JP7602227B2 - Geopolymer-based lightweight fireproof material - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. ・2019 Research Reports of the Architectural Institute of Japan, Chugoku Branch, Vol. 43, pp. 41-44, pp. 45-48, Architectural Institute of Japan, Chugoku Branch, General Incorporated Association, Published on February 29, 2020 (Reiwa 2) ・2019 Architectural Institute of Japan, Chugoku Branch, Hiroshima Institute of Technology, held on February 29, 2020 (Reiwa 2)

The present invention relates to a geopolymer-based lightweight fireproof material suitable for use as a fireproof coating for steel-frame structures.

In recent years, geopolymers, which are mainly made from waste and by-products, have been attracting attention as low-carbon binders. Geopolymers are made by hardening active fillers such as fly ash and blast furnace slag powder in an alkaline solution environment through a condensation polymerization reaction without using cement clinker. The _CO2 emission intensity of geopolymer cement is about 20% of that of Portland cement, and that of geopolymer concrete is 30-60% of that of Portland cement concrete. For this reason, research and development of geopolymers is being actively conducted both domestically and internationally in order to reduce the environmental load of cement and concrete and to expand the use of waste. In addition, unlike the hydration reaction of Portland cement, the condensation polymerization reaction of geopolymers does not produce Ca(OH) ₂ crystals, so they have better fire resistance and acid resistance than Portland cement hardened bodies, and are expected to be used in high temperature and acidic environments.

On the other hand, the Building Standards Act requires the use of fire-resistant coating materials for steel-framed structures to ensure safety in the event of a fire. Currently, cement-based fire-resistant coating materials are the mainstream, but as mentioned above, geopolymer-based fire-resistant coating materials are in demand from the perspective of waste utilization and reducing environmental impact.
Lightweight fireproof coating materials are necessary. The present inventors proposed a method for foaming geopolymers in Patent Document 1, and clarified that the strength of the hardened porous geopolymer body is reduced after it is heated, and the specific strength is increased.
However, the hardened porous geopolymer remains problematic in that it can crack and deform when exposed to heat.

Patent No. 6430268

The problem that this invention aims to solve is to provide a geopolymer-based lightweight fire-resistant material that is less likely to crack or deform when exposed to heat.

According to one aspect of the present invention, there is provided a geopolymer-based lightweight fire-resistant material comprising:
A geopolymer-based lightweight fireproof material having a density of 1.0 g/cm3 or ^less , which is obtained by adding an alkaline solution to a mixture containing an active filler, a non-active filler, a lightweight fireproof aggregate, and a foaming agent, kneading the mixture, and curing the mixture.
The active filler is a mixture of at least one first active filler selected from fly ash, finely ground molten slag from municipal waste incineration ash, and finely ground molten slag from sewage sludge incineration ash, and at least one second active filler selected from finely ground blast furnace slag and metakaolin, the mass ratio of the second active filler being 10 to 20 mass% based on 100 mass% of the total amount of the active filler and the inactive filler;
The inactive filler is a stone powder that does not harden in the alkaline solution or that, even if hardened, has a compressive strength of 5 MPa or less and maintains its physical and chemical properties even when heated to 1000°C, and the mass ratio of the inactive filler is 20 to 50 mass% based on 100 mass% of the total amount of the inactive filler and the active filler;
The lightweight refractory aggregate maintains its physical and chemical properties even when heated to 1000°C, has a density of 1.65 g/cm3 ^or less, has a particle size distribution in which the proportion of particle sizes of 5 mm or more is 0 mass% and the proportion of particle sizes of less than 0.15 mm is 5 mass% or less, and when the total volume of the lightweight refractory aggregate, the active filler, and the inactive filler is 100 volume%, the volume proportion of the lightweight refractory aggregate is 40 to 60 volume%. This is a geopolymer-based lightweight refractory material.

The geopolymer-based lightweight fireproof material of the present invention is less likely to crack or deform when exposed to heat. Therefore, the geopolymer-based lightweight fireproof material of the present invention is suitable as a fireproof coating material for steel frame structures.

