Soil strength improving agent, method for manufacturing soil strength improving agent, method for modifying soil, modified soil

Abstract

The present invention aims to provide a novel ground strength improving agent that can improve ground strength while reducing the amount of cement used and fixing a large amount of calcium carbonate in the soil, a method for producing this ground strength improving agent, a ground modification method, and modified ground modified by the ground modification method. [Solution] The soil strength is improved by applying calcium carbonate raw materials, mainly composed of calcium carbonate, in an application ratio of 20-45% by weight, cement in 35-60% by weight, hemihydrate gypsum in 15-40% by weight, and metal salts consisting of alkali metal or alkaline earth metal halides in 1-5% by weight.

Description

Technical Field

[0001] The present invention relates to a ground strength improving agent for improving ground strength by applying it to soil, a manufacturing method for manufacturing the ground strength improving agent, a ground improvement method, and a modified ground modified by the ground improvement method.

Background Art

[0002] The global warming phenomenon is caused by various factors overlapping, but the theory that greenhouse gases such as carbon dioxide (CO2) emitted into the atmosphere due to human industrial activities is a major factor has become the mainstream. Therefore, reducing the emissions of carbon dioxide has become an international issue. Also, research is being conducted on means for recovering the emitted carbon dioxide.

[0003] As a means for recovering carbon dioxide, for example, a method (chemical adsorption method) of bringing carbon dioxide into contact with an alkaline aqueous solution to dissolve carbon dioxide has been developed. In this chemical adsorption method, carbon dioxide is selectively recovered by heat-treating the aqueous solution in which carbon dioxide is dissolved, and it is supposed to be buried underground in the state of liquefied carbon dioxide gas.

[0004] However, in this chemical adsorption method, the heat energy consumed when separating carbon dioxide from the aqueous solution in which carbon dioxide is dissolved increases, so the treatment cost becomes high. Also, since the land suitable for burying carbon dioxide is limited, the transportation cost of liquefied carbon dioxide gas also becomes high.

[0005] Regarding this point, in Patent Document 1 below, a means for obtaining calcium carbonate by bringing calcium-containing powder into contact with carbon dioxide in water and manufacturing a cement powder composition by mixing cement clinker and gypsum is disclosed.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-152631 [Overview of the project] [Problems that the invention aims to solve]

[0007] Patent Document 1 describes a method for fixing carbon dioxide by converting it into calcium carbonate and then using this calcium carbonate as a cement composition.

[0008] However, mortar and concrete structures cast using cement compositions containing calcium carbonate tended to experience a decrease in strength as the amount of calcium carbonate increased, because calcium carbonate itself does not undergo a hydration reaction.

[0009] The present invention was developed to solve the aforementioned technical problems, and aims to provide a novel ground strength improving agent that can improve ground strength while reducing the amount of cement used and fixing a large amount of calcium carbonate in the soil, a method for producing this ground strength improving agent, a ground modification method, and modified ground modified by the ground modification method. [Means for solving the problem]

[0010] The ground strength improving agent of the present invention, which solves the aforementioned technical problems, is a ground strength improving agent for improving ground strength by application to soil, and comprises 20 to 45% by weight of a calcium carbonate raw material mainly composed of calcium carbonate, 35 to 60% by weight of cement, and 15 to 40% by weight of hemihydrate gypsum, and further comprises 1 to 5% by weight of a metal salt consisting of an alkali metal or alkaline earth metal halide (hereinafter referred to as "the ground strength improving agent of the present invention").

[0011] In the ground strength improving agent of the present invention, a preferred embodiment is one in which the weight ratio of calcium carbonate raw material to cement is 1:1 ± 0.1.

[0012] In the ground strength improving agent of the present invention, a preferred embodiment is one in which the metal salt is selected from at least one of sodium chloride, potassium chloride, calcium chloride, or magnesium chloride.

[0013] The present invention provides a method for producing a ground strength improving agent that solves the aforementioned technical problems, characterized by producing the ground strength improving agent by performing a calcium carbonate production step to obtain a calcium carbonate raw material by contacting a calcium source containing calcium oxide or calcium hydroxide with carbon dioxide in water, and a mixing step to mix cement, hemihydrate gypsum, and a metal salt with the calcium carbonate raw material (hereinafter referred to as the "production method of the present invention").

[0014] In the manufacturing method of the present invention described above, it is preferable to use by-product calcium contained in industrial by-products as the calcium source.

[0015] In the manufacturing method of the present invention described above, it is preferable to use Beckendust, paper sludge incineration ash, or stainless steel slag as the by-product calcium.

[0016] The present invention provides a soil modification method for improving soil strength, characterized by applying the following to the soil: 20-45% by weight of calcium carbonate raw material mainly composed of calcium carbonate, 35-60% by weight of cement, 15-40% by weight of hemihydrate gypsum, and 1-5% by weight of a metal salt consisting of an alkali metal or alkaline earth metal halide (hereinafter referred to as "the present invention modification method").

