Carbonation curing method for precast member

Abstract

To provide a carbonation curing method for a precast member, which improves the carbonation curing efficiency of the precast member including γ - C2S.SOLUTION: A carbonation curing method for a precast member includes an air-curing step of air-curing a precast member C of a cement hardened body containing γ - C2S in a state in which an outer face of the precast member C is exposed to the atmosphere, a negative-pressure curing step of covering the outer face of the precast member C with a curing sheet 1 after the air-curing step and sucking air in the curing sheet 1 to bring the inside of the curing sheet 1 into a negative-pressure state lower than the atmosphere pressure, and a carbonation curing step of blowing gas containing carbon dioxide into the curing sheet 1 after the negative-pressure curing step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for carbonation curing of precast components containing γC2S. [Background technology]

[0002] Carbonation curing is currently being studied to improve the durability of precast concrete containing γ-phase dicalcium silicate (γ-2CaO·SiO2, hereafter referred to as γCS). Carbonation (neutralization) curing of concrete incorporating γCS has been shown to improve material barrier properties by densifying pores and chemical stability by improving leaching resistance. Furthermore, since constructing the entire component from highly durable materials is not always economical, it is important to improve the quality of the surface layer, which is the first line of defense for corrosion-causing substances. Furthermore, for concrete containing rebar, neutralization of only the surface layer is useful because it prevents carbonation from progressing deeper than the surface rebar and neutralizes below the cover of the surface rebar. This is useful because it maintains the passive film on the cover rebar while densifying the pore structure of the γCS, improving durability.

[0003] Patent Document 1 discloses a carbonation curing method for precast concrete containing γC2S (γ-belite), in which the cementitious material is demolded and then cured in the atmosphere at room temperature and normal pressure, and then carbonation curing is carried out after the material is 7 days old, thereby carbonate the surface layer of the concrete and increasing its resistance to calcium elution, etc. Patent Document 2 also discloses a carbonation curing method in which precast components are covered with a curing sheet, which is suctioned with a suction device to create a vacuum, and carbon dioxide is blown into the curing sheet, thereby densifying the components. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-182583 [Patent Document 2] Japanese Patent Application Publication No. 2023-169081 Summary of the Invention [Problem to be solved by the invention]

[0005] According to Patent Document 1, carbonation curing up to 28 days of age allows the thickness of the densified layer of concrete (carbonation depth) to be increased to 5 mm to 10 mm, but does not specify how to improve the efficiency of the curing period. Furthermore, Patent Document 2 does not specify how to improve the efficiency of the curing period for precast members containing γC2S, and like Patent Document 1, does not specify how to improve the efficiency of the curing period. Therefore, there is a problem in that it is not possible to improve the efficiency of carbonation curing for precast members containing γC2S.

[0006] The present invention has been devised in consideration of the above-mentioned problems, and its purpose is to provide a method for carbonation curing of precast members that improves the efficiency of carbonation curing of precast members containing γC2S. [Means for solving the problem]

[0007] The carbonation curing method for precast components in the first invention is characterized by comprising: an air curing step in which a precast component of a cement hardened body containing γCS is air-cured with its outer surface exposed to the atmosphere; a negative pressure curing step in which, after the air curing step, the outer surface is covered with a curing sheet and the air within the curing sheet is sucked out, thereby creating a negative pressure within the curing sheet that is lower than atmospheric pressure; and a carbonation curing step in which, after the negative pressure curing step, a gas containing carbon dioxide is blown into the curing sheet.

[0008] The carbonation curing method for precast members according to the second invention is characterized in that in the negative pressure curing step, the outer surface is covered with a curing sheet so that a desiccant is contained within the curing sheet.

[0009] The carbonation curing method for precast components in the third invention is characterized in that, in the first or second invention, in the negative pressure curing process, the air is continuously or intermittently sucked in without sealing the curing sheet. [Effects of the Invention]

[0010] According to the first to third inventions, the carbonation curing method includes an air curing step in which the precast member is subjected to air curing with its outer surface exposed to the atmosphere, a negative pressure curing step in which the outer surface of the precast member is covered with a curing sheet and a negative pressure is created within the curing sheet, and a carbonation curing step in which a gas containing carbon dioxide is blown into the curing sheet. This allows a densified layer of a predetermined carbonation depth to be formed on the surface of the precast member in a short period of time. This improves the efficiency of carbonation curing of precast members containing γCS.

