WO2018030728A1 - Ultra-high-performance fiber-reinforced concrete and manufacturing method therefor - Google Patents

Abstract

The present invention relates to an ultra-high-performance fiber-reinforced concrete and a manufacturing method therefor, wherein in a cement composite formed by mixing cement, a zirconium-containing silica micropowder, fine aggregate, a filler, a shrinkage-reducing agent, a high-performance water-reducing agent, mixing water, macro steel fiber, micro steel fiber, and an antifoaming agent, mixing is carried out such that the range of the specific surface area of the silica micropowder is 80,000-150,000 cm²/g, and the shape factor of the steel fiber is 60-100 and a crack inducer for inducing microcracks is mixed in a ratio of 0.5-2% with respect to the total volume.

Description

Ultra-high performance fiber reinforced concrete and its manufacturing method

The present invention relates to an ultra-high performance fiber reinforced concrete and a method of manufacturing the same, and more particularly, to limit the shape coefficient of steel fiber to increase the fluidity without lowering the compressive strength and to artificially induce microcracks by crack derivatives. The present invention relates to an ultra-high performance fiber reinforced concrete and its manufacturing method for increasing tensile properties by having a strain hardening phenomenon and multiple fine crack distributions in tensile behavior.

Although concrete, which is economically and durable, is widely used as a material for structures, it has defects that are small in its tensile strength and flexural strength and are prone to cracking.

Therefore, in order to solve the problems of the concrete, fiber reinforced concrete in which various fibers such as steel fibers or organic fibers are mixed with the cement composite is being developed. Among them, the compressive strength is 120 MPa or more, the tensile strength is 5 MPa or more, and the flexural tensile strength There is an increasing demand for Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with a strength of 30 MPa or more.

Ultra-high performance fiber reinforced concrete has a very low water / binder ratio, formulation design based on the closest packing theory, excellent rheological properties using high performance water reducing agents, homogeneous properties and hydration formation using only fine aggregates without thick aggregates. High temperature curing conditions are basically required.

However, the fiber reinforced concrete is not added to the fiber due to the lack of viscosity of the concrete because the fiber is added to the mixing of the general concrete, thereby failing to secure sufficient toughness.

In general, the fine particles of siliceous powder (specific surface area 2000,000 cm ² / g) blended with fiber-reinforced concrete are much smaller than the cement particles (specific surface area 35,000 cm ² / g). As the main component has amorphous SiO ₂ component, the concrete structure is densified by producing calcium silicate (CSH) hydrate due to calcium hydroxide (Ca (OH) ₂ ) and pozzolanic reaction produced by cement hydration.

However, since fiber reinforced concrete uses a high proportion of silica fine powder of 20-30% of cement weight to realize ultra high strength, the viscosity of concrete is increased and the production time of concrete is lengthened to secure predetermined fluidity. Although special mixers such as high speed mixers or shear mixers have to be used and expensive high performance sensitizers have to be used in large amounts, there is a case where the fibers are not evenly dispersed due to lack of fluidity.

Due to this, the condensation hardening time is long, which is disadvantageous for winter construction, and the self-shrinkage is increased due to the activation of the hydration reaction, and the dispersibility of the fiber is deteriorated. Mass production of concrete is difficult and manufacturing costs increase.

On the other hand, in terms of the toughness of the concrete structure, as shown in Fig. 1, the cement composite is tough because the steel fiber is first drawn out from the concrete before the yield strength of the steel fiber is reached and fractured upon bending failure of the ultra-high performance fiber reinforced cement composite. You can see the effect.

It can be seen that the behavior of the fiber in the cement composite is largely dependent on the interfacial phase, and the dominating behavior is due to the adhesion performance between the fiber and the cement matrix and the fracture of the fiber.

And, it can be seen that the durability of concrete is very closely related to the crack width. The self-healing performance of concrete depends on the crack width. In ultra-high fibre-reinforced concrete with low water binder ratio, controlling the crack width has a very close effect on durability and self-softening performance.

As a result, it is time to improve the tensile performance of the ultra-high-performance fiber reinforced concrete inherently by controlling the interfacial properties and adhesion between the fiber and the cement matrix and the crack width of the concrete itself.

The present invention is to solve such a conventional problem, it is an object of the present invention to secure the dispersibility of the fiber and at the same time tensile strength and strength to specify the shape coefficient of the steel fiber in order to secure the dispersibility of the conventional fiber reinforced concrete It is to improve toughness.

Another object of the present invention is to improve the interfacial properties and adhesion deterioration phenomenon between the steel fibers and the cement matrix generated in the conventional fiber reinforced concrete, and to prevent a sudden decrease in tensile performance due to the occurrence of macro cracks.

According to the characteristics of the present invention for achieving the above object, the ultra-high performance fiber reinforced concrete of the present invention is cement, zirconium-containing silica fine powder, fine aggregate, filler, shrinkage reducing agent, high performance water reducing agent, compounding water, macro steel fiber, micro steel fiber In the cement composite formed by mixing at least one or more of an antifoaming agent, the specific surface area of the silica fine powder is in the range of 80,000 cm ² / g or more and 150,000 cm ² / g or less, and the shape coefficient of the steel fiber is 60 or more and 100 or less. It is preferable.

When the steel fiber of the present invention has the same shape factor, it is preferable that the steel fiber includes a relatively small diameter steel fiber.

In the steel fiber of the present invention, the micro steel fiber is mixed at 25% to 35%, and the macro steel fiber is mixed at 65% to 75%.

In the steel fiber of the present invention, it is preferable to mix 0.5% of the shape coefficient 80 (d0.2mm × L16mm) and 1.5% of the shape coefficient 100 (d0.2mm × L20mm).

