KR102292424B1 - Hybrid fiber-reinforced mortar composition containing steel fiber and carbon fiber, and cement composite with improved flexural performance - Google Patents

Abstract

A hybrid fiber reinforced mortar composition according to the present invention comprises reinforced fiber comprising steel fiber and carbon fiber, cement, fine aggregate, and water. A cement composite manufactured by the composition has effects of excellent compressive strength and drastically high bending performance, bending toughness, and deformation performance, and has an effect of minimizing reduction of fluidity compared to a conventional carbon fiber reinforced mortar composition.

Description

Hybrid fiber-reinforced mortar composition containing steel fiber and carbon fiber, and cement composite with improved flexural performance prepared therefrom

The present invention relates to a hybrid fiber-reinforced mortar (cement) composition comprising steel fibers and carbon fibers and a cement (mortar) composite having improved flexural performance prepared therefrom, in particular, mechanical properties such as flexural performance, flexural strength, and flexural toughness It relates to a hybrid fiber-reinforced mortar (cement) composition comprising improved steel fibers and carbon fibers, and a cement (mortar) composite prepared therefrom.

Cement-based composites have been widely used worldwide as a major construction material for buildings and civil structures due to their excellent compressive strength. However, the conventional cement-based composite is not only weak in flexural strength and tensile strength, but also has disadvantages in that it has brittle properties such as low ductility and insufficient deformability. Accordingly, studies were attempted to improve the bending performance of cement-based composites through various reinforcing materials.

Steel fiber (SF) is a reinforcing material used in civil engineering and construction fields, and is a material of steel fiber, iron-based fiber used for fiber-reinforced mortar or concrete. Steel fiber is used to overcome brittleness, the greatest weakness of concrete, and is used to maintain the best condition for various structures.

Carbon fiber (CF) refers to a fiber composed of at least 92% or more of carbon elements, and can be roughly divided into polyacrylonitrile (PAN)-based, pitch-based and rayon-based depending on the manufacturing method and raw material. According to the fiber length, it can be divided into short fiber and long fiber. In the early stages of development, there were some difficulties in using large-scale construction materials such as construction materials due to the increased economic burden. In particular, carbon fiber is a promising new material that can be called a 21st century high-tech composite with high tensile strength and tensile modulus. In addition, carbon fiber has light weight, high strength, high elasticity, and excellent corrosion resistance, and has been widely used in the aerospace industry in recent years, is attracting attention.

However, the conventional carbon fiber reinforced cement composite has a problem of lowering compressive strength and still requires higher flexural and tensile strength characteristics, and for various reasons such as inter-matrix adhesion strength problems and problems with fiber mixing, the performance is not practical for commercialization. The reality is that it is still lacking.

Korean Patent No. 10-0857475

It is an object of the present invention to provide a hybrid fiber-reinforced mortar composition comprising steel fibers and carbon fibers, and a composite prepared therefrom, which have excellent compressive strength while at the same time significantly improving flexural strength, flexural toughness and deformability.

Another object of the present invention is to provide a hybrid fiber-reinforced mortar composition comprising steel fibers and carbon fibers, which can minimize the decrease in fluidity compared to the case of the conventional carbon fiber-reinforced mortar composition, and a composite having improved bending performance prepared therefrom. will be.

The hybrid fiber-reinforced mortar composition according to the present invention includes reinforcing fibers including steel fibers and carbon fibers, cement, and water.

In one embodiment of the present invention, in the reinforcing fiber, the volume ratio of the steel fiber to the carbon fiber may be 1:0.1-2 at 25°C and 1 atm.

In an example of the present invention, the average diameter of the steel fibers may be 200 to 900 μm, and the average diameter of the carbon fibers may be 1 to 15 μm.

In an example of the present invention, the average length of the steel fibers may be 10 to 100 mm, and the average length of the carbon fibers may be 3 to 24 mm.

The hybrid fiber-reinforced mortar composition according to an embodiment of the present invention may include 0.5 to 50 parts by weight of the reinforcing fiber and 50 to 800 parts by weight of the cement based on 100 parts by weight of the water.

The hybrid fiber-reinforced mortar composition according to an embodiment of the present invention may further include a strength reinforcing agent, wherein the strength reinforcing agent is an alkanolamine-based compound; and a carboxylic acid-based polymer of Formula 1 below; It may include any one or more selected from among.

[Formula 1]

In Formula 1, 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 each independently hydrogen, alkali metal, ammonium or organic An amine group, and when X is a hydrogen or methyl group, Z is -CH ₂ COOM ₁ Or, when X is -COOM ₁ , Z is a hydrogen or methyl group, wherein M ₁ is hydrogen, an alkali metal, ammonium or an organic amine group, t and u are independently integers from 0 to 15, and P ₁ O and P ₂ O are each independently one or more repeating units of an oxy (C2-C4) alkylene group, and a mixture of two or more. It is added in a block form or randomly, 1 and m are independently integers from 1 to 100, and p, q, r and s are independently from 10 to 1,000.

In one embodiment of the present invention, the alkanolamine-based compound is N-methyl-N-ethanolamine, N-ethyl-N-ethanolamine, N-propyl-N-ethanolamine, N-isopropyl-N-ethanol It may include any one or two or more selected from amine, N,N-diethanolamine, N,N-diisopropanolamine, triethanolamine, diisopropylethanolamine and diethanolamine.

