Consolidating material, method for constructing earth structures using the same, and ground improvement method

Abstract

This invention provides a sustainable and environmentally friendly consolidating material that can be supplied stably and does not cause environmental problems such as environmental pollution or increased carbon dioxide emissions, thereby enabling not only carbon neutrality but also carbon negativity, as well as a method for constructing soil structures and a ground improvement method using this material. [Solution] This solidifying material is mainly composed of silica-containing combustion products, which are obtained by partially burning and cooling land-derived waste and contain SiO2 and carbon as active ingredients. The amorphous silica in the silica-containing combustion products undergoes a hydration reaction and solidifies, thereby enabling carbon negativity.

Description

Technical Field

[0001] The present invention relates to a solidifying material that enables carbon negativity by using a material containing metals such as silica contained in industrial waste derived from terrestrial products and calcium derived from industrial waste such as industrial waste derived from marine products, a method for constructing an earth structure using the same, and a ground improvement method.

[0002] With the movement such as the Paris Agreement, today, countermeasures against global warming have become a common issue for the world, and the issue of reducing CO2 emissions in industrial activities is widely recognized. From such a perspective, the present inventors have conducted research on a solidifying material that enables the realization of carbon negativity, which can be said to be a more ultimate goal than achieving carbon neutrality, in order to contribute to environmental protection, and have completed the present invention.

[0003] Carbon negativity means a state where the amount of absorption exceeds the amount of emissions of greenhouse gases including CO2. That is, carbon negativity aims to make the CO2 emissions negative (minus). There is a term "carbon neutral" that is very similar to carbon negativity. Carbon neutral means a state where the difference between the CO2 emissions and the absorption amount is substantially zero. That is, it indicates a state of "emissions = absorption amount" where all the CO2 emitted in corporate business activities and the like is absorbed by some method. Since carbon negativity is a concept of "emissions < absorption amount", it can be said to be a state that is one step further from carbon neutrality.

[0004] For example, the terrestrial plants used in the present invention absorb and fix CO2 in the atmosphere by photosynthesis during the growth process. Therefore, unlike cement that emits a large amount of CO2 during production, it is a material that can realize carbon negativity where the amount of CO2 fixation exceeds the emissions.

Background Art

[0005] In Japan, where cities are built on soft ground such as river basins, numerous cases of damage due to soil liquefaction and sliding failure have been reported following major earthquakes. Against this backdrop, ground improvement methods such as cement mixing and chemical grouting are being implemented.

[0006] Cement-improved soil is soil that has been treated with 5-15% (50-200 kg / m³) of its dry mass. 3 It is made by adding a suitable amount of water to cement (mainly ordinary Portland cement), mixing, and compacting it to solidify it. The purposes of ground improvement using cement-based consolidating materials are diverse, including earthquake resistance and liquefaction countermeasures, and it is used in a wide range of improvement sites. On the other hand, it is known that the carbon dioxide emissions during the manufacturing process of ordinary Portland cement are estimated to be about 800 kg / t, which is quite high.

[0007] In response to this, currently, in order to reduce carbon dioxide emissions, blast furnace cement mixed with blast furnace slag or fly ash cement mixed with fly ash are being used instead of ordinary Portland cement. However, the carbon dioxide emissions during the manufacturing process of blast furnace slag and fly ash are approximately 20 kg / t and 25 kg / t, respectively, and it is known that the total carbon dioxide emissions during the manufacturing process of cement using these as admixtures are approximately 500 to 600 kg / t.

[0008] Furthermore, during the manufacturing process of ordinary Portland cement, trivalent chromium contained in the raw materials oxidizes, producing hexavalent chromium, a harmful substance that does not exist in nature. While sufficient hydration can be achieved in concrete products and structures, in cement-improved soil, sufficient hydration cannot be achieved due to the chemical composition of the soil, the heterogeneity of the ground, or the construction method. This raises concerns that hexavalent chromium may leach out, potentially causing environmental pollution.

[0009] Furthermore, since blast furnace slag and fly ash are by-products obtained from the Earth's resources, there is a possibility that their supply may become unavailable in the future. Specifically, fly ash is a by-product obtained when burning coal ash to generate electricity, but in recent years, there has been a shift from coal-fired power generation to renewable energy sources such as solar and wind power, so it is expected that the supply will decrease in the future. Similarly, blast furnace slag is a by-product generated when iron is melted and reduced from iron ore in a blast furnace, but because blast furnaces emit large amounts of carbon dioxide, there is a shift towards electric arc furnaces using renewable energy, and in addition, the recycling of waste iron is progressing, in which case electric arc furnaces are used. Therefore, the supply of blast furnace slag will also tend to decrease in the future.

[0010] The combustion temperature of ordinary Portland cement is around 1,300°C, while that of coal-fired power plants and blast furnaces is 1,500°C.

[0011] On the other hand, chemical grouting involves injecting a gelling liquid through injection pipes installed in the ground, replacing the pore water between soil particles and solidifying the ground. While chemical grouting was traditionally used as a temporary auxiliary method, recent technological improvements have increased its durability, leading to its use in liquefaction countermeasures and seismic reinforcement work. Among the solution-type grouting materials that offer good durability, there are activated silica colloid systems, and among the suspension-type grouting materials, there is ultrafine particle composite silica. However, activated silica colloid systems use colloidal silica obtained by removing the alkali from water glass with ion exchange resin and then curing it by heat as the main component, which tends to result in high carbon dioxide emissions during the manufacturing process. On the other hand, ultrafine particle composite silica uses granulated blast furnace slag as the main component, and therefore faces the same challenges as the blast furnace slag mentioned above.

[0012] Furthermore, studies are being conducted on producing highly active clinker by mixing ash obtained from burning plants with cement and firing it. However, since cement is used as the base material, it cannot be said that the reduction in carbon dioxide emissions is significant. In addition, a technology is being considered to use a mixture of rice husk ash and cement as a ground improvement material. However, since it is used as a cement admixture, it cannot be said that the reduction in carbon dioxide emissions is significant, and the improvement strength tends to decrease as the ash replacement rate increases, it is difficult to say that a sufficient pozzolanic reaction is being obtained.

[0013] Regarding conventional technologies for ground improvement using waste materials, for example, Patent Document 1 describes a technology using coal ash. However, coal ash is produced as a residue after extracting iron by melting iron ore at high temperatures of 1000°C to 1360°C, and its production itself consumes a huge amount of energy, so it cannot be considered a material that reduces CO2. Non-Patent Document 1 describes a ground improvement technology using materials derived from land and marine waste by the present inventors, but this technology is a technology that reduces CO2, and does not relate to research that has progressed to the development of specific methods for making the project carbon negative. Furthermore, Non-Patent Document 2 describes a technology related to river embankment materials using papermaking incineration ash. However, this is a technology related to the effective utilization of papermaking waste materials that are artificially generated in the papermaking industry, and is different from the technology that uses waste materials that deteriorate under natural conditions, as in the present invention. Furthermore, Non-Patent Document 3 describes a conventional technology related to the effective utilization of seashells. However, this technology utilizes carbon dioxide generated during the calcination of oyster shells to activate charcoal, aiming to produce high-performance charcoal and effectively utilize calcium components. Activation is a reaction operation that transforms carbonaceous raw materials into porous materials, and is different from the carbon-negative technology using land-derived waste in the present invention. Furthermore, Non-Patent Document 4 describes concrete mixed with granulated rice husk charcoal, but this technology involves mixing rice husk charcoal, obtained by carbonizing rice husks, into concrete to add a self-curing function to the concrete by utilizing the water retention properties of the rice husk charcoal, and is different from the present invention. Furthermore, Non-Patent Document 5 describes concrete mixed with charcoal powder as an admixture. However, as mentioned above, this technology is also different from the present invention. The same applies to Non-Patent Document 6.

