JP7709334B2 - Rapid hardening admixture and rapid hardening cement composition - Google Patents

Description

The present invention relates to a rapid-hardening admixture and a rapid-hardening cement composition for use in the fields of civil engineering, construction, etc.

In recent years, the environments in which concrete structures are used have become more diverse, and from the perspective of the life cycle cost of structures, there is a demand for highly durable concrete that can withstand a variety of environments.

Carbonation is one of the main causes of the deterioration of concrete's durability. Carbonation is a deterioration phenomenon caused by calcium hydroxide reacting with carbon dioxide in the air and becoming carbonated.

The problem with neutralizing concrete is rusting of the reinforcing bars used as reinforcing materials in reinforced concrete structures. The expansion pressure caused by rusting can damage the adhesion between the reinforcing bars and the concrete, causing cracks in the concrete and being one of the causes of the loss of durability of concrete structures.

In addition, concrete structures constructed during Japan's period of rapid economic growth are now in need of repair due to deterioration such as carbonation, and the number of areas requiring repairs is expected to continue to increase in the future.

When deteriorated concrete has progressed to the point of cracking due to neutralization, repair methods include chipping off the deteriorated areas, removing the rust from the reinforcing bars, and then pouring the concrete again. It is desirable to use highly durable concrete in the repair areas to prevent premature deterioration.

For such repairs, a method has been proposed in which a cement composition consisting of cement and a polymer is used to improve adhesion and crack resistance to the repair surface and slow the progression of carbonation (see, for example, Patent Document 1).

However, in recent years, it has become clear that the penetration of moisture from rain, etc., has a significant impact on the corrosion of rebars in reinforced concrete structures, and therefore not only the carbonation inhibition effect but also the resistance of carbonized concrete to moisture penetration has become important.

In addition, when repairing major roads, etc., there is a strong desire to complete construction as soon as possible to alleviate traffic congestion, and materials with rapid hardening properties are required. For these reasons, there has been a demand for the development of an admixture that combines rapid hardening, carbonation inhibition effects, and resistance to water penetration after carbonation.

Japanese Patent Application Publication No. 5-24899

Under the circumstances described above, the objective of the present invention is to provide a rapid-hardening admixture that combines rapid hardening, carbonation inhibition effects, and resistance to water penetration after carbonation, and a rapid-hardening cement composition that uses the admixture.

As a result of intensive research to solve the above problems, we have developed a technology that combines a non-hydraulic compound containing Li in a specific ratio with a rapid hardening component, which exhibits strength development in a short period of time, carbonation inhibition effect due to densification of the non-hydraulic composition as it is carbonized, and furthermore, resistance to moisture penetration after carbonation. 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, wherein the non-hydraulic compound contains Li, and the Li content is 0.001 to 1.0 mass % in terms of oxide. A rapid hardening admixture containing an alkali metal salt and/or an alkaline earth metal salt.
[2] The rapid hardening admixture according to [1] above, which contains, as a chemical composition in 100 parts by mass of the cement admixture, 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 to 10 parts by mass of Al ₂ O ₃ .
[3] The rapid-hardening admixture according to [1] or [2] above, wherein the alkali metal salt and the alkaline earth metal salt are nitrites and/or nitrates, respectively.
[4] The rapid hardening admixture according to any one of [1] to [3] above, further comprising a hardening regulator, the hardening regulator being one or more selected from the group consisting of inorganic carbonates, organic acids and salts of the organic acids.
[5] A rapid-hardening cement composition comprising cement and the rapid-hardening admixture according to any one of [1] to [4] above.

By using the rapid-hardening admixture and rapid-hardening cement composition of the present invention, it is possible to provide an admixture and a cement composition using the admixture that combine rapid hardening, carbonation inhibition effects, and water penetration resistance after carbonation.

The present invention will now be described in detail.
In this specification, parts and percentages are by weight unless otherwise specified.

