JP2024024029A - cement admixture - Google Patents

Abstract

[Problem] To provide a cement admixture that quickly develops excellent strength. The cement admixture contains gypsum, and the dissolution rate of the gypsum in a saturated calcium hydroxide solution at 20° C. is 30 mg/(100 mL/min) or more and 100 mg/(100 mL/min) or less. [Selection diagram] None

Description

The present invention relates to cement admixtures.

A technique related to a cement admixture containing gypsum is described in Patent Document 1 (Japanese Unexamined Patent Publication No. 157129/1983). This document describes a method for producing a cement quick-hardening material, in which a cement quick-hardening material made of calcium aluminate and gypsum is mixed with a small amount of water in the presence of sulfuric acid. It is said that it is possible to produce cement-curing materials with easy control of pot life and excellent strength.

Japanese Unexamined Patent Publication No. 54-157129

However, as a result of the present inventor's study of the cement rapid hardening material described in Patent Document 1, it was found that there is still room for improvement in terms of developing excellent strength at an early stage.

According to the present invention, the cement admixture shown below is provided.

1. A cement admixture containing gypsum,
A cement admixture having a dissolution rate of the gypsum of 30 mg/(100 mL/min) or more and 100 mg/(100 mL/min) or less, as measured according to Method 1 below.
(Method 1)
(1) Into a 200 mL beaker, put 100 mL of a saturated calcium hydroxide solution whose temperature is controlled to 20°C.
(2) Put a stirring bar into the beaker, stir it on a magnetic stirrer, add 4g of the gypsum sample, and measure the elapsed time from the time it was added.
(3) Immediately after a specified time has elapsed from the time of charging, the beaker is removed from the stirrer and the beaker is placed in a JIS P 3801 No. Filter with suction through 5C filter paper.
(4) Collect 10 mL of the filtrate into a 20 mL volumetric flask, add 1 mL of 3.18% hydrochloric acid solution, and make up the volume with pure water.
(5) Collect 5 mL of the solution obtained in (4) into a 200 mL volumetric flask, and make up the volume with pure water.
(6) The solution obtained in (5) is injected into an ion chromatogram (Ion chromatograph manufactured by Shimadzu Corporation, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) When the specified time in (3) is 5 minutes and 10 minutes later, the SO ₄ ^2- ion is quantified by the steps (4) to (6), and the dissolution rate is determined based on the following formula. seek.
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 proportion of particles of 1.0 μm or more and 10 μm or less in the plaster is 30 volume % or more and 80 volume % or less. Cement admixtures listed in .
3. the gypsum is granular;
1. The median diameter d ₅₀ of the plaster is 5 μm or more and 15 μm or less. or 2. Cement admixtures listed in .
4. Further comprising SiO ₂ 1. to 3. Cement admixture according to any one of the above.

According to the present invention, it is possible to obtain a cement admixture that quickly develops excellent strength.

Embodiments of the present invention will be described below. In addition, unless otherwise specified, "~" in a numerical range represents the above to the following, and includes both ends of the range. Moreover, in this embodiment, the composition can contain each component alone or in combination of two or more.

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

(Method 1)
(1) Into a 200 mL beaker, put 100 mL of a saturated calcium hydroxide solution whose temperature is controlled to 20°C.
(2) Put a stirrer in a beaker, stir it on a magnetic stirrer, add 4g of gypsum sample, and measure the elapsed time from the time it was added.
(3) Immediately after the specified time has elapsed from the time of pouring, remove the beaker from the stirrer and place it in JIS P 3801 No. Filter with suction through 5C filter paper.
(4) Collect 10 mL of the filtrate into a 20 mL volumetric flask, add 1 mL of 3.18% hydrochloric acid solution, and make up the volume with pure water. Here, 3.18% hydrochloric acid can be obtained, for example, by diluting commercially available 35% hydrochloric acid 1/11 times.
(5) Collect 5 mL of the solution obtained in (4) into a 200 mL volumetric flask, and make up the volume with pure water.
(6) The solution obtained in (5) is injected into an ion chromatogram (Ion chromatograph manufactured by Shimadzu Corporation, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) After 5 minutes and 10 minutes after the specified time in (3), quantify SO ₄ ^2- ions using the steps (4) to (6), respectively, and calculate the dissolution rate 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 present inventors have discovered that excellent strength can be developed early by setting the dissolution rate of gypsum contained in a cement admixture into a saturated calcium hydroxide solution at 20°C within a specific range. The reason for this is not necessarily clear, but it is thought to be because it has appropriate handling properties and reaction activity that is appropriate for early strength development.

