JPH0891885A - Production of cement composition - Google Patents

Abstract

PURPOSE: To provide a cement composition capable of producing mortar or concrete extremely superior in fluidity. CONSTITUTION: This producing method of the cement composition is composed of totally 100 pts.wt. consisting of 50-92 pts.wt. Portland cement, 5-25 pts.wt. silica fume and 3-25 pts.wt. lime stone fine powder. In the cement production process, the silica fume is charged into a finishing mill for pulverizing cement clinker, etc., and the silica fume is mixed at the same time as pulverizing of the cement clinker, etc., and also it is dispersed and next the lime stone fine powder having a specific particle size distribution is mixed with the pulverized product produced by the finishing mill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cement composition for high strength having excellent fluidity.

[0002]

2. Description of the Related Art In order to obtain high strength concrete,
Using a high-performance water reducing agent and a high-performance AE water reducing agent (hereinafter, these two types may be collectively referred to as "high-performance water reducing agent"), the water-cement ratio should be as small as possible within the range in which the kneaded product can be compactly molded. Doing is the most effective and common method. However, if the water-cement ratio is reduced, the viscosity of the kneaded material increases, resulting in concrete with poor fluidity and workability. Further, if the water-cement ratio is reduced,
It becomes concrete that is no longer flowable and cannot be molded by ordinary pouring or compaction.

As a means for solving this, there is a method of using silica fume as an admixture. Silica fume is a by-product of the production of metallic silicon and ferrosilicon,
It is a spherical and ultrafine silica having a specific surface area of about 20 m ² / g and an average particle diameter of about 0.1 μm. By using silica fume and a high-performance water reducing agent together, the viscosity of concrete can be reduced and the fluidity can be improved, so that it is possible to produce concrete with a lower water cement ratio.

The action of this silica fume is said to be due to the ball bearing effect derived from its spherical shape.
Furthermore, since silica fume is a finer powder than cement particles, it is said that it has an effect of filling the spaces between cement particles to densify the structure of the hardened body and an effect of increasing the strength of the hardened body by the pozzolan reaction.

The effect of improving the fluidity and the effect of increasing the strength by the silica fume are remarkable when the water-cement ratio is small. Therefore, compressive strength 800 kgf / cm ²
At present, the most effective and general method is to use silica fume as an admixture and add a high-performance water-reducing agent as a technique for imparting fluidity in high-strength concrete with a low water cement ratio of at least a certain level. .

However, compared with general concrete of ordinary strength, it has a large viscosity and is inferior in pumpability and workability. Therefore, there is a strong demand for the development of concrete with lower viscosity, and there is an example in which fly ash or blast furnace slag fine powder is used as an admixture to reduce viscosity and improve pumpability and workability.

Silica fume comes in three forms: powder, granules and slurries. Slurry silica fume has problems that silica fume easily precipitates, its concentration is difficult to control, and it may be frozen in winter. Furthermore, when applied to high-strength concrete, since the amount of cement is large and the amount of water is small compared to that, the silica fume slurry must have a high concentration, but as a result, it becomes a slurry with strong viscosity and Not practical for plant applications. Therefore, the silica fume that is practically used is a powdery or granular silica fume.

[0008] Granular silica fume has the advantage that it can be used with the same transportation, metering, and charging equipment as powder materials such as cement, but it is inferior in dispersibility because it is a granule as compared with powdery silica fume, and it can be used in concrete. Poor improvement in fluidity and strength.

[0009] Although powdery silica fume has an excellent effect of improving fluidity and strength as compared with granules, it is difficult to handle because it is an ultrafine powder, so existing transportation, metering and addition equipment for a concrete manufacturing plant can be used as it is. Used and cannot be added to the mixer. Therefore, the concrete mixer is put into the concrete mixer manually or by newly installing special addition equipment.

[0010]

The most general and effective method for increasing the strength of concrete is to reduce the water-cement ratio as much as possible within the range where compact molding is possible. If silica fume and a high-performance water reducing agent are used together, it is possible to produce concrete with a lower water cement ratio, and in high strength concrete with a low water cement ratio of compressive strength of about 800 kgf / cm ² or more,
As a technique for imparting fluidity, a method of using silica fume as an admixture and adding a high-performance water reducing agent is currently the most effective and general method. However, there are the following problems.

Dispersion of Silica Fume Since silica fume is ultrafine particles, it is usually in an aggregated state. At first glance, not only granular silica fume but also powdery silica fume seems to have a small degree of aggregation, but it is an aggregate of ultrafine particles. Unless these aggregated silica fumes are sufficiently dispersed in concrete, the effects of improving fluidity and strength cannot be effectively obtained.

