JP2023028439A - Cement admixture and cement composition - Google Patents

Abstract

To provide a cement admixture and a cement composition that enable the production of a concrete secondary product having both neutralization resistance and improved productivity.SOLUTION: Provided is a cement admixture, which is a cement admixture containing a neutralization suppression component containing a non-hydraulic compound and a high-early-strength component containing an expansive material component, and in which, a content ratio of Li in the neutralization-suppression component is 0.001 to 1.0 mass% in terms of oxide, and the non-hydraulic compound contains one kind, or two or more kinds selected from the group consisting of γ-2CaO-SiO2, 3CaO-2SiO2, α-CaO-SiO2, and calcium magnesium silicate.SELECTED DRAWING: None

Description

The present invention relates primarily to cement admixtures and cement compositions used in the civil engineering and construction industries.

Steam curing at normal pressure is often used in the production of conventional concrete products. In this steam curing, the concrete placed in the formwork is left in the curing chamber, and the steam generated by the boiler is introduced here to raise the temperature of the concrete in the formwork under humidified conditions. This is a method of promoting the sum reaction to hasten the development of strength.
In particular, in recent years, the precasting of concrete has progressed, and the method of manufacturing concrete products in a factory, transporting them to a construction site and assembling them is increasing. Such precast concrete products are subjected to steam curing for the purpose of improving productivity.
However, secondary concrete products subjected to steam curing tend to have coarser textures and are more susceptible to neutralization than those cured in water.

For steam curing, for example, concrete is poured into a formwork, compacted, and precured at room temperature for about 2 to 4 hours. Next, the introduction of steam is started, the temperature is raised at a rate of 15 to 20° C./hour, and isothermal curing is performed by maintaining the curing temperature at about 50 to 80° C. for 2 to 4 hours. After that, the supply of steam is stopped, and the curing is completed after a slow cooling period by natural cooling.
That is, since the steam curing period usually requires about 18 to 20 hours, only one product can be manufactured with one formwork per day, which poses a problem in terms of productivity.

As a means of shortening the steam curing time, super fast-strength expansive materials mainly composed of quicklime, anhydrous gypsum, or alkali metal sulfates, and hydraulic compositions that combine specific compounds such as glycerin and alkali metal sulfates. Although quick-strength materials and the like are known (see, for example, Patent Document 1), their performance was not sufficient.
Therefore, a mixed pulverized product of gypsum having a Blaine specific surface area of 2500 to 9000 cm ² /g and glycerin is included, and the content of glycerin is 0.1 to 10 parts by mass in a total of 100 parts by mass of gypsum and glycerin. A high-strength cement admixture characterized by is proposed (see Patent Document 2).

Japanese Patent Application Laid-Open No. 2001-294460 Retable 2014/112487

An object of the present invention is to provide a cement admixture and a cement composition that enable the production of secondary concrete products having both neutralization resistance and improved productivity.

The inventors of the present invention have made various efforts to solve the above problems, and as a result, have solved the above problems with a cement admixture containing a specific neutralization inhibiting component and a specific early strength component. We have found that we can obtain it, and have completed the present invention. The gist of the present invention is as follows.
[1] A cement admixture containing a neutralization-inhibiting component containing a non-hydraulic compound and an early-strength component containing an expansive material, wherein the content of Li in the neutralization-inhibiting component is 0.001 to 1.0% by mass in terms of oxide, and the non-hydraulic compound is a group consisting of γ-2CaO.SiO ₂ , 3CaO.2SiO ₂ , α-CaO.SiO ₂ and calcium magnesium silicate. Cement admixture characterized by containing one or more selected from.
[2] The chemical composition of the neutralization-suppressing component is 0.001 to 1.0 parts by mass of Li ₂ O, 45 to 70 parts by mass of CaO, relative to 100 parts by mass of the total amount of the neutralization suppressing component. The cement admixture according to [1] above, containing 29 to 54 parts by mass of SiO ₂ and 0 to 10 parts by mass of Al ₂ O ₃ .
[3] The chemical composition of the early-strength component contains 30 parts by mass or more of an expansive component, 15 parts by mass or more of anhydrous gypsum, quicklime, and inorganic sulfate, per 100 parts by mass of the total amount of the early-strength component. , slaked lime, formate, and cement admixture according to the above [1] or [2] containing one or more selected from the group consisting of acetate.
[4] A cement composition containing cement and the cement admixture according to any one of [1] to [3] above, wherein the cement admixture is 1 to 35 parts per 100 parts by mass of cement. Cement composition containing parts by mass.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a cement admixture and a cement composition that enable the production of secondary concrete products having both neutralization resistance and improved productivity.

