JP6913531B2 - Manufacturing method of precast concrete members - Google Patents

Description

The present disclosure relates to a method for manufacturing a precast concrete member.

Hardened cement bodies typified by precast concrete are used for various purposes and are also widely used as structural materials for buildings, and hardened cement bodies with high strength are desired.
When the concrete composition and water are kneaded, the mass ratio of water and a binder which is a material that undergoes a hydration reaction in concrete such as cement and silica fume (hereinafter referred to as water / binder ratio) may be used. Unless otherwise specified, the water / binder ratio in the present specification is based on mass), the distance between the particles becomes narrower, and the hydration product is precipitated and filled in the liquid phase portion. Therefore, it is known that the structure becomes dense and a hardened concrete body having high compressive strength can be obtained.
Further, by heating and curing the obtained hardened concrete body at a high temperature, it can be expected that the strength of the hardened concrete body is further improved and a high-strength precast concrete member (hereinafter, may be simply referred to as a concrete member) can be obtained. ..
If a high-strength concrete member is obtained, the column cross section of the structure can be reduced and the load-bearing area of the column can be increased, which is useful for the construction of a high-rise structure. In addition, the distance between the pillars of the building can be increased, and the degree of freedom in the plan of the building can be increased, which is a great advantage.

Typical concrete members, whereas the compressive strength is ^{20N / mm 2 ~50N / mm 2} , in recent years, as high-strength concrete members, compressive strength is desired 100 N / mm ² or more members.
For general concrete members, steam curing at around 50 ° C. may be carried out in order to secure strength at the time of demolding when the outside air temperature is low such as in winter. On the other hand, an ultra-high-strength precast concrete member produced by using a material having a small water-bonding material ratio as a concrete composition may be subjected to high-temperature heat curing such as steam curing and autoclave curing for the purpose of increasing strength. .. This is because the hardened concrete body is heat-cured at a high temperature to promote the hydration reaction of the binder such as cement inside the hardened concrete body and the reaction between the components, and as a result, the densification of the structure progresses. It is thought that this is to do.

Since high-strength precast concrete members are used as structural materials such as columns and beams, they are often large as members. Generally, in the production of a cured product, it is known that the strength of the obtained cured product increases as the maximum temperature in curing increases. However, according to the study by the present inventors, for the purpose of efficiently producing a high-strength precast concrete member, a large-sized hardened concrete body is rapidly heated to a temperature exceeding 90 ° C., for example, a maximum temperature of 95 ° C. to 180 ° C. It was found that the expected effect of improving the strength may not be obtained when the temperature is raised to a high temperature and the curing is performed at a high temperature.

This is considered to be due to the following factors.
That is, when the maximum temperature during high-temperature curing exceeds 90 ° C, especially when the rate of temperature rise when reaching the maximum temperature is high, it is compared with the normal curing performed at the maximum temperature of 90 ° C or less. As a result, in a concrete member having a large cross-sectional size, a temperature difference is likely to occur between the surface and the inside of the hardened concrete body during high-temperature curing, and a large temperature stress due to the temperature difference is generated. That is, when the temperature rises, the compressive stress due to expansion is larger near the surface of the cured product than inside, and the vicinity of the center of the cured product, which has a relatively small expansion strain, is pulled from the surroundings, resulting in tensile stress. Occurs. On the contrary, when the temperature is lowered, tensile stress is generated near the surface and compressive stress is generated near the center. In a concrete member having a large cross-sectional dimension, when the maximum temperature during high-temperature curing is high, or when the rate of temperature rise or decrease is large, the temperature gradient becomes large, so that this temperature stress becomes large. Since the tensile strength of concrete is as small as 1/10 of the compressive strength, it is considered that the cause is that undesired fine cracks are generated in the portion where the temperature stress of the above tension exceeds the tensile strength of concrete. ..

As a method of manufacturing ultra-high-strength concrete members by controlling the thermal conductivity, when manufacturing concrete members, a plurality of heat insulating members are laminated so as to overlap each other, and heat insulating as a curing material whose heat transfer rate can be changed. The process of constructing the mold, the process of covering the surface of the cast ultra-high-strength concrete with a curing material by placing ultra-high-strength concrete in the constructed heat-insulating mold, and the process of curing the ultra-high-strength concrete. At that time, a method for manufacturing an ultra-high-strength concrete member has been proposed, which comprises a step of sequentially removing a plurality of heat insulating members laminated so as to be overlapped and gradually changing the heat transfer rate of the curing material. For example, see Patent Document 1).

Japanese Patent No. 4999608

However, the manufacturing method described in Patent Document 1 requires a heat insulating formwork having a complicated structure in order to change the heat transfer coefficient to the hardened concrete body, and involves a complicated process such as removing a plurality of heat insulating members over time. Therefore, there is a problem in productivity.

The problem to be solved by one embodiment of the present invention is that even when the concrete member is cured at a high temperature, the occurrence of cracks due to the internal temperature gradient is suppressed, and a high-strength precast concrete member can be manufactured with high productivity. It is to provide a method of manufacturing a precast concrete member.

The disclosure includes the following embodiments:
<1> A step of putting the concrete composition into a mold, curing it to a strength that allows it to be demolded, and demolding it to obtain a hardened concrete body, and a temperature gradient of at least a part of the surface of the obtained hardened concrete body. A method for manufacturing a precast concrete member, which comprises a step of coating with a layer for relaxing the temperature and curing at a high temperature to obtain a precast concrete member.