The ultra high performance fiber reinforced concrete of the present invention preferably further includes a crack inducer for inducing microcracks in the cement composite.

The crack derivative of the present invention is preferably composed of polystyrene beads.

The crack derivatives of the present invention are preferably mixed at 0.5 to 2% of the total volume.

The crack derivative of the present invention preferably includes a first surface layer comprising a crack promoter applied to the surface to promote microcracking.

The crack derivative of the present invention includes a second surface layer which is applied to the surface of the first surface layer and dissolved for a predetermined time by moisture.

The method for producing ultra-high performance fiber reinforced concrete of the present invention is a cement composite by mixing at least one or more of cement, fine silica powder, fine aggregate, filler, shrinkage reducing agent, high performance water reducing agent, blended water, macro steel fiber, micro steel fiber, and antifoaming agent. In the manufacturing method of the super high-performance fiber-reinforced concrete to be formed, 25 parts by weight of fine silica powder having a specific surface area of 80,000 cm ² / g or more and 150,000 cm ² / g or less based on 100 parts by weight of cement, 20 parts by weight of filler, quartz sand It is preferable to make it mix by 110 weight part, to make the ratio of compounding water-binder to be 0.20, and to mix and manufacture steel fiber whose shape coefficient is 60 or more and 100 or less.

Method for producing ultra-high performance fiber reinforced concrete of the present invention is a mortar manufacturing step of mixing evenly silica fine powder, quartz powder, quartz sand for 20 seconds to 30 seconds at a speed of 10 ~ 20rpm; A first mixing step of mixing the mortar with a blending water-binder ratio of 0.20 and mixing the high-performance water reducing agent, the antifoaming agent, and the shrinkage reducing agent with 1.9 parts by weight of the binder at a speed of 20-50 rpm in a mixer for 2 minutes to 5 minutes. And it is preferable to include a second mixing step of mixing the steel fiber for 1 minute to 3 minutes at a speed of 20 to 50 rpm.

The second mixing step of the present invention preferably further comprises mixing a crack derivative for inducing microcracks in the cement composite.

In the second mixing step of the present invention, the crack derivative is preferably mixed at a ratio of 2 to 3% of the total volume.

According to the ultra-high performance fiber-reinforced concrete and the manufacturing method thereof according to the present invention, the specific surface area of the fine silica-like powder to control the fluidity of the cement composite, and the range of the shape coefficient of the steel fiber affecting the dispersion and compressive strength of the fiber It is limited in combination to secure the dispersibility of the steel fiber and the fluidity of the cement composite and at the same time has the advantage of improving the tensile strength and toughness.

In addition, since the viscosity decreases compared to the existing high performance fiber reinforced concrete, the fluidity is improved, and thus, the amount of expensive high performance water reducing agent required to secure the same workability can be reduced, thereby reducing the manufacturing cost of the UHPC.

In addition, the microcracks are artificially formed between the crack inductor and the cement matrix to induce the growth of large cracks into the microcracks, and the crack propagation is prevented by the tensile force of the microfibers around the crack inductor. There is an advantage to improve.

In addition, since one end of the microfiber around the crack inductor is affected by the discontinuous interface property, the adhesion strength between the microfiber and the cement matrix is improved, thereby controlling the crack width and increasing the pull energy of the fiber, thereby greatly improving tensile strength and toughness. There is this.

In addition, since the tensile strength is improved compared to the existing technology, the mixing ratio (volume) of the steel fibers required to secure the same performance can be reduced by about 0.5%, thereby reducing manufacturing costs and improving workability.

1 is a view showing a fracture state of ultra-high performance fiber reinforced concrete according to the prior art.

Figure 2 is a graph illustrating the relationship between the fine silica powder specific surface area and the water adsorption amount of ultra-high performance fiber reinforced concrete according to the present invention.

Figure 3 is a graph of the relationship between the specific surface area and fluidity or viscosity of the fine silica powder of ultra-high performance fiber reinforced concrete according to the present invention.

Figure 4 is a graph illustrating the relationship between the specific surface area and the compressive strength of the fine silica powder of ultra-high performance fiber reinforced concrete according to the present invention.

5 is a graph illustrating the relationship between the specific surface area and the amount of high performance water reducing agent of the ultra high performance fiber reinforced concrete according to the present invention.

Figure 6 is an evaluation of the material separation state by visual observation in the flow test (KS L 5105) of ultra-high performance fiber reinforced concrete according to the present invention.

7 is a graph illustrating the correlation between the shape coefficient of the steel fiber of the high-performance fiber reinforced concrete according to the present invention, the specific surface area of the fine silica powder and the compressive strength.

8 is a view showing a direct tensile test body and a tensile test device of ultra-high performance fiber reinforced concrete according to the present invention.

9 is a graph illustrating the relationship between the shape coefficient and tensile strength of steel fibers of ultra-high performance fiber reinforced concrete according to the present invention.

Figure 10a is a schematic diagram showing the crack propagation state of a general ultra-high performance fiber reinforced concrete.

Figure 10b is a graph showing the tensile behavior of the general ultra-high performance fiber reinforced concrete.

11a is a graph illustrating the relationship between the compressive strength and the tensile strength of the cement composite hybridized by the shape coefficients in the shape coefficient 60 of the steel fiber of the ultra-high performance fiber reinforced concrete according to the present invention.

11b is a graph illustrating the relationship between the compressive strength and the tensile strength of the cement composite hybridized by the shape coefficient of the steel fiber of the ultra-high performance fiber reinforced concrete according to the present invention.

