Reducing agent, cement composition, ground improvement material, and improved ground soil

Abstract

To provide a reducing material and a ground improvement material capable of sufficiently suppressing the elution amount of hexavalent chromium, and to provide a cement composition and a ground improvement soil capable of sufficiently suppressing the elution amount of hexavalent chromium.SOLUTION: A reducing material includes a sulfite, a sulfur component comprising at least one of sulfur and a sulfur compound, in which the sulfur compound releases at least one of HS- ions and S2- ions when contacted with water. A cement composition includes a sulfite, a sulfur component comprising at least one of sulfur and a sulfur compound, and cement. A ground improvement material includes sulfite, a sulfur component comprising at least one of sulfur and a sulfur compound, and cement. A ground improvement soil includes the ground improvement material and a ground improvement object soil.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a reducing agent, a cement composition, a ground improvement material, and improved soil.

Background Art

[0002] Cement clinker is produced using limestone, clay, silica, iron oxide, etc. as main raw materials. In addition to these main raw materials, various industrial by-products and industrial wastes are effectively used as raw fuels in the production of cement clinker. Therefore, depending on the selection of raw materials, trace amounts of heavy metals such as cadmium, chromium, lead, and molybdenum derived from various raw fuels may be mixed into the cement clinker. Thus, techniques are known that use various reducing agents to reduce heavy metal ions derived from cement clinker and reduce their elution amounts. (Patent Documents 1 to 4).

[0003] For example, in Patent Document 1, a technique is proposed in which ferrous sulfate and sulfite are mixed and used as a solidifying agent when solidifying soft ground, thereby reducing hexavalent chromium to trivalent chromium and suppressing the elution of hexavalent chromium. In Patent Document 2, a technique is proposed in which a ground improvement material having a specific pH and redox potential and containing a predetermined amount of MgO is used to suppress the elution of hexavalent chromium. In Patent Document 3, a technique is proposed in which an elution amount of selenium(IV) is suppressed using a reducing agent containing an iron compound. In Patent Document 4, a technique is proposed in which a heavy metal immobilizing agent containing a predetermined amount of calcium sulfide is used to suppress the elution of heavy metals. Patent Document 5 discloses a cement additive containing bassanite or calcium polysulfide and sulfur, and Patent Document 6 discloses a cement additive containing calcium sulfite, which is a by-product when producing a lime sulfur mixture.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] As described above, various components have been proposed as reducing agents for hexavalent chromium. However, as part of environmental protection, it is expected that there will be an even stronger demand in the future to establish a technology that can further reduce the elution amount of hexavalent chromium from soil improvement soil. Therefore, the present disclosure provides a reducing agent capable of sufficiently suppressing the elution amount of hexavalent chromium. In addition, a soil improvement material, a cement composition, and soil improvement soil capable of sufficiently suppressing the elution amount of hexavalent chromium are provided. [Means for Solving the Problems

[0006] In one aspect, the present disclosure includes a sulfite and a sulfur component composed of at least one of sulfur and sulfur compounds, and the sulfur compound releases at least one of HS - ions and S 2- ions when contacted with water, and provides a reducing agent. This reducing agent can sufficiently suppress the elution amount of hexavalent chromium from hexavalent chromium-containing substances such as soil by the interaction between the sulfite and the sulfur component. As an example of the above interaction in the reducing agent, hydrogen sulfide ions (HS - ) and sulfide ions (S 2-) may be involved. That is, when the soil becomes alkaline due to the action of cement or the like, it is considered that the sulfur component gradually dissolves in water and releases hydrogen sulfide ions and sulfide ions. The released hydrogen sulfide ions and sulfide ions themselves also reduce hexavalent chromium, but also have the effect of increasing the solubility of coexisting sulfites. Due to such interactions, the reduction of hexavalent chromium by the reducing agent is promoted, and the elution amount of hexavalent chromium can be reduced. Note that the mechanism for reducing the elution amount of hexavalent chromium is not limited to this.

