Ground improvement material slurry, ground improvement material cured product, and ground improvement method

Abstract

A ground improvement material slurry, which is a ground improvement material slurry containing calcium aluminate, gypsum, and cement in water or an aqueous solution, the calcium aluminate having a glassification rate of 70% or more, a CaO / Al2O3 molar ratio of 1.0 to 2.7, and an impurity content of 15% by mass or less, the total amount of chlorine contained in the aforementioned calcium aluminate and the aforementioned gypsum and the aforementioned cement being 20 ppm to 2000 ppm, and the oxidation-reduction potential of the aforementioned ground improvement material slurry being -0.4 to 0.1 V.

Description

TECHNICAL FIELD

[0001] The present application relates to a ground improvement material slurry, a ground improvement material cured product, and a ground improvement method. BACKGROUND

[0002] As one of the ground improvement methods, a grout injection method of injecting a curing agent into a ground is known. In addition, various ground injection materials for this method are known. The grout injection method using a ground injection material is different from a method of using a high-pressure jet to disturb a ground while improving the ground, such as a high-pressure jet grouting method, and has advantages such as being able to improve the ground while disturbing the ground as little as possible, and compact equipment. Therefore, there are many practical benefits.

[0003] Until now, various ground injection materials have been known. For example, a technique of mixing a specific 2-liquid (one of the 2-liquids contains cement) as a mixture, and injecting the mixture into a ground as a ground injection material is known.

[0004] As one example, a 2-liquid type ground injection agent of a rapid hardening material slurry and a cement slurry is described in Patent Literature 1. Here, the rapid hardening agent slurry contains calcium aluminate, gypsum, a carbonate of an alkali metal, sodium aluminate, a retarder, and water, the calcium aluminate contains Si02and MgO as chemical components, the contained molar ratio of Al203and MgO (Al203 / MgO) is 17 to 60, and the contained molar ratio of Si02and MgO (Si02 / MgO) is 2.0 to 7.5. In addition, the cement slurry contains cement and water.

[0005] As another example, mixing an aqueous slurry A and an aqueous slurry B as a ground injection material is described in Patent Literature 2. Here, the aqueous slurry A contains 100 parts by mass of calcium aluminate, 20 to 300 parts by mass of gypsum, 0.5 to 15 parts by mass of one or more selected from the group consisting of a carbonate, a hydrogen carbonate, or a sulfate of an alkali metal, 0.5 to 15 parts by mass of sodium aluminate, and 0.1 to 10 parts by mass of a retarder. In addition, the aqueous slurry B contains 100 to 2200 parts by mass of cement with respect to 100 parts by mass of the calcium aluminate in the aqueous slurry A.

[0006] For the 2-liquid type ground injection material described in the above-described patent literatures, it is generally intentionally designed so that each liquid has sufficient fluidity before the 2-liquids are mixed, and so that curing is rapidly performed after the 2-liquids are mixed. Therefore, in the 2-liquid type ground injection material, the liquid of at least one of the 2-liquids is generally easily gelled or cured in a relatively short time before being mixed with the liquid of the other.

[0007] In this regard, Patent Literature 3 describes a ground injection material that can exhibit a ground improvement effect immediately after ground injection and ensure a sufficient pot life before ground injection, and provides a novel 2-liquid type ground injection material that includes an A liquid, which is a mixed slurry of a powder material A containing calcium aluminate and a carboxylate and water, and a B liquid, which is a mixed slurry of a powder material B containing cement and water, wherein the A liquid and the B liquid are mixed, and a gel time measured by a specific procedure is 1 second or more and 30 seconds or less. However, none of these patents describes a ground improvement material having a rust-preventing effect on a metal member such as a reinforced concrete, a rock bolt, or the like, which requires durability for a tunnel structure.

[0008] Prior Art Documents

[0009] Patent Literature

[0010] Patent Literature 1: Japanese Patent Application Publication No. 2017-154948

[0011] Patent Literature 2: Japanese Patent Application Publication No. 2014-109012

[0012] Patent Literature 3: WO 2020 / 121738 SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] As a result of research by the inventors of the present application, it was found that the ground improvement material described in Patent Literature 3 above has room for improvement in terms of being able to improve good permeability and initial strength enhancement in balance and impart a rust-preventing effect on a metal member present in a ground.

[0015] Therefore, an object of the present application is to provide a ground improvement material slurry that exhibits good permeability when injected into a ground, can achieve a good initial strength enhancement effect, and can impart a rust-preventing effect on a metal member present in a ground.

