Cement admixture and hydraulic composition

Abstract

To provide a cement admixture capable of imparting rapid strength development and sufficient usable life to a cement-based hydraulic composition without using lithium carbonate, and also to provide a hydraulic composition using the admixture.SOLUTION: A cement admixture includes (A) calcium aluminates, (B) a sulfate, and (C) a zinc compound. A hydraulic composition includes the cement admixture and Portland cement.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cement admixture for imparting rapid hardening properties to various hydraulic compositions, and to a hydraulic composition using said admixture. [Background technology]

[0002] In emergency construction, waterproofing work, and spraying work to prevent spalling, concrete and mortar are required to have fast hardening, rapid setting, and rapid setting properties. To impart these properties to cement, calcium aluminates and gypsum (calcium sulfate) have long been used in combination. In the three-component system of cement, calcium aluminates, and gypsum, the addition of lithium carbonate was previously essential to achieve both strength development and usable life. It is known that without the addition of lithium carbonate, sufficient strength does not develop even after hardening (Patent Document 1, etc.).

[0003] On the other hand, while lithium is not as scarce as rare earth elements, it is often present in dilute concentrations in seawater and is difficult to recover; it is sometimes mined concentrated in salt lakes and rock salt, making it rare and expensive. Furthermore, with the recent trend toward reducing CO2 emissions, demand for lithium batteries has rapidly increased, causing the price of lithium carbonate to rise significantly, making it difficult to use as a construction material. While carbonates of the same alkali metals as lithium have been studied as alternatives to lithium carbonate, no results have yet been obtained that could serve as a suitable substitute for lithium carbonate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-335620 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a cement admixture that does not use lithium carbonate and can impart rapid strength development and sufficient usable life to a cement-based hydraulic composition, and a hydraulic composition using the admixture. [Means for solving the problem]

[0006] The present inventors have found that by blending calcium aluminates, sulfates, and zinc compounds, cement admixtures can be obtained that can provide rapid strength development and sufficient working life. They have also found that the strength development can be further enhanced by using alkali metal sulfates and / or aluminum sulfate as sulfates.

[0007] That is, the present invention provides the following [1] to [7]. [1] A cement admixture containing (A) calcium aluminates, (B) sulfates, and (C) zinc compounds. [2] (B) The sulfate salt contains one or more selected from alkali metal sulfates and aluminum sulfate, and the content of the one or more selected from alkali metal sulfates and aluminum sulfate is 0.5% or more and 30% or less in terms of molar content relative to the sulfate salt. [1] The cement admixture according to [1]. [3] The cement admixture according to [1], wherein (B) the sulfate contains one or more selected from alkaline earth metal sulfates, alkali metal sulfates, and aluminum sulfate. [4] (B) The cement admixture according to [1] or [3], wherein the sulfate salt contains calcium sulfate and one or more selected from alkali metal sulfates and aluminum sulfate. [5] (B) The cement admixture according to [1] or [3], wherein the sulfate salts include calcium sulfate and alkali metal sulfate salts, and the content of the alkali metal sulfate salts is 0.5% or more and 30% or less in terms of molar content relative to the total content of calcium sulfate and alkali metal sulfate salts. [6] (C) The cement admixture according to any one of [1] to [5], wherein the zinc compound is one or more selected from basic zinc carbonate, zinc oxide, zinc nitrate, zinc sulfate, zinc sulfide, and zinc hydroxide. [7] A hydraulic composition containing the cement admixture according to any one of [1] to [6] and Portland cement. [Effects of the Invention]

[0008] The cement admixture of the present invention can impart excellent rapid hardening properties, particularly rapid strength development and sufficient usable life, to hydraulic compositions such as concrete and mortar. Therefore, concrete and mortar containing the cement admixture are useful as rapid-hardening, rapid-hardening, or quick-setting concrete compositions or mortar compositions. DETAILED DESCRIPTION OF THE INVENTION

[0009] The cement admixture of the present invention is an admixture that can impart excellent rapid hardening properties to hydraulic compositions such as concrete and mortar without containing lithium carbonate. One aspect of the present invention is a cement admixture containing (A) calcium aluminates, (B) a sulfate, and (C) a zinc compound.

[0010] (A) Calcium aluminates impart rapid hardening properties to mortar or concrete. "Calcium aluminates" is a general term for compounds, solid solutions, glassy substances, or mixtures thereof that contain at least CaO and Al2O3 as their main components. Examples of such calcium aluminates include CA2(CaO·2Al2O3), CA(CaO·Al2O3), C 12 A7(12CaO・7Al2O3), C3A(3CaO・Al2O3), C 11 A7·CaF2(11CaO·7Al2O3·CaF2), C 11Examples of suitable calcium aluminates include A7·CaCl2 (11CaO·7Al2O3·CaCl2), NC8A3 (Na2O·8CaO·3Al2O3), Irwin (3CaO·3Al2O3·CaSO4), and alumina cement. Known equipment such as an electric furnace or kiln can be used to fire calcium aluminates. A conventional grinding machine can be used for pulverization. The calcium aluminates used in the present invention are those with a Blaine specific surface area of ​​4000 cm2, which is considered to be suitable for rapid hardening. 2 / g or more is preferred. The calcium aluminates are contained in the cement admixture of the present invention in an amount of preferably 30 to 80 mass %, more preferably 40 to 70 mass %. The content of calcium aluminates in the hydraulic composition is preferably 5 to 40 mass %, more preferably 7 to 30 mass %, from the viewpoint of obtaining excellent short-term strength and not reducing long-term strength.

