Construction methods and methods for reducing carbon dioxide emissions

Abstract

To provide a construction method capable of reducing discharge of CO2 while maintaining the strength of the ground, and a method for reducing discharge of carbon dioxide, although conventionally the reduction of the amount of a ground solidification material used for solidification of soil for the purpose of reduction in discharge of CO2 has resulted in lowering of the ground strength.SOLUTION: A construction method includes mixing a soil constituting the ground and a molten slag to prepare a primary mixture, adding one or more selected from a cement and a cement-based solidification material to the primary mixture, and mixing the mixture to solidify the ground.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a construction method and a method for reducing carbon dioxide emissions. [Background technology]

[0002] As a ground improvement method (construction method) for solidifying the soil that makes up the ground, a method using cement or cement-based solidifying material (hereinafter also referred to as ground solidifying material) is known (see, for example, Non-Patent Documents 1 and 2). According to Non-Patent Documents 1 and 2, the strength of soil (ground) is improved by hardening due to the hydration reaction of cement and a decrease in water content due to the immobilization of water as bound water. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Ground Improvement Manual Using Cement-Based Solidifying Agents, 5th Edition, pp. 44-45, published by the Japan Cement Association. [Non-Patent Document 2] Soil stabilization techniques for road earthworks, pages 10-11, published by the Highway Technology Research Institute Co., Ltd. [Overview of the project] [Problems that the invention aims to solve]

[0004] The manufacturing of the soil solidification materials used in Non-Patent Documents 1 and 2 generates large amounts of carbon dioxide (CO2). Reducing CO2 emissions is a global goal. Reducing the amount of soil solidification materials used to solidify soil will lead to a reduction in CO2 emissions. However, reducing the amount of soil solidification material used will decrease the strength of the ground.

[0005] This invention has been made in view of the above circumstances, and aims to provide a construction method and a method for reducing carbon dioxide emissions that can reduce CO2 emissions while maintaining the strength of the ground. [Means for Solving the Problem]

[0006] In order to solve the above problem, the present invention has the following aspects. [1] A construction method, comprising: mixing soil constituting the ground and molten slag to obtain a primary mixture; and adding one or more ground solidification materials selected from cement and cement-based solidification materials to the primary mixture, followed by mixing to solidify the ground. [2] The construction method according to [1], wherein a ratio of the volume of the molten slag to the volume of the soil in the primary mixture is 1:99 to 50:50. [3] The total volume of the primary mixture is 1m 3 The construction method according to [1] or [2], wherein the addition amount of the ground solidification material is 200 kg or less. [4] The construction method according to [1] or [2], wherein the soil is cohesive soil.

[0007] [5] A method for reducing carbon dioxide emissions in a construction method of solidifying the ground, comprising: mixing soil constituting the ground and molten slag to obtain a primary mixture; and adding one or more ground solidification materials selected from cement and cement-based solidification materials to the primary mixture, followed by mixing, wherein compared with the usage amount of the ground solidification material when the molten slag is not used, the usage amount of the ground solidification material is reduced, so that carbon dioxide emissions derived from production of the ground solidification material can be reduced, which is the method for reducing carbon dioxide emissions. [6] The method for reducing carbon dioxide emissions according to [5], wherein a carbon dioxide fixing material capable of immobilizing carbon dioxide is further added to the primary mixture. [Effect of the Invention]

[0008] According to the construction method and the method for reducing carbon dioxide emissions of the present invention, CO2 emissions can be reduced while maintaining the strength of the ground. [Brief Description of the Drawings]

[0009] [Figure 1]This is a graph showing the uniaxial compressive strength at 3 days of age when blast furnace cement is used as a ground solidifying material. [Figure 2] This is a graph showing the uniaxial compressive strength at 7 days of age when blast furnace cement is used as a ground solidifying material. [Figure 3] This is a graph showing the uniaxial compressive strength at 28 days of age when blast furnace cement is used as a ground solidifying material. [Figure 4] This is a graph showing the uniaxial compressive strength at 3 days of age when a cement-based solidifying material is used as a ground solidifying material. [Figure 5] This is a graph showing the uniaxial compressive strength at 7 days of age when a cement-based solidifying material is used as a ground solidifying material. [Figure 6] This is a graph showing the uniaxial compressive strength at 28 days of age when a cement-based solidifying material is used as a ground solidifying material. [Figure 7] This is a graph showing the relationship between moisture content and uniaxial compressive strength at 3 days of age when blast furnace cement is used as a ground solidifying material. [Figure 8] This is a graph showing the relationship between moisture content and uniaxial compressive strength at 7 days of age when blast furnace cement is used as a ground solidifying material. [Figure 9] This is a graph showing the relationship between moisture content and uniaxial compressive strength at 28 days of age when blast furnace cement is used as a ground solidifying material. [Figure 10] This is a graph showing the relationship between moisture content and uniaxial compressive strength at 3 days of age when a cement-based solidifying material is used as a ground solidifying material. [Figure 11] This is a graph showing the relationship between moisture content and uniaxial compressive strength at 7 days of age when a cement-based solidifying material is used as a ground solidifying material. [Figure 12] This is a graph showing the relationship between moisture content and uniaxial compressive strength at 28 days of age when a cement-based solidifying material is used as a ground solidifying material. MODE FOR CARRYING OUT THE INVENTION