12 is a view showing an embodiment of the crack inductor of ultra-high performance fiber reinforced concrete according to the present invention.

13 is a graph showing the flexural tensile strength and equivalent flexural tensile strength (V _f = 2%) of the ultra-high performance fiber reinforced concrete according to the present invention.

Figure 14 is a graph showing the bending stress-strain (V _f = 2%) state of the ultra-high performance fiber reinforced concrete according to the present invention.

15a and 15b are graphs showing the tensile behavior of ultra-high performance fiber reinforced concrete for the state containing no crack derivatives and 2% containing crack derivatives, respectively.

Figure 16a and 16b is a view showing a cross-sectional state of the ultra-high performance fiber-reinforced concrete for the state that does not include the crack guide and 2% containing the crack guide.

Figure 17 is a schematic diagram showing the microcracks propagation state of the crack inductor of ultra-high performance fiber reinforced concrete according to the present invention.

18 is an enlarged view of a portion of FIG.

19 is a cross-sectional view showing a crack derivative showing another embodiment of ultra-high performance fiber reinforced concrete according to the present invention.

The present invention is a super high-performance fiber reinforced concrete formed by mixing at least one or more of cement, zirconium-containing silica fine powder, fine aggregate, filler, shrinkage reducing agent, high performance water reducing agent, blended water, steel fiber, and antifoaming agent, The specific surface area is in the range of 80,000 cm ² / g or more and 150,000 cm ² / g or less, and the shape factor of the steel fiber is 60 or more and 100 or less, and the steel fibers having a shape factor of 60 to 80 are mixed at a volume ratio of 25% to 35%, and the shape Steel fibers having a coefficient of 81 to 100 are mixed at a volume ratio of 65% to 75%, and a crack inducer for inducing microcracks in the cement composite is further included, and the crack inducer is applied to a surface to include a crack promoter for promoting microcracks. It provides an ultra-high performance fiber reinforced concrete comprising a first surface layer.

Description of the present invention is only an embodiment for structural or functional description, the scope of the present invention should not be construed as limited by the embodiments described in the text. That is, since the embodiments may be variously modified and may have various forms, the scope of the present invention should be understood to include equivalents capable of realizing the technical idea. In addition, the objects or effects presented in the present invention does not mean that a specific embodiment should include all or only such effects, the scope of the present invention should not be understood as being limited thereby.

On the other hand, the meaning of the terms described in the present application should be understood as follows.

Terms such as "first" and "second" are intended to distinguish one component from another component, and the scope of rights should not be limited by these terms. For example, the first component may be named a second component, and similarly, the second component may also be named a first component.

When a component is referred to as being "connected" to another component, it should be understood that there may be other components in between, although it may be directly connected to the other component. On the other hand, when a component is referred to as being "directly connected" to another component, it should be understood that there is no other component in between. On the other hand, other expressions describing the relationship between the components, such as "between" and "immediately between" or "neighboring to" and "directly neighboring to", should be interpreted as well.

Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "comprise" or "have" refer to a feature, number, step, operation, component, part, or feature thereof. It is to be understood that the combination is intended to be present and does not exclude in advance the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof.

In each step, an identification code (e.g., a, b, c, etc.) is used for convenience of description, and the identification code does not describe the order of the steps, and each step clearly indicates a specific order in context. Unless stated otherwise, they may occur out of the order noted. That is, each step may occur in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. Generally, the terms defined in the dictionary used are to be interpreted to coincide with the meanings in the context of the related art, and should not be interpreted as having ideal or excessively formal meanings unless clearly defined in the present application.

The present invention relates to a material design method for increasing proper fluidity while reducing excessive viscosity of ultra-high performance fiber reinforced concrete (hereinafter referred to as “UHPC”), and a material capable of increasing fluidity while lowering viscosity without decreasing compressive strength. And formulation design.

In general, as long as the dispersion coefficient of the fiber is secured in the fiber reinforced concrete, the tensile strength and toughness of the steel fiber increase as the shape factor (fiber length / diameter) of the steel fiber increases. However, in actual production of UHPC, the larger the steel fiber shape coefficient, the worse the dispersibility of the fiber and the lower the tensile strength and toughness. Therefore, it is very important to select the shape coefficient of the steel fiber when manufacturing the UHPC.

Conventional UHPC uses a lot of steel fibers with a shape factor of 60 (12 mm in length and 0.2 mm in diameter). However, since USiPC uses fine silica-like powders, when the steel fiber with a shape factor of 60 or more is used, the dispersibility of fibers deteriorates and tension Strength and toughness are rather lowered.

The siliceous fine powder has an excessive viscosity because the specific surface area is very high (200,000 cm ² / g) and the water adsorption amount is very high (50 ~ 70 cm ³ / g) to absorb the blended water and high performance water reducing agent.

Therefore, it is necessary to reduce the viscosity of UHPC and to ensure proper fluidity by reducing the amount of water absorbed by the blending water and the high performance water reducing agent by using a binder having a small water adsorption amount.

(1) Specific surface area range of fine siliceous powder

First, in order to examine the effect of the specific surface area of the silicate fine powder on the flowability or viscosity and compressive strength of UHPC, the cement composite was prepared by the following method and the compressive strength and viscosity were measured.

