KR102175574B1 - Mortar composition comprising carbon fiber coated with silica nanoparticles and fiber reinforced mortar produced therefrom - Google Patents

Abstract

A mortar composition according to the present invention contains carbon fibers coated with silica nanoparticles, admixtures, cement, aggregate, and water, and a carbon fiber reinforced mortar manufactured from the same has an effect of having excellent compressive strength and flexural strength, and thus has an effect of having excellent dispersibility even when carbon fibers are contained, and having excellent workability due to high fluidity.

Description

Mortar composition comprising carbon fiber coated with silica nanoparticles and fiber reinforced mortar produced therefrom.

The present invention relates to a mortar composition comprising carbon fibers coated with silica nanoparticles and a carbon fiber reinforced mortar prepared therefrom.

Cement mortar or concrete, which is one of the major construction materials, is a construction material with superior mechanical performance and high durability compared to other construction materials, but its flexural strength and tensile strength are about 1/10 of the compressive strength, and under the action of bending and tensile loads. Therefore, it has a brittle property in which the stress rapidly decreases after the initial cracking occurs. In order to compensate for these shortcomings, there is a fiber-reinforced cement composite material that improves brittleness by mixing various fibers, and research on this has been actively conducted mainly in advanced countries such as North America, Europe, and Japan. Even in Korea, cement composite materials using various fibers as cement reinforcing materials have been reviewed, but the development of fiber-reinforced cement composite materials that can be commercialized is insufficient.

On the other hand, carbon fiber (CF) refers to a fiber composed of at least 92% or more carbon elements, and is classified into polyacrylonitrile (PAN)-based, pitch-based, and rayon-based, etc. depending on the manufacturing method and raw material. Can be, and can be divided into short fibers and long fibers according to the fiber length. In the early stages of development, due to the increased economic burden, large-scale applications such as construction materials were somewhat difficult, but the mechanical properties of carbon fiber and the mechanical properties such as chemical stability were high, and thus, it is attracting much attention at home and abroad as a cement reinforcement. In particular, carbon fiber is a promising new material that can be called a high-tech composite material of the 21st century with high tensile strength and tensile modulus.

Therefore, recently, research for the development of carbon fiber reinforced cement composites (CFRCC) mixed with carbon fibers is being conducted, and carbon fibers are used as cement composites to improve flexural strength and tensile strength. . By including the fiber, such a composite material can suppress local destruction due to an impact load, and improve bending toughness and resistance to impact.

However, until now, carbon fiber-reinforced cement composites have various problems due to carbon fiber mixing, such as a problem of lowering compressive strength, a problem of matrix and adhesion strength, a problem of lowering dispersibility and workability due to agglomeration of fibers in the manufacturing process. As side effects are accompanied, there is a limit to commercialization, and research to overcome this is needed.

Korean Registered Patent Publication No. 10-0857475

An object of the present invention is a mortar composition with remarkably high adhesion strength due to dense bonding of carbon fibers on a matrix in the mortar composition, and remarkably improved mechanical properties of the mortar by dispersing carbon fibers evenly on the matrix, and a carbon fiber reinforced mortar prepared therefrom Is to provide.

Another object of the present invention is to provide a mortar composition and a carbon fiber-reinforced mortar made of the mortar composition capable of minimizing a decrease in compressive strength while having excellent flexural strength.

Another object of the present invention is to provide a mortar composition having excellent dispersibility of components in the composition and high fluidity and excellent workability.

The mortar composition according to the present invention includes a carbon fiber coated with silica nanoparticles, an admixture, a cement, an aggregate, and water.

In one example of the present invention, the carbon fiber may be coated by bonding silica nanoparticles to the surface of the carbon fiber by a reaction of a silane coupling agent and a curing agent.

In an example of the present invention, the silica nanoparticles may be chemically bonded to the surface of the carbon fiber by using a material bonded by the reaction of the silane coupling agent and the curing agent as a linker, and the functional group of the silane coupling agent It is bonded to the silica nanoparticles, and the functional group of the curing agent may be bonded to the surface of the carbon fiber.

In one example of the present invention, the silane coupling agent may be represented by the following formula (1), and the curing agent may include a diamine-based compound. In the following formula (1), X is selected from an epoxy group or a (C1-C30) alkyl group substituted with a glycidoxy group, and R is independently selected from a linear or branched (C1-C7) alkyl group.

[Formula 1]

X-Si-(OR) ₃

In one example of the present invention, the silane coupling agent may include glycidoxyalkyl alkoxysilane, and the diamine-based compound may include alkylenediamine.

In an example of the present invention, the admixture may include inorganic particles having an average particle diameter of 0.01 to 100 μm and a specific surface area of 3 to 1 million cm ² /g.

In one example of the present invention, the admixture may include any one or two or more selected from silica fume, pozzolan, fly ash, blast furnace slag, volcanic glass and rice husk ash.

The mortar composition according to an embodiment of the present invention may further include a strength reinforcing agent, and the strength reinforcing agent may include an alkanolamine-based compound; And a carboxylic acid polymer of the following formula (2); Any one or more selected from among may be included. In Formula 2 below, R ₁ , R ₂ and R ₄ are each independently hydrogen or a methyl group, R ₃ is hydrogen or a (C1-C30) aliphatic hydrocarbon group, and M are independently of each other hydrogen, alkali metal, ammonium or organic When X is a hydrogen or methyl group, Z is -CH ₂ COOM _1, or when X is -COOM ₁ , Z is hydrogen or methyl, and M ₁ is hydrogen, alkali metal, ammonium or organic amine group, t and u are each independently an integer of 0 to 15, and P ₁ O and P ₂ O are each independently a mixture of one or two or more repeating units of an oxy(C2-C4)alkylene group, and two or more It is added in a block form or added in a random form, and 1 and m are each independently an integer of 1 to 100, and p, q, r and s are each independently 10 to 1,000.

[Formula 2]

In one example of the present invention, the alkanolamine compound is N-methyl-N-ethanolamine, N-ethyl-N-ethanolamine, N-propyl-N-ethanolamine, N-isopropyl-N-ethanol Any one or two or more selected from amine, N,N-diethanolamine, N,N-diisopropanolamine, triethanolamine, diisopropylethanolamine, and diethanolamine may be included.

In an example of the present invention, the strength reinforcing agent may be included in an amount of 0.01 to 5% by weight based on the total weight of the composition.

The mortar composition according to an embodiment of the present invention may include 0.1 to 5% by weight of carbon fiber, 0.5 to 15% by weight of admixture, 30 to 80% by weight of aggregate, 10 to 50% by weight of cement, and the balance of water.

The present invention provides a carbon fiber reinforced mortar made of the mortar composition.

The carbon fiber reinforced mortar according to an example of the present invention may have a compressive strength of 20 MPa or more at 28 days of age, and a flexural strength of 3 MPa or more by the center point loading method.

The method for producing a strength reinforcing fiber for mortar according to the present invention includes a coating step of coating a coating mixture including silica nanoparticles, a silane coupling agent, and a curing agent on the surface of the carbon fiber, and heat treatment of the coating mixture coated on the carbon fiber. And a heat treatment step.

The method of manufacturing the strength reinforcing fiber for mortar according to an embodiment of the present invention may further include a surface treatment step of treating the surface of the carbon fiber with an inorganic acid before the coating step.

