JP7731964B2 - Cement composition - Google Patents

Description

The present invention relates to a cement admixture.

Technology related to cement admixtures containing gypsum is described in Patent Document 1 (JP 54-157129 A). This document describes a method for producing a cement hardening agent in which a cement hardening agent consisting of calcium aluminate and gypsum is mixed with a small amount of water in the presence of sulfuric acid. It is claimed that this method makes it easy to adjust the working life of the cement and produces a cement hardening agent with excellent strength development.

Japanese Unexamined Patent Publication No. 54-157129

However, as a result of the inventor's investigation into the cement quick-hardening additive described in Patent Document 1, it was found that there is still room for improvement in terms of quickly developing excellent strength.

According to the present invention, the following cement admixture is provided.

1. A cement admixture containing gypsum,
The cement admixture, wherein the dissolution rate of the gypsum, measured according to the following method 1, is 30 mg/(100 mL min) or more and 100 mg/(100 mL min) or less.
(Method 1)
(1) Place 100 mL of saturated calcium hydroxide solution adjusted to 20°C into a 200 mL beaker.
(2) A stirring bar is placed in the beaker and stirred on a magnetic stirrer, and 4 g of the gypsum sample is added, and the elapsed time from the addition is measured.
(3) Immediately after a specified time has elapsed since the addition, the beaker is removed from the stirrer and the mixture is subjected to suction filtration using JIS P 3801 No. 5C filter paper.
(4) 10 mL of the filtrate is placed in a 20 mL volumetric flask, and 1 mL of 3.18% hydrochloric acid solution is added, followed by diluting the solution with pure water.
(5) 5 mL of the solution obtained in (4) is placed in a 200 mL volumetric flask and made up to the volume with pure water.
(6) The solution obtained in (5) is injected into an ion chromatogram (Shimadzu Corporation, Ion Chromatograph, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) When the specified time in (3) is 5 minutes and 10 minutes, the amount of SO ₄ ^2- ions is determined by the procedures in (4) to (6), and the dissolution rate is calculated based on the following formula.
Dissolution rate (mg/(100 mL·min))=(SO ₄ ^2- ion concentration after 10 minutes−SO ₄ ^2- ion concentration after 5 minutes)/5
2. The gypsum is granular,
1. The cement admixture according to 1., wherein the proportion of particles having a size of 1.0 μm or more and 10 μm or less in the gypsum is 30% by volume or more and 80% by volume or less.
3. The gypsum is granular,
3. The cement admixture according to 1. or 2., wherein the gypsum has a median diameter _d50 of 5 μm or more and 15 μm or less.
4. The cement admixture according to any one of 1. to 3., further comprising _SiO2 .

The present invention makes it possible to obtain a cement admixture that quickly develops excellent strength.

Embodiments of the present invention are described below. Note that unless otherwise specified, the "to" symbol in a numerical range indicates a range from above to below, and includes both of the values on either end. Furthermore, in this embodiment, the composition may contain each component alone or in combination of two or more types.

(Cement admixture)
In this embodiment, the cement admixture contains gypsum, and the dissolution rate of the gypsum measured by the following method 1 is 30 mg/(100 mL min) or more and 100 mg/(100 mL min) or less.

(Method 1)
(1) Place 100 mL of saturated calcium hydroxide solution adjusted to 20°C into a 200 mL beaker.
(2) A stirring bar is placed in a beaker and stirred on a magnetic stirrer, and 4 g of a gypsum sample is added, and the elapsed time from the addition is measured.
(3) Immediately after the specified time has elapsed since the addition, remove the beaker from the stirrer and filter the contents under suction using JIS P 3801 No. 5C filter paper.
(4) 10 mL of the filtrate was placed in a 20 mL volumetric flask, and 1 mL of 3.18% hydrochloric acid solution was added, followed by diluting the solution with pure water. 3.18% hydrochloric acid can be obtained, for example, by diluting commercially available 35% hydrochloric acid by 1/11.
(5) 5 mL of the solution obtained in (4) is placed in a 200 mL volumetric flask and made up to the volume with pure water.
(6) The solution obtained in (5) is injected into an ion chromatogram (Shimadzu Corporation, Ion Chromatograph, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) When the specified time in (3) is 5 minutes and 10 minutes, the amount of SO ₄ ^2- ions is determined by the procedures in (4) to (6), and the dissolution rate is calculated based on the following formula.
Dissolution rate (mg/(100 mL·min))=(SO ₄ ^2- ion concentration after 10 minutes−SO ₄ ^2- ion concentration after 5 minutes)/5

