JPH07138060A - Admixture for concrete, concrete mixture using the same and production of concrete - Google Patents

Abstract

PURPOSE:To obtain an admixture for concrete capable of expressing a high initial strength, increasing fluidity of a kneaded concrete mixture to require no compacting process and resistance against separation of materials by using starch or modified starch as a component. CONSTITUTION:This admixture for concrete comprises starch and/or modified starch. E.g. following methods (a)-(b) are used to mix and knead the admixture. At first, (a) cement based powder, a fine aggregate, water, a water reducing agent and a thickener are mixed and kneaded and a coarse aggregate is further added and mixed and kneaded. Then, (b) the cement based powders, the fine aggregate and the coarse aggregate are mixed and kneaded and mixing water which is separately prepared by mixing the water reducing agent and the thickener. Then, the cement based powder, the fine aggregate, the coarse aggregate, the thickener and a portion (almost one half) of mixing water are mixed and kneaded. To this mixture, the rest of mixing water containing the water reducing agent is added and mixed and kneaded. Further, (d) the cement based powder, the fine aggregate, the coarse aggregate, water, the water reducing agent and the thickener are mixed and kneaded at once.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel admixture for concrete, a concrete kneaded product using the same, and a method for producing concrete. In particular, the fluidity of the concrete kneaded product is increased, and vibrations, etc. TECHNICAL FIELD The present invention relates to a novel admixture for concrete which does not require a compaction step due to the method, has improved material separation resistance, and realizes cost reduction, a concrete kneaded product using the admixture, and a method for producing concrete.

[0002]

2. Description of the Related Art Conventionally, the following concretes have been proposed as concretes that do not require a compaction step due to vibration or the like.

(I) Compaction-free concrete with a large amount of powder (for example, annual report of concrete engineering)
1989 P699-704 Ozawa et al. “Development of high performance concrete”) (ii) Compaction-free concrete using a separation reducing agent such as a cellulosic thickener (for example, Annual Report of Concrete Engineering 1992 P325-330 Yamakawa et al. “ Basic properties of thickeners for high-fluidity concrete ")

[0004]

Among the above-described conventional compaction-free concretes, compaction-free concrete having a large amount of powder has the following problems.

Since many materials are used, process control is complicated.

[0006] Concrete properties vary greatly depending on the material used and are difficult to manage (for example, changes in fresh properties of concrete such as slump flow due to changes in surface water ratio of sand, etc.).

Since it is necessary to mix a large amount of fly ash, slag, etc. that do not contribute to the initial strength for the purpose of increasing the viscosity of concrete, the initial hardening strength of concrete is low.

In addition, the compaction unnecessary concrete using the separation reducing agent has the following problems.

[0009] Depending on the type of the separation reducing agent, air bubbles having a large diameter are carried, so that the freeze-thaw resistance of the obtained concrete is poor.

The cost of the thickener is high, and the material cost as concrete is 1.5 to 100% when the separation reducing agent is not used.
It doubles.

Depending on the type of separation reducing agent, there is a problem of compatibility with the water reducing agent, and it is difficult to select the material.

It is an object of the present invention to provide an admixture for concrete which solves the problems of the conventional compaction-free concrete, a concrete kneaded product using the admixture, and a method for producing concrete.

[0013]

The admixture for concrete according to claim 1 comprises starch and / or modified starch.

A concrete kneaded product according to a second aspect is a kneaded product of cement-based powder, aggregate and water, further comprising the admixture for concrete according to the first aspect.

In the method for producing concrete according to claim 3, the concrete kneaded product obtained by kneading cement-based powder, starch and / or modified starch, aggregate, water and a water-reducing agent is poured into a mold to be molded. Is characterized by.

A method for producing concrete according to a fourth aspect is the method according to the third aspect, wherein the starch and / or the modified starch is 20 to 1000 per 1 m ³ of the concrete kneaded material.
It is characterized by using 0 g.

The method for producing concrete according to claim 5 is the method according to claims 3 and 4, wherein the cement-based powder is Portland cement, or Portland cement and fly ash, blast furnace slag powder, silica fume, natural minerals and the like. It is characterized in that it is a mixed powder with powder.

The method for producing concrete according to claim 6 is the method according to any one of claims 3 to 5, wherein when the concrete kneaded product is poured into a mold to be molded, the mold or concrete kneaded product is compacted by an external force. It is characterized by being cured without being poured.

