Method for manufacturing cement-based solidifying agents

Abstract

To provide a manufacturing method for stably producing cement-based solidifying agents with guaranteed quality. To provide a manufacturing method that avoids problems during storage of thiosulfate salts. [Solution] The present invention provides a method for producing a cement-based solidifying material, which involves a mixing operation in which one or more components constituting a cement composition are mixed with an aqueous solution of thiosulfate to obtain a mixture, a water removal operation in which water is removed from the mixture to obtain a solid mixture, and a grinding operation in which the solid mixture is ground, performed in this order or simultaneously. It is preferable to introduce the components into a grinding device and, within the grinding device, spray the aqueous solution onto the components and grind the components while mixing them with the aqueous solution.

Description

[Technical Field]

[0001] This invention relates to a method for producing cement-based solidification materials. [Background technology]

[0002] A known method for solidifying soft ground involves adding solidifying agents such as cement-based solidifying agents. Various substances may be added to cement-based solidifying agents depending on their application; for example, thiosulfate is sometimes used as such a substance. Thiosulfate has a high chromium content even in small amounts. 6+ Because it exhibits a reducing effect, cement-based solidifying agents containing thiosulfates can reduce Cr from soil. 6+ This can suppress the elution of certain substances.

[0003] For example, Patent Document 1 describes a cement admixture that develops strength after concrete is constructed. The document states that this cement admixture is obtained by adding thiosulfate dissolved in mixing water.

[0004] Patent document 2 describes a ground improvement material containing a cement-based solidifying agent. The document states that this ground improvement material can be obtained by mixing the cement-based solidifying agent with a thiosulfate dissolved in water. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-56879 [Patent Document 2] Japanese Patent Publication No. 2024-90693 [Overview of the project] [Problems that the invention aims to solve]

[0006] Cr by cement-based solidification agent 6+To improve the ability to suppress elution, for example, increasing the amount of thiosulfate added to the solidifying agent could be considered. However, since thiosulfate is expensive, in reality, there is a demand to reduce the amount added. Furthermore, when using thiosulfate in powder form, it was not easy to thoroughly mix the cement-based solidifying agent and thiosulfate depending on the mixer. Furthermore, thiosulfates are known to be hygroscopic. Therefore, when storing thiosulfates in powder form, equipment such as dehumidifiers to control humidity is essential. This contributes to the high cost of installing and maintaining storage facilities. Moreover, if the amount of thiosulfate added is increased, the mixing equipment must be enlarged, which also increases costs. Therefore, the object of the present invention is to stably produce a cement-based solidifying agent with guaranteed quality while solving the storage problems of thiosulfates. [Means for solving the problem]

[0007] The present invention relates to a mixing operation in which one or more components constituting a cement composition are mixed with an aqueous solution of a thiosulfate to obtain a mixture, A water removal operation to remove water from the mixture to obtain a solid mixture, The present invention provides a method for producing a cement-based solidifying material, which involves performing a grinding operation to pulverize the aforementioned solid mixture in this order, or simultaneously. [Effects of the Invention]

[0008] According to the present invention, it is possible to stably manufacture cement-based solidifying materials with guaranteed quality. Furthermore, by storing the thiosulfate as an aqueous solution, it is possible to avoid problems during storage. [Modes for carrying out the invention]

[0009] The present invention relates to a method for producing a cement-based solidifying material. The cement-based solidifying material obtained by this production method preferably contains any optional components constituting a cement composition and a thiosulfate. Details of each component will be described later. Hereinafter, the method for producing a cement-based solidifying material will be described based on preferred embodiments thereof. This production method encompasses (I) a method of performing the following operations (a) to (c) in this order (hereinafter, this embodiment is also referred to as "the first embodiment"), and (II) a method of performing the following operations (a) to (c) simultaneously (hereinafter, this embodiment is also referred to as "the second embodiment"). In any of the embodiments, it is possible to stably produce a cement-based solidifying material with guaranteed quality. Furthermore, troubles during storage of the thiosulfate can be avoided.

