JP2023169081A - Carbonation curing method for precast concrete member - Google Patents

Abstract

To provide a carbonation curing method for concrete members that can be performed even at a factory or a construction site and enables CO2 to be efficiently immobilized using a simple facility.SOLUTION: In a carbonation curing method for precast concrete members, the precast concrete members are covered with an airtight curing sheet 2, and a gas including carbon dioxide is blown into the curing sheet 2 to produce calcium carbonate in the precast concrete members 1, immobilizing carbon dioxide. The curing sheet 2 is a heat-retentive sheet 2' with insulation capabilities. The heat of hydration of the precast concrete members 1 is used to promote the calcium carbonate producing reaction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a carbonation curing method for precast concrete members.

In recent years, the demand for CO ₂ reduction has been increasing in order to realize a carbon-neutral society by 2050. The construction industry deals with hardened cement parts such as concrete parts, so efforts have been made to reduce the carbon content of materials for the past year. Furthermore, various techniques have been proposed for fixing CO ₂ in various processes from the manufacture of cement to its use.

However, carbonation promotes the carbonation of concrete members, and there are concerns about corrosion of reinforcing bars in concrete members, so there are many challenges in promoting this method. On the other hand, attempts have also been made to construct internal reinforcing materials for concrete structures using non-corrosive materials (for example, CFCC slabs (precast PC floor slabs) using carbon fiber composite cable CFCC (registered trademark) as tendons). It is thought that combining this technology with these technologies will contribute to reducing CO ₂ emissions.

As for the current carbonation curing method of cement hardened material, for example, Patent Document 1 discloses a concrete water storage structure that has a storage area capable of storing water, and the inner wall surface of the storage area is made of cement-based hardened material. A carbonation curing method for carbonation of a concrete water storage structure, comprising: a depressurization step of reducing the pressure in the space by making the storage area a closed space; and a water injection step of pouring carbon dioxide-dissolved water into the storage area. A chemical curing method is disclosed (see claim 1 of patent document 1, paragraphs [0025] to [0038] of the specification, FIGS. 2 to 4, etc.).

However, the carbonation curing method for concrete water storage structures described in Patent Document 1 solves the problem of water leaching in large concrete water storage structures that are expected to be used for long periods of time in contact with water. The purpose of this method is to densify the surface of a concrete structure in order to achieve this, and there is a problem in that it can only be applied to concrete water storage structures because carbon dioxide is supplied using carbon dioxide-dissolved water.

Further, Patent Document 2 discloses a method for producing a hardened product, in which a cement mixture containing cement and water is placed, demolded, an alkaline solution is supplied as curing water, and then carbonation curing is performed. (See claims 1, 2, and 4 of the scope of claims of Patent Document 2, paragraphs [0010] to [0023] of the specification, etc.).

However, in the method for producing a hardened product described in Patent Document 2, an alkaline solution is applied to cure the cement mixture immediately after demolding, in order to simply densify only the very surface layer of the hardened cement product and improve durability. It is supplied as water, impregnated, and densified through carbonation and curing.

Furthermore, the method for producing a cured body described in Patent Document 2 does not specifically consider the method of supplying carbon dioxide, and what kind of equipment performs carbonation curing in the actual manufacturing process of components in factories and on-site. There was a problem as to whether the construction should be carried out using

Furthermore, Patent Document 3 describes a carbonation curing equipment used for producing carbonated concrete, in which living organisms housed in a carbonation curing tank whose interior is a shielded space are carbonated and cured. A method is disclosed (see claim 1 of the claims of Patent Document 3).

However, the carbonation curing tank described in Patent Document 3 is a box-shaped container like a container, and when the living body is stored in the curing tank, a surplus space is created, which is inefficient. Changing the size and shape of the curing tank depending on the shape and number of curing bodies requires equipment installation costs and requires a place to store the curing tank during periods when it is not in use. Therefore, there is a problem in that the curing method occupies more space than the minimum necessary curing space depending on the shape of the living body, and is subject to restrictions depending on the amount and shape.

Similarly, when attempting to carry out carbonation curing in large quantities or for a long period of time using a curing tank, there is a problem in that there are restrictions on the number and duration of carbonation curing that can be carried out compared to the case where only the target organisms are stored. was there.

