JPH05262546A - Cement admixture and cement composition - Google Patents

Abstract

PURPOSE:To provide a cement admixture and a cement composition capable of reducing both the salt damage and carbonatization of concrete which can be used in the fields of civil engineering and construction where such deterioration must be avoided as far as possible. CONSTITUTION:The objective cement admixture comprises hydrotalcite, an expanding admixture and/or a rapid hardening admixture and the cement admixture and cement constitute the objective cement composition. The cement admixture according to the present invention has excellent ability to capture anions such as chloride or carbonate ion, thus can prevent the damage by saline salt and carbonatization over a wide range of fields.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cement admixture and a cement composition, and more particularly to a cement admixture and a cement composition mainly used in the field of civil engineering and construction.

The concrete in the present invention is a general term for paste, mortar and concrete.

[0003]

2. Description of the Related Art Recently, early deterioration of a concrete structure, which has been considered to be semi-permanently durable, has become a social problem.

The causes of deterioration of concrete are known to be salt damage, carbonation, alkali-aggregate reaction, and the like, and they are widely highlighted every time early deterioration comes to the surface.

On the other hand, many proposals have hitherto been made on the method of suppressing the reaction of alkaline aggregate and the development of the material thereof (Japanese Patent Laid-Open No. 3-224635, Annual Report of Concrete Engineering 13- 1 1992 745-570). However, not many proposals have been made regarding methods and materials for suppressing salt damage and carbonation, and at present, there is no proposal for materials that simultaneously suppress salt damage and carbonation of concrete.

In view of the above-mentioned circumstances, the present inventors have made various studies including simultaneously suppressing salt damage and carbonation of concrete, and preventing these deteriorations as much as possible. As a result, by using a specific cement admixture, the inventors have obtained knowledge that the above problems can be solved and completed the present invention.

[0007]

Means for Solving the Problems That is, the present invention is a cement admixture containing hydrotalcite, a cement expansive material and / or a cement rapid hardening material, which contains cement and the cement admixture. It is a cement composition obtained.

The present invention will be described in detail below.

The hydrotalcite according to the present invention is
Is a collective term of non-stoichiometric compound represented by _{^{- [M 1-X 2+ M}} X 3+ (OH) 2] X + [A X / N N- · mH 2 O] X. Where X is 0 <X
≦ 0.33.

Further, M ²⁺ is Mg ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni
²⁺ , Cu ²⁺ , Zn ^{2+ and} other divalent metals, M ³⁺ is Al ³⁺ , F
Trivalent metals such as e ³⁺ , Cr ³⁺ , Co ³⁺ and In ³⁺ are shown.

Furthermore, A ^{N-is OH -, F -, Cl -} , Br -, NO 3 -,
It shows N-valent anions such as CO ₃ ²⁻ and SO ₄ ²⁻ . Of these, as the N-valent anion, OH ⁻ , F ⁻ , Br ⁻ , NO ₃ ⁻ , and SO ₄ ²⁻ are preferable, and OH ⁻ , NO ₃ ⁻ , and SO ₄ ²⁻ are more preferable. When the N-valent anion is Cl ⁻ or CO ₃ ²⁻ , it is not possible to expect a suppressing effect, and there is a possibility that ion exchange with other anions in the concrete structure may be carried out to promote corrosion of the reinforcing bar. Also, when the N-valent anions are F ⁻ and Br ⁻ , although Cl ⁻ and CO ₃ ²⁻ that contribute to salt damage and carbonation can be expected to be collected, F ⁻ and Br ⁻ released by the ion exchange action May corrode rebar in concrete structures.

Hydrotalcite means that when it is produced or when a substance containing a large amount of it is used,
The presence of impurities of other components is not particularly limited, either crystalline or amorphous can be used, but crystalline is preferably used.

The particle size of hydrotalcite is 0.1 to 100 μm
It is preferable that If it is less than 0.1 μm, the amount of kneading water increases, which may adversely affect the physical properties such as strength. If it exceeds 100 μm, the surface area decreases and the suppression effect may become insufficient. The amount of hydrotalcite used is preferably 0.1 to 30 parts by weight, more preferably 1 to 15 parts by weight, and most preferably 2 to 5 parts by weight, based on 100 parts by weight of cement. If it is less than 0.1 part by weight, the suppressing effect is not sufficient, and if it exceeds 30 parts by weight, the amount of kneading water increases, which may cause a problem in long-term durability.

Here, as cement, normal, early strength,
Examples include various portland cements such as ultra-rapid strength, moderate heat and sulfate resistance, various mixed cements obtained by mixing these portland cements with blast furnace slag, fly ash or silica, and alumina cement.

In the present invention, in addition to hydrotalcite, cement expansive material and / or cement rapid hardening material are used in combination with the cement.

