JP7596586B1 - Manufacturing method for precast remaining formwork panels - Google Patents

Abstract

[Problem] To provide a method for manufacturing a precast remaining form panel that can manufacture a lightweight precast remaining form panel, improve the water impermeability of the main body of the precast concrete panel, and prevent cracks that occur over time. [Solution] The method for manufacturing a precast remaining form panel is a method for manufacturing a water impermeable precast remaining form panel using volcanic lapilli and volcanic ash as lightweight aggregates, and includes a mixing step of mixing concrete raw materials containing cement, volcanic lapilli as coarse aggregate and volcanic ash as fine aggregate with mixing water to obtain a fluidized cement composition, and an insulation curing step of allowing the temperature of the fluidized cement composition poured into the molding form to drop naturally to the outside air temperature without reheating the fluidized cement composition from the outside, thereby preventing the bleeding phenomenon in which the fluidized cement composition is discharged outside the molding form. [Selected Figure] Figure 1

Description

The present invention relates to a method for manufacturing a precast remaining form panel that can suppress cracks caused by alkali-aggregate reaction.

Precast remaining form panels are made of concrete. Conventionally, cracks that occur when making precast remaining form panels and cracks that occur due to deterioration of concrete after constructing a wall (remaining form) made with precast remaining form panels have been problems. Alkali-aggregate reaction is known as a concrete deterioration phenomenon. In alkali-aggregate reaction, the alkaline aqueous solution contained in concrete reacts with aggregates such as gravel and sand, causing expansion and cracks due to expansion. One type of alkali-aggregate reaction is the alkali-silica reaction, which is a reaction between silica minerals in the aggregate and alkaline components in the concrete, producing silica gel, which absorbs water and expands inside the concrete. The pressure of the expansion causes cracks from the inside. Cracks include tortoiseshell-shaped cracks that occur on the surface due to the expansion of concrete, and cracks that occur perpendicular to or parallel to the reinforcing bars or horizontally.

When cracks occur in the precast remaining form panels, the remaining formwork, which is made up of the precast remaining form panels, may suffer from frost damage, salt damage, efflorescence, etc. In order to prevent such cracks, frost damage, salt damage, efflorescence, etc., the inventor has proposed a method for manufacturing a precast remaining form panel to seal voids formed in the precast remaining form panels, such as capillary voids (for example, Patent Document 1).

The method for manufacturing a precast remaining form panel described in Patent Document 1 includes a step of pouring a fluidized cement composition obtained by mixing concrete raw materials containing cement, gravel, and sand, 5% to 40% by weight of limestone fine powder relative to the cement in the concrete raw materials, and mixing water, or a fluidized cement composition obtained by mixing mortar raw materials containing cement and sand, 5% to 40% by weight of limestone fine powder relative to the cement in the mortar raw materials, and mixing water, into a molding form, a molding step of molding the fluidized cement composition poured into the molding form, and a curing step of hardening the fluidized cement composition. In this method for manufacturing a precast remaining form panel, in the molding step and the curing step, excess water containing calcium hydroxide dissolved from the cement is pushed up to the back side in the mixing water, and is stored in the entire back area of the panel body, covering the back side of the panel body with the excess water, and the excess water is present so as to fill capillary voids formed inside the panel body. When the cement in the fluidized cement composition hardens, a waterproof layer is formed over the entire back surface of the panel body, preventing the carbon dioxide in the outside air from reacting chemically with calcium hydroxide and forming a permeable fine powder layer of calcium carbonate over the entire back surface of the panel body, while at the same time naturally blocking capillary voids and the like.

Patent No. 7314430

Conventional manufacturing methods were effective in sealing capillary voids, but they could not completely seal the capillary voids, and moisture could penetrate into the precast remaining formwork panel through the formed capillary voids, react with silica minerals, and cause an alkali-silica reaction. Furthermore, as moisture continues to penetrate, it can accelerate the alkali-silica reaction and cause cracks after several years. In light of this, there was a need for a manufacturing method for precast remaining formwork panels that could completely seal the capillary voids in precast concrete panels, prevent moisture from penetrating, and suppress expansion cracks caused by alkali-silica reaction.