In addition, although this is fine within a factory where the equipment and site are secured, the number of transports may increase if the target organisms are transported while continuing carbonation curing, or if carbonation curing is carried out at the construction site to which they are being transported. There were problems such as expansion of site area and uneconomical problems.

As a general characteristic of concrete members, those with high strength have a dense pore structure and therefore have low air permeability and water permeability. In other words, if carbonation is intended, if the strength of the concrete member is high, the permeation of carbon dioxide will be inhibited, resulting in a problem that the area for carbonation will become smaller.

JP2015-54806A JP2013-107284A Japanese Patent Application Publication No. 2012-126623

Therefore, the present invention has been devised in view of the above-mentioned problems, and its purpose is to minimize the space required for carbonation curing and reduce the number of items that can be stored. The purpose of the present invention is to provide a carbonation curing method for precast concrete members that can efficiently fix carbon dioxide in a simple facility that can be used in factories, construction sites, etc., and requires a small site.

The carbonation curing method for a precast concrete member according to claim 1 includes covering the precast concrete member with a vacuum pack and suctioning it with a suction device to bring the precast concrete member into a state at a pressure lower than the surrounding atmospheric pressure, and then releasing carbon dioxide into the vacuum pack. The method is characterized in that calcium carbonate is generated in the precast concrete member by blowing a gas containing the above into the precast concrete member, thereby fixing carbon dioxide.

The carbonation curing method for concrete members according to claim 2 is the carbonation curing method for concrete members according to claim 1, in which the vacuum pack is further covered with a heat-insulating sheet having heat insulating properties, and the precast concrete member is hydrated. It is characterized by promoting the reaction that produces calcium carbonate with heat.

The carbonation curing method for concrete members according to claim 3 is the carbonation curing method for concrete members according to claim 1, in which calcium hydroxide water is added to the surface of the precast concrete member in advance before inserting it into the vacuum pack. After spraying or after injecting calcium hydroxide water into the vacuum pack, carbon dioxide is supplied to generate calcium carbonate in the precast concrete member and fix carbon dioxide.

The carbonation curing method for a concrete member according to claim 4 is the carbonation curing method for a concrete member according to claim 3, wherein the precast concrete member is carbonated in the vacuum pack while carbonation curing of the precast concrete member is progressing in the vacuum pack. The method is characterized in that calcium hydroxide water is injected, and then carbon dioxide is supplied to generate calcium carbonate in the precast concrete member and fix carbon dioxide.

The carbonation curing method for concrete members according to claim 5 is the carbonation curing method for concrete members according to claim 3, which includes sucking out excess calcium hydroxide water after injecting calcium hydroxide water into the vacuum pack. Then, by supplying carbon dioxide to form a layer densified with calcium carbonate on the surface layer of the precast concrete member, carbon dioxide is trapped in the pores of the precast concrete member and the precast concrete is It is characterized by continuing the production of calcium carbonate inside the member.

The carbonation curing method for concrete members according to claim 6 is the carbonation curing method for concrete members according to claim 3, wherein calcium hydroxide water is injected into the vacuum pack and carbon dioxide is supplied a predetermined number of times. or until a predetermined carbonation depth is reached, calcium carbonate is generated in the precast concrete member and carbon dioxide is fixed.

The carbonation curing method for concrete members according to claim 7 is the carbonation curing method for concrete members according to claim 1, wherein an exhaust device capable of adjusting the humidity in the vacuum pack is provided, and the relative humidity in the curing sheet is adjusted. is adjusted to 40% or more and 70% or less to produce calcium carbonate in the precast concrete member and fix carbon dioxide.

The carbonation curing method for concrete members according to claim 8 is the carbonation curing method for concrete members according to claim 1, in which carbon dioxide in the vacuum pack is sucked to reduce the pressure. The vacuum pack is opened after the temperature becomes below a predetermined value.

The carbonation curing method for a precast concrete member according to claim 9 is the carbonation curing method for a concrete member according to claim 1, wherein a non-corrosive material with no fear of corrosion is used as an internal reinforcing material of the precast concrete member. It is characterized by

A carbonation curing method for a precast concrete member according to claim 10 is a carbonation curing method for a concrete member according to claim 1, in which irregularities are provided on the outer surface of the precast concrete member, and a gas containing carbon dioxide is blown into the carbonation curing method for a concrete member. The method is characterized in that calcium carbonate is generated in the irregularities of the precast concrete member to fix carbon dioxide.