[0010] First, the first embodiment will be described. In this embodiment, the following operations (a) to (c) are performed in this order. If necessary, additional operations may be performed between the respective operations. (a) Mixing operation (b) Moisture removal operation (c) Pulverization operation Hereinafter, each of these operations will be described.

[0011] [Mixing Operation] In this operation, one or more components constituting a cement composition are mixed with an aqueous solution of a thiosulfate to obtain a mixture. Alternatively, a cement composition and an aqueous solution of a thiosulfate may be mixed to obtain a mixture. Details of the latter case will be described later. First, the constituent components of the cement composition, which is one of the raw materials of the cement-based solidifying material, are prepared. The type of the constituent components of the cement composition used in this production method is not particularly limited. For example, cement clinker, gypsum, slag and the like can be used. Hereinafter, these constituent components will be described.

[0012] Various cement clinkers can be used as the cement clinker constituting the cement composition, such as ordinary cement clinker, rapid-hardening cement clinker, moderate-heat cement clinker, and low-heat cement clinker. These cement clinkers can be those specified in JIS R5210:2019, for example. These cement clinkers can be used individually or in combination of two or more. From the viewpoint of effectively solidifying the target soil, it is particularly preferable that the cement clinker be at least one selected from ordinary cement clinker and rapid-hardening cement clinker.

[0013] The cement composition preferably contains a predetermined amount of cement clinker. Specifically, from the viewpoint of effectively solidifying the target soil, it is preferable to use cement clinker such that its content in the cement composition is 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. The cement clinker may also be used such that its content in the cement composition is, for example, 95% by mass or less.

[0014] As the gypsum that constitutes the cement composition, for example, anhydrous gypsum powder, hemihydrate gypsum powder, and dihydrate gypsum powder can be used. These gypsums can be used individually or in combination of two or more. From the viewpoint of effectively solidifying the target soil, it is particularly preferable to use anhydrous gypsum powder as the gypsum.

[0015] It is preferable that the gypsum has a Blaine specific surface area value within a predetermined range. Specifically, from the viewpoint of effectively solidifying the target soil, the Blaine specific surface area of ​​the gypsum should be 2000 cm². 2 It is preferable that the amount be 4000 cm or more. 2 It is even more preferable that it be 4500 cm or more per gram. 2 It is even more preferable that the amount is greater than or equal to / g. There is no particular limit on the upper limit of the Blaine specific surface area of ​​gypsum. The Blaine specific surface area of ​​gypsum can be measured in accordance with JIS R5201:2015 "Physical Testing Methods for Cement".

[0016] The cement composition preferably contains a predetermined amount of gypsum. Specifically, from the viewpoint of effectively solidifying the target soil, it is preferable to use gypsum such that the gypsum content in the cement composition is 2% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. From a similar viewpoint, it is preferable to use gypsum such that the gypsum content in the cement composition is 30% by mass or less, more preferably 25% by mass or less, and even more preferably 15% by mass or less.

[0017] As the slag that makes up the cement composition, for example, blast furnace slag can be used. Blast furnace slag is slag that is generated as a by-product in blast furnaces at steel mills and the like. As blast furnace slag, for example, commercially available granulated blast furnace slag or slag specified in JIS A6206:2013 can be used. Since blast furnace slag contains sulfur, if heavy metals such as hexavalent chromium are present in the solidified soil, the sulfur can reduce them to trivalent chromium, thereby suppressing the leaching of hexavalent chromium from the solidified soil to below environmental standards. From the viewpoint of making this effect significant, the sulfur content in the blast furnace slag is preferably 0.1% by mass or more. When the solidification material of the present invention contains blast furnace slag, Cr is obtained from the soil after solidification treatment. 6+ From the viewpoint of suppressing the leaching of blast furnace slag and suppressing excessive long-term strength enhancement, it is preferable to use blast furnace slag in the cement composition such that its content is between 1% by mass and 50% by mass.

