Steel fiber reinforced concrete

Abstract

To provide steel fiber-reinforced concrete with higher dispersibility of steel fibers, excellent compression strength, flexure strength and flexure toughness.SOLUTION: Steel fiber-reinforced concrete comprises cement, water, coarse aggregate, fine aggregate, chemical admixture and steel fiber and the dispersion ratio of the steel fiber defined by the following formula (1) is equal to or greater than 60%. (where, in the formula (1), FD is the dispersion ratio (%) of the steel fiber, VD is the mass (g) of the steel fiber not bound and VA is the mass (g) of the entire steel fiber (the total of the bundle of the steel fiber and the steel fiber not bound).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to steel fiber reinforced concrete.

Background Art

[0002] In recent years, fiber reinforced concrete having both ultra-high strength, high fluidity, high fire resistance, and high toughness, and using synthetic fibers and steel fibers in combination has been developed and put into practical use. Fiber reinforced concrete can improve mechanical properties such as flexural and tensile toughness compared to ordinary concrete. Also, it is known that the dispersibility and orientation of fibers affect the flexural and tensile toughness of fiber reinforced concrete.

[0003] For example, in order to improve the brittle fracture of concrete, steel fiber reinforced concrete in which steel fibers (about 0.62 mm to 0.75 mm in diameter and about 30 mm to 60 mm in length) are incorporated into concrete is known. As the original form of steel fibers, generally, in order to facilitate handling and suppress the generation of fiber balls in which steel fibers become lumps, bundles of steel fibers are used. The bundle of steel fibers is formed by fixing a plurality of steel fibers with a water-soluble adhesive. To disperse the steel fibers in concrete, the bundle of steel fibers is mixed into the concrete and stirred for a certain period of time with a mixer or an agitator truck. As a result, the above-mentioned adhesive melts in the concrete, and the bundle of steel fibers is broken up by the impact of aggregates or the like, and the steel fibers are dispersed in the concrete (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The dispersibility of steel fibers in concrete is known to affect the mechanical properties of steel fiber-reinforced concrete. For example, when steel fibers are used at 80 kg / m 3 and in the case of ultra-high-strength fiber-reinforced concrete with a design standard strength of 120 N / mm 2 , there has been a problem that when the dispersibility of steel fibers is low, the mechanical properties such as compressive strength, flexural strength, and flexural toughness tend to decrease.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide steel fiber-reinforced concrete having high dispersibility of steel fibers and excellent compressive strength, flexural strength, and flexural toughness.

Means for Solving the Problems

[0007] The present invention has the following aspects. [1] A steel fiber-reinforced concrete containing cement, water, coarse aggregate, fine aggregate, a chemical admixture, and steel fibers, wherein the dispersion rate of the steel fibers defined by the following formula (1) is 60% or more ri , The content of the steel fiber is 40 kg / m 3 or more and 80 kg / m 3 or less. Among the steel fibers, the diameter of the non-bundled steel fibers is 0.50 mm or more and 1.00 mm or less, the length is 30 mm or more and 80 mm or less, and the aspect ratio (length / diameter) is 40 or more and 80 or less. Steel fiber-reinforced concrete.

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Figure 1

Advantages of the Invention

[0008] According to the present invention, it is possible to provide steel fiber-reinforced concrete having high dispersibility of steel fibers and excellent compressive strength, flexural strength, and flexural toughness.

Brief Description of the Drawings

[0009]

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] Hereinafter, steel fiber-reinforced concrete according to an embodiment of the present invention will be described. Note that this embodiment is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

[0011] [Steel Fiber-Reinforced Concrete] The steel fiber-reinforced concrete of this embodiment includes cement, water, coarse aggregate, fine aggregate, chemical admixture, and steel fibers.

[0012] As the cement, medium heat Portland cement and low heat Portland cement are preferable in terms of low heat of hydration.

[0013] The water content may be, for example, such that the water-binder ratio is 15% by mass or more and 65% by mass or less. The lower the water-binder ratio, the higher the compressive strength of the steel fiber-reinforced concrete.