[0010] <<Construction Method>> The construction method of the present invention involves mixing soil constituting the ground with molten slag to obtain a primary mixture, and then adding one or more ground solidification materials selected from cement and cement-based solidification materials to the primary mixture and mixing to solidify the ground. The construction method of the present invention involves adding a ground solidification agent to a primary mixture of soil and molten slag, thereby reducing the amount of ground solidification agent used compared to cases where molten slag is not used, while still achieving a predetermined strength (for example, 200 kN / m² in uniaxial compressive strength of the structure). 2 The above-mentioned ground conditions can be obtained. Therefore, the amount of ground solidification material used can be reduced while maintaining the strength of the ground, and CO2 emissions from the manufacture of ground solidification material can be reduced. In addition, the construction method of the present invention further reduces and offsets CO2 emissions originating from the production of the ground solidification material by adding and mixing a carbon dioxide fixative that can fix carbon dioxide to the primary mixture.

[0011] <Saturday> In this specification, "soil" refers to soil, and includes clayey soil, sandy soil, and gravelly soil. Clayey soil is a general term for soil with small particle sizes. In this specification, "cohesive soil" means soil containing 50% by mass or more of soil particles (fine-grained components) with a particle size of 75 μm or less. "Sandy soil" refers to soil that contains 50% or more by mass of particles with a particle size of 75 μm or larger (coarse-grained material) and whose particle size is 2.0 mm or less. "Gravelous soil" refers to soil with a particle size greater than 2.0 mm. The particle size of gravelous soil is generally 75 mm or less. Clayey soils generally have relatively low ground strength, and it is often necessary to increase the ground strength. For this reason, clayey soil is preferred as a soil type.

[0012] <Molten slag> Molten slag is produced by melting industrial waste, sludge, and other incinerated materials at temperatures above 1300°C, then cooling and solidifying them. Examples of industrial waste include municipal solid waste. Examples of sludge include organic sludge and sewage sludge. Note that molten slag is different from blast furnace slag, which will be discussed later.

[0013] Molten slag is used, for example, in precast concrete products, backfill materials, topsoil, and fertilizers. Commercially available molten slag may be used, and examples of commercially available molten slag include NS Eco Sand (registered trademark) from Nippon Steel Engineering Co., Ltd.

[0014] <Ground solidification material> Soil solidification materials are mixed into the ground to solidify the soil and improve its strength. Examples of ground solidification materials include one or more selected from cement and cement-based solidification materials.

[0015] Examples of cement include Portland cement, blended cement, eco-cement, and special cement. Portland cement includes various types such as ordinary, rapid-hardening, very rapid-hardening, moderate-heat, low-heat, and sulfate-resistant types.

[0016] Ordinary Portland cement is the most common type of cement, most widely used for construction or finished products. High-early-strength Portland cement is a type of cement that achieves high strength early on and continues to increase in strength over the long term. Ultra-high-early-strength Portland cement is a cement with an even higher alite (C3S) content and finer particle size than regular high-early-strength Portland cement. Ultra-high-early-strength Portland cement achieves the 3-day strength of regular high-early-strength Portland cement in just one day. Moderate-heat Portland cement has reduced levels of C3S and aluminate (C3A) and increased levels of beelite (C2S) to lower the heat of hydration. As a result, it has low initial strength but high long-term strength. Low-heat Portland cement has a higher C2S content than moderate-heat Portland cement to reduce the heat of hydration, with a C2S content of 40% by mass or more. Low-heat Portland cement is characterized by good strength development in the high-strength range and easy acquisition of high fluidity in concrete with a low water-to-powder ratio. Sulfate-resistant Portland cement is a type of cement with reduced reactivity to sulfates by decreasing the amount of C3A. It is suitable for construction in areas with sulfate-containing soil and also exhibits excellent resistance to seawater.

[0017] Examples of blended cements include blast furnace cement, silica cement, and fly ash cement. Blast furnace cement is cement mixed with blast furnace slag. Blast furnace slag is formed when non-iron components such as silica contained in iron ore, and coke ash, are combined with limestone, which is used as a secondary raw material. Blast furnace slag has latent hydraulic properties and gradually hardens when stimulated by Portland cement. Blast furnace cement has low initial strength but high long-term strength. Blast furnace cement is classified into three types—Type A, Type B, and Type C—depending on the amount of blast furnace slag mixed in (JIS R5211:2009). Blast furnace cement type A... Blast furnace slag content: 5-30% by mass Blast furnace cement type B... Blast furnace slag content: 10-60% by mass Blast furnace cement type C... Blast furnace slag content: 60-70% by mass

[0018] Silica cement is a type of cement made by mixing high-purity silica powder with other materials. Silica cement is used in products that require autoclave curing. Fly ash cement is cement mixed with fly ash, which is produced when pulverized coal is burned. Fly ash cement has high long-term strength and can be used to create highly durable structures.

