acetate can be adjusted, thereby improving the stability of the gel and the final MgO crystal quality. When the amount of acetic acid added is small, the number of carboxyl groups contained in the sol system is small, and the carboxyl groups and Mg 2+ The average distance between them is long, which leads to slow complexation of magnesium acetate. 2+ The ions are over-hydrolyzed to form unstable MgO gel, accompanied by precipitation. The final result is that only part of the carbon fiber surface is covered by gel. As the acetic acid content increases, the number of carboxyl groups in the system increases, and the carboxyl groups and Mg 2+The distance between them is shortened, resulting in an increase in the polycondensation and complexation rate of magnesium acetate, and a good balance is maintained with the hydrolysis reaction. This is conducive to the uniform dispersion of magnesium acetate colloidal particles in the system, thereby forming a uniformly distributed fine MgO crystal coating on the carbon fiber surface. However, when acetic acid is added too much, the number of carboxyl groups in the system is greatly increased, resulting in an extremely fast complexation rate, a small number of initial MgO cores, and a fast growth rate of the core, and finally forming agglomeration of MgO. In the process of preparing the MgO coating, a suitable acetic acid complexing agent concentration can balance the hydrolysis and complexation reaction in the sol-gel, and finally obtain a better coating effect.

[0084] 3. In order to quantify the effect of different acetic acid molar contents on the quality of MgO coating on the carbon fiber surface, thermogravimetric (TG) analysis tests were performed. The results are shown in Figure 5 As shown, at 600°C, the carbon fiber begins to decompose, and the decomposition is completed at about 850°C, and the remaining mass is the mass of MgO. It can be seen that in this embodiment, a relatively ideal MgO coating can be obtained under different acetic acid molar contents, but with the increase of acetic acid molar content, the MgO content on the surface of the carbon fiber shows a trend of first increasing and then decreasing. When the molar ratio of magnesium acetate hydrate: acetic acid: anhydrous ethanol is 1:6:29, the MgO residual amount has a maximum value of 10.42%, that is, the molar ratio of magnesium acetate hydrate, acetic acid, and anhydrous ethanol is 1:6:29 as the optimal parameter, at this time, a coating with the most MgO nanoparticles and a more uniform coating can be obtained.

[0085] Example 3

[0086] This embodiment provides four methods for preparing functionalized fiber materials, including the following steps:

[0087] Step a: pretreating the carbon fiber (length 3 mm) by heating it at 350° C. for 2.5 h in a muffle furnace to obtain pretreated carbon fiber.

[0088] Step b, according to a volume ratio of 1.066:1, aluminum sec-butoxide and sec-butanol are mixed, and then deionized water (the ratio of its volume to the sum of the volumes of aluminum sec-butoxide and sec-butanol is 1:4.144) is added, and stirred at 85° C. for 2 hours to obtain a mixed solution; then 1.0 mol / L nitric acid solution (with a volume ratio of 0.025:1 to the mixed solution) is added to the mixed solution, and stirring is continued at 85° C. for 4 hours, and the resulting solution is refluxed overnight to obtain an AlOOH solution.

[0089] Step c, soaking the treated carbon fiber in the AlOOH solution for 7 minutes and drying it at 85°C.

[0090] Step d: soaking the dried product in the AlOOH solution again for 7 minutes, and then drying it again at 85° C. to obtain a functionalized fiber material precursor.

[0091] Step e: heating the functionalized fiber material precursor at 550°C, 650°C and 750°C for 2.5 hours respectively to form a coating on the surface of the carbon fiber to obtain three functionalized fiber materials, denoted as Al 2 O 3 @CF.

[0092] In addition, step e is not performed to obtain a functionalized fiber material precursor, which is recorded as an unheated functionalized fiber material.

[0093] The following tests were performed on the three functionalized fiber materials and the unheated functionalized fiber material:

[0094] 1. Carry out XRD test, the results are as follows Figure 6 As shown, Al can be formed under different conditions. 2 O 3 Specifically, α-Al 2 O 3 Crystal, ŋ-Al 2 O 3 When the heating temperature rises to 650℃, the characteristic peak of AlOOH disappears, and AlOOH loses water to generate Al 2 O 3 This means that the coating is completely transformed from amorphous state to Al at 650℃. 2 O 3 When the heating temperature is increased to 750℃, α-Al 2 O 3 and ŋ-Al 2 O 3 The peak intensity of the aluminum oxide nanoparticles is weakened. Therefore, the transformation process of aluminum oxide nanoparticles is that as the temperature increases, AlOOH dehydrates to form Al 2 O 3 .

