Accelerator for blast furnace cement, spray material, and sprayed concrete

Abstract

To provide an accelerator for blast furnace cement that offers superior early strength development and rapid setting, effectively reducing the generation of hydrogen sulfide gas.SOLUTION: An accelerator for blast furnace cement contains 40-70 pts.mass of calcium aluminate and 2.5-40 pts.mass of alkali metal salt.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an accelerator for blast-furnace cement, a spraying material, and a sprayed concrete. [Background technology]

[0002] Conventionally, in order to prevent the collapse of exposed natural ground such as in tunnel excavation, a method of spraying quick-setting concrete in which an accelerator is mixed into the concrete has been used. In this method, materials are measured and mixed in a measuring plant installed at the excavation site to prepare the shotcrete, which is then pumped and mixed with the accelerator pumped from the other side of the junction pipe, and sprayed onto the natural ground until a specified thickness is reached.

[0003] As quick-setting admixtures, there have been proposed a liquid quick-setting admixture comprising a combination of a fluoride-containing water-soluble aluminum complex obtained by the reaction of aluminum sulfate with hydrofluoric acid, aluminum hydroxide, and phosphorous acid and / or an organic acid salt thereof (see Patent Document 1); a concrete quick-setting admixture containing at least one selected from the group consisting of aluminum fluoride, an acidic or basic solution of aluminum, lithium silicate, and lithium aluminate (see Patent Document 2); and a liquid quick-setting admixture comprising a fluoride-containing water-soluble aluminum salt obtained by the reaction of aluminum sulfate with hydrofluoric acid, aluminum hydroxide, and lithium hydroxide, lithium carbonate, lithium sulfate, or the like (see Patent Document 3).

[0004] On the other hand, in recent years, there has been a demand to reduce the amount of cement used in order to reduce carbon dioxide emissions, and the use of by-products such as blast furnace cement has been considered. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-193388 A [Patent Document 2] JP 2001-130935 A [Patent Document 3] JP 2005-89276 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, blast-furnace slag cement has the problem that it is difficult to obtain short-term strength, and there is also concern that hydrogen sulfide gas derived from the blast-furnace slag in the blast-furnace slag cement may be generated depending on the combination with the quick-setting admixture used.

[0007] In view of the above, an object of the present invention is to provide an accelerated setting admixture for blast-furnace cement which is excellent in short-term strength development and rapid setting properties and can suppress the generation of hydrogen sulfide gas. [Means for solving the problem]

[0008] As a result of intensive research conducted by the present inventors in light of the above problems, they found that a blast furnace cement quick-setting admixture containing a predetermined amount of calcium aluminate and an alkali metal salt can solve the above problems, and thus completed the present invention.

[0009] [1] A blast furnace cement accelerator containing 40 to 70 parts by mass of calcium aluminate and 2.5 to 40 parts by mass of an alkali metal salt. [2] The quick-setting admixture for blast-furnace slag cement according to the above item [1], which comprises a combination of material A containing the calcium aluminate and material B containing the alkali metal salt. [3] The quick-setting admixture for blast-furnace cement according to [1] or [2] above, wherein the alkali metal salt is one or more selected from the group consisting of sodium carbonate, potassium carbonate, and sodium sulfate. [4] The quick-setting admixture for blast-furnace cement according to the above [2] or [3], wherein the B material is a slurry containing water. [5] The quick-setting admixture for blast-furnace cement according to any one of the above [2] to [4], wherein the pH of the material B is 6 or more. [6] A spraying material comprising the quick-setting admixture for blast-furnace slag cement according to any one of [1] to [5] above and blast-furnace slag cement. [7] The spraying material according to the above [6], wherein the amount of blast furnace slag in the blast furnace cement is 30 to 90 mass %. [8] Shotcrete containing the spraying material described in [6] or [7] above. Effect of the Invention

[0010] According to the present invention, it is possible to provide an accelerated setting admixture for blast-furnace cement which is excellent in short-term strength development and rapid setting properties and which can suppress the generation of hydrogen sulfide gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to the embodiment. In addition, "%" in this specification is based on mass unless otherwise specified.

