JP2020083660A - Cement admixture, expansion material, and cement composition - Google Patents

Abstract

To provide a cement admixture capable of providing a large volume of expansion to concrete during an initial material age (ex. 2 to 7 days of material age) after concrete placement, curbing dry-shrinkage distortion, and preventing lowering of long-term strength development.SOLUTION: A cement admixture of this invention contains free lime, a hydraulic compound, and anhydrite, and includes SrO as chemical component.SELECTED DRAWING: None

Description

The present invention relates to a cement admixture, an expansive material, and a cement composition used in the field of civil engineering/construction, for example.

Reducing cracks in cement/concrete is important from the viewpoint of reliability, durability, aesthetics, etc. of concrete structures, and further technological development of cement admixtures that have the effect of improving these, that is, cement-based expansive materials Is desired.

So far, concrete expansive materials having excellent expansion properties with a small amount of addition (Patent Document 1), expansive materials for cement in which the surface of free lime is coated with calcium carbonate (Patent Document 2), and the like have been proposed. In recent years, it has been proposed to use an expansive material and a shrinkage reducing agent together (Patent Document 3).
On the other hand, a digestion-resistant calcia clinker composed of a solid solution of calcia and strontium oxide has been proposed (Patent Document 4).

Japanese Patent No. 4244261 JP, 54-93020, A JP, 2003-12352, A JP-A-57-205363

Conventional expansive materials have the property of expanding up to 7 days old. However, there is a problem that the drying shrinkage behavior is not so different from that when the expansive material is not mixed. Further, the combined use of the expansive material and the shrinkage-reducing agent is effective in suppressing the dry shrinkage, but there is a problem that the long-term strength development property is lowered.
The digestive resistant calcia clinker described in Patent Document 4 is intended to be used as a basic refractory raw material, and there is no description about use as an expansive material for suppressing cracking of cement/concrete.

From the above, the present invention imparts a large expansion to the cement/concrete over the initial age (for example, 2 to 7 days of age) after placing the cement/concrete, suppresses dry shrinkage strain, and exhibits long-term strength development. It is an object of the present invention to provide a cement admixture, an expansive material, and a cement composition capable of suppressing the deterioration of the cement content.

As a result of intensive studies in view of the above problems, the present inventors have found that the problems can be solved by a cement admixture containing free lime, a hydraulic compound, and anhydrous gypsum, and containing SrO as a chemical component. Completed the invention. That is, the present invention is as follows.

[1] A cement admixture containing free lime, a hydraulic compound, and anhydrite, and containing SrO as a chemical component.
[2] The cement admixture according to [1], wherein the content of SrO is 0.001 to 5.0 parts by mass based on 100 parts by mass of the cement admixture.
[3] The cement admixture according to [1] or [2], further containing ZrO ₂ as a chemical component.
[4] The cement admixture according to [3], wherein the content of ZrO ₂ is 0.0001 to 5.0 parts by mass with respect to 100 parts by mass of the cement admixture.
[5] The cement admixture according to any one of [1] to [4], which has a Blaine specific surface area of 2,000 to 6,000 cm ² /g.
[6] On a volume basis, the content of particles of 10 μm or less is 30 to 60% by volume, and the ratio (A/B) of the content A of 100 μm or less and the content B of particles of 10 μm or less is 1.5. The cement admixture according to any one of [1] to [5], which is ˜4.0.
[7] as the hydraulic _{compound, 3CaO · 3Al 2 O 3 ·} CaSO 4, 3CaO · SiO 2, 2CaO · SiO 2, 4CaO · Al 2 O 3 · Fe 2 O 3, 6CaO · 2Al 2 O 3 · Fe 2 _{O 3, 6CaO · Al 2 O} 3 · Fe 2 O 3, and containing one or more selected from the group consisting of _{2CaO · Fe 2 O 3 [1} ] ~ according to any one of [6] Cement admixture.
[8] An expansive material comprising the cement admixture according to any one of [1] to [7].
[9] A cement composition containing the cement admixture according to any one of [1] to [7].

