JP2023028445A - Rapid-hardening admixture material and rapid-hardening cement composition - Google Patents

Abstract

To provide an admixture material for repair material that has both rapid-hardening property and neutralization suppression effect, and furthermore moisture permeation resistance after neutralization.SOLUTION: Provided is a rapid-hardening admixture material which contains a cement admixture material, and alkali metal salt and/or alkaline earth metal salt, and in which the cement admixture material contains one kind of or two or more kinds of non-hydraulic compounds selected from a group consisting of γ-2CaO-SiO2, 3CaO-2SiO2, α-CaO-SiO2, and calcium magnesium silicate, and the non-hydraulic compound contains Li and a content ratio of the Li is 0.001 to 1.0 mass% in terms of oxide.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a quick-hardening admixture and a quick-hardening cement composition used in the fields of civil engineering, construction and the like.

In recent years, the environments in which concrete structures are used have diversified, and from the viewpoint of the life cycle cost of structures, there is a demand for highly durable concrete that can cope with various environments.

One of the important causes of deterioration of durability of concrete is neutralization. Neutralization is a degradation phenomenon caused by calcium hydroxide reacting with carbon dioxide in the atmosphere and being carbonated.

The problem with neutralization of concrete is the rusting of reinforcing bars used as reinforcing materials in reinforced concrete structures. This is one of the causes of deterioration of the durability of concrete structures.

In addition, concrete structures built during Japan's period of high economic growth now require repair due to deterioration such as neutralization. be.

As a repair method for deteriorated concrete, if cracking has progressed due to neutralization, the deteriorated part must be removed, the rust of the reinforcing bar must be removed, and then concrete must be placed again. First of all, it is desirable that the concrete used for the repaired part is highly durable so as not to cause premature deterioration.

In such repairs, a method has been proposed in which a cement composition consisting of cement and a polymer is used to improve adhesion to the repaired surface and crack resistance and delay the progress of neutralization (for example, Patent Document 1). reference).

However, in recent years, it has become clear that penetration of moisture, such as raindrops, has a great effect on reinforcement corrosion in reinforced concrete structures. Moisture permeation resistance has become important.

Also, in the repair of main roads and the like, early completion of construction is strongly desired in order to alleviate traffic congestion, and materials having rapid hardening properties are required. For these reasons, there has been a demand for the development of an admixture that has both rapid hardening properties, an effect of suppressing neutralization, and resistance to moisture permeation after neutralization.

JP-A-5-24899

Under the circumstances as described above, the present invention provides a rapid-hardening admixture having both rapid-hardening property, neutralization-inhibiting effect, and water penetration resistance after neutralization, and a rapid-hardening cement composition using the said admixture. The task is to provide

As a result of intensive research to solve the above problems, it was found that by combining a non-hydraulic compound containing Li at a predetermined ratio and a rapid hardening component, the strength development in a short time and the carbonation of the non-hydraulic composition We have developed a technique to exhibit the effect of suppressing the neutralization and further the moisture permeation resistance after the neutralization by the densification accompanying the densification. The gist of the present invention is as follows.
[1] A cement admixture containing one or more non-hydraulic compounds selected from the group consisting of γ-2CaO.SiO ₂ , 3CaO.2SiO ₂ , α-CaO.SiO ₂ and calcium magnesium silicate. a cement admixture containing Li in the non-hydraulic compound and having a Li content of 0.001 to 1.0% by mass in terms of oxide, and an alkali metal salt and/or an alkaline earth metal salt; A quick-hardening admixture containing
[2] The chemical composition in 100 parts by mass of the cement admixture is 0.001 to 1.0 parts by mass of Li ₂ O, 45 to 70 parts by mass of CaO, 29 to 54 parts by mass of SiO ₂ and Al ₂ O. The rapid-hardening admixture according to [1] above, containing 0 to 10 parts by mass of ₃ .
[3] The quick-hardening admixture according to [1] or [2] above, wherein the alkali metal salt and alkaline earth metal salt are respectively nitrite and/or nitrate.
[4] The above [1] to [3], further containing a curing modifier, wherein the curing modifier is one or more selected from the group consisting of inorganic carbonates, organic acids and salts of said organic acids. ] The quick-hardening admixture according to any one of the above.
[5] A quick-hardening cement composition comprising cement and the quick-hardening admixture according to any one of [1] to [4] above.

