Quick-setting agent for pozzolanic material-containing cement, spray material, and sprayed concrete

Abstract

To provide a quick-setting agent for pozzolanic material-containing cement with superior strength development and quick-setting properties, capable of reducing the elution of hexavalent chromium.SOLUTION: A quick-setting agent for pozzolanic material-containing cement comprises 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 a pozzolanic substance-containing cement quick-setting admixture, 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 fly ash and silica fume 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, cement containing pozzolanic substances such as fly ash and silica fume has the problem that it is difficult to obtain sufficient strength. In addition, there is a concern that hexavalent chromium may be eluted 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 a pozzolanic substance-containing quick-setting admixture for cement that is excellent in strength development and quick-setting properties and can inhibit the elution of hexavalent chromium. [Means for solving the problem]

[0008] As a result of intensive research conducted by the present inventors in light of the above problems, they have found that a pozzolanic substance-containing quick-setting admixture for cement containing prescribed amounts of calcium aluminate and an alkali metal salt can solve the above problems, and have completed the present invention.

[0009] [1] A pozzolanic substance-containing cement quick-setting admixture 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 pozzolanic substance-containing quick-setting admixture for 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 pozzolan-containing quick-setting admixture for 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 pozzolanic substance-containing quick-setting admixture for cement according to any one of the above [1] to [3], further containing calcium hydroxide. [5] The pozzolanic substance-containing quick-setting admixture for cement according to any one of the above [2] to [4], wherein the material B is a slurry containing water. [6] The pozzolanic substance-containing quick-setting admixture for cement according to any one of the above [2] to [5], wherein material B has a pH of 6 or higher. [7] A spraying material comprising the pozzolanic substance-containing cement quick-setting admixture according to any one of the above [1] to [6] and pozzolanic substance-containing cement. [8] The spraying material according to [7] above, wherein the amount of the pozzolanic substance in the pozzolanic substance-containing cement is 30 to 90 mass %. [9] Shotcrete containing the spraying material described in [7] or [8] above. Effect of the Invention

[0010] According to the present invention, it is possible to provide a pozzolanic substance-containing quick-setting admixture for cement which is excellent in strength development and quick-setting properties and which can inhibit the elution of hexavalent chromium. 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] [Pozzolanic substance-containing cement accelerator] The quick-setting admixture for pozzolanic substance-containing cement according to this embodiment contains 40 to 70 parts by mass of calcium aluminate and 2.5 to 40 parts by mass of an alkali metal salt. The pozzolanic substance-containing cement in the present invention is a pozzolanic substance-containing cement obtained by mixing a pozzolanic substance such as volcanic ash or coal ash with silica cement as specified in JIS R 5212:2009 "Silica cement" or fly ash cement as specified in JIS R 5213:2009 "Fly ash cement", or ordinary Portland cement, and containing a pozzolanic substance in an amount equal to or greater than the amount specified in the above JIS.

[0013] The pozzolanic substance is a material containing a substance that exhibits a pozzolanic reaction with the hydration products of cement, and examples of such a material include fly ash, silica fume, metakaolin, volcanic ash, coal ash, diatomaceous earth, silica clay, tass, and zeolite.

[0014] The calcium aluminate contained in the pozzolanic substance-containing cement quick-setting admixture according to this embodiment is a general term for a compound which has CaO and Al2O3 as its main components and has hydration activity, and is a compound in which part of the 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 small amounts of these are dissolved in a substance mainly composed of CaO and Al2O3, and the calcium aluminate may be either crystalline or amorphous.

[0015] 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.

[0016] The pozzolanic substance-containing quick-setting admixture for cement according to the present embodiment contains 40 to 70 parts by mass of calcium aluminate. If the calcium aluminate content is less than 40 parts by mass, the strength development and quick-setting ability may not be sufficiently exhibited, and there is a risk of elution of hexavalent chromium. If the calcium aluminate content exceeds 70 parts by mass, the strength development and quick-setting ability may not be sufficiently exhibited. The calcium aluminate content is preferably 45 to 65 parts by mass, and more preferably 50 to 60 parts by mass. If the calcium aluminate content is within the above range, it is easy to achieve better strength development and quick-setting ability.

[0017] The CaO / Al2O3 molar ratio of calcium aluminate is not particularly limited, but from the viewpoints of 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.

[0018] 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.

[0019] 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.

