Method for curing concrete structure and method for producing precast concrete product

Abstract

To provide a method for curing a concrete structure, capable of increasing compressive strength of a concrete structure to a level comparable to that of water curing by sprinkling curing, and to provide a method for producing a precast concrete product using the same.SOLUTION: A method according to the present invention for curing a concrete structure obtained by placing concrete material into a mold and then demolding includes a sprinkling-and-curing step of sprinkling curing water containing a surfactant onto a surface of the concrete structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for curing a concrete structure and a method for manufacturing a precast concrete product. [Background technology]

[0002] Precast concrete products are concrete structures that are manufactured in advance in a factory or other facility. They are obtained by pouring a concrete composition into a formwork, subjecting it to a primary curing process, and then demolding it. Precast concrete products are stored in a stockyard for a specified period of time before being shipped.

[0003] When precast concrete products are stored until their guaranteed strength age, the concrete structure obtained after demolding is subjected to secondary curing as a second curing step. Examples of secondary curing include air curing, in which the concrete structure is left in an environment where it is in direct contact with the outside air, and underwater curing, in which the concrete structure is immersed in water.

[0004] However, air curing is prone to thermal cracks on the surface of the concrete structure due to the temperature difference between the concrete structure and the outside air, and fine cracks are likely to occur due to the evaporation of moisture as the concrete dries, which not only damages the appearance of the precast concrete product surface but also affects its durability. Compared to air curing, underwater curing increases the strength and durability of precast concrete products and does not damage the appearance of the precast concrete product surface, but requires the installation of dedicated facilities, which makes it subject to space restrictions.

[0005] Therefore, in order to solve the above problems, water spray curing, in which curing water is sprayed onto the concrete structure obtained after demolding, has been considered as a secondary curing method (for example, Non-Patent Document 1). Water spray curing is a curing method in which moisture is supplied by spraying water onto the concrete structure using a sprinkler, sprayer, etc. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Effect of Water Spray Curing on Secondary Curing of Precast Concrete, Abstracts of the 74th Annual Conference of the Japan Society of Civil Engineers, Vol. V-266, 2019 (Yamazaki Ryuji, Uno Hiroshiki, Hashimoto Shinichiro, Date Shigeyuki) Summary of the Invention [Problem to be solved by the invention]

[0007] However, although the water spray curing described in Non-Patent Document 1 increases the strength of the concrete structure compared to air curing, it is difficult to increase the strength of the concrete structure compared to underwater curing. Therefore, there is room for improvement in conventional water spray curing, and it has not yet been put to practical use.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a method for curing a concrete structure that can increase the compressive strength of a concrete structure by water spray curing to the same extent as by underwater curing, and a method for manufacturing a precast concrete product using this method for curing a concrete structure. [Means for solving the problem]

[0009] The method for curing a concrete structure according to the present invention is a method for curing a concrete structure obtained by pouring concrete material into a formwork and then removing the formwork, and includes a spray curing step of spraying curing water containing a surfactant onto the surface of the concrete structure.

[0010] The method for curing a concrete structure according to the present invention, configured as described above, allows the curing water to easily penetrate the surface of the concrete structure, thereby easily increasing the compressive strength of the concrete structure. Therefore, the method for curing a concrete structure according to the present invention makes it possible to increase the compressive strength of the concrete structure by water spray curing to the same extent as by underwater curing.

[0011] In the method for curing a concrete structure according to the present invention, in the water spray curing step, the curing water may be sprayed onto the concrete structure within 60 minutes after the concrete structure is removed from the formwork.

[0012] The method for curing a concrete structure according to the present invention, which has such a configuration, makes it possible to increase the compressive strength of the concrete structure in an early stage to the same extent as underwater curing.

[0013] In the method for curing a concrete structure according to the present invention, in the water spray curing step, the curing water may be sprayed onto the concrete structure for at least 10 minutes.