By using the quick-hardening admixture and the quick-hardening cement composition of the present invention, an admixture and the admixture having both rapid hardening property, neutralization suppressing effect, and water permeation resistance after neutralization can be obtained. The cement composition used can be provided.

The details of the present invention are described below.
Parts and percentages in this specification are based on mass unless otherwise specified.

[Rapid hardening admixture]
The quick-hardening admixture of the present invention comprises a cement admixture and an alkali metal salt and/or an alkaline earth metal salt.

<Cement admixture>
The cement admixture according to the present embodiment is one or more non-hydraulic compounds selected from the group consisting of γ-2CaO·SiO ₂ , 3CaO·2SiO ₂ , α-CaO·SiO ₂ , and calcium magnesium silicate. including.
Further, the cement admixture according to the present embodiment is characterized by further containing Li in the non-hydraulic compound and having a content of 0.001 to 1.0% in terms of oxide. It is presumed that this predetermined amount of Li promotes the formation of vaterite, which is a type of calcium carbonate, among the carbonation of CSH (calcium silicate hydrate). It is thought that a more dense cured state can be easily obtained by.
The content of Li is 0.001 to 1.0%, preferably 0.005 to 1.0%, preferably 0.010 to 1.0% in terms of oxide, from the viewpoint that the above effects are likely to be achieved. It is more preferably 0.90%, even more preferably 0.015 to 0.80%. If the Li content is less than 0.001% in terms of oxide, the effect of promoting carbonation cannot be obtained. On the other hand, if it exceeds 1.0%, the cost becomes high. The content of Li in terms of oxide can be measured by the method described in Examples.
Here, "contains Li in the non-hydraulic compound" means that the non-hydraulic compound contains Li ₂ O as a chemical composition (existence can be confirmed by ICP emission spectroscopic analysis), but X-ray diffraction It refers to a state in which Li ₂ O is not identified by measurement (a clear peak of Li ₂ O is not observed), and simply refers to a state in which a non-hydraulic compound and a Li compound are not physically mixed. Such a state can be obtained by mixing each raw material and heat-treating it at a high temperature of 1,000° C. or higher. Each component and the like will be described below.

(γ-2CaO-SiO ₂ )
γ-2CaO.SiO ₂ is a compound represented _by 2CaO.SiO ₂ and is known as a low temperature phase _. It is completely different from β-2CaO·SiO ₂ . All of these are represented by 2CaO.SiO ₂ , but have different crystal structures and densities.

( _3CaO.2SiO2 )
3CaO.2SiO ₂ is a mineral containing CaO in pseudowollastonite and is called rankinite. Although it is a chemically stable mineral with no hydration activity, it has a large effect of promoting carbonation (salting).

(α-CaO.SiO ₂ )
α-CaO·SiO ₂ (α-type wollastonite) is a compound represented by CaO·SiO ₂ and is known as a high-temperature phase. β-CaO·SiO ₂ is a low-temperature phase. They are completely different. All of these are represented by CaO.SiO ₂ , but have different crystal structures and densities.

Naturally occurring wollastonite is the low temperature phase β-CaO.SiO ₂ . β-CaO SiO ₂ has needle- _like crystals and is used as an inorganic fibrous material such as wollastonite fiber. There is no salinization promoting effect.

(calcium magnesium silicate)
Calcium magnesium silicate is a general term for CaO--MgO-- _SiO.sub.2 -based compounds, and in the present embodiment, it is Merwinite _represented by 3CaO.MgO.2SiO.sub.2 ( _{C.sub.3MS.sub.2 )} . Mervinite achieves a large carbonation (salt) promoting effect.

The above non-hydraulic compounds may be one or two or more, and the content of Li in the non-hydraulic compound is as described above. The content of refers to the content of Li in terms of oxide with respect to the total of two or more non-hydraulic compounds.