According to the inventions according to claims 1 to 10, carbon dioxide can be efficiently fixed with a simple facility that can be implemented even at a construction site, and precast concrete members can be densified and of high quality. Further, according to the inventions according to claims 1 to 10, the space required for carbonation curing is minimized, the number of storage organisms that can be normally stored is not reduced, and the carbonation curing equipment itself The site required for storage is smaller than that required for curing tanks, and carbon dioxide can be efficiently fixed in simple facilities that can be implemented at factories, construction sites, etc. In addition, according to the inventions according to claims 1 to 10, carbonation curing can be continued even during factory storage, transportation, and temporary storage on site, and the carbonation area can be increased. , it is possible to densify and improve the quality of precast concrete members in a time-efficient manner.

In particular, according to the invention according to claim 2, since the precast concrete member is covered with a heat insulating sheet, it is possible to promote the reaction of producing calcium carbonate with the heat of hydration of the precast concrete member. By fixing carbon dioxide, precast concrete parts can be made denser and of higher quality.

In particular, according to the invention according to claim 3, since calcium hydroxide water is sprayed onto the surface of the precast concrete member or calcium hydroxide water is injected into the vacuum pack, calcium carbonate is generated on the surface of the precast concrete member. can be done efficiently.

In particular, according to the invention according to claim 4, calcium hydroxide and carbon dioxide gas in the precast concrete member are reacted without supplying calcium hydroxide water at the beginning of the curing period, so that the surface layer of the precast concrete member is densely formed. Calcium carbonate can be efficiently produced without inhibiting further carbonation, and as a result, a large amount of carbon dioxide can be fixed.

In particular, according to the invention according to claim 5, after the excess calcium hydroxide water is sucked and discharged, carbon dioxide is supplied to form a densified layer of calcium carbonate on the surface layer of the precast concrete member. , carbon dioxide can be trapped within the pores of the precast concrete member to continue the production of calcium carbonate inside the precast concrete member.

In particular, according to the invention according to claim 6, since the injection of calcium hydroxide water and the supply of carbon dioxide are repeated until reaching a predetermined number of times or until reaching a predetermined carbonation depth, A layer of desired thickness of calcium carbonate can be produced to immobilize more carbon dioxide, resulting in a densified, high quality precast concrete component.

In particular, according to the invention according to claim 7, the relative humidity, which is the humidity that promotes the production of calcium carbonate, is adjusted to 40% or more and 70% or less, resulting in the production of calcium carbonate in the precast concrete member. can be carried out efficiently and a large amount of carbon dioxide can be fixed.

In particular, according to the invention according to claim 8, since unreacted carbon dioxide gas is recovered, carbon dioxide is not released into the atmosphere, reducing carbon dioxide emissions and preventing global warming. can contribute.

In particular, according to the invention according to claim 9, since the internal reinforcing material of the concrete structure is replaced with a non-corrosive material such as carbon fiber, aramid fiber, or glass fiber, which is free from corrosion concerns, carbonation curing is not necessary. Even if the carbonated region reaches the internal reinforcing material of the concrete structure, it will not corrode, so structural performance can be maintained.

In particular, according to the tenth aspect of the invention, the surface area of the precast concrete member on which carbon dioxide acts can be increased, so that calcium carbonate can be efficiently generated in the precast concrete member and carbon dioxide can be fixed.

FIG. 1 is a sectional view schematically showing the configuration of a carbonation curing facility used in the method for carbonation and curing of concrete members according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the configuration of a carbonation curing facility used in the method for carbonation and curing of concrete members according to the second embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the carbonation curing method for a precast concrete member according to the present invention will be described in detail with reference to the drawings.

[First embodiment]
A cement carbonation curing method according to a first embodiment of the present invention will be described using FIG. 1. FIG. 1 is a cross-sectional view schematically showing the configuration of a carbonation curing facility used in the carbonation curing method for precast concrete members according to the first embodiment of the present invention.

