JP6559644B2 - Reclaimed soil manufacturing system and method - Google Patents

Description

  The present invention relates to a reclaimed soil production system and a reclaimed soil production method for producing high-quality reclaimed soil by modifying and neutralizing alkaline construction sludge having a hydrogen ion concentration index (pH) of less than 12.

  Construction sludge discharged from construction sites often contains cement and lime components, and usually exhibits alkalinity with a pH of about 9-12. Such construction sludge is brought into an intermediate treatment plant, and is further reused or disposed of in landfill after the addition of quicklime and cement-based solidification material, and the reforming and solidification treatment. This modified and solidified construction sludge after treatment has a problem that its use is limited because the pH is often higher than 12 due to the added quicklime and cement-based solidified material, and it exhibits strong alkali. ing.

  Many techniques have been developed to address this problem. Specifically, a technique for producing a neutral solidified material having a pH in the range of 5.8 to 8.6 and a technique for adding a sulfate having strong acidity have been proposed (for example, see Patent Document 1). ). Also proposed is a method of neutralizing the solidified product by blowing carbon dioxide into the sludge slurry, aeration curing, or finely granulating so as to enclose air when kneading and granulating. (For example, refer to Patent Document 2).

JP2012-092180A JP-A-7-323299 Japanese Patent Application Laid-Open No. 2011-25211 JP-A-9-10732

  Here, as for the technology related to the neutral solidifying material disclosed in Patent Document 1, neutralization is performed by adding an acidic sulfate (such as aluminum sulfate) to a method using a neutral gypsum-based solidifying material or an alkaline solidifying material. How to do is shown. However, adding a neutral solidifying material to construction sludge already exhibiting alkalinity does not lead to neutralization of construction sludge. In addition, a method of neutralizing by further adding sulfate or the like showing strong acidity has been proposed, but the formation of a hydrate that contributes to solidification is inhibited by a strong acid, and a predetermined solidification strength cannot be obtained. It becomes a hindrance in producing high-quality recycled soil.

  Patent Document 2 proposes a method in which carbon dioxide gas is blown into sludge slurry, neutralized and then dehydrated, and further dried or baked at a high temperature of 200 ° C. or higher for reuse. In this method, water is added once to make sludge into a slurry, and after neutralization, it is dehydrated, and further dried or baked at a high temperature. It cannot be said that it is an economical processing method commensurate with the processing cost.

  Patent Document 3 discloses that strong alkalinity is obtained by adding chloride as a primary treatment to strong alkaline construction sludge having a pH of 12.5 or more, and adding a chloride or a phosphate compound as a secondary treatment after 1-2 days. A method for suppressing the generation of hydroxide is shown. Furthermore, a method is shown in which sodium aluminate is added in the primary treatment to accelerate the hydration reaction and shorten the aeration curing period. In this method, a method of adding a chloride has been proposed. However, the addition of a chloride causes the occurrence of salt damage and there is a concern that it may adversely affect the surrounding environment more than an alkali. In addition, the method of promoting the hydration reaction with sodium aluminate increases the cost of the drug. Furthermore, in the method of reducing the pH by aeration curing with backhoe, the pH reduction effect is low, and the reduction in pH per month is limited to about 1.5 at most. Therefore, it is difficult to say that it is a high-quality and highly reliable neutralization technology for construction sludge. Moreover, it is intended for construction sludge having a pH of 12.5 or higher, and is different from the applicable range of pH targeted by the present invention.

Further, in Patent Document 4, solidification is achieved by kneading and granulating industrial waste such as sludge, blast furnace cement and fly ash with a reverse flow high speed mixer, and finely squeezing so as to enclose air. A technique for bringing the alkalinity of a processed product closer to neutrality is disclosed. In this method, it is necessary to use a special mixer, and the effect of reducing the pH is limited to a little less than 1 in 2 weeks. Further, there is no specific method for reliably lowering the pH to 8.6 or lower.
An object of the present invention is to provide a reclaimed soil production system and a reclaimed soil production method for neutralizing alkaline construction sludge inexpensively and reliably and producing high-quality reclaimed soil.

That is, the present invention includes the following matters.
[1] Stirring means for stirring alkaline construction sludge to which a water-absorbing modifier is added, a first curing area for curing the construction sludge stirred in the stirring means until it becomes semi-solid, and the first The loosening granulation means for loosening the construction sludge that has become semi-solid in one curing area, and the construction sludge refined by the loosening granulation means is further cured to promote the hydration reaction A second curing area to be regenerated, and carbon dioxide contact means for neutralizing the construction sludge by bringing carbon dioxide into contact with the construction sludge whose hydration reaction has been promoted in the second curing area. Soil production system.

  [2] The reclaimed soil production system according to [1], wherein a cement-based solidifying material is further added to the construction sludge by the stirring means.

  [3] The recycled soil production system according to [1] or [2], wherein the construction sludge stirred by the stirring means has a hydrogen ion concentration index of 9 or more and less than 12.

  [4] The carbon dioxide contact means neutralizes the construction sludge by bringing the carbon dioxide into direct contact with the construction sludge whose hydration reaction has been promoted in the second curing area. The recycled soil manufacturing system according to any one of to [3].