The present invention will be described in detail below.
Parts and percentages in this specification are based on mass unless otherwise specified.

[Cement admixture]
The cement admixture of the present invention comprises a neutralization inhibiting component containing a non-hydraulic compound and an early strength component containing an expansive component.

<Neutralization suppression component>
The neutralization-inhibiting component in the present invention contains a non-hydraulic compound, and the non-hydraulic compound is a group consisting of γ-2CaO·SiO ₂ , 3CaO·2SiO ₂ , α-CaO·SiO ₂ , and calcium magnesium silicate. Contains one or more selected from
In addition to the above compounds, β-type or α-type dicalcium silicate 2CaO.SiO ₂ , tricalcium silicate 3CaO.SiO ₂ , β-type wollastonite (β-CaO · SiO ₂ ), calcium silicates such as 12CaO·7Al ₂ O ₃ , 11CaO·7Al ₂ O ₃ ·CaF ₂ , 3CaO·Al ₂ O ₃ and other calcium aluminates, galenite 2CaO·Al ₂ O ₃ ·SiO ₂ , anode Calcium aluminosilicate such _as site _{CaO.Al2O3.2SiO2} , _melilite which is a mixed crystal of _achermanite 2CaO.MgO.2SiO2 and galenite _{2CaO.Al2O3.SiO2} , free lime, _{free magnesia} , calcium ferrite 2CaO - _{Fe2O3 , calcium} aluminoferrite _{4CaO.Al2O3.Fe2O3 ,} leucite _{( K2O} , _{Na2O ) .Al2O3.SiO2 ,} spinel _{MgO.Al2O3 ,} and Magnetite Fe ₃ O ₄ or the like can be added.

The chemical composition of the neutralization suppressing component is 0.001 to 1.0 parts by mass of Li ₂ O, 45 to 70 parts by mass of CaO, and 29 parts by mass of SiO ₂ with respect to 100 parts by mass of the total amount of the neutralization suppressing component. 54 parts by mass and preferably 0 to 10 parts by mass of Al ₂ O ₃ . Within the above range, neutralization can be effectively suppressed.
In particular, the content of Li ₂ O _is extremely important in the neutralization-suppressing component of the present invention. Even if it exceeds 0 parts by mass, the neutralization resistance is lowered. Note that the content of Li ₂ O has almost no effect on the cohesion, strength, and expansion coefficient.
The mechanism by which the neutralization resistance is improved when the Li ₂ O content is in the range of 0.001 to 1.0 parts by mass is not clear, but the process in which the calcium silicate hydrate is carbonated It is presumed that the formation of vaterite, which is a type of calcium carbonate, is accelerated, thereby obtaining a denser hardened state. On the other hand, if the content of Li ₂ O is outside the above range, it is known that the amount of vaterite produced decreases, densification does not effectively contribute, and neutralization resistance is considered to decrease.

