JP7605838B2 - Cement admixture and cement composition - Google Patents

Description

The present invention relates to cement admixtures and cement compositions that are primarily used in the fields of civil engineering and construction.

Conventionally, the most common method for promoting the waterproofing of cement concrete has been to use water-reducing agents or high-performance water-reducing agents, as specified in JIS A 6204 "Chemical admixtures for concrete," in order to reduce the water-to-cement ratio as much as possible.

On the other hand, methods for improving waterproofing without reducing the water-to-powder ratio include, for example, an admixture made by mixing a calcium sulfoaluminate compound with baked white clay (see Patent Document 1), a method in which a water repellent and a carbonated admixture are mixed with cement (see Patent Document 2), coating a filler (aggregate) with a water repellent (see Patent Document 3), and applying a water repellent to the surface of hardened cement concrete (see Patent Document 4).

However, cement concrete is prone to cracking due to hardening shrinkage and drying shrinkage, making it difficult to make cement concrete waterproof.

JP 2006-219319 A JP 2012-111640 A Japanese Patent Application Publication No. 1-317140 JP 2004-231488 A

The present invention aims to provide a cement admixture and a cement composition that improve the waterproofing properties of concrete.

The inventors discovered that the problem could be solved by combining a specific hydraulic compound, free lime, anhydrous gypsum, and alumina-silica powder, and thus completed the present invention. That is, the present invention is as follows.

[1] A cement admixture comprising: (A) one or more hydraulic compounds selected from the group consisting of ielimite, calcium silicate, and calcium aluminoferrite; (B) free lime; (C) anhydrous gypsum; and (D) alumina-silica powder.
[2] The cement admixture according to [1], having a Blaine specific surface area of 4,500 cm ² /g or more.
[3] The cement admixture according to [1] or [2], comprising, as chemical components, 40 to 65 parts by mass of CaO, 5 to 15 parts by mass of Al _{2 O 3} , 5 to 30 parts by mass of SiO 2, and 20 to 30 parts by mass of SO ₃ .
[4] (A) 15 to 20% by mass of hydraulic compound, (B) 25 to 43% by mass of free lime, (C) 25 to 35% by mass of anhydrous gypsum, and (D) 17 to 28% by mass of alumina-silica powder, [1] to [3]. The cement admixture according to any one of the above.
[5] A cement composition comprising the cement admixture according to any one of [1] to [4] and cement.

According to the present invention, it is possible to provide a cement admixture and a cement composition that improve the waterproofing properties of concrete.

The following describes in detail an embodiment of the present invention (the present embodiment), but the present invention is not limited to this embodiment. In this specification, "parts" and "%" are based on mass unless otherwise specified. In addition, "cement concrete" is a general term for cement paste, mortar, and concrete.

[Cement admixture]
The cement admixture of the present embodiment contains (A) one or more hydraulic compounds selected from the group consisting of ielimite, calcium silicate, and calcium aluminoferrite, (B) free lime, (C) anhydrous gypsum, and (D) alumina-silica powder.
By containing the above four types, it is possible to enhance the waterproofing properties of concrete, and in particular, it is possible to activate the reaction of the cement admixture and the cement composition containing the cement admixture at an appropriate time, thereby preventing cracks in the cement concrete and imparting waterproofing properties.
Each component will be described below.

(A) Hydraulic compound:
The hydraulic compound of this embodiment is one or more selected from the group consisting of eelimite, calcium silicate, and calcium aluminoferrite.
These hydraulic compounds produce ettringite, calcium silicate hydrate, calcium aluminosilicate hydrate, and calcium aluminate hydrate, which fill the voids and make the structure denser and more waterproof. It can be improved.

(Elimite)
Eelimite, also known as calcium sulfoaluminate or auyne, is a mineral with the chemical formula _{3CaO.3Al 2} O 3.CaSO ₄ .

Elimite is produced by mixing raw materials such as limestone, sulfate raw materials such as gypsum, and alumina raw materials such as bauxite in a molar ratio of CaO: _CaSO4 : _Al2O3 of 3:1: ₃ , firing the mixture at about 1500°C in a kiln or the like, and pulverizing the mixture.

It is preferable to use a mixture of C1, which has a Blaine specific surface area value (JIS R5201, hereinafter referred to as the Blaine value) of 2,000 to 4,000 ^cm2 /g, and C2, which has a Blaine value of 5,000 to 8,000 ^cm2 /g, as Elimite. The mixing ratio C1/C2 of C1 and C2 is preferably 2 to 5, and more preferably 2.5 to 3.5. By making it 2 or more, a good waterproofing effect can be expected without decreasing the reaction rate. If it is 5 or less, the bleeding water of the cement concrete is reduced, and a waterproofing effect can be expected by reducing cavities caused by the bleeding water.