[0011] In particular, according to the second aspect of the present invention, during the negative pressure curing process, the outer surface of the precast member is covered with a curing sheet so that the desiccant is contained within the curing sheet. This prevents moisture from escaping from the precast member under negative pressure or the humidity inside the curing sheet from increasing due to the influence of liquefied carbon dioxide gas used to supply carbon dioxide, and prevents a decrease in the rate of carbonation. This further improves the efficiency of carbonation curing of precast members containing γCS.

[0012] In particular, according to the third invention, in the negative pressure curing process, the air inside the curing sheet is continuously or intermittently suctioned without sealing the curing sheet. In other words, a negative pressure state is maintained inside the curing sheet by degassing. Therefore, compared to when the curing sheet is sealed under negative pressure, it is difficult to suppress the escape of moisture from the precast material, and the pores in the surface layer are more likely to dry out, forming pore voids and creating a negative pressure state. This further improves the efficiency of carbonation curing of precast materials containing γCS. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a carbonation curing method for precast members according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of a specimen of a precast member used in this example. [Figure 3] FIG. 3 is a graph showing the experimental results of the carbonation (carbonation) depth for this example. [Figure 4] FIG. 4 is a graph showing the experimental results of the compressive strength for this example. DETAILED DESCRIPTION OF THE INVENTION

[0014] An example of a carbonation curing method for a precast member C according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the components in each drawing are shown schematically for the purpose of explanation, and the size of each component and the size comparison between components may differ from those shown in the drawings.

[0015] (Carbonation curing method for precast member C) The carbonation curing method for the precast member C (hereinafter also simply referred to as the carbonation curing method) is carried out using a carbonation curing system 100, as shown in FIG. 1, for example.

[0016] First, the precast member C and the carbonation curing system 100 used in the carbonation curing method will be described.

[0017] <Precast member C> Precast component C is a hardened cement composite containing γC2S (γ-2CaO·SiO2), and concrete or mortar is used. Here, γC2S refers to the γ phase of di-calcium silicate.

[0018] When used as a structure, the precast member C may be a hardened cement body that uses a non-corrosive material such as carbon fiber, aramid fiber, or glass fiber as an internal reinforcement material that does not corrode, or a hardened cement body that uses a corrosive material such as steel bars.

[0019] The outer surface of each precast member C is partially or entirely covered with an airtight protective sheet 1. In the example of Figure 1, each precast member C is covered with a separate protective sheet 1, but multiple precast members C stacked vertically may be covered with a single protective sheet 1.

[0020] A plurality of precast members C may be stacked, for example, via spacers C'. As the spacers C', for example, a member having enough rigidity to support the precast members C from below may be used, and a member of the same quality as the precast members C may also be used.

[0021] <Carbonation Curing System 100> The carbonation curing system 100 includes, for example, a curing sheet 1, a carbon dioxide supply device 2, a suction device 3, an exhaust device 4, a carbon dioxide intake device 5, and a carbon dioxide concentration measuring device 6. The carbonation curing system 100 is, for example, portable.

[0022] The carbonation curing system 100 covers, for example, a precast component C, which is the object of carbonation curing, with a curing sheet 1, and creates a negative pressure inside the curing sheet 1 that is lower than atmospheric pressure by sucking the air inside the curing sheet 1 using a suction device 3. Then, a gas containing carbon dioxide is blown into the curing sheet 1 using a carbon dioxide supply device 2, generating calcium carbonate near the surface of the precast component C and immobilizing the carbon dioxide. This allows the surface of the precast component C to be carbonated. In the following explanation, the gas containing carbon dioxide will be simply referred to as carbon dioxide.

