Ground materials and ground formation methods

Abstract

When using waste materials containing solidified cement as ground material after carbonization, the contamination of the soil by hexavalent chromium is suppressed. [Solution] The ground material includes a CO2-fixing material obtained by reacting CO2 with crushed waste materials containing cement solidified material, and blast furnace slag fine powder.

Description

[Technical Field]

[0001] This disclosure relates to ground materials and ground formation methods. [Background technology]

[0002] Cement raw materials contain naturally occurring trivalent chromium. Some of the trivalent chromium is oxidized to hexavalent chromium during the cement firing process. Hexavalent chromium is highly toxic to humans.

[0003] Crushed concrete or mortar waste is sometimes used as backfill material, roadbed material, etc. When crushed waste containing cement solidified material is used as ground material, it is necessary to suppress the leaching of hexavalent chromium from the cement solidified material.

[0004] Patent Document 1 discloses a method for detoxifying construction waste containing soluble hexavalent chromium, which includes micronizing the construction waste containing soluble hexavalent chromium and adding iron(II) sulfate in the presence of water that dissolves the soluble hexavalent chromium.

[0005] Patent Document 2 discloses a method for producing recycled concrete material, which includes adding sodium sulfite as a reducing agent to recycled concrete material obtained by crushing and intermediate-treating concrete blocks, thereby detoxifying soluble hexavalent chromium.

[0006] Patent Document 3 discloses a method for suppressing the elution of hexavalent chromium from recycled aggregate, which includes mixing recycled aggregate produced from concrete waste with an acidic soil material, and reducing or adsorbing the hexavalent chromium eluted from the recycled aggregate with the acidic soil material.

[0007] Patent Document 4 discloses a method for preventing the leaching of hexavalent chromium from a solidified product containing hexavalent chromium using cement, wherein the cement is adjusted to have a total amount of C3S and C3A of 70% by weight or more, and the method includes mixing 25 to 80 parts by weight of slag with 100 parts by weight of cement before solidification.

[0008] Patent Document 5 discloses a method for reducing hexavalent chromium, which involves contacting an alkaliphilic Cellulomonas microorganism with a hydraulic substance containing hexavalent chromium and whose aqueous solution is alkaline. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2001-121109 [Patent Document 2] Japanese Patent Publication No. 2010-201333 [Patent Document 3] Japanese Patent Publication No. 2011-217772 [Patent Document 4] Japanese Patent Publication No. 2000-308863 [Patent Document 5] International Publication No. 2011 / 148512 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] To reduce atmospheric carbon dioxide (CO2), CO2-fixed materials, which are produced by reacting CO2 with crushed waste materials containing solidified cement, are being used as ground materials. It is known that the amount of hexavalent chromium leached from solidified cement increases with carbonation.

[0011] This disclosure was made under the circumstances described above. The problem that this disclosure aims to solve is to suppress soil contamination by hexavalent chromium when using waste materials containing cement solidified material as ground material after carbonization. [Means for solving the problem]

[0012] The following embodiments are included as specific means for solving the aforementioned problems. <1> A CO2 immobilization material obtained by reacting crushed waste materials containing cement solidified products with CO2, and fine powder of blast furnace slag, and a ground material. <2> The ground material according to <1>, wherein the waste material containing the cement solidified product is a concrete waste material. <3> The ground material according to <1> or <2>, which contains 1 to 10 parts by mass of the fine powder of blast furnace slag with respect to 100 parts by mass of the CO2 immobilization material. <4> The specific surface area of the fine powder of blast furnace slag is 4000 cm 2 / g or more, and the ground material according to any one of <1> to <3>. <5> A ground formation method including embedding the ground material according to any one of <1> to <4> at a destination.

Effect of the Invention

[0013] According to the present disclosure, when using waste materials containing cement solidified products as a ground material after carbonation, soil contamination by hexavalent chromium can be suppressed.

Brief Description of the Drawings

[0014] [Figure 1] It is a scatter diagram showing the relationship between the CO2 fixation amount of concrete crushed material and the elution amount of hexavalent chromium. [Figure 2] It is a scatter diagram showing the concentration of hexavalent chromium in the test solution when a hexavalent chromium elution test is performed using a mixture of a CO2 immobilization material and BFS-40 as a sample. [Figure 3] It is a scatter diagram showing the concentration of hexavalent chromium in the test solution when a hexavalent chromium elution test is performed using a mixture of a CO2 immobilization material and BFS-80 as a sample.