[0016] MEANS FOR SOLVING THE PROBLEMS

[0017] As a result of intensive research by the inventors of the present application, it was found that a ground improvement material slurry containing a specific calcium aluminate, gypsum, and cement, and exhibiting a specific chlorine content and a specific oxidation-reduction potential can exhibit good permeability and an initial strength enhancement effect, and can impart a rust-preventing effect on a metal member, thereby completing the present application.

[0018] That is, the gist of the present application is as follows.

[0019] [1] A ground improvement material slurry, which is a ground improvement material slurry containing calcium aluminate, gypsum, and cement in water, the calcium aluminate having a glass transition rate of 70% or more, a CaO / Al203molar ratio of 1.0 to 2.7, and an impurity content of 15% by mass or less, wherein the total amount of chlorine contained in the calcium aluminate and the gypsum and the cement is 20 ppm to 2000 ppm, and the oxidation-reduction potential of the ground improvement material slurry is -0.4 to 0.1 V.

[0020] [2] The ground improvement material slurry as claimed in [1], further comprising a coagulation accelerator.

[0021] [3] The ground improvement material slurry as claimed in [1] or [2], further comprising alum.

[0022] [4] The ground improvement material slurry as claimed in any one of [1] to [3], further comprising an additive, the additive being at least one selected from the group consisting of a sulfate other than gypsum, a sulfite, and a thiosulfate.

[0023] [5] The ground improvement material slurry as claimed in [4], wherein the sulfate is at least one selected from the group consisting of ferrous sulfate and ferric sulfate, the thiosulfate is at least one selected from the group consisting of sodium thiosulfate and calcium thiosulfate, and the sulfite is at least one selected from the group consisting of sodium sulfite and calcium sulfite.

[0024] [6] The ground improvement material slurry as claimed in [4] or [5], wherein the thiosulfate, the sulfite, and boron are contained in the additive, and when the content of the thiosulfate in the additive is set to X (% by mass) and the content of the sulfite is set to Y (% by mass), X and Y satisfy 10 ≤ X / Y ≤ 100.

[0025] [7] The ground improvement material slurry as claimed in [6], wherein the content of the boron is 0.01 mg / L or more and 5.0 mg / L or less as measured in accordance with JIS K 0102.

[0026] [8] A ground improvement material cured product, which comprises a cured product of the ground improvement material slurry as claimed in any one of [1] to [7].

[0027] [9] A ground improvement method, wherein a ground is improved by the ground improvement material slurry as claimed in any one of [1] to [7].

[0028] Effects of the Invention

[0029] According to the present application, it is possible to provide a ground improvement material slurry which exhibits good permeability at the time of injection into a ground, which can obtain an initial strength improvement effect well, and which can impart a rust-preventing effect to a metal member present in the ground. DETAILED DESCRIPTION

[0030] Hereinafter, the embodiments of the present application will be described in detail.

[0031] In the present specification, for a value which can vary depending on a temperature condition, unless otherwise specified, the value under the condition of 20°C is adopted.

[0032] The ground improvement material slurry of the present embodiment contains calcium aluminate, gypsum, and cement in water. It is preferable to further contain a setting regulator or the like. It is more preferable to further contain alum or the like. It is further more preferable to contain an additive. Hereinafter, the components, properties, and the like of the ground improvement material slurry will be described.

[0033] • Calcium Aluminate

[0034] The so-called calcium aluminate, in the technical field of hydraulic materials, refers to a general term of a substance which contains aluminum oxide (Al203) and calcium oxide (CaO) as main components, and which has hydration activity. Here, the "main components" means that the total content of aluminum oxide and calcium oxide in the calcium aluminate as a whole is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0035] For the calcium aluminate, typically, aluminum oxide and calcium oxide (and, depending on the case, silicon dioxide (Si02) or the like) are mixed as a mixture, the mixture is subjected to firing and / or melting, and then cooled to obtain. For the firing and melting, a rotary kiln, an electric furnace, or the like can be used. As the CaO raw material, for example, limestone, a calcium carbonate such as a shell, calcium hydroxide such as slaked lime, and calcium oxide such as quicklime can be cited. As the Al203raw material, for example, industrial by-products such as bauxite and aluminum residue, and aluminum powder can be cited.

[0036] As the calcium aluminate, either of crystalline and amorphous can be used. From the viewpoint of further improving the solidification property after injection into a ground, amorphous calcium aluminate, such as amorphous calcium aluminate manufactured by quenching after melting, is preferable.

[0037] The CaO / Al203molar ratio in the calcium aluminate is preferably 1.0 to 2.7, and more preferably 1.7 to 2.5. By appropriately adjusting the molar ratio, it is possible to improve the initial strength of the cured product, and in addition, it is possible to obtain a ground improvement effect at an earlier stage.