[0012] [Accelerating agent for blast furnace cement] The quick-setting admixture for blast-furnace cement according to the present embodiment contains 40 to 70 parts by mass of calcium aluminate and 2.5 to 40 parts by mass of an alkali metal salt. Note that the blast-furnace cement in the present invention refers to blast-furnace cement as specified in JIS R 5211:2009 "Blast-furnace cement" or blast-furnace cement obtained by mixing blast-furnace slag with ordinary Portland cement or the like and containing blast-furnace slag in an amount equal to or greater than the amount specified in the JIS.

[0013] The calcium aluminate contained in the quick-setting admixture for blast furnace cement according to this embodiment is a general term for a compound having CaO and Al2O3 as main components and having hydration activity, and is a compound in which a portion of CaO and / or Al2O3 is replaced with an alkali metal oxide, an alkaline earth metal oxide, silicon oxide, titanium oxide, iron oxide, an alkali metal halide, an alkaline earth metal halide, an alkali metal sulfate, an alkaline earth metal sulfate, or the like, or a substance in which a small amount of these are dissolved in a substance mainly composed of CaO and Al2O3, and calcium aluminate may be either crystalline or amorphous.

[0014] Specific examples of crystalline materials include CaO, Al2O3, and R2O (Na2O, K2O, Li2O), and include C3A and C, which is a solid solution of alkali metals. 14 RA5, CA, C 12 A7 and C 11 Examples include A7·CaF2, C4A·Fe2O3, and C3A3·CaSO4, but amorphous calcium aluminate is preferred because of its good quick-setting properties. In addition, in the case of amorphous calcium aluminate, it is preferable that the vitrification rate is 80% or more.

[0015] The quick-setting admixture for blast furnace cement according to the present embodiment contains 40 to 70 parts by mass of calcium aluminate. If the content of calcium aluminate is less than 40 parts by mass, the short-term strength development and quick-setting property may not be fully exhibited, and hexavalent chromium may be eluted. If the content of calcium aluminate exceeds 70 parts by mass, the short-term strength development and quick-setting property may not be fully exhibited. In addition, the content of calcium aluminate is preferably 45 to 65 parts by mass, more preferably 50 to 60 parts by mass. If the content of calcium aluminate is within the above range, it is easy to improve the short-term strength development and quick-setting property.

[0016] The CaO / Al2O3 molar ratio of calcium aluminate is not particularly limited, but from the viewpoint of short-term strength development and suppression of elution of hexavalent chromium, the molar ratio is preferably 1.3 to 3.0, more preferably 1.6 to 2.7.

[0017] Methods for obtaining calcium aluminate include heat treating CaO raw materials such as calcium carbonate and calcium hydroxide with Al2O3 raw materials such as bauxite in a rotary kiln, electric furnace, etc. Specifically, the raw materials are mixed in a predetermined ratio, heated and melted in an electric furnace, etc., and quenched by contacting with compressed air or water, etc. The CaO / Al2O3 molar ratio can be adjusted by adjusting the ratio of the raw materials, and the vitrification rate can be adjusted by the temperature during heating and melting and the cooling method.

[0018] When calcium aluminate is obtained industrially, it may contain impurities. Specific examples of impurities include SiO2, Fe2O3, MgO, TiO2, MnO, Na2O, KO, Li2O, S, PO5, and F, but the presence of these impurities is not a problem as long as they do not substantially impede the object of the present invention. Specifically, it is not a problem as long as the total amount of these impurities is 10% or less.

[0019] The Blaine specific surface area value (Blaine value) of calcium aluminate is not particularly limited, but is usually 3,000 to 9,000 cm 2 / g is preferable, and 4,000 to 8,000 cm 2 / g is more preferable. By the Blaine value being within the above range, the handleability can be improved. The Blaine specific surface area is measured based on the specific surface area test described in JIS R 5201:2015 "Physical test method for cement".

[0020] The quick-setting admixture for blast-furnace cement according to the present embodiment contains an alkali metal salt in an amount of 2.5 to 40 parts by mass. If the content of the alkali metal salt is less than 2.5 parts by mass, the short-term strength development may be insufficient, and if it exceeds 40 parts by mass, the short-term strength development and quick-setting property may be insufficient. The content of the alkali metal salt is preferably 3 to 30 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 8 to 15 parts by mass.