[Rapid hardening admixture]
The rapid 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 this embodiment contains 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.
The cement admixture according to this embodiment is characterized in that the non-hydraulic compound further contains Li, and the content of Li is 0.001 to 1.0% in terms of oxide. It is presumed that this predetermined amount of Li promotes the production of vaterite, a type of calcium carbonate, during the carbonation of C-S-H (calcium silicate hydrate), and it is believed that a denser hardened state can be easily obtained by carbonation (salt) curing.
From the viewpoint of easily achieving the above-mentioned effect, the Li content is 0.001 to 1.0% in terms of oxide, preferably 0.005 to 1.0%, more preferably 0.010 to 0.90%, and even more preferably 0.015 to 0.80%. If the Li content is less than 0.001% in terms of oxide, the carbonation promotion effect cannot be obtained. On the other hand, if it exceeds 1.0%, the cost becomes high. The Li content in terms of oxide can be measured by the method described in the examples.
Here, "Li is contained in the nonhydraulic compound" means that the nonhydraulic compound contains _Li2O as a chemical composition (its presence can be confirmed by ICP atomic emission spectroscopy), but _Li2O is not identified by X-ray diffraction measurement (no clear peak for _Li2O is observed), and it means that the nonhydraulic compound and the Li compound are not simply physically mixed together. This state can be obtained by mixing the respective raw materials and subjecting them to a heat treatment at a high temperature of 1,000°C or higher. Each component will be explained below.

(γ-2CaO・SiO ₂ )
γ- _2CaO.SiO2 is known as a low-temperature phase among the compounds expressed as _2CaO.SiO2 , and is completely different from the high-temperature phases α-2CaO.SiO2, α'- _2CaO.SiO2 , and _β - _2CaO.SiO2 . Although all of these are expressed as _2CaO.SiO2 , their crystal structures and densities are different.

(3CaO・2SiO ₂ )
_3CaO.2SiO2 is a mineral called rankinite, which is a pseudowollastonite containing CaO. It is a chemically stable mineral with no hydration activity, but has a large effect of promoting carbonation (salt).

(α-CaO・SiO ₂ )
α-CaO.SiO ₂ (α-type wollastonite) is known as a high-temperature phase among the compounds expressed as CaO.SiO ₂ , and is completely different from the low-temperature phase β-CaO.SiO _2. Although both are expressed as CaO.SiO ₂ , they have different crystal structures and densities.

Naturally occurring wollastonite is a low-temperature phase of β- _CaO.SiO2 . β- _CaO.SiO2 has needle-shaped crystals and is used as an inorganic fibrous material such as wollastonite fiber, but it does not have the carbonation (salt) promoting effect of α- _CaO.SiO2 according to this embodiment.

(Calcium Magnesium Silicate)
Calcium magnesium silicate is a general term for CaO-MgO- _SiO2 compounds, but in this embodiment, merwinite represented by _{3CaO.MgO.2SiO2} ( _C3MS2 ) is preferred, as merwinite achieves a large carbonation ( _salt ) promotion effect.

The above non-hydraulic compounds may be one type or two or more types, and the Li content in the non-hydraulic compounds is as described above. However, when there are two or more types of non-hydraulic compounds, the Li content refers to the Li oxide content relative to the total of the two or more types of non-hydraulic compounds.

Among the above non-hydraulic compounds, γ- _2CaO.SiO2 is particularly preferred because it requires less energy to grind than other compounds due to the powdering phenomenon called dusting that occurs during production, it has a large effect of promoting carbonation (salt) over a long period of time, and when combined with blast furnace cement at a low water-binder ratio, it has a very large effect of inhibiting carbonation.

