Method for producing soil cement, and method for reducing carbon dioxide emissions

Abstract

To provide a method for producing soil cement that can reduce a weight of soil cement while increasing its strength, or can make soil cement impermeable while increasing its strength, and a method for reducing carbon dioxide emissions.SOLUTION: In a method for producing soil cement containing soil material, cement-based solidification material, and water, the soil material, cement-based solidification material, water, and powdered biochar are mixed to produce soil cement.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing soil cement that is suitable for making soil cement lightweight, impermeable, and strong, and a method for reducing carbon dioxide emissions. [Background technology]

[0002] Conventionally, in building redevelopment and reconstruction projects, the basement of the existing building may be deep and the basement of the new building may be shallow. In such cases, the basement space (basement floor) of the existing building is often backfilled with concrete or liquefied treated soil (see, for example, Patent Document 1), and the new building is often supported by a direct foundation on the underground framework and foundation of the existing building. FIG. 9 is a vertical cross-sectional view of an underground space showing an example of such a case. As shown in this figure, a basement 4 (existing foundation) of an existing building 3 is provided on an existing pile 2 driven into a supporting layer 1 of the ground G. The upper part of the basement 4 is backfilled with backfill material 5 (liquefied treated soil), and a mat slab 7 of a new building 6 is constructed on top of it.

[0003] In such a plan, the weight of the material used to backfill the underground space must be deducted from the bearing capacity of the existing foundation when designing. In other words, the weight of the material used to backfill must be counted as part of the weight of the new building. Therefore, in order to effectively utilize the bearing capacity of the existing foundation, the material used to backfill should have high compressive strength and low density (lightweight).

[0004] As a lightweight backfill material, for example, soil-cement type aerated soil mixture is known (for example, see Non-Patent Document 1).

[0005] On the other hand, in excavation and retaining works, as shown in FIG. 10, a retaining wall 8 is constructed to construct the underground part of the structure, and the ground G (excavation bottom 9) surrounded by the retaining wall 8 is often excavated. In order to stop the seepage flow in the highly permeable ground, a retaining wall called a water cutoff wall or a water shielding wall may be constructed on the ground using an impermeable material. As the impermeable material, steel sheet piles, steel pipe sheet piles, cast-in-place reinforced concrete, and soil cement are used. Soil cement is composed of soil, cement, and water, and is an intermediate material between ground materials and concrete materials, and is also used in ground improvement works and backfilling works. In addition to the ingenuity of the materials and mix of soil cement, methods for improving the water cutoff property of soil cement include inserting steel sheet piles, steel pipe sheet piles, and high-density polyethylene sheets into the soil cement when used in excavation and retaining works. It is known that the water cutoff property of soil cement increases as the sand content of the constituent soil decreases (for example, see Non-Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2021-169749 A [Non-patent literature]

[0007] [Non-Patent Document 1] Public Works Research Center website, "Foam Mixture Earthwork Method", [online], [Retrieved August 1, 2023], Internet<URL:https: / / www.pwrc.or.jp / fukyuu / higradesoil / kihou.html> [Non-Patent Document 2] "Basic Experiments on the Material Properties of Soil-Cement Diaphragm Walls", Takeo Suzuki and Masamitsu Kunito, "Soil and Foundations, 42-3(434)", pp.19-22, Geotechnical Society of Japan, 1994. Summary of the Invention [Problem to be solved by the invention]

[0008] However, there is an upper limit to the strength of foamed soil (unconfined compressive strength of about 1000 kPa) (see, for example, Non-Patent Document 1). With ordinary soil cement, it is possible to achieve unconfined compressive strength of 1000 kPa or more by adjusting the amount of solidifying agent added, but there is a problem that increasing the amount of solidifying agent added leads to an increase in the amount of CO2 emitted during cement production and transportation, which increases the environmental load. For this reason, there has been a demand for technology that can reduce the weight and increase the strength of soil cement without increasing the amount of solidifying agent added.

[0009] As mentioned above, the water-stopping ability of soil cement increases the lower the sand content of the soil that makes it up, but the soil composition at the current site varies, and the amount of solidifying material added may need to be adjusted to achieve the required strength. Increasing the amount of solidifying material added leads to an increase in the amount of CO2 emitted during cement production and transportation, which increases the environmental burden. For this reason, there was a demand for technology that could make soil cement impermeable and strong without increasing the amount of solidifying material added.