The method of manufacturing the strength reinforcing fiber for mortar according to an embodiment of the present invention may further include a pH control step of adjusting the pH of the coating mixture to 4 or less before the coating step.

The carbon fiber reinforced mortar made of the mortar composition according to the present invention has a remarkably high adhesion strength due to the dense bonding of carbon fibers on the matrix in the mortar composition, and the mechanical properties of the mortar are remarkably improved because the carbon fibers are evenly dispersed on the matrix. It works.

In addition, the carbon fiber reinforced mortar made of the mortar composition according to the present invention has excellent compressive strength and flexural strength.

In addition, the mortar composition according to the present invention has excellent dispersibility and high fluidity even when carbon fibers are contained, and thus has excellent workability.

1 is a schematic view showing a principle of coating silica nanoparticles on carbon fibers in a carbon fiber coated with silica nanoparticles according to the present invention.
2 is a process diagram schematically showing a method of manufacturing a carbon fiber coated with silica nanoparticles according to the present invention.
FIG. 3 is a scanning electron microscope image observing carbon fibers (a) not coated with silica nanoparticles, carbon fibers acid-treated with nitric acid (b), and carbon fibers coated with silica nanoparticles (c).
FIG. 4 is an FT-IR analysis result (a) for carbon fibers coated with silica nanoparticles, and an FT-IR analysis result (b) for carbon fibers coated with silica nanoparticles of Example 1, Example In 1, the result of FT-IR analysis of carbon fibers in the specimen obtained by reacting the carbon fibers coated with silica nanoparticles with the components in the mortar composition (c).
5 is a result showing the flow performance of the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13.
6 is an image showing the results of analyzing the microstructure of the fracture surface of specimens prepared with the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13 using a scanning electron microscope.
7 is an image image of a surface portion of specimens made of the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13.
8 is a graph showing the compressive strength of specimens prepared with mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13.
9 is a graph showing the flexural strength of specimens prepared with the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13.

Hereinafter, a mortar composition including carbon fibers coated with silica nanoparticles according to the present invention and a carbon fiber reinforced mortar manufactured therefrom will be described in detail with reference to the accompanying drawings.

The drawings described in this specification are provided as an example in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings to be presented and may be embodied in other forms, and the drawings may be exaggerated to clarify the spirit of the present invention.

Unless otherwise defined, technical terms and scientific terms used in the present specification have the meanings commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings A description of known functions and configurations that may unnecessarily obscure will be omitted.

The singular form of terms used in the present specification may be interpreted as including the plural form unless otherwise indicated.

Unless otherwise defined, the unit of% used in this specification means% by weight.

The present invention relates to a mortar composition and a strength reinforcing fiber prepared therefrom, and by using a carbon fiber coated with silica nanoparticles and an admixture to be described later, problems such as reduced dispersibility and agglomeration of carbon fibers are prevented, and prior art In contrast, the mechanical properties (compression strength, flexural strength, impact resistance, etc.) of the steel beam reinforcing material produced by curing are remarkably improved.

In particular, the mortar according to the present invention has mechanical properties such as compressive strength, flexural strength, impact resistance, adhesion strength, etc. as the carbon fibers are densely and firmly dispersed on the matrix in the mortar composition, and the bonding strength between the interface between the carbon fibers and the matrix is remarkably high. This is remarkably excellent.

Hereinafter, the mortar composition according to the present invention will be described in detail.

The mortar composition according to the present invention includes silica nanoparticles-coated carbon fiber (CF), admixture, cement, aggregate, and water.

The carbon fiber is preferably coated by bonding silica nanoparticles to the surface of the carbon fiber by a reaction of a silane coupling agent and a curing agent. Specifically, the silica nanoparticles may be chemically bonded to the surface of the carbon fiber by using a material to which the silane coupling agent and the curing agent are reacted and bonded as a linker. At this time, the functional group of the silane coupling agent is bonded to the silica nanoparticles, and the functional group of the curing agent is bonded to the surface of the carbon fiber. If this is satisfied, compared to the case where the silica nanoparticles are not coated on the carbon fiber or the silica nanoparticles are coated by other means, the introduction amount of the silica nanoparticles bonded to the surface of the carbon fiber can be further improved. In particular, the matrix and carbon fibers in the composition can maintain a stronger bonding force for a longer period of time, and the carbon fibers are densely and firmly dispersed due to high affinity with the cement component in the matrix, and the bonding strength between the carbon fibers and the matrix is remarkably high. Mechanical properties such as, flexural strength, impact resistance, and adhesion strength are significantly improved. In addition, compared to the case where the silica nanoparticles are not coated on the carbon fiber or the case where the silica nanoparticles are coated by other means, the fluidity of the mortar composition can be further improved, thereby increasing work efficiency.

The silane coupling agent may be bonded to silica nanoparticles, and may preferably be represented by Formula 1 below, and the curing agent may include a diamine compound.

[Formula 1]

X-Si-(OR) ₃

In Formula 1, X is selected from a (C1-C30) alkyl group, preferably a (C1-C15) alkyl group, more preferably a (C1-C5) alkyl group substituted with an epoxy group or a glycidoxy group, and R is independently It is selected from a linear or branched (C1-C7) alkyl group, preferably a (C1-C5) alkyl group, and more preferably a (C1-C3) alkyl group.

As a specific example, the silane coupling agent may include any one or more selected from glycidoxyalkyl alkoxysilane and epoxyalkyl alkoxysilane. At this time, the number of carbon atoms of the alkyl is (C1-C30), preferably (C1-C15), more preferably (C1-C5), and the number of carbon atoms of the alkoxy is (C1-C7), preferably (C1 -C5), More preferably, (C1-C3) is mentioned. More specifically, the silane coupling agent is glycidoxypropyltrimethoxysilane, glycidoxypropylmethyldiethoxysilane, glycidoxypropyldiethoxysilane, and glycidoxypropyltriene. Glycidoxypropyltriethoxysilane, glycidoxypropyltrimethoxysilane, glycidoxypropyldiethoxysilane, glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclo Selected from hexyl) ethyltrimethoxysilane (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) It can be illustrated that includes any one or two or more. However, this has been described as a preferred example, and the present invention is not necessarily limited thereto.

As a specific example, the diamine-based compound may include alkylenediamine, wherein the number of carbon atoms of the alkyl is (C1-C12), preferably (C1-C6), more preferably (C1-C3) Can be mentioned. More specifically, the alkylenediamine is ethylenediamine, butane-1,4-diamine, pentane-1,5-diamine, hexa Methylenediamine (Hexamethylenediamine), phenylenediamine (Phenylenediamine) and the like may be mentioned. However, this has been described as a preferred example, and the present invention is not necessarily limited thereto.

Referring to FIG. 1, as an example, when a carbon fiber coated with silica nanoparticles is specifically described, a plurality of methoxy groups of glycidoxypropyltrimethoxysilane are bonded to silica nanoparticles, and the epoxy group of glycidoxy is ring-opening reaction Thus, it is bonded to the amine group of ethylenediamine, and other amine groups of the ethylenediamine are bonded to the surface of the carbon fiber.

As described above, the silica nanoparticles are bonded to the carbon fiber by using the compound produced by the reaction of the silane coupling agent and the curing agent as a linker, so that the amount of silica nanoparticles introduced can be further improved, and a stronger binding force can be maintained for a longer period. , It is possible to implement more excellent mechanical properties with a high affinity with the cement component in the mortar composition matrix.