[0021] From the viewpoint of early strength development at an age of 10 minutes to 24 hours, the alkali metal salt is preferably one or more selected from the group consisting of sodium carbonate, potassium carbonate, and sodium sulfate, and from the viewpoint of suppressing generation of hydrogen sulfide gas, sodium carbonate or potassium carbonate is more preferable.

[0022] The quick-setting admixture for blast furnace cement according to the present embodiment can contain aluminum sulfate. The content of aluminum sulfate is not particularly limited, but is preferably 1 to 20 parts by mass, more preferably 3 to 10 parts by mass, and even more preferably 5 to 8 parts by mass, relative to 100 parts by mass of calcium aluminate. When the content of aluminum sulfate is within the above range, it is easy to improve short-term strength development and quick-setting properties. In addition, the aluminum sulfate is preferably in the form of a powder, more preferably a 14 to 18 hydrate, and even more preferably less than 50% of the particles have a particle size of 150 μm or less.

[0023] The blast furnace cement quick-setting admixture may contain slaked lime. The content of slaked lime is not particularly limited, but is preferably 1 to 30 mass%, and more preferably 3 to 15 mass%. When the content of slaked lime is within the above range, the adhesion is improved, making it easier to suppress rebound.

[0024] The quick-setting admixture for blast furnace cement may further contain an alkaline earth metal salt. The alkaline earth metal salt may include carbonates such as calcium carbonate, and sulfates such as calcium sulfate. The content of the alkaline earth metal salt is not particularly limited, but is preferably 3 to 50 mass%, and more preferably 5 to 30 mass%, from the viewpoint of long-term strength development and adhesion.

[0025] The quick-setting admixture for blast-furnace cement according to this embodiment is preferably composed of a combination of material A containing calcium aluminate and material B containing an alkali metal salt. By the quick-setting admixture for blast-furnace cement being composed of a combination of material A and material B, storage stability is improved, and when the amount of blast-furnace slag in the blast-furnace cement fluctuates or when the temperature conditions change, the additive ratios of material A and material B can be increased or decreased to adjust the physical properties to suit the environmental conditions. Material A can contain aluminum sulfate and the like in addition to calcium aluminate, and material B can contain calcium sulfate and the like in addition to the alkali metal salt.

[0026] The content of calcium aluminate in material A is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass.

[0027] The Blaine value of material A is not particularly limited, but is in the range of 3,000 to 9,000 cm 2 / g is preferable, and 4,000 to 8,000 cm 2 When the Blaine value is within the above range, the handleability can be improved.

[0028] Material B is preferably a slurry containing water. When material B is a slurry, it tends to have good mixability and produce less dust when mixed with material A and added to concrete as a quick-setting agent for blast-furnace cement. As a feature of the slurry, the solid content of material B is preferably 1 to 50 mass%, and more preferably 3 to 30 mass%. When the solid content is within the above range, it is easy to improve pumpability.

[0029] It is more preferable that the pH of material B is 6 or more. When material B has a pH of 6 or more, it is easy to suppress the amount of hydrogen sulfide gas generated. The pH of material B can be measured using a pH meter.

[0030] [Spraying material] The spraying material according to the present embodiment contains the quick-setting admixture for blast-furnace cement of the present invention and blast-furnace cement. Usually, depending on the combination of blast-furnace cement and quick-setting admixture, there is a concern that hydrogen sulfide gas derived from blast-furnace cement may be generated. However, since the spraying material according to the present invention contains the quick-setting admixture for blast-furnace cement of the present invention and blast-furnace cement, it is excellent in short-term strength development and quick setting, and can suppress the generation of hydrogen sulfide gas.

[0031] The content of the quick-setting admixture for blast-furnace cement in the spraying material is preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of blast-furnace cement. When the content of the quick-setting admixture for blast-furnace cement is within the above range, it is easy to achieve excellent short-term strength development and quick setting properties, and it is easy to suppress the generation of hydrogen sulfide gas.