[0038] The content of impurities (components other than CaO and Al2O3) in the calcium aluminate is preferably 15% by mass or less, more preferably 10% by mass or less. By making the impurities 15% by mass or less, the initial strength of the cured product can be improved, and the ground improvement effect can be obtained earlier. Here, as the impurities, silicon oxide, magnesium oxide, sulfur oxide, and the like can be typically given. In addition, as the impurities, organic substances, alkali metal oxides, alkaline earth metal oxides, titanium oxide, iron oxide, alkali metal halides, alkaline earth metal halides, alkali metal sulfates, products in which these are substituted or solid-solved in part of CaO or Al2O3, and the like can be given. Of course, the impurities are not limited to these.

[0039] The content of impurities in the calcium aluminate can be determined by fluorescence X-ray analysis.

[0040] In terms of reactivity, the glassification rate of the calcium aluminate is preferably 70% or more, more preferably 90% or more. By making this value appropriate, the ground improvement effect can be obtained earlier. For the glassification rate, for a measurement sample, the main peak area S of a crystalline mineral is determined in advance using powder X-ray diffraction, and then, after heating at 1000°C for 2 hours, the main peak area S0 of the crystalline mineral after heating is determined using powder X-ray diffraction at a slow cooling rate of (1 to 10°C) / minute, and using these values of S0 and S, the glassification rate χ is calculated using the following formula.

[0041] Glassification rate χ (%) = 100 x (1 - S / S0)

[0042] In terms of initial strength development, for the particle size of the calcium aluminate, the Blaine specific surface area value (JIS R 5201) is preferably 3000 cm 2 / g or more, more preferably 5000 cm 2 / g or more. The upper limit is, for example, 9000 cm 2 / g or less. By making this value moderately large, the initial strength of the cured product can be improved, and the ground improvement effect can be obtained earlier.

[0043] As a specific example of the calcium aluminate, alumina cement can be given. That is, as a calcium aluminate raw material, commercially available alumina cement or the like can be used.

[0044] As a specific example of the alumina cement, alumina cement No. 1, alumina cement No. 2, and the like can be given. These can be purchased from Denka Corporation, AGC Inc.

[0045] The ground improvement material slurry can contain only one calcium aluminate, or two or more calcium aluminates that differ in properties. The amount of calcium aluminate in the powder of the ground improvement material slurry is, for example, 5% by mass or more and 80% by mass or less, preferably 10% by mass or more and 75% by mass or less, and more preferably 15% by mass or more and 70% by mass or less. By appropriately adjusting the amount of calcium aluminate, the balance between the speed of curing and the initial strength, and the like, are good. In addition, the early ground improvement effect is easily obtained further.

[0046] • gypsum

[0047] The ground improvement material slurry is designed to have a long pot life by containing gypsum, and the operability is improved.

[0048] The gypsum that can be used is not particularly limited. In addition, different types of gypsum can be used in combination. As examples of gypsum, hemihydrate gypsum and anhydrous gypsum can be given. In terms of strength development, anhydrous gypsum is preferred. As anhydrous gypsum, more specifically, hydrogen fluoride by-product anhydrous gypsum and natural anhydrous gypsum can be given.

[0049] From the viewpoint of initial strength development, the particle size of the gypsum is preferably 3000 cm 2 / g or more, and more preferably 5000 cm 2 / g or more. In addition, from the viewpoint of further long pot life, the value is preferably 30000 cm 2 / g or less, and more preferably 20000 cm 2 / g or less.

[0050] The amount of gypsum in the ground improvement material slurry is 5% by mass or more and 80% by mass or less, preferably 10% by mass or more and 75% by mass or less, and more preferably 15% by mass or more and 70% by mass or less. As another viewpoint, in the ground improvement material slurry, the amount of gypsum relative to calcium aluminate is preferably 50% by mass or more and 250% by mass or less, and more preferably 70% by mass or more and 200% by mass or less, relative to 100% by mass of calcium aluminate. By moderately increasing the amount of gypsum, a long pot life can be obtained. In addition, by moderately reducing the amount of gypsum, the initial strength of the cured product can be improved. That is, the ground improvement effect is easily obtained earlier.

[0051] • cement

[0052] The cement that can be used is not particularly limited. Specifically, various Portland cements such as ordinary, early-strength, ultra-early-strength, low-heat, and moderate-heat cements, various blended cements obtained by mixing blast furnace slag, fly ash, or silica in these Portland cements, filler cements obtained by mixing limestone powder, gypsum, blast furnace slow-cooling slag fine powder, and the like, and Portland cements manufactured using municipal waste incineration ash, sewage sludge incineration ash as raw materials, and the like, as well as commercially available cement-based solidification materials, commercially available microparticle cements, and the like (note that high-alumina cement, which is calcium aluminate, is preferably excluded from the cement here) can be mentioned.