[0023] Here, "negative pressure state" refers to a state where the pressure is reduced below atmospheric pressure. More specifically, this refers to the vacuums described in, for example, ISO 3529-1 or JIS Z 8161-2, and includes low vacuums of 100 kPa to 100 Pa. Furthermore, by supplying carbon dioxide into the curing sheet 1 while maintaining a negative pressure lower than the surrounding atmospheric pressure, even if it does not reach a vacuum state, carbon dioxide can also be supplied into the pores of the precast member C, and a certain amount of calcium carbonate production can be promoted.

[0024] Therefore, the carbonation curing method of the present invention enables carbonation curing using the portable carbonation curing system 100, so no special location is required for carbonation curing even if the shape or quantity of the precast component C to be cured changes.

[0025] <Protection Sheet 1> The curing sheet 1 covers the outer surface of the precast member C. The curing sheet 1 maintains the interior at a negative pressure lower than atmospheric pressure, thereby enabling the precast member C to be negative-pressure cured.

[0026] The curing sheet 1 may be any packing material that is impermeable and gas-blocking, preventing water vapor and carbon dioxide from passing through to the outside air during the curing period of the precast member C, and that can maintain a negative pressure state. The curing sheet 1 may be, for example, a flexible bag or a box assembled from rigid sheets. The inside of the curing sheet 1 may be sealed, or it may be unsealed and partly open to the outside.

[0027] The protective sheet 1 is made of, for example, a resin material, and in addition to a resin sheet including a polyethylene sheet, a resin film including a nylon poly film in which a nylon resin film and a polyethylene resin film are laminated may be used.

[0028] <Carbon dioxide supply device 2> The carbon dioxide supplying device 2 is connected to the protective sheet 1 and supplies carbon dioxide into the protective sheet 1. As the carbon dioxide supplying device 2, for example, a known carbon dioxide generating device such as a liquefied carbon dioxide type may be used.

[0029] <Suction device 3> The suction device 3 is connected to the curing sheet 1 and is a device that sucks air from within the curing sheet 1 to create or maintain a negative pressure state. A known vacuum pump, for example, may be used as the suction device 3. For example, when the curing sheet 1 is not sealed, the suction device 3 sucks in a volume of air that is greater than the amount of air flowing into the curing sheet 1, thereby maintaining a negative pressure state within the curing sheet 1.

[0030] <Exhaust device 4> The exhaust device 4 is connected to the suction device 3 and is a device that exhausts the air discharged from the protective sheet 1 and adjusts the humidity inside the protective sheet 1. As the exhaust device 4, for example, a known air conditioning device may be used.

[0031] <Carbon dioxide inhalation device 5> The carbon dioxide intake device 5 is connected to the exhaust device 4 and is a device that collects air exhausted from the curing sheet 1. The carbon dioxide intake device 5 sucks in and collects excess carbon dioxide that did not contribute to the carbonation of the precast members C. The carbon dioxide intake device 5 may be connected to, for example, the carbon dioxide supply device 2. In this case, the carbonation curing system 100 can circulate the collected carbon dioxide and supply it into the curing sheet 1. As the carbon dioxide intake device 5, for example, a known compression tank or the like may be used.

[0032] <Carbon dioxide concentration measuring device 6> The carbon dioxide concentration measuring device 6 is a device that measures the carbon dioxide concentration within the protective sheet 1. As the carbon dioxide concentration measuring device 6, for example, a known carbon dioxide concentration meter may be used.

[0033] Next, as the carbonation curing method of this embodiment, we will explain the operation method of the carbonation curing system 100. The operation method of the carbonation curing system 100 includes, for example, an air curing step, a negative pressure curing step, and a carbonation curing step.

[0034] The negative pressure curing step and the carbonation curing step may be repeated until carbonation is completed to a predetermined carbonation depth. For example, the negative pressure curing step may be repeated for 3.5 to 7 days, and the carbonation curing step may be repeated for 3.5 to 7 days, for a total of 7 to 14 days. Furthermore, although an example in which concrete is used as the precast member C will be described, other hardened cement products such as mortar may also be used.

[0035] <Advance preparation> The worker mixes 1% to 40% γCS in binder ratio with fresh concrete as the target of the carbonation curing method, and pours it into a pre-arranged formwork. The worker then demolds the poured concrete after one day. The worker may also demold the concrete after subjecting it to atmospheric steam curing.