[0010] The present invention has been made in consideration of the above, and aims to provide a method for producing soil cement that can reduce weight and strength, or can make soil cement impermeable and strong, and a method for reducing carbon dioxide emissions. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems and achieve the objectives, the soil cement manufacturing method of the present invention is a method for producing soil cement containing soil material, cement-based solidification material, and water, and is characterized in that the soil cement is produced by mixing the soil material, the cement-based solidification material, water, and powdered biochar.

[0012] Another soil cement manufacturing method according to the present invention is characterized in that, in the above-mentioned invention, soil material, cement-based solidification material, water, and powdered biochar are mixed to produce soil cement with higher strength than soil cement that does not contain biochar.

[0013] In addition, another soil cement manufacturing method according to the present invention is characterized in that, in the above-mentioned invention, it has a step of determining the wet density corresponding to the strength of the soil cement by applying the target soil cement strength to a previously obtained relationship between the strength and wet density of the soil cement, a step of determining the amount of biochar to be added corresponding to the wet density of the soil cement by applying the determined wet density of the soil cement to a previously obtained relationship between the wet density of the soil cement and the amount of biochar to be added, and a step of producing soil cement of the target strength using the determined amount of biochar to be added.

[0014] Another soil cement manufacturing method according to the present invention is characterized in that, in the above-mentioned invention, it includes a step of determining the amount of biochar to be added corresponding to the wet density of the soil cement by applying the target wet density of the soil cement to the relationship between the wet density of the soil cement and the amount of biochar to be added that has been obtained in advance, and a step of manufacturing soil cement having the target wet density using the determined amount of biochar to be added.

[0015] In addition, another soil cement manufacturing method according to the present invention is characterized in that, in the above-mentioned invention, it has a step of determining the permeability coefficient corresponding to the strength of the soil cement by applying the target soil cement strength to a previously obtained relationship between the soil cement strength and permeability coefficient, a step of determining the amount of biochar to be added corresponding to the permeability coefficient of the soil cement by applying the determined permeability coefficient of the soil cement to a previously obtained relationship between the soil cement permeability coefficient and the amount of biochar to be added, and a step of producing soil cement of the target strength using the determined amount of biochar to be added.

[0016] Another soil cement manufacturing method according to the present invention is characterized in that, in the above-mentioned invention, it includes a step of determining the amount of biochar to be added according to the hydraulic conductivity of the soil cement by applying the hydraulic conductivity of a target soil cement to the relationship between the hydraulic conductivity of the soil cement and the amount of biochar to be added that has been previously obtained, and a step of manufacturing soil cement with the target hydraulic conductivity using the determined amount of biochar to be added.

[0017] In addition, the carbon dioxide emission reduction method of the present invention is a method for reducing carbon dioxide emissions from soil cement in the above-mentioned invention, characterized in that soil cement is produced by the above-mentioned soil cement production method. Effect of the Invention

[0018] According to the method for producing soil cement of the present invention, which is a method for producing soil cement containing an earthen material, a cement-based solidification material, and water, the soil cement is produced by mixing the earthen material, the cement-based solidification material, water, and powdered biochar, and therefore, it is possible to simultaneously achieve a reduction in weight of the soil cement and an increase in strength. It is also possible to simultaneously achieve a reduction in water permeability of the soil cement and an increase in strength.

[0019] In addition, according to another soil cement manufacturing method of the present invention, by mixing earthen material, cement-based solidification material, water, and powdered biochar, the strength of the soil cement is increased compared to that of soil cement that does not contain biochar, thereby achieving the effect of realizing a soil cement with a higher strength than that of soil cement that does not contain biochar.

[0020] In addition, another soil cement manufacturing method according to the present invention includes the steps of: determining the wet density corresponding to the strength of the soil cement by applying the target soil cement strength to a previously obtained relationship between the strength and wet density of the soil cement; determining the amount of biochar to be added corresponding to the wet density of the soil cement by applying the determined wet density of the soil cement to a previously obtained relationship between the wet density of the soil cement and the amount of biochar to be added; and producing soil cement of the target strength using the determined amount of biochar to be added, thereby achieving the effect of easily producing soil cement of the target strength and wet density.