SEM photo of fly ash. SEM photo of ground granulated blast furnace slag. A photo of granular and powdered perlite. Photo of fine powder of perlite raw stone and crushed stone powder. Photographs showing the process of producing hardened geopolymer foam. Photographs showing a method for measuring the temperature of the back surface, which is the surface opposite to the heated surface, during a one-sided heating test. 1 is a graph showing the relationship between the dimensional reduction rate after heating in a full surface heating test and the mass ratio of stone powder (inactive filler). 1 is a graph showing the relationship between the density increase rate after heating in a full surface heating test and the mass ratio of stone powder (inactive filler). 1 is a graph showing the relationship between the rate of change in bending strength before and after heating in a full surface heating test and the mass ratio of stone powder (inactive filler). 1 is a graph showing the relationship between the ratio of compressive strength before and after heating in a full surface heating test and the mass ratio of stone powder (inactive filler). Graph showing the relationship between the specific compressive strength before heating and the mass ratio of stone powder (inactive filler) in a full surface heating test (only examples). Photographs showing the appearance of a test specimen before and after full surface heating (Example). Photographs showing the appearance of a test specimen before and after full surface heating (Comparative Example 1). Photographs showing the appearance of a test specimen before and after full surface heating (Comparative Example 2). SEM photo showing the internal structure of the geopolymer foamed hardened body without stone powder (non-reactive filler) and lightweight aggregate. 1 is a graph showing the relationship between the density reduction rate after heating and the mass ratio of stone powder (inactive filler) in a one-sided heating test. Photographs showing the occurrence of cracks and warping in a test specimen after one-sided heating (Example). Photographs showing the occurrence of cracks and warping on a test specimen after one-sided heating (Comparative Example). Graph showing the relationship between the warpage of the test specimen after one-sided heating and the mass fraction of stone powder (inactive filler). Graph showing the temperature rise on the back side of a test specimen when heated on one side.

The geopolymer-based lightweight fireproof material of the present invention is obtained by adding an alkaline solution to a mixture containing an active filler, an inactive filler, a lightweight fireproof aggregate, and a foaming agent, kneading the mixture, and curing the mixture. One embodiment of the material is described below.

1. Materials used 1.1 Active filler JIS II type fly ash (hereinafter referred to as "FA") was mainly used. When FA alone is used as an active filler for geopolymer (hereinafter referred to as "GP"), the setting time of GP is long in a normal temperature environment, and the strength development is small. Therefore, in order to increase the strength development of the GP hardened body and match the foaming speed and setting speed of GP, JIS 3000 class granulated blast furnace slag (hereinafter referred to as "BFS") was used in combination. If BFS is not used in combination, settlement due to expansion occurs immediately after foaming, or the foam shrinks significantly after curing. However, if the mass ratio of BFS is too high, C-A-S-H gel is generated in the hardening reaction, and the fire resistance of GP decreases.
Here, as mentioned above, BFS is used to increase the strength development of the GP hardened body, and metakaolin (hereinafter referred to as "MK") is also known to have the effect of increasing the strength development of the GP hardened body. Therefore, MK can be used in place of BFS or in combination with BFS. Also, FA has a lower strength development than BFS and MK, but the finely ground molten slag powder of municipal waste incineration ash and the finely ground molten slag powder of sewage sludge incineration ash have the same strength development as FA. Therefore, the finely ground molten slag powder of municipal waste incineration ash and/or the finely ground molten slag powder of sewage sludge incineration ash can be used in place of FA or in combination with FA.
That is, in the present invention, the active filler is a mixture of at least one first active filler selected from FA, fine powder of molten slag from municipal waste incineration ash, and fine powder of molten slag from sewage sludge incineration ash, and at least one second active filler selected from BFS and MK. The mass ratio of the second active filler, which acts to increase the strength expression of the GP hardened body, is 10 to 20 mass% in terms of the total amount of the active filler and the inactive filler (hereinafter, the total amount of the active filler and the inactive filler is referred to as "powder") 100 mass%. If the ratio of the second active filler is less than 10 mass%, sufficient strength cannot be obtained. On the other hand, if the mass ratio of the second active filler is more than 20 mass%, problems such as a decrease in the fire resistance of GP when BFS is added, and a decrease in the waste utilization effect of the present invention when MK is added occur.
In the examples of the present invention described later, the mass ratio of the second active filler, BFS, was set to 15 mass %.
The chemical compositions and physical properties of FA and BFS are shown in Table 1. FA is a spherical particle with a particle size of 30 μm or less as shown in Figure 1, while BFS is a particle with random particle size and shape as shown in Figure 2.

