INORGANIC EXPANDABLE REFRACTORY COMPOSITION

Abstract

The present invention provides a refractory composition containing expandable powder that consists of an alkali metal oxide and silicon oxide and is coated onto a steel frame structure of a building or a structure requiring fire prevention or fireproofing in order to prevent the strength or resistance force of the structure from being deteriorated by high-temperature heat in case of fire. The refractory composition of the present invention specifically consists of 1 wt % to 50 wt % of expandable powder composed of silicate, 20 wt % to 80 wt % of silicate binder, 0.05 wt % to 5 wt % of stabilizer, and 0.01 wt % to 10 wt % of fiber.

Claims

1. An inorganic expandable refractory composition comprising expandable powder consisting of a dry silicate.

2. The inorganic expandable refractory composition of claim 1, wherein the expandable powder of a silicate consists of 10 wt % to 50 wt % of an alkali metal oxide, 30 wt % to 80 wt % of silicon oxide and 0.1 wt % to 20 wt % of water.

3. The inorganic expandable refractory composition of claim 1, wherein the silicate is at least one selected from the group consisting of sodium silicate, potassium silicate and lithium silicate.

4. The inorganic expandable refractory composition of claim 1, wherein the expandable powder further includes at least one of a foaming auxiliary material and a refractory auxiliary material.

5. The inorganic expandable refractory composition of claim 4, wherein the foaming auxiliary material is at least one selected from the group consisting of potassium bicarbonate, calcium bicarbonate, sodium bicarbonate, magnesium bicarbonate and ammonium bicarbonate.

6. The inorganic expandable refractory composition of claim 4, wherein the refractory auxiliary material is at least one selected from the group consisting of an antimony compound, aluminum hydroxide, magnesium hydroxide, calcium carbonate, boric acid, borax, a kaoline-group mineral, bentonite, clay, ettringite, a phosphate, a phosphorous-based flame retardant, a halogen-based flame retardant and a thermally curable resin.

7. The inorganic expandable refractory composition of claim 1, wherein the expandable powder further comprises at least one selected from the group consisting of an organic silane-based coupling agent, a titanate-based coupling agent, a zirconate-based coupling agent, a silicone-based water repelling agent and a fluorine-based water repelling agent to provide hydrophobicity.

8. The inorganic expandable refractory composition of claim 1, wherein the refractory composition consists of 1 wt % to 70 wt % of the expandable powder, 20 wt % to 80 wt % of a silicate binder, 0.05 wt % to 10 wt % of a stabilizer and 0.01 wt % to 10 wt % of fiber.

9. The inorganic expandable refractory composition of claim 8, wherein the silicate is at least one selected from the group consisting of sodium silicate, potassium silicate and lithium silicate.

10. The inorganic expandable refractory composition of claim 8, further comprising at least one of a foaming auxiliary material and a refractory auxiliary material.

11. The inorganic expandable refractory composition of claim 10, wherein the foaming auxiliary material is at least one selected from the group consisting of potassium bicarbonate, calcium bicarbonate, sodium bicarbonate, magnesium bicarbonate and ammonium bicarbonate.

12. The inorganic expandable refractory composition of claim 10, wherein the refractory auxiliary material is at least one selected from the group consisting of an antimony compound, aluminum hydroxide, magnesium hydroxide, calcium carbonate, boric acid, borax, a kaoline-group mineral, bentonite, clay, ettringite, a phosphate, a phosphorous-based flame retardant, a halogen-based flame retardant and a thermally curable resin.

13. The inorganic expandable refractory composition of claim 8, further comprising at least one selected from the group consisting of an organic silane-based coupling agent, a titanate-based coupling agent, a zirconate-based coupling agent, a silicone-based water repelling agent and a fluorine-based water repelling agent to provide hydrophobicity.

14. The inorganic expandable refractory composition of claim 8, wherein the stabilizer is at least one selected from the group consisting of a cellulose-based viscosity agent, a silicon-based viscosity agent, an inorganic-base viscosity agent, an organic-base viscosity agent, a dispersant, an anti-layer separation agent, an antifoaming agent, stearic acid, paraffin-based wax, a surfactant, a silicone-based water repelling agent, a fluorine-based water repelling agent and a silane-coupling agent.

15. The inorganic expandable refractory composition of claim 8, wherein the fiber is at least one selected from the group consisting of organic-base fiber or inorganic-base fiber.