[0021] In addition, another soil cement manufacturing method according to the present invention includes a step of determining the amount of biochar to be added that corresponds to the wet density of the soil cement by applying the target wet density of the soil cement to the previously obtained relationship between the wet density of the soil cement and the amount of biochar to be added, and a step of producing soil cement having the target wet density using the determined amount of biochar to be added, thereby achieving the effect of easily producing soil cement having the target wet density.

[0022] In addition, another soil cement manufacturing method of the present invention includes a step of determining the permeability coefficient corresponding to the strength of the soil cement by applying the target soil cement strength to the previously obtained relationship between the soil cement strength and permeability coefficient, a step of determining the amount of biochar to be added corresponding to the permeability coefficient of the soil cement by applying the determined permeability coefficient of the soil cement to the previously obtained relationship between the soil cement strength and the amount of biochar to be added, and a step of producing soil cement of the target strength using the determined amount of biochar to be added, thereby achieving the effect of easily producing soil cement of the target strength and permeability coefficient.

[0023] In addition, another soil cement manufacturing method according to the present invention includes a step of determining the amount of biochar to be added that corresponds to the hydraulic conductivity of the soil cement by applying the hydraulic conductivity of the target soil cement to the previously obtained relationship between the hydraulic conductivity of the soil cement and the amount of biochar to be added, and a step of producing soil cement with the target hydraulic conductivity using the determined amount of biochar to be added, thereby achieving the effect of easily producing soil cement with the target hydraulic conductivity.

[0024] Furthermore, according to the carbon dioxide emission reduction method of the present invention, which is a method for reducing carbon dioxide emissions from soil cement, soil cement is produced by the above-mentioned soil cement production method, and therefore carbon dioxide can be fixed within the soil cement by using biochar, thereby achieving the effect of reducing the carbon dioxide emissions from the soil cement. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram showing an embodiment of a method for producing soil cement according to the present invention. [Diagram 2] FIG. 2 is a table showing an example of soil cement mix proportion, wet density, and unconfined compressive strength. [Diagram 3] Figure 3 shows an example of the relationship between the wet density and unconfined compressive strength of biochar soil cement (solidification agent added amount: 150 kg / m3). [Figure 4] FIG. 4 is a diagram showing an example of the relationship between the wet density of biochar soil cement (solidification agent added amount: 150 kg / m3) and the amount of biochar added. [Diagram 5] FIG. 5 is a table showing an example of soil cement mix proportion, permeability coefficient, and unconfined compressive strength. [Figure 6] FIG. 6 is a diagram showing an example of the relationship between the unconfined compressive strength of biochar soil cement (solidification agent added amount 80 kg / m3) and the amount of biochar added. [Figure 7]FIG. 7 is a graph showing an example of the relationship between the permeability coefficient and unconfined compressive strength of biochar soil cement (solidification agent added amount: 80 kg / m3). [Figure 8] FIG. 8 is a diagram showing an example of the relationship between the hydraulic conductivity of biochar soil cement (solidification material added amount: 80 kg / m3) and the amount of biochar added. [Figure 9] FIG. 9 shows an example of a conventional existing underground space being backfilled with liquefied treated soil. [Figure 10] FIG. 10 is a diagram showing an example of ground excavation for a conventional earth-retaining construction using an earth-retaining wall. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the method for producing soil cement and the method for reducing carbon dioxide emissions according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment.

[0027] <Embodiment 1> First, a first embodiment of the present invention will be described. The method for producing soil cement according to the first embodiment of the present invention is to produce lightweight, high-strength soil cement by mixing soil material, cement-based solidification material, water, and powdered biochar that fixes carbon in a natural state. Examples of soil cement include fluidized soil, lean cement milk, cement-based ground improvement material, and cement-based earth retaining material.

[0028] As shown in Fig. 1, in the method for producing soil cement according to the first embodiment, first, a target strength (unconfined compressive strength) or density (wet density) of the soil cement is set (step S1). Next, an amount of biochar to be added that corresponds to the set strength or density is determined (step S2). Next, the determined amount of biochar is added to the soil cement and mixed (step S3). In this way, a soil cement having the target strength or density is produced.