[0007] In the above reducing agent, the content of the sulfur component with respect to a total of 100 parts by mass of the sulfite and the sulfur component is preferably 1 to 85 parts by mass. Also, it is preferable that the content of the sulfite is more than the content of the sulfur component. Thereby, the elution amount of hexavalent chromium can be further reduced. Note that the "sulfur component" in the present disclosure is sulfur and HS - ions and S 2- ions and is only a sulfur compound that releases at least one of them.

[0008] In the above reducing agent, it is preferable that the sulfite contains calcium sulfite. Thereby, the elution amount of hexavalent chromium can be further reduced.

[0009] In one aspect, the present disclosure provides a cement composition containing any of the above reducing agents and cement. Since this cement composition contains any of the above reducing agents, the elution amount of hexavalent chromium can be sufficiently reduced. In another aspect, the present disclosure provides a cement composition containing a sulfite, a sulfur component composed of at least one of sulfur and a sulfur compound, and cement, and the sulfur compound releases at least one of HS - ions and S 2- ions when contacted with water. Since this cement composition contains both a sulfite and a sulfur component, the elution amount of hexavalent chromium can be sufficiently reduced.

[0010] In one aspect, the present disclosure provides a ground improvement material containing any of the above reducing materials. Since this ground improvement material contains any of the above reducing materials, the elution amount of hexavalent chromium can be sufficiently reduced. In another aspect, the present disclosure provides a ground improvement material containing a sulfite and a sulfur component composed of at least one of sulfur and sulfur compounds, and the sulfur compound releases at least one of HS - ions and S 2- ions when contacting water. Since this ground improvement material contains both a sulfite and a sulfur component, the elution amount of hexavalent chromium can be sufficiently reduced.

[0011] The above ground improvement material further contains blast furnace slag powder, and the total content of the sulfite and the sulfur component is preferably 0.1 to 30% by mass of the content of the reducing material, and the content of the blast furnace slag powder is 5 to 30% by mass. Thereby, while maintaining the elution amount of hexavalent chromium low, the usage amounts of the sulfite and the sulfur component can be reduced.

[0012] In one aspect, the present disclosure provides a ground improved soil containing any of the above ground improvement materials and the soil to be improved. Since this ground improved soil contains any of the above ground improvement materials, the elution amount of hexavalent chromium can be sufficiently reduced.

Advantages of the Invention

[0013] It is possible to provide a reducing material capable of sufficiently suppressing the elution amount of hexavalent chromium. Further, it is possible to provide a ground improvement material, a cement composition, and a ground improved soil capable of sufficiently suppressing the elution amount of hexavalent chromium.

Brief Description of the Drawings

[0014]

Figure 1

Modes for Carrying Out the Invention

[0015] Embodiments of the present disclosure will be described below. However, the following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content.

[0016] A reducing material according to an embodiment includes a sulfite and a sulfur component composed of at least one of sulfur and sulfur compounds, and the sulfur compound releases at least one of HS - ions and S 2- ions when contacting water. By using this reducing material as a ground improvement material, an excellent effect of suppressing the elution of hexavalent chromium can be obtained. This reducing material is particularly suitable for use as a cement-based ground improvement material. Note that the sulfur component in this specification corresponds only to sulfur and sulfur compounds.

[0017] The sulfite is not particularly limited, and for example, it can include at least one selected from the group consisting of calcium sulfite (e.g., hemihydrate), sodium sulfite, magnesium sulfite, calcium bisulfite (Ca(HSO2)2), sodium bisulfite, and magnesium bisulfite. Among these, it is preferable to include calcium sulfite. Thereby, when used as a reducing material for a ground improvement material, the elution amount of hexavalent chromium can be further reduced.