16. The inorganic expandable refractory composition of claim 8, further comprising a filler.

17. The inorganic expandable refractory composition of claim 16, wherein the filler is at least one selected from the group consisting of cement, plaster, dolomite, synthetic silica, perlite, fly ash, vermiculite, aluminum oxide, magnesium oxide and carbon black.

Description

MODE FOR DISCLOSURE

[0022] One embodiment according to an inorganic expandable refractory composition of the present invention includes expandable powder formed by a dry silicate, and the expandable powder of a silicate may consist of 10 wt % to 50 wt % of an alkali metal oxide, 30 wt % to 80 wt % of silicon oxide and 0.1 wt % to 20 wt % of water.

[0023] The silicate used in the present invention is a compound represented by M.sub.2O.nSiO.sub.2.xH.sub.2O, wherein M is an alkali metal belonging to group 1A of the periodic table, and n and x are integers. The alkali metal belonging to group 1A includes lithium, sodium, potassium and the like, and one or more types thereof may be mixed and used. For example, the silicate may be at least one selected from the group consisting of sodium silicate, potassium silicate and lithium silicate.

[0024] Such a silicate has moisture content of 40 wt % to 70 wt %, and has an expandable coefficient of linear expansion due to a glass substance-based property. Accordingly, when the silicate is heated, a foam having cells inside is formed as the silicate goes through foam expansion.

[0025] However, when a silicate expands, cells produced inside are not able to form a fine-sized honeycomb structure, and continuously expand and combine with surrounding cells due to weak cell barriers, and as a result, a foam that is non-uniform and has large pores is formed. Such a phenomenon causes cracks in the foam or decline in the heat insulation and fire resisting capacity, therefore the silicate is unable to properly exhibit its capacity.

[0026] In order to improve such a problem, embodiments of the present invention control cell sizes and expansion uniformity using particle sizes and amounts of the expandable powder, a coefficient of linear expansion of the silicate and the moisture content acting as an expansion agent, and provide changes in the strength of cells produced from the expansion.

[0027] In the present invention, particle sizes of the expandable powder affect cell sizes, and since large particle sizes of expandable powder lead to formation of large cells, and small particle sizes of expandable powder lead to formation of small cells, this is a natural principle, and therefore, additional descriptions will not be included. However, when the sizes are too big, a honeycomb structure is difficult to form, and accordingly, particle sizes are preferably 5 mm or less.

[0028] Moisture content of the silicate acts as an expansion agent of the silicate, and for securing expansion sizes and uniformity, powder may be prepared by controlling moisture amount through drying. The expandable powder dried as above is mixed with the silicate to be used as a refractory composition in a steel frame structure and the like. The silicate used as a binder is also dried after being coated on a steel frame structure, but is not 100% dried in a natural state, and is solidified in a state having approximately 10 wt % or more moisture. The expandable powder prepared in advance is dried to have lower moisture content, for example, up to 5 wt % to 7 wt %, and in case of fire, the expandable powder expands to a smaller size than the silicates used as a binder in the coated refractory composition of the present invention. As a result, fine expanded cells of the expandable powder are distributed into expanded cells of the silicate used as a binder due to the difference in the magnitude of linear expansion even if they are the same material, thereby honeycomb-structured fine cells are obtained which enhances effects of heat insulation and fire resisting capacity. At the same time, foam uniformity is obtained. As described above, when a silicate is used alone, a foam that is non-uniform and has large pores is formed causing cracks or declined heat insulation leading to quick heat transfer to the inside, and as a result, a non-uniform phenomenon, in which parts touched by flames start to expand first, is observed. However, in the present invention, expandable powder prevents flames from rapidly spreading to the inside, and overall uniform expansion and cells are formed starting from the surface. As a result, such an effect prevents cracks in the foam and thereby effective fire resisting capacity is obtained.

[0029] In the present invention, expandable powder has a correlation with a mixed state of a prepared refractory composition and additional mixtures, therefore suitable dry % is determined from a condition of a refractory composition to be finally prepared.

[0030] Since expandable powder is prepared from silicate, initial content is almost determined. For example, a silicate is generally as in the following Table 1 depending on the type.

