JP2019045195A - Evaluation method of silica fume, method of producing concrete composition, concrete composition and concrete cured body - Google Patents

Abstract

To provide a concrete composition capable of forming a concrete cured body using the concrete composition whose water/binder ratio is 0.2 or less and which has excellent liquidity and high strength, and also to provide the concrete cured body, an evaluation method of silica fume and a method of producing the concrete composition.SOLUTION: Silica fume 1 g is dispersed in a 100 g of water, and the particle size distribution is measured using the obtained silica fume liquid dispersion as a measuring object. An ultrasonic liquid dispersion obtained by applying ultrasonic frequencies selected from 15 kHz to 50 kHz to the further obtained silica fume liquid dispersion for 540 seconds is used as the measuring object, then the particle size distribution is measured.SELECTED DRAWING: None

Description

  The present disclosure relates to a method for evaluating silica fume, a method for producing a concrete composition, a concrete composition and a cured concrete.

Hardened concrete, represented by precast concrete, is used in various applications, is also widely used as a structural material for buildings, and a hardened hard body is desired.
The mass ratio of water to the binder in the concrete composition, ie, cement, silica fume, blast furnace slag, fly ash, and other materials that react with water in concrete (hereinafter referred to as water / binder ratio) may be referred to as the present specification. If the water / binder ratio in the paper is particularly low as far as the weight is concerned, the distance between the particles will be narrow, and the hydration product will precipitate and fill in the liquid phase part. It is known that the structure becomes dense and concrete with high compressive strength can be obtained.
Such a concrete composition with a low water / binder ratio does not have sufficient flowability because the water content is small, and for example, the water / binder ratio is 0.2 or less for the purpose of strengthening. In the case of using a large amount of surfactant for the purpose of improving the fluidization, the mixture can not be uniformly mixed or the viscosity of the mixed mixture becomes extremely high, which is practically sufficient. At present, liquidity can not be obtained. Moreover, it is unpreferable also from a viewpoint of strength maintenance of the concrete hardening body obtained to increase content of surfactant which is a component which does not participate in hardening.

On the other hand, for the purpose of improving fluidity and strengthening, a technique has been proposed in which silica fume having a spherical particle shape is replaced by about 5% to 25% of cement, and silica fume having an average particle diameter of about 0.2 μm is previously added to cement. There are commercially available mixed cements mixed with about 10% to 20%. A concrete composition containing commercially available silica fume is a cement composition obtained by adsorbing spherical cement-based silica fume having an average particle diameter of submicron SiO ₂ as a main component on the surface of cement particles or in the liquid phase. Improves slippage between particles to lower the viscosity of the mixture, and SiO ₂ in silica fume causes pozzolanic reaction with calcium hydroxide generated by hydration of cement to form hydrate and densify It is thought that it is expected that it contributes to the strength improvement of the concrete hardening body obtained. Such silica fume concrete composition was used, adapted to be widely applied to design strength ^60N / mm ^{2 ~150N} / mm 2 as high strength concrete.

However, according to the study of the present inventors, the concrete composition containing the already mentioned commercially available silica fume is to be further strengthened, that is, to have a strength range such that the design standard strength exceeds 150 N / mm ^2. It was found that when the water / binder ratio is reduced to 0.2 or less, preferably about 0.15 or less, practically preferable fluidity can not be obtained.
It is also considered to increase the mixing ratio of silica fume to improve the fluidity, but the surfactant necessary for the fluidity improvement is adsorbed to the silica fume and the addition amount increases, or the aggregation of the fine silica fume occurs to cause the flow On the contrary, there are new problems such as a decrease in the effect of improving the property and a delay in setting due to the addition of a large amount of surfactant.

For this reason, various methods have been proposed in which the flowability when silica particles such as silica fume are blended in a concrete composition is evaluated or judged in advance.
For example, a method of quantifying free water amount by centrifuging a cement paste containing silica fume and measuring separated water content and a method of applying silica fume having a free water amount of 8% or more to a concrete composition have been proposed. For example, refer to Patent Document 1 and Patent Document 2.).
In addition, a sample slurry is prepared by kneading silica fume and water having a water powder ratio of 350% to 450%, and a water reducing agent with a mass conversion of 3% to less than 5% with respect to silica fume, and then the rotational viscosity A method for evaluating the quality of silica fume, which measures the viscosity of a sample slurry using a meter, has been proposed (see, for example, Patent Document 3).
In addition, as a means for improving the fluidity of concrete compositions, a method for producing a silica slurry suitable for concrete compositions has been proposed, which includes grinding raw material silica slurry containing silica fume using a grinding medium (for example, See Patent Document 4).

JP 2008-230891 A JP, 2008-230892, A Japanese Patent Application Laid-Open No. 2007-70133 JP, 2011-64647, A

However, in the techniques described in Patent Document 1 and Patent Document 4, although focusing only on the flowability of the silica fume-containing slurry, no consideration is given to the strength of the cured body of the concrete composition containing the silica fume-containing slurry.
Moreover, in the technique described in Patent Document 2, as an evaluation related to the viscosity of cement paste, a cement paste containing a water reducing agent is centrifuged to evaluate by free water amount, but a polycarboxylic acid-based water reduction used for evaluation There are a plurality of agents having different formulations, and there is a problem that the cement also has a characteristic that changes slightly, even for each batch. Therefore, it is a more indirect evaluation of physical properties by silica fume, and it can not be said that it can be properly evaluated.
The silica fume-containing slurry described in Patent Document 3 has good fluidity, but the hardened body of the concrete composition containing the silica fume has a compressive strength of about 160 N / mm ² and is targeted to be 200 N in the present disclosure. It is difficult to obtain a cured product having a high strength exceeding 1 mm ² / mm ² .

An object of an embodiment of the present invention is to provide a method of evaluating silica fume which can be suitably used for a concrete composition which has good fluidity and can form a high-strength hardened concrete, and a method of producing the concrete composition. It is.
The object of another embodiment of the present invention is to provide a concrete composition and a concrete composition having a water / binder ratio of 0.2 or less, good fluidity, and capable of forming a high-strength hardened concrete body. An object of the present invention is to provide a high-strength concrete cured product which is a cured product.

As a result of intensive investigations, the present inventors selected a silica fume capable of achieving both flowability and high strength by a simple evaluation method in a concrete composition containing silica fume, and by using this silica fume, one of the above-mentioned problems was achieved. I found that I could solve it.
That is, the means for solving the problem includes the following embodiments.

A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and the obtained silica fume dispersion is A and B, assuming that the 50% integrated particle size of the silica fume obtained by measuring the particle size distribution is an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds. The evaluation method of the silica fume which includes confirming whether and satisfy | fills following formula (I) and Formula (II).
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)

<2> A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and the obtained silica fume dispersion is A and B, assuming that the 50% integrated particle size of the silica fume obtained by measuring the particle size distribution is an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds. And selecting a silica fume satisfying the following formulas (I) and (II):
A method of producing a concrete composition comprising cement, aggregate, silica fume and water, wherein a water / binder ratio is 0.2 or less on a mass basis.
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)

<3> cement, aggregate, silica fume, and water, and the water / binder ratio is 0.2 or less on a mass basis,
The 50% cumulative particle diameter of the silica fume obtained by measuring the particle size distribution by using 1 g of the silica fume dispersed in 100 g of water and measuring the particle size distribution with the silica fume dispersion as the measurement target is A, and the silica fume dispersion obtained above The ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds is a measurement target, and the 50% cumulative particle diameter of silica fume obtained by measuring the particle size distribution is B. The concrete composition whose said B is a silica fume which satisfy | fills following formula (I) and Formula (II).
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)
<4> The concrete composition according to <3>, wherein the ratio of spherical particles to all particles of silica fume included in a viewing angle is 90% or more when the silica fume is observed by a scanning electron microscope.
<5> The ratio of particles having a particle diameter of 0.1 μm or more and 10 μm or less with respect to all particles of silica fume is 90% or more, and the average particle diameter obtained by particle size distribution measurement is 0.2 μm or more 1 .5 The concrete composition according to <3> or <4>, which is 5 μm or less.
<6> The hardened concrete body according to any one of <3> to <5>, wherein the aggregate includes coarse aggregate.
It is a hardened | cured material of the concrete composition as described in any one of <7><3>-<6>, and the concrete hardened body whose compressive strength in 28 days of materials is 250 Mpa or more.