According to the present invention, a large expansion is imparted to the cement/concrete over the initial age (for example, 2 to 7 days of age) after placing the cement/concrete, to suppress the dry shrinkage strain and to exhibit the long-term strength development property. It is possible to provide a cement admixture, an expansive material, and a cement composition capable of suppressing the decrease.

Hereinafter, the cement admixture, the expansive material, and the cement composition according to the embodiment of the present invention will be described.
The parts and% used in this specification are based on mass unless otherwise specified. The cement/concrete in the present invention is a general term for cement paste, mortar and concrete.

[1. Cement admixture and expansive material]
The cement admixture according to this embodiment contains free lime, a hydraulic compound, and anhydrite, and contains SrO as a chemical component.

(Free lime)
Free lime is usually called f-CaO (free lime). By containing free lime in the cement admixture according to the present embodiment, expansion characteristics are imparted, and as a result, drying shrinkage is suppressed.
The content of free lime is preferably 10 to 95 parts, and more preferably 40 to 90 parts, relative to 100 parts of the cement admixture. By containing 10 to 95 parts, the effect of suppressing dry shrinkage can be exhibited without causing a decrease in long-term strength expression.
During firing during the production of the cement admixture, by raising the firing temperature, or by appropriately adjusting the blending amount and particle size of the input raw materials other than the CaO raw material, the crystal particle size of free lime in the cement admixture Can be increased or the content can be increased.

(Hydraulic compound)
The hydraulic compound according to this embodiment, Irimaito represented by _{3CaO · 3Al 2 O 3 · CaSO} 4, in 3CaO · _SiO 2 _{(C 3} S for short) and 2CaO · _{SiO 2 (C} 2 S for short) calcium silicate _{represented, 4CaO · Al 2 O 3 ·} Fe 2 O 3 (C 4 AF for short) and _{6CaO · 2Al 2 O 3 · Fe} 2 O 3 (C 6 a 2 F abbreviated), 6CaO · Al ₂ Calcium aluminoferrite represented by O ₃ ·Fe ₂ O ₃ (abbreviated as C ₆ AF), calcium ferrite such as 2CaO·Fe ₂ O ₃ (abbreviated as C ₂ F), or the like, and one of these or It is preferable to include two or more kinds. Among _{them, 3CaO · 3Al 2 O 3 ·} CaSO 4, C 4 AF, it is preferred to include one or more of _{C 2} S.

The content of the hydraulic compound is preferably 2 to 45 parts, more preferably 5 to 30 parts, still more preferably 7 to 20 parts, based on 100 parts of the cement admixture. A high expansion characteristic can be imparted by being 2 to 45 parts.

(Anhydrous gypsum)
The content of anhydrous gypsum is preferably 3 to 50 parts, more preferably 10 to 40 parts, and even more preferably 20 to 30 parts with respect to 100 parts of the cement admixture.
When the content of anhydrous gypsum in the cement admixture is low, an amount of anhydrous gypsum in the range of 3 to 50 parts per 100 parts of the cement admixture can be added separately.

(SrO)
The cement admixture according to the present embodiment contains SrO as a chemical component. When a certain amount of SrO is dissolved in the cement admixture (or expansion material), the drying shrinkage (after 7 days of age) can be reduced. It also makes it possible to improve storage stability.

The content of SrO is preferably 0.001 to 5.0 parts by mass, more preferably 0.001 to 0.5 parts by mass, and 0.005 parts by mass with respect to 100 parts by mass of the cement admixture. It is more preferably 0.5 to 0.5 parts by mass. In particular, when it is 0.001 to 0.5 parts by mass, the effect of reducing drying shrinkage becomes better.

(Other ingredients)
The cement admixture according to the present embodiment preferably further contains ZrO ₂ as a chemical component. The content of ZrO ₂ is preferably 0.001 to 5.0 parts by mass, more preferably 0.0001 to 0.1 parts by mass, and more preferably 0.001 to 5.0 parts by mass with respect to 100 parts by mass of the cement admixture. It is more preferably 0003 to 0.05 parts by mass. Especially when it is 0.0001 to 0.1 parts by mass, the fluidity can be improved.