Furthermore, in recent years, there has been a demand for lightweight precast remaining formwork panels, as crack formation is suppressed and the transportation of precast remaining formwork panels is done manually. Specifically, there is a demand to reduce the weight from the current 21 kg to around 16 kg.

The present invention aims to provide a method for manufacturing a precast remaining form panel that can produce a lightweight precast remaining form panel and can suppress cracking caused by alkali-aggregate reaction over time.

The method for producing a precast remaining form panel according to the present invention is a method for producing a non-permeable precast remaining form panel using volcanic lapilli and volcanic ash as aggregates, and includes a mixing step of mixing concrete raw materials containing cement, the volcanic lapilli as coarse aggregate, and the volcanic ash as fine aggregate with mixing water for hydration reaction that has been heated to a temperature of 60°C to 85°C in advance to obtain a fluidized cement composition with a mixing temperature of 15°C to 45°C corresponding to an outside air temperature of 0°C to 40°C, and a mixing step of placing the fluidized cement composition in a molding form designed so that the back surface of the panel body faces upward and is maintained horizontally after the mixing step. A cement composition is poured into the mixing water, and excess water containing calcium hydroxide dissolved from the cement is pushed up toward the rear surface of the panel body, so that the excess water is stored over the entire rear surface of the panel body, covering the rear surface of the panel body, and the excess water fills capillary voids formed inside the panel body. In order to do this, vibration is applied to the fluidized cement composition poured into the molding form to mold the fluidized cement composition poured into the molding form, and after the step of molding the fluidized cement composition, the fluidized cement composition poured into the molding form is reheated from the outside. The present invention includes a heat-retaining and curing step of allowing the temperature of the fluidized cement composition in the molding form to drop naturally to an outside air temperature over a period of 3 hours or more without heating, thereby preventing a bleeding phenomenon in which a mixing water for a hydration reaction containing calcium hydroxide dissolved from the fluidized cement composition expands in volume and is discharged to the outside of the molding form, thereby preventing the occurrence of capillary voids in the fluidized cement composition and hardening the fluidized cement composition until a demolding strength is ensured, and a demolding step of removing the molding form after the heat-retaining and curing step. When the fluidized cement composition hardens in the heat-retaining and curing step, the fluidized cement composition The alkaline components contained in the cement composition react chemically with the silica contained in the volcanic gravel and volcanic ash to produce alkaline silica gel, forming a waterproof layer over the entire back surface of the panel body, which prevents the carbon dioxide in the outside air from reacting chemically with the calcium hydroxide to form a permeable fine powder layer of calcium carbonate over the entire back surface of the panel body. At the same time, the capillary voids are almost completely blocked by the waterproof layer, dramatically improving the impermeability of the panel body and preventing expansion cracks caused by the alkali-silica reaction of the coarse aggregate of the volcanic gravel and the fine aggregate of the volcanic ash over time.

The manufacturing method of the precast remaining formwork panel according to the present invention is characterized in that, in the process of molding the fluidized cement composition, a stainless steel connecting fitting is embedded in the back surface of the panel body.

The manufacturing method for the precast remaining form panel according to this embodiment uses concrete raw materials that contain cement, volcanic gravel as a coarse aggregate, and volcanic ash as a fine aggregate. Because volcanic gravel and volcanic ash are lightweight aggregates, the manufactured precast remaining form panel is lighter than conventional panels.