[0018] In addition to the cement clinker, gypsum, and slag mentioned above, other components may be used. The cement composition may include, for example, limestone and fly ash. These other components may be present in the cement composition in a total amount of 50% by mass or less.

[0019] Along with a cement composition, an aqueous solution of thiosulfate, which is one of the raw materials of the cement-based solidifying material, is prepared. Thiosulfate exhibits high Cr 6+ reduction effects even in a small amount, so it is used for the purpose of suppressing the elution of Cr from soil. 6+ It is also used for the purpose of improving the strength development property of the soil to be subjected to solidification treatment.

[0020] Cr 6+ While it is effective to use thiosulfate to obtain a solidifying material with improved elution suppression performance, thiosulfates such as sodium thiosulfate are known to have deliquescence. For this reason, thiosulfate takes in water present in the air and changes from a solid to a liquid. If the solidifying material solidifies due to the deliquesced liquid, it causes a decrease in strength properties and the like, so the deliquescence of thiosulfate is not preferable from the viewpoint of successfully performing the solidification treatment of the target soil. Therefore, in order to improve the Cr 6+ elution suppression performance of the solidifying material by adding thiosulfate, it is essential to store thiosulfate in an apparatus equipped with dehumidification equipment or the like for the purpose of preventing deliquescence of thiosulfate. However, this contributes to an increase in the cost required for installation and maintenance of dehumidification, so storage that does not require such equipment has been demanded. Furthermore, since the amount of thiosulfate powder added to the cement-based solidifying material is small relative to the solidifying material, high-performance mixing equipment is required. For this reason, it has also been demanded to enhance the mixability between thiosulfate and the cement composition. As a result of intensive studies by the present inventor regarding improving these points, it has been found that by using an aqueous solution of thiosulfate as a raw material instead of solid thiosulfate, the Cr 6+ reduction effect of thiosulfate is not reduced, and a solidifying material with improved Cr 6+ elution suppression performance can be produced. Furthermore, it has been found that storing thiosulfate in the state of an aqueous solution prevents the deliquescence of thiosulfate, thereby making it unnecessary to introduce new dehumidification equipment separate from storage facilities. From such a viewpoint, in the present production method, it is preferable to use thiosulfate in the state of an aqueous solution.

[0021] Examples of thiosulfate salts that can be used include alkali metal salts and alkaline earth metal salts of thiosulfate. Examples of alkali metal salts of thiosulfate include sodium thiosulfate and potassium thiosulfate. Examples of alkaline earth metal salts of thiosulfate include magnesium thiosulfate. The thiosulfate may be an anhydrous form, or it may be a hydrate such as a monohydrate, tetrahydrate, pentahydrate, or heptahydrate. Here, "hydrate" refers to a substance obtained by the deliquescent formation of thiosulfate, i.e., a substance obtained by thiosulfate incorporating water from the air, which has different properties. In this specification, "thiosulfate" refers to the anhydrous form of thiosulfate unless otherwise specified. Cr 6+ From the viewpoint of successfully obtaining a cement-based solidifying agent with improved elution suppression ability, the use of sodium thiosulfate is particularly preferred.

[0022] There are no particular restrictions on the form of the thiosulfate before dissolution. Powdered thiosulfate may be used. In this case, the average particle size of the particles constituting the thiosulfate powder can be, for example, 5 μm to 40 μm. This average particle size can be adjusted, for example, by grinding or sieving a commercially available product. The average particle size of thiosulfate can be measured, for example, using a laser diffraction particle size distribution analyzer. The average particle size is the volume cumulative particle size D at a cumulative volume of 50%. 50 That is the case.

[0023] An aqueous solution of thiosulfate can be prepared by dissolving thiosulfate in water. One method of dissolution is to stir the water, then add the thiosulfate and stir again.

