Expansive admixture

Abstract

To provide an expansive admixture which allows expansion performance to be easily controlled even when blast furnace cement is used, and has the initial strength development.SOLUTION: An expansive admixture contains a quicklime-sintered material and anhydrous gypsum. In the anhydrous gypsum, the percentage content of particles of less than 10 μm is 77-85 mass%; the percentage content of particles of 10 μm-100 μm is 15-23 mass%; the maximum particle size is 100 μm or less; and the median size (D50) of the anhydrous gypsum is 1 μm or more and less than 5 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an expansive additive used to suppress cracking in concrete. [Background technology]

[0002] After hardening, concrete shrinks when it dries in an air environment due to evaporation of water from the surface, reducing the internal moisture content. If the stress caused by shrinkage exceeds the tensile strength of the concrete, cracks will occur. When cracks occur in concrete structures that contain steel, deterioration factors can easily reach the steel, causing corrosion and reducing the durability of the structure. For this reason, it is common to mix expansive additives into the concrete to expand it in advance and reduce cracks caused by shrinkage.

[0003] Two types of expansive additives are typically used for concrete: ettringite-based expansive additives, which contain ettringite products such as calcium sulfoaluminate as their active ingredient, and lime-based expansive additives, which contain free quicklime (free lime). Of these, lime-based expansive additives are known to have high hydration activity and are particularly effective in suppressing large initial shrinkage of concrete. As lime-based expansive additives, those using expansive compositions in which free quicklime is encapsulated in alite have been proposed (e.g., Patent Documents 1 and 2). Furthermore, an expansive additive with little temperature dependency has been proposed, based on the particle size of expansive fired materials containing free quicklime (Patent Document 3).

[0004] Meanwhile, in recent years, blended cements such as blast furnace cement and fly ash cement have been attracting attention as alternatives to Portland cement, with a view to reducing carbon dioxide emissions. Among these, blast furnace cement is a cement made by mixing Portland cement with ground granulated blast furnace slag, a by-product of steelworks. The addition of ground granulated blast furnace slag reduces the amount of Portland cement used and also reduces carbon dioxide emissions. Cement made with ground granulated blast furnace slag is standardized as blast furnace cement in JIS R 5201. However, the hydration reaction of blast furnace cement proceeds more slowly than that of ordinary Portland cement, and the initial strength development is also slower. When using such blast furnace cement, it is difficult to control the expansion performance of concrete. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 50-24320 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-201603 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-129210 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides an expanding material that can easily control expansion performance and exhibits good subsequent strength development even when using blast furnace cement. [Means for solving the problem]

[0007] The inventors of the present invention have conducted extensive research into the behavior of expansion when an expansive agent is added to blast furnace cement, and have found that when blast furnace cement is used, the anhydrous gypsum in the expansive agent has a large effect on expansion performance. Further research has revealed that this is closely related to the particle size of the coarse particles in the anhydrous gypsum, and that the above problem can be solved by adjusting the particle size of the anhydrous gypsum to a predetermined particle content, thereby completing the invention. The present invention is as follows: [1] to [5]. [1] An expanding material containing calcined lime and anhydrous gypsum, wherein the anhydrous gypsum has a particle content of less than 10 μm of 77 to 85% by mass, a particle content of 10 μm to 100 μm of 15 to 23% by mass, and a maximum particle size of 100 μm or less. [2] The median diameter (D 50 The expanding material according to [1], wherein the particle size is 1 μm or more and less than 5 μm. [3] The expansive material according to [1] or [2], characterized in that the mass ratio of the quicklime calcined product to the anhydrous gypsum is quicklime calcined product:anhydrous gypsum=67:33 to 76:24. [4] A cement composition comprising cement and the expanding material according to any one of [1] to [3]. [5] The cement composition according to [4], wherein the cement is blast furnace cement. [Effects of the Invention]

[0008] By using the expansive additive of the present invention, it is possible to easily obtain good expansion performance and strength development, especially when using blast furnace slag cement. As a result, even when using blast furnace slag cement, shrinkage-compensating concrete that meets the standards of the Japan Society of Civil Engineers can be easily produced. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention provides an expanding agent containing quicklime calcined product and anhydrous gypsum, wherein the anhydrous gypsum has a particle content of less than 10 μm of 77 to 85 mass %, a particle content of 10 μm to 100 μm of 15 to 23 mass %, and a maximum particle size of 100 μm or less. Furthermore, the expanding agent preferably has a mass ratio of the quicklime calcined product to the anhydrous gypsum of quicklime calcined product:anhydrous gypsum=67:33 to 76:24. This will be explained in detail below.