The method for producing concrete according to claim 7 is the method according to any one of claims 3 to 6, wherein after molding, the maximum temperature is 3 at normal pressure.
Normal temperature and high temperature curing of 5 to 95 ° C and / or 1 atm or more 1
It is characterized by performing high-temperature and high-pressure curing at 00 ° C or higher.

The present invention will be described in detail below.

[0021] Of the starch and / or modified starch constituting the admixture for concrete of the present invention, the raw material plant of starch is not particularly limited, and various plant-derived starches can be used. On the other hand, as modified starch, α-modified starch due to α-formation (micelle disintegration) of starch, starch degradation product by decomposition of molecular starch (molecular chain cleavage), roasted dextrin, acid-treated starch derivative of starch (functional group addition) (Esterified starch, etherified starch) Grafting of starch by grafting (branch addition) Starch Crosslinked of starch by cross-linking (molecular chain bond) Starch oxidized by starch oxidation (structure change) Starch (hypochlorite oxidized starch, For example, dialdehyde starch) can be used.

The concrete kneaded product of the present invention is prepared and molded using the admixture for concrete comprising such starch and / or modified starch, for example, according to the method for producing concrete of the present invention.

As the concrete kneading procedure in the present invention, for example, the following methods (a) to (d) can be adopted.

(A) Cement-based powder, fine aggregate, water, water-reducing agent and thickener are kneaded, and coarse aggregate is further added thereto and kneaded.

(B) Cement-based powder, fine aggregate and coarse aggregate are kneaded, and kneading water obtained by mixing a water reducing agent and a thickener with water is added and kneaded. (c) Cement-based powder, fine aggregate, coarse aggregate, thickener and a part (about half amount) of the kneading water containing the water reducing agent are kneaded, and the remaining part of the kneading water further containing the water reducing agent And knead.

(D) Cement-based powder, fine aggregate, coarse aggregate,
Knead water, water reducer and thickener at once.

Here, as the cement-based powder, one of Portland cement alone, or powder such as fly ash, blast furnace slag powder, silica fume, and natural mineral powder is used.
A mixed powder of one kind or two or more kinds and Portland cement can be mentioned. When using fly ash etc. together, the ratio is 50 per 100 parts by weight of Portland cement.
It is preferable that the amount is less than or equal to parts by weight. The amount of cement-based powder is preferably 300 kg / m ³ or more, and when initial strength is taken into consideration, it is preferably 400 kg / m ³ or more.

If the amount of starch and / or modified starch added is too small, sufficient separation resistance cannot be obtained, and if it is too large, the fluidity is impaired. Therefore, the amount of starch and / or modified starch is preferably 20 to 10000 g, particularly about 200 to 1200 g, per 1 m ^{3 of the} concrete kneaded product obtained.

If the amount of the water reducing agent is too small, the fluidity is insufficient, and if it is too large, the resistance to separation is impaired. Therefore,
The water reducing agent is preferably 0.1 to 10% by weight, more preferably 1.0 to 5% by weight, based on the cement-based powder. As the water-reducing agent to be used, any of those conventionally used generally can be preferably used. For example, naphthalene sulfonic acid formalin high-condensation salt-based high-performance water reducing agent,
Examples include melamine sulfonic acid-based high-performance water reducing agents, polycarboxylic acid salt-based polymer compound high-performance AE water reducing agents, lignin sulfonate-based AE water reducing agents, and oxycarboxylate-based AE water reducing agents.

The amount of aggregate and kneading water with respect to the cement-based powder can be set to the same ratio as in the conventional case, but the ratio of fine aggregate to coarse aggregate is increased in consideration of material separation resistance. Is preferred.

The prepared concrete kneaded product can be cast into a mold without being compacted by an external force such as vibration. After casting, in the case of on-site casting, air curing, sprinkling curing, sheet curing, etc., and for concrete products, normal temperature and high temperature curing with maximum temperature of 35 to 95 ° C. And / or high temperature and high pressure curing of 1 atm or more and 100 ° C or more. Do.

Since the concrete kneaded product according to the present invention can increase the initial strength, it can be removed from the mold at an early stage and the production efficiency is significantly improved.

[0033]

[Function] The properties required for the production of a compacted concrete kneaded product are that it has a high fluidity so that it can be spread to every corner of the form, and that the materials in the concrete kneaded product do not separate. 2 of having separation resistance
It is a point.