[0014] Thus, while incinerated ash from land-derived waste such as plants is used as a soil modifier and concrete additive, an effective formulation for using it as a solidifying agent with soil solidification as the main component has not been established. Similarly, incinerated ash from seashells is used as a concrete additive and a soil pH adjuster and solidifying agent, but its solidification mechanism is due to the reaction of the lime obtained by calcination with moisture in the ground to become slaked lime, or the decrease in water content due to the effect of heat generation, which is different from the mechanism by which amorphous silica obtained by burning land-derived waste is solidified in the present invention. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Patent No. 4728829 [Patent Document 2] Patent No. 5751923 [Non-patent literature]

[0016] [Non-Patent Document 1] Gemmyture, Naoaki Suemasa, Takamitsu Sasaki, Koichi Nagao, Sugar Cane Bagasse Ash: An In-depth Study and Its Feasibility for Permeation Grouting, The 79th Annual Conference of the Japan Society of Civil Engineers, 2024. [Non-Patent Document 2] Seiji Tomohisa, Kohei Sawa, Nagahide Naito, Shinya Kuroda, Hiroyuki Nakagawa, "A Study on the Strength Characteristics of River Embankment Materials," December 2006, Akashi National College of Technology Research Bulletin [Non-Patent Document 3] Takamune Yaegashi, "Resource Utilization of Seashells and Enhancement of Charcoal Functionality through Integrated Firing Technology (First Report)," 2008, Iwate Prefectural Industrial Technology Center Research Report. [Non-Patent Document 4] Hideo Ogata, Kuzuo Hattori, Ryuichi Takada, "Basic Properties of Concrete Mixed with Granulated Rice Husk Charcoal", Transactions of the Japan Concrete Institute, Vol.28, No.1, 2006

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0017] As described above, various studies have been conducted on materials used for the construction of earth structures and ground improvement. However, materials that can be stably supplied and do not cause environmental problems such as environmental pollution and an increase in carbon dioxide emissions have not been obtained.

[0018] Therefore, an object of the present invention is to provide a solidifying material excellent in sustainability and environmental performance that enables not only carbon neutrality but also carbon negativity by using a material that can be stably supplied and does not cause environmental problems such as environmental pollution and an increase in carbon dioxide emissions, a method for constructing an earth structure using the same, and a ground improvement method.

Means for Solving the Problems

[0019] As a result of investigations to solve the above problems, the inventors of the present invention have found that the above problems can be solved by using a solidifying material mainly composed of a silica-containing combustion product containing SiO2 and carbon obtained by partially burning and cooling waste derived from terrestrial products, and preferably further containing a Ca-containing combustion product containing metals such as Ca obtained by burning waste derived from terrestrial or marine products.

[0020] In the present invention, for example, a composition obtained by burning a silica-containing waste derived from terrestrial products and a Ca-containing waste derived from marine products is used as the main component. Among these, a carbon compound and amorphous silica obtained from the waste of terrestrial products are used as the main agents, and a Ca-containing combustion product obtained from the waste of marine products is used as a reactant to form a solidifying material. As a result, it is possible to obtain an earth structure capable of reducing CO2 emissions, achieving not only carbon neutrality but also carbon negativity, and a solidifying material applicable to the improvement of ground by various construction methods.

[0021] That is, the present invention provides a carbon-negative solidifying material made of geopolymers derived from terrestrial or marine products, which is a sustainable material with a low environmental impact, in place of ordinary Portland cement, blast furnace slag, fly ash, etc., which can cause global warming by generating a large amount of CO2 and have problems in environmental issues, environmental load, and supply sustainability. Specifically, examples of waste from terrestrial products include cereal plants such as rice, wheat, sugarcane, corn, vetiver, rice husk, and bamboo, and also include banana plants such as bananas. In addition, waste from wood such as coniferous trees, broad-leaved trees, and their fallen leaves can also be used. Furthermore, those containing a large amount of calcium or aluminum, such as cow dung, chicken dung, eggs, and eggshells, which contain a large amount of silica, also belong to these. Additionally, examples of waste from marine products include shells such as scallops and oysters, those containing calcium, and those containing a large amount of metals such as magnesium chloride generated when producing salt.

[0022] To utilize land-derived waste as a solidifying agent according to the present invention, these wastes are partially combusted and cooled to retain amorphous silica while leaving carbon behind, thereby generating silica-containing combustion products with SiO2 and carbon as active ingredients.

[0023] Of these, amorphous silica reacts with Ca to produce calcium silicate and solidify (pozzolanic reaction). The remaining carbon content does not offer any strength advantage, but it functions as a filler, and SiO2 reacts with Ca to bind this filler, thereby contributing to the development of strength. In other words, in the solidifying material of the present invention, carbon can be considered to play the role of aggregate in concrete.

[0024] For example, when wood and materials primarily composed of carbon compounds (such as wood) are burned in an oxygen-deficient environment, only carbon atoms remain as solids, while other atoms become gaseous molecules and detach. This process is called carbonization.

[0025] Even if charcoal consisting solely of carbon is crushed and mixed with calcium, the required strength cannot be expected to be achieved. The same is true for complete combustion of land-derived waste. Raw plant waste consists mostly of carbon. However, as shown in Table 3 below, in the case of partially combusted plant waste, the total volume is reduced and carbon is released into the atmosphere as CO2, so the residual carbon is small, but carbon, SiO2, and other metal components are concentrated and remain at high concentrations. Since residual carbon itself does not directly contribute to the development of strength, if the amount of carbon is too high relative to SiO2, the required strength cannot be obtained. Conversely, if the residual carbon is too low, the required strength cannot be obtained either. The carbon content due to partial combustion is determined by the combustion temperature and combustion time. When the combustion temperature is constant, the residual carbon content is high if the combustion time is short, and low if the combustion time is long. Also, when the combustion time is constant, the carbon content is small if the combustion temperature is high, and large if the combustion temperature is low (Figure 2).

[0026] Figure 1 shows an explanatory diagram illustrating the relationship between the combustion temperature and cooling conditions of silica and its crystal structure. From Figure 1, it can be seen that silica becomes solution silica at high temperatures, and various crystal structures can be obtained by slow cooling. It is thought that the crystallinity changes depending on the combustion conditions (combustion time and cooling time) of waste plants (Figure 2). Steel can be given as an example of a material whose properties change due to heat treatment (Tables 1 and 2). The crystal structure of iron changes with temperature. At room temperature, it exhibits a structure called ferrite, and its crystal structure is a body-centered cubic lattice. Above 911°C, it changes to a structure called austenite, and its crystal structure becomes a face-centered cubic lattice. Furthermore, in the temperature range just before it becomes liquid, from above 1,392°C to 1,536°C, it becomes a structure called delta-ferrite, and its crystal structure returns to a body-centered cubic lattice.

[0027] [Table 1]

[0028] Furthermore, it is known that the properties of iron change depending on the rate of cooling.

[0029] [Table 2]

[0030] In this invention, problems arise because the chemical composition differs depending on the type of waste, and even for the same type of waste, the degree of deterioration differs depending on the disposal conditions and duration. Therefore, in order to effectively utilize waste as a binding agent, it is necessary to conduct chemical tests and combustion tests on each type of waste and use a composition that is appropriate for its intended purpose. Furthermore, it is necessary to confirm the use of waste as a binding agent material through combustion tests and solidification tests.

[0031] Burning plants releases CO2 into the atmosphere, but this is part of the natural carbon cycle where plants absorb CO2 from the atmosphere through photosynthesis during their growth. This combustion does not increase the amount of CO2 in the air. Therefore, it is a carbon-neutral or carbon-negative emission.