In an example of the present invention, the strength reinforcing agent may be included in the composition in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the water.

The present invention also provides a hybrid fiber-reinforced mortar prepared by curing the hybrid fiber-reinforced mortar composition.

The hybrid fiber-reinforced mortar according to the present invention has a compressive strength of 25 MPa or more based on KS F ISO 679 test at 28 days of age, and a flexural strength of 4 MPa or more based on the 4-point flexural load test suggested by KS F 2566 and ASTM C 1609 regulations, The flexural toughness may be 10 J (kN·mm) or more.

In addition, the present invention provides a method for producing a hybrid fiber-reinforced mortar comprising the step of preparing a fiber-reinforced mortar by curing the hybrid fiber-reinforced mortar composition.

The composite prepared from the hybrid fiber-reinforced mortar composition comprising steel fibers and carbon fibers according to the present invention has excellent compressive strength and at the same time has the effect of remarkably high flexural strength, flexural toughness and deformability.

In addition, the composite prepared from the hybrid fiber-reinforced mortar composition comprising the steel fiber and the carbon fiber according to the present invention has the effect of minimizing the decrease in fluidity compared to the case of the conventional carbon fiber-reinforced mortar composition.

1 shows the results of a fluidity test for the hybrid fiber-reinforced mortar compositions of Examples 1 to 3 and Comparative Example 2.
2 shows the results of measuring the compressive strength of cement composites cured with the hybrid fiber-reinforced mortar compositions of Examples 1 to 3 and Comparative Example 2.
3 is a set-up view of the specimen shape and specifications (a) and test equipment for the bending performance test for the cement composite cured with the hybrid fiber-reinforced mortar composition of Examples 1 to 3 and Comparative Example 2; (b) is shown.
4 is a load-deflection curve for measuring bending toughness - a conceptual diagram of calculation.
5 shows the results of measuring the flexural strength of cement composites cured with the hybrid fiber-reinforced mortar compositions of Examples 1 to 3, Comparative Examples 1 and 2;
6 shows the results of measuring the bending toughness of the cement composites cured with the hybrid fiber-reinforced mortar compositions of Examples 1 to 3 and Comparative Example 2.
7 is an image showing crack propagation and fracture patterns of the side surfaces of each specimen after completion of the bending performance test.
8 is an image showing the fracture state of the crack surface in each specimen after completion of the bending performance test.

Hereinafter, a hybrid fiber-reinforced mortar composition comprising steel fibers and carbon fibers and a composite with improved bending performance prepared therefrom will be described in detail with reference to the accompanying drawings.

The drawings described in this specification are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention is not limited to the drawings 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 in technical terms and scientific terms used in this specification, those of ordinary skill in the art to which this invention belongs have the meanings commonly understood, and in the following description and accompanying drawings, the subject matter of the present invention Descriptions of known functions and configurations that may unnecessarily obscure will be omitted.

A singular form of a term used herein may be construed to include a plural form unless otherwise indicated.

In the present specification, the unit of % used without special mention means % by weight unless otherwise specified.

The present invention relates to a hybrid fiber-reinforced mortar composition and a cement composite prepared therefrom, and more preferably, a strength reinforcing agent such as a carboxylic acid-based polymer or an alkanolamine-based compound having a specific structure to be described later by including steel fibers and carbon fibers together. By additionally including, the compressive strength and bending performance of the material is significantly improved compared to the prior art. In particular, the cement composite prepared with the hybrid fiber-reinforced mortar composition according to the present invention has a high deformability, and when used for structures requiring dynamic loads such as earthquakes, shocks, explosion loads, wind loads, etc., the evacuation time before the collapse of the structure It has the effect of securing sufficient time to reach.

That is, in the cement according to the present invention, fibers of different properties, specifically macro-scale steel fibers and micro-scale carbon fibers, are used on the matrix, so that each fiber is densely and firmly dispersed to prevent sudden brittle fracture due to impact. It has very stable properties.

The hybrid fiber-reinforced mortar composition according to the present invention includes reinforcing fibers including steel fibers and carbon fibers, cement, fine aggregate, and water.

In the reinforcing fiber, the composition ratio of the steel fiber to the carbon fiber may be appropriately adjusted, but preferably, the volume ratio of the steel fiber to the carbon fiber is 1:0.1 to 2, more preferably 1:0.2 to 1 at 25° C. and 1 atm. can be good When this is satisfied, it is possible to maximize the compressive strength and flexural performance while minimizing the decrease in fluidity of the composition. In particular, when the volume ratio of steel fiber to carbon fiber is 1:0.2 to 1 at 25°C and 1 atm, that is, when the amount of steel fiber mixed is greater than that of carbon fiber, there is an effect of remarkably improving flexural toughness among bending performance.

The steel fiber (SF) may be a commonly known material used as a reinforcing material in civil engineering and construction fields, and for example, may be an iron-based fiber used as a reinforcing material of a construction material.

The average length of the steel fibers can be appropriately adjusted as long as mechanical properties such as bending performance and impact resistance can be improved without problems due to a decrease in compressive strength, etc. In terms of higher bending performance, for example, it may be 10 to 100 mm, preferably 20 to 60 mm.

