JP7199942B2 - Ultra-high-strength concrete and its mixing method - Google Patents

Description

The present invention relates to ultra-high strength concrete and its preparation method.

By lowering the water-binder ratio in concrete, the compressive strength of the concrete can be increased. However, when the water-binder ratio is low, the concrete is more likely to explode when exposed to high temperatures, such as in the event of a fire.
As a technique for suppressing explosion, a method of adding organic fibers to concrete is known, and organic fibers are often added to high-strength concrete. Examples of organic fibers include polyolefin fibers such as polypropylene and polyethylene, polyvinyl alcohol fibers (vinylon fibers), polyacetal fibers, and the like (Patent Document 1).
In addition, it has been proposed to combine organic fibers and steel fibers in concrete (Patent Documents 2 and 3).

Japanese Patent No. 4608176 Japanese Patent Application Laid-Open No. 2002-193654 Japanese Patent No. 4071983

In recent years, ultra-high-strength concrete having a design standard strength of 100 N/mm ² or more has come to be applied to members such as RC columns of super-super-high-rise RC buildings.
The addition of steel fibers to ultra-high-strength concrete is considered to be effective in suppressing the extension of period due to cracking during earthquakes in super-high-rise RC buildings and the decrease in yield strength due to edge crushing during extreme earthquakes. In particular, if the steel fiber content is higher than 0.5% by volume, for example about 1.0% by volume, it is considered possible to remarkably improve the performance as a member.
However, when the steel fiber content is increased in ultrahigh-strength concrete, it is difficult to secure the gap passageability that ensures filling in the gaps between the densely arranged column main reinforcing bars and shear reinforcing bars.
It is conceivable to reduce the amount of coarse aggregate in order to ensure pore permeability. However, if the amount of coarse aggregate is reduced to the extent that pore permeability can be secured, the amount of shrinkage of concrete increases, leading to a decrease in crack resistance.
Patent Literatures 1 to 3 do not discuss a mixing design for achieving both the interstitial property and crack resistance of concrete.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultra-high-strength concrete that has excellent interstitial properties and crack resistance despite a high content of steel fibers, and a method for mixing the same. do.

The present invention has the following aspects.
[1] Cement, silica fume, water, coarse aggregate, fine aggregate, chemical admixture, steel fiber, and organic fiber, water binder ratio is 25% by mass or less, the steel An ultra-high-strength concrete having a fiber content of more than 0.5% by volume and not more than 2% by volume,
The organic fibers comprise polypropylene fibers,
The maximum dimension of the coarse aggregate is 15 mm or less,
Super high-strength concrete having a unit coarse aggregate bulk volume of 0.3 to 0.4 m ³ /m ³ .
[2] The ultra-high-strength concrete of [1], wherein the mixing ratio of the organic fibers is 0.14 to 0.58% by volume.
[3] The ultra-high strength concrete of [1] or [2], wherein the steel fibers have a diameter of 0.15 to 0.9 mm and a length of 12 to 32 mm.
[4] Cement, silica fume, water, coarse aggregate, fine aggregate, chemical admixture, steel fiber, and organic fiber are blended, and the water binder ratio is 25% by mass or less, the above A method for mixing ultra-high-strength concrete with a steel fiber content of more than 0.5% by volume and not more than 2% by volume, comprising:
Using at least polypropylene fiber as the organic fiber,
The maximum dimension of the coarse aggregate is 15 mm or less,
Calculate the target value _V'bG of the unit coarse aggregate bulk volume of the ultra-high-strength concrete by the following formula (1), and set the blending amount of the coarse aggregate so that the target value _V'bG is obtained. How to mix high-strength concrete.
V′ _bG =V _bG −(K _S ·2r _G /3r _F −1)·V _F /G _S (1)
Here, V' _bG represents the target value (m ³ /m ³ ) of the unit coarse aggregate bulk volume of the ultra-high strength concrete,
V _bG indicates a number of 0.5 to 0.56 (m ³ /m ³ ) in the range of standard values of unit coarse aggregate bulk volume (m ³ /m ³ ) of ultra-high strength concrete,
K _S is an influence coefficient and indicates a number from 0.8 to 1,
r _G indicates the radius (mm) of the coarse aggregate calculated from the total coarse aggregate surface area obtained from the particle size distribution of the coarse aggregate, assuming that the coarse aggregate is spherical,
r _F represents the radius (mm) of the steel fiber calculated assuming that the steel fiber has a cylindrical shape,
_VF indicates the mixing ratio (% by volume) of the steel fibers,
_GS indicates the actual volume ratio (volume %) of the coarse aggregate.
[5] The method of mixing ultra-high-strength concrete according to [4], wherein the mixing ratio of the organic fibers is 0.14 to 0.58% by volume.
[6] The method of mixing ultrahigh-strength concrete according to [4] or [5], wherein the steel fibers have a diameter of 0.15 to 0.9 mm and a length of 12 to 32 mm.

