JP2003171154A - Cement admixture and cement composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a cement admixture mainly used in civil engineering and building industries, which gives a cement composition exhibiting strengths nearly equivalent to those of a cement composition obtained by using a limestone fine powder and having material separation resistance and a function to suppress neutralization, and to provide the cement composition. <P>SOLUTION: The cement admixture contains gehlenite characterized in that the Blaine specific surface area is ≥3,000 cm<SP>2</SP>/g and the degree of vitrification is ≤10%. The cement composition contains cement and the cement admixture. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention mainly relates to a cement admixture and a cement composition used in the civil engineering and construction industry. Parts and% in the present invention are based on mass unless otherwise specified.

[0002]

[Prior art and its problems] Currently, European standards (EN
The standardization of cement is the basic idea, and the internationalization of cement standards is being promoted. Cement is roughly classified into strength classes, and a system that allows the selection of a suitable cement according to the purpose. Specifically, they are roughly divided into 32.5N / mm ² class, 42.5N / mm ² class, and 52.5N / mm ² class (Koji Goto,
Shunsuke Habara, Internationalization of Cement Standards-Outline and Direction of European Standards-Cement / Concrete, No.631, pp1-8,
1999).

On the other hand, in Japan, the quality of cement has been designed based on the JIS standard. As a result, cement with good strength development under uniform specifications has been evaluated as good cement. As a result, Japanese cement is EN
When classified by standard, all are 42.5N / mm ² class or 52.5N
Only cement equivalent to / mm ² class is present, and even if a concrete mix with a design strength that is not very high is attempted to be mixed, in most cases, the strength tends to be excessive.

Prevention of excessive strength is important from the viewpoint of preventing excessive heat of hydration associated therewith, and from the viewpoint of minimizing the shrinkage ratio as much as possible.

On the other hand, it is conceivable to use a cement having a high strength development property to reduce the amount of unit cement so as to mix and design a concrete having a not so high design strength. There was a problem that the amount becomes small, the materials are easily separated, and the concrete has a high bleeding rate, that is, so-called "Shabcon".

When a concrete structure is constructed by using such concrete, macroscopic defects are likely to occur, and it is difficult to construct a durable concrete structure. .

As described above, the EN standard is 32.5 N / mm ² which makes it easy to mix and design concrete whose design strength is not so high.
The feature is that a class of cement is prepared.

The mainstream of this cement is limestone mixed cement. The limestone mixed cement is a mixture of Portland cement with a large amount of fine limestone powder, and is a cement that can realize both prevention of excess strength and improvement of material separation resistance. Limestone fine powder can be regarded as an inactive powder from the viewpoint of strength development, and has an advantage of giving only material separation resistance and not generating extra strength or heat of hydration.

Under such circumstances, research on limestone-mixed cement has been actively conducted in Japan. However, for Japan, which has few resources, limestone is a valuable natural resource, and its use simply by mixing it with concrete leads to exhaustion of resources, so there is a strong demand for more effective use as an industrial raw material.

Further, the limestone-mixed cement has a problem that it is easily neutralized.

Neutralization is important because it may reduce the durability of reinforced concrete structures, and today, as with limestone-mixed cement, prevention of excess strength and improvement of material separation resistance can both be achieved. Moreover, the development of a cement having a resistance to neutralization superior to that of a limestone-mixed cement is awaited.

The present inventor has conducted various studies to solve the above-mentioned problems of limestone-mixed cement, and as a result, specific gerenicite is equivalent to limestone fine powder in terms of strength development and material separation resistance. Therefore, the present invention has been completed by finding that there is a neutralization suppressing function.

[0013]

Means for Solving the Problems That is, the present invention is a cement admixture containing a grenite having a Blaine specific surface area value of 3,000 cm ² / g or more and a vitrification rate of 10% or less,
A cement composition containing cement and the cement admixture.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

Gerenite used in the present invention means 2CaO.
・ A compound represented by Al ₂ O ₃・ SiO ₂ (C ₂ AS), whose Blaine specific surface area value (hereinafter referred to as Blaine value) is 3,000 cm ² / g
With the above, the vitrification rate is 10% or less. The Blaine value of gehlenite is 3,000 cm ² / g or more, 4,000 cm ²
/ g or more is preferable, and 5,000 cm ² / g or more is more preferable. If the Blaine value is less than 3,000 cm ² / g, a sufficient neutralization suppressing effect may not be obtained. Further, the vitrification ratio of the gehlenite used in the present invention needs to be 10% or less. If the vitrification ratio exceeds 10%, a sufficient neutralization suppressing effect may not be obtained. Vitrification rate (X) is X (%) =
It is calculated as (1-S / S ₀ ) × 100. Here, S is the area of the main peak of gehlenite in the cement admixture determined by the powder X-ray diffraction method, and S ₀ is the cement admixture heated at 1,000 ° C. for 3 hours and then cooled at 5 ° C./min. It represents the area of the main peak of gehlenite that was cooled at a speed.