  [5] The carbon dioxide contact means includes a rotary mixer for charging the construction sludge whose hydration reaction has been promoted in the second curing area, and neutralization of the construction sludge is carried out in the carbon dioxide in the mixer. The reclaimed soil production system according to [4], which is performed by injecting or press-fitting gas and stirring in a sealed state.

  [6] The carbon dioxide contact means includes a pit in which the construction sludge whose hydration reaction is promoted in the second curing area is thinly laid in a loosely packed state, and the carbon dioxide gas from above the pit into the pit. The regeneration according to [4], wherein the construction sludge is neutralized by curing the construction sludge for a certain period in the pit into which the carbon dioxide gas has flowed. Soil production system.

  [7] The carbon dioxide contact means includes a space, a supply pipe that supplies the carbon dioxide to the space, and an input unit that inputs the construction sludge in which the hydration reaction has been promoted in the second curing area. The construction sludge is neutralized by introducing the construction sludge into the space supplied from the supply pipe and filled with the carbon dioxide gas by the introduction unit and curing the construction sludge for a certain period of time. [4] The reclaimed soil manufacturing system according to [4].

[8] A reforming and solidifying step in which a water-absorbing modifier is added to and mixed with alkaline construction sludge;
A reforming solidification curing step for curing the construction sludge treated in the reforming solidification step until it becomes semi-solid, and a loosening of the construction sludge that has become a semisolid state in the reforming solidification curing step. A loosening granulation step, a hydration reaction promoting curing step for further curing the construction sludge refined in the loosening granulation step to promote a hydration reaction, and a hydration in the hydration reaction promotion curing step A method for producing reclaimed soil, comprising: a carbon dioxide gas contact step in which carbon dioxide gas is brought into contact with the construction sludge whose reaction has been promoted to neutralize the construction sludge.

  [9] The method for producing reclaimed soil according to [8], wherein a cement-based solidified material is further added to the construction sludge in the modified solidification step.

  [10] The method for producing reclaimed soil according to [8] or [9], wherein the construction sludge used in the reforming and solidifying step has a hydrogen ion concentration index of 9 or more and less than 12.

  [11] Any one of [8] to [10], wherein in the carbon dioxide contact step, the construction sludge is neutralized by bringing the carbon dioxide into direct contact with the construction sludge whose hydration reaction has been promoted. The method for producing recycled soil according to claim 1.

  [12] In the carbon dioxide gas contact step, the construction sludge in which the hydration reaction has been promoted is put into a rotary mixer, and carbon dioxide gas is introduced or injected into the rotary mixer and stirred in a sealed state. The method for producing recycled soil according to [11].

  [13] In the carbon dioxide contact step, the construction sludge in which the hydration reaction has been promoted is spread in a thin and loosely packed state, and the carbon dioxide is introduced from above to be cured [11] The reclaimed soil manufacturing method as described.

  [14] The reclaimed soil production according to [11], wherein in the carbon dioxide contact step, the construction sludge whose hydration reaction has been promoted is placed on the space filled with the carbon dioxide and cured. Method.

  According to the invention according to the present invention, alkaline construction sludge having a hydrogen ion concentration index (pH) of less than 12 can be modified and neutralized to produce high-quality recycled soil.

It is a figure which shows the mixer used for the rapid contact method which concerns on embodiment. It is a figure which shows the pit used for the flow-down contact method which concerns on embodiment. It is a figure which shows the space used for the pool contact method which concerns on embodiment. 3 is a table showing the measurement results of pH in Example 1. 10 is a table showing test results of Example 2. 6 is a diagram showing a cylinder used in a test of Example 4. FIG. In the test of Example 4, it is a figure which shows the condition which the carbon dioxide gas flows down and contacts to a fine-grain solidified soil. It is a figure which shows the confirmation test result of the pH reduction effect by the flowing-down contact method which concerns on Example 4. FIG.

Hereinafter, a reclaimed soil manufacturing system and a reclaimed soil manufacturing method according to embodiments of the present invention will be described with reference to the drawings. First, construction sludge discharged at the construction site is transported to an intermediate treatment facility. Here, the construction sludge transported to the intermediate treatment facility already contains cement, lime, and the like, and exhibits an alkalinity of pH 9 or more and less than 12. The corn index of this construction sludge is less than 200 kN / m ² .

(Step S1: reforming and solidifying step)
Next, after putting this construction sludge into a mud storage tank, 20-150 kg / m < ³ > of a water absorbing modifier is added to the construction sludge in the mud tank. As the water absorption modifier, for example, a PS (paper sludge) ash-based water absorption modifier is used. The PS ash-based water-absorbing modifier is a mud modifier that utilizes the porous properties of PS ash, and has a humidity control function that quickly absorbs excess moisture in construction sludge. The pH of the PS ash-based water-absorbing modifier is 10 to 11, and the material itself exhibits alkalinity, but has a property that the pH gradually decreases with time.

  Next, the construction sludge with the water-absorbing modifier added is agitated. Examples of the stirring means include bucket mixing using a backhoe, or mixing using a machine such as a badge-type kneader or a twin-screw kneader.

  If stirring is continued, excess water in the construction sludge is absorbed by the water-absorbing modifier, and the viscosity of the construction sludge increases. Thereby, the loosening granulation process in step S3 becomes easy and it becomes easy to refine. Moreover, the carbon dioxide contact neutralization process in subsequent step S5 is also facilitated.