The method for manufacturing a precast remaining formwork panel according to the present invention involves mixing concrete raw materials containing cement, volcanic lapilli coarse aggregate, and volcanic ash fine aggregate with mixing water for hydration reaction that has been heated to a temperature of 60°C to 85°C in advance, to obtain a fluidized cement composition with a mixing temperature of 15°C to 45°C corresponding to an outside air temperature of 0°C to 40°C, and allowing the temperature of the fluidized cement composition in the forming formwork to drop naturally to the outside air temperature over a period of 3 hours or more without reheating the fluidized cement composition from the outside. This prevents the bleeding phenomenon, in which the mixing water for hydration reaction containing calcium hydroxide dissolved from the fluidized cement composition expands in volume and is discharged outside the forming formwork, thereby preventing the generation of capillary voids in the fluidized cement composition, and since moisture does not penetrate into the inside of the panel body, alkali-silica reaction does not occur in the coarse aggregate of volcanic lapilli and the fine aggregate of volcanic ash, and prevents expansion cracks caused by the alkali-silica reaction. Therefore, the precast remaining formwork panels are prevented from undergoing expansion cracks over time.

In addition, in the manufacturing method of the precast remaining form panel using this concrete raw material, the excess water containing calcium hydroxide dissolved from the cement is pushed up to the rear side in the mixing water during the heat retention curing process, and is stored on the entire rear surface of the panel body, covering the rear surface of the panel body with the excess water, and the excess water is present so as to fill voids such as capillary voids formed inside the panel body. When the fluidized cement composition hardens, the alkaline component contained in the fluidized cement composition reacts chemically with the silica contained in the volcanic gravel and volcanic ash to generate alkaline silica gel, forming a waterproof layer on the entire rear surface of the panel body, and it is possible to prevent the formation of a permeable calcium carbonate fine powder layer on the entire rear surface of the panel body. The waterproof layer almost completely blocks voids such as capillary voids, dramatically improving the impermeability of the panel body.

In the manufacturing method of the precast remaining form panel according to the present invention, in the pouring step, the stainless steel connecting fittings can be embedded in a predetermined position in the fluidized cement composition so that they protrude from the back surface of the panel body. Even in this case, the gap formed between the embedded part of the connecting fittings and the panel body is almost completely sealed by the waterproof layer, dramatically improving the water impermeability of the panel body.

1A and 1B are diagrams showing a precast remaining form panel according to an embodiment of the present invention, in which (a) shows a cross-sectional view and (b) shows a rear view. FIG. 2 is an enlarged view of a connected portion of a precast remaining formwork panel according to an embodiment of the present invention. 1A, 1B, and 1C are diagrams for explaining a manufacturing process of a precast remaining form panel according to an embodiment of the present invention. 1A and 1B are diagrams showing a remaining formwork constructed by a remaining formwork construction method according to an embodiment of the present invention, in which (a) is a cross-sectional view and (b) is a front view.

The manufacturing method of the precast remaining formwork panel according to the present invention will be described with reference to Figures 1 to 4, taking the manufacturing method of the precast remaining formwork panel as an example. In addition, in the drawings, the horizontal direction of the precast remaining formwork is indicated as the width direction X, the vertical direction is indicated as the height direction Y, and the thickness direction is indicated as the front-rear direction Z.

In the manufacturing method of the precast remaining form panel according to this embodiment, a non-water-permeable precast remaining form panel 1 shown in FIG. 1 is manufactured. As shown in FIG. 1(a), this precast remaining form panel 1 comprises a precast remaining form panel body 2 (hereinafter also referred to as the panel body 2), a plurality of connecting fittings 3 provided at predetermined positions on the back surface 2a of the panel body 2, and a waterproof layer 4 formed on the back surface 2a, etc., of the panel body 2. This precast remaining form panel 1 is a non-water-permeable precast remaining form panel that uses volcanic gravel and volcanic ash as lightweight aggregate.

[Panel body 2]
1(a) and (b), the panel body 2 is rectangular, and a panel body 2 having a height of 300 mm and a width of 900 mm is used, for example. Two connected metal fittings 3 are provided in the width direction X and the height direction Y on the back surface 2a of the panel body 2. The connected metal fittings 3 are provided so as to protrude from the back surface 2a of the panel body 2. A plurality of reinforcing bars 5 are provided inside the panel body 2 in the width direction X and the height direction Y to ensure the strength of the panel body 2. The size (height and width) of the panel body 2 can be changed as appropriate.

