Solidification material, solidified soil, and soil solidification method

Abstract

To provide a solidification material capable of temporarily increasing a foundation strength but suppressing it in the long term.SOLUTION: The solidification material contains a cement clinker in which a C3S content is 50 mass% or more, gypsum, and a CaCO3 content. The solidification material contains the cement clinker of 40 mass% or more and 75 mass% or less, the gypsum of 5 mass% or more and 20 mass% or less, and the CaCO3 content of 20 mass% or more and 50 mass% or less. Preferably, the plaster is made of at least one or more of the group consisting of anhydrous gypsum, dihydrate gypsum, hemihydrate gypsum, and recycled gypsum generated as a recycled product of a gypsum board. Preferably, the CaCO3 content is made of at least one or more of the group consisting of a limestone, and a product obtained by carbonizing a fine article or a crushed article generated during crushing of waste concrete.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solidification material and solidified soil obtained by solidification treatment using the solidification material. The present invention also relates to a soil solidification treatment method using the solidification material. [Background technology]

[0002] Adding solidification materials to soil is a widely used method for solidifying soil contained in soft ground. In ground improvement work using solidification materials, there are cases where it is desired to increase the ground strength over the long term, and cases where it is desired to temporarily increase the ground strength but suppress it over the long term, for example, to accommodate design changes or changes in use.

[0003] As a solidification material that can be used in the latter case, for example, Patent Document 1 proposes a solidification material containing ordinary Portland cement and fly ash. The document states that this solidification material can reduce the strength of ground that is 28 days old to an appropriate level.

[0004] Patent Document 2 proposes a solidification material containing a long-term strength suppressing material such as Portland cement or slag, and a fluidizing material such as fly ash. The document states that the long-term strength suppressing material and fluidizing material delay the hardening of Portland cement, thereby suppressing the increase in ground strength over the long term.

[0005] Patent Document 3 proposes a soil improvement material containing Portland cement, and states that the soil improvement material may contain admixtures such as fly ash and blast furnace slag powder, and that the addition of such admixtures can suppress an increase in ground strength over the long term. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2-34546 [Patent Document 2] Japanese Patent Application Publication No. 10-158049 [Patent Document 3] Japanese Patent Application Publication No. 11-35939 Summary of the Invention [Problem to be solved by the invention]

[0007] When soft ground is solidified, the strength of the ground generally tends to increase by 1.1 to 2.0 times from 7 to 28 days. Furthermore, the strength of the ground also tends to increase by a similar amount from 28 to 91 days, so there is a demand for continued suppression of the strength of the ground at 91 days. However, in Patent Documents 1 to 3, the ground strength was measured only up to 7 or 28 days, so it is unclear whether the ground strength is suppressed after that. Furthermore, there is a possibility that the ground strength will increase in the long term due to the pozzolanic reaction caused by fly ash. Therefore, an object of the present invention is to provide a solidification material that can temporarily increase ground strength but suppress it in the long term. [Means for solving the problem]

[0008] The present invention provides a solidification material containing cement clinker having a C3S content of 50% by mass or more, gypsum, and a CaCO3-containing material, The above problem is solved by providing a solidification material containing 40% by mass or more and 80% by mass or less of the cement clinker, 5% by mass or more and 20% by mass or less of the gypsum, and 20% by mass or more and 50% by mass or less of the CaCO3-containing material. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a solidification material that can temporarily increase ground strength while suppressing it in the long term. Furthermore, according to the present invention, it is possible to provide solidified soil that has been solidified using the solidification material. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments. The present invention relates to a cement-based solidification material. The solidification material of the present invention is used in a wide range of applications, such as solidification of general soft soils such as sandy soils and clayey soils, as well as muddy materials with high water content and organic matter-containing soils.

[0011] The inventors of the present invention have conducted extensive research into the formulation of a solidification material that can temporarily increase ground strength while suppressing it in the long term. As a result, they have surprisingly found that when the solidification material contains predetermined amounts of cement clinker, gypsum, and CaCO3-containing material, the above-mentioned problems can be solved extremely effectively. The solidifying material of the present invention contains all of the above-mentioned cement clinker, gypsum, and CaCO3-containing material. Each of these components will be explained below.

[0012] The solidifying material of the present invention preferably contains cement clinker as one of its materials. As the cement clinker, any cement clinker known in the art can be used without any particular limitation. For example, ordinary Portland cement clinker, high-early-strength Portland cement clinker, moderate-heat Portland cement clinker, low-heat Portland cement clinker, etc. can be used. As these cement clinkers, for example, those specified in JIS R5210:2019 can be used. These cement clinkers can be used alone or in combination of two or more types.