[0019] Ecocement is a type of cement made using at least 500 kg (dry weight) of waste materials such as municipal solid waste incineration ash and sewage sludge per ton of product. Ecocement is classified into ordinary ecocement and rapid-setting ecocement depending on the amount of chloride ions in the cement. Ordinary eco-cement is an eco-cement that has been dechlorinated during the manufacturing process, with a chloride ion content of 0.1% or less. Ordinary eco-cement has properties similar to ordinary Portland cement in terms of both setting time and mortar compressive strength. Rapid-setting eco-cement is an eco-cement with a chloride ion content of 0.5% to 1.5%. Rapid-setting eco-cement is a cement that exhibits rapid hardening properties and takes advantage of its ability to develop strength quickly.

[0020] Special cements are manufactured as non-JIS standard products and include white Portland cement, alumina cement, ultrafast-setting cement, colloidal cement, oil well cement, low-heat cement, and high-belite cement. High-belite cement is a cement formulated for low-heat applications, with the high heat-generating aluminate (C3A) phase of the cement components minimized, and belite (C2S), which has low heat of hydration, becoming the main component. Because high-belite cement suppresses heat of hydration, it is easy to produce concrete with good fluidity. High-belite cement is suitably used for large structures.

[0021] Portland cement generates carbon dioxide during the thermal decomposition of limestone (CaCO3 → CaO + CO2↑) and the fuel required for firing during the manufacturing process. On the other hand, blast furnace slag powder, which is an admixture in blast furnace cement, does not require firing, and therefore the amount of carbon dioxide emitted during cement production can be reduced in proportion to the amount of blast furnace slag used. For this reason, blast furnace cement is preferred as the cement in this embodiment, and blast furnace cement type B or blast furnace cement type C, which have a high amount of blast furnace slag mixed in, is more preferred. Cement may be used alone or in combination of two or more types. Alternatively, instead of using a blended cement, such as blast furnace cement, a mixture of cement other than blast furnace cement and blast furnace slag may be used during construction.

[0022] Cement-based solidifying agents are solidifying agents that use cement as a base and add various active ingredients to effectively improve the ground. Examples of active ingredients include inorganic compounds containing sulfates. Commercial cement-based solidifying agents may be used, and examples of commercially available cement-based solidifying agents include the GeoSet® series from Taiheiyo Cement Corporation.

[0023] As a ground solidification material, a cement-based solidification material is preferred because it can further increase the strength of the ground, a cement-based solidification material made from blast furnace cement is more preferred because it can further reduce CO2 emissions, a cement-based solidification material made from blast furnace cement type B or blast furnace cement type C is even more preferred, and a cement-based solidification material made from blast furnace cement type C is particularly preferred.

[0024] In the construction method of this embodiment, soil and molten slag are mixed to obtain a primary mixture. Since the water content of molten slag is lower than that of soil, the water content of the primary mixture can be reduced. Furthermore, by mixing molten slag, which has a low fine particle content, with soil, the particle size composition of the primary mixture changes, and a compaction effect can be expected. As a result, the efficiency of ground reinforcement by adding a ground solidification agent can be further increased.

[0025] The ratio of the volume of molten slag to the volume of soil in the primary mixture is preferably, for example, 1:99 to 50:50, more preferably 10:90 to 50:50, and even more preferably 25:75 to 50:50. When the ratio of the volume of molten slag to the volume of soil is above the lower limit, the amount of soil solidification material used to obtain ground of a predetermined strength can be further reduced, and CO2 emissions can be further reduced. In addition, when the ratio of the volume of molten slag to the volume of soil is above the lower limit, the strength of the ground can be further increased when the same amount of soil solidification material is used. When the ratio of the volume of molten slag to the volume of soil is below the upper limit, the amount of soil that can be treated can be further increased. Therefore, more improved ground can be obtained.

[0026] The method for obtaining the primary mixture is not particularly limited, and one method is to stir and mix the soil and molten slag. In this case, the soil may be excavated in situ, then the molten slag may be added and stirred, or the molten slag may be sprinkled on the surface of the soil, and then the soil and molten slag may be stirred and mixed to obtain the primary mixture. Mixing machines for combining soil and molten slag include, for example, backhoes, self-propelled soil improvement machines, wheeled stabilizers, crawler stabilizers, mud carriers, and soil rimers.

[0027] The soil solidification agent is added to the primary mixture and mixed. At this time, the total volume of the primary mixture is 1 m³. 3 The amount of soil solidification agent added is preferably 200 kg or less, more preferably 180 kg or less, and even more preferably 150 kg or less. Total volume of primary mixture 1 m³ 3 If the amount of ground solidification material added is below the above upper limit, the amount of ground solidification material used can be further reduced, and CO2 emissions originating from the manufacture of ground solidification material can be further reduced. From the perspective of maintaining the strength of the ground, the total volume of the primary mixture is 1 m³. 3 The amount of ground solidification material added is preferably 20 kg or more, more preferably 30 kg or more, and even more preferably 50 kg or more.

