Expansive admixture

Abstract

To provide an expansive admixture exhibiting early strength manifestation while maintaining its excellent expansion performance.SOLUTION: The expansive admixture includes 30 to 55 mass% of an expansive composition, 25 to 60 mass% of gypsum, and 10 to 30 mass% of calcium aluminate. The expansive admixture further includes one species or at least two species of metal salts selected from the group consisting of: an alkali metal sulfate such as sodium sulfate and potassium sulfate; an alkali metal carbonate such as lithium carbonate, sodium carbonate, and potassium carbonate; calcium nitrate; calcium nitrite; and aluminum sulfate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an expansive admixture used for the purpose of suppressing cracks in mortar, concrete, etc. [Background technology]

[0002] In order to improve the durability of various materials and buildings, such as mortar and concrete, which use 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 concrete expansive additives. These expansive additives are broadly divided into those containing quicklime as the active ingredient and those containing calcium sulfoaluminate as the active ingredient. Of these, those containing quicklime as the active ingredient generally have high reactivity, leading to excellent early expansion and the expectation of relatively large expansion amounts, making them 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] Meanwhile, in precast concrete (PCa) manufactured at concrete product factories, various admixtures are used for the purposes of cost reduction, high performance, energy conservation, etc., and expansive additives are also widely used to suppress cracking. Examples of admixtures other than expansive additives include blast furnace slag fine powder, silica fume, fly ash, siliceous fine powder, limestone fine powder, high-strength admixtures, early-strength admixtures, and colorants (Non-Patent Document 1). In recent years, in order to improve productivity, shorter strength development times are required to increase formwork turnover rates. For this purpose, early-strength admixtures are used, but when used in combination with expansive additives, two silos are required. Without a silo, the admixtures must be added manually, which makes the addition process cumbersome and difficult to manage. Therefore, a method for achieving both expansive performance and early-strength development with a single material has been desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-127372 [Patent Document 2] Japanese Patent Application Publication No. 2018-131359 [Non-patent literature]

[0006] [Non-Patent Document 1] Shinji Tsuchida, "Manufacturing of Precast Concrete," Concrete Engineering, 2000 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the problem to be solved by the present invention is to provide an expansive admixture that can obtain early strength development while ensuring good expansion performance. [Means for solving the problem]

[0008] As a result of extensive research into the constituent components of expansive admixtures, the present inventors have found an expansive admixture that can solve the above problems. That is, the present invention is as described in the following [1] to [5]. [1] An expansive admixture containing 30 to 55 mass% of an expansive composition, 25 to 60 mass% of gypsum, and 10 to 30 mass% of calcium aluminate. [2] The expansive admixture of [1] further contains 0.1 to 3.0 mass% of one or more metal salts selected from alkali metal sulfates such as sodium sulfate and potassium sulfate, alkali metal carbonates such as lithium carbonate, sodium carbonate and potassium carbonate, calcium nitrate, calcium nitrite, and aluminum sulfate. [3] Mortar or concrete containing the expansive admixture of [1] or [2]. [4] A method for producing precast concrete, characterized by containing the expansive admixture of [1] or [2] and steam curing at a maximum temperature of 40 to 80°C. [5] Compressive strength at 5 hours is 10N / mm 2 The expansion amount at 5 hours is 150 x 10 -6 The method for producing precast concrete according to [4], characterized by the above. [Effects of the Invention]

[0009] By using the expansive admixture of the present invention, it is possible to obtain mortar or concrete that is excellent in early strength development while ensuring good expansion performance. By using the expansive admixture of the present invention in precast concrete, it is possible to increase the rotation speed of the formwork, thereby improving productivity. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Expansive admixture> The expansive admixture of the present invention is characterized by containing 30 to 55 mass % of an expansive composition, 25 to 60 mass % of gypsum, and 10 to 30 mass % of calcium aluminate.

[0011] The expandable composition of the present invention contains free quicklime (f-CaO) as an active ingredient. The free quicklime content is preferably 30 to 80 mass %, more preferably 40 to 70 mass %. In addition to the free quicklime, the composition may contain one or more hydraulic compounds such as calcium silicates such as CaO·2SiO2 (C2S) and CaO·3SiO2 (C3S), calcium aluminoferrites such as 4CaO·Al2O3·Fe2O3 (C4AF) and 6CaO·2Al2O3·Fe2O3 (C6A2F), and calcium sulfoaluminates such as 3CaO·3Al2O3·CaSO4 (aouin). The fineness of the expandable composition is 2000 to 7000 cm2 in terms of Blaine specific surface area. 2 / g is preferred, and 3000 to 6500 cm 2 / g is more preferred.