ADVANTAGE OF THE INVENTION According to this invention, although the steel fiber content is high, the ultra-high strength concrete which is excellent in gap permeability and crack resistance, and its mixing method can be provided.

It is a figure explaining the box-shaped container used for the excitation box filling test in the Example. 4 is a graph showing the results (filling height before and after vibration) of a vibration box filling test in Examples. 4 is a graph showing measurement results of autogenous shrinkage strain in Examples.

The following term definitions apply throughout the specification and claims.
"Concrete" includes fresh and hardened concrete.
"Ultra-high-strength concrete" refers to concrete having a design standard strength of 100 N/mm ² or more.
"Water binder ratio" indicates the ratio (mass %) of water to the total mass of binders in fresh concrete.
A "binder" is a material that hydrates in concrete, such as cement, silica fume, slag, fly ash, and the like.
"Ratio of steel fibers mixed" indicates the volume ratio (% by volume) of steel fibers to the total volume of the remainder after removing steel fibers and organic fibers from concrete.
"Organic fiber mixing rate" indicates the ratio (volume %) of the volume of the organic fiber to the total volume of the remainder after removing the steel fiber and the organic fiber from the concrete.

(ultra high strength concrete)
The ultra-high strength concrete of the present invention (hereinafter also referred to as "this concrete") includes cement, silica fume, water, coarse aggregate, fine aggregate, chemical admixture, steel fibers, organic including fibers.

As the cement, moderate heat Portland cement and low heat Portland cement are preferable because of their low heat of hydration.

Silica fume may be known silica fume for concrete.
The content of silica fume is preferably 9 to 20% by mass with respect to the mass of cement. If the content of silica fume is within the above range, the fluidity and pore passability of the present concrete are more excellent.

The water content is such that the water binder ratio is 25% by mass or less. The water binder ratio is preferably 15 to 25% by mass, more preferably 15 to 20% by mass.
If the water binder ratio is 25% by mass or less, it is easy to obtain a compressive strength exceeding 100 N/mm ² . When the water-binder ratio is 15% by mass or more, the mixing ratio of steel fibers has a large effect on the interstitial property, and the usefulness of the present invention is high.

Coarse aggregates include hard sandstone crushed stone, andesite crushed stone, rhyolite crushed stone, and the like.
The surface dry density of coarse aggregate may be, for example, 2.55-2.7 g/cm ³ .
The coarseness of the coarse aggregate may be, for example, 6-6.6.

The maximum dimension of coarse aggregate is 15 mm or less. The maximum size of the coarse aggregate is the nominal size of the smallest size sieve through which 90% by mass or more of the coarse aggregate passes. If the maximum dimension of the coarse aggregate is 15 mm or less, the interstitial property can be ensured even if the unit coarse aggregate bulk volume is 0.3 m ³ /m ³ or more.
As coarse aggregate having a maximum dimension of 15 mm or less, for example, coarse aggregate having a maximum dimension of 15 mm, coarse aggregate having a maximum dimension of 13 mm, and the like are commercially available.