[0011] (B) Sulfates, when used in combination with calcium aluminates, produce ettringite, which increases the short-term strength of rapid-hardening mortar or rapid-hardening concrete. The sulfate is preferably an inorganic sulfate, and more preferably a metal sulfate. Specifically, it is preferable to contain one or more selected from alkaline earth metal sulfates, alkali metal sulfates, and aluminum sulfate. Here, the alkaline earth metal sulfate is preferably calcium sulfate. Examples of the alkali metal sulfate include sodium sulfate and potassium sulfate. From the viewpoint of short-term strength development, it is preferable to use one or more sulfates selected from alkali metal sulfates and aluminum sulfate. The content of one or more selected from alkali metal sulfates and aluminum sulfate is preferably 0.5% to 30% in terms of molar content relative to the sulfate. The molar content of each sulfate is expressed as an anhydrous salt. As the sulfate, it is more preferable to use calcium sulfate in combination with one or more selected from alkali metal sulfates and aluminum sulfate, from the viewpoint of short-term strength development. From the viewpoint of strength development, the sulfates more preferably include calcium sulfate and alkali metal sulfates. The content of the alkali metal sulfate is preferably 0.5% or more and 30% or less, more preferably 5% or more and 20% or less, and even more preferably 7% or more and 15% or less, in terms of molar content relative to the total content of calcium sulfate and alkali metal sulfate. The content of sulfate in the cement admixture of the present invention is preferably 25 to 60 mass %, more preferably 30 to 55 mass %. The content of the sulfate in the hydraulic composition is preferably 5 to 35 mass %, more preferably 5 to 30 mass %, from the viewpoint of obtaining excellent short-term strength. The mass ratio of the sulfate to the total amount of the sulfate and calcium aluminates (sulfate / (sulfate+calcium aluminates)) is preferably 30% by mass to 60% by mass, and more preferably 30% by mass to 50% by mass, from the viewpoint of excellent strength development and suppression of excessive expansion.

[0012] (C) By using a zinc compound, it is possible to impart rapid strength development and sufficient usable life to hydraulic compositions such as concrete and mortar without adding lithium carbonate. The zinc compound can be one or more selected from basic zinc carbonate, zinc oxide, zinc nitrate, zinc sulfate, zinc sulfide, and zinc hydroxide. Among these, basic zinc carbonate and zinc oxide are more preferred from the viewpoint of safety. The zinc compound is preferably contained in the cement admixture of the present invention in an amount of 0.02 to 6 mass %, more preferably 0.03 to 2 mass %. The content of the zinc compound in the hydraulic composition is preferably 0.001 to 1 mass %, more preferably 0.02 to 0.3 mass %, from the viewpoint of obtaining excellent short-term strength.

[0013] In addition to the above components, the cement admixture of the present invention may contain expansive agents, water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, air-entraining agents, antifoaming agents, retarders, accelerators, thickeners, foaming agents, foaming agents, water repellents, re-emulsifiable powdered resins, various pozzolanic substances, finely divided slag powder, fillers (extenders), fibers, etc. However, lithium carbonate does not need to be used.

[0014] The cement admixture of the present invention can be produced by mixing the above components. It is preferable to produce the cement admixture in advance and add it to concrete or mortar at the construction site. However, it can also be added to concrete or mortar at the construction site.

[0015] Another aspect of the present invention is a hydraulic composition containing the cement admixture and Portland cement. Any type of Portland cement can be used, but high-early-strength Portland cement and normal Portland cement are preferred in terms of rapid hardening.

[0016] The content of the cement admixture in the hydraulic composition of the present invention is preferably 15 to 60 parts by mass relative to 100 parts by mass of the hydraulic composition.

[0017] Hydraulic compositions include concrete compositions and mortar compositions, and these compositions can contain fine aggregates, coarse aggregates, expansive additives, water-reducing agents, air-entraining agents, high-performance water-reducing agents, air-entraining agents, antifoaming agents, retarders, accelerators, thickeners, foaming agents, foaming agents, water-repellents, re-emulsifiable powdered resins, various pozzolanic substances, finely divided slag powder, fibers, etc. Examples of high-performance water-reducing agents include polycarboxylic acid-based water-reducing agents, naphthalene-based water-reducing agents, melamine-based water-reducing agents, and aminosulfonic acid-based water-reducing agents. Examples of retarders include hydroxycarboxylic acids such as citric acid and citrates, and hydroxycarboxylic acid salts.