[0014] Examples of the coarse aggregate include crushed hard sandstone, crushed andesite, crushed rhyolite, etc. The oven-dry density of the coarse aggregate is, for example, 2.55 g / cm 3 or more and 2.7 g / cm 3 or less. The coarse particle ratio of the coarse aggregate is, for example, 6 or more and 6.6 or less.

[0015] The maximum size of the coarse aggregate is typically preferably 25 mm or less, and more preferably 20 mm or less. The maximum size of the coarse aggregate is the size indicated by the nominal size of the sieve through which 90% by mass or more of the coarse aggregate passes. Examples of the coarse aggregate with a maximum size of 20 mm or less include commercially available coarse aggregates with a maximum size of 20 mm, a maximum size of 15 mm, a maximum size of 13 mm, etc.

[0016] The content of the coarse aggregate in the steel fiber reinforced concrete of this embodiment is such that the unit bulk volume of the coarse aggregate in the steel fiber reinforced concrete is 0.3 kg / m 3 or more and 0.5 kg / m 3 or less, preferably 0.33 kg / m 3 or more and 0.43 kg / m 3 or less. When the unit bulk volume of the coarse aggregate in the steel fiber reinforced concrete is at least the lower limit value, the resistance to material segregation is excellent. The actual volume ratio of the coarse aggregate in the steel fiber reinforced concrete of this embodiment is, for example, 58% by volume, and further 58% by volume or more and 64% by volume or less.

[0017] Examples of the fine aggregate include crushed sand, mountain sand, land sand, etc. The oven-dry density of the fine aggregate is, for example, 2.55 g / cm 3 or more and 2.7 g / cm 3 or less. The content of the fine aggregate is set in consideration of the fine aggregate ratio.

[0018] In the steel fiber-reinforced concrete of this embodiment, the fine aggregate ratio may be, for example, 35% or more and 65% or less.

[0019] The chemical admixture includes at least one of a high-performance water reducer and a high-performance AE water reducer (hereinafter, these are also collectively referred to as "high-performance (AE) water reducer"), and a thickening agent. The chemical admixture may contain other chemical admixtures as necessary within a range that does not impair the effects of the present invention.

[0020] The high-performance (AE) water reducer is used for the purpose of improving the workability of the steel fiber-reinforced concrete of this embodiment. The definitions of the high-performance water reducer and the high-performance AE water reducer conform to JIS A 6204. Examples of the high-performance water reducer include those having a polycarboxylic acid ether-based main component and those having a polycarboxylic acid copolymer main component. Examples of the high-performance AE water reducer include those having a polycarboxylic acid-based main component.

[0021] The thickening agent is used for the purpose of increasing the viscosity of the steel fiber-reinforced concrete of this embodiment and enhancing the resistance to material separation. The thickening agent is not particularly limited as long as it can be blended into concrete. Examples of the thickening agent include those having a cellulose-based main component.

[0022] The high-performance (AE) water reducer and the thickening agent may be separately used for the preparation of the steel fiber-reinforced concrete of this embodiment, or may be used for the preparation of the steel fiber-reinforced concrete of this embodiment as a high-performance (AE) water reducer containing a thickening agent (hereinafter, also referred to as "thickening agent-containing high-performance (AE) water reducer"). Preferably, it is used for the preparation of the steel fiber-reinforced concrete of this embodiment as a thickening agent-containing high-performance (AE) water reducer.

[0023] As the thickener-containing high-performance (AE) water reducer, commercially available products can be used. Examples of commercially available products of the thickener-containing high-performance water reducer include "Mighty 21-V" of Kao Corporation. Examples of commercially available products of the thickener-containing high-performance AE water reducer include "Master Glenium 6520" of BASF Japan Ltd.

[0024] The content of each of the high-performance (AE) water reducer and the thickener can be appropriately selected according to the type of each of the high-performance (AE) water reducer and the thickener so as to obtain a desired effect. The total content of the high-performance (AE) water reducer and the thickener, or the content of the thickener-containing high-performance (AE) water reducer is, for example, about 0.3% by mass or more and 0.9% by mass or less based on the total mass of the cement in terms of solid content.

