JPH07115900B2 - Chlorine ion scavenger - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chlorine ion scavenger containing hydrocalumite as an active ingredient. Further, it relates to a chlorine ion scavenger effective for suppressing the corrosion of reinforcing bars due to chlorine ions in concrete.

[Prior Art] Recently, in concrete structures, corrosion of rebars caused by chlorine ions mixed in during pouring or entering from the outside during pouring, so-called salt damage, has become a social problem.

It is said that such problems are largely due to the use of sea sand due to resource depletion of river sand and mountain sand as aggregates and the large use of calcium chloride-based admixtures.

On the other hand, due to such raw material circumstances, when chloride ions are mixed into concrete in a positive and large amount, for example, calcium chloride solution for adhesion of sea water droplets, prevention of road freezing and snow melting May be sprayed.

Conventionally, as a method of coping with such salt damage of concrete, a rust preventive material such as calcium nitrite is used, a structure is covered, repairing after deterioration is merely taken as a coping treatment. Absent.

However, it is desirable to avoid chlorine ions mixed in the raw materials, such as using well washed sea sand,
This has limitations and is often uneconomical.

By the way, hydrocalumite is a kind of divalent-trivalent metal complex hydroxide, is a layered crystalline compound in the form of Ca-Al complex hydroxide, and is known to have anion exchange property. . Hydrotalcite, which is a Mg-Al-based composite hydroxide, belongs to the same category as such compounds, and is used as a resin additive.

[Problems to be Solved by the Invention] Today, effective measures for preventing or suppressing salt damage in concrete structures have not been established. This requires removal or containment of chloride ions, which is technically possible but often not economically feasible.

The hydrotalcite is well known as a resin additive because of its excellent ability to collect chlorine ions, but its application as a cement additive has not been attempted. The reason for this is that the inclusion of Mg ^{++ in} the cement is not desirable.

On the other hand, hydrocalumite is a compound similar to hydrotalcite, but its industrial utility has not been found to date.

The inventors of the present invention, in view of the above problems, have made intensive studies, and a certain kind of hydrocalumite has excellent chlorine ion-scavenging ability and is useful as an additive to a cement material, without any adverse effect. That is, the present invention has been completed.

That is, an object of the present invention is to provide a chloride ion scavenger useful for preventing or suppressing corrosion of reinforcing bars in a concrete structure due to salt damage or the like.

Chlorine ions scavenger [Means for Solving the Problems] The present invention is to provide the following general _{formula: 3CaO · Al 2 O 3 ·} CaX 2 / m · nH 2 O [ wherein, X is a monovalent Or represents a divalent anion, m represents the valence of the anion, and n
Representing ≤20] is used as an active ingredient.

Hereinafter, the present invention will be described in detail.

The hydrocalumite according to the present invention is represented by the above general formula in an oxide form, and X represents a monovalent or divalent anion,
When other anions are present, they have anion exchange properties.

Hydrocalumite varies depending on the production method and its substance, but the Ca / Al molar ratio is almost 2, and n, which indicates the amount of water of crystallization, is often up to 15, but in the present invention, it includes up to 20. sell.

The anion, X, for example, _{^{NO 3 -, NO 2 -,}} OH -, CH 3 CO
O ^-, CO ₃ ^2-, but SO ₄ ^2-is typical, particularly in the present invention NO
₃ ^-, NO ₂ ^- or OH ^- it is preferably a monovalent anion, and they no problem even one or two or more.

Therefore, in the present invention, these are referred to as nitric acid type hydrocalumite, nitrite type hydrocalumite, or hydroxy type hydrocalumite.

Hydrocalumite is a water-containing crystalline compound having a layered structure, which can be easily identified by X-ray diffraction, and water of crystallization is dehydrated in a temperature range of about 300 ° C.

Chlorine type non hydrocalumite, especially the above-mentioned nitric acid type, nitrite-type or hydroxyl type hydrocalumite is to anion exchange upon contact with chlorine ions _{^{NO 3 -, NO 2 -,}} OH
^- to liberate, Cl ^- markedly superior to the action of collecting.

Such Cl ^- capturing ability is the same even in mortar and concrete, and the collected Cl ^- is supported in hydrocalumite unlike free Cl ^- and is, so to speak, inactive. Has no action to induce corrosion.

