KR101292173B1 - Hybrid ultra-high performance fiber reinforced cementitious composites using the twist and straight type steel fiber and method for it - Google Patents

Abstract

The present invention relates to ultra-high-performance concrete incorporating hybrid fibers, which will be described in more detail. The long fibers of the torsional cross section are mixed to improve the mechanical properties of the concrete based on the shape of the torsional cross section, as well as controlling macro cracks. The present invention relates to an ultra-high performance fiber reinforced concrete composition using hybrid steel fibers that can improve the mechanical performance of ultra-high performance concrete by incorporating and blending short fibers of a circular cross section, and a method of manufacturing the same.

Description

HYBRID ULTRA-HIGH PERFORMANCE FIBER REINFORCED CEMENTITIOUS COMPOSITES USING THE TWIST AND STRAIGHT TYPE STEEL FIBER AND METHOD FOR IT}

The present invention relates to an ultra-high performance fiber reinforced concrete composition using a hybrid steel fiber and a method for manufacturing the same, and more particularly, to high crack resistance performance against macro cracking of torsion steel fibers having micro crack prevention and high pull-out performance of straight steel fibers. It relates to a composition and a manufacturing method for improving the mechanical performance of ultra-high performance fiber reinforced concrete using.

Concrete is widely used in the construction of concrete structures together with steel as an economical and durable construction material. However, concrete has inherent defects that are small in tensile strength and flexural strength, and are prone to cracking, and brittle failure of concrete has been a problem due to an increase in compressive strength due to the practical use of high strength concrete.

Meanwhile, in order to prevent brittle fracture of concrete, fiber reinforced concrete (Fiber Reinforced Concrete) manufactured by mixing steel fiber in volume of 1% (75kg / ㎥) or less in general concrete is applied to some concrete structures. It is used. Such steel fibers are mostly made of straight steel fibers having a circular cross section and hook-type steel fibers having bent ends. In general, the steel fibers are those having a tensile strength of 1,500 MPa or less, lengths of about 10 mm to 30 mm, and diameters of about 0.45 mm to 1.0 mm.

However, the 1% fiber mixing does not sufficiently prevent brittle fracture of high-strength concrete, and thus, the structure is immediately destroyed when an earthquake or repetitive and impact load of a vehicle, fire, and natural degradation occur.

In addition, in the case of using the conventional circular fiber for ultra-high strength concrete that is more than 180MPa conventionally (Patent No. 10-0620866; steel fiber reinforced cement composite and its manufacturing method), the fiber is broken before the cement composite is broken due to the lack of tensile strength of the fiber. Reaching the yield strength has a problem that does not help to improve the bending or tensile strength.

In addition, even when steel fiber with tensile strength of 2,000 MPa or more is used, when circular fiber is used, the steel fiber is first pulled out of concrete before it breaks due to reaching the yield strength during bending or tensile failure. There was a problem that does not contribute significantly to toughness improvement.

Therefore, the present inventors have conducted research and experiments to overcome the problems of the conventional general concrete, fiber reinforced concrete and ultra high strength fiber reinforced concrete mentioned above, and as a result, when using hybrid reinforcing fiber mixed with long and short fibers, Bending strength and ductility effect are significantly improved than that of steel fiber, and the straight short fiber is used to prevent micro cracks of the matrix, and torsional long fiber is used to improve adhesion strength to the matrix and to improve frictional adhesion. The purpose of the present invention is to provide ultra-high-performance concrete with excellent mechanical performance by using the high crack resistance against macro cracks by improving the pullout resistance.

Ultra high-performance fiber reinforced concrete composition using the hybrid steel fiber of the present invention as a means for achieving the above object, in the super-high-performance concrete composition containing the reinforcing fiber, the reinforcing fiber is composed of steel fibers, the reinforcing fibers and the amount of circular cross section The end portion is fixed and rotated so that the outer periphery of the hybrid fiber is mixed with the reinforcing fiber of the twisted cross-section twisted in the longitudinal direction continuously.