[0018] Each sulfite may be a commercially available product synthesized chemically or may be a naturally occurring one. Calcium sulfite may be, for example, calcium sulfite anhydride and / or calcium sulfite hemihydrate contained in gypsum generated in a flue gas desulfurization process or the like. Calcium sulfite is preferably in powder form. Ordinary calcium sulfite can be used. For example, the pH of the supernatant after adding 10 g of calcium sulfite to 100 g of distilled water and stirring may be less than 9, or may be less than 8.5. The oxidation-reduction potential (ORP) of the same supernatant may exceed 50 mV, or may be 100 mV or more.

[0019] Sulfur is so-called elemental sulfur and is different from sulfur compounds. Examples of sulfur include those produced from natural sulfur, those obtained from pyrite, and those obtained as by-products in the desulfurization process during petroleum refining. From the perspective of cost, it is preferable that the reducing agent contains sulfur obtained from by-products among the above-mentioned sulfur.

[0020] When the reducing agent of this embodiment is used as, for example, a cement-based ground improvement material, sulfur is gradually dissolved by the moisture in the soil made alkaline by cement to release hydrogen sulfide ions (HS - ) and sulfide ions (S 2- ). It is considered that the released hydrogen sulfide ions and sulfide ions themselves also reduce hexavalent chromium, but also have the effect of increasing the solubility of coexisting sulfite. It is considered that the reduction of hexavalent chromium is promoted by such an interaction between sulfur and sulfite.

[0021] A sulfur compound is one that releases at least one of HS - ions and S 2- ions when contacted with water. The temperature of the water here is 20°C. Examples of such sulfur compounds include sulfides, specifically, potassium sulfide (K2S), manganese sulfide (MnS), iron sulfide (FeS), calcium sulfide (CaS), sodium disulfide (Na2S2), and iron disulfide (FeS2). Such sulfur compounds can also promote the reduction of hexavalent chromium by interaction with sulfite, and can sufficiently reduce the elution amount of hexavalent chromium. The reducing agent may contain both sulfur and sulfur compounds as sulfur components, or may contain either one of them.

[0022] The content of the sulfur component relative to 100 parts by mass in total of the sulfite and the sulfur component in the reducing material is not particularly limited. For example, from the perspective of further reducing the elution amount of hexavalent chromium from the ground improvement soil, the content of the sulfite may be more than the content of the sulfur component. From the perspective of further reducing the elution amount of hexavalent chromium from the ground improvement soil at a material age of 7 to 28 days, the content is, for example, 1 to 85 parts by mass, preferably 5 to 70 parts by mass, more preferably 10 to 60 parts by mass, still more preferably 15 to 45 parts by mass, particularly preferably 19 to 40 parts by mass, and most preferably 25 to 35 parts by mass.

[0023] From the perspective of increasing the uniaxial compression strength of the ground improvement soil, the content of the sulfur component relative to 100 parts by mass in total of the sulfite and the sulfur component is, for example, 1 to 95 parts by mass, preferably 21 to 90 parts by mass, more preferably 26 to 85 parts by mass, still more preferably 45 to 80 parts by mass, and particularly preferably 55 to 75 parts by mass. The contents of the sulfur component (sulfur and sulfur compounds) and the sulfite can be determined, for example, by the XRD-Rietveld method.

[0024] The reducing material may contain components other than the sulfite and the sulfur component. Such components include hydroxides, chlorides, carbonates, sulfates, etc. Specifically, calcium hydroxide, ferrous chloride, calcium carbonate, magnesium hydroxide, ferrous sulfate, calcium sulfate, etc. are included. Calcium sulfate includes dihydrate (gypsum), hemihydrate (plaster of Paris), and anhydride (anhydrite). The reducing material may contain at least one of the above components, or may contain two or more of them. The total content of the sulfite and the sulfur component in the reducing material may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more. The reducing material may consist only of the sulfite and the sulfur component.