[0020] 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".

[0021] The pozzolanic substance-containing quick-setting admixture for cement according to this embodiment contains 2.5 to 40 parts by mass of an alkali metal salt. If the content of the alkali metal salt is less than 2.5 parts by mass, the strength development may be insufficient, and if it exceeds 40 parts by mass, the strength development and quick-setting properties may be insufficient, and hexavalent chromium may be eluted. The content of the alkali metal salt is preferably 3 to 38 parts by mass, more preferably 5 to 35 parts by mass, and even more preferably 8 to 30 parts by mass.

[0022] From the viewpoint of short-term strength development, such as 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, from the viewpoint of suppressing elution of hexavalent chromium, it is more preferable that the alkali metal salt be sodium carbonate and / or sodium sulfate, and from the viewpoint of long-term strength development, it is even more preferable that the alkali metal salt be sodium carbonate.

[0023] The pozzolanic substance-containing quick-setting admixture for cement according to this embodiment preferably further contains calcium hydroxide. By further containing calcium hydroxide, it is easy to improve the strength development, and also to improve adhesion and suppress rebound. The content of calcium hydroxide is preferably 0.5 to 30 parts by mass, more preferably 1 to 25 parts by mass, and further preferably 3 to 20 parts by mass.

[0024] The pozzolanic substance-containing cement quick-setting admixture according to this 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 achieve better strength development and quick-setting properties. Moreover, 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.

[0025] The pozzolanic substance-containing cement quick-setting admixture may further contain an alkaline earth metal salt other than calcium hydroxide. The alkaline earth metal salt other than calcium hydroxide may include carbonates such as calcium carbonate and sulfates such as calcium sulfate. The content of the alkaline earth metal salt other than calcium hydroxide is not particularly limited, but from the viewpoint of long-term strength development and adhesion, it is preferably 3 to 50 mass%, more preferably 5 to 30 mass%.

[0026] The quick-setting admixture for pozzolanic substance-containing cement according to this embodiment preferably comprises a combination of material A containing calcium aluminate and material B containing an alkali metal salt. By comprising material A and material B in the quick-setting admixture for pozzolanic substance-containing cement, storage stability is improved, and when the amount of pozzolanic substance in the pozzolanic substance-containing cement fluctuates or when temperature conditions change, the addition rates of materials A and B can be increased or decreased to adjust the physical properties to suit the environmental conditions. Material A can contain calcium hydroxide, aluminum sulfate, etc. in addition to calcium aluminate, and material B can contain calcium hydroxide, etc. in addition to alkali metal salts.

[0027] 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.

[0028] 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.

[0029] 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 pozzolanic substance-containing cement as a quick-setting additive for pozzolanic substance-containing cement. As a feature of the slurry, material B has a solids concentration of preferably 1 to 50 mass%, more preferably 3 to 30 mass%. When the solids concentration is within the above range, it is easy to improve pumpability.

[0030] It is more preferable that the pH of material B is 6 or more. When the pH of material B is 6 or more, the amount of hexavalent chromium eluted is easily suppressed. The pH of material B can be measured using a pH meter.

[0031] [Spraying material] The spraying material according to the present embodiment contains the quick-setting admixture for pozzolanic substance-containing cement of the present invention and pozzolanic substance-containing cement. By containing the quick-setting admixture for pozzolanic substance-containing cement of the present invention and pozzolanic substance-containing cement, the spraying material has excellent strength development and quick-setting properties and can suppress elution of hexavalent chromium.

[0032] The content of the pozzolanic substance-containing quick-setting admixture for 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 the pozzolanic substance-containing cement. When the content of the pozzolanic substance-containing quick-setting admixture for cement is within the above range, it is easy to achieve excellent strength development and quick-setting properties, and it is easy to suppress the elution of hexavalent chromium.

[0033] The amount of the pozzolanic substance in the pozzolanic substance-containing cement is preferably 3 to 90 mass %, and more preferably 5 to 70 mass %. When the amount of the pozzolanic substance is within the above range, it is easy to suppress the elution of hexavalent chromium.

[0034] [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 immediately before spraying to prepare a quick-setting admixture for pozzolanic substance-containing cement, mixing the admixture with pozzolanic substance-containing cement, and spraying the mixture. The sprayed concrete has excellent strength development and quick-setting properties, and can suppress elution of hexavalent chromium.