[0032] The amount of blast furnace slag in the blast furnace cement is preferably 30 to 90 mass%, more preferably 40 to 70 mass%. When the amount of blast furnace slag is within the above range, it is easy to suppress the generation of hydrogen sulfide gas and the elution of hexavalent chromium.

[0033] [Shocked concrete] The sprayed concrete according to the present embodiment contains the spraying material of the present invention. The sprayed concrete can be obtained, for example, by mixing material A and material B just before spraying to prepare a quick-setting admixture for blast-furnace cement, mixing the quick-setting admixture with blast-furnace cement, and spraying the mixture. The sprayed concrete has excellent short-term strength development and quick-setting properties, and can suppress the generation of hydrogen sulfide gas.

[0034] The content of the sprayed material in the shotcrete is preferably 10 to 30 mass%, more preferably 15 to 25 mass%. When the content of the sprayed material is within the above range, it is easy to achieve excellent short-term strength development and quick setting properties, and it is easy to suppress the generation of hydrogen sulfide gas.

[0035] The water-cement ratio of the sprayed concrete is preferably 30 to 70%, more preferably 40 to 60%, based on the blast-furnace cement in the sprayed material. By having the water-cement ratio within the above range, it is easy to achieve excellent short-term strength development and quick setting, and it is easy to suppress the generation of hydrogen sulfide gas.

[0036] In practice, sprayed concrete uses aggregate, but the aggregate is not particularly limited, and preferably has low water absorption and high aggregate strength. The maximum size of the aggregate is not particularly limited as long as it can be sprayed. River sand, mountain sand, sea sand, lime sand, and silica sand can be used as fine aggregate, and river gravel, mountain gravel, and lime gravel can be used as coarse aggregate, and crushed sand and crushed stone can also be used.

[0037] The content of aggregate in the shotcrete is preferably 60 to 80 mass %, and more preferably 65 to 75 mass %. EXAMPLES

[0038] The present invention will be described in more detail below using examples and comparative examples. However, the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention.

[0039] [Experimental Example 1] <Preparation of Accelerator for Blast-furnace Slag Cement> A slurry (material B) was prepared by adding and mixing alkali metal salt and calcium sulfate in the ratios shown in Table 1 so that the total amount of alkali metal salt and calcium sulfate was 20 parts by mass per 100 parts by mass of water. The prepared slurry and calcium aluminate (material A) were mixed so that the ratios of each component were as shown in Table 1, to prepare a quick-setting admixture for blast-furnace cement. The prepared quick-setting admixture for blast-furnace cement was immediately used in the preparation of the spraying material described below.

[0040] <Materials used> Calcium aluminate: Amorphous calcium aluminate made by melting calcium carbonate and aluminum oxide in an electric furnace and quenching them so that the CaO / Al2O3 molar ratio is 2.3. The vitrification rate is 97% (measured by powder X-ray diffraction) and the Blaine value is 5,800 cm 2 / g, amorphous. Alkali metal salts: Sodium sulfate, anhydrous, 98% purity, industrial raw material. Calcium sulfate: anhydrous calcium sulfate, natural product, Blaine value 4,500 cm 2 / g, industrial raw materials.

[0041] <Preparation of spraying materials> 400g of ordinary Portland cement (manufactured by Denka Co., Ltd.) and 400g of ground granulated blast furnace slag (manufactured by Esment Kanto Co., Ltd.: product name Esment 4000) were mixed to prepare blast furnace cement (blast furnace slag content 50% by mass), 2,000g of fine aggregate (river sand from the Hime River water system in Niigata Prefecture) and water were added to make a water-cement ratio of 50%, and the mixture was kneaded. 10 parts by mass of the prepared blast furnace cement quick-setting admixture was added to 100 parts by mass of the blast furnace cement to prepare a spray material. The prepared spray material was immediately used in the following tests.

[0042] <Coagulation test> The prepared spray material was quickly sprayed onto a formwork measuring 30 cm in length, 30 cm in width, and 10 cm in depth, and the Proctor penetration resistance was measured over time from the addition of the accelerator, reaching 3.5 N / mm 2 The time when this occurs is the starting time, 28.0N / mm 2 The time when the reaction time reached the end was determined as the termination time. The results are shown in Table 1 below.