[0025] The method for manufacturing the reducing material is not particularly limited, and it may be manufactured by mixing each raw material (sulfite and sulfur component), or it may be manufactured by mixing while pulverizing part or all of the raw materials. Further, it may be manufactured by mixing slurry-like raw materials. The reducing material may be a solid such as a powder or may be in a slurry state.

[0026] The ground improvement material according to one embodiment includes the above-mentioned reducing material, cement, and gypsum. By including the reducing material, the elution amount of hexavalent chromium can be maintained at a sufficiently low level over a long period from the short-term material age. In a modified example, the ground improvement material includes a sulfite, a sulfur component, cement, and gypsum. Since this ground improvement material contains a sulfite and a sulfur component, the elution amount of hexavalent chromium can be maintained at a sufficiently low level over a long period from the short-term material age.

[0027] The total content of the sulfite and the sulfur component in the ground improvement material is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, still more preferably 1.0 to 8% by mass, particularly preferably 1.5 to 5% by mass, and most preferably 2 to 4% by mass. As a result, the elution amount of hexavalent chromium can be sufficiently reduced while maintaining the uniaxial compressive strength of the improved ground.

[0028] The lower limit of the content of the sulfite in the ground improvement material is not particularly limited. For example, the lower limit of the content may be 0.1% by mass, 0.5% by mass, 1% by mass, 1.5% by mass, or 2% by mass. The lower limit of the content of the sulfur component in the ground improvement material is also not particularly limited, and the lower limit of the content may be 0.1% by mass, 0.15% by mass, 0.5% by mass, 0.75% by mass, or 1% by mass. By including the sulfite and the sulfur component within such a range, the elution amount of hexavalent chromium from the improved ground can be sufficiently reduced.

[0029] The gypsum may be any of dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum. From the viewpoint of the strength development property of the ground improvement material, it is preferable to contain dihydrate gypsum or anhydrous gypsum. For example, when obtaining the ground improvement material, gypsum containing dihydrate gypsum and anhydrous gypsum may be used. From the viewpoint of the strength development property of the ground improved soil, the content of gypsum in the ground improvement material is, for example, 1 to 25% by mass, preferably 3 to 20% by mass, more preferably 4 to 15% by mass, and still more preferably 5 to 12% by mass.

[0030] The cement may be various Portland cements specified in JIS R5210:2003 "Portland Cement". Among these, from the viewpoints of easy availability and high compressive strength at a short age, it is preferable to contain at least one of ordinary Portland cement and early-strength Portland cement. The total chromium amount of the cement may be, for example, 30 to 250 mg / kg, or may be 50 to 200 mg / kg, from the viewpoint of easy availability. The water-soluble hexavalent chromium amount of the cement may also be, for example, 3 to 40 mg / kg, or may be 5 to 30 mg / kg, from the same viewpoint. Note that the total chromium amount of the cement is measured in accordance with the method described in JIS R5202:2010, and the water-soluble hexavalent chromium amount is measured in accordance with the method described in Cement Association Standard Test Method I-51-1981.

[0031] The content of cement in the ground improvement material is, for example, 50 to 98% by mass, preferably 70 to 95% by mass, and more preferably 75 to 90% by mass. When the content of cement is less than 50% by mass, the strength of the ground improved soil tends to be difficult to develop. On the other hand, when the content of cement exceeds 98% by mass, the elution amount of hexavalent chromium from the ground improved soil may increase depending on the content of hexavalent chromium in the cement.

[0032] Cement clinker can also be used as a substitute for cement. When using cement clinker, it is preferable to use it after adjusting to an appropriate fineness.

[0033] The ground improvement material may further contain blast furnace slag powder. The content of the blast furnace slag powder is, for example, 1 to 50% by mass, preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. When the content of the blast furnace slag is within such a range, the elution amount of hexavalent chromium from the ground improvement soil can be further suppressed, and the amount of reducing agent used can be reduced.