[0024] In this procedure, it is preferable to mix an aqueous solution in which the concentration of thiosulfate is within a predetermined range with the components of the cement composition. Specifically, Cr 6+From the viewpoint of successfully obtaining a solidifying agent with improved elution suppression ability, it is preferable to prepare the aqueous solution so that the concentration of thiosulfate is 0.1% by mass or more, more preferably 10.0% by mass or more, and even more preferably 25.0% by mass or more. Furthermore, from the viewpoint of reducing manufacturing costs, it is preferable to prepare the aqueous solution so that the concentration of thiosulfate is 50.0% by mass or less, more preferably 45.0% by mass or less, and even more preferably 40.0% by mass or less.

[0025] Once the components of the cement composition and aqueous solutions of thiosulfate are prepared, they are mixed to obtain a mixture. The mixing may be done by adding all the components of the cement composition and the aqueous solution of thiosulfate all at once, or by adding the aqueous solutions sequentially to one or more of the components. Conversely, one or more of the components may be added sequentially to the aqueous solution of thiosulfate. The aqueous solutions may be sprayed during the addition process. In the case of sequential addition, there are no particular restrictions on the order in which the constituent components and the aqueous solutions of thiosulfate are added. For example, consider a case where the cement composition consists of components A, B, and C. When these components are added and mixed sequentially with aqueous solutions of thiosulfate, for example, component A and the aqueous solution of thiosulfate may be mixed first, and then components B and C may be added and mixed further. Alternatively, component A and component B may be mixed first, then the aqueous solution of thiosulfate may be added and mixed, and then component C may be added and mixed further. Even when the cement composition consists of four or more components, the same approach can be followed for mixing. When an aqueous solution of thiosulfate is added sequentially to the components of a cement composition, the addition of the aqueous solution of thiosulfate to the components may be continuous or intermittent. Even when the aqueous solution is added intermittently, if there is a short period of time during which the aqueous solution is not added that can be considered as continuous addition, it shall be considered as continuous addition. The same applies when the components of the cement composition are added sequentially to the aqueous solution of thiosulfate. Mixing can be carried out using general mixing equipment such as a V-type mixer, a Prussia mixer, a Henschel mixer, and a ribbon mixer. Alternatively, as described in the second embodiment, it can be carried out using equipment equipped with a mixing mechanism and a grinding mechanism.

[0026] In this operation, it is preferable to mix the components of the cement composition with the aqueous solution of thiosulfate used to produce the cement-based solidifying material so that the amount of aqueous solution of thiosulfate used is within a predetermined range. Specifically, Cr 6+ From the viewpoint of successfully obtaining a solidifying agent with improved elution suppression ability, provided that the concentration of thiosulfate is within the above-mentioned range, it is preferable to use 1 L or more of an aqueous solution of thiosulfate to produce 1 ton of cement-based solidifying agent, more preferably 2 L or more, even more preferably 3 L or more, and even more preferably 5 L or more. Furthermore, from the viewpoint of reducing manufacturing costs, it is also possible to use 65 L or less, 60 L or less, or 55 L or less of an aqueous solution of thiosulfate to produce 1 ton of cement-based solidifying agent.

[0027] In this operation, it is preferable to mix the components of the cement composition with an aqueous solution of thiosulfate so that the thiosulfate content in the mixture falls within a predetermined range. Specifically, Cr 6+ From the viewpoint of successfully obtaining a solidifying agent with improved elution suppression ability, it is preferable to mix the mixture so that the thiosulfate content in the mixture is 0.10% by mass or more, more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more. Furthermore, from the viewpoint of reducing manufacturing costs, the thiosulfate content in the mixture may be 20.00% by mass or less, 10.00% by mass or less, 5.00% by mass or less, or 3.00% by mass or less.