Mode for Carrying Out the Invention

[0015] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0016] In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. In numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced by the values ​​shown in the examples.

[0017] In this disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" may be A alone, B alone, or a combination of A and B.

[0018] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0019] When referring to the amount of each component in a composition in this disclosure, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0020] <Ground materials> The ground material of this disclosure includes at least a CO2-fixing material obtained by reacting CO2 with crushed waste materials including cement solidified material, and blast furnace slag fine powder. Hereinafter, "CO2 fixation material obtained by reacting CO2 with crushed waste materials containing cement solidified material" will simply be referred to as "CO2 fixation material."

[0021] According to the ground material disclosed herein, when waste materials containing cement solidified material are carbonated and then used as ground material, soil contamination by hexavalent chromium can be suppressed. The mechanism is presumed to be as follows.

[0022] In the soil, hexavalent chromium leached from the cement solidified material constituting the CO2 fixation material and thiosulfate ions leached from the blast furnace slag fine powder undergo a reaction represented by the following chemical equation, reducing hexavalent chromium to trivalent chromium. As a result, the hexavalent chromium concentration decreases, and soil contamination by hexavalent chromium is suppressed. 3S2O3 2- +8Cr 6+ +15H2O→6SO4 2- +8Cr 3+ +30H +

[0023] The following describes in detail each of the materials constituting the ground material of this disclosure.

[0024] [CO2 fixation material] Examples of waste materials containing cement solidified material, which is a raw material for CO2 fixation, include concrete waste, mortar waste, and cement paste hardened waste.

[0025] Waste materials containing cement solidified material are crushed to an appropriate particle size for use as a ground material. Crushing increases the specific surface area of ​​the waste materials containing cement solidified material, which increases their reactivity with CO2.

[0026] The particle size of the crushed waste material and the CO2 fixation material are not restricted and should be selected according to the intended use of the ground material, the properties of the destination where it will be buried, the type of burial method, the size of the machinery used for burial, etc. The particle size of the crushed waste material and the CO2 fixation material are, for example, the particle size of the fine aggregate and the particle size of the coarse aggregate. When using the ground material disclosed herein as sand for sand compaction, it is preferable that the particle size of the crushed waste material and the CO2 fixation material fall within the particle size standards described in the Japanese Geotechnical Society's "Design and Construction Manual for Sand Compaction Pile Construction by Backfilling."

[0027] The reaction of crushed waste materials with CO2 may be carried out by placing the crushed waste materials in the atmosphere or by exposing them to a CO2-containing gas. As the CO2-containing gas, exhaust gas generated from coal-fired power plants, LNG-fired power plants, cement plants, steel mills, oil refineries, waste incineration plants, etc., may be used. The carbonation process of crushed waste materials can reduce the amount of CO2 in the environment, or it can reduce the amount of CO2 emitted into the atmosphere from power plants, factories, treatment plants, etc.

[0028] [Blast furnace slag fine powder] The quality of blast furnace slag fine powder (e.g., density, specific surface area) is not limited and should be selected according to the particle size of the CO2 fixation material, the mixing ratio with the CO2 fixation material, etc. Examples of blast furnace slag fine powder include blast furnace slag fine powders 3000, 4000, 6000, and 8000 as specified in JIS A6206:2013 "Blast furnace slag fine powder for concrete".

[0029] From the viewpoint of thiosulfate ion elution efficiency, blast furnace slag fine powder is preferable as long as it has a high specific surface area, with a specific surface area of ​​4000 cm² being preferable. 2 It is preferable that the amount is 1 / g or more. The specific surface area of ​​blast furnace slag fine powder is 10,000 cm², from the perspective of workability when manufacturing ground materials. 2 It is preferable that the amount be less than / g.

[0030] The amount of blast furnace slag powder used is not limited and should be selected according to the particle size of the CO2 fixation material, the specific surface area of ​​the blast furnace slag powder, and other factors.