The content of coarse aggregate is such that the unit coarse aggregate bulk volume of the concrete is 0.3 to 0.4 m ³ /m ³ . The unit coarse aggregate bulk volume is preferably 0.33 to 0.37 m ³ /m ³ .
When the unit coarse aggregate bulk volume is 0.3 m ³ /m ³ or more, crack resistance is excellent. When the unit coarse aggregate bulk volume is 0.4 m ³ /m ³ or less, the interstitial property is excellent.

Examples of fine aggregates include crushed sand, mountain sand, land sand, and the like.
The surface dry density of the fine aggregate may be, for example, 2.55-2.7 g/cm ³ .

As the chemical admixture, a known one can be used, including high performance water reducing agents, high performance AE water reducing agents and the like. Any one of these chemical admixtures may be used alone, or two or more may be used in combination.

The concrete preferably contains at least a superplasticizer as a chemical admixture. Examples of high-performance water reducing agents include those containing polycarboxylic acid ether as the main component and those containing polycaribonic acid copolymer as the main component.
When the solid content of the main component is about 30%, the content of the superplasticizer is, for example, about 1 to 5% by mass with respect to the mass of cement.

Examples of the steel material that constitutes the steel fiber include ordinary steel material, stainless steel, etc., and those having alkali resistance are preferable.
Moreover, from the viewpoint of rust prevention, it is preferable that the surface of the steel material is plated with zinc.
Examples of the shape of the steel fiber include hook type, straight type, wave type, and the like. The hook type is preferable in terms of improving the adhesion between concrete and steel fibers and improving the toughness of concrete.
As the steel fibers, for example, those commercially available as steel fibers for steel fiber reinforced concrete can be used.

The length of the steel fibers is preferably 12-32 mm, more preferably 24-32 mm. If the steel fiber length is within the above range, the concrete will have better interstitial properties and crack resistance. The length of the steel fiber is measured with a vernier caliper or the like.
The diameter of the steel fibers is preferably 0.15-0.9 mm, more preferably 0.38-0.75 mm. If the steel fiber diameter is within the above range, the concrete will have better interstitial properties and crack resistance. The diameter of the steel fiber is measured with a vernier caliper or the like.

In the present concrete, the mixing ratio of steel fibers is preferably more than 0.5% by volume and 2% by volume or less, more preferably 0.7 to 1.2% by volume. When the content of steel fibers exceeds 0.5% by volume, the concrete has excellent toughness and crack resistance. If the mixing ratio of steel fibers is 2% by volume or less, sufficient interstitial permeability can be ensured.

Organic fibers include polypropylene fibers. Polypropylene fibers are less expensive than other organic fibers and are economically efficient.
Polypropylene fibers are fibers that contain polypropylene.
Polypropylene includes homopolymers of propylene, copolymers of propylene and other monomers, and the like. Other monomers include olefins other than propylene (such as ethylene).

The polypropylene fiber may consist of only polypropylene, or may be a fiber containing polypropylene and other resins.
Other resins include, for example, polyolefin resins other than polypropylene (polyethylene, etc.), polyvinyl alcohol resins, and the like.
The ratio of polypropylene in the polypropylene fibers is preferably 45% by mass or more with respect to the total mass of the polypropylene fibers.

The dry density of polypropylene fibers is preferably 0.91 g/cm ³ . If the dry density is 0.91, the dispersibility of fibers in concrete is more excellent. Dry density is measured according to JIS L 1015.

The length of the polypropylene fiber is preferably 9-11 mm, more preferably 9.5-10.5 mm. If the length of the polypropylene fiber is within the above range, the interstitial property and the dispersibility of the fiber in concrete are more excellent. The length of polypropylene fiber is measured according to JIS L 1015.
The moisture content of the polypropylene fiber is preferably 20-40%, more preferably 30-40%. If the moisture content of the polypropylene fiber is within the above range, the dispersibility of the fiber in concrete is more excellent. The moisture content of polypropylene fibers is measured according to JIS L 1015.

The cross-sectional shape of the polypropylene fiber may be circular, irregular, hollow, or the like.
When the polypropylene fiber contains another resin, the polypropylene fiber may be a fiber made of a mixed resin of polypropylene and another resin, or a composite fiber having a layer made of polypropylene and a layer made of another resin. . Examples of the form of the composite fiber include side-by-side type, core-sheath type, split type, and the like.
Polypropylene fibers can be produced, for example, by the method described in Japanese Patent No. 3889946.