The non-hydraulic compound according to this embodiment is obtained by mixing a CaO raw material, a _SiO2 raw material, a MgO raw material, and a Li raw material in a predetermined molar ratio and subjecting the mixture to a heat treatment at a high temperature of 1000°C or higher.
Examples of CaO raw materials include 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, etc. In order to reduce non-energy-derived _CO2 emissions during heat treatment, one or more types selected from industrial by-products containing CaO, such as by-product slaked lime, fine powder generated from waste concrete mass, municipal waste incineration ash, and sewage sludge incineration ash, can be used. Among these, the use of by-product slaked lime, which has a lower amount of impurities than other industrial by-products, is more preferable.
Examples of _SiO2 raw materials include silica stone, clay, and various siliceous dusts generated as industrial by-products, such as silica fume and fly ash.
Examples of the MgO raw material include magnesium hydroxide, basic magnesium carbonate, and dolomite. Examples of the Li raw material include lithium carbonate. If the CaO raw material, _SiO2 raw material, and MgO raw material contain Li, it is not necessary to add the Li raw material.

Examples of by-product slaked lime include acetylene by-product slaked lime such as by-product slaked lime produced in the acetylene gas production process by the calcium carbide method (wet type and dry type depending on the acetylene gas production method), by-product slaked lime contained in dust captured in the wet dust collection process of a calcium carbide electric furnace, etc. 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% (preferably 0.1 to 3.0%) iron oxide. These proportions can be confirmed by fluorescent X-ray measurement and mass loss determined by differential thermogravimetric analysis (TG-DTA) (Ca(OH) ₂ : around 405°C to 515°C, CaCO ₃ : around 650°C to 765°C). The volume average particle size measured by the laser diffraction/scattering method is about 50 to 100 μm. Furthermore, the moisture content measured by the loss on drying method in JIS K 0068 "Method for measuring moisture content of chemical products" is preferably 10% or less. In addition, sulfur compounds such as CaS, Al ₂ S ₃ , and CaC ₂ ·CaS may be contained, but it is preferable that the content is 2% or less.

The heat treatment at high temperatures of 1,000°C or higher mentioned above is not particularly limited, but can be carried out, for example, in a rotary kiln or electric furnace. The heat treatment temperature is not uniquely determined, but is usually carried out in the range of about 1,000 to 1,800°C, and often in the range of about 1,200 to 1,600°C.

In this embodiment, industrial by-products containing the non-hydraulic compounds described above can also be used. In this case, impurities will coexist. Examples of such industrial by-products include steel slag.

The CaO raw material, _SiO2 raw material, and MgO raw material may contain impurities, but _these do not pose any particular problem as long as they do not impair the effects of the present invention. Specific examples of impurities include _Al2O3 , _Fe2O3 , _TiO2 , _MnO , _Na2O , _K2O , _{S, P2O5 , F} , _B2O3 , and chlorine. 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 , and sulfur compounds such as the above-mentioned CaS, Al ₂ S ₃ , and CaC _2.CaS .

Of these impurities, the content of S (sulfur) in the non-hydraulic compound is preferably 1.0% or less, more preferably 0.7% or less, and even more preferably 0.5% or less, calculated as oxide (SO ₃ ). By having the content be 1.0% or less, a sufficient carbonation (salt) promotion effect can be obtained, and the setting and hardening 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) may be present in the non-hydraulic compound at about 2% calculated as oxide.

In addition, in order to make the cement admixture more likely to exhibit its effects, the chemical composition preferably contains 0.001 to 1.0 part of Li ₂ O, 45 to 70 parts of CaO, 29 to 54 parts of SiO ₂ , and 0 to 10 parts of Al ₂ O ₃ per 100 parts of the cement admixture. The Li ₂ O content can be measured by the method described in the examples below. CaO, SiO ₂ , and Al ₂ O ₃ can be measured by fluorescent X-rays.
As a chemical composition, it is more preferable that, in 100 parts of the cement admixture, Li ₂ O is 0.002 to 0.5 parts, CaO is 60 to 70 parts, SiO ₂ is 30 to 45 parts, and Al ₂ O ₃ is 0.5 to 5 parts. Furthermore, as a chemical composition, in 100 parts of the cement admixture, the total of Li ₂ O, CaO, SiO ₂ , and Al ₂ O ₃ is preferably 90 parts or more, and more preferably 95 to 100 parts.

Methods for quantifying the non-hydraulic compounds in this admixture include the Rietveld method using powder X-ray diffraction.