[0031] From the viewpoint of the reduction efficiency of hexavalent chromium, the amount of blast furnace slag fine powder used is preferably 1 part by mass or more per 100 parts by mass of CO2 immobilization material, and a larger amount is preferable. From the viewpoint of workability when burying the ground material, the amount of blast furnace slag fine powder used is preferably 10 parts by mass or less per 100 parts by mass of CO2 fixation material. The amount of blast furnace slag fine powder used is preferably 1 to 10 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 3 to 10 parts by mass, per 100 parts by mass of CO2 fixation material. Here, the masses of the CO2 fixation material and blast furnace slag powder are the masses in their naturally dried state.

[0032] [Other materials] The ground material of this disclosure may include materials other than CO2 fixation material and blast furnace slag fine powder. Examples of such materials include sand, blast furnace slag, stone, and water.

[0033] The ground material disclosed herein may be a dry material or a slurry. The ground material of this disclosure may be a non-hardening composition or a water-hardening composition. One example of an embodiment of the ground material of this disclosure is a dry, non-hardening composition that can be used as a substitute for natural sand.

[0034] <Ground formation method> The ground formation method of this disclosure includes burying the ground material of this disclosure at a destination. In this disclosure, the term "ground formation" includes ground stabilization, ground reinforcement, ground backfilling, and ground improvement. The destination of the ground formation method of this disclosure is not limited. Examples include residential areas, commercial areas, industrial areas, agricultural areas, roads, airports, and ports.

[0035] There are no restrictions on the construction method used to bury the ground materials. Examples include the sand compaction pile method and the sand drain method. Ground materials may be manufactured in a factory and transported to the destination, or they may be manufactured on-site at the destination. [Examples]

[0036] <Experiment 1> The crushed concrete was crushed to the particle size of fine aggregate, contacted with CO2 gas for carbonation, and a CO2 immobilization material was obtained. The amount of CO2 immobilized was controlled by the length of the time of contacting with CO2 gas. The amount of CO2 immobilized in the CO2 immobilization material was determined by a thermogravimetric analysis of the ignition loss test. Using the CO2 immobilization material as a sample, a hexavalent chromium elution test was carried out in accordance with Notification No. 46 of the Environment Agency. The results are shown in Fig. 1.

[0037] As shown in Fig. 1, there was a positive correlation between the amount of CO2 immobilized and the amount of hexavalent chromium eluted in the cement solidified product. It was confirmed that the amount of hexavalent chromium eluted increased with the carbonation of the cement solidified product.

[0038] <Experiment 2> The crushed concrete was crushed to the particle size of fine aggregate, contacted with CO2 gas for carbonation, and a CO2 immobilization material was obtained. 1 part by mass, 2 parts by mass, 3 parts by mass, 5 parts by mass or 10 parts by mass of blast furnace slag fine powder was mixed with 100 parts by mass of the CO2 immobilization material in a natural drying state. The blast furnace slag fine powder was BFS-40 (specific surface area 4000 cm 2 / g) and BFS-80 (specific surface area 8000 cm 2 / g), and two types were used. Three samples were prepared for each mixing ratio. Using each mixture as a sample, a hexavalent chromium elution test was carried out in accordance with Notification No. 46 of the Environment Agency, and the hexavalent chromium concentration in the test solution was measured. The results are shown in Table 1 and Figs. 2 to 3.

[0039]

Table 1

[0040] There was a negative correlation between the addition amount of the blast furnace slag fine powder and the hexavalent chromium concentration. From the viewpoint of the reduction efficiency of hexavalent chromium, it can be said that the larger the addition amount of the blast furnace slag fine powder, the more preferable. The hexavalent chromium concentration in the test solution was lower for BFS-80 than for BFS-40. It can be said that the higher the specific surface area of the blast furnace slag fine powder, the higher the efficiency of reducing hexavalent chromium to trivalent chromium.

Claims

1. CO2 ２ CO reacted with ２ Immobilization material and, Contains blast furnace slag fine powder, ground material.

2. The ground material according to claim 1, wherein the waste material containing the cement solidified material is concrete waste.

3. The aforementioned CO ２ The ground material according to claim 1, comprising 1 to 10 parts by mass of the blast furnace slag fine powder per 100 parts by mass of the immobilization material.

4. The specific surface area of ​​the aforementioned blast furnace slag fine powder is 4000 cm². ２ The ground material according to claim 1, wherein the amount is 1 / g or more.

5. The process includes burying the ground material described in any one of claims 1 to 4 at the destination. Ground formation method.

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