(Calcium Silicate)
Calcium silicate is a general term for CaO- _SiO2 systems and is not particularly limited, but _2CaO.SiO2 and _3CaO.SiO2 are generally well known.

From the viewpoint of reaction rate, calcium silicate preferably has a Blaine value of 2000 to 4500 cm ² /g, and more preferably 2500 to 4000 cm ² /g.

(Calcium Aluminoferrite)
Calcium aluminoferrite is a general term for compounds _whose main components are _{CaO , Al2O3 , and Fe2O3} , and _known examples include 4CaO.Al2O3.Fe2O3 ( _C4AF ) _{, 6CaO.2Al2O3.Fe2O3} ( _C6A2F ), _{and 6CaO.Al2O3.2Fe2O3 ( C6AF2} ).

The calcium aluminoferrite of the present embodiment is obtained by mixing a raw material containing calcia (CaO raw material), a raw material containing alumina (Al ₂ O ₃ raw material), a raw material containing ferrite (Fe ₂ O ₃ raw material), etc., and subjecting the mixture to a heat treatment such as firing in a kiln or an electric furnace.

From the viewpoint of pot life, calcium aluminoferrite preferably has a Blaine value of 2000 to 7000 cm ² /g, and more preferably 3000 to 6000 cm ² /g.

Of the above hydraulic compounds, from the standpoint of the timing of the hydration reaction and imparting expansion properties, it is preferable for the composition to contain 50% or more of eelimite, and it is even more preferable for the composition to contain 70% or more.

(B) Free Lime:
Free lime is usually called f-CaO (free lime). By including free lime in the cement admixture according to the present embodiment, it is possible to supply calcium consumed in the reaction of hydraulic substances. In addition, the free lime provides expansion properties, thereby suppressing drying shrinkage.

From the viewpoint of long-term strength and expansiveness, the fineness of the free lime is preferably 2000 to 7000 cm ² /g, more preferably 3000 to 6000 cm ² /g, in Blaine value.

(C) Anhydrous Gypsum:
The anhydrite may be of any crystal structure, and the inclusion of anhydrite can improve the overall strength from the initial stage to the long term.

From the viewpoint of reactivity, the fineness of the anhydrous gypsum is preferably 2000 to 5000 cm ² /g, more preferably 2500 to 4500 cm ² /g, in Blaine value.

(D) Alumina Silica Powder Examples of the alumina silica powder include fly ash, ground granulated blast furnace slag, metakaolin, silica fume, sewage sludge, volcanic ash, activated clay, and calcined clay.

From the viewpoint of packing into the hardened body structure, the fineness of the alumina-silica powder is preferably 2500 cm ² /g or more, and more preferably 3500 cm ² /g or more, in Blaine value.

The specific surface area of the cement admixture is preferably 4,500 cm ² /g or more, more preferably 4,500 to 5,500 cm ² /g, in Blaine value. By having a specific surface area of 4,500 cm ² /g or more, a better waterproofing effect can be expected.

From the viewpoint of good waterproofing effect and strength development, the chemical components of the cement admixture are preferably 40 to 65 parts CaO, 5 to 15 parts Al ₂ O ₃ , 5 to 30 parts SiO ₂ , and 20 to 30 parts SO _3. The contents of the chemical components can be determined by fluorescent X-rays.

From the viewpoint of a better waterproofing effect, it is preferable that the cement admixture contains (A) 15 to 20 mass% of hydraulic compound, (B) 25 to 43 mass% of free lime, (C) 25 to 35 mass% of anhydrous gypsum, and (D) 17 to 28 mass% of alumina-silica powder.
These contents are preferably determined by calculation based on the identification results of the chemical components and powder X-ray diffraction.

The cement admixture of the present embodiment as described above can improve the waterproofing of cement concrete, so it is preferable to use it as a waterproofing cement admixture. In addition, since it also exhibits good expansion properties, it is more preferable to use it as an expansion material or a waterproofing expansion material.

[Cement composition]
The cement composition according to this embodiment contains the cement admixture of the present invention and cement.
The amount of the cement admixture used is preferably 0.6 to 20 parts, more preferably 1.0 to 10 parts, per 100 parts of cement. When the amount is 0.6 to 20 parts, good waterproofing effect and strength can be obtained.

Here, the cement is not particularly limited, and ordinary cement can be used. Specific examples include various Portland cements such as normal, early strength, low early strength, low heat, and medium heat, various mixed cements in which Portland cement is mixed with blast furnace slag, fly ash, or silica, filler cements in which limestone powder or ground cooled blast furnace slag powder is mixed, waste-recycling cement, so-called ecocement, etc., and one or more of these can be used in combination.