[0028] In the construction method of this embodiment, the reduction in the amount of ground solidification material used is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and particularly preferably more than 50% by mass, compared to the amount of ground solidification material used when molten slag is not used. If the reduction in the amount of ground solidification material used is equal to or greater than the above lower limit, CO2 emissions originating from the manufacture of ground solidification material can be further reduced. From the viewpoint of maintaining the strength of the ground, the upper limit of the reduction in the amount of ground solidification material used is preferably, for example, 80% by mass. The reduction in the amount of soil solidification material used is, for example, when the unconfined compressive strength of the mixture (structure) after 7 days of mixing soil and soil solidification material is 200 kN / m². 2In this case, the amount of ground solidification material to be used and the uniaxial compressive strength of the structure 7 days after mixing the primary mixture and the ground solidification material is 200 kN / m 2 This can be calculated from the amount of ground solidification material used in such cases. The uniaxial compressive strength of the structure can be measured in accordance with the method described in "Strength Test Method for Improved Structures Using Cement-Based Solidifying Agents L-01:2006," a standard test method specified by the Japan Cement Association.

[0029] <Carbon dioxide fixed product> In the construction method of this embodiment, it is preferable to further add a carbon dioxide fixative capable of fixing carbon dioxide to the primary mixture. By further adding and mixing the carbon dioxide fixative to the primary mixture, the CO2 emissions originating from the production of the ground solidification material can be further reduced and offset. The carbon dioxide fixative is not particularly limited as long as it is a substance that can fix carbon dioxide, for example, biochar. In this specification, biochar refers to a solid material produced by heating biomass at a temperature exceeding 350°C under an oxygen concentration controlled to a level that does not cause combustion.

[0030] When adding carbon dioxide fixative to a primary mixture, the carbon dioxide fixative is mixed with the ground solidification material before being added. The amount of carbon dioxide fixative added to mix with the ground solidification material varies depending on the amount of carbon dioxide fixed by the carbon dioxide fixative. For example, in the case of biochar, 18 kg or more is preferred, 20 kg or more is more preferred, and 25 kg or more is even more preferred, per 100 kg of ground solidification material. If the amount of carbon dioxide fixative added is above the lower limit mentioned above, CO2 emissions originating from the production of the ground solidification material can be further reduced. There is no particular upper limit to the amount of carbon dioxide fixative added; for example, it may be 100 kg or less per 100 kg of ground solidification material.

[0031] Methods for reducing carbon dioxide emissions The method for reducing carbon dioxide emissions according to the present invention is a method for reducing carbon dioxide emissions in a construction method for solidifying the ground, which comprises mixing soil constituting the ground and molten slag to obtain a primary mixture, and adding one or more ground solidifying materials selected from cement and cement-based solidifying materials to the primary mixture followed by mixing to solidify the ground. The method for reducing carbon dioxide emissions according to the present invention reduces the usage amount of a ground solidifying material relative to the usage amount of the ground solidifying material when no molten slag is used, thereby reducing carbon dioxide emissions derived from the production of the ground solidifying material. The soil, molten slag and ground solidifying material are the same as the soil, molten slag and ground solidifying material in the construction method described above.

[0032] The carbon dioxide emissions of the present embodiment are the total amount of carbon dioxide emitted in the step of producing molten slag, the step of producing a ground solidifying material, and the construction method described above (hereinafter also referred to as the ground improvement step). In the step of producing molten slag, carbon dioxide is emitted when incineration ash is melted in the process of incinerating industrial waste and sludge to obtain incineration ash. Let this emission amount be X (kg). Note that the mass of carbon dioxide emitted when producing 1 kg of molten slag is substantially zero when considering heat utilization obtained during production. In the step of producing a ground solidifying material, a large amount of carbon dioxide is emitted when cement is fired. Let this emission amount be Y (kg). Note that the mass of carbon dioxide emitted when producing 1 kg of the ground solidifying material is 470 g. In the ground improvement step, carbon dioxide is emitted when mixing soil, molten slag and the ground solidifying material. Let this emission amount be Z (kg). Let S (kg) be the total amount of carbon dioxide emissions of the present embodiment, then S is represented by S=(X+Y+Z). From the viewpoint of increasing ground strength, increasing the addition amount of molten slag can reduce the usage amount of the ground solidifying material, but in terms of carbon dioxide emissions, X increases. However, due to the relationship X<<Y, for S, the amount of decrease in Y is extremely larger than the amount of increase in X, and as a result, S decreases. As described above, reducing the addition amount of the ground solidification material when obtaining ground having a predetermined strength can significantly reduce carbon dioxide emissions. In addition, by further adding a carbon dioxide immobilizing material capable of immobilizing carbon dioxide to the primary mixture and mixing the resulting mixture, S can be further reduced, and carbon dioxide emissions can be reduced to 0 (zero) or -(negative).