Here, it is preferable to use a length of the reinforcing fiber of the torsional cross section longer than the reinforcing fiber of the circular cross section. That is, the reinforcing fiber of circular cross section is used as short fiber, and the reinforcing fiber of torsional cross section is used as long fiber.

On the other hand, the ultra-high performance fiber reinforced concrete manufacturing method using the hybrid steel fiber of the present invention is based on 100 parts by weight of cement 100 to 130 parts by weight, 10 to 30 parts by weight of reactive powder, 10 to 30 parts by weight filler and 0.05 to 1 weight of the middle agent Preparing a mortar including a part; Mixing the blended water and mortar so that the ratio of the blended water consisting of 90% by weight to 99.5% by weight of water and 0.5% to 10% by weight of the reducing agent and the binder of the mortar (sum of cement and reactive powder) is 0.2 or less. step; Mixing the hybrid reinforcing fibers in the mixture of the blended water and mortar, but injecting the hybrid reinforcing fibers mixed by adding 1 to 5 vol% of the total concrete to 100 vol%; After performing the wet curing for 1 to 3 days for the blended water and the mortar mixture is added to the hybrid reinforcing fiber, and performing steam curing for 2 to 4 days at a temperature of 60 ℃ to 110 ℃; including It features.

Wherein the mortar preparing step includes mixing the mixture constituting the mortar at a speed of 20 rpm to 40 rpm for 7 to 15 minutes; The mixing step of the blended water and mortar includes mixing for 7 minutes to 20 minutes at a speed of 80rpm to 120rpm and then mixing for 2 to 5 minutes at a speed of 40rpm to 60rpm; Mixing the hybrid reinforcing fiber in the blended water and mortar is mixed for 3 to 10 minutes at a speed of 30rpm to 50rpm; characterized in that it comprises a.

The ultra high performance fiber reinforced concrete composition and its manufacturing method using the hybrid steel fiber of the present invention are intended to improve the mechanical properties of the ultra high performance fiber reinforced concrete composition by the hybrid form and shape of the steel fiber, the mechanical adhesion performance with the hardened cement To improve the mechanical performance of ultra-high performance fiber reinforced concrete by mixing the torsional fiber of torsional cross section and mixing the torsional fiber of torsional cross section with long fiber to control all cracks, There is this.

1 is a photograph showing the reinforcing fibers of the torsional cross section which is one configuration of the present invention,
Figure 2 is a photograph showing a reinforcing fiber of a circular cross section which is one configuration of the present invention,
Figure 3 is a perspective view showing a state before manufacturing the reinforcing fiber of the torsional short-lived which is one configuration of the present invention.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, terms and words used in the present specification and claims are to be construed in accordance with the principles of the present invention, on the basis that the inventor can properly define the concept of a term in order to best explain his invention It should be construed as meaning and concept consistent with the technical idea of.

The present invention is a super high-performance concrete composition in which the reinforcing fibers are blended, the reinforcing fibers are composed of steel fibers, the reinforcing fibers of the circular cross section and both ends are fixed to rotate so that the outer circumference is twisted in the longitudinal direction continuously It is characterized in that the hybrid fiber in which the reinforcing fiber of the torsional cross section is mixed.

The reinforcing fiber is composed of steel fiber bar, the steel fiber may be manufactured by cutting, casting, etc. thin carbon steel, the aspect ratio (length ratio of the length to the cross-sectional value) is about 30 to 100 Can be. Preferably, the reinforcing fiber according to the present invention has a diameter of 0.16 to 0.30 mm, a length of 20 to 150 mm, and a reinforcing fiber having a twisting cross section is 2 to 12 per 35 mm number of twists. When manufactured in such a diameter, length and twisted state, the tensile strength of the steel fiber can be determined to be 1300 ~ 3800 MPa, so that the effect can be sufficiently exhibited in the fiber reinforced ultra-high performance concrete.