The Blaine specific surface area of the present cement admixture is not particularly limited, but is preferably 1,500 cm ² /g or more, and the upper limit is preferably 8,000 ^{cm 2} /g or less. Of these, 2,000 to 6,000 ^{cm 2} /g is more preferable, and 4,000 to 6,000 cm ² /g is most preferable. With a Blaine specific surface area of 1,500 cm ² /g or more, good material separation resistance is obtained, and the carbonation (salt) promotion effect is sufficient. Furthermore, with a Blaine specific surface area of 8,000 cm ² /g or less, the grinding power required for grinding is not large, which is economical, and weathering is suppressed, thereby suppressing deterioration of quality over time.

<Alkali Metal Salt and/or Alkaline Earth Metal Salt>
The 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, etc., of which nitrites and nitrates are preferred.
The nitrites and/or nitrates (hereinafter referred to as "nitrates") used in the present invention are not particularly limited so long as they impart rapid hardening properties when mixed with cement. Specific examples include alkali metal salts or alkaline earth metal salts of nitrites and nitrates, and of these, the use of lithium salts, sodium salts, potassium salts, 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 preferred since they do not promote the alkali-aggregate reaction. In particular, when lithium nitrite is used, the rapid hardening property is most remarkable and therefore it is 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 rapid-hardening admixture. If it is 5 parts or more, sufficient rapid hardening is obtained, and if it is 70 parts or less, the fluidity of the concrete is not impaired, which is advantageous in terms of construction.

<Cure regulator>
The rapid hardening admixture of the present invention may contain a hardening regulator.
The hardening regulator is not particularly limited, but is preferably one or more selected from the group consisting of inorganic carbonates, organic acids and salts of the organic acids.
For example, inorganic carbonates include alkali metal carbonates and bicarbonates, and organic acids include oxycarboxylic acids such as citric acid, tartaric acid, gluconic acid, and malic acid, as well as alkali metal salts, alkaline earth metal salts, aluminum salts, and ammonium salts thereof.

The amount of hardening regulator to be used is not particularly limited, but it is usually preferable to use 5 parts or less per 100 parts of the rapid-hardening admixture, more preferably 2 parts or less, and particularly preferably 0.1 to 1 part. . If the hardening regulator is insufficient, the pot life may be shortened, and if too much is added, the strength expression may be insufficient.

<Retarder>
The rapid hardening admixture of the present invention may contain a retarder.
The retarder used in the present invention is not particularly limited, but it is used to adjust the setting of cement and not to impair the fluidity of concrete during construction, and can also be called a setting regulator. Both organic and inorganic retarders can be used.

Specific examples of the organic substance that can be used include organic acids such as carboxylic acids, oxymonocarboxylic acids, oxypolycarboxylic acids, and polycarboxylic acids, or salts thereof.
The carboxylic acid may be a saturated or unsaturated carboxylic acid, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, and heptanoic acid, and the oxymonocarboxylic acid may be 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 co-condensates of acrylic acid and maleic anhydride.

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

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

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

The amount of 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 rapid hardening admixture.

[Rapid hardening cement composition]
The rapid-hardening cement composition of the present invention comprises cement and the above-mentioned rapid-hardening admixture.
The amount of the rapid-hardening admixture used in the rapid-hardening cement composition of the present invention is not particularly limited, but is usually preferably 3 to 20 parts, more preferably 7 to 15 parts, per 100 parts of the cement composition consisting of cement and the rapid-hardening admixture. When it is 3 parts or more, the effect of the present invention can be sufficiently obtained, and when it is 20 parts or less, the 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 a cement containing Portland cement, and examples thereof include various Portland cements such as ordinary, early strength, extra early strength, low heat, and medium heat Portland cements, various mixed cements in which granulated blast furnace slag, fly ash, or silica is mixed with any of these Portland cements, and limestone filler cements in which limestone powder or the like is mixed with Portland cement.