The inventors have discovered that by setting the dissolution rate of the gypsum contained in the cement admixture in a saturated calcium hydroxide solution at 20°C within a specific range, it is possible to quickly develop excellent strength. While the reason for this is not entirely clear, it is thought to be due to the fact that the admixture has adequate reactivity for early strength development while maintaining adequate handleability.

From the viewpoint of improving the strength of the cement composition, the dissolution rate of gypsum is 30 mg/(100 mL min) or more, preferably 50 mg/(100 mL min) or more, more preferably 60 mg/(100 mL min) or more, and even more preferably 70 mg/(100 mL min) or more.
From the viewpoint of improving the reactivity and handling time of the cement composition, the dissolution rate of gypsum is 100 mg/(100 mL min) or less, preferably 95 mg/(100 mL min) or less, more preferably 90 mg/(100 mL min) or less, even more preferably 85 mg/(100 mL min) or less, and still more preferably 80 mg/(100 mL min) or less.

The type of gypsum is not limited, and can be, for example, one or more selected from anhydrous gypsum (CaSO ₄ ) and gypsum hemihydrate. From the viewpoint of improving the strength of the cement composition, the gypsum preferably contains anhydrous gypsum, and more preferably is anhydrous gypsum. Examples of anhydrous gypsum include anhydrous gypsum produced by hydrofluoric acid and natural anhydrous gypsum. From the viewpoint of improving the strength of the cement composition, anhydrous gypsum produced by hydrofluoric acid is preferred.

The shape of the gypsum is not limited, but is preferably granular from the viewpoint of stably improving the strength of the cement composition.
In this case, the proportion of particles in the gypsum having a particle size in the range of 1.0 μm or more and 10 μm or more is preferably 30 vol% or more, more preferably 40 vol% or more, and even more preferably 50 vol% or more, relative to the total gypsum, from the viewpoint of improving the strength of the cement composition, and is preferably 80 vol% or less, and more preferably 70 vol% or less.

From the viewpoint of improving the strength of the cement composition, the median diameter _d50 of the gypsum is preferably 5 μm or more, more preferably 6 μm or more, and is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, and still more preferably 8 μm or less.

Here, the particle size distribution of the gypsum can be obtained by measuring the particle size distribution on a volume basis using a commercially available laser diffraction particle size distribution measuring device (for example, HORIBA LA-960).

From the viewpoint of improving the strength of the cement composition, the content of gypsum in the cement admixture is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 98% by mass or more, based on the total mass of the cement admixture.
There is no upper limit to the amount of gypsum contained in the cement admixture, and it is 100% by mass or less, but it may be, for example, 99% by mass or less, or may be, for example, 98% by mass or less.

The cement admixture may be composed of gypsum or may contain components other than gypsum.
For example, the cement admixture may further contain SiO ₂ (silica) from the viewpoint of improving the handling properties of the cement composition.
When the cement admixture contains _SiO2 , the silica is, for example, granular. The median diameter _d50 of the silica can be approximately the same as the median diameter _d50 of the gypsum.
Furthermore, from the viewpoint of improving the strength of the cement composition, it is preferable that the cement admixture does not contain fluorite (CaF ₂ ).