For the example of FIG. 1, since the silane coupling agent and the curing agent are combined in a 1:1 equivalent ratio, the carbon fiber coated with silica nanoparticles can be prepared by appropriately adjusting the weight ratio of each component to be a 1:1 equivalent ratio during manufacture. I can. However, the equivalent ratio may vary depending on the number of functional groups that can be combined with the silane coupling agent and the curing agent used, and the weight ratio is not limited largely and can be appropriately controlled because it varies depending on the type of the silane coupling agent and the curing agent. However, this is only described as a preferred example, and does not need to be limited to a 1:1 equivalent ratio, and of course, the content ratio can be appropriately changed according to circumstances.

In addition, the amount of the silane coupling agent used for the carbon fiber may be appropriately adjusted according to the specific type of the silane coupling agent, for example, 0.001 to 10 parts by weight, specifically 0.01 to 5 parts by weight of the silane coupling agent per 100 parts by weight of the carbon fiber. It can be used in parts by weight. However, this has been described as a preferred example, and the present invention is not necessarily limited thereto.

In addition, the content of the silica nanoparticles for the carbon fiber may be appropriately adjusted, and for example, the silica nanoparticles may be used in an amount of 0.001 to 10 parts by weight, specifically 0.01 to 5 parts by weight, based on 100 parts by weight of the carbon fiber. However, this has been described as a preferred example, and the present invention is not necessarily limited thereto.

The carbon fiber may be used as a reinforcing material in various fields, for example, it may be a carbon fiber that can be used as a reinforcing material for construction materials. A preferred example thereof may be a polyacrylonitrile (PAN)-based carbon fiber, and when a polyacrylonitrile-based carbon fiber is used, the above-described effects can be properly implemented, so it is preferable.

The average length of the carbon fibers can be appropriately adjusted as long as mechanical properties such as flexural strength and impact resistance can be improved without causing problems due to deterioration of dispersibility, fluidity, workability, and compressive strength. For example, it may be 3 to 24 mm, preferably 4 to 16 mm. However, since this has been described as a preferred example, of course, the present invention is not necessarily limited thereto.

The average diameter of the carbon fiber can be appropriately adjusted as long as mechanical properties such as flexural strength and impact resistance can be improved without causing problems due to a decrease in dispersibility, fluidity, workability, and compressive strength. Examples include 1 to 15 μm, specifically 3 to 12 μm, but are not limited thereto.

The average density of the carbon fibers may be appropriately adjusted so long as mechanical properties such as flexural strength and impact resistance can be improved without causing problems due to a decrease in workability such as dispersibility, fluidity, and flowability, and compressive strength. It may be, for example, 1.3 to 2.5 g/cm ³ , specifically 1.5 to 2.1 g/cm ³ , but is not limited thereto.

Tensile strength, tensile modulus, and elongation of the carbon fiber are flexural strength, impact resistance, etc. without causing fatal problems due to deterioration of dispersibility, fluidity, workability and compressive strength, etc. As long as the mechanical properties of the material can be improved, it may be appropriately adjusted, and examples include, but are not limited to, 3,000 to 10,000 MPa, 100 to 500 GPa, and 1 to 5%, respectively.

The average particle diameter of the silica nanoparticles is a nano unit, and the specific value is not limited thereto, but it may be 1 to 50 nm, preferably 3 to 30 nm, more preferably 10 to 20 nm. If this is satisfied, silica nanoparticles are better bonded to the carbon fiber by using the compound produced by the reaction of the silane coupling agent of Formula 1 and the curing agent as a linker, so that the above-described effect may be better implemented.

The admixture (混和材) is that its own volume is included in the volume when mixing in the composition, and is classified as different from the admixture (混和劑) which may be considered to be substantially not included in the volume. As a specific example, the admixture includes any one or two or more selected from silica fume, pozzolan, fly ash, blast-furnace slag, volcanic glass and rice husk ash, etc. It can, and a preferred embodiment may be a silica fume. Examples of the admixture include an air entraining agent (AE agent), a water reducing agent, an AE water reducing agent, and a foaming agent.

In the mortar composition according to the present invention, the content of carbon fiber, admixture, aggregate, cement, water, etc., is not limited, but, for example, 0.1 to 5% by weight of carbon fiber, 0.5 to 15% by weight of admixture based on the total weight of the composition %, 30 to 80% by weight of aggregate, 10 to 50% by weight of cement and the remaining amount of water, preferably 0.1 to 3% by weight of carbon fiber, 1 to 10% by weight of admixture, 40 to 70% by weight of aggregate, 20 to 40% by weight of cement And it may be desirable to include the remaining amount of water. Here, the water may be adjusted so that the total weight of the composition is 100% by weight, and examples thereof include 3 to 30% by weight, specifically 5 to 50% by weight.

In the case of the carbon fiber, if too much is contained in the mortar composition, there may be a risk that dispersibility, fluidity, workability, etc., and compressive strength may decrease, so 5% by weight or less, preferably 3, based on the total weight of the composition. It may be good to be less than or equal to 1.6% by weight, more preferably less than or equal to 1.6%, very preferably less than or equal to 1.2% by weight. Here, the lower limit value of the carbon fiber may be sufficient as long as it can realize the above-described effect, for example, 0.1% by weight, specifically 0.3% by weight. However, since this has been described as a preferred example, of course, the present invention is not necessarily limited thereto.

In the present invention, by using an admixture together with the above-described silica nanoparticle-coated carbon fiber, it is excellent in dispersibility, agglomeration of carbon fibers is prevented, and mechanical properties such as compressive strength and flexural strength are significantly improved. If admixtures are not used, dispersibility is poor, agglomeration of carbon fibers may occur, and excellent mechanical properties are not properly realized by the carbon fibers coated with silica nanoparticles.

In terms of properly implementing the above-described effect, the admixture preferably includes inorganic particles having an average particle diameter of 0.01 to 100 µm and a specific surface area of 3,000 to 1,000,000 cm ² /g. Specific types of admixtures for this may include those containing one or two or more selected from silica fume, pozzolan, fly ash, blast furnace slag, volcanic glass and rice husk ash. Preferably, the admixture is silica fume or volcanic glass, and more preferably silica fume is better, and if this is satisfied, the effect of the admixture described above can be realized higher. As a preferred example, in terms of high implementation of the above-described effect, the average particle diameter is 0.01 to 100 µm, specifically 0.01 to 10 µm, and a specific surface area of 30,000 cm ² /g or more, specifically 100,000 cm ² /g or more, more specifically Inorganic particles of 150,000 cm ² /g or more are preferable, and the upper limit value is not limited, but an example may be 1 million cm ² /g, specifically 500,000 cm ² /g.

Various types of cement may be used, for example, ordinary Portland cement, medium heat Portland cement, crude steel Portland cement, ultra-rough steel Portland cement, sulfate-resistant Portland cement, white Portland cement, oil well cement, colloidal cement, blast furnace cement, ply -Ash cement, silica cement, ultra-low heat-generating cement, geothermal cement, RCCP cement, alumina cement, ultra-fast-hardening cement, low alkali cement for GRC, etc., and of course, various kinds of cement can be used. .