The cement admixture according to the present embodiment preferably has a Blaine specific surface area of 2,000 to 6,000 cm ² /g, more preferably 2,500 to 5,000. When the Blaine specific surface area is 2,000 to 6,000 cm ² /g, it is possible to prevent the concrete structure from being broken due to expansion over a long period of time, and to maintain good expansion performance.
In addition, the Blaine specific surface area value in this specification can be calculated|required based on JISR5201 (physical test method of cement).

Further, from the viewpoints of reducing slump loss, securing expansion amount even when added in a small amount, and preventing pop-out, the content rate of particles having a particle size of 10 μm or less is 30 to 60% by volume, and the content rate of particles having a particle size of 100 μm or less is used. The ratio (A/B) of A and the content B of particles of 10 μm or less is preferably 1.5 to 4.0. The content of particles of 10 μm or less is 20 to 60% by volume, and the ratio (A/B) of the content A of particles of 100 μm or less and the content B of particles of 10 μm or less is 1.8 to 3.0. More preferably.
In addition, the content of particles in the present invention is such that the cement admixture is dispersed in ethanol for 1 minute by ultrasonic waves using a laser diffraction/scattering type particle size distribution measuring device, and then the sample refractive index is 1.770 and the dispersion medium is It is calculated based on the particle size distribution measured on a volume basis under the condition that the refractive index is 1.360.
The cement admixture of the present invention is obtained by appropriately mixing and firing CaO raw material, Al ₂ O ₃ raw material, Fe ₂ O ₃ raw material, SiO ₂ raw material, CaSO ₄ raw material, SrO raw material, and ZrO ₂ raw material.

Examples of the CaO raw material include limestone and slaked lime, examples of the Al ₂ O ₃ raw material include bauxite and aluminum residual ash, examples of the Fe ₂ O ₃ raw material include copper kalami and commercially available iron oxide, and examples of the SiO ₂ raw material include silica stone. Examples of CaSO ₄ raw materials include gypsum dihydrate, gypsum hemihydrate, and gypsum anhydrate.

The SrO raw material is not particularly limited, but examples thereof include celestite, strontium stone, strontium oxide, and strontium carbonate.
The ZrO ₂ raw material is not particularly limited, but examples thereof include zirconium oxide, zirconium hydroxide, zirconium carbonate, zirconium oxychloride, zirconium sulfate, zirconium acetate, organic acid zirconium, and zircon sand.
When SrO or ZrO ₂ is contained in the CaO raw material, the Al ₂ O ₃ raw material, the SiO ₂ raw material, or the CaSO ₄ raw material, it is not necessary to newly add the SrO raw material or the ZrO ₂ raw material.

These raw materials may contain impurities, but there is no particular problem as long as the effects of the present invention are not impaired. Examples of the impurities include MgO, TiO ₂ , MnO, P ₂ O ₅ , Na ₂ O, K ₂ O, Li ₂ O, sulfur, fluorine and chlorine.

The cement admixture can be produced by mixing the above raw materials so that the desired mineral composition and SrO have the desired chemical composition, appropriately pulverizing, and then firing.
The firing method is not particularly limited, but it is preferable to use an electric furnace, a kiln, or the like to perform firing at a temperature of 1,100 to 1,600°C, and more preferably 1,200 to 1,500°C. If it is less than 1,100°C, the expansion performance is not sufficient, and if it exceeds 1,600°C, anhydrous gypsum may decompose.
Moreover, when pulverizing, it is preferable to carry out by a known method so that the Blaine specific surface area becomes 2,000 to 6,000 cm ² /g.