[0029] In the above step S2, it is desirable to obtain in advance the relationship between the strength and wet density of the soil cement and the relationship between the wet density of the soil cement and the amount of biochar added by a blending test as described below. In this way, the wet density according to the strength of the soil cement can be obtained by applying the target strength of the soil cement to the previously obtained relationship between the strength and wet density of the soil cement. In addition, the amount of biochar added according to the wet density of the soil cement can be obtained by applying the obtained wet density of the soil cement to the previously obtained relationship between the wet density of the soil cement and the amount of biochar added. This makes it possible to easily design and manufacture soil cement with a target strength or wet density. In addition, by using biochar with carbon fixed as an additive, the CO2 emissions from the soil cement can be reduced. In other words, CO2 can be fixed in the soil cement.

[0030] (Verification of the effect of adding biochar through blending tests: wet density and unconfined compressive strength) Next, we will explain the verification of the effect of adding biochar through a mixing test using soil cement. The soil cement was made by mixing air-dried silica sand No. 7, clay (made from wood-bush clay and kaolin clay in a mass ratio of 1:1), and water in a mass ratio of 4:1:2.15, and adding a solidification agent (solidification agent added amount 150 kg / m 3 The muddy water was mixed with water and the cement milk was poured into the concrete. Blast-furnace cement type B (cement-based solidification material) was used as the solidification material. The water content of the adjustment muddy water and the water-cement ratio of the cement milk were both 43%.

[0031] The biochar used was powdered biochar with a particle size of 5 mm or less. Biochar is a material that fixes carbon using sawdust generated during the sawing of coniferous and broadleaf trees. In the blending test, biochar that could reduce the CO2 (carbon dioxide) emissions of the solidification material by 100, 200, 400, and 1000% was weighed and added to the soil cement after preparation. The CO2 emissions of the solidification material were set at 0.5 g-CO2 / g based on Reference 1 below. The amount of CO2 fixed by biochar was assumed to be 2.51 g-CO2 / g, based on the calculation method in Reference 2 below. In Figure 2, the reduction rate of CO2 emissions of the solidification material (CN: carbon neutral) is shown along with the amount of biochar added. The amount of solidification material and biochar added was 1 m of adjusted mud water. 3 The amount added is based on the amount of the additive.

[0032] [Reference 1] "Global warming prevention measures in the construction field (February 2007)", Ministry of Land, Infrastructure, Transport and Tourism, [online], [searched November 7, 2022], Internet<URL:https: / / www.mlit.go.jp / singikai / infra / kankyou / 6 / images / 04.pdf> [Reference 2] "Methodology for the application of biochar to agricultural land (November 9, 2020)", Ministry of Agriculture, Forestry and Fisheries, Environmental Policy Office, [online], [searched November 7, 2022], Internet <URL:https: / / www.maff.go.jp / j / kanbo / kankyo / seisaku / climate / biochar / attach / pdf / top-4.pdf>

[0033] Figure 2 shows the soil-cement mix, wet density and unconfined compressive strength results. The sample names in Figure 2 are shown as a combination of the solidification agent additive amount (BB) and the solidification agent's CO2 emission reduction rate (carbon neutral rate: CN rate). For example, sample number 2, with the sample name "BB150-CN100", has a solidification agent additive amount (BB) of 150 kg / m 3This means that the CO2 emission reduction rate (CN rate) of the solidification material is 100%.

[0034] According to the table in Figure 2, the wet density of soil cement decreases with the addition of biochar. On the other hand, the unconfined compressive strength of soil cement increases with the addition of biochar. Therefore, it is possible to simultaneously reduce the weight and increase the strength of soil cement by adding biochar to soil cement. Furthermore, it is believed that the tendency for the wet density of soil cement to decrease and the unconfined compressive strength to increase with the addition of biochar will be the same even if the amount of solidification agent added and the mass ratio of soil, water, and solidification agent in the soil cement are changed.

[0035] As a secondary effect of adding biochar, the CO2 emissions from the soil cement are reduced, which leads to a reduction in the environmental impact. Therefore, the soil cement produced by the present invention can be said to be an environmentally friendly lightweight material that fixes any amount of CO2. Because it is a lightweight material, it is suitable as soil cement to be used for backfilling work of existing buildings, etc.