[0036] <Air curing process> In the air curing process, workers air-cure the demolded concrete until it is 8 days old. Air curing includes curing exposed to the air at ambient temperature as well as atmospheric steam curing. In other words, it does not interfere with the demolding process or finishing processes such as drying, which are commonly performed with precast concrete. In the air curing process, moisture near the surface of precast component C dissipates as it dries. However, since it takes a considerable amount of time for moisture to dissipate from inside the component, the air curing process does not inhibit the concrete from developing strength.

[0037] <Negative pressure curing process> In the negative pressure curing process, the workers performed air curing until the material was 8 days old, and the compressive strength was 23N / mm 2 For precast component C that has developed a degree of deterioration, the entire outer surface is covered with curing sheet 1, and a negative pressure state lower than atmospheric pressure is maintained within curing sheet 1 by suction using suction device 3, and negative pressure curing is carried out for up to 15 days. Because curing sheet 1 is used in the negative pressure curing process, negative pressure curing can be carried out under normal conditions without being restricted by the work site or stock status.

[0038] During the negative pressure curing process, workers may cover the outer surface of the precast component C so that a desiccant (not shown) is contained within the curing sheet 1. In this case, high humidity inside the curing sheet 1 due to the evaporation of water from the precast component C under negative pressure or the influence of liquefied carbon dioxide gas to supply carbon dioxide can be suppressed, and the rate of carbonation is less likely to decrease. This further improves the efficiency of carbonation curing of precast component C containing γCS. Note that silica gel, for example, may be used as the desiccant. Using a desiccant eliminates the need for drying equipment, reducing equipment costs.

[0039] Alternatively, the worker may continuously or intermittently suction the air from within the curing sheet 1 without sealing it. In other words, a negative pressure state is maintained within the curing sheet 1 by degassing. In this case, compared to when the curing sheet 1 is sealed under negative pressure, it is difficult to suppress the escape of moisture from the precast component C, and the pores in the surface layer tend to dry out, forming pore voids and creating a negative pressure state. This further improves the efficiency of carbonation curing of precast component C containing γCS.

[0040] <Carbonation curing process> In the carbonation curing process, the worker supplies carbon dioxide mixed with carbon dioxide through a path that has been previously connected between the curing sheet 1 and the carbon dioxide supply device 2. By filling the curing sheet 1 with carbon dioxide, the minimum necessary carbonation curing can be ensured, and carbonation can be completed without excess or deficiency on the surface layer of the precast member C.

[0041] Specifically, by supplying carbon dioxide into the curing sheet 1, the carbon dioxide is drawn into the pore spaces of the precast component C covered by the curing sheet 1 as the pressure returns from a negative state to atmospheric pressure, allowing the carbon dioxide to physically act within the pore spaces. In this case, a densified layer of a predetermined carbonation depth can be formed on the surface of the precast component C in a short period of time. This improves the efficiency of carbonation curing of the precast component C containing γCS. The benefits of carbonation curing of the precast component C according to the present invention will be explained in the examples below.

[0042] When the inside of the curing sheet 1 is wet, the pore spaces of the precast member C are also wet, preventing carbon dioxide from penetrating, and carbonation in the pore spaces is difficult to progress. Furthermore, when the inside of the curing sheet 1 is bone dry, carbon dioxide can penetrate the pore spaces, but if it is so dry that no liquid (pore solution) exists in the pore spaces, the carbonation reaction with calcium ions dissolved in the pore solution does not occur, preventing carbonation. Therefore, it is preferable that the relative humidity in the curing sheet 1 be between 40% and 70% RH.

[0043] Through the above steps, the operation of the carbonation curing system 100 of this embodiment is completed, and the carbonation curing method is completed.

