Explosion-proof panel and method for producing the same

Abstract

To provide an explosion-proof panel composed of a cured body of a cement composition having high compressive strength and excellent impact resistance, and to provide a method for producing the explosion-proof panel.SOLUTION: An explosion-proof panel 1 is composed of a cured body of a cement composition, wherein: the cement composition comprises cement, silica fume having a BET specific surface area of 15 to 25 m2 / g, an inorganic powder having a 50% cumulative particle diameter of 0.8 to 5 μm, an aggregate A having a maximum particle diameter of 1.2 mm or less, heat-resistant foamed beads having an average particle diameter of 1.5 to 4.5 mm, a high-range water-reducing agent, a defoaming agent, metal fibers, and water; in 100 vol% of the total amount of the cement, the silica fume, and the inorganic powder, a ratio of the cement is 55 to 65 vol%, a ratio of the silica fume is 5 to 25 vol%, and a ratio of the inorganic powder is 15 to 35 vol%; and a ratio of the heat-resistant foamed beads in the cement composition is 7.0 to 27.0 vol%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an explosion-proof panel and a method for manufacturing an explosion-proof panel. [Background technology]

[0002] Concrete structures are expected to be damaged by explosions caused by explosives or gases, or by terrorist attacks. In general concrete structures, explosions can cause total destruction of the structure or localized destruction such as peeling off of the backing, which can harm people and equipment inside the structure. Patent Document 1 describes an explosion-proof panel having excellent impact resistance and fire resistance, which is an explosion-proof panel made of a cementitious hardened body, and the cementitious hardened body is made of cement, a material having a BET specific surface area of ​​15 to 25 m 2 The document describes an explosion-proof panel characterized by being a hardened product of a cement composition containing silica fume in an amount of 0.8 to 5 μm / g, inorganic powder having a 50% cumulative particle size by volume of 0.8 to 5 μm, aggregate A having a maximum particle size of 1.2 mm or less, a high-performance water-reducing agent, an antifoaming agent, metal fibers, organic fibers, and water, wherein the cement accounts for 55 to 65% by volume, the silica fume for 5 to 25% by volume, and the inorganic powder for 15 to 35% by volume, out of a total of 100% by volume of the cement, the silica fume, and the inorganic powder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-116470 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an explosion-proof panel which is made of a hardened product of a cement composition having high compressive strength and which has excellent impact resistance, and a method for producing the explosion-proof panel. [Means for solving the problem]

[0005] The present inventors have conducted extensive research to solve the above problems, and have found that cement, a BET specific surface area of ​​15 to 25 m 2 The present inventors have found that the above-mentioned objects can be achieved by a hardened cement composition comprising silica fume in an amount of 0.8 to 5 μm, an inorganic powder having a 50% cumulative particle size by volume of 0.8 to 5 μm, aggregate A having a maximum particle size of 1.2 mm or less, heat-resistant foamed beads having an average particle size of 1.5 to 4.5 mm, a high-performance water-reducing agent, an antifoaming agent, fibers, and water, wherein, out of a total of 100% by volume of cement, silica fume, and inorganic powder, the proportion of cement is 55 to 65% by volume, the proportion of silica fume is 5 to 25% by volume, and the proportion of inorganic powder is 15 to 35% by volume, and the proportion of heat-resistant foamed beads in the cement composition is 7.0 to 27.0% by volume, and have completed the present invention. That is, the present invention provides the following [1] to [5]. [1] An explosion-proof panel made of a hardened cement composition, wherein the cement composition is cement, a BET specific surface area of ​​15 to 25 m 2 1. An explosion-proof panel comprising: silica fume in an amount of 0.8 to 5 μm / g; inorganic powder having a 50% cumulative particle size by volume of 0.8 to 5 μm; aggregate A having a maximum particle size of 1.2 mm or less; heat-resistant foamed beads having an average particle size of 1.5 to 4.5 mm; a high-performance water-reducing agent; an antifoaming agent; fibers; and water; wherein, in a total of 100% by volume of the cement, the silica fume, and the inorganic powder, the proportion of the cement is 55 to 65% by volume, the proportion of the silica fume is 5 to 25% by volume, and the proportion of the inorganic powder is 15 to 35% by volume; and the proportion of the heat-resistant foamed beads in the cement composition is 7.0 to 27.0% by volume. [2] The explosion-proof panel according to [1], wherein the rate of thermal dimensional change of the heat-resistant foam beads when left standing at a temperature of 180°C for 168 hours is within the range of ±1.0%.