[0028] The cement composition may contain only an aqueous solution of thiosulfate, or it may also contain an aqueous solution containing other substances. From the viewpoint of successfully obtaining a mixture of the components of the cement composition and an aqueous solution of thiosulfate, it is preferable to stir the components while adding the aqueous solution to them. Once a sufficient amount of the mixture has been obtained, stop adding the aqueous solution of thiosulfate and stop mixing.

[0029] The above explanation pertains to the case where the components of the cement composition are mixed with an aqueous solution of thiosulfate. However, as mentioned above, the cement composition may also be mixed with an aqueous solution of thiosulfate. In this case, first, a cement composition, which is one of the raw materials for cement-based solidifying agents, is prepared. There are no particular restrictions on the type of cement composition used in this manufacturing method. For example, a cement composition containing cement and gypsum can be used.

[0030] As the cement constituting the cement composition, various types of Portland cement can be used, such as ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, and low-heat Portland cement, as well as blended cements such as blast furnace cement, fly ash cement, and silica fume cement. These cements can be used individually or in combination of two or more types. From the viewpoint of effectively solidifying the target soil, it is particularly preferable that the cement be at least one selected from ordinary Portland cement, rapid-hardening Portland cement, and blast furnace cement.

[0031] It is preferable that the concrete surface area of ​​the cement is within a predetermined range. Specifically, from the viewpoint of effectively solidifying the target soil, the concrete surface area of ​​the cement should be 2000 cm². 2 It is preferable that it be 2500 cm or more per gram. 2 It is even more preferable that it be 3000 cm or more per gram. 2 It is even more preferable that the amount is 6000 cm² or more. From the viewpoint of manufacturing costs and ensuring slurry fluidity in high-temperature environments, the specific surface area of ​​the cement's Blaine is 6000 cm². 2 It is preferable that the value be less than or equal to 5500 cm². 2It is even more preferable that it be less than or equal to / g, and 5000cm 2 It is even more preferable that the value be less than or equal to / g. The Blaine specific surface area of ​​cement can be measured in accordance with JIS R5201:2015 "Physical Testing Methods for Cement".

[0032] The cement composition preferably contains a predetermined amount of cement. Specifically, from the viewpoint of effectively solidifying the target soil, the cement composition preferably contains 30% by mass or more of cement, more preferably 40% by mass or more, and even more preferably 50% by mass or more. There is no particular upper limit on the cement content in the cement composition. For example, the cement composition may contain 95% by mass or less of cement.

[0033] The gypsum used in the cement composition can be the same type as the gypsum described above. While cement generally contains gypsum, the gypsum present in the cement is not included in the gypsum described above. In other words, the gypsum is added separately from the cement. Furthermore, the same components as those described above can be used for other components that the cement composition may contain, as well as for aqueous solutions of thiosulfates.

[0034] The same mixing method as described above can be used for mixing the cement composition and the aqueous solution of thiosulfate. For example, the mixing may be carried out by adding the cement composition and the aqueous solution of thiosulfate all at once, or by adding the aqueous solution to the cement composition sequentially. Conversely, the cement composition may be added to the aqueous solution of thiosulfate sequentially. Furthermore, the cement composition and the aqueous solution of thiosulfate can be prepared under the same mixing conditions as described above.

[0035] [Moisture removal operation] Once the mixture is obtained, it is then subjected to the following operation. This operation involves removing water from the mixture to obtain a solid mixture. The removal of water is performed to eliminate excessive aggregation of the mixture and to facilitate the grinding operation described later.

[0036] To remove water, a heating and drying method can be employed. In this case, known drying apparatus can be used. Specifically, methods such as blowing hot air onto the mixture, blowing dry gas onto it, heating with a heater, irradiation with infrared rays, and irradiation with microwaves can be used.