The average diameter of the steel fibers can be appropriately adjusted as long as mechanical properties such as bending performance and impact resistance can be improved without causing problems due to a decrease in compressive strength, etc., but preferably with carbon fibers in micro units In terms of higher bending performance due to the incorporation of

The average density of the steel fibers can be appropriately adjusted as long as mechanical properties such as bending performance and impact resistance can be improved without problems due to a decrease in compressive strength, for example, 3,000 to 15,000 kg/m ³ , specifically 5,000 to 10,000 kg / m ^{3 It} may be mentioned, but is not limited thereto, of course.

The tensile strength, tensile modulus, and elongation of the steel fiber do not cause fatal problems due to a decrease in compressive strength, etc., and mechanical properties such as bending performance and impact resistance can be improved. The degree may be appropriately adjusted, and examples thereof include 500 to 2,000 MPa, 100 to 500 GPa, and 1 to 5%, respectively, but are not limited thereto.

The carbon fiber (CF) may be used as a reinforcing material in various fields, and for example, may be a carbon fiber which may be used as a reinforcing material of a construction material. A preferred example thereof may include polyacrylonitrile (PAN)-based carbon fibers, and when polyacrylonitrile-based carbon fibers are used, it is preferable to properly implement the above-described effects.

The average length of the carbon fibers can be appropriately adjusted as long as mechanical properties such as bending performance and impact resistance can be improved without causing problems due to a decrease in compressive strength, etc., but preferably for mixing with steel fibers. In terms of higher bending performance, for example, it may be 3 to 24 mm, preferably 4 to 16 mm.

The average diameter of the carbon fibers can be appropriately adjusted as long as mechanical properties such as bending performance and impact resistance can be improved without problems due to a decrease in compressive strength, etc., but preferably with macro unit steel fibers In terms of higher bending performance due to the incorporation of

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

Tensile strength, tensile modulus, and elongation of the carbon fiber do not cause fatal problems due to lowering of compressive strength, and mechanical properties such as bending performance and impact resistance can be improved. If there is enough, it can be appropriately adjusted, and examples thereof include 3,000 to 10,000 MPa, 100 to 500 GPa, and 1 to 5%, respectively, but are not limited thereto.

In the hybrid fiber-reinforced mortar composition according to the present invention, the composition ratio of reinforcing fibers, cement, fine aggregate, and water is not particularly limited, but for example, the composition comprises 0.5 to 50 parts by weight of reinforcing fiber, 50 to 50 parts by weight of cement, based on 100 parts by weight of water. It may include 800 parts by weight and 100 to 1,000 parts by weight of fine aggregate, specifically, 0.5 to 20 parts by weight of reinforcing fiber, 100 to 600 parts by weight of cement, and 200 to 800 parts by weight of fine aggregate based on 100 parts by weight of water. When carbon fibers are contained in the composition as the above-mentioned composition ratio, it is possible to prevent deterioration of dispersibility, fluidity, workability, etc. due to excessive use, and deterioration of mechanical properties such as compressive strength.

Preferably, the hybrid fiber-reinforced mortar composition is capable of not only improving properties such as compressive strength and flexural performance, but also improving adhesion strength while further improving the affinity between the cement component and other dispersed components of the matrix, particularly the fibers on the matrix. In the aspect, it is preferable to further include any one or more strength reinforcing agents selected from carbonic acid-based polymers and alkanolamine-based compounds.

As the strength reinforcing agent, the carbonic acid-based polymer is preferably represented by the following formula (1).

[Formula 1]

In Formula 1, 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 each independently hydrogen, alkali metal, ammonium or organic An amine group, and when X is a hydrogen or methyl group, Z is -CH ₂ COOM ₁ Or, when X is -COOM ₁ , Z is a hydrogen or methyl group, wherein M ₁ is hydrogen, an alkali metal, ammonium or an organic amine group, t and u are independently integers from 0 to 15, and P ₁ O and P ₂ O are each independently one or more repeating units of an oxy (C2-C4) alkylene group, and a mixture of two or more. It is added in a block form or randomly, 1 and m are independently integers from 1 to 100, and p, q, r and s are independently from 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 particularly limited, and 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 can In addition, each value of p, q, r and s is not particularly limited, and may be, for example, independently of each other from 10 to 1,000. In addition, the weight average molecular weight of the carbonic acid-based polymer may be appropriately adjusted according to each value of Chemical Formula 9, and for example, may have a range of 10,000 to 200,000 g/mol. However, it goes without saying that this is only described as a specific example, and the present invention is not limited thereto.

As the strength reinforcing agent, various types of alkanolamine-based compounds may be used as long as they are alkanol-based compounds having an amine group. For example, N-methyl-N-ethanolamine, N-ethyl-N-ethanolamine, N-propyl-N-ethanol Contains any one or two or more selected from amine, N-isopropyl-N-ethanolamine, N,N-diethanolamine, N,N-diisopropanolamine, triethanolamine, diisopropylethanolamine and diethanolamine can be heard However, this is only described as a preferred example, and the present invention is not necessarily limited thereto.