A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and the obtained silica fume dispersion is A and B, assuming that the 50% integrated particle size of the silica fume obtained by measuring the particle size distribution is an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds. The evaluation method of the silica fume which includes confirming whether and satisfy | fills following formula (III) and Formula (IV).
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)
A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and the obtained silica fume dispersion is A and B, assuming that the 50% integrated particle size of the silica fume obtained by measuring the particle size distribution is an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds. And selecting a silica fume satisfying the following formulas (III) and (IV):
A method of producing a concrete composition comprising cement, aggregate, silica fume and water, wherein a water / binder ratio is 0.2 or less on a mass basis.
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)

<10> cement, aggregate, silica fume, and water, the water / binder ratio is 0.2 or less on a mass basis, and the silica fume is obtained by dispersing 1 g of the silica fume in 100 g of water; The 50% cumulative particle size of the silica fume obtained by measuring the particle size distribution with the target silica fume dispersion as the measurement target is A, and the obtained silica fume dispersion is given an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz for 540 seconds. When the 50% cumulative particle diameter of silica fume obtained by measuring the particle size distribution is B, the above-mentioned A and B are expressed by the following formulas (III) and (IV). Concrete composition which is a filling silica fume.
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)

The present inventors focused on the silica fume used for the concrete composition, and the performance of the concrete composition was achieved by using a very spherical shape and using silica fume which contains no secondary aggregate or contains very little, if any. A method for evaluating silica fume, etc., has been found that can be significantly improved, and silica fume suitable for concrete compositions can be easily selected.
Hereinafter, the 50% cumulative particle diameter of silica fume obtained by measuring the particle size distribution in the dispersion of silica fume may be simply abbreviated as “50% cumulative particle diameter”.
In the present specification, the 50% integrated particle diameter, so-called median diameter, obtained by measuring the particle size distribution of the silica fume dispersion to which ultrasonic waves have been applied was considered as the average primary particle diameter of the silica fume.

  Heretofore, it has been known that fluidity is improved by replacing a part of cement with small particle size silica fume. However, when the water / binder ratio of the concrete composition decreases to 0.2 or less due to high strength, the liquid phase extremely decreases, the distance between cement particles becomes narrow, and fine particles that are not adsorbed to cement particles Secondary aggregates tend to form, and the generation of aggregates rather increases the viscosity. Therefore, there has been a demand for a simple method of selecting a suitable silica fume for a concrete composition which does not contain a secondary aggregate and has a form of spherical particles, in which silica fume particles are monodispersed.

Although the effect concerning the evaluation method of silica fume suitable for a concrete composition is not clear, it is considered as follows.
According to the study of the present inventors, ultrasonic dispersion is mentioned as a suitable method for crushing secondary aggregates of silica fume particles.
Therefore, first, an aqueous dispersion of silica fume particles is prepared.
Then, the silica fume which is likely to form aggregates will form secondary aggregates in water at the time of preparation of the aqueous dispersion. However, it has been found that spherical silica fume particles excellent in dispersibility are easily dispersed uniformly without aggregation of the particles even when the aqueous dispersion is prepared. It has also been found that the dispersibility depends on the size of the average primary particle size of silica fume.
First, silica fume to be evaluated is dispersed in water, the particle size distribution is measured, and the average particle size is determined from the 50% integrated particle size. Then, when ultrasonic waves are applied to the aqueous dispersion of silica fume prepared in the same manner, secondary aggregates of silica fume are crushed and the particles are uniformly dispersed. Here, the average particle size is determined from the 50% cumulative particle size of the particle size distribution of the dispersion to which ultrasonic waves have been applied.
If the ratio between the 50% cumulative particle diameter of the simple aqueous dispersion and the 50% cumulative particle diameter of the dispersion to which ultrasonic waves have been applied, obtained as described above, is within the predetermined range, from the beginning Silica fume is found to be silica fume particles that do not impair the flowability of the concrete composition, do not contain secondary aggregates, or are within an acceptable range, and contain only water dispersion and ultrasonic wave-applied dispersion If the ratio to the 50% cumulative particle size determined from the particle size distribution with the product exceeds a predetermined range, the silica fume contains secondary aggregates in excess of the allowable amount and is inferior in fluidity when it is added to the concrete composition It can be estimated.
Therefore, according to the evaluation method of silica fume of the present disclosure, it is considered that it is possible to select a silica fume which can form a hardened high-strength concrete without reducing the flowability of the concrete composition by a simple method. ing.

Although the effect of the concrete composition of the present disclosure is not clear, it is considered as follows.
Silica fume has attracted attention as a preferable binder contained in a concrete composition. Since silica fume is in the form of fine particles, it is generally highly cohesive. As a silica fume used for a concrete composition, for example, the average value of the primary particle diameter of the silica fume estimated by measuring the specific surface area by BET method is preferably about 1 to 2 μm. However, it is considered that fine silica fume particles tend to aggregate, and the apparent particle size of the silica fume containing the aggregates is several μm or more.
When silica fume is included in a concrete composition, it is preferable that the aggregate is broken in a mixing process, but a generally used concrete mixer has almost no ability to crush fine particle aggregates such as silica fume, and a concrete composition In the mixing of the above, the silica fume aggregate having a high specific surface area may first adsorb moisture, resulting in a decrease in fluidity.

Therefore, assuming that the 50% integrated particle size obtained from the particle size distribution of the silica fume dispersion to which ultrasonic waves have been applied is the particle size of the monodispersed primary particles, it is obtained from the particle size distribution of the aqueous dispersion of silica fume to which ultrasonic waves are not applied. By comparing the 50% cumulative particle diameter with each other, the difference between the above is within a predetermined range, and the influence of silica fume on the fluidity of the concrete composition is evaluated in advance. Here, focusing on the fact that the dispersibility depends on the average primary particle size, the 50% integrated particle size determined from the particle size distribution of the silica fume dispersion is divided into the range of the particle size of the primary particles, We believe that more accurate methods for evaluating silica fume have become possible.
The concrete composition of the present disclosure contains silica fume whose 50% integrated particle size obtained from the particle size distribution of the silica fume dispersion before and after application of ultrasonic waves is within a predetermined range, preferably by a scanning electron microscope When observed, the ratio of spherical particles to the total particles of silica fume contained in the viewing angle is 90% or more, that is, it is spherical, that is, contains silica fume which does not form aggregates, so water / binder Even when the ratio is small, the flowability is good, and at the time of forming a hardened body, silica fume showing spherical and well dispersed state is uniformly dispersed with cement particles, and is contained in SiO ₂ contained in silica fume and cement components react, silicate hydrate produced under normal pressure (C-S-H: x (CaO) · y (SiO 2) z (H 2 _O)) is generated, in order to form a dense tissue scaffolds, according to the concrete composition of the present disclosure high strength concrete hardened body is estimated to be obtained.
Note that the present disclosure is not limited to the above estimation mechanism.

According to one embodiment of the present invention, provided are a method of evaluating silica fume that can be suitably used for a concrete composition that has good fluidity and can form a high-strength hardened concrete, and a method of producing the concrete composition. be able to.
Moreover, according to another embodiment of the present invention, a concrete composition and concrete composition having a water / binder ratio of 0.2 or less, good fluidity, and capable of forming a high-strength hardened concrete body It is possible to provide a high-strength concrete cured body which is a cured product of the object.