[Connected metal fitting 3]
The connected metal fitting 3 comprises a hook portion 6 and an embedded portion 7 connected to both ends of the hook portion 6 (FIG. 1(a)). The connected metal fitting 3 is provided on the panel body 2 with the embedded portion 7 embedded inside the panel body 2 and the hook portion 6 protruding from the back surface 2a of the panel body 2. The connected metal fitting 3 can be made of metal, and is preferably made of a material with excellent corrosion resistance, such as stainless steel (SUS304).

[Waterproof layer 4]
The waterproof layer 4 is formed by a chemical reaction between the alkaline component contained in the fluidized cement composition C and the silica contained in the volcanic lapilli and volcanic ash to produce alkaline silica gel, and is composed of a water-insoluble layer . As shown in Figure 2, the waterproof layer 4 is formed not only over the entire back surface 2a of the panel body 2, but also in the capillary gap 9A and the gap 9B formed between the embedded portion 7 of the connected metal fitting 3 and the panel body 2.

Next, we will explain the manufacturing method for precast remaining formwork panels.

The manufacturing method of the precast remaining form panel according to the present embodiment is a method for manufacturing a non-permeable precast remaining form panel 1. The manufacturing method of the precast remaining form panel includes a mixing step of mixing concrete raw materials including cement, volcanic gravel as coarse aggregate and volcanic ash as fine aggregate with mixing water for hydration reaction that has been heated to a predetermined temperature in advance to obtain a fluidized cement composition C having a predetermined mixing temperature corresponding to an outside air temperature of 0°C to 40°C, a pouring step of pouring the fluidized cement composition C into a molding form 22 after the mixing step, a molding step of molding the fluidized cement composition C poured into the molding form 22, a heat retention curing step of naturally lowering the temperature of the poured fluidized cement composition C to the outside air temperature over a predetermined time or more without reheating the poured fluidized cement composition C from the outside, and hardening the fluidized cement composition C, and a demolding step of removing the molding form 22 after the heat retention curing step. In the manufacturing method of the recast remaining formwork panel of the present invention, no heating is performed during the mixing process, except for heating the mixing water for the hydration reaction to raise its temperature.

[Mixing process]
In the mixing step, concrete raw materials including cement, volcanic gravel as coarse aggregate, and volcanic ash as fine aggregate are mixed with mixing water for hydration reaction that has been heated to a temperature of 60° C. to 85° C. in advance, to obtain a fluidized cement composition having a mixing temperature of 15° C. to 45° C. corresponding to an outside air temperature of 0° C. to 40° C. In addition, when the outside air temperature is 0° C. in winter, the mixing temperature is preferably 15° C. higher than 0° C., and when the outside air temperature is 40° C. in summer, the mixing temperature is preferably 5° C. higher than 40° C.

[Insertion process]
In the pouring step, as shown in FIG. 3, the panel body 2 is formed using a molding form 22. The molding form 22 is designed so that the back surface 2a of the panel body 2 faces upward and is maintained horizontally. The upper side of the molding form 22 is the back surface 2a side of the panel body 2. Specifically, as shown in FIG. 3(a), a mixture with the fluidized cement composition C is poured into the molding form 22 installed on a stand 21 equipped with a vibration device 20, and the fluidized cement composition C is vibrated by the vibration device 20. Then, excess water containing calcium hydroxide dissolved from the fluidized cement composition C is pushed up to the back surface 2a side of the panel body 2. Then, this excess water is interposed so as to fill the capillary gap 9A formed inside the panel body 2 and the gap 9B formed between the embedded part 7 of the connected metal fitting 3 and the panel body 2, and the entire back surface of the panel body 2 is covered with excess water containing calcium hydroxide.