<2> The step of covering with a layer for relaxing the temperature gradient and curing at a high temperature to obtain a precast concrete member includes a step of covering at least a part of the hardened concrete with a heat insulating material. How to manufacture precast concrete members.
<3> In the step of covering with a layer that relaxes the temperature gradient and curing at high temperature to obtain a precast concrete member, the hardened concrete is cured at high temperature by providing a means that does not come into direct contact with high temperature steam or hot air. The method for manufacturing a precast concrete member according to <1>, which includes a step.

The problem to be solved by one embodiment of the present invention is that even when the concrete member is cured at a high temperature, the occurrence of cracks due to the internal temperature gradient is suppressed, and a high-strength precast concrete member can be manufactured with high productivity. It is to provide a method of manufacturing a precast concrete member. According to the method for producing a hardened cement product of the present invention, even when a cement composition having a water / binder ratio of 0.2 or less is used, the local strength is caused by a decrease in the fluidity of the cement composition. An extremely high-strength cement hardened product is produced without causing variation in the above.

1 (A), 1 (B), and 1 (C) are perspective views showing an example of a mode in which a hardened concrete body is covered with a heat insulating material, respectively. It is a perspective view which shows an example of the aspect which coated the concrete hardened body with the silicone resin sheet as a means which high temperature steam or hot air does not come into direct contact with. FIG. 3 (A) is a perspective view showing an example of a mode in which a hardened concrete body is surrounded by a metal tsuitate as a means that high-temperature steam or hot air does not come into direct contact with, and FIG. 3 (B) is a hardened concrete. It is a schematic cross-sectional view which shows an example of the mode in which a body is surrounded by a metal tsuitate, and high-temperature steam is supplied. It is a graph which shows the time-dependent change of the surface temperature and the center temperature of the concrete hardened body in Example 1 and the concrete hardened body in Comparative Example 1 in an autoclave.

The numerical range described by using "~" in the present specification represents a numerical range including the numerical values before and after "~" as the lower limit value and the upper limit value.
In the present specification, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.
Further, in the present specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. Means.
In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. .. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[Manufacturing method of precast concrete members]
The method for producing a precast concrete member of the present disclosure includes a step of putting a concrete composition into a mold, curing it to a strength that allows it to be demolded, and demolding it to obtain a hardened concrete body, and a surface of the obtained hardened concrete body. At least a part of the above is covered with a layer that relaxes the temperature gradient, and is cured at a high temperature to obtain a precast concrete member.
The method for manufacturing a concrete member of the present disclosure may have steps other than the above.

Although the action of the present invention is not clear, it is considered as follows.
By curing the concrete member at a high temperature, the hardening reaction of the concrete composition and the densification of the structure proceed.
When the size of the concrete member to be manufactured is small, the hardened concrete body forming the concrete member is easily affected by the atmospheric temperature up to the center thereof. However, when the size of the hardened concrete body becomes large, for example, when the thickness is 100 mm or more for a rectangular parallelepiped or the diameter is 100 mm or more for a cylinder, the temperature difference between the surface and the center of the hardened concrete body tends to increase. ..
When curing a large-sized hardened concrete body at high temperature, high-temperature steam, high-temperature hot air, or radiant heat from a heater for curing the hardened concrete body is localized on the surface of the hardened concrete body, especially a part of the surface. By directly hitting the concrete, the surface of the hardened concrete locally suddenly becomes hot, the temperature gradient between the surface of the hardened concrete and the center of the hardened concrete becomes large, and the high-temperature steam or the like directly touches and heats the concrete. There is also a temperature difference between the region and the surrounding region. Therefore, there is a concern that cracks, that is, fine cracks, may occur due to non-uniform heating in the surface region and the depth direction of the cured product.

In the method for producing a concrete member of the present disclosure, by having a step of covering at least a part of the surface of the hardened concrete body with a layer that relaxes the temperature gradient, a local abrupt local surface of the hardened concrete body described above is provided. The temperature rise is suppressed, the non-uniformity of the temperature on the surface of the cured product, and the temperature gradient between the surface and the center of the cured product are alleviated.
Therefore, according to the manufacturing method in the present disclosure, the effect of improving the strength of the concrete member in the high temperature curing is achieved, and the occurrence of undesired fine cracks and the like due to the temperature gradient in the concrete member and the occurrence of fine cracks and the like. It is considered that the decrease in strength of the concrete member due to the above is effectively suppressed.
The present disclosure is not limited to the above estimation mechanism.

As another means of preventing the hot steam, hot air, or radiant heat from the heater from directly touching the surface of the hardened concrete, the hardened concrete can be used at a hot steam supply port or at a high temperature. It is conceivable to place it at a sufficient distance from the hot air outlet or a heat source such as a heater. However, in that case, there is a problem that productivity can be lowered because only a very small number of hardened concrete bodies can be arranged in the heating zone as compared with the manufacturing method of the present disclosure.