[0032] Table 3, described later, shows the results of X-ray fluorescence (XRF) analysis of sugarcane waste (SCB: Sugar Cone Bagasse) (hereinafter also referred to as "SCB"). Sugarcane waste (raw material SCB) was burned at 400°C for 6 hours using a muffle oven, and then rapidly cooled to produce sugarcane combustion products (SCBA: Sugar Cone Bagasse Ash) (hereinafter also referred to as "SCBA") containing amorphous silica. XRF analysis and XRD (X-ray diffraction) analysis were performed, and the results shown in Table 3 were obtained. When raw raw material SCB is burned, CO2 is released into the atmosphere. As mentioned above, this CO2 is absorbed by plants through photosynthesis during growth and fixed inside the plants, so burning it and releasing it into the atmosphere does not increase the amount of CO2 in the atmosphere. In other words, it can be said to be a carbon-neutral release. Raw sugarcane (sugarcane waste) is mostly composed of carbon (91%), but when sugarcane is burned as described above, the yield is small, and about 3% of the combustion material remains. Unburned substances such as silica and aluminum remain in this combustion material and become concentrated, with the proportion of SiO2 reaching 40%. By cooling this, amorphous silica is produced. When Ca acts on this amorphous silica, calcium silicate is formed by pozzolanic action and solidifies. However, the remaining carbon does not solidify itself but is thought to become the base of the solidified product. Therefore, if the carbon content of the combustion product is too high or too low, the strength will not be obtained, so it is preferable to perform combustion so that the carbon content is at the optimal value (Figure 2, Table 4). The composition and crystallographic properties of the material can be analyzed by XRF analysis and XRD analysis. The former allows for non-destructive and rapid analysis and can detect a wide range of elements from low atomic number (such as sodium) to high atomic number (such as uranium). The latter can provide detailed information regarding crystal structure, phase composition, and crystallographic properties.

[0033] The combustion tests in this invention can utilize muffle furnaces, electric ovens, kilns, and the like. Typically, electric ovens and muffle furnaces are used for burning materials. Electric ovens, also known as laboratory ovens, are designed for low-temperature operations such as drying, sterilization, and material testing, and usually operate between 70°C and 250°C. In contrast, muffle furnaces are designed for high-temperature applications, reaching up to 1700°C, and are used in processes such as annealing, crystal growth, and incineration. Muffle furnaces are designed with insulation to minimize heat loss and ensure uniform heating, making them suitable for precise high-temperature operations. Kilns (calcination kilns) used to produce clinker, the base material for cement, can also be used. In this invention, furnaces that can control predetermined temperatures and calcination times, and that can also be rapidly cooled, are highly applicable.

[0034] In other words, the present invention is a solidifying material whose main component is a silica-containing combustion product obtained by partially burning and cooling land-derived waste, with SiO2 and carbon as active ingredients. The aforementioned silica-containing combustion product is characterized by the fact that the amorphous silica undergoes a hydration reaction and solidifies, thereby enabling carbon negativity.

[0035] The solidifying agent of the present invention preferably further contains an alkaline component, and the alkaline component is preferably a Ca-containing combustion product obtained by burning Ca-containing waste derived from land products and / or marine products.

[0036] The consolidating agent of the present invention preferably further contains one or more alkaline agents from among (i) to (iii) below. (i) An alkaline agent having gypsum and / or MgO as active ingredients. (ii) An alkaline agent containing one or more of Ca salts, Mg salts, Al salts, carbonates, and bicarbonates as active ingredients. (iii) An alkaline agent having one or more of lime, cement, caustic alkali, water glass, and silica colloid as active ingredients.

[0037] The solidifying material of the present invention comprises the silica-containing combustion product, the Ca-containing combustion product, and water. When the mass of the mixed powder consisting of amorphous silica in the silica-containing combustion product and the Ca-containing combustion product is P, and the mass of water is W, it is preferable that the water-to-powder ratio W / P is in the range of 30 to 1000%, and the molar ratio of SiO2 to CaO contained in the mixed powder, SiO2 / CaO, is in the range of 0.05 to 10.0.

[0038] The consolidating material of the present invention preferably further contains one or more of the natural and artificial pozzolans.

[0039] The consolidating material of the present invention is suitably used for constructing soil structures or as a ground consolidating material.

[0040] In the solidifying material of the present invention, the degree of partial combustion in the silica-containing combustion product can be adjusted by the combustion time and / or combustion temperature.

[0041] The present invention relates to a method for designing the compound composition of a solidifying material, and is a method for designing the compound composition of a solidifying material. This method is characterized by conducting combustion tests on each type of land-derived waste and then conducting strength tests on the resulting silica-containing combustion products to determine a compound formulation of the solidifying material that provides the desired strength.

[0042] The present invention relates to a method for constructing soil structures, characterized by the use of the above-mentioned consolidating material to construct environmentally friendly soil structures with low alkalinity.

[0043] In the method for constructing an earth structure according to the present invention, it is preferable that the earth structure is a ground protection structure, a block-shaped structure, a coastal structure, or a seabed structure.

[0044] The ground improvement method of the present invention is characterized by using the above-mentioned consolidating material to improve the ground by a block method, a ground injection method, a high-pressure injection method, a high-density method, or a fluidized soil method. [Effects of the Invention]

[0045] According to the present invention, by using a material that can be supplied stably and does not cause environmental problems such as environmental pollution or increased carbon dioxide emissions because it solidifies without using cement, it is possible to provide a sustainable and environmentally friendly solidifying material that can achieve not only CO2 reduction and carbon neutrality, but also carbon negativity, as well as a method for constructing soil structures and a ground improvement method using the same.

[0046] The solidifying material of the present invention is mainly composed of combustion products containing silica derived from land-based waste products that fix atmospheric CO2 through photosynthesis during their growth process, and further forms a solidified body containing combustion products containing metals such as calcium derived from marine waste products, etc. Therefore, it is also useful from the viewpoint that these wastes can be recycled in a carbon-negative manner. [Brief explanation of the drawing]

[0047] [Figure 1] This is an explanatory diagram showing the relationship between the combustion temperature and cooling conditions of silica and its crystal structure. [Figure 2] This is an explanatory diagram showing an example of the distribution of combustion time, residual carbon content, and solidification strength. [Figure 3] This graph shows the results of the thermal analysis of CaCO3. [Figure 4] This is a photographic illustration showing an example of Okinawan sugarcane fiber powder. [Figure 5] This is a photographic diagram showing an example of the powder produced after combustion. [Figure 6] This graph shows the XRD pattern of combustion products produced by slow cooling. [Figure 7] This graph shows the XRD pattern of combustion products due to rapid cooling. [Figure 8] This is a photographic illustration showing an example of a scallop shell. [Figure 9] This is a photographic diagram showing an example of scallop shells that have been crushed and then calcined. [Figure 10] This graph shows the TGA analysis results for scallop shells. [Figure 11] This is a photographic diagram showing the results of the solidification confirmation test. [Figure 12] This graph shows the results of a uniaxial compression test. [Figure 13] This is a photographic diagram showing the situation after the compression test. [Figure 14] This graph shows the relationship between age of the wood and unconfined compressive strength. [Figure 15] This is a photographic diagram showing actual images (top image) and 1000x microscope images (bottom image) of SCBA, CCA (corn cob ash), and BSC (blast furnace slag cement) ash. [Figure 16] This graph shows the particle size distribution of each material. [Figure 17] These are explanatory diagrams and photographs showing soil samples. [Figure 18] This is a photographic diagram showing microscopic images and EDX analysis results of SCBA. [Modes for carrying out the invention]

[0048] The embodiments of the present invention will be described in detail below. The solidifying agent of the present invention mainly comprises a silica-containing combustion product, which has SiO2 and carbon as active ingredients, obtained by partially burning and cooling land-derived waste. The amorphous silica in this silica-containing combustion product undergoes a hydration reaction and solidifies, thereby enabling carbon negativity. In particular, the solidifying agent of the present invention includes a combustion product obtained by partially burning and cooling a mixture of land-derived waste and land and / or marine-derived waste containing at least Ca. The amorphous silica and carbon contained in this combustion product are the main components, and a Ca-containing combustion product containing Ca is used as the reactant.

