Reducing material and its manufacturing method, cement composition, and ground improvement material

Abstract

To provide a reduction material capable of reducing occurrence of granular floating matters on a surface of slurry when being formed into the slurry.SOLUTION: There is provided a reduction material including sulfur particles, a Ca-containing object, and a reaction product of them. In the reduction material, with a total amount of the sulfur particles, a Ca-containing object, and reaction product of them as a reference, a dissolution ratio of the sulfur particles, a Ca-containing object, and reaction product to water in a prescribed condition is 3 mass% or greater. The reduction material may satisfy the following formula (1). The formula (1) is WLRa≥(WLS×RS+WLCa×RCa) / (RS+RCa)+0.5. In formula (1), WLRa, WLS, and WLCa indicate, respectively, the dissolution ratio of the reduction material, the sulfur particles before reaction, and the Ca-containing object before reaction to water under the prescribed condition, and RS and RCa respectively indicate a molar ratio of the sulfur particles before reaction and the Ca-containing object before reaction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a reducing agent and a method for producing the same, a cement composition, and a ground improvement material. [Background technology]

[0002] Cement clinker is produced using limestone, clay, silica, iron oxide, etc. as primary raw materials. In addition to these primary raw materials, various industrial by-products and industrial waste are also effectively utilized as raw materials and fuels in the production of cement clinker. Therefore, depending on the raw materials selected, cement clinker may be contaminated with small amounts of heavy metals, such as cadmium, chromium, lead, and molybdenum, derived from the various raw materials and fuels. Therefore, a technique is known in which heavy metal ions derived from cement clinker are reduced by using a reducing agent containing sulfur to reduce the amount of elution (see, for example, Patent Document 1). Meanwhile, a known method of ground improvement involves excavating the ground while injecting a solidification slurry for ground improvement into the ground, stirring and mixing the excavated soil and the solidification slurry, and solidifying the mixture (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-145077 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-346108 Summary of the Invention [Problem to be solved by the invention]

[0004] When heavy metal components such as hexavalent chromium are contained in a cement composition containing cement clinker and in soil to be improved (soil to be improved), the elution of heavy metals such as hexavalent chromium can be suppressed by using a reducing agent containing sulfur. However, for example, when a slurry method such as that described in Patent Document 2 is applied to ground improvement, the sulfur contained in the reducing agent floats to the surface of the slurry, and there is a concern that the sulfur will not be uniformly dispersed in the slurry, resulting in an uneven distribution of the reducing agent in the improved soil. Ground improvement and cement composition construction are often carried out on a large scale, and there is a concern that uneven distribution of the reducing agent will result in variations in the effect of suppressing the elution of heavy metal components.

[0005] Therefore, the present invention aims to provide a reducing agent capable of reducing the granular suspended matter that forms on the surface of a slurry when the slurry is made, and a method for producing the same. The present invention also provides a cement composition and a ground improvement material that can improve the uniformity of distribution of the reducing agent by using such a reducing agent. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above object, the inventors discovered that the dispersibility of the reducing material in water can be improved by reacting sulfur particles with a Ca-containing material, and thus completed the present invention.

[0007] In one aspect, the present invention relates to a method for producing a water-soluble polymer comprising: a sulfur particle, a Ca-containing material, and a reaction product thereof; and a method for producing a water-soluble polymer comprising the sulfur particle, the Ca-containing material, and the reaction product under predetermined conditions, the method comprising: Ra ) is 3 mass % or more.

[0008] Sulfur particles have poor dispersibility in water, and when made into a slurry, the sulfur particles float to the surface of the slurry. However, the above-mentioned reducing material containing the reaction product of sulfur particles and Ca-containing material has excellent dispersibility in water. The reason for this is presumed to be as follows. Sulfur particles are inherently hydrophobic and therefore tend to float on the surface of water. However, by reacting the sulfur particles with the Ca-containing material, the surface of the sulfur particles is modified to become hydrophilic, making them more easily dispersible in water. Here, in the above-mentioned reducing material, the solubility ratio in water of the reducing material containing the reaction product of sulfur and Ca-containing material (WL Ra ) is 3 mass % or more. In such a reducing agent, the surface of the sulfur particles is sufficiently modified, and the dispersibility in water is sufficiently good. Therefore, when the reducing agent is made into a slurry, it is thought that the particulate suspended matter that appears on the surface of the slurry can be reduced.

[0009] In one aspect, the present invention provides a reducing material that contains sulfur particles, a Ca-containing material, and a reaction product thereof, and satisfies the following formula (1): WL Ra ≧(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )+0.5···(1) In the above formula (1), WL Ra , W.L. S and WL Ca indicate the dissolution ratios of the reducing material, sulfur particles before reaction, and Ca-containing materials before reaction in water under the specified conditions, respectively, and R S and R Ca and indicate the molar ratio of sulfur particles before the reaction to the Ca-containing material before the reaction, respectively.