[0033] In the method for reducing carbon dioxide emissions of the present embodiment, the reduction amount of the usage amount of the ground solidification material is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 50% by mass or more, and particularly preferably more than 50% by mass, relative to the usage amount of the ground solidification material when molten slag is not used. When the reduction amount of the usage amount of the ground solidification material is equal to or more than the above lower limit, CO2 emissions derived from the production of the ground solidification material can be further reduced. The reduction amount of the usage amount of the ground solidification material can be determined, for example, based on the usage amount of the ground solidification material when the unconfined compressive strength of the mixture (structure) 7 days after mixing soil and the ground solidification material is 200kN / m 2 and the usage amount of the ground solidification material when the unconfined compressive strength of the structure 7 days after mixing soil, molten slag and the ground solidification material is 200kN / m 2 . The unconfined compressive strength of the structure can be measured in accordance with the method described in "Strength Test Method for Improved Ground by Cement-based Solidification Material L-01:2006", which is a standard test method specified by the Cement Association of Japan.

[0034] In the primary mixture of soil and molten slag, the ratio of the volume of molten slag to the volume of soil is preferably, for example, 1:99 to 50:50, more preferably 10:90 to 50:50, and even more preferably 25:75 to 50:50. When the ratio of the volume of molten slag to the volume of soil is above the lower limit, the amount of soil solidification material used to obtain ground of a predetermined strength can be further reduced, and CO2 emissions can be further reduced. In addition, when the ratio of the volume of molten slag to the volume of soil is above the lower limit, the strength of the ground can be further increased when the same amount of soil solidification material is used. When the ratio of the volume of molten slag to the volume of soil is below the upper limit, the amount of soil that can be processed can be further increased. Therefore, more improved ground can be obtained.

[0035] Total volume of primary mixture: 1 m³ 3 The amount of ground solidification material used is preferably 200 kg or less, more preferably 180 kg or less, and even more preferably 150 kg or less. If the amount of ground solidification material used is below the above upper limit, carbon dioxide emissions can be further reduced. The lower limit of the amount of ground solidification material used is, for example, 20 kg, from the viewpoint of obtaining ground of a predetermined strength.

[0036] In this embodiment, the method for reducing carbon dioxide emissions preferably involves further adding a carbon dioxide fixative capable of fixing carbon dioxide to the primary mixture. By further adding and mixing the carbon dioxide fixative to the primary mixture, CO2 emissions originating from the production of the ground solidification material can be further reduced and offset. The carbon dioxide fixative is not particularly limited as long as it is a substance that can fix carbon dioxide, for example, biochar.

[0037] When adding carbon dioxide fixative to a primary mixture, the carbon dioxide fixative is mixed with the ground solidification material before being added. The amount of carbon dioxide fixative added to mix with the ground solidification material varies depending on the amount of carbon dioxide fixed by the carbon dioxide fixative. For example, in the case of biochar, 18 kg or more is preferred, 20 kg or more is more preferred, and 25 kg or more is even more preferred, per 100 kg of ground solidification material. If the amount of carbon dioxide fixative added is above the lower limit mentioned above, CO2 emissions originating from the production of the ground solidification material can be further reduced. There is no particular upper limit to the amount of carbon dioxide fixative added; for example, it may be 100 kg or less per 100 kg of ground solidification material.

[0038] The construction method of the present invention involves adding and mixing a ground solidification agent to a primary mixture of soil and molten slag, thereby enabling the production of ground with a predetermined strength even when the amount of ground solidification agent used is reduced. The construction method of the present invention can reduce the amount of ground solidification material used compared to the amount used when molten slag is not used, and therefore can reduce the amount of carbon dioxide emitted during the manufacture of ground solidification material. The construction method of the present invention utilizes molten slag, thereby effectively making use of incinerated waste ash and contributing to a reduction in the burden on the global environment. The present invention provides a method for reducing carbon dioxide emissions, which, by using molten slag, can reduce the amount of ground solidification material used in the ground improvement process and reduce the amount of carbon dioxide emissions generated by the manufacture of the ground solidification material. The present invention's method for reducing carbon dioxide emissions contributes to reducing the burden on the global environment by reducing the amount of carbon dioxide emitted during the manufacture of ground solidification materials. [Examples]

[0039] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. The materials used are as follows.

[0040] [Materials used] <Saturday> Cohesive soil (loam soil, unconfined compressive strength 121 kN / m²) 2 ). <Molten slag> Molten slag: NS Eco Sand (registered trademark), Nippon Steel Engineering Co., Ltd. <Ground solidification material> Cement: Blast furnace cement type B, UBE Mitsubishi Cement Corporation. Cement-based solidifying agent: Geoset (registered trademark) 200, Taiheiyo Cement Corporation.

[0041] <<Uniaxial compressive strength of the ground>> The unconfined compressive strength of the ground was measured in accordance with the method described in "Strength Test Method for Improved Ground with Cement-Based Solidifying Agents L-01:2006," a standard test method stipulated by the Japan Cement Association. Specifically, the measurement was performed using the following procedure.