Next, a method for producing the cement admixture will be described.
The method for producing a cement admixture may include, for example, preparing gypsum having a solubility within a specific range. When the cement admixture contains a component other than gypsum, the method may also include mixing the gypsum with the component other than gypsum.
In this embodiment, the dissolution rate of gypsum can be controlled by, for example, appropriately selecting a gypsum preparation method, etc. Among these, appropriately adjusting the particle size, particle size distribution, etc. of gypsum can be cited as a factor for achieving a desired dissolution rate of gypsum.
The particle size and particle size distribution of the cement admixture can be adjusted by performing a pulverization and classification process. There are no limitations on the pulverization and classification methods, and known pulverization and classification methods can be used. For example, a ball mill or roller mill can be used as the pulverization method, and an air classifier can be used as the classification method.

(Cement composition)
In this embodiment, the cement composition includes the cement admixture in this embodiment and cement.
In this embodiment, since the cement composition contains the above-mentioned cement admixture, excellent strength can be developed early. Furthermore, according to this embodiment, for example, it is possible to stably control the usable life of the cement composition, for example, to stably extend it.

The term "cement" in this embodiment is not limited to, but includes, for example, various types of Portland cement specified by the Japanese Industrial Standards (JIS), including normal, early-strength, medium-heat, and low-heat cements; various blended cements containing blast furnace slag, fly ash, and silica; filler cements containing limestone powder and slowly cooled blast furnace slag powder; and environmentally friendly cements (ecocements) made from municipal waste incineration ash and sewage sludge incineration ash. Other examples include cements specified by the overseas EN197-2000 standard and all types of cement specified by the Chinese GB standard, and one or more of these can be used.

More specifically, the cement composition contains water. There are no restrictions on the amount of water used, but typically the water/cement composition ratio may be, for example, about 8 to 80%, or may be, for example, 25 to 70%, or, for example, 30 to 60% of the cement composition.

The cement composition is specifically a rapid hardening cement, and in this case, for example, the cement admixture in this embodiment may be a rapid hardening agent. Here, the rapid hardening agent refers to a component that quickly generates a rapid hardening hydrate such as ettringite and imparts rapid hardening to cement concrete.
When the cement admixture is a hardening agent, the hardening agent preferably contains at least the above-mentioned gypsum and calcium aluminate. Regarding the content of these components in the hardening agent, when the hardening agent contained in the hardening cement is taken as 100 parts by mass, the total amount of calcium aluminate and gypsum is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and can be 100 parts by mass. In other words, the hardening agent according to this embodiment can be composed only of calcium aluminate and gypsum.

(Calcium aluminate)
Calcium aluminate is a mineral that can be obtained by synthesizing, for example, CaO raw material, Al ₂ O ₃ raw material, and optionally SiO ₂ raw material in an electric furnace or kiln at 1,200 to 1,900° C., followed by rapid cooling.
The calcium aluminate may have a composition of, for example, 35 to 60 mass % CaO, 35 to 55 mass % Al ₂ O ₃ , and 1 to 15 mass % SiO ₂ .
Exemplary chemicals include 3CaO· _Al2O3 , 12CaO· _7Al2O3 , 11CaO· _7Al2O3 · _CaF2 , CaO· _Al2O3 , 2CaO· _Al2O3 · _SiO2 , CaO· _Al2O3 · _2SiO2 , _3CaO · _3Al2O3 · _CaF2 , _{and 3CaO ·2Na2O · 5Al2O3 ,} and may contain _one or more of these. Of _{these, 12CaO·7Al2O3 is preferred .}
The amount of calcium aluminate in the rapid hardening cement is, for example, 2 parts by mass or more and preferably 30 parts by mass or less, and for example, 5 parts by mass or more and 20 parts by mass or less, based on 100 parts by mass of the rapid hardening cement. By setting the amount of calcium aluminate within the above range, a rapid hardening cement having an excellent balance between short-term strength and expansion rate after curing can be obtained.
Calcium aluminate can be used in either a crystalline or vitreous form, but vitreous form obtained by quenching the melt in an electric furnace or the like is preferred, and when the vitreous content is 60 mass % or more, excellent short-term strength development is achieved.
The fineness of calcium aluminate is preferably 3,000 cm ² /g or more and 9,000 cm ² /g or less, and more preferably 4,000 cm ² /g or more and 7,000 cm ² /g or less, in Blaine value.