The volume ratio of steel fibers to polypropylene fibers (steel fibers/polypropylene fibers) is preferably 0.9 to 14.3, more preferably 1.6 to 4.1. If the volume ratio of steel fibers to polypropylene fibers is within the above range, the concrete will have better explosion resistance, toughness and crack resistance.

In this concrete, the mixing ratio of organic fibers is preferably 0.14 to 0.58% by volume, more preferably 0.29 to 0.44% by volume. If the mixing ratio of the organic fiber is 0.14% by volume or more, the explosion resistance is excellent. If the mixing ratio of organic fibers is 0.58% by volume or less, it is easy to ensure sufficient interstitial permeability.

This concrete contains cement, silica fume, water, coarse aggregate, fine aggregate, chemical It can be prepared by blending an admixture, steel fibers, organic fibers, and optionally other ingredients.

In the present concrete described above, the maximum dimension of the coarse aggregate is 15 mm or less, and the unit coarse aggregate bulk volume is 0.3 to 0.4 m ³ /m ³ , so the water binder ratio is 25 Although it is as low as mass% or less and the steel fiber content is as high as more than 0.5% by volume and not more than 2% by volume, it is excellent in gap permeability and crack resistance.
This is believed to be due to the following reasons.
Coarse aggregate having a maximum dimension of 15 mm or less is more effective in suppressing shrinkage of concrete than coarse aggregate having a maximum dimension of more than 15 mm, for example, 20 mm. Therefore, while ensuring sufficient cracking resistance, the unit coarse aggregate bulk volume is reduced to 0.3 to 0.4 m ³ /m ³ to increase the fluidity of the remainder after removing the steel fibers from the concrete. can be done. The unit coarse aggregate bulk volume of general ultrahigh-strength concrete is about 0.5 to 0.56 m ³ /m ³ .
Since the fluidity of the remainder of this concrete after removing the steel fibers is high, sufficient fluidity can be ensured even though it contains a large amount of steel fibers.
In addition, in the present concrete, the water binder ratio is as low as 25% by mass or less, and the steel fiber mixing ratio is as high as 0.5% by volume or more and 2% by volume or less, so excellent strength (for example, JIS A 1108 A compressive strength of 110 to 180 N/mm ² at a material age of 28 days (4 weeks) or a material age of 56 days (8 weeks) measured according to the method is obtained. Moreover, since it contains polypropylene fibers as organic fibers, it has explosion resistance and is excellent in economic efficiency.

(Method for mixing ultra-high-strength concrete)
The method for preparing the ultra-high-strength concrete of the present invention comprises blending cement, silica fume, water, coarse aggregate, fine aggregate, chemical admixture, steel fibers, and organic fibers, and This is a method of mixing ultra-high-strength concrete having a material ratio of 25% by mass or less and a steel fiber content of more than 0.5% by volume and not more than 2% by volume.
Other ingredients may be blended with cement, silica fume, coarse aggregate, fine aggregate, chemical admixture, steel fiber, and organic fiber.
Cement, silica fume, coarse aggregate, fine aggregate, chemical admixture, steel fiber, organic fiber and other components are the same as above.

Further, in the preparation method of the present invention, the target value _V'bG of the unit coarse aggregate bulk volume of the ultrahigh-strength concrete is calculated by the following formula (1), and the coarse aggregate is adjusted so that the target value _V'bG is obtained. Set the blending amount of the material.

V′ _bG =V _bG −(K _S ·2r _G /3r _F −1)·V _F /G _S (1)
Here, V' _bG represents the target value (m ³ /m ³ ) of the unit coarse aggregate bulk volume of the ultra-high strength concrete,
V _bG indicates a number of 0.5 to 0.56 (m ³ /m ³ ) in the range of standard values of unit coarse aggregate bulk volume (m ³ /m ³ ) of ultra-high strength concrete,
K _S is an influence coefficient and indicates a number from 0.8 to 1,
r _G indicates the radius (mm) of the coarse aggregate calculated from the total coarse aggregate surface area obtained from the particle size distribution of the coarse aggregate, assuming that the coarse aggregate is spherical,
r _F represents the radius (mm) of the steel fiber calculated assuming that the steel fiber has a cylindrical shape,
_VF indicates the mixing ratio (% by volume) of the steel fibers,
_GS indicates the actual volume ratio (volume %) of the coarse aggregate.
The volume fraction of coarse aggregate is measured according to JIS A 1104.