[0006] [3] A method for manufacturing the explosion-proof panel described in [1] or [2] above, comprising: a molding step of pouring the cement composition into a formwork to obtain an unhardened molded body; a room temperature curing step of subjecting the unhardened molded body to sealed curing or air curing at 10 to 40°C for 24 hours or more, and then removing it from the formwork to obtain a hardened molded body; and a heat curing step of subjecting the hardened molded body to either steam curing or hot water curing at 70°C or more but less than 100°C for 6 hours or more, or autoclave curing at 100 to 200°C for 1 hour or more, to obtain the explosion-proof panel. [4] A high-temperature heating process in which the explosion-proof panel after the heat curing process is heated at 150 to 200°C for 24 hours or more (excluding heating by autoclave curing). The method for manufacturing the explosion-proof panel according to [3] above, [5] The method for manufacturing an explosion-proof panel according to [3] or [4], further comprising a water absorption step of making the hardened molded body absorb water between the room temperature curing step and the heat curing step. [Effects of the Invention]

[0007] The explosion-proof panel of the present invention is made of a hardened cement composition that has high compressive strength and excellent impact resistance, and therefore concrete structures constructed using the panel (for example, explosion-proof walls or storage facilities for explosives, etc.) can protect people and equipment from flying debris generated by an explosion. Furthermore, because the explosion-proof panel of the present invention has excellent strength, it is possible to reduce the thickness of the panel and thereby achieve weight reduction, which significantly reduces the workload involved in transporting the panel to a construction site and in assembling and installing an explosion-proof wall or a storage facility for explosives or the like using the panel. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing an example of an explosion-proof panel of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] The explosion-proof panel of the present invention is an explosion-proof panel made of a hardened cement composition, wherein the cement composition is made of cement, a BET specific surface area of ​​which is 15 to 25 m 2 The cement composition contains silica fume in an amount of 0.8 to 5 μm / g, inorganic powder with a 50% cumulative particle size by volume of 0.8 to 5 μm, aggregate A with a maximum particle size of 1.2 mm or less, heat-resistant foamed beads with an average particle size of 1.5 to 4.5 mm, a high-performance water-reducing agent, an antifoaming agent, fibers, and water, and the cement ratio is 55 to 65 vol%, the silica fume ratio is 5 to 25 vol%, and the inorganic powder ratio is 15 to 35 vol%, of a total of 100 vol% of the cement, silica fume, and inorganic powder, and the heat-resistant foamed beads ratio is 7.0 to 27.0 vol% in the cement composition. The cement composition used in the present invention will be described in detail below. In this specification, "explosion-proof" means an application for preventing damage caused by an explosion. Furthermore, the term "cement composition" includes both a fluid form before hardening and a form after hardening.

[0010] The type of cement is not particularly limited, and various types of Portland cement can be used, such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, sulfate-resistant Portland cement, low-heat Portland cement, etc. These may be used alone or in combination of two or more. Among these, it is preferable to use moderate-heat Portland cement or low-heat Portland cement from the viewpoint of improving the fluidity of the cement composition before hardening.

[0011] The BET specific surface area of ​​silica fume is 15 to 25 m 2 / g, preferably 17 to 23 m 2 / g, particularly preferably 18 to 22 m 2 / g. The specific surface area is 15m 2 If the specific surface area is less than 25 m / g, the strength development of the cement composition will decrease. 2 If the saturation coefficient exceeds 1 / g, the fluidity of the cement composition before hardening decreases.

[0012] Examples of inorganic powders having a 50% cumulative volume particle size of 0.8 to 5 μm (hereinafter sometimes abbreviated as "inorganic powders") include quartz powder (silica powder), volcanic ash, fly ash (classified or pulverized), slag powder, limestone powder, feldspar powder, mullite powder, alumina powder, silica sol, carbide powder, nitride powder, etc. These may be used alone or in combination of two or more. Among these, it is preferable to use quartz powder or fly ash from the viewpoint of improving the fluidity of the cement composition before hardening and improving the strength development of the cement composition. In this specification, the inorganic powder having a 50% volume cumulative particle size of 0.8 to 5 μm does not include cement.

[0013] The 50% volume cumulative particle size of the inorganic powder is 0.8 to 5 μm, preferably 1 to 4 μm, more preferably 1.1 to 3.5 μm, and particularly preferably 1.2 μm or more and less than 3 μm. If the particle size is less than 0.8 μm, the fluidity of the cement composition before hardening decreases. If the particle size exceeds 5 μm, the strength development of the cement composition decreases. The 50% volume cumulative particle size of the inorganic powder can be determined using a commercially available particle size distribution measuring device (for example, Nikkiso Co., Ltd., product name "Microtrac HRA Model 9320-X100"). Specifically, a cumulative particle size curve is created using a particle size distribution analyzer, and the 50% volume cumulative particle size can be determined from the cumulative particle size curve. 3 0.06 g of a sample is added to the mixture, and the mixture is ultrasonically dispersed for 90 seconds using an ultrasonic dispersing device (for example, Nippon Seiki Seisakusho, product name "US300"), and then the resultant is measured.

[0014] The maximum particle size of the inorganic powder is preferably 15 μm or less, more preferably 14 μm or less, and particularly preferably 13 μm or less, from the viewpoint of further improving the strength development of the cement composition. The 95% volume cumulative particle size of the inorganic powder is preferably 8 μm or less, more preferably 7 μm or less, and particularly preferably 6 μm or less, from the viewpoint of further improving the strength development of the cement composition.

[0015] The inorganic powder is preferably one containing SiO2 as a main component (for example, quartz powder). The SiO2 content in the inorganic powder is preferably 50 mass% or more, more preferably 60 mass% or more, and particularly preferably 70 mass% or more. If the content is 50 mass% or more, the strength development of the cement composition is further improved.