Among the above non-hydraulic compounds, especially γ-2CaO SiO ₂ is accompanied by a pulverization phenomenon called dusting during production, so it requires less energy for pulverization than other compounds, and carbonation (salification) occurs over a long period of time. It is preferable in that it has a large acceleration effect and, on the other hand, has a very large neutralization suppressing effect when combined with blast-furnace cement at a low water binder ratio.

The non-hydraulic compound according to the present embodiment is obtained by blending CaO raw material, SiO ₂ raw material, MgO raw material and Li raw material in a predetermined molar ratio and heat-treating the mixture at a high temperature of 1000° C. or higher.
CaO raw materials include, for example, calcium carbonate such as limestone, calcium hydroxide such as slaked lime, by-product slaked lime such as acetylene by-product slaked lime, fine powder generated from waste concrete mass, and the like. One selected from industrial by-products containing CaO, such as by-product slaked lime, fine powder generated from waste concrete masses, municipal waste incineration ash and sewage sludge incineration ash, for the reduction of non-energy-derived CO ₂ emissions during heat treatment. Alternatively, two or more types can be used. Among them, it is more preferable to use by-product slaked lime, which contains less impurities than other industrial by-products.
Examples of SiO ₂ raw materials include silica stone, clay, and various siliceous dusts generated as industrial by-products such as silica fume and fly ash.
Examples of MgO raw materials include magnesium hydroxide, basic magnesium carbonate, and dolomite. Moreover, lithium carbonate etc. can be mentioned as a Li raw material. If the CaO raw material, SiO ₂ raw material, or MgO raw material contains Li, it is not necessary to newly add the Li raw material.

As by-product slaked lime, by-product slaked lime produced in the acetylene gas production process by the calcium carbide method (there are wet and dry products depending on the acetylene gas production method), and the wet dust collection process of the calcium carbide electric furnace. Examples include acetylene by-product slaked lime such as by-product slaked lime contained in the dust captured by. The by-product slaked lime contains, for example, 65 to 95% (preferably 70 to 90%) calcium hydroxide, 1 to 10% calcium carbonate, and 0.1 to 6.0% iron oxide (preferably contains 0.1 to 3.0%). These ratios are determined by fluorescent X-ray measurement and differential thermogravimetric analysis (TG-DTA) for weight loss (Ca(OH) ₂ : around 405°C to 515°C, CaCO ₃ : around 650°C to 765°C). can be confirmed. The volume average particle diameter measured by laser diffraction/scattering method is about 50 to 100 μm. Furthermore, in JIS K 0068 "Method for measuring water content of chemical products", the moisture content measured by the loss-on-drying method is preferably 10% or less. Further, sulfur compounds such as CaS, Al ₂ S ₃ and CaC ₂ ·CaS may be contained, but the content is preferably 2% or less.

The above heat treatment at a high temperature of 1,000° C. or higher is not particularly limited, but can be performed, for example, by using a rotary kiln or an electric furnace. Although the heat treatment temperature is not uniquely determined, it is usually performed in the range of about 1,000 to 1,800.degree. C., and often in the range of about 1,200 to 1,600.degree.

This embodiment can also use industrial by-products containing the non-hydraulic compounds previously described. In this case, impurities coexist. Such industrial by-products include steelmaking slag and the like.

The CaO raw material, the SiO ₂ raw material, and the MgO raw material may contain impurities, but they pose no particular problem as long as they do not impair the effects of the present invention. Specific examples of impurities include Al ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , MnO, Na ₂ O, K ₂ O, S, P ₂ O ₅ , F, B ₂ O ₃ and chlorine. be done. Coexisting compounds include free calcium oxide, calcium hydroxide, calcium aluminate, calcium aluminosilicate, calcium ferrite, calcium aluminoferrite, calcium phosphate, calcium borate, magnesium silicate, leucite (K ₂ O, Na ₂ O).Al ₂ O ₃ .SiO ₂ , spinel MgO.Al ₂ O ₃ , magnetite Fe ₃ O ₄ , sulfur compounds such as CaS, Al ₂ S ₃ and CaC ₂ .CaS mentioned above.