Hereinafter, the method for manufacturing the concrete member of the present disclosure will be described in order of steps.
[Step of putting the concrete composition into a mold, curing it to a strength that allows it to be removed from the mold, and removing the mold to obtain a hardened concrete body: Step (A)]
In this step (A), a concrete composition containing a binder and water is kneaded by a conventional method and put into a mold having a size and shape suitable for the purpose of the concrete member.
In the manufacturing method of the present disclosure, for the purpose of manufacturing a high-strength concrete member, at least cement as a binder, aggregate and water are contained, and the water / binder ratio (mass standard) is 20% or less. It is preferable to use a certain concrete composition.

[Components of hardened concrete]
As the material used for the hardened concrete of the present disclosure, as described in detail below, a material having a low water / binder ratio is preferable.
(Water / binder ratio)
The concrete composition used in the hardened concrete of the present disclosure is preferably a composition having a water / binder ratio (mass ratio) of 20% or less, and at least water, cement, aggregate, and optionally. , Silica fume and other binders may be contained, and a water reducing agent or the like may be contained depending on the purpose.
The water / binder ratio is preferably 20% or less, more preferably 17% or less, and the target compressive strength of the hardened concrete body is 200 N / N /, from the viewpoint of the strength of the obtained hardened concrete body. In ^{the case of mm 2} or more, it is more preferably 13% or less. From the viewpoint of fluidity, the water / binder ratio is preferably 8% or more.
The binder in the present specification includes cement which is the main component of the hardened concrete and fine powder (solid content) which is involved in the hardening reaction of the hardened cement such as silica fume, slag and fly ash which are generally used together with cement. Used in the sense. In addition, aggregates, surfactants added for improving fluidization, etc. are not included in the binders in the present specification.

(cement)
The cement used in the production method of the present disclosure is not particularly limited, and can be appropriately selected from various cements according to the purpose. As the cement, any known cement such as ordinary Portland cement, moderate heat Portland cement, low heat Portland cement, and early strength Portland cement can be preferably used.
Further, Portland cement containing silica fume in advance may be used. Portland cement containing silica fume is also available as a commercially available product, and examples thereof include Ube-Mitsubishi Cement Co., Ltd., trade names: Silica Fume Cement Super, Silica Fume Cement, and Pacific Cement Co., Ltd .: Silica Fume Premix Cement.

(Silica fume)
The concrete composition can contain silica fume as a binder from the viewpoint of further improving the strength of the obtained concrete member.
The silica fume preferably used may be in the form of powder, slurry or granules. As the silica fume, generally used ferrosilicon or silica fume produced as a by-product during the production of metallic silicon (average particle size: 0.1 μm to 0.2 μm, pH 5 to 10) is preferable.
The particle size of silica fume in the present specification is a value obtained by calculating the specific surface area of silica fume particles by the BET method on the assumption that the particles are spherical, and from the calculated specific surface area and the density of the particles. Is used.

When the concrete composition contains silica fume, the content is preferably 5% by mass to 35% by mass, more preferably 10% by mass to 30% by mass, based on the total binder in the concrete composition. In order to contain 5% by mass to 35% by mass of silica fume in the total binder, 5% by mass to 35% by mass of the cement as the binder may be replaced with silica fume. The content of silica fume referred to here refers to the total amount of silica fume when a plurality of types of silica fume are used in combination. When the content of silica fume is in the above range, the effect of improving fluidity and the effect of improving strength are sufficiently exhibited.
As described above, some commercially available cements contain silica fume in advance, and when such cement is used, it is added in consideration of the content of silica fume contained in advance. It is necessary to calculate the replacement amount of silica fume to be contained.

Further, from the viewpoint of strength development, the silica fume _{preferably contains silicon dioxide (SiO 2} ) in an amount of 85% or more by mass ratio. When the content of SiO _{2 in} the silica fume is 85% by mass or more, SiO ₂ in the silica fume causes a pozzolan reaction with calcium hydroxide generated in the hydration reaction of cement to generate hydrate and densify. The effect is sufficiently obtained, and the effect of improving the strength can be expected.
Further, when the particle size of the silica fume particles is within the above range, the reaction activity is high and the strength development is more excellent. In addition, since the shape of the silica fume particles is spherical, the flow during preparation of the concrete composition due to the bearing effect. The properties are improved, and the decrease in kneadability is suppressed.

(Other binders)
In addition to cement and silica fume used as desired, the hardened concrete body of the present disclosure is used in an appropriate amount by appropriately selecting other binders according to the use of the concrete member as long as the effect is not impaired. You may.
Examples of other binders include silica fine powder obtained by finely pulverizing crystalline silica, slag such as blast furnace slag fine powder, limestone fine powder, and fly ash.
The content of the binder other than cement and silica fume is preferably 70% by mass or less for the blast furnace slag fine powder and 30% by mass or less for the other binders with respect to the total binder.

(aggregate)
The concrete composition for producing a hardened concrete body contains an aggregate. Examples of the aggregate include fine aggregate and coarse aggregate. The strength of the hardened concrete is further improved by containing the aggregate.