Moreover, since hydrocalumite is a basic substance in addition to its main component being the same as the cement component,
It does not hinder the physical properties of cement.

The hydrocalumite according to the present invention can be easily synthesized, for example, by mixing an aqueous solution of sodium aluminate and, if necessary, an aqueous solution or slurry of caustic alkali and calcium salt in a predetermined molar ratio to cause a precipitation reaction. However, the cement additive mainly contains hydrocalumite and includes those having Cl ^- capturing ability.

When used as a cement additive, the reaction product is preferably a fine powder having a fineness of cement particles or less, preferably an average particle diameter of 10 μm or less.

The cement additive according to the present invention is mainly used for the purpose of suppressing corrosion of reinforcing bars due to salt damage etc. of concrete structures, and in order to effectively exhibit its function, its use mode needs to be particularly limited. However, it may include, for example, the following: alone or in the cement composition (eg,
Dispersant, water reducing agent, hardening retarder, hardening accelerator, etc.) are mixed together to suppress free chlorine ions in concrete in advance.

Used as an injection material alone or together with other additives in the concrete body where corrosion of the reinforcing bars is feared due to salt damage.

It is used as a cross-section restoration material or surface restoration material with other additives for the concrete skeleton that has deteriorated due to salt damage and has its surface peeled.

Therefore, as can be seen from the above, in the chlorine ion scavenger according to the present invention, it is not necessarily pure in terms of chemical composition that hydrocalumite is used as an active ingredient, and X-ray diffraction is used as the main composition. It can be specified and has a Cl ^- scavenging ability. On the other hand, when it is used as a chlorine ion scavenger, alone or in combination with other additives, it is used in a cement material. Means to include.

[Action] The chlorine ion scavenger according to the present invention contains hydrocalumite as an active ingredient, and can easily collect Cl ⁻ in concrete by its anion exchange action, so that corrosion of rebar in a concrete structure is caused. Can be suppressed.

Such chlorine-scavenging ability is more preferable for those having monovalent anions such as OH ⁻ , NO ₃ ⁻ , and NO ₂ ⁻ than those having divalent anions having strong intercalation force for hydrocalumite as exchangeable anions. .

In addition, these anions released as a result of chlorine collection,
In particular, NO ₂ ^- is because an effect of suppressing or preventing the corrosion of reinforcing steel can exhibit more excellent function as a cement additive.

[Examples] In order to describe the present invention more specifically, examples will be described below.

Examples 1 to 4 A. Synthesis of a sample of the cement additive (a) nitrate type Hydrocalumite _{Ca (NO 3) 2 · 4H} 2 O, and 57kg was dissolved in water 60 kg, prepared calcium nitrate solution (A solution) To do.

23.4 kg of Al ₂ O ₃ 25.6 wt% and NaO 21.1 wt% sodium aluminate solution 23.4 kg, liquid NaOH solution (48%) 10.2 kg and water 293.3 k
A sodium aluminate solution (solution B) containing g is prepared.

Then, the solution B was charged into the reaction tank, and the solution A was fed through a metering pump with stirring and added.

Then, the mixture was heated to 50 ° C. and the reaction was continued for 4 hours to crystallize the gel. The molar composition of the starting material was CaO / Al ₂ O _{3
= 4, Na 2 O / NO} 3 - was 0.30.

After completion of the reaction, solid-liquid separation was carried out, and after washing, it was dried at 50 ° C. for 20 hours. After drying, it was ground to 150 mesh (this is referred to as Sample 1).

Sample 1 is X-ray diffraction, infrared absorption spectrum measurement, TG
-DTA be nitrate type Hydrocalumite _{[3CaO · Al 2 O 3 ·} Ca (NO 3) 2 · 11H 2 O] was observed by analysis of the measurement and chemical composition.

(B) Add 270 ml of concentrated nitric acid, 0.68 kg of sodium aluminate (Na ₂ O: 21.9% by weight, Al ₂ O ₃ : 15.0% by weight) liquid and 2 kg of water to 3.6 kg of slaked lime slurry of 8.23% by weight of nitric acid type hydrocalumite. And reacted at 50 ° C. for 8 hours under stirring. Then, the same post-treatment as in the above-mentioned method for synthesizing hydrocalumite was performed to obtain a sample powder.
And).