Therefore, in the conventional general compaction-free concrete kneaded product, an admixture having a water reducing effect is added to ensure high fluidity, and at the same time, powder such as fly ash or blast furnace slag powder is separated from the separation reducing agent. Separation resistance is secured by the addition of. Thus, conventionally, in order to obtain a general compaction-free concrete kneaded product, it is necessary to mix powder such as fly ash and blast furnace slag powder, but these powders do not contribute to the initial strength. Therefore, sufficient strength at the time of demolding could not be secured, and it was unsuitable for concrete products. Further, some of the separation reducing agents include those entraining air bubbles in the concrete kneaded product and those causing delay in setting of the concrete kneaded product, so that it was not possible to secure sufficient demolding strength. Further, the separation reducing agent and the water reducing agent are compatible with each other, and in some cases, the concrete kneaded product may become stiff. Further, since the conventional separation reducing agent is expensive, the material cost of the concrete becomes considerably high, which hinders the spread of compacted concrete.

On the other hand, in the present invention, a water reducing agent which is generally used is added in order to ensure high fluidity in the concrete kneaded product, and starch and / or starch is added in order to ensure separation resistance. By adding the modified starch, a compaction-free concrete kneaded product can be obtained which can omit the compaction step due to external force such as vibration when the concrete kneaded product is poured into the mold. In the present invention, by adding this starch and / or modified starch, without mixing powders such as fly ash and blast furnace slag powder that do not contribute to the initial strength, or by suppressing the mixing amount low, concrete kneaded materials It secures separation resistance, and because this starch and / or modified starch is inexpensive, it can reduce the material cost, and also causes air bubbles to be entrapped in the concrete mixture and delay the setting. Therefore, it is possible to overcome the problems of initial strength and low freeze-thaw resistance, which have been problems in the past, and to secure sufficient strength during demolding. Further, the fluctuation of the concrete property due to the fluctuation of the material property can be made very small.

[0036]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Materials used in Examples and Comparative Examples are as follows. Cement-based powder: Early strength Portland cement (hereinafter referred to as "H cement") Ordinary Portland cement (hereinafter referred to as "N cement") Fly ash (produced at thermal power plant, Blaine value 3180 cm ² / g)
, Hereinafter referred to as "F". ) Blast furnace slag (from steel mill, Blaine value 4000 cm ² /
g, hereinafter referred to as "B". ) Separation-reducing agent according to the present invention: Etherified starch (hereinafter referred to as "ET") α-modified starch (hereinafter referred to as "α") Esterified starch (hereinafter referred to as "ES") Dextrin (hereinafter referred to as "D") Water reducing agent: naphthalenesulfonic acid type water reducing agent (“Mighty 150” manufactured by Kao Co., Ltd.) Melamine sulfonic acid type water reducing agent (NMB Co., Ltd.)
"NL4000" manufactured by NL) Separation reducing agent according to comparative example: Acrylic polymer separation reducing agent (hereinafter referred to as "AC") Methylcellulose separation reducing agent (hereinafter referred to as "MC") Fine aggregate: Kisarazu Sanzan (Surface dry specific gravity 2.62, water absorption rate 1.56, coarse particle rate 2.9
7) Coarse aggregate: Crushed stone from Hachioji (maximum size 20mm, surface dry specific gravity 2.67, water absorption rate 0.
60, coarse grain ratio 6.10) Examples 1 to 17 Cement-based powder, fine aggregate and coarse aggregate were kneaded with a pan-type forced kneading mixer for 30 seconds, and tap water was then mixed with a separation reducing agent and a water reducing agent. A concrete kneaded product having the composition shown in Table 1 was kneaded for 2 minutes while adding the above materials.

This concrete kneaded product was cast into a mold without vibration, and after casting, steam curing was performed under the following conditions without compaction by an external force such as vibration. The compressive strength was measured after time and after 28 days. In addition, the compressive strength was measured 28 days after the casting when the standard curing was performed under the following conditions.

Steam curing conditions Preliminary: 20 ° C., 3 hours Temperature rising: 10 ° C./hour Holding: 60 ° C., 3 hours Cooling: 10 ° C./hour Standard curing conditions Demolding in 1 day after molding, up to a prescribed number of days in 20 ° C. water Curing In addition, fresh properties (slump flow, air content, separation resistance) were examined.

The material separation reduction property was measured by an L-type flow tester, and the ratio of (rough aggregate ratio at input portion (%))-(rough aggregate ratio at flow tip portion (%)) was 5%. Within ○○, 5-1
0% was evaluated as ◯, 10 to 15% was evaluated as Δ, and 15% or more was evaluated as x.

