JP4509015B2 - Cement admixture and cement composition - Google Patents

Description

  The present invention mainly relates to a cement admixture and a cement composition used in the civil engineering and construction industries.

  In recent years, there has been an increasing demand for improving the durability of concrete structures in the civil engineering and construction fields.

One of the causes of deterioration of concrete structures is salt damage in which reinforcing steel corrosion becomes obvious due to the presence of chloride ions. A method to give chloride ion penetration resistance to concrete structures as a method to suppress the salt damage. There is.
As a method for suppressing chloride ion penetration into the inside of a hardened concrete and imparting chloride ion penetration resistance, a method of reducing the water / cement ratio is known (see Non-Patent Document 1).

On the other hand, a method of adding nitrite has also been proposed for the purpose of rust prevention of reinforcing bars (see Patent Documents 1 to 4).
However, although nitrite exhibits a rust prevention effect, it does not exhibit a shielding effect against chloride ions entering from the outside.

A method of adding nitrous acid type hydrocalumite has also been proposed (see Patent Document 5).
Nitrous acid type hydrocalumite has a problem that although it exhibits an antirust effect, the hardened cement mixed with this nitrite type tends to be porous, and rather allows permeation of chloride ions from the outside. It was.

On the other hand, 3CaO · Al ₂ O ₃ · 6H ₂ O has been proposed as an expansion material that generates ettringite in combination with gypsum (see Patent Literature 6 and Patent Literature 7).

JP 47-035020 A JP-A-53-003423 Japanese Patent Laid-Open No. 01-103970 Japanese Patent Laid-Open No. 03-224635 Japanese Patent Laid-Open No. 04-154648 Koichi Kishitani, Noriaki Nishizawa et al., "Durability series of concrete, salt damage (I)", Gihodo Publishing, pp.49-54, May 1986 JP-A-53-085822 JP-A-12-302502

  The present invention provides a cement admixture and a cement composition for civil engineering and building applications.

The present invention is a cement admixture containing a _{3CaO · Al 2 O 3 · 6H} 2 O and nitrite, is _{3CaO · Al 2 O 3 · 6H} 2 O BET specific surface area value of 2m ² / g or more The cement admixture, wherein the nitrite is lithium nitrite and / or calcium nitrite, and the mixing ratio of 3CaO · Al ₂ O ₃ · 6H ₂ O and nitrite is Al ₂ The cement admixture having a molar ratio of O ₃ / NO ₂ of 1/4 to 4/1, a cement composition containing cement and the cement admixture, and cement, 3CaO · Al ₂ O ₃ · A cement composition containing 6H ₂ O and nitrite.

  By using the cement admixture of the present invention, it has excellent rust prevention effect, shielding effect of chloride ions entering from the outside, and less leaching of Ca ions from hardened cement concrete, There are effects such as the ability to suppress crystallization.

Unless otherwise specified, parts and percentages in the invention are shown on a mass basis.
The cement concrete in the present invention is a general term for cement paste, cement mortar, and concrete.

In civil engineering and architectural uses, there are modes of use that are transported from the ready-mix factory to the construction site and placed in large quantities.
In such a form of use, the pot life needs to be equal to or greater than that of cement, the pot life needs to be secured for at least 1 hour, and preferably secured for 3 hours or more. .

3CaO · Al ₂ O ₃ · 6H ₂ O (hereinafter referred to as C ₃ AH ₆ ) has a composition in the vicinity of 3 in terms of a CaO / Al ₂ O ₃ molar ratio, and calcium aluminum containing 6 mol of bound water. It is a kind of hydrated hydrate. In the present invention, calcium aluminate hydrate containing about 6 mol of bound water can also be used.
C ₃ AH ₆ can be synthesized by hydrating a calcium aluminate compound. At this time, when 3CaO · Al ₂ O ₃ is used as the calcium aluminate compound, a highly pure C ₃ AH ₆ can be synthesized.
It can also be synthesized by a method of reacting calcium hydroxide and aluminum hydroxide in water, and can also be synthesized by a method of reacting calcium hydroxide and alkali metal aluminate in water.
The specific surface area of the C ₃ AH ₆ is, BET specific surface area value (hereinafter, referred to as BET) is preferably not less than 2m ² / g in, 3m ² / g or more is more preferable. If it is less than 2 m ² / g, sufficient chloride ion shielding effect may not be obtained.