[0044] After the carbonation curing process was completed, the compressive strength of precast element C was approximately 100 N / mm2 in the carbonated area on the surface. 2 and 24N / mm, which is the design standard for the strength level of general concrete members. 2 ~50N / mm 2 In this respect, a layer with a higher strength can be formed compared to the conventional technology, which has a strength of about 100 N / mm 2 In order to provide concrete members with a strength of approximately 100 N / mm, it is common to add silica fume or increase the amount of cement used, which significantly increases material costs. In addition, there is a concern that the silica fume may become granulated if transported over a long period of time, resulting in variations in quality. On the other hand, the carbonation curing method of the present invention can easily achieve a surface compressive strength of approximately 100 N / mm without using silica fume.2 This allows us to provide precast components C of 31.6N / mm², which improves economy and quality stability. In addition, in the internal uncarbonated area, self-hydration continues, resulting in a compressive strength of approximately 31.6N / mm². 2 This region also achieves the strength level of the above design criteria.

[0045] Furthermore, if the precast component C includes exposed connecting rebars, carbonation curing can be limited by covering the surface of the rebars with sealing or the like, which is useful because it prevents problems such as the loss of the passive film on the rebars due to carbonation.

[0046] (Variations of carbonation curing method for precast materials) The carbonation curing system 100 may further include, for example, a calcium hydroxide water supply device 7. The carbonation curing system 100 performs further carbonation curing by supplying calcium hydroxide water (lime water) to the precast member C in which carbon dioxide has been fixed via the calcium hydroxide water supply device 7, thereby forming an even stronger and denser layer on the surface of the carbonated layer.

[0047] The calcium hydroxide water supply device 7 is a device that supplies calcium hydroxide water to the precast members C. At this time, the supply of calcium hydroxide water and carbon dioxide promotes carbonation of the surface layer of the precast members C, producing calcium carbonate. The calcium hydroxide water supply device 7 may be configured, for example, with a known tank for storing calcium hydroxide water and a water pump.

[0048] The calcium hydroxide solution may be water (recovered water) from which aggregate has been removed, such as wastewater from washing vehicles and mixers at ready-mix concrete plants and precast product plants, or from laitance treatment water. Recovered water is divided into highly alkaline supernatant water containing calcium hydroxide eluted from cement, and sludge water containing sludge solids (mostly hydration products, with some aggregate particles), with supernatant water being preferred. The plant is required to neutralize the recovered water before discharging it for general use. Using the recovered water as carbonated curing water reduces the consumption of recovered water and neutralizes any remaining water, reducing the amount of reagents used during the neutralization process.

[0049] During the carbonation curing process, workers may supply carbon dioxide into the curing sheet 1 to promote carbonation, and then supply calcium hydroxide water to the same curing sheet 1 through a path that connects the curing sheet 1 and the calcium hydroxide water supply device 7 in advance. In this case, the precast component C undergoes further carbonation curing, and a densified layer approximately three times the design strength is formed on the surface of the carbonated layer formed by contact with carbon dioxide. Furthermore, this densified layer significantly reduces the penetration of corrosion-causing substances compared to the carbonated layer. This improves the quality of the surface layer of the precast component C containing γCS. Furthermore, because the depth of the carbonated layer does not exceed a maximum of approximately 30 mm from the surface, increasing the cover depth beyond this maintains an alkaline environment around the surface rebar and maintains the integrity of the passive film. This improves the durability of the precast component C containing γCS and rebar.

[0050] In the precast member C, calcium hydroxide water dissolves in the pore solution, causing a reaction between calcium ions and carbon dioxide to form carbon dioxide. Therefore, a higher temperature facilitates the dissolution of calcium hydroxide water and also increases the rate of the carbonation reaction of the dissolved calcium ions. For example, the carbonation rate at 40°C is about twice as fast as that at 20°C. Therefore, in the carbonation curing method according to this embodiment, it is preferable to supply carbon dioxide while maintaining the temperature inside the curing sheet 1 higher than the ambient temperature.

[0051] Furthermore, in the carbonation curing process, the worker may blow carbon dioxide into the calcium hydroxide water supplied into the curing sheet 1. Specifically, calcium hydroxide water is sprayed onto the precast components C in the curing sheet 1 to allow them to absorb the water, and then carbon dioxide is supplied into the curing sheet 1 to promote carbonation of the surface layer of the precast components C. As a result, carbon dioxide is blown into the calcium hydroxide water on the surface of the precast components C, producing calcium carbonate.