[0053] Various cements and various blended cements can be used after being micronized. In addition, cements prepared by increasing or decreasing the amount of components (for example, gypsum and the like) used in ordinary cements can be used. The cement can be used alone or in combination with two or more kinds. Among them, blast furnace cement is preferred because of its low content of hexavalent chromium.

[0054] The amount of the cement in the ground improvement material slurry is 10% by mass or more and 60% by mass or less, preferably 15% by mass or more and 40% by mass or less, and more preferably 20% by mass or more and 35% by mass or less.

[0055] • Coagulation accelerator

[0056] A coagulation accelerator can also be included for the purpose of adjustment of the pot life, adjustment of the solidification property, and the like. Note that the coagulation accelerator can be included in advance, or can be added at the time of preparation, in particular.

[0057] As the coagulation accelerator, aluminates such as sodium aluminate and potassium aluminate, carbonates such as sodium carbonate and potassium carbonate, oxycarboxylic acids or salts thereof, hydroxides such as sodium hydroxide and potassium hydroxide, aluminum sulfate, iron (III) sulfate, silicates such as sodium silicate and potassium silicate, phosphates such as sodium phosphate, calcium phosphate, and magnesium phosphate, borates such as lithium borate and sodium borate, and the like, and sugars and the like can be mentioned.

[0058] A commercially available product can also be used as the coagulation accelerator. As the commercially available product, for example, Denka Setter D-100, D-300, and the like manufactured by Denka Co., Ltd. can be mentioned.

[0059] In the case where the ground improvement material slurry contains a coagulation adjusting agent, the amount thereof is only required to be appropriately adjusted based on the desired pot life, solidification property, and the like. Specifically, the amount of the coagulation adjusting agent is preferably used so as to be 0.0005 mass% or more and 2 mass% or less, more preferably 0.001 mass% or more and 1.5 mass% or less, and even more preferably 0.002 mass% or more and 1 mass% or less, in the total components of the ground improvement material slurry other than water. That is, in the case where the coagulation adjusting agent is contained in advance, the amount of the coagulation adjusting agent with respect to the total ground improvement material slurry is preferably the above-described degree. In addition, in the case where the coagulation adjusting agent is prepared separately, the amount of the coagulation adjusting agent in the total of the ground improvement material slurry and the coagulation adjusting agent is preferably the above-described degree.

[0060] • alum

[0061] The ground improvement material slurry preferably contains alum. The inventors of the present application have found that, by containing alum, it is possible to accelerate solidification even more. Also, it is possible to obtain the ground improvement effect even earlier.

[0062] The alum that can be used is not particularly limited. For example, various alums such as potassium alum, chrome alum, and iron alum can be given. In addition, alunite can also be given. Here, alunite refers to a natural substance in the component range of [(K, Na) (Al, Fe) 3 (SO4) 2 (OH) 6]. Also, unground alunite powder obtained by pulverizing alunite, calcined alunite powder obtained by calcining alunite at a temperature of 800°C or lower and pulverizing it, and the like can also be used. As the alum, it is preferable to use commonly commercially available potassium alum and calcined alunite powder. In addition, there are alums that contain anhydrous salts and crystal water, but all of them can be used as they are.

[0063] The amount of alum in the ground improvement material slurry is, for example, 0.3 parts by mass or more and 10 parts by mass or less, and preferably 0.5 parts by mass or more and 5 parts by mass or less, with respect to 100 parts by mass of cement. By moderately using a large amount of alum, it is possible to accelerate solidification even more. In addition, by moderately using a small amount of alum, it is possible to suppress unintended changes over time (for example, reduction in flowability, solidification), and the like.

[0064] • additive

[0065] The additive is at least one selected from the group consisting of sulfates other than gypsum, sulfites, and thiosulfates. The amount of the additive (total amount in the case where there are a plurality of kinds) in the ground improvement material slurry is 0.0001 mass% or more and 10 mass% or less, preferably 0.001 mass% or more and 8 mass% or less, and more preferably 0.01 mass% or more and 5 mass% or less.

[0066] The additive can be composed of a liquid composition containing a sulfate other than gypsum.

[0067] Further, the additive can be composed of a liquid composition containing a thiosulfate, a sulfite, and boron. Thereby, dispersibility in cement can be improved. The liquid additive can be composed of an aqueous solution containing these components and water.

[0068] The solid component concentration of the liquid additive can be appropriately changed according to the purpose. The lower limit of the solid component concentration of the additive is, for example, 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more. Thereby, the effect of the additive can be sufficiently obtained. On the other hand, the upper limit of the solid component concentration of the additive is, for example, 60% by mass or less, preferably 50% by mass or less, and more preferably 45% by mass or less. Thereby, the liquid stability of the additive can be improved.