1.2 Alkaline solution In the present invention, an alkaline solution that is usually used for producing a GP hardened body can be used. That is, as the alkaline solution in the present invention, at least one selected from the group consisting of silicates, hydroxides, and carbonates of alkali metals can be used.
In the present examples and comparative examples, the alkaline solution was previously examined so that the foaming rate and the setting rate of GP were matched to increase the amount of expansion due to foaming of GP and to prevent or reduce the decrease in strength after heating. As a result, a mixture of commercially available sodium silicate ( _SiO2 28.6 mass%, _Na2O 12.0%, molar ratio 2.5, density 1.46 g/ ^cm3 ) and a 10M aqueous solution of caustic soda (density 1.33 g/ ^cm3 ) in a volume ratio of 4:1 was used as the alkaline solution.

1.3 Aggregate
In the present invention, lightweight refractory aggregate is added as aggregate to suppress shrinkage, cracking, and irregular deformation that occur in the GP hardened body when it is heated at high temperatures. Here, the "lightweight refractory aggregate" in the present invention refers to an aggregate having a density of 1.65 g/cm3 or ^less , a particle size distribution in which the proportion of particles with a particle size of 5 mm or more is 0 mass %, and the proportion of particles with a particle size of less than 0.15 mm is 5 mass % or less. The fire resistance of the lightweight aggregate is such that the physical and chemical properties are maintained even when heated to 1000°C. Specifically, it is such that the aggregate does not decompose or melt, does not change in size or shape, and does not become brittle even when heated to 1000°C.
When such a lightweight refractory aggregate is added in an appropriate amount, it restrains the shrinkage of the GP matrix, so that cracks and irregular deformation due to shrinkage can be suppressed. In order to fully exert such effects, in the present invention, the lightweight refractory aggregate is added so that the volume ratio of the lightweight refractory aggregate is 40 to 60 volume % when the total volume of the lightweight refractory aggregate, the active filler, and the inactive filler is taken as 100 volume %. If the volume ratio of the lightweight refractory aggregate is less than 40 volume %, the effect of suppressing the above-mentioned shrinkage, cracks, and irregular deformation cannot be sufficiently obtained. On the other hand, if the volume ratio of the lightweight refractory aggregate is more than 60 volume %, the strength of the GP decreases, so that cracks and irregular deformation are more likely to occur. In addition, if the volume ratio of the lightweight refractory aggregate is more than 60 volume %, even if the GP is foamed by adding a foaming agent, air bubbles leak out and it is difficult to expand, making it difficult to reduce the weight of the GP.
In the examples of the present invention, granular perlite (hereinafter referred to as "granular P") was used as the lightweight refractory aggregate. The density of this granular P was 0.12 g/ ^cm3 , and the particle size distribution was >5.0 mm (0 mass%), 5.0-2.5 mm (10 mass%), 2.5-1.25 mm (43 mass%), 1.25-0.63 mm (45 mass%), 0.63-0.15 mm (1.5 mass%), and <0.15 mm (0.5 mass%). In the examples of the present invention, the volume fraction of granular P was 48-50 volume%.
On the other hand, in the comparative example, in addition to granular P, powdered perlite (hereinafter referred to as "powdered P") and silica sand were used as aggregates. The density of powdered P was 0.09 g/cm ³ , and the particle size distribution was >1.25 mm (2.0 mass%), 1.2 to 0.63 mm (25.0 mass%), 0.63 to 0.15 mm (66.0 mass%), and <0.15 mm (7.0 mass%). The density of silica sand was 2.59 g/cm ³ , and the particle size distribution was 0.63 mm or more (0 mass%), 0.63 to 0.315 mm (33 mass%), 0.315 to 0.15 mm (66 mass%), and <0.15 mm (1 mass%). Photographs of granular perlite and powdered perlite are shown in FIG. 3. Granular P and powdered P are made by heating and rapidly cooling pearlite ore, and are so-called lightweight aggregates.