As shown in FIG. 1, in the carbonation curing method for precast concrete members according to the present embodiment (hereinafter also simply referred to as carbonation curing method), a precast concrete member 1 is covered with a curing sheet 2 made of a resin sheet such as a polyethylene sheet. Cover the container, and blow gas containing carbon dioxide from the carbon dioxide supply device 3 that supplies carbon dioxide to generate calcium carbonate and fix carbon dioxide.

Here, the hardened cement body to be cured in the carbonation curing method according to the present embodiment is assumed to be a precast concrete member.

Further, the curing sheet 2 is not limited to a resin sheet such as a polyethylene sheet, and may be a resin film. In short, the curing sheet 2 only needs to have a certain degree of airtightness to prevent water vapor and carbon dioxide from permeating to the outside air during the curing period of the precast concrete member. Further, it is preferable to place a weight 4 such as a scaffolding board on the edge of the curing sheet 2 to prevent the curing sheet 2 from rolling up.

Therefore, since carbonation curing can be performed using the curing sheet 2, carbonation curing can be performed even if the shape or quantity of the precast concrete member 1, which is the body to be cured, changes, compared to the case where carbonation curing is not performed. It does not require a special place to do it. Further, since carbonation curing is performed using the curing sheet 2, a special place for storing the curing sheet 2 is not required during the period when carbonation curing is not performed.

However, in the precast concrete member 1, Ca(OH) ₂ dissolves in the pore solution and Ca ²⁺ reacts with CO ₂ to carbonate, so the higher the temperature, the easier it is to dissolve from the precast concrete member. In addition, the higher the temperature, the faster the reaction rate of carbonation of Ca ²⁺ after dissolution. For example, it is known that the carbonation rate at 40°C is about twice as fast as the carbonation rate at 20°C. Therefore, in the carbonation curing method according to the present embodiment, it is preferable to supply carbon dioxide gas while maintaining the temperature inside the curing sheet 2 higher than the ambient temperature.

(thermal sheet)
However, providing heating facilities is costly in order to be viable at construction sites. Therefore, in the carbonation curing method according to the present embodiment, the curing sheet 2 is a thermal insulation sheet 2 having heat insulation properties, which is made by laminating a resin film such as polyethylene, a metal foil such as aluminum foil, and a heat insulating material such as urethane foam. ' is preferable. This is because the heat of the hydration reaction of the precast concrete member 1 can be insulated and the carbonation reaction can be promoted. Of course, the heat retaining sheet 2' is not particularly limited as long as it has a heat insulating property by having a heat insulating layer such as a heat insulating material or an air layer.

Although the example is shown in which the weights 4 are placed on the curing sheet 2, the heat insulating sheet 2' has some weight and there is little risk of it being rolled up and the airtightness being impaired. Therefore, the weight 4 can be omitted by using the heat retaining sheet 2' as the curing sheet 2.

(spray of calcium hydroxide water)
In the carbonation curing method according to the present embodiment, calcium hydroxide Ca(OH) ₂ water (lime water) is sprayed on the precast concrete member 1 to absorb water, and carbon dioxide CO ₂ is supplied to the surface layer of the precast concrete member 1. Promotes carbonation. That is, in the carbonation curing method according to the present embodiment, carbon dioxide is blown into lime water on the surface of the precast concrete member 1 to generate calcium carbonate CaCO ₃ . The chemical formula is as follows.
Ca(OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O

Furthermore, in the carbonation curing method according to the present embodiment, the spraying of this calcium hydroxide water and the supply of carbon dioxide are repeated to generate more calcium carbonate in the precast concrete member 1 and fix more carbon dioxide. It is preferable.

However, as the carbonation of the surface layer of the precast concrete member 1 progresses, the surface layer of the precast concrete member 1 also becomes denser, and further carbonation is also inhibited. Therefore, in the carbonation curing method according to the present embodiment, at the beginning of the curing period, carbon dioxide is supplied without spraying calcium hydroxide Ca(OH) ₂ water, and then, calcium hydroxide is added to the precast concrete member 1. It is preferable to repeat the spraying of water and the supply of carbon dioxide.

Note that, as the calcium hydroxide, water (recovered water) obtained by removing aggregates from washing wastewater from transport vehicles and mixers of ready-mixed concrete factories or precast product factories, or laitance treated water may be used. The recovered water is divided into highly alkaline supernatant water containing calcium hydroxide etc. eluted from cement, and sludge water containing sludge solids (mostly hydration products, some aggregate fine particles), and is preferably It is supernatant water. The factory is required to neutralize the recovered water before discharging it as general wastewater, and by using it as carbonated curing water, the recovered water will not be consumed or even if it remains, it will act on the neutral side. The amount of reagent used during neutralization treatment is reduced.