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, More preferably, it is 70 mg/(100 mL/min) or more.
From the viewpoint of making the reactivity and handling time of the cement composition more favorable, 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. /(100 mL·min) or less, more preferably 85 mg/(100 mL·min) or less, even more preferably 80 mg/(100 mL·min) or less.

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

Although the shape of the gypsum is not limited, it is preferably granular from the viewpoint of stably improving the strength of the cement composition.
At this time, the proportion of particles having a particle size in the range of 1.0 μm or more and 10 μm or more in the plaster is preferably 30% by volume or more based on the entire plaster, more preferably It is 40 volume% or more, more preferably 50 volume% or more, and preferably 80 volume% or less, and more preferably 70 volume% or less.

In addition, from the viewpoint of improving the strength of the cement composition, the median diameter _d50 of the plaster is preferably 5 μm or more, more preferably 6 μm or more, and preferably 15 μm or less, more preferably 12 μm or less, More preferably, it is 10 μm or less, and even more preferably 8 μm or less.

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

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, and even more preferably 95% by mass based on the entire cement admixture. % or more, even more preferably 98% by mass or more.
There is no upper limit to the content of gypsum in the cement admixture, and it is 100% by mass or less, but may be, for example, 99% by mass or less, or, 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 making the handling of the cement composition more favorable.
When the cement admixture contains _SiO2 , the shape of the silica is, for example, granular. Further, the median diameter d ₅₀ of silica can be, for example, approximately the same as the median diameter d ₅₀ of gypsum.
Further, 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 a cement admixture will be explained.
A method for producing a cement admixture includes, for example, preparing gypsum having a solubility within a specific range. Moreover, when the cement admixture contains a component other than gypsum, it may include a step of mixing gypsum and a component other than gypsum.
Here, in this embodiment, it is possible to control the dissolution rate of gypsum by appropriately selecting a method for preparing gypsum, for example. Among these, appropriately adjusting the particle size, particle size distribution, etc. of gypsum can be cited as a factor for achieving a desired level of dissolution rate of gypsum.
Further, the particle size and particle size distribution of the cement admixture can be adjusted by performing a crushing and classification process. The method of pulverization and classification is not limited, and it is possible to use known pulverization and classification methods. For example, the pulverization method may be a ball mill or roller mill, and the classification method may be an air classifier, etc. can be mentioned.

(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 at an early stage. Further, according to the present embodiment, it is also possible to stably control, for example, stably increase the pot life of the cement composition.

The "cement" used in this embodiment is not limited to, but includes, for example, various kinds of normal, early-strength, medium-heat, and low-heat Portland cements defined by the Japanese Industrial Standards (JIS), blast furnace slag, fly ash, Various mixed cements containing silica, filler cements containing limestone powder, slowly cooled blast furnace slag powder, etc., and environmentally friendly cement (ecocement) made from municipal waste incineration ash and sewage sludge incineration ash. All kinds of cements such as Further, cements defined by overseas EN197-2000 and all kinds of cements defined by China's GB standards can be mentioned, and one or more of these can be used.

The cement composition also more specifically includes water. Although the amount of water used is not limited, usually the water/cement composition ratio may be, for example, about 8 to 80%, or, for example, 25 to 70%, or, for example, 30% to the cement composition. It may be up to 60%.