[0069] The sulfate can contain at least one selected from the group consisting of ferrous sulfate and iron sulfate. These can be used alone or in combination of two or more. Thereby, rusting of the reinforcing bar can be suppressed, and bleeding of the cured body is reduced.

[0070] The thiosulfate can contain at least one selected from the group consisting of sodium thiosulfate and calcium thiosulfate. These can be used alone or in combination of two or more. Thereby, rusting of the reinforcing bar can be suppressed, and bleeding of the cured body is reduced.

[0071] As the sulfite, at least one selected from the group consisting of sodium sulfite and calcium sulfite can be contained. These can be used alone or in combination of two or more. Thereby, bleeding of the cured body is reduced.

[0072] The additive contains a thiosulfate and a sulfite and boron, and the content of the thiosulfate in the additive is set to X (% by mass), and the content of the sulfite is set to Y (% by mass). In the additive, X and Y can be, for example, composed so as to satisfy 10 ≤ X / Y ≤ 100, preferably so as to satisfy 15 ≤ X / Y ≤ 70, and more preferably so as to satisfy 20 ≤ X / Y ≤ 50. By being within the above range, a balance between rusting suppression of the reinforcing bar and bleeding rate reduction can be achieved.

[0073] One of the methods of measuring the content of the sulfite and the thiosulfate in the additive is as follows.

[0074] (1) First, 10 ml of a sample containing the additive is moved into a volumetric flask using a pipette, water is added so that the total amount becomes 500 ml, and they are mixed while being sealed to obtain a mixture.

[0075] (2) Then, about 100 ml of water was added to a 300-ml conical beaker, and 20 ml of the mixture of (1) was added using a pipette to obtain a sample. Two samples of this were prepared.

[0076] (3) To one of the samples of (2), 5 ml of 20% acetic acid was added and mixed.

[0077] (4) To the other sample of (2), 5 ml of 20% acetic acid and 5 ml of 37% formalin were added and mixed, and left to stand for 2 to 3 minutes.

[0078] (5) The sample of (3) was titrated with N / 10 iodine solution using a starch solution as an indicator, and the amount added was set as A ml. Similarly, the sample of (4) was titrated, and the amount added was set as B ml.

[0079] (6) The content of sulfite, thiosulfate in the additive was calculated based on the following formula.

[0080] • Na2S203: w / w% = B x f x 3.953 ÷ specific gravity

[0081] • Na2SO3: w / w% = (A - B) x f x 1.576 ÷ specific gravity

[0082] • f: factor of N / 10 iodine solution

[0083] The lower limit of the content of boron in the additive is, for example, 0.01 mg / L or more, preferably 0.05 mg / L or more, and more preferably 0.1 mg / L or more. Thereby, it is possible to improve the initial strength and reduce bleeding. On the other hand, the upper limit of the content of boron is, for example, 5.0 mg / L or less, preferably 3.0 mg / L or less, and more preferably 1.0 mg / L or less. Thereby, it is possible to reduce the environmental load.

[0084] The content of boron can be measured by ICP emission spectrometry according to JIS K 0102.

[0085] In the present embodiment, for example, the content of sulfite in the additive, X / Y, and the content of boron can be controlled by appropriately selecting the kind, the blending amount, the preparation method of the additive, and the like of each component included in the additive. Among them, for example, it is possible to cite adding sulfite as a source of sulfite ions, and appropriately adding water and the like as elements for setting the content of sulfite in the additive, X / Y, and the content of boron to desired numerical ranges.

[0086] • Water

[0087] As described above, the ground improvement material slurry is a slurry-like substance obtained by mixing calcium aluminate, gypsum, and cement with water and, as necessary, additives and the like. The amount of water when mixing calcium aluminate, gypsum, and cement with water as the ground improvement material slurry can be appropriately adjusted depending on the desired fluidity, pumpability, injectability into the ground, and the like. The amount of water in the entire ground improvement material slurry can be adjusted, for example, so as to be 10 mass% or more and 95 mass% or less, and preferably so as to be 50 mass% or more and 90 mass% or less.

[0088] Note that the solid component concentration of the ground improvement material slurry is 10 mass% or more and 80 mass% or less, preferably 15 mass% or more and 50 mass% or less, and more preferably 20 mass% or more and 40 mass% or less.