Kneadability The conventional method of adding silica fume to Portland cement has a problem of poor kneadability in a mixer.
In particular, the load on the mixer at the initial stage of kneading is extremely large until the silica fume and the superplasticizer are dispersed in the kneaded product. Therefore, in kneading with a mixer, kneading cannot be performed unless the kneading amount of one time is considerably reduced from the capacity of the mixer, and moreover, the kneading time is long in order to loosen agglomerated silica fume and disperse it in concrete sufficiently. It is necessary to take measures such as increasing the amount of high-performance water reducing agent.

Fluidity and Viscosity Although an improvement in fluidity that cannot be obtained only by using a high-performance water-reducing agent can be obtained by using silica fume, high-strength concrete containing silica fume has a large viscosity, which makes pumpability and construction difficult. In order to secure the liquidity, the slump flow must have a high fluidity of about 40 cm or more. From this, too, the amount of the high-performance water reducing agent to be added must be increased. Also, slump flow 40 cm
Even if the above is the case, concrete is still more viscous than general strength concrete, and there is a demand for concrete with lower viscosity in order to improve pumpability and workability.
Therefore, as a conventional technique, fly ash or blast furnace slag fine powder is used as an admixture to reduce viscosity, pump pumpability and workability, but there is an example in which setting is delayed and strength development is reduced. There is a problem.

Setting retardation In order to make the concrete have a low water cement ratio and fluidity, it is necessary to add a high-performance water reducing agent or a high-performance AE water reducing agent having a strong powder particle dispersing action. I won't. However, the high-performance water reducing agent and the high-performance AE water reducing agent both have a strong dispersing action and a strong setting retarding action. As a result, the setting of concrete is significantly delayed.
Moreover, the lower the water-cement ratio, the larger the amount of the high-performance water reducing agent used to obtain fluidity, and the larger the delay in setting. If the delay in setting is large, there is a problem that cracks and other defects are likely to occur in the concrete due to the effects of the load being applied to the formwork for a long time and the sinking of the concrete being large. In addition, there is a problem that it interferes with the next construction process.

Manufacturing cost The kneading property of concrete is poor, the kneading amount in the mixer is small, and the kneading must be performed for a long time.
Further, since it is necessary to add a large amount of expensive high-performance water-reducing agent, there arises a problem that productivity of concrete decreases, supply capacity of concrete decreases, and manufacturing cost increases.

Silica Fume Addition Method Prior art powdered silica fume or granular silica fume is added to the concrete mixer in batches together with other concrete materials. Granular silica fume can be used with conventional cement and admixture transportation and metering equipment, but it is inferior in dispersibility because it is granules compared to powdery silica fume, and it has the effect of improving the fluidity and strength properties of concrete. Inferior. The powdery silica fume has an excellent effect of improving the fluidity and the strength as compared with the granular form, but since it is an ultrafine powder, it has poor handling and cannot be used as it is with the existing conveying and measuring devices. Therefore, it is necessary to manually load or newly install a special transfer and weighing device.

[0017]

A method for producing a cement composition according to claim 1 is such that 50 to 92 parts by weight of Portland cement, 5 to 25 parts by weight of silica fume, and limestone fine powder 3 are used.
A method for producing a cement composition containing 25 to 25 parts by weight in total of 100 parts by weight, wherein silica fume is added to a finishing mill in which cement clinker and the like are crushed in the cement manufacturing process, and the cement clinker is added. Silica fume is mixed and dispersed at the same time as pulverization such as, and then limestone fine powder having a specific particle size distribution is mixed with a pulverized product produced by a finishing mill.

The method for producing the cement composition according to claim 2 is
A method for producing a cement composition comprising 50 to 92 parts by weight of Portland cement, 5 to 25 parts by weight of silica fume, and 3 to 25 parts by weight of fine limestone powder in a total amount of 100 parts by weight, which is a finishing mill. It is characterized in that pulverized Portland cement is mixed with silica fume and limestone fine powder having a specific particle size distribution by using a mixer.

As the Portland cement, there can be used ordinary Portland cement, early strength Portland cement, super early strength Portland cement, moderate heat Portland cement and the like.

As the limestone fine powder, according to claim 3,
Those having a particle size distribution in which 90% or more of particles of 20 μm or less, 65% or more of particles of 10 μm or less, 40% to 90% of particles of 5 μm or less, and 25% or less of particles of 1 μm or less are preferable. The fine limestone powder is preferably obtained by crushing natural limestone and then classifying the limestone to have the above particle size.