(Fine aggregate)
As the fine aggregate, good quality and solid natural sand, crushed sand, and processed sand are used. The type and content of the fine aggregate may be appropriately selected according to the target strength of the hardened cement, but when crushed sand or processed sand is used, the corners are treated or the particle size is adjusted. It is effective to use the ones that have been made.
When a fine aggregate _{containing a large amount of SiO 2} is used as the fine aggregate, it _{behaves in the same manner as the SiO 2} derived component contained in silica fume, and the constituent components of the fine aggregate are slightly cured at high temperature. However, since it reacts, it is effective in increasing strength. More specifically, it is preferable to use a fine aggregate containing 70% or more of _{SiO 2, for example, rhyolite or quartz-based aggregate.}

(Coarse aggregate)
When a coarse aggregate is used as the aggregate in addition to the fine aggregate, a good quality and solid coarse aggregate may be used. The maximum size of the coarse aggregate requires that the particle size (maximum particle size) be 20 mm or less, and preferably the maximum size is 15 mm or less. The rock type may be appropriately selected from general rocks such as hard sandstone, andesite, and rhyolite according to the target strength. When the concrete composition contains a coarse aggregate, the strength of the obtained cured product is further improved.

(Other ingredients)
Depending on the purpose, the concrete composition may further contain other components commonly used in the concrete composition, such as a water reducing agent, a retarding agent, and a defoaming agent.

In this step (A), first, the concrete composition for producing the above-mentioned hardened concrete is uniformly mixed to prepare a fluid slurry.
Mixing can be done by a conventional method. That is, there is a method of preparing a slurry by adding a binder such as cement, an aggregate, water and other additives added if desired to a mixer and mixing them. Further, first, the aggregate may be mixed with a mixer, then cement and silica fume may be added to the mixer and mixed, and then water may be added and mixed, and the materials may be sequentially added and mixed. It is also possible to prepare a slurry by kneading 50% by mass to 90% by mass of the material with water, and then adding the residual binder and mixing.
When preparing the slurry, any component such as an antifoaming agent and a water reducing agent can be added as needed.

The prepared slurry is put into a mold and cured over time until it reaches a demolding strength to form a hardened concrete body.
When the concrete composition is put into the mold, after the slurry is put into the mold, a step such as defoaming may be further performed according to a conventional method.
In this step (A), it is preferable that the concrete composition charged into the formwork is hardened with self-heating and placed in the formwork until the demolding strength is reached to obtain a hardened concrete body. The hardened concrete body thus obtained is subjected to the next step.
After the concrete composition is put into the mold, it may be left at room temperature (25 ° C.) until it hardens with self-heating.
The holding time in the mold at room temperature until the mold removal strength is reached is generally 12 hours to 24 hours. If the setting is delayed, it may be about 24 hours to 72 hours, and if there is a margin in the process, the holding time may be set to one week.
Further, for example, the hardened concrete body can be heated at a low temperature under the temperature condition of 40 ° C. to 50 ° C. for each formwork to shorten the time until the demolding strength is reached.

The term "demolding strength" as used herein means that the hardened concrete obtained by hardening the concrete composition has a self-retaining shape when the formwork is removed, and is gripped for transportation. It means that the strength is such that cracks do not occur even when the concrete is gripped or stacked by means. More specifically, the demolding strength depends on the compressive strength of 5 N / mm ² or more from the viewpoint that the demolded concrete surface is not scratched, and from the viewpoint of whether or not the member can be lifted. Although the required strength is different, it generally refers to developing a strength ^{of 15 N / mm 2 or more.}

[Step of coating at least a part of the surface of the obtained hardened concrete body with a layer that relaxes the temperature gradient and curing at high temperature to obtain a precast concrete member: step (B)]
The hardened concrete obtained in the previous step (A) is cured at a high temperature.
The high-temperature curing in the present specification is used to include heat curing (normal pressure heating curing), steam curing (normal pressure steam heating curing), and autoclave curing (high-pressure steam heating curing).
This step (B) may be performed at any timing as long as the hardened concrete body is obtained. For example, it may be carried out immediately on the hardened concrete body obtained in the step (A), or after a lapse of time, for example, after the self-heated concrete hardened body has cooled to room temperature, and a large number of cases may be carried out. After producing the hardened concrete body, a plurality of hardened bodies may be put together.

The high-temperature curing in the present specification refers to normal-pressure high-temperature curing under a temperature condition of 70 ° C. or higher and high-pressure high-temperature curing under a temperature condition of 100 ° C. or higher.
Examples of the high-temperature curing mode include heating curing (normal pressure heating curing), steam curing (normal pressure steam heating curing), autoclave curing (high pressure steam heating curing), and the like.
The conditions for high temperature curing will be described below.

(Atmospheric pressure heating curing)
Normal pressure heating curing is a curing method in which a hardened concrete body is heated under normal pressure conditions.
As a heating method, for example, a method of heating a hardened concrete body at normal pressure in a heating zone, a method of preventing the hardened concrete body from drying extremely, and for example, a planar heating element that generates heat by energization, etc. There is a method of heating by attaching the above to the surface of the cured product. Examples of the heating means include a planar heating element, a rubber heater, a jet heater, and the like, and examples thereof include a method of heating from the outside by these heating means. In addition, as a means for the hardened concrete body not to dry extremely, a state in which the whole or most of the hardened concrete body is covered with a formwork having an effect of suppressing the dissipation of water, such as a steel formwork or a wooden formwork. The means to do so can be mentioned.
As another means for preventing the hardened material from being extremely dried, there is a means for arranging the hardened concrete body in an atmosphere in which water vapor is present. One aspect of atmospheric heating curing is a means of using steam as a heating means and heating with steam in an unsealed atmosphere, and a method of heating with steam in an unsealed atmosphere is a method of heating with steam. Sometimes referred to as curing or simply steam curing. That is, the "steam curing" in the present specification means a curing in which steam is supplied and heated under a normal pressure atmosphere.