[0095] 2. Perform SEM and EDS tests, the results are as follows Figure 7 As shown in Table 1, the results show that when not heated, the coating on the surface of the carbon fiber is extremely uneven and rough. After heating, the coating on the surface of the carbon fiber becomes smooth. In this embodiment, relatively good coatings can be obtained at the above different heating temperatures. Figure 7 (b) in the above equation, Figure 7 (c) and Figure 7 The coating on the carbon fiber surface in (d) is more completely wrapped. According to the EDS results in Table 1, Figure 7 (a) and Figure 7The Al element distribution in (d) is more uniform and dense. The mass fraction of Al element in (d) is as high as 13.23%, which is close to the mass fraction of Al element in the unheated functionalized fiber material. According to the analysis of XRD, SEM and EDS results, 750℃ is the best heating temperature to obtain uniform and dense Al 2 O 3 Dense coating.

[0096] Table 1. EDS results

[0097]

[0098] Example 4

[0099] This embodiment provides five methods for preparing functionalized fiber materials, including the following steps:

[0100] Step a: pretreating the carbon fiber (length 3 mm) by heating it at 350° C. for 2.5 h in a muffle furnace to obtain pretreated carbon fiber.

[0101] Step b, according to a volume ratio of 1.066:1, aluminum sec-butoxide and sec-butanol are mixed, and then deionized water (the ratio of its volume to the total volume of aluminum sec-butoxide and sec-butanol is 1:4.144) is added, and stirred at 85° C. for 2 hours to obtain a mixed solution; then 1.0 mol / L nitric acid solution (with a volume ratio of 0.025:1 to the mixed solution) is added, and stirring is continued at 85° C. for 4 hours, and the resulting solution is refluxed overnight to obtain an AlOOH solution.

[0102] Step c, soaking the treated carbon fiber in the AlOOH solution for 5 minutes and drying at 85°C.

[0103] Step d: soaking the dried product in the AlOOH solution again for 5 minutes, and then drying it again at 85° C. to obtain a functionalized fiber material precursor.

[0104] Step e: heating the functionalized fiber material precursors at 750° C. for 2.5 hours to form a coating on the surface of the carbon fiber to obtain a functionalized fiber material.

[0105] The above steps are repeated, but the only difference from the above steps is that the soaking time in step c and step d is 7 minutes, to obtain a functionalized fiber material.

[0106] The above steps are repeated, but the only difference from the above steps is that the soaking time in step c and step d is 9 minutes, to obtain a functionalized fiber material.

[0107] The above steps are repeated, but the only difference from the above steps is that the soaking time in step c and step d is 11 minutes, to obtain a functionalized fiber material.

[0108] The above steps were repeated, but the only difference from the above steps was that the soaking time in step c and step d was 13 minutes, to obtain a functionalized fiber material.

[0109] The above five functionalized fiber materials were tested as follows:

[0110] 1. Perform SEM and EDS tests, the results are as follows Figure 8 As shown in Table 2, it can be seen that different immersion times can form Al on the surface of carbon fiber. 2 O 3 Coating, but longer (11min) or shorter (5min) time will cause Al 2 O 3 The coating is not completely wrapped around the carbon fiber, and part of the carbon fiber surface is exposed. The time is 7min or 9min, Al 2 O 3 The coating completely and evenly wrapped the carbon fiber. When the immersion time was 11 minutes, Al 2 O 3 Coating agglomeration. From the EDS results in Table 2, it can be found that when the immersion time is 11 minutes, the Al element in the functionalized fiber material accounts for the largest proportion, reaching 20.47%; when the immersion time is 9 minutes, the Al element accounts for the smallest proportion.

[0111] Table 2. EDS results

[0112]

[0113] 2. In order to calculate the Al content on the carbon fiber surface under different immersion times 2 O 3 The thickness of the coating was obtained by measuring the diameter of 20 functionalized fibers by SEM and subtracting the diameter of the original carbon fiber (without coating). 2 O 3 Coating thickness distribution diagram, the results are as follows Fig. 9 As the immersion time increases from 5 min to 13 min, Al 2 O 3 The thickness of the coating showed a trend of increasing first and then decreasing. When the time was 11 minutes, the coating was the thickest at 1221nm. 2 O 3 The coating thickness is reduced to 791nm. At first, as time goes by, the coating on the carbon fiber surface changes from thin to thick. 2 O 3If the coating is too thick, the tensile stress generated during shrinkage is too large, which leads to the generation and growth of cracks and eventually some macroscopic peeling. Based on SEM, EDS analysis and diameter statistics, the optimal immersion time is 11 minutes.