The content of minerals in the cement admixture manufactured as described above can be confirmed by a conventional analysis method. For example, it is possible to quantify the mineral by applying the powdered X-ray diffractometer to the crushed sample, confirming the produced mineral, and analyzing the data by the Rietveld method. Further, the amount of minerals can be calculated by using the chemical components and the results of powder X-ray diffraction identification. In the present embodiment, it is preferable to calculate the amount of minerals based on the chemical composition and the identification result of the powder X-ray diffraction.
The content of the chemical component can be determined by fluorescent X-ray.

The cement admixture according to the present embodiment preferably contains particles in which free lime, hydraulic compound, anhydrite, and SrO are present in the same particle. Further, when ZrO ₂ is contained, it is preferable that this also be present in the same particle.
Whether free lime, hydraulic compound, anhydrous gypsum, SrO, and ZrO ₂ are present in the same particle can be confirmed by an electron microscope or the like. Specifically, a cement admixture is embedded in a resin, subjected to surface treatment with an argon ion beam, and while observing the structure of the particle cross section, free lime, hydraulic compound, anhydrous gypsum by elemental analysis, and It can be confirmed whether SrO and ZrO ₂ are present in the same particle.

The cement admixture according to the present embodiment as described above is preferably used as an expansive material, for example. That is, the expansive material according to the present embodiment is made of the cement admixture described above. This makes it possible to impart a large expansion to the concrete over the initial age (for example, 2 to 7 days of age) after placing the concrete, to suppress the dry shrinkage strain, and to suppress the deterioration of long-term strength development.

[3. Cement composition]
The cement composition according to the present embodiment contains the cement admixture described above. Here, as the cement used in the cement composition, normally, early strength, ultra-early early strength, low heat, and various portland cement such as moderate heat, these Portland cement, blast furnace slag, fly ash, or mixed silica. Various types of mixed cement, filler cement mixed with limestone powder and blast furnace slowly cooled slag fine powder, and Portland cement such as environmentally friendly cement (eco-cement) manufactured from municipal waste incineration ash and sewage sludge incineration ash are raw materials. One or more of these can be used. The cement admixture may be the expansive material according to this embodiment.

In the present embodiment, in addition to cement, cement admixture, and coarse aggregate such as sand and coarse aggregate such as sand, fast strengthening agent, rapid hardening material, water reducing agent, AE water reducing agent, high performance water reducing agent, high Performance AE water reducing agent, superplasticizer, antifoaming agent, thickening agent, rust preventive, antifreezing agent, shrinkage reducing agent, coagulation reducing agent, heat of hydration inhibitor, polymer emulsion, clay minerals such as bentonite, hydrotal One or two of the group consisting of anion exchangers such as sites, slag such as granulated blast furnace slag fine powder and blast furnace slowly cooled slag fine powder, limestone fine powder, siliceous fine powder, gypsum, and calcium silicate. It is possible to use two or more kinds in combination as long as the object of the present invention is not substantially impaired. Further, as the organic material, it is possible to use together with a fibrous substance such as vinylon fiber, acrylic fiber, carbon fiber or the like.

The use amount (mixing amount) of the cement admixture (or expanding material) is not particularly limited because it changes depending on the mixing of concrete, but usually a cement composition containing cement and the cement admixture (or expanding material). In 100 parts by mass, 3 to 12 parts by mass is preferable, and 4 to 7 parts by mass is more preferable. When the amount is 3 parts by mass or more, sufficient expansion performance can be obtained. Further, when the amount is 12 parts by mass or less, overexpansion does not occur and expansion cracks can be prevented from occurring in concrete.

"Experimental example 1"
After CaO raw material, Al ₂ O ₃ raw material, Fe ₂ O ₃ raw material, SiO ₂ raw material, CaSO ₄ raw material, and SrO raw material were blended so as to have the mineral proportions and the chemical component proportions shown in Table 1, after mixing and pulverizing A clinker was synthesized by firing at 1,350° C., and crushed to have a Blaine specific surface area of 3,000 cm ² /g using a ball mill to prepare a cement admixture.
Using this cement admixture, 7 parts by mass of the cement admixture is used in 100 parts by mass of the cement composition consisting of cement and the cement admixture, and the water/cement composition ratio=50% by mass, the cement composition/sand. Mortar with a ratio of 1/3 (mass ratio) was prepared in a room at 20° C., and the rate of change in length and the compression strength were measured.
Further, for the cement admixture, the ratio (A/B) of the content A of particles of 100 μm or less and the content B of particles of 10 μm or less was obtained.