The aggregates may be used in various fields as long as they are used in fields such as concrete or mortar, and may include fine aggregates (such as sand), coarse aggregates (such as gravel), or a mixture of these aggregates. The specific gravity of the aggregate is not largely limited, and an example may be 2.5 to 3.5. As a specific example of the aggregate, there may be various things such as river sand, river gravel, sea sand, sea gravel, land sand, land gravel, mountain sand, mountain gravel, and the like. Specific examples of fine aggregates include sand, and coarse aggregates include gravel. However, this is only described as a specific example, of course, the present invention is not interpreted as being limited thereto.

The mortar composition according to a preferred example is a carbonic acid-based in terms of improving properties such as compressive strength and flexural strength, as well as improving adhesion between the cement component of the matrix and other dispersed components, especially the affinity between carbon fibers. Any one or more selected from a polymer and an alkanolamine-based compound may be further included.

In the present invention, when a carboxylic acid-based polymer is further used as the strength reinforcing agent, it is preferable to use a carboxylic acid-based polymer represented by Formula 2 below.

[Formula 2]

In Formula 2, R ₁ , R ₂ and R ₄ are each independently hydrogen or a methyl group, R ₃ is hydrogen or a (C1-C30) aliphatic hydrocarbon group, and M are independently of each other hydrogen, alkali metal, ammonium or organic When X is a hydrogen or methyl group, Z is -CH ₂ COOM _1, or when X is -COOM ₁ , Z is hydrogen or methyl, and M ₁ is hydrogen, alkali metal, ammonium or organic amine group, t and u are each independently an integer of 0 to 15, and P ₁ O and P ₂ O are each independently a mixture of one or two or more repeating units of an oxy(C2-C4)alkylene group, and two or more It is added in a block form or added in a random form, and 1 and m are each independently an integer of 1 to 100, and p, q, r and s are each independently 10 to 1,000.

p, q, r, and s represent the appearance fraction (molar ratio) of each repeating unit in the polymer. The ratio of p, q, r and s is not significantly limited, for example, 1:0.2-5:0.2-5:0.2-5, preferably 1:0.5-2:0.2-1.2:0.21.2 days I can. In addition, each value of p, q, r and s is not significantly limited, and for example, may be 10 to 1,000 independently of each other. In addition, the weight average molecular weight of the carboxylic acid-based polymer may be appropriately adjusted according to each value of Formula 1, for example, may have a range of 10,000 to 200,000. However, this is only described as a specific example, of course, the present invention is not interpreted as being limited thereto.

In particular, when the mortar composition according to the present invention contains both the carboxylic acid polymer and the alkanolamine compound represented by Formula 2 as a strength reinforcing agent, the carbon fiber reinforced mortar prepared by curing is cemented in the matrix with remarkably high compressive strength. It is possible to significantly improve the adhesion strength while further improving the affinity between the carbon fiber and the carbon fiber, and improve the fluidity when mixing each component in the composition manufacturing process. Specifically, when the carboxylic acid polymer represented by Formula 2 and the alkanolamine compound are used together, compressive strength is remarkably improved, whereas the carboxylic acid polymer or alkanolamine compound represented by Formula 2 as a strength reinforcing agent When used alone, the compressive strength is significantly lowered. That is, only when the carboxylic acid-based polymer and the alkanolamine-based compound represented by Formula 2 are used together, the effect of remarkably increasing the compressive strength as well as high bending strength is realized.

Various types of the alkanolamine-based compound may be used, for example, N-methyl-N-ethanolamine, N-ethyl-N-ethanolamine, N-propyl-N-ethanolamine, N-isopropyl-N -Ethanolamine, N,N-diethanolamine, N,N-diisopropanolamine, triethanolamine, diisopropylethanolamine, diethanolamine, and the like may contain any one or two or more selected from. However, this has been described as a preferred example, and the present invention is not necessarily limited thereto.

When the strength reinforcing agent is used, the content of the strength reinforcing agent is not largely limited, but it is contained in an amount of 0.01 to 5% by weight, preferably 0.1 to 3% by weight, based on the total weight of the composition. It can be good in terms of what it can be.

When the strength reinforcing agent includes both the carboxylic acid-based polymer and the alkanolamine-based compound represented by Formula 2, the weight ratio thereof is not largely limited, for example 1:0.2 to 5, preferably 1:0.5 to 2, More preferably, 1:0.7 to 1.5 are mentioned. If this is satisfied, the above-described flexural strength and compression strength may be further increased.

The mortar composition according to an embodiment of the present invention may further include an admixture, and the admixture may further include a water reducing agent, an AE water reducing agent, an air entraining agent (AE agent), a foaming agent, a defoaming agent, and the like. When the admixture is further used, the content of the admixture is not limited, and for example, it may be preferably used in an amount of 0.01 to 5% by weight, specifically 0.1 to 3% by weight, based on the total weight of the composition.

In addition, the mortar composition according to an example of the present invention may further include other additives, and for example, various things such as a surfactant, a curing accelerator, and a fluidizing agent may be mentioned. When other additives are further used, the content of the additives is not greatly limited, but may be used in an amount of 0.01 to 5% by weight, specifically 0.1 to 3% by weight, based on the total weight of the composition. However, in addition to this, a variety of known things for improving performance can be used in various amounts.

The present invention provides a carbon fiber coated with the silica nanoparticles, that is, a strength reinforcing fiber for mortar and a method for producing the same.

The method for producing a strength reinforcing fiber for mortar according to the present invention includes a coating step of coating a coating mixture including silica nanoparticles, a silane coupling agent, and a curing agent on the surface of the carbon fiber, and heat treatment of the coating mixture coated on the carbon fiber. And a heat treatment step.

The coating mixture includes silica nanoparticles, a silane coupling agent, and a curing agent, and each component may be dissolved or dispersed in a solvent (dispersion medium). That is, the coating mixture may include silica nanoparticles, a silane coupling agent, a curing agent, and a solvent. The content of the solvent may be such that components such as silica nanoparticles, silane coupling agent, and curing agent can be easily dissolved/dispersed.For example, the solvent is 10 to 90% by weight, specifically, 20 to the total weight of the coating mixture. It may be used in an amount of to 80% by weight, but is not limited thereto.

The solvent may be in a liquid form such as water and an organic solvent in which each component is well dissolved/dispersed, and may be a mixed solvent including water and an organic solvent. In the case of a mixed solvent of water and an organic solvent, the weight ratio thereof is not greatly limited, and for example, 1:0.5-2 may be mentioned. Examples of the organic solvent include lower alcohols such as methanol, ethanol, and propanol; Oxygen-containing aprotic polar solvent; Or a mixture thereof; may be mentioned.

The composition ratio of the silica nanoparticles, the silane coupling agent, and the curing agent in the coating mixture may be appropriately adjusted to satisfy the composition ratio of the carbon fiber coated with the silica nanoparticles as described above. As a specific example, 0.5 to 10 parts by weight of a silane coupling agent and 0.01 to 3 parts by weight of a curing agent may be used based on 100 parts by weight of the silica nanoparticles.

The method of manufacturing a strength reinforcing fiber for mortar according to an embodiment of the present invention may further include a pH control step of adjusting the pH of the coating mixture to 4 or less, specifically, 3 or less, before the coating step. By controlling the pH of the coating mixture to 4 or less, the bonding reaction between the functional group of the silane coupling agent and the silica nanoparticles can be improved. The pH control means may be exemplified by a method of adding a known acid to the coating mixture, and specific examples of the acid include inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid, but are not limited thereto.