However, for the generation of calcium carbonate by spraying calcium hydroxide water, it is important whether the calcium hydroxide solution exists in the pores of the precast concrete member 1, so if the precast concrete member 1 is completely dry, the solution will disappear. Dissolution does not proceed. On the other hand, if the precast concrete member 1 is in a wet state, gas cannot enter.

Therefore, in the carbonation curing method according to the present embodiment, as shown in FIG. 1, an exhaust device 5 that can adjust the humidity inside the curing sheet 2 (thermal sheet 2') is provided to promote the production of calcium carbonate. The relative humidity in the curing sheet 2 (thermal sheet 2') is adjusted to 40% or more and 70% or less to generate calcium carbonate in the precast concrete member 1 and fix carbon dioxide. Of course, it depends on the water-cement ratio W/C of the precast concrete member 1, the type of cement used, and the type of admixture, so it is preferable to appropriately determine and adjust the humidity at which calcium carbonate production is promoted through experiments or the like.

( _CO2 concentration)
In addition, in the carbonation curing method according to the present embodiment, a carbon dioxide concentration measuring device 6 is provided to measure the carbon dioxide concentration in the curing sheet 2 (thermal sheet 2'), and the carbon dioxide concentration is determined by the carbon dioxide concentration as the production of calcium carbonate is promoted. Calcium carbonate is generated in the precast concrete member 1 to fix carbon dioxide.

However, if the curing sheet 2 (thermal insulation sheet 2') is filled with carbon dioxide _CO2 , the excess that does not contribute to carbonation of the precast concrete member 1 when the curing sheet 2 (thermal insulation sheet 2') is opened There is concern that more carbon dioxide CO ₂ will be released into the atmosphere.

Therefore, in the carbonation curing method according to the present embodiment, a carbon dioxide intake device 7 is provided to suck and recover gaseous carbon dioxide in the curing sheet 2 (thermal sheet 2') connected to an exhaust device 5 etc. The calcium hydroxide solution and unreacted carbon dioxide gas in the sheet 2 (thermal sheet 2') are recovered. Further, as shown in FIG. 1, the carbon dioxide recovered by the carbon dioxide intake device 7 may be connected to the carbon dioxide supply device 3 or the like so that it can be supplied again, or it may be compressed and stored in a cylinder or the like. I don't mind.

(Non-corrosive material)
The precast concrete member 1 to be carbonated and cured in the carbonation and curing method according to the present embodiment has been described above without any particular limitation. However, the precast concrete member 1 cured by the carbonation curing method according to the present embodiment uses a non-corrosive material such as carbon fiber, aramid fiber, or glass fiber as an internal reinforcing material without fear of corrosion when used as a structure. Preferably, it is a used concrete member. As described in the background art, when a concrete structure internally reinforced with steel materials such as reinforcing bars is carbonated and cured, carbonation promotes the carbonation of the concrete members, and there is a concern that the steel materials in the concrete members may corrode. Ru.

However, in the carbonation curing method according to the present embodiment, when the precast concrete member 1 to be cured is used as a concrete structure, the internal reinforcing material of the precast concrete member 1 is carbon fiber, aramid fiber, glass fiber, etc. Use non-corrosive materials. As a result, even if the carbonated region reaches the internal reinforcing material of the structure due to active carbonation curing, corrosion will not occur, so that structural performance can be maintained.

[Second embodiment]
A carbonation curing method for a precast concrete member according to a second embodiment of the present invention will be described using FIG. 2. FIG. 2 is a cross-sectional view schematically showing the configuration of a carbonation curing facility used in the method for carbonation and curing of precast concrete members according to the second embodiment of the present invention. The difference between the cement carbonation curing method according to the second embodiment and the cement carbonation curing method according to the first embodiment described above is that the precast concrete member 1 is covered with a vacuum pack 8 and suction is carried out using a suction machine 9. Since carbon dioxide is fixed in a vacuum and low pressure state, this point will be mainly explained, and the same components will be given the same reference numerals and the explanation will be omitted.