In particular, in the composition according to the present invention, when a strength reinforcing agent including both the carboxylic acid-based polymer and the alkanolamine-based compound represented by Formula 1 is used, the affinity between the cement and the fibers in the matrix is further improved with significantly higher compressive strength. It is possible to significantly improve the adhesion strength while doing this. In addition, it is possible to improve fluidity when mixing each component in the composition manufacturing process, and in particular, steel fibers and carbon fibers having different sizes induce a better crosslinking role with each other on the matrix, resulting in higher bending performance and very high compression. strength performance can be realized. Specifically, when the carboxylic acid-based polymer represented by Formula 1 and the alkanolamine-based compound are used together, compressive strength is remarkably improved, while the carboxylic acid-based polymer or alkanolamine-based compound represented by Formula 1 as a strength reinforcing agent is used together. When used alone, the compressive strength may decrease. That is, when the carboxylic acid-based polymer and the alkanolamine-based compound represented by Formula 1 are used together, the effect of significantly increasing the compressive strength as well as the high bending performance is realized.

When the strength reinforcing agent is used, the content thereof is not particularly limited, but 0.1 to 50 parts by weight, preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight based on 100 parts by weight of water. Hybrid fiber-reinforced mortar composition It may be good in terms of cost and the effect of using the above-described strength reinforcing agent can be properly implemented.

When both the carboxylic acid-based polymer and the alkanolamine-based compound represented by Formula 1 are included as the strength reinforcing agent, the weight ratio thereof is not particularly limited, and for example, 1:0.2-5, preferably 1:0.5- 2, More preferably, 1:0.7-1.5 are mentioned. When this is satisfied, the improvement of the aforementioned flexural strength and compressive strength may be further increased.

The hybrid fiber-reinforced mortar composition according to an embodiment of the present invention may further include an admixture, and when this is satisfied, mechanical properties such as compressive strength, flexural strength, flexural toughness, and tensile strength can be further improved. 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 addition, various known admixtures may be used, and the present invention is not limited thereto. At this time, the content of the admixture is not particularly limited, and for example, it may be used in an amount of 0.01 to 30 parts by weight, specifically 0.1 to 20 parts by weight, and more specifically 0.1 to 5 parts by weight based on 100 parts by weight of water.

The hybrid fiber-reinforced mortar composition according to an embodiment of the present invention may further include an admixture, and when this is satisfied, mechanical properties such as compressive strength, flexural strength, flexural toughness, and tensile strength can be further improved. That is, since the admixture is used together with the reinforcing fibers, the dispersibility is excellent, the aggregation of the fibers is minimized, the mechanical properties such as compressive strength and flexural strength are significantly improved, and the adhesion strength between the matrix and the fibers is significantly increased after curing. do. Admixtures (混和材) are classified as being different from admixtures (混和材), whose volume is included in the volume when mixed in the composition, and which can be regarded as substantially not included in the volume. In this case, the content of the admixture is not particularly limited, and for example, may be used in an amount of 0.01 to 30 parts by weight, specifically 0.1 to 20 parts by weight, and more specifically 0.1 to 5 parts by weight based on 100 parts by weight of water. In terms of implementing the above-described effect well, the admixture may preferably include inorganic particles having an average particle diameter of 0.01 to 100 μm and a specific surface area of 30 to 1 million cm ^{2 /g.} Specific types of the admixture for this purpose include those containing any one or two or more selected from silica fume, pozzolan, fly ash, blast furnace slag, volcanic glass and rice husk ash. More preferably, the admixture is preferably silica fume or volcanic glass, and more preferably silica fume. As a preferred example, in terms of high implementation of the above-described effects, the average particle diameter is 0.01 to 100 μm, specifically 0.01 to 10 μm, and the specific surface area is 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 may be preferable, and in this case, the upper limit is not limited, but an example may be 1 million cm ² /g, specifically 500,000 cm ² /g.

As the fine aggregate, a variety of materials may be used as long as they are used in construction and civil engineering fields such as concrete or mortar, and specific examples of the fine aggregate include sand. The specific gravity of the fine aggregate is not particularly limited, and may be, for example, 2.5 to 3.5. However, this is only described as a specific example, and the present invention is not limited thereto.

The hybrid fiber-reinforced mortar composition according to an embodiment of the present invention may further include coarse aggregate. The coarse aggregate may be used in various ways as long as it is used in construction and civil engineering fields such as concrete or mortar, and specific examples of the coarse aggregate include gravel. The specific gravity of the coarse aggregate is not particularly limited, and may be, for example, 2.5 to 3.5. The amount of the coarse aggregate used is not particularly limited, and may be, for example, 100 to 1,000 parts by weight, specifically 200 to 800 parts by weight, based on 100 parts by weight of water. However, this is only described as a specific example, and the present invention is not limited thereto.

The hybrid fiber-reinforced mortar composition according to an embodiment of the present invention may further include other additives, for example, various types of surfactants, curing accelerators, fluidizing agents, and the like. When other additives are further used, their content is not significantly limited, but 0.01 to 50 parts by weight, preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight based on 100 parts by weight of water. for example. However, it goes without saying that, in addition to this, various known materials for improving performance may be used in various amounts.

The method for preparing the composite with the hybrid fiber-reinforced mortar composition according to the present invention is not particularly limited as long as it is a means to ensure that each component is well mixed and cured, and a known method may be used. For example, when an admixture is used, the method for producing the composite includes the steps of b1) preparing a first mixture by dry-mixing the admixture and cement, b2) preparing a second mixture by mixing fibers with the first mixture, b3) mixing water with the second mixture, and b4) curing.