[0016] In the cement composition, the proportion of cement is 55 to 65 volume %, preferably 57 to 63 volume %, of the total amount of cement, silica fume, and inorganic powder (100 volume %). If the proportion is less than 55 volume %, the strength development of the cement composition decreases. If the proportion is more than 65 volume %, the fluidity of the cement composition before hardening decreases. The proportion of silica fume is 5 to 25% by volume, preferably 7 to 23% by volume, of the total amount of cement, silica fume, and inorganic powder (100% by volume). If the proportion is less than 5% by volume, the strength development of the cement composition decreases. If the proportion is more than 25% by volume, the fluidity of the cement composition before hardening decreases. The proportion of the inorganic powder is 15 to 35% by volume, preferably 17 to 33% by volume, of the total amount of cement, silica fume, and inorganic powder (100% by volume). If the proportion is less than 15% by volume, the strength development of the cement composition decreases. If the proportion is more than 35% by volume, the fluidity of the cement composition before hardening decreases.

[0017] Examples of aggregate A include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, natural emery sand, artificial fine aggregate (for example, slag fine aggregate, fired fine aggregate obtained by firing fly ash, etc., artificial (man-made) emery sand, and coarsely crushed alumina or carbides (for example, silicon carbide, boron carbide, etc.)), recycled fine aggregate, and mixtures thereof. The maximum particle size of the aggregate A is 1.2 mm or less, preferably 1.1 mm or less, and particularly preferably 1.0 mm or less. If the maximum particle size is 1.2 mm or less, the strength development of the cement composition is improved. From the viewpoint of improving the fluidity of the cement composition before hardening and improving the strength development of the cement composition, it is preferable that the particle size distribution of aggregate A is such that the proportion of aggregate with a particle size of 0.6 mm or less is 95 mass% or more, the proportion of aggregate with a particle size of 0.3 mm or less is 40 to 50 mass%, and the proportion of aggregate with a particle size of 0.15 mm or less is 6 mass% or less. The proportion of aggregate A in the cement composition is preferably 7.0 to 27.0 vol%, more preferably 9.0 to 25.0 vol%, even more preferably 11.0 to 22.0 vol%, and particularly preferably 14.0 to 19.0 vol%. If the proportion is 7.0 vol% or more, the amount of shrinkage of the hardened product of the cement composition is reduced. If the proportion is 27.0 vol% or less, the strength development of the cement composition is further improved.

[0018] Examples of heat-resistant foam beads include those made of synthetic resins such as polyester, polystyrene, polypropylene, and urethane. From the viewpoint of further improving the impact resistance of the hardened cement composition, it is preferable that the heat-resistant foamed beads have a thermal dimensional change rate within the range of ±1.0% when left standing at a temperature of 180°C for 168 hours. Here, the thermal dimensional change rate can be calculated using the following formula (1) in accordance with, for example, "JIS K 6767 (Foamed plastics - Polyethylene - Testing method)". Heat dimensional change rate (%) = (dimension of heat-resistant foamed beads after standing (mm) - dimension of heat-resistant foamed beads before standing (mm)) / dimension of heat-resistant foamed beads before standing (mm) × 100

[0019] The average particle size of the heat-resistant foamed beads is 1.5 to 4.5 mm, preferably 1.8 to 4.2 mm, and more preferably 2.5 to 3.5 mm. If the average particle size is less than 1.5 mm, the impact resistance of the hardened body of the cement composition will decrease. If the average particle size is more than 4.5 mm, the strength development of the cement composition will decrease, and the impact resistance of the hardened body of the cement composition will also decrease. In this specification, the average particle size of the heat-resistant expanded beads is, for example, the average value of the measured values ​​obtained by measuring the diameters of at least 50 heat-resistant expanded beads using an image analyzer or the like.

[0020] The proportion of heat-resistant foam beads in the cement composition is 7.0 to 27.0 vol%, preferably 9.0 to 25.0 vol%, more preferably 12.0 to 23.0 vol%, and particularly preferably 15.0 to 20.0 vol%. If the proportion is less than 7.0 vol%, the impact resistance of the hardened body of the cement composition will decrease. If the proportion is more than 27.0 vol%, material separation will occur, making it difficult to mold the cement composition.

[0021] The total amount of aggregate A and heat-resistant foamed beads in the cement composition is preferably 20.0 to 40.0% by volume, more preferably 22.0 to 38.0% by volume, even more preferably 30.0 to 37.0% by volume, and particularly preferably 32.0 to 36.0% by volume. If this ratio is 20.0% by volume or more, the calorific value of the cement composition is reduced, and the shrinkage of the hardened body of the cement composition is reduced. If this ratio is 40.0% by volume or less, the compressive strength of the cementitious hardened body is increased. The proportion of the heat-resistant foamed beads in a total of 100% by volume of aggregate A and heat-resistant foamed beads is preferably 20.0 to 80.0% by volume, more preferably 25.0 to 75.0% by volume, even more preferably 35.0 to 65.0% by volume, and particularly preferably 40.0 to 60.0% by volume. If the proportion is 20% by volume or more, the impact resistance of the hardened body of the cement composition is improved. If the proportion is 80% by volume or less, material separation is less likely to occur.