In addition, in the present invention, it is also possible to mix fine aggregate with the rapid-hardening cement composition consisting of cement and the rapid-hardening admixture of the present invention. The type of fine aggregate is not particularly limited, but examples that can be used include lime sand, silica sand, river sand, sea sand, mountain sand, crushed sand, etc., 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, one or more of the following may be used in the rapid hardening admixture and rapid hardening cement composition of the present invention, including water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, high-performance air-entraining water reducing agents, defoamers, 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, within a range that does not substantially impair the object of the present invention.

In the present invention, the amount of water used is preferably 20 to 60 parts per 100 parts of the rapid hardening cement composition. If the amount of water is 20 parts or more, sufficient fluidity is obtained, and if the amount 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 some or all of the materials may be mixed in advance. Any existing device can be used as a mixer, such as a tilting mixer, omni mixer, Henschel mixer, V-type mixer, and Nauta mixer.

Experimental Example 1
(1) Preparation of Cement Admixtures Cement admixtures 1 to 15 were prepared as follows.

(1-1) Cement admixtures 1 to 3 (Li-containing γ-2CaO/SiO ₂ )
First-grade reagent calcium carbonate and first-grade reagent silicon dioxide were mixed in a molar ratio of 2:1, and then first-grade reagent lithium carbonate was mixed in so that the Li content of the mixture, calculated as oxide (Li ₂ O), was as shown in Table 1 (internal substitution).The mixture was then heat-treated at 1,400°C for 2 hours and allowed to cool to room temperature to produce cement admixtures 1 to 3 with Blaine specific surface areas of 4,000 cm ² /g.

(1-2) Cement admixture 4-6 (Li-containing 3CaO.2SiO ₂ )
First-grade reagent calcium carbonate and first-grade reagent silicon dioxide were mixed in a molar ratio of 3:2, and then first-grade reagent lithium carbonate was mixed in so that the Li content of the mixture, converted into oxide (Li ₂ O), was as shown in Table 1 (internal substitution).The mixture was then heat-treated at 1,400°C for 2 hours and allowed to cool to room temperature to produce cement admixtures 4 to 6 with Blaine specific surface areas of 4,000 cm ² /g.

(1-3) Cement admixtures 7 to 9 (Li-containing α-CaO/SiO ₂ )
First-grade reagent calcium carbonate and first-grade reagent silicon dioxide were mixed in a 1:1 molar ratio, and then first-grade reagent lithium carbonate was mixed in so that the Li content of the mixture, converted into oxide (Li ₂ O), was as shown in Table 1 (internal substitution).The mixture was then heat-treated at 1,500°C for 2 hours and allowed to cool to room temperature to produce cement admixtures 7 to 9 with Blaine specific surface areas of 4,000 cm ² /g.

(1-4) Cement admixture 10 to 12 (Li-containing 3CaO·MgO·2SiO ₂ )
First-grade reagent calcium carbonate, first-grade reagent magnesium oxide, and first-grade reagent silicon dioxide were mixed in a molar ratio of 3:1:2, and then first-grade reagent lithium carbonate was mixed in so that the Li content of the mixture, converted into oxide (Li ₂ O), was as shown in Table 1 (internal substitution).The mixture was then heat-treated at 1,400°C for 2 hours and allowed to cool to room temperature to produce cement admixtures 10 to 12 with Blaine specific surface areas of 4,000 cm ² /g.

(1-5) Cement admixture 13 (β-2CaO.SiO ₂ )
First-grade reagent calcium carbonate and first-grade reagent silicon dioxide were mixed in a molar ratio of 2:1, heat-treated at 1,400°C for 2 hours, allowed to cool to room temperature, pulverized, and the same heat treatment _was repeated until the peak of γ-2CaO·SiO2 was no longer observed by XRD. After the peak of only β-2CaO· _SiO2 was observed, a cement admixture 13 with a Blaine specific surface area of 4,000 ^cm2 /g was produced.