In a more specific and preferred example, the method for preparing the coating mixture may include: a) preparing a first mixture of a silane coupling agent and a solvent; b) controlling the pH of the first mixture; c) preparing a second mixture by mixing silica nanoparticles with the first mixture whose pH is controlled; d) preparing a coating mixture by mixing a curing agent with the second mixture. As a specific example, step a) may be stirred at 4 to 30°C for 5 to 60 minutes to prepare a first mixture, and step b) is added with acid and stirred at 50 to 90°C for 5 to 20 hours The pH can be controlled, and the step c) is stirred at 50 to 90°C for 12 to 48 hours to prepare a second mixture, and the d) step is stirred at 30 to 60°C for 0.5 to 5 hours Coating mixtures can be prepared. However, since the temperature and time conditions can be appropriately controlled so that dissolution, dispersion and/or reaction occur well, the present invention is not limited thereto.

The method of manufacturing the strength reinforcing fiber for mortar according to a preferred example may further include a surface treatment step of treating the surface of the carbon fiber with an inorganic acid before the coating step. Before the silica nanoparticles are coated on the surface of the carbon fiber, when the surface of the carbon fiber is modified with an inorganic acid, the formation of surface irregularities and surface roughness are improved. By improving the bonding, it is possible to implement high adhesion characteristics through high physical bonding with high chemical bonding as described above. As an example of the inorganic acid, nitric acid, sulfuric acid, hydrochloric acid, or a mixed acid thereof may be mentioned.

In the coating step, the coating means and specific conditions of the coating may be any known coating means and conditions. Specifically, various coating means, such as brush application, spray application, and immersion, are exemplified.

In the heat treatment step, the curing speed of the coating mixture applied to the carbon fiber may be increased through heat treatment, and for example, the heat treatment may be performed at 50 to 100° C. for 0.5 to 3 hours.

The mortar composition according to the present invention can be prepared through various preparation methods, and publicly known literature can be referred to, and in particular, it may be preferable in terms of securing dispersibility, fluidity, workability, etc. to use the following method. It goes without saying that the present invention is limited and not interpreted.

A method for preparing a mortar composition according to an embodiment of the present invention includes: a) dry mixing an admixture, cement, and aggregate to prepare a first mixture, b) mixing carbon fibers with the first mixture to prepare a second mixture And c) mixing water into the second mixture.

When the mortar composition includes an alkanolamine-based compound or a strength reinforcing agent such as a carboxylic acid-based polymer of Formula 2, in step c), a strength reinforcing agent may be further mixed with the second mixture.

In addition, when the mortar composition further includes other additives, other additives may be further mixed with the first mixture in step a) and/or step b).

The present invention can provide a carbon fiber reinforced mortar made of the above-described mortar composition. The carbon fiber reinforced mortar may be prepared by curing the above-described mortar composition under appropriate conditions. Curing conditions of the mortar composition are well known in the art, so it is safe to refer to the known literature.

The carbon fiber reinforced mortar according to an example of the present invention may have a compressive strength of 20 MPa or more, preferably 25 MPa or more, more preferably 30 MPa or more, very preferably 35 MPa or more, at 28 days of age, and The flexural strength according to the point loading method may be 3 MPa or more, preferably 3.5 MPa or more, and more preferably 4 MPa or more. Here, the upper limit value of the compressive strength and the upper limit value of the flexural strength are not limited because the higher the value is, the better, for example, 70 MPa and 15 MPa, respectively. The compressive strength or the flexural strength may be measured according to KS L ISO 679 regulations.

Hereinafter, the present invention will be described in detail through examples, but these are for explaining the present invention in more detail, and the scope of the present invention is not limited by the following examples.

[Examples 1 to 4]

A mortar (Carbon fiber reinforced mortar, CFRM) composition including carbon fiber, admixture (silica fume), cement, fine aggregate, admixture, and water was prepared in the composition ratio of Table 1 below.

Specifically, for the prevention of fiber ball and uniform distribution, cement, silica fume, and fine aggregate were first added to the mixer and mixed for 30 seconds with dry bibeam, and then carbon fibers were added and mixed for 90 seconds. . Subsequently, water and an admixture were further added to the mixer and further mixed for 150 seconds. After stopping for 30 seconds, the attached mortar was removed, and finally, the mixer was operated again and mixed for 60 seconds. The total mixing time was about 5 minutes, and the target flow was blended to be about 190±10 mm or more.

Carbon fiber Silica fume cement Fine aggregate Admixture water (wt%) (vol%) (wt%) Example 1 0.40 0.50 1.10 20.98 66.25 0.22 11.05 Example 2 0.80 1.00 1.10 20.90 65.99 0.22 10.99 Example 3 1.20 1.50 1.10 20.81 65.73 0.22 10.94 Example 4 1.60 2.00 1.09 20.73 65.46 0.22 10.90 ※ wt% represents the mass fraction of the object relative to the total weight of the mortar composition, and vol% represents the volume (volume) fraction of the object relative to the total volume of the mortar composition at 25°C and 1 atm.

And the carbon fiber, admixture, cement and fine aggregate used are specifically as follows.

<Carbon fiber>

As the carbon fiber, a carbon fiber coated with silica nanoparticles prepared in Fig. 2 and the following method using a polyacrylonitrile-based (PAN-based) high-strength carbon fiber having the characteristics of Table 2 below was used.

[Table 2] Carbon fiber

3.6 g of glycidoxypropyl trimethoxysilane (GPTMS) was added to a mixture of 150 ml ethanol and 150 ml distilled water, and after uniformly mixing, nitric acid was added so that the pH was 2, and then at 70°C for 12 hours. While stirring. Subsequently, 445.5 g of colloidal silica sol (SS-SOL 30A, S-Chemtech) in which 30% by weight of silica nanoparticles having an average particle diameter of 15 nm was dispersed was further added to the mixture and reacted at 70° C. for 24 hours. In addition, 0.54 g of ethylene diamine (EDA), a curing agent, was added dropwise for the purpose of opening the epoxy group of glycidoxypropyltrimethoxysilane, and further stirred at 40° C. for 2 hours to prepare a coating mixture.

After removing impurities attached to the carbon fibers having the characteristics of Table 2 with acetone, the carbon fibers are oxidized by supporting the carbon fibers in a nitric acid solution for 24 hours to increase surface activity, and then the oxidized carbon fibers are washed with distilled water. And sufficiently dried in an oven at 110° C. to prepare acid-treated carbon fibers.

Then, 200 g of the acid-treated carbon fiber was supported on the coating mixture for 12 hours to attach the silica nanoparticles to the surface of the carbon fiber, and the carbon fiber was surface-modified to be hydrophilic, and then at 80°C using an oven. Cured and heat treated for hours. Subsequently, the heat-treated carbon fiber was washed with distilled water and then dried at 120° C. for 2 hours to prepare a carbon fiber coated with silica nanoparticles.

<Cement and admixture>

As the cement and the admixture, ordinary Portland cement (OPC) and silica fume having the characteristics of Table 3, respectively, were used. At this time, the average particle diameter of the silica fume is 0.15 μm (particles exceeding 45 μm are less than 0.1% by weight of the total silica fume).