Further, the cement composition is specifically a rapidly hardening cement, and in this case, for example, the cement admixture in this embodiment may be a rapidly hardening material. Here, the rapid hardening material refers to a component that generates a rapid hardening hydrate such as ettringite at an early stage and imparts rapid hardening to cement concrete.
When the cement admixture is a rapidly hardening material, it is preferable that the rapidly hardening material contains at least the above-mentioned gypsum and calcium aluminate. Regarding the content of these components in the rapidly hardening material, the total amount of calcium aluminate and gypsum is preferably 80 parts by mass or more when the rapidly hardening material contained in the rapidly hardening cement is 100 parts by mass. , more preferably 90 parts by mass or more, and can also be 100 parts by mass. That is, the rapidly hardened material according to this embodiment may be made of only calcium aluminate and gypsum.

(calcium aluminate)
Calcium aluminate can be obtained, for example, by synthesizing a CaO raw material, an Al ₂ O ₃ raw material, and optionally a SiO ₂ raw material, etc. in an electric furnace or kiln at 1,200 to 1,900°C, and then rapidly cooling the mixture. It is a mineral.
As for the composition of calcium aluminate, for example, CaO may be 35% by mass or more and 60% by mass or less, Al ₂ O ₃ may be 35% by mass or more and 55% by mass or less, and SiO ₂ may be 1% by mass or more and 15% by mass or less. can.
Exemplary _{chemicals include 3CaO.Al2O3 ,} 12CaO.7Al2O3 _{, 11CaO.7Al2O3.CaF2 , CaO.Al2O3 , 2CaO.Al2O3.SiO2 , CaO -Al2O3.2SiO2 , 3CaO.3Al2O3.CaF2 , 3CaO.2Na2O.5Al2O3 ,} etc., and _{one or} more of the _above may be included. Among these, it is preferable to include 12CaO.7Al ₂ O ₃ .
The blending amount of calcium aluminate in the quick-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, based on 100 parts by mass of the quick-hardening cement. The content is preferably 20 parts by mass or less. By setting the amount of calcium aluminate within the above numerical range, a rapidly hardening cement with a better balance between short-term strength and expansion rate after curing can be obtained.
As calcium aluminate, it is possible to use either crystalline or vitreous forms, but vitreous ones obtained by rapidly cooling the molten material in an electric furnace or the like are preferable, and if the vitreous content is 60% by mass or more, it is short-lived. Excellent time-strength development.
The fineness of calcium aluminate is preferably 3,000 cm ² /g or more and 9,000 cm ² /g or less, 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 mentioned above. Specific examples of such components include setting regulators; water reducers; high performance water reducers; AE (Air Entraining) agents; AE water reducers; high performance AE water reducers; thickeners; rust preventives; antifreeze agents; heat of hydration. Inhibitors; polymer emulsions; clay minerals such as bentonite and montmorillonite; ion exchangers such as zeolite, hydrotalcite, and hydrocalumite; sulfates such as aluminum sulfate and sodium sulfate; phosphates; boric acid, and other groups One or more materials selected from:

In the cement composition, the respective materials may be mixed at the time of construction, or some or all of the materials may be mixed in advance.

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

Further, the curing method for the cement composition is not limited, and any curing method generally performed such as normal temperature/normal pressure curing, steam curing, high temperature/high pressure steam curing, pressurized curing, etc. can be applied.

Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and the present invention includes modifications, improvements, etc. within a range that can achieve the purpose of the present invention.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the description of these Examples.
Hereinafter, unless otherwise specified, each operation was performed at room temperature and normal pressure.

(Raw materials used)
Cement admixtures The cement admixtures used in each example are as follows.
Cement admixture 1: Type II anhydrite, pH 3.3, main component CaSO ₄
Cement admixture 2: Type II anhydrite, pH 6.0, main component CaSO ₄
Cement admixture 3: Type II natural anhydrite, pH 8.5, main component CaSO ₄

(Example 1)
Cement admixture 1 was ground in a ball mill to prepare a cement admixture having the characteristics shown in Table 1.

(Example 2, Comparative Example 1)
Cement admixtures 2 and 3 were obtained in the same manner as in Example 1 except that the cement admixtures listed in Table 1 were used.
The obtained cement admixtures of Examples and Comparative Examples were evaluated as follows.

Here, each cement admixture was analyzed using 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 cement admixture was measured in accordance with JIS R 9101 (chemical analysis method for gypsum).