[0089] • Method for producing ground improvement material slurry

[0090] The method for producing the ground improvement material slurry is not particularly limited. It is only necessary to mix calcium aluminate, gypsum, and cement with water to produce the ground improvement material slurry. Note that, in the case where the ground improvement material slurry contains a set-controlling agent, it is preferable to obtain the ground improvement material slurry in the order of first putting the set-controlling agent into water and then putting the other components into water, from the viewpoint of production stability, prevention of unintended setting, and gelation, and the like. In addition, in the case of using alum, it is possible to include alum in the powder component (solid component) of the ground improvement material slurry in advance, or to add alum as another material at the time of production. In addition, in the case of using an additive, it is preferable to obtain the ground improvement material slurry in the order of first putting the additive into water and then putting the other components into water. At the time of mixing, various kinds of stirrers and the like known in the technical field can be used.

[0091] Note that the ground improvement material slurry can contain other components than calcium aluminate, gypsum, cement, water, a set-controlling agent, alum, a sulfate, a thiosulfate, a sulfite, and boron, within a range that does not excessively reduce the effects of the present application. As the "other components", for example, carbonates, heavy metal carbonates, calcium hydroxide, magnesium hydroxide, alkali hydroxides, and the like can be given.

[0092] In the present application, it is found that the chlorine content of calcium aluminate, gypsum, and cement contained in the ground improvement material slurry affects the strength (initial good strength improvement effect) and permeability, and rust prevention effect. That is, the amount of chlorine contained in the ground improvement material slurry is preferably 20 to 2000 ppm, more preferably 50 to 1500 ppm, further preferably 90 to 1000 ppm, and still further preferably 90 to 500 ppm. The amount of chlorine contained in the ground improvement material slurry can be adjusted, for example, by adding a mixture containing chlorine when the ground improvement material slurry is prepared. In addition, the amount of chlorine can be measured using the method described in the examples below. If the amount of chlorine contained in the ground improvement material slurry is less than 20 ppm, the strength of the ground improvement material slurry decreases (particularly, the initial strength improvement effect is not obtained), and there is a possibility of promoting rust. In the case where the amount of chlorine is greater than 2000 ppm, there is also a possibility of promoting rust. In addition, there is a possibility of reducing permeability.

[0093] Also, from the viewpoint of contributing to good permeability in the ground improvement material slurry and preventing rusting of the reinforcing steel, the oxidation-reduction potential of the ground improvement material slurry is preferably -0.4 to 0.1 V, and more preferably -0.3 to -0.1 V. The oxidation-reduction potential can be measured by using an oxidation-reduction potential (ORP) meter. Also, for the oxidation-reduction potential to be -0.4 to 0.1 V, the slurry can be adjusted by bubbling oxygen or the like. If the oxidation-reduction potential is less than -0.4 V or greater than 0.1 V, a stable oxidation film cannot be formed on the surface of the reinforcing steel, there is a possibility of promoting rust and not being able to prevent rusting of the reinforcing steel. In addition, there is a possibility of reducing permeability.

[0094] The ground improvement material slurry can be obtained as a cured product. That is, a ground improvement material cured product containing the cured product of the above-described ground improvement material slurry of the present application can be obtained. Thereby, the ground can be improved. In addition, by the above-described ground improvement material slurry of the present application, a ground improvement method for improving the ground can be provided.

[0095] As described above, the ground improvement material slurry can be a 1 liquid type, and for example, can also be a 2 liquid type. In the case of a 2 liquid type, for example, two liquids, an A material containing calcium aluminate and gypsum in water or an aqueous solution, and a B material containing cement in water or an aqueous solution, can be prepared separately, and by mixing, a ground improvement material slurry can be obtained.

[0096] In the case of the 2-liquid type, more specifically, a 2-liquid type ground improvement material slurry is combined from an A material and a B material, the A material contains calcium aluminate and gypsum in water or an aqueous solution, the glass transition rate of the calcium aluminate is 70% or more, the CaO / Al203molar ratio is 1.0 to 2.7, and the impurity content is 15% by mass or less, the B material contains cement in water or an aqueous solution, the total amount of chlorine contained in the calcium aluminate and the gypsum and the cement is 20 ppm to 2000 ppm, and the oxidation-reduction potential of the ground improvement material slurry when the A material and the B material are mixed is -0.4 to 0.1 V.

[0097] The method of mixing the A material and the B material and the specific steps of improving the ground by the A material and the B material are not particularly limited and various methods known in the technical field of ground improvement can be applied. For example, (i) a so-called 2-shot method in which the A material and the B material are mixed and injected into the ground at the front end portion using a double pipe, (ii) a so-called 1.5-shot method in which the A material and the B material are mixed on the way from the injection pump to the injection pipe and injected, (iii) a 1-shot method in which the A material and the B material are mixed in a mixing tank such as a stirrer, and the like can be adopted. In implementing these methods, known injection pumps and the like can be used.