[0052] Alternatively, calcium hydroxide water may be supplied into the curing sheet 1 while the precast components C are undergoing carbonation curing within the curing sheet 1, and then carbon dioxide may be supplied to generate calcium carbonate in the precast components C and immobilize the carbon dioxide. In this case, carbonation proceeds before the surface layer of the precast components C becomes densified. This further improves the efficiency of carbonation curing of the precast components C containing γCS.

[0053] Alternatively, without using the calcium hydroxide water supply device 7, calcium hydroxide water may be sprayed onto the outer surface of the precast component C, and then the precast component C with the calcium hydroxide water sprayed onto its outer surface may be inserted into the curing sheet 1, and carbon dioxide gas may be supplied by creating a negative pressure inside the curing sheet 1. In this case as well, the action of the calcium hydroxide water sprayed on the outer surface can promote the production of calcium carbonate and fix the carbon dioxide.

[0054] Furthermore, in the carbonation curing method according to this embodiment, the spraying of calcium hydroxide water and the supply of carbon dioxide may be repeated to generate more calcium carbonate and immobilize more carbon dioxide in the precast component C. However, as carbonation of the surface layer of the precast component C progresses, the surface layer of the precast component C also becomes more densified, which may inhibit further carbonation. Therefore, in the carbonation curing method according to this embodiment, it is preferable to supply carbon dioxide without spraying calcium hydroxide water at the beginning of the curing period, and then to repeatedly spray calcium hydroxide water and supply carbon dioxide to the precast component C. It is preferable to repeat the supply of calcium hydroxide water and carbon dioxide a predetermined number of times until the densification of the precast component C through the generation of calcium carbonate and the immobilization of carbon dioxide reach a certain depth from the surface. This thickens the layer of calcium carbonate generated, allowing more carbon dioxide to be immobilized.

[0055] Furthermore, after calcium hydroxide water is supplied into the curing sheet 1, the excess calcium hydroxide water may be sucked out and then carbon dioxide may be supplied from the carbon dioxide supply device 2. In this case, a densified calcium carbonate layer is formed on the surface of the precast member C, and carbon dioxide is trapped in the pores contained in the calcium carbonate layer, allowing the generation of calcium carbonate inside the precast member C to continue.

[0056] According to this embodiment, the carbonation curing method includes an air curing step in which the precast component C is air-cured with its outer surface exposed to the atmosphere, a negative-pressure curing step in which the outer surface of the precast component C is covered with a curing sheet 1 and a negative pressure is created inside the curing sheet, and a carbonation curing step in which a gas containing carbon dioxide is blown into the curing sheet 1. This allows a densified layer of a predetermined carbonation depth to be formed on the surface of the precast component C in a short period of time. This improves the efficiency of carbonation curing of the precast component C containing γCS.

[0057] Furthermore, according to this embodiment, in the negative pressure curing process, the outer surface of the precast component C is covered so that the desiccant is contained within the curing sheet 1. This prevents moisture from escaping from the precast component C under negative pressure or the humidity inside the curing sheet 1 from increasing due to the influence of liquefied carbon dioxide gas used to supply carbon dioxide, and the rate of carbonation is less likely to decrease. This further improves the efficiency of carbonation curing of precast component C containing γCS.

[0058] Furthermore, according to this embodiment, in the negative pressure curing process, the curing sheet 1 is not sealed and the air inside the curing sheet 1 is continuously or intermittently suctioned. In other words, a negative pressure state is maintained inside the curing sheet 1 by degassing. Therefore, compared to when the curing sheet 1 is sealed under negative pressure, it is difficult to suppress the escape of moisture from the precast component C, and the pores in the surface layer tend to dry out, forming pore voids and creating a negative pressure state. This further improves the efficiency of carbonation curing of precast component C containing γCS. [Example]

[0059] The carbonation curing method of the present invention was compared with other methods in terms of the carbonation (carbonation) depth from the surface of a rectangular pillar and the compressive strength when carbonation curing was performed, to confirm the efficiency of carbonation curing. In this example, the carbonation curing method of the present invention was designated as the present invention example, an example in which the present invention was applied to a cured body that did not contain γCS was designated as comparative example 1, and other methods were designated as comparative examples 2 to 3. Furthermore, the carbonation depth was compared between the present invention example and comparative examples 1 to 3, and the compressive strength was compared between the present invention example and comparative examples 2 and 3.

