Solidified soil and method for manufacturing the same

Abstract

To provide: a solidified soil capable of contributing to carbon negative by effectively using plants, such as bamboo; and a method for manufacturing the solidified soil.SOLUTION: A solidified soil is made by solidification in which as a solidification material and a water-absorbing material, a carbonized material made by carbonizing a plant-based ingredient is added to a viscous soil whose moisture ratio is adjusted. The solidified soil substantially achieves carbon negative.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to solidified treated soil capable of carbon negativity and a method for producing the same.

Background Art

[0002] Conventionally, soft high water content cohesive soil typified by dredged clay generated in port construction has been effectively utilized as solidified treated soil having a predetermined strength by adding a cement-based solidifying material and performing solidification treatment (for example, see Patent Document 1).

[0003] However, since cement is used as a solidifying material for such solidified treated soil, carbon dioxide (CO2), which is a greenhouse gas, is emitted during the production, transportation, and construction of cement. Therefore, from the perspective of preventing global warming, reduction of cement usage and use of blast furnace cement or the like with a small CO2 emission amount during cement production are required.

[0004] On the other hand, in the field of concrete, technological development for realizing carbon neutrality has been actively carried out. As an example, by mixing a carbonizing material into concrete, carbon is fixed in the concrete, and carbon negativity is realized by the amount of fixed carbon exceeding the amount of CO2 emitted by the production of the concrete or the like.

[0005] In addition, in order to achieve carbon neutrality, reduction of CO2 emissions by absorption of carbon dioxide through photosynthesis of plants such as trees is effective. In particular, plants with a high growth rate such as bamboo are relatively easy to grow and are expected to contribute to the realization of carbon neutrality by increasing the quantity.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, plants with a high growth rate such as bamboo are often difficult to use as building materials, etc. Due to their high growth rate, there has been a problem that they are often left unattended due to a shortage of administrators.

[0008] In addition, plants with a high growth rate such as bamboo have a balanced growth amount and withered and dead amount due to their high growth rate, and there has been a risk that they do not actually contribute much to the reduction of CO2 emissions because CO2 is emitted during the incineration and disposal of withered and dead materials.

[0009] Furthermore, plants with a high growth rate such as bamboo may also inhibit the growth of other plants because of their strong reproductive ability.

[0010] Therefore, in order for plants with a high growth rate such as bamboo to contribute to the realization of carbon neutrality, it is desired to construct a suitable cycle of felling and tree planting through appropriate management of bamboo forests, etc., and effectively utilize the materials generated by felling.

[0011] Therefore, in view of such conventional problems, the present invention has been made for the purpose of providing solidified treated soil that can effectively utilize plants such as bamboo and contribute to carbon negativity, and a method for manufacturing the same.

Means for Solving the Problems

[0012] The feature of the invention according to claim 1 for solving the above-described conventional problems is that in the solidified treated soil obtained by adding a solidifying material to cohesive soil with an adjusted water content ratio and subjecting it to solidification treatment, a carbonized material formed by carbonizing a plant material is added as a water absorbent material.

[0013] The feature of the invention according to claim 2 is that, in addition to the configuration of claim 1, the carbonized material is bamboo charcoal.

[0014] The feature of the invention according to claim 3 is that, in addition to the configuration of claim 1, the carbonized material is rice husk charcoal.

[0015] The feature of the invention according to claim 4 is that, in addition to the configuration of any one of claims 1 to 3, the solidifying material is blast furnace cement in which blast furnace slag is mixed with cement.

[0016] The feature of the invention according to claim 5 is that, in addition to the configuration of any one of claims 1 to 3, the carbonized material is carbonized at a combustion temperature of 300 to 800 °C.

[0017] The feature of the invention according to claim 6 is in a method for producing solidified treated soil in which a solidifying material is added to cohesive soil with an adjusted water content ratio and solidified, after uniformly mixing the cohesive soil and the solidifying material, adding and mixing a carbonized material formed by carbonizing a plant-based material.

[0018] The feature of the invention according to claim 7 is that, in addition to the configuration of claim 6, the carbonized material is carbonized at a combustion temperature of 300 to 800 °C.

Advantages of the Invention

[0019] The solidified treated soil according to the present invention has the following effects by having the configuration according to claim 1. (1) Due to the high water absorption of the carbonized material, the apparent water content ratio can be reduced, the trafficability of the cohesive soil can be improved, and since the apparent water content ratio decreases by adsorbing free water in the dredged soil with the carbonized material, a predetermined strength can be exhibited even with a small amount of a solidifying material such as cement. Therefore, the amount of carbon dioxide generated during cement production can be reduced accordingly. (2) By using a carbonized material made of a plant-based material as a water absorbent, the amount of CO2 absorbed during the growth process of the plant-based material is considered to be fixed in the solidified treated soil, and the carbon fixed in the carbonized material is fixed in the solidified treated soil. The amount of CO2 corresponding to the amount of fixed carbon is stored in the solidified treated soil, and the amount of CO2 stored in the solidified treated soil exceeds the amount of CO2 emitted during the production of the solidified treated soil, realizing carbon negativity. (3) The carbonized material also has an adsorption effect on heavy metals such as arsenic and hexavalent chromium, similar to its water absorption performance. By solidifying it with cement or the like, these heavy metals can be insolubilized.