The cement composition may contain components other than those described above. Specific examples of such components include one or more materials selected from the group consisting of set retarders; water reducing agents; high-performance water reducing agents; air entraining (AE) agents; air entraining water reducing agents; high-performance air entraining water reducing agents; thickeners; rust inhibitors; antifreeze agents; hydration heat inhibitors; polymer emulsions; clay minerals such as bentonite and montmorillonite; ion exchangers such as zeolites, hydrotalcites, and hydrocalumite; sulfates such as aluminum sulfate and sodium sulfate; phosphates; and boric acid.

When mixing cement compositions, the individual ingredients may be mixed at the time of construction, or some or all of them may be mixed in advance.

The method for mixing the cement composition is not limited and may be any commonly used method. Any existing mixing device can be used as the mixing device, such as a tilting mixer, omni mixer, V-type mixer, Henschel mixer, or Nauta mixer.

In addition, there are no restrictions on the method of curing the cement composition, and any of the commonly used curing methods, such as room temperature and atmospheric pressure curing, steam curing, high temperature and high pressure steam curing, and pressurized curing, can be applied.

The above describes embodiments of the present invention, but these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements that achieve the objectives of the present invention are included in the present invention.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.
Unless otherwise specified, all operations were carried out at room temperature and pressure.

(Raw materials used)
plaster
The gypsum used in each example is as follows:
Gypsum 1: Type II anhydrite, pH 3.3, main component CaSO ₄
Gypsum 2: Type II anhydrite, pH 6.0, main component CaSO ₄
Gypsum 3: Type II natural anhydrite, pH 8.5, main component CaSO ₄

Example 1
Gypsum 1 was pulverized in a ball mill . The properties of gypsum 1 after pulverization are shown in Table 1.

(Example 2, Comparative Example 1)
The same procedure as in Example 1 was carried out except that the gypsum shown in Table 1 was used .
The obtained gypsum of each of the examples and comparative examples was evaluated as follows.

Each gypsum was analyzed by the following method. The analysis results are shown in Table 1.
(component analysis)
The chemical composition was analyzed in accordance with JIS R 5202 "Method for chemical analysis of Portland cement."
(pH)
The pH of each gypsum was measured in accordance with JIS R 9101 (method for chemical analysis of gypsum).

(dissolution rate)
(1) 100 mL of saturated calcium hydroxide solution adjusted to 20°C was placed in a 200 mL beaker.
(2) A stirring bar was placed in a beaker and stirred on a magnetic stirrer, and 4 g of a gypsum sample was added, and the elapsed time from the addition was measured.
(3) After a specified time had elapsed since the addition, the beaker was immediately removed from the stirrer and subjected to suction filtration using JIS P 3801 No. 5C filter paper.
(4) 10 mL of the filtrate was placed in a 20 mL volumetric flask, and 1 mL of 3.18% hydrochloric acid solution was added, followed by diluting the mixture with pure water.
(5) 5 mL of the solution obtained in (4) was placed in a 200 mL volumetric flask and made up to the volume with pure water.
(6) The solution obtained in (5) was injected into an ion chromatogram (Shimadzu Corporation, Ion Chromatograph, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) When the specified time in (3) was 5 minutes and 10 minutes, the SO ₄ ^2- ions were quantified in the same manner as in (4) to (6), and the dissolution rate was calculated based on the following formula.
Dissolution rate (mg/(100 mL·min))=(SO ₄ ^2- ion concentration after 10 minutes−SO ₄ ^2- ion concentration after 5 minutes)/5

(particle size distribution)
The particle size distribution of the particles was measured on a volume basis using a laser diffraction particle size distribution measuring device (HORIBA, LA-960).