The silica fume may be used in the form of powder or granules. Further, the silica fume preferably contains SiO _{2 in an amount} of 80 parts by weight or more and has a specific surface area of 1.5 to 3.0 m ² / g measured by a nitrogen adsorption method.

[0022]

[Function] High strength concrete, especially compressive strength 800 kg
As a technique for imparting fluidity to high-strength concrete of f / cm ² or more, a method of using silica fume as an admixture and adding a high-performance water reducing agent is currently the most effective and general method.

However, even by the above method, since the viscosity is higher than that of general ordinary strength concrete, the kneading property in the mixer is poor, and the amount of the kneaded material with respect to the mixer capacity is significantly reduced, and compared with general concrete. Unless the kneading time is significantly lengthened, it is impossible to obtain concrete that is homogeneous and has sufficient fluidity. Further, in order to make the concrete have a low water-cement ratio and be fluid, it is necessary to mix silica fume and to add a high-performance water reducing agent having a strong dispersing effect of powder particles. As a result, the setting of concrete is greatly delayed due to the strong setting retarding action which the high-performance water reducing agent has at the same time as the dispersing action. Moreover, the lower the water-cement ratio, the more the amount of the high-performance water reducing agent used for obtaining the fluidity increases, which causes a problem of delaying the setting. Furthermore, the smaller the water-cement ratio, the more expensive high-performance water-reducing agent is required to obtain the fluidity, and the higher the material cost of concrete becomes.

Portland cement 50, such as the cement composition produced by the method of claim 1 or claim 2.
~ 92 parts by weight, 5 to 25 parts by weight of silica fume, and 3 to 25 parts by weight of fine limestone powder having a specific particle size distribution are used as a binder to add silica fume to Portland cement according to the prior art. The fluidity is improved as compared with the method, and the amount of the superplasticizer required to obtain a certain concrete fluidity can be reduced. In addition, when the concrete is mixed, it has the effect of shortening the time until the material is homogeneously mixed and in a fluidized state, and further has the effect of reducing the load on the mixer.

Therefore, as compared with the conventional technique of adding silica fume to Portland cement, the amount of the high-performance water reducing agent necessary for obtaining the same fluidity can be reduced, which is advantageous in terms of cost. Further, the fluidization at the time of kneading is fast and the load on the mixer can be reduced, so that the kneading amount can be increased once and the kneading time can be shortened, thus improving the productivity,
It will be industrially advantageous.

In the cement composition produced by the method according to claim 1 or 2, if the content of Portland cement is less than 50 parts by weight, the high strength developing property is deteriorated, and if it is more than 92 parts by weight. Since the proportions of silica fume and limestone fine powder are reduced, a cement composition, which is a feature of the present invention, has high strength, high flowability, good kneading properties, and no significant delay in setting cannot be obtained. A particularly preferable amount of Portland cement is 70 to 90 parts by weight.

When the amount of silica fume is less than 5 parts by weight, the effect of improving strength and fluidity due to silica fume cannot be obtained, and even when it is more than 25 parts by weight, the improvement of strength and fluidity by silica fume is 5 to 25 parts by weight. The amount tends to be lower than that of the compounded amount, and silica fume is expensive, which is uneconomical. A particularly preferable amount of silica fume is 5 to 20 parts by weight.

If the amount of the fine limestone powder blended is less than 3 parts by weight, a cement composition having high strength, high fluidity, good kneading properties and no significant delay in setting, which is a feature of the present invention, cannot be obtained. If the amount is more than 25 parts by weight, the strength developability will be poor. A particularly suitable amount of limestone fine powder is 3 to 1
2.5 parts by weight.

The fluidity-improving effect and kneading-improving effect of silica fume-added cement by this limestone fine powder are
It is remarkably expressed by the limestone fine powder having the specific particle size distribution described in claim 3. The specific particle size distribution for producing the above effect cannot be specified only by the fineness (blaine specific surface area) of the specific surface area by the air permeation method which has been conventionally performed. That is, even if the limestone fine powders have the same Blaine specific surface area but do not have the specific particle size distribution specified in claim 3,
It is not possible to obtain a remarkable effect in improving the fluidity and kneading property of the silica fume-added cement.