[0036] (Example of lightweight and strong soil cement) Next, examples of lightweight and strong soil cement will be described. FIG. 3 shows the relationship between the unconfined compressive strength (strength) and wet density of soil cement containing added biochar (hereinafter referred to as biochar soil cement). FIG. 4 shows the relationship between the wet density of biochar soil cement and the amount of added biochar. Both are created by plotting the results of the above-mentioned blending test. The dashed lines in the figure are regression lines of the respective relationships obtained by regression analysis. The regression equation representing the regression line may be a regression line equation or a regression curve equation. In the example of FIG. 3, a regression curve is used, and in the example of FIG. 4, a regression line is used. The amount of added biochar can be determined using the regression line or the regression equation representing the regression line. Below, examples of the use of FIG. 3 and FIG. 4 (Examples 1-1 and 1-2) are explained.

[0037] (Example 1-1) For example, when a new building is to be supported by a direct foundation, the required strength of the soil cement to support it (target soil cement strength) is set based on the required bearing capacity of the soil. If the required strength of the soil cement is 1300 kPa in unconfined compressive strength, the regression line in Figure 3 is used to determine the soil cement wet density as 1.74 g / cm 3 Next, based on Figure 4, the amount of biochar needed to achieve a desired wet density is read. Using the regression line in Figure 4, the wet density is 1.74 g / cm 3 The amount of biochar to be added to satisfy the following is approximately 258 kg. 3 By adding more than 258 kg of biochar, the wet density is 1.74 g / cm 3 The soil cement will have a uniaxial compressive strength of 1300 kPa and a CO2 fixation rate of 647 kg or more (CN rate of 863% or more). It is also possible to check whether the weight of the new building and the wet density of the designed biochar soil cement can be supported by the existing foundation.

[0038] (Example 1-2) Alternatively, the wet density of the soil cement (target wet density of soil cement) can be set considering the weight of the new building against the bearing capacity of the existing foundation, and the corresponding amount of biochar to be added can be read. For example, to effectively utilize the existing foundation, the wet density of the soil cement can be set to 1.70 g / cm 3 If the regression line in Figure 4 is used, the soil cement 1 m 3 For this, it is sufficient to add 422 kg or more of biochar. In this case, the amount of CO2 fixed in the soil cement is 1,058 kg or more (CN ratio 1,411% or more).

[0039] According to the present Examples 1-1 and 1-2, the weight of soil cement can be reduced by adding an amount of biochar set based on the relationship between the unconfined compressive strength and wet density of soil cement and the relationship between the wet density of soil cement and the amount of biochar added at the time of soil cement production. In addition, since the strength of soil cement is increased by adding biochar, there is no need to adjust the amount of solidifying agent separately. In other words, by adding biochar to soil cement, the weight of soil cement can be reduced and the strength can be increased at the same time. As a secondary effect of adding biochar, the CO2 emissions from soil cement are reduced, which also leads to a reduction in the environmental load.

[0040] <Embodiment 2> Next, a second embodiment of the present invention will be described. The method for producing soil cement according to the second embodiment of the present invention involves mixing an earthen material, a cement-based solidification material, water, and powdered biochar that has fixed carbon in a natural state to produce soil cement that has improved water-stopping properties, is impermeable, and has high strength. Examples of soil cement include fluidized soil, lean cement milk, cement-based ground improvement materials, and cement-based earth retaining materials.

[0041] The second embodiment will be described below taking as an example a case where it is applied to soil cement in a soil cement wall constructed on the ground for the purpose of achieving a water-stopping effect in excavation and retaining works and the like. First, the target strength (uniaxial compressive strength) or hydraulic conductivity of the soil cement is set. Next, the amount of biochar to be added that corresponds to the set strength or hydraulic conductivity is determined. Next, the determined amount of biochar is added to the soil cement and mixed to produce soil cement having the target strength or hydraulic conductivity. This makes it possible to simultaneously make the soil cement impermeable and increase its strength.

[0042] When determining the amount of biochar to be added, it is desirable to obtain in advance the relationship between the strength and hydraulic conductivity of the soil cement and the relationship between the hydraulic conductivity of the soil cement and the amount of biochar to be added by a blending test as described below. In this way, the hydraulic conductivity corresponding to the strength of the soil cement can be obtained by applying the target strength of the soil cement to the previously obtained relationship between the strength and hydraulic conductivity of the soil cement. In addition, the amount of biochar to be added corresponding to the hydraulic conductivity of the soil cement can be obtained by applying the obtained hydraulic conductivity of the soil cement to the previously obtained relationship between the hydraulic conductivity of the soil cement and the amount of biochar to be added. This makes it possible to easily design and manufacture soil cement with the target strength or hydraulic conductivity. In addition, by using biochar with carbon fixed as an additive, the CO2 emissions from the soil cement can be reduced. In other words, CO2 can be fixed in the soil cement.