(Preparation of mortar)
270 g of cement admixture (rapid hardening material) (containing 135 g of gypsum and 135 g of calcium aluminate in each of the Examples and Comparative Examples) , 630 g of cement, 1,350 g of fine aggregate, and 306 g of water were mixed at room temperature of 20°C to prepare mortar, and the compressive strength was measured.

(Materials used)
Calcium aluminate : CaO-Al ₂ O ₃ -SiO ₂ amorphous material, CaO 47%, Al ₂ O ₃ 47%, SiO ₂ 3%, others 3%. Density 2.85 g/cm ³ , Blaine specific surface area 5000 cm ² /g, amorphousness 90%
Cement: High-early-strength Portland cement manufactured by Denka (Blaine specific surface area: 4500 cm ² /g, density: 3.12 g/cm ³ )
Fine aggregate: river sand from Himekawa, Itoigawa City, Niigata Prefecture, surface-dried, density 2.62 g/cm ³ , maximum aggregate size 5 mm
Water: Tap water

( Calcium aluminate , cement density and Blaine specific surface area)
The density and Blaine specific surface area of each of the calcium aluminates and cements were measured in accordance with JIS R5201 (physical testing method for cement).

<Compression strength>
Test specimens measuring 4 x 4 x 16 cm were prepared in accordance with JIS R 5201, and the compressive strength after 3 hours was measured.

As can be seen from Table 1, in each example, the cement composition had excellent strength and was able to achieve high strength in as little as three hours.

Claims (4)

A cement composition comprising a cement admixture and cement,
The cement composition is a rapid hardening cement ,
The cement admixture is a hardening agent, and the hardening agent consists of calcium aluminate and gypsum only.
The content of the gypsum in the rapid hardening material is 50% by mass or more and 98% by mass or less,
The amount of calcium aluminate in the rapid hardening cement is 2 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the rapid hardening cement,
The dissolution rate of the gypsum, measured according to the following method 1, is 30 mg/(100 mL min) or more and 100 mg/(100 mL min) or less,
The calcium aluminate has a composition of 35% by mass or more and 60% by mass or less of CaO, 35% by mass or more and 55% by mass or less of Al ₂ O ₃ , and 1% by mass or more and 15% by mass or less of SiO ₂ .
(Method 1)
(1) Place 100 mL of saturated aqueous calcium hydroxide solution adjusted to 20°C into a 200 mL beaker.
(2) A stirring bar is placed in the beaker and stirred on a magnetic stirrer, and 4 g of the gypsum sample is added, and the elapsed time from the addition is measured.
(3) Immediately after a specified time has elapsed since the addition, the beaker is removed from the stirrer and the mixture is subjected to suction filtration using a JIS P 3801 No. 5C filter paper.
(4) 10 mL of the filtrate is placed in a 20 mL volumetric flask, and 1 mL of 3.18% hydrochloric acid aqueous solution is added, followed by diluting the solution with purified water.
(5) 5 mL of the solution obtained in (4) is placed in a 200 mL volumetric flask and made up to the volume with pure water.
(6) The solution obtained in (5) is injected into an ion chromatogram (Shimadzu Corporation, Ion Chromatograph, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) When the specified time in (3) is 5 minutes and 10 minutes, the amount of SO ₄ ^2- ions is determined by the procedures in (4) to (6), and the dissolution rate is calculated based on the following formula.
Dissolution rate (mg/(100 mL·min))=(SO ₄ ^2- ion concentration after 10 minutes−SO ₄ ^2- ion concentration after 5 minutes)/5 the gypsum is granular,
2. The cement composition according to claim 1, wherein the proportion of particles having a size of 1.0 μm or more and 10 μm or less in the gypsum is 30% by volume or more and 80% by volume or less. the gypsum is granular,
The cement composition according to claim 1 or 2, wherein the gypsum has a median diameter d ₅₀ of 5 μm or more and 15 μm or less. 4. The cement composition of claim 1, wherein the cement admixture further comprises _SiO2 .