Manufacturing method 1 is based on 100 parts by weight of cement, 25 parts by weight of fine silica powder having a different specific surface area, 20 parts by weight of a filler of quartz powder (99% of SiO ₂ , 4 μm average particle diameter) and 20 parts by weight of quartz sand having a particle size of 5 mm or less. Mortar was prepared by mixing 110 parts by weight and mixing evenly for 15 seconds at 15 rpm. The ratio of the mixture water-binding agent was 0.20, and the binder was 1.9 parts by weight of the high-performance water reducing agent, antifoaming agent, and shrinkage reducing agent at 30 rpm for 3 minutes. After mixing for a while, a steel fiber having a shape factor of 60 (diameter 0.2 mm, length 12 mm) was added to 2% of the cement composite and mixed for 2 minutes at a speed of 20 rpm to produce a steel fiber reinforced cement composite, which was described in the test method described below. Accordingly, a viscosity and slump flow test were performed.

Then, the cement composite was wet cured for 2 days, steam curing was performed at 90 ° C. for 3 days, and then the compressive strength was measured according to the test method described below.

In the test method, the plastic viscosity was measured using a Brookfield viscometer using a Linder spindle immediately after the fiber-reinforced cement composite was prepared for the viscosity test. And, the slump flow test measured the diameter of the concrete spread in a circular shape by KS F 2594. The compressive strength test was performed in accordance with KS F 2405 using Φ100 * 200mm circumferential concrete specimens.

According to the results of the experiment as described above, according to the graph of the relationship between the fine silica powder specific surface area and the water adsorption amount shown in FIG. 2, it can be seen that the water adsorption amount is rapidly decreased from the specific surface area of 150,000 cm ² / g or less.

And, according to the graph of the relationship between the specific surface area and fluidity or viscosity of the fine silica powder shown in Fig. 3, the larger the specific surface area, the smaller the slump flow and the higher the viscosity, and the specific surface area is 150,000 cm ² / g or less. It can be seen that the slump flow increased rapidly and the viscosity decreased.

This is similar to the result of the water adsorption amount. When the water adsorption amount is small, the adsorption of the blended water and the high performance water reducing agent decreases, so that the viscosity of the UHPC decreases and the slump flow increases.

And, Fig. According to the relationship graph of the specific surface area and compressive strength of the siliceous fine powder shown in Fig. 4, by a specific surface area 100,000cm ² / g of the fine silica powder to be a reduction in the compressive strength very little, a specific surface area of 80,000 cm ² / g UHPC using silica fine powder has a compressive strength of 186 MPa, which is about 8% higher than the specific surface area of 200,000 cm ² / g, and the compressive strength of UHPC using silica fine powder with a specific surface area of 50,000 cm ² / g is about 156 MPa. It can be confirmed that the strength decrease of about 33% occurs.

Accordingly, it can be seen from the above results that UHPC can be produced with a compressive strength of 180 MPa or more when using a fine silica powder with a specific surface area of 80,000 cm ² / g.

According to the above results, it can be seen that the specific surface area of silica fine powder having no problem in compressive strength and fiber dispersibility in manufacturing UHPC ranges from 80,000 cm ² / g to 150,000 cm ² / g.

(2) High performance water reducing agent according to specific surface area of fine silica powder

In order to examine the relationship between the specific surface area of fine silica powder and the use of high performance water reducing agent of UHPC, cement composites were prepared by the following method and the compressive strength and viscosity were measured.

25 parts by weight of fine silica powder having a specific surface area based on 100 parts by weight of cement, 20 parts by weight of a filler having a quartz powder (99% of SiO2, an average particle size of 4 μm), and 110 parts by weight of quartz sand having a particle size of 5 mm or less. , The ratio of the blended water-binding material is 0.20. Under these mixing conditions, the amount of high-performance water reducing agent required to secure slump flow of 650 mm was investigated according to the specific surface area of fine silica lipid powder. The high performance water reducing agent used a polycarboxylic acid system of 30% of the solid component.

The experimental results are shown in FIG. 5. As shown, the larger the specific surface area of the fine silica powder, the higher the amount of high performance water reducing agent required to secure a certain fluidity. In particular, the use of high performance water reducing agents has increased rapidly from the specific surface area of 180,000 cm ² / g. For example, UHPC using silicate powder with a specific surface area of 230,000 cm ² / g requires 2.09 times more high-performance water reducing agent to achieve the same workability than UHPC using silicate powder with a specific surface area of 80,000 cm ² / g. .

Therefore, the condition for optimizing the amount of expensive high performance water reducing agent is preferably 150,000 cm ² / g or less of the specific surface area of the fine siliceous powder.

In the case of using the fine siliceous powder having an appropriate specific surface area, the viscosity of the cement composite is lowered to improve the fluidity, thereby reducing the cost of manufacturing UHPC by reducing the amount of expensive high performance water reducing agent.

(3) Shape factor range of steel fiber

In order to investigate the effect of the shape coefficient of steel fiber on the fiber dispersibility and compressive strength, the cement composite was prepared by the following method and the fiber dispersibility, compressive strength and tensile strength were measured.

In the manufacturing method 2, the diameter of 0.2 mm was fixed in the manufacturing method 1 described above, and the shape factors 50 (length 10 mm), 70 (length 14 mm), 80 (length 16 mm), 90 (length 18 mm), 100 (length 20 mm), Steel fiber with 110 (length 22mm) and 120 (length 24mm) was added to prepare a UHPC, and the dispersibility and compressive strength of the fiber were evaluated according to the following test method.

The fiber dispersibility of the UHPC was evaluated for material separation by visual observation in a flow test (KS L 5105). By visual observation, it was evaluated by classifying the grade 1 (excellent), 2 (normal), 3 (defect) according to the fiber agglomeration state in the cement composite (see Fig. 6).

Here, Grade 1 is a state in which fibers are homogeneously dispersed in manufacturing UHPC, Grade 2 is a state of fiber ball and material separation slightly, Grade 3 is a very bad state of fiber dispersion due to fiber agglomeration. Divided into.