1.4 Admixture (a) Foaming Agent In the present invention, a foaming agent is added to reduce the weight of the GP. As disclosed in the above-mentioned Patent Document 1, at least one foaming agent selected from metal silicon (Si), metal aluminum (Al) and hydrogen peroxide (H ₂ O ₂ ) can be used. The foaming agent can be added in an external amount of 0.5 to 3 mass% relative to 100 mass% of the powder.
Here, in the case of strongly alkaline GP, the foaming time of metallic aluminum and hydrogen peroxide is within 10 minutes, so a special kneading and molding method is required. In contrast, the foaming time of metallic silicon is more than 30 minutes at room temperature of 20° C. Therefore, in the present examples and comparative examples, a commercially available silicon reagent (metallic silicon, density 2.33 g/cm ³ , fineness 150 μm or less, purity 95%) was used as the foaming agent.
In the following description, GP that has been foamed with a foaming agent to make it porous is referred to as "GP foamed hardened body."

(b) Foam stabilizer Strongly alkaline GP has a fast foaming reaction rate, which easily leads to the formation and escape of large bubbles, and the distribution of bubbles is easily uneven. This reduces the final expansion amount of GP, and the generation of large interconnected voids reduces the insulation properties and strength. Therefore, in the present examples and comparative examples, commercially available zinc stearate (density 1.09 g/cm ³ ) was added as a foam stabilizer to reduce the size of the bubbles and improve the uniformity of the bubble distribution.
In the present invention, the addition of a foam stabilizer is not essential, but it is preferable to add a foam stabilizer for the reasons described above. As the foam stabilizer, in addition to the above-mentioned zinc stearate, dodecylbenzenesulfonate, triethanolamine, etc. can be added, and the addition ratio can be 0.5 to 2 mass% based on 100 mass% of the powder.

(c) Inactive filler (stone powder)
When GP is heated, the raw material is dehydrated (bound water) and cracks occur due to shrinkage. Therefore, in the present invention, a part of the active filler is replaced with an inactive filler. Here, The "inactive filler" in the present invention is a filler that does not harden in the above-mentioned alkaline solution, or that has a compressive strength of 5 MPa or less even after hardening, and has physical and chemical properties that are not affected even when heated to 1000°C. In the present invention, the inactive filler is used in such a manner that the mass ratio of the inactive filler is 20 to 50 mass % based on 100 mass % of the powder. Mass ratio of the inactive filler If the mass ratio of the inactive filler is less than 20% by mass, the effect of suppressing cracks due to shrinkage cannot be sufficiently obtained. On the other hand, if the mass ratio of the inactive filler exceeds 50% by mass, the mass ratio of the active filler is accordingly reduced. The strength of the GP decreases. Since the inactive filler is a substitute for the active filler, there is no restriction on its size, but it is preferable that it is the same as or slightly larger than the active filler, and expressed in terms of specific surface area, is about 2000 to 4000 cm ² /g. It is preferable that there is.
As the inactive filler, limestone powder, which is easily decomposed by heating, cannot be used, and typically siliceous stone powder can be used. In the present examples and comparative examples, perlite obtained by crushing perlite ore with a ball mill is used. Two types of stone powder were used: raw stone powder (hereinafter referred to as "PP") and crushed stone powder (hereinafter referred to as "CSP"). CSP is waste generated during the production of crushed stone and crushed sand. Figure 4 shows the photographs of the two types of stone powder, and Table 2 shows the chemical compositions of the two types of stone powder.