On the other hand, the length of the hybrid reinforcing fiber is preferably limited to 20 to 150mm. If less than 20mm, it is insignificant to express an effect on strength expression and crack control in cement paste. This is because agglomeration may occur and dispersibility may decrease, and dispersibility may decrease due to an increase in specific gravity.

The torsional fiber of the torsional cross section as shown in Figure 3 is characterized in that the torsional cross-section is formed by rotating both ends are fixed to the straight fiber 100 formed with a plurality of convex borders in the longitudinal direction so that a plurality of acids are formed in the cross-section There is this.

As shown in FIG. 1, the outer periphery of the reinforcing fiber having a torsional cross-section is formed by using a straight fiber 100 having a plurality of convex edges formed in a longitudinal direction so that a plurality of acids are formed in the cross section. The circumferential length of is to be increased to eventually form a torsional cross section.

This twisting cross section is designed to improve the adhesion performance of the reinforcing fiber and the cement hardened body by the increased circumferential length. In other words, the technical characteristics of enhancing the adhesion performance with the cement hardened body was introduced while not affecting the aspect ratio in the reinforcing fiber.

Eventually, in one configuration of the present invention, as shown in FIG. 1, the reinforcing fiber having a torsional cross section is a straight steel fiber in which a plurality of convex edges are formed in a longitudinal direction such that a plurality of acids are formed in a cross section having a predetermined length as shown in FIG. 3. The torsional cross section that maximizes the contact area with the cement hardened body is produced by the torsion in the steel fiber in such a way that both ends are fixed to each other while the ends thereof are fixed.

In Fig. 1, the twisted state (called 4 PITCH state) is shown four times at a constant length (35mm) at the top, and the twisted state six times (6 PITCH state) at a constant length (35mm) at the bottom. ).

Of course, it will be possible to form a torsional cross section according to the use or the like two or more times as desired. In case of forming more than 12 torsional cross sections at 35mm, the excessive twisting causes the tensile strength of the reinforcing fiber itself to be lowered, and cement mortar is hard to be filled to every corner of the reinforcing fiber and bubbles are easily generated. Bars do not function in high-performance concrete, so limited. Herein, when the shape ratio is formed to be 100 or less, the cross-sectional dimension and the length have the maximum value. Therefore, when the maximum value (shape ratio 100) is used, the number of braids of the reinforcing fibers is preferably 12 or less.

When the steel fibers are twisted to form a torsional cross section many times in this way, the circumferential area is naturally increased, and the fiber reinforcement is ultimately strengthened through the crosslinking effect of the cement composites in contact with each other in the cracked surface when cracking occurs in the unsolidified cement composite. It is possible to enhance the reinforcing effect of ultra-high performance concrete.

In particular, in the present invention, it is preferable to use a length of the reinforcing fiber of the torsional cross section longer than the reinforcing fiber of the circular cross section.

That is, the reinforcing fiber of circular cross section is used as short fiber, and the reinforcing fiber of torsional cross section is used as long fiber. This prevents agglomeration due to the relatively short length by using the reinforcing fiber of the circular cross section as a short fiber, and improves the toughness, bending strength, etc. in the cement paste due to the use of the reinforcing fiber of the torsional cross section as the long fiber. By reinforcing the control of micro cracks, hybrid fibers improve the durability by controlling cracks of various shapes and sizes in cement paste.

As described above, the hybrid reinforcing fiber may be included in an amount of 1 to 5 vol% based on 100 vol% of the total concrete when the super high-performance steel fiber reinforcing concrete composition is blended. This is because the mixing effect is insignificant when less than 1 vol%, and the strength is lowered due to aggregation of fibers when the volume exceeds 5 vol%.

On the other hand, the present invention proposes a super high-performance fiber reinforced concrete manufacturing method using a hybrid steel fiber, it is prepared by blending cement, reactive powder, sand, filler, thickener, water reducing agent and hybrid reinforcing fiber.