In the carbonation curing method according to the second embodiment, the precast concrete member 1 is covered with a vacuum pack 8 and suctioned by a suction device (not shown) to keep the precast concrete member 1 in a state where the pressure is lower than the surrounding atmospheric pressure (vacuum state). A gas containing carbon dioxide is blown into the vacuum pack 8 to generate calcium carbonate in the precast concrete member 1 and fix carbon dioxide.

(vacuum pack)
The vacuum pack 8 is made of a highly airtight resin film such as a nylon poly film in which a nylon resin film and a polyethylene resin film are laminated. Of course, the vacuum pack according to the present invention may be any pack material as long as it has a predetermined airtightness that can maintain a vacuum state.

Here, the vacuum is not limited to an ultra-high vacuum of 10 ^-5 Pa or less, but also includes a low vacuum of 100 kPa to 100 Pa. Furthermore, even if the inside of the vacuum pack 8 is not brought to a vacuum state, if the inside of the vacuum pack 8 is brought into a low pressure state lower than the surrounding atmospheric pressure, and carbon dioxide gas is supplied with negative pressure inside the vacuum pack 8, the inside of the pores of the precast concrete member 1 can be filled. can also supply carbon dioxide and promote the production of calcium carbonate to a certain extent.

Therefore, since carbonation curing can be performed using the vacuum pack 8, carbonation curing can be performed even if the shape or quantity of the precast concrete member 1 to be cured changes compared to the case where carbonation curing is not performed. It does not require a special place to do it. Further, since carbonation curing is performed in the vacuum pack 8, a special place for storing the curing sheet is not required during the period when carbonation curing is not performed.

(thermal sheet)
Further, in the carbonation curing method according to the present embodiment, similarly to the carbonation curing method according to the first embodiment, the vacuum pack 8 is further covered with a heat insulating sheet 2' having heat insulating properties, and the precast concrete member 1 is The heat of hydration promotes the reaction that produces calcium carbonate. This is because there is no need to provide heating facilities or the like.

(Injection of calcium hydroxide water)
Furthermore, in the carbonation curing method according to the present embodiment, after calcium hydroxide water is injected into the vacuum pack 8 using the calcium hydroxide water injection device 10, carbon dioxide containing carbon dioxide is added from the carbon dioxide supply device 3 in a vacuum state. Carbon dioxide is supplied into the vacuum pack 8 by blowing a gas into the vacuum pack 8. This is because, similarly to the carbonation curing method according to the first embodiment, carbon dioxide can be fixed by promoting the production of calcium carbonate as shown in the above chemical formula.

However, without using the calcium hydroxide water injection device 10, after spraying calcium hydroxide water on the outer surface of the precast concrete member 1, the precast concrete member 1 with the calcium hydroxide water sprayed on the outer surface is vacuum packed 8. Alternatively, the carbon dioxide gas may be supplied by inserting the gas into the vacuum pack 8 and keeping the inside of the vacuum pack 8 in a low pressure state. Similarly, the action of lime water sprayed on the outer surface can promote the production of calcium carbonate and fix carbon dioxide.

However, as described above, as the carbonation of the surface layer of the precast concrete member 1 progresses, the surface layer of the precast concrete member 1 also becomes denser, and further carbonation is also inhibited. Therefore, in the carbonation curing method according to the present embodiment, calcium hydroxide water is injected into the vacuum pack 8 while carbonation curing of the precast concrete member 1 is progressing in the vacuum pack 8, and then carbon dioxide is supplied. Calcium carbonate is generated in the precast concrete member 1 to fix carbon dioxide.

That is, at the beginning of the curing period, carbon dioxide is supplied into the vacuum pack 8 in a vacuum state without injecting calcium hydroxide water, and after that, calcium hydroxide water is injected into the precast concrete member 1, and carbon dioxide is injected into the precast concrete member 1. It is preferable to repeat the feeding.

In addition, the injection of calcium hydroxide water and the supply of carbon dioxide are carried out at a predetermined time until the precast concrete member 1 is densified by the production of calcium carbonate and the carbon dioxide is immobilized (neutralized) to a certain depth from the surface. It is preferable to repeat the process several times. This is because the layer of calcium carbonate that is produced becomes thicker and more carbon dioxide can be fixed.