<Early strength component>
The early strength component in the present invention essentially contains an expanding component. The expansive material is defined in JIS A 6202, and is an admixture that, when mixed with cement and water, produces ettringite, calcium hydroxide, etc. through a hydration reaction and has the effect of expanding concrete or mortar. Examples of the expansion material component include calcium sulfoaluminate expansion material, ettringite-lime composite expansion material, and lime expansion material.
In the present invention, the content of the expansive agent in the early strength component is preferably 30 parts by mass or more with respect to 100 parts by mass of the early strength component. When the expansive component is 30 parts by mass or more, there are effects of improving crack resistance and suppressing neutralization.
From the above viewpoints, it is more preferable that the content of the expanding material component is 40 parts by mass or more.
The upper limit of the expansion material component is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, in order to ensure the contents of other components described later.

The particle size of the expanding material component used in the present invention is not particularly limited, but the Blaine specific surface area value is preferably in the range of 2,000 cm ² /g or more and 25,000 cm ² /g or less, and 2,200 cm 2 /g or more. ² /g or more and 15,000 cm ² /g or less is more preferable, and 2,400 cm ² /g or more and 10,000 cm ² /g or less is even more preferable. Bleeding can be suppressed when the Blaine specific surface area value of the expansive material is equal to or higher than the above lower limit. Further, when the Blaine specific surface area value of the expansive material is equal to or less than the above upper limit value, sufficient expansibility can be obtained.

The early strength component preferably contains anhydrite in addition to the expansive component. Anhydrous gypsum is considered to have the action of forming ettringite and the like, which are quick-hardening hydrates, together with the hydration of calcium aluminate.
The content of anhydrite is preferably 15 parts by mass or more with respect to 100 parts by mass of the early strength component. When it is 15 parts by mass or more, the short-term strength and the post-curing expansion rate are well balanced. From the above point of view, the content of anhydrous gypsum is more preferably 18 parts by mass or more, more preferably 20 parts by mass or more.
The upper limit of the anhydrous gypsum is preferably 30 parts by mass or less, more preferably 28 parts by mass or less, in order to ensure the contents of the expanding material component and other components described later.
The fineness of the anhydride gypsum is preferably 3,000 cm ² /g or more and 9,000 cm 2 /g or less, more preferably 4000 ^{cm 2 /} g or more and 7000 cm ² /g or less, in Blaine specific surface area value.

Quick lime, inorganic sulfate, slaked lime, formate, and acetate may be added to the early-strength component in addition to the expansive component and anhydrous gypsum.
Examples of inorganic sulfates include alkali metal salts, alkaline earth metal salts, and ammonium salts of thiosulfate. More specifically, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, lithium thiosulfate, and calcium thiosulfate. , and magnesium thiosulfate. Among them, sodium thiosulfate, potassium thiosulfate and ammonium thiosulfate are preferred, and sodium thiosulfate is particularly preferred.
Examples of the formate include alkali metal formate, alkaline earth metal formate, and more specific examples include sodium formate, potassium formate, calcium formate, magnesium formate, and the like. Among them, sodium formate and calcium formate are preferred, and calcium formate is particularly preferred.
Calcium acetate is suitable as the acetate.
You may use these compounds individually by 1 type or in combination of 2 or more types. The total amount of these compounds is preferably in the range of 0.2 to 3.2 parts by mass, and in the range of 0.5 to 3.0 parts by mass, per 100 parts by mass of the early strength component. It is even more preferable to have

<Ratio of neutralization-suppressing component to early-strength component>
The ratio of the neutralization-suppressing component and the early-strength component is not particularly limited as long as the effects of both components are exhibited. /early strength component ratio (mass ratio) is preferably in the range of 30/70 to 70/30, more preferably in the range of 40/60 to 60/40.

[Cement composition]
The cement composition of the present invention contains cement and the cement admixture described above. The content of the cement admixture is preferably in the range of 1 to 35 parts by mass, more preferably in the range of 3 to 35 parts by mass, and more preferably 5 to 30 parts by mass with respect to 100 parts by mass of cement. It is more preferably in the range, and particularly preferably in the range of 10 to 30 parts by mass.
When the content of the cement admixture is within the above range, the neutralization depth is good and the daily expansion rate can be kept low. Also, 14-day compressive strength can be maintained.