[0010] In the reducing material, the solubility ratio of the reducing material containing the reaction product of sulfur and the Ca-containing material in water is sufficiently larger than the solubility ratios of sulfur and the Ca-containing material, respectively, as expressed by the above formula (1). When formula (1) is satisfied, the surface of the sulfur particles is sufficiently modified, and the dispersibility in water is sufficiently good. Therefore, when the reducing material is made into a slurry, it is thought that the particulate floating matter that appears on the surface of the slurry can be reduced.

[0011] In one aspect, the present invention provides a reducing material obtained by reacting sulfur particles with a Ca-containing material in the presence of water for at least one minute. It is believed that in such a reducing material, the surfaces of the sulfur particles are sufficiently modified by the reaction of the Ca-containing material. Therefore, the dispersibility in water is sufficiently improved. This is believed to reduce particulate floating matter that appears on the surface of the slurry when the reducing material is made into a slurry.

[0012] The Ca-containing material preferably contains at least one selected from the group consisting of calcium oxide, calcium carbonate, calcium chloride, calcium hydroxide, calcium sulfide, calcium sulfate, and calcium sulfite, which can further improve the dispersibility of the reducing agent in water.

[0013] The Ca-containing material preferably contains calcium sulfite and / or calcium hydroxide, which can further improve the dispersibility of the reducing agent in water.

[0014] The Ca-containing material preferably contains calcium sulfite and / or calcium sulfide. Calcium sulfite and calcium sulfide have the effect of suppressing the elution of hexavalent chromium. Therefore, by including calcium sulfite and / or calcium sulfide, the elution of hexavalent chromium can be further reduced while suppressing the generation of granular suspended matter on the surface of the slurry.

[0015] The Ca-containing material is preferably contained in raw concrete sludge and / or clinker dust, which allows the production cost of the reducing material to be sufficiently low.

[0016] In one aspect, the present invention provides a cement composition containing any one of the reducing agents described above. The reducing agent contained in this cement composition has excellent dispersibility in water as described above. Therefore, this cement composition can improve the uniformity of distribution of the reducing agent.

[0017] In one aspect, the present invention provides a ground improvement material containing any one of the reducing materials described above. As described above, the reducing material contained in this ground improvement material has excellent dispersibility in water. Therefore, even when used as a slurry, such a ground improvement material can improve the uniformity of the distribution of the reducing material. Therefore, even when used in a ground improvement method using a slurry, the variation in the properties of the ground improvement soil can be sufficiently reduced.

[0018] In one aspect, the present invention provides a method for producing a reducing material, which includes a step of mixing sulfur particles with a Ca-containing material and reacting them in the presence of water for at least one minute. It is believed that in this step, the surface of the sulfur particles is sufficiently modified by the reaction with the Ca-containing material. Therefore, the reducing material obtained through this step has sufficiently good dispersibility in water. This is believed to reduce particulate floating matter that appears on the surface of the slurry when the reducing material is made into a slurry. [Effects of the Invention]

[0019] The present invention provides a reducing agent capable of reducing particulate suspended matter that forms on the surface of a slurry when the slurry is formed, and a method for producing the same. Furthermore, by using such a reducing agent, it is possible to provide a cement composition and a ground improvement material that can improve the uniformity of distribution of the reducing agent. [Brief explanation of the drawings]

[0020] [Figure 1]1 is a photograph showing the dispersibility of the reducing material of Example 2 in water. [Figure 2] 1 is a photograph showing the dispersibility of the reducing agent of Comparative Example 1 in water. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes embodiments of the present invention. However, the following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to the following contents.

[0022] The reducing material according to one embodiment includes sulfur particles, a Ca-containing material, and a reaction product thereof, and is characterized by a solubility ratio (WL) of the sulfur particles, the Ca-containing material, and the reaction product in water under a predetermined condition (A) based on the total amount of the sulfur particles, the Ca-containing material, and the reaction product. Ra ) is 3 mass % or more.

[0023] In this specification, the solubility in water (WL) under a given condition (A) is Ra ) is derived by the following procedure. First, 4 g of the reducing agent and 100 mL of distilled water (20°C) are introduced into a 200 mL beaker and stirred at 20°C for 30 minutes (rotation speed: 240 rpm) using a 30 mm long magnetic stirrer. Then, the obtained dispersion is filtered through filter paper (membrane filter, manufactured by ADVANTEC, cellulose acetate type, pore size: 0.45 μm, diameter: 47 mm), and the recovered solid content is dried for 15 hours in a dryer set at 40°C. The mass of the dried product thus obtained (water content: 4 mass% or less) is defined as D Ra When [g] is used, WL Ra is {(4-D Ra ) / 4}×100.