In order to obtain the cement composition of the present invention which has high strength, high fluidity and good kneading property, limestone fine powder is used as defined in claim 3.
Particle size distribution of the limestone fine powder specified in 1., ie, 1 μm to 1
There is a peak of frequency of particle size distribution within the range of about 0 μm,
It cannot be obtained unless it has a sharp particle size distribution in which the particle size is distributed in a relatively narrow range. The effect of the present invention can be obtained by combining the fine limestone powder having this specific particle size distribution with Portland cement and silica fume to produce a cement composition by the production method according to claim 1 or 2. Therefore, in the case where the particle size distribution specified in claim 3 is deviated, that is, there is no peak of frequency of particle size distribution within a range of about 1 μm to 10 μm, and a particle size distribution in a wide range has a flat particle size distribution. However, the cement composition of the present invention having high strength, high fluidity and good kneading properties cannot be obtained.

It is known that limestone fine powder generally has an action of promoting the setting of cement. However, the use of limestone fine powder having a specific particle size distribution and settling delay has an effect of setting the limestone fine powder originally. Due to the synergistic effect with the effect that the added amount of high-performance water reducing agent that has an effect can be reduced,
It is possible to greatly suppress the delay in setting of concrete, which has been a problem in the prior art.

When silica fume is added and a high-performance water-reducing agent is used to make a high-strength concrete having a low water-cement ratio, an inorganic substance such as limestone fine powder which is considered to have no reactivity is internally added to cause a decrease in strength. Is also concerned. However, in the present invention using the limestone fine powder having a specific particle size distribution, there is no large decrease in strength, and particularly when the addition amount of the limestone fine powder having a specific particle size distribution is 10% or less, it is equivalent to that not adding it. The above strength is exhibited.

Further, in the present invention using the limestone fine powder having the specific particle size distribution, the viscosity of the concrete becomes small, and it has an effect that the workability can be made excellent as compared with the case where it is not used.

Further, in the present invention using a limestone fine powder having a specific particle size distribution, since the limestone fine powder does not generate heat of hydration, it has an effect of reducing heat generation of concrete, and high strength concrete having a large amount of unit cement. It has the effect of suppressing the decrease in strength and the occurrence of cracks due to temperature rise, which is a problem with.

[0035]

EXAMPLES Examples of mortar and concrete using the cement composition produced according to the present invention are shown below. First, the experimental method will be described item by item.

1. Materials Used (Including Materials Used in Comparative Examples) 1.1 Materials Used in Cement Composition (1) Portland Cement NP (Normal Portland Cement) (Specific Gravity: 3.1)
6) HP (early strong Portland cement) (specific gravity: 3.1)
4) MP (moderate heat Portland cement) (specific gravity: 3.
20) (2) Silica fume: Elchem 940U (specific gravity 2.
2, BET specific surface area 2.0 m ² / g) (3) Fine limestone powder having specific particle size distribution Limestone was crushed with a ball mill and prepared to have a specific particle size distribution using a classifier.

A) Limestone fine powder having specific particle size distribution used in Examples GL: 20 μm or less 95% by weight, 10 μm or less 65% by weight, 5 μm or less 40% by weight, 1 μm or less 13% by weight. Blaine specific surface area is 5
It is 280 cm ² / g.

GL: 98 wt% when 20 μm or less,
87 wt% for 10 μm or less, 55 wt% for 5 μm or less,
Below 1 μm has a particle size distribution of 15 wt%. The Blaine specific surface area is 7730 cm ² / g.

GL: 20 wtm or less is 100 wt
%, Less than 10 μm is 99 wt%, less than 5 μm is 87 wt
%, 1 μm or less has a particle size distribution of 25 wt%. The Blaine specific surface area is 17,000 cm ² / g.

B) Limestone fine powder having no specific particle size distribution used in the comparative example BL: 66 wt% below 20 μm, 49 wt% below 10 μm, 38 wt% below 5 μm, 19 wt% below 1 μm. Blaine specific surface area is 5
It is 040 cm ² / g.

BL: 77 wt% at 20 μm or less,
62 wt% for 10 μm or less, 47 wt% for 5 μm or less,
Particle sizes of 1 μm or less have a particle size distribution of 16 wt%. The Blaine specific surface area is 7670 cm ² / g.

BL: 98 wt% of 20 μm or less,
86 wt% for 10 μm or less, 75 wt% for 5 μm or less,
Particle sizes of 1 μm or less have a particle size distribution of 32 wt%. The Blaine specific surface area is 16820 cm ² / g.

BL: 64 wt% is 20 μm or less,
40 wt% for 10 μm or less, 26 wt% for 5 μm or less,
Below 1 μm has a particle size distribution of 7 wt%. The Blaine specific surface area is 3710 cm ² / g.