[Table 3] Cement and silica fume

<fine aggregate>

As the fine aggregate, silicon dioxide (SiO ₂ ) specified in KS L ISO 679 is contained, and standard yarn, which is a fine aggregate having the characteristics of Table 4 below, was used.

[Table 4] Fine aggregate

In addition, the mortar composition was cured according to KSL ISO 679 test regulations in the following manner to prepare a specimen.

<Admixture>

As the admixture, a polycarboxylic acid-based high-performance air entraining and water reducing agent having the characteristics of Table 5 was used.

[Table 5] Admixture

[Example 5]

In Example 3, it was carried out in the same manner as in Example 3, except that the carboxylic acid-based polymer of Formula 1, which is the first strength reinforcing agent, was further used as the composition ratio of Table 6 below. At this time, the carboxylic acid-based polymer of Formula 1 was prepared by the following method.

<Carbon acid-based polymer manufacturing process>

Into a glass reactor equipped with a thermometer, stirrer, dropping funnel, nitrogen inlet pipe, and reflux cooling device, 120 parts by weight of maleic anhydride and 90 parts by weight of distilled water are injected and completely dissolved, and then allyl alcohol-polyoxyethylene glycol (average addition of allyl alcohol-ethylene oxide 20 moles of moles) 220 parts by weight and 250 parts by weight of allyl alcohol-polyoxyethylene glycol sulfoethoxyester (average number of moles added of allyl alcohol-ethylene oxide 10 moles), and nitrogen-substituting in the reactor under stirring to raise the temperature to 80°C under a nitrogen atmosphere I did. Next, 80 parts by weight of methacrylic acid and 100 parts by weight of an aqueous ammonium sulfate solution (5.5 wt%) as an initiator were added dropwise for 6 hours. After the addition of the monomer initiator was completed, 55 parts by weight of a 2 wt% aqueous ammonium sulfate solution was added dropwise for 1 hour, and the unreacted monomer was completely polymerized while maintaining at 80° C. for 2 hours. After cooling the reaction mixture to room temperature, 300 parts by weight of distilled water was added, and 270 parts by weight of caustic soda (50 wt% aqueous solution) was slowly added to the water-soluble copolymer having a weight average molecular weight of 19,500 g/mol and a polydispersity of 2.25. A carboxylic acid polymer was obtained.

[Example 6]

In Example 3, it was carried out in the same manner as in Example 3, except that the second strength reinforcing agent triethanolamine was further used as the composition ratio of Table 6 below. At this time, the carboxylic acid-based polymer of Formula 1 was prepared by the following method.

[Example 7]

In Example 3, it was carried out in the same manner as in Example 3, except that the carboxylic acid polymer of Formula 1 as the first strength reinforcing agent and triethanolamine as the second strength reinforcing agent were further used as the composition ratio of Table 6 below. At this time, the carboxylic acid-based polymer of Formula 1 was prepared by the method described in Example 5.

Carbon fiber Silica fume cement Fine aggregate Admixture water Carboxylic acid polymer Triethanolamine (wt%) (vol%) (wt%) Example 5 1.2 1.5 1.10 20.98 66.25 0.22 9.25 1.0 - Example 6 1.2 1.5 1.10 20.90 65.99 0.22 9.59 - 1.0 Example 7 1.2 1.5 1.10 20.81 65.73 0.22 9.94 0.6 0.4 ※ wt% represents the mass fraction of the object relative to the total weight of the mortar composition, and vol% represents the volume (volume) fraction of the object relative to the total volume of the mortar composition at 25°C and 1 atm.

[Comparative Examples 1 to 4]

Examples 1 to 4, except that the carbon fiber without silica nanoparticles, that is, the carbon fiber of Table 2, was used instead of the carbon fiber coated with the silica nanoparticles with the carbon fiber. Each was performed in the same manner as in Example 4.

[Comparative Examples 5 to 8]

Examples 1 to 4 were carried out in the same manner as in Examples 1 to 4, except that no admixture (silica fume) was used. At this time, the content of the unused admixture (silica fume) was added to the cement content and adjusted to be 100% by weight.

[Comparative Examples 9 to 12]

In Comparative Examples 1 to 4, each was carried out in the same manner as in Comparative Examples 1 to 4, except that no admixture (silica fume) was used. At this time, the content of the unused admixture (silica fume) was added to the cement content and adjusted to be 100% by weight.

[Comparative Example 13]

In Example 1, except that the carbon fiber and admixture (silica fume) was not used, it was carried out in the same manner as in Example 1. At this time, the content of unused carbon fibers and admixtures (silica fume) was added to the cement and adjusted to be 100% by weight.

Hereinafter, the mortar compositions according to Examples 1 to 7 and Comparative Examples 1 to 13 will be described with reference to the drawings, wherein the amount of carbon fibers incorporated in each drawing is vol% (0.5%, 1.0%, 1.5%) , 2.0%).

<Surface structure analysis of carbon fiber>

The carbon fiber coated with the silica nanoparticles of Example 1, the acid-treated carbon fiber of Example 1, and the carbon fiber of Comparative Example 1 were each treated with an ultra high resolution scanning electron microscope (UHR-SEM) (MIRA LMH). , TESCAN) was used to analyze the surface of the carbon fiber. At this time, the analysis was carried out at an ACC voltage of 10 kv, and after coating a carbon fiber sample with platinum under argon (Ar) gas, by observing the surface of the carbon fiber at 5,000 magnification, silica nanoparticles on the surface of the carbon fiber Whether or not was adhered, adhesion uniformity and the like were observed. The results are shown in FIG. 3.

In Figure 3, (a) is a carbon fiber not coated with silica nanoparticles, (b) is a carbon fiber acid-treated with nitric acid, (c) is a scanning electron microscope image of the carbon fiber coated with silica nanoparticles. .

Compared with the carbon fiber not coated with the silica nanoparticles of (a), it can be seen that the carbon fiber acid-treated with nitric acid of (b) has a string formed in the axial direction, so that the surface roughness of the carbon fiber is formed and increased. . The surface roughness of the carbon fiber is increased through acid treatment, and the introduction of hydrophilic groups such as COOH and OH to the surface of the carbon fiber through an oxidation reaction and the content of the hydrophilic group are increased. It can be, and the adhesion content can be improved.

(c) shows that the silica nanoparticles are coated on the carbon fiber, and it can be seen that the silica nanoparticles are uniformly dispersed and bonded to the surface of the carbon fiber.

<Surface component analysis of carbon fiber>

The carbon fibers coated with the silica nanoparticles of Example 1, the carbon fibers in the specimen obtained by reacting the carbon fibers coated with the silica nanoparticles in Example 1 with the components in the mortar composition, and the silica nanoparticles of Comparative Example 1 were not coated. Each of the carbon fibers was analyzed for surface components of the carbon fibers using a Fourier transform infrared spectoscopy (FT-IR) (Cary 630, Agilent Technologies). At this time, a wavelength range in the range of 400 to 4,000 cm ^-1 was measured with the device to qualitatively analyze whether the particles bonded to the surface of the carbon fiber were silica nanoparticles. The results are shown in FIG. 4.