-Atmospheric pressure steam curing-
Normal pressure steam curing, which is one aspect of normal pressure heating curing, can be performed by a conventional method. Specifically, for example, steam produced in a boiler can be introduced into a tank for curing a hardened concrete body by an introduction pipe, a temperature sensor is installed in the tank, and the temperature in the tank is set. There is a method of performing steam curing by opening and closing the steam supply valve so as to have a history.

The heating temperature conditions in normal pressure heating and curing and the heating time at the temperature are appropriately adjusted according to the composition, shape, size, and desired compressive strength of the hardened concrete.
The heating temperature (maximum heating temperature at the time of curing) is usually preferably in the temperature range of 100 ° C. to 210 ° C., more preferably in the temperature range of 150 ° C. to 190 ° C. when a heating means other than steam is used.
The heat curing time (curing time) is preferably the time to reach a predetermined temperature inside the hardened concrete body, and for example, the curing time can be 6 hours to 100 hours.
In the present specification, the curing time in each high-temperature curing refers to the time during which the heating temperature (maximum heating temperature at the time of curing) is maintained.

The rate of temperature rise in normal pressure heating is arbitrary. However, if the temperature is raised rapidly, a temperature imbalance in the hardened concrete body is likely to occur, which may lead to non-uniformity of the curing reaction.
Generally, it is preferable to raise the temperature under the condition that the maximum heating temperature is reached in 2 hours to 15 hours.
Specifically, when a heating means other than steam is used, the heating rate is preferably about 5 ° C./hr to 120 ° C./hr, and more preferably about 10 ° C./hr to 60 ° C./hr.

Further, in the case of steam curing using steam as the heating means, the maximum heating temperature at the time of curing is preferably in the temperature range of 70 ° C. to 100 ° C., and more preferably in the temperature range of 80 ° C. to 95 ° C.
When steam is used as the heating means, the rate of temperature rise is preferably about 5 ° C./hr to 60 ° C./hr, and more preferably about 10 ° C./hr to 40 ° C./hr.
The curing time of atmospheric pressure heating with steam is preferably 2 hours to 72 hours, and more preferably 6 hours to 72 hours.

(High pressure steam heating curing)
High-pressure steam heating curing is a curing performed by arranging a hardened concrete body in an autoclave device, and is usually cured by high-temperature steam under a pressure higher than normal pressure in a closed autoclave device.
The heating temperature is preferably in the temperature range of 105 ° C. to 300 ° C., more preferably 130 ° C. to 250 ° C., and even more preferably 150 ° C. to 200 ° C.
As the high pressure condition in the high pressure steam heating curing, the pressure condition exceeding the normal pressure and 10 MPa or less is preferable, the pressure condition of 0.2 MPa to 5 MPa is more preferable, and the addition of 0.4 MPa to 2 MPa is preferable in the autoclave apparatus. Pressure conditions are more preferred.
The curing time in the high-pressure steam heating curing is preferably 2 hours to 72 hours, more preferably 6 hours to 60 hours.

The rate of temperature rise in high-pressure steam heating is arbitrary, but as with normal-pressure steam curing, if the temperature is raised rapidly, temperature imbalance in the hardened concrete tends to occur, resulting in non-uniformity of the curing reaction. There is a concern that it will invite. Therefore, the rate of temperature rise is preferably about 5 ° C./hr to 120 ° C./hr, and more preferably about 10 ° C./hr to 60 ° C./hr.
The boosting speed in the autoclave apparatus is preferably about 0.05 MPa / hr to 1 MPa / hr, and more preferably about 0.1 MPa / hr to 0.5 MPa / hr.
In high-pressure steam heating curing, it is also possible to adjust the temperature conditions in the autoclave device by adjusting the pressure gradient in the device.

The temperature condition in the high temperature curing represents the set temperature of the autoclave device or the temperature in the curing tank in the case of high-pressure steam heating curing in the autoclave. The temperature condition in the case of atmospheric heating curing refers to the ambient temperature or the surface temperature of the hardened concrete body measured by using a means of a temperature measuring sensor such as a thermocouple. The temperature condition in the case of atmospheric steam curing refers to the temperature in the curing tank measured by means of a temperature measuring sensor such as a thermocouple or the surface temperature of the hardened concrete.
Since the strength is improved by setting the temperature near the center of the hardened concrete body to a predetermined temperature, the temperature at the center promotes the hardening of the hardened concrete body even when the temperature gradient is relaxed, and the structure of the hardened concrete body is reduced. It is preferable to heat and cure to a temperature sufficient to densify the concrete.

As will be described later, the effect of relaxing the temperature gradient can be confirmed by measuring the surface temperature of the hardened concrete body and the temperature near the center of the hardened concrete body.
The relationship between the surface temperature of the hardened concrete body and the temperature at the center of the hardened concrete body can be obtained by experimental measurement in advance. It can also be estimated from the size of the cured product and the thermal characteristics of the cured product, that is, the heat transfer coefficient, the thermal conductivity, and the heat capacity of the cured concrete body.