1.2 Materials other than cement composition used for mortar and concrete Fine aggregates: Kisarazu mountain sand (specific gravity 2.63, water absorption 1.
77%) Coarse aggregate: Crushed stone from Hachioji (maximum size 20 mm, specific gravity 2.68, water absorption 0.83%) High-performance AE water reducing agent: polycarboxylic acid kneading water: tap water 2. Measuring method of particle size distribution of limestone fine powder having specific particle size distribution A laser diffraction / scattering particle size distribution measuring device (French CI
It was performed using LAS CILAS 850B). At the same time, the fineness (specific surface area) by the Blaine air permeation method was also measured.

3. Cement composition manufacturing method The cement composition manufacturing method is as follows.

(1) Manufacturing method 1 (example of manufacturing method of claim 2) Various powder materials such as Portland cement, silica fume and limestone fine powder are mixed with a ski type shovel impeller type high speed mixer (manufactured by Taiheiyo Kiko Co., Ltd .: Plowshare). Mixer). However, this method only shows an example of the mixer, and does not limit the type and model of the mixer.

(2) Production Method 2 (Production Method of Claim 1) In a cement factory, silica fume is supplied together with Portland cement raw materials such as clinker and gypsum to a finishing mill in the cement production process, and silica fume is mixed with Portland cement particles. The limestone fine powder having a specific particle size distribution was added to and mixed with the silica-fume mixed cement produced by mixing and dispersing with the above.

(3) Manufacturing Method 3 (Comparative Example) For the purpose of comparison, manufacturing method 3 is a conventional method in which cement, silica fume and the like are separately charged into a concrete mixer.

4. Mortar Composition The composition of the mortar used in Examples and Comparative Examples is as follows. Note that W is the amount of water, C is the amount of cement composition, and S is the amount of fine aggregate.

Formulation I: W / C = 22% S / C = 1.
4. Addition amount of high-performance AE water reducing agent: C × 1.2% Blend II: W / C = 25% S / C = 1.6 Addition amount of high-performance AE water reducing agent: C × 1.2% Mixing of concrete Mixing of concrete used in Examples and Comparative Examples is as follows.

[0051]

[Table 1]

6. Mortar kneading method For kneading the mortar, a Hobart mixer (capacity 4.7 liters) was used and kneading was performed for 3 minutes.

7. Kneading method of concrete Forcible kneading is performed by using a forced kneading pan type mixer (capacity 50 liters), and kneading is performed by mortar kneading 1
Minutes, and after the coarse aggregate was added, kneading was further performed for 2 minutes.

8. Evaluation method of various properties of mortar and concrete (1) Evaluation method of fluidity of mortar The evaluation of fluidity of mortar is made by a mini slump cone (top 5 cm in diameter, bottom 10 cm in cone shape with height 15 cm).
The final spread diameter (mini slump flow) of the mortar was evaluated when the mortar was packed in and the corn was pulled up.

(2) Method for evaluating the fluidity and viscosity of concrete The fluidity of concrete is the spread of the sample after the slump test of concrete, that is, the slump flow, when the addition amount of the high-performance AE water reducing agent is constant. It was evaluated by. When the addition amount of the high performance AE water reducing agent was adjusted so that the slump flow was 60 ± 3 cm, the fluidity was evaluated by the addition amount of the high performance AE water reducing agent. In addition, even if the slump flow is the same, the properties of concrete differ greatly depending on the viscosity. Therefore, in some cases, the O funnel flow time was measured as an index of viscosity.

(3) Method of evaluating kneadability In mortar and concrete having a low water-cement ratio, it takes some time after the kneading by the mixer is started until the fluidity of the kneaded material is exhibited. The longer this time, the heavier the load on the mixer, and the longer the kneading time. Therefore, in this example, the kneadability of concrete was evaluated by measuring the time required for the mortar material to be fluidized (mortar kneading time) in 1 minute of the mortar kneading, and used as an index of kneadability. did. That is, the shorter the kneading time of the mortar, the better the kneading property. The mortar kneading time was measured under the condition that the concrete slump flow after kneading with the amount of the high-performance AE water reducing agent was constant at 60 ± 3 cm.

(4) Setting Property of Concrete The setting property was measured according to the setting test of concrete by ASTM C 403 Proctor penetration resistance method.

(5) Compressive strength properties After kneading concrete, it was poured into a steel mold of φ10 × 20 cm and lightly tapped with a wooden hammer for compaction. The material was removed from the mold at the age of 1 day and thereafter cured in water at 20 ° C. until the age of the test material. In the compressive strength test, the loading surface is polished and the loading speed is JI
S A 1108 Concrete compressive strength test method.