Next, a small amount of cement-based solidifying material, specifically 10 to 100 kg / m ^{3, is} added to the stirring mud storage tank, and stirring is continued. In this way, by using a combination of the water-absorbing modifier and the cement-based solidifying material, the pH of the modified solidified soil can be suppressed to less than 12. Here, as the cement-based solidifying material, blast furnace cement type B is suitable in that it suppresses an increase in pH. Lime / cement composite materials contain many lime components and are not suitable for cement-based solidification materials.

In addition, although it is possible to add only a cement-type solidification material and to perform a solidification process, since a cement addition amount increases with 100-150 kg / m < ³ >, there exists a concern of high-calcification. Furthermore, when only cement is added, unevenness of improvement tends to occur, and the quality of the finely ground solidified soil tends to vary. That is, there is a risk of reacting with the water around the cement immediately and forming lumps and fist-sized lumps. Therefore, the dispersibility of construction sludge can be improved by using a combination of a water-absorbing modifier and a cement-based solidifying material in the reforming and solidifying step (step S1).

Further, the modification treatment can be performed even if only the water-absorbing modifier is added, but the amount of the modifier is increased (200 to 300 kg / m ³ ), so that the material cost becomes high. For this reason, the cost concerning a modification | reformation process can be reduced by combining and using a cement-type solidification material.

(Step S2: Modified solidification curing process)
Next, when the construction sludge that has undergone reforming and solidification treatment (hereinafter referred to as reforming and solidifying soil) is piled up and cured in the stockyard (first curing area), the curing reaction of the reforming and solidifying soil during curing. As the time progresses, the properties change from sludge to plastic and semi-solid over time. The time required for the property to change to a semi-solid varies greatly depending on the amount of the modifying material or the solidifying material added, but is approximately several hours to one week. In addition, what does not solidify even after a curing period of 1 week is not suitable for loosening granulation described later, and therefore reprocessing (re-addition of a solidifying material or the like) is required.

(Step S3: loosening granulation process)
The modified solidified soil that has become semi-solid is undergoing a hydration reaction, and if it is cured as it is, it will solidify in the form of a lump. Therefore, after passing through the loosening granulation step (step S3) described below, it is necessary to complete the solidification again in the hydration reaction promotion curing step (step S4).

The suitability of loosening granulation is determined by the cone index test method (JIS A 1228). Usually, if the corn index of the modified solidified soil is 100 kN / m ² or more, loosening granulation is possible, but more refined construction sludge (hereinafter referred to as loosening granulated soil) is produced by loosening granulation. to is preferably cone index modifying solidification soil is less than 400 kN / m ² or more 1800kN / m ^2. The machine used for the loosening granulation process (the loosening granulation means) may be a backhoe, but a soil improvement machine (plant) having a crushing function is suitable.

  By performing the loosening granulation, the modified solidified soil that has become a semi-solid soil mass is crushed and becomes a finely ground loosening granulated soil. For this reason, the loosened granulated soil is adjusted to a particle size that is easy to be used as reclaimed soil, while increasing the surface area of the particles and being in contact with air or carbon dioxide gas.

Here, the loose granulated soil is in a state where it is easy to dry because the surface area is increased. At the same time, it reacts with carbon dioxide in the air and is in a state where the pH is easily reduced.
Next, the loose granulated soil is sifted. Thereby, coarse-grained soil can be repelled by sifting (size-regulating action). Moreover, evaporation of moisture is promoted by exposure to air when sieving (air drying action). Furthermore, since it contacts with carbon dioxide in the air, the neutralization reaction proceeds (alkali neutralization action).

(Step S4: Hydration reaction promotion curing process)
The loose granulated soil immediately after the loose granulation is in a wet state. For this reason, if it neutralizes by exposing to a carbon dioxide gas immediately after a loosening granulation process, the loosening granulated soil will soften again (confirmed by experiment). This is because water is generated along with the neutralization reaction as shown in the following formula.

[Neutralization reaction of alkali lime with carbon dioxide]
Ca (OH) ₂ + CO ₂ = CaCO ₃ + H ₂ O
As this neutralization reaction formula shows, the more the Ca (OH) ₂ component (that is, the alkali lime component) contained in the modified solidified soil, the higher the pH and the greater the amount of water produced by the neutralization reaction. . As shown also in the Example mentioned later, it has been confirmed by experiment that the softening phenomenon accompanying neutralization of quicklime is more remarkable than other solidification materials. Therefore, it is not preferable to use quick lime in the reforming and solidifying step (step S1) from the viewpoint of preventing the occurrence of the softening phenomenon when contacting carbon dioxide.

  On the other hand, it is known that cement hydration continues for several hours to several months. This is the reason why the strength of concrete is regulated by the age of 28 days. The cement hydration reaction is a reaction in which a component in the cement (a clinker compound containing a component such as calcium or silicon) reacts with water to generate calcium silicate hydrate or the like. The hydrate is a solid crystallized from water.

  In this hydration reaction accelerating curing step (step S4), by utilizing the characteristics of the hydration reaction of cement in which free water (liquid) is taken into the solidified body as a hydrated crystal as the hydration reaction proceeds. Immobilize moisture. Specifically, the loosened granulated soil finely divided in a wet state is cured again in the curing stock yard (second curing area) to promote the hydration reaction, and the excess water is fixed as crystal water. Thus, the moist soil becomes smooth by providing a curing period again after the loosening granulation step (step S3). That is, the construction sludge is changed from the loosened granulated soil to the fine-grained solidified soil in which the solidification of the loosened granulated soil is completed.