[0043] (Verification of the effect of adding biochar through blending tests: Permeability coefficient and unconfined compressive strength) Next, we will explain the verification of the effect of adding biochar through a mixing test using soil cement. The soil cement was made by mixing air-dried silica sand No. 7, clay (made from wood-bush clay and kaolin clay in a mass ratio of 1:1), and water in a mass ratio of 4:1:2.15, and adding a solidification agent (solidification agent added amount 80 kg / m 3 The muddy water was mixed with water and the cement milk was poured into the concrete. Blast-furnace cement type B (cement-based solidification material) was used as the solidification material. The water content of the adjustment muddy water and the water-cement ratio of the cement milk were both 43%.

[0044] The biochar used was powdered biochar with a particle size of 5 mm or less. Biochar is a material that fixes carbon using sawdust generated during the sawing of coniferous and broadleaf trees. In the blending test, biochar that could reduce the CO2 (carbon dioxide) emissions of the solidification material by 100, 400, and 1000% was weighed and added to the soil cement after preparation. The CO2 emissions of the solidification material were set at 0.5 g-CO2 / g based on the above-mentioned Reference 1. The amount of CO2 fixed by biochar was assumed to be 2.51 g-CO2 / g, based on the calculation method in the above-mentioned Reference 2. Figure 5 shows the reduction rate of CO2 emissions of the solidification material (CN: carbon neutral) along with the amount of biochar added. The amount of solidification material and biochar added was 1 m of adjusted mud water. 3 The amount added is based on the amount of the additive.

[0045] Figure 5 shows the results of soil-cement mix, hydraulic conductivity and unconfined compressive strength. The sample names in Figure 5 are shown as a combination of the solidification material addition amount (BB) and the solidification material's CO2 emission reduction rate (carbon neutral rate: CN rate). For example, sample number 7, named "BB80-CN100", is a sample with a solidification material addition amount (BB) of 80 kg / m 3 This means that the CO2 emission reduction rate (CN rate) of the solidification material is 100%.

[0046] According to the table in Figure 5, the hydraulic conductivity of soil cement increased to the same level or 10 times that of normal soil cement with the addition of biochar. -9 The unconfined compressive strength of soil cement is on a downward trend, showing an order of magnitude increase. On the other hand, as shown in Figure 6, the addition of biochar increases the unconfined compressive strength of soil cement to a maximum of twice that of normal soil cement (sample number 6: BB80-CN0) (sample number 9: BB80-CN1000). The dashed line in Figure 6 is the regression equation obtained by regression analysis. Therefore, when using soil cement with added biochar for an earth retaining wall, the "design standard strength of soil cement is 3,000 kN / m 2The upper limit is 500 kN / m when the original ground is sandy soil, gravel soil, or clayey soil (excluding clay). 2 , 300 kN / m for clay 2 This fully meets the criteria stated above.

[0047] [Reference 3] "Earth Retaining Design Guidelines," Architectural Institute of Japan, November 2017

[0048] From the above results, it is possible to simultaneously make soil cement impermeable and increase its strength by adding biochar to the soil cement. As a secondary effect of adding biochar, the CO2 emissions from the soil cement are reduced, which leads to a reduction in the environmental impact. Therefore, the soil cement produced by the present invention can be said to be an environmentally friendly impermeable material that fixes an arbitrary amount of CO2. As it is an impermeable material, it is suitable as a soil cement to be used in earth retaining wall construction.

[0049] (Example of impermeability and strength improvement of soil cement) Next, an example of making soil cement impermeable and strong will be described. FIG. 7 shows the relationship between the unconfined compressive strength and the hydraulic conductivity of soil cement containing added biochar (hereinafter referred to as biochar soil cement). FIG. 8 shows the relationship between the hydraulic conductivity of biochar soil cement and the amount of added biochar. Both are created by plotting the results of the above-mentioned blending test. The dashed lines in the figure are regression lines of each relationship obtained by regression analysis. The regression equation representing the regression line may be a regression line equation or a regression curve equation. In the example of FIG. 7, a regression curve is used, and in the example of FIG. 8, a regression line is used. The amount of added biochar can be determined using the regression line or the regression equation representing the regression line. Below, we will explain examples of the use of FIG. 7 and FIG. 8 (Examples 2-1 and 2-2).