[0014] The method for curing a concrete structure according to the present invention, which has such a configuration, makes it possible to increase the compressive strength of the concrete structure in an early stage to the same extent as underwater curing.

[0015] In the method for curing a concrete structure according to the present invention, the surfactant may be an amine-based surfactant or a sulfosuccinate-based surfactant.

[0016] With this configuration, the method for curing a concrete structure according to the present invention allows the curing water to penetrate more easily into the surface of the concrete structure, and therefore makes it possible to increase the strength of the concrete structure more quickly to the same extent as underwater curing.

[0017] In the method for curing a concrete structure according to the present invention, the curing water may contain bubbles.

[0018] According to the above-described configuration of the method for curing a concrete structure of the present invention, bubbles adhere to the surface of the concrete structure, thereby keeping the surface of the concrete structure warm, thereby suppressing surface cracks.

[0019] In the method for curing a concrete structure according to the present invention, the amount of surfactant contained in the curing water is 0.2 mass % or more and 4.0 mass % or less based on the total amount of the curing water.

[0020] With this configuration, the method for curing a concrete structure according to the present invention allows curing water to penetrate more easily into the surface of the concrete structure, and therefore makes it possible to increase the compressive strength of the concrete structure more quickly, to the same extent as underwater curing.

[0021] The method for manufacturing a precast concrete product according to the present invention includes a pouring step in which concrete material is poured into a formwork, a primary curing step in which primary curing is carried out after pouring, a demolding step in which the concrete is demolded to obtain a concrete structure, and a spray curing step in which curing water containing a surfactant is sprayed onto the surface of the concrete structure.

[0022] According to the above-described configuration, the method for manufacturing precast concrete products of the present invention makes it possible to manufacture precast concrete products by water spray curing, which have increased compressive strength to the same extent as precast concrete products manufactured by underwater curing. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a method for curing a concrete structure that can increase the compressive strength of a concrete structure by water spray curing to the same extent as by underwater curing, and a method for manufacturing a precast concrete product that utilizes the method for curing a concrete structure. DETAILED DESCRIPTION OF THE INVENTION

[0024] The method for curing a concrete structure and the method for manufacturing a precast concrete product according to this embodiment will be described below.

[0025] <Curing method for concrete structures> The method for curing a concrete structure according to this embodiment is a method for curing a concrete structure obtained by pouring concrete material into a formwork and then removing the formwork, and includes a spray curing step in which curing water containing a surfactant is sprayed onto the surface of the concrete structure.

[0026] The concrete material may include cement, aggregate, and water.

[0027] The cement is not particularly limited, and examples thereof include Portland cements such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, low-heat Portland cement, moderate-heat Portland cement, and sulfate-resistant Portland cement as defined in JIS R 5210:2019; mixed cements such as blast-furnace cement, fly ash cement, and silica cement; white Portland cement, ultra-high-speed hardening cement, and alumina cement. One type of cement may be used alone, or two or more types may be used in combination.

[0028] Fine aggregate and / or coarse aggregate can be used as aggregate. Fine aggregate is defined as aggregate that passes entirely through a 10 mm mesh sieve and at least 85% by mass passes through a 5 mm mesh sieve, while coarse aggregate is defined as aggregate that is retained by at least 85% by mass on a 5 mm mesh sieve (JIS A 0203:2019).

[0029] Examples of fine aggregates include naturally occurring sands such as river sand, land sand, mountain sand, sea sand, crushed sand, and crushed limestone sand, as specified in JIS A 5308:2024 Appendix JA Aggregates for Ready-Mixed Concrete; sands derived from slags such as blast furnace slag, electric furnace oxidized slag, and ferronickel slag; recycled aggregates; artificial lightweight aggregates; and recycled aggregates. Silica sand produced by crushing and classifying silica may also be used. One type of fine aggregate may be used alone, or two or more types may be used in combination.

