Cement admixture

Abstract

To provide a cement admixture that can suppress the bleeding of mortar and concrete while exhibiting a good restricted expansion ratio.SOLUTION: A cement admixture comprising an expander and aluminum sulfate, in which the expander is 80-99 pts.mass and the aluminum sulfate is 1-20 pts.mass in 100 pts.mass of the cement admixture. In the cement admixture, the aluminum sulfate has 10-100 mass% of sieve residue of 150 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cement admixture used for the purpose of inhibiting cracking in mortar, concrete, etc. [Background technology]

[0002] To improve the durability of various materials and buildings, such as mortar and concrete, which contain cement as a binder phase, particularly concrete architectural structures, it is essential to suppress cracks that occur due to hardening shrinkage and drying shrinkage. A particularly effective means of suppressing cracks is the use of expansive additives. These expansive additives are broadly divided into those containing quicklime as the active ingredient and those containing substances that form ettringite through hydration, such as calcium sulfoaluminate. Among these, those containing quicklime as the active ingredient generally have high reactivity, leading to excellent early expansion and the potential for relatively large expansion. Therefore, they are particularly suitable for suppressing large initial shrinkage of concrete.

[0003] However, in recent years, as expansive additives have been applied to a variety of uses, there has been a demand for additional functions in addition to expansion performance. In response to such demands, for example, expansive additives for fair-faced concrete and expansive additives for underwater non-segregating concrete have been proposed (Patent Documents 1 and 2).

[0004] On the other hand, when mortar or concrete is poured, a phenomenon called bleeding can occur, in which floating water appears on the concrete surface. If this bleeding occurs in large quantities, the path created when the water in the mortar or concrete comes to the surface can impair the density of the structure of the mortar or concrete, potentially resulting in a decrease in strength after hardening. In addition, the occurrence of bleeding water can cause the dimensions of the poured structure to be smaller than expected.

[0005] One known method for suppressing such bleeding is to add a polymer thickener or the like to mortar or concrete (Patent Document 3). Examples of polymer thickeners include methyl cellulose, polyvinyl alcohol, and starch. However, it is known that adding a required amount of a polymer thickener or the like to effectively prevent bleeding poses problems such as a decrease in fluidity due to an increase in viscosity, or a decrease in the strength of the hardened mortar or concrete. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-127372 [Patent Document 2] Japanese Patent Application Publication No. 2018-131359 [Patent Document 3] Japanese Patent Application Publication No. 8-26803 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a new cement admixture that solves the above-mentioned problems. Specifically, the present invention provides a cement admixture that exhibits a good coefficient of restrained expansion and can suppress bleeding of mortar and concrete. [Means for solving the problem]

[0008] That is, the present invention provides the following [1] to [3]. [1] A cement admixture containing an expanding material and aluminum sulfate, wherein the expanding material is 80 to 99 parts by mass and the aluminum sulfate is 1 to 20 parts by mass per 100 parts by mass of the cement admixture. [2] The cement admixture according to [1], wherein the aluminum sulfate has a 150 μm sieve residue of 10 to 100 mass %. [3] Mortar or concrete containing the cement admixture of [1] or [2]. [Effects of the Invention]

[0009] By using the cement admixture of the present invention, it is possible to obtain mortar or concrete that exhibits a good restrained expansion rate and has a small amount of bleeding. DETAILED DESCRIPTION OF THE INVENTION

[0010] The cement admixture of the present invention contains an expanding material and aluminum sulfate, and is characterized in that the expanding material is present in an amount of 80 to 99 parts by mass and the aluminum sulfate is present in an amount of 1 to 20 parts by mass per 100 parts by mass of the cement admixture. The details will be explained below.

[0011] The expanding agent used in the present invention can be any of those containing free quicklime (f-CaO) as the active ingredient, those containing calcium sulfoaluminate such as 3CaO·3Al2O3·CaSO4 (aluminium), and those containing both free quicklime and calcium sulfoaluminate as active ingredients. In particular, those that exhibit an expanding effect by increasing the volume due to hydration of free quicklime are preferred. The free quicklime content in the expanding agent is preferably 30 to 80% by mass, more preferably 40 to 70% by mass.

[0012] In addition to the above components, the expansive material of the present invention contains hydraulic compounds such as calcium silicates such as CaO·2SiO2 (C2S) and CaO·3SiO2 (C3S), CaO·Al2O3 (CA), 12CaO·7Al2O3 (C 12 A7), calcium aluminates such as 3CaO·Al2O3 (C3A), and calcium aluminoferrites such as 4CaO·Al2O3·Fe2O3 (C4AF) and 6CaO·2Al2O3·Fe2O3 (C6A2F) may be included. The content of the hydraulic compound in the expansive material is preferably 3 to 40 mass%, more preferably 5 to 30 mass%.

[0013] The expanding agent of the present invention preferably further contains gypsum. Examples of gypsum include gypsum hemihydrate, gypsum dihydrate, and anhydrous gypsum, with anhydrous gypsum being particularly preferred. The gypsum content in the expanding agent is preferably 2 to 30% by mass, more preferably 3 to 25% by mass.

[0014] The fineness of the expansive material is 2000 to 7000 cm in terms of Blaine specific surface area. 2 / g is preferred, and 3000 to 6500 cm 2 / g is more preferable, 4000~6000cm 2 / g is more preferred.