[0060] The specimens were made by pouring mortar with a water-cement ratio of 55%, high-early-strength cement, and γC2S (30% cement replacement) to form square columns measuring 40 mm wide x 40 mm deep x 160 mm high, as shown in Figure 2. In Comparative Example 1 only, a square column of the same shape was formed without replacing γC2S.

[0061] In the carbonation curing method used in this example, two opposing sides (40 mm deep x 160 mm high) of the surface of the rectangular column of the specimen, which was removed from the form after one day of age, were exposed, and the other four sides were sealed, thereby promoting neutralization on only the two side surfaces.

[0062] The carbonation curing conditions are as shown in Table 1. The material age in the table refers to the number of days elapsed since the day the specimen was demolded (material age 0 days). The carbonation curing process was carried out for each specimen up to three cycles. The specimens used in each cycle were independent of each other.

[0063] [Table 1]

[0064] For the invention example and comparative example 1, one cycle of carbonation curing was carried out by carrying out an air curing step at material ages 1 to 7 days, a negative pressure curing step at material ages 8 to 14 days, and a carbonation curing step at material ages 15 to 21 days. Furthermore, two cycles of carbonation curing were carried out by carrying out a negative pressure curing step at material ages 22 to 28 days after one cycle of carbonation curing, and a further carbonation curing step at material ages 29 to 35 days.

[0065] In Comparative Example 2, no air curing step was performed. Specifically, as a one-cycle carbonation curing method, a carbonation curing step was performed at material ages 1 to 7 days, a negative pressure curing step was performed at material ages 8 to 14 days, and a carbonation curing step was performed at material ages 15 to 21 days. Furthermore, as a two-cycle carbonation curing method, after one carbonation curing cycle, a negative pressure curing step was performed at material ages 22 to 28 days, and a carbonation curing step was further performed at material ages 29 to 35 days. Furthermore, as a three-cycle carbonation curing method, after two carbonation curing cycles, a negative pressure curing step was performed at material ages 36 to 42 days, and a carbonation curing step was further performed at material ages 43 to 49 days.

[0066] In Comparative Example 3, the air curing step and the negative pressure curing step were not performed. Specifically, as a one-cycle carbonation curing method, a drying step was performed at material ages 1 to 7 days and a carbonation curing step was performed at material ages 8 to 14 days. Furthermore, as a two-cycle carbonation curing method, after one cycle of carbonation curing, a drying step was performed at material ages 15 to 21 days and a carbonation curing step was further performed at material ages 22 to 28 days.

[0067] In the air curing step of the invention example and comparative example 1, the test specimen was left uncovered with the outer surface exposed to the atmosphere without being covered with the curing sheet 1. In the drying step of comparative example 3, the test specimen was covered and sealed with the curing sheet 1, and silica gel (desiccant) was enclosed within the curing sheet 1 at an average temperature of 18.5°C and an average relative humidity of 50.6%RH. The material used for the curing sheet 1 was ONy15 / LDPE20 / L-LDPE70 (low-density polyethylene).

[0068] In the negative pressure curing process of the invention example and comparative example 1, the curing sheet 1 was left open, and the air inside the curing sheet 1 was sucked out to maintain the air pressure at approximately -0.095 MPa to -0.080 MPa. Silica gel (desiccant) was enclosed inside the curing sheet 1 under conditions of an average temperature of 20°C and an average relative humidity of 60% RH.

[0069] In the carbonation curing process of the present invention examples and comparative examples 1 to 3, the curing sheet 1 was sealed, and gas containing carbon dioxide generated from liquefied carbon dioxide was supplied into the curing sheet 1 by repeatedly sealing and leaving it for 7 days at an average temperature of 20.3°C and an average relative humidity of 50.1%RH.