[0037] The heating temperature of the mixture is not particularly limited, as long as it is sufficient to remove the water from the mixture. From the viewpoint of successfully removing water from the mixture, it is preferable to heat the mixture to 50°C or higher, more preferably to 70°C or higher, and even more preferably to 80°C or higher. From the viewpoint of suppressing a deterioration in cement quality, it is preferable to heat the mixture to 200°C or lower, more preferably to 150°C or lower, and even more preferably to 100°C or lower. The drying time in this operation can be adjusted as appropriate depending on the type of drying apparatus and the heating temperature. When heating the mixture at the above-mentioned temperature range, it is preferable to dry the mixture for 0.5 minutes or more, more preferably 1 minute or more, and even more preferably 2 minutes or more. In the same case, it is preferable to dry the mixture for 10 minutes or less, more preferably 8 minutes or less, and even more preferably 5 minutes or less.

[0038] By removing water from the mixture in this way, a solid mixture is obtained. The solid mixture may have all the water removed from it, or some of the water may remain. If the solid mixture contains water, it is preferable that its content be between 0.1% by mass and 10.0% by mass of the solid mixture, from the viewpoint of facilitating the grinding operation described later.

[0039] [Crushing operation] Once a solid mixture is obtained, it is then subjected to the following operation. In this operation, the solid mixture is crushed by a predetermined means. Through crushing, a cement-based solidifying agent is obtained.

[0040] For grinding, a method using grinding media can be employed. In this case, milling equipment such as bead mills and ball mills can be used.

[0041] In this operation, it is preferable to crush the solid mixture so that the cement-based solidifying agent is of a predetermined size. When the obtained cement-based solidifying material is in powder form, the sieve residue after sieving with a mesh size of 90 μm is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, when the cement-based solidifying material is 100 parts by mass or less. Having the sieve residue within this range allows for effective solidification of the target soil. The sieve residue of the cement-based solidifying agent shall be measured in accordance with JIS R 5201:2015.

[0042] In this way, the desired cement-based solidifying material can be obtained.

[0043] Next, a second embodiment will be described. This embodiment differs from the first embodiment only in the manner in which operations (a) to (c) described above are performed; otherwise, it is the same as the first embodiment. Specifically, this embodiment performs operations (a) to (c) described above simultaneously. In this embodiment, the various conditions for the mixing operation, moisture removal operation, and grinding operation, such as the type and concentration of raw materials, as well as the mixing and drying conditions, can be the same as in the first embodiment.

[0044] When mixing, dewatering, and grinding operations are performed simultaneously, each operation may be started at the same time, or each operation may be started separately and then performed simultaneously. In either case, it is preferable to perform each operation simultaneously until the desired cement-based solidifying material is obtained. Each operation may be performed continuously or intermittently. If performed intermittently, the intervals between operations can be set to be short enough to be considered as if they were performed continuously. When performing multiple operations simultaneously, you may perform only these operations, or you may also perform other operations.

[0045] In this embodiment, each operation is performed simultaneously, and it is preferable to perform these operations within a predetermined crushing device from the viewpoint of successfully obtaining the target cement-based solidification material. When manufacturing cement-based solidifying agents, there are typically two methods: manufacturing the agent at the factory, or mixing the cement composition and other raw materials at the shipping base (service station). In the former case, the raw materials are mixed and ground very uniformly within the cement mill, making uneven distribution of thiosulfate unlikely. In contrast, in the latter case, the mixing equipment at the shipping base does not have the same mixing performance as the cement mill. In this manufacturing method, as mentioned above, thiosulfate is used, and the performance of the mixing equipment when adding thiosulfate powder and aqueous solution at the shipping base was insufficient. Insufficient mixing is undesirable from the standpoint of stably manufacturing cement-based solidifying agents with guaranteed quality, and improvement in this area was desired. In addressing this issue, the inventors conducted thorough research and discovered that by simultaneously performing the above-mentioned operations within a device equipped with a watering mechanism, a mixing mechanism, a drying mechanism, and a crushing mechanism, it is possible to stably produce a cement-based solidifying material with guaranteed quality. They also found that by utilizing existing equipment at a cement plant, the introduction of new equipment can be eliminated.