[0015] The aluminum sulfate used in the present invention is not particularly limited, but may be an industrially produced or commercially available powder, such as aluminum sulfate, which is used as a flocculant for water purification.

[0016] With regard to the particle size of aluminum sulfate, from the viewpoint of reducing the bleeding rate and the slump properties of fresh concrete, the 150 μm sieve residue is preferably 10 to 100 mass%, more preferably 20 to 90 mass%, and even more preferably 40 to 80 mass%.

[0017] The contents of the expanding agent and aluminum sulfate in the cement admixture are 80 to 99 parts by mass of the expanding agent and 1 to 20 parts by mass of aluminum sulfate per 100 parts by mass of the cement admixture. If the aluminum sulfate content is less than 1 part by mass, the bleeding suppression effect cannot be obtained, while if the aluminum sulfate content exceeds 20 parts by mass, there is a risk that the restrained expansion performance cannot be ensured and the fresh properties may deteriorate. The aluminum sulfate content is more preferably 3 to 18 parts by mass, and even more preferably 5 to 15 parts by mass.

[0018] In addition to the above-mentioned components, the cement admixture of the present invention may contain various additives in combination, provided that the advantages of the present invention are not impaired. Examples of such additives include water-reducing agents, air-entraining agents, foaming agents, shrinkage-reducing agents, waterproofing agents, rust inhibitors, thickeners, polymers for cement admixture, water-retaining agents, pigments, water-repellents, and anti-efflorescence agents.

[0019] The amount of the cement admixture of the present invention added to mortar or concrete is preferably 3 to 15 mass % and more preferably 5 to 10 mass % relative to the cement in the mortar or concrete. The unit amount in concrete is 10 to 30 kg / m 3 is preferred. [Example]

[0020] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0021] Example 1 First, the expansive material and aluminum sulfate were mixed to prepare a cement admixture. The expansive material used was a quicklime-based expansive material (free quicklime content: 50% by mass, Blaine specific surface area: 5,130 cm). 2 / g). The aluminum sulfate used was a commercially available aluminum sulfate (17% alumina) with particle size adjustment (150 μm sieve residue 60% by mass). As a comparative example, a mixture was also prepared using sodium sulfate (Miura salt, commercially available product) instead of aluminum sulfate. Table 1 shows the prepared cement admixtures.

[0022] [Table 1]

[0023] These cement admixtures were added and concrete was prepared in a 10°C environment. Ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) was used as the cement, Kakegawa mountain sand as the fine aggregate, and Sakuragawa crushed stone 2005 as the coarse aggregate. The concrete mix is ​​shown in Table 2. 0.7% by mass of a high-performance water-reducing agent was added to the total amount of cement and cement admixtures.

[0024] [Table 2]

[0025] <Evaluation test> The concrete thus produced was tested for slump, bleeding rate, initial setting time, and restrained expansion rate using the following test methods. (1) Slump The test was conducted in accordance with "JIS A 1101 Slump Test for Concrete." (2) Breeding test Measurements were taken using a φ12.5cm summit mold in accordance with "JCI-S-015 Concrete Bleeding Test Method Using Small Containers." (3) Coagulation test The test was conducted in accordance with "JIS A 1147 Concrete Setting Test Method." (4) Restrained expansion test The concrete prepared in a 10°C environment was cast into specimens in a 20°C environment, and tests were then conducted in accordance with "JIS A 6202 Expansive Additives for Concrete, Appendix B."

[0026] <Test Results> The test results are shown in Table 3. It was found that when a cement admixture containing a specified amount of aluminum sulfate was used as an expansive agent, a bleeding reduction effect could be achieved. When Admixture H, containing 24 parts by mass of aluminum sulfate, was used, bleeding was sufficiently reduced, but the slump dropped significantly and the restrained expansion rate also decreased. Furthermore, when using only an expansive agent or a cement admixture containing sodium sulfate, a sufficient bleeding reduction effect could not be achieved.

[0027] [Table 3]

[0028] Example 2 Next, the effect of particle size of aluminum sulfate used as cement admixture was evaluated. The particle size adjusted aluminum sulfate is shown in Table 4.

[0029] [Table 4]

[0030] These aluminum sulfates were mixed with the expansive agent used in Example 1 to prepare cement admixtures. Table 5 shows the prepared cement admixtures.

[0031] [Table 5]

[0032] The prepared cement admixture was added, and concrete was prepared in the same manner as in Example 1, and each evaluation test was carried out.

[0033] <Test Results> The test results are shown in Table 6.

[0034] [Table 6]

Claims

1. A cement admixture containing an expansive material and aluminum sulfate, the expansive material containing free lime (f-CaO) as an active ingredient, 3CaO.3Al ２ O ３ CaSO ４ The expanding agent is either one containing calcium sulfoaluminate such as (Auin) as an active ingredient, or one containing both free quicklime and calcium sulfoaluminate as active ingredients, The aluminum sulfate has a 150 μm sieve residue of 10 to 100 mass %; A cement admixture characterized in that the expanding material is 80 to 99 parts by mass and the aluminum sulfate is 1 to 20 parts by mass per 100 parts by mass of the cement admixture.

2. 2. Mortar or concrete containing the cement admixture according to claim 1.

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