9. Examples and Comparative Examples with Mortar Examples 1 to 5 and Comparative Examples 1 to 9 In a fluidity test of a mortar using a cement composition prepared by mixing Moderate heat Portland cement, silica fume and limestone fine powder for 7 minutes by the manufacturing method 1. The results are shown in Table 2.
Shown in.

Also, in Examples 5, 8 and 9 to which the comparative limestone fine powder of Table 2 was not added, the cement composition was prepared for 7 minutes by the production method 1 except that the limestone fine powder was not used. Mixed and prepared. The mortar formulation is Formula I.

[0061]

[Table 2]

From the comparison between Examples 1 to 3 and Comparative Example 5, it can be seen that the addition of fine limestone powder to the cement composition containing silica fume improves the fluidity of the cement composition containing silica fume. However, from the comparison of Examples 1 to 3 and Comparative Examples 1 to 4, even if the specific surface area of the limestone fine powder is about the same, the fluidity improving effect is greatly different, and the limestone fine powder having the specific particle size distribution of the present invention is obtained. It can be seen that the fluidity of the mixed cement composition is remarkably good.

That is, 90% or more of particles of 20 μm or less and 65% of particles of 10 μm or less in limestone fine powder.
% Or more and 5 μm or less particles are in the range of 40 to 90%, and 1 μm or less particles have a particle size distribution of 25% or less, a large fluidity improving effect is obtained, and more preferably 20 μm or less. 95% or more of particles, and 10
80% or more of particles having a size of μm or less, 50 to 90% of particles having a size of 5 μm or less, and 2% of particles having a size of 1 μm or less.
When the particle size distribution is 5% or less, a greater effect of improving fluidity can be obtained.

From the comparison between Examples 4 and 5 and Comparative Examples 8 and 9, it can be seen that, even when NP and HP other than MP are used, the fluidity improving effect can be obtained as in Examples 1 to 3. Further, from the comparison between Examples 4 and 5 and Comparative Examples 6 and 7,
In the cement composition in which the limestone fine powder having the specific particle size distribution of the present invention is mixed, it is possible to obtain remarkably good results in fluidity. Even if the specific surface area of the limestone fine powder is about the same, it does not have the specific particle size distribution of the present invention. It can be seen that the limestone fine powder does not effectively improve the fluidity.

Examples 6 to 9 and Comparative Examples 10 to 11 In the mortar, the mixing ratio of silica fume in the cement composition was changed in the range of 0 to 30 parts by weight, and the strength properties were examined. The cement composition was manufactured by mixing and preparing for 7 minutes by the manufacturing method 1. The mortar composition is Compound II, and the limestone fine powder in the cement composition is GL.
Was fixed at 10 parts by weight. Table 3 shows the compressive strength of the mortar after 28 days of age.

[0066]

[Table 3]

From Table 3, the mixing ratio of silica fume is 5
It can be seen that the amount of up to 25 parts by weight is effective for improving the strength. When the mixing ratio of the silica fume exceeds 25 parts by weight and reaches 30 parts by weight, the strength improving effect is no longer great, and the silica fume is expensive, which is uneconomical. Regarding the mixing ratio of silica fume in the cement composition, 5 to 25 parts by weight of the present invention is effective, and more preferably 5 to 20 parts by weight is effective.

10. EXAMPLES AND COMPARATIVE EXAMPLES BY CONCRETE Examples 10 and 11 and Comparative Examples 12 to 14 Moderate heat Portland cement, silica fume and limestone fine powder having a specific particle size distribution are mixed and prepared by Manufacturing Method 1 for 7 minutes. (Examples 10 and 11), and a comparative cement composition prepared by mixing in the same manner except that a comparative limestone fine powder having no specific particle size distribution was used instead of the limestone fine powder having a specific particle size distribution (comparative). The fluidity of concrete using Examples 12 and 13) was investigated.

Further, a case where no fine powder of limestone was added was also carried out as a comparative example (Comparative Example 14). Comparative Example 14 was prepared by mixing for 7 minutes by the manufacturing method 1 in the same manner as the other, except that the mixing ratio of the cement composition was moderate heat Portland cement: silica fume 9: 1.

The concrete composition was the same except that the type of cement composition was different. The concrete composition was 22% of the water-cement ratio of the composition 2, and the amount of the high-performance AE water reducing agent added was C × 1.3% (C is the amount of the cement composition). Table 4 shows the slump flow measurement results.