(1-6) Cement admixture 14 (γ-2CaO.SiO ₂ )
Reagent grade calcium carbonate and reagent grade silicon dioxide were mixed in a molar ratio of 2:1, heat-treated at 1,400°C for 2 hours, and allowed to cool to room temperature to produce γ-2CaO·SiO2 with a Blaine specific surface area of _4,000 ^cm2 /g.

(1-7) Cement admixture 15 (Li ₂ O + γ-2CaO.SiO ₂ )
Reagent grade calcium carbonate and reagent grade silicon dioxide were mixed in a molar ratio of 2:1, heat-treated at 1,400°C for 2 hours, and allowed to cool to room temperature to produce γ-2CaO·SiO2 with a Blaine specific surface area of _4,000 ^cm2 /g.
Also, first-grade reagent lithium carbonate was heat-treated at 1,400° C. for 2 hours and allowed to stand until it cooled to room temperature to prepare Li ₂ O powder.
Li ₂ O powder (first-grade lithium carbonate heat-treated at 1,400° C. for 2 hours) was mixed with the above γ-2CaO.SiO ₂ so that the Li ₂ O content was 0.1% (internal substitution) to prepare a cement admixture.

The oxide-equivalent Li content of each cement admixture was measured by an ICP optical emission spectrometer (VISTA-PRO, manufactured by Hitachi High-Tech Science Corporation). It was confirmed that the Li content was the same as the amount of the feed amount by the absolute calibration curve method using a diluted ICP mixture solution of SPEX XSTC-22. The measurement conditions were as follows.
・Li measurement wavelength: 670.783nm
・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 (5-point calibration curve of 0 mg/L, 0.1 mg/L, 0.5 mg/L, 1 mg/L, 5 mg/L)
・Quantitative analysis using absolute calibration curve method

(2) Carbonation reaction rate evaluation of admixtures 5 g of each admixture was weighed into an evaporating dish and carbonation cured for 7 days in accordance with JIS A 1153 (room temperature 20 ° C, relative humidity 60%, 5% _-CO2 concentration). After 7 days of carbonation curing, a differential thermogravimetric analysis (TG) was performed using a differential thermogravimetric analyzer (NETZSCH, 2020SA type) with a sample weight of 50 ± 2 mg, a heating rate of 10 ° C / min from room temperature to 1,000 ° C, and a nitrogen flow environment. The amount of CaCO ₃ produced (carbonation reaction rate) was calculated from the following formula, with the weight loss near 650 ° C to 765 ° C in the TG curve being the weight loss due to decarbonation of CaCO _3. The results are shown in Table 1.
Carbonation reaction rate (%) = [ _ΔmCaCO3 /( _m0 - _m1,000 )] x 100.09/44.01 x 100
( _ΔmCaCO3 : amount of decarbonated calcium carbonate (mg), _m0 : amount of sample used in measurement (mg), _m1,000 : amount of mass reduction up to 1,000°C (mg))

(3) Measurement of vaterite content by XRD measurement The vaterite content of the admixture after the 7-day carbonation curing was measured by powder X-ray diffraction (Rigaku Corporation, SmartLab). A predetermined amount of an internal standard substance such as aluminum oxide or magnesium oxide was added to the cement admixture, and the mixture was thoroughly mixed in an agate mortar, after which powder X-ray diffraction measurement was performed. The measurement results were analyzed using quantitative software to determine the vaterite content. The quantitative software used was "Smartlab Studio II" manufactured by Rigaku Corporation. The results are shown in Table 1.

Experimental Example 2 (Experiments No. 2-1 to 2-31)
A rapid hardening admixture was prepared by mixing 70 parts of the cement admixture shown in Table 1 with 30 parts of lithium nitrite. Furthermore, a cement composition was prepared using the rapid hardening admixture in the formulation of Table 2 and the remainder was 100 parts as cement, with a water/cement composition ratio of 50% and a cement composition/sand ratio of 1/3, and the compressive strength and carbonation depth at ages of 1 day and 28 days were measured. The results are shown in Table 2.