1 is a scanning photomicrograph of silica fume A used in the concrete composition of Example 1. FIG. It is a scanning electron micrograph of the silica fume B containing the secondary aggregate used for the concrete composition of the comparative example 1. FIG. It is a scanning electron micrograph of the silica fume C containing the secondary aggregate used for the concrete composition of Comparative Example 2. 5 is a graph showing the particle size distribution of silica fume A used in the concrete composition of Example 1. FIG. It is a graph showing the particle size distribution of silica fume B used for the concrete composition of comparative example 1. It is a graph showing the particle size distribution of the silica fume C used for the concrete composition of Comparative Example 2.

Hereinafter, the evaluation method of the silica fume of this indication, the manufacturing method of a concrete composition, a concrete composition, and a concrete hardening object are each demonstrated in detail. The present disclosure is not limited to the embodiments disclosed below, and various modifications can be made without departing from the scope of the present disclosure.
The numerical range shown using "-" in this specification means the range which includes the numerical value described before and after "-" as minimum value and the maximum value, respectively.
In the present specification, the term "process" is included in the term if the intended purpose of the process is achieved, even if it can not be clearly distinguished from other processes, as well as independent processes.
In the present specification, when referring to the amount of each component in the composition, when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified, a plurality of components present in the composition Means the total amount of

[Concrete composition]
The concrete composition which is one embodiment in the present disclosure (hereinafter sometimes referred to as the first embodiment) contains cement, aggregate, silica fume and water, and the water / binder ratio is on a mass basis. Of the silica fume dispersed in 100 g of water, and the particle size distribution of the obtained silica fume dispersion is measured, and the 50% cumulative particle diameter of the silica fume is A. A 50% integrated particle diameter of silica fume obtained by measuring the particle size distribution of an ultrasonic dispersion liquid obtained by applying ultrasonic waves of a frequency selected from 15 kHz to 50 kHz for 540 seconds to the obtained silica fume dispersion liquid as a measurement target When it is set to B, it is a concrete composition whose said A and said B are the silica fume which satisfy | fills following formula (I) and Formula (II).
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)

In the concrete composition of the present disclosure, when the particle size satisfies the formula (II), when the silica fume contained in the concrete composition is observed with a scanning electron microscope, spherical particles relative to all particles of silica fume contained in a viewing angle The ratio of is preferably 90% or more on the basis of the number.
In addition, the term "concrete composition" in this specification is used in the meaning which also includes the "mortar composition" which contains only a fine aggregate as an aggregate and does not contain a coarse aggregate.

(Silica fume)
When the particles of silica fume contained in the concrete composition of the present disclosure are observed, most of them, specifically, a scanning electron micrograph (hereinafter may be referred to as a SEM photograph) can be observed within a viewing angle. The silica fume particles are spherical particles of 90% or more based on the number of all particles, and do not contain or have less than 10% of irregular shaped particles such as secondary aggregates.
The silica fume satisfies the above conditions, and most of the particles of the silica fume are spherical particles independently existing, thereby containing the silica fume, the cement, the aggregate and the water, and the water / binder ratio (mass basis) The fluidity of the concrete composition having a value of 0.2 or less is maintained in a good range of workability.

FIG. 1 is a SEM photograph of silica fume particles contained in the concrete composition of Example 1 described later. As apparent from FIG. 1, it can be seen that most of the silica fume contained in the viewing angle of the SEM photograph is spherical particles. In addition, the SEM photograph shown in FIG. 1 was image | photographed in the state which made the silica fume particle | grains as a measuring object adhere to a carbon tape (5 mm x 5 mm).
The sample to be measured is prepared by placing silica fume particles on the carbon tape described above, pressing the surface on which the particles are placed with a spoon to press the particles against the carbon tape, and then removing excess particles with a blower It did.
The SEM photograph shown in FIG. 1 is a photograph taken at 20000 × magnification using SU 8230 manufactured by Hitachi High-Technologies Corp. as a scanning electron microscope.

The silica fume contained in the concrete composition of the present disclosure may be used in the form of powder, slurry or granules.
Silica fume has a ratio of particles with a particle size of 0.1 μm to 10 μm with respect to all particles of silica fume of 90% or more, and an average particle size obtained by particle size distribution measurement of 0.2 μm to 1.5 μm It is preferable from the viewpoint that the fluidity of the obtained cement slurry is better.
That is, the graph when the particle size distribution is measured has a shape close to a normal distribution, and fine particles less than 0.1 μm and large particle diameters exceeding 10 μm are not present, or the content is less than 10% The particles have a high degree of dispersion, and the average particle diameter obtained by the particle size distribution measurement is preferably 0.1 μm to 3.0 μm, and more preferably 0.1 μm to 1.5 μm.

  In addition, as the said Formula (I) and Formula (II) are clear from the range prescribed | regulated by Formula (II), the comparatively large particle | grains of the range whose average primary particle size is 1.0 micrometer-2.0 micrometers as a silica fume. It defines the diameter. The evaluation method of relatively fine silica fume particles having an average primary particle size of less than 1.0 μm will be described later.

As the silica fume, silica fume (average particle size: 0.1 μm to 0.2 μm, pH 5 to 10) by-produced during production of ferrosilicon and metal silicon generally used, silica fume derived from zirconia (average particle size: 0.22 μm to 1.0 μm, pH 2 to 4), etc. Among them, when observing the SEM photograph, select the silica fume whose ratio of spherical particles to all particles of silica fume included in the viewing angle is 90% or more on the basis of number It may be used as it is.
The particle size of silica fume in the present specification can be determined from a particle size distribution based on a number basis measured by a laser diffraction type particle size distribution analyzer (for example, MT3300EXII manufactured by Microtrack Bell Co., Ltd.).

The content of the silica fume is preferably 10% by mass to 30% by mass, and more preferably 10% by mass to 20% by mass, in the entire binder in the concrete composition. In order to contain 10% by mass to 30% by mass of the silica fume in the entire binder, 10% by mass to 30% by mass of the cement as the binder may be replaced with silica fume. In addition, content of the silica fume said here refers to the total amount, when using together multiple types of silica fume. When the content of the silica fume is in the above-mentioned range, the flowability improvement effect of the concrete composition and the strength improvement effect of the obtained cured concrete can be sufficiently exhibited.
As described above, some commercially available cements contain silica fume in advance, and when using such cement, it is added in consideration of the content of silica fume contained in advance. It is necessary to calculate the replacement amount of silica fume to be contained. If the particle shape of the silica fume contained in the commercially available cement is outside the range specified in the present disclosure, there is a concern that favorable flowability can not be obtained, and therefore the particle shape of the silica fume in the cement containing silica fume is spherical particles. It is preferable to confirm and use.

In addition, from the viewpoint of the hardenability of the concrete composition, the silica fume contains 80% or more by mass ratio of silicon dioxide (SiO ₂ ), and is preferably 90% or more, and has a specific surface area of 3 m by BET method. is preferably ² / ^{g~25m 2} / ^g, and more preferably 5m ² / g~15m 2 / g.
When the content of SiO ₂ is 80% by mass or more, the reactivity is sufficiently obtained, and the strength improvement effect of the obtained cured concrete is sufficiently exhibited. In addition, when the specific surface area is in the above range, the flowability and the kneadability are well maintained.

(Water / binder ratio)
The concrete composition of the present disclosure is preferably a composition having a water / binder ratio of 0.2 or less, has appropriate flowability, and is easy to obtain a high-strength concrete cured body, The range of 0.08 to 0.17 is more preferable, and the range of 0.09 to 0.13 is more preferable.
The binder in the present specification includes cement which is a main component contained in a concrete composition, silica fume generally used together with cement, fine powder (solid content) involved in hardening of cement hardened body such as slag and fly ash. It is
In addition, aggregate, surfactant etc. which are added for fluidization improvement are not included in the binder in this specification.

(cement)
There is no restriction | limiting in particular in the cement contained in the concrete composition of this indication, According to the objective, it can select suitably from various cements.
As cements, known cements such as ordinary Portland cement, moderate heat Portland cement, low heat Portland cement, and early-strength Portland cement can be suitably used. Among them, low heat Portland cement can be preferably mentioned.
Alternatively, Portland cement containing silica fume in advance may be used. However, as described above, it is necessary to be used paying attention to the particle shape of silica fume contained in cement. When using a portland cement containing silica fume, as described above, the content of silica fume is determined in advance in consideration of the content of silica fume contained in the cement.