In FIG. 4, (a) is an FT-IR analysis result of a carbon fiber coated with silica nanoparticles, (b) is an FT-IR analysis result of a carbon fiber coated with silica nanoparticles of Example 1. , (c) is the result of FT-IR analysis of carbon fibers in the specimen obtained by reacting the carbon fibers coated with silica nanoparticles with the components in the mortar composition in Example 1.

Compared to the carbon fiber without the silica nanoparticles of (a), the carbon fiber coated with the silica nanoparticles of (b) has a strong absorption due to the Si-O-Si stretching vibration at 1,040 cm ^-1 . As the peak is confirmed, it can be seen that silica nanoparticles are attached to the carbon fiber.

On the other hand, (c) is a carbon fiber in the specimen, it can be confirmed that the absorption peak (Papadakis, VG et al. 1989) due to the CO stretching vibration at 1,437 cm ^-1 was generated. This is confirmed as the CO of calcium carbonate produced by the reaction of CSH with carbon dioxide (CO ₂ ) in the atmosphere, and is the basis for confirming whether CSH is produced. In addition, silica nanoparticles are properly attached to the surface of the carbon fiber, which can be seen as a result of the hydrophilic modification of the surface of the carbon fiber by acid treatment. On the other hand, in the case of the carbon fiber not coated with the silica nanoparticles, it can be seen that peaks due to stretching vibration were not formed at 1,040 cm ^-1 and 1437 cm ^-1 .

<liquidity analysis>

In order to evaluate the flow performance of the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13, the flow test was measured according to KS L 5105 using a flow table and a flow cone specified in KS L 5111. Specifically, immediately after the mortar composition was discharged, it was poured into a conical mold having a lower diameter of 100±0.5 mm, an upper diameter of 70±0.5 mm, and a height of 50±0.5 mm and compacted 20 times. After lifting the conical mold, immediately dropping a height of 12.7 mm 25 times for 15 seconds, and then measuring the flow value, and measuring the diameter in three diagonal directions passing through the center when the spreading stops after dropping, and the average value is the flow value It was set as. The results are shown in FIG. 5.

In FIG. 5, in the case of the ordinary mortar composition of Comparative Example 13 in which carbon fibers and silica fume were not used, the flow value was 192 mm, which satisfies the target flow value of 190 mm or more, so that the flow performance was good. On the other hand, in the case of Comparative Examples 5 to 8 in which silica fume was not used and carbon fibers coated with silica nanoparticles were used, the flow value was 114 to 160 mm, and silica fume was not used and silica nanoparticles were not coated. In the case of Comparative Examples 9 to 12 in which carbon fibers were used, the flow value was measured to be lower, 110 to 146 mm. From this, it can be confirmed that the silica nanoparticles coated on the surface of the carbon fiber have a higher flow value.

In addition, from the case of Examples 1 to 4 along with the above results, it can be seen from FIG. 5 that there is substantially no change in the flow value according to the use of silica fume.

<Microstructure Analysis in Mortar>

Specimens prepared with the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13 were analyzed for microstructures of their fracture surfaces using a scanning electron microscope.

The thickness between the interface of the fiber and the cement matrix is about 10-50 μm, and the thickness of this interface can affect the strength and durability. As shown in FIG. 6, when carbon fibers coated with silica nanoparticles and silica fume are used, it can be seen that large and small CSH are uniformly distributed in a rough shape on the surface of the fiber, and pores are hardly observed. . This is considered to be due to the formation of a large number of crystals of the cement hydration product around and uniform dispersion in the cement matrix due to high affinity.

On the other hand, when silica fume was not used and carbon fibers coated with silica nanoparticles were used, although C-S-H was somewhat bonded to the surface of the fiber, microscopic cracks between the fiber and the cement matrix were observed.

When carbon fiber and silica fume without silica nanoparticles are used, CSH is slightly bonded to the surface of the fiber, but sufficient strength is not secured, and fiber debonding or pulling ( The separation between the fiber and the cement matrix was observed due to the pull out phenomenon.

When carbon fiber without silica nanoparticles was used and silica fume was not used, it was found that the shape of the fiber surface was very clean and fairly smooth, and it was observed that fine pores were formed around the cement hydrate. In addition, since crystals of the cement hydration product were difficult to occur, the affinity was low, and the interfacial bonding between the fibers and the cement matrix was low, and thus the dispersion of the fibers was not smooth, and agglomeration phenomenon was confirmed.

<Mortar surface image analysis>

In order to confirm the degree of dispersion of the carbon fibers in the matrix of the mortar, imaging images of the surface portion of the specimens made of the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13 were observed.

As a result, as shown in FIG. 7, it can be confirmed that the carbon fibers coated with silica nanoparticles and Examples 1 to 4 in which the silica fume are used are evenly dispersed in the mortar prepared by curing. have.

On the other hand, in Comparative Examples 1 to 12 in which carbon fibers not coated with silica nanoparticles were used or silica fume was not used, carbon fibers were not evenly dispersed, and there were relatively many areas and carbon fibers. It can be seen that there are many small areas.

<Analysis of compressive strength and flexural strength of mortar>

In order to perform the compressive and flexural strength tests of the specimens prepared from the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13, a mortar specimen was prepared and the strength at the age of 28 was measured. The results are shown in Figure 8.

Specifically, for the compressive strength and flexural strength tests, a 40×40×160 mm mold was prepared in accordance with the KS L ISO 679 (2016) test method, and a hexahedral specimen was used with a mortar composition and cured.

In the case of flexural strength, a specimen is installed on a steel roller with a circular cross section using a universal testing machine (UTM) (UT-100F, MTDI Co) with a capacity of 100 kN, and the load is controlled in the center at 50 N/s. The flexural strength was measured by the point loading method, and the value was calculated from Equation 1 below.

[Equation 1]

In Equation 1, f _r is the flexural strength (MPa), P is the maximum load (N), L is the distance between points (mm), b is the width of the specimen (mm), and h is the height (mm) of the specimen.

In the case of compressive strength, the flexural strength was first measured using the universal testing machine, and the fractured specimen was mounted on a pressing mold for compressive strength measurement to measure the compressive strength. The loading speed of the compressive strength was applied at a constant speed under the condition of 2,400 N/s, and the compressive strength was calculated from Equation 2 below.

[Equation 2]

In Equation 2, f _cu is the compressive strength (MPa), P is the maximum load (N), b is the width of the specimen (40 mm), and h is the height of the specimen (40 mm).

8 is a graph showing the compressive strength of specimens made of the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13.

After measuring the flexural strength, the compressive strength of the common mortar of Comparative Example 13 at 28 days of age, when each of the three fractured specimens was measured twice, was measured at an average level of 30.6 MPa. Examples 1 to 4 in which silica fume was used and carbon fibers coated with silica nanoparticles were used have a compressive strength of about 28 to 38 MPa, whereas silica fume was used and carbon fibers not coated with silica nanoparticles were used. Comparative Examples 1 to 4 had a lower compressive strength of about 25 to 35 MPa.

In general, when fibers are incorporated into the mortar composition, it has been reported that the dispersibility of the fibers is reduced and agglomeration occurs, which is greatly affected by the decrease in compressive strength. It can be seen that when silica fume is not used, the compressive strength is significantly reduced in both the case where the silica nanoparticles are coated on the carbon fiber to about 30 MPa or less and the case where it is not coated. Silica fume, which is a silica fume having an average particle diameter of 0.15 µm and a large specific surface area distributed in the pores in the specimen, serves as a source of hydration, and promotes the hydration reaction to close the pores and reduce fine bubbles, thereby coating the silica nanoparticles. It is believed that the compressive strength is improved by the carbon fiber.