[0012] The expandable composition of the present invention is produced by firing raw materials containing calcium raw materials such as limestone, quicklime, and slaked lime. In addition to the calcium raw materials, silica raw materials, alumina raw materials, and iron oxide raw materials are also used. Examples of silica raw materials include silica powder and diatomaceous earth. Examples of alumina raw materials include alumina, bauxite, band shale, aluminum ash, aluminum dross, coal ash, and clay. Examples of iron oxide raw materials include iron oxide, red iron oxide, copper slag, and steelmaking slag. A rotary kiln or an electric furnace is used for firing. The firing temperature is preferably 1100 to 1500°C. After firing, the fired clinker is crushed and classified to obtain a desired powder size.

[0013] Examples of gypsum in the present invention include gypsum hemihydrate, gypsum dihydrate, anhydrous gypsum, etc., and anhydrous gypsum is particularly preferred. In addition to natural gypsum and by-product gypsum, particle-size-adjusted waste gypsum can also be used. The fineness of the gypsum is 4,000 to 10,000 cm in terms of Blaine specific surface area. 2 / g is preferred, and 5000 to 8000 cm 2 / g is more preferred.

[0014] The calcium aluminate in the present invention is a compound consisting of CaO and Al2O3, and examples thereof include CaO·2Al2O3 (CA2), CaO·Al2O3 (CA), and 12CaO·7Al2O3 (C 12 A7), 3CaO·Al2O3 (C3A), etc. Also, amorphous calcium aluminate can be used. It contains one or more of these. In particular, those containing CA as the main component are preferred. Also, commercially available alumina cement can be used as calcium aluminate.

[0015] The CaO content of calcium aluminate is preferably 20 to 70 mass%, more preferably 30 to 60 mass%, and particularly preferably 35 to 45 mass%. The calcium aluminate may contain small amounts of impurities such as SiO2, MgO, K2O, Na2O, Fe2O3, TiO2, MnO, Cr2O3, V2O5, NiO, SrO, BaO, P2O5, ZrO2, and CeO2. The fineness of calcium aluminate is 3000 to 8000 cm2 in terms of Blaine specific surface area. 2 / g is preferred, and 4000 to 7000 cm 2 / g is more preferred.

[0016] The blending ratios of the expansive admixture of the present invention are 30 to 55 mass% of the expansive composition, 25 to 60 mass% of the gypsum, and 10 to 30 mass% of the calcium aluminate. If the expansive composition is less than 30 mass%, expansion performance cannot be ensured. If the gypsum is less than 25 mass%, strength development under steam curing conditions decreases and the fresh properties of the concrete also deteriorate. If the calcium aluminate is less than 10 mass%, early strength development decreases significantly. By using the above blending ratios, concrete with good expansion performance and excellent early strength development can be obtained.

[0017] Furthermore, the expansive admixture of the present invention may contain, as an accelerator component, one or more metal salts selected from alkali metal sulfates such as sodium sulfate and potassium sulfate, alkali metal carbonates such as lithium carbonate, sodium carbonate and potassium carbonate, calcium nitrate, calcium nitrite, and aluminum sulfate. Among these, sodium sulfate is particularly preferred. Addition of a metal salt such as sodium sulfate can further enhance early strength development. The content of the metal salt in the expansive admixture is preferably 0.1 to 3.0% by mass, more preferably 0.2 to 2.0% by mass.

[0018] In addition to the above-mentioned components, the expansive 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, setting retarders, waterproofing agents, rust inhibitors, thickeners, polymers for cement admixture, water-retaining agents, pigments, water-repellents, and anti-efflorescence agents.

[0019] By adding the expansive admixture of the present invention to mortar or concrete, it is possible to obtain mortar or concrete that is excellent in early strength development while maintaining good expansion performance. The amount of expansive admixture added to mortar or concrete is preferably 3 to 25 mass % relative to the cement in the mortar or concrete, more preferably 5 to 20 mass %. Furthermore, the unit amount in concrete is 20 to 60 kg / m 3 is preferable, and 30 to 50 kg / m 3 is more preferred.