  By providing this hydration reaction promotion curing process (step S4), the softening phenomenon at the time of carbon dioxide gas contact can be prevented in the next carbon dioxide gas contact process (step S5). In addition, it is desirable to perform the curing in the hydration reaction promoting curing process (step S4) until two weeks or more have elapsed after the cement-based solidifying material is added in the modified solidification process (step S1). The stock yard (first curing area) and the curing stock yard (second curing area) may be the same place or different places.

(Step S5: Carbon dioxide contact process)
Next, carbon dioxide gas is directly exposed to the finely ground solid soil in a smooth state. As specific methods, the following three methods, i) rapid contact method, b) falling contact method, and c) pool contact method, can be considered. By combining these methods alone or in combination, the pH of the reclaimed soil can be neutralized to 8.6 or less.

(B) Rapid contact method In the rapid contact method, recycled soil is produced using a mixer. Here, FIG. 1 (a) is a perspective view showing a rotary mixer used in the rapid contact method, FIG. 1 (b) is a view from above, and FIG. 1 (c) is a cross-sectional view thereof. FIG. In this rapid contact method, first, finely ground solidified soil is put into a rotary mixer 2, and carbon dioxide gas is allowed to flow into the mixer 2 into which the finely ground solidified soil is charged. Next, the mixer 2 is sealed and stirred for 5 to 30 minutes. Thereby, the pH of the fine-grained solidified soil whose pH has been lowered to less than 11 can be lowered to 8.6 or less. However, in the case of finely ground solid soil with a lot of water, care must be taken because the finely ground solidified soil may be weakened due to the generation of water accompanying neutralization. Moreover, in the fine-grained solid soil having a pH of 11 or more, the pH may not be 8.6 or less due to a rebound phenomenon. In that case, the pH can be reduced in a shorter time by filling the mixer into which the finely ground solidified soil is filled with carbon dioxide and contacting the finely ground solidified soil with carbon dioxide in a pressurized state.

(B) Flow-down contact method In the flow-down contact method, first, a sealed pit 12 with a lid 18 as shown in FIG. 2 is prepared, and a fine solidified soil 14 is laid thinly and loosely on the pit 12. The fine-grained solidified soil 14 is preferably laid at 70 cm or less. Next, carbon dioxide gas is allowed to flow into the pit 12 from the flow path 16 located above the pit 12 and is left as it is for 6 hours or more. According to this flow-down contact method, carbon dioxide gas heavier than air is gradually submerged from the surface of the fine-grained solidified soil 14 downwards so as to sew the voids of the fine-grained solidified soil 14, and the recycled soil is neutralized. Is manufactured. When the finely ground solidified soil 14 becomes densely packed, it is only neutralized up to about 15 cm from the surface layer, so care must be taken, but by increasing the contact time, it is possible to produce a reclaimed soil that has been neutralized to a deeper location. it can.
Note that the pit 12 used in the flow-down contact method is sufficient if it is a space that can be sealed, and for example, a dump box may be used as the pit.

(C) Pool Contact Method First, as shown in FIG. 3, a space 20 like a swimming pool is created, and a supply pipe 22 and a belt conveyor 24 for supplying carbon dioxide gas are arranged above the space 20. In addition, a lid 26 for sealing the space 20 is prepared.

  Next, the upper opening of the space 20 is covered with a lid 26 to seal the space 20. Here, the upper opening of the space 20 is not completely closed, and a gap 21 is left so that the finely ground solidified soil 28 can be supplied to the space 20 later. Next, carbon dioxide gas is supplied to the space 20 through the supply pipe 22, and the space 20 is filled with carbon dioxide gas. Next, the belt conveyor 24 is driven, and the fine-grained solidified soil 28 is gradually put into the space 20 filled with carbon dioxide gas, and the fine-grained solidified soil 28 is left as it is for 6 hours or more. As a result, since the finely ground solidified soil 28 and carbon dioxide are uniformly contacted, the finely ground solidified soil can be efficiently neutralized and a reclaimed soil having a pH of 8.6 or less can be produced.

The means for supplying the finely ground solidified soil 28 to the space 20 may not necessarily be the belt conveyor 24 as long as it has such a function.
In the pool contact method, a vibration screen may be installed below the gap 21. Thereby, the efficiency of the neutralization reaction can be improved.

According to the reclaimed soil production system and reclaimed soil production method of the present embodiment, a reclaimed soil production system and a reclaimed soil production method for neutralizing alkaline construction sludge inexpensively and reliably and producing high quality reclaimed soil are provided. can do.
Moreover, according to the recycled soil manufacturing system and the recycled soil manufacturing method of the present embodiment, the effects listed below can be obtained.

(1) Significantly contributes to the recycling of construction sludge Conventionally, recycled soil made from construction sludge has been limited in use because it exhibits alkali, but as described above, the pH is neutralized to 8.6 or less. By doing so, the use range of reclaimed soil is greatly expanded.