Comparing Examples 10 and 11 in Table 4 with Comparative Example 14, the fluidity of the concrete using the cement composition of the present invention using the limestone fine powder having a specific particle size distribution is the same as that of the limestone fine powder. It can be seen that it is greatly improved compared to the one not used. In addition, Examples 10 and 11 and Comparative Example 12,
When compared with No. 13, in the case of limestone fine powder having a particle size distribution different from that of the present invention, even limestone fine powder having a specific surface area similar to that of limestone fine powder having a specific particle size distribution which is a feature of the present invention Shows that the effect of improving the fluidity of concrete is inferior.

[0072]

[Table 4]

Examples 12 to 17, Comparative Examples 15 and 16 According to the composition of the present invention, a large slump flow can be obtained as compared with the case of using the conventional cement composition. Therefore, when the same slump flow is used, the high-performance AE water reducing agent necessary for improving the fluidity may be small.

In order to demonstrate this, the amount of the high-performance AE water reducing agent required to obtain a slump flow of 60 cm when the mixing ratio of limestone fine powder was changed was measured. The results are shown in Table 5.

The concrete mixing condition is that the water cement ratio of mixing 2 is 22%. For limestone fine powder having a specific particle size distribution, GL was used, and the mixing ratio was changed.
The mixing ratio of the cement compositions in Examples 12 to 17 and Comparative Examples 15 and 16 is limestone having a specific particle size distribution with respect to A, where A is the mixing ratio of ordinary Portland cement and silica fume. The mixing ratio of the fine powder was adjusted to 0 to 25%. The manufacturing method of the cement composition was the manufacturing method 1. Also,
The mixing time was 7 minutes.

From Table 5, the cement compositions of Examples 12 to 17 in which limestone fine powder having a specific particle size distribution was mixed,
Limestone fine powder for comparison Compared with no addition (Comparative Example 15) or small amount (Comparative Example 16), the amount of high-performance AE water reducing agent required to obtain a slump flow of 60 cm may be small, and limestone fine powder having a specific particle size distribution It can be seen that the larger the amount of powder added, the smaller the amount of water reducing agent required.

Further, the kneading time of the mortar is shorter in the cement composition of the present invention in which 3% or more of limestone fine powder having a specific particle size distribution is mixed, as compared with the non-mixed comparative example, and the kneading property is remarkably improved. I understand. Especially 5%
It is effective when mixed as above.

The O funnel run-down time, which is an index of the viscosity of concrete, was measured in Comparative Example 15 using a cement composition mixed with fine limestone powder having a specific particle size distribution.
It can be seen that the flowing time is shorter and the viscosity of the concrete is lower than that of the case where no addition is made. The decrease in viscosity is greater as the mixing ratio of fine limestone powder having a specific particle size distribution is higher.

As described above, the cement composition in which the limestone fine powder having the specific particle size distribution is mixed has the effect of reducing the high-performance AE water reducing agent necessary for obtaining a predetermined slump flow, the effect of improving the kneading property, and the viscosity. Although it has a reducing effect, the mixing ratio of fine limestone powder having a specific particle size distribution is 3
Effective at ~ 25%.

[0080]

[Table 5]

Examples 18 to 23, Comparative Examples 17 and 18 Table 6 shows the results obtained by examining the setting properties and strength properties of concrete using the cement composition of the present invention prepared by mixing and adjusting limestone fine powder having a specific particle size distribution. Show. The concrete composition and the like are the same as those in Table 5.

It can be seen that the setting time of concrete becomes shorter as the mixing ratio of fine limestone powder having a specific particle size distribution increases. Acceleration of setting time is effective at a mixing ratio of limestone fine powder of 3% or more.

Further, it is understood that the compressive strength does not decrease even when fine limestone powder having a specific particle size distribution is mixed, up to a mixing ratio of 10% as compared with the case where no addition is made.

[0084]

[Table 6]

Examples 24 and 25, Comparative Examples 19 and 20 Cement compositions in which the type of Portland cement was changed were produced by mixing for 7 minutes in Production Method 1, and the concrete properties were examined. Formula 1 with W / C = 25%, high performance A
E The amount of the water reducing agent was adjusted so that the slump flow was 60 cm. GL was used as the limestone fine powder having a specific particle size distribution. The composition of the cement composition of the example is Portland cement: silica fume: GL = 80: 10: 10,
The composition of the cement composition of the comparative example is Portland cement: silica fume = 90: 10. The results are shown in Table 7.

From Table 7, it can be seen that even in early-strength Portland cement and ordinary Portland cement, the concrete using the cement composition of the present invention uses a cement composition which does not use limestone fine powder having a specific particle size distribution for comparison. It is clear that it is superior in kneading property and fluidity as compared with conventional concrete.