[0017] In the modification method of the present invention, the application ratio of calcium carbonate raw material, cement, hemihydrate gypsum, and metal salt is applied to 1 m of soil. 3 A preferred application rate is 100 to 200 kg per unit area.

[0018] The improved ground of the present invention for solving the above technical problem is the improved ground modified by the above-described method for modifying the soil of the present invention, characterized in that the soil pH is 8 to 10 (hereinafter referred to as "the improved ground of the present invention").

Advantages of the Invention

[0019] According to the present invention, while reducing the amount of cement used, a large amount of calcium carbonate can be fixed in the soil, and the ground strength can be improved.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0021] <The ground strength improving agent of the present invention, the manufacturing method of the present invention> The ground strength improving agent of the present invention comprises 20 to 45% by weight of a calcium carbonate raw material, 35 to 60% by weight of cement, 15 to 40% by weight of hemihydrate gypsum, and 1 to 5% by weight of a metal salt. Further, in the manufacturing method of the present invention, the ground strength improving agent of the present invention is manufactured by performing a "calcium carbonate manufacturing step" and a "mixing step".

[0022] -Calcium carbonate manufacturing step- In the calcium carbonate manufacturing step, a "calcium carbonate raw material" is obtained by bringing a calcium source containing calcium oxide or calcium hydroxide into contact with carbon dioxide in water. A means for generating calcium carbonate by introducing a gas containing carbon dioxide into an alkaline aqueous solution in which calcium ions are dissolved (Ca 2+ +CO3 2- →CaCO3) is already known.

[0023] ·Calcium carbonate raw material Here, as the calcium carbonate raw material contained in the ground strength improver of the present invention, heavy calcium carbonate produced from crushed limestone or light calcium carbonate produced by sintering, hydrating, and carbonating limestone can also be used. However, since the present invention has an aspect of carbon dioxide recovery and fixation, it is preferable to produce a calcium carbonate raw material using by-product calcium such as Becken dust discharged from a limestone firing facility (Becken buffer furnace), incineration ash of paper sludge discharged in the papermaking process, and stainless slag discharged in the stainless steel manufacturing process as a calcium source.

[0024] These by-product calciums contain about 40 to 60% by weight of a calcium component (mainly calcium oxide) as the main component, and in addition, metal oxides such as silica, alumina, and iron oxide are contained. In addition, when carrying out the manufacturing method of the present invention, it is not necessary to remove these metal oxides from the by-product calcium. Therefore, the blending amount of the calcium carbonate raw material in the ground strength improver of the present invention is set to a weight ratio of 20 to 45% by weight regardless of the presence or absence of metal oxides in the calcium carbonate raw material.

[0025] -Mixing step- In the mixing step, "cement", "hemihydrate gypsum", and "metal salt" are mixed with the calcium carbonate raw material obtained in the calcium carbonate production step. After mixing cement, hemihydrate gypsum, and metal salt with the calcium carbonate raw material, the ground strength improver of the present invention is obtained by stirring until it becomes uniform in a mill or a mixer.

[0026] ·Cement Examples of cement include various Portland cements such as ordinary Portland cement, early strength Portland cement, medium heat Portland cement, low heat Portland cement, sulfate resistant Portland cement, etc., and mixed cements such as blast furnace cement, fly ash cement, silica cement, etc., and eco-cement, etc. These cements can be appropriately selected and used singly or in combination of two or more according to the ground strength and hardening speed required when carrying out the modification method of the present invention described later.

[0027] ·Hemihydrate plaster Hemihydrate gypsum (calcium sulfate hemihydrate (CaSO4·1 / 2H2O)) is a mineral also known as calcined gypsum. Upon contact with water, it undergoes a hydration reaction, precipitating and solidifying needle-shaped crystals of dihydrate gypsum (CaSO4·2H2O). Hemihydrate gypsum plays a role in improving the ground strength (especially the initial ground strength) when implementing the ground modification method of the present invention, which will be described later.

[0028] Although some cements contain gypsum components, in this invention, the mixing ratio of hemihydrate gypsum is based on the net amount of hemihydrate gypsum added, and the gypsum components contained in the cement are not added to the amount of hemihydrate gypsum added.

[0029] • Metal salts The metal salt is a halide of an alkali metal or alkaline earth metal. Suitable examples of metal salts include sodium chloride, potassium chloride, calcium chloride, or magnesium chloride. The metal salt plays a role in suppressing hardening inhibition caused by organic matter ions in the soil during the soil modification method described later.

[0030] Although calcium carbonate raw materials and cement may contain metal salts, in this invention the blending ratio of metal salts is based on the net amount of metal salts blended, and metal salts contained in the calcium carbonate raw materials or cement are not added to the blending amount of metal salts.