(2) Recyclable soil can be produced at low cost Existing facilities (intermediate treatment plant and reclaimed soil production yard) and machines (backhoes, soil improvement machines, or mud kneaders) can be used as they are and are relatively inexpensive. In addition, since only highly versatile materials (water-absorbing modifier, cement-based solidifying material, and carbon dioxide gas) are used, the production cost of recycled soil can be reduced.

(3) High versatility If the construction sludge has a pH of less than 12, it is possible to produce a regenerated soil that has been neutralized reliably.

(4) Mass disposal is possible if a certain area of yard is secured If facilities for reforming and solidifying construction sludge, facilities for loosening granulation, facilities for contacting carbon dioxide gas, and yards for curing each soil can be secured A large amount of reclaimed soil can be produced in a short period of time.

(5) Reclaimed soil is neutral and high quality Reclaimed soil produced by the reclaimed soil production system and the reclaimed soil production method of this embodiment shows a neutral range of pH = 5.8 to 8.6. The corn index is a high quality reclaimed soil that secures 800 kN / m ² or more. Furthermore, since it is subjected to a solidification process using a hydration reaction by cement, it does not re-mudder even if it is watered or submerged.

(6) Low environmental load The reclaimed soil produced by the reclaimed soil production system and the reclaimed soil production method of this embodiment is a material that is environmentally friendly because it has a neutral pH.

(7) Carbon dioxide emission reduction effect can be expected Since carbon dioxide reacts with alkali (calcium hydroxide) in the soil to fix it as calcium carbonate, it can be expected to reduce carbon dioxide emission.

  In the reforming and solidifying step (step S1) of the above-described embodiment, the water absorbing modifier and the cement-based solidifying material may be simultaneously added and mixed. However, a greater strength development effect can be obtained when the cementation solidifying material is added and the mixing treatment is performed after the water-absorbing modifier is preceded as in the above-described embodiment. Moreover, you may perform the mixing process by adding the water absorbing modifier and the cement-based solidifying material in one pack and filling the flexible container.

  Moreover, in the above-mentioned embodiment, although the case where the blast furnace cement B type is used as a cement-type solidification material is mentioned as a main example, when it is desired to shorten the curing period, early-strength cement or ground improvement special cement May be used.

In the modified solidification step (step S1) of the above-described embodiment, the amount of cement-based solidification material added varies depending on the pH of the raw mud. Specifically, the higher the pH of the raw mud, the more solidified components contained in the construction sludge. Therefore, when the pH of the raw mud is high, the amount of cement-based solidified material added at the intermediate treatment plant is reduced. (25-50 kg / m ³ ). On the other hand, when the pH of the raw mud is not high and the construction sludge is almost neutral, solidification by a reliable hydration reaction can be expected by adding a large amount of cement-based solidifying material (50-100 kg / m ³ ). . In addition, according to the past results, it has been experimentally found that the pH of the modified solidified soil is 12 or less if the cement addition amount is suppressed to 100 kg / m ³ .

In the above-described embodiment, promoting drying during curing is also effective from the viewpoint of promoting reduction in pH and preventing softening during carbon dioxide gas contact. As a measure, it is also possible to use the following methods together (of course, it is not an essential condition).
(A) Fluffing the loose-granulated soil with a sieve (regulating action).
(B) Exposure to air when sieving to promote moisture evaporation (air drying action).
(C) The neutralization reaction is advanced by contacting with carbon dioxide in the air (alkali neutralization action).
(D) Spread the soil as thin and wide as possible to promote air contact.
(E) Dry the soil positively using a blower or warm air.
(F) Prevent rainwater from entering in covered facilities.

  The period of the hydration reaction promotion curing process (step S4) can also be shortened by positively performing the processes (A) to (F). At this stage, it is ideal to lower the pH of the fine-grained solidified soil to 11 or less.

  Moreover, you may provide a drying process further between the process of step S1-5 of the above-mentioned embodiment. While the construction sludge changes its properties through the treatment and curing in steps S1 to S5, the pH is slightly lowered due to contact reaction with carbon dioxide contained in the air (atmosphere). Although depending on the degree of air contact and the curing method, the pH is usually lowered by about 0.5 to 1 from the initial state (the pH is 11.5 or less). By incorporating a drying step more actively, the pH can be further lowered by about 0.5 to 1 (confirmed by experiments).

In addition, the recycled soil production system / recycled soil production method of the present invention is a treated product obtained by subjecting construction sludge, which is industrial waste, to dehydration or solidification in an intermediate treatment facility, or construction generated soil (construction residual soil). Can also be used.
Next, examples of experiments conducted using the method for producing recycled soil according to the embodiment will be described.

[Example 1]
About three kinds of construction sludges A, B, and C having different pHs, PS ash-based water-absorbing modifier and cement-based solidified material (in this case, blast furnace cement type B) was added, or quick lime was added. The pH was measured. In addition, the measurement of pH was based on "The soil suspension pH test method (JGS 0211)" of the Geotechnical Society.

The table shown in FIG. 4 shows the measurement results of pH in Example 1. As shown in the table of FIG. 4, when quicklime is added, the pH exceeds 12 in all cases. On the other hand, when the water-absorbing modifier and the cement-based solidifying material are added, there are cases where the pH is less than 12. For example, the pH is relatively low construction sludge A of the original mud, water absorption modifiers to 150 kg / m ^3, even when the cement solidifying material 100 kg / m ³ was added, pH is settled to less than 12. Even in the construction sludge C, in which the pH of the raw mud is relatively high, the pH is below 12 in the case where 75 kg / m ^{3 of} cement-based solidifying material is added. Thus, compared with quicklime, the case where the water-absorbing modifier and the cement-based solidifying material are added can largely suppress the increase in pH.