[0114] Example 5

[0115] This embodiment provides a method for preparing cement mortar, comprising the following steps:

[0116] (1) Preparation of functional fiber materials based on carbon fibers of different lengths

[0117] Carbon fibers with lengths of 3 mm, 6 mm, and 12 mm were placed in a muffle furnace and heated at 350° C. for 2.5 h for pretreatment to obtain three types of pretreated carbon fibers (respectively designated as CF-3, CF-6, and CF-12).

[0118] Magnesium acetate hydrate, acetic acid and anhydrous ethanol were mixed in a molar ratio of 1:6:29 to obtain a magnesium oxide precursor solution.

[0119] The three pretreated carbon fibers were immersed in the above-mentioned magnesium oxide precursor solution for 5 min, then placed in an oven and baked at 85 °C for 24 h, and finally heated in a tube furnace under vacuum and 400 °C (heating rate of 5 °C / min) for 1 h to form a MgO coating on the surface of carbon fibers of different lengths, and three functionalized fiber materials were obtained, which were respectively recorded as MgO@CF-3, MgO@CF-6, and MgO@CF-12.

[0120] (2) Preparation of cement mortar based on functionalized fiber materials of different lengths

[0121] In parts by mass, 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand are mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water and MgO@CF-3 (0.02 parts) are mixed and stirred evenly to obtain a second mixed solution; the second mixed solution is added to the first mixed solution and stirred rapidly for 1 minute to obtain a cement mortar based on MgO@CF-3 (which may be referred to as a MgO@CF-3 group) (if all the raw materials are mixed and stirred at the same time, it will cause uneven distribution of the functionalized fiber material and agglomeration, and then introduce too many weak interface areas, which will seriously damage the mechanical properties of the cement mortar. However, the present embodiment improves the process, that is, the aggregate and the cementitious material are first stirred for 1 minute, and the functionalized fiber material and water are mixed and stirred evenly, and then the mixture of the functionalized fiber material and water is added to the mixture of the aggregate and the cementitious material and stirred rapidly for 1 minute. In this way, the functionalized fiber material is evenly dispersed and the mechanical properties are significantly improved);

[0122] At the same time, 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water and MgO@CF-6 (0.02 parts) were mixed and stirred evenly to obtain a second mixed solution; the second mixed solution was added to the first mixed solution and quickly stirred for 1 minute to obtain a cement mortar based on MgO@CF-6 (which can be called MgO@CF-6 group);

[0123] By weight, 1 part of cement, 0.1 part of silica fume, and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water and MgO@CF-12 (0.02 parts) were mixed and stirred evenly to obtain a second mixed solution; the second mixed solution was added to the first mixed solution and quickly stirred for 1 minute to obtain a cement mortar based on MgO@CF-12 (which can be referred to as a MgO@CF-12 group);

[0124] By weight, 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water and CF-3 (0.02 parts) were mixed and stirred evenly to obtain a second mixed solution; the second mixed solution was added to the first mixed solution and quickly stirred for 1 minute to obtain a CF-3-based cement mortar (which may be referred to as a CF-3 group);

[0125] By weight, 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water and CF-6 (0.02 parts) were mixed and stirred evenly to obtain a second mixed solution; the second mixed solution was added to the first mixed solution and quickly stirred for 1 minute to obtain a CF-6-based cement mortar (which may be referred to as a CF-6 group);

[0126] By weight, 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water and CF-12 (0.02 parts) were mixed and stirred evenly to obtain a second mixed solution; the second mixed solution was added to the first mixed solution and quickly stirred for 1 minute to obtain a CF-12-based cement mortar (which may be referred to as a CF-12 group);

[0127] 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed solution; then 0.48 parts of water were added to the first mixed solution and stirred rapidly for 1 minute to obtain a cement mortar (for comparison, it can be called PC group);

[0128] The above cement mortar was tested as follows:

[0129] 1. After curing different cement mortars for 28 days, the tensile strength test was carried out. The results are as follows: Fig.10 As shown in the figure, it can be seen that after the carbon fiber surface is coated with MgO coating, the tensile strength of cement mortar can be improved (that is, the tensile strength of concrete obtained after cement mortar curing is improved). Specifically, MgO nanoparticles react with water to generate Mg(OH) 2 , volume expansion, can effectively fill the gap between carbon fiber and cement matrix interface. At the same time, MgO can also react with Al in cement matrix 2 O 3 、SiO 2 The reaction produces magnesium aluminate spinel (MgAl 2 O 4 ) and magnesium silicate (MgSiO 3 ), these hard compounds can fill the micro cracks in the cement matrix. In addition, the MgO coating helps to improve the physical friction and chemical bonding between the carbon fiber and the cement matrix, thereby effectively improving the tensile strength.