(dissolution rate)
(1) In a 200 mL beaker, 100 mL of a saturated calcium hydroxide solution whose temperature was controlled to 20° C. was placed.
(2) A stirrer was placed in a beaker, stirred on a magnetic stirrer, 4 g of a cement admixture sample was added, and the elapsed time from the time of addition was measured.
(3) Immediately after the specified time has elapsed from the time of pouring, remove the beaker from the stirrer and place it in JIS P 3801 No. Suction filtration was performed using 5C filter paper.
(4) 10 mL of the filtrate was collected in a 20 mL volumetric flask, 1 mL of 3.18% hydrochloric acid solution was added, and the volume was diluted with pure water.
(5) 5 mL of the solution obtained in (4) was collected into a 200 mL volumetric flask and diluted with pure water.
(6) The solution obtained in (5) was injected into an ion chromatogram (Ion chromatograph, PIA-1000, Personal Ion Analyzer, manufactured by Shimadzu Corporation), and SO ₄ ^2- ions were quantified.
(7) When the specified time in (3) is 5 minutes and 10 minutes later, the SO ₄ ^2- ions are quantified by the steps (4) to (6), respectively, and the dissolution rate is calculated based on the following formula. I asked for it.
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 analyzer (manufactured by HORIBA, LA-960).

(Preparation of mortar)
Mortar was prepared by mixing 135 g of cement admixture, 135 g of rapidly hardening material, 630 g of cement, 1350 g of fine aggregate, and 306 g of water at a room temperature of 20° C., and the compressive strength was measured.

(Materials used)
Rapidly hardened material: CaO--Al ₂ O ₃ --SiO ₂ -based amorphous material with 47% CaO, 47% Al ₂ O ₃ , 3% SiO ₂ , and 3% others. Density 2.85g/cm ³ , Blaine specific surface area 5000cm ² /g, amorphousness 90%
Cement: Early strength Portland cement manufactured by Denka (Brain specific surface area 4500cm ² /g, density 3.12g/cm ³ )
Fine aggregate: River sand from Himekawa, Itoigawa City, Niigata Prefecture, surface dry, density 2.62g/cm ³ , maximum aggregate size 5mm
Water: tap water

(Sudden hardening material, cement density and Blaine specific surface area)
The density and Blaine specific surface area of each of the above-mentioned rapidly hardening materials and cement were measured based on JIS R5201 (physical testing method for cement).

<Compressive strength>
Based on JIS R 5201, a 4 x 4 x 16 cm test specimen was prepared, and the compressive strength was measured after 3 hours.

From Table 1, in each Example, the cement composition was excellent in strength and was able to develop high strength as early as 3 hours.

Claims (1)

A cement admixture containing gypsum,
A cement admixture having a dissolution rate of the gypsum of 30 mg/(100 mL/min) or more and 100 mg/(100 mL/min) or less, as measured according to Method 1 below.
(Method 1)
(1) Into a 200 mL beaker, put 100 mL of a saturated calcium hydroxide solution whose temperature is controlled to 20°C.
(2) Put a stirring bar into the beaker, stir it on a magnetic stirrer, add 4g of the gypsum sample, and measure the elapsed time from the time it was added.
(3) Immediately after a specified time has elapsed from the time of charging, the beaker is removed from the stirrer and the beaker is placed in a JIS P 3801 No. Filter with suction through 5C filter paper.
(4) Collect 10 mL of the filtrate into a 20 mL volumetric flask, add 1 mL of 3.18% hydrochloric acid solution, and make up the volume with pure water.
(5) Collect 5 mL of the solution obtained in (4) into a 200 mL volumetric flask, and make up the volume with pure water.
(6) The solution obtained in (5) is injected into an ion chromatogram (Ion chromatograph manufactured by Shimadzu Corporation, PIA-1000, Personal Ion Analyzer) to quantify SO ₄ ^2- ions.
(7) When the specified time in (3) is 5 minutes and 10 minutes later, the SO ₄ ^2- ion is quantified by the steps (4) to (6), and the dissolution rate is determined based on the following formula. seek.
Dissolution rate (mg/(100 mL min)) = (SO ₄ ^2- ion concentration after 10 minutes - SO ₄ ^2- ion concentration after 5 minutes) / 5