[0042] [Example 1] Prepare 500g of a primary mixture by mixing soil and molten slag in a volume ratio of 50:50, and the volume of the primary mixture is 1m³ 3 For each primary mixture, a soil solidification agent (blast furnace cement) was added in proportions of 50 kg, 100 kg, and 150 kg, respectively. The mixture was then stirred and mixed uniformly in a mixer (4.7 L Hobart-type soil mixer, rotational motion 120-300 rpm, orbital motion 30-125 rpm) in a room at 20°C to obtain improved soil. The improved soil was placed in a mold fitted with a cylindrical collar measuring 5 cm in diameter and 10 cm in height, and test specimens were prepared by compacting it using a 1.5 kg rammer. The compaction method involved dropping a 1.5 kg hammer from a height of 20 cm, compacting the soil in three layers. Each layer was compacted 12 times. The amount of improved soil added to the mold was adjusted so that each layer compacted was approximately one-third of the height of the specimen after compaction. Notches were made at the end of each layer using a spatula or similar tool to ensure good contact with the layer above. After compacting three layers, the collar was removed and the excess soil on top of the mold was carefully scraped off with a straight edge. Holes created on the surface due to sand grains, etc., were filled with the fine-grained portion of the improved soil, and the surface was smoothed to the same height as the top of the mold. The prepared specimens were covered with polyethylene film, secured with rubber bands to prevent surface drying, and left to cure until the next day. After one day, the specimens were removed from the mold and sealed in a constant temperature and humidity chamber at 20±3°C and a relative humidity of 95% or higher to prevent moisture evaporation. Uniaxial compression tests were performed on each specimen after 3, 7, and 28 days of age, in accordance with the method described in JIS A1216:1998 "Uniaxial Compression Test Method for Soil". The uniaxial compressive strength was calculated as the arithmetic mean of the measurement results of three specimens under identical conditions. The results are shown in Figures 1-3.

[0043] [Example 2] Except for using a volume ratio of 75:25 between soil and molten slag, specimens were prepared in the same manner as in Example 1, and the uniaxial compressive strength was measured. The results are shown in Figures 1-3.

[0044] [Comparative Example 1] Except for using only soil (volume ratio 100:0) and not molten slag, specimens were prepared in the same manner as in Example 1, and the uniaxial compressive strength was measured. The results are shown in Figures 1 to 3.

[0045] As shown in Figure 1, at 3 days of age, 100 kg / m³ of ground solidification material is used. 3 It was confirmed that adding it in this proportion increases the unconfined compressive strength, i.e., the ground strength. It was also confirmed that the higher the proportion of molten slag in the primary mixture, the greater the increase in unconfined compressive strength. As shown in Figure 2, it was confirmed that the uniaxial compressive strength was higher at 7 days of age compared to 3 days of age. Furthermore, it was confirmed that Example 1 had a higher uniaxial compressive strength than Example 2. As shown in Figure 3, it was confirmed that the uniaxial compressive strength was higher at 28 days of age compared to 7 days of age. Furthermore, the uniaxial compressive strength was significantly higher in Example 1 than in Example 2. Furthermore, the uniaxial compressive strength is 300 kN / m 2 To achieve the above, in the case of Comparative Example 1, 150 kg / m³ of ground solidification material was used. 3 The above proportions are necessary for addition, but in the case of Example 2, it is 120 kg / m³. 3A small amount of additive is sufficient (reduction of ground solidification material by 20% by mass), and in the case of Example 1, 75 kg / m 3 It was found that such a small amount of additive was sufficient (a reduction of 50% by mass in the amount of ground solidification material). In other words, the required strength (uniaxial compressive strength of 300 kN / m) was achieved. 2 It was found that to obtain the desired ground conditions, the greater the amount of molten slag included in the primary mixture, the less mass of ground solidification material can be added. This is thought to be because the water content of molten slag is lower than that of soil, thus reducing the water content of the primary mixture. In addition, by mixing molten slag with a low fine particle content with soil, the particle size composition of the primary mixture changes, which is expected to have a compaction effect and thus increase the efficiency of ground reinforcement through the addition of ground solidification material.

[0046] [Example 3] Except for using a cement-based solidification material as the ground solidification agent, specimens were prepared in the same manner as in Example 1, and their uniaxial compressive strength was measured. The results are shown in Figures 4 to 6.

[0047] [Example 4] Except for using a cement-based solidification material as the ground solidification agent, specimens were prepared in the same manner as in Example 2, and their uniaxial compressive strength was measured. The results are shown in Figures 4 to 6.

[0048] [Comparative Example 2] Except for using a cement-based solidification material as the ground solidification agent, specimens were prepared in the same manner as in Comparative Example 1, and their uniaxial compressive strength was measured. The results are shown in Figures 4 to 6.

[0049] [Example 5] Molten slag was spread in an outdoor yard so that the volume ratio of soil to molten slag was 75:25, and the total volume of the primary mixture of soil and molten slag was 1 m³. 3 Further cement-based solidifying agent was spread so that the mass of the cement-based solidifying agent relative to the primary mixture was 100 kg. The primary mixture and the cement-based solidifying agent were mixed using a crawler-type stabilizer to obtain improved soil. Using the improved soil obtained, specimens were prepared in the same manner as in Example 1, and the unconfined compressive strength was measured for specimens at 3 days and 7 days of age, in the same manner as in Example 1. For the unconfined compressive strength, three specimens were prepared at each of four different yards, and the arithmetic mean of these three specimens was used. The results are shown in Figures 4-5.