[0022] The high-performance water-reducing agent may be a naphthalenesulfonic acid-based, melamine-based, polycarboxylic acid-based, or other high-performance water-reducing agent. Among these, polycarboxylic acid-based high-performance water-reducing agents are preferred from the viewpoint of improving the fluidity of the cement composition before hardening and improving the strength development of the cement composition. The amount of the high-range water-reducing agent is preferably 0.2 to 1.5 parts by mass, more preferably 0.3 to 1.2 parts by mass, calculated as solid content, per 100 parts by mass of the total amount of cement, silica fume, and inorganic powder. If the amount is 0.2 parts by mass or more, the water-reducing performance is improved, and the fluidity of the cement composition before hardening is improved. If the amount is 1.5 parts by mass or less, the strength development of the cement composition is further improved.

[0023] As the defoaming agent, commercially available products can be used. The amount of antifoaming agent blended is preferably 0.001 to 0.1 parts by mass, more preferably 0.01 to 0.07 parts by mass, and particularly preferably 0.01 to 0.05 parts by mass, relative to 100 parts by mass of the total amount of cement, silica fume, and inorganic powder. If the amount is 0.001 parts by mass or more, the strength development of the cement composition is improved. If the amount exceeds 0.1 parts by mass, the effect of improving the strength development of the cement composition reaches a plateau.

[0024] The cement composition contains fibers from the viewpoint of improving the bending strength and breaking energy of the hardened product of the cement composition and thereby increasing the impact resistance of the explosion-proof panel. Examples of fibers include metal fibers, organic fibers, carbon fibers, etc. These may be used alone or in combination of two or more. The proportion of fibers in the cement composition is preferably 0.3 to 4.0% by volume, more preferably 1.0 to 3.8% by volume, and particularly preferably 1.5 to 3.5% by volume. If the proportion is 0.3% by volume or more, the bending strength and impact resistance of the hardened product of the cement composition are improved. If the proportion is 4.0% by volume or less, the bending strength and impact resistance of the hardened product of the cement composition can be improved without reducing the fluidity and workability of the cement composition before hardening.

[0025] Examples of metal fibers include steel fibers, stainless steel fibers, and amorphous fibers. These may be used alone or in combination of two or more. Among these, steel fibers are preferred in terms of their excellent strength, cost, and availability. From the viewpoints of preventing separation of the metal fibers in the cement composition and improving the bending strength and impact resistance of the hardened cement composition, the dimensions of the metal fibers are preferably 0.01 to 1.0 mm in diameter and 2 to 30 mm in length, more preferably 0.05 to 0.5 mm in diameter and 5 to 25 mm in length. The aspect ratio of the metal fibers (fiber length / fiber diameter) is preferably 20 to 200, more preferably 40 to 150. Furthermore, the shape of the metal fibers is preferably a shape that provides some kind of physical adhesive force (for example, a spiral or wavy shape) rather than a straight shape. A spiral or other shape ensures stress between the metal fibers and the matrix as they are pulled out, improving the bending strength of the hardened cement composition.

[0026] The organic fiber may be any fiber that can withstand the heating in the method for manufacturing the explosion-proof panel of the present invention described below, and examples thereof include aramid fiber, polyparaphenylene benzobisoxazole fiber, polyethylene fiber, polyallylate fiber, polypropylene fiber, and polyvinyl alcohol fiber. The cement composition containing organic fibers can further enhance the fire resistance of the explosion-proof panel. Among them, polypropylene fibers are preferred from the viewpoints of ease of availability and improving the fire resistance of the hardened body of the cement composition. Examples of carbon fibers include PAN-based carbon fibers and pitch-based carbon fibers. The dimensions of the organic fibers and carbon fibers are preferably 0.005 to 1.0 mm in diameter and 2 to 30 mm in length, more preferably 0.01 to 0.5 mm in diameter and 5 to 25 mm in length, from the viewpoints of preventing material separation of these fibers in the cement composition and improving the fracture energy of the hardened body. The aspect ratio (fiber length / fiber diameter) of the organic fibers and carbon fibers is preferably 20-200, and more preferably 30-150.

[0027] The water is not particularly limited, and tap water, sludge water, etc. can be used. The amount of water is preferably 10 to 20 parts by mass, more preferably 11 to 18 parts by mass, and particularly preferably 12 to 16 parts by mass, relative to 100 parts by mass of the total amount of cement, silica fume, and inorganic powder. If the amount is 10 parts by mass or more, the fluidity of the cement composition before hardening is improved. If the amount is 20 parts by mass or less, the strength development of the cement composition is further improved.

[0028] The compressive strength of the hardened body obtained by hardening the mortar made of the cement composition (not including aggregate B described later) is preferably 280 N / mm 2 More preferably, 290N / mm 2 More than 300N / mm 2 That's all.

[0029] The cement composition of the present invention may contain aggregate B having a maximum particle size of more than 1.2 mm and not more than 13 mm. Examples of aggregate B include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, natural emery sand, artificial fine aggregate (for example, slag fine aggregate, fired fine aggregate obtained by firing fly ash, etc., and artificial (man-made) emery sand), recycled fine aggregate, river gravel, mountain gravel, land gravel, crushed stone, artificial coarse aggregate (for example, slag coarse aggregate, fired coarse aggregate obtained by firing fly ash, etc.), recycled coarse aggregate, coarsely crushed alumina or carbide (for example, silicon carbide, boron carbide, etc.), and mixtures thereof. The maximum particle size of aggregate B is 13 mm or less, preferably 12 mm or less, more preferably 11 mm or less, and particularly preferably 10 mm or less. If the maximum particle size is 13 mm or less, the strength development of the cement composition is improved.