Therefore, it can be seen that the effect of the silica nanoparticle coating of the carbon fiber is greatly realized only when the silica fume is used together and the carbon fiber coated with the silica nanoparticles is used.

In addition, it can be seen from FIG. 8 that the compressive strength of the carbon fiber is better at less than 2 vol% (1.6 wt%), so that the amount of carbon fiber coated with silica nanoparticles is less than 2 vol% (1.6 wt%). It can be seen that it is more preferable in terms of improving strength.

9 is a graph showing the flexural strength of specimens prepared with the mortar compositions of Examples 1 to 4 and Comparative Examples 1 to 13.

The flexural strength of the common mortar of Comparative Example 13 at 28 days of age, when each of three specimens was measured twice, was measured at an average of 3.1 MPa.

In particular, it can be seen from FIG. 9 that when the silica fume is not used and the carbon fiber is used at 2 vol% (1.6 wt%) or more, the flexural strength is reduced rather than when the carbon fiber is used at 1.5 vol% (1.2 wt%) or less. I can. On the other hand, when silica fume is used, it can be seen that the flexural strength increases even if the carbon fiber exceeds 1.5 vol% (1.2 wt%) and is used in 2 vol% (1.6 wt%).

Therefore, it can be seen that only when carbon fiber and silica fume are used together can have high flexural strength even at a high mixing amount of carbon fiber exceeding 1.5 vol% (1.2 wt%).

Strength enhancer Compressive strength Flexural strength Carbonic acid polymer (wt%) Triethanolamine (wt%) (MPa) Example 3 - - 32.9 5.9 Example 5 1.0 - 35.6 6.0 Example 6 - 1.0 34.8 5.9 Example 7 0.6 0.4 41.7 6.2

In addition, as a result of measuring the compressive strength and flexural strength of the specimen prepared with the mortar composition according to Examples 5 to 7, each component was used alone in the group in which the carboxylic acid polymer and triethanolamine were combined. Example 6 was not significantly improved in compressive strength compared to Example 3. On the other hand, Example 7 in which both the carboxylic acid-based polymer and triethanolamine were used, surprisingly, while maintaining the level of excellent flexural strength, it was confirmed that the compressive strength was significantly improved compared to Examples 5 and 6 in which each component was used alone. .

Therefore, when a carboxylic acid polymer or triethanol amine is used as a strength reinforcing agent, the compressive strength is improved, and in particular, it can be seen that the effect of remarkably improving the compressive strength while maintaining excellent flexural strength is realized by the use of the carboxylic acid polymer and triethanolamine together.

Claims (17)

Including carbon fiber coated with silica nanoparticles, strength reinforcing agent, admixture, cement, aggregate, and water,
The strength enhancer is an alkanolamine-based compound; And a carboxylic acid polymer of the following formula (2); Mortar composition comprising any one or more selected from.
[Formula 2]

(In Chemical Formula 2,
R1, R ₂ and R ₄ are each independently hydrogen or a methyl group, R ₃ is hydrogen or a (C1-C30) aliphatic hydrocarbon group,
M are independently of each other hydrogen, alkali metal, ammonium or organic amine groups,
When X is hydrogen or a methyl group, Z is -CH ₂ COOM _1, or when X is -COOM ₁ , Z is a hydrogen or methyl group, where M ₁ is hydrogen, an alkali metal, ammonium or an organic amine group,
t and u are each independently an integer from 0 to 15,
P _1O and P _2O are each independently a mixture of one or two or more repeating units of an oxy(C2-C4)alkylene group, and if two or more are added in a block form or added in a random form,
1 and m are each independently an integer of 1 to 100,
p, q, r and s are each independently 10 to 1,000) The method of claim 1,
The carbon fiber is a mortar composition in which silica nanoparticles are bonded to the surface of the carbon fiber by a reaction of a silane coupling agent and a curing agent to be coated. The method of claim 2,
The silica nanoparticles are chemically bonded to the surface of the carbon fiber by using a material bonded by the reaction of the silane coupling agent and the curing agent as a linker,
A mortar composition in which a functional group of the silane coupling agent is bonded to the silica nanoparticles, and a functional group of the curing agent is bonded to the surface of the carbon fiber. The method of claim 3,
The silane coupling agent is represented by the following formula (1), and the curing agent is a mortar composition comprising a diamine compound.
[Formula 1]
X-Si-(OR) ₃
(In Formula 1,
X is selected from an epoxy group or a (C1-C30) alkyl group substituted with a glycidoxy group,
R is independently selected from straight or branched (C1-C7) alkyl groups) The method of claim 4,
The silane coupling agent includes a glycidoxyalkyl alkoxysilane,
The diamine-based compound is a mortar composition comprising an alkylenediamine. The method of claim 1,
The admixture is a mortar composition comprising inorganic particles having an average particle diameter of 0.01 to 100 μm and a specific surface area of 3 to 1 million cm ² /g. The method of claim 6,
The admixture is a mortar composition comprising any one or two or more selected from silica fume, pozzolan, fly ash, blast furnace slag, volcanic glass, and rice husk ash. delete The method of claim 1,
The alkanolamine-based compound is N-methyl-N-ethanolamine, N-ethyl-N-ethanolamine, N-propyl-N-ethanolamine, N-isopropyl-N-ethanolamine, N,N-diethanol Mortar composition comprising any one or two or more selected from amine, N,N-diisopropanolamine, triethanolamine, diisopropylethanolamine and diethanolamine. The method of claim 1,
The strength reinforcing agent is a mortar composition comprising 0.01 to 5% by weight based on the total weight of the composition. The method of claim 1,
The mortar composition is a mortar composition comprising 0.1 to 5% by weight of carbon fiber, 0.5 to 15% by weight of admixture, 30 to 80% by weight of aggregate, 10 to 50% by weight of cement, and the balance of water. A carbon fiber reinforced mortar made of the mortar composition of any one of claims 1 to 7 and 9 to 11. The method of claim 12,
Carbon fiber reinforced mortar with a compressive strength of 20 MPa or more at 28 days of age, and a flexural strength of 3 MPa or more by the center point loading method. A coating step of coating a coating mixture comprising the mortar composition of any one of claims 1 to 7 and 9 to 11 on the surface of carbon fibers, and
Method for producing a strength reinforcing fiber for mortar comprising a heat treatment step of heat-treating the coating mixture coated on the carbon fiber. The method of claim 14,
Before the coating step,
Method for producing a strength reinforcing fiber for mortar further comprising a surface treatment step of treating the surface of the carbon fiber with an inorganic acid. The method of claim 14,
Before the coating step,
Method for producing a strength reinforcing fiber for mortar further comprising a pH control step of adjusting the pH of the coating mixture to 4 or less. The method of claim 14,
The silane coupling agent is represented by the following formula (1), and the curing agent is a method for producing a strength reinforcing fiber for a mortar comprising a diamine compound.
[Formula 1]
X-Si-(OR) ₃
(In Formula 1,
X is selected from an epoxy group or a (C1-C30) alkyl group substituted with a glycidoxy group,
R is independently selected from straight or branched (C1-C7) alkyl groups)

Images