[0031] <Method of modification according to the present invention> In the soil modification method of the present invention, the following components are applied to the soil: calcium carbonate raw material at a ratio of 20-45% by weight, cement at 35-60% by weight, hemihydrate gypsum at 15-40% by weight, and metal salt at 1-5% by weight. When each component (calcium carbonate raw material, cement, hemihydrate gypsum, and metal salt) is applied to the soil, it undergoes a hydration reaction upon contact with moisture in the soil, hardening and improving the soil strength.

[0032] As for application methods, each component may be scattered on the soil surface, but in order to improve soil permeability, it is preferable to add each component to the collected soil, mix them, and then backfill the site where the soil was collected or use it as cover soil for other land.

[0033] The order in which each component is applied to the soil is not particularly limited. However, it is preferable to pre-mix and thoroughly stir each component to ensure that there is no imbalance in the distribution of each component in the soil. In this regard, it is preferable to use the soil strength improving agent of the present invention when carrying out the humidification method of the present invention.

[0034] Furthermore, there are no particular limitations on the amount of each component applied to the soil. It has been observed that the stronger the soil tends to be as the amount applied to the soil increases, so the application amount should be determined according to the required soil strength. Specifically, for 1 m of soil... 3 It has been confirmed that applying 100-200 kg per unit area improves ground strength to a level equivalent to or greater than that achieved with conventional soil modification methods using cement-based solidifying agents.

[0035] <Modified ground according to the present invention> The modified ground of the present invention refers to soil or ground modified by the modification method of the present invention. The modification method of the present invention requires less cement component compared to conventional cement-based solidifying agents. Therefore, while the pH of soil modified by conventional soil modification methods using cement-based solidifying agents exceeds 11, the soil pH of the modified ground of the present invention is close to neutral, at 8 to 10.

[0036] [Examples 1-4, Comparative Examples 1 and 2] Table 1 below shows the composition of the ground strength improving agents of the present invention according to Examples 1 to 4, and the properties of the modified ground according to the present invention when the modification method of the present invention is carried out using each ground strength improving agent of the present invention. Light calcium carbonate was used as the calcium carbonate raw material, ordinary Portland cement as the cement, and a 1:1 mixture of sodium chloride and calcium chloride as the metal salt. Furthermore, sandy clay (moisture content 40%) collected from agricultural land was used as the soil. In addition, the modification method of the present invention was performed on 1 m of soil. 3This was carried out by mixing 150 kg of the ground strength improving agent of the present invention per unit area and stirring thoroughly.

[0037] In addition, the ground strength was measured based on a plate load test (at 14 days old), and the soil pH was measured using a pH meter (Sato Keiryoki Seisakusho Handy pH Meter SK-620PHII) after the collected soil was air-dried, five times the amount of water was added and stirred, and the supernatant liquid was measured after 1 hour (at 14 days old).

[0038] [Table 1]

[0039] As shown in Table 1 above, the modified ground obtained by the modification method of the present invention using the ground strength improving agent of the present invention according to Examples 1 to 4 was found to have ground strength equivalent to or greater than that of soil modified using a commercially available cement-based solidifying agent (Comparative Example 2). Furthermore, the soil pH of the modified ground of the present invention was closer to neutral than that of soil modified using a commercially available cement-based solidifying agent, confirming that the range of secondary uses of the modified ground of the present invention, such as for agricultural land, is broadened.

[0040] On the other hand, soil modified with Comparative Example 2, which had the same composition as the ground strength improver of the present invention except for the absence of metal salts, showed lower ground strength compared to Examples 1-3. This is presumed to be due to the inhibition of hardening by organic matter ions contained in the soil. It has been confirmed that similar results are obtained when using potassium chloride or magnesium chloride as the metal salt.

[0041] [Examples 5-9, Comparative Examples 3, 4] Table 2 below shows the composition of the ground strength improving agents of the present invention for Examples 5 to 9, and the properties of the modified ground of the present invention when the modification method of the present invention is carried out using each of the ground strength improving agents of the present invention. Other conditions were the same as those for Examples 1 to 3 above.

[0042] [Table 2]

[0043] The results in Table 2 above show that increasing the amount of calcium carbonate raw material tends to decrease ground strength, while increasing the amount of cement tends to increase the alkalinity of the soil pH.

[0044] In light of the ground strength and soil pH of the modified ground of the present invention, it is preferable that the amount of calcium carbonate raw material and cement in the ground strength improver of the present invention be approximately equal. Specifically, it is preferable that the weight ratio of calcium carbonate raw material to cement be 1:1 ± 0.1 (1:0.9 to 1.1).