[0098] In other words, it can be (1) the A material and the B material are mixed before being injected into the ground as a mixture, the mixture is injected into the ground, or it can also be (2) the A material and the B material are separately pressure-fed, and mixed in the ground at the moment of injection into the ground or after injection into the ground.

[0099] The mixing ratio of the A material and the B material can be appropriately adjusted depending on the desired curing speed, pressure-feedability, and the like. For the mixing ratio of the A material : B material, typically, 20 : 80 to 80 : 20, and preferably around 30 : 70 to 70 : 30 by volume.

[0100] Note that in the case of the 1-liquid type, it is directly injected into the ground by a known method.

[0101] The above describes the embodiments of the present application, but these are examples of the present application and various configurations other than the above can be adopted. In addition, the present application is not limited to the above-described embodiments and modifications and the like within the scope of achieving the object of the present application are included in the present application.

[0102] Example

[0103] The embodiments of the present application are described in detail based on the examples and comparative examples. Note that the present application is not limited to the examples.

[0104] "Experimental Example 1"

[0105] (Preparation of ground improvement material slurry)

[0106] First, calcium aluminate, gypsum, cement, and potassium alum were mixed using a ProShear mixer (Model WB, manufactured by Pacific Machine Works Co., Ltd.). Then, a coagulation accelerator (Denka Setter D-100, manufactured by Denka Co., Ltd.) and the above mixture were sequentially added to water, and the mixture was sufficiently kneaded to obtain a ground improvement material slurry. The amounts of the respective components in the ground improvement material slurry are shown in Table 1. The chlorine content was determined for the calcium aluminate, gypsum, and cement, and the remainder was adjusted by adding a chlorine-containing admixture (material name: sodium chloride) at the time of mixing the powders. The ORP of the prepared ground improvement material slurry was adjusted by bubbling oxygen.

[0107] As the gypsum, natural anhydrite was used, which had a Blaine specific surface area value of 5000 cm 2 / g.

[0108] As the cement, ordinary Portland cement (manufactured by Denka Co., Ltd.) was used in Experiments No. 1-1 to 1-5, 1-7 to 1-12, and 1-14, and in Experiments No. 1-6 and 1-13, a trial cement was used (a cement prepared using a cement plant's blended raw material and various commercially available pure chemicals in the adjustment of chemical components, and using pure anhydrite for the adjustment of the SO3 amount, which had a chlorine content of 1.5 ppm and a Blaine value of 3,450 cm 2 / g).

[0109] In addition, as the calcium aluminate, calcium carbonate and alumina were used as raw materials. By changing the CaO / Al203molar ratio, melting at 1650°C, and adjusting the cooling rate, calcium aluminate having the vitrification rates shown in Table 1 was prepared. The Blaine specific surface area value was 5000 to 6000 cm 2 / g. In Experiments No. 1-5 and 1-12, silica sand, magnesium oxide, and sulfur oxide were added so as to have the amounts shown in Table 1, and then fired.

[0110] As the impurities of the calcium aluminate, silicon oxide, magnesium oxide, and sulfur oxide were determined by fluorescence X-ray analysis, and the total amount thereof (impurity content) was calculated.

[0111] (Initial strength)

[0112] The strength was determined in accordance with JIS R 5201. Specifically, using the composition of the ground improvement material slurry, a test body having a length of 4 cm, a width of 4 cm, and a height of 16 cm was prepared, and the compressive strength was determined after 30 minutes, 1 hour, and 1 day from the preparation of the ground improvement material slurry.

[0113] Then, the increase rate of the initial strength during the period from the age of 1 hour to the age of 1 day is calculated from the following formula 1. [Formula 1] Increase rate of compressive strength (times) = (compressive strength at the age of 1 day - compressive strength at the age of 1 hour) / compressive strength at the age of 1 hour

[0114] (Measurement of penetration length)

[0115] A vinyl bag of 5 cm in diameter is filled with sand for penetration length measurement to a depth of 20 cm, and 200 ml of the slurry of the ground improvement material just prepared is injected from the upper surface and allowed to naturally penetrate, and the penetration length is measured. Note that the penetration length is preferably 20 cm or more. As the sand for measurement, a mixture (particle size adjusted product) of Kikugawa sand and mined lime sand manufactured by Denka Corporation is used.

[0116] (Chlorine concentration)

[0117] The chlorine concentration is measured in accordance with JIS R 5202 for calcium aluminate, gypsum, and cement, and the total amount of chlorine is calculated.