(Other binder)
The concrete composition of the present disclosure may be added to cement and silica fume, and other binders may be appropriately selected and used in appropriate amounts, as needed, as long as the effects are not impaired.
Other binders include fine powder of silica obtained by finely pulverizing crystalline silica, slag such as fine powder of blast furnace slag, fine powder of limestone, fly ash and the like.
The content of the binder other than cement and silica fume is preferably 10% by mass or less of the total binder.

(aggregate)
The concrete composition contains an aggregate. As aggregate, fine aggregate is preferable. Moreover, you may also contain a coarse aggregate.

(1. fine aggregate)
Fine aggregate is made of high quality and firm natural sand, crushed sand and processed sand. The type and content of fine aggregate may be selected appropriately according to the strength of the cement hardened material to be targeted, but in the case of using crushed sand or processed sand, the treated ones of the corners or those having adjusted the particle size It is effective to use etc.
When fine aggregate with more SiO ₂ as component is used as fine aggregate, it behaves the same as SiO ₂ derived component contained in silica fume, and when the component of fine aggregate performs high temperature curing etc. However, because it reacts, it is effective for strength enhancement. More specifically, it is preferable to use a fine aggregate containing 70% or more of SiO ₂ , for example, a quartz-based aggregate such as rhyolite.

(2. Coarse aggregate)
When coarse aggregate is used as the aggregate in addition to fine aggregate, a high quality and firm coarse aggregate may be used. The largest dimension of the coarse aggregate needs to have a particle size (maximum particle size) of 20 mm or less, and preferably, the largest dimension is 15 mm or less. The rock type may be appropriately selected from general ones such as hard sandstone, andesite and rhyolite according to the target strength.

(Other ingredients)
The concrete composition may further contain other components usually used in the concrete composition, such as a water reducing agent, a retarder, an antifoaming agent and the like, depending on the purpose.

[Hardened concrete]
The concrete cured product of the present disclosure is a cured product of the concrete composition of the present disclosure described above, and has a compressive strength of at least 250 MPa at a material age of 28 days.
The cured concrete of the present disclosure contains cement, aggregate, silica fume, and water, and the concrete composition of the present disclosure mixed with a water / binder ratio (mass basis) of 0.2 or less. It can be obtained by putting it in a frame and curing it.
The molded body charged into the mold and cured can be subjected to known curing. By curing, the strength of the obtained cured concrete can be further improved.
There is no restriction | limiting in particular in the curing method of a concrete molded object, A well-known curing method can be suitably selected and applied according to the intended purpose etc. of a hardening object.
As a known curing method, for example, atmospheric pressure steam curing performed in a temperature range of 70 ° C. to 100 ° C. for 2 hours to 72 hours, heat curing heated in a temperature range of 100 ° C. to 400 ° C. for 2 hours to 72 hours, in an autoclave And high pressure steam curing under high pressure conditions.
The cured concrete, which is a cured product of the concrete composition of the present disclosure having a water / binder ratio of 0.2 or less on a mass basis by performing known steam curing, has a compressive strength of 250 MPa or more at a material age of 28 days Become a high-strength cured product.

In the production of a cured concrete, first, the above-mentioned concrete composition is uniformly mixed to prepare a fluid slurry.
The mixing can be carried out by a conventional method. That is, it is a method of preparing a slurry by charging and mixing cement, aggregate, silica fume, water and other additives optionally added to a mixer. In addition, first, after mixing the aggregate, cement and silica fume are added and mixed, and then the materials may be sequentially added and mixed, for example, water may be added and mixed; It is also possible to prepare a slurry by mixing and mixing% by mass to 90% by mass with water, and then charging and mixing the remaining binder.
An antifoamer, a water reducing agent, etc. may be included at the time of preparation of a slurry as needed.

The prepared slurry is introduced into a mold and hardened to form a concrete molding. After the slurry is introduced into the mold, steps such as degassing may be further performed according to a conventional method.
It is preferable not to demold until the concrete composition put into the formwork hardens with self heat generation and a concrete molded body is formed, and the hardened concrete molded body thus obtained is described above. It is preferable to be subjected to a known curing step such as
There is no particular limitation on the curing method, and a known curing method such as standard curing or steam curing may be applied. In addition, multiple curing such as steam curing and heating curing may be performed sequentially.

  Preferably, the cured concrete obtained by performing the curing step is subjected to a surface treatment step in which the surface is covered with a coating material for suppressing water dissipation and water absorption, or the surface is impregnated with a treatment agent. It is also good.

[Concrete composition]
As another embodiment of the concrete composition of the present disclosure (hereinafter sometimes referred to as a second embodiment), it comprises cement, aggregate, silica fume and water, and the water / binder ratio is on a mass basis Of the silica fume dispersed in 100 g of water, and the particle size distribution of the obtained silica fume dispersion is measured, and the 50% cumulative particle diameter of the silica fume is A. A 50% integrated particle diameter of silica fume obtained by measuring the particle size distribution of an ultrasonic dispersion liquid obtained by applying ultrasonic waves of a frequency selected from 15 kHz to 50 kHz for 540 seconds to the obtained silica fume dispersion liquid as a measurement target When it is set to B, the concrete composition whose said A and said B are the silica fume which satisfy | fills following formula (III) and Formula (IV) is mentioned.
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)

  The definitions of the above formulas (III) and (IV) in the second embodiment relate to silica fume having an average primary particle size of 0.1 μm or more and less than 1.0 μm. That is, silica fume having an average primary particle size of less than 1.0 μm tends to aggregate as compared to silica fume having an average primary particle size of 1.0 μm or more, but the larger the secondary particle size of the aggregate is, the more the fluidity is impaired. Therefore, the ratio of the 50% cumulative particle diameter A in the aqueous dispersion to the 50% cumulative particle diameter B determined after the application of ultrasonic waves, represented by the formula (III), is defined by the above-mentioned equation (I) From the above range, good dispersibility is exhibited even in the case of being larger, and the concrete composition of the second embodiment of the present disclosure also exhibits fluidity without any problem in practical use.

The cement, aggregate, water, other optional components, and the water / binder ratio that can be used in the concrete composition of the second embodiment are the same as the concrete composition of the first embodiment described above. Preferred examples are also the same. The silica fume which can be used in the concrete composition of the second embodiment is the same as the silica fume exemplified in the concrete composition of the first embodiment described above, except that the average primary particle diameter is different.
Therefore, also in the concrete composition of the second embodiment, the aggregate can take an aspect including coarse aggregate.

The concrete composition of the second embodiment of the present disclosure can form a hardened body of high strength like the concrete composition of the first embodiment described above, the concrete of the second embodiment of the present disclosure It is preferable that the concrete cured body which is a hardened | cured material of a composition is 250 MPa or more in compressive strength in 28 days of material age similarly to the hardened | cured material of the concrete composition of 1st embodiment of this indication as stated above.
Such a hardened concrete body contains cement, aggregate, silica fume and water, and the concrete composition according to the second embodiment of the present disclosure has a water / binder ratio (mass basis) of 0.2 or less. The materials can be mixed, introduced into a mold, and cured.

[Evaluation method of silica fume]
Next, the evaluation method of the silica fume of this indication is described. In the method of evaluating silica fume according to the present disclosure, when particles having an average primary particle size of 1.0 μm or more and 2.0 μm or less are used (first embodiment) and an average primary particle size of silica fume used is 0 In the case of using particles of 1 μm or more and less than 1.0 μm (second embodiment), evaluation is performed using different evaluation criteria.
First, a first embodiment of the silica fume evaluation method of the present disclosure will be described.