[0045] [Examples 10-13, Comparative Example 5] Table 3 below shows the composition of the ground strength improving agents of the present invention for Examples 10 to 13, and the properties of the modified ground of the present invention when the modification method of the present invention is carried out using each of the ground strength improving agents of the present invention. Other conditions were the same as those for Examples 1 to 3 above.

[0046] [Table 3]

[0047] The results in Table 3 above confirm that increasing the amount of hemihydrate gypsum tends to improve ground strength. However, it has also been confirmed that excessively high amounts of hemihydrate gypsum can cause expansion problems, so it is preferable to use an amount of hemihydrate gypsum of 15-40% by weight (more preferably 15-25% by weight).

[0048] [Examples 14-16] Table 4 below shows the composition of the soil strength improving agents of the present invention for Examples 14 to 16, and the properties of the modified soil of the present invention when the modification method of the present invention was carried out using each soil strength improving agent of the present invention (the results of Example 2 are also shown for reference). The calcium carbonate raw materials used in Examples 14 to 16 were all obtained by carbonated the calcium components contained in by-product calcium (Beckendust, paper sludge incineration ash, stainless steel slag) as a calcium source. Other conditions were the same as in Examples 1 to 3 above.

[0049] [Table 4]

[0050] As shown in the results in Table 4, it was confirmed that the modified soil of the present invention, which was modified with the ground strength improving agent of the present invention that includes by-product calcium carbonate as a calcium source, as in Examples 14-16, tended to have higher ground strength compared to the modified soil of the present invention modified with the ground strength improving agent of the present invention according to Example 2, which uses light calcium carbonate as a calcium carbonate raw material.

[0051] This is likely because ceramic components such as alumina and silica contained in the by-product calcium act as fillers, improving the ground's strength.

[0052] [Examples 17, 18] Table 5 below shows the properties of the modified soil of the present invention when the modification method of the present invention is carried out using the soil strength improving agent of the present invention according to Example 2 (the results of Example 2 are also shown for reference).

[0053] [Table 5]

[0054] The results in Table 5 show that increasing the amount of the soil strength improving agent of the present invention applied to the soil tends to improve the soil strength of the modified soil of the present invention.

[0055] Furthermore, the present invention can be implemented in various other forms without departing from its spirit or main features. Therefore, the embodiments described above are merely illustrative in all respects and should not be interpreted restrictively. The scope of the present invention is defined by the claims and is not restricted in any way by the text of the specification. Moreover, any modifications or changes falling within the equivalent scope of the claims are all within the scope of the present invention. [Industrial applicability]

[0056] The present invention can be suitably used as a means to improve ground strength.

Claims

1. A soil strength improving agent for improving the strength of the ground when applied to the soil, 20-45% by weight of calcium carbonate raw material, which has calcium carbonate as its main component, 35-60% by weight of cement, 15-40% by weight of hemihydrate gypsum, It is equipped with, A ground strength improving agent characterized by comprising 1 to 5% by weight of a metal salt consisting of an alkali metal or alkaline earth metal halide.

2. In the ground strength improving agent according to claim 1, A ground strength improver in which the weight ratio of calcium carbonate raw material to cement is set to 1:1 ± 0.

1.

3. In the ground strength improving agent according to claim 1, A ground strength improver in which the metal salt is at least one selected from sodium chloride, potassium chloride, calcium chloride, or magnesium chloride.

4. A method for producing a ground strength improving agent according to any one of claims 1 to 3, A calcium carbonate production process that obtains a calcium carbonate raw material by contacting a calcium source containing calcium oxide or calcium hydroxide with carbon dioxide in water, A mixing process in which calcium carbonate raw material is mixed with cement, hemihydrate gypsum, and a metal salt, A method for producing a ground strength improving agent, characterized by performing the following steps.

5. In the method for producing a ground strength improving agent according to claim 4, A method for producing a ground strength improver that uses by-product calcium contained in industrial by-products as a calcium source.

6. In the method for producing a ground strength improving agent according to claim 5, A method for producing a ground strength improver using Beckendust, paper sludge incineration ash, or stainless steel slag as by-product calcium.

7. A method for improving soil strength, 20-45% by weight of calcium carbonate raw material, which is mainly composed of calcium carbonate. Cement is 35-60% by weight. Hemihydrate gypsum is 15-40% by weight. A metal salt consisting of an alkali metal or alkaline earth metal halide is present in 1 to 5% by weight. A soil modification method characterized by applying the substance to the soil in a manner that results in a specific application ratio.

8. In the ground modification method described in claim 7, For the calcium carbonate raw materials, cement, hemihydrate gypsum, and metal salts in the aforementioned application ratios, 1 m³ of soil ３ A soil modification method that involves applying 100 to 200 kg per unit area.

9. Modified ground modified by the ground modification method described in claim 7 or 8, Modified soil characterized by a soil pH of 8 to 10.

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