[0046] From this viewpoint, in this embodiment, it is preferable to perform each of the above operations within the grinding device. The term "grinding device" here refers to a device equipped with a water spraying mechanism, a mixing mechanism, a drying mechanism, and a grinding mechanism. For example, a finishing mill can be used as such a device. A finishing mill is a device used in the finishing process after the firing of cement. It is a mill device, such as a bead mill or ball mill, that is equipped with a water spraying mechanism. The water spraying mechanism is installed in the finishing mill to lower the temperature inside the mill. The water spraying mechanism is attached to the inner surface of the finishing mill, such as the ceiling and side walls, and has a mechanism to spray liquid onto the contents inside the mill. This suppresses the conversion of dihydrate gypsum contained in the cement-based solidifying material to hemihydrate gypsum, thereby maintaining the quality of the solidifying material.

[0047] When performing this operation using such a pulverizing device, it is preferable to specifically introduce one or more components constituting the cement composition into the pulverizing device, and then, within the pulverizing device, spray an aqueous solution of thiosulfate onto the components and pulverize the components while mixing them with the aqueous solution. The material can be introduced into the grinding device using the introduction mechanism provided in the grinding device. The spraying of an aqueous solution of thiosulfate onto the components of the cement composition may also be carried out using the spraying mechanism provided in the grinding device. Depending on the volume of the grinding device, the spraying may be carried out from one location in the grinding device or from multiple locations. The spraying may be carried out under the same conditions as described in the mixing operation of the first embodiment. Note that the amount of aqueous solution of thiosulfate used to produce 1 ton of cement-based solidifying material as described above refers to the total amount used until the cement-based solidifying material is discharged from the grinding device. The mixing of the components of the cement composition with an aqueous solution, and the pulverization of the components, may be carried out using the mixing mechanism and pulverization mechanism provided in the pulverizing device.

[0048] As described above, the desired cement-based solidifying material can be obtained. In either the first or second embodiment, a cement-based solidifying material with guaranteed quality can be stably produced by thoroughly mixing the cement composition with an aqueous solution of thiosulfate. Furthermore, in both the first and second embodiments, since the thiosulfate is stored and used as an aqueous solution, problems during storage can be avoided.

[0049] The cement-based solidifying agent obtained by this manufacturing method is Cr 6+ This material offers improved ability to suppress leaching. When using this cement-based solidifying agent, the solidifying agent and water (mixing water) are mixed to produce a cement-based solidifying agent slurry. This slurry is then mixed with the soil to be treated, or added to the soil in powder form and mixed. This allows the soil to be solidified.

[0050] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. [Examples]

[0051] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0052] [Examples 1 to 4] (1) Mixing operation, moisture removal operation and grinding operation A cement composition (containing 92% ordinary Portland cement and 8% anhydrous gypsum) was prepared. Along with this, anhydrous sodium thiosulfate was dissolved in water to prepare an aqueous solution of sodium thiosulfate. This aqueous solution was stored in air. The concentration of sodium thiosulfate in this aqueous solution was 2.7 mol / L (30%). The ball mill was started, and its mixing and grinding mechanisms were activated. Stainless steel balls were used. The temperature inside the ball mill was set to 100°C. The cement composition was introduced into the ball mill under these conditions, and an aqueous solution of sodium thiosulfate was continuously sprayed onto the cement composition using a water sprayer installed on the ceiling of the mill. The amount of aqueous solution added was set so that the sodium thiosulfate content (%) in the mixture of the cement composition and the aqueous solution was as shown in Table 1. Table 1 shows the amount (L) of aqueous solution added to produce 1 ton of the target cement-based solidifying material. The mixture was heated and dried for 30 minutes while mixing. A grinding operation was performed simultaneously. The grinding was carried out so that when the cement-based solidifying material was 100 parts by mass, the residue on a 90 μm sieve of the cement-based solidifying material was 5 parts by mass or less. The aqueous solution of sodium thiosulfate was continuously sprayed while mixing and grinding were taking place. In this way, the target cement-based solidifying material was obtained.