[0024] If the reaction between sulfur particles and Ca-containing materials does not proceed sufficiently (i.e., the amount of reaction product is small), and the surface of the sulfur particles is not sufficiently modified, the dissolution ratio (WL Ra On the other hand, if the reaction product between sulfur particles and Ca-containing materials is sufficiently generated (= the amount of reaction product is large), the dissolution ratio (WLRa ) tends to increase. From the viewpoint of further improving the dispersibility in water and further reducing the amount of suspended particulate matter that occurs on the surface of the slurry when it is made into a slurry, the dissolution ratio (WL Ra ) is preferably 3.5% by mass or more, more preferably 5% by mass or more, and more preferably 7% by mass or more.

[0025] On the other hand, from the viewpoint of smoothly producing reducing materials, the melting ratio (WL Ra ) is, for example, 90 mass % or less, preferably 70 mass % or less, more preferably 50 mass % or less, even more preferably 30 mass % or less, and particularly preferably 10 mass % or less. The reducing material according to this embodiment may satisfy the following formula (1). This makes it possible to further reduce particulate suspended matter that occurs on the surface of the slurry. The meanings, preferred embodiments, and numerical ranges of each symbol in formula (1) are as explained in the following embodiments.

[0026] A reducing material according to another embodiment contains sulfur particles, a Ca-containing material, and a reaction product thereof, and satisfies the following formula (1). WL Ra ≧(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )+0.5···(1) Here, in the above formula (1), WL Ra , W.L. S and WL Ca indicate the dissolution ratios (mass basis) of the reducing material, sulfur particles before reaction, and Ca-containing substances before reaction in water under the specified conditions (A), respectively, and R S and R Ca and indicate the molar ratio of sulfur particles before the reaction to the Ca-containing material before the reaction, respectively.

[0027] WL in the above formula (1) Ra is the dissolution ratio (WL Ra ) and is derived using the procedure described above. Sand WL Ca is the dissolution ratio of sulfur particles before reaction and Ca-containing substances before reaction in water under the specified condition (A), and WL Ra That is, instead of 4 g of reducing agent, 4 g of sulfur particles before reaction is used, and the mass of the dried material (water content: 4 mass% or less) obtained by the same procedure as above is calculated as D S When [g] is used, WL S is {(4-D S ) / 4} × 100. In addition, the mass of the dried material (water content: 4 mass% or less) obtained by the same procedure as above using 4 g of Ca-containing material before reaction instead of 4 g of reducing agent is calculated as D Ca When [g] is used, WL Ca is {(4-D Ca ) / 4}×100.

[0028] If the reaction between sulfur particles and Ca-containing materials is not sufficiently advanced (i.e., the amount of reaction product is small), and the surface of sulfur particles is not sufficiently modified, WL Ra and the value of "(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca On the other hand, if the reaction products between sulfur particles and Ca-containing materials are sufficiently generated (= the amount of reaction products is large), the difference between the WL Ra The value of "(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )" in the above formula (1). S ×R S +WL Ca ×R Ca ) / (R S +R Ca )" value plus "0.5" RaSince the value of is larger, the reaction product between the sulfur particles and the Ca-containing material is sufficiently generated, and the surface of the sulfur particles is sufficiently modified. This is thought to result in sufficiently good dispersibility in water, which can reduce the amount of particulate floating matter that appears on the surface of the slurry when it is made into a slurry.

[0029] From the viewpoint of further reducing particulate suspended matter generated on the surface of the slurry, the reducing agent preferably satisfies formula (2), and more preferably formula (3). WL Ra ≧(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )+1.2···(2) WL Ra ≧(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )+1.5···(3)

[0030] WL in the above formula (1), (2) or (3) Ra The upper limit of (WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )+10" or "(WL S ×R S +WL Ca ×R Ca ) / (R S +R Ca )+8" is also acceptable.

[0031] The sulfur particles in each of the above-described embodiments are not particularly limited and may be composed of elemental sulfur or may contain impurities other than sulfur. The sulfur particles may be, for example, those produced from natural sulfur, those obtained from pyrite, or those obtained as a by-product of the desulfurization process during petroleum refining. The sulfur particles may be one of these alone or a combination of two or more. From the viewpoint of cost, it is preferable that the sulfur particles include those obtained from by-products. The size of the sulfur particles is not particularly limited.

[0032] The Ca-containing material in each of the above-described embodiments may be in the form of particles (Ca-containing particles), similar to sulfur. The Ca-containing material is preferably poorly soluble in water having a pH of 7 or higher. This allows the surface of the sulfur particles to be sufficiently modified. The Ca-containing material is not particularly limited, and examples thereof include various Ca salts such as calcium oxide, calcium carbonate, calcium chloride, calcium hydroxide, calcium sulfide, calcium sulfate, calcium sulfite, calcium nitrate, and calcium nitrite. Calcium sulfate may include any of a dihydrate (gypsum dihydrate), a hemihydrate (gypsum hemihydrate), and an anhydrous (gypsum anhydrite).