Generally, it is difficult to confirm from the surface of the precast concrete member 1 how deep the carbonation depth has reached. However, by enclosing multiple specimens in a vacuum pack 8 and performing carbonation curing under the same conditions as the precast concrete member 1, the carbonation depth can be determined by taking out the specimens and checking. Repeat injection of calcium hydroxide water and supply of carbon dioxide until it is confirmed that the depth has been reached. Through such an experiment, the necessary number of times can be confirmed and set in advance according to the water-cement ratio W/C of the precast concrete member 1, the type of cement used, and the type of admixture.

Furthermore, after injecting calcium hydroxide water into the vacuum pack 8, excess calcium hydroxide water is sucked and discharged, and then carbon dioxide is supplied from the carbon dioxide supply device 3 to carbonate the surface layer of the precast concrete member 1. Forms a densified layer of calcium. By doing so, carbon dioxide can be trapped in the pores of the precast concrete member 1 with the densified layer of calcium carbonate, and the production of calcium carbonate inside the precast concrete member 1 can be continued. .

(Suction of excess carbon dioxide)
In the carbonation curing method according to the present embodiment, when finishing the carbonation curing, the carbon dioxide in the vacuum pack 8 is sucked in by the carbon dioxide suction device 7 described above so that the pressure is lower than a predetermined value (for example, After the vacuum is reduced to a low vacuum level (below the level of low vacuum), the vacuum pack 8 is opened. This is to prevent excess carbon dioxide that did not contribute to carbonation of the precast concrete member 1 from being released into the atmosphere when the vacuum pack 8 is opened.

(Providing unevenness on the surface of the non-care body)
Next, a modification of the carbonation curing method for precast concrete members according to the first and second embodiments of the present invention will be described. In the carbonation curing method for a precast concrete member according to a modified example, irregularities are provided on the outer surface of the precast concrete member 1, which is a living body, and calcium carbonate is generated in the precast concrete member 1 by blowing gas containing carbon dioxide. to fix carbon dioxide. This is to increase the carbonation area by increasing the surface area on which carbon dioxide acts compared to a normal product shape. Of course, the degree of unevenness may be of any value as long as it satisfies the performance required for the structure.

Furthermore, if the precast concrete member that is the living body is a product with pores, the pipes buried to form the pores are removed during the manufacturing process of the precast concrete member to expose the precast concrete member, and carbon dioxide is removed. It is also possible to increase the surface area on which the particles act.

According to the carbonation curing method for precast concrete members according to the first and second embodiments of the present invention described above, carbon dioxide can be efficiently fixed in a simple facility that can be carried out both in a factory and at a construction site. This allows the precast concrete member 1 to be densified and of high quality.

Further, according to the carbonation curing method according to the first and second embodiments, carbonation curing of the precast concrete member 1 can be continued even during factory storage, transportation, or temporary storage on site, and The precast concrete member 1 can be densified and of high quality efficiently.

Moreover, according to the carbonation curing method according to the first and second embodiments, since the heat insulating sheet 2' is used to cover the precast concrete member 1, the reaction that produces calcium carbonate can be promoted by the heat of hydration of the precast concrete member 1. It is possible to efficiently fix a large amount of carbon dioxide without installing heating facilities, making precast concrete parts denser and of higher quality.

Furthermore, according to the carbonation curing method according to the first and second embodiments, since calcium hydroxide water is sprayed onto the surface of the precast concrete member 1 or calcium hydroxide water is injected into the vacuum pack 8, the precast concrete member 1 is Calcium carbonate can be efficiently generated on the surface of the member 1.

Moreover, according to the carbonation curing methods according to the first and second embodiments, calcium hydroxide in the precast concrete member 1 is allowed to react with carbon dioxide gas without supplying calcium hydroxide water at the beginning of the curing period. Therefore, calcium carbonate can be efficiently generated without further carbonation being inhibited by the densification of the surface layer of the precast concrete member 1, and as a result, a large amount of carbon dioxide can be fixed.

Furthermore, according to the carbonation curing methods according to the first and second embodiments, since unreacted carbon dioxide gas is recovered, carbon dioxide is not released into the atmosphere, reducing carbon dioxide emissions. can contribute to the prevention of global warming.