In the first embodiment of the method for evaluating silica fume, 1 g of silica fume is dispersed in 100 g of water, and the 50% cumulative particle diameter of silica fume obtained by measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A. The ultrasonic dispersion obtained by applying ultrasonic waves of a frequency selected from 15 kHz to 50 kHz to the obtained silica fume dispersion for 540 seconds is a measurement target, and the 50% cumulative particle diameter of the silica fume obtained by measuring the particle size distribution is And B includes confirming whether or not A and B satisfy the following formulas (I) and (II).
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)

The particle size distribution measurement of the silica fume contained in the dispersion liquid can be performed according to the method of the laser diffraction scattering type using a micro track bell product MT3300EXII apparatus. The measurement is performed at normal temperature: 25 ° C. The particle size distribution is on a number basis.
As shown in the formula (II), the definition represented by the formula (I) is an evaluation method applied to silica fume particles having a 50% integrated particle size of 1.0 μm or more and 2.0 μm or less.

In the silica fume satisfying the above formula (I), the 50% cumulative particle diameter of the silica fume obtained from the particle size distribution before and after crushing the aggregate by applying ultrasonic waves does not change significantly, and the ultrasonic wave is not Even when not applied, it means that there is almost no secondary aggregate, and each particle maintains a good monodispersed state. Therefore, it is evaluated that the silica fume which satisfies the above-mentioned formula (I) can be expected to obtain good fluidity by using it as it is in a concrete composition without special treatment.
On the other hand, when the formula (I) is not satisfied, it is indicated that the silica fume is a larger secondary aggregate before ultrasonication, and such a silica fume is contained as it is in a concrete composition. Water is first adsorbed inside the silica fume aggregate, and it is evaluated that a decrease in fluidity is a concern due to the secondary aggregate.
As the value of [A / B] in the formula (I) is closer to 1.0, the average particle size before and after the application of ultrasonic waves, that is, there is no fluctuation of the peak value in the particle size distribution, and the dispersion state of untreated silica fume It shows that it is good.

In addition, as in the below-mentioned Example, time to give ultrasonic vibration was evaluated by 180 seconds, 360 seconds, and 540 seconds. As a result, the same tendency was observed in all cases, and it was confirmed that the dispersion state of silica fume can be estimated before and after the application of ultrasonic vibration.
In the present disclosure, data after application of ultrasonic vibration for 540 seconds, in which the case of evaluation with an aqueous dispersion without ultrasonic vibration application is most prominent, is adopted as an evaluation criterion.

The value of [A / B] in the formula (I) has a more preferable range depending on the average particle size of the silica fume. The smaller the particle size, the easier the aggregation, and the larger the particle size, the smaller the cohesiveness. Therefore, it is preferable to select the value of A / B appropriately according to the particle size.
For example, when the average particle size of silica fume is relatively large, ie, 1.0 μm or more and 2.0 μm or less, and the 50% integrated particle size is relatively large, that is, when the formula (II) described above is satisfied, the aqueous dispersion described above is The relationship [A / B] between the 50% integrated particle size A measured as a target and the 50% integrated particle size B measured for an ultrasonic dispersion preferably satisfies the following formula (I-2) It is more preferable to satisfy the formula (I-3).
[A / B] ≦ 4 Formula (I-2)
[A / B] ≦ 3 formula (I-3)

Next, a second embodiment of the silica fume evaluation method of the present disclosure will be described.
In a second embodiment of the method for evaluating silica fume, 50% integrated particle diameter of silica fume obtained by measuring 1% of silica fume dispersion obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution of the obtained silica fume dispersion is A. The ultrasonic dispersion obtained by applying ultrasonic waves of a frequency selected from 15 kHz to 50 kHz to the obtained silica fume dispersion for 540 seconds is a measurement target, and the 50% cumulative particle diameter of the silica fume obtained by measuring the particle size distribution is It is an evaluation method of silica fume including confirming whether said A and said B satisfy following formula (III) and a formula (IV), when it is referred to.
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)

Also, when the 50% cumulative particle size of silica fume is 0.1 μm or more and less than 1.0 μm, that is, when the formula (IV) is satisfied, the average particle size A measured for the aqueous dispersion described above and The relationship [A / B] with the average particle diameter B measured for the acoustic dispersion liquid satisfies the formula (III) described above and preferably satisfies the formula (IV-2).
[A / B] ≦ 200 formula (IV-2)

  As described above, according to the silica fume evaluation method of the present disclosure, a large amount of equipment is not required, and for example, commercially available silica fume has a low water / binder ratio and high strength concrete hardening by a simple method. An assessment can be made as to whether it is suitable for the preparation of concrete compositions from which the body can be produced.

[Method of producing concrete composition]
Next, a method of producing the concrete composition of the present disclosure will be described. In the method of producing a concrete composition of the present disclosure, when particles having an average primary particle size of 1.0 μm to 2.0 μm are used (first embodiment), an average primary particle of silica fume used is used. In the case of using particles having a diameter of 0.1 μm or more and less than 1.0 μm (the second embodiment), it is a production method of producing a concrete composition using the selected silica fume, which is evaluated based on different evaluation criteria.
First, a first embodiment of the method for producing a concrete composition of the present disclosure will be described.

1st embodiment of the manufacturing method of the concrete composition of this indication disperse | distributes 1 g of silica fume in 100 g of water, 50% integrated particle size of the silica fume obtained by measuring a particle size distribution by making the obtained silica fume dispersion liquid into a measuring object 50% of the silica fume obtained by measuring the particle size distribution by using an ultrasonic dispersion having a diameter of A and applying ultrasonic waves of a frequency selected from 15 kHz to 50 kHz for 540 seconds to the obtained silica fume dispersion When the cumulative particle diameter is B, it has a step of selecting silica fume in which the A and B satisfy the following formula (I) and formula (II):
A method of producing a concrete composition comprising cement, aggregate, silica fume and water, wherein a water / binder ratio is 0.2 or less on a mass basis.
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)

That is, prior to the production of a concrete composition containing cement, aggregate, silica fume and water, and having a water / binder ratio of 0.2 or less on a mass basis, first, 1 g of silica fume used is added to 100 g of water The 50% cumulative particle diameter of the silica fume obtained by dispersing and measuring the particle size distribution with the obtained silica fume dispersion as the measurement object is A, and the obtained silica fume dispersion has an ultra-high frequency selected from 15 kHz to 50 kHz. Assuming that a 50% integrated particle size of silica fume obtained by measuring an ultrasonic dispersion to which a sound wave is applied for 540 seconds is a measurement target, and B represents the following formula (I) and the following formula (I) The silica fume satisfying the formula (II) is selected.
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)

In the case where silica fume having relatively 50% cumulative particle diameter of 1.0 μm or more and 1.0 μm or less and 2.0 μm or less is used as the silica fume by passing through the above steps, the water / binder ratio is 0.2 or less on a mass basis It is possible to select a silica fume suitable for the production of a concrete composition capable of producing a high strength hardened body.
Therefore, by including the silica fume selected through the above-described steps, it is possible to easily manufacture a concrete composition which is excellent in fluidity at the time of driving and which can manufacture a high-strength hardened concrete.

Next, a second embodiment of the method for producing a concrete composition of the present disclosure will be described.
In the second embodiment of the method for producing a concrete composition, the 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target The ultrasonic dispersion obtained by applying ultrasonic waves of a frequency selected from 15 kHz to 50 kHz to the obtained silica fume dispersion for 540 seconds is used as a measurement target, and the 50% cumulative particle diameter of silica fume obtained by measuring particle size distribution Where A and B each have a step of selecting a silica fume satisfying the following formulas (III) and (IV): cement, aggregate, silica fume, and water; It is a manufacturing method of the concrete composition whose ratio of binder / binder is 0.2 or less on a mass basis.
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)

In the case of using silica fume having relatively fine particles with a 50% integrated particle size of 0.1 μm or more and less than 1.0 μm as the silica fume, the water / binder ratio is 0.2 or less on a mass basis by passing through the above steps. Suitable silica fumes can be selected for the production of concrete compositions which can produce certain high strength hardened bodies.
Therefore, by including the silica fume selected through the above-described steps, it is possible to easily manufacture a concrete composition which is excellent in fluidity at the time of driving and which can manufacture a high-strength hardened concrete.