<Materials used>
Cement: Commercially available, ordinary Portland cement Nitrates: Commercially available, lithium nitrite Retarder: Commercially available, citric acid Water: Tap water Fine aggregate: ISO 679 compliant, standard sand

<Measurement method>
Compressive strength: A 4 x 4 x 16 cm test specimen was prepared, and the strength was measured at 1 day and 28 days according to JIS A 1108. The casting temperature was 20°C.
Carbonation depth: 4 x 4 x 16 cm test specimens were prepared and aged in water at 20°C for 28 days, after which accelerated carbonation was carried out in an environment of 30°C, relative humidity of 60%, and carbon dioxide concentration of 10%. After 6 months, the test specimens were cut into slices, and a phenolphthalein solution was applied to the cross sections to measure the carbonation depth from the surface to the colored part, and the carbonation inhibition effect was evaluated.

Experimental Example 3 (Experiment No. 3-1 to 3-9)
A rapid hardening admixture was prepared by mixing 70 parts of the admixture type shown in Table 3 with 30 parts of lithium nitrite, and mixing the retarder of the type and amount shown in Table 3. Next, the fluidity retention rate was evaluated using a composition consisting of 10 parts of the rapid hardening admixture and 90 parts of cement. The results are shown in Table 3. The other evaluation items were the same as those in the previous examples.
Fluidity retention: Evaluated by the change in flow value over time at an environmental temperature of 20° C. Based on the flow test of JIS R 5201, it was calculated from the flow values immediately after kneading and after 30 minutes had elapsed.
Fluidity retention rate = (flow value after 30 minutes/flow value immediately after kneading) x 100

<Materials used>
Retarder A: Commercially available product, citric acid retarder B: Commercially available product, gluconic acid retarder C: Commercially available product, sodium gluconate retarder D: Commercially available product, tartaric acid retarder E: A mixture of retarder A and retarder D in a 1:1 ratio (by weight)

Experimental Example 4 (Experiment No. 4-1 to 4-10)
The concrete containing the above rapid hardening admixture was evaluated for its resistance to material (moisture) movement depending on whether it was neutralized or not. Note that the test specimens used were completely neutralized.

Using the rapid-hardening admixtures shown in Table 4, 100 parts of cement composition consisting of normal cement and rapid-hardening admixtures were mixed in the amounts shown in Table 4 to prepare cylindrical mortar specimens of Φ100 x 200 mm in accordance with JIS R 5201. The sides of the specimens were sealed with aluminum tape, and the top and bottom were left open. The specimens were immersed in a water bath up to 1 cm below the bottom, and split after 24 hours of immersion. The depth of water penetration was measured using calipers. The results are shown in Table 4.

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

The rapid hardening admixture and rapid hardening cement composition of the present invention can achieve short-term strength and exhibit excellent carbonation inhibition effects. Furthermore, they also have excellent resistance to moisture penetration after carbonation, making them suitable as concrete materials in civil engineering or construction, particularly as repair materials.

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, wherein the non-hydraulic compound contains Li, the Li content being 0.001 to 1.0 mass% in terms of oxide, and an alkali metal salt and/or an alkaline earth metal salt, wherein the presence of Li ₂ O contained as a chemical composition in the non-hydraulic compound can be confirmed by ICP emission spectrometry, but Li ₂ O cannot be identified by X-ray diffraction measurement. The rapid hardening admixture according to claim 1, wherein the chemical composition of 100 parts by mass of the cement admixture (excluding cement admixtures in a state in which a non-hydraulic compound and a Li compound are physically mixed) 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 to 10 parts by mass of Al ₂ O ₃ . The rapid hardening admixture according to claim 1 or 2, wherein the alkali metal salt and the alkaline earth metal salt are nitrites and/or nitrates, respectively. The rapid hardening admixture according to any one of claims 1 to 3 further contains a hardening regulator, and the hardening regulator is one or more selected from the group consisting of inorganic carbonates, organic acids, and salts of the organic acids. A rapid hardening cement composition comprising cement and the rapid hardening admixture according to any one of claims 1 to 4.