If the influence coefficient K _S is 0.8 or more, the obtained ultra-high-strength concrete has excellent pore permeability. If the influence coefficient K _S is less than 1, the crack resistance of the resulting ultrahigh-strength concrete is excellent. The influence coefficient K _S is preferably 0.9.

The maximum dimension of coarse aggregate used in general high-flow steel fiber reinforced concrete with a design standard strength of less than 100 N / mm ² is 20 mm, and by equivalent surface area replacement for such high-flow steel fiber reinforced concrete In the formulation design method, the influence coefficient K _S is about 1 to 1.35.
The present inventors have found that when the maximum dimension of coarse aggregate is 15 mm or less, the unit coarse aggregate bulk volume required to ensure interstitial permeability is smaller than that of general high-flow steel fiber reinforced concrete. Therefore, the influence coefficient K _S was set to 0.8 or more and less than 1.

The preferable range of water binder ratio and steel fiber mixing ratio is the same as above.
Preferred blending amounts of silica fume, fine aggregate, chemical admixture, organic fiber, etc. are the same as in the present concrete.

In the mixing method of the present invention described above, the maximum size of the coarse aggregate is set to 15 mm or less, and the blending amount of the coarse aggregate is set so as to achieve the target value _V'bG calculated by the above formula (1). Therefore, although the water binder ratio is low at 25% by mass or less and the steel fiber content is high at more than 0.5% by volume and up to 2% by volume, ultra-high strength concrete with excellent gap passage and crack resistance is produced. Can be compounded.
In addition, the resulting ultra-high-strength concrete has a low water-binder ratio of 25% by mass or less and a high content of steel fibers of more than 0.5% by volume and 2% by volume or less, and thus has excellent compressive strength. Moreover, since it contains polypropylene fibers as organic fibers, it has explosion resistance and is excellent in economic efficiency.

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these.

(Material used)
Table 1 shows the materials used in the examples.

(Formulation 1-7)
<Preparation of ultra-high-strength concrete>
According to Table 2, each material was kneaded according to the following procedure to prepare ultra-high strength concrete.
W/C was set assuming a design standard strength of 100 N/mm ² or more. W/C is the mass ratio of water (W) to silica fume premixed cement (C) and corresponds to the water binder ratio. The steel fiber loadings of 40 kg/m ³ and 80 kg/m ³ correspond to steel fiber loadings of 0.5% by volume and 1% by volume, respectively. The mixing amounts of organic fibers (polyacetal fibers) of 3.1 kg/m ³ and 3.9 kg/m ³ correspond to the mixing rates of organic fibers of 0.2% by volume and 0.3% by volume, respectively.
For kneading, a forced twin-screw kneading mixer was used. Silica fume premixed cement (C) and fine aggregate (S) were charged, and after dry kneading, water (W) and chemical admixture (SP) were added and kneaded to obtain mortar. Next, coarse aggregate (G) was charged and kneaded to obtain concrete. Further, polyacetal fiber (PA) and steel fiber (SF) were added and kneaded for 90 seconds to obtain ultra-high strength concrete containing steel fiber.