TABLE-US-00001 TABLE 1 Category Type 1 Type 2 Foundry Type 3 Type 4 SiO.sub.2 % 36 to 38 34 to 36 30 to 33 28 to 30 23 to 25 Na.sub.2O % 17 to 18 14 to 15 12 to 14 9 to 10 6 to 7 Other % 0.3 or less 0.3 or less 0.3 or less 0.3 or less 0.3 or less H.sub.2O % 43.7 to 47 48.7 to 52 52.7 to 58 59.7 to 63 67.7 to 71

[0031] In Table 1, expandable powder is dried to have moisture content of 10% or less for preparation, and accordingly, wt % changes as in the following Table 2 when the expandable powder is dried based on a final moisture amount of 10% or less.

TABLE-US-00002 TABLE 2 Type 1 Type 2 Foundry Type 3 Type 4 SiO.sub.2 % 36 38 34 36 30 33 28 30 23 25 Na.sub.2O % 17 18 14 15 12 14 9 10 6 7 Other % 0 0.3 0 0.3 0 0.3 0 0.3 0 0.3 H.sub.2O % 5.89 6.25 5.33 5.7 4.66 5.25 4.11 4.48 3.22 3.58 Total 58.89 62.55 53.33 57 46.66 52.55 41.11 44.78 32.22 35.88 SiO.sub.2 % 61.13 60.75 63.75 63.16 64.29 62.80 68.11 66.99 71.38 69.68 Na.sub.2O % 28.87 28.78 26.25 26.32 25.72 26.64 21.89 22.33 18.62 19.51 Other % 0.00 0.48 0.00 0.53 0.00 0.57 0.00 0.67 0.00 0.84 H.sub.2O % 10.00 9.99 9.99 10.00 9.99 9.99 10.00 10.00 9.99 9.98 Total 100 100 100 100 100 100 100 100 100 100

[0032] When prepared, the content by default changes according to the changes in the moisture amount.

[0033] According to one embodiment of the present invention, the expandable powder may be prepared by drying a silicate, and may further include at least one of a foaming auxiliary material and a refractory auxiliary material. An alkali metal of group 1A is included as the foaming auxiliary material, silicon oxide may be included as the refractory auxiliary material, and content of the expandable powder changes depending on the mixing. The alkali metal oxide affects performance and form of foaming, and the silicon oxide affects strength of foamed cells, and when the alkali metal oxide is included in greater than 50 wt %, cracks in the cells occur when foaming, and when the silicon oxide is included in greater than 80 wt %, foaming force is weak and effects thereof are small.

[0034] In the present invention, the foaming auxiliary material of the expandable powder may be a bicarbonate compound, for example, at least one selected from the group consisting of potassium bicarbonate, calcium bicarbonate, sodium bicarbonate, magnesium bicarbonate and ammonium bicarbonate. When controlling only the moisture, moisture distribution may be non-uniform depending on the drying condition and type. When fine adjustment for foaming is specifically required, uniformity for moisture may be provided by maximal drying, and in this case, sizes and forms of the foaming may be controlled to some degree by the mixed amount of the bicarbonate-based compound. In other words, the bicarbonate-based compound is dissolved in the silicate as much as the required size of foamed cells, and then the resulting mixture is maximally dried. Herein, the suitable amount of the bicarbonate-based compound with respect to the silicate is largely from 0.1 wt % to 20 wt % although it may vary depending on the type of the silicate. Having the amount in less than 0.1 wt % does not have big impact on foaming, but when the amount is greater than 20 wt %, sizes of the foamed cells are too large.

[0035] According to the present invention, a refractory auxiliary material may be added when preparing the expandable powder. A refractory auxiliary material or a heat resisting auxiliary is added to make the cells formed from the expansion of the expandable powder by flames harder and prevent the expanded cells from being melted at high temperatures, or to enhance a flame retarding property. It is preferable to use as the refractory auxiliary material at least one selected from the group consisting of antimony compounds, aluminum hydroxide, magnesium hydroxide, calcium carbonate, boric acid, borax, kaoline-group minerals such as kaolinite, montmorillonite, dickite, illite, sericite and halloysite, bentonite, clay, ettringite, phosphates, phosphorous-based flame retardants, halogen-based flame retardants and thermally curable resins. In the present invention, the refractory auxiliary material is preferably approximately 0.1 wt % to 50 wt %, and when the content is 0.1 wt % or less, the effects are insignificant, and when the content is greater than 50 wt %, foaming capacity declines as the strength of the foamed cells increases.