In the present invention, nitrite is used in combination with C ₃ AH ₆ .
Nitrite means alkali metal nitrites such as sodium nitrite, potassium nitrite and lithium nitrite, alkaline earth metal nitrites such as calcium nitrite and magnesium nitrate, and zinc nitrite, aluminum nitrite, And iron nitrite. Among them, it is preferable to select lithium nitrite or calcium nitrite because there is no adverse effect on other physical properties and an effect of suppressing the alkali-silica reaction can be expected.

The mixing ratio of C ₃ AH ₆ and nitrite is not particularly limited, but usually, the molar ratio of Al ₂ O ₃ / NO ₂ is preferably 1/4 to 4/1, and preferably 1/2 to 2 / 1 is more preferable. When the mixture ratio of C ₃ AH ₆ and nitrite is more than 1/4 by the molar ratio of Al ₂ O ₃ / NO ₂ , the shielding effect of chloride ions entering from the outside becomes insufficient In addition, the Ca leaching suppression effect may not be expected. On the contrary, if C ₃ AH ₆ exceeds 4/1 in the molar ratio of Al ₂ O ₃ / NO ₂ , the rust prevention effect is insufficient. Or the suppression effect of alkali-silica reaction may not be expected.

  As the cement used in the present invention, various portland cements such as normal, early strength, super early strength, low heat, and moderate heat, and various mixed cements obtained by mixing these portland cements with blast furnace slag, fly ash, or silica, Portland cement such as filler cement mixed with limestone powder, blast furnace slow-cooled slag fine powder, etc., and environmentally friendly cement (eco-cement) manufactured from municipal waste incineration ash and sewage sludge incineration ash 1 type or 2 types or more can be used.

The cement admixture of the present invention contains C ₃ AH ₆ and nitrite.
Although the usage-amount of a cement admixture is not specifically limited, Usually, 1-20 parts are preferable in a cement composition which consists of a cement and a cement admixture, and 3-10 parts are more preferable. If the amount of cement admixture is small, sufficient rust prevention effect, chloride ion shielding effect, Ca ion leaching inhibition effect, and alkali-silica reaction inhibition effect may not be obtained. May appear and sufficient pot life may not be secured.

In the present invention, cement and a cement admixture are blended, and cement, C ₃ AH ₆ , and nitrite are used in combination to form a cement composition.

The water / binder ratio of the cement composition of the present invention is preferably 25 to 70%, more preferably 30 to 65%. If the blending amount of water is small, the pumpability and workability may be reduced or shrinkage may be caused. If the blending amount of water is excessive, the strength development may be degraded.
Here, the binder in the present invention refers to cement, C ₃ AH ₆ , and nitrite, and includes any material exhibiting latent hydraulic properties such as slag or pozzolana that is blended as necessary.

  The cement admixture and cement composition of the present invention may be mixed at the time of construction, or may be partially or wholly mixed in advance.

  In the present invention, in addition to cement, cement admixture, and fine aggregates such as sand and coarse aggregates such as gravel, expansion material, rapid hardener, water reducing agent, AE water reducing agent, high performance water reducing agent, high performance AE Water reducing agent, antifoaming agent, thickening agent, conventional rust inhibitor, antifreeze agent, shrinkage reducing agent, polymer emulsion, setting modifier, clay minerals such as bentonite, anion exchanger such as hydrotalcite, blast furnace water granulation One or more of the group consisting of slag such as slag fine powder and blast furnace slow-cooled slag fine powder, limestone fine powder, and pozzolanic substances such as fly ash and silica fume are used for the purpose of the present invention. It can be used in combination as long as it does not substantially inhibit.

  Hereinafter, although an example and a comparative example are given and the contents are explained in detail, the present invention is not limited to these.

Experimental example 1
C ₃ AH ₆ and nitrite A shown in Table 1 were mixed at a molar ratio of Al ₂ O ₃ / NO ₂ of 1/2 to prepare a cement admixture.
C ₃ AH ₆ is a method of hydrating 3CaO · Al ₂ O ₃ , a method of reacting aluminum hydroxide and calcium hydroxide, and a method of reacting reagent primary sodium aluminate and calcium hydroxide. Was synthesized.
Use this cement admixture to prepare a cement composition by blending 7 parts of cement admixture in 100 parts of cement composition obtained by mixing cement and cement admixture, and add mortar with a water / binder ratio of 0.5. Prepared according to JIS R 5201.
Using this mortar, the antirust effect, compressive strength, chloride penetration depth, and Ca ion leaching were examined. The results are also shown in Table 1.