Above, the carbonation curing method for precast concrete members according to the first and second embodiments of the present invention has been explained in detail, but the embodiments described above or illustrated are all examples of concrete methods for carrying out the present invention. This is merely an illustration of an embodiment. Therefore, the technical scope of the present invention should not be construed as being limited by these.

1: Precast concrete member 2: Curing sheet 2': Heat retention sheet (curing sheet)
3: Carbon dioxide supply device 4: Weight 5: Exhaust device 6: Carbon dioxide concentration measuring device 7: Carbon dioxide suction device 8: Vacuum pack 9: Suction device 10: Calcium hydroxide water injection device

The carbonation curing method for precast concrete members according to claim 1 includes covering the entire outer surface of the precast concrete member with a vacuum pack made of a highly airtight resin film and sucking it with a suction device to lower the precast concrete member from surrounding atmospheric pressure. The method is characterized in that a gas containing carbon dioxide is blown into the vacuum pack in a low pressure state to generate calcium carbonate in the precast concrete member and fix carbon dioxide.

The carbonation curing method for concrete members according to claim 7 is the carbonation curing method for concrete members according to claim 1, wherein an exhaust device capable of adjusting the humidity in the vacuum pack is provided, and the relative humidity in the vacuum pack is adjusted. is adjusted to 40% or more and 70% or less to produce calcium carbonate in the precast concrete member and fix carbon dioxide.

Claims (10)

The precast concrete member is covered with a vacuum pack and suction is performed using a suction device to lower the pressure of the precast concrete member than the surrounding atmospheric pressure, and a gas containing carbon dioxide is blown into the vacuum pack to inject calcium carbonate into the precast concrete member. A carbonation curing method for precast concrete members characterized by generating carbon dioxide and fixing it. Carbonation of a precast concrete member according to claim 1, characterized in that the vacuum pack is further covered with a heat insulating sheet having heat insulating properties to promote a reaction that generates calcium carbonate by heat of hydration of the precast concrete member. Curing method. After spraying calcium hydroxide water on the surface of the precast concrete member before inserting it into the vacuum pack, or after injecting calcium hydroxide water into the vacuum pack, carbon dioxide is supplied to the precast concrete member. The carbonation curing method for precast concrete members according to claim 1, characterized in that carbon dioxide is immobilized by producing calcium carbonate therein. Injecting calcium hydroxide water into the vacuum pack during carbonation curing of the precast concrete member in the vacuum pack, and then supplying carbon dioxide to generate calcium carbonate in the precast concrete member. The carbonation curing method for a precast concrete member according to claim 3, further comprising fixing carbon dioxide. After injecting calcium hydroxide water into the vacuum pack, excess calcium hydroxide water is sucked and discharged, and then carbon dioxide is supplied to form a densified layer of calcium carbonate on the surface layer of the precast concrete member. Carbonation of a precast concrete member according to claim 3, characterized in that by forming carbon dioxide in the pores of the precast concrete member to continue the production of calcium carbonate inside the precast concrete member. Curing method. Repeating the injection of calcium hydroxide water into the vacuum pack and the supply of carbon dioxide until a predetermined number of times or until a predetermined carbonation depth is reached to generate calcium carbonate in the precast concrete member. The carbonation curing method for a precast concrete member according to claim 3, further comprising fixing carbon dioxide. An exhaust device that can adjust the humidity in the vacuum pack is provided, and the relative humidity in the curing sheet is adjusted to 40% or more and 70% or less to generate calcium carbonate and fix carbon dioxide in the precast concrete member. The carbonation curing method for precast concrete members according to claim 1, characterized in that: The precast concrete member according to claim 1, characterized in that, when finishing carbonation curing, the vacuum pack is opened after the carbon dioxide in the vacuum pack is sucked and the pressure becomes below a predetermined value. carbonation curing method. The carbonation curing method for a precast concrete member according to claim 1, characterized in that a non-corrosive material with no fear of corrosion is used as an internal reinforcing material for the precast concrete member. According to claim 1, wherein the outer surface of the precast concrete member is provided with unevenness, and a gas containing carbon dioxide is blown into the outer surface of the precast concrete member to generate calcium carbonate on the unevenness of the precast concrete member and fix carbon dioxide. carbonation curing method for precast concrete parts.

Images