<Evaluation>
Slump flow, flow time, air content, concrete temperature, unit volume mass, filling time/height of box-shaped container, excitation filling time/height, and compressive strength of mixed ultra-high-strength concrete containing steel fiber was measured. In addition, preparation 1 without steel fiber (0 vol% steel fiber content), preparation 1 (0.5 vol% steel fiber content), preparation 5 without steel fiber (0 vol% steel fiber content) volume %), formulation 5 (steel fiber content of 1 volume %), and formulation 6 without steel fiber (steel fiber content of 0 volume %) were measured for autogenous shrinkage strain.
Slump flow and flow time were measured according to JIS A 1150, air content according to JIS A 1128, concrete temperature according to JIS A 1156, unit volume mass according to JIS A 1116, and compressive strength according to JIS A 1108.
The filling time/height and the vibrating filling time/height were measured by a vibrating box filling test method based on the standards of the Japan Society of Civil Engineers (JSCE-F511-2012, JSCE-F701-2016).
Autogenous shrinkage strain is described in Japan Concrete Institute: Superfluid Concrete Research Committee Report (II), pp. 209-210, 1994.5 [Appendix 1] (tentative name) In accordance with the self-shrinkage test method for high-flow concrete, the embedded strain gauge KM-100BT manufactured by Tokyo Sokki Kenkyusho is placed in a 10 x 10 x 40 cm test piece. It was installed in the center and measured, and the value was evaluated at the age of 7 days.

In the vibration box filling test, a box-shaped container 1 as shown in FIG. 1 is used. The bottom surface 2 of the box-shaped container 1 is made of a vibration-proof rubber mat, and the side walls 3 are made of a transparent acrylic plate. The interior of the box-shaped container 1 is partitioned into chambers A and B by a partition 4 . A bar-shaped vibrator 5 is arranged in the A chamber. The vibrator 5 is a hand-held vibrator of an externally driven electric motor conforming to JIS A 8610, having a nominal diameter of 28 mm, a length of 580 mm or more, and a frequency of about 200 Hz. A gate G is provided at the lower end of the partition 4, and the gate G is provided with a flow obstacle 6. - 特許庁The gate G can be opened and closed by moving a partition plate 7 arranged along the partition 4 up and down. The unit of numerical values indicating dimensions in the drawing is mm. Since the minimum distance between mechanical joints embedded in the precast member may be less than 40 mm, the flow obstacle 6 was set to obstacle R2 (D13 reinforcing bars x 3, 35 mm intervals).
In the vibrating box filling test, with the gate G closed, concrete is poured up to the upper end of the A chamber, and the tip of the vibrator 5 is placed at a height of 100 mm from the lower end of the A chamber. Next, open the gate G, let the concrete flow from the A chamber to the B chamber without vibrating the vibrator 5, and the height from the lower end to the upper end of the concrete that has flowed into the B chamber (filling height before vibration) to measure. Next, the vibrator 5 is vibrated to measure the height from the lower end to the upper end of the concrete that has flowed into the B chamber (filling height after vibration).

Table 3 shows the measurement results of slump flow, flow time, air content, concrete temperature, unit mass, filling time/height, excitation filling time/height, and compression strength. FIG. 2 shows the filling height (filling height before vibration) and the vibration filling height (filling height after vibration). FIG. 3 shows a graph in which the unit coarse aggregate bulk volume (m ₃ /m ₃ ) of each formulation is plotted on the horizontal axis and the autogenous shrinkage strain is plotted on the vertical axis from the measurement results of the autogenous shrinkage strain.
Slump flow, air content and compressive strength satisfied the required quality. Regarding the compressive strength, the formulation with a steel fiber content of 1.0% by volume was approximately the same as the formulation with a steel fiber content of 0.5% by volume, considering the effect of the amount of air on the compressive strength.

Of the formulations with a steel fiber content of 1.0% by volume, formulation 4 with a unit coarse aggregate bulk volume of 0.45 m ³ /m ³ caused clogging in the vibrating box filling test. On the other hand, preparations 5 to 7 did not cause clogging, the filling height with vibration reached 300 mm, and they were excellent in gap passageability.
From the comparison of formulations 5 to 6 and formulation 7, it was confirmed that the smaller the water binder ratio, the higher the filling height before vibration (the higher the gap permeability). It is presumed that the viscosity of the base concrete affected the pore permeability.
Formulations 1-3 with 0.5 volume percent steel fiber loading did not show any interstitial problems. However, compared to Formulations 5-7, the toughness of concrete is inferior due to the low content of steel fibers.
In FIG. 3, it can be seen that autogenous shrinkage strain increases as the unit coarse aggregate bulk volume decreases from the comparison of the mixture with a steel fiber content of 0% by volume. In addition, from the comparison of Formulation 1 with steel fibers removed, Formulation 1, and Formulation 5, by increasing the steel fiber mixing rate, even if the unit coarse aggregate bulk volume is reduced, the unit coarse aggregate bulk volume It can be seen that the autogenous shrinkage strain can be suppressed to the same extent as when the is large.