[0130] The figure below compares the tensile strength variation trend of cement mortar reinforced with carbon fiber (CF) and functionalized fiber material (MgO@CF) at different carbon fiber lengths. The tensile strength data were fitted, as shown in the figure below. Fig.11 The fitting curves shown show that, at the same dosage of CF and MgO@CF, with the increase of carbon fiber length, the tensile strength of cement mortar based on CF and cement mortar based on MgO@CF both show a trend of first increasing and then decreasing. When the carbon fiber length is in the range of 0-12mm, the tensile strength of cement mortar based on MgO@CF is higher than that of cement mortar based on CF. According to the fitting relationship, the tensile strength of cement mortar based on MgO@CF reaches a maximum value of 3.96MPa at a carbon fiber length of 8.30mm, and the tensile strength of cement mortar based on CF reaches a maximum value of 3.14MPa at a fiber length of 9.50mm.

[0131] 2. Test the drying shrinkage rate of the sample according to GB-T 29417-2012 "Test Method for Drying Shrinkage and Cracking Performance of Cement Mortar and Concrete". The sample size is 160mm×40mm×40mm. The test block cast with the above cement mortar is demoulded after curing for 2 days in a natural environment. The demoulded test block is first cured in water at 20±2℃ for 1 day, and the water stains are wiped off and the initial length L is tested with a comparator. 0 , and pay attention to the direction and position of the calibration test block, which will remain unchanged in the future. Transfer the test block to a curing box with a temperature of 20±2℃ and a relative humidity of 60%±5% and cure it to the specified age, and test its length L t During the test, mark the surface of the test block, always keep the same side of the test block facing the tester, and keep the same end of the test block facing up, to ensure the accuracy of the test results. The drying shrinkage calculation formula is as follows:

[0132]

[0133] Where: ——Drying shrinkage of the specimen at age t;

[0134] ——The measured length of the specimen at age t (mm);

[0135] ——Measurement value of the initial length of the test piece (mm);

[0136] ——The reference length of the test piece (250mm).

[0137] The results are as follows Fig.12 As shown, on the 1st to 3rd day, the drying shrinkage strains of the 7 groups of specimens almost overlapped. This may be because the specimens are in the early stage of hydration reaction and the fibers have not yet been effectively connected to the cement matrix. However, the bonding strength between the carbon fiber and the matrix is ​​insufficient at this time, so the drying shrinkage rates of the groups are almost the same. As the age increases, the bonding strength increases, and the carbon fiber will prevent or reduce shrinkage deformation to a certain extent. Therefore, the drying shrinkage rate of the group with added carbon fiber is significantly lower than that without added carbon fiber. When the carbon fiber length is 3mm and 6mm, the drying shrinkage strain of the carbon fiber group containing MgO coating (MgO@CF group) is significantly lower than that of the carbon fiber group; when the carbon fiber length is 12mm, the drying shrinkage strains of the two are almost the same. Mg(OH) generated by the reaction of MgO with water 2 It will bring about a 117% molar volume expansion, and at the same time improve the interfacial bonding between carbon fiber and cement matrix, so that at the same fiber length, the shrinkage resistance of the MgO@CF group is better than that of the CF group. In addition, based on the blank group, the shrinkage performance improvement rate of CF and MgO@CF with incorporation lengths of 3mm, 6mm and 12mm was calculated. For the CF group, as the length of carbon fiber increases, the shrinkage resistance also increases. For the MgO@CF group, when the fiber length is 3mm and 6mm, the shrinkage resistance of the specimen is improved, but when the fiber length is 12mm, the shrinkage resistance of the specimen decreases and is lower than that of the CF group with the same length. As mentioned earlier, Mg(OH) 2 It will bring about a 117% molar volume expansion and improve the interfacial bonding between carbon fiber and cement matrix, so that at the same fiber length, the anti-shrinkage performance of the MgO@CF group is better than that of the CF group.