[Example 2]
FIG. 5 is a table showing test results when actual construction sludge is processed based on the recycled soil manufacturing method described in the present embodiment. In addition, the recycled soil manufacturing method of this Embodiment is not limited to a present Example.

The used construction sludge (raw mud) has the characteristics of pH = 10.7 and corn index qc = 45 kN / m ² . The reclaimed soil was manufactured by adding the treatment or curing in Steps S1 to 5 shown in the embodiment of the present invention to this construction sludge, and the result was evaluated in Step S6. Specific methods and procedures are shown below.

  Step S1 (modified solidification treatment): A 5 kg sample is taken for each case (No. 1 to 17), and a PS ash-based water-absorbing modifier and a solidifying material are added to the sample under the blending conditions shown in FIG. Mixed. Mixing was performed carefully using a soil mixer for 10 minutes.

Step S2 (modified solidification curing): In the modified solidification curing, a sample was spread on a bat and covered with a vinyl sheet from above to maintain a sealed state.
Step S3 (relief granulation treatment): A corn test was performed using the sample that had passed the predetermined curing period in step S3. The test was based on the compacted soil cone index test method (JIS A1228). The corn index described below was also obtained by the same method.

  Next, the sample was put into a soil mixer and stirred at a high speed for 1 minute to loosen it. Judgment of the possibility of granulation was performed visually, and the case where the soil mass was made fine was “◯”, and the others were “x”.

Step S4 (hydration reaction accelerated curing): The sample was sealed in the same manner as the modified solidification curing in step S2 for the hydration reaction accelerated curing.
Step S5 (carbon dioxide contact process): 2L (liter) is taken from the sample that has undergone the curing period of step S4, placed in a plastic bag, and air is sufficiently discharged from the plastic bag. 5 times the volume of the sample taken) was filled into a plastic bag. The opening of the plastic bag was tied and kept in a sealed state so as to keep contact with carbon dioxide for a predetermined time. Also, take 100 mL of the same sample, put it in another small plastic bag, fill it with 5 times the volume of carbon dioxide, and keep the plastic bag sealed for 30 minutes and shake it by hand to soften the sample. It was judged visually whether or not. Cases that were not softened were marked as “◯”, and cases that were softened due to moisture generation were marked as x.

Step S6 (evaluation): “◯” indicates a determination when the cone index is 800 kN / m ² or more in the cone test performed immediately after the process of step S5, and “×” indicates a determination when the cone index is less than that. It was. In addition, the sample after the process of step S5 is transferred to another plastic bag, and after further sealing and curing as it is for one week, the pH is measured (in consideration of the rebound phenomenon), and the determination is made when the pH is 8.6 or less. “◯”, otherwise the judgment was “x”.
Hereinafter, the knowledge obtained from the results shown in the table of FIG. 5 will be shown.

  First, when looking at the case (No. 9 to 11) in which only quick lime was added in the modified solidification treatment in Step S1 and the case (No. 12 to 14) in which only the blast furnace B cement was added, Except for 12, the pH immediately after addition of the solidifying material is higher than 12. Further, the evaluation of step S6 is “x” in either case (or both) of pH or qc in any case, and does not satisfy the target. Therefore, it turns out that a favorable result is not obtained in the solidification process only with quicklime or a cement-type solidification material.

Next, no. Focus on cases 15-17. These cases are cases where only the water absorption modifier is added. Only 17 satisfies the evaluation of step S6. However, since it is not satisfactory unless the amount of water-absorbing modifier added is as large as 300 kg / m ³ , it is not economical.

  And No. which added water-absorbing modifier and blast furnace B cement. In 1 to 8, the pH after the treatment of [1] is less than 12 in all cases. However, No. which does not provide the curing period of step S2. In No. 1, the loosening granulation was “x”, and the carbon dioxide contact / curing treatment in step S5 was performed in that state, so the pH in step S6 was “x” (pH 9.9). That is, it can be seen from this case that the pH does not drop efficiently unless the sample is refined by loosening granulation.

  Next, no. Focus on cases 2-8. In step S4, the curing period was set to 0 day, 3 days, and 7 days, respectively. In 2, 3, and 4, the cone index in step S6 was “x”. This is because the hydration reaction promoting curing time in step S4 is too short. No. In 5-8, the cone index of step S6 is “◯”, and the softening phenomenon does not occur in step S5. Therefore, it can be seen that it is appropriate to set the curing period in step S4 to 14 days (2 weeks) or longer.

  And the contact time of the carbon dioxide gas in step S5 is different from each other. 5-8, the pH of step S6 is “x” in the contact time of 2, 4 hours, and “◯” in the case where the contact time is 6 hours or more. This shows that the contact time of carbon dioxide gas is preferably 6 hours or longer.