[Embedding process]
3(b) and 3(c), after the pouring step, the connected metal fittings 3 attached to the reinforcing bars 5 are embedded in the fluidized cement composition C poured into the molding formwork 22. Specifically, the connecting portion of the hook portion 6 and the embedded portion 7 and the embedded portion 7 are pushed to a predetermined position in the fluidized cement composition C, and the hook portion 6 of the connected metal fittings 3 are embedded so as to protrude from the back surface 2a of the panel main body 2. Note that if the connected metal fittings 3 are not formed integrally with the panel main body 2, the embedding step is not performed.

[Insulation and curing process]
In the heat-retaining curing step, the fluidized cement composition C is hardened until the demolding strength is ensured. Specifically, the fluidized cement composition C, which has been poured into the molding form 22 and is at a temperature higher than the outside air temperature, is allowed to naturally drop in temperature to the outside air temperature over 3 hours or more without reheating from the outside. When the temperature is naturally lowered to the outside air temperature, the mixing water for the hydration reaction, which contains calcium hydroxide dissolved from the fluidized cement composition C, expands in volume and is discharged to the outside of the molding form 22, thereby preventing the bleeding phenomenon. By preventing bleeding, the generation of capillary voids 9A and voids 9B in the fluidized cement composition C is prevented.

In the heat-retaining curing process, excess water containing calcium hydroxide dissolved from the cement is pushed up toward the back surface 2a of the mixing water, and is stored in the entire back surface 2a of the panel body 2. The excess water covers the back surface 2a of the panel body 2 and fills the capillary gaps 9A and gaps 9B formed inside the panel body 2. When the fluidized cement composition C hardens, the alkaline component contained in the fluidized cement composition C reacts chemically with the silica contained in the volcanic gravel and volcanic ash to generate alkaline silica gel, forming a waterproof layer 4 over the entire back surface 2a of the panel body 2. This prevents the formation of a permeable calcium carbonate fine powder layer over the entire back surface 2a of the panel body 2. Furthermore, the waterproof layer 4 almost completely blocks the capillary gaps and gaps 9B.

[Mold removal process]
In the demolding process, the molding formwork 22 is removed after a heat retention and curing process is performed for a predetermined time.

Next, a construction method using the precast remaining form panel 1 manufactured by the above-mentioned manufacturing method will be described. The cement-based binder used in the remaining form construction method can be anything that contains moisture and hardens over time, such as concrete, mortar, and aerated mortar. In this embodiment, an example will be described in which ready-mix concrete 12 is used as the cement-based binder.

In the construction method according to this embodiment, as shown in FIG. 4(b), precast remaining form panels 1 are stacked to construct a remaining form 10. In this precast remaining form panel 1, a waterproof layer 4 is formed on the entire back surface 2a of the panel body 2, in the capillary gaps 9A, and in the gaps 9B. When constructing the remaining form 10, as shown in FIG. 4(a), the precast remaining form panel 1 is fixed to the front surface of the wooden form 13 by connecting the steel connecting fittings (separators) 11 connected to the connecting fittings 3 and the wooden form (plywood) 13.

Next, the cement-based solidifying material casting process is carried out. Specifically, ready-mixed concrete 12 is cast between the remaining precast formwork panel 1 and the wooden formwork 13 (Figure 4(a)). The ready-mixed concrete 12 is cast so that it comes into contact with the waterproof layer 4 formed on the back surface 2a of the panel body 2.

After pouring the ready-mixed concrete 12, the ready-mixed concrete 12 is hardened (cement-based binder hardening process). At this time, the waterproof layer 4 is formed in the capillary voids 9A and voids 9B, so moisture in the ready-mixed concrete 12 is prevented from penetrating into the inside of the panel body 2 through the capillary voids 9A and voids 9B. This prevents moisture from being released and evaporated from the ready-mixed concrete 12, and prevents cracks due to drying shrinkage in the ready-mixed concrete 12.

Next, we will explain the effects of the manufacturing method for precast remaining formwork panels according to this embodiment.