<Cement>
The cement used in the present invention is not particularly limited, and usually various types of cement such as high-early strength, ultra-early strength, low heat and moderate heat, and blast furnace slag, fly ash, silica fume, etc. are mixed with these cements. There are various types of mixed cement, environment-friendly cement (eco-cement) manufactured from municipal waste incineration ash and sewage sludge incineration ash, and commercially available fine-particle cement. It is also possible to use In addition, those adjusted by increasing or decreasing the amount of components (for example, gypsum, etc.) normally used in cement can also be used.
In the present invention, it is preferable to select ordinary Portland cement or early-strength Portland cement from the viewpoints of heat of hydration, drying shrinkage, and filling properties.

The cement used in the present invention preferably has a Blaine specific surface area value of 2,500 cm ² /g or more and 7,000 cm ² /g or less, and 2,750 cm ² from the viewpoint of production cost and strength development. /g or more and 6,000 cm ² /g or less, and more preferably 3,000 cm ² /g or more and 4,500 cm ² /g or less.
The Blaine specific surface area value is determined according to JIS R 5201 (physical test method for cement).

The present invention will be further described below based on experimental examples of the present invention, but the present invention is not limited thereto.

[Evaluation method]
(1) Setting time Measured according to JIS A 1147:2007.
(2) Compressive strength Measured according to JIS A 1108:2018. The measurement was performed after curing in air for 14 days after steam curing.
(3) Length change rate Measured after 1 day of material age in accordance with JIS A 6202:2017 B method. In the table, it is described as a one-day expansion rate.
(4) Accelerated neutralization After steam curing, after curing in the air at 20°C until the material age is 14 days, accelerated neutralization is performed until the material age is 13 weeks in an environment of 30°C, relative humidity of 60%, and carbon dioxide gas concentration of 5%. A 1% alcohol solution of phenolphthalein was applied to the cracked surface of the concrete to confirm the neutralization depth.

Experimental Example 1 (No. 1-1 to 1-5)
(1) Preparation of Neutralization Inhibiting Material Reagent grade 1 calcium carbonate and reagent grade 1 silicon dioxide are mixed at a molar ratio of 2:1, and the content of Li in the mixture is an oxide (Li ₂ O ) Reagent class 1 lithium carbonate was mixed so as to be 0.1% by mass (internal substitution) in terms of conversion, 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 neutralization inhibitor (Li-containing γ-2CaO·SiO ₂ ) was prepared.
(2) Preparation of early-strength admixture 52 parts by mass of calcium sulfoaluminate expanding material, 24 parts by mass of quicklime, and 24 parts by mass of anhydrous gypsum are blended, and anhydrous sodium thiosulfate is blended to 0.5% by mass. was blended to prepare an early-strength admixture.
(3) Preparation of cement admixture Using the neutralization inhibitor as the neutralization inhibitor and the early strength admixture as the early strength ingredient, A cement admixture with a ratio (mass ratio) of 50/50 was prepared.
(4) Preparation of concrete composition 150 kg/m ³ of water, 350 kg/m ³ of cement, 824 kg/m ³ of fine aggregate, and 1018 kg/m ³ of coarse aggregate were blended, and the cement admixture was added to 100 mass of cement. 0 parts by mass, 5 parts by mass, 15 parts by mass, 30 parts by mass, and 40 parts by mass, respectively, and mixed using a forced twin-screw mixer to obtain a concrete composition. Table 1 shows the results of evaluation by the above method. The temperature during mixing was set at 10° C., and various measurements were performed after curing the concrete composition under the following conditions.
(curing method)
Concrete was poured into a formwork, compacted, and precured at 20°C for 2 hours. Next, steam ventilation was started, the temperature was raised at a rate of 20°C/hour, and isothermal curing was performed at 50°C for 2.5 hours. After that, the supply of steam was stopped, and slow cooling was performed by natural cooling.