[0030] From the viewpoint of cost reduction, the maximum particle size of aggregate B is a value exceeding 1.2 mm, preferably 3 mm or more, more preferably 5 mm or more, and particularly preferably 7 mm or more. In this specification, when the maximum particle size of aggregate B is 5 mm or more, the "maximum particle size" refers to the particle size of aggregate B indicated by the nominal size of the smallest sieve among those that will pass 90% or more by mass of the total aggregate B (generally known as the definition of the maximum particle size of coarse aggregate).

[0031] The minimum particle size of aggregate B is preferably greater than the maximum particle size of aggregate A, more preferably 2 mm or more, even more preferably 3 mm or more, even more preferably 4 mm or more, and particularly preferably 5 mm or more (in this case, it corresponds to coarse aggregate). In this specification, the minimum particle size of aggregate B refers to the particle size of aggregate B when it reaches 15% by mass of the total aggregate B when accumulated from the smallest particle size to the largest particle size.

[0032] In the present invention, the total ratio of aggregate A and aggregate B in the cement composition is preferably 25 to 40% by volume, more preferably 28 to 38% by volume, and particularly preferably 30 to 36% by volume. If this ratio is 25% by volume or more, the calorific value of the cement composition is reduced, and the shrinkage of the hardened product of the cement composition is reduced. If this ratio is 40% by volume or less, the strength development of the cement composition can be improved. The ratio of aggregate B to the total amount of aggregate A and aggregate B is preferably 40% by volume or less, more preferably 30% by volume or less, and particularly preferably 25% by volume or less. If the ratio is 40% by volume or less, the strength development of the cement composition can be improved.

[0033] The method for producing an explosion-proof panel made of the hardened product of the above-mentioned cement composition will be described in detail below. An example of a method for manufacturing an explosion-proof panel of the present invention includes a molding step of pouring a cement composition into a formwork to obtain an unhardened molded body, a room temperature curing step of sealing and air-curing the unhardened molded body at 10 to 40°C for 24 hours or more, and then removing it from the formwork to obtain a hardened molded body, and a heat curing step of subjecting the hardened molded body to either steam curing or hot water curing at 70 to 100°C for 6 hours or more, or autoclave curing at 100 to 200°C for 1 hour or more, or both, to obtain an explosion-proof panel made of a hardened cement composition. Each step will be explained in detail below.

[0034] [Molding process] This step involves pouring the cement composition into a formwork to obtain an unhardened molded body. The method for mixing the cement composition before pouring is not particularly limited. The equipment used for mixing is also not particularly limited, and conventional mixers such as an omni mixer, a pan mixer, a twin-shaft mixer, and a tilting mixer can be used. Furthermore, the pouring (molding) method is also not particularly limited. The unhardened molded body in this step may be made of a cement composition in which the air bubbles have been reduced or removed. By reducing or removing the air bubbles in the cement composition, the strength development of the cement composition can be further improved. Methods for reducing or removing bubbles in a cement composition include (1) mixing the cement composition under reduced pressure, (2) reducing the pressure of the mixed cement composition before pouring it into a formwork to degas it, and (3) reducing the pressure of the cement composition after pouring it into a formwork to degas it.

[0035] [Room temperature curing process] In this step, the uncured molded body is subjected to sealed curing or air curing at 10 to 40°C (preferably 15 to 30°C) for 24 hours or more (preferably 24 to 72 hours, more preferably 24 to 48 hours), and then removed from the formwork to obtain a cured molded body. If the curing temperature is 10°C or higher, the curing time can be shortened. If the curing temperature is 40°C or lower, the compressive strength of the hardened body of the cement composition (explosion-proof panel) can be increased. If the curing time is 24 hours or more, defects such as chips and cracks are less likely to occur in the hardened molded body when it is demolded. In this step, the cured molded body preferably has a compressive strength of 20 to 100 N / mm 2 , more preferably 30 to 80N / mm 2 When the compressive strength reaches 20 N / mm, the cured molded body is preferably removed from the mold. 2 If the compressive strength is 100 N / mm or more, defects such as chipping or cracking are unlikely to occur in the hardened molded body when it is demolded. 2 If the above conditions are met, the cured molded body can absorb water with less effort in the water absorption step described below.

[0036] [Heat curing process] In this step, the hardened molded body obtained in the previous step (room temperature curing step or water absorption step) is subjected to either steam curing or hot water curing at a temperature of 70°C or higher but lower than 100°C (preferably 75 to 95°C, more preferably 80 to 92°C) for 6 hours or more, or autoclave curing at 100 to 200°C (preferably 160 to 190°C) for 1 hour or more, to obtain an explosion-proof panel made of a hardened cement composition. In this step, when only steam curing or hot water curing is performed, the curing time is preferably 24 hours or more, more preferably 24 to 96 hours, and particularly preferably 36 to 72 hours. When only autoclave curing is performed, the curing time is preferably 8 to 60 hours, and more preferably 12 to 48 hours. When both steam curing or hot water curing and autoclave curing are performed (for example, when steam curing or hot water curing is performed followed by autoclave curing), the curing time for steam curing or hot water curing is preferably 6 to 72 hours, and more preferably 12 to 48 hours, and the curing time for autoclave curing is preferably 1 to 24 hours, and more preferably 4 to 18 hours. In this step, if the curing temperature is within the above range, the curing time can be shortened and the strength development of the cement composition can be improved. In addition, in this step, if the curing time is within the above range, the strength development of the cement composition can be improved.