Among these impurities, the content of S (sulfur) in the non-hydraulic compound is preferably 1.0% or less, more preferably 0.7% or less in terms of oxide (SO ₃ ). , and more preferably 0.5% or less. When the content is 1.0% or less, a sufficient effect of promoting carbonation (salting) can be obtained, and the setting and curing properties can be kept within an appropriate range. The content of S in terms of oxide (SO ₃ ) can be measured by fluorescent X-ray measurement. Note that S (sulfur) in the non-hydraulic compound may be present as long as it is about 2% in terms of oxide.

In addition, from the viewpoint of making the effect more likely to be expressed in the present cement admixture, the chemical composition is 0.001 to 1.0 parts of Li ₂ O, 45 to 70 parts of CaO, in 100 parts of the cement admixture. It preferably contains 29 to 54 parts of SiO ₂ and 0 to 10 parts of Al ₂ O ₃ . The Li ₂ O content can be measured by the method described in Examples below. Also, CaO, SiO ₂ and Al ₂ O ₃ can be measured by fluorescent X-rays.
As for the chemical composition, 0.002 to 0.5 parts of Li ₂ O, 60 to 70 parts of CaO, 30 to 45 parts of SiO ₂ and 0.5 to 5 parts of Al ₂ O ₃ are contained in 100 parts of the cement admixture. It is more preferable to include a part. Furthermore, as a chemical composition, the total of Li ₂ O, CaO, SiO ₂ and Al ₂ O ₃ in 100 parts of the cement admixture is preferably 90 parts or more, more preferably 95 to 100 parts. .

As a method for quantifying the non-hydraulic compound in the present admixture, the Rietveld method using powder X-ray diffractometry may be used.

Although the Blaine specific surface area of the present cement admixture is not particularly limited, it is preferably 1,500 cm ² /g or more, and the upper limit is preferably 8,000 cm ² /g or less. Among them, 2,000 to 6,000 cm ² /g is more preferable, and 4,000 to 6,000 cm ² /g is most preferable. When the Blaine specific surface area is 1,500 cm ² /g or more, good material separation resistance is obtained, and the carbonation (salt) promotion effect is sufficient. In addition, when it is 8,000 cm ² /g or less, the power required for pulverization is not large, which is economical, and weathering is suppressed, so that deterioration of quality over time can be suppressed.

<Alkali metal salt and/or alkaline earth metal salt>
Alkali metal salts and alkaline earth metal salts that can be used in the present invention are not particularly limited, and include nitrites, nitrates, sulfates, carbonates, acetates, and the like. Preferably.
The nitrite and/or nitrate (hereinafter referred to as "nitrates") used in the present invention is not particularly limited as long as it imparts rapid hardening when mixed with cement. Specifically, Alkali metal salts or alkaline earth metal salts of nitrites and nitrates may be mentioned, of which the use of lithium, sodium, potassium and calcium salts is economically preferred.
In the present invention, one or more of these can be used, but lithium salts and calcium salts are more preferable because they do not promote the alkali-aggregate reaction. Rapid hardening is most prominent and most preferred.

The amount of alkali metal salt and/or alkaline earth metal salt used is not particularly limited, but is preferably 5 to 70 parts, more preferably 20 to 50 parts, per 100 parts of the quick-hardening admixture. When it is 5 parts or more, sufficient rapid hardening is obtained, and when it is 70 parts or less, the fluidity of concrete is not impaired, which is advantageous in terms of construction.

<Curing modifier>
The quick-hardening admixture of the present invention may contain a hardening modifier.
Although the curing modifier is not particularly limited, it is preferably one or more selected from the group consisting of inorganic carbonates, organic acids and salts of said organic acids.
For example, inorganic carbonates include carbonates and bicarbonates of alkali metals, and organic acids include oxycarboxylic acids such as citric acid, tartaric acid, gluconic acid and malic acid, alkali metal salts thereof, and alkali metal salts. Examples include earth metal salts, aluminum salts, ammonium salts and the like.

Although the amount of the curing modifier is not particularly limited, it is usually preferably used within 5 parts, more preferably within 2 parts, and 0.1 part with respect to 100 parts of the quick-hardening admixture. It is particularly preferred to be used in the range of to 1 part. . If the curing modifier is insufficient, the pot life may be shortened.