When aggregate is additionally used in the present invention, the aggregate may be mixed in each step, but preferably, the aggregate may be mixed in the preparation of the first mixture in step b1).

When the hybrid fiber-reinforced mortar composition includes a strength reinforcing agent such as an alkanolamine-based compound or a carboxylic acid-based polymer of Formula 1, the strength reinforcing agent may be further mixed with the second mixture in step b3).

In addition, when the hybrid fiber-reinforced mortar composition further includes other additives, other additives may be further mixed with the first mixture in step b1) and/or step b2).

The curing conditions of step b4), for example, temperature, pressure, humidity, time, etc. are well known in the art, so it is okay to refer to the literature.

The composite prepared from the hybrid fiber-reinforced mortar composition according to an example of the present invention has a compressive strength at 28 days of age of 25 MPa or more, preferably 35 MPa or more, more preferably 40 MPa or more based on KS F ISO 679 test. and the flexural strength may be 4 MPa or more, preferably 5 MPa or more, more preferably 6.5 MPa or more, based on the 4-point flexural load test suggested by KS F 2566 and ASTM C 1609 regulations, and the flexural toughness is 10 J (kN · mm) or more, preferably 15 J (kN·mm), and more preferably 25 J (kN·mm) or more. Here, the upper limit of the compressive strength, the upper limit of the flexural strength, and the upper limit of the flexural toughness are not limited because the higher the better, for example, 70 MPa, 15 MPa, and 60 J (kN·mm), respectively. The compressive strength or the bending strength may be measured in accordance with KS L ISO 679 regulations.

Hereinafter, the present invention will be described in detail by way of Examples, but these are for describing the present invention in more detail, and the scope of the present invention is not limited by the Examples below.

[Examples 1 to 3, Comparative Examples 1 and 2]

Hybrid fiber-reinforced mortar compositions of Examples 1 to 3 including steel fibers, carbon fibers, admixtures, cement and water at the composition ratios shown in Table 1 below were prepared. In addition, a hybrid fiber-reinforced mortar composition of Comparative Example 1 and Comparative Example 2 in which carbon fiber was not used but the same as in Example 1 but in which no steel fiber was used was prepared with the composition ratio shown in Table 1 below.

Specifically, cement and fine aggregate were first put into the mixer and mixed for 30 seconds at a low speed, and then the corresponding fibers were added as shown in Table 1 to ensure fiber dispersibility and mixed with dry bibim for 90 seconds. Then, more water and an admixture were added to the mixer, and the mixture was further mixed immediately for 90 seconds. After stopping for 30 seconds, the attached composition was removed, and finally, the mixer was operated again and mixed at high speed for 60 seconds to prepare a hybrid fiber-reinforced mortar composition. The total mixing time at this time was about 5 minutes.

In order to properly cure the hybrid fiber-reinforced mortar composition prepared in this way, the composition is filled in a mold and sufficiently minced, and then covered with a plastic sheet for 24 hours before demolding to suppress rapid evaporation of moisture. made to be After demolding, the cured hybrid fiber-reinforced mortar composition was air dry cured for 3 days, 7 days and 28 days, respectively, and the curing temperature was controlled at room temperature (20±2° C.).

reinforcing fiber admixture cement fine aggregate water Gross weight (kg) steel fiber carbon fiber (vol%, at 25°C, 1 atm) (kg) Comparative Example 1 9.6 100 0 9.675 645 1,290 297 Comparative Example 2 0 100 Example 1 75 25 Example 2 50 50 Example 3 25 75

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

<Steel fiber and carbon fiber>

As shown in Table 2 below, steel fibers having a diameter of 0.5 mm, a length of 30 mm, and a tensile strength of 1,100 MPa were used. A bundle type made by attaching them to each other was used. In addition, as shown in Table 2 below, carbon fibers having a diameter of 0.007 mm, a length of 6 mm, a tensile strength of 4,900 MPa, and an elastic modulus of 230 GPa were used.

Characteristics Macro steel fiber (SF) Micro carbon fiber (CF) Shape Hooked-end Straight Length, l (mm) 30 6 Diameter, d (mm) 0.5 0.007 Aspect ratio (l/d) 60 857 Density (kg/m ³ ) 7,850 1,800 Tensile strength (MPa) 1,100 4,900 Elastic modulus (GPa) > 210 230 Elongation (%) > 3.5 2.1

<Cement and admixture>

As the cement, Ordinary Portland Cement (OPC) having a specific gravity of 3.13 and a fineness of 3,860 cm ^{2 /g was used.} The admixture (superplasticizer, SP) was a polycarboxylic acid-based, high-performance AE water reducing agent having a specific gravity of 1.04, a pH of 5.0±1.5, and a light yellow liquid to facilitate the fluidity of the composition.

<fine aggregate>

As the fine aggregate, silicon dioxide (SiO ₂ ) specified in KS L ISO 679 is contained, and a standard yarn having an average particle diameter of 2 mm or less, a density of 2.65 g/cm ³ , and a fineness modulus (FM) of 2.78 was used.

Hereinafter, the results of testing various properties of the mortars prepared by curing the compositions according to Examples 1 to 3, Comparative Examples 1 and 2 will be described below.