[0030] The coarse aggregate is not particularly limited, and examples thereof include natural aggregates such as river gravel, mountain gravel, and sea gravel, as specified in JIS A 5308:2024 Appendix JA Aggregates for Ready-Mixed Concrete, artificial aggregates such as crushed stone such as sandstone, hard limestone, basalt, and andesite, and recycled aggregate, etc. One type of coarse aggregate may be used alone, or two or more types may be used in combination.

[0031] The water is not particularly limited, and examples thereof include tap water, industrial water, recycled water, groundwater, river water, and rainwater. The water preferably does not contain organic matter, chloride ions, sodium ions, potassium ions, and the like, which have adverse effects on the hydration reaction of the cement composition and on the concrete, or contains only trace amounts of such ions. The water is more preferably tap water or industrial water of stable quality.

[0032] The concrete material may contain admixtures as needed. Examples of admixtures include air-entraining agents, air-entraining water-reducing agents, high-performance water-reducing agents, superplasticizers, separation-reducing agents, set retarders (e.g., tartaric acid), set accelerators (e.g., aluminum sulfate), quick-setting agents, shrinkage-reducing agents, foaming agents, and waterproofing agents. One type of admixture may be used alone, or two or more types may be used in combination.

[0033] Furthermore, concrete materials may contain admixtures as needed. Examples of admixtures include inorganic fine powders such as fly ash, silica fume, cement kiln dust, blast furnace fume, ground granulated blast furnace slag, ground granulated blast furnace slag, ground granulated converter slag, gypsum hemihydrate, expansive additives, limestone fine powder, quicklime fine powder, and dolomite fine powder, as well as inorganic fillers such as sodium bentonite, calcium bentonite, attapulgite, sepiolite, activated clay, acid clay, allophane, imogolite, shirasu (volcanic ash), shirasu balloons, kaolinite, metakaolin (calcined clay), synthetic zeolite, artificial zeolite, mordenite, and clinoptilolite. These admixtures may be used singly or in combination.

[0034] The watering method in the watering curing step is not particularly limited, and examples thereof include methods of watering using a hose, shower, sprinkler, sprayer, etc.

[0035] In the method for curing a concrete structure according to this embodiment, from the viewpoint of increasing the compressive strength of the concrete structure quickly to the same extent as underwater curing, in the spray curing step, the curing water is sprayed onto the concrete structure preferably within 60 minutes after the form is removed, more preferably within 30 minutes after the form is removed, and particularly preferably within 10 minutes after the form is removed.

[0036] In the method for curing a concrete structure according to this embodiment, from the viewpoint of increasing the compressive strength of the concrete structure quickly to the same extent as underwater curing, in the spray curing step, curing water is preferably sprayed on the concrete structure for at least 10 minutes, more preferably for at least 30 minutes.

[0037] Examples of surfactants include amine surfactants and sulfosuccinate surfactants. Among these, from the viewpoint of increasing the compressive strength of the concrete structure quickly to the same extent as in underwater curing, the surfactant is preferably an amine surfactant or sulfosuccinate surfactant, and more preferably an amine surfactant. The surfactant may be used alone or in combination of two or more types.

[0038] Examples of amine surfactants include triethanolamine, short-carbon-chain amine oxide surfactants, long-carbon-chain amine oxide surfactants, and tripropanolamine. Among these, from the viewpoint of increasing the compressive strength of concrete structures quickly to the same extent as underwater curing, the amine surfactant is preferably triethanolamine, a short-carbon-chain amine oxide surfactant, or a long-carbon-chain amine oxide surfactant, and more preferably a short-carbon-chain amine oxide surfactant or a long-carbon-chain amine oxide surfactant. One type of amine surfactant may be used alone, or two or more types may be used in combination.