[0013] Cement clinker generally contains C3S, C2S, C3A and C4AF as typical mineral compositions. The respective contents of C3S, C2S, C3A and C4AF can be calculated by the Bogue formula. The Bogue formula is a widely used formula for calculating the content ratio of main minerals in cement clinker from the content ratio of chemical composition. By using the Bogue formula shown below, the contents of tricalcium silicate (3CaO·SiO2, denoted as C3S), dicalcium silicate (2CaO·SiO2, denoted as C2S), tricalcium aluminate (3CaO·Al2O3, denoted as C3A) and tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3, denoted as C4AF) in cement clinker can be calculated. The chemical formula represents the content ratio (mass %) of each compound shown by the chemical analysis value according to JIS R 5204:2019 "Fluorescent X-ray Analysis Method for Cement".

[0014] <Bogue formula> C3S [mass%] = (4.07 × CaO [mass%]) - (7.60 × SiO2 [mass%]) - (6.72 × Al2O3 [mass%]) - (1.43 × Fe2O [mass%]) - (2.85 × SO3 [mass%]) C2S [mass%] = (2.87 × SiO2 [mass%]) - (0.754 × C3S [mass%]) C3A [mass%] = (2.65 × Al2O3 [mass%]) - (1.69 × Fe2O3 [mass%]) C4AF [mass%] = 3.04 × Fe2O3 [mass%]

[0015] In the solidifying material of the present invention, it is preferable that the contents of C3S, C2S, C3A and C4AF in the cement clinker are respectively within a predetermined range. Since the minerals contributing to the expression of initial strength and long-term strength are different, by setting the content suitable for the expression of the target strength, a solidifying material that can temporarily increase the ground strength but can be suppressed in the long term can be obtained. Specifically, from the viewpoint of temporarily increasing the initial strength of the ground, the C3S content in the cement clinker is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more. From the viewpoint of making such an advantage more pronounced, the higher the C3S content in the cement clinker, the better, but it may be 75% by mass or less.

[0016] The C2S content in cement clinker is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of suppressing an increase in the long-term strength of the ground. From the viewpoint of making such advantages more pronounced, the lower the C2S content in cement clinker, the better, but it may be 0.1% by mass or more.

[0017] The C3A content in cement clinker is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more, from the viewpoint of temporarily increasing ground strength and suppressing it in the long term. Also, from the viewpoint of suppressing heat generation during solidification treatment, the C3A content in cement clinker is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0018] From the viewpoint of enhancing chemical resistance, the C4AF content in the cement clinker is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 6% by mass or more. Also, from the viewpoint of suppressing heat generation during solidification treatment, the C4AF content in the cement clinker is preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 9% by mass or less.

[0019] As the cement clinker having the above-mentioned composition, for example, ordinary Portland cement clinker and high-early-strength Portland cement clinker can be used. From the viewpoint of temporarily increasing the ground strength and suppressing it in the long term, it is preferable to use high-early-strength Portland cement clinker as the cement clinker. Alternatively, it is also preferable to use a combination of various cement clinkers so that the C3S content in the cement clinker is 50 mass% or more, from the viewpoint of temporarily increasing the ground strength and suppressing it in the long term.

[0020] The solidification material of the present invention preferably contains a predetermined amount of cement clinker. Specifically, from the viewpoint of temporarily increasing ground strength and suppressing it in the long term, the solidification material preferably contains 40% by mass or more of cement clinker, more preferably 45% by mass or more, and even more preferably 50% by mass or more. From the same viewpoint, the solidification material preferably contains 80% by mass or less of cement clinker, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less.

[0021] The solidifying material of the present invention preferably contains gypsum as one of its materials. As the gypsum, any gypsum known in the art can be used without any particular limitation. The gypsum may be a natural product or a synthetic product. As the gypsum, for example, anhydrous gypsum, dihydrate gypsum, hemihydrate gypsum, and recycled gypsum containing these can be used. Recycled gypsum refers to gypsum produced as a recycled product of gypsum board. These gypsums can be used alone or in combination of two or more types. From the viewpoint of temporarily increasing ground strength and suppressing it in the long term, it is preferable that the gypsum is composed of at least one selected from the group consisting of gypsum anhydride, gypsum dihydrate, and gypsum hemihydrate, and it is particularly preferable that the gypsum is composed of gypsum dihydrate.

[0022] The solidification material of the present invention preferably contains a predetermined amount of gypsum. Specifically, from the viewpoint of temporarily increasing ground strength and suppressing it in the long term, the solidification material preferably contains 5% by mass or more of gypsum, more preferably 8% by mass or more, and even more preferably 10% by mass or more. From the same viewpoint, the solidification material preferably contains 20% by mass or less of gypsum, more preferably 18% by mass or less, and even more preferably 15% by mass or less.