The present invention will now be described in detail with reference to examples.
(Experimental Example 1)
A cement admixture (expansive waterproofing agent) was prepared by mixing (A) hydraulic compound, (B) free lime, (C) anhydrous gypsum, and (D) alumina-silica powder in the proportions shown in Table 1. 3.5 parts of this admixture was mixed with 100 parts of cement, and concrete was obtained by kneading the mixture with a slump of 12±2.5 cm, air content of 4.5±1.5%, W/C of 60%, and s/a of 48%.
The cement was 288 kg/m ³ , the fine aggregate was 865 kg/m ³ , the coarse aggregate was 987 kg/m ³ , and the water was 173 kg/m ³ .
The water permeability and compressive strength of the obtained concrete were measured. In addition, 10 parts of the cement admixture were mixed with 100 parts of cement, and the length change rate of the concrete prepared in the same manner was measured. The results are shown in Table 1.

<Materials used>
Water: Tap water Cement: Ordinary Portland cement, specific gravity 3.16
(A) Hydraulic compound: Eelimite (crystalline 3CaO.3Al ₂ O _{3.CaSO 4} , loss on ignition 1.0%, Blaine value 5500 cm ² /g)
(B) Free lime: Limestone powder was calcined at 1300°C in an electric furnace and pulverized (Blaine value: 4500 ^cm2 /g)
(C) Anhydrous gypsum: commercially available product (Blaine value 4000 cm ² /g)
(D) Alumina-silica powder: fly ash (type II fly ash as defined in JIS A 6201 "fly ash for concrete", Blaine value 3,500 cm ² /g)
Fine aggregate: Natural sand from Himekawa River, Niigata Prefecture, specific gravity 2.62
Coarse aggregate: Crushed stone from Himekawa, Niigata Prefecture, maximum size 25 mm, specific gravity 2.64

<Evaluation method>
Slump: Measured according to JIS A 1101 Air volume: Measured according to JIS A 1128

Permeability ratio: After pouring the concrete, a cylindrical specimen measuring φ100mm x 100mm was used, cured in water at 20°C for 7 days, and a permeability test was conducted. The test method was the output method, and a water pressure of 1.0 MPa was applied to the outer surface of the specimen for 500 hours, and the amount of water that oozed out was measured and used as the permeability. The permeability without cement admixture was used as the denominator, and the value obtained by dividing the value was used as the permeability ratio.

Compressive strength: Measured in accordance with JIS A 1108 at a material age of 28 days.
Length change rate: The length change rate at 7 days was measured according to JIS A 6202. The evaluation was as follows: a length change rate of 200×10 ⁻⁶ or more was good, 150×10 ⁻⁶ or more but less than 200×10 ⁻⁶ was acceptable, and less than 150×10 ⁻⁶ was unacceptable.

(Experimental Example 2)
The same procedure as in Example 1 was repeated except that concrete was prepared using a cement admixture prepared by mixing (A) hydraulic compound, (B) free lime, (C) anhydrous gypsum, and (D) alumina-silica powder in the ratios shown in Table 2, and various evaluations were carried out. The results are also shown in Table 2.

(Experimental Example 3)
The same procedure as in Example 1 was carried out except that the hydraulic compound (A) in Experiment No. 1-6, ie, ie, eirimite, was replaced with calcium silicate (Experiment No. 3-1) and calcium aluminoferrite (Experiment No. 3-2) to prepare concrete as a cement admixture, and various evaluations were carried out. The results are shown in Table 3.

(Experimental Example 4)
The same procedure as in Example 1 was carried out except that the fly ash, which is the alumina-silica powder (D) in Experiment No. 1-6, was replaced with ground granulated blast furnace slag (Experiment No. 4-1), burned white clay (Experiment No. 4-2), and silica fume (Experiment No. 4-3) as cement admixtures, concrete was prepared, and various evaluations were performed. The results are shown in Table 4.

The cement admixture of the present invention can, for example, improve the waterproofing properties of cement concrete and prevent cracking.

INDUSTRIAL APPLICABILITY The present invention is effective mainly as a cement admixture and a cement composition that promote the waterproofing of cement concrete used in the fields of civil engineering and construction.

Claims (4)

(A) one or more hydraulic compounds selected from the group consisting of eelimite, calcium silicate, and calcium aluminoferrite, (B) free lime, (C) anhydrous gypsum, and (D) alumina-silica powder ;
(A) a cement admixture comprising 15 to 20 mass% of a hydraulic compound, (B) 25 to 43 mass% of free lime, (C) 25 to 35 mass% of anhydrous gypsum, and (D) 17 to 28 mass% of an alumina-silica powder . 2. The cement admixture according to claim 1, having a Blaine specific surface area of 4,500 cm ² /g or more. The cement admixture according to claim 1 or 2, comprising, as chemical components, 40 to 65 parts by mass of CaO, 5 to 15 parts by mass of Al ₂ O ₃ , 5 to 30 parts by mass of SiO ₂ , and 20 to 30 parts by mass of SO ₃ . A cement composition comprising the cement admixture according to any one of claims 1 to 3 and cement.