[0039] The surfactant may be a commercially available surfactant. Examples of commercially available surfactants include Cadenax DM10D-W (manufactured by Lion Specialty Chemicals Co., Ltd.), Cadenax DM12D-W(C) (manufactured by Lion Specialty Chemicals Co., Ltd.), and Repearl 870P (manufactured by Lion Specialty Chemicals Co., Ltd.). Commercially available surfactants that contain at least 10% by mass of the main component may be used.

[0040] The amount of surfactant contained in the curing water is preferably 0.2% by mass or more and 4.0% by mass or less, and more preferably 0.2% by mass or more and 2.0% by mass or less, based on the total amount of curing water, from the viewpoint of increasing the compressive strength of the concrete structure quickly to the same extent as in underwater curing.

[0041] In one aspect of the curing method for a concrete structure according to this embodiment, the curing water contains bubbles in order to suppress surface cracking. That is, bubbles may be generated in the curing water, and then the curing water may be sprayed onto the surface of the concrete structure. The method for generating bubbles in the curing water is not particularly limited, and examples thereof include passing the curing water through a pump; heating the curing water; adding a foaming agent to the curing water; pumping compressed air and the curing water through a column filled with metal mesh or beads; and stirring the curing water at high speed.

[0042] In another aspect of the curing method for a concrete structure according to the present embodiment, the curing water sprayed on the surface of the concrete structure contains bubbles. That is, bubbles may be generated in the sprayed curing water after the curing water is sprayed on the surface of the concrete structure. The method for generating bubbles in the sprayed curing water is not particularly limited, and examples thereof include a method in which the curing water is left to stand.

[0043] When bubbles are generated in the curing water, the expansion ratio is preferably 5.0 to 50.0 times, more preferably 10.0 to 20.0 times, the volume of the curing water before foaming, from the viewpoint of promoting the heat retention effect.

[0044] From the viewpoint of suppressing surface cracking, the temperature of the curing water is preferably 5°C or higher and 65°C or lower, and more preferably 20°C or higher and 40°C or lower.

[0045] The method for curing a concrete structure according to this embodiment is a method for curing a concrete structure obtained by pouring concrete material into a formwork and then removing the formwork, and includes a spray curing step in which curing water containing a surfactant is sprayed onto the surface of the concrete structure. This makes it easier for the curing water to penetrate the surface of the concrete structure than when ordinary water is used as the curing water, making it easier to increase the compressive strength of the concrete structure. Therefore, spray curing can increase the compressive strength of the concrete structure to the same extent as underwater curing.

[0046] In the curing method for a concrete structure according to this embodiment, the curing water is sprayed onto the concrete structure within 60 minutes of demolding in the spray curing step, thereby enabling the compressive strength of the concrete structure to be increased quickly to the same extent as underwater curing.

[0047] In the curing method for a concrete structure according to this embodiment, the curing water is sprayed onto the concrete structure for at least 10 minutes during the spray curing process, thereby enabling the compressive strength of the concrete structure to be increased quickly to the same level as that achieved by underwater curing.

[0048] In the method for curing a concrete structure according to this embodiment, the surfactant is an amine-based surfactant or a sulfosuccinate-based surfactant, which allows the curing water to penetrate more easily into the surface of the concrete structure, thereby enabling the strength of the concrete structure to be increased more quickly to the same extent as in underwater curing.

[0049] In the method for curing a concrete structure according to this embodiment, the curing water contains bubbles, which adhere to the surface of the concrete structure, thereby keeping the surface warm and preventing surface cracks.

[0050] In the method for curing a concrete structure according to this embodiment, the amount of surfactant contained in the curing water is 0.2% by mass or more and 4.0% by mass or less relative to the total amount of the curing water, which allows the curing water to penetrate more easily into the surface of the concrete structure, and therefore it is possible to increase the strength of the concrete structure by spray curing to a level similar to that achieved by underwater curing.