  The materials used in the method of producing a concrete composition of the present disclosure are the same as the materials described in the section of the concrete composition of the present disclosure described above, and preferred embodiments are also the same.

The method of producing a concrete composition of the present disclosure can include other steps applied to the production of a general concrete composition.
That is, water is mixed in an appropriate amount with respect to cement, aggregate, and silica fume selected in the above step to prepare a concrete composition having a water / binder ratio (mass basis) of 0.2 or less. At this time, additives such as an antifoaming agent and a water reducing agent may be contained, if necessary.
The prepared concrete composition can be introduced into a formwork, hardened to form a concrete molded body, and cured, whereby it can be used for the production of the above-described hardened concrete body.

Since the concrete composition obtained by the production method of the present disclosure contains good silica fume in a dispersed state, it is possible to rapidly and uniformly mix even when the water / binder ratio is low to obtain a fluid slurry. it can.
The mixing can be carried out by a conventional method. That is, it is a method of preparing a slurry by charging and mixing cement, aggregate, silica fume, water and other additives optionally added to a mixer. At this time, coarse aggregate may be blended as aggregate.
The concrete composition obtained by the manufacturing method of the present disclosure has a water / binder ratio of 0.2 or less, but contains silica fume which is excellent in dispersibility and hardly contains secondary aggregates. Excellent flowability, uniformly injected into the mold.

  Since the concrete composition of the present disclosure is excellent in fluidity even when the water / binder ratio is 0.2 or less, it can be rapidly added to the form, and furthermore, as described above, the concrete composition of the present disclosure Hardened concrete obtained from materials is uniform and high in strength. Further, silica fume suitable for such a concrete composition can be easily selected by the silica fume evaluation method of the present disclosure.

  EXAMPLES Hereinafter, although the evaluation method of the silica fume of this indication, the manufacturing method of a concrete composition, a concrete composition, and a hardened | cured material are further explained in detail with an example, this indication is not restrict | limited to the following description. .

(Example 1, Comparative Examples 1 and 2)
[Composition of concrete composition]
<Material used>
(cement)
Cement: Low heat portland cement
(Brand name: Ube Mitsubishi Cement Co., Ltd., density: 3.24 g / cm ³ )
(Silica fume)
Silica fume A: SF-Silicafume (trade name: manufactured by Sakai Industry Co., Ltd., average particle size 0.15 μm, silicon dioxide content: 95% by mass, BET specific surface area: 7 m ² / g, density 2.3 g / cm ³ )
Silica fume B: SF-AN (trade name: manufactured by Sakai Industry Co., Ltd., average particle size 0.15 μm, silicon dioxide content: 95% by mass, BET specific surface area: 14 m ² / g, density 2.2 g / cm ³ )
Silica fume C: AGCSF (trade name: manufactured by Asahi Glass Ceramics Co., Ltd., average particle size 0.15 μm, silicon dioxide content: 95% by mass, BET specific surface area: 11 m ² / g, density 2.2 g / cm ³ )
(water)
Water: Tap water (fine aggregate)
Fine aggregate: Quartz-based fine aggregate (particle size D50: 212 μm, density: 2.6 g / cm ³ )
(Other additives)
Admixture: Carboxylic acid-based high performance water reducing agent: SSP-104T, trade name: manufactured by Takemoto Yushi Co., Ltd. Defoamer: AFK-2, trade name: manufactured by Takemoto Yushi Co., Ltd.

Table 1 below shows the preparation conditions of the concrete compositions of Examples and Comparative Examples. The details of each material used for the preparation are as described above.
In Table 1 below, “C ×” in the content indicates that the content ratio of each component to cement (abbreviated as C), and “S / C” indicates the content ratio of fine aggregate / cement. Show.

[Evaluation of silica fume]
(1. Shape observation by SEM)
With respect to the above silica fume A, silica fume B and silica fume C, a small amount of particles of 0.1 g or less is attached to a carbon tape (Nisshin EM Co., Ltd. product, NEMTAPE: trade name) of 5 mm × 5 mm in size. An SEM image (20,000 ×) was taken using a resolution scanning electron microscope (SU 8230, manufactured by Hitachi High-Technologies Corp.) to observe the particle shape.

FIG. 1 is a SEM photograph of silica fume A. From FIG. 1, it was confirmed that silica fume A is a particle group having a wide particle diameter of about 0.1 μm to about 10 μm. Almost all the particles that can be observed at the viewing angle were confirmed to be spherical particles, and the ratio of spherical particles to the total particles observed was over 99%. Thus, it can be seen that silica fume A is a silica fume compatible with the concrete composition of the present disclosure.
Using silica fume A, the concrete composition of Example 1 was prepared by the method described later according to the recipe of Table 1.

FIG. 2 is a SEM photograph of silica fume B. From FIG. 2, it was confirmed that silica fume B is a particle group having a wide particle diameter of about 0.1 μm to about 10 μm. As for particles that can be observed at a viewing angle, spherical particles were deformed or aggregated, and it was confirmed that a large number of non-spherical particles were present, and the ratio of spherical particles to all particles observed was 70% or less. Thus, it can be seen that silica fume B is a silica fume that is not compatible with the concrete composition of the present disclosure.
The concrete composition of Comparative Example 1 was prepared by the method described later according to the recipe of Table 1 using silica fume B.

FIG. 3 is a SEM photograph of silica fume C. From FIG. 3, it was confirmed that the silica fume C is a particle group having a wide particle diameter of about 0.1 μm to about 10 μm. With respect to particles that can be observed at a viewing angle, spherical particles were deformed or aggregated, and it was confirmed that a large number of non-spherical particles were present, and the ratio of spherical particles to the total particles observed was 85% or less. Thus, it can be seen that silica fume C is a silica fume that is not compatible with the concrete composition of the present disclosure.
Using silica fume C, a concrete composition of Comparative Example 2 was prepared by the method described later according to the recipe of Table 1.

(2. Evaluation by average particle size from particle size distribution)
1 g of each of the above silica fume A, silica fume B and silica fume C was dispersed in 99 g of water and stirred to prepare an aqueous dispersion of silica fume.
The particle size distribution of the obtained aqueous dispersion was measured using a laser diffraction type particle size distribution analyzer (manufactured by Micro Track Bell Co., Ltd., MT3300EXII).
Next, after applying ultrasonic vibration of 40 kHz for 180 seconds to the obtained aqueous dispersion of silica fume using MT3300EXII manufactured by Micro Track Bell Co., Ltd., the particle size is the same as the method for the aqueous dispersion. The distribution was measured. The particle size distribution was similarly measured by changing the time of applying ultrasonic vibration to 360 seconds and 540 seconds. The laser diffraction type particle size distribution analyzer used in the evaluation is an apparatus having a function of applying ultrasonic waves to the dispersion.

First, silica fume A was evaluated.
These results are shown in the graph of FIG.
The average particle diameter based on the peak particle diameter obtained from the particle size distribution is shown in Table 2 below.
From the results of FIG. 4 and Table 2, in the case of silica fume A, the average particle diameter A obtained from the particle size distribution of the aqueous dispersion is 1.676 μm and the average particle size obtained after applying ultrasonic waves for 540 seconds The particle size B is 1.597 μm, and the value of [average particle size A / average particle size B] is 1.052, which satisfies the condition of the formula (I) defined by the silica fume evaluation method of the present disclosure. I understand that.
Further, from the dispersed state in the graph of FIG. 4, the silica fume A confirmed from FIG. 4 as being within the scope of the present disclosure according to the evaluation method of the above-mentioned silica fume is shown in FIG. It can be seen that most of the particles in the viewing angle are silica fume A, which is spherical particles.