[0050] As shown in Figure 4, at 3 days of age, 100 kg / m³ of ground solidification material is used. 3 It was confirmed that adding the material at this ratio could increase the unconfined compressive strength. Furthermore, the amount of ground solidification material added was 150 kg / m³. 3 As a result, it was confirmed that the specimens in Examples 3 and 4 achieved more than 1.3 times the strength of the specimens in Examples 1 and 2. This means that cement-based solidifying agents can increase the strength of the ground more effectively than blast furnace cement. The specimens in Example 5 showed a large variation in unconfined compressive strength. This is thought to be due to variations in the soil quality (cohesive soil) of the yard.

[0051] As shown in Figure 5, it was confirmed that the unconfined compressive strength was higher at 7 days of age compared to 3 days of age. Furthermore, it was confirmed that the unconfined compressive strength was higher in Example 3 than in Example 4. In particular, when the ground solidification material was 150 kg / m 3 When added in this proportion, the specimen of Example 3 had more than twice the uniaxial compressive strength compared to the specimen of Example 1. The specimens in Example 5 showed greater variation in uniaxial compressive strength compared to the specimens in Example 4.

[0052] As shown in Figure 6, it was confirmed that the uniaxial compressive strength was higher at 28 days of age compared to 7 days of age. Furthermore, the uniaxial compressive strength was significantly higher in Example 3 than in Example 4. For example, a uniaxial compressive strength of 400 kN / m 2 To achieve the above, in the case of Comparative Example 2, the amount of ground solidification material used was 150 kg / m³. 3 The above proportions are necessary for addition, but in the case of Example 4, it is 100 kg / m 3A small amount of additive is sufficient (reduction of ground solidification material: 33% by mass), and in the case of Example 3, 75 kg / m 3 It was found that such a small amount of additive was sufficient (a reduction of 50% by mass in the amount of ground solidification material). In other words, the required strength (uniaxial compressive strength of 400 kN / m) was achieved. 2 It was found that the greater the amount of molten slag in the primary mixture, the less mass of ground solidification material can be added in order to obtain the desired ground conditions.

[0053] [Experimental Examples 1-4] (Relationship between water content and uniaxial compressive strength) The water content of each specimen was measured using the water content measuring instrument described in JIS A1216:1998 "Method for uniaxial compression testing of soil". 150 kg / m³ of improved soil was added to Example 1, Example 2, and Comparative Example 1. 3 Figures 7-9 show the relationship between the water content and unconfined compressive strength of specimens prepared by adding a ground solidification agent (blast furnace cement) as Experimental Example 1. 100 kg / m³ of improved soil was added to Example 1, Example 2, and Comparative Example 1. 3 Figures 7-9 show the relationship between the water content and unconfined compressive strength of specimens prepared by adding a ground solidification agent (blast furnace cement) as Experimental Example 2. 50 kg / m³ of improved soil was added to Example 1, Example 2, and Comparative Example 1. 3 Figures 7-9 show the relationship between the water content and unconfined compressive strength of specimens prepared by adding a ground solidification agent (blast furnace cement) as Experimental Example 3. Figures 7-9 show the relationship between the water content and unconfined compressive strength of specimens prepared without adding a soil solidification agent to the improved soil of Example 1, Example 2, and Comparative Example 1, as Experimental Example 4.

[0054] As shown in Figure 7, it was confirmed that, at 3 days of age, the greater the amount of soil solidification agent added and the lower the water content of the specimen, the higher the unconfined compressive strength. Furthermore, the water content was lower the more molten slag was used, and in each experimental example, the water content was lowest in Example 1, followed by Example 2, and then Comparative Example 1. Furthermore, in Experimental Example 4, the specimens in Example 1 in which no soil solidification agent was added to the improved soil showed a decrease in unconfined compressive strength.

[0055] As shown in Figure 8, it was confirmed that the unconfined compressive strength was higher at 7 days of age compared to 3 days of age. Furthermore, it was confirmed that the lower the moisture content, the higher the unconfined compressive strength.

[0056] As shown in Figure 9, it was confirmed that the unconfined compressive strength was higher at 28 days of age compared to 7 days of age. Furthermore, it was confirmed that the lower the moisture content, the more significantly the unconfined compressive strength was increased. It was confirmed that the uniaxial compressive strength of the specimens in Experimental Example 4 was independent of the age of the wood.