[0051] <Manufacturing method for precast concrete products> The method for manufacturing a precast concrete product according to this embodiment includes a pouring step in which concrete material is poured into a formwork, a primary curing step in which primary curing is carried out after pouring, a demolding step in which the concrete is demolded to obtain a concrete structure, and a spray curing step in which curing water containing a surfactant is sprayed onto the surface of the concrete structure.

[0052] The concrete material may be the same as the concrete material used in the curing method for a concrete structure according to the present embodiment.

[0053] The casting step is carried out by pouring concrete material into a formwork.

[0054] The primary curing step is carried out by subjecting the poured concrete material to primary curing after the pouring step.

[0055] The primary curing is not particularly limited, and examples thereof include formwork curing, heat curing, and heat-retaining curing.

[0056] The heat curing is not particularly limited, and examples thereof include steam curing, hot water curing, hot air curing, and autoclave curing.

[0057] The curing temperature in the primary curing is not particularly limited, and may be, for example, 5°C or higher and 80°C or lower.

[0058] The holding time for the primary curing is not particularly limited, and may be, for example, 5 hours or more and 72 hours or less at a curing temperature of 5° C. or more.

[0059] The demolding step is carried out by demolding the concrete material that has been subjected to the primary curing step, thereby obtaining a concrete structure.

[0060] The timing of demolding is not particularly limited, and may be, for example, a time when the concrete structure has enough strength to prevent harmful damage when it is lifted after demolding.

[0061] The water spray curing step is carried out by spraying curing water containing a surfactant onto the surface of the concrete structure.

[0062] The water spray curing step can be carried out in the same manner as the curing method for a concrete structure according to the present embodiment described above.

[0063] Examples of the timing for sprinkling water include the time when the concrete structure is transported to a stockyard or a transport vehicle after the concrete material that has been subjected to primary curing has been demolded, the time when the concrete structure is stored in a stockyard, etc. Among these, from the viewpoint of early shipping of precast concrete products, the timing for sprinkling water is preferably the time when the concrete structure is transported to a stockyard or a transport vehicle after the concrete material that has been subjected to primary curing has been demolded.

[0064] The method for manufacturing a precast concrete product according to this embodiment includes a pouring step in which concrete material is poured into a formwork, a primary curing step in which primary curing is carried out after pouring, a demolding step in which the concrete is demolded to obtain a concrete structure, and a spray curing step in which curing water containing a surfactant is sprayed onto the surface of the concrete structure. This makes it possible to manufacture precast concrete products with increased compressive strength by spray curing, to the same extent as precast concrete products manufactured by underwater curing.

[0065] The method for curing a concrete structure and the method for manufacturing a precast concrete product according to the present invention are not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0066] The present invention includes the following aspects. [1] A method for curing a concrete structure obtained by pouring concrete material into a formwork and then removing the formwork, comprising: A method for curing a concrete structure, comprising a water spray curing step of spraying curing water containing a surfactant onto the surface of the concrete structure. [2] The method for curing a concrete structure according to [1], wherein in the water spray curing step, the curing water is sprayed onto the concrete structure within 60 minutes after demolding. [3] The method for curing a concrete structure according to [1] or [2], wherein the curing water is sprayed onto the concrete structure for at least 10 minutes in the spray curing step. [4] The method for curing a concrete structure according to any one of [1] to [3], wherein the surfactant is an amine-based surfactant or a sulfosuccinate-based surfactant. [5] The method for curing a concrete structure according to any one of [1] to [4], wherein the curing water contains bubbles. [6] The method for curing a concrete structure according to any one of [1] to [5], wherein the amount of surfactant contained in the curing water is 0.2 mass % or more and 4.0 mass % or less based on the total amount of the curing water. [7] A pouring step of pouring concrete material into a formwork; After pouring, a primary curing process is performed. a demolding step of obtaining a concrete structure by demolding; and a spray curing step of spraying curing water containing a surfactant onto the surface of the concrete structure. [Example]

[0067] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0068] [Examples 1 to 36] <Preparation of curing water> Using water and each surfactant shown in Table 1, the surfactant was added to the water to give the concentration shown in Tables 3 to 8, and the mixture was mixed at a water temperature of 20°C to obtain curing water.