In addition, in the formulation in which the steel fiber mixing ratio V _F is 1 (% by volume) and the unit coarse aggregate bulk volume V′ _bG of the steel fiber-containing ultra-high strength concrete is 0.4 (m ³ /m ³ ), the above The values in equation (1) are _VbG of 0.5, _rG of _4.24 , _rF of 0.31, VF of _0.0102 , GS of 0.6, and _KS of 0. .9.

According to the study by the present inventors, the type of organic fiber does not affect the interstitial property and the crack resistance, or has a slight effect. Polyacetal fibers were used as the organic fibers in Formulations 1-7, but it has been confirmed that similar results can be obtained when the polyacetal fibers are replaced with polypropylene fibers.

Claims (4)

Cement, silica fume, water, coarse aggregate, fine aggregate, chemical admixture, steel fiber, and organic fiber, with a water binder ratio of 25% by mass or less, containing the steel fiber Ultra high-strength concrete having a ratio of more than 0.50% by volume and 2% by volume or less and a mixing ratio of the organic fiber of 0.14 to 0.58% by volume ,
The steel fibers have a length of 12 to 32 mm,
The organic fibers contain polypropylene fibers, and the polypropylene fibers have a length of 9 to 11 mm,
The volume ratio of the steel fibers to the polypropylene fibers (the steel fibers/the polypropylene fibers) is 0.9 to 14.3,
The maximum dimension of the coarse aggregate is 15 mm or less,
Super high-strength concrete having a unit coarse aggregate bulk volume of 0.3 to 0.4 m ³ /m ³ . The ultra-high strength concrete according to claim 1, wherein said steel fibers have a diameter of 0.15-0.9 mm . Cement, silica fume, water, coarse aggregate, fine aggregate, chemical admixture, steel fiber, and organic fiber are blended, and the water binder ratio is 25% by mass or less, and the steel fiber ratio is 25% by mass or less. A mixing ratio of more than 0.5% by volume and 2% by volume or less , and a mixing ratio of the organic fiber of 0.14 to 0.58% by volume.
The steel fibers have a length of 12 to 32 mm,
At least polypropylene fibers are used as the organic fibers, and the length of the polypropylene fibers is 9 to 11 mm,
The volume ratio of the steel fibers to the polypropylene fibers (the steel fibers/the polypropylene fibers) is 0.9 to 14.3,
The maximum dimension of the coarse aggregate is 15 mm or less,
Calculate the target value _V'bG of the unit coarse aggregate bulk volume of the ultra-high-strength concrete by the following formula (1), and set the blending amount of the coarse aggregate so that the target value _V'bG is obtained. How to mix high-strength concrete.
V′ _bG =V _bG −(K _S ·2r _G /3r _F −1)·V _F /G _S (1)
Here, V' _bG represents the target value (m ³ /m ³ ) of the unit coarse aggregate bulk volume of the ultra-high strength concrete,
V _bG is a standard value of unit coarse aggregate bulk volume (m ³ /m ³ ) of ultra-high strength concrete and indicates 0.5 ,
K _S is the influence coefficient and indicates 0.9 ;
r _G indicates the radius (mm) of the coarse aggregate calculated from the total coarse aggregate surface area obtained from the particle size distribution of the coarse aggregate, assuming that the coarse aggregate is spherical,
r _F represents the radius (mm) of the steel fiber calculated assuming that the steel fiber has a cylindrical shape,
_VF indicates the mixing ratio (% by volume) of the steel fibers,
_GS indicates the actual volume ratio (volume %) of the coarse aggregate. The method for preparing ultra-high strength concrete according to claim 3 , wherein the steel fibers have a diameter of 0.15-0.9 mm .

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