<Retardant>
The quick-setting admixture of the present invention may contain a retardant.
The retarder used in the present invention is not particularly limited, but it is for adjusting the setting of cement and not impairing the fluidity of concrete during construction, and can also be called a setting adjusting agent. Both organic and inorganic retardants can be used.

Specific examples of organic substances that can be used include organic acids such as carboxylic acids, oxymonocarboxylic acids, oxypolycarboxylic acids, polycarboxylic acids, and salts thereof.
Carboxylic acids include saturated or unsaturated carboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, and heptanoic acid. Examples include heptonic acid, gluconic acid, and glycolic acid.

Examples of oxypolycarboxylic acids include malic acid, tartaric acid, and citric acid, and examples of polycarboxylic acids include cocondensates of acrylic acid and maleic anhydride.

In addition, salts of the above organic acids can also be used, for example alkali metal salts such as lithium, sodium and potassium, alkaline earth metal salts such as magnesium and calcium, and zinc, copper, aluminum and ammonium salts. and the like.

Specific examples of inorganic substances include inorganic acids such as phosphoric acid, hydrofluoric acid, and boric acid, phosphates, zinc oxide, lead oxide, and silicofluorides such as magnesium silicofluoride and sodium silicofluoride, and ice. Fluorine-containing minerals such as crystallite and calcium fluoroaluminate can be used.

In the present invention, one or more of these can be used, but it is particularly preferred to use citric acid or its salts, gluconic acid or its salts, and tartaric acid or its salts.

The amount of the retarder used is not particularly limited, but is preferably 0.1 to 10 parts, more preferably 0.3 to 5 parts, per 100 parts of the quick-hardening admixture.

[Quick-hardening cement composition]
The quick-hardening cement composition in the present invention contains cement and the above-described quick-hardening admixture.
The amount of the quick-hardening admixture used in the quick-hardening cement composition of the present invention is not particularly limited, but usually 3 to 20 parts per 100 parts of the cement composition comprising cement and the quick-hardening admixture. parts are preferred, and 7 to 15 parts are more preferred. When the amount is 3 parts or more, the effects of the present invention are sufficiently obtained, and when the amount is 20 parts or less, long-term strength development is not impaired.

<Cement>
The cement used in the present invention is not particularly limited, but it is preferable to use cement containing Portland cement. Examples include various mixed cements obtained by mixing water granulated slag, fly ash, or silica, or limestone filler cements obtained by mixing Portland cement with limestone powder or the like.

In addition, in the present invention, it is possible to mix fine aggregates with a quick-hardening cement composition comprising cement and the quick-hardening admixture of the present invention, and the type of fine aggregates is not particularly limited. , silica sand, river sand, sea sand, mountain sand, crushed sand, etc. can be used, and the maximum particle size is preferably 5 mm or less, more preferably 2.5 mm or less.

In the present invention, in addition to aggregates such as sand and gravel, water reducing agents, AE water reducing agents, high performance AE water reducing agents, high performance AE water reducing agents and antifoaming agents are added to the quick-hardening admixture and the quick-hardening cement composition of the present invention. agents, thickeners, rust inhibitors, antifreeze agents, expansion agents, shrinkage reducing agents, polymer emulsions, clay minerals such as bentonite and zeolite, and ion exchangers such as hydrotalcite, etc. can be used as long as the object of the present invention is not substantially impaired.

The amount of water used in the present invention is preferably 20 to 60 parts of water per 100 parts of the quick-hardening cement composition. When the amount of water is 20 parts or more, sufficient fluidity is obtained, and when it is 60 parts or less, sufficient strength is ensured.

In the present invention, the method of mixing each material is not particularly limited, and each material may be mixed at the time of construction, or may be partially or wholly mixed in advance. As a mixing device, any existing device can be used, for example, a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, a Nauta mixer, and the like can be used.

Experimental example 1
(1) Production of Cement Admixtures Cement admixtures 1 to 15 were produced as follows.