[0050] (Example 2-1) For example, when constructing a soil cement wall in an excavation and retaining wall construction, the necessary strength of the soil cement to satisfy the required load capacity (target soil cement strength) is set based on the required load capacity. If the required soil cement strength is 600 kPa or more in unconfined compressive strength, then, using Figure 7, the soil cement permeability coefficient is 4.32 x 10 -9 m / s or less. Next, based on Figure 8, the amount of biochar needed to add to satisfy the specified hydraulic conductivity is calculated. Hydraulic conductivity: 4.32×10 -9 The amount of biochar to be added to satisfy the above condition is about 149 kg. 3 By adding 149 kg or more of biochar, the hydraulic conductivity is increased to 4.32 × 10 -9 This soil cement simultaneously satisfies both the axial compressive strength and unconfined compressive strength of 600 kPa. The amount of CO2 fixed in the soil cement at this time is 374 kg or more (CN ratio of 935% or more).

[0051] (Example 2-2) Alternatively, the hydraulic conductivity of the soil cement (the target hydraulic conductivity of the soil cement) can be set, and the corresponding amount of biochar to be added can be read. For example, if the soil cement is expected to have a water-stopping effect, the hydraulic conductivity can be set to 1×10 -8 m / s or less, if the regression equation in Figure 8 is used, 3 For this, it is sufficient to add 84 kg or more of biochar. In this case, the amount of CO2 fixed in the soil cement is 212 kg or more (CN ratio of 530% or more).

[0052] According to Examples 2-1 and 2-2, the soil cement can be made impermeable by adding an amount of biochar set based on the relationship between the unconfined compressive strength of the soil cement and the coefficient of permeability, and the relationship between the coefficient of permeability of the soil cement and the amount of biochar added, at the time of soil cement production. In addition, since the strength of the soil cement is increased by adding biochar, there is no need to adjust the amount of solidifying agent separately. In other words, by adding biochar to the soil cement, it is possible to simultaneously make the soil cement impermeable and increase its strength. As a secondary effect of adding biochar, the CO2 emissions from the soil cement are reduced, which also leads to a reduction in the environmental load.

[0053] As described above, the method for producing soil cement according to the present invention is a method for producing soil cement containing soil material, cement-based solidification material, and water, and produces soil cement by mixing soil material, cement-based solidification material, water, and powdered biochar, thereby simultaneously achieving weight reduction and high strength of the soil cement. In addition, it is possible to simultaneously achieve water impermeability and high strength of the soil cement.

[0054] In addition, according to another soil cement manufacturing method of the present invention, soil material, cement-based solidification material, water, and powdered biochar are mixed to produce soil cement with higher strength than soil cement that does not contain biochar, thereby achieving soil cement with higher strength than soil cement that does not contain biochar.

[0055] In addition, another soil cement manufacturing method according to the present invention includes a step of determining the wet density corresponding to the strength of the soil cement by applying the target soil cement strength to a previously obtained relationship between soil cement strength and wet density, a step of determining the amount of biochar to be added corresponding to the wet density of the soil cement by applying the determined wet density of the soil cement to a previously obtained relationship between the soil cement wet density and the amount of biochar to be added, and a step of producing soil cement of the target strength using the determined amount of biochar to be added, so that soil cement of the target strength and wet density can be easily produced.

[0056] In addition, another soil cement manufacturing method according to the present invention includes a step of determining the amount of biochar to be added that corresponds to the wet density of the soil cement by applying the target wet density of the soil cement to the previously obtained relationship between the wet density of the soil cement and the amount of biochar to be added, and a step of producing soil cement having the target wet density using the determined amount of biochar to be added, thereby making it possible to easily produce soil cement having the target wet density.