[0037] [High temperature heating process] This step is an optional step in which the explosion-proof panel after the heat curing step is heated at 150 to 200°C (preferably 170 to 190°C) for 24 hours or more (preferably 24 to 72 hours, more preferably 36 to 48 hours) (excluding heating due to autoclave curing). By carrying out this step, the strength (compression strength) of the explosion-proof panel can be further improved. The heating in this step is usually carried out in a dry atmosphere (in other words, in a state where water or water vapor is not artificially supplied). If the heating temperature is 150°C or higher, the heating time can be shortened. If the heating temperature is 200°C or lower, the compression strength of the explosion-proof panel can be improved. If the heating time is 24 hours or more, the compression strength of the explosion-proof panel can be further improved.

[0038] [Water absorption process] A water absorption step may be included between the room temperature curing step and the heat curing step, in which the hardened molded body obtained in the room temperature curing step is allowed to absorb water. Examples of methods for making the hardened molded body absorb water include a method of immersing the molded body in water. In the method of immersing the molded body in water, from the viewpoint of increasing the amount of water absorption in a short time and increasing the compressive strength of the hardened cement composition, the following methods are preferred: (1) a method of immersing the molded body in water under reduced pressure, (2) a method of immersing the molded body in boiling water and then lowering the water temperature to 40°C or less while the molded body is still immersed, (3) a method of immersing the molded body in boiling water, removing the molded body from the boiling water, and then immersing the molded body in water at 40°C or less, (4) a method of immersing the molded body in water under pressure, or (5) a method of immersing the molded body in an aqueous solution in which an agent for improving the water permeability of the molded body is dissolved.

[0039] The method for immersing the molded body in water under reduced pressure includes a method using equipment such as a vacuum pump or a large reduced pressure vessel. The method for immersing the molded body in boiling water may be carried out using equipment such as a high-temperature, high-pressure vessel or a hot water bath. The time for which the hardened molded body is immersed in water under reduced pressure or boiling water is preferably 3 minutes or more, more preferably 8 minutes or more, and particularly preferably 20 minutes or more, from the viewpoint of increasing the water absorption rate. The upper limit of the time is preferably 60 minutes, more preferably 45 minutes, from the viewpoint of increasing the compressive strength of the hardened cement composition.

[0040] The water absorption rate in the water absorption step is preferably 0.2 vol% or more, more preferably 0.3 to 2.0 vol%, and particularly preferably 0.35 to 1.7 vol%, expressed as the ratio of water to 100 vol% of a hardened molded body having a diameter of 50 mm x 100 mm, when the cement composition does not contain coarse aggregate (when the cement composition does not contain aggregate B, or when aggregate B in the cement composition does not fall under the category of coarse aggregate); and is preferably 0.2 vol% or more, more preferably 0.3 to 2.0 vol%, and particularly preferably 0.35 to 1.7 vol%, expressed as the ratio of water to 100 vol% of a hardened molded body having a diameter of 100 mm x 200 mm, when the cement composition contains coarse aggregate (when aggregate B in the cement composition falls under the category of coarse aggregate). If the water absorption rate of these is 0.2% by volume or more, the compressive strength of the hardened body of the cement composition can be increased.

[0041] The explosion-proof panel of the present invention is made of a hardened cement composition having high compressive strength, and therefore is less susceptible to cracking. Furthermore, since the explosion-proof panel of the present invention is made of a hardened cement composition having high compressive strength, its thickness can be reduced. As a result, the explosion-proof panel can be made lighter, facilitating the construction of explosion-proof walls and storage facilities for explosives, etc. Furthermore, the explosion-proof panel of the present invention has excellent impact resistance.

[0042] The shape of the explosion-proof panel of the present invention may be determined appropriately to match the shape of the structure to be constructed using the panel, but from the standpoint of versatility, it may also be a rectangular (square or oblong) plate shape, such as the explosion-proof panel 1 shown in Figure 1. From the viewpoint of strength and impact resistance, the thickness of the explosion-proof panel is preferably 6 cm or more, more preferably 8 cm or more, and particularly preferably 10 cm or more, and from the viewpoint of ease of manufacturing and improved workability due to lighter weight, the thickness is preferably 30 cm or less, more preferably 25 cm or less, and even more preferably 20 cm or less. Furthermore, from the viewpoint of ease of handling, the vertical and horizontal dimensions of the explosion-proof panel are preferably 3 m or less, more preferably 2.5 m or less, and particularly preferably 2 m or less, and from the viewpoint of work efficiency, they are preferably 1 m or more, more preferably 1.5 m or more, and particularly preferably 2 m or more.