(1-1) Cement admixtures 1 to 3 (Li-containing γ-2CaO SiO ₂ )
First-grade reagent calcium carbonate and reagent first-grade silicon dioxide were mixed at a molar ratio of 2:1, and the content of Li in the mixture in terms of oxide (Li ₂ O) was calculated as shown in Table 1 (of which Cement admixtures 1 to 3 having a Blaine specific surface area of 4,000 cm ² /g were mixed with reagent grade 1 lithium carbonate so as to have a split substitution), heat-treated at 1,400° C. for 2 hours, and left to stand at room temperature. was made.

(1-2) Cement admixtures 4 to 6 (Li-containing 3CaO 2SiO ₂ )
First-grade reagent calcium carbonate and reagent first-grade silicon dioxide are mixed at a molar ratio of 3:2, and the content of Li in the mixture is calculated in terms of oxide (Li ₂ O) described in Table 1 (inner division substitution), heat-treated at 1,400° C. for 2 hours, left to stand at room temperature, and cement admixtures 4 to 6 having a Blaine specific surface area of 4,000 cm ² /g. made.

(1-3) Cement admixtures 7 to 9 (Li-containing α-CaO SiO ₂ )
First-grade reagent calcium carbonate and reagent first-grade silicon dioxide were mixed at a molar ratio of 1:1, and the content of Li in the mixture was determined in terms of oxide (Li ₂ O) described in Table 1 (of which Cement admixtures 7 to 9 having a Blaine specific surface area of 4,000 cm ² /g were mixed with reagent grade 1 lithium carbonate so as to have a split substitution), heat-treated at 1,500° C. for 2 hours, and left to stand at room temperature. was made.

(1-4) Cement admixtures 10 to 12 (Li-containing 3CaO/MgO/2SiO ₂ )
Reagent grade 1 calcium carbonate, reagent grade 1 magnesium oxide, and reagent grade 1 silicon dioxide are mixed in a molar ratio of 3:1:2, and the content of Li in the mixture is adjusted to oxide (Li ₂ O ) Reagent class 1 lithium carbonate was mixed so that the conversion would be as described in Table 1 (internal substitution), heat treated at 1,400 ° C. for 2 hours, left to stand at room temperature, and Blaine specific surface area was 4,000 cm ² / g of cement admixtures 10 to 12 were produced.

(1-5) Cement admixture 13 (β-2CaO/SiO ₂ )
Reagent grade 1 calcium carbonate and reagent grade 1 silicon dioxide are mixed at a molar ratio of 2:1, heat-treated at 1,400° C. for 2 hours, allowed to stand at room temperature, pulverized and analyzed by XRD to obtain γ-2CaO SiO. The same heat treatment was repeated until the peak of ₂ was no longer confirmed. After confirming the peak of β-2CaO·SiO ₂ alone, a cement admixture 13 having a Blaine specific surface area of 4,000 cm ² /g was produced.

(1-6) Cement admixture 14 (γ-2CaO/SiO ₂ )
Reagent grade 1 calcium carbonate and reagent grade 1 silicon dioxide were mixed at a molar ratio of 2:1, heat-treated at 1,400°C for 2 hours, and left to stand at room temperature to obtain a Blaine specific surface area of 4,000 cm ² /g. of γ-2CaO SiO ₂ was produced.

(1-7) Cement admixture 15 (Li ₂ O+γ-2CaO.SiO ₂ )
Reagent grade 1 calcium carbonate and reagent grade 1 silicon dioxide were mixed at a molar ratio of 2:1, heat-treated at 1,400°C for 2 hours, and left to stand at room temperature to obtain a Blaine specific surface area of 4,000 cm ² /g. of γ-2CaO SiO ₂ was produced.
Lithium carbonate of reagent grade 1 was heat-treated at 1,400° C. for 2 hours and left to stand at room temperature to prepare Li ₂ O powder.
Li ₂ O powder (reagent class 1 lithium carbonate heat-treated at 1,400 ° C. for 2 hours) is added to the above γ-2CaO SiO ₂ so that Li ₂ O becomes 0.1% (internal substitution). A cement admixture was produced by internal mixing.