[0036] According to one embodiment of the present invention, a method of providing hydrophobicity may be used when preparing the expandable powder. This is due to the fact that a silicate is hydrophilic to water. The method of providing hydrophobicity includes mixing a water repelling agent such as a silicone-based water repelling agent or a fluorine-based water repelling agent in approximately 0.01 wt % to approximately 10 wt %, or using a coupling agent such as silane, and the coupling agent may include, for example, an organic silane-based coupling agent including iso-octyltrimethoxysilane, methyltrimethoxysilane, octyltrietoxysilane, 3-aminopropyltriethoxysilane, 3-glycidyloxytriethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(2-methoxy-ethoxy)silane and the like, a titanate-based coupling agent including neopentyl(diallyl)oxy, trineodecano titanate, neopentyl(diallyl)oxy, tri(dodecyl)benzene-sulfonyl titanate, neopentyl(diallyl)oxy, tri(dioctyl)phosphate titanate, neopentyl(diallyl)oxy, tri(dioctyl)pyro-phosphato titanate, neopentyl(diallyl)oxy, tri(N-ethylenediamino)ethyl titanate, neopentyl(diallyl)oxy, tri(m-amino)phenyl titanate and the like, and a zirconate-based coupling agent including neopentyl(diallyl)oxy, trineodecano zirconate, neopentyl(diallyl)oxy, tri(dodecyl)benzene-sulfonyl zirconate, neopentyl(diallyl)oxy, tri(dioctyl)phosphate zirconate, neopentyl(diallyl)oxy, tri(dioctyl)pyro-phosphato zirconate, neopentyl(diallyl)oxy, tri(N-ethylenediamino)ethyl zirconate, neopentyl(diallyl)oxy, tri(m-amino)phenyl zirconate and the like, and the like. Using the above in an amount of less than 0.01 wt % is not effective, and using in an amount of greater than 10 wt % lowers economic feasibility compared to effects.

[0037] In addition, according to one embodiment of the present invention, the inorganic expandable refractory composition consists additionally of 20 wt % to 80 wt % of a silicate binder, 0.05 wt % to 10 wt % of a stabilizer and 0.01 wt % to 10 wt % of fiber besides the 1 wt % to 70 wt % of the expandable powder.

[0038] According to the present invention, the expandable powder is prepared by drying a silicate, and the expandable powder prepared as above is mixed again with a silicate binder to prepare a refractory composition. Herein, the silicate binder also expands in flames, and therefore, a foaming auxiliary material and a refractory auxiliary material are added for controlling expansion capacity and strength against flames. However, the preparation process is the same as the preparation process of the expandable powder prepared from a silicate as described above, and therefore, the same description will not be repeated.

[0039] Meanwhile, in the refractory composition according to the present invention, the stabilizer is used for securing workability and physical properties that the refractory composition needs to have to be used as paints or mastics. The stabilizer is preferably at least one selected from the group consisting of a cellulose-based viscosity agent, a silicon-based viscosity agent, an inorganic-base viscosity agent, an organic-base viscosity agent, a dispersant, an anti-layer separation agent, an antifoaming agent, stearic acid, paraffin-based wax, a surfactant, a silicone-based water repelling agent, a fluorine-based water repelling agent and a silane-coupling agent. The amount of the stabilizer used is preferably from 0.05 wt % to 10 wt %. Adding in less than 0.05 wt % is not effective, and adding in greater than 10 wt % inhibits fire resisting capacity, therefore, adding within the above-mentioned range is favorable.

[0040] The fiber in the refractory composition of the present invention may be at least one selected from among organic substance-based fiber such as polyethylene, polypropylene, polyester and nylon, or inorganic substance-based fiber such as glass fiber, mineral wool and zirconium. The fiber is preferably added in a range of 0.01 wt/o to 10 wt %, and adding in less than 0.01 wt % is not effective, and adding in greater than 10 wt % decreases workability due to excess use of fiber.

[0041] The organic substance-based may be mixed for securing physical properties that need to be exhibited during or after coating on a steel frame structure and the like, and the inorganic substance-based is used for securing physical properties when brought into contact with fire causing expansion of the refractory composition.