In the manufacturing method for precast remaining form panels according to this embodiment, concrete raw materials are used that contain cement, volcanic gravel as a coarse aggregate, and volcanic ash as a fine aggregate. Because volcanic gravel and volcanic ash are lightweight aggregates, the manufactured precast remaining form panels are lighter than conventional panels. Specifically, the weight of precast remaining form panels manufactured by the manufacturing method for precast remaining form panels according to this embodiment is 30 to 40 percent lighter than when conventional gravel or sand is used.

The precast remaining form panel 1 of this embodiment is made by mixing concrete raw materials containing volcanic lapilli as a coarse aggregate and volcanic ash as a fine aggregate with mixing water for hydration reaction that has been heated in advance, to obtain a fluidized cement composition with a mixing temperature of 15°C to 45°C, which corresponds to an outside air temperature of 0°C to 40°C, and allowing the temperature to rise naturally to the outside air temperature without heating, whereby the alkaline component contained in the fluidized cement composition C chemically reacts with the silica contained in the volcanic lapilli and volcanic ash to produce alkaline silica gel, forming a waterproof layer 4 over the entire back surface 2a of the panel main body 2, and the capillary gap 9A and the gap 9B (not shown in the drawing) formed between the embedded portion 7 of the connected metal fittings 3 and the panel main body 2 are almost completely blocked by the water- insoluble waterproof layer 4. In this way, by forming the waterproof layer 4, it is possible to prevent the formation of a water-permeable fine powder layer of calcium carbonate over the entire back surface 2a of the panel body 2, and it almost completely blocks the capillary gap 9A and the gap 9B formed between the embedded portion 7 of the connected metal fitting 3 and the panel body 2. This prevents moisture from penetrating into the panel body 2, prevents alkali-silica reaction of the coarse aggregate of the volcanic lapilli and the fine aggregate of the volcanic ash, inhibits expansion cracks caused by the alkali-silica reaction, and inhibits expansion cracks that occur over time.

Furthermore, the formation of the waterproof layer 4 prevents the formation of a water-permeable fine powder layer of calcium carbonate over the entire back surface 2a of the panel body 2, and by almost completely sealing the capillary gap 9A and the gap 9B formed between the embedded portion 7 of the connected metal fitting 3 and the panel body 2, the water impermeability of the panel body 2 can be dramatically improved. As the water impermeability of the panel body 2 is dramatically improved, this is particularly suitable for a panel body 2 that is thin.

In the manufacturing method of the precast remaining form panel according to this embodiment, concrete raw materials containing volcanic gravel as a coarse aggregate and volcanic ash as a fine aggregate are used, so that the hydration reaction is significantly faster than when, for example, silica fine powder is used, and the waterproof layer 4 can be formed on the back surface 2a of the panel body 2 and on the capillary voids 9A and voids 9B in a short time. In addition, since the hydration reaction is not slowed down even at low temperatures (for example, 5 degrees), the manufacturing method according to this embodiment is particularly useful when manufacturing the panel body 2 at low temperatures.

In addition, the manufacturing method of the precast remaining form panel according to this embodiment contributes to energy saving because the temperature of the fluidized cement composition C is naturally lowered to the outside temperature over a period of 3 hours or more during the thermal curing process without reheating the fluidized cement composition C from the outside. The construction method using the precast remaining form panel 1 according to this embodiment maintains the appearance of the remaining form 10 after construction, and can maintain the remaining form 10 stably for a long period of time without reducing its durability.

In addition, in the precast remaining form panel 1 used in this embodiment, the waterproof layer 4 is formed and the capillary voids 9A and voids 9B of the panel body 2 are almost completely blocked, so that the water in the poured fresh concrete 12 is prevented from being suddenly released and evaporated from the capillary voids 9A during the cement-based hardening material hardening process. Therefore, the fresh concrete 12 gradually hardens and becomes less likely to crack, and cracks are prevented from occurring in the panel body 2 after the remaining formwork 10 is constructed. In this way, the effect of making it less likely to crack by the gradual hardening of the fresh concrete 12 is effective when constructing the remaining formwork 10 in the summer or when constructing the remaining formwork 10 in a sunny location.