[0033] From the viewpoint of sufficiently suppressing the leaching of Cr(VI) from the ground improvement soil, the Ca-containing material preferably contains at least one selected from the group consisting of calcium hydroxide, calcium sulfide, and calcium sulfite, and more preferably contains calcium sulfide and / or calcium sulfite.

[0034] The Ca-containing material may be contained in raw concrete sludge and / or clinker dust, which reduces the procurement cost of the Ca-containing material and the manufacturing cost of the reducing material.

[0035] In order to sufficiently suppress the elution of hexavalent chromium from the soil when the reducing agent is used as a soil improvement material, the Ca-containing material may contain sulfite. Examples of sulfite include calcium sulfite and calcium bisulfite (Ca(HSO2)2). Each sulfite may be a commercially available chemically synthesized product or a naturally occurring product. The calcium sulfite may be, for example, calcium sulfite anhydride and / or calcium sulfite hemihydrate, which are contained in gypsum generated in a flue gas desulfurization process or the like.

[0036] The reaction products contained in the reducing material in each of the above-described embodiments may include, for example, a complex oxide having S (sulfur), Ca (calcium), and O (oxygen) as constituent elements. Such a reaction product may, for example, adhere to the surface of sulfur particles. This is thought to modify the surface of the sulfur particles and make them hydrophilic. However, such complex oxides may be present in trace amounts that are not detectable by analysis such as XRD, or may be in a crystalline form (amorphous) that is difficult to detect by such analysis.

[0037] The blending ratio of the sulfur particles and the Ca-containing material when preparing the reducing material, and the content ratios of the sulfur particles, the Ca-containing material, and the reaction product in the reducing material are not particularly limited. From the viewpoint of achieving a sufficiently high level of both dispersibility of the reducing material in water and reduction of elution of hexavalent chromium, the molar content ratio of the Ca-containing material based on the sulfur particles contained in the reducing material may be 0.2 to 5, 0.5 to 3, or 1.5 to 2. Furthermore, the blending molar ratio of the Ca-containing material based on the sulfur particles when preparing the reducing material may be 0.2 to 5, 0.5 to 3, or 1.5 to 2.

[0038] When the reducing material contains calcium sulfite as a Ca-containing substance, the content of the sulfur particles relative to 100 parts by mass of the total of the sulfur particles and calcium sulfite is preferably 1 to 85 parts by mass, more preferably 5 to 70 parts by mass, more preferably 10 to 60 parts by mass, and even more preferably 15 to 45 parts by mass, from the viewpoint of further reducing the elution of hexavalent chromium from the ground improvement soil at an age of 7 to 28 days.

[0039] The reducing material may be composed of sulfur particles, Ca-containing materials, and their reaction products, or may contain components other than the sulfur particles, Ca-containing materials, and their reaction products. Examples of such components include hydroxides, chlorides, carbonates, and sulfates (excluding Ca-containing materials). Specific examples include ferrous chloride, magnesium hydroxide, and ferrous sulfate. The reducing material may contain at least one of the above-mentioned components.

[0040] An example of a method for producing a reducing material according to each of the above-described embodiments includes a step of mixing sulfur particles and a Ca-containing material and reacting the sulfur particles and the Ca-containing material in the presence of water for at least one minute. In this step, for example, a composite oxide containing S (sulfur), Ca (calcium), and O (oxygen) as constituent elements may be produced as a reaction product on the surface of the sulfur particles, thereby modifying the surface. This allows a reducing material with excellent dispersibility in water to be obtained. The mixing may be performed by stirring water containing the sulfur particles and the Ca-containing material using a stirrer or stirring blades. For example, the sulfur particles and the Ca-containing material may be mixed in advance and then contacted with water vapor. Furthermore, in the above step, a mixture containing the sulfur particles and the Ca-containing material may be prepared, and then the mixture may be introduced into water and mixed. Alternatively, the sulfur particles and the Ca-containing material may be introduced into water separately and mixed. When mixing the sulfur particles and the Ca-containing material, the molar ratio of the Ca-containing material to the sulfur particles may be 0.2 to 5, 0.5 to 3, or 1.5 to 2.

[0041] From the viewpoint of further reducing particulate suspended matter on the surface of the slurry when the slurry is prepared using the reducing material, the lower limit of the reaction period of the sulfur particles and the Ca-containing material may be 1 minute, 5 minutes, 10 minutes, 30 minutes, 3 hours, 6 hours, 12 hours, 24 hours, 3 days, or 7 days. From the viewpoint of production efficiency of the reducing material, the upper limit of the reaction period of the sulfur particles and the Ca-containing material may be, for example, 30 days, 3 weeks, 2 weeks, or 7 days.