[0042] According to one embodiment of the present invention, additional treatment may be carried out on the expandable powder depending on the method of use of the refractory composition. Expandable powder starts from a silicate, and therefore, may be melted and gelated again in a silicate binder used when preparing the refractory composition as described above. Methods to eliminate such problems include a method of respectively preparing a refractory composition including expandable powder and not including expandable powder, and mixing the expandable powder to a steel frame structure at the time of working. Expandable powder is dissolved or gelated in a refractory composition to which a silicate binder is mixed, however, this phenomenon does not occur in a short time. This is because expandable powder is a powder in a rigidly hard state with moisture inside being controlled, and therefore, only a small part of the surface is melted during the working time of fireproof coating process and while being coated on a steel frame structure and then dried, and accordingly, this does not affect fire resisting capacity.

[0043] According to an embodiment of the present invention, the refractory composition may further include a thermoplastic and thermally curable binder as necessary for reinforcing water resistance and chemical resistance.

[0044] The inorganic expandable refractory composition of the present invention prepared as above improves a problem of foamed cells that a silicate has and forms uniform foam layer honeycomb-structured cells, does not produce toxic gas during expansion unlike fireproof paints, and does not experience damages in the expanded cells caused by flames, and consequently, has excellent fire resisting capacity to high temperature and long-term heating.

[0045] The present invention will be described in detail with reference to examples and experimental examples as follows based on the descriptions provided above, however, the scope of the present invention is not limited thereto.

Examples 1 to 6

Preparation of Binder for Expandable Powder of Present Invention

[0046] To a silicate, a foaming auxiliary material, a refractory auxiliary material, a water repelling agent and the like were introduced in order, and the mixture was sufficiently stirred for 4 hours at a rate of 1,000 rpm or higher to prepare a binder for expandable powder.

TABLE-US-00003 TABLE 3 Category Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Sodium Silicate 100 (Number 1) Sodium Silicate 100 98 96 91 (Number 2) Potassium Silicate 100 Ammonium Bicarbonate 2 2 2 Borax 2 2 Silicone-based Water 5 Repelling Agent (unit: wt %)

Examples 7 to 16

Preparation of Expandable Powder of Present Invention

[0047] The binders for expandable powder prepared in Examples 1 to 6 were dried to moisture content listed in Table 4. The drying may be carried out in various ways including hot blast, far-infrared rays, microwave and the like, and after drying, the particles were ground using a grinder so that particles sizes of 325 mesh or smaller became 90 wt % or greater, to prepare the expandable powder.

TABLE-US-00004 TABLE 4 Example 7 Dry Example 1 to moisture content of 7 wt % Example 8 Dry Example 2 to moisture content of 7 wt % Example 9 Dry Example 3 to moisture content of 7 wt % Example 10 Dry Example 4 to moisture content of 7 wt % Example 11 Dry Example 4 to moisture content of 5 wt % Example 12 Dry Example 5 to moisture content of 7 wt % Example 13 Dry Example 5 to moisture content of 5 wt % Example 14 Dry Example 6 to moisture content of 7 wt % Example 15 Dry Example 6 to moisture content of 5 wt % Example 16 Hydrophobic treatment of surface of Example 11 with methoxysilane

[0048] However, in Example 16, a process of hydrophobic treatment of surface of expandable particles prepared in Example 11 with methoxysilane was added.

Examples 16 to 27

Preparation of Inorganic Expandable Refractory Composition of Present Invention

[0049]