This sample 2 is a nitric acid type hydrocalumite [3CaO ・ Al ₂ O ₃・ Ca (NO ₃ ) ₂・ 11H with high crystallinity measured by XRD etc.
₂ O] was recognized.

(C) 0.68 kg of the same sodium aluminate solution and 4 kg of water were added to 1.76 kg of a calcium nitrite solution containing 30% by weight of nitrite-type hydrocalumite at 50 ° C.
The reaction was carried out under stirring for 4 hours.

Then, the same post-treatment was performed to obtain a sample powder (this is referred to as sample 3).

The sample 3 is that nitrite type Hydrocalumite _{[3CaO · Al 2 O 3 ·} Ca (NO 2) 2 · 11H 2 O] was observed by measuring the XRD or the like.

(D) Nitric acid-nitrite mixed hydrocalumite 8.085% by weight To 184 g of slaked lime slurry, 88 g of 30% by weight calcium nitrite solution, 11 ml of concentrated nitric acid and 200 ml of water are added.

Then, 68 g of the same sodium aluminate solution as described above was added to this slurry and reacted at 50 ° C. for 4 hours with stirring. Then, the same post-treatment was performed to obtain a sample powder (this is referred to as sample 4).

This sample 4 is a mixed hydrocalumite [3CaO ・ Al ₂ O ₃・ Ca (NO ₃ , NO ₂ ) ₂ mixture of nitric acid and nitrous acid measured by XRD etc.
・ 11H ₂ O] was recognized.

B.Cl ^- Evaluation sample 2.0kg of adsorption capacity is taken up in 100ml beaker, the predetermined concentration NaCl solution
Add 20 ml and stir at room temperature for 4 hours. Next, the Cl content of the solid phase that had been subjected to solid-liquid separation and thoroughly washed with distilled water was determined by fluorescent X-ray analysis, and the Cl ^- adsorption capacity of each sample was checked.
The results are shown in Table 1.

C. Evaluation of Cl Adsorption Ability in Cement (a) Preparation of Specimen Mortar Specimen mortar was prepared according to JIS A5308. Ordinary portrad cement 420g, fine aggregate [frame stone from Ariake, specific gravity 2.5
4, water absorption 0.8% by weight, coarse particle ratio 3.19, compounding ratio (4.75 ~ 2.83
mm: 2.83 to 1.16 mm: 1.16 to 0.6 mm: 0.6 to 0.3 mm = 10: 25: 25: 1
5)] 945 g and the above-mentioned synthetic hydrocalumite sample 84 g are added and kneaded for 30 seconds by a kneading machine.

Then, 210 g of 1.5 wt% NaCl water is added, and the mixture is kneaded for 30 seconds, rested for 20 seconds, and then stirred with a spoon for 2-3 times.

Then, after kneading for 120 seconds, the mortar was
X 160 mm).

Approximately 3 hours later, trimmed and unframed for 24 hours
Immerse in l distilled water and incubate at 20 ℃ ± 3 ℃.

(B) Evaluation of Cl ^- collection The amount of chlorine ions eluted in the distilled water in which the sample is immersed is sampled in an amount of 1 ml every predetermined time (day) and measured with an ion chromatograph analyzer. The results are shown in Table 2.

[Effect of the Invention] The cement additive according to the present invention contains hydrocalumite as an active ingredient and has an excellent ability to collect chlorine ions. When this is added to cement and used, the corrosion of reinforcing bars in concrete structures can be suppressed or prevented.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Koshimizu 9-15-1, Kameido, Koto-ku, Tokyo Within Nippon Kagaku Kogyo Co., Ltd. (72) Inventor Shozo Takatsu 9-15-1, Kameido, Koto-ku, Tokyo Within Nippon Kagaku Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A following general _{formula: 3CaO · Al 2 O 3 ·} CaX 2 / m · nH 2 O
[Wherein, X represents a monovalent or divalent anion, m represents a valence of the anion, and n ≦ 20], and the active ingredient is hydrocalumite. Collecting agent. 2. The chlorine ion scavenger according to claim 1, wherein X is at least one selected from OH ⁻ , NO ₃ ^{− and} NO ₂ ⁻ . 3. A chloride ion scavenger which is used by adding the chloride ion scavenger according to claim 1 to a cement material.