[0070] The evaluation methods for this example were the carbonation depth measured from the side surface in the depth direction and the compressive strength against a load measured from the side surface in the depth direction. Since the carbonation depth measured from two opposing side surfaces in the depth direction can be evaluated up to 20 mm, which corresponds to half of a 40 mm width as shown in Figure 2, 20 mm was set as the upper evaluation limit for the carbonation depth. After completing each cycle for the present invention example and comparative examples 1 to 3, the square columns were split into four equal parts, and the cross sections were contacted with a phenolphthalein solution to measure the carbonation depth. Furthermore, the compressive strength of the specimens with the dimensions shown in Figure 2 was measured using a 5000 kN pressure tester.

[0071] First, the experimental results of the neutralization depth are shown in Figure 3.

[0072] The carbonation depth of the inventive example was 19.6 mm at the end of one cycle and 20.0 mm (upper evaluation limit) at the end of two cycles. The carbonation depth of comparative example 1 was 11.0 mm at the end of one cycle and 14.5 mm at the end of two cycles. The carbonation depth of comparative example 2 was 10.7 mm at the end of one cycle, 18.6 mm at the end of two cycles, and 20.0 mm (upper evaluation limit) at the end of three cycles. The carbonation depth of comparative example 3 was 14.2 mm at the end of one cycle and 18.6 mm at the end of two cycles.

[0073] That is, it was found that the carbonation depth of the Inventive Example improved earlier than that of Comparative Examples 1 to 3. In particular, the carbonation depth of the Inventive Example was 19.6 mm after one cycle, confirming that carbonation had progressed more than that of Comparative Examples 2 and 3, which had a carbonation depth of 18.6 mm after two cycles. This is thought to be because the pore spaces of the specimen dried during the air curing process, making it easier for carbon dioxide to be mixed in. Furthermore, the carbonation depth of the Inventive Example was more than twice as deep as that of Comparative Example 1, confirming that carbonation had progressed more. This is thought to be because the addition of γCS facilitated the progress of carbonation.

[0074] As described above, according to the carbonation curing method of the present invention, a densified layer of a predetermined neutralization depth can be formed on the surface of the precast component C in a short period of time, thereby improving the efficiency of carbonation curing of the precast component C containing γC2S.

[0075] Next, the results of the compressive strength experiment are shown in Figure 4.

[0076] The compressive strength of the example of the present invention was 98.7 N / mm at the end of one cycle. 2 At the end of the second cycle, the force was 106.2N / mm 2 The compressive strength of Comparative Example 2 was about 63.4 N / mm at the end of one cycle. 2 At the end of the second cycle, the force was 108.8N / mm 2 At the end of the third cycle, the force was 114.6N / mm 2 The compressive strength of Comparative Example 3 was 81.7 N / mm at the end of one cycle. 2 At the end of the second cycle, the force was 107.8N / mm 2 It was.

[0077] That is, similar to the results of comparing the carbonation depth, it was found that the compressive strength of the inventive example improved earlier than that of comparative examples 2 and 3. This is thought to be because the dense region increased in response to the increase in the carbonation depth region, resulting in an increase in compressive strength. Furthermore, it is clear from previous literature that the specimens of the inventive example had a dense pore structure due to their high compressive strength, which naturally resulted in improved resistance to salt penetration.

[0078] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0079] 100 Carbonation Curing System 1. Protective sheet 2 Carbon dioxide supply device 3 Suction device 4. Exhaust system 5. Carbon dioxide inhalation device 6. Carbon dioxide concentration measuring device 7. Calcium hydroxide water supply device C Precast members

Claims

1. γC 2 an air curing step of air curing a precast member of a cement hardened body containing S with its outer surface exposed to the atmosphere; After the air curing process, a negative pressure curing process is performed in which the outer surface is covered with a curing sheet and the air in the curing sheet is sucked to create a negative pressure state in the curing sheet that is lower than atmospheric pressure. After the negative pressure curing step, a carbonation curing step of blowing a gas containing carbon dioxide into the curing sheet; Having A carbonation curing method for precast components, characterized by:

2. In the negative pressure curing step, the outer surface is covered so that the desiccant is contained within the curing sheet.

2. The carbonation curing method for precast members according to claim 1,

3. In the negative pressure curing step, the air is continuously or intermittently sucked without sealing the curing sheet.

3. The carbonation curing method for precast members according to claim 1 or 2, characterized in that:

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