As shown in Table 1 below with respect to the fiber dispersibility of UHPC, it was evaluated that the fiber dispersibility was lowered as the shape coefficient of the steel fiber increased and the specific surface area of the fine silica powder was increased.

This is because the larger the specific surface area of the fine siliceous powder, the higher the amount of adsorption of the high-performance sensitizer and the blended water and the excessive viscosity to the UHPC. For example, if the shape factor of the steel fiber is 60 or less, there is no problem in dispersibility of the steel fiber regardless of the specific surface area of the fine silicate powder, but the steel fiber in UHPC using the fine silicate powder having a specific surface area of 180,000 cm ² / g or more from the shape factor 70 Problems have been shown to occur in the dispersibility of. It was found that the fiber dispersibility of UHPC was lowered regardless of the specific surface area of fine silicate powder at the shape coefficient of steel fiber over 110. According to the above results, it can be seen that the specific surface area of the fine siliceous powder and the shape coefficient of the steel fiber should be specified dependently, not independently of each other.

As shown in FIG. 7, the compressive strength was hardly changed regardless of the specific surface area of the fine silica powder in the range of 50 to 100, but the fine silica powder was used when the shape coefficient of the steel fiber 110 was used. It can be seen that the compressive strength is lowered regardless of the specific surface area of. This is because when the shape coefficient of the steel fiber is larger than a certain amount, the fiber is not dispersed well when the UHPC is manufactured.

Therefore, the shape coefficient of the steel fiber which does not affect the compressive strength is preferably 100 or less.

In addition, a direct tensile test was performed on the cement composite prepared by the production method 2 to confirm the influence of the shape coefficient of the steel fiber on the direct tensile strength of the UHPC.

The direct tensile test used a direct tensile test specimen and a tensile test apparatus shown in FIG. The direct tension tester was manufactured with a hinge and supporting condition in consideration of the effects of secondary bending stress occurring during the test and the accuracy of the initial specimen mounting. The direct tensile test of the UHPC was carried out using a 300 kN universal material tester, loaded at a loading speed of 0.4 mm / min, and two LVDTs were installed at a range of 175 mm to measure displacement in a narrow cross section in the test specimen.

As shown in FIG. 9 according to the test result, it can be seen that the direct tensile strength increases as the shape coefficient of the steel fiber increases in the range of 50 and 100. This is because the crosslinking effect of the steel fiber increases as the shape coefficient increases.

In particular, the change in direct tensile strength between the shape coefficients 50 and 60 is large, and it is analyzed that the shape coefficient of the minimum steel fiber should be 60 or more in order to fully exhibit the crosslinking action of the steel fiber in the direct tensile strength behavior of UHPC. In addition, it can be seen that the direct tensile strength of the UHPC using the steel fiber having a shape factor of 110 was greatly reduced.

Tensile strength is almost the same regardless of the specific surface area of fine silica powder at shape coefficients of 50 and 60, but when steel fibers with a shape coefficient of 70 or more are used, the tensile strength is large from the specific surface area of more than 180,000 cm ² / g of fine silica powder. It tends to be lowered.

This is because the silicate fine powder has a specific surface area of more than 180,000cm ² / g and the moisture adsorption amount is more than 47cm ² / g, so that the amount of adsorption of high performance water sensitizer and blending water increases during the manufacturing process of UHPC. This is because the UHPC was produced because the fiber dispersibility is irregular because of this decrease, and this phenomenon occurs even more than a certain number of steel fiber shape coefficient.

Therefore, the UHPC blend preferably has a shape coefficient of steel fiber in the range of 60 to 100 in the specific surface area of the fine siliceous powder of 80,000 cm ² / g to 150,000 cm ² / g. In addition, it is preferable that the specific surface area of the fine silica powder and the shape coefficient of the steel fiber are specified independently, not independently of each other.

Specific surface area of fine silica powder (cm 2 / g)	Shape factor of steel fiber (L / d)
	60	70	80	90	100	110	120
50,000	One	One	One	One	One	2	2
80,000	One	One	One	One	One	2	2
100,000	One	One	One	One	One	2	2
130,000	One	One	One	One	One	2	3
150,000	One	One	One	One	One	2	3
180,000	One	2	2	2	2	3	3
200,000	One	2	2	2	3	3	3
230,000	One	2	2	3	3	3	3

(4) Change in tensile strength characteristics with diameter change at same shape factor

In order to examine the tensile strength characteristics according to the diameters of the steel fibers with the same shape coefficients, the cement composites were prepared by the following manufacturing method, and the compressive and direct tensile strengths were measured.

In the manufacturing method 3, the shape coefficient of the steel fiber is fixed to 100, and the diameter of the steel fiber is 0.16mm × length 16mm, diameter 0.18mm × length 18mm, diameter 0.20mm × length 20mm, diameter 0.22mm × length 22mm, diameter 0.25mm × length 25mm Set to.

And, based on 100 parts by weight of cement, 25 parts by weight of a fine powder of 150,000 cm 2 / g silicate powder, 20 parts by weight of a filler having a quartz powder (99% of SiO ₂ , an average particle diameter of 4 μm), and a quartz having a particle size of 5 mm or less. Sand is composed of 110 parts by weight and mixed evenly for 15 seconds at a speed of 15rpm to prepare a mortar. After mixing for 3 minutes at a speed of 30rpm, the steel fiber was added to 2% of the cement composite and mixed for 2 minutes at a speed of 20rpm to prepare a steel fiber reinforced cement composite, and then a slump flow test was performed. Then, the cement composite was wet cured for 2 days, and the compressive strength and direct tensile strength of steam curing at 90 ° C. for 3 days were measured.