<Liquidity test>

Fluidity tests were performed on the hybrid fiber-reinforced mortar compositions of Examples 1 to 3 and Comparative Example 2, and “Flow table for use in tests of hydraulic cement” in KS L 5111 It was tested according to the test method of KS L 5105 of “Testing method for compressive of hydraulic cement mortar”. Immediately after the composition was discharged, it was poured into a conical mold with a lower diameter of 100±0.5 mm, an upper diameter of 70±0.5 mm, and a height of 50±0.5 mm in two layers and compacted 20 times. The table flow value of the composition was calculated as an average of 4 diameters in different directions after falling from a height of 12.7 mm at a speed of 25 for 15 seconds, and the results are shown in FIG. 1 .

As shown in FIG. 1 , the flow value of Example 1, in which the volume ratio of steel fiber to carbon fiber was 75:25, was superior to that of Example 2, in which the volume ratio of steel fiber to carbon fiber was 50:50, and Example 3, in which the volume ratio of steel fiber to carbon fiber was 25:75. and the flow value of Comparative Example 2 in which only carbon fiber was used among the reinforcing fibers was the lowest. Therefore, it can be confirmed from FIG. 1 that the fluidity is better when the mixing ratio of the steel fiber among the reinforcing fibers is higher. This is because carbon fiber has a higher fiber aspect ratio than steel fiber and absorbs some of the mixing water, so it is judged that the dispersibility of the fiber tends to decrease as the mixing rate of carbon fiber increases. , it can be seen that it is very disadvantageous in terms of fluidity due to the non-hydrophilicity and fiber aggregation of carbon fibers.

<Compressive strength test>

Compressive strength was tested on the composite material cured with the hybrid fiber-reinforced mortar composition of Examples 1 to 3 and Comparative Example 2, and for each sample, a mold was manufactured according to the test method of KS L ISO 679, and the age of 28 The strength at work was measured. At this time, the compressive strength of the 40×40×160 mm cubic specimen that was cured was measured using a universal testing machine (MTDI Co., Ltd, Korea, UT-100F) with a capacity of 100 kN, and the loading rate was 2,400 N/s. It was measured by applying pressure at a constant speed under the conditions of . And the compressive strength was calculated through Equation 1 below, and the result is shown in FIG. 2 .

[Formula 1]

In Equation 1, f _cu is the compressive strength (MPa), P is the maximum load obtained in the test (N), b is the width of the specimen (40 mm), h is the height of the specimen (40 mm).

As shown in FIG. 2, at 28 days of age, the compressive strengths of Comparative Example 1 in which only steel fibers among the reinforcing fibers were used and Comparative Example 2 in which only carbon fibers among the reinforcing fibers were used were 45.2 MPa and 35.4 MPa, respectively, whereas The compressive strength of Example 1 with a volume ratio of 75:25 was the best at 47.0 MPa. In addition, the compressive strength of Example 1 in which the volume ratio of steel fiber to carbon fiber was 75:25 was superior to that of Example 2 in which the volume ratio of steel fiber to carbon fiber was 50:50 and Example 3 in which the volume ratio was 25:75. This is considered to be due to the fact that the interfacial bonding force between the fibers and the matrix in the mortar after curing is further improved as the surface hydrophilic properties of the steel fibers are superior to that of the carbon fibers.

<Bending performance test and crack characteristic evaluation>

Examples 1 to 3 The flexural performance was tested for the composite cured with the hybrid fiber-reinforced mortar composition of Example 3 and Comparative Example 2, and a beam specimen having a size of 100 × 100 × 400 mm presented in ASTM C 1609 and KS F 2566 was manufactured and the flexural strength and flexural toughness were measured at the age of 28 days. Figure 3 (a) is the shape and specifications of the specimen used in the bending performance test, Figure 3 (b) shows the set-up state of the test equipment. Specifically, the flexural performance test was applied as a four-point flexural load test using a universal material testing machine (Instron Co., Ltd, 5597) with a capacity of 2,500 kN, and two linear variable displacement transducers installed in the center of both sides of the specimen. , LVDT) was used to measure deflection and breaking load. The deflection rate was controlled by displacement at a constant load rate of 0.2 mm/min until the specimen was broken at 1/1,500 spans per minute, and the load was measured through a load cell with a capacity of 850 kN.

The flexural strength was calculated using Equation 2 below at the maximum load. In Equation 2 below, f' _r is the equivalent flexural strength (MPa), δ _tb is the deflection of 1/150 of the span (mm), l is the span (mm), b is the average width of the fracture section (mm), and h is the fracture The average height (mm) of the section, A _b represents the area (kN·mm, J) of the load-deflection curve up to _{δ tb} in FIG. 4 as flexural toughness. At this time, the bending toughness was calculated by accumulating the sum of the _{area under the load-deflection curve of FIG. 4 (A b} ) until the deflection suggested in ASTM C 1609 and KS F 2566 was 1/150 (2 mm) of the span.

[Formula 2]

1. Flexural strength

As shown in FIG. 5 , the average flexural strengths of Comparative Example 1 in which only steel fibers among the reinforcing fibers were used and Comparative Example 2 in which only carbon fibers among the reinforcing fibers were used at the age of 28 days were measured to be 5.85 MPa and 4.8 MPa, respectively. On the other hand, the average flexural strength of Example 1, in which steel fibers and carbon fibers were used together, in which the volume ratio of steel fibers to carbon fibers was 75:25, was the highest at 8.16 MPa. In addition, from Examples 1 to 3, as the mixing ratio of the steel fiber compared to the carbon fiber increased, the bending sensitivity was further increased. This is because the mixed fiber prevents crack propagation by the bridging effect and improves flexural strength through the redistribution of stress. Through the combination of carbon fibers, it was possible to significantly increase the flexural strength compared to the case where one type of fiber was used.

