JPH0524893A - Cement admixture and cement composition - Google Patents

Abstract

PURPOSE:To provide the title admixture and composition to be used in the construction industry with the need for high-early strength concrete and long age strength concrete. CONSTITUTION:The objective cement admixture containing, as active ingredient, calcium aluminate containing >0.1wt.% but <2wt.% of a R2O (R is alkali metal) and the other objective cement composition prepared by incorporating cement with the present cement admixture. Use of the present admixture will desirably regulate the working life of the cement composition. The concrete from the present composition is good in strength developability and high in long term strength. There is no concern for alkali-aggregate reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cement admixture and a cement composition used in the fields of civil engineering and construction where early and long-term strength is required.

[0002]

_2. Description of the Related Art Conventionally, it is known that calcium carbonate such as 12CaO.7Al ₂ O ₃ and alumina cement, Portland cement, gypsum and the like are mixed to prepare a rapid hardening cement.

Further, it is known that calcium aluminate and alkali carbonate are combined and mixed with cement to be used as a cement for spraying immediately after tunnel excavation (Japanese Patent Publication No. 3-21497).

However, since the conventional calcium aluminate is less reactive, long-term over expansive ettringite _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O) is generated, thereby hardened cement paste is inflated breaking There were many problems, such as that, or the concrete sprayed in the tunnel came off.

In order to solve the above problems, it has been proposed to use calcium aluminate containing a large amount of Na ₂ O as a cement admixture (Japanese Patent Laid-Open No. 2-258659).

[0006] However, if a large amount of R ₂ O is contained in this way, the furnace at the time of production will be severely damaged, which is not practical, and the alkali that reacts with R ₂ O and the reactive aggregate in the concrete Aggregate reaction occurred, a turtle-like crack was generated for a long period of time, and the strength was greatly reduced.

The alkali-aggregate reaction means that the alkali in Portland reacts with a rock-forming mineral in the aggregate to form an alkali silicate gel, which causes excessive expansion of concrete, resulting in concrete powder. It is an action that induces harmful phenomena such as aging, cracking, bending, and collapse.

The reactive aggregates include protein stones, siliceous magnesitic limestone, cryptocrystalline rhyolite, andesite,
Examples thereof include tuff, quartz andesite, porphyrite, and rocks containing these.

In the past, the use of these reactive aggregates was extremely rare, but at present, it is very common due to the exhaustion of aggregates, and the alkaline aggregate reaction is a major problem. Has become.

As a result of various studies to solve the above-mentioned problems, the present invention has been completed by obtaining the finding that the use of a specific calcium aluminate does not cause a decrease in strength over an early period or a long period of time. Came to.

[0011]

That is, the present invention provides R ₂ O (R
Is a cement admixture containing, as an active ingredient, calcium aluminate containing more than 0.1% by weight and less than 2% by weight of alkali metal, and a cement composition obtained by mixing cement with the cement admixture.

The present invention will be described in detail below.

[0013] (hereinafter referred to as CA) calcium aluminate according to the present invention, R ₂ O containing (R is an alkali metal) are those amounts of less than 2% by weight greater than 0.1% by weight of, R ₂ O
Is preferably 0.4 to 1.6% by weight, more preferably 0.6 to 1.4% by weight. When the R ₂ O content is 0.1% by weight or less, the reactivity of CA is small, so that the initial strength is low and the long-term strength is also low. When it is 2% by weight or more, the furnace is seriously damaged during the production of CA, and CA containing such a high concentration of R ₂ O can cause a large decrease in strength when used in concrete. The molar ratio CaO / Al ₂ O ₃ of CaO and Al ₂ O ₃ in the CA is preferably 0.5 to 3, more preferably from 1 to 2.5, most preferably 1.5 to 2. If it is less than 0.5, it is difficult to obtain sufficient initial strength, and if it exceeds 3, it tends to be difficult to secure working time. Such CA is a calcareous raw material,
It can be produced by using an aluminous raw material and an R ₂ O raw material.

As the R ₂ O raw material, for example, carbonates of alkali metals such as sodium carbonate, potassium carbonate and lithium carbonate can be used.

As the calcareous raw material, limestone, quick lime, slaked lime and the like can be used.

As the alumina raw material, aluminum oxide, aluminum hydroxide or the like can be used.