The cement expansive material used in the present invention is a compound that is mixed with cement to give expansivity, and as a component,
Auin mineral, calcium oxide-based, calcined alum system, magnesia, crystalline or amorphous, or calcium aluminate -CaSO ₄ system is a mixture of both, as well as _four systems such as CaSO, expanded by the reaction It is one that produces ettringite and Ca (OH) ₂ , which are hydrates, and also includes ones that produce hydroxides, such as iron powder. Among them, it is preferable to use a hain mineral-based or calcium oxide-based material, which is usually used as a cement expansive material, from the viewpoint of its stability. In particular,
Commercially available products such as "Denka CSA" manufactured by Denki Kagaku Kogyo Co., Ltd. and "Onoda Expan" manufactured by Onoda Cement Co., Ltd. can be used.

The amount of the cement expanding agent used is preferably 5 to 20 parts by weight, and 7-1 to 100 parts by weight of cement.
More preferably 8 parts by weight, most preferably 9 to 15 parts by weight. If it is less than 5 parts by weight, the effect of dimensional stabilization is insufficient, and if it exceeds 20 parts by weight, abnormal expansion may occur.

The cement quick-hardening material used in the present invention is a material which is mixed with cement to give quick-hardening property. Among the cement quick-hardening materials, it is particularly preferable to use a material containing calcium aluminates as a main component. Here, the calcium aluminates are usually produced at a high temperature in an electric furnace or a rotary kiln, and either crystalline or amorphous can be used. The presence of impurities is also not particularly limited.
As crystalline calcium aluminates, CaO is C,
When Al ₂ O ₃ is A, those shown as CA, C ₅ A ₃ , C ₁₂ A ₇ , C ₃ A, and the like, and when Fe ₂ O ₃ is F, SO ₃ is S, and halogen is X , Other components other than C and A are present in the crystal, C ₁₁ A
₇ CaX ₂ , C ₃ A ₃ CaX ₂ , C ₄ AF, C ₄ A ₃ S and the like can be mentioned. Typical examples of amorphous calcium aluminates include those having the same composition as crystalline, but they are amorphized by rapid cooling and cannot be identified by X-ray as they are. From the viewpoint of reactivity, the CaO content in the calcium aluminate is preferably 30 to 60% by weight, more preferably 38 to 52% by weight.

In the present invention, one or more of the above calcium aluminates can be used. It is also possible to use these calcium aluminates in combination with an inorganic sulfate to prepare a cement rapid hardening material.

Here, examples of the inorganic sulfates include alkali metal or alkaline earth metal sulfates.
It is preferable to use anhydrous, semi-water, and dihydrated calcium sulfate, and among them, it is more preferable to use a sparingly soluble or insoluble substance such as anhydrous type II gypsum.

The amount of inorganic sulfate used is preferably 50 to 300 parts by weight, and particularly preferably 100 to 200 parts by weight, based on 100 parts by weight of calcium aluminate. If the amount is less than 50 parts by weight, the strength development is not sufficient, and if it exceeds 300 parts by weight, the dimensional stability of the cured product of the hydraulic composition may be deteriorated.

The amount of cement rapid hardening material used is 100
The amount is preferably 5 to 50 parts by weight, more preferably 10 to 40 parts by weight, most preferably 15 to 35 parts by weight, based on parts by weight. If it is less than 5 parts by weight, rapid hardening is insufficient, and if it exceeds 50 parts by weight, long-term durability may be a problem.

In the present invention, when a cement rapid hardening material is used, it is preferable to use a setting retarder together. Here, the setting retarder is an admixture which controls the hydration reaction of cement and delays the setting time and initial hydration rate of concrete. Specifically, citric acid, tartaric acid, gluconic acid,
Organic acids such as succinic acid and maleic acid, or salts thereof, alkali carbonate, phosphoric acid or salts thereof, boric acid, alkali borate, silicofluoride, starch, sugar, and alcohols and mixtures thereof. Of these, the use of organic acids is preferred.

The setting retarder is preferably used in an amount of about 0.1 to 30 parts by weight based on 100 parts by weight of cement and cement rapid hardening material in total. Outside this range, it is difficult to obtain an appropriate pot life.

Further, when the cement expansive material and the cement rapid hardening material are used in combination, the method of use strongly influences the material to be used and the compatibility between the two. The total amount of cement rapid hardening material is preferably 5 to 30 parts by weight, more preferably 7 to 20 parts by weight. If it is less than 5 parts by weight, the effect of dimensional stabilization is insufficient, and if it exceeds 30 parts by weight, abnormal expansion may occur. Incidentally, the respective proportions when the cement expansive material and the cement rapid hardening material are used in combination are not particularly limited,
It is optional. When using cement expansive material and / or cement rapid hardening material in combination with cement, especially when a large amount is used, it is necessary to select materials so that negative factors such as abnormal expansion do not occur.