[0138] 3. After curing different cement mortars for 28 days, test blocks were obtained and the specific surface area (BET) test was performed. The results are shown in Table 3. It can be seen that the maximum average pore size of the test blocks is the PC group, reaching 24.4106nm. The average pore sizes of the CF-3, CF-6, CF-12, MgO@CF-3, and MgO@CF-6 groups decrease in turn, and the average pore size of the MgO@CF-12 group (i.e., the test blocks obtained by curing cement mortar based on MgO@CF-12) increases to 24.0407. The trend of the average pore size change is the same as the drying shrinkage rate. Therefore, the addition of CF and MgO@CF affects the drying shrinkage performance of the specimen by affecting the internal pores of the cement mortar.

[0139] Table 4. BET test results

[0140]

[0141] 4. According to the provisions of GB-T17671-1999 "Test Method for Cement Mortar Strength (ISO Method)", the flexural strength performance test of the specimens cured for 28 days under standard conditions was carried out, and the test results were fitted. The results are as follows: Fig.13 As shown in the figure, the flexural strength of cement mortar based on MgO@CF first increases and then decreases with the length of carbon fiber, and in the length range of 0-12 mm, the flexural strength of cement mortar based on MgO@CF is greater than that of cement mortar based on CF. It can be seen that MgO@CF can effectively increase the flexural strength of cement mortar.

[0142] 5. According to the provisions of GB-T17671-1999 "Test Method for Cement Mortar Strength (ISO Method)", the broken semi-prism specimens were subjected to compression tests, and the test results were fitted to obtain the following: Fig.14 From the fitting curves shown, it can be seen that the compressive strength of the cement mortar based on CF and the cement mortar based on MgO@CF first increases and then decreases with the increase of carbon fiber length, and the intersection is obtained at (11.53, 36.57). When the carbon fiber length is 0-11.53mm, the compressive strength of the cement mortar based on MgO@CF is greater than that of the cement mortar based on CF. Similar to the tensile strength and drying shrinkage properties, the MgO coating on the surface of the carbon fiber will make the compressive strength of the cement mortar based on MgO@CF reach the maximum value first. When the carbon fiber length is 5.97mm, the compressive strength of the cement mortar based on MgO@CF reaches the maximum value of 48.98MPa.

[0143] It can be seen from the above test results that the introduction of the functionalized fiber material provided by the present invention into cement mortar can significantly enhance the tensile strength, flexural strength and compressive strength of cement mortar, and the functionalized fiber material improves the drying shrinkage performance of cement mortar by improving the porosity of cement mortar. Among them, the MgO@CF-3 group has the best performance in tensile strength and compressive strength. Compared with the CF-3 group, the tensile strength and compressive strength increased by 45.45% and 20.02%, respectively. The flexural strength of the MgO@CF-12 group reached the maximum, an increase of 46.04% compared with the CF-12 group. The drying shrinkage performance of the MgO@CF-6 group was most significantly improved, with an improvement rate of 15.89% compared with the PC group.

[0144] Example 6 Chloride ion binding performance test of functionalized fiber material

[0145] (1) Preparation of functional fiber materials

[0146] Step a: pretreating the carbon fiber (length 3 mm) by heating it at 350° C. for 2.5 h in a muffle furnace to obtain three kinds of pretreated carbon fibers.

[0147] Step b, according to a volume ratio of 1.066:1, aluminum sec-butoxide and sec-butanol are mixed, and then deionized water (the ratio of its volume to the sum of the volumes of aluminum sec-butoxide and sec-butanol is 1:4.144) is added, and stirred at 85° C. for 2 hours to obtain a mixed solution; then a 1.0 mol / L nitric acid solution (with a volume ratio of 0.025:1 to the mixed solution) is added to the mixed solution, and stirring is continued at 85° C. for 4 hours, and the resulting solution is refluxed overnight to obtain an AlOOH solution.

[0148] Step c, soaking the treated carbon fiber in the AlOOH solution for 11 minutes and drying at 85° C.;

[0149] Step d, soaking the dried product in the AlOOH solution again for 11 minutes, and then drying it again at 85° C. to obtain a functionalized fiber material precursor;

[0150] Step e: heating the functionalized fiber material precursor at 750° C. for 2.5 h to form a coating on the surface of the carbon fiber to obtain a functionalized fiber material, denoted as Al 2 O 3 @CF.