[0043] Concrete structures constructed using the explosion-proof panel of the present invention include explosion-proof walls formed by connecting explosion-proof panels vertically and horizontally. If the thickness of the explosion-proof wall is desired to be greater (for example, 30 cm or more), it may be constructed by stacking multiple explosion-proof panels. Furthermore, in order to construct a storage facility for explosive substances such as gunpowder, the explosion-proof panel of the present invention can be used as a member for the wall and roof (and floor, if necessary) of the storage facility. [Example]

[0044] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Cement A: Low-heat Portland cement manufactured by Taiheiyo Cement Corporation, density: 3.22 g / cm 3 (2) Cement B: ordinary Portland cement manufactured by Taiheiyo Cement Corporation, density: 3.15 g / cm 3 (3) Silica fume; BET specific surface area: 20 m 2 / g, density: 2.36g / cm 3 , (4) Inorganic powder; quartz fine powder, density: 2.68g / cm 3 50% volume cumulative particle size: 2 μm, maximum particle size: 12 μm, 95% volume cumulative particle size: 5.8 μm, SiO2 content: 90 mass% or more (5) Aggregate A: Fine aggregate, silica sand, surface dry density: 2.62 g / cm 3 , maximum particle size 1.0 mm, particles with a particle size of 0.6 mm or less: 98% by mass, particles with a particle size of 0.3 mm or less: 45% by mass, particles with a particle size of 0.15 mm or less: 3% by mass (6) Aggregate: Fine aggregate, mountain sand, surface dry density: 2.59 g / cm3 , (7) Coarse aggregate: crushed stone, surface dry density: 2.64 g / cm 3 , (8) Metal fiber: Taiheiyo Cement Corporation, UFC steel fiber, diameter: 0.2 mm, length: 15 mm, density: 7.84 g / cm 3 (9) Polycarboxylic acid-based high-performance water reducer; manufactured by FLORIC Co., Ltd., trade name "FLORIC SF500U", solid content: 28.4% by mass (10) Defoamer: Pozzolith Solutions, trade name "Master Air 404" (11) Air-entraining agent: manufactured by Pozzolith Solutions, Inc., trade name "Master Air 202" (12) Water: Tap water (13) Heat-resistant foam beads A: Polyester foam beads, average particle size: 1.0 mm, bulk density: 0.30 g / cm 3 (14) Heat-resistant foam beads B: Polyester foam beads, average particle size: 2.0 mm, bulk density: 0.20 g / cm 3 (15) Heat-resistant foam beads C; polyester foam beads, average particle size: 3.0 mm, bulk density: 0.15 g / cm 3 (16) Heat-resistant foam beads D; polyester foam beads, average particle size: 4.0 mm, bulk density: 0.10 g / cm 3 (17) Heat-resistant foam beads E; polyester foam beads, average particle size: 5.0 mm, bulk density: 0.05 g / cm 3 When heat-resistant foamed beads A to E were left to stand for 168 hours at a temperature of 180°C, the thermal dimensional change rates measured in accordance with JIS K 6767 (expanded plastics - polyethylene - testing methods) were all within the range of ±1.0%.

[0045] [Preparation of powder raw materials] Cement A, silica fume, and inorganic powder were mixed so that the proportion of cement was 60% by volume, the proportion of silica fume was 10% by volume, and the proportion of inorganic powder was 30% by volume, out of a total of 100% by volume of the powder raw materials (cement A, silica fume, and inorganic powder), to prepare a powder raw material (shown as "powder" in Table 1). [Examples 1 to 6] The powdered raw materials in the cement composition (shown as "powder" in Table 1), water, aggregate A (fine aggregate: silica sand), and the heat-resistant foam beads of the type shown in Table 1 were mixed in amounts such that the respective proportions were as shown in Table 1. The powder raw materials, aggregate A, and heat-resistant foam beads were charged into an omnimixer and dry mixed for 15 seconds. Next, water, a polycarboxylic acid-based high-performance water-reducing agent, and an antifoaming agent were charged into the omnimixer in the amounts shown in Table 1 and mixed for 4 minutes. After mixing, any mixture adhering to the side walls of the omnimixer was scraped off, and the mixture was mixed for another 2 minutes. Thereafter, the steel fibers were added to the omnimixer in an amount such that the ratio of the steel fibers in the cement composition was the ratio shown in Table 1, and the mixture was further mixed for 2 minutes.

[0046] The resulting kneaded product was cast into a cylindrical mold of φ50 × 100 mm to obtain an uncured molded body. After casting, the uncured molded body was subjected to sealed curing at 20 ° C for 48 hours, and then demolded to obtain a cured molded body. The molded body was immersed in water for 30 minutes in a depressurized desiccator (pressure inside the desiccator: -0.1 MPa). The depressurization was performed using an "Aspirator (AS-01)" manufactured by AS ONE Corporation. After immersion, the molded body was steam cured at 90°C for 48 hours, then cooled to 20°C, and heated at 180°C for 48 hours. The compressive strength of the molded body (hardened body of the cement composition) after heating was measured in accordance with "JIS A 1108:2018 (Test method for compressive strength of concrete)". In addition, the Young's modulus of the molded body after heating was measured in accordance with "JIS A 1149:2017 (Test method for static elastic modulus of concrete)".