[0087]

[Table 7]

Examples 26 to 30 and Comparative Examples 21 and 22 Table 8 shows the results of examining the properties of cement compositions obtained by changing the production method with concrete. Here, with the compounding 2 having a water cement ratio of 22%, the addition amount of the high-performance AE water reducing agent was C × 1.
3% (C is the amount of the cement composition) was kept constant.

From Table 8, it can be seen that as the mixing time in Manufacturing Method 1 becomes longer, the mortar kneading time becomes shorter and the concrete slump flow also increases. This is in a cement composition containing silica fume,
It is shown that the agglomeration of silica fume is sometimes loosened, and the more homogeneously dispersed, the more the kneadability of mortar in the mortar pre-kneading and the fluidity of concrete are improved. Further, the cement composition mixed and manufactured by the manufacturing method 2 in which silica fume was added to the finishing mill at the time of cement manufacturing exhibited the same kneadability and fluidity as those mixed by the manufacturing method 1 for 7 minutes or more.

Comparing Comparative Example 22 with Examples 26 to 30, in the conventional manufacturing method 3 in which limestone fine powder having a specific particle size distribution is not used, and cement and silica fume are separately charged into a concrete mixer, the present invention is used. It can be seen that the kneadability and fluidity are inferior as compared with the case of using the cement composition produced by. In Comparative Example 22, since the mortar flow time exceeded 1 minute in the concrete mortar pre-kneading, the kneading time after the addition of the coarse aggregate was shortened to 1 minute 40 seconds, 20 seconds, and the total kneading time was different. Same as 3 minutes.

Comparing Comparative Example 21 with Examples 26-30, the cement composition of Examples 26-30 consisting of Portland cement, silica fume and limestone fine powder having a specific particle size distribution was obtained by the production method of the present invention. Then, it is understood that the kneading property and the fluidity are remarkably improved by the method of separately introducing the respective constituent materials constituting the cement composition into the concrete mixer.

[0092]

[Table 8]

[0093]

As described above, according to the cement composition produced by the production method according to claims 1 to 3, silica fume is used as an admixture in Portland cement which has been used in conventional high strength concrete, and high performance water reduction is achieved. It is possible to produce mortar or concrete having excellent fluidity and kneadability, which could not be obtained by a method of reducing the water-cement ratio with an agent. Moreover, according to the cement composition produced by the method of the present invention, the addition amount of the high-performance water reducing agent can be small and the limestone fine powder in the composition has a setting promoting action, which causes a problem in the conventional technique. The delay in setting due to the existing high-performance water reducing agent can be greatly reduced. Further, compared with the conventional method of using silica fume as an admixture in Portland cement, the strength is equivalent or higher and the heat of hydration can be reduced. Further, compared to the conventional method of using silica fume as an admixture in Portland cement, the cement composition of the present invention has a rapid fluidization of the kneaded product during concrete kneading, and a large load on the mixer is less, so that it is industrial. High strength in favor of
Can produce high-fluidity concrete.

Conventionally, special equipment was required to separately add silica fume to the mixer. However, if the composition of the present invention mixed with silica fume is used, existing concrete plant equipment can be used and no special equipment is required. It also has an effect.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuro Asakura 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Cement Research Institute

Claims (3)

[Claims] 1. Portland cement 50-92 parts by weight, silica fume 5-25 parts by weight and limestone fine powder 3
A method for producing a cement composition comprising 25 parts by weight to 100 parts by weight in total, wherein silica fume is added to a finishing mill in which cement clinker or the like is crushed in the cement manufacturing process, and the cement clinker is added. A method for producing a cement composition, characterized in that silica fume is mixed and dispersed at the same time as pulverization such as the above, and then fine powder of limestone having a specific particle size distribution is mixed with the pulverized product produced by a finishing mill. 2. Portland cement 50-92 parts by weight, silica fume 5-25 parts by weight and limestone fine powder 3
A method for producing a cement composition containing 25 parts by weight to 100 parts by weight in total, wherein silica fume and limestone fine powder having a specific particle size distribution are mixed with Portland cement crushed by a finishing mill. A method for producing a cement composition, which comprises mixing using 3. The limestone fine powder according to claim 1, wherein the limestone fine powder having the specific particle size distribution is 20 μm.
90% or more of particles of m or less and 65 of particles of 10 μm or less
% To 5 μm particles in the range of 40 to 90%, 1
A method for producing a cement composition, which has a particle size distribution in which particles having a size of μm or less are 25% or less.