[0151] (2) Preparation of cement paste

[0152] By mass, 1 part of cement, 0.48 parts of water, 0.35 parts of NaCl solution (concentration of 1 mol / L) and Al 2 O 3@CF (0.0078 parts) was mixed and stirred evenly to obtain cement paste.

[0153] At the same time, only change Al 2 O 3 The dosage of @CF was 0.0156, 0.0312, 0.0467, 0.0623 and 0.0779 parts respectively for the preparation of cement paste, and a total of 6 types of cement paste were prepared.

[0154] The above six cement pastes were tested for water-soluble chloride ion concentration:

[0155] This test method refers to the relevant chapters of the method for testing the water-soluble chloride ion content of hardened concrete in JGJ / T 322-2013 "Technical Specifications for the Detection of Chloride Ion Content in Concrete" and JTJ27-98 "Test Specifications for Concrete in Water Transport Engineering". The specific test process is to grind the test block that has been cured to a certain age and take samples. The obtained powder is placed in an oven at 60°C for drying, sieved, and 3g of powder and 80mL of deionized water are weighed to prepare the test water-soluble chloride ion content. - The sample with 0.02 mol / L AgNO 3 The solution is titrated with chloride ions. The consumed AgNO is finally recorded. 3 Volume, water-soluble Cl - The content is calculated as follows:

[0156]

[0157] Where: P—Cl - content(%);

[0158] C—molar concentration of the silver nitrate solution used (0.01 mol / L);

[0159] V—the volume of silver nitrate solution consumed (mL);

[0160] M—Cl - Molar mass (35.5 g / mol);

[0161] m—weight of powder taken (3g).

[0162] The results are shown in Table 5. It can be seen that with the increase of Al 2 O 3 @With the increase of CF dosage, the free chloride ion content in cement paste gradually decreases and is lower than 0.006%.

[0163] Table 5. Chloride ion concentration test results in Example 6 (28 days)

[0164]

[0165] Example 7

[0166] This embodiment provides a method for preparing cement mortar, comprising the following steps:

[0167] (1) Preparation of functional fiber materials based on carbon fibers of different lengths

[0168] Carbon fibers with lengths of 3 mm, 6 mm, and 12 mm were placed in a muffle furnace and heated at 350° C. for 2.5 h for pretreatment to obtain three types of pretreated carbon fibers (respectively designated as CF-3, CF-6, and CF-12).

[0169] Step b: providing an AlOOH solution, the preparation method of which is the same as that of Example 6.

[0170] Step c, soaking the three treated carbon fibers in the AlOOH solution for 11 minutes and drying them at 85° C.;

[0171] Step d, soaking the dried product in the AlOOH solution again for 11 minutes, and then drying it again at 85° C. to obtain a functionalized fiber material precursor;

[0172] Step e: The functionalized fiber material precursors are respectively placed at a temperature of 750° C. and heated for 2.5 h to form a coating on the surface of the carbon fiber to obtain three functionalized fiber materials, which are respectively denoted as Al 2 O 3 @CF-3, Al 2 O 3 @CF-6, Al 2 O 3 @CF-12.

[0173] (2) Preparation of cement mortar based on functionalized fiber materials of different lengths

[0174] The only difference from Example 5 is that MgO@CF-3, MgO@CF-6, and MgO@CF-12 are replaced by Al 2 O 3 @CF-3, Al 2 O 3 @CF-6, Al 2 O 3 @CF-12, respectively based on Al 2 O 3 @CF-3 cement mortar, based on Al 2 O 3 @CF-6 cement mortar, based on Al 2 O 3 @CF-12 cement mortar.

[0175] The above cement mortar was tested as follows:

[0176] 1. After curing different cement mortars, the flexural strength and compressive strength tests were carried out. The results are as follows: Fig.15 and Fig.16 As shown. Fig.15 It can be seen that compared with the PC group (its composition and preparation method are shown in Example 5), CF and Al 2 O 3 The addition of @CF significantly improves the flexural and compressive strength of cement mortar. For flexural strength, when the carbon fiber lengths are 3mm, 6mm, and 12mm, respectively, based on Al 2 O 3 The flexural strength of cement mortar with @CF was increased by 4.89%, 17.29% and 21.21% respectively compared with that of PC group. 2 O 3 The flexural strength of cement mortar based on Al@CF is 22.49% and 4.94% higher than that based on CF, respectively. 2 O 3 Can react with Ca(OH) 2 The reaction generates calcium aluminate hydrate, so that the functionalized fiber material provided by the present invention is chemically bonded to the cement-based material. 2 O 3 @CF group, as the length of carbon fiber increases, its flexural strength also increases. This means that the longer the carbon fiber, the better the bridging effect. Fig.16 It can be seen that adding CF or Al into cement mortar 2 O 3 @CF can improve the compressive strength of cement mortar. 2 O 3 @CF-3 Group and Al 2 O 3 The increases in compressive strength of the @CF-6 group were 26.24% and 19.46%, respectively.