[0020] Furthermore, in the present invention, by adopting the configuration described in claim 2, it is possible to cut down the abandoned bamboo forests that have become a problem nationwide and effectively utilize them as bamboo charcoal, thereby contributing to the proper management of the abandoned bamboo forests. In addition, since bamboo forests grow rapidly, the growth and harvesting cycle can be accelerated, and CO2 can be efficiently absorbed and stored.

[0021] Furthermore, in the present invention, by adopting the configuration described in claim 3, rice husks can be effectively utilized.

[0022] Moreover, in the present invention, by adopting the configuration described in claim 4, the carbonized material exhibits the effect as an alkali stimulant, and the strength increase can be achieved by promoting the strength development of the blast furnace slag fine powder.

[0023] Also, in the present invention, by adopting the configuration described in claim 5, the water absorption of the carbonized material can be enhanced, and the modification of the solidified treated soil and the promotion of carbon negativity can be achieved.

[0024] The method for manufacturing the solidified treated soil according to the present invention can improve the workability and manufacture a solidified treated soil that is substantially carbon negative by adopting the configuration described in claim 6.

[0025] Also, in the present invention, by adopting the configuration described in claim 7, the water absorption of the carbonized material can be improved.

Brief Description of the Drawings

[0026]

Figure 1

Embodiments for Carrying Out the Invention

[0027] Next, embodiments of the solidified treated soil according to the present invention will be described.

[0028] This solidified treated soil is obtained by adding a solidifying agent such as cement, a water-absorbing material, and, if necessary, other additives to cohesive soil with an adjusted water content ratio such as dredged soil, and then subjecting it to solidification treatment.

[0029] For the cohesive soil, dredged soil generated in port construction or the like is used, and the water content ratio is adjusted to be equal to or higher than the liquid limit. Generally, the water content ratio of dredged soil after dredging is about 0.9 to 1.3 times the liquid limit, so basically no adjustment is required, but the water content ratio is adjusted according to the situation.

[0030] As the solidifying agent, cement such as ordinary Portland cement or blast furnace slag cement is used, and an amount such that the ratio of the free water amount in the dredged soil to the solidifying agent (water-solidifying agent ratio W / C) is 0.45 or more is made into powder and added.

[0031] Note that the free water amount of the dredged soil is calculated as the free water amount of the dredged soil = the water content of the dredged soil - (the water amount corresponding to the plastic limit of the dredged soil + the water absorption amount of the carbonized material).

[0032] Note that when using blast furnace slag cement as the solidifying agent, from the viewpoint of reducing CO2 emissions, it is desirable to use blast furnace type B cement mixed with 30 to 60% of blast furnace slag or blast furnace type C cement mixed with 60 to 70% of blast furnace slag.

[0033] As the water-absorbing material, a carbonized material obtained by carbonizing plant materials such as bamboo charcoal, black charcoal, sawdust charcoal, powdered charcoal, rice husk smoked charcoal, and rice straw-derived materials is used. Since this carbonized material has a large number of cavities derived from bundle sheath cells, it exhibits a water absorption rate of about 10 to 15%.

[0034] In order to enhance the water absorption property, it is preferable that this carbonized material be fired within a carbonization temperature range of 300 to 800 °C and have a particle size of about 0.25 mm to 20 mm. Note that when the particle size is 0.25 mm or less, there is a risk of moisture absorption and agglomeration in the natural state, and it is desirable not to use it from the perspective of material management.

[0035] Note that the addition amounts of the solidifying material and the water-absorbing material are set so that the CO2 emission amount (=cement addition amount × CO2 emission amount per unit) during the production of the solidified treated soil does not exceed the CO2 storage amount (carbonized material addition amount × carbon content × carbon residual rate × 44 / 12).

[0036] The CO2 emission amount per unit of each member is shown below.

Table 1

[0037] Next, the manufacturing method of this solidified treated soil will be described.

[0038] First, adjust the water content ratio of cohesive soil such as dredged soil serving as the base material to be equal to or higher than the liquid limit as required. Generally, the water content ratio of dredged soil after dredging is about 0.9 to 1.3 times the liquid limit, so adjustment may not be necessary, but the water content ratio is adjusted in consideration of the conditions at the construction site and the water absorption rate of the solidifying material and the water-absorbing material used.

[0039] More specifically, adjust the water content ratio so that the free water amount of the dredged soil = the water content of the dredged soil - (the water amount corresponding to the plastic limit of the dredged soil + the water absorption amount of the carbonized material).

[0040] Next, add cement such as ordinary Portland cement or blast furnace slag cement as a solidifying material to the cohesive soil adjusted to a predetermined water content ratio, and stir well to mix uniformly.

[0041] At that time, the solidifying material is added in powder form in an amount such that the ratio of the free water amount in the dredged soil to the solidifying material (water-solidifying material ratio W / C) is 0.45 or more.