[0049] The consolidating material of the present invention is used for constructing soil structures or as a ground consolidating material, and in particular, it has a lower alkali content than cement and is used for constructing environmentally friendly soil structures. Examples of such soil structures include ground protection structures (retaining walls), block-shaped structures (blocks), coastal structures, and seabed structures, which are used to construct solidified bodies on the ground surface or seabed. Specifically, the consolidating material of the present invention is used as a consolidating material in chemical grouting methods, high-pressure jet mixing methods, high-density methods, fluidized soil methods, or mixed soil improvement methods, and can be used to improve the ground by block methods (where blocks are used to construct earth retaining materials, wave-dissipating blocks (tetrapods), coastal protective walls), ground injection methods, high-pressure jet methods, high-density methods, or fluidized soil methods.

[0050] Furthermore, the consolidating material of the present invention can be described as a geopolymer that uses land or marine waste, which is an environmentally friendly and sustainable material, instead of blast furnace slag or fly ash. Geopolymers are a general term for silicate complexes produced by mixing activated fillers such as blast furnace slag or fly ash with alkaline solutions such as water glass or sodium hydroxide. When blast furnace slag is used, an amorphous calcium silicate substance is produced, and when fly ash is used, an amorphous aluminosilicate substance is produced. Concrete using geopolymers does not use any cement, so carbon dioxide emissions during cement production can be reduced, and it has excellent compressive strength, acid resistance, and durability, and also has the function of immobilizing harmful metals such as heavy metals during the hardening process, so it is expected to have expanded applications in acidic environments and in the field of environmental remediation.

[0051] Here, we will explain conventional technologies using waste materials. Patent Document 1 describes a technology for a hydraulic composition and a method for producing the same, using industrial waste, particularly coal ash, as a raw material. Granulated blast furnace slag is obtained as an industrial by-product without using cement, which generates a large amount of CO2 during production. Because CaO reacts with the contained SiO2 and solidifies due to latent hydraulic properties, solidifying materials using granulated blast furnace slag are known to be a technology that reduces CO2. On the other hand, granulated blast furnace slag requires a high temperature of 1300 to 1600°C to melt the iron ore, which requires a large amount of energy, and crushing it also requires large equipment and energy. In Patent Document 1, coal ash is used instead of granulated blast furnace slag, and the raw materials are calcined within the combustion temperature range without melting, and then mixed with CaO and solidified by a hydration reaction similar to that of granulated blast furnace slag. However, coal ash may not always be available in a stable supply from the perspective of preventing global warming. In contrast, the present invention is a technology that uses amorphous silica obtained by burning land-derived waste as its main material, and further uses a material obtained by burning Ca-containing waste derived from marine products, etc., to solidify through a hydration reaction. Since these wastes absorb and fix CO2 from the atmosphere through photosynthesis during their generation process, the solidifying material not only reduces the emission of greenhouse gases, including CO2, which causes global warming, but also enables the realization of carbon neutrality and carbon negativity.

[0052] The technology described in Patent Document 2 is a method for effectively utilizing seashells by crushing them and firing the resulting powder mixture with coal ash at a temperature of 1000 to 1400°C. In contrast, the present invention uses land-derived waste without using coal ash, and as mentioned above, it is an invention that differs in both its composition and effect.

[0053] Non-patent document 2 describes the use of paper mill incineration ash. Paper mill incineration ash is an artificial material and does not deteriorate or vary in quality depending on the disposal period or conditions, unlike marine or land-based waste in the present invention, which is subject to natural phenomena. Land-based waste in the present invention easily loses moisture during disposal, or easily deteriorates or decomposes in the short term due to natural conditions, causing changes in its composition.

[0054] Furthermore, Non-Patent Document 3 relates to a concrete admixture mixed with charcoal powder, and is different from the carbon-negative solidifying agent of the present invention, which itself is the main component.

[0055] Furthermore, Non-Patent Document 4 relates to the use of rice husk ash as a concrete admixture, and, as mentioned above, is a different technology from the present invention. The inventors have conducted research and development on the resource recovery of waste derived from marine or land products, as described above, from a carbon-negative perspective, with regard to soil structures and ground improvement applications, identified the problems and solutions, and invented a specific method for this purpose.

[0056] First, the amorphous silica that serves as the main component in the solidifying agent of the present invention can be obtained from edible plant waste of grasses such as rice and wheat husks, sugarcane, and corn, as well as waste derived from land products that contain a large amount of amorphous silica, such as bamboo, Japanese pampas grass, vetiver grass, and fallen leaves of deciduous and coniferous trees. In particular, it is preferable that the amorphous silica component mainly consists of amorphous silica derived from grasses or bamboo. In the present invention, a silica-containing combustion product with SiO2 and carbon as active ingredients obtained by partially burning and cooling this material can be used. In recent years, bamboo damage has become a problem in neglected forests, but if such bamboo is used as a material for the solidifying agent of the present invention, it will also be useful as a countermeasure against bamboo damage. By partially burning these plants at an appropriate temperature and cooling them, a silica-containing combustion product containing amorphous silica and carbon can be obtained.

[0057] As shown in Figure 1, it is known that the crystalline structure of silica differs depending on the temperature and time of combustion and the cooling method after combustion. The most important element in this invention is obtaining amorphous silica and carbon by partially burning and cooling waste such as plants that contain silica. Although it is known that the silica in grasses, which contain a large amount of silica, is amorphous silica, a composition containing amorphous silica and carbon as active ingredients can be obtained by appropriate treatment. In this invention, it is required that of the amorphous silica and carbon compound, which are the main components, the carbon compound will not be completely burned and will be present in a content that forms the base of the solidified product, and that amorphous silica will be obtained by appropriate combustion temperature and time, and that this will react with Ca-containing combustion products obtained by calcining shellfish waste, etc., and together with the carbon compound, will be present in a content that is useful for solidification. For this reason, it is necessary to burn it within a predetermined temperature range and for a predetermined time. This is based on the formation of calcium silicate and subsequent solidification.

[0058] The strength of the solidified material obtained in this way varies depending on the ratio and concentration of carbon, amorphous silica, and Ca compounds. Furthermore, the ratio of carbon and amorphous silica varies depending on the type of plants and other materials contained in the waste, its disposal conditions, disposal time, combustion temperature, and combustion time. The carbon forms the base of the solidified material, and the amorphous silica reacts with Ca to form calcium silicate, which together with the carbon forms a gelled solid.

[0059] To partially combust waste materials such as plants, leaving a sufficient carbon content to achieve the necessary strength for the solidified material without completely turning it into incinerated ash, the combustion temperature and combustion time are relevant. In other words, the degree of partial combustion in silica-containing combustion products can be adjusted by the combustion time and / or combustion temperature. If the combustion temperature is too high, the combustion time should be shortened; if the combustion temperature is too low, the combustion time should be lengthened. These factors vary depending on the type of plant material and the waste conditions, so combustion tests, mix design tests, and strength tests are necessary. Here, we will explain using examples of tests on woody materials and sugarcane ash (SCBA) as a guideline.

[0060] [Table 3]

[0061] [Table 4]

[0062] Amorphous silica can be obtained with the component combinations shown in Table 5 at a combustion temperature of 400°C or higher but less than 700°C.

[0063] In the case of charcoal, black charcoal can be obtained by carbonizing logs of Japanese cedar, pine, sawtooth oak, and Japanese oak at around 400-600°C and then slowly cooling them. In the case of hard logs such as oak and chestnut, white charcoal can be obtained by carbonizing them at a carbonization temperature of approximately 1000°C and then cooling them. From the above, amorphous silica can be obtained from soft to hard plant waste at combustion temperatures in the range of 400-1000°C without completely burning the carbon. In addition, calcium-rich waste such as seashells, chicken shells, and cow and chicken manure can also have calcium produced from CaCO3 at around 900°C.