CA is a mixture of the above-mentioned R ₂ O raw material, calcareous raw material, and aluminous raw material, which are mixed at a predetermined ratio, and melted by using, for example, a direct-current type melting furnace or a high-frequency furnace. Is produced by blowing off compressed air or high-pressure water or pouring it into water. CA is preferably amorphous rather than crystalline from the viewpoint of improving the strength development of the concrete in the initial stage. Specifically, the vitrification rate of CA is preferably 50% or more, more preferably 70% or more, and 90%.
The above is the most preferable.

The vitrification rate is measured by heating the amorphous material at 1,000 ° C. for 2 hours, then slowly cooling it at a cooling rate of 5 ° C./minute, and measuring the main peak of the crystalline mineral by powder X-ray diffraction. The area S ₀ was obtained, and the vitrification rate X was obtained from the main peak area S of the crystal in the amorphous material.

[0019]

[Equation 1]

A typical example of the CA according to the present invention is alumina cement. However, the vitrification rate of alumina cement does not exceed 25%, and it is preferable to use CA with a higher vitrification rate by further increasing the cooling rate [1964, issued by Academic Press Corp. Limited of the City of London,
HFW Taylor, The Chemistry of Cement, Volume 2, Volume 16
page〕.

Although the amorphous forming region of pure calcium aluminate is only around CaO / Al ₂ O ₃ of 12/7, general industrial raw materials include SiO ₂ , MgO, Fe ₂ O ₃ , And TiO ₂
Naturally, impurities such as are included, but these impurities are
Since the amorphous forming region is expanded, its presence is preferable if the content is less than 10% by weight, and no problem occurs in strength development.

In the production of CA, it is preferable to add calcium fluoride, cryolite, aluminum fluoride and the like, which are general glass fluxes, since the amorphous melting point is lowered. The finer the particle size of CA is, the better the reactivity is, which is preferable. The Blaine specific surface area is 3,000 cm ^2.
/ g or more is preferable.

In the present invention, the combined use of CA and gypsum is preferable from the viewpoint of reduction of shrinkage and improvement of workability.

Here, the gypsums include di-water, semi-water,
Various types of gypsum such as type II and type III anhydrous are listed, and naturally occurring gypsum, chemical gypsum such as phosphoric acid, excretion, and hydrofluoric acid gypsum, or those obtained by heat-treating these can be used. Yes, it is not affected by the type and amount of impurities normally contained. Of these, type II anhydrous gypsum is particularly excellent in terms of initial strength development and workability. In particular, since type II anhydrous gypsum is by-produced in a large amount from the hydrofluoric acid generation step, it is most convenient to use as it is or to neutralize free H ₂ SO ₄ minutes with limestone, quick lime, slaked lime, etc. Is. The particle size of gypsum is usually 3,000 c
It is preferably ground to m ² / g or more, more preferably 6,000 cm ² / g or more. The amount of gypsum used is preferably 30 to 300 parts by weight, more preferably 50 to 200 parts, and most preferably 100 to 150 parts by weight, based on 100 parts by weight of CA. If it is less than 30 parts by weight, the shrinkage is large, and if it exceeds 300 parts by weight, the strength tends to decrease for a long time due to the expansion of the unreacted gypsum due to the reaction.

In the present invention, the amount of the cement admixture used is preferably 3 to 50 parts by weight based on 100 parts by weight of the total amount of the cement and the cement admixture. When the amount is less than 3 parts by weight, the strength development is low, and when the amount exceeds 50 parts by weight, it is not preferable in terms of workability.

Here, as the cement, various portland cements such as normal, early strength, super early strength and moderate heat, and various mixed cements in which silica, blast furnace slag or fly ash are mixed can be used.

The cement admixture or cement composition of the present invention can be used in combination with various setting modifiers to control the setting time.

Examples of the coagulation modifier include aluminates such as sodium aluminate and potassium aluminate, carbonates such as sodium carbonate and potassium carbonate, hydroxides such as sodium hydroxide and potassium hydroxide, and zinc silicofluoride. Inorganic salts such as silicofluorides such as magnesium silicofluoride and sodium silicofluoride, and organic acids such as citric acid, gluconic acid, and tartaric acid, or their organic salts such as calcium salts, sodium salts, and potassium salts Therefore, they can be used alone or in combination of two or more. Of these, the combined use of an alkali carbonate and an organic acid compound is most preferable because it shows a rapid curing reaction after the coagulation. The amount of the coagulation modifier used is preferably 0.1 to 100 parts by weight with respect to 100 parts by weight of CA. If it is less than 0.1 part by weight, workability is poor, and if it exceeds 100 parts by weight, initial strength development is not preferable.