That is, for example, a premixing mortar material, which is a mixture of cement, sand, reactive powder, filler, and thickener, is mixed evenly with a high speed mixer, mixed with a high speed mixer, and then mixed with a high speed mixer. The hybrid fiber is added to the mixture, mixed again, and then manufactured through a curing period.

Specifically, the premixing mortar material is to place a storage site for the material constituting the construction site, to reduce the cost and minimize the weighing error and to reduce the mixing time.

For example, 100 to 130 parts by weight of sand, 10 to 30 parts by weight of reactive powder, 10 to 30 parts by weight of filler, and 0.05 to 1 part by weight of thickener based on 100 parts by weight of cement. Prepared by mixing evenly for 15 minutes.

In order to secure the fluidity and workability of the premixed mortar material thus prepared, water (typically distilled water is preferred) and a polycarboxylic high performance water reducing agent or a naphthalene high performance water reducing agent having a solid content of 30 to 40% by weight Prepare the blended water so that the ratio is 90 to 99.5% by weight and 0.5 to 10% by weight, respectively. Mix for 7-15 minutes at 20-40 rpm.

The hybrid reinforcing fiber is added to the mixture of mortar and the blended water so mixed in 1 to 5% by volume in the mixture and mixed for 3 to 10 minutes at a speed of 30 to 50rpm.

In this way, the final mixture was subjected to wet curing for 1 to 3 days, and then steam curing was performed at a high temperature of 60 to 110 ° C. for 2 to 4 to activate the hydration reaction of cement and the Pozzolanic reaction of reactive powder. By performing for days, ultra-high performance concrete is produced.

The sand is quartz sand (90 wt% or more of SiO 2) having a size of 5 mm or less, and about 100 parts by weight to 130 parts by weight based on 100 parts by weight of cement. The reason for using sand of 5 mm or less is to secure the homogeneity of the cement composite and improve its strength.

The reactive powder is a mineral admixture such as silica fume, blast furnace slag, fly ash and the like. Such reactive powder is used in about 10 to 30 parts by weight based on 100 parts by weight of cement. Since the reactive powder is composed of spherical particles, the workability is improved by reducing friction of the steel fiber reinforced cement composite (steel fiber reinforced concrete), the fiber dispersibility is increased by increasing the viscosity of the paste, and the strength by the pozzolanic reaction It serves to improve.

In general, the reactive powder has the advantage of increasing the long-term strength by the pozzolanic reaction which reacts with calcium hydroxide (Ca (OH) 2), a hydration reaction product of cement, to produce calcium silicate salt (3CaO2SiO23H2O) and calcium aluminate salt (3CaOAl2O3). However, since the amount of cement used decreases as early as the age of the reactive powder, the initial strength of the concrete decreases, so the construction period is long, and there is a disadvantage in that a lot of shrinkage occurs. In order to solve such problems as the initial strength decrease due to the reactive powder, steam curing is performed at a high temperature of 60 to 120 ° C. at an early stage so that the hydration reaction of the cement and the pozzolan reaction of the reactive powder are activated. By such a technical configuration, not only the hydration reaction of cement proceeds quickly, but calcium hydroxide is almost consumed by the pozzolanic reaction, thereby overcoming the initial drop in strength of the steel fiber reinforced cement composite, and at the same time, it is possible to realize super strength.

The filler is 10 to 30 parts by weight of quartz powder (SiO 2 95% or more) or limestone fine powder (CaCO 3 or more 75% or more) based on 100 parts by weight of cement.

The use of such a filler prevents destruction of the interface region by a filler action filled in the interface region between the cement paste and the aggregate or the interface region between the cement paste and the fiber, thereby improving the strength of the steel fiber reinforced cement composite.