2. Flexural toughness

As shown in FIG. 6 , the average flexural toughness of Comparative Example 1 in which only steel fibers among the reinforcing fibers were used and Comparative Example 2 in which only carbon fibers among the reinforcing fibers were used at the age of 28 days were 8.16 kN·mm and 27.9 kN·mm, respectively. The average flexural toughness of Example 2, in which steel fiber and carbon fiber were used together, in which the volume ratio of steel fiber to carbon fiber was 50:50, was the highest at 35.7 kN·mm, which was the highest in Comparative Example 2 in which only carbon fiber was used among the reinforcing fibers and reinforcement Compared with Comparative Example 1 in which only steel fibers were used among the fibers, the results were approximately 4.4 times and 1.3 times higher, respectively. This difference is considered to have a synergistic effect between the strength-enhancing effect of micro-sized carbon fibers and the toughness-enhancing effect of macro-sized steel fibers. Therefore, it can be seen that the composite material prepared with the hybrid fiber-reinforced composition according to the present invention has high flexural strength as described above, and, in particular, has high flexural toughness to improve deformation performance and has high crack resistance.

As such, it can be seen that the composite material prepared from the hybrid fiber-reinforced mortar composition according to the present invention has high deformability, and is particularly effective when used in structures requiring dynamic loads such as earthquakes, impacts, blast loads, and wind loads.

3. Crack propagation and fracture patterns

After completion of the flexural performance test, crack propagation and fracture patterns of the side surfaces of each specimen were observed, and this is shown as an image in FIG. 7 .

As shown in FIG. 7 , the cracks of all specimens occurred almost similarly and appeared as vertical cracks propagating from the bottom to the top, and as the load increased, the cracks finally fractured at the compression edge of the compression part. Comparative Example 2, in which only carbon fiber was used among the reinforcing fibers, did not cause a sudden load reduction, but showed a brittle fracture behavior. On the other hand, in the case of Examples 1 to 3, in which steel fibers and carbon fibers were used together, the residual strength after the maximum load due to the crosslinking role of the fibers in transferring the tensile stress across the internal cracks occurring between the fibers and the cement matrix. showed ductile fracture behavior. It is judged that this fracture behavior is the result of reinforcing the brittle properties of Comparative Example 2 in which only carbon fibers among the reinforcing fibers were used, but the steel fibers and carbon fibers were reinforced with the role of fiber bridging in the specimen. From this, in the case of a hybrid fiber-reinforced specimen in which steel fibers and carbon fibers are used together, micro carbon fibers with a relatively short length control the propagation of micro-cracks by narrowing the distance between the fibers, and macro steel fibers with a long length increase the distance between the fibers. It can be seen that it effectively controls the growth of macro cracks due to their widening.

4. Crack Surface Observation

8 shows the fracture state of the crack surface in each specimen after completion of the bending performance test.

As shown in FIG. 8 , in Comparative Example 1 (a) in which only steel fibers were used, steel fibers were distributed at very wide intervals along the crack surface, and in Comparative Example 2 (c) in which only carbon fibers were used, carbon fibers were narrowly spaced. It can be seen that the distribution of On the other hand, in the case of Example (b) in which steel fibers and carbon fibers are used together, it can be seen that the steel fibers are widely distributed along the crack surface and carbon fibers are distributed at narrow intervals at the same time. This shows that the failure mechanism is mainly due to the pull-out phenomenon of the fibers, not the rupture of the fibers. In the general case where fibers are not reinforced, cracks occur and fracture when subjected to a load, whereas fiber-reinforced composites transmit tensile force to the fibers constraining the crack, increasing the proof strength and reaching the maximum load. As a result, the fibers begin to be pulled out one by one near the tensile edge, and the yield strength gradually decreases. This is thought to be because the fibers suppress the internal cracks that occur between the cement matrices, and at the same time, the fibers act as a bridge to transmit the tensile stress across the cracks, thereby inhibiting the growth of cracks. It can be seen that when used, it is more effective.

[Example 4]

In Example 1, the same procedure as in Example 1 was performed, except that the carboxylic acid-based polymer of Chemical Formula 1 as the first strength reinforcing agent was further used as the composition ratio in Table 3 below. In this case, the carboxylic acid-based polymer of Formula 1 was prepared as follows.

<Carbon acid-based polymer manufacturing process>

120 parts by weight of maleic anhydride and 90 parts by weight of distilled water were injected into a glass reactor equipped with a thermometer, stirrer, dropping funnel, nitrogen inlet tube and reflux cooling device and completely dissolved, and then allyl alcohol-polyoxyethylene glycol (Allyl alcohol-ethylene oxide average addition 20 moles) 220 parts by weight and 250 parts by weight of allyl alcohol-polyoxyethylene glycol sulfoethoxyester (allyl alcohol-ethylene oxide average added mole number of 10 moles) are added, and the inside of the reactor is replaced with nitrogen under stirring, and the temperature is raised to 80° C. under a nitrogen atmosphere. did. Then, 80 parts by weight of methacrylic acid and 100 parts by weight of an aqueous solution of ammonium sulfate (5.5 wt%) as an initiator were added dropwise over 6 hours. After completion of the dropping of the monomer initiator, 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 80° C. for 2 hours. After the reaction mixture was cooled 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 polydispersity of 2.25. A carbonic acid-based polymer was obtained.