The results are shown in Table 1.

[0042]

[Table 1]

Comparative Example 1 The fresh properties and the compressive strength were examined in the same manner as in Example 1 except that modified starch was not used, the concrete composition shown in Table 2 was used, and vibration molding which has been conventionally performed was adopted. The results are shown in Table 2.

The slump of this concrete kneaded material was 10 cm.

Comparative Examples 2 to 6 Fresh properties and compressive strength were examined in the same manner as in Example 1 except that the modified starch was not used and the concrete composition shown in Table 2 was used. The results are shown in Table 2.

Comparative Example 7 Fresh properties and compressive strength were examined in the same manner as in Example 11 except that the modified starch was not used and the concrete composition shown in Table 2 was used. The results are shown in Table 2.

Comparative Example 8 Fresh properties and compressive strength were examined in the same manner as in Example 1 except that the concrete mix shown in Table 2 was used without using the water reducing agent, and the results are shown in Table 2. The concrete kneaded product had a slump of 2 cm and could not be molded without compaction, so vibration molding was required.

Comparative Examples 9, 10 and 11 The same procedure as in Example 1 was carried out except that the separation reducing agent shown in Table 2 was used in place of the modified starch and the type of the water reducing agent was changed and the formulation shown in Table 2 was used. The fresh properties and compressive strength were examined, and the results are shown in Table 2.

In Comparative Example 11, since the slump was 0 cm due to the stiffness of the kneaded material, compaction was performed by vibration.

Comparative Examples 12 and 13 Fresh properties and compressive strength were examined in the same manner as in Example 11 except that the separation reducing agent was not used and the formulation shown in Table 2 was used. The results are shown in Table 2.

[0051]

[Table 2]

From the results shown in Tables 1 and 2, the following is clear.

That is, by comparing the examples with the comparative examples 2 to 7, the results of tests carried out by confirming the amount of cement and the presence or absence of modified starch are confirmed, but the modified starches of the comparative examples 2 to 7 without addition of modified starch are confirmed. However, even if the amount of cement is increased to increase the paste content, it is not possible to prevent the material separation.On the other hand, in the case of adding the modified starch of the example, the material separation is hardly recognized and the strength is improved. Also has a sufficient value which is equal to or higher than that of Comparative Example 1 in which vibration compaction was performed, and the strength at the time of demolding can be adjusted by the cement amount and the water cement ratio.

Comparison between Examples 2, 4 and 5 and Comparative Examples 3, 5 and 6 confirms the results of the test conducted by the value of the fine aggregate ratio and the presence or absence of denatured starch. 3,
The modified starches of Nos. 5 and 6 which do not contain the modified starch cannot prevent the material separation even if the fine aggregate ratio is increased, whereas the modified starches of Examples 3, 4, and 5 are the materials. Almost no separation was observed, and the strength was equal to or higher than that of Comparative Example 1 and had a sufficient value.

Comparison of Examples 2, 6 and 7 with Comparative Example 8 confirms the results of the test conducted with the addition ratio of the water reducing agent as a factor. Since it was impossible to mold without compaction due to insufficient fluidity, and vibration molding was required, Example 2,
The water-reducing agents of Nos. 6 and 7 have sufficient fluidity, can be molded without compaction, and have strength equivalent to or higher than Comparative Example 1 and sufficient. . The size of the slump flow can be adjusted by the addition ratio of the water reducing agent.

Comparison between Examples 2, 8, 9 and 10 and Comparative Example 3 confirms the results of the test conducted by using the modified starch addition rate as a factor. In the case of Comparative Example 3 without modified starch, the material separation cannot be prevented, whereas in the case of the modified starches of Examples 2, 8, 9 and 10, the material separation was hardly observed and the strength was high. In comparison, Comparative Example 1 has a value equal to or higher than that of Comparative Example 1 and a sufficient value. It should be noted that when the addition rate of the modified starch is small, a separation tendency is observed, and conversely, when it is large, the viscosity is increased and the fluidity tends to be lowered.

In Comparative Example 9, since the water reducing agent was added excessively, the setting was delayed and the initial strength was small. In Comparative Example 10, since the separation reducing agent entrains air, the amount of air is large. In Comparative Example 11, the compatibility between the separation reducing agent and the water reducing agent is poor, and the kneaded product becomes stiff, so compaction is required. In Comparative Examples 12 and 13, the initial strength is low due to the addition of a large amount of powder such as fly ash and blast furnace slag.