The thickener is used to impart viscosity to the cement matrix. Cellulose thickener or acryl thickener is used in an amount of 0.05 to 1 parts by weight based on 100 parts by weight of cement. Such thickeners serve to improve fiber dispersibility of steel fiber reinforced cement composites.

Reducing agents are used to ensure the fluidity of the cement matrix. In the steel fiber reinforced cement composite, 0.5 to 10 parts by weight of a polycarboxylic acid-based high performance water reducing agent or a naphthalene-based high performance water reducing agent having a solid content of 30 to 40% by weight based on 100 parts by weight of cement is used. Such a water reducing agent serves to improve the workability and fiber dispersibility of the steel fiber reinforced cement composite.

In general, in the steel fiber-reinforced cement composites, the fiber ball phenomenon occurs when a large amount of steel fiber is used because the specific gravity and aspect ratio of the steel fiber are different from the particles of the material constituting the cement matrix. It is known that it does not exhibit the inherent performance of steel fiber reinforced cement composites, but rather cause brittle fracture and durability degradation.

However, the steel fiber-reinforced cement composite can secure high fiber dispersibility by using the above-described thickener and water reducing agent, so that a high toughness can be realized by adding a large amount of steel fiber to the steel fiber-reinforced cement composite without fiber aggregation as described below.

100: straight fiber

Claims (9)

In the ultra-high performance concrete composition in which reinforcing fibers are blended,
The reinforcing fiber is composed of steel fibers,
A hybrid reinforcing fiber in which a reinforcing fiber having a circular cross section and a reinforcing fiber having a torsional cross section twisted in the longitudinal direction to be fixed and rotated at both ends thereof are mixed, wherein the hybrid reinforcing fiber has a length of 20 to 150 mm. , The diameter is 0.16 ~ 0.30mm, characterized in that 1 to 5vol% is blended with respect to 100vol% of concrete,
The hybrid reinforcing fiber, so that the length of the reinforcing fiber of the torsional cross section longer than the reinforcing fiber of the circular cross section, the reinforcing fiber of the circular cross section is made of short fibers to control the micro cracks, The torsional cross-section of the reinforcing fiber is ultra-high performance fiber reinforced concrete composition using a hybrid steel fiber, characterized in that composed of long fibers to control the macro (macro) cracks.
delete delete delete delete delete delete Preparing a mortar including 100 to 130 parts by weight of sand, 10 to 30 parts by weight of reactive powder, 10 to 30 parts by weight of filler, and 0.05 to 1 part by weight of a thickener based on 100 parts by weight of cement;
Mixing the blended water and mortar so that the ratio of the blending water consisting of 90% by weight to 99.5% by weight of water and 0.5% to 10% by weight of a reducing agent and the binder of the mortar (sum of cement and reactive powder) is 0.2 or less. step;
Mixing the hybrid reinforcing fiber of claim 1 in the mixture of the blended water and mortar, but adding a hybrid reinforcing fiber for mixing by mixing 1 ~ 5vol% with respect to 100vol% of the total concrete; And
After performing the wet curing for 1 to 3 days for the blended water and the mortar mixture into which the hybrid reinforcing fiber is added, characterized in that it comprises the step of steam curing for 2 to 4 days at a temperature of 60 ℃ to 110 ℃ Ultra-high performance fiber reinforced concrete manufacturing method using a hybrid steel fiber.
The method of claim 8,
The mortar preparing step includes mixing the mixture constituting the mortar at a speed of 20 rpm to 40 rpm for 7 to 15 minutes;
The mixing step of the blended water and mortar includes mixing for 7 minutes to 20 minutes at a speed of 80rpm to 120rpm and then mixing for 2 to 5 minutes at a speed of 40rpm to 60rpm;
Mixing the hybrid reinforcing fiber in the blended water and mortar mixing for 3 to 10 minutes at a speed of 30rpm to 50rpm; Ultra-high performance fiber reinforced concrete manufacturing method using a hybrid steel fiber, characterized in that it comprises a.

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