According to the test results, even if the shape coefficients of the steel fibers are the same, the use of small diameter steel fibers directly affects the tensile strength improvement, in particular, using steel fibers having a diameter of 0.16 mm and a length of 16 mm as shown in Table 2 below. The direct tensile strength of UHPC is greatly increased to 20.1 MPa. On the contrary, the compressive strength and the direct tensile strength were slightly decreased when the steel fibers of 0.25 mm diameter and 25 mm length were used.

Steel fiber type	Slump Flow (mm)	Compressive strength (MPa)	Direct tensile strength (MPa)
d0.16 x L16	620	196	20.1
d0.18 x L18	635	196	19.7
d0.20 × L20	650	196	18.7
d0.22 x L22	660	189	18.1
d0.25 x L25	660	179	16.7

The smaller the diameter, the higher the tensile strength of UHPC, even if the steel fiber of the same shape factor increases. As the diameter of the fiber decreases, the adhesion area increases due to the increase of the specific surface area of the fiber mixed with the steel fiber and the cement composite. This is because the stress redistribution in the cement composite is caused by the crosslinking action of the fiber after cracking.

(5) Direct tensile strength change by hybrid steel fiber

As shown in Figure 10a and Figure 10b, the effect of the microfiber restrains the micro-cracking at the beginning of the crack during the direct tensile failure behavior, macro cracks having a certain size as the microcracks advance In the case of -cracking), the tensile energy and toughness of the fiber are greatly increased by the crosslinking action of the macrofiber.

Therefore, in order to confirm that the tensile strength is directly improved by the hybrid steel fiber, a cement composite in which a steel fiber having a shape factor of 60 (d0.2mm × L13mm) and a shape factor of 80 (d0.2mm × L16mm) is hybridized, and a shape factor of 80 (d0). Experimental results on the compressive and direct tensile strengths of the cement composite hybridized with steel fibers of .2 mm × L16mm) and shape factor 100 (d0.2mm × L20mm) are shown in FIGS. 11A and 11B, respectively.

According to the experimental results, it can be seen that the shape factor of the fiber has little effect on the compressive strength, UHPC hybridization of the microfiber and macrofiber is a shape factor 60 (d0.2mm × L13mm) that is used a lot in the existing UHPC It can be seen that the direct tensile strength is increased than when using the fiber.

In addition, when the micro steel fibers and the macro steel fibers are mixed, it can be seen that the mixing of the micro steel fibers in the range of 25% to 35% and the macro steel fibers in the range of 65% to 75% is advantageous for improving the direct tensile strength. .

Also, shape factor 80 (d0.2mm × L16mm) and shape factor 100 (d0.2mm × L20mm) than UHPC which hybridizes steel fibers of shape factor 60 (d0.2mm × L13mm) and shape factor 80 (d0.2mm × L16mm). Hybrid steel fiber) is advantageous in terms of tensile steel performance, and it can be seen that incorporating a large proportion of macro steel fiber is more effective in increasing the direct tensile strength of UHPC.

As a result, it can be seen that the hybrid steel fiber is advantageous to combine the steel fiber with the highest possible shape factor, in particular, the shape factor 80 (d0.2mm × L16mm) 0,5% and the shape factor 100 (d0.2mm × L20mm) 1.5 The direct tensile strength of UHPC hybridized with% steel fiber is very high at 19.2 MPa, which is 143% higher than the existing UHPC tensile strength.

In addition, UHPC that hybridized steel fibers with a shape factor of 80 (d0.2mm × L16mm) and shape factor 100 (d0.2mm × L20mm) had a tensile strength of 1.5% (Vf) when compared to conventional UHPCs using steel fibers 2.0% (Vf). The result of high strength shows that even if the mixing ratio of steel fiber decreases by 0.5% (39kg / m ³ ), the same performance can be secured, which can greatly reduce the manufacturing cost of UHPC. That is, in consideration of manufacturing cost, it is preferable to mix the shape coefficient 80 0.5% and the shape coefficient 100 1.0% with each other.

Micro fiber (A)	Macro fiber (B)	Incorporation Rate of Steel Fibers (Vf)			Direct tensile strength (MPa)
		A	B	A + B
d0.2 * L16	d0.2 * L20	0.25	0.75	One	11.3
		0.3	1.0	1.3	12.7
		0.5	1.0	1.5	15.6
		0.75	0.75	1.5	14.9
		0.5	1.5	2.0	19.2
		1.0	1.0	2.0	18.4
d0.2 * L13	-	One	-	One	6.2
		1.3	-	1.3	7.8
		1.5	-	1.5	10.9
		2.0	-	2.0	13.4
d0.2 * L20	-	One	-	One	11.1
		1.3	-	1.3	12.8
		1.5	-	1.5	15.1
		2.0	-	2.0	18.7

(6) Evaluation of Improvement of Tensile Performance by Induction of Artificial Microcrack Distribution

As shown in FIGS. 10A and 10B, in the initial tensile cracking behavior, micro-cracking occurs at the beginning of cracking in the UHPC, and then fracture starts as the microcracks develop into macro-cracking. .

 In the early stage of cracking, the microfibers confine the cracks, and when the major cracks are propagated, the tensile energy and toughness of the fibers are greatly increased by the crosslinking action of the macrofibers.

Therefore, concrete is prepared by mixing microfibers and macrofibers at an appropriate ratio, and artificially induces micro cracks by inserting a separate crack inductor capable of inducing the growth of microcracks, thereby improving adhesion to the surrounding cement matrix. In addition, it is possible to further improve the tensile performance by controlling the crack width by further inducing microcracks from the first crack.