[0064] Furthermore, by conducting combustion tests on each type of land-derived waste to confirm the content of its components, and then performing strength tests using a solidifying material primarily composed of the resulting silica-containing combustion products, it is possible to determine a compound formulation of a solidifying material that will provide the required solidifying strength for the intended purpose.

[0065] Specifically, if the combustion temperature is between 400°C and 700°C, for example between 400°C and 500°C, the combustion product containing amorphous silica can be obtained without rapid cooling after combustion, but rapid cooling is more preferable. If the combustion temperature is 700°C or higher, it can be obtained by rapid cooling after combustion. Here, in this invention, rapid cooling means rapidly cooling the combustion product by either immersing it in water immediately after combustion or by a water cooling method in which pressurized water is injected into the combustion product. By processing in this way, amorphous silica can be obtained efficiently.

[0066] As shown in Table 5, the chemical components of the combustion product ash vary greatly depending on the type of plant. Therefore, the type and amount of the alkali stimulant reagent can be appropriately set according to the purpose. For this reason, it is preferable that the solidifying agent of the present invention further contains an alkaline component.

[0067] [Table 5]

[0068] In the present invention, it is preferable to use a Ca-containing combustion product obtained by burning land and / or marine waste containing Ca as the alkaline component (alkaline stimulant) used as a reactant in the solidifying material. The Ca-containing combustion product acts as an alkaline stimulant and contains at least Ca, thereby enabling a hardening effect. It is preferable that the Ca-containing combustion product further contains Mg and / or Al, thereby improving the hardening properties and allowing adjustment of the strength of the solidified material.

[0069] Specifically, the Ca-containing combustion product is derived from marine or land waste such as seashells rich in Ca, such as oysters and scallops, chicken shells, as well as plants and chicken manure rich in Mg and Al, and sewage sludge. It can be obtained by crushing one or more of these materials into powder and heating and burning it until no further weight loss is observed. It is preferable that the combustion components such as plants, chicken manure, and sewage sludge contain carbon, amorphous silica, and Ca.

[0070] In other words, as shown in Table 6, from the viewpoint of stability of component composition, CaO derived from seashells is highly effective as a Ca-containing combustion product, but chicken manure and cow manure can also be used. Furthermore, the solidification characteristics can be modified by adding metals that act as crosslinking points for the geopolymer, such as bittern or incinerated sewage sludge ash.

[0071] [Table 6]

[0072] To convert CaCO3 from seashells, chicken shells, cow dung, and other materials used as Ca-containing combustion products into CaO, combustion at approximately 900°C is sufficient, as shown in Figure 3.

[0073] When using the solidifying agent of the present invention, an appropriate amount of Ca-containing combustion product, such as CaO derived from seashells, which acts as an alkaline stimulant, is added to the combustion product of amorphous silica, which is the main component. By adding water to the amorphous silica combustion product and the Ca-containing combustion product, a pozzolanic reaction occurs, and a gelled product mainly of calcium silicate complex can be obtained, and a hardened body can be obtained. The amount of Ca-containing combustion product to be added is determined according to the content of amorphous silica in the silica-containing combustion product containing amorphous silica, and the pozzolanic reaction occurs when an appropriate amount is added.

[0074] As a specific reaction, for example, first, by calcining seashells, the main component of seashells, CaCO3, is decarboxylated to obtain CaO. When this is mixed with combustion products obtained by partially burning and cooling plant waste, etc., and water, CaO becomes Ca(OH)2, and the pH becomes about 12. Due to the stimulation of this alkali, the amorphous silica contained in the silica-containing combustion products derived from plant waste, etc., dissolves into particles of about 1 nm. Along with this dissolution, metallic ions such as calcium, aluminum, and magnesium are released from the Ca-containing combustion products obtained from waste such as seashells. When the silica and these metallic ions reach a certain concentration, the silica crosslinks via the metallic ions and polymerizes, forming a silicate complex. In the case of calcium-based silica, tobermorite (Ca5(Si6O) 18 H2)·4H2O), and in aluminum-based systems, kaolinite (Al4Si4O 10 (OH)8) In magnesium-based systems, it forms a semicrystalline form of dolomite (CaMg(CO3)2).

[0075] Thus, this invention recycles waste generated during daily activities such as food production, and there is little risk of raw material depletion. Furthermore, since the combustion products derived from plant waste can be obtained from biomass power generation, and the combustion temperature for each raw material is around 900°C, the carbon dioxide emissions generated during implementation are not only significantly lower than those generated in the process of obtaining cement, blast furnace slag, and fly ash, but also have the advantage of achieving carbon negativity because plants absorb CO2 from the air through photosynthesis during the production process.

[0076] As mentioned above, when burning silica-containing plant waste at 400°C to less than 700°C to obtain amorphous silica combustion products, it is necessary to separately burn CaCO3 derived from seashells, etc., to obtain CaO in order to obtain Ca-containing combustion products, which complicates the process. In such cases, if the combustion product components obtained by combustion can be known in advance, it is effective to obtain the solidifying material of the present invention by mixing the waste materials that will be the raw materials for the main agent and the reactant, i.e., plant waste and Ca-containing waste, in a predetermined weight ratio, burning them at 400 to 1000°C, and cooling them to obtain a solidifying material composition. For example, the solidifying material of the present invention may be a clinker obtained by mixing plant waste and Ca-containing waste, partially burning them at 900°C or higher, and then cooling them. In this case, by adding chicken manure or bittern containing SO3, CaCO3 becomes CaSO4. This CaSO4 has the effect of contributing to the rise of initial strength. From this, it can be seen that adding gypsum as an additive is effective in increasing initial strength.

[0077] The solidifying agent of the present invention may contain a mixture obtained by cooling amorphous silica and carbon-containing silica combustion products derived from plant waste, and Ca-containing combustion products derived from Ca-containing waste, and water. In the present invention, when the mass of the mixed powder consisting of amorphous silica obtained by burning plants, etc., and Ca-containing combustion products is P, and the mass of water is W, the water-to-powder ratio W / P is preferably in the range of 30 to 1000%, more preferably in the range of 40 to 1000%, and particularly preferably in the range of 50 to 800%. Furthermore, the molar ratio of SiO2 to CaO contained in the above mixed powder, SiO2 / CaO, is preferably in the range of 0.05 to 10.0, and more preferably in the range of 0.1 to 5.0, from the viewpoint of obtaining latent hydraulic properties through hydration reactions. This molar ratio of SiO2 / CaO of the mixed powder can be determined, for example, by XRF (X-ray fluorescence) analysis. Note that in the above, Ca-containing combustion products may also be Ca and Al-containing combustion products.

[0078] Furthermore, in the consolidating material of the present invention, the strength of the consolidated soil can be adjusted by adjusting the content of MgO and / or Al2O3 in the consolidating material, and consequently, the rate of strength development and the rate of strength rise can be adjusted.

[0079] In other words, in the present invention, as described above, combustion tests are performed for each type of land-derived waste at 400 to 1000°C depending on the type of plant, and as described above, blending tests of Ca-containing combustion products and strength tests are performed thereon, thereby obtaining a blended composition that provides the strength required for the purpose.

[0080] Table 7 shows the compositional components of the combustion test results for plant waste and seashell waste. The SiO2 and CaO contained in the combustion composition of sugarcane (SCBA), a plant waste, and the CaO contained in scallop shells (hereinafter also referred to as "SS"), a Ca-containing waste, undergo a hydration reaction, resulting in strength in the presence of residual carbon. The chemical composition (mass%) of blast furnace slag is also shown in Table 7. For reference, the composition of fly ash, which is silica that undergoes hydration bonding, is also shown.