[0042] The reaction temperature is, for example, 10° C. or higher, preferably 20° C. or higher, more preferably 30° C. or higher, even more preferably 40° C. or higher, and particularly preferably 50° C. or higher. The upper limit of the reaction temperature may be 90° C., 85° C., or even 80° C. The pH of the water used in the above step may be preferably 7 to 13, more preferably 10 to 13, from the viewpoint of allowing the reaction between the sulfur particles and the Ca-containing material to proceed sufficiently.

[0043] The mass ratio of water to the mass of the solid material containing sulfur particles and a Ca-containing material may be 0.2 to 2, or may be 0.4 to 1. This allows the solid material to be sufficiently dispersed in water while allowing the reaction between sulfur and the Ca-containing material to proceed smoothly. The solid material may contain only sulfur particles and a Ca-containing material, or may contain other components.

[0044] A reducing material according to yet another embodiment can be obtained by mixing sulfur particles and a Ca-containing material and reacting them for at least 1 minute. The reaction time is calculated from the time when the sulfur particles, the Ca-containing material, and water are present. The lower limit of the reaction time (period) may be 5 minutes, 10 minutes, 30 minutes, 3 hours, 6 hours, 12 hours, 24 hours, 3 days, or 7 days. The upper limit of the reaction time (period) may be, for example, 30 days, 3 weeks, 2 weeks, or 7 days, from the viewpoint of production efficiency of the reducing material. This reducing material may also contain sulfur particles, a Ca-containing material, and a reaction product thereof. For example, the reaction product may be attached to the surface of the sulfur particles. The types of sulfur particles and the Ca-containing material, as well as their molar ratios and content ratios, are the same as those in the above-described embodiment. The reaction conditions may be the same as those in the above-described production method. That is, the reaction temperature is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher. The upper limit of the reaction temperature may be 90°C or 80°C. The reducing material and the manufacturing method thereof according to the above-described embodiments are applicable to the reducing material of this embodiment.

[0045] It is believed that the surfaces of the sulfur particles of such a reducing agent are sufficiently modified by reaction with the Ca-containing material. Therefore, the dispersibility in water is sufficiently good. It is believed that when such a reducing agent is made into a slurry, it can reduce the amount of particulate floating matter that appears on the surface of the slurry.

[0046] The reducing agent in each of the above embodiments may be in powder form or may be a slurry (reducing agent slurry) in which solids are dispersed in water. The reducing agent can be suitably used as a ground improvement material or a cement composition. The reducing agent has excellent dispersibility in water. Therefore, uneven distribution of the reducing agent can be suppressed when used in various applications. Therefore, the occurrence of variations in properties and poor appearance due to uneven distribution of the reducing agent can be sufficiently suppressed. For example, when a ground improvement material containing such a reducing agent is applied to a slurry construction method, granular floating matter on the surface of the slurry is sufficiently reduced, improving the appearance during construction. Furthermore, the ground improvement material can stably suppress the amount of hexavalent chromium leaching from solidification-treated soil.

[0047] A cement composition according to one embodiment may include cement or cement clinker and the reducing material according to any of the above-described embodiments. Such a cement composition includes a reducing material that is highly dispersible in water. Therefore, the uniformity of distribution of the reducing material can be improved. Such a cement composition can be suitably used as a ground improvement material.

[0048] The ground improvement material according to one embodiment may be a cement-based ground improvement material containing cement or cement clinker and any of the reducing materials described above. It is believed that the sulfur particles contained in the reducing material gradually dissolve in the water in the soil that has been made alkaline by the cement, releasing hydrogen sulfide ions. Furthermore, the released hydrogen sulfide ions themselves reduce hexavalent chromium. When the reducing material contains sulfite, the hydrogen sulfide ions also have the effect of increasing the solubility of sulfite. This further promotes the reduction of hexavalent chromium.

[0049] The ground improvement material (cement composition) may contain cement or cement clinker, the reducing agent of any of the above-described embodiments, and gypsum. The content of the reducing agent in the ground improvement material (cement composition) is preferably 0.5 to 30 mass%, more preferably 1 to 20 mass%, even more preferably 2 to 15 mass%, and particularly preferably 3 to 10 mass%. This makes it possible to sufficiently suppress the elution of hexavalent chromium while maintaining the solidification strength of the ground improvement soil.

[0050] When the reducing agent contains calcium sulfite as a Ca-containing substance, the lower limit of the calcium sulfite content in the ground improvement material (cement composition) may be, for example, 0.1 mass%, 1 mass%, 2 mass%, 3 mass%, or 4 mass%. The lower limit of the sulfur particle content in the ground improvement material may be, for example, 0.1 mass%, 0.5 mass%, 1 mass%, 2 mass%, or 4 mass%. By containing calcium sulfite and sulfur particles within such ranges, the elution of hexavalent chromium from the ground improvement soil can be sufficiently suppressed.