2. Preparation of GP foamed hardened body As a mixing method, the materials other than the alkaline solution (active filler, aggregate, stone powder, foaming agent, foam stabilizer) were mixed in a mortar mixer for 3 minutes, then the alkaline solution was added and mixed for another 2 minutes. As shown in Figure 5 (a), the mold was filled with the sample to about half, and immediately vibration compaction was performed with a table vibrator for 30 seconds. After that, the test specimen was placed in a drying box at 80 ° C without being removed from the mold. Foaming was completed after about 1 hour (see Figure 5 (b)). After foaming was completed, the specimen was removed from the drying box and the excess higher than the mold was cut off as shown in Figure 5 (c). After that, the specimen was removed from the mold, sealed with plastic wrap, and high-temperature curing was continued for a specified time, and curing was continued for 27 days in the sealed air at 20 ° C and 60% R.H.
A 4x4x16 cm rectangular columnar specimen was used for the full-surface heating test, and a 20x20x3 cm flat plate specimen was used for the single-sided heating test. The flat plate specimen was also used for measuring thermal conductivity.

3. Heating method and performance test At the age of 28 days, the surface condition of the specimen was photographed, and the dimensions, bulk density, bending strength, compressive strength and thermal conductivity were measured. In the strength test, three rectangular column specimens of 4 x 4 x 16 cm were used, and the bending strength was measured by the three-point method using a universal testing machine. Furthermore, the compressive strength was measured using six folded pieces after the bending test using a universal testing machine. In addition, the thermal conductivity before heating was measured using the heat flow meter method (HFM method) using a flat plate specimen of 20 x 20 x 3 cm.
The remaining specimens were subjected to a heating test. A small electric heating furnace was used for the full surface heating test, which heated the entire surface of the specimen. The temperature was raised to 1000°C at a rate of 5°C/min in the electric furnace, and the temperature was maintained for 5 hours. The specimens were then allowed to cool naturally in the furnace. After cooling to room temperature, the same measurements as before heating were performed.
In the single-sided heating test, a 20x20x3cm flat plate specimen was heated to 945°C for 1 hour in an electric furnace according to the standard heating curve of ISO834. During single-sided heating, a thermocouple was attached to the back surface, which is the opposite side of the heated surface, to monitor the temperature of the back surface, as shown in Figure 6. After single-sided heating and cooling, the dimensions, bulk density, and warpage of the flat plate specimen were measured, and the crack conditions on the heated surface and back surface were photographed. The length and width of the flat plate specimen were measured at the middle position in the thickness direction. The thermal conductivity of a part of the heated flat plate specimen after heating was also measured by the above-mentioned HFM method.
The moisture state of the specimens before the heating test was either air-dried (air-dried) or bone-dry (absolutely dry). The air-dried specimens were 28 days old, and the bone-dry specimens were 28-day old air-dried specimens that were dried at 100±5°C for one day.

4. Formulation of GP foamed cured material Table 3 shows the formulation of the GP foamed cured material subjected to the full surface heating test, and Table 4 shows the formulation of the GP foamed cured material subjected to the one-sided heating test.
Here, in Tables 3 and 4, "mass ratio" refers to the mass ratio (mass%) in 100% mass of powder (BFS+FA+stone powder), "volume ratio" refers to the volume ratio (volume%) when the total volume of powder (BFS+FA+stone powder) and aggregate is 100% by volume, "addition ratio" refers to the external ratio (mass%) to 100% mass of powder (BFS+FA+stone powder). Also, "mass ratio of alkaline solution to powder" refers to the mass of alkaline solution/mass of powder (BFS+FA+stone powder).

In the formulations of the Examples, the mass percentage of CSP was 20-40 mass%, the mass percentage of BFS was 15 mass%, and the mass percentage of granular P was 8 mass%. As a result, the volume percentage of granular P was 48-50 volume%. In the Comparative Examples, GP foamed hardened bodies were produced without the addition of stone powder, aggregate, or BFS, or with the addition of powdered P or silica sand. In the formulations of the Examples and Comparative Examples, the addition ratios of the foaming agent and foam stabilizer were appropriately adjusted depending on the temperature at the time of specimen preparation.
The moisture state of the specimens before the performance measurement and heating was air-dried or bone-dry. The high-temperature curing time of the specimens measured in the air-dry state was 12 hours, while the high-temperature curing time of the other specimens was 24 hours.