[0057] In addition, another soil cement manufacturing method of the present invention includes a step of determining the permeability coefficient corresponding to the strength of the soil cement by applying the target soil cement strength to the previously obtained relationship between the soil cement strength and permeability coefficient, a step of determining the amount of biochar to be added corresponding to the permeability coefficient of the soil cement by applying the determined permeability coefficient of the soil cement to the previously obtained relationship between the soil cement strength and the amount of biochar to be added, and a step of producing soil cement of the target strength using the determined amount of biochar to be added, so that soil cement of the target strength and permeability coefficient can be easily produced.

[0058] In addition, another soil cement manufacturing method according to the present invention includes a step of determining the amount of biochar to be added that corresponds to the hydraulic conductivity of the soil cement by applying the hydraulic conductivity of the target soil cement to the previously obtained relationship between the hydraulic conductivity of the soil cement and the amount of biochar to be added, and a step of producing soil cement with the target hydraulic conductivity using the determined amount of biochar to be added, thereby making it possible to easily produce soil cement with the target hydraulic conductivity.

[0059] Furthermore, according to the carbon dioxide emission reduction method of the present invention, which is a method for reducing carbon dioxide emissions from soil cement, soil cement is produced by the above-mentioned soil cement production method, and carbon dioxide can be fixed within the soil cement by using biochar, thereby reducing the carbon dioxide emissions from the soil cement.

[0060] The "Sustainable Development Goals (SDGs)" are 17 international goals that were adopted at the United Nations Summit in September 2015. The soil cement manufacturing method and carbon dioxide emission reduction method according to the present embodiment can contribute to the achievement of the 17 SDGs, for example, goal 11, "Sustainable cities and towns." [Industrial Applicability]

[0061] As described above, the soil cement manufacturing method and carbon dioxide emissions reduction method of the present invention are useful as backfill material used in building redevelopment and reconstruction projects, and are particularly suitable for making soil cement lighter, more impermeable, and stronger. [Explanation of symbols]

[0062] 1 Support layer 2 Existing piles 3 Existing buildings 4 Bottom board 5 Backfill material 6 New Building 7. Mat Slab 8 Retaining wall 9 Root cutting bottom

Claims

1. A method for producing soil cement containing a soil material, a cement-based solidification material, and water, comprising the steps of: A method for producing soil cement, comprising mixing soil material, a cement-based solidification material, water, and powdered biochar to produce soil cement.

2. The method for producing soil cement according to claim 1, characterized in that the soil cement is made stronger by mixing soil material, cement-based solidification material, water, and powdered biochar, compared to soil cement that does not contain biochar.

3. 2. The method for producing soil cement as described in claim 1, further comprising the steps of: determining a wet density corresponding to the strength of the soil cement by applying a target soil cement strength to a previously obtained relationship between soil cement strength and wet density; determining an amount of biochar to be added corresponding to the wet density of the soil cement by applying the determined wet density of the soil cement to a previously obtained relationship between soil cement wet density and an amount of biochar to be added; and producing soil cement of the target strength using the determined amount of biochar to be added.

4. 2. The method for producing soil cement as described in claim 1, characterized in that it comprises the steps of: determining the amount of biochar to be added according to the wet density of the soil cement by applying the target wet density of the soil cement to the relationship between the wet density of the soil cement and the amount of biochar to be added that has been obtained in advance; and producing soil cement having the target wet density using the determined amount of biochar to be added.

5. 2. A method for producing soil cement as described in claim 1, comprising the steps of: determining the permeability coefficient corresponding to the strength of the soil cement by applying the target soil cement strength to a previously obtained relationship between the strength and permeability coefficient of the soil cement; determining the amount of biochar to be added corresponding to the permeability coefficient of the soil cement by applying the determined permeability coefficient of the soil cement to a previously obtained relationship between the permeability coefficient of the soil cement and the amount of biochar to be added; and producing soil cement of the target strength using the determined amount of biochar to be added.

6. 2. The method for producing soil cement as described in claim 1, characterized in that it comprises the steps of: determining the amount of biochar to be added according to the hydraulic conductivity of the soil cement by applying the hydraulic conductivity of the target soil cement to the relationship between the hydraulic conductivity of the soil cement and the amount of biochar to be added that has been obtained in advance; and producing soil cement with the target hydraulic conductivity using the determined amount of biochar to be added.

7. A method for reducing carbon dioxide emissions from soil cement, comprising: A method for reducing carbon dioxide emissions, comprising producing soil cement by the method for producing soil cement according to any one of claims 1 to 6.

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