Various other admixtures may be used in combination with the cement admixture or cement composition of the present invention. Other various admixtures include, for example, silica sand, natural sand, aggregates such as gravel, glass fibers, carbon fibers,
And fibers such as steel fiber, high-molecular polymer emulsion or latex, colorant, fluidizing agent, rust preventive, inseparable admixture in water such as methyl cellulose, thickener, water retention agent, waterproofing agent such as sodium silicate, A foaming agent, a foaming agent and the like can be used, and one kind or two or more kinds thereof can be used together within a range not substantially impairing the object of the present invention.

Any existing stirring device can be used as the mixing device used when producing the cement admixture or cement composition of the present invention. For example, a tilting barrel mixer, an omni mixer manufactured by Chiyoda Giken Kogyo Co., Ltd., a V-type mixer, a Henschel mixer, a Nauta mixer and the like can be used. In addition, the respective materials may be mixed at the time of construction, or a part or all of them may be mixed in advance.

The actual construction method of the cement composition of the present invention may be based on the conventional construction method of mortar or concrete.

[0032]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 Calcium carbonate and alumina, which are commercially available special grade reagents, were mixed so that the molar ratio of CaO / Al ₂ O ₃ was 12/7, and further, sodium carbonate, potassium carbonate, and lithium carbonate, which were the special grade reagents, were mixed. Was mixed in a predetermined amount in terms of oxide. Put 500g of each of them into a carbon crucible and put them in a high frequency furnace for about 1,600
After being melted by heating at 0 ° C., it was put into water and rapidly cooled to synthesize various CAs. Table 1 shows the analysis results of the synthesized CA.

[0034]

[Table 1]

Further, the vitrification rate of these CAs is determined by powder X
It was measured by a line diffractometer. As a result, it was found that all CAs were 100% vitrified glass.
Further, each of these CAs was ground to a BET specific surface area of 0.4 m ² / g to obtain a cement admixture. 10 parts by weight of this cement admixture was added to 100 parts by weight of the total amount of cement and the cement admixture to obtain a cement composition. Using this cement composition, a 1: 2 mortar was prepared according to JIS R5201 “Cement physical testing method”, and 4 × 4
A 16 cm mortar specimen was molded. The thus-prepared mortar specimen was cured for 24 hours at 20 ° C. in wet air and then at 20 ° C. in water. Using the mortar specimen that had been cured, a compressive strength test was immediately carried out in a thermostatic chamber at 20 ° C. In addition, the setting time was measured by placing 200 g of mortar immediately after kneading in a plastic container in a thermostatic chamber at 20 ° C.
The temperature was set until the temperature of the mortar increased by inserting a thermocouple. The results are shown in Table 2.

[0036]

[Table 2]

Example 2 The industrial raw materials shown in Table 3 were mixed so as to have the composition shown in Table 4, and the mixture was melted in a direct current melting furnace with a maximum power load of 5,000 kVA, and the cooling rate was changed. , CA respectively
Were produced in 3 ton increments. The same procedure as in Example 1 was carried out except that these CAs were used. The results are shown in Table 5.

<Material used> Quick lime: manufactured by Denki Kagaku Kogyo Alumina: Showa Denko Sodium carbonate: Asahi Glass Co., Ltd.

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

Example 3 Using CA of K 5 and K 10 of Example 1, gypsum was compounded as shown in Table 6 to obtain a cement admixture. To 85 parts by weight of cement, mix 15 parts by weight of the cement admixture,
The same procedure as in Example 1 was performed except that opal which was a reactive aggregate was used as the aggregate. The results are shown in Table 6.

<Materials used> Gypsum: Type II anhydrous gypsum manufactured by Sankei Gypsum Co., BET
Specific surface area 0.45 m ² / g

[0044]

[Table 6]

Example 4 The CA E, gypsum, and setting modifier of Example 2 are listed in Table 7.
Example 3 was carried out in the same manner as in Example 3 except that the formulation shown in was used. The results are also shown in Table 7.

<Materials used>

[0047]

[Table 7]

[0048]

As described above in detail, by using the cement admixture of the present invention, (1) pot life can be adjusted arbitrarily. (2) Good strength development. (3) High long-term strength. (4) There is no concern about alkali-aggregate reaction. The effects such as

Claims (2)

[Claims] 1. A cement admixture containing calcium aluminate as an active ingredient, containing more than 0.1% by weight and less than 2% by weight of R ₂ O (R is an alkali metal). 2. A cement composition comprising a mixture of cement and the cement admixture according to claim 1.