[0081] [Table 7]

[0082] In the table, SCBA+SS represents the composition of the combustion product of a mixed waste of plant waste (sugarcane) and seashell waste (scallop shells). Since blast furnace slag (hereinafter also referred to as "BS") is already known to solidify through a hydration reaction, a formulation of SCBA and SS that undergoes a hydration reaction can be established by setting the mixing ratio of SCBA and SS such that the ratio of SiO2 to CaO in blast furnace slag is approximately the same as the ratio of SiO2 to CaO in SCBA+SS in the present invention.

[0083] After the combustion test, a strength test is performed to determine the mass percentage of SCBA and SS and the combustion conditions that yield the desired strength q1 (Figure 2). The strength varies depending on the type and disposal conditions of the waste, as well as the combustion conditions (combustion temperature Q and combustion time T). Therefore, Q and T are adjusted, and strength tests are performed, for example, qu = 1 M / m 2 You should set Q and T to be such (Figure 2).

[0084] For example, if we keep Q constant and vary T to create a graph of uniaxial intensity qu, as shown in Figure 2, we can obtain the range of T where qu is at its maximum value and the range of T where a predetermined intensity is obtained. From Figure 2, we can obtain the range of T1 to T2 where the intensity is q2 or greater, or the range of T3 to T4 where the intensity is q1. Also, if we keep T constant, we can plot qu on the horizontal axis with Q as the horizontal axis and set Q and T in the same way. In this way, it is possible to set Q and T.

[0085] In this way, data can be accumulated on combustion conditions that yield the necessary intensity for various types of waste and disposal conditions.

[0086] Figure 3 shows the TGA analysis results for scallop shells. Thermogravimetric analysis (TGA), a type of calorimetry, is a method for measuring the weight change when a sample is heated under specific conditions.

[0087] The solidifying material of the present invention, obtained by partially burning and cooling the aforementioned waste material, contains CaO, SiO2, Al2O3, MgO, and Fe2O3. As shown in Table 7, it has a chemical composition similar to blast furnace slag, possesses latent hydraulic properties due to hydration reactions, and hardens when water is added. Therefore, in the solidifying material of the present invention, it is considered that solidification strength can be obtained by hydration reactions by adding water to the silica-containing combustion product containing amorphous silica as the main component and the Ca-containing combustion product as the reactant, or by adding an alkaline agent as an auxiliary agent.

[0088] As an alkaline agent that produces hydration bonds, (i) An alkaline agent having gypsum and / or MgO as active ingredients. (ii) An alkaline agent containing one or more of Ca salts, Mg salts, Al salts, carbonates, and bicarbonates as active ingredients. (iii) An alkaline agent having one or more of lime, cement, caustic alkali, water glass, and silica colloid as active ingredients. These can be listed, and one or more of these can be used.

[0089] Furthermore, aggregates such as sand may be added to the consolidating material of the present invention. In addition, the consolidating material of the present invention may be mixed with natural pozzolans containing amorphous silica such as volcanic ash, or with artificial pozzolans such as fly ash (coal ash), blast furnace slag, converter slag, silica fume, and paper mill incineration ash. By including one or more of these, the strength can be further improved.

[0090] Based on the above, the solidified material according to the present invention, which uses combustion products of waste materials such as plants, or even more so, waste materials such as shellfish, can achieve carbon negativity. By further adding natural or artificial pozzolanes containing amorphous silica to this mixture, carbon neutrality can be achieved depending on the amount added. Of course, adding a large amount of the above-mentioned natural or artificial pozzolanes will result in a low-carbon solidifying material.

[0091] [Example of combustion test] (Production of combustion products (SCBA) from sugarcane fiber powder) First, we will explain in detail the formation of amorphous silica through the combustion of plant waste such as agricultural products. The fiber powder made from sugarcane bagasse from Okinawa Prefecture, as shown in Figure 4, was heated at a rate of 10°C / min to 400-900°C and partially combusted in a high-temperature electric furnace for 6 hours while maintaining that temperature. Subsequently, the combustion product (SCBA) obtained from the partial combustion, as shown in Figure 5, was subjected to slow cooling or rapid cooling. Slow cooling refers to allowing the incinerated ash (combustion product) obtained from the combustion to cool at room temperature (approximately 20°C), while rapid cooling is a method of spraying cooling water at high pressure immediately after removing the incinerated ash obtained from the combustion from the furnace, and is a process used in the production of blast furnace granulated slag.

[0092] The purpose of rapid cooling is to generate amorphous SiO2. Silica structures include quartz, tridymite, cristobalite, and amorphous silica, and this structure is determined by the combustion temperature, pressure, and cooling time. As a general trend, the higher the combustion temperature and pressure and the longer the cooling time, the higher the crystallinity in the order of quartz > tridymite > cristobalite > amorphous silica, and of these, amorphous (non-crystalline) silica has the highest reactivity. Note that SiO2 incorporated into plants is basically in an amorphous state (Figure 1).

[0093] Figure 6 shows the XRD (X-ray diffraction) observation results for different combustion temperatures under slow cooling. Below 700°C, the material basically becomes amorphous without the need for rapid cooling, but above 800°C, the formation of cristopalite was observed.

[0094] Figure 7 shows the XRD observation results for different combustion temperatures after rapid cooling. It can be confirmed that the material is in an amorphous state at all temperatures.

[0095] (Preparation of combustion products (SS) from scallop shells) Next, we will explain in detail the generation of calcium-containing incineration ash (combustion product) by calcining seashell waste. Scallop shells (SS) shown in Figure 8 were ground into a powder by grinding as a pretreatment. This powder was heated in a high-temperature electric furnace at a heating rate of 10°C / min to 900°C and burned for 2 hours while maintaining that temperature. The combustion products obtained from the combustion, shown in Figure 9, were then slowly cooled. Figure 10 shows the results of TGA (Thermogravimetric Analysis) performed on scallop shells rich in CaCO3. The weight decreased rapidly due to an endothermic reaction when the reference temperature exceeded 600°C, and the weight decrease ceased when it reached approximately 740°C. This indicates that the combustion temperature needs to be set to 740°C or higher in order to obtain CaO.

[0096] Furthermore, in order to efficiently obtain CaO by burning oyster shells, it is necessary to burn them at a temperature of 900°C or higher for one hour. In this experiment, the combustion temperature was set to 900°C and the combustion time to 2 hours. Although the combustion temperature and time required to obtain CaO from chicken shells are the same as for oyster shells, the pre-treatment crushing process is easier to perform with chicken shells.

[0097] (Solidification test) A solidification test was conducted using SCBA and SS, the two combustion products obtained in the above combustion experiment. The components of SCBA and SS are shown in Table 7.

[0098] The purpose of the solidification test is to understand the effects of the presence or absence of SCBA and differences in moisture content on solidification. Table 8 shows the sample preparation conditions for the solidification test. For Case 1-1 and Case 1-2, 2.1g of SS and 2.9g of SCBA were mixed to a total of 5.0g. This mixing ratio was chosen so that the overall proportion of components would be similar to the chemical composition of blast furnace slag (BS) shown in Table 7. Table 7 also shows the chemical composition of the mixed combustion product. In contrast, for Case 1-3 and Case 1-4, only SS was mixed without SCBA. Distilled water (W) was then added to achieve two different water-to-powder ratios (W / P = 120% and W / P = 200%) and mixed in beakers. Subsequently, the mixture was stirred using a metal spoon. A solidification test was conducted on all four cases after 7 days.

[0099] [Table 8]

[0100] Figure 11 shows photographs of each case after 0 days of curing (immediately after mixing). The method for evaluating solidification was to insert a bamboo skewer into the sample in the beaker, shake the beaker by hand, and visually check whether the hole made by the bamboo skewer was filled in. If the hole was completely filled, it was marked "×", if the hole remained but was shallow, it was marked "△", if the hole remained, it was marked "〇", and if it was judged to have solidified visually before inserting the bamboo skewer it was marked "◎".