<Materials used>
C ₃ AH _{6 B} : 3CaO · Al ₂ O ₃ hydrated and synthesized, BET 2m ² / g
C ₃ AH ₆ B: synthesized by reacting 0.1 mol of aluminum hydroxide and 0.3 mol of calcium hydroxide in 1,000 cc of pure water while heating to 50 ° C., BET ³ m ² / g
C ₃ AH ₆ C: synthesized by reacting 0.5 mol of sodium aluminate and 1 mol of calcium hydroxide in 1,000 cc of pure water while heating to 50 ° C., BET ⁵ m ² / g
Nitrite A: Lithium nitrite, Commercial cement: Normal Portland cement, Commercial fine aggregate: Standard sand water used in JIS R 5201: Tap water

<Measurement method>
Corrosion protection: as mortar endogenous chloride ions, confirm the anticorrosive effect in accelerated test by the 10 kg / m ³ and comprising as the chloride ion addition, it puts reinforcing steel round bars heated curing in 50 ° C. did. When the rust did not occur in the reinforcing bars, it was good. When the rust occurred within 1/10 of the area, it was acceptable. When the rust exceeded the 1/10 area, it was not acceptable.
Compressive strength: Measure compressive strength at age 28 days according to JIS R 5201.
Chloride penetration depth: A 10cmφ × 20cm cylindrical mortar specimen that evaluates chloride ion penetration resistance and shows the shielding effect of chloride ions was prepared. After water curing at 20 ° C and immersion for 12 weeks in simulated seawater, which is a 3.5% salt solution at 30 ° C, the chloride penetration depth was measured. The chloride penetration depth was determined by the fluorescein-silver nitrate method, the portion of the cross section of the mortar specimen where the tea did not change was regarded as the chloride penetration depth, and the average value was obtained by measuring 8 points with calipers.
Ca ion leaching: Shows Ca ion leaching suppression effect. A 4 × 4 × 16 cm mortar specimen was immersed in 10 liters of pure water for 28 days, and determination was made by measuring the concentration of Ca ions dissolved in the liquid phase.

Experimental example 2
The same operation as in Experimental Example 1 was conducted except that C ₃ AH ₆ B was used and the nitrite shown in Table 2 was used in combination. The results are also shown in Table 2.

<Materials used>
Nitrite B: Reagent primary sodium nitrite Citrate C: Reagent primary potassium nitrite nitrite D: Reagent primary calcium nitrite Nitrate E: Mixture of 50 parts nitrite A and 50 parts nitrite D

Experimental example 3
The test was conducted in the same manner as in Experimental Example 1 except that the cement admixture shown in Table ₃ consisting of C ₃ AH ₆ B and nitrite A and having a Al ₂ O ₃ / NO ₂ molar ratio of 1/2 was used. It was. For comparison, a conventional rust preventive material was used in the same manner. The results are also shown in Table 3.

<Materials used>
Conventional rust preventive: nitrite hydrocalumite, commercial product

  By using the cement admixture of the present invention, it has an excellent rust preventive effect and a chloride ion shielding effect, and in addition, an Ca ion leaching suppression effect and an alkali-silica reaction suppression effect can also be obtained. In order to achieve the effect, it is suitable for applications such as offshore structures, seawall structures, floor slab concrete, etc. mainly in the civil engineering and construction industries.

Claims (6)

A cement admixture containing 3CaO · Al ₂ O ₃ · 6H ₂ O and nitrite. The cement admixture according to claim 1, wherein the BET specific surface area value of 3CaO · Al ₂ O ₃ · 6H ₂ O is 2 m ² / g or more.   The cement admixture according to claim 1 or 2, wherein the nitrite is lithium nitrite and / or calcium nitrite. The mixing ratio of 3CaO · Al ₂ O ₃ · 6H ₂ O and nitrite is 1/4 to 4/1 in terms of a molar ratio of Al ₂ O ₃ / NO _2. The cement admixture according to Item.   A cement composition comprising cement and the cement admixture according to any one of claims 1 to 4. A cement composition comprising cement, 3CaO · Al ₂ O ₃ · 6H ₂ O, and nitrite.