(Material used)
CaO raw material: limestone Al ₂ O ₃ raw material: bauxite Fe ₂ O ₃ raw material: iron oxide SiO ₂ raw material: silica stone CaSO ₄ raw material: dihydrate gypsum SrO raw material: strotian stone ZrO ₂ raw material: zircon sand sand: JIS standard sand cement: ordinary Portland cement, commercial product

(Test method)
Chemical composition: determined from fluorescent X-rays.
Ratio (A/B) of content rate A of particles of 100 μm or less and content rate B of particles of 10 μm or less: Laser diffraction/scattering particle size distribution analyzer LA-920 manufactured by HORIBA was used. The cement admixture was dispersed in ethanol for 1 minute by ultrasonic waves, and a volume-based particle size distribution was measured under the conditions of a sample refractive index of 1.770 and a dispersion medium refractive index of 1.360. From the particle size distribution, the content A of particles of 100 μm or less and the content B of particles of 10 μm or less were obtained, and A/B was calculated. Mineral composition: Calculated based on chemical composition and powder X-ray diffraction identification results.
Compressive strength: A test piece of 4×4×16 cm was prepared in accordance with JIS R 5201, and the compressive strength at 7 days (7d) and 28 days (28d) of age was measured.

"Experimental example 2"
Experiment No. 1-5, except that the ZrO ₂ raw material was further used and the amount of SrO was adjusted to change the amounts of SrO and ZrO ₂ in the clinker as shown in Table 2 below. A similar experiment was conducted. The results are shown in Table 2.
(Test method)
Flow test: Mortar was kneaded in accordance with JIS R 5201-2015 "Physical test method for cement", and 15-point flow value immediately after kneading was measured. The composition of temperature, humidity and mortar was the same as in the compressive strength test. Standard sand was used in the test.

With the cement admixture of the present invention, it is possible to impart large expansion and suppression of dry shrinkage strain to concrete from the age of 2 to 7 days after placing concrete, and there is no decrease in long-term strength development, so in the field of civil engineering and construction. It can be used widely.

Claims (9)

A cement admixture containing free lime, a hydraulic compound, and anhydrous gypsum, and containing SrO as a chemical component. The cement admixture according to claim 1, wherein the content of SrO is 0.001 to 5.0 parts by mass with respect to 100 parts by mass of the cement admixture. The cement admixture according to claim 1 or 2, further comprising ZrO ₂ as a chemical component. The cement admixture according to claim 3, wherein the content of ZrO ₂ is 0.0001 to 5.0 parts by mass with respect to 100 parts by mass of the cement admixture. Blaine specific surface area, a cement admixture according to any one of claims 1 to 4 is 2,000~6,000cm ² / g. On a volume basis, the content of particles of 10 μm or less is 30 to 60% by volume, and the ratio (A/B) of the content A of particles of 100 μm or less and the content B of particles of 10 μm or less is 1.5 to. The cement admixture according to claim 1, wherein the cement admixture is 4.0. The water as a hydraulic _{compound, 3CaO · 3Al 2 O 3 ·} CaSO 4, 3CaO · SiO 2, 2CaO · SiO 2, 4CaO · Al 2 O 3 · Fe 2 O 3, 6CaO · 2Al 2 O 3 · Fe 2 O 3, _{6CaO · Al 2 O 3 · Fe} 2 O 3, and 2CaO · _Fe 2 _{O 3} 1 kind selected from the group consisting of or containing two or more cement admixture according to any one of claims 1 to 6 .. An expansive material comprising the cement admixture according to any one of claims 1 to 7. A cement composition comprising the cement admixture according to any one of claims 1 to 7.