[Example 5]

In Example 1, it was carried out in the same manner as in Example 1, except that triethanolamine, a second strength reinforcing agent, was further used as the composition ratio in Table 3 below.

[Example 6]

The same procedure as in Example 1 was carried out in Example 1, except that the carboxylic acid-based polymer of Chemical Formula 1 as the first strength reinforcing agent and triethanolamine as the second strength reinforcing agent were further used as the composition ratios shown in Table 3 below.

kg reinforcing fiber admixture cement fine aggregate water strength enhancer Carbonic acid polymer triethanolamine Example 4 9.6 9.675 645 1,290 297 12 - Example 5 - 12 Example 6 6 6

Hereinafter, the compressive strength and flexural strength of the cement prepared by curing the compositions according to Examples 1 and 4 to 6 were measured, which were measured in the same manner as in the compressive strength test and the bending performance test.

Strength modifier (wt%) compressive strength flexural strength Carbonic acid polymer triethanolamine (MPa) Example 1 - - 47.0 8.16 Example 2 1.24 - 51.1 8.23 Example 3 - 1.24 50.2 8.21 Example 4 0.62 0.62 56.9 8.97

As a result of measuring the compressive strength and flexural strength of the specimens prepared from the compositions according to Examples 1 and 4 to 6, in the group in which the carboxylic acid-based polymer and triethanolamine were combined, each component was used alone 2 and Example 3 did not show significant improvement in compressive strength compared to Example 1. On the other hand, Example 4, in which both the carbonic acid-based polymer and triethanolamine were used, surprisingly improved the compressive strength significantly compared to Examples 2 and 3 in which each component was used alone while maintaining a high level of flexural strength.

Therefore, when a carbonic acid-based polymer or triethanolamine is used as a strength reinforcing agent, not only the compressive strength is improved, but especially, when a carbonic acid-based polymer and triethanolamine are used together, it can be confirmed that the compressive strength is significantly improved while maintaining excellent flexural strength. .

Claims (11)

Reinforcing fibers including steel fibers and carbon fibers, strength reinforcing agents, cement, fine aggregates and water,
The strength reinforcing agent is an alkanolamine-based compound; and a carboxylic acid-based polymer of Formula 1 below. A hybrid fiber-reinforced mortar composition comprising.
[Formula 1]

(In Formula 1,
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,
M is independently of each other hydrogen, alkali metal, ammonium or organic amine group,
When X is hydrogen or a methyl group, Z is -CH ₂ COOM ₁ Or, when X is -COOM ₁ , Z is hydrogen or a methyl group, wherein M ₁ is hydrogen, an alkali metal, ammonium or an organic amine group,
t and u are independently integers from 0 to 15;
P ₁ O and P ₂ O are independently of each other one type or a mixture of two or more repeating units of an oxy (C2-C4) alkylene group, and in the case of two or more types, are added in a block form or are added randomly,
1 and m are independently integers from 1 to 100;
p, q, r and s are each independently from 10 to 1,000) According to claim 1,
In the reinforcing fiber, the volume ratio of the steel fiber to the carbon fiber is 1:0.1 to 2 at 25° C. and 1 atm hybrid fiber-reinforced mortar composition. According to claim 1,
The average diameter of the steel fiber is 200 to 900 ㎛, the average diameter of the carbon fiber is 1 to 15 ㎛ hybrid fiber reinforcement mortar composition. 4. The method of claim 3,
The average length of the steel fibers is 10 to 100 mm, and the average length of the carbon fibers is 3 to 24 mm hybrid fiber reinforcement mortar composition. According to claim 1,
The composition is a hybrid fiber-reinforced mortar composition comprising 0.5 to 50 parts by weight of the reinforcing fiber, 50 to 800 parts by weight of the cement, and 100 to 1,000 parts by weight of the fine aggregate based on 100 parts by weight of the water. delete According to 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 A hybrid fiber-reinforced mortar composition comprising any one or two or more selected from amine, N,N-diisopropanolamine, triethanolamine, diisopropylethanolamine and diethanolamine. According to claim 1,
The strength reinforcing agent is a hybrid fiber-reinforced mortar composition comprising 0.1 to 20 parts by weight based on 100 parts by weight of the water. A hybrid fiber-reinforced mortar composite prepared by curing the mortar composition of any one of claims 1 to 5, 7 and 8. 10. The method of claim 9,
At 28 days of age, the compressive strength is 25 MPa or more based on the KS F ISO 679 test, the flexural strength is 4 MPa or more based on the 4-point flexural load test suggested by KS F 2566 and ASTM C 1609, and the flexural toughness is 10 J (kN·mm) ) or more hybrid fiber reinforced mortar composites. A method for producing a hybrid fiber-reinforced mortar composite comprising a composite manufacturing step of preparing a fiber-reinforced cement composite by curing the mortar composition of any one of claims 1 to 5, 7 and 8.

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