[0023] The solidifying material of the present invention preferably contains a CaCO3-containing material as one of its ingredients. The CaCO3-containing material may contain at least CaCO3, and various compounds can be used without particular limitations. The CaCO3-containing material may be a natural or synthetic product. Examples of the CaCO3-containing material include compositions and mixtures containing CaCO3, as well as CaCO3 itself. Examples of compositions or mixtures containing CaCO3 include limestone and carbonated fines and crushed materials generated during the crushing of waste concrete. These CaCO3-containing materials may be used alone or in combination. The term "limestone" as used herein encompasses limestone itself and pulverized limestone. Limestone itself and pulverized limestone can be distinguished by their respective average particle sizes. Specifically, the average particle size of limestone itself is preferably greater than 1000 μm and not greater than 1000 mm. The average particle size of pulverized limestone is preferably 0.01 μm or greater and not greater than 1000 μm. The "average particle size" in this specification can be determined by particle size measurement using sieving. As a specific method, for example, the sieving test method for aggregates in JIS A 1102:2014 can be used, and measurements can be made in the same manner as for sieving tests for fine aggregates. When the CaCO3-containing material is a composition or mixture containing CaCO3, the proportion of CaCO3 contained in the CaCO3-containing material is preferably 50 mass% or more. The CaCO3 itself used as the CaCO3-containing material includes, for example, synthetic CaCO3 obtained by blowing CO2 into an aqueous suspension of Ca(OH)2.

[0024] In the solidifying material of the present invention, it is preferable that the CaCO3-containing material has a Blaine specific surface area within a predetermined range. Specifically, from the viewpoint of improving the ease of handling, the Blaine specific surface area of ​​the CaCO3-containing material is 10,000 cm 2 / g or less 2000cm 2 / g or more is preferable. The Blaine specific surface area of ​​CaCO3-containing material can be measured in accordance with JIS R5201:2015 "Physical testing methods for cement."

[0025] In order to keep the Blaine specific surface area within the above range, temporarily increase the ground strength, and then suppress it in the long term, it is preferable to adjust the average particle size of the CaCO3-containing material, for example. Specifically, from the viewpoint of improving the Blaine specific surface area, the average particle size of the CaCO3-containing material is preferably 1000 μm or less, more preferably 500 μm or less, even more preferably 300 μm or less, and even more preferably 100 μm or less. The smaller the average particle size of the CaCO3-containing material, the better, but it may be 1 μm or more.

[0026] In order to make the above-mentioned advantages more pronounced and to temporarily increase ground strength while suppressing it in the long term, it is preferable that the CaCO3-containing material be composed of at least one of the group consisting of limestone and carbonated fine particles and crushed material generated when crushing waste concrete, and it is particularly preferable that the CaCO3-containing material be composed of limestone.

[0027] The solidification material of the present invention preferably contains a predetermined amount of CaCO3-containing material. Specifically, from the viewpoint of temporarily increasing ground strength and suppressing it in the long term, the solidification material preferably contains 20 mass% or more of CaCO3-containing material, more preferably 30 mass% or more, and even more preferably 40 mass% or more. Furthermore, from the viewpoint of not excessively reducing the initial strength, the solidification material preferably contains 50 mass% or less of CaCO3-containing material.

[0028] The solidification material of the present invention preferably has a ratio of the total content of cement clinker and gypsum to the content of CaCO3-containing material within a predetermined range. By replacing a portion of the cement clinker and gypsum, which greatly contribute to soil solidification, with CaCO3-containing material, it becomes easier to balance temporary improvement in ground strength with long-term suppression. Furthermore, carbon dioxide emissions can be reduced. Specifically, from the viewpoint of suppressing ground strength in the long term and reducing carbon dioxide emissions, the ratio of the content of CaCO3-containing material to the total content of cement clinker and gypsum (hereinafter also referred to as "ratio A") is preferably 0.1 or more, more preferably 0.4 or more, and even more preferably 0.6 or more. Furthermore, from the viewpoint of not excessively reducing the early strength, it is preferable that ratio A is less than 1.0.

[0029] The solidifying material of the present invention may contain other components in addition to the above-mentioned cement clinker, gypsum, and CaCO3-containing material, as long as the effects of the present invention are not impaired. Examples of other components include blast furnace slag, fly ash, clinker dust, and minerals such as allophane. These components may be used alone or in combination.