[0034] The fineness of the ground improvement material is not particularly limited, but the Blaine specific surface area is 1000 to 6000 cm 2 / g, preferably 2000 to 5500 cm 2 / g, more preferably 3000 to 5000 cm 2 / g, and even more preferably 4000 to 4500 cm 2 / g. If it is within such a range, the elution amount of hexavalent chromium can be suppressed while maintaining the strength of the ground improvement soil.

[0035] The method for manufacturing the ground improvement material is not particularly limited, and it may be manufactured by mixing raw materials adjusted to a predetermined fineness, or it may be manufactured by mixing and pulverizing part or all of the raw materials. The ground improvement material may be manufactured by mixing the above-mentioned reducing agent and raw materials other than the reducing agent, or the raw materials of the reducing agent, that is, sulfite, sulfur component, and raw materials other than the reducing agent may be blended and mixed simultaneously for preparation. That is, the ground improvement material of the present disclosure is not limited to that prepared using a reducing agent containing sulfite and sulfur component, and may be prepared by separately mixing sulfite and sulfur component with other raw materials.

[0036] The cement composition according to one embodiment contains the above-mentioned reducing agent, cement, and gypsum. By containing the above-mentioned reducing agent, this cement composition can sufficiently reduce the elution amount of hexavalent chromium. In a modified example, the cement composition contains sulfite, a sulfur component composed of at least one of sulfur and sulfur compounds, and cement. This cement composition can also sufficiently reduce the elution amount of hexavalent chromium by containing sulfite and sulfur component.

[0037] The total content of sulfite and sulfur components in the cement composition is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, still more preferably 1.0 to 8% by mass, particularly preferably 1.5 to 5% by mass, and most preferably 2 to 4% by mass. By this, the elution amount of hexavalent chromium from the structure manufactured using the cement composition can be sufficiently reduced.

[0038] The lower limit of the content of sulfite in the cement composition is not particularly limited. For example, the lower limit of the content may be 0.1% by mass, may be 0.5% by mass, may be 1% by mass, may be 1.5% by mass, or may be 2% by mass. The lower limit of the content of the sulfur component in the cement composition is also not particularly limited, and the lower limit of the content may be 0.1% by mass, may be 0.15% by mass, may be 0.5% by mass, may be 0.75% by mass, or may be 1% by mass. By containing sulfite and the sulfur component within such a range, the elution amount of hexavalent chromium from the structure manufactured using the cement composition can be sufficiently reduced.

[0039] The gypsum and cement contained in the cement composition can be the same as those of the above-mentioned ground improvement material. The manufacturing method of the cement composition is not particularly limited, and it may be manufactured by mixing raw materials adjusted to a predetermined powder fineness, or may be manufactured by mixing and pulverizing part or all of the raw materials. For example, the cement composition may be manufactured by mixing the above-mentioned reducing material and raw materials other than the reducing material, or the raw materials of the reducing material, that is, sulfite, sulfur component, and raw materials other than the reducing material may be simultaneously blended, mixed, and prepared. That is, the cement composition of the present disclosure is not limited to the one prepared using a reducing material containing sulfite and sulfur components, and may be the one prepared by separately mixing sulfite and sulfur components with other raw materials.

[0040] The ground improvement soil according to one embodiment includes the above-mentioned ground improvement material and the soil to be improved. Such ground improvement soil is obtained by mixing the above-mentioned ground improvement material and the soil to be improved. 1 m of the soil to be improved 3The content of the ground improvement material for [object] is, for example, 20 to 500 kg, preferably 50 to 450 kg, more preferably 50 to 400 kg, and even more preferably 100 to 350 kg.

[0041] The soil to be improved is not particularly limited, and may be, for example, volcanic ash clay (e.g., Kanto loam) for which it is relatively difficult to suppress the elution of hexavalent chromium. By using the ground improvement material according to the present 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.