[Example 3]
Example 3 shows an example in which alkaline soil is neutralized by a rapid contact method.
Construction sludge produced by the treatment method shown in the embodiment of the present invention is charged with 20 L (liter) of finely ground solid soil having a pH = 11.1 into a drum mixer having a capacity of 140 L, and carbon dioxide gas is supplied into the drum mixer at 25 L / min. Filled at flow rate for 6 minutes. The mixer was covered, the mixer was rotated for 10 minutes, the finely ground solidified soil was stirred, and carbon dioxide contact was attempted. As a result, the pH of the soil after 3 days was 8.5. Moreover, when the corn penetration | invasion test of this neutral reproduction | regeneration soil was implemented, the corn index was 2350 kN / m < ² >. As described above, it was confirmed that high quality neutral reclaimed soil having a pH of 8.6 or less and a corn index of 800 kN / m ² or more can be produced by a rapid contact method.

On the other hand, using a solidified material mainly composed of quick lime, 20 L of fine-grained solidified soil having a modified solidification treatment with pH = 11.4 is put into the same drum mixer, and carbon dioxide gas is supplied into the drum mixer at 25 L / Filled for 6 minutes at a flow rate of minutes. The mixer was covered and the mixer was rotated for 30 minutes, and the finely ground solidified soil was stirred to contact carbon dioxide. As a result, the pH of the soil after 3 days was 10.5, and 8.6 or less could not be achieved. Furthermore, this reclaimed soil was weakened, and the cone penetration test was conducted, and the cone index was 656 kN / m ² . As described above, in the soil modified by the solidified material mainly composed of quicklime, the target values in both pH and corn index could not be achieved by the rapid contact method.

[Example 4]
Example 4 shows an example in which fine sludge soil with a pH of 11.4 produced from construction sludge by the treatment method described in the embodiment of the present invention is neutralized by the falling contact method. As a test procedure of Example 4, first, as shown in FIG. 6, three cylinders 31 each having a height of 1 m prepared by connecting eight acrylic columns 31 a of φ100 mm × 125 mm were prepared. The target fine-grained solidified soil 33 was put into the inside. Here, the volume of the fine-grained solidified soil 33 put into each cylinder 31 is as follows.
Volume of fine-grained solidified soil 33 = 5 cm × 5 cm × 3.14 × 100 cm
= 7,850 cm ³ (mL) ≒ 8L

  Next, a 45 L plastic bag 35 filled with 40 L of carbon dioxide gas was prepared, and the plastic bag 35 was put on the upper end of each cylinder 31 as shown in FIG. As a result, the carbon dioxide gas in the plastic bag 35 flows down into contact with the fine-grained solidified soil 33. Here, the flow-down contact is performed at a rate of 5 times, because carbon dioxide gas is 40 L while the fine solidified soil 33 in the cylinder 31 is 8 L.

  In the test of Example 4, it was confirmed that the upper part of the cylinder 31 became whitish with moisture after 30 minutes from the flow-down contact. It was allowed to stand overnight, and 18 hours after the flow contact, One cylinder 31 was disassembled into individual columns 31a. At this time, the carbon dioxide in the plastic bag 35 was almost consumed.

  Next, no. The fine solidified soil 33 in the eight columns 31a constituting one cylinder 31 is put in a plastic bag 35, and the pH of the fine solidified soil 33 in each column 31a is set to 1 day and 3 days after flowing-down contact. It was measured.

In addition, no. Two cylinders 31 were disassembled, and the pH of the finely ground solidified soil 33 in each column 31a was measured.
Further, 3 days after the flow contact, No. 3 cylinders 31 were refilled with 40 L of carbon dioxide. That is, no. 3 cylinders 31 were filled with a total of 80 L of carbon dioxide gas. No. 4 days after the flow-down contact. When the third cylinder 31 was disassembled, some carbon dioxide in the plastic bag 35 still remained. In addition, no. The pH of the finely ground solidified soil 33 in each column 31a constituting the three cylinders 31 was also measured.

  FIG. 8 is a graph showing the test results of Example 4. As shown in the graph of FIG. 8, when the flow-down contact method is performed according to the procedure described in Example 4, it can be seen that the fine-grained solid soil 33 having a depth of 50 to 70 cm in a 1 m cylinder 31 is neutralized. . Moreover, the effect of neutralization appears even one day after the flow-down contact. Furthermore, it was confirmed that the rebound was small even after 3 days had passed since the flow-down contact, and that the reduction depth of the pH was increased by additional filling with carbon dioxide gas.

[Example 5]
Example 5 shows an example in which fine sludge soil of pH = 11.1 produced from construction sludge by the treatment method shown in the embodiment of the present invention is neutralized by a downflow contact method at an actual scale level. As a test procedure of Example 5, first, 3.3 m ³ of finely ground solid soil having a pH of 11.1 was put into a tank of a dump truck (watertight vessel car) having a capacity of 8.4 m ³ . The average layer thickness of the finely ground solidified soil charged in the tank is 30 cm. Table 1 shows the specifications of the tank.

Carbon dioxide gas was injected into the tank at 5.1 m ³ , and then cured for 3 days in a sealed state to produce reclaimed soil. Thereafter, samples at 5 points (samples 1 to 5) were randomly extracted from the recycled soil dumped up, and the pH was measured. The results are shown in Table 2.

According to Table 2, the pH was below 8.6 at all points, and the average pH = 8.3 was obtained. Moreover, as a result of conducting a cone test on this recycled soil, a result having a cone index of 918 kN / m ² was obtained.