[0010] The term "quicklime calcined product" used in the present invention refers to a calcined product containing quicklime (free quicklime; f-CaO) as a primary component. Specifically, it refers to quicklime obtained by calcining a CaO raw material such as limestone, and a calcined product containing free quicklime as a primary component. Calcination is performed in a calcining furnace such as a rotary kiln or electric furnace at a temperature of 1100 to 1500°C. The free quicklime content in the quicklime calcined product is preferably 50% or more, more preferably 60% or more. Components other than free quicklime preferably include hydraulic compounds such as CaO·3SiO2, 4CaO·Al2O3·Fe2O3, 3CaO·Al2O3, and 3CaO·3Al2O3·CaSO4. The quicklime calcined product may contain small amounts of impurities derived from the raw materials, such as MgO, KO, Na2O, MnO, TiO2, and SO3. The calcined quicklime is crushed and used as a powder. The fineness of the calcined quicklime is 2000 to 5000 cm in terms of Blaine specific surface area. 2 / g is preferred.

[0011] The anhydrous gypsum used in the present invention can be either natural gypsum or industrially produced or by-product chemical gypsum. Also, waste gypsum recycled from gypsum boards can be used. The particle size of the anhydrous gypsum is characterized by the content of particles less than 10 μm being 77 to 85 mass %, the content of particles between 10 μm and 100 μm being 15 to 23 mass %, and the maximum particle size being adjusted to 100 μm or less. By adjusting the content of particles between 10 μm and 100 μm to 15 to 23 mass %, it becomes easy to control the expansion performance even when blast furnace cement is used. Furthermore, since excessive expansion is likely to occur when particles exceeding 100 μm are included, the maximum particle size is adjusted to 100 μm or less. Furthermore, the median diameter (D50 ) is preferably 1 μm or more, more preferably 2 μm or more, and is preferably less than 5 μm, more preferably less than 4 μm.

[0012] The method for adjusting the particle size of anhydrous gypsum is not particularly limited, but examples include a method of adjusting by grinding and classifying while measuring the particle size, or a method of separating the ground material into powders of 10 μm or more and powders of less than 10 μm using a sieve or classifier, and then mixing and adjusting the respective powders to achieve a predetermined particle size distribution. For grinding, various grinders such as a rod mill, ball mill, vertical roller mill, hammer mill, jaw crusher, and jet mill can be used. For classification, various classifiers such as a vibrating sieve including an ultrasonic sieve, a rotary sieve (trommel), an air separator, and a centrifuge can be used. For mixing, various mixers (mixers) can be used, such as a gravity mixer such as a V-type mixer or a tilting concrete mixer, a Henschel mixer, a ribbon mixer, a pan-type concrete mixer, a Hugmill mixer, and a hand mixer. The particle content can be determined by a sieving test using a vacuum suction dry sieving device (air jet sieve) with sieves having openings appropriate for each particle size range. Furthermore, particle size distributions such as particle size distribution and average particle size can be measured using a laser diffraction particle size distribution analyzer.

[0013] The ratio of quicklime calcined product to anhydrous gypsum in the expansive additive of the present invention is preferably a mass ratio of quicklime calcined product to anhydrous gypsum of quicklime calcined product:anhydrous gypsum = 67:33 to 76:24. By adjusting the mass ratio within this range, even when blast-furnace cement is used, sufficient expansion performance can be obtained and mortar concrete with good strength development can be obtained. The mass ratio is more preferably 68:32 to 75:25, and even more preferably 69:31 to 74:26. ​​The expansive additive of the present invention can be suitably used as an expansive additive for blast-furnace cement.

[0014] In addition to the above, admixtures commonly used in mortar and concrete can be added to the expansive additive of the present invention, provided that they do not impair the effects of the present invention. Examples of admixtures include dispersants, waterproofing agents, pigments, water repellents, foaming agents, foaming agents, defoamers, retarders, hardening accelerators, shrinkage reducers, hydration heat inhibitors, thickeners, water retention agents, and rust inhibitors. One or more of these admixtures can be added. Furthermore, various Portland cements, ecocements, stone powder, clay mineral powders, slag powders, fly ash, silica fume, and the like can also be added as fillers to the extent that they do not impair the effects of the present invention. However, the amount of admixtures other than calcined lime and anhydrous gypsum added to the expansive additive is preferably less than 10% by mass, more preferably less than 5% by mass. Conversely, the content of calcined lime and anhydrous gypsum in the expansive additive is preferably 90% by mass or more, more preferably 95% by mass or more.

[0015] The cement used in the cement composition of the present invention can be various types of Portland cement, including normal, early-strength, ultra-early-strength, low-heat, and moderate-heat cements, as well as blended cements. Since the expansive additive of the present invention is specifically formulated to exhibit good expansion performance when used with blast-furnace cement, it is particularly preferable to use Type A blast-furnace cement. Type A refers to blast-furnace cement with a blast-furnace slag replacement rate of more than 5% and not more than 30%.