[0053] [Comparative Examples 1 to 4] In Example 1, sodium thiosulfate powder was used instead of an aqueous solution of sodium thiosulfate. This powder had been stored in a dehumidifier set at 20°C. The powder was introduced into the ball mill together with the cement composition. Except for these steps, the desired cement-based solidifying material was obtained in the same manner as in Example 1.

[0054] 〔evaluation〕 The sodium thiosulfate content in the cement-based solidifying materials of the examples and comparative examples was measured according to the following method. Furthermore, using the cement-based solidifying agent obtained in the examples and comparative examples, solidified soil was prepared according to the following method and its unconfined compressive strength was measured. In addition, Cr was measured from the solidified soil according to the following method. 6+ The amount of elution was measured.

[0055] [Sodium thiosulfate content] After the cement-based solidifying agent was obtained, 100g of the agent was taken from the sampling point (slider) of the ball mill before it was recovered from the ball mill. The sodium thiosulfate content in this cement-based solidifying agent was measured in accordance with JIS R 5202:2015.

[0056] [Uniaxial compressive strength] The soil to be solidified is Kanto loam (produced in Koza District, Kanagawa Prefecture, with a water content of 87.0% and a wet density of 1.415 g / cm³). 3 I prepared ). Using this soil and the cement-based solidifying agents obtained in the examples and comparative examples, cylindrical specimens with a diameter of 5 cm and a height of 10 cm were prepared in accordance with JGS 0821:2009 "Method for preparing specimens of stabilized soil without compaction," yielding three specimens for each cement-based solidifying agent. The amount of cement-based solidifying agent added to the soil was 200 kg / m³. 3 The obtained specimens were cured for 7 days in a sealed state at a temperature of 20°C and a humidity of 90%RH. The unconfined compressive strength of the solidified soil was measured in accordance with JIS A 1216:2020.

[0057] [Cr 6+ Elution amount] The solidified soil, prepared and cured according to the aforementioned "uniaxial compressive strength," was measured in accordance with JIS R 5202:2015.

[0058] [Table 1]

[0059] As is clear from the results shown in Table 1, the solidified soils using the cement-based solidifying agents of Examples 1 to 4 exhibited high unconfined compressive strength. Furthermore, the small degree of variation in the sodium thiosulfate content in the cement-based solidifying agents of Examples 1 to 4 indicates that the quality of the solidifying agents was ensured. Furthermore, the aqueous solutions of sodium thiosulfate used in Examples 1 to 4 were stored in air, whereas the sodium thiosulfate powder used in Comparative Examples 1 to 4 was stored in a dehumidifying device. This shows that the aqueous solution was easier to store than the powder. From the above, it can be seen that this manufacturing method allows for the stable production of cement-based solidifying agents with guaranteed quality, and also helps to avoid problems during the storage of sodium thiosulfate.

Claims

1. A mixing operation to obtain a mixture by mixing one or more components constituting the cement composition with an aqueous solution of thiosulfate, A water removal operation to remove water from the mixture to obtain a solid mixture, A method for producing a cement-based solidifying material, comprising performing a grinding operation to pulverize the solid mixture in this order, or simultaneously.

2. The manufacturing method according to claim 1, comprising introducing the aforementioned component into a grinding device, and within the grinding device, spraying the aqueous solution onto the component and grinding the component while mixing it with the aqueous solution.

3. The manufacturing method according to claim 1 or 2, comprising mixing the aqueous solution having a thiosulfate concentration of 0.1% by mass or more and 50.0% by mass or less with the component.

4. The manufacturing method according to claim 3, wherein in the mixing operation, 1 L or more and 65 L or less of the aqueous solution is used to produce 1 ton of the cement-based solidifying material.

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