Further, in the present invention, aggregates such as silica sand, natural sand, and gravel, fibrous substances such as glass fibers, carbon fibers, and steel fibers, polymer emulsions and latexes of polymers, AE agents, and water reducing agents. , AE water reducing agent, superplasticizer, rust preventive, non-separable admixture in water such as methyl cellulose, thickener, water retention agent, waterproofing agent such as sodium silicate, foaming agent, foaming agent, antifreezing agent, and water Among alkaline substances such as calcium oxide and the like, one kind or two or more kinds can be used in combination unless the object of the present invention is substantially impaired.

Since the hydrotalcite according to the present invention can easily collect chlorine ions and carbonate ions in concrete by an ion exchange reaction, it is possible to suppress carbonation and salt damage of concrete. Is.

That is, chlorine ions and carbonate ions in concrete are anions in hydrotalcite, for example,
It is ion-exchanged with hydroxide ions and nitrate ions. This action keeps the alkalinity of concrete and suppresses corrosion of reinforcing bars.

[0029]

EXAMPLES The present invention will now be described in more detail by way of examples.

Example 1 Hydrotalcite's ability to adsorb chlorine ions and carbonate ions was confirmed. That is, 1 g of hydrotalcite is added to 0.1N
-NaCl aqueous solution and 0.1N-Na ₂ CO ₃ aqueous solution in 50 ml,
The ion concentration in the aqueous solution after 24 hours, the chloride ion and the carbonate ion concentration were measured by potentiometric titration. As a result, 0.1N-
The chloride ion of the NaCl aqueous solution itself was 3,600 mg / l, but when hydrotalcite was added, it became 2,900 mg / l, and the carbonate ion of the 0.1N-Na ₂ CO ₃ aqueous solution itself was 5,400 m.
It was g / l, but it was 4,100 when hydrotalcite was added.
It became mg / l.

<Materials used> Hydrotalcite: product name “KW-100” manufactured by Kyowa Chemical Industry Co., Ltd.
0 "to 0.1N- nitrate 24 hour immersion treated Mg-Al-NO ₃ system,
Average particle size 45 μm or less NaCl: Wako Pure Chemical Industries, Ltd. reagent first grade Na ₂ CO ₃ : 〃

Example 2 Mortars were kneaded by using the composition shown in Table 1 to prepare a cylindrical specimen having a diameter of 10 cm and a height of 20 cm. Temperature 20 ℃, Humidity 60
% Pre-curing of this specimen for 28 days, then
Curing was carried out for 3 months in an environmental test room at a temperature of 30 ° C., a humidity of 60% and a carbon dioxide concentration of 5%. Then, the specimen was sliced into pieces, coated with phenolphthalein, and the depth up to the discolored portion was measured to be the penetration depth of carbon dioxide gas from the surface of the specimen. A caliper was used for the measurement, and measurement was carried out at four points per circumference, and the average value was taken as the penetration depth of carbon dioxide. The results are also shown in Table 1.

<Materials used> Cement: Ordinary Portland cement made by Denki Kagaku Kogyo Aggregate: Light aggregate made by Sanki Kogyo Co., Ltd., product name “Sankiraite YO4”, main component SiO ₂ cement expansion material: Denki Kagaku Kogyo Product name "Denka CS
A ", calcium sulfoaluminate-based cement rapid hardening material: 〃" Dencaplacto-1 ", calcium aluminate-based water: tap water Others are the same as in Example 1

[0034]

[Table 1]

Example 3 A test piece was prepared in the same manner as in Example 2 using the formulations shown in Table 2.
Preliminary curing for 7 days in water at a temperature of 20 ℃,
It was immersed in 5% saline for 3 months. Cut the test piece into slices, apply a 1N silver nitrate aqueous solution, and then spray a 10% potassium chromate solution to measure the depth to the discolored point,
The procedure was performed in the same manner as in Example 2 except that the depth from the surface of the specimen was such that chlorine ions were included. The results are also shown in Table 2.

<Materials used> Salt: manufactured by Wako Pure Chemical Industries, Reagent grade 1 Others are the same as in Example 2.

[0037]

The hydrotalcite of the present invention has an excellent ability to collect anions such as chlorine ions and carbonate ions,
When added to concrete alone or as a composition, it exerts a marked effect of suppressing salt damage and carbonation in various aspects.

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C04B 28/02

Claims (2)

[Claims] 1. A cement admixture containing hydrotalcite and a cement expansive material and / or a cement rapid hardening material. 2. A cement composition comprising cement and the cement admixture according to claim 1.