[0042] As described above, the embodiments of the present disclosure have been described, but the present disclosure is not limited to the above-described embodiments. For example, the use of the reducing material is not limited to being used as a ground improvement material or a cement composition, and it may be blended with incineration ash, construction-generated soil, or the like.

Examples

[0043] Hereinafter, the content of the present disclosure will be described in detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0044] [Preparation of Ground Improvement Material] The following raw materials were prepared. · Cement: Ordinary Portland cement (total chromium content: 65.5 mg / kg, water-soluble hexavalent chromium content: 5.8 mg / kg) · Anhydrous gypsum: Natural anhydrous gypsum · Calcium sulfite hemihydrate: Manufactured by Wako Pure Chemical Industries, Ltd., for chemical use (The pH of the supernatant after adding 10 g of this product to 100 g of distilled water and stirring was 8.40, and the oxidation-reduction potential (ORP) of the same supernatant was 260 mV.) · Ferrous sulfate: Manufactured by Wako Pure Chemical Industries, Ltd. · Sulfur: Manufactured by Wako Pure Chemical Industries, Ltd., for chemical use · Calcium sulfide-containing substance: Prepared by mixing gypsum and a carbon source and firing at 950 °C, and the content of CaS was 95% by mass and the content of anhydrous gypsum was 5% by mass. Blast furnace slag powder: K-ment (product name, manufactured by Kobe Steel Slag Products Co., Ltd.) - Soil to be improved: Kanto loam

[0045] The above-mentioned raw materials were mixed at the same time in the ratio shown in Table 1 to prepare the ground improvement materials of Examples 1 to 16 and Comparative Examples 1 to 7. In Table 1, "Ca sulfite" indicates the mixing ratio of calcium sulfite hemihydrate. In this manner, the ground improvement materials containing the reducing materials shown in Table 1 were prepared. In Example 10, the mixing ratio of the calcium sulfide-containing material was 2 mass%. In Table 1, the value obtained by converting the mixing ratio of the calcium sulfide-containing material into calcium sulfide is shown in the "Ca sulfide" column. In addition, the "natural anhydrous gypsum" column of Example 10 in Table 1 shows the total value of the mixing ratio of natural anhydrous gypsum and the ratio of anhydrous gypsum derived from the calcium sulfide-containing material.

[0046] [Table 1]

[0047] [Preparation and evaluation of ground improvement soil] The amount of soil improvement material mixed for the target soil (Kanto loam) is 3 300kg / m 3 The soil improvement materials of each Example and Comparative Example were mixed so that the above ratio was obtained, and mixed for 3 minutes with a Hobart mixer. Mixing was stopped once at 1 minute 30 seconds during mixing, and the soil adhering to the paddle and ball was scraped off. After mixing was completed, the mixture was packed in three layers using a rammer into a cylindrical formwork with a diameter of 50 mm and a height of 100 mm, and then sealed and cured at 20°C for 7 days and 28 days.

[0048] Regarding the ground-improved soils of the above-mentioned material ages, an elution test was conducted in accordance with the Environmental Agency Notification No. 46 (August 23, 1991), and the elution amount of hexavalent chromium was measured. For the measurement, a vacuum degassing was carried out overnight by an aspirator, and the dried improved soil sample was used. The elution amount of hexavalent chromium was determined by quantifying the concentration of hexavalent chromium in the filtrate after leaching by the diphenylcarbazide spectrophotometric method of 65.2.1 of JIS K0102:2016. Among the operations of the quantitative measurement, the interval until 1 mL of diphenylcarbazide solution (10 g / L) was added after adding 3 mL of sulfuric acid (1+9) was within 20 seconds. In addition, the uniaxial compressive strength of the ground-improved soil was measured in accordance with JIS A1216 "Test Method for Uniaxial Compression of Soils". Table 2 shows the composition of the reducing agent, the blending amounts of the reducing agent and slag powder in the ground-improving material, and the measurement results of the elution amount of hexavalent chromium and the uniaxial compressive strength of the ground-improved soil in each example and comparative example. In the column of "Composition of reducing agent", the mass ratio of each component based on the total of calcium sulfite, sulfur, calcium sulfide and ferrous sulfate was shown. In addition, in the column of "CaS" in Example 10, the mass ratio of calcium sulfide contained in the calcium sulfide-containing substance was shown.