[0020] The expansive admixture of the present invention is particularly effective when used in precast concrete manufactured in a concrete product factory. Concrete products containing the expansive admixture can achieve a compressive strength of 10 N / mm in 5 hours by steam curing at a maximum temperature of 40 to 80°C. 2 Since the strength development of the above can be achieved, it is possible to manufacture formwork twice a day, which increases productivity. In addition, the expansion amount at 5 hours of age is 150 x 10 -6Concrete having the above properties can be obtained, and has a sufficient crack suppression effect. [Example]

[0021] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0022] (Preparation of Expandable Composition) A mixture of industrial quicklime, silica stone, alumina shale, and iron oxide was fired in an electric furnace at 1400°C to obtain a fired product containing 60% by mass of free quicklime. The main minerals contained in this fired product other than free lime are calcium silicate (3CaO SiO2), calcium aluminoferrite (4CaO Al2O3 Fe2O3), etc. This fired product was pulverized in a ball mill to obtain a Blaine specific surface area of ​​3500±200 cm2. 2 The particle size was adjusted to 1 / g to obtain an expandable composition.

[0023] (Preparation of expansive admixture) The prepared expandable composition, gypsum, calcium aluminate, and sodium sulfate were used to prepare an expandable admixture. As the gypsum, anhydrous gypsum (Blaine specific surface area: 7000 cm) was used. 2 The calcium aluminate used was a calcium aluminate containing 38% CaO by mass (Blaine specific surface area: 5100 cm), which was produced by calcining limestone and calcined bauxite. 2 These were mixed in a mixer at a predetermined mixing ratio to obtain an expansive admixture.

[0024] (Concrete preparation) The mixing amount of expansive admixture is 40 kg / m 3Concrete with a slump of 3.0±1.5 cm was prepared using the above method. 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 1. A high-performance water-reducing agent (Pozzolith Solutions' "Mastergranium 8000S") was added at 0.85% by mass relative to the total amount of cement and expansive admixture. The concrete was mixed in a concrete mixer, packed into a formwork, and steam-cured for 5 hours under the following conditions: a pre-setting time of 1 hour, a heating rate of 30°C / hour, a maximum temperature of 50°C, and a maximum temperature hold time of 3 hours. After demolding, the concrete was subjected to testing.

[0025] [Table 1]

[0026] (Evaluation test) The concrete was subjected to a compressive strength test and a restrained expansion test. The test methods are shown below. (1) Compression strength test The test was conducted in accordance with "JIS A 1108 Compressive Strength Test of Concrete." (2) Restrained expansion test The concrete was cast, and then, in accordance with "JIS A 6202 Expansive Materials for Concrete, Appendix B," strain gauges were attached to the restraining device used in Method A to measure the amount of expansion.

[0027] <Example 1> The mixing ratio of the expansive admixture and the test results are shown in Table 2. The concrete using the expansive admixture prepared within the range of the present invention had a compressive strength of 10N / mm 2 This is sufficient strength to remove the precast concrete formwork. The expansion amount was also 150 x 10 - 6 As shown above, it is clear that all of them have good expansion performance.

[0028] [Table 2]

[0029] <Example 2> Next, tests were conducted on expansive admixtures containing metal salts. The same materials as in Example 1 were used except for the metal salts. The blending ratios of the expansive admixtures and the test results are shown in Table 3. Glauber's salt (commercially available) was used as the sodium sulfate, aluminum sulfate (commercially available) was used as the aluminum sulfate, and a reagent was used as the lithium carbonate. In particular, it was found that when an expansive admixture containing sodium sulfate was used, good early strength development was achieved while maintaining expansion performance.

[0030] [Table 3]

Claims

1. An expansive admixture comprising 30 to 45 mass% of an expansive composition, 45 to 55 mass% of gypsum, and 10 to 20 mass% of calcium aluminate.

2. The expansive admixture according to claim 1 further contains 0.1 to 3.0 mass% of one or more metal salts selected from sodium sulfate, potassium sulfate, lithium carbonate, sodium carbonate, potassium carbonate, calcium nitrate, calcium nitrite and aluminum sulfate.

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

4. A method for producing precast concrete, comprising containing the expansive admixture according to claim 1 or 2 and steam curing at a maximum temperature of 40 to 80°C.

5. The compressive strength at 5 hours is 10 N / mm2 or more, and the expansion amount at 5 hours is 150 x 10 －６ 5. The method for producing precast concrete according to claim 4, comprising the steps of:

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