[0057] [Experimental Examples 5-10] The water content of each specimen was measured using the water content measuring instrument described in JIS A1216:1998 "Method for uniaxial compression testing of soil". 150 kg / m³ was added to the improved soil of Examples 3, 4, and Comparative Example 2. 3 Figures 10-12 show the relationship between the water content and unconfined compressive strength of specimens prepared by adding a ground solidification agent (cement-based solidification agent) as Experimental Example 5. 100 kg / m³ of improved soil was added to the improved soil of Examples 3, 4, and Comparative Example 2. 3 Figures 10-12 show the relationship between the water content and unconfined compressive strength of specimens prepared by adding a ground solidification agent (cement-based solidification agent) as Experimental Example 6. 50 kg / m³ of improved soil was added to the soils of Examples 3, 4 and Comparative Example 2. 3 Figures 10-12 show the relationship between the water content and unconfined compressive strength of specimens prepared by adding a ground solidification agent (cement-based solidification agent) as Experimental Example 7. Figures 10-12 show the relationship between the water content and unconfined compressive strength of specimens prepared without adding a soil solidification agent to the improved soil of Example 3, Example 4, and Comparative Example 2, as Experimental Example 8. The relationship between the water content and uniaxial compressive strength of the specimens in Example 5 is shown in Figures 10-12 as Experimental Example 9. Figures 10-12 show the relationship between the water content and unconfined compressive strength of specimens prepared from soil samples taken from two different outdoor yards, as Experimental Example 10. The water content was measured using the same method as in Experimental Examples 1-4.

[0058] As shown in Figure 10, in Experimental Example 5, it was confirmed that the uniaxial compressive strength could be increased at 3 days of age. In Experimental Example 6, it was confirmed that the uniaxial compressive strength was increased in the specimen with the lowest moisture content. Furthermore, the water content was lower the more molten slag was used, and in each experimental example, the water content was lowest in Example 3, followed by Example 4, and then Comparative Example 2. Experimental examples 7 and 8 showed similar uniaxial compressive strengths regardless of water content. Experimental examples 9 and 10 confirmed that lower water content is associated with higher unconfined compressive strength.

[0059] As shown in Figure 11, at 7 days of age, it was confirmed that the uniaxial compressive strength of the specimens using improved soil in Examples 3 and 4 of Experimental Examples 5 and 6 was significantly higher compared to the case at 3 days of age. In Experimental Example 7, it was confirmed that the uniaxial compressive strength was increased in the specimens using the improved soil from Examples 3 and 4. In other experimental cases, no improvement in uniaxial compressive strength was observed compared to the case with 3 days of age.

[0060] As shown in Figure 12, at 28 days of age, it was confirmed that the uniaxial compressive strength of the specimen using the improved soil in Example 3 of Experimental Examples 5 and 6 was significantly higher compared to the case at 7 days of age. Of the experimental examples 5 and 6, it was confirmed that the uniaxial compressive strength was increased in the specimens using the improved soil of Example 4. In the seven experimental examples, it was confirmed that the unconfined compressive strength was increased in the specimens using the improved soil in Examples 3 and 4. Other experimental examples confirmed that the uniaxial compressive strength of the specimens is independent of the age of the wood.

[0061] As shown in Experimental Examples 1 to 10, it was confirmed that by mixing molten slag with soil to obtain a primary mixture and reducing the water content, the uniaxial compressive strength of the specimens could be increased when a soil solidification agent was added to the primary mixture and stirred. Furthermore, it was confirmed that by using a large amount of molten slag, the uniaxial compressive strength of the test specimen could be increased even with a reduction in the amount of ground solidification material added. Thus, it was confirmed that reducing the amount of ground solidification material used can reduce the carbon dioxide emissions generated by the manufacture of ground solidification material, thereby contributing to a reduction in the burden on the global environment.

Claims

1. A primary mixture is obtained by mixing the soil constituting the ground with molten slag, and one or more ground solidification materials selected from cement and cement-based solidification materials are added to the primary mixture and mixed to solidify the ground. A construction method in which the aforementioned soil is cohesive soil.

2. A primary mixture is obtained by mixing the soil constituting the ground with molten slag, and one or more ground solidification materials selected from cement and cement-based solidification materials are added to the primary mixture and mixed to solidify the ground. A construction method in which, when mixing the soil and the molten slag, the soil is excavated in its original location before the molten slag is added.

3. A primary mixture is obtained by mixing the soil constituting the ground with molten slag, and one or more ground solidification materials selected from cement and cement-based solidification materials are added to the primary mixture and mixed to solidify the ground. A construction method comprising further adding a carbon dioxide fixative capable of fixing carbon dioxide to the primary mixture.

4. The construction method according to any one of claims 1 to 3, wherein the ratio of the volume of molten slag to the volume of soil in the primary mixture is 1:99 to 50:

50.

5. The total volume of the primary mixture is 1 m³ ３ The construction method according to any one of claims 1 to 3, wherein the amount of the ground solidification material added is 200 kg or less.

6. A method for reducing carbon dioxide emissions in a construction method in which soil constituting the ground and molten slag are mixed to obtain a primary mixture, and one or more ground solidification materials selected from cement and cement-based solidification materials are added to the primary mixture and mixed to solidify the ground, Compared to the amount of ground solidification material used when the molten slag is not used, the amount of ground solidification material used is reduced, and carbon dioxide emissions originating from the manufacture of the ground solidification material are reduced. A method for reducing carbon dioxide emissions, comprising further adding a carbon dioxide fixative capable of fixing carbon dioxide to the primary mixture.

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