(Coating with a layer that reduces the temperature gradient)
There is no particular limitation on the method of covering the hardened concrete body with a layer that relaxes the temperature gradient during the above-mentioned high-temperature curing, and various methods are adopted as long as it is possible to prevent only the surface of the hardened concrete body from rapidly becoming high in temperature. can do. Therefore, the coating method of the hardened concrete body may be appropriately selected according to the conditions of high temperature curing, the shape and size of the hardened concrete body, and the like.
Above all, the step (B) preferably includes a step of coating at least a part of the hardened concrete body with a heat insulating material.
In addition, as one of another preferable embodiments, the step (B) includes an embodiment in which the hardened concrete is cured at a high temperature by providing a means that does not come into direct contact with high-temperature steam or hot air.

(The process of covering at least a part of the hardened concrete with a heat insulating material)
As one aspect of coating with a layer that alleviates the temperature gradient, a step of coating at least a part of the hardened concrete body with a heat insulating material can be mentioned.
The heat insulating material is not particularly limited as long as it does not deteriorate at the heating temperature of high temperature curing and is composed of a material having low thermal conductivity. As the heat insulating material, a heat insulating material composed of an inorganic material other than a metal having high thermal conductivity is preferable, and from the viewpoint of lower thermal conductivity, an inorganic porous plate containing bubbles is also preferable. Examples of the heat insulating material include calcium silicate board, lightweight cellular concrete board, gypsum board, wood wool cement board and the like. Further, a housing made of these heat insulating materials, a prism having a space in which a hardened concrete body can be placed, a cylinder, and the like can also be suitably used as the heat insulating material.
FIG. 1 is a perspective view showing an example of a state in which at least a part of the hardened concrete body 12 is covered with the heat insulating material 14.
FIG. 1A is a perspective view showing a mode in which the outer periphery of the columnar concrete hardened body 12 is covered with a cylindrical heat insulating material 14. FIG. 1B is a perspective view showing an embodiment in which the outer circumference of a rectangular parallelepiped concrete hardened body 12 is covered with a prismatic heat insulating material 14 having a space inside. FIG. 1C is a perspective view showing a mode in which a plate-shaped heat insulating material 14 is placed on the top surface of a rectangular parallelepiped hardened concrete body 12 and only the top surface is covered with the heat insulating material 14.
According to the present embodiment, the necessary relaxation of the temperature gradient is achieved in any of the above-described high temperature curing embodiments.

(A process of high-temperature curing by providing a means for the hardened concrete body to prevent direct contact with high-temperature steam or hot air)
In the present embodiment, the hardened concrete body is subjected to high-temperature curing by providing means for which high-temperature water steaming or hot air does not come into direct contact.
As a means by which high-temperature steam or hot air does not come into direct contact with the hardened concrete body, for example, at least one of radiant heat from a heater, warm air, and high-temperature steam in steam curing does not come into direct contact with the surface of the hardened concrete body. If so, there is no particular limitation.

One means is to coat the hardened concrete with a sheet having high heat resistance and impermeable to water or a sheet made of a material having low thermal conductivity.
By coating the surface of the hardened concrete with a sheet such as a silicone resin sheet, carbon fiber sheet, heat-resistant felt, or glass cloth, high-temperature steam, radiant heat from the heater, etc. can come into direct contact with the surface of the hardened concrete. It is suppressed. Therefore, the rapid temperature rise of the surface of the hardened concrete body is suppressed, and the temperature gradient between the surface and the central portion of the hardened concrete body is relaxed.
FIG. 2 shows a perspective view of a hardened concrete body 12 coated with a silicone resin sheet 16 as an example of the present embodiment. In the embodiment shown in FIG. 2, a sheet having a width of 1000 mm, a length of 2000 mm, and a thickness of 1 mm is used as the silicone resin sheet. The size of the silicone resin sheet is appropriately selected according to the size of the hardened concrete.
The thickness of the silicone resin sheet is preferably 0.5 mm to 3 mm from the viewpoint of heat resistance, durability, flexibility (shape followability), and the like.
As the covering sheet, a commercially available resin sheet or the like may be used, and as a commercially available product, for example, a silicon sheet can be purchased from Daiichi Co., Ltd.

Further, as another means, there is a means of providing a support in the peripheral portion of the hardened concrete body. This embodiment is preferably used for high temperature curing using steam such as atmospheric pressure steam curing and autoclave curing.
The material constituting the tsuitate is not particularly limited as long as it has heat resistance and can block water vapor. As the tsuitate, for example, from the viewpoint of durability, a metal plate, gypsum board, stone plate, calcium silicate plate, lightweight aerated concrete plate, wood wool cement plate, etc. mentioned as the above-mentioned heat insulating materials are also used as the material of the tsuitate. obtain.
FIG. 3A is a perspective view showing a state in which the peripheral portion of the hardened concrete body 12 is surrounded by a metal tsuitate 18, and FIG. 3B is a hardened concrete body in an autoclave (not shown). 12 is a schematic cross-sectional view showing a state surrounded by the tsuitate 18. FIG. 3B shows a cross section of a steam supply port (steam pipe) 20 that supplies steam into the autoclave. As described in FIG. 3B, the presence of the strut 18 prevents the high-temperature steam ejected from the steam pipe 20 from directly touching the surface of the hardened concrete.
In the embodiment shown in FIG. 3, the hardened concrete body 12 is arranged on the panel 22, and a spacer 24 is provided on the panel 22 to provide a space between the panel 22 and the hardened concrete body 12. ing. By providing a space between the panel 22 and the hardened concrete body 12, water vapor easily wraps around the bottom surface of the hardened concrete body 12, and the hardened concrete body 12 is heated more uniformly by the water vapor.
The mode of the abutment shown in FIG. 3 is an example. For example, the abutment may have a shape provided on the peripheral portion and the bottom surface of the hardened concrete body as the shape of the housing, and at least a part of the periphery of the hardened concrete body. Specifically, for example, it may be provided only on the steam supply port side to which steam is supplied.