[0051] The gypsum may be any of gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. From the viewpoint of the strength development of the ground improvement material (cement composition), it is preferable to contain gypsum dihydrate or anhydrous gypsum. For example, when obtaining the ground improvement material (cement composition), gypsum obtained by mixing gypsum dihydrate and anhydrous gypsum may be used. From the viewpoint of the strength development of the improved soil, the gypsum content in the ground improvement material (cement composition) is, for example, 1 to 25 mass%, preferably 3 to 20 mass%, more preferably 4 to 15 mass%, and even more preferably 5 to 12 mass%.

[0052] The cement may be any of the various Portland cements specified in JIS R5210:2003 "Portland Cement." Among these, ordinary Portland cement or high-early-strength Portland cement is preferred from the viewpoints of availability and increasing compressive strength at short ages. The total chromium content in the cement may be, for example, 30 to 250 mg / kg or 50 to 200 mg / kg from the viewpoint of availability. Similarly, the amount of water-soluble hexavalent chromium in the cement may be, for example, 3 to 40 mg / kg or 5 to 30 mg / kg from the viewpoint of similar availability. The total chromium content of the cement is measured in accordance with the method described in JIS R5202:2010, and the amount of water-soluble hexavalent chromium is measured in accordance with the method described in Cement Association Standard Test Method I-51-1981.

[0053] The content of cement or cement clinker in the ground improvement material (cement composition) is, for example, 50 to 98% by mass, preferably 70 to 95% by mass, and more preferably 75 to 90% by mass. If the content of cement or cement clinker is less than 50% by mass, the strength of the improved soil tends to be difficult to exhibit. On the other hand, if the content of cement or cement clinker exceeds 98% by mass, the amount of hexavalent chromium eluted from the improved soil may increase depending on the hexavalent chromium content of the cement or cement clinker. When cement clinker is used, it is preferable to adjust it to an appropriate fineness before use.

[0054] The ground improvement material (cement composition) may further contain blast furnace slag powder. The content of the blast furnace slag powder is, for example, 1 to 50 mass%, preferably 5 to 30 mass%, and more preferably 10 to 20 mass%. When the content of the blast furnace slag is within this range, the amount of hexavalent chromium eluted from the ground improvement soil can be further suppressed, and the amount of reducing agent used can be reduced.

[0055] The fineness of the ground improvement material (cement composition) is not particularly limited, but the Blaine specific surface area is preferably 1000 to 6000 cm 2 / g, preferably 2000 to 5500 cm 2 / g, and more preferably 3000 to 5000 cm 2 / g, and more preferably 4000 to 4500 cm 2 Within this range, the amount of hexavalent chromium eluted can be suppressed while maintaining the strength of the ground improvement soil.

[0056] The method for producing the ground improvement material (cement composition) is not particularly limited, and it may be produced by mixing raw materials adjusted to a predetermined fineness, or by grinding some or all of the raw materials while mixing them.

[0057] The improved soil obtained by the soil improvement material includes the above-mentioned soil improvement material and the soil to be improved. The improved soil may be obtained by injecting a slurry-like soil improvement material into the ground and mixing it (slurry method). Because the soil improvement material contains a reducing material that has excellent dispersibility in water, even if it is in a slurry form, it is possible to prevent granular floating matter from being generated on the surface of the slurry. This prevents the segregation of the reducing material in the improved soil, which causes variations in the appearance and quality of the improved soil. For example, it is possible to sufficiently prevent the amount of hexavalent chromium leaching from increasing due to a localized decrease in the content of the reducing material.

[0058] 1m of soil to be improved 3 The content of the soil improvement material in terms of solid content relative to the above is, for example, 20 to 500 kg, preferably 50 to 450 kg, more preferably 50 to 400 kg, and further preferably 100 to 350 kg.

[0059] The soil to be improved is not particularly limited, and may be volcanic ash clayey soil (e.g., Kanto loam), which is relatively difficult to suppress the elution of hexavalent chromium. By using the soil improvement material according to this embodiment, it is possible to sufficiently suppress the elution of hexavalent chromium from the improved soil while maintaining a high compressive strength of the improved soil.