[0069] <Preparation of test specimen> Using the raw materials shown in Table 1 and in accordance with the formulations shown in Table 2, test specimens for each example were prepared by the following method.

[0070] Specifically, cement and fine aggregate were first dry-mixed for 15 seconds using a mixing mixer (a mechanical mixer specified in JIS R 5201), after which water and admixtures were added and mixed for 90 seconds to obtain concrete material. The resulting concrete material was poured into a cylindrical formwork (φ50 × 100 mm) and steam-cured as the primary curing under conditions of a curing temperature of 60°C to 70°C and an insulation time of 5.5 hours. After that, the concrete was demolded when the surface temperature of the steam-cured concrete material had dropped to 65°C or below, and a test specimen was obtained.

[0071] After demolding, the surfaces of the test specimens were subjected to water spray curing by spraying curing water at a rate of 0.68 L / min and a water temperature of 20°C on the surfaces of the test specimens for 10 minutes using a sprayer at the times shown in Tables 3 to 6, thereby obtaining test specimens for each example.

[0072] [Examples 37 to 47] Each surfactant was added to water to give the concentration shown in Table 7, and the resulting curing water was foamed by passing it through a pump at a flow rate of 5 to 10 L / min. The test specimens of Examples 37 to 47 were obtained in the same manner as in Examples 1 to 36, except that the surfaces of the test specimens were subjected to water spray curing at the timings shown in Table 7.

[0073] The foaming curing water was measured for its defoaming time and foaming ratio. The defoaming time was measured by filling a measuring cylinder with foam up to the 800 ml position and measuring the time it took for the foam to decrease to a volume of 400 ml. The foaming ratio was measured by first filling a measuring cylinder with foam up to the 800 cm 3 The foam with the adjusted expansion ratio was placed in a container, and the mass of the foam was measured. Next, 800 g of water alone was placed in the container, and the mass of the water was measured, and the mass of the water was divided by the mass of the foam. The results of the defoaming time and expansion ratio are shown in Table 9.

[0074] [Comparative Examples 1 to 3] Test specimens of Comparative Examples 1 to 3 were obtained in the same manner as in Examples 1 to 3, except that only the water shown in Table 1 was used as the curing water.

[0075] [Comparative Examples 4 to 13] Test specimens of Comparative Examples 4 to 13 were obtained in the same manner as in Examples 37 to 47, except that instead of water spray curing, the test specimens were immersed in foamed curing water in an amount 5 to 10 times the volume of the test specimen and cured (hereinafter referred to as foam immersion curing) according to the conditions shown in Table 8.

[0076] [Reference example 1] A test specimen of Reference Example 1 was obtained in the same manner as in Example 1, except that after demolding, air curing was carried out instead of water spray curing.

[0077] [Reference example 2] A test specimen for Reference Example 2 was obtained in the same manner as in Example 1, except that instead of water spray curing, the test specimen was subjected to underwater curing by immersing it in water in an amount 5 to 10 times the volume of the test specimen.

[0078] [Contact angle] The contact angle of the curing water immediately after spraying was measured for each of the test specimens of Examples and Comparative Examples 1 to 3 to evaluate the ease of penetration of the curing water into the test specimen surface. The contact angle was measured by first dripping the curing water onto the surface of a glass slide and then observing the dripped curing water using a contact angle meter (B100, manufactured by Asumi Co., Ltd.). The contact angle measurement results are shown in Tables 3 to 8.

[0079] [Compression strength] The compressive strength of the test specimens of each Example, Comparative Example, and Reference Example was measured by a method in accordance with JIS R 5201. The compressive strength measurement results for each Example, Comparative Example, and Reference Example are shown in Tables 3 to 8.