Next, silica fume B was evaluated in the same manner as silica fume A.
The results for silica fume B are shown in the graph of FIG.
The average particle diameter based on the peak particle diameter obtained from the particle size distribution is shown in Table 2 below.
From the results of FIG. 5 and Table 2, in the case of silica fume B, the average particle diameter A obtained from the particle size distribution of the aqueous dispersion is 25.74 μm, and after applying ultrasonic waves for 540 seconds, the average particle size obtained from the particle size distribution The particle diameter B is 1.443 μm, and the value of [average particle diameter A / average particle diameter B] is 17.838, which satisfies the condition of the formula (I) defined by the silica fume evaluation method of the present disclosure. I understand that there is not.
The silica fume B having the dispersed state as shown in FIG. 5 is the same as the particles observed in the SEM photograph of FIG. 2, and it can be seen that it contains many aggregates.

Silica fume C was evaluated in the same manner as silica fume A.
The results for silica fume C are shown in the graph of FIG.
The average particle diameter based on the peak particle diameter obtained from the particle size distribution is shown in Table 2 below.
From the results of FIG. 6 and Table 2, in the case of silica fume C, the average particle diameter A obtained from the particle size distribution of the aqueous dispersion is 14.3 μm and the average particle size obtained after applying ultrasonic waves for 540 seconds The particle size B is 1.584 μm, the value of [average particle size A / average particle size B] is 9.028, and the condition of the formula (I) defined by the method for evaluating silica fume of the present disclosure is satisfied. I understand that there is not.
Silica fume C having a dispersed state as shown in FIG. 6 is the same as the particles observed in the SEM photograph of FIG. 3 and although somewhat better than silica fume B, it can be seen that aggregates are also observed .

From these results, it can be seen that the 50% integrated particle size (B) obtained after application of ultrasonic waves satisfies the above-mentioned formula (II) for all of the silica fumes A, B and C.
Furthermore, it was confirmed that the silica fume A satisfying the value of the above-mentioned formula (I) does not form aggregates even in the aqueous dispersion.
On the other hand, silica fume B and silica fume C, which do not satisfy formula (I), form aggregates of about 20 μm to 40 μm in the aqueous dispersion prior to application of ultrasonic vibration, and are used as they are in concrete compositions Is found to be unsuitable.

<Preparation of Concrete Composition>
(1. Preparation of slurry)
According to the preparation conditions of the concrete composition described in Table 1 above, Hobart mixer (HL-200 manufactured by Hobart Japan Co., Ltd .: trade name, volume: water, cement, aggregate, and respective amounts of silica fume). The slurry was prepared by stirring for 10 minutes at a speed of 270 rpm (rotational speed / minute) after charging the whole amount using 10 L (liter).

(2. Physical property evaluation of slurry)
Table flow of the obtained slurry was measured according to JIS R5201 (2015). The results are shown in Table 3 below.
The target value of the table flow was 200 mm, and the slurries of the concrete compositions of Example 1, Comparative Example 1 and Comparative Example 2 all achieved the target value, and showed fluidity with no problem in practical use.

(3. Production of a cured product)
The obtained slurry was introduced into a cylindrical mold having a diameter of 50 mm and a height of 100 mm, and defoaming was performed by penetrating the rod and moving it up and down.
This was left to stand for 5 to 7 days to be naturally cured, and after confirming the curing, it was taken out from the mold and a molded body was obtained.
The obtained molded product was heated to a maximum temperature of 90 ° C. at a temperature rising rate and a temperature falling rate of 10 ° C./hr, and steam curing was performed for 72 hours to obtain a cured concrete.

(4. Strength test of hardened concrete)
Based on JIS A 1108 (2006), the compressive strength of a material having a material age of 28 days was measured according to JIS A 1108 (2006). The results are shown in Table 3.
In addition, in the concrete composition of the prescription of Table 1, the cement was not substituted to silica fume, ie, the concrete composition which does not contain silica fume was prepared, and the result evaluated like Example 1 is a table as a reference example. It is written along with 3.

From Table 3, it became clear that the slurry by the concrete composition of Example 1 showed favorable fluidity | liquidity, and the obtained hardened | cured material showed very high compressive strength with 292 Mpa.
On the other hand, although the slurries of the concrete compositions of Comparative Example 1 and Comparative Example 2 also exhibited fluidity with no problem in practical use, they have lower values than the fluidity in Example 1, and the compression of the obtained cured body The strength was also inferior to the cured body obtained by the concrete composition of Example 1.
From these results, it can be seen that by selecting silica fume that does not contain aggregates, good fluidity of the slurry is achieved and the strength of the resulting cured product is higher.
In addition, silica fume which does not contain aggregates, which show a dispersion state suitable for preparation of a concrete composition, is simply evaluated from the calculation result of the average particle diameter obtained by the particle size distribution before and after the ultrasonic wave application of the water dispersion. It turns out that it can choose.

(Examples 2, 3 and Comparative Example 3)
[Composition of concrete composition]
<Material used>
(cement)
Cement: Low heat portland cement
(Brand name: Ube Mitsubishi Cement Co., Ltd., density: 3.24 g / cm ³ )
(Silica fume)
Silica fume D: sf-r (average particle size 0.15 μm, silicon dioxide content: 95% by mass, BET specific surface area: 19 m ² / g, density 2.3 g / cm ³ )
Silica fume E: micro silica 940 U, average particle size 0.15 μm, silicon dioxide content: 95% by mass, BET specific surface area: 23 m ² / g, density 2.3 g / cm ³ )
Silica fume F: Micro silica 971 U, average particle size 0.15 μm, silicon dioxide content: 95% by mass, BET specific surface area: 23 m ² / g, density 2.3 g / cm ³ )
(water)
Water: Tap water (fine aggregate)
Fine aggregate: Quartz-based fine aggregate (particle size D50: 212 μm, density: 2.6 g / cm ³ )
(Other additives)
Admixture: Carboxylic acid-based high performance water reducing agent: SSP-104T, trade name: manufactured by Takemoto Yushi Co., Ltd. Defoamer: AFK-2, trade name: manufactured by Takemoto Yushi Co., Ltd.

The preparation conditions of the concrete composition of Example 2, Example 3, and Comparative Example 3 are shown in Table 4 below. The details of each material used for the preparation are as described above.
In Table 1 below, “C ×” in the content indicates that the content ratio of each component to cement (abbreviated as C), and “S / C” indicates the content ratio of fine aggregate / cement. Show.

[Evaluation of silica fume]
(1. Evaluation by average particle size from particle size distribution)
1 g of each of the above silica fume D, silica fume E and silica fume F was dispersed in 99 g of water and stirred to prepare an aqueous dispersion of silica fume.
The particle size distribution of the obtained aqueous dispersion was measured using a laser diffraction type particle size distribution analyzer (manufactured by Micro Track Bell Co., Ltd., MT3300EXII).
Next, after applying ultrasonic vibration of 40 kHz for 540 seconds to the obtained aqueous dispersion of silica fume using MT3300EXII manufactured by Micro Track Bell Co., Ltd., the particle size is the same as the method for the aqueous dispersion. The distribution was measured to obtain 50% cumulative particle size.

  In addition, it is possible to adjust the ultrasonic frequency which is more likely to resonate. By using an ultrasonic homogenizer us-150t (trade name) manufactured by Nippon Seiki Seisakusho Co., Ltd. The particle size distribution was similarly measured by applying ultrasonic vibration for a second to obtain a 50% integrated particle size. When this is compared with the result measured by the laser diffraction type particle size distribution analyzer obtained above, almost the same result is obtained, and according to the ultrasonic vibration applying apparatus, the same result is obtained at a shorter ultrasonic application time. It was suggested that it could be obtained.

First, silica fume D was evaluated.
The 50% cumulative particle size obtained from the particle size distribution is shown in Table 3 below.
From the results of Table 3, in the case of silica fume D, the 50% integrated particle size A obtained from the particle size distribution of the aqueous dispersion is 50 μm, and 50% integrated particle size B obtained from the particle size distribution after applying ultrasonic waves. Is 0.29 μm, the value of [A / B] is 172, and it is understood that any condition of the formula (III) and the formula (IV) defined by the evaluation method of silica fume of the present disclosure is satisfied. .