The oxide-equivalent Li content in each cement admixture was measured by an ICP emission spectrometer (VISTA-PRO, manufactured by Hitachi High-Tech Science). Then, from the absolute calibration curve method using a diluted SPEX company XSTC-22 ICP mixed solution, it was confirmed that the Li content was the same as the charged amount. In addition, the measurement conditions are as follows.
・ Li measurement wavelength: 670.783 nm
・ BG correction: fitting curve method ・ Standard solution for calibration curve: SPEX XSTC-22 ICP mixed solution diluted and used Calibration curve range: 0-5 mg / L (0 mg / L, 0.1 mg / L, 0. 5 mg/L, 1 mg/L, 5 mg/L 5-point calibration curve)
・Quantification by absolute calibration curve method

(2) Evaluation of carbonation reaction rate of admixture 5 g of each admixture was weighed in an evaporating dish and subjected to carbonation curing for 7 days according to JIS A 1153 (room temperature 20 ° C., relative humidity 60%, 5%-CO ₂ concentration )bottom. After carbonation curing for 7 days, using a differential thermogravimetric analysis (manufactured by NETZSCH, model 2020SA), the sample weight was 50 ± 2 mg, the temperature was raised from room temperature to 1,000 ° C. at a rate of 10 ° C./min, and under a nitrogen flow environment. Thermogravimetric analysis (TG) was performed. For the amount of CaCO ₃ produced (carbonation reaction rate), the carbonation reaction rate of each sample was calculated from the following formula, assuming that the weight loss in the vicinity of 650° C. to 765° C. in the TG curve was the weight loss due to decarboxylation of CaCO ₃ . Table 1 shows the results.
Carbonation reaction rate (%) = [Δm _CaCO3 / (m ₀ - m _1,000 )] x 100.09/44.01 x 100
(Δm _CaCO3 : amount of decarboxylation of calcium carbonate (mg), m ₀ : amount of sample used for measurement (mg), m _1,000 : amount of mass loss up to 1,000° C. (mg))

(3) Measurement of vaterite content by XRD measurement The vaterite content of the admixture after the carbonation curing for 7 days was measured by powder X-ray diffraction (manufactured by Rigaku, SmartLab). A predetermined amount of an internal standard substance such as aluminum oxide or magnesium oxide was added to the cement admixture, thoroughly mixed in an agate mortar, and then subjected to powder X-ray diffraction measurement. The measurement results were analyzed with quantitative software to determine the vaterite content. Rigaku's "Smartlab Studio II" was used as the quantification software. Table 1 shows the results.

Experimental Example 2 (Experiment Nos. 2-1 to 2-31)
70 parts of the cement admixture shown in Table 1 and 30 parts of lithium nitrite were mixed to obtain a quick-hardening admixture. Furthermore, a mortar with a water/cement composition ratio of 50% and a cement composition/sand ratio of 1/3 was prepared using the rapid-hardening admixture having the composition shown in Table 2 and a cement composition with the remainder being 100 parts as cement. After preparation, the compressive strength and neutralization depth at 1 day and 28 days of material age were measured. The results are also shown in Table 2.

<Materials used>
Cement: commercial product, ordinary Portland cement Nitrates: commercial product, lithium nitrite retardant: commercial product, citric acid water: tap water Fine aggregate: ISO679 compliant, standard sand

<Measurement method>
· Compressive strength: A specimen of 4 × 4 × 16 cm was produced, and the strength was measured according to JIS A 1108 at the age of 1 day and at the age of 28 days. The casting temperature was 20°C.
・ Neutralization depth: A specimen with a size of 4 × 4 × 16 cm was prepared, cured in water at 20 ° C until the age of 28 days, and then placed in an environment of 30 ° C, relative humidity of 60%, and carbon dioxide gas concentration of 10%. Promoted neutralization. After 6 months, the specimen was cut into round slices, a phenolphthalein solution was applied to the cross section, and the neutralization depth from the surface to the colored portion was measured to evaluate the neutralization inhibitory effect.