[0042] Then, after the cohesive soil and the solidifying agent are uniformly mixed, a predetermined amount of a carbonized material obtained by carbonizing a plant material as a water absorbent is newly added, and the mixture is stirred again.

[0043] In addition, since there is a risk that the mixing with the solidifying agent may not be uniform after dredging due to the water absorption property of the carbonized material when adding the water absorbent, the water absorbent is added after the cohesive soil and the solidifying agent are uniformly mixed.

[0044] The solidified soil configured in this way adds a carbonized material obtained by carbonizing a plant material as a water absorbent. As a result, the plant material absorbs CO2 during the growth process and is added to the solidified soil in a state where carbon is fixed as a carbonized material after logging. By doing so, more CO2 can be stored in the solidified soil than the amount of CO2 emitted during the production of the solidified soil, and carbon negativity can be realized. By using these solidified soils as landfill materials for artificial islands or backfill materials for revetments, CO2 can be permanently sealed.

[0045] Furthermore, due to the high water absorption property of the carbonized material, this solidified soil can reduce the apparent water content ratio of the dredged soil, and accordingly, the amount of the solidifying agent used can be reduced, and the amount of CO2 in the production of the solidifying agent can be reduced, and at the same time, the strength of the solidified soil can be improved.

[0046] The following shows a comparison of the substantial CO2 emissions between the present invention and the conventional solidified soil.

[0047]

Table 2

[0048] In particular, by carbonizing the carbonized material by firing in the temperature range of 300 to 800 °C, the water absorption property of the carbonized material can be improved, and the reduction effect of the amount of CO2 due to water absorption and the strength improvement effect of the solidified soil can be promoted.

[0049] In addition, in this solidified treated soil, the carbonized material can exhibit the effect as an alkali stimulant and promote the strength development of the fine powder of blast furnace slag, thereby increasing the strength.

[0050] Furthermore, this solidified treated soil also has the effect that the carbonized material adsorbs heavy metals such as arsenic and hexavalent chromium. By solidifying with cement or the like, these heavy metals can be insolubilized.

[0051] Also, in this solidified treated soil, by using bamboo charcoal as a water absorbent, the standing bamboo forests and the like can be harvested and effectively utilized as bamboo charcoal, contributing to the proper management of the bamboo forests.

[0052] Furthermore, by using bamboo charcoal as a water absorbent, a stable cycle of bamboo forest harvesting and reforestation is established, thereby promoting carbon dioxide absorption by bamboo with a fast growth rate and contributing to the realization of carbon neutrality.

[0053] Moreover, since the carbonized material is alkaline, this solidified treated soil also functions as an alkali stimulant. When using blast furnace slag cement as a solidifying material, the fine powder of blast furnace slag contained in the blast furnace slag cement has "latent hydraulicity" that exhibits strength development by the hydration reaction in an alkaline environment. Therefore, by mixing the carbonized material, the strength development of the fine powder of blast furnace slag is promoted, and the strength can be increased. Accordingly, the amount of the fine powder of blast furnace slag, which is a carbon-negative material in the solidifying material, can be increased.

[0054] Fig. 1 shows a graph showing the relationship between the addition amount of the solidifying material (cement) and the strength in the solidified treated soil of the present invention and the conventional one. In the figure, the symbol N in the legend represents the conventional solidified treated soil using ordinary Portland cement as the solidifying material, the symbol BB represents the conventional solidified treated soil using blast furnace B-type cement as the solidifying material, the symbol BC represents the conventional solidified treated soil using blast furnace C-type cement as the solidifying material, and the symbol BB+Ch represents the solidified treatment according to the present invention using blast furnace B-type cement as the solidifying material and adding a carbonized material made of a plant-based material as a water absorbent.

[0055] As shown in FIG. 1, when the addition amount of the solidifying agent is the same, it was confirmed that the strength of the solidification treatment according to the present invention is higher than that of other conventional solidified treated soils.

[0056] In addition, in the above-described embodiment, the case where cement is used as the solidifying agent has been described, but it can also be applied to solidified treated soils using other solidifying agents.

Claims

1. In the solidified soil obtained by adding a solidifying agent to cohesive soil with adjusted water content and subjecting it to solidification treatment, the solidified soil is characterized in that a carbonized material obtained by carbonizing a plant material is added as a water absorbent.

2. The solidified soil according to Claim 1, wherein the carbonized material is bamboo charcoal.

3. The solidified soil according to Claim 1, wherein the carbonized material is rice husk charcoal.

4. The solidified soil according to any one of Claims 1 to 3, wherein the solidifying agent is blast furnace cement in which blast furnace slag is mixed with cement.

5. The solidified soil according to any one of Claims 1 to 3, wherein the carbonized material is carbonized at a combustion temperature of 300 to 800°C.

6. In a method for producing solidified soil by adding a solidifying agent to cohesive soil with adjusted water content and solidifying it, the method for producing solidified soil is characterized in that after uniformly mixing the cohesive soil and the solidifying agent, a carbonized material obtained by carbonizing a plant material is added and mixed.

7. The method for producing solidified soil according to Claim 6, wherein the carbonized material is carbonized at a combustion temperature of 300 to 800°C.

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