By providing the abutment, the high temperature steam is suppressed from directly touching the surface of the hardened concrete body, the rapid temperature rise of the surface of the hardened concrete body is suppressed, and the temperature gradient between the surface and the center of the hardened concrete body is increased. It will be relaxed.

The concrete member obtained by the manufacturing method of the present disclosure is heated to obtain the strength improving effect up to the center of the concrete member by high temperature curing, and the temperature gradient between the surface and the center of the hardened concrete body at the time of curing is high. It will be relaxed. Therefore, according to the manufacturing method of the present disclosure, the occurrence of fine cracks in the central portion of the hardened concrete due to the temperature gradient is suppressed, an excellent strength improving effect is obtained, and a high-strength concrete member is manufactured.

According to the method for manufacturing a concrete member of the present disclosure, it is possible to mass-produce a concrete member having a high compressive strength by the above-mentioned simple process, and the timing of high-temperature curing after obtaining a demoldable concrete hardened body is arbitrary. Therefore, it is possible to manufacture a highly productive and high-strength precast concrete member.

In particular, in the case of a concrete member having a large cross-sectional area such as a thickness of 100 mm or more, a difference in temperature between the surface and the central portion is likely to occur, so that the cross-sectional area useful as a structural material is large. The method for manufacturing a concrete member of the present disclosure is particularly useful for manufacturing a concrete member.

According to the method for producing a concrete member of the present disclosure, it is possible to produce a concrete member having a uniform structure and high compressive strength by suppressing the occurrence of undesired fine cracks and the like. Further, the manufactured concrete member is mainly applied to a structural member of a building, but since it has high strength, it can be utilized for a non-structural member by taking advantage of this feature, and its use is wide.
In particular, when a concrete member is used as a structural member of a building, it is required to have a large thickness because it is used for columns, beams, etc. It can be said that the effect of the manufacturing method of the present disclosure is remarkable when applied.

Hereinafter, the method for manufacturing the concrete member of the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the description according to the following examples.

(Examples 1 to 3, Comparative Examples 1 to 3)
[Concrete composition formulation]
Cement: L cement (Product name: Ube Mitsubishi, density 3.24 g / cm ³ )
(Low heat Portland cement): 1133 kg / m ³
Silica fume: Elchem 940U (trade name: manufactured by Elchem, average particle size 0.1 μm,
Silicon dioxide content: 95.4% by mass, BET specific surface area: 21.2 m ² / g)
: 200kg / m ³
Water: Tap water: 160 kg / m ³
Fine aggregate: Mikawa silica sand (particle size D50 212 μm,
Density 2.6 g / cm ³ ): 384 kg / m ³
Coarse aggregate: Crushed stone 1505 (maximum size 15 mm,
Density 2.61 g / cm ³ ): 605 kg / m ³
Admixture: SSP-104 (trade name: manufactured by Takemoto Oil & Fat Co., Ltd.): 85 kg / m ³
(Water / binder ratio: 12%)

[Manufacturing of hardened concrete: Step (A)]
(Adjustment of slurry)
Regarding the concrete composition of the above-mentioned composition, water, cement, aggregate, and silica fume are added in the amounts described in the above [Concrete composition composition] to a vertical mixer (SK-81 mixer manufactured by SK Mixer Co., Ltd., capacity 30 L) and an omni-mixer. (OM-10E capacity 10 L manufactured by Chiyosa Machinery Co., Ltd.) was used for kneading under the following conditions.
(1) In a vertical mixer, perform dry kneading for 30 seconds, add water, stir at low speed (speed: 110 rpm: rotation speed / minute) for 3 minutes, scrape off, and then scrape off at medium speed (speed::) for another 5 minutes. It was stirred at 215 rpm).
The mixture was put into an omnimixer and kneaded with the omnimixer for 3 minutes (speed: 300 rpm) to prepare a slurry.

(Injection of concrete composition into formwork)
In Example 1, the obtained slurry was put into a cylindrical mold having a diameter of 350 mm and a height of 1000 mm, and defoaming was performed by penetrating a rod and moving it up and down.
Similarly, in the second embodiment, the material is put into a rectangular mold having a height of 500 mm × a width of 500 mm × a length of 2000 mm, and in the third embodiment, the material is put into a rectangular mold having a height of 1000 mm × a width of 1000 mm × a length of 3000 mm. , The mold was vibrated to defoam.

(Demolding, preparation of hardened concrete)
This was left to stand for 5 to 7 days to be naturally cured, and after confirming that it had reached the mold removal strength, it was taken out from the mold to obtain a concrete molded body.