[0101] The solidification evaluation for Case 1-1 and Case 1-2, which included SCBA, was "◎". In Case 1-1, the sample was so hard that it was impossible to insert the bamboo skewer all the way to the bottom. Next, in Case 1-2, less force was required to insert the bamboo skewer compared to Case 1-1, allowing it to reach the bottom of the beaker. Also, water came out of the hole created when the bamboo skewer was inserted, suggesting a high water content. On the other hand, the solidification evaluation for Case 1-3, which did not include SCBA, was "〇", while the solidification evaluation for Case 1-4 was "△". In Cases 1-3 and 1-4, less force was required to insert the bamboo skewer compared to Cases 1-1 and 1-2. Also, the resistance when inserting the bamboo skewer in Case 1-4 felt weaker than in Case 1-3. This is thought to be due to the higher water content of the sample in Case 1-4. Furthermore, it was found that SCBA significantly affects the solidification process based on its presence or absence. In this test, solidification was determined using bamboo skewers, but accurate measured values ​​can also be obtained using the Yamanaka penetration test or a bender element.

[0102] (Uniaxial compression test) Next, we will describe the uniaxial compression test of the improved soil according to the present invention, which was prepared based on the results of the solidification judgment test described above. Table 9 shows the conditions for preparing the test specimens. SS and SCBA, used in the solidification test, were used, and the mass of the mixed powder, obtained by mixing these two components, was defined as P. The test specimens were 15 mm in diameter and 30 mm in height, prepared using silica sand No. 6, and had a relative density of 60%. The amount of consolidating agent added was determined by two different ratios, P / S, where S is the mass of silica sand No. 6, and further, the water-to-powder ratio (W / P) in the consolidating agent was used as a reference. The test specimens were prepared by mixing and compaction, with a curing period of 7 days. Subsequently, a uniaxial compression test was performed at a compression rate of 0.3 mm / min.

[0103] [Table 9]

[0104] Figure 12 shows the results of the compression test. The unconfined compressive strength was 71 kPa for Case 2-1, 17 kPa for Case 2-2, 954 kPa for Case 2-3, and 246 kPa for Case 2-4. Figure 13 shows photographs of each case after the unconfined compression test.

[0105] The results of the uniaxial compression test revealed that Cases 2-3 and 2-4, which had a higher amount of consolidating agent added, had higher maximum stresses compared to Case 2-2, which had a lower amount of consolidating agent added. Furthermore, comparing Case 2-3 and Case 2-4, it was found that Case 2-3, which had a lower W / P value, had a higher uniaxial compressive strength. From the above, it was found that the consolidation strength differs depending on the material composition, water content, and water / solids ratio.

[0106] Next, an alkaline agent was added to the SS and SCBA combination, and the effect of the alkaline agent was confirmed in a solidification test. As a result, as shown in Table 10, evaluations that were previously △ or × became ○ or ◎, indicating a significant improvement.

[0107] [Table 10]

[0108] As shown in Table 10, it was found that solidification performance could be improved by changing the chemical composition. Therefore, we mixed various combustion products shown in Table 6 with SCBA and investigated the effect of chemical composition on solidification characteristics. For comparison, a solidified body using ordinary Portland cement (OPC) was also prepared.

[0109] Table 11 shows the composition of the solidifying agent. The water-to-powder ratio (W / P) of the solidifying agent was set to 100%, and the test specimens were prepared by mixing soil and solidifying agent in a volume ratio of 1:1. The soil used for the test specimens was a mixture of silica sand No. 5 and clay in a mass ratio of 7:3.

[0110] [Table 11]

[0111] Figure 14 shows the relationship between age and unconfined compressive strength. At 28 days of age, the unconfined compressive strength of specimens using solidifying agents derived from land or marine products (Cases 4-1 to 4-3) was higher than that of specimens using OPC (Case 4-4). This is likely because OPC has a lower ratio of SiO2 to Al2O3, CaO, and MgO compared to solidifying agents derived from land or marine products, and therefore could not form a sufficient silicate complex. When comparing solidifying agents derived from land or marine products, Case 4-2, which contains the most MgO, showed the highest unconfined compressive strength.

[0112] The uniaxial compressive strength at 28 days of age for Case 4-1 and Case 4-2 is higher than that of OPC (Case 4-4), although the uniaxial compressive strength in the early stages of age tends to be lower. However, in Case 4-3, which contains a large amount of Al2O3, the uniaxial compressive strength is higher than that of OPC from the initial stage up to 28 days of age.

[0113] Thus, the differing rates and speeds of strength development are thought to be due to the ion exchange action of the soil and the proportions of Al2O3, CaO, and MgO contained in the solidifying agent, as well as their respective ionization tendencies. Therefore, it is desirable to determine an appropriate mixing ratio according to the desired strength and purpose of the improvement.

[0114] (Combustion tests of materials and combustion products) The raw materials used in this experiment were sugarcane waste and corn waste. The aim was to reuse sugarcane bagasse (the residue left after pressing) and corn cobs to process them into plant-derived pozzolanes. For this purpose, the raw materials / moist materials were placed in a drying oven for several hours to dry completely, and then pulverized in a pulverizer. Pulverization increases the surface area of ​​the material, improving its flammability and reactivity.

[0115] Biomass energy production is being utilized as a solution to address increasing waste generation. One method of converting biomass into energy is direct combustion or combustion followed by steam turbine power generation. By controlling parameters within the incinerator, the temperature suitable for combustion can be maintained. To simulate this type of combustion on a laboratory scale, an electric furnace with variable temperature control was used.

[0116] The optimal combustion temperature varies depending on the raw material. Different temperatures and combustion times were tested for both sugarcane bagasse and corn cob. It was found that combustion at 400°C for 6 hours was optimal for producing sugarcane bagasse ash (combustion product) (SCBA), and combustion at 700°C for 3 hours was optimal for producing corn cob ash (combustion product) (CCA). The physical and chemical properties of the materials were analyzed by various tests. Microscopic images and laser diffraction tests were performed for physical properties, and energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence analysis (XRF), and X-ray diffraction (XRD) were performed for chemical properties. Blast furnace slag cement (BSC) was also tested as a comparison. Figure 15 shows actual images and 1000x microscope images of the ash. Both ashes exhibited an angular shape, and as shown in the particle size distribution graph in Figure 16, they were found to be composed of ash of various particle sizes.

[0117] Table 12 shows the chemical analysis results. Figure 17 shows an explanatory diagram and photograph of the prepared uniaxial compression test sample. The sample used was silica sand No. 6 with a relative density of 60%. Some alkalis show different reactions when mixed with combustion products of different plant waste materials. Through investigation, it became clear that calcium oxide is optimal for SCBA and magnesium oxide is optimal for CCA.

[0118] [Table 12]

[0119] [Soil stabilization test] Conventionally, cement weight ratios of 4% to 16% have been used for soil stabilization, with water-cement ratios varying from 1.0 to above. Considering this, this study applied powder weight ratios of 5% and 15%. Specifically, 5g of combustion product powder was mixed per 100g of a soil sample of silica sand No. 6 with a relative density of 60%. While volume is usually the dominant unit in soil stabilization, using mass improves the accuracy of material comparisons, considering the difference in specific gravity between cement and combustion products. A water-cement ratio of 1.0 was deemed insufficient for sample preparation and was increased to 1.2. After curing the samples in a humid environment for 7 days, uniaxial compression tests were conducted. The tests continued at a rate of 1% strain / min until the sample fractured or reached 15% strain, whichever came first. Table 13 shows the uniaxial compressive strength of each sample. Three tests were performed for each sample, and the average strength was calculated.