[0118] (Rusting rate of reinforcing steel)

[0119] A φ 19 mm round steel buried to a depth of 18 cm is filled with the ground improvement material slurry to a thickness of 10 mm, and after water curing at 20°C for 28 days, accelerated neutralization is performed for 12 weeks in an environment of 30°C, 60% relative humidity, and 5% carbon dioxide concentration. In addition, in the accelerated neutralization test, the test body is taken out every 3 weeks, and immersed in water for 1 day at 20°C to perform the accelerated neutralization test. After the test, the round steel is taken out, derusted with a 10% diammonium citrate solution, and the weight (m2) of the round steel after the test is measured, and the rusting rate of the reinforcing steel is calculated from the change in the weight (m1) of the round steel before the test by the following formula.

[0120] Rusting rate of reinforcing steel (%) = [(m1 - m2) / m1] x 100

[0121] The composition of the ground improvement material slurry, the above measurement / evaluation results, and the like are summarized in Tables 1 and 2.

[0122] [Table 1]

[0123]

[0124] [Table 2]

[0125]

[0126] For the ground improvement material slurry containing the specific calcium aluminate, gypsum, and cement, showing the specific chlorine content, and exhibiting the specific oxidation-reduction potential, both the permeability and the initial strength (e.g., 1 day strength) are good, and the rusting of the reinforcing steel present in the ground can also be inhibited. That is, it is confirmed that excellent performance as a ground injection material is exerted. Note that for Experiment Nos. 1-10, 1-12, 1-13, although the improvement rate of the initial strength is very high, the compression strength itself at the age of 1 day is very small, and thus it cannot be considered to be excellent.

[0127] "Experiment Example 2"

[0128] The ground improvement material slurry was prepared according to the formulation shown in Table 3. In the ground improvement material slurry, the additive was first mixed in water so as to be 0.002%, and otherwise, the chlorine amount was adjusted to 100 ppm, and the oxidation-reduction potential was adjusted to -0.1 V according to the same preparation method as in Experiment Example 1. As the calcium aluminate, a calcium aluminate having a glass transition rate of 97%, a CaO / Al203molar ratio of 2.2, and an impurity content of 2% was used.

[0129] (Permeation rate)

[0130] The permeation rate was measured according to JIS A 1123.

[0131] (Rusting rate of reinforcing steel)

[0132] The same test as in Experiment Example 1 was performed to measure the rusting rate of the reinforcing steel.

[0133] The composition of the ground improvement material slurry, the measurement, the evaluation results, and the like, which were the same as in Experiment Example 1, are summarized in Table 3.

[0134] [Table 3]

[0135]

[0136] The ground improvement material slurry containing the specific additive can reduce the permeation rate, and can also further inhibit the rusting of the reinforcing steel present in the ground. That is, it is confirmed that more excellent performance as a ground injection material is exerted.

[0137] Industrial applicability

[0138] According to the present application, a ground improvement material slurry capable of exerting good permeability and initial strength improvement effects, and imparting a rust-preventing effect to reinforcing steel present in a ground, can be appropriately used mainly in the field of civil engineering.

Claims

1. A foundation amendment slurry, comprising calcium aluminate, gypsum, and cement in water, wherein the calcium aluminate has a glass transition rate of ≥70%, a CaO / Al₂O₃ molar ratio of 1.0~2.7, and an impurity content of ≤15% by mass. The total amount of chlorine contained in the calcium aluminate, gypsum, and cement is 20ppm to 2000ppm, and the oxidation-reduction potential of the foundation improvement material slurry is -0.4 to 0.1V.

2. The foundation improvement material slurry as described in claim 1, further comprising a setting regulator.

3. The foundation improvement slurry as described in claim 1 or 2, further comprising alum.

4. The foundation improvement material slurry as described in claim 1 or 2, further comprising an additive, said additive being at least one selected from the group consisting of sulfates, sulfites and thiosulfates other than gypsum.

5. The foundation improvement material slurry as described in claim 4, wherein, The sulfate is selected from at least one of the groups consisting of ferrous sulfate and ferric sulfate, the thiosulfate is selected from at least one of the groups consisting of sodium thiosulfate and calcium thiosulfate, and the sulfite is selected from at least one of the groups consisting of sodium sulfite and calcium sulfite.

6. The foundation improvement material slurry as described in claim 4, wherein, The additive contains the thiosulfate, the sulfite, and boron, and when the content of the thiosulfate in the additive is set to X% by mass and the content of the sulfite by mass is set to Y%, X and Y satisfy 10≤X / Y≤100.

7. The foundation improvement slurry as described in claim 6, wherein, The boron content, as determined according to JIS K 0102, is 0.01 mg / L to 5.0 mg / L.

8. A solidified foundation amendment, comprising the solidified foundation amendment slurry according to any one of claims 1 to 7.

9. Foundation improvement methods, among which, The foundation is improved by using the foundation improvement material slurry according to any one of claims 1 to 7.

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