[0025] Examples of the steel material constituting the steel fiber include ordinary steel materials and stainless steels. The above-mentioned steel material preferably has alkali resistance. Also, from the viewpoint of rust prevention, those with zinc plating on the surface of the steel material are preferable. Examples of the shape of the steel fiber include hook type, straight type, and corrugated type. The hook type is preferable in terms of improving the adhesion between the concrete and the steel fiber and improving the toughness of the concrete. As the steel fiber, for example, commercially available steel fibers for steel fiber reinforced concrete can be used.

[0026] The steel fiber reinforced concrete of the present embodiment includes bundles of steel fibers and steel fibers that are not bundled and are separated from the bundles of steel fibers.

[0027] In the steel fiber reinforced concrete of the present embodiment, the dispersion rate of the steel fibers defined by the following formula (1) is 60% or more, preferably 80% or more, and more preferably 90% or more. When the dispersion rate of the steel fibers is 60% or more, the compressive strength, flexural strength, and flexural toughness coefficient of the steel fiber reinforced concrete are excellent. Note that there is no standardized method for evaluating the dispersibility of steel fibers. Therefore, in this embodiment, a steel fiber dispersibility rate for evaluating the dispersibility is defined as follows. By the washing analysis test method specified in JSCE-F 554-1999 "Test Method for Steel Fiber Content in Steel Fiber Reinforced Concrete", while washing the steel fiber reinforced concrete placed in a metal cylindrical container with a capacity of 6 L or more with water, the steel fibers are separated, collected, and dried. The dried steel fibers are sorted into bundled steel fibers and unbundled steel fibers, and the dispersibility rate of the steel fibers is calculated using the following formula (1).

[0028] [Number] (However, in formula (1), F D is the dispersibility rate (%) of the steel fibers, A D is the mass (g) of the unbundled steel fibers, and V A is the mass (g) of all the steel fibers (the total of the bundled steel fibers and the unbundled steel fibers).)

[0029] Among the steel fibers, it is preferable that the diameter of the unbundled steel fibers (loose steel fibers) is 0.50 mm or more and 1.00 mm or less. If the diameter of the unbundled steel fibers is less than 0.50 mm, the specific surface area of the steel fibers per unit amount increases, and the fluidity of the steel fiber reinforced concrete deteriorates. If the diameter of the unbundled steel fibers exceeds 1.00 mm, the number of steel fibers per unit amount is small, and the flexural toughness obtained by the steel fibers bridging when cracks occur becomes small.

[0030] Among the steel fibers, it is preferable that the length of the unbundled steel fibers (loose steel fibers) is 30 mm or more and 80 mm or less. If the length of the unbundled steel fibers is less than 30 mm, the anchorage length of the steel fibers is short, and the flexural toughness of the steel fiber reinforced concrete obtained by the steel fibers bridging when cracks occur becomes small. If the length of the unbundled steel fibers exceeds 80 mm, the filling property of the steel fiber reinforced concrete into narrow parts and the like is poor.

[0031] The steel fiber content in the steel fiber reinforced concrete of this embodiment is 40 kg / m 3 More than 80kg / m 3 The steel fibre content is preferably 40 kg / m 3 If the steel fiber content is less than 80kg / m, the number of steel fibers per unit weight is small, and the bending toughness of the steel fiber reinforced concrete obtained by bridging the cracks caused by the steel fibers is small. 3 If the ratio exceeds this value, the number of steel fibers per unit weight becomes large, and the fluidity of the steel fiber reinforced concrete becomes poor.

[0032] The steel fiber reinforced concrete of this embodiment may further contain components other than the above components.

[0033] The steel fiber reinforced concrete of this embodiment has steel fibers of 80 kg / m 3 The design strength is 120N / mm 2 In this case, it is preferable that the compressive strength, bending strength and bending toughness are 90% or more compared to when the dispersion rate of the steel fibers is 100%.

[0034] An example of a method for measuring the compressive strength of steel fiber reinforced concrete is JIS A1108-2018 "Test method for compressive strength of concrete."

[0035] An example of a method for measuring the bending strength of steel fiber reinforced concrete is JSCE-G552-2013 "Test method for bending strength and bending toughness of steel fiber reinforced concrete" (Japan Society of Civil Engineers standard).