[0120] SCBA exhibited the highest strength among the three materials tested, even surpassing commercially available blast furnace slag cement (BSC) in Case 3. This superior performance is thought to be due to its high silica and alumina content, which played a significant role in the silica hydration bonding. In this process, a strong chain polymer was formed, significantly improving its mechanical properties. These hypotheses were further supported by Figure 18, which shows microscopic images of SCBA alongside energy-dispersive X-ray spectroscopy (EDX) analysis results. The images confirmed the presence of silicate hydrate polymers in the sample, providing clear evidence of successful polymerization.

[0121] [Table 13]

[0122] In contrast, while CCA did not achieve a comparable increase in strength, its composition has clear advantages. CCA contains a large amount of potassium oxide, which gives it a natural alkalinity. The pH values ​​of CCA and SCBA were measured at 11.4 and 10.7, respectively, suggesting that CCA has potential applications beyond strength enhancement.

[0123] The high pH value of CCA suggests its potential benefits in applications requiring pH adjustment. Peat soils are known to be difficult to treat because the presence of humic acids inhibits chemical reactions. Soil stabilization cannot be achieved unless these acids are neutralized. As a result, significantly larger amounts of binders are required to neutralize the acids and stabilize the soil. Since neutralization is essential to promote chemical reactions, strongly alkaline CCA could potentially be used as a soil remediation agent before mixing in the binders needed for stabilization. This approach could reduce the amount of binders used, ultimately lowering the environmental impact and contributing to CO2 reduction.

[0124] Figure 16 shows that SCBA has a finer particle size compared to BSC, which is used as a suspension grout, and exhibits extremely good permeability when used for ground injection. In other words, the consolidating material of the present invention has a wide range of applicability depending on the ground conditions.

[0125] The evaluation of SCBA and CCA indicates promising potential as alternative, environmentally friendly geopolymer precursor materials (materials consisting of combustion products containing amorphous silica that undergo hydration bonding with alkali). SCBA exhibits performance equivalent to or better than conventional materials, and further improvements in design and optimization are expected to enhance its performance. Since CCA is largely composed of alkaline materials, it may be considered for various applications, such as soil pH remediation. Overall, the performance differences between SCBA and CCA highlight the diverse functionalities of these plant-derived ashes. Furthermore, as mentioned above, SCBA has a lower alkalinity compared to cement-based materials, making it suitable for low-alkali ground improvement and favorable for plant growth.

[0126] Because these combustion products are derived from plants considered food sources, they are classified as renewable resources. Furthermore, the raw materials used in this study will remain readily available, and their supply may even increase. By reusing discarded plant components, it becomes possible to realize a more sustainable and environmentally friendly future.

[0127] The growing demand for sustainable and environmentally friendly construction methods is seeking innovative materials that can replace conventional binders such as cement in soil stabilization. Plant-derived combustion products are attracting attention as potential geopolymer precursors due to their rich silica and alumina content. Cereals, sugar crops, and vegetables are the top three most produced crops in the world, with corn being the most produced of the cereals. These agricultural by-products, which are often discarded as waste, can be activated with alkaline solutions to produce geopolymers. Geopolymers are durable, cost-effective, and environmentally friendly materials that improve soil properties.

[0128] The inventors of this invention completed the present invention by investigating the potential use of sugarcane bagasse ash and corn cob ash as geopolymer precursors for soil stabilization applications. To evaluate the mechanical properties of these plant-derived ashes, comparative analyses were conducted with blast furnace slag cement. The results revealed that they achieved performance levels equivalent to or exceeding those of cement-based stabilizers, demonstrating their ability to improve soil strength and stability. Furthermore, the use of these combustion products significantly reduces carbon dioxide emissions, mitigating the environmental burden associated with cement production. By reusing agricultural waste, this invention is expected to contribute not only to waste management but also to sustainable construction methods.

[0129] This invention demonstrates the potential of sugarcane bagasse ash and corn cob ash to advance environmentally friendly geotechnical solutions. Furthermore, it discovers broader application possibilities using plant-derived geopolymer technology, paving the way for a more sustainable and resource-efficient approach to infrastructure development.

[0130] The ground improvement method of the present invention uses the consolidating material of the present invention when improving the ground by methods such as chemical injection, block method, ground injection method, high-pressure jet mixing method, high-pressure jet method, densification method, fluid soil method, or mixing and stirring system ground improvement method. The material can be supplied stably, and the material used absorbs and fixes CO2 during its formation, so the consolidated material can be carbon negative and does not cause environmental problems such as environmental pollution or increased carbon dioxide emissions. For this reason, it is excellent in terms of sustainability and environmental friendliness, and is also useful from the viewpoint of resource recovery of waste.

[0131] Furthermore, the solidifying material of the present invention is low in alkalinity because it solidifies without the use of cement. Therefore, it does not leach out much alkali. This solidifying material of the present invention can be used as a block, and can also be used as a fluid material to form soil structures in the ground or on land, and can also form solidified bodies on coastlines and seabeds. In this case, plants can be grown on the surface, and furthermore, since it does not cause bleaching, artificial reefs can be constructed without adversely affecting corals and other organisms.

Claims

1. A SiO2 obtained by partially burning waste derived from grasses containing amorphous silica at a combustion temperature in the range of 400 to 1000°C until the amount of carbon contained in the waste exceeds 0% and becomes 20% or less, and then cooling the waste. ２ and a solidifying material mainly composed of silica-containing combustion products with carbon as an active ingredient, Furthermore, it contains an alkaline component as a reactant, but does not contain cement. A solidifying material characterized in that the amorphous silica in the silica-containing combustion product undergoes a hydration reaction and solidifies, thereby enabling carbon negativity.

2. The solidifying material according to claim 1, wherein the alkaline component is a Ca-containing combustion product obtained by burning Ca-containing waste derived from land products and / or marine products.

3. Furthermore, the consolidating material according to claim 1 further comprises one or more alkaline agents from (i) to (iii) below. (i) An alkaline agent containing gypsum and / or MgO as active ingredients. (ii) An alkaline agent containing one or more of Ca salts, Mg salts, Al salts, carbonates, and bicarbonates as active ingredients. (iii) An alkaline agent containing one or more of lime, caustic alkali, water glass, and silica colloid as active ingredients.

4. The mixture contains the silica-containing combustion product, the Ca-containing combustion product, and water, and when the mass of the mixed powder consisting of a mixture of amorphous silica in the silica-containing combustion product and the Ca-containing combustion product is P and the mass of water is W, the water-to-powder ratio W / P is in the range of 30 to 1000%, and the mixed powder contains SiO ２ The molar ratio of CaO to SiO ２ The consolidating material according to claim 2, wherein the amount of CaO is in the range of 0.05 to 10.

0.

5. Furthermore, the consolidating material according to claim 1 further comprises one or more of the natural and artificial pozzolanes.

6. The soil stabilizer according to claim 1, used for constructing soil structures or as a ground stabilizer.

7. The solidifying material according to claim 1, wherein the degree of partial combustion in the silica-containing combustion product is adjusted by the combustion time and / or combustion temperature.

8. A method for designing the composition of a solidifying agent according to claim 1, A method for designing the formulation of a solidifying agent, characterized by conducting combustion tests on each of the aforementioned land-derived waste products and performing strength tests on the resulting solidifying agent mainly composed of the silica-containing combustion products, thereby determining a formulation of the solidifying agent that provides the required strength.

9. A method for constructing an earth structure, characterized by constructing an environmentally friendly earth structure with low alkalinity using the consolidating material described in claim 1.

10. The method for constructing an earth structure according to claim 9, wherein the earth structure is a ground protection structure, a block-shaped structure, a coastal structure, or a seabed structure.

11. A ground improvement method characterized by using the consolidating material described in claim 1 to improve the ground by a block method, a ground injection method, a high-pressure jet method, a high-density method, or a fluidized soil method.

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