The cement admixture of the present invention (hereinafter referred to as the present admixture) is mainly composed of gerenite.
The presence of impurities is not particularly limited, and does not cause any particular problem as long as the object of the present invention is not substantially impaired. Specific examples thereof include, for example, MgO, TiO ₂ , MnO, and Na.
₂ O, S, Cr ₂ O ₃ , P ₂ O ₅ , Fe ₂ O _{3 and the} like. The coexisting compounds are CaO ・ SiO ₂ (CS), 2CaO ・ SiO
Calcium silicates such as ₂ (C ₂ S) and 3CaO ・ SiO ₂ (C ₃ S), magnesium silicates such as MgO ・ SiO ₂ (MS) and 2MgO ・ SiO ₂ (M ₂ S), and 2CaO ・ MgO ・Akermanite represented by 2SiO ₂ (C ₂ MS ₂ ), 3CaO ・ MgO ・ 2SiO ₂ (C ₃ M
S ₂ ) Merwinite represented by CaO ・ MgO ・
Examples include calcium magnesium silicate such as Monticellite represented by SiO ₂ (CMS). The amount of the admixture of the present invention used is not particularly limited, but usually 5 to 40 parts is preferable, and 10 to 30 parts is more preferable, in 100 parts of the cement composition comprising cement and the admixture. If it is less than 5 parts, the effect of the present invention, that is, the effect of suppressing neutralization may not be sufficiently obtained, and if it exceeds 40 parts, the strength development may be deteriorated.

As the cement used in the present invention, various kinds of portland cements such as normal, early strength, ultra-early strength, low heat, and moderate heat are mixed, and granulated blast furnace slag, fly ash, or silica is mixed with these portland cements. Examples include various mixed cements and limestone filler cements in which limestone powder and the like are mixed, and one or more of these can be used.

In the present invention, the cement and the admixture are used in combination as a cement composition. In the cement composition of the present invention, the respective materials may be mixed at the time of construction, or a part or all of them may be mixed in advance. The particle size of the cement composition of the present invention is not particularly limited because it depends on the purpose and application to be used, but usually, the Blaine value is preferably 3,000 to 8,000 cm ² / g, and 4,000 to 6,000 cm ² / g. Is more preferable. If it is less than 3,000 cm ² / g, strength development may not be sufficiently obtained.
If it exceeds 0 cm ² / g, workability may deteriorate.

In the present invention, in addition to cement, the present admixture, aggregates such as sand and gravel, a water reducing agent, a high performance water reducing agent, an AE water reducing agent, a high performance AE water reducing agent, an expanding material, a quick hardening material, and a dewatering material. One or more of foaming agents, thickeners, rust preventives, antifreeze agents, polymer emulsions, setting regulators, clay minerals such as bentonite, and anion exchangers such as hydrotalcite, etc. It can be used within a range not substantially impairing the object of the invention.

In the present invention, the method of mixing the respective materials is not particularly limited, and the respective materials may be mixed at the time of construction, or some or all of them may be mixed in advance. . As the mixing device, any existing device can be used, and for example, a tilting barrel mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer can be used.

[0021]

EXAMPLES The present invention will be further described below based on experimental examples of the present invention.

Experimental Example 1 In 100 parts of a cement composition comprising cement and the present admixture,
Using the admixtures in the amounts shown in Table 1, a mortar with a water / cement composition ratio of 50% and a cement composition / sand ratio of 1/3 was prepared and subjected to compressive strength and accelerated neutralization tests. went. The results are also shown in Table 1. For comparison, the same procedure was performed using limestone instead of the admixture. The results are also shown in Table 1.

<Materials used> Cement: Ordinary Portland cement, manufactured by Denki Kagaku Kogyo Co., Ltd., specific gravity 3.15 2CaO.Al ₂ O ₃ .SiO ₂ : Reagent first grade calcium carbonate, aluminum oxide and silicon dioxide 2: 1: 1 Mixed at a molar ratio of 2 and heat treated at 1,400 ° C for 2 hours. Synthetic main admixture A: 2CaO ・ Al ₂ O ₃・ SiO ₂ crushed product, vitrification rate 0
%, Blaine value 4,000 cm ² / g Limestone: Limestone fine powder, crushed limestone from the Aomi mine, Blaine value 4,000 cm ² / g Water: Tap water sand: JIS standard sand

<Measurement method> Compressive strength: Measured according to JIS R 5201, 28 days old strength accelerated neutralization: After curing at 20 ° C in water until 28 days old, temperature 30 ° C, relative humidity 60% Confirmed by applying 1% alcohol solution of phenolphthalein to the mortar cross section after accelerated neutralization for 4 weeks under the condition of carbon dioxide concentration of 5%.

[0025]

[Table 1]

Experimental Example 2 The procedure of Experimental Example 1 was repeated except that 25 parts of the admixture shown in Table 2 was used in 100 parts of the cement composition. The results are shown in Table 2.
Also described in.

<Materials used> This admixture B: 2CaO · Al ₂ O ₃ · SiO ₂ crushed product, vitrification rate 0
%, Blaine value 3,000 cm ² / g This admixture C: 2CaO ・ Al ₂ O ₃・ SiO ₂ ground product, vitrification rate 0
%, Blaine value 5,000 cm ² / g Main admixture D: 2CaO ・ Al ₂ O ₃・ SiO ₂ ground product, vitrification rate 0
%, Blaine value 6,000 cm ² / g This admixture E: 2CaO ・ Al ₂ O ₃・ SiO ₂ crushed product, vitrification rate 10
%, Blaine value 4,000 cm ² / g This admixture F: 2CaO ・ Al ₂ O ₃・ SiO ₂ crushed product, vitrification rate 20
%, Blaine value 4,000 cm ² / g

[0028]

[Table 2]

[0029]

EFFECTS OF THE INVENTION By using the present admixture, it is possible to obtain a cement composition having a high material separation resistance and being hardly neutralized.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Nakajima             2209 Aomi, Aomi-cho, Aomi-cho, Nishikubiki-gun, Niigata Prefecture             Denki Kagaku Co., Ltd. Aomi factory F-term (reference) 4G012 PB05 PB06 PC01 PC13

Claims (2)

[Claims] 1. A cement admixture containing gehlenite having a Blaine specific surface area value of 3,000 cm ² / g or more and a vitrification rate of 10% or less. 2. A cement composition comprising cement and the cement admixture according to claim 1.