[High temperature curing of hardened concrete: Step (B)]
(Covering of hardened concrete with heat insulating material)
In Example 1, the hardened concrete after demolding was inserted into the space of a cylindrical covering material having an inner diameter of 350 mm, which was produced by a lightweight cellular concrete panel having a thickness of 50 mm (described as ALC in Table 2).
In Example 2, the hardened concrete body after demolding was inserted into the space of a prismatic covering material having internal dimensions of 500 mm in width × 500 mm in length × 2000 mm in height, which was produced by a lightweight cellular concrete panel having a thickness of 50 mm.
In Example 3, the hardened concrete body after demolding was inserted into the space of a prismatic covering material having an inner dimension of 1000 mm in width × 1000 mm in length × 3000 mm in height, which was produced by a lightweight cellular concrete panel having a thickness of 50 mm.
In Comparative Examples 1 to 3, the hardened concrete obtained in Examples 1 to 3 was subjected to high temperature curing under the same conditions as in Examples 1 to 3 without being covered with a heat insulating material.

(High pressure steam heating curing)
The obtained hardened concrete was placed in an autoclave, heated at a heating rate of 10 ° C./hr until the maximum temperature reached 90 ° C., and subjected to high-pressure steam heating curing for 72 hours. Then, the concrete member was obtained by cooling to room temperature (25 ° C.) at a temperature lowering rate of 10 ° C./hr.

(Evaluation of crack index)
In the temperature stress analysis of the concrete member after steam curing, the temperature history and the crack index inside the concrete member at the program temperature of steam curing were obtained.
The analysis method is the three-dimensional finite element method (FEM), and the analysis software is ASTEA MACS Ver. 9.1.2 (Computational Mechanics Research Center Co., Ltd.) was used.
Table 1 below shows the standard crack occurrence probability and safety factor γ _{cr in} a general bar arrangement structure, and the evaluation rank in the present disclosure. Table 2 below shows the results of analysis of the concrete members obtained by the manufacturing methods of each Example and Comparative Example by the analysis method described below.

The crack occurrence is checked by the following equation using the minimum value of the crack index.
I _cr (t) ≧ γ _cr
Here, I _cr (t): crack index I _cr (t) = f _tk (t) / σ _t (t)
f _tk (t): Tensile strength of hardened concrete on t days of age σ _t (t): Maximum main tensile stress of concrete on t days of age γ _cr : Safety factor for crack occurrence probability

As the tensile strength of the hardened concrete, the split tensile strength obtained by the JIS A1113 (2006) split tensile strength test method for concrete can be applied. Further, the maximum principal tensile stress degree can be obtained from the result of FEM analysis using the analysis code of ASTEA MACS.

In the above evaluation, if it is rank C or higher, it is evaluated as a concrete member with a crack index that can withstand general use, and if it is rank B or higher, it is evaluated as a concrete member with a crack index that can withstand use as a structural material. ..
From the results in Table 1, all of the concrete members obtained by the manufacturing methods of Examples 1 to 3 have realized a crack index that can withstand use as a structural material.
On the other hand, the concrete members obtained by the production methods of Comparative Examples 1 to 3 had a low crack index and did not reach a sufficient level as a structural material.

(Temperature analysis of concrete members)
The measurement results of the surface temperature and the internal temperature of the hardened concrete used in the methods of Example 1 and Comparative Example 1 in the above-mentioned high-temperature curing are shown in the graph of FIG.
As is clear from FIG. 4, with respect to the increase in the curing temperature, in the hardened concrete in the production method of Example 1, the increase in surface temperature is slower than that in Comparative Example 1, and the surface temperature and the center temperature are higher. It can be seen that the difference is smaller and the temperature gradient is relaxed.
From this, it is presumed that the result of relaxing the temperature gradient of the hardened concrete in the high temperature curing has an influence on the improvement of the crack index.

By comparing the above Examples and Comparative Examples, it can be seen that the concrete member obtained by the method for manufacturing the concrete member of the present disclosure suppresses the occurrence of cracks due to the temperature gradient.

12 Concrete hardened body 14 Insulation material 16 Silicone resin sheet 18 Tsuitate 20 Steam supply port (steam pipe)
22 Panel 24 Spacer

Claims (3)

The process of putting the concrete composition into the formwork, curing it to a strength that allows it to be demolded, and demolding it to obtain a hardened concrete body.
At least a part of the surface of the resulting concrete cured body was coated with a layer of mitigating the temperature gradient, and a high temperature curing, possess obtaining a precast concrete member,
The step of coating with a layer that relaxes the temperature gradient and curing at a high temperature to obtain a precast concrete member includes a step of coating at least a part of the cured concrete body with an inorganic porous plate containing bubbles.
Manufacturing method of precast concrete members. The process of putting the concrete composition into the formwork, curing it to a strength that allows it to be demolded, and demolding it to obtain a hardened concrete body.
It has a step of covering at least a part of the surface of the obtained hardened concrete body with a layer that relaxes a temperature gradient and curing it at a high temperature to obtain a precast concrete member.
The step of covering with a layer that relaxes the temperature gradient and curing at high temperature to obtain a precast concrete member is a step of providing a tsuitate to the hardened concrete body as a means to prevent direct contact with high temperature steam or hot air and curing at high temperature. Including ,
Manufacturing method of precast concrete members. The precast concrete member according to claim 2, wherein the material of the abutment is at least one selected from the group consisting of a metal plate, gypsum board, stone plate, calcium silicate plate, lightweight cellular concrete plate and wood wool cement plate. Production method.

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