In order to investigate the effect of artificial microcracks induction on tensile performance, cement composites were prepared by the following method and tensile strength and tensile behavior of cement composites were measured.

In the manufacturing method 3, cement, fine silica powder, fine aggregate, and filler are placed in a mixer and mixed at a speed of 15 rpm for 30 seconds. Then, the flowable mixture including the blended water, the high performance water reducing agent, and the antifoaming agent and the shrinkage reducing agent is added to the mixer, and mixed at a speed of 30 rpm for 3 minutes until the mixture is brought into a fluid state.

Then, the macro steel fibers, micro steel fibers, and crack derivatives are added to the mixer, followed by mixing at 20 rpm for 2 minutes. At this time, the crack derivative is preferably mixed at a rate of 0.5 to 2% of the total volume.

When the mixing is completed, the mixture is poured into the formwork and then wet curing, ultra-high-performance fiber-reinforced concrete can be produced by curing by steam curing for 2 to 4 days at a temperature of 60 ℃ ~ 110 ℃.

An experimental example of the cement composite thus prepared is as follows.

First, a macro steel fiber having a diameter of 0.2 mm and a length of 19.5 mm (shape ratio 97.5) and a micro steel fiber having a diameter of 0.2 mm and a length of 16.3 mm were mixed, and a polystyrene bead having a three-dimensional shape having a particle diameter of 2 mm (see FIG. 12) was formed. Experimental results for ultra high-performance fiber reinforced concrete prepared by mixing 2% by volume.

In the experimental example, when mixed with straight steel fibers of different lengths, as shown in FIG. 13, the microfibers constrain the microcracks and the major fissures are the interface between the cement matrix and the steel fiber even in the stress- swallowing section at the same time as the macrofibers crosslinking. It can be seen that the tensile strength and toughness are improved by minimizing fracture.

According to FIG. 14, when the microfibers and the macrofibers are mixed, the tensile strength is improved by 27% compared to the case of using only the single length steel fiber, and it can be seen that the stress-swept section is greatly improved.

Figure 15a is a graph showing the tensile behavior of the cement composite containing no crack derivatives, Figure 15b is a graph showing the tensile behavior of the cement composite containing 1% crack derivatives.

And, Figure 16a is a view showing a cross section of the cement composite containing no crack derivatives, Figure 16b is a view showing a cross section of the cement composite containing 1% crack derivatives.

In the case of FIG. 16A, the number of cracks was 12 and the average width of the cracks was 65 μm. In FIG. 16B, the number of cracks was 18 and the average width of the cracks was 40 μm. Therefore, it can be seen that more microcracks are induced in the cement composite including the crack derivatives, and that the crack width is relatively small.

According to the experimental results as described above, the change in tensile performance due to artificial defects induced by crack induction is described as follows.

As shown in FIGS. 17 and 18, since the crack inductor 10 has low adhesive strength with the cement matrix, the first crack generated by the external force is induced by inducing microcracks in advance before cracks are generated in the cement hardened body. By inducing a large number of microcracks around the crack inductor 10 to form a strain hardening and a plurality of fine crack distribution serves to improve the tensile strength and toughness.

In general, the initial cracking during fracture behavior by direct tension is determined by the properties of the cement matrix rather than by the influence of fibers, and initial cracking occurs at the beginning of reloading at the interface with voids or foreign materials present in the cement matrix. The initial crack then connects or merges with progressively adjacent cracks to evolve into narrow, short microscopic cracks. Later, as the deformation increases in the cement composite, cracks generated at the initial stage of loading progress or new cracks are additionally developed, which eventually develops into mat cracks, and local deformation occurs intensively. When the macro crack occurs, the first occurrence of the first crack may be a starting point for increasing the crack width and progressing from the microcracks to the major cracks.

Therefore, in FIG. 17, the crack derivative 10 mixed in the cement composite in advance forms microcracks between the cement matrix and the pre-formed microcracks during the curing process. This leads to the development of microcracks around the crack derivatives 10.

As a result, by inducing the external force to advance the microcracks around the crack inductor 10, the time of occurrence of the first crack having a large crack width is delayed, thereby preventing the occurrence of large cracks, thereby improving tensile strength and toughness. .

And, as shown in FIG. 18, the crack inductor 10 functions to improve the adhesion of the microfiber 20 to reduce the progress of the microcracks. In general, the adhesion between the steel fibers and the cement matrix depends on the interfacial properties between the steel fibers and the matrix.

Accordingly, the adhesion between the steel fibers and the cement matrix may be influenced by the adhesion between the continuous interface and the discontinuous interface. Some of the microfibers 20 may be cracked derivatives due to microcracks formed around the crack inductor 10. It may be located at the discontinuous interface where one end is exposed at the point of contact with 10).

In general, the continuous interface is only affected by the properties between the steel fiber and the cement matrix, but the discontinuous interface is also affected by the properties of the interface connection point, so the adhesion is relatively high.

That is, one end of the microfiber 20 exposed by the discontinuous interface has a characteristic that the adhesion is very high compared to the continuous interface because the end is bent or adhered at the discontinuous interface to act as a kind of ring.

As a result, the crack inducer 10 forms microcracks in the surrounding cement matrix to induce the growth of large cracks into microcracks, and the microcracks induced around the crack inductor 10 are formed by the adhesion of the microfibers 20. By preventing progression, tensile performance and toughness of the entire concrete structure can be improved.

Figure 19 shows another embodiment of the crack inductor of the ultra-high performance fiber reinforced concrete of the present invention. Crack inducing body 10 according to another embodiment may include a first surface layer 11 or a second surface layer 12 on the surface.