Experimental Example 3 (Experiment Nos. 3-1 to 3-9)
70 parts of the admixture shown in Table 3 and 30 parts of lithium nitrite were blended, and a retarder of the type and amount shown in Table 3 was blended to prepare a quick-hardening admixture. Next, a composition comprising 10 parts of the quick-hardening admixture and 90 parts of cement was used to evaluate fluidity retention. Table 3 shows the results. Other evaluation items are the same as those in the above example.
- Fluidity retention rate: Evaluated by the change in flow value over time at an ambient temperature of 20°C. Based on the flow test of JIS R 5201, it was calculated from the flow value immediately after kneading and after 30 minutes.
Fluid retention = (flow value after 30 minutes / flow value immediately after kneading) x 100

<Materials used>
Retardant A: commercial product, citric acid retardant B: commercial product, gluconic acid retardant C: commercial product, sodium gluconate retardant D: commercial product, tartaric acid retardant E: retarder A and retarder D 1: 1 (mass ratio) mixture

Experimental Example 4 (Experiment Nos. 4-1 to 4-10)
The mass (moisture) transfer resistance of the concrete to which the above quick-hardening admixture was added was evaluated depending on whether it was neutralized or not. The neutralized test specimens used were completely neutralized.

Using the rapid-hardening admixture shown in Table 4, the rapid-hardening cement admixture was blended in the amount shown in Table 4 in 100 parts of the cement composition consisting of ordinary cement and the rapid-hardening admixture, and JIS R 5201. A cylindrical test piece of mortar Φ100×200 mm was prepared according to. The sides of the specimen were sealed with aluminum tape, and the top and bottom surfaces were opened. As for the water absorption method, the lower surface of the test piece was immersed in a water bath up to 1 cm, and the test piece was split 24 hours after the immersion, and the penetration depth of water was measured using a vernier caliper. Table 4 shows the results.

From the results in Table 1, it can be seen that the quick-hardening admixture of the present invention has a high carbonation reaction rate and a high production amount of vaterite.
The results in Table 2 also show that the mortars prepared using these quick-hardening admixtures of the present invention have a high compressive strength and a small neutralization depth. That is, it can be seen that the use of the quick-hardening admixture of the present invention exhibits strength development in a short period of time and good resistance to neutralization.
In contrast, the cement admixtures 13 to 15 presented as comparative examples have low compressive strength and deep neutralization depths.
Moreover, from the results in Table 3, it can be seen that the addition of the retarder improves the fluidity retention rate.
Furthermore, from the results in Table 4, it can be seen that the quick-hardening cement composition using the quick-hardening admixture of the present invention has a shallow water penetration depth and excellent water penetration resistance.

According to the quick-hardening admixture and the quick-hardening cement composition of the present invention, short-term strength can be achieved, and an excellent neutralization suppressing effect can be exhibited. Furthermore, since it is excellent in moisture permeation resistance after neutralization, it is suitable as a concrete material in civil engineering or construction, especially as a repair material.

Claims (5)

A cement admixture containing one or more non-hydraulic compounds selected from the group consisting of γ-2CaO·SiO ₂ , 3CaO·2SiO ₂ , α-CaO·SiO ₂ , and calcium magnesium silicate, A cement admixture containing Li in a non-hydraulic compound and having a Li content of 0.001 to 1.0% by mass in terms of oxide, and an alkali metal salt and/or an alkaline earth metal salt. A rapid hardening admixture. The chemical composition in 100 parts by mass of the cement admixture is 0.001 to 1.0 parts by mass of Li ₂ O, 45 to 70 parts by mass of CaO, 29 to 54 parts by mass of SiO ₂ , and 0 parts by mass of Al ₂ O _3. The quick-hardening admixture according to claim 1, containing up to 10 parts by mass. 3. The quick-hardening admixture according to claim 1, wherein said alkali metal salt and alkaline earth metal salt are respectively nitrite and/or nitrate. 4. The composition according to any one of claims 1 to 3, further comprising a curing modifier, wherein said curing modifier is one or more selected from the group consisting of inorganic carbonates, organic acids and salts of said organic acids. The quick-hardening admixture described in . A quick-hardening cement composition comprising cement and the quick-hardening admixture according to any one of claims 1 to 4.