TABLE-US-00005 TABLE 5 Refractory Expandable Auxiliary Category Powder Silicate Binder Material Stabilizer Fiber Filler Example 16 20% (Example 7) Sodium Magnesium HEC 1% Ceramic Fiber 2% Silicate 72% Hydroxide 5% Example 17 20% (Example 8) Sodium Magnesium HEC 1% Ceramic Fiber Silicate 72% Hydroxide 5% Example 18 20% (Example 9) Sodium Magnesium HEC 1% Ceramic Fiber Silicate 72% Hydroxide 5% Example 19 15% (Example 10) Sodium Aluminum Paraffin 1% Glass Fiber 2% Silicate 72% Hydroxide 10% Example 20 15% (Example 11) Sodium Aluminum Paraffin 1% Glass Fiber 2% Silicate 72% Hydroxide 10% Example 21 15% (Example 12) Sodium Aluminum Paraffin 1% Glass Fiber 2% Silicate 72% Hydroxide 10% Example 22 15% (Example 13) Sodium Aluminum Paraffin 1% Glass Fiber 2% Silicate 72% Hydroxide 10% Example 23 15% (Example 14) Sodium Calcite 20% Stearic Acid 1% Glass Fiber 2% Expanded Silicate Perlite 5% Example 24 15% (Example 15) Sodium Calcite 20% Stearic Acid 1% Glass Fiber 2% Expanded Silicate Perlite 5% Example 25 15% (Example 13) Sodium Calcite 20% HPC 1% Glass Fiber 2% Expanded Silicate Perlite 5% Example 26 15% (Example 15) Sodium Calcite 20% HPC 1% Glass Fiber 2% Expanded Silicate Perlite 5% Example 27 15% (Example 16) Sodium Calcite 20% HPC 1% Glass Fiber 2% Expanded Silicate Perlite 5% Comparative None Sodium calcite 20% HPC 1% Glass Fiber 2% Expanded Example 1 Silicate Perlite 5% Comparative None Sodium calcite 20% Stearic Acid 1% Glass Fiber 2% Expanded Example 2 Silicate Perlite 5% (Unit: wt %) HEC = hydroxyethylcellulose, HPC = hydroxypropylcellulose

Experimental Example 1

Fire Resisting Capacity Comparison

[0050] A fire resisting capacity experiment on the refractory compositions prepared in Examples 16 to 24 and Comparative Examples 1 and 2 were carried out based on a standard heating curve temperature defined in KS F 2257 in accordance with the Ministry of Construction and Transportation Notice, and coating was carried out so that the thickness of a dried coated film on a H beam was from 12.0 mm to 12.1 mm. Fire resisting capacity was examined with criteria of 3 hours and 538 C. or lower.

TABLE-US-00006 TABLE 6 Category Example 16 Example 17 Example 18 Example 19 Example 20 Example 21 Sample 60 Minutes 110 108 106 107 103 104 Temperature 120 Minutes 258 247 257 241 237 237 ( C.) 180 Minutes 531 518 528 514 497 495 Foam Layer Outer Appearance Favorable Favorable Favorable Favorable Excellent Favorable Crack Occurrence None None None None None None Comparative Comparative Category Example 22 Example 23 Example 24 Example 1 Example 2 Sample 60 Minutes 96 98 91 487 418 Temperature 120 Minutes 233 235 227 641 (Finish) 578 (Finish) ( C.) 180 Minutes 467 473 442 Foam Layer Outer Appearance Excellent Favorable Excellent Poor Poor Crack Occurrence None None None Occurred Occurred

Experimental Example 2

Comparison of Long-Term Safety

[0051] For the refractory compositions prepared in Examples 25 to 27, viscosity comparison over time was carried out, and safety of the expandable powder and the silicate of the present invention was examined. Viscosity was measured using a VT-04F viscometer manufactured by RION of Japan.

TABLE-US-00007 TABLE 7 Time of After After After 60 After 90 After 150 Category Preparation 1 Day 1 Week Days Days Days Example 25 15,370 Impossible to Measure Example 26 15,150 15,350 23,800 Impossible to Measure Example 27 15,160 15,190 15,170 15,330 15,730 15,920 (Unit: CPS)

[0052] From the results of Table 6, it was seen that, when using the inorganic expandable powder of the present invention, uniform foam layer honeycomb-structured expanded cells were formed and effects were bigger compared to Comparative Examples 1 and 2 using a silicate alone. In addition, more favorable results were obtained as the foaming auxiliary material was used, which indicates that it is more effective in obtaining expandable powder having uniform foamed cells. Particularly, fire resisting capacity was more enhanced when adding a refractory auxiliary material such as boric acid.

[0053] Results of Table 7 indicate safety on the use of the expandable powder and the silicate depending on hydrophobic treatment on the inorganic expandable powder of the present invention. As described above, inorganic expandable powder is made from a silicate, and therefore, is readily dissolved in silicate, and gelated by absorbing the silicate. However, with the hydrophobic treatment as in Example 26 or Example 27, such a phenomenon is prevented, and the expandable powder may be used for a long period of time. When the expandable powder is immediately used after mixing, no big problems occur even without hydrophobic treatment, and therefore, hydrophobic treatment is not absolutely necessary.