The first surface layer 11 is a layer to which a cracking accelerator, such as a dehumidifier, is applied, so as to reduce the water-bonding material ratio around the crack derivative 10 during the concrete curing process, so that cracking is more smoothly generated.

The second surface layer 12 is a layer applied to the surface of the first surface layer 11 and is a surface layer dissolved for a predetermined time by moisture. The second surface layer 12 may delay the time that the first surface layer 11 is exposed during the concrete curing time so that the first surface layer 11 may be exposed in the curing state having a low moisture content so that the crack may be more smoothly generated. .

(7) Mixing design and manufacturing method of ultra high performance fiber reinforced concrete

Considering the experimental results as described above, the mixing design and manufacturing method of the ultra-high performance fiber reinforced concrete as follows will be described.

Ultra high-performance fiber reinforced concrete of the present invention can be prepared by mixing at least one or more of cement, fine silica powder, fine aggregate, filler, shrinkage reducing agent, high performance water reducing agent, compounded water, macro steel fiber, micro steel fiber, antifoaming material.

The specific surface area of the fine silica powder of the ultra-high performance fiber reinforced concrete of the present invention is in the range of 80,000 cm ² / g or more and 150,000 cm ² / g and preferably in the shape coefficient of the steel fiber of 60 or more and 100 or less. However, the specific surface area of the fine silica powder and the shape coefficient of the steel fiber are preferably specified dependently, and the steel fiber preferably has a relatively small diameter when the shape coefficient is the same.

When the micro steel fibers and the macro steel fibers are mixed, it is preferable to combine the steel fibers having a high shape coefficient with each other, in particular, the shape coefficient 80 (d0.2mm × L16mm) 0.5% and the shape coefficient 100 (d0.2mm × L20mm) 1.5% It is preferable to mix the steel fibers.

The ultra-high performance fiber reinforced concrete of the present invention may further include a crack derivative for inducing artificial microcracks. The crack derivatives have a three-dimensional shape with a particle diameter of 2 to 5 mm, and may be formed in various shapes such as spheres and polyhedrons.

In more detail, the crack inductor is preferably a spherical body formed of polystyrene, and is preferably mixed at a ratio of 0.5 to 2% of the total volume.

The surface of the crack derivative may be provided with a first surface layer having a dehumidifying function and a second surface layer applied to the surface of the first surface layer and dissolved for a predetermined time by moisture.

Method of producing ultra high performance fiber reinforced concrete of the present invention is cement 100 parts by weight a specific surface area of the parts of the reference 80,000cm ² / g or more 150,000cm (SiO ₂ 99% a ² / g or less siliceous fine powder 25 parts by weight of quartz powder quality, 20 parts by weight of a filler having an average particle diameter of 4 μm) and 110 parts by weight of quartz sand having a particle size of 5 mm or less are mixed evenly for 20 seconds to 30 seconds at a speed of 10 to 20 rpm, preferably 15 rpm to prepare a mortar.

Then, the ratio of the mixing water-binder to the prepared mortar is 0.20, and the high-performance water reducing agent, the antifoaming agent, and the shrinkage reducing agent, which are 1.9 parts by weight of the binder, are mixed in a mixer at a speed of 20 to 50 rpm for 2 to 3 minutes.

Then, the steel fiber having a shape coefficient of 60 or more and 100 or less is added to 2% of the total volume of the cement composite and mixed for 1 minute to 3 minutes at a speed of 20 to 50 rpm. At this time, the crack derivatives may be mixed at a ratio of 0.5 to 2% of the total volume.

When the mixing is completed, the mixture is poured into the formwork and then wet curing, ultra-high-performance fiber-reinforced concrete can be produced by curing by steam curing for 2 to 4 days at a temperature of 60 ℃ ~ 110 ℃.

Although described above with reference to the preferred embodiment of the present application, those skilled in the art various modifications and changes to the present application without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

The present invention relates to ultra-high performance fiber reinforced concrete and a method of manufacturing the same.

Claims (5)

1. In the ultra-high performance fiber reinforced concrete formed by mixing at least one of cement, zirconium-containing silica powder, fine aggregate, filler, shrinkage reducing agent, high performance water reducing agent, blended water, steel fiber, and antifoaming agent,

   The specific surface area of the fine siliceous powder is 80,000 cm ² / g or more and 150,000 cm ² / g or less,

   The shape coefficient of the steel fiber is 60 or more and 100 or less, the steel fibers having a shape coefficient of 60 to 80 are mixed in a volume ratio of 25% to 35%, the steel fibers having a shape coefficient of 81 to 100 are mixed in a volume ratio of 65% to 75%,

   Further comprising a crack derivative for inducing microcracks in the cement composite,

   The crack derivative is

   A first surface layer comprising a crack promoter applied to the surface to promote microcracking;

   Ultra high performance fiber reinforced concrete.
2. The method of claim 1,

   The steel fiber is

   Steel fibers with a shape factor of 80 are mixed at a volume ratio of 25% to 35%,

   Mixing steel fiber with shape factor 100 at 65% ~ 75% volume ratio

   Ultra high performance fiber reinforced concrete.
3. The method of claim 1,

   The crack derivative is

   Composed of polystyrene beads

   Ultra high performance fiber reinforced concrete.
4. The method of claim 1,

   The crack derivative is

   Mixed at 0.5 to 2% of the total volume

   Ultra high performance fiber reinforced concrete.
5. The method of claim 1,

   The crack derivative is

   A second surface layer applied to the surface of the first surface layer and dissolved for a predetermined time by moisture;

   Ultra high performance fiber reinforced concrete.

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