[0060] Although several embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. For example, the use of the reducing material is not limited to a ground improvement material or a cement composition, and the reducing material may be mixed with incineration ash, construction soil, etc. [Example]

[0061] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0062] [Adjustment of reducing material] The following raw materials were prepared: Calcium sulfite hemihydrate: Wako Pure Chemical Industries, Ltd., chemical grade (When 10 g of this product was dispersed in 100 g of distilled water, the pH of the supernatant was 8.40, and the oxidation-reduction potential (ORP) of the supernatant was 260 mV.) Sulfur: Wako Pure Chemical Industries, Ltd., powder, chemical grade Calcium hydroxide: Wako Pure Chemical Industries, Ltd., chemical grade

[0063] In each example, the blending ratio (R S ,R Ca The above-mentioned raw materials (50 g in total) were mixed in a 250 ml plastic container, and water was added to make the water-to-powder ratio (W / P) = 0.6 (mass ratio), and the mixture was sealed in a 250 ml plastic container and reacted under the treatment conditions shown in Table 1. During the period (number of days) shown in Table 1, the plastic container was left to stand without any particular stirring. After the reaction, the solid content obtained by filtration was dried for 15 hours in a dryer set at 40°C and recovered. The dried product thus obtained (moisture content: 4 mass% or less) was used as the reducing material for each example.

[0064] On the other hand, in each comparative example, the above-mentioned raw materials were blended in the blending ratio (molar ratio) shown in Table 1 to prepare the reducing material of each comparative example.

[0065] [WL Ra , W.L. S and WL Ca Derivation of The melting ratios (WLRa , W.L. S and WL Ca ) was derived. WL Ra and WL S is the dissolution ratio of sulfur particles used as a reducing agent and raw material in water under the specified condition (A), and WL Ca is the solubility ratio of calcium sulfite hemihydrate, calcium hydroxide, or a mixture thereof used as a raw material in water under the specified conditions (A). Ra , W.L. S and WL Ca The derivation method of each parameter is as explained in the "Description of the Preferred Embodiments." The derivation results are shown in Table 1.

[0066] [Table 1]

[0067] The reducing materials of Examples 1 to 8 were obtained by mixing sulfur particles and a Ca-containing material (one or both of calcium sulfite hemihydrate and calcium hydroxide) and reacting them under the treatment conditions shown in Table 1. The dissolution ratio (WL Ra ) was 3 mass% or more, and the relationship of the above formula (1) was satisfied. Qualitative analysis by XRD was carried out on the reducing materials obtained in Examples 1 and 4. As a result, in both cases, no substances other than sulfur, calcium sulfite, and calcium hydroxide, which were the raw materials used, were detected.

[0068] [Evaluation of dispersibility] A ground improvement material was prepared by mixing 10% by mass of anhydrous gypsum (natural anhydrous gypsum), the amount of reducing agent shown in Table 2, and the remainder being ordinary Portland cement (total chromium content: 65.5 mg / kg, water-soluble hexavalent chromium content: 5.8 mg / kg). 100 g of this ground improvement material and 80 g of tap water were placed in a plastic container and mixed for 1 minute 30 seconds at 250 rpm using a chemical stirrer. The mixture was then left to stand, and the surface condition of the slurry was visually evaluated. The evaluation criteria were as follows. The results are shown in Table 2.

[0069] A: There is absolutely no floating of solids. B: Almost no floating of solids. C: There is a small amount of solid matter floating. D: A large amount of floating solids is present.

[0070] FIG. 1 is a photograph of the surface of the slurry of Example 2. As shown in FIG. 1 and Table 2, in the slurries of Examples 1 to 8, there was little or no floating of solids on the surface. Furthermore, when the treatment conditions were high temperature, the surface condition of the slurry could be improved even with a short treatment time (Examples 3 and 6). FIG. 2 is a photograph of the surface of the slurry of Comparative Example 1. As shown in FIG. 2 and Table 2, in Comparative Example 1, in which only sulfur was added, and in Comparative Examples 2 to 6, in which sulfur and a Ca-containing material were mixed and not subjected to the specified treatment, a small amount or a large amount of floating of solids was confirmed on the surface of the slurry. From these results, it is presumed that by mixing sulfur particles with a Ca-containing material and performing the specified treatment, the very surface of the sulfur particles was modified to a hydrophilic substance, improving the dispersibility when the particles were made into a slurry.

[0071] [Table 2]

[0072] [Evaluation of elution amount of hexavalent chromium] The soil to be improved (Kanto loam) was mixed with the soil improvement materials of each example and each comparative example prepared as described above, and the amount of the soil improvement materials was adjusted to 1 m 3 300kg / m 3 The soil improvement materials of each Example and Comparative Example were mixed in a Hobart mixer so that the above ratio was achieved. Mixing was carried out for a total of 3 minutes, with the soil adhering to the paddle and ball being scraped off at the 1 minute 30 second mark. After mixing was completed, the mixture was packed into a cylindrical formwork measuring 50 mm in diameter and 100 mm in height using a rammer in three layers, and then sealed and cured at 20°C for 7 and 28 days.