<Materials used>
・Cement: Commercially available ordinary Portland cement Density 3.14 g/cm ³
・Water: Tap water ・Fine aggregate: River sand from Himekawa water system, Itoigawa City, Niigata Prefecture, density 2.62 g/cm ³ , maximum particle size 5 mm
・Coarse aggregate: River gravel from Himekawa water system, Itoigawa City, Niigata Prefecture, density 2.64 g/cm ³ , maximum particle size 25 mm

Experimental example 2 (No. 2-1 to 2-6)
(1) Preparation of Neutralization Inhibiting Material Reagent grade 1 calcium carbonate and reagent grade 1 silicon dioxide are mixed at a molar ratio of 2:1, and the content of Li in the mixture is an oxide (Li ₂ O ) Reagent class 1 lithium carbonate is mixed so that the conversion becomes 0.0005%, 0.002%, 0.15%, 0.9%, 1.0%, 1.1% (internal substitution) Then, the material was heat-treated at 1,400° C. for 2 hours and allowed to stand to room temperature to prepare a neutralization inhibitor having a Blaine specific surface area of 4,000 cm ² /g.
(2) Preparation of early-strength admixture Same as in Example 1.
(3) Preparation of cement admixture Same as in Example 1.
(4) Preparation of concrete composition Water 150 kg/m ³ , cement 350 kg/m ³ , fine aggregate 824 kg/m ³ , and coarse aggregate 1018 kg/m ³ are blended, and the above cement mixture with different Li content is mixed. 30 parts by mass of each material was mixed with 100 parts by mass of cement to obtain a concrete composition. Table 2 shows the results of evaluation by the above method. The method of preparing the concrete composition and the curing conditions were the same as in Example 1.

From the results of Table 1, the cement composition containing 1 to 35 parts by mass of the cement admixture of the present invention with respect to 100 parts by mass of cement has a small value of neutralization depth and good neutralization resistance It can be seen that In addition, it is possible to maintain a high compressive strength, and it is clear from the results of the initial setting time and the daily expansion rate that the productivity is excellent.
Furthermore, from the results in Table 2, it was found that the content of lithium was within an appropriate range, resulting in extremely good neutralization resistance. It is clear that it can be improved.

According to the cement admixture of the present invention and the cement composition using the cement admixture, a secondary concrete product having high neutralization resistance can be obtained with high productivity. Therefore, it is a very useful technique, especially in the precast method and the like.

Claims (4)

A cement admixture containing a neutralization inhibiting component containing a non-hydraulic compound and an early strength component containing an expansive component, wherein the content of Li in the neutralization inhibiting component is an oxide 0.001 to 1.0% by mass in terms of conversion, and the non-hydraulic compound is selected from the group consisting of γ-2CaO·SiO ₂ , 3CaO·2SiO ₂ , α-CaO·SiO ₂ , and calcium magnesium silicate. A cement admixture characterized by containing one or more types. The chemical composition of the neutralization suppressing component is 0.001 to 1.0 parts by mass of Li ₂ O, 45 to 70 parts by mass of CaO, and SiO ₂ with respect to 100 parts by mass of the total amount of the neutralization suppressing component. The cement admixture according to claim 1, containing 29 to 54 parts by mass and 0 to 10 parts by mass of Al ₂ O ₃ . The chemical composition of the early-strength component contains 30 parts by mass or more of an expansive component and 15 parts by mass or more of anhydrous gypsum relative to the total amount of 100 parts by mass of the early-strength component, and further comprises quicklime, inorganic sulfate, slaked lime, 3. The cement admixture according to claim 1, comprising one or more selected from the group consisting of formate and acetate. A cement composition containing cement and the cement admixture according to any one of claims 1 to 3, containing 1 to 35 parts by mass of the cement admixture with respect to 100 parts by mass of cement. cement composition.