Next, silica fume E was evaluated in the same manner as silica fume D.
The 50% cumulative particle size obtained from the particle size distribution is shown in Table 5 below.
From the results of Table 5, in the case of silica fume E, the 50% integrated particle size A obtained from the particle size distribution of the aqueous dispersion is 90 μm and 50% integrated particles obtained from the particle size distribution after applying ultrasonic waves for 540 seconds. The diameter B is 0.5 μm, the value of [A / B] is 180, and any condition of the formula (III) and the formula (IV) defined by the evaluation method of silica fume of the present disclosure is satisfied. I understand.

Silica fume F was evaluated in the same manner as silica fume D.
The 50% cumulative particle size obtained from the particle size distribution is shown in Table 5 below.
From the results of Table 5, in the case of silica fume F, the average particle size A obtained from the particle size distribution of the aqueous dispersion is 150 μm, and after applying ultrasonic waves for 540 seconds, the average particle size B obtained from the particle size distribution is 0.45 μm, the value of [A / B] is 333 and the condition of the formula (III) defined by the evaluation method of silica fume of the present disclosure is satisfied, but the condition of the formula (IV) is not satisfied Recognize.

From these results, it was confirmed that neither silica fume D nor silica fume E formed excessive aggregates in the aqueous dispersion.
On the other hand, silica fume F has a diameter of 300 times or more that of primary particles in an aqueous dispersion prior to application of ultrasonic vibration, and the formation of aggregates is remarkable, and is not suitable for use in concrete compositions as it is I understand.

<Preparation of Concrete Composition>
(1. Preparation of slurry)
According to the preparation conditions of the concrete composition described in Table 1 above, Hobart mixer (HL-200 manufactured by Hobart Japan Co., Ltd .: trade name, volume: water, cement, aggregate, and respective amounts of silica fume). The slurry was prepared by stirring for 10 minutes at a speed of 270 rpm (rotational speed / minute) after charging the whole amount using 10 L (liter).

(2. Physical property evaluation of slurry)
Table flow of the obtained slurry was measured according to JIS R5201 (2015). The results are shown in Table 6 below.
The target value of the table flow was 200 mm, and the slurries of the concrete compositions of Example 1, Comparative Example 1 and Comparative Example 2 all achieved the target value, and showed fluidity with no problem in practical use.

(3. Production of a cured product)
The obtained slurry was introduced into a cylindrical mold having a diameter of 50 mm and a height of 100 mm, and defoaming was performed by penetrating the rod and moving it up and down.
This was left to stand for 5 to 7 days to be naturally cured, and after confirming the curing, it was taken out from the mold and a molded body was obtained.
The obtained molded product was heated to a maximum temperature of 90 ° C. at a temperature rising rate and a temperature falling rate of 10 ° C./hr, and steam curing was performed for 72 hours to obtain a cured concrete.

(4. Strength test of hardened concrete)
Based on JIS A 1108 (2006), the compressive strength of a material having a material age of 28 days was measured according to JIS A 1108 (2006). The results are shown in Table 6.

From Table 6, it became clear that the slurry by the concrete composition of Example 2 and Example 3 showed favorable fluidity, and the obtained hardened body showed higher compressive strength than Comparative Example 3. .
On the other hand, although the slurry by the concrete composition of Comparative Example 3 also showed fluidity with no problem in practical use, it is a value lower than the fluidity in Examples 2 and 3 and the compression of the obtained cured body The strength was also inferior to the hardened body obtained by the concrete composition of Example 2 and Example 3.
From these results, even if it is fine silica fume having a 50% cumulative particle size of less than 1.0 μm, do not contain aggregates, or select silica fume whose inclusion degree is within the allowable range. It can be seen that good fluidity of the slurry is achieved and the strength of the resulting cured body is higher.
In addition, an average particle size distribution obtained before and after ultrasonication of the aqueous dispersion is obtained that does not contain aggregates, or contains an acceptable range of silica fume, which exhibits a dispersion state suitable for preparation of a concrete composition. From the calculation result of the particle diameter, it is understood that it can be easily evaluated and selected.

Claims (10)

A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and 15 kHz to 50 kHz in the silica fume dispersion obtained above When an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from among the above is applied for 540 seconds is used as a measurement target and 50% cumulative particle diameter of silica fume obtained by measuring particle size distribution is B, The evaluation method of the silica fume including confirming whether it satisfy | fills following formula (I) and Formula (II).
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II) A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and 15 kHz to 50 kHz in the silica fume dispersion obtained above When an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from among the above is applied for 540 seconds is used as a measurement target and 50% cumulative particle diameter of silica fume obtained by measuring particle size distribution is B, Selecting a silica fume satisfying the following formulas (I) and (II):
A method of producing a concrete composition comprising cement, aggregate, silica fume and water, wherein a water / binder ratio is 0.2 or less on a mass basis.
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II) Containing cement, aggregate, silica fume and water, the water / binder ratio is 0.2 or less on a mass basis,
The 50% cumulative particle diameter of the silica fume obtained by measuring the particle size distribution by using 1 g of the silica fume dispersed in 100 g of water and measuring the particle size distribution with the silica fume dispersion as the measurement target is A, and the silica fume dispersion obtained above The ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds is a measurement target, and the 50% cumulative particle diameter of silica fume obtained by measuring the particle size distribution is B. The concrete composition whose said B is a silica fume which satisfy | fills following formula (I) and Formula (II).
[A / B] ≦ 5.0 Formula (I)
1.0 μm ≦ B ≦ 2.0 μm Formula (II)   The concrete composition according to claim 3, wherein when the silica fume is observed with a scanning electron microscope, the ratio of spherical particles to all particles of silica fume included in a viewing angle is 90% or more. Said silica fume is
The ratio of particles having a particle size of 0.1 μm or more and 10 μm or less to all the particles of silica fume is 90% or more,
The concrete composition according to claim 3 or 4, wherein the average particle diameter obtained by the particle size distribution measurement is 0.2 μm or more and 1.5 μm or less.   The concrete composition according to any one of claims 3 to 5, wherein the aggregate comprises coarse aggregate.   It is a hardened | cured material of the concrete composition of any one of Claims 3-6, The concrete hardened body whose compressive strength in 28 days of materials is 250 Mpa or more.
A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and 15 kHz to 50 kHz in the silica fume dispersion obtained above When an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from among the above is applied for 540 seconds is used as a measurement target and 50% cumulative particle diameter of silica fume obtained by measuring particle size distribution is B, The evaluation method of the silica fume including confirming whether it satisfy | fills following formula (III) and Formula (IV).
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV) A 50% cumulative particle diameter of silica fume obtained by dispersing 1 g of silica fume in 100 g of water and measuring the particle size distribution with the obtained silica fume dispersion as a measurement target is A, and 15 kHz to 50 kHz in the silica fume dispersion obtained above When an ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from among the above is applied for 540 seconds is used as a measurement target and 50% cumulative particle diameter of silica fume obtained by measuring particle size distribution is B, Selecting a silica fume satisfying the following formulas (III) and (IV):
A method of producing a concrete composition comprising cement, aggregate, silica fume and water, wherein a water / binder ratio is 0.2 or less on a mass basis.
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV) Containing cement, aggregate, silica fume and water, the water / binder ratio is 0.2 or less on a mass basis,
The 50% cumulative particle diameter of the silica fume obtained by measuring the particle size distribution by using 1 g of the silica fume dispersed in 100 g of water and measuring the particle size distribution with the silica fume dispersion as the measurement target is A, and the silica fume dispersion obtained above The ultrasonic dispersion liquid to which an ultrasonic wave of a frequency selected from 15 kHz to 50 kHz is applied for 540 seconds is a measurement target, and the 50% cumulative particle diameter of silica fume obtained by measuring the particle size distribution is B. The concrete composition whose said B is a silica fume which satisfy | fills following formula (III) and Formula (IV).
[A / B] ≦ 300 Formula (III)
0.1 μm ≦ B <1.0 μm formula (IV)