[0030] Blast furnace slag is a by-product of blast furnaces in steelworks, etc. As the blast furnace slag, for example, commercially available granulated blast furnace slag or slag specified in JIS A6206:2013 can be used. Blast furnace slag contains sulfur, and when heavy metals such as hexavalent chromium are present in the soil, the sulfur reduces the heavy metals to trivalent chromium, thereby suppressing the elution of heavy metals from the soil after solidification treatment to below environmental standards. To maximize this effect, the sulfur content of the blast furnace slag is preferably 0.1% by mass or more. When the solidification material of the present invention contains blast furnace slag, it is preferable that the solidification material contains blast furnace slag in an amount of 1% by mass or more and 50% by mass or less, from the viewpoint of suppressing the leaching of heavy metals from the soil after solidification treatment and suppressing excessive increase in long-term strength.

[0031] The solidifying material of the present invention preferably contains as little fly ash as possible. Specifically, from the viewpoint of reducing the pozzolanic reaction caused by fly ash and suppressing the ground strength in the long term, the solidifying material preferably contains 30% by mass or less of fly ash, more preferably 20% by mass or less. The lower the fly ash content, the better, but it may be 5% by mass or more.

[0032] The solidifying material of the present invention can be produced, for example, by mixing the above-mentioned materials in a known mixer. There are no particular limitations on the type of mixer. Alternatively, the solidifying material can be produced by mixing and grinding the materials using a grinder such as a ball mill.

[0033] Solidified soil can be obtained by mixing soil with the solidification material of the present invention and solidifying the soil. Examples of soil that can be solidified include sandy soil, clayey soil, Kanto loam, black soil, and humus soil. The amount of solidification material to be added can be changed as appropriate depending on the type and properties of the soil to be solidified. Generally, the amount of solidification material to be added is determined based on the type and properties of the soil to be solidified. 3 The upper limit of the amount of solidification material to be added varies depending on the type of soil and the construction method, but it is recommended to use 50 kg or more per 1 m of soil to be solidified. 3 Preferably, the amount of solidification material added is 400 kg or less, more preferably 350 kg or less, and even more preferably 300 kg or less. By setting the amount of solidification material added as described above, it is possible to obtain solidified treated soil having the strength described below. In this way, the solidified treated soil of the present invention is specified by its manufacturing method, because it is not realistic to specify the components that make up the solidified treated soil of the present invention and their contents, and there are impossible circumstances that make it necessary to use such expressions.

[0034] There are no particular limitations on the means for mixing the solidification material with the soil to be solidified. For example, devices or methods commonly used in the technical field can be used, such as backhoes, backhoes with mixing buckets, stabilizers, self-propelled soil improvers, stationary mixers, Hobart mixers, trencher-type agitation mixers, deep mixers, power blenders, and plant mixers.

[0035] It is preferable that the solidification-treated soil produced using the solidification material of the present invention has suppressed ground strength over the long term. Whether or not the ground strength has been suppressed over the long term can be determined using the unconfined compressive strength at 91 days of age as an indicator. In other words, it is preferable that the solidification material of the present invention is made so that the unconfined compressive strength at 91 days of age of the solidification-treated soil obtained by mixing the solidification material with soil and solidifying the soil is within a predetermined range. Specifically, it is preferable that the unconfined compressive strength at 91 days of age of the solidification-treated soil is 200 kN / m 2 More than 400kN / m 2 Preferably, it is less than 250 kN / m 2 More than 350kN / m 2 It is more preferable that: The unconfined compressive strength of solidified soil can be measured based on JIS A 1216:2020.

[0036] Although ground strength can be temporarily increased, the ratio of the unconfined compressive strength at 28 days to that at 91 days can be used as an indicator of whether it can be suppressed in the long term. Specifically, from the perspective of balancing the temporary increase in ground strength with the long-term suppression, the ratio of the unconfined compressive strength at 91 days to the unconfined compressive strength at 28 days (hereinafter also referred to as "91d / 28d") is preferably less than 1.40, more preferably less than 1.30, and even more preferably less than 1.20. 91d / 28d may also be 1.00 or greater.

[0037] Although ground strength can be temporarily increased, the ratio of the unconfined compressive strength at 7 days to that at 91 days can also be used as an indicator of whether it can be suppressed in the long term. Specifically, from the perspective of balancing the temporary increase in ground strength with the long-term suppression, the ratio of the unconfined compressive strength at 91 days to the unconfined compressive strength at 7 days (hereinafter also referred to as "91d / 7d") is preferably 2.50 or less, more preferably 2.00 or less, and even more preferably 1.80 or less. 91d / 7d may also be 1.20 or more.