5. Test Results and Discussion 5.1 Full-surface Heating Test Table 5 shows the changes in dimensions, density, and strength before and after the full-surface heating test.

When the GP foamed hardened material was heated at 1000°C, the dimensions were reduced, while the density and compressive strength were increased. In particular, the compressive strength after heating was 1.3 times or more that before heating. Regarding the bending strength, both the comparative example and the example specimens had a lower bending strength after heating than before heating. This is because the distribution and dimensions of cracks that occurred before and after heating greatly affected the bending strength, and there was variation in the bending strength of the specimens.
Fig. 7 shows the relationship between the mass fraction of stone powder and the rate of dimensional reduction after heating, without distinguishing between different types of stone powder. As shown in the figure, the higher the mass fraction of stone powder, the smaller the dimensional change after heating. Also, Fig. 8, which shows the relationship between the mass fraction of stone powder and the rate of density increase after heating, shows that the density change after heating is smaller as the mass fraction of stone powder increases. Therefore, it can be said that adding an appropriate amount of stone powder has the effect of suppressing the dimensional change of the GP foamed hardened body due to heating.
FIG. 9 shows the relationship between the mass ratio of stone powder and the rate of change in bending strength after heating. Although there is some variation, the higher the mass ratio of stone powder, the greater the rate of increase in bending strength after heating. Similarly, as shown in FIG. 10, the ratio of compressive strength after heating to before heating increases with an increase in the mass ratio of stone powder. Since cracks have a significant effect on the strength of the hardened body, these results suggest that the higher the mass ratio of stone powder, the greater the effect of suppressing cracking caused by heating. However, according to FIG. 11, the specific compressive strength before heating tends to decrease as the mass ratio of stone powder increases. In other words, by increasing the mass ratio of stone powder, the strength of the GP foamed hardened body after heating can be increased, but excessive addition reduces the strength before heating.

Even in the case of the test specimens in the examples, the dimensional change after heating all over is somewhat large. In addition, the bending strength before heating is not high. This is because part of the active filler is replaced with stone powder, which is an inactive filler. However, if fibers are added as in conventional molded plate fireproof coating materials, the dimensional change in each direction can be suppressed to less than 1% even when heated all over, and bending strength can be improved.

Figures 12A to 12C show the occurrence of cracks and irregular deformation in each specimen after it was subjected to full heating at 1000° C. As shown in Figure 12A, in the example of the present invention in which the mass fraction of CSP is 20 to 40 mass % and the volume fraction of granular P is 48 to 50 volume %, almost no cracks or irregular deformation occurred in the specimen.
On the other hand, in Comparative Examples 4, 7, and 11, in which no granular P was added, Comparative Example 5, in which no CSP was added, Comparative Example 6, in which the mass ratio of PP was low at 6 mass%, and Comparative Example 8, in which powdered P was added instead of granular P, cracks and warping were confirmed to occur after heating.
When the GP foamed hardened material is heated to 1000°C, the incomplete products of the condensation polymerization reaction, N-A-S-H gel and C-A-S-H gel, are dehydrated and decomposed, melted and sintered, and the volume decreases (see Figure 13). This decrease in volume is thought to be the main cause of cracks and irregular deformation.
On the other hand, when a suitable amount of stone powder and granular P is added, a framework structure is formed inside the GP foamed hardened body by these inactive fillers and granular refractory aggregates. That is, a refractory particle framework (refractory particle framework structure) having a continuous particle size from small particles to large particles is formed from the small inactive filler particles and the relatively large lightweight aggregate particles, and the product of the condensation polymerization reaction of the active filler is filled into the gaps of this particle framework. And, due to the framework effect of this framework structure, even if the condensation polymerization reaction product shrinks