As explained above, by using the construction method according to this embodiment, deterioration of the precast remaining formwork panel 1 due to salt damage or frost damage can be prevented, cracks can be prevented from occurring in the precast remaining formwork, and the surface of the remaining formwork can be prevented from becoming contaminated.

Although the present embodiment has been described above, it is possible to select from the configurations described in the above embodiment or to change to other configurations as appropriate without departing from the spirit of the present invention.

In this embodiment, in the manufacturing method of the precast remaining form panel, the aggregate used in the concrete raw material can be only volcanic gravel and volcanic ash. In this embodiment, an example has been described in which the connected metal fittings 3 are embedded so as to protrude from the back surface 2a of the panel body 2 and are formed integrally, but it is also possible to attach the connected metal fittings after the panel body is formed. For example, screw holes are formed in each of the four corners of the back surface of the panel body, and the connected metal fittings are fixed into these screw holes.

1 Precast remaining formwork panel (panel)
2. Precast remaining formwork panel body (panel body)
2a Back (reverse side)
3 Connectable metal fitting 4 Waterproof layer 5 Reinforcing bar 6 Hook portion 7 Buried portion 9A Capillary gap 9B Gap (gap formed between buried portion 7 and panel body 2)
10 Remaining formwork 11 Connecting metal fitting (separator)
12. Ready-mix concrete (cement-based binder)
13 Wooden formwork (plywood)
20 Vibration device 21 Platform 22 Forming mold C Fluidized cement composition X Width direction Y Height direction Z Front-rear direction

Claims (2)

A method for manufacturing a precast remaining form panel using only volcanic gravel and volcanic ash as aggregate, comprising the steps of:
A mixing process of mixing concrete raw materials including cement, the volcanic gravel as a coarse aggregate, and the volcanic ash as a fine aggregate with mixing water for hydration reaction that has been heated to a temperature of 60°C to 85°C in advance, to obtain a fluidized cement composition having a mixing temperature of 15°C to 45°C, which is higher than the outside air temperature;
a step of pouring the fluidized cement composition into a molding form designed so that the rear surface of the panel body faces upward and is maintained horizontally after the mixing step, and vibrating the fluidized cement composition poured into the molding form, so that excess water containing calcium hydroxide dissolved from the cement in the mixing water is pushed up toward the rear surface of the panel body, thereby being stored over the entire rear surface of the panel body, covering the rear surface of the panel body with the excess water, and filling capillary voids formed inside the panel body , thereby molding the fluidized cement composition poured into the molding form;
a heat retention curing step of naturally lowering the temperature of the fluidized cement composition in the molding form to an outside temperature over a period of 3 hours or more without externally reheating the fluidized cement composition charged into the molding form, thereby preventing the occurrence of capillary voids in the fluidized cement composition and hardening the fluidized cement composition until a demolding strength is ensured, while preventing the volume expansion of the mixing water for hydration reaction containing calcium hydroxide dissolved from the fluidized cement composition and causing a bleeding phenomenon in which the mixing water is discharged to the outside of the molding form.
A demolding process of removing the molding form after the heat retention and curing process,
When the fluidized cement composition hardens in the heat retention curing process, the alkaline component contained in the fluidized cement composition reacts chemically with the silica contained in the volcanic lapilli and volcanic ash to generate alkaline silica gel, forming a waterproof layer over the entire back surface of the panel body, which prevents the carbon dioxide in the outside air from reacting chemically with the calcium hydroxide to form a permeable fine powder layer of calcium carbonate over the entire back surface of the panel body, and at the same time, the capillary voids are almost completely blocked by the waterproof layer, dramatically improving the impermeability of the back surface of the panel body and suppressing expansion cracks caused by the alkali-silica reaction of the coarse aggregate of the volcanic lapilli and the fine aggregate of the volcanic ash over time.
A method for manufacturing a precast remaining form panel, comprising: In the step of molding the fluidized cement composition, a stainless steel connecting fitting is embedded in the back surface of the panel body.
The method for manufacturing a precast remaining form panel according to claim 1 .

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