[0038] In order to bring the unconfined compressive strength, 91d / 28d and 91d / 7d of the solidified soil at 91 days into the above-mentioned ranges, it is preferable to appropriately adjust, for example, the content of each material contained in the solidification material of the present invention and the amount of solidification material added to the soil.

[0039] The solidified soil produced using the solidification material of the present invention is controlled so that the initial strength and long-term strength development are appropriate, so although the ground strength is temporarily high, it is suppressed in the long term. [Example]

[0040] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0041] [Examples 1 to 3 and Comparative Examples 1 and 2] (1) Manufacturing of solidification materials High-early-strength Portland cement clinker was used as the cement clinker, dihydrate gypsum (manufactured by Toho Zinc Co., Ltd.) was used as the gypsum, and crushed limestone (Blaine specific surface area: 6500 cm) was used as the CaCO3-containing material. 2 / g, average particle size: 12 μm, CaCO3 content: 99% were prepared. The mineral composition of the high-early-strength Portland cement clinker is shown in Table 1. The chemical composition of each material is shown in Table 2. The materials were mixed in the mass ratios shown in Table 3 to obtain solidification materials A to E. The amount of SO3 contained in solidification materials A to E is also shown in Table 3. The chemical composition of each material was measured using an X-ray fluorescence analyzer (Panalytical, model number: Axios mAX). The mineral composition of the high-early-strength Portland cement clinker was calculated from the measured chemical composition of the clinker using the Bogue formula described above.

[0042] (2) Soil to be solidified Sand-mixed silt (produced in Ishikawa Prefecture, moisture content: 212.1%, wet density: 1.205 g / cm 3 Grain size composition: Gravel 0.0%, Sand 14.3%, Silt 47.6%, Clay 38.1%)

[0043] (3) Preparation of solidified soil The solidified soil obtained using solidification materials A to E was molded in accordance with JGS 0821:2009 "Test specimen preparation method for stabilized soil without compaction," and three cylindrical specimens with a diameter of 5 cm and a height of 10 cm were obtained for each solidification material. The amount of solidification materials A to E added to the soil was 150 kg / m 3 The obtained specimens were sealed and cured at a temperature of 20°C and a humidity of 90%RH for 7, 28, and 91 days, respectively.

[0044] (4) Evaluation The unconfined compressive strength and hexavalent chromium elution amount of the solidified soil at ages of 7 days, 28 days, and 91 days were measured using the following methods. The results are shown in Table 4.

[0045] [Uniaxial compressive strength] The unconfined compressive strength of the solidified soil was measured in accordance with JIS A 1216:2020.

[0046] [Heavy metal element elution amount] The amount of heavy metal elements leached from the solidified soil was measured in accordance with the Environment Agency Notification No. 46 (1991). Table 4 shows the soil environmental standards.

[0047] [Table 1]

[0048] [Table 2]

[0049] [Table 3]

[0050] [Table 4]

[0051] As is clear from the results shown in Table 4, the solidified soils using the solidification materials of Examples 1 to 3 have reduced ground strength over the long term compared to the solidification treated soil using the solidification material of Comparative Example 1. It is also clear that the solidified soils using the solidification materials of Examples 1 to 3 have higher initial ground strength compared to the solidification treated soil using the solidification material of Comparative Example 2. Furthermore, the amount of hexavalent chromium eluted from the solidified soils was within the soil environmental standards in all cases. From the above, it can be seen that the solidification materials of Examples 1 to 3 can temporarily increase the ground strength and suppress it in the long term.

Claims

1. C ３ Cement clinker having an S content of 50% by mass or more, gypsum, and CaCO ３ A solidification material including an inclusion, The cement clinker is 40% by mass or more and 80% by mass or less, the gypsum is 5% by mass or more and 20% by mass or less, and the CaCO ３ A solidification material containing 20% ​​by mass or more and 50% by mass or less of an inclusion.

2. The solidification material according to claim 1, wherein the gypsum is at least one selected from the group consisting of anhydrous gypsum, dihydrate gypsum, hemihydrate gypsum, and recycled gypsum produced as a recycled product of gypsum board.

3. CaCO ３ 3. The solidification material according to claim 1 or 2, wherein the inclusions are at least one of the group consisting of limestone and carbonated fine particles and crushed materials generated when crushing waste concrete.

4. 1m of soil ３ A solidified soil obtained by mixing 50 kg or more of the solidification material according to claim 1 or 2 with the soil and solidifying the soil, The unconfined compressive strength at 91 days is 200 kN / m ２ More than 400kN / m ２ Below is the solidified treated soil.

5. A method for solidifying soil, comprising mixing the solidification material according to claim 1 or 2 with soil to solidify the soil.

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