[0080] [Compression strength enhancement effect] From the compressive strength results obtained above for each Example, Comparative Example, and Reference Example, the compressive strength enhancement effect was calculated using the following formula (I): The compressive strength enhancement effect means the ratio of the difference between the compressive strength of a test specimen subjected to water curing or foam immersion curing and the compressive strength of a test specimen subjected to air curing to the difference between the compressive strength of a test specimen subjected to water curing and the compressive strength of a test specimen subjected to air curing. EE={(σ s -σ a ) / (σ w -σ a )}×100 (I) where EE is the compressive strength enhancement effect (%), and σ s is the compressive strength (N / mm 2 ) and σ a is the compressive strength (N / mm 2 ) and σ w is the compressive strength (N / mm 2 The results of the compressive strength enhancing effect in each example and each comparative example are shown in Tables 3 to 8.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] [Table 6]

[0087] [Table 7]

[0088] [Table 8]

[0089] [Table 9]

[0090] As can be seen from Tables 3 to 8, the curing methods for concrete structures of the Examples satisfying all of the configurations of the present invention have lower contact angles of the curing water immediately after spraying than the contact angles of Comparative Examples 1 to 3, which used the water shown in Table 1 as the curing water, and therefore it can be said that the curing water easily penetrates the surface of the concrete structure. Furthermore, the curing methods for concrete structures of the Examples satisfying all of the configurations of the present invention had a greater effect in increasing compressive strength than the curing methods for concrete structures of the Comparative Examples, which used the same spraying timing. From this, it can be said that the curing method for concrete structures of the present invention can increase the compressive strength of concrete structures by spraying curing to the same extent as underwater curing.

[0091] As can be seen from Table 9, as the amount of surfactant contained in the curing water increases, the defoaming time and foaming ratio tend to increase, but when the amount of surfactant exceeds 4.0 mass%, the defoaming time and foaming ratio become almost constant. From this, it can be said that the method for curing a concrete structure according to the present invention, by setting the amount of surfactant contained in the curing water to 0.2 mass% or more and 4.0 mass% or less relative to the total amount of curing water, can make the bubbles contained in the curing water last longer and can more efficiently suppress surface cracks of the concrete structure.

[0092] Furthermore, as described above, it can be said that the curing method for concrete structures in each Example that satisfies all of the configurations of the present invention allows the curing water to easily penetrate the surface of the concrete structure, and that the compressive strength was more effective than the curing methods for concrete structures in each Comparative Example that used the same timing of water spraying. Therefore, it can be said that the method for manufacturing precast concrete products according to the present invention is capable of manufacturing precast concrete products that have increased compressive strength by water spray curing to the same extent as precast concrete products manufactured by underwater curing.

Claims

1. A method for curing a concrete structure obtained by pouring concrete material into a formwork and then removing the formwork, comprising: A method for curing a concrete structure, comprising a water spray curing step of spraying curing water containing a surfactant onto the surface of the concrete structure.

2. 2. The method for curing a concrete structure according to claim 1, wherein in the water spray curing step, the curing water is sprayed onto the concrete structure within 60 minutes after the form is removed.

3. 3. The method for curing a concrete structure according to claim 1, wherein the curing water is sprayed onto the concrete structure for at least 10 minutes in the water spray curing step.

4. 4. The method for curing a concrete structure according to claim 3, wherein the surfactant is an amine-based surfactant or a sulfosuccinate-based surfactant.

5. The method for curing a concrete structure according to claim 4, wherein the curing water contains foam.

6. 5. The method for curing a concrete structure according to claim 4, wherein the amount of the surfactant contained in the curing water is 0.2 mass % or more and 4.0 mass % or less based on the total amount of the curing water.

7. a pouring step of pouring concrete material into a formwork; After pouring, a primary curing process is performed. a demolding step of obtaining a concrete structure by demolding; and a spray curing step of spraying curing water containing a surfactant onto the surface of the concrete structure.

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