[0036] An example of a method for measuring the bending toughness of steel fiber reinforced concrete is JSCE-G552-2013 "Test method for bending strength and bending toughness of steel fiber reinforced concrete" (Japan Society of Civil Engineers standard).

[0037] In the steel fiber reinforced concrete of the present embodiment described above, it contains cement, water, coarse aggregate, fine aggregate, chemical admixture, and steel fiber, and since the dispersion rate of the steel fiber defined by the above formula (1) is 60% or more, the steel fiber has high dispersibility, and it is possible to provide steel fiber reinforced concrete excellent in compressive strength, flexural strength, and flexural toughness.

[0038] (Mixing method of steel fiber reinforced concrete) The mixing method of the steel fiber reinforced concrete of the present embodiment is a method of blending cement, water, coarse aggregate, fine aggregate, chemical admixture, and steel fiber to prepare steel fiber reinforced concrete in which the dispersion rate of the steel fiber defined by the above formula (1) is 60% or more. Other components may be blended together with cement, coarse aggregate, fine aggregate, chemical admixture, and steel fiber.

[0039] In the mixing method of the steel fiber reinforced concrete of the present embodiment, cement, water, coarse aggregate, fine aggregate, chemical admixture, and steel fiber are stirred and mixed so that the dispersion rate of the steel fiber defined by the above formula (1) is 60% or more.

[0040] In the mixing method of the steel fiber reinforced concrete of the present embodiment, first, all materials other than the additive (cement, water, coarse aggregate, fine aggregate, chemical admixture) are put into a mixer, and these are kneaded to prepare base concrete. Next, the base concrete is discharged into a truck agitator, and the additive is put into the base concrete and these are kneaded. Next, steel fiber is put into the base concrete to which the additive has been added, and after the addition is completed, predetermined kneading is performed by high-speed stirring (for example, 15 rpm). By adjusting the high-speed stirring time, the dispersion rate of the steel fiber is made within the target range.

Examples

[0041] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples. The materials used in the test examples are shown in Table 1.

[0042]

Table 1

[0043] (Test Example) In this test example, for steel fiber-reinforced concrete (design standard strength 120 N / mm 3 ) with steel fibers mixed in at a content of 80 kg / m 2 , the mix proportion was studied.

[0044] <Mix Proportion of Steel Fiber-Reinforced Concrete> Table 2 shows the mix proportion of steel fiber-reinforced concrete. The mix proportion name is composed of "W / C - unit volume of coarse aggregate (m 3 / m 3 ) - content of steel fibers (kg / m 3 ) - type of chemical admixture". W / C is the mass ratio of water (W) to cement (C), corresponding to the water-binder ratio. W / C was set assuming a design standard strength of 120 N / mm 2 . The content of steel fibers of 80 kg / m 3 corresponds to a mixing ratio of 1.02% by volume. In this test example, the dispersion ratio of the steel fibers defined by the above formula (1) was set to 20% - 100%. In Table 2, "s / a" indicates the fine aggregate ratio.

[0045]

Table 2

[0046] <Mixing> For mixing, a twin-shaft forced mixer (manufactured by Taiheiyo Kiko Co., Ltd., model: SD-55) with a nominal capacity of 0.055 m 3 was used. Cement (C) and fine aggregate (S) were charged and dry-mixed. Then, water (W) and chemical admixture (SP) were charged and mixed to form mortar. Next, coarse aggregate (G) was charged and mixed to form high-strength concrete. Further, steel fibers (ST) were charged and mixed for 10 seconds to 180 seconds to form steel fiber-reinforced concrete.

[0047] <Evaluation> For each mixture of steel fiber reinforced concrete, the compressive strength, flexural strength, and flexural toughness were evaluated. The compressive strength was evaluated in accordance with JIS A1108 - 2018 "Test Method for Compressive Strength of Concrete". The flexural strength was evaluated in accordance with JSCE - G552 - 2013 "Test Method for Flexural Strength and Flexural Toughness of Steel Fiber Reinforced Concrete" (Japan Society of Civil Engineers Standard). The flexural toughness was evaluated in accordance with JSCE - G552 - 2013 "Test Method for Flexural Strength and Flexural Toughness of Steel Fiber Reinforced Concrete" (Japan Society of Civil Engineers Standard). The flexural toughness coefficient was calculated from the area enclosed by the load - deflection curve up to a deflection of 2 mm, and then evaluated. The evaluation results are shown in Figures 1 to 3.