[0177] The compressive failure morphology of ordinary cement mortar (such as PC group cement mortar in Example 5) is as follows Fig.17 As shown in (a), it presents a typical brittle shear failure mode, with a large degree of damage and a chamfered cone-shaped failure. The surrounding parts peel off from top to bottom, and the failure surface is clean and tidy with almost no debris. This is because cement mortar itself is a brittle material with very small lateral restraint force. Under the action of two-way compression force, the four surfaces perpendicular to the pressure surface are prone to cracks and damage, and the material is easy to fall off. Based on CF and Al 2 O 3After the @CF cement mortar was cured, the specimens did not fall off, only vertical cracks or oblique cracks appeared on the surface, and the integrity was good. This shows that carbon fiber plays a role of connecting inside the cement mortar specimen, providing lateral constraints during the compression process, which is conducive to improving the compressive ultimate bearing capacity of the specimen.

[0178] Example 8

[0179] (1) Preparation of cement paste and related tests

[0180] MgO@CF (wherein the length of CF is 3 mm, and MgO@CF is prepared by the method in Example 5) and Al 2 O 3 @CF (wherein the length of CF is 3 mm and is prepared by the method in Example 6) are mixed in mass ratios of 1:9, 3:7, 5:5, 7:3 and 9:1 to obtain functionalized fiber material 1, functionalized fiber material 2, functionalized fiber material 3, functionalized fiber material 4 and functionalized fiber material 5, respectively.

[0181] By mass, 1 part of cement, 0.48 parts of water, 0.35 parts of NaCl solution (concentration of 1 mol / L) and functionalized fiber material 1 (0.02 parts) were mixed and stirred evenly to obtain cement paste 1; at the same time, the functionalized fiber material 1 was replaced by functionalized fiber material 2, functionalized fiber material 3, functionalized fiber material 4 and functionalized fiber material 5 to obtain cement paste 2, cement paste 3, cement paste 4 and cement paste 5 respectively. Then the chloride ion binding performance test was carried out. The results are shown in Table 6. When the curing age was 28 days, the free chloride ion concentration of each group was far below 0.06%, and when Al 2 O 3 When the CF content is reduced to a certain proportion, the concentration of free chloride ions in cement paste no longer increases with the increase of Al 2 O 3 @CF content decreases with the decrease, and is around 0.056%.

[0182] Table 6. Chloride ion concentration test results in Example 8 (28 days)

[0183]

[0184] (2) Preparation of cement mortar and related tests

[0185] 1 part of cement, 0.1 part of silica fume and 1 part of quartz sand were mixed and stirred for 1 minute to obtain a first mixed liquid; 0.48 parts of water and functionalized fiber material 1 (0.02 parts) were mixed and stirred evenly to obtain a second mixed liquid; the second mixed liquid was added to the first mixed liquid and quickly stirred for 1 minute to obtain cement mortar 1; at the same time, the functionalized fiber material 1 was replaced with functionalized fiber material 2, functionalized fiber material 3, functionalized fiber material 4 and functionalized fiber material 5, respectively, to obtain cement mortar 2, cement mortar 3, cement mortar 4 and cement mortar 5, respectively.

[0186] 1. After 28 days of curing, the flexural strength and compressive strength tests were carried out on cement mortar 1, cement mortar 2, cement mortar 3, cement mortar 4 and cement mortar 5. The results are as follows: Fig.18 As shown in the figure, it can be seen that with the increase of MgO@CF content, the flexural strength of cement mortar decreases continuously. 2 O 3 When the content ratio of MgO@CF and Al is 1:9, 3:7, 5:5, 7:3, and 9:1, the flexural strength increases by 25.12%, 17.29%, 6.36%, 2.94%, and -0.65%, respectively. It can be seen that the flexural strength of the specimen is mainly controlled by the MgO content. 2 O 3 When the CF content ratio is 9:1, the flexural strength is 6.09MPa, slightly lower than the PC group 6.13Mpa. When the content ratio of the two is 1:9, the flexural strength reaches the maximum value of 7.67MPa.