[0049]

Table 2

[0050] From the results shown in Table 2, the ground-improving materials using only calcium sulfite (Comparative Examples 1 and 2) were able to reduce the elution amount of hexavalent chromium from the ground-improved soil more than the ground-improving materials containing only sulfur (Comparative Example 3), the ground-improving materials containing only ferrous sulfate (Comparative Examples 4 to 6), and the ground-improving materials containing a combination of sulfur and ferrous sulfate (Comparative Example 7). And in the ground-improving materials containing a combination of calcium sulfite and sulfur (Examples 1 to 9), although the blending amount of the reducing agent was equal to or less than that in the case of using only calcium sulfite, the elution amount of hexavalent chromium could be reduced to be equal to or less than that. Similarly, in the ground-improving material containing a combination of calcium sulfite and calcium sulfide (Example 10), the elution amount of hexavalent chromium could also be reduced.

[0051] Also, when the addition amount of the reducing material is the same, it was confirmed that when the content of calcium sulfite with respect to sulfur increases, the effect of suppressing the elution of hexavalent chromium tends to increase (for example, comparison between Examples 3 and 7 and Examples 5 and 8). On the other hand, when the content of sulfur with respect to calcium sulfite increases, the uniaxial compressive strength tends to increase (for example, comparison between Examples 3 and 7 and Examples 5 and 8). Furthermore, the ground improvement materials blended with slag powder (Examples 12, 15, and 16) were able to further reduce the elution amount of hexavalent chromium compared to the case where slag powder was not blended (Examples 5, 8, and 9).

[0052] Figure 1 is a graph plotting the results of Examples 1 to 9 and Comparative Examples 1 to 3. The plots of double circles (◎) indicate that the elution amount of hexavalent chromium was less than the quantification lower limit value (0.002 mg / L) until the age of 28 days. The plots of single circles (〇) indicate that the elution amount of hexavalent chromium was below the environmental standard value (0.05 mg / L) until the age of 28 days. On the other hand, the cross marks (×) indicate that the elution amount of hexavalent chromium at the age of 28 days exceeded the environmental standard value.

[0053] The density and Blaine specific surface area of the ground improvement materials of several examples were measured. The Blaine specific surface area was measured in accordance with JIS R5201:2015 "Physical Test Methods for Cement". The results were as shown in Table 3.

[0054]

Table 3

Claims

1. A reducing material containing calcium sulfite and elemental sulfur.

2. The reducing material according to Claim 1, wherein the content of the elemental sulfur is 1 to 85 parts by mass with respect to a total of 100 parts by mass of the calcium sulfite and the elemental sulfur.

3. The reducing material according to Claim 1 or 2, wherein the content of the calcium sulfite is greater than the content of the elemental sulfur.

4. A reducing material according to any one of claims 1 to 3, further comprising a sulfur compound that releases at least one of HS － ions and S ２－ ions when in contact with water.

5. A cement composition containing the reducing material according to any one of Claims 1 to 4 and cement.

6. A cement composition containing calcium sulfite, elemental sulfur, and cement.

7. A ground improvement material containing the reducing material according to any one of Claims 1 to 4.

8. A ground improvement material containing calcium sulfite and elemental sulfur.

9. Further containing blast furnace slag powder, The ground improvement material according to Claim 7 or 8, wherein the total content of the calcium sulfite and the elemental sulfur is 0.1 to 30% by mass, and the content of the blast furnace slag powder is 5 to 30% by mass.

10. A ground-improved soil containing the ground improvement material according to any one of Claims 7 to 9 and soil to be ground-improved.

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