As is clear from the above, starch and /
Or, by adding an appropriate amount of modified starch and commonly used water reducing agents, excellent fluidity and separation resistance,
Moreover, it is possible to obtain concrete that does not require compaction and that has sufficient strength even at the time of demolding.

As is clear from Examples 12 to 17, fly ash, blast furnace slab and the like can be used in combination as the cement-based raw material, and various modified starches other than etherified starch can also be used as the separation reducing agent. It can be used.

[0060]

As described in detail above, the admixture for concrete of the present invention has an excellent effect of reducing separation, and also has good compatibility with a water reducing agent, and the water reducing agent can be arbitrarily selected.
Since it has neither setting retardation nor air entrainment, the mixing of concrete can be easily set. Therefore, the admixture for concrete of the present invention is very easy to use, as long as it is necessary to use a water reducing agent in combination with the conventional concrete mixture, if necessary.

Further, since starch and / or modified starch are relatively low in cost, cost advantages can be expected.

According to the concrete kneaded product of the present invention using the admixture for concrete of the present invention or the method for producing concrete of the present invention, it is possible to produce concrete having a high initial strength and not requiring compaction. Therefore, it is possible to overcome the noise pollution at the time of vibration molding, the shortage of employees, and the low initial strength, which have been problems in the past. Can be manufactured.

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[Procedure amendment]

[Submission date] December 7, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

Materials used in Examples and Comparative Examples are as follows. Cement-based powder: Early strength Portland cement (hereinafter referred to as "H cement") Ordinary Portland cement (hereinafter referred to as "N cement") Fly ash (produced at thermal power plant, Blaine value 3180 cm ² / g)
, Hereinafter referred to as "F". ) Blast furnace slag (from steel mill, Blaine value 4000 cm ² /
g, hereinafter referred to as "B". ) Separation-reducing agent according to the present invention: Etherified starch (hereinafter referred to as "ET") α-modified starch (hereinafter referred to as "α") Esterified starch (hereinafter referred to as "ES") Dextrin (hereinafter referred to as "D") Water reducing agent: naphthalenesulfonic acid type water reducing agent (“Mighty 150” manufactured by Kao Co., Ltd.) Melamine sulfonic acid type water reducing agent (NMB Co., Ltd.)
"NL4000" manufactured by NL) Separation reducing agent according to Comparative Example: Acrylic polymer separation reducing agent (hereinafter referred to as "AC") Cellulose separation reducing agent (hereinafter referred to as "MC") Fine aggregate: Kisarazu Sanzan (Surface dry specific gravity 2.62, water absorption rate 1.56, coarse particle rate 2.9
7) Coarse aggregate: Crushed stone from Hachioji (maximum size 20mm, surface dry specific gravity 2.67, water absorption rate 0.
60, coarse grain ratio 6.10) Examples 1 to 17 Cement-based powder, fine aggregate and coarse aggregate were kneaded with a pan-type forced kneading mixer for 30 seconds, and tap water was then mixed with a separation reducing agent and a water reducing agent. A concrete kneaded product having the composition shown in Table 1 was kneaded for 2 minutes while adding the above materials.

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Claims (7)

[Claims] 1. An admixture for concrete, which comprises starch and / or modified starch. 2. A kneaded product of cement-based powder, aggregate and water, further comprising the admixture for concrete according to claim 1. 3. A method for producing concrete, which comprises molding a concrete kneaded product obtained by kneading cement-based powder, starch and / or modified starch, aggregate, water and a water reducing agent into a formwork. . 4. The method for producing concrete according to claim ³ , wherein 20 to 10000 g of starch and / or modified starch is used per 1 m ³ of concrete kneaded material. 5. The cement-based powder is Portland cement, or a mixed powder of Portland cement and powder of fly ash, blast furnace slag powder, silica fume, natural minerals or the like. Or the method for producing concrete according to 4. 6. The method according to claim 3, wherein when the concrete kneaded product is poured into a mold to be molded, the mold or the concrete kneaded product is cured as it is without being compacted by an external force. The method for producing the concrete according to any one of 1. 7. The molding according to claim 3, wherein after molding, normal temperature and high temperature curing at a maximum temperature of 35 to 95 ° C. at normal pressure and / or high temperature and high pressure curing at 1 atm to 100 ° C. is performed. The method for producing concrete according to any one of items.