[0047] Furthermore, in the same manner as for the above-mentioned heated molded body (hardened body of the cement composition), a flat plate specimen measuring 500 mm in length, 500 mm in width, and 100 mm in thickness was prepared. 150 g of C-4 explosive was placed directly on the approximate center of the top surface (a plane measuring 500 mm long x 500 mm wide) of the flat plate specimen, and then detonated. The depth of the crater-like damage on the top surface where the C-4 bomb was placed (shown as "crater depth" in Table 2) was measured. In addition, the depth of spalling fracture that occurred on the surface (bottom surface) opposite the top surface where the C-4 bomb was placed (shown as "spaul depth" in Table 2) was measured. In Table 2, cases where no spalling fracture occurred on the opposite surface (bottom surface) are indicated as "-". In addition, in assessing explosion resistance, a specimen in which a crater appeared on the top surface when the C-4 bomb was placed, but no peeling or failure occurred on the opposite surface (bottom surface) (shown as "surface failure" in Table 2) was evaluated as "Good," while a specimen in which a crater appeared on the top surface when the C-4 bomb was placed, and peeling or failure occurred on the opposite surface (bottom surface) (shown as "reverse surface peeling" in Table 2) was evaluated as "Poor." In addition, fractures that penetrated the flat plate specimen were evaluated as "surface peeling + penetration."

[0048] [Comparative Example 1] Ordinary Portland cement (shown as "powder" in Table 1), water, pit sand (fine aggregate), and coarse aggregate were mixed in amounts such that the ratios shown in Table 1 were obtained. To mix, ordinary Portland cement, pit sand, and coarse aggregate were placed in a forced mixing pan mixer and dry mixed for 15 seconds. Next, water and air-entraining agent were added to the forced mixing pan mixer in the amounts shown in Table 1 and mixed for 2 minutes. After mixing, any mixture adhering to the side walls of the forced mixing pan mixer was scraped off, and the mixture was mixed for an additional 30 seconds. The kneaded material thus obtained was subjected to sealed curing at 20°C for 28 days, and then demolded to obtain a hardened molded body (hardened cement composition). The obtained molded body was subjected to measurement of compressive strength and the like in the same manner as in Example 1. [Comparative Examples 2 to 3, 5 to 6] A hardened product of the cement composition was obtained in the same manner as in Example 1. A molded product (hardened product of the cement composition) was obtained after heating. The obtained molded product was subjected to measurement of compressive strength and the like in the same manner as in Example 1. Comparative Example 4 The cement composition was kneaded in the same manner as in Example 1 except that no fine aggregate was used, but separation of the materials occurred and molding was not possible. The results are shown in Table 2.

[0049] [Table 1]

[0050] [Table 2]

[0051] From Table 2, it can be seen that the explosion-proof panel of the present invention does not experience peeling on the back surface and has excellent impact resistance. On the other hand, in Comparative Examples 1 to 3 and 5 to 5, even though the compressive strength of the cement compositions was the same, peeling occurred on the back surface, and it is clear that the impact resistance was poor. [Explanation of symbols]

[0052] 1 Explosion-proof panel

Claims

1. An explosion-proof panel made of a hardened cement composition, The cement composition comprises cement, a BET specific surface area of ​​15 to 25 m ２ / g of silica fume, inorganic powder having a 50% volume cumulative particle size of 0.8 to 5 μm, aggregate A having a maximum particle size of 1.2 mm or less, heat-resistant foamed beads having an average particle size of 1.5 to 4.5 mm, a high-performance water-reducing agent, a defoamer, fibers, and water; The cement comprises 55 to 65% by volume, the silica fume comprises 5 to 25% by volume, and the inorganic powder comprises 15 to 35% by volume, based on a total volume of 100% by volume of the cement, the silica fume, and the inorganic powder; and An explosion-proof panel characterized in that the proportion of the heat-resistant foam beads in the cement composition is 7.0 to 27.0 volume %.

2. 2. The explosion-proof panel according to claim 1, wherein the heat-resistant foamed beads have a dimensional change rate of within ±1.0% when left to stand at a temperature of 180°C for 168 hours.

3. A method for manufacturing the explosion-proof panel according to claim 1 or 2, comprising: a molding step of casting the cement composition into a formwork to obtain an unhardened molded body; a room temperature curing step of subjecting the uncured molded body to sealed curing or air curing at 10 to 40°C for 24 hours or more, and then removing the uncured molded body from the formwork to obtain a cured molded body; a heat curing step of subjecting the cured molded body to steam curing or hot water curing at 70°C or higher but lower than 100°C for 6 hours or more, and / or autoclave curing at 100 to 200°C for 1 hour or more, to obtain the explosion-proof panel; A method for manufacturing an explosion-proof panel, comprising:

4. a high-temperature heating step of heating the explosion-proof panel after the heat curing step at 150 to 200°C for 24 hours or more (excluding heating by autoclave curing); The method for manufacturing the explosion-proof panel according to claim 3, comprising:

5. 4. The method for manufacturing an explosion-proof panel according to claim 3, further comprising a water absorption step for allowing the hardened molded body to absorb water between the room temperature curing step and the heat curing step.

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