[0043] <Compressive strength test> The prepared spray material was quickly sprayed onto a triple-section formwork measuring 4 cm length x 4 cm width x 16 cm depth, and the compressive strength was measured at 10 minutes, 3 hours, 24 hours, and 7 days after the addition of the quick-setting admixture. The results are shown in Table 1. In the present invention, the compressive strengths at 10 minutes, 3 hours, and 24 hours are indicators of short-term strength, and the compressive strength at 7 days is an indicator of long-term strength.

[0044] <Amount of eluted hexavalent chromium> The prepared spraying material was quickly sprayed onto the formwork after preparation, and the amount of hexavalent chromium eluted from the sprayed concrete, which had an age of 3 hours depending on the time elapsed since the addition of the accelerator, was measured based on the method specified in the "Elution Test to be carried out at the Mix Design Stage, Notification No. 46 of the Environment Agency, dated August 23, 1991. The results are shown in Table 1.

[0045] <Amount of hydrogen sulfide gas generated> In a 20℃ environment, 100g of blast furnace cement and 50g of water were added to a vinyl bag measuring 340mm long x 230mm wide to prepare a cement paste, and after 1 minute, 10g of the prepared blast furnace cement quick-setting agent was added and the bag was closed. After 10 minutes, 1mL of gas was collected from the bag and the amount of hydrogen sulfide gas was quantified by gas chromatography. The results are shown in Table 1. The detection limit of hydrogen sulfide gas by this method is 20ppb.

[0046] [Table 1]

[0047] [Experimental Example 2] Material A was prepared by mixing calcium aluminate and aluminum sulfate (aluminum sulfate 14-18 hydrate, purity 98%, industrial raw material) in the ratio shown in Table 2. In addition, various alkali metal salts were added and mixed in the ratios shown in Table 2 so that the total amount of various alkali metal salts was 20 parts by mass per 100 parts by mass of water, to prepare a slurry (material B). Materials A and B thus prepared were mixed so that the components were in the ratios shown in Table 2 to prepare an accelerated setting admixture for blast furnace cement, and each test was carried out in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0048] <Alkali metal salt> Sodium carbonate: 98% purity, industrial raw material, Blaine value 1,500 cm 2 / g. Potassium carbonate: 98% purity, industrial raw material, Blaine value 2,200 cm 2 / g. Sodium sulfate: anhydrous, purity 98%, industrial raw material, Blaine value 1,400 cm2 / g.

[0049] [Table 2]

[0050] [Experimental Example 3] Each test was carried out in the same manner as in Experimental Example 2, except that the blast-furnace slag content in the blast-furnace slag cement was changed using the blast-furnace slag cement accelerator prepared in the same manner as in Experimental Example 2. The results are shown in Table 3.

[0051] [Table 3] [Industrial Applicability]

[0052] The quick-setting admixture for blast-furnace cement of the present invention can be suitably used for cement concrete to be sprayed onto exposed natural ground surfaces such as tunnels for roads, railways, and waterways, and slopes.

Claims

1. A quick-setting admixture for blast furnace cement, comprising 40 to 70 parts by mass of calcium aluminate and 2.5 to 40 parts by mass of an alkali metal salt.

2. 2. The quick-setting admixture for blast furnace cement according to claim 1, comprising a combination of material A containing the calcium aluminate and material B containing the alkali metal salt.

3. 3. The quick-setting admixture for blast furnace cement according to claim 1, wherein the alkali metal salt is one or more selected from the group consisting of sodium carbonate, potassium carbonate, and sodium sulfate.

4. The quick-setting admixture for blast furnace cement according to claim 2, wherein the material B is a slurry containing water.

5. The quick-setting admixture for blast furnace cement according to claim 4, wherein the pH of the B material is 6 or more.

6. A spraying material comprising the quick-setting admixture for blast-furnace slag cement according to claim 1 or 2 and blast-furnace slag cement.

7. The spraying material according to claim 6, wherein the amount of blast furnace slag in the blast furnace cement is 30 to 90 mass%.

8. A sprayed concrete comprising the spraying material according to claim 6.

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