[0073] For each of the improved soil samples at the above ages, a leaching test was conducted in accordance with Environment Agency Notification No. 46 (August 23, 1991) to measure the amount of hexavalent chromium leaching. The improved soil samples used for the measurements were dried overnight by vacuum degassing using an aspirator. The amount of hexavalent chromium leaching was determined by quantifying the hexavalent chromium concentration in the filtrate after immersion using the diphenylcarbazide spectrophotometric method in accordance with JIS K0102:2016, section 65.2.1. The quantitative measurement procedure involved adding 3 mL of sulfuric acid (1+9) and then adding 1 mL of diphenylcarbazide solution (10 g / L) within a 20-second interval. The measurement results are shown in Table 3.

[0074] [Table 3]

[0075] As shown in Table 3, the soil improvement materials of each example were able to sufficiently reduce the amount of Cr(VI) elution. Furthermore, the reducing material of Example 6, despite the reaction period under the treatment conditions being only one day, reduced the amount of Cr(VI) elution to a level equal to or greater than that of Examples 4 and 5. From this, it is thought that a higher reaction temperature between sulfur particles and Ca-containing materials tends to result in a better Cr(VI) elution suppression effect.

Claims

1. Contains sulfur particles, Ca-containing substances, and reaction products thereof, The solubility ratio (WL) of the sulfur particles, the Ca-containing material, and the reaction product in water, which is determined under the following predetermined condition (A) based on the total amount of the sulfur particles, the Ca-containing material, and the reaction product: Ｒａ ) is 3 mass% or more. [Predetermined condition (A): 4 g of the reducing agent and 100 mL of distilled water (20° C.) are placed in a 200 mL beaker and stirred at 20° C. for 30 minutes using a 30 mm long magnetic stirrer (rotation speed: 240 rpm). Thereafter, the obtained dispersion is filtered through a filter paper (membrane filter, cellulose acetate type, pore size: 0.45 μm, diameter: 47 mm), and the recovered solid content is dried for 15 hours in a dryer set at 40° C. The mass of the obtained dried product (water content: 4% by mass or less) is represented by D Ｒａ When [g], WL Ｒａ is {(4-D Ｒａ ) / 4} × 100.

2. A reducing material containing sulfur particles, Ca-containing materials, and reaction products thereof, and satisfying the following formula (1): WL Ｒａ ≧(WL Ｓ ×R Ｓ +WL Ｃａ ×R Ｃａ ) / (R Ｓ +R Ｃａ )+0.5・・・(1) [In formula (1), WL Ｒａ , W.L. Ｓ and W.L. Ｃａ respectively indicate the dissolution ratios in water of the reducing agent, the sulfur particles before the reaction, and the Ca-containing substance before the reaction, which are determined under the following predetermined condition (A), and R Ｓ and R Ｃａ and represent the molar ratio of the sulfur particles before the reaction to the Ca-containing material before the reaction, respectively. Predetermined condition (A): 4 g of the reducing agent, 4 g of the sulfur particles before the reaction, or 4 g of the Ca-containing material before the reaction, and 100 mL of distilled water (20°C) are introduced into a 200 ml beaker, and the mixture is stirred at 20°C for 30 minutes using a magnetic stirrer with a length of 30 mm (rotation speed: 240 rpm). Thereafter, the obtained dispersion is filtered with filter paper (membrane filter, cellulose acetate type, pore size: 0.45 μm, diameter: 47 mm), and the recovered solid content is dried for 15 hours in a dryer set at 40° C. The masses of the dried products (water content: 4 mass% or less) obtained when using the reducing agent, the sulfur particles before the reaction, and the Ca-containing material before the reaction are respectively represented by D Ｒａ [g], D Ｓ [g], and D Ｃａ When [g], WL Ｒａ is {(4-D Ｒａ ) / 4}×100, WL Ｓ is {(4-D Ｓ ) / 4} × 100 、 W.L. Ｃａ is {(4-D Ｃａ ) / 4} × 100.

3. 3. The reducing material according to claim 1, wherein the Ca-containing substance comprises at least one selected from the group consisting of calcium oxide, calcium carbonate, calcium chloride, calcium hydroxide, calcium sulfide, calcium sulfate, and calcium sulfite.

4. The reducing material according to any one of claims 1 to 3, wherein the Ca-containing material includes calcium sulfite and / or calcium hydroxide.

5. The reducing material according to any one of claims 1 to 4, wherein the Ca-containing material includes calcium sulfite and / or calcium sulfide.

6. The reducing material according to any one of claims 1 to 5, wherein the Ca-containing material is contained in raw concrete sludge and / or clinker dust.

7. A cement composition comprising the reducing material according to any one of claims 1 to 6.

8. A ground improvement material comprising the reducing material according to any one of claims 1 to 6.

9. A method for producing a reducing material that is a dry material, comprising a step of mixing sulfur particles and a Ca-containing material in the presence of water having a pH of 7 to 13, at a molar ratio of the Ca-containing material to the sulfur particles of 0.2 to 5, and reacting the mixture at a temperature of 10 to 90°C for 1 minute or more.

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