[0016] The amount of the expansive material added to the cement composition is preferably 5 to 10 mass % and more preferably 6 to 9 mass % based on the total amount of cement and expansive material (binder equivalent) from the viewpoint of expansion performance and strength development. The cement composition is used as mortar or concrete by kneading it with aggregate (fine aggregate, coarse aggregate) and water. When the cement composition is used as concrete, the amount of the expansive material to be mixed is 10 ... 3 The mixing amount of the aggregate is preferably 10 to 30 kg per m, more preferably 15 to 25 kg per m. The mixing amount of the aggregate is 500 to 1400 kg / m for both fine aggregate and coarse aggregate. 3 is preferable, and more preferably 600 to 1000 kg / m 3The fine aggregate ratio is preferably 10 to 60%. [Example]

[0017] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0018] (calcined quicklime) The main raw material was limestone, and to make it easier to burn, silica, alumina, and iron oxide were mixed and fired at 1400°C in an electric furnace. The resulting fired mass was crushed and Free Calcined quicklime (f-CaO) containing 65% by mass (Blaine specific surface area 3000 cm 2 The main minerals contained in this burned lime product, other than free lime, were 20 mass% tricalcium silicate (3CaO SiO2), 5 mass% ferrite phase (4CaO Al2O3 Fe2O3), 3 mass% aluminate phase (3CaO Al2O3), and 2 mass% periclase (MgO).

[0019] (Anhydrite) Granular anhydrous gypsum (hydrofluoric anhydrous gypsum manufactured by Asahi Glass Co., Ltd.; commercially available product) was crushed, and the 100 μm whole product was separated using a sieve into crushed products of 10 μm or more and crushed products of less than 10 μm. The respective powders were mixed to a predetermined ratio. Table 1 shows the particle content of each anhydrous gypsum used in the test. The average particle diameter (median diameter; D 50 ) was measured using a laser diffraction particle size distribution analyzer (manufactured by Japan Laser Co., Ltd.; HELOS).

[0020] [Table 1]

[0021] (expansive material) The above burned quicklime was mixed with each of the five types of anhydrous gypsum shown in Table 1 to prepare expansive additives. The formulations of each expansive additive are shown in Table 2.

[0022] [Table 2]

[0023] (Preparation of mortar specimens) Mortar was prepared by adding the expansive additives shown in Table 2, cement equivalent to blast furnace cement type A, which was a mixture of equal parts of ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) and blast furnace cement type B (manufactured by Taiheiyo Cement Corporation, slag replacement rate 45%), fine aggregate, and water, and mixing for 3 minutes. The mortar mix was 450g of cement and expansive additive combined, 1350g of standard sand, and 225g of water. Various properties were evaluated using the prepared mortar specimens. The evaluation test items are listed below.

[0024] (Evaluation test) (1) Compression strength test Specimens were prepared in accordance with JIS A 1132 "Method of preparing specimens for strength tests of concrete," and after 24 hours they were demolded and then underwater cured until they were 7 days old. The compressive strength of the specimens at 7 days old was measured in accordance with JIS A 1108 "Testing method for compressive strength of concrete." (2) Restrained expansion rate test The test was conducted in accordance with Method A of JIS A 6202 "Expansive additive for concrete," and the restrained expansion rate at 7 days of age was determined.

[0025] The test results are shown in Table 3. The compressive strength ratio is the strength of the mortar specimen without the addition of expansive additive (45 N / mm 2 ) is the ratio to The restrained expansion of concrete containing expansive additives and the restrained expansion ratio of shrinkage-compensating concrete (150-250 x 10) -6 ) in order to obtain expansion performance that satisfies the above, the mortar restrained expansion rate test is 600 × 10 -6 The expansion coefficient of the specimens using the expansive additive of the present invention (Nos. 1-2 to 1-4) all showed sufficient expansion coefficients. In addition, the compressive strength at 7 days was also higher than the compressive strength of the specimens without the addition of expansive additive (45 N / mm 2 ) and the strength development was also good.

[0026] [Table 3]

[0027] Example 2 CS3 shown in Table 1 was used as a particle-size-adjusted expansive additive, and the mixing ratio with burned quicklime was examined. The expansive additives tested are shown in Table 4. Mortar specimens were prepared and evaluation tests were carried out in the same manner as in Example 1. The test results are shown in Table 5. As shown in Table 5, it was confirmed that all of the additives exhibited good expansion performance and strength development.

[0028] [Table 4]

[0029] [Table 5]

Claims

1. An expanding material comprising calcined lime and anhydrous gypsum, wherein the anhydrous gypsum has a particle content of less than 10 μm of 77 to 85% by mass, a particle content of 10 μm to 100 μm of 15 to 23% by mass, and a maximum particle size of 100 μm or less.

2. The median diameter (D ５０ 2. The expanding material according to claim 1, wherein the particle size is 1 μm or more and less than 5 μm.

3. The expanding material according to claim 1, characterized in that the mass ratio of the quicklime calcined product to the anhydrous gypsum is quicklime calcined product:anhydrous gypsum=67:33 to 76:

24.

4. A cement composition comprising cement and the expanding material according to any one of claims 1 to 3.

5. 5. The cement composition of claim 4, wherein the cement is a blast furnace cement.

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