[0048] From the results shown in Figures 1 to 3, in the case of steel fiber reinforced concrete with a design standard strength of 120 N / mm 3 using 80 kg / m of steel fibers, if the dispersion rate of the steel fibers is 60% or more, it was found that the compressive strength, flexural strength, and flexural toughness can be ensured at 90% or more compared to the case where the dispersion rate of the steel fibers is 100%. 2

[0049] [Examples] Assuming actual construction work, steel fiber reinforced concrete with a design standard strength of 120 N / mm 3 using 80 kg / m of steel fibers was prepared. 2 The materials used in the examples are shown in Table 3.

[0050]

Table 3

[0051] <Mixing of Steel Fiber Reinforced Concrete> The mixing of steel fiber reinforced concrete is shown in Table 4.

[0052]

Table 4

[0053] <Mixing (Mixing machine) For mixing, a twin - shaft forced mixer (manufactured by Koyo Machinery Industry Co., Ltd.) with a nominal capacity of 5 m 3 was used. (Mixing method) Materials other than additives were put into the above twin - shaft forced mixer and mixed for 300 seconds. After the mixing was completed, the concrete was loaded into the truck agitator, polyacetal fibers were put into the truck agitator, and high - speed stirring was carried out for 120 seconds with the truck agitator. After that, steel fibers were put in, and high - speed stirring was carried out with the truck agitator for a predetermined time. The high - speed stirring was stopped halfway, and the concrete was sampled for 0.1 m 3 minutes to check the dispersion ratio of the steel fibers. The results are shown in Figure 4. From the relationship between the dispersion ratio of the steel fibers shown in Figure 4 and the high - speed stirring time, it was found that when the high - speed stirring time is 180 seconds or more, the dispersion ratio of the steel fibers becomes 84.5%. That is, when the high - speed stirring time is 180 seconds or more, it is considered that the steel fiber - reinforced concrete obtained can ensure 90% or more of the compressive strength, flexural strength, and flexural toughness compared with the case where the dispersion ratio of the steel fibers is 100%.

Claims

1. A steel fiber-reinforced concrete comprising cement, water, coarse aggregate, fine aggregate, a chemical admixture, and steel fibers, wherein the dispersion ratio of the steel fibers defined by the following formula (1) is 60% or more, the content of the steel fibers is 40 kg / m³ or more and 80 kg / m³ or less, and among the steel fibers, the diameter of the non-bundled steel fibers is 0.50 mm or more and 1.00 mm or less, the length is 30 mm or more and 80 mm or less, and the aspect ratio (length / diameter) is 40 or more and 80 or less. 【Number 1】 (However, in formula (1), FD is the dispersion ratio (%) of the steel fibers, AD is the mass (g) of the non-bundled steel fibers, and VA is the mass (g) of all the steel fibers (the total of the steel fiber bundles and the non-bundled steel fibers).)

2. A steel fiber-reinforced concrete comprising cement, water, coarse aggregate, fine aggregate, a chemical admixture, and steel fibers, wherein the dispersion ratio of the steel fibers defined by the following formula (1) is 60% or more, when 80 kg / m³ of steel fibers are used and the design standard strength is 120 N / mm², the compressive strength, flexural strength, and flexural toughness are 90% or more with respect to the case where the dispersion ratio of the steel fibers is 100%, and among the steel fibers, the diameter of the non-bundled steel fibers is 0.50 mm or more and 1.00 mm or less, the length is 30 mm or more and 80 mm or less, and the aspect ratio (length / diameter) is 40 or more and 80 or less. 【Number 2】 (However, in formula (1), FD is the dispersion ratio (%) of the steel fibers, AD is the mass (g) of the non-bundled steel fibers, and VA is the mass (g) of all the steel fibers (the total of the steel fiber bundles and the non-bundled steel fibers).)

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