[0035] The content of the spraying material in the shotcrete is preferably 10 to 30 mass%, more preferably 15 to 25 mass%. When the content of the spraying material is within the above range, it is easy to achieve excellent strength development and quick setting properties, and it is easy to suppress the elution of hexavalent chromium.

[0036] The water-cement ratio of the sprayed concrete is preferably 30 to 70%, more preferably 40 to 60%, based on the pozzolanic substance-containing cement in the sprayed material. By having the water-cement ratio within the above range, it is easy to achieve excellent strength development and quick setting, and it is easy to suppress the elution of hexavalent chromium.

[0037] 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.

[0038] The content of aggregate in the shotcrete is preferably 60 to 80 mass %, and more preferably 65 to 75 mass %. EXAMPLES

[0039] 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.

[0040] [Experimental Example 1] <Preparation of cement accelerator containing pozzolanic substance> A slurry (material B) was prepared by adding and mixing an alkali metal salt and calcium hydroxide in the ratios shown in Table 1 so that the total amount of the alkali metal salt and calcium hydroxide was 20 parts by mass per 100 parts by mass of water. The prepared slurry and calcium aluminate (material A) were mixed in the ratios of each component shown in Table 1 to prepare a pozzolanic substance-containing quick-setting admixture for cement. The prepared pozzolanic substance-containing quick-setting admixture for cement was immediately used in the preparation of the spraying material described below.

[0041] <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 salt: Sodium carbonate, purity 98%, industrial raw material, Blaine value 1,500 cm 2 / g. Calcium hydroxide: Industrial product, purity 98%, Blaine value 6,000.

[0042] <Preparation of spraying materials> A pozzolanic cement containing cement (fly ash content 50% by mass) was prepared by mixing 400g of ordinary Portland cement (manufactured by Denka) and 400g of fly ash (JIS II type) as a pozzolanic material, and then 2,000g of fine aggregate (river sand from the Himekawa River system in Niigata Prefecture) and water were added to give a water-cement ratio of 50% and kneaded. 10 parts by mass of the prepared quick-setting admixture for pozzolanic cement was added to 100 parts by mass of the pozzolanic cement to prepare a spraying material. The prepared spraying material was immediately used in the following tests.

[0043] <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 2The 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.

[0044] <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 28 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 28 days is an indicator of long-term strength.

[0045] <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.

[0046] [Table 1]

[0047] [Experimental Example 2] Except for using the alkali metal salts shown below as the alkali metal salts, pozzolanic substance-containing quick-setting admixtures for cement were prepared in the same manner as in Experimental Example 1, and tests were 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 cm 2 / g.

[0049] [Table 2]

[0050] [Experimental Example 3] Using a pozzolanic substance-containing cement quick-setting admixture prepared in the same manner as in Experimental Example 2, tests were carried out in the same manner as in Experimental Example 2, except that the pozzolanic substances in the pozzolanic substance-containing cement were changed in their amounts as shown below. The results are shown in Table 3.

[0051] <Pozzolanic substances> Fly ash: JIS type II product. Silica fume: JIS granular product. Metakaolin: Industrial product, calcined kaolin, SiO2 52%, Al2O3 43%, moisture 0.5%, pH 5.0.

[0052] [Table 3] [Industrial Applicability]

[0053] The pozzolanic substance-containing cement quick-setting admixture 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 pozzolan-containing cement quick-setting admixture containing 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 pozzolanic substance-containing cement quick-setting admixture according to claim 1, which comprises a combination of material A containing the calcium aluminate and material B containing the alkali metal salt.

3. 3. The pozzolanic substance-containing cement quick-setting admixture 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. 3. The pozzolanic substance-containing cement quick-setting admixture according to claim 1 or 2, further comprising calcium hydroxide.

5. 3. The pozzolanic substance-containing quick-setting admixture for cement according to claim 2, wherein the material B is a slurry containing water.

6. 6. The pozzolanic substance-containing quick-setting admixture for cement according to claim 5, wherein the pH of material B is 6 or higher.

7. A spraying material comprising the pozzolanic substance-containing cement quick-setting admixture according to claim 1 or 2 and pozzolanic substance-containing cement.

8. The spraying material according to claim 7, wherein the amount of the pozzolan substance in the pozzolan-containing cement is 30 to 90 mass %.

9. A sprayed concrete comprising the sprayed material according to claim 7.

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