[0018] The method for producing hydraulic compositions such as mortar or concrete is not particularly limited, and the materials may be mixed in a conventional mixer installed in a ready-mix concrete plant or construction site. [Example]

[0019] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0020] <Materials used> (A) Calcium aluminates: Alumina cement (limestone and aluminous shale, respectively, with a specific surface area of ​​1000-2000 cm 2 The mixture was crushed to about 1 / g, mixed, and adjusted to CaO: 38%, Al2O3: 54%, SiO2: 4%. It was fired in an electric furnace at 1650°C for 60 minutes. After cooling, it was crushed in a vibration mill and crushed to a powder with a Blaine specific surface area of ​​5500 cm 2 / g.) (B) Gypsum: Hydrofluoric anhydrous gypsum manufactured by Asahi Glass Co., Ltd. was used. It was pulverized in a vibration mill and had a Blaine specific surface area of ​​7500 cm. 2 / g. Sodium sulfate: Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Potassium sulfate: Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Aluminum sulfate: Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (C) Zinc oxide: Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Basic zinc carbonate: Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Other additives Lithium carbonate: monohydrate manufactured by Livent Corporation Citric acid: monohydrate manufactured by Showa Kako Co., Ltd. Water reducing agent: Pacific Materials NF-200 Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) High-early-strength Portland cement (manufactured by Taiheiyo Cement Corporation) Blast-furnace cement type B (manufactured by Taiheiyo Cement Corporation) Aggregate: Silica sand: JIS standard sand (manufactured by the Cement Association) Water: Tap water

[0021] <Manufacturing method for cement admixture> The above components (A) to (C) were mixed using a Loedige mixer in the proportions shown in Tables 1 and 2 to prepare a cement admixture. Furthermore, the cement admixture and cement were mixed in the proportions shown in Tables 1 and 2 to prepare a rapid-setting cement. <Mortar manufacturing> The rapid-hardening cement, aggregate, and water were mixed for 2 minutes using a hand mixer in a 20°C constant temperature testing room to prepare mortar samples.

[0022] <Compression strength> Conforms to JIS A 1108, except that the specimen dimensions are Φ50 x h100mm. For the 6-hour and 24-hour periods, the specimen is demolded immediately before the test and tested with unbonded capping. For the 7-day period, the specimen is demolded 24 hours after molding and then underwater cured. The compressed surface is polished before testing. <Condensation end time> Measured in accordance with JIS A 1147. <Test conditions and evaluation> The amount of retarder (citric acid) was adjusted so that the final setting time was between 60 and 90 minutes. Under these conditions, the compressive strength was considered to be acceptable if it was 6 hours ≥ 18 MPa, 24 hours ≥ 30 MPa, and 7 days ≥ 40 MPa.

[0023] The results are shown in Tables 1 and 2. As is clear from Tables 1 and 2, in Comparative Example 1, which did not contain either lithium carbonate or the zinc compound of the present invention, the short-term strength (6-hour and 24-hour compressive strength) did not reach the target acceptable strength, whereas in Examples 1 to 8 of the present invention, despite not containing lithium carbonate, all of them exhibited high short-term strength development and met the target strength, similar to Comparative Examples 2 and 3, which used lithium carbonate. Furthermore, when calcium sulfate and one or more selected from alkali metal sulfates and aluminum sulfate were contained as sulfates, high short-term strength development was demonstrated even when the amount of the cement admixture of the present invention added was relatively small, as in Examples 1 to 4 and 7.

[0024] [Table 1]

[0025]

Table 2

Claims

1. A cement admixture containing (A) calcium aluminates, (B) sulfates, and (C) zinc compounds.

2. 2. The cement admixture according to claim 1, wherein the sulfate (B) comprises one or more selected from alkali metal sulfates and aluminum sulfate, and the content of the one or more selected from alkali metal sulfates and aluminum sulfate is 0.5% or more and 30% or less in terms of molar content relative to the sulfate.

3. 2. The cement admixture according to claim 1, wherein the sulfate (B) comprises one or more selected from the group consisting of alkaline earth metal sulfates, alkali metal sulfates, and aluminum sulfate.

4. 2. The cement admixture according to claim 1, wherein the sulfate (B) comprises calcium sulfate and one or more selected from the group consisting of alkali metal sulfates and aluminum sulfate.

5. 2. The cement admixture according to claim 1, wherein the (B) sulfate comprises calcium sulfate and an alkali metal sulfate, and the content of the alkali metal sulfate is 0.5% or more and 30% or less in terms of molar content relative to the total content of calcium sulfate and the alkali metal sulfate.

6. 2. The cement admixture according to claim 1, wherein the zinc compound (C) is one or more selected from the group consisting of basic zinc carbonate, zinc oxide, zinc nitrate, zinc sulfate, zinc sulfide, and zinc hydroxide.

7. A hydraulic composition comprising the cement admixture according to any one of claims 1 to 6 and Portland cement.

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