[0187] It can be found in the compressive strength results that MgO@CF and Al 2 O 3 The compressive strength of each group with different proportions of MgO@CF was much higher than that of the PC group (its composition and preparation method were the same as those in Example 5). 2 O 3 When the ratio of @CF is 9:1, the compressive strength is the highest, reaching 44.05MPa. When the ratio of the two is 1:9 and 7:3, the compressive strength is smaller, reaching 38.97MPa and 38.65MPa respectively.

[0188] The compressive failure forms of each group of specimens are as follows: Fig.19 As shown, it can be seen that changing the MgO@CF and Al 2 O 3 The proportion of @CF had no significant effect on the apparent failure morphology, and all groups showed a non-brittle failure mode.

[0189] 2. After 28 days of curing, the tensile strength of cement mortar 1, cement mortar 2, cement mortar 3, cement mortar 4 and cement mortar 5 was tested. The results are as follows: Fig. 20 As shown, compared with the PC group (whose composition and preparation method are the same as in Example 5), MgO@CF and Al 2 O 3 The tensile strength of each group with different proportions of MgO@CF was significantly improved. 2 O 3 When the @CF dosage ratio is 1:9, 3:7, 5:5, 7:3, and 9:1, the tensile strength is increased by 86.40%, 72.52%, 62.32%, 33.39%, and 82.94% respectively compared with the PC group.

[0190] 3. The drying shrinkage performance test was carried out on cement mortar 1, cement mortar 2, cement mortar 3, cement mortar 4 and cement mortar 5. The results are as follows: Fig.21 As shown, compared with the PC group (whose composition and preparation method are the same as in Example 5), MgO@CF and Al 2 O 3 The drying shrinkage strain of each group with different proportions of MgO@CF was significantly reduced, but the difference between them was not large. 2 O 3 The drying shrinkage performance first increases and then decreases as the proportion of MgO@CF is reduced. 2 O 3 When the doping ratio of MgO@CF and Al is 5:5, the improvement rate reaches a maximum of 11.45%. 2 O 3 @When the CF dosage ratio is 9:1, the minimum is 7.13%.

[0191] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A cement mortar, characterized in that: The cement mortar comprises a first component and a second component; In parts by mass, the first component includes 1 part of cement, 0.01-0.2 parts of silica fume, 0.5-2 parts of quartz sand, and 0.35-0.55 parts of water; The mass of the second component accounts for 0.5%-8% of the mass of the cement; The second component comprises at least one of the following functionalized fiber material a, functionalized fiber material b and functionalized fiber material c: Functionalized fiber material a: comprising carbon fiber, and a functional material coating located on the surface of the carbon fiber, wherein the functional material coating comprises magnesium oxide; Functionalized fiber material b: comprising carbon fiber, and a functional material coating located on the surface of the carbon fiber, wherein the functional material coating comprises aluminum oxide; Functionalized fiber material c: comprising carbon fiber, and a functional material coating located on the surface of the carbon fiber, wherein the functional material coating comprises magnesium oxide and aluminum oxide; The length of the carbon fiber is 3-12 mm.

2. The cement mortar according to claim 1, characterized in that: The preparation method of the functionalized fiber material a comprises the following steps: Mixing a magnesium source, acetic acid and a first organic solvent to obtain a magnesium oxide precursor solution; The carbon fiber is immersed in the magnesium oxide precursor solution, dried, and then heated at a first preset temperature for a first preset time to obtain the functionalized fiber material a.

3. The cement mortar according to claim 2, characterized in that: The molar ratio of the magnesium source, acetic acid and the first organic solvent is 1:(1-9):29, the magnesium source includes magnesium acetate hydrate, the first organic solvent includes ethanol, the first preset temperature is 300-500° C., and the first preset time is 1 hour.

4. The cement mortar according to claim 1, characterized in that: The preparation method of the functionalized fiber material b comprises the following steps: Step A, providing AlOOH solution and carbon fiber; Step B, soaking the carbon fiber in the AlOOH solution for a preset time and drying it; Step C, soaking the dried product again in the AlOOH solution for a preset time, and then drying it again; Step D: Repeat step C several times to obtain a functionalized fiber material precursor; Step E: heating the functionalized fiber material precursor at a second preset temperature for a second preset time to obtain the functionalized fiber material b.

5. The cement mortar according to claim 4, characterized in that: In step B and step C, the preset time is 3-11 minutes; in step E, the second preset temperature is 550-750° C., and the second preset time is 2.5 hours.

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