[Example 6]
In Example 6, a case where neutralization is performed by the pool contact method will be described. In Example 6, the dump truck tank (capacity 8.4 m ³ ) used in Example 5 was first filled with 8 m ^{3 of} carbon dioxide, and the tank filled with the carbon dioxide was described in the embodiment of the present invention. The finely ground solid soil having a pH of 11.3 produced by the treatment method of 3.3 m ³ was gently added over 4 hours. In addition, 4 m ³ of carbon dioxide gas was replenished in four portions every hour during charging. After the addition of finely ground solid and filling with carbon dioxide, the lid was covered and cured overnight to produce reclaimed soil. Thereafter, samples at 5 points (samples 1 to 5) were randomly extracted from the recycled soil dumped up, and the pH was measured. The results are shown in Table 3.

According to Table 3, the pH was below 8.6 at all points, and the average pH = 8.0 was obtained. Further, as a result of conducting a cone test on this recycled soil, a result having a cone index of 1370 kN / m ² was obtained.

2 Mixer 12 Pit 20 Space 31 Cylinder

Claims (14)

A stirring means for stirring alkaline construction sludge to which a water-absorbing modifier is added;
A first curing area for curing the construction sludge stirred in the stirring means until it becomes semi-solid;
Loosening granulation means for loosening and finely pulverizing the construction sludge that has become semi-solid in the first curing area;
A second curing area for further curing the construction sludge refined by the loosening granulation means to promote a hydration reaction;
A reclaimed soil production system comprising carbon dioxide gas contact means for bringing carbon dioxide into contact with the construction sludge whose hydration reaction has been promoted in the second curing area to neutralize the construction sludge.   The recycled soil production system according to claim 1, wherein a cement-based solidifying material is further added to the construction sludge by the stirring means.   The recycled soil production system according to claim 1 or 2, wherein the construction sludge stirred by the stirring means has a hydrogen ion concentration index of 9 or more and less than 12.   The carbon dioxide contact means neutralizes the construction sludge by bringing the carbon dioxide into direct contact with the construction sludge whose hydration reaction has been promoted in the second curing area. The reclaimed-soil manufacturing system as described in any one of Claims. The carbon dioxide contact means includes
A rotary mixer for feeding the construction sludge whose hydration reaction has been promoted in the second curing area;
5. The reclaimed soil production system according to claim 4, wherein the construction sludge is neutralized by flowing or press-fitting the carbon dioxide gas into the mixer and stirring in a sealed state. The carbon dioxide contact means includes
A pit in which the construction sludge whose hydration reaction has been promoted in the second curing area is thinly laid in a loosely packed state;
A flow path for allowing the carbon dioxide gas to flow into the pit from above the pit,
5. The reclaimed soil production system according to claim 4, wherein the construction sludge is neutralized by curing the construction sludge for a certain period in the pit into which the carbon dioxide gas has flowed. The carbon dioxide contact means includes
Space,
A supply pipe for supplying the carbon dioxide gas to the space;
A charging unit for charging the construction sludge whose hydration reaction has been promoted in the second curing area into the space;
The neutralization of the construction sludge is performed by introducing the construction sludge into the space that is supplied from the supply pipe and filled with the carbon dioxide gas, and curing the construction sludge for a certain period. The recycled soil manufacturing system according to claim 4. A reforming and solidifying process in which a water-absorbing modifier is added to and mixed with alkaline construction sludge;
A reforming solidification curing step for curing the construction sludge treated in the reforming solidification step until it becomes semi-solid;
A loosening granulation step of loosening and finely pulverizing the construction sludge that has become semi-solid in the modified solidification curing step;
A hydration reaction promoting curing step of further curing the construction sludge refined in the loosening granulation step to promote a hydration reaction;
A method for producing reclaimed soil, comprising: a carbon dioxide gas contact step in which carbon dioxide gas is brought into contact with the construction sludge whose hydration reaction has been promoted in the hydration reaction promotion curing step to neutralize the construction sludge.   The method for producing reclaimed soil according to claim 8, wherein a cement-based solidifying material is further added to the construction sludge in the modified solidification step.   The method for producing reclaimed soil according to claim 8 or 9, wherein the construction sludge used in the reforming and solidifying step has a hydrogen ion concentration index of 9 or more and less than 12.   The said carbon dioxide gas contact process WHEREIN: The said carbon dioxide is directly contacted with the said construction sludge in which the hydration reaction was accelerated | stimulated, The said construction sludge is neutralized, It is any one of Claims 8-10 characterized by the above-mentioned. Reclaimed soil production method.   In the carbon dioxide gas contact step, the construction sludge whose hydration reaction has been promoted is put into a rotary mixer, carbon dioxide gas is introduced or injected therein, and stirred in a sealed state. 11. The method for producing recycled soil according to item 11.   12. The regeneration according to claim 11, wherein, in the carbon dioxide contact step, the construction sludge whose hydration reaction has been promoted is spread in a thin and loosely packed state in a pit, and is cured by flowing the carbon dioxide from above. Soil manufacturing method.   12. The method for producing reclaimed soil according to claim 11, wherein, in the carbon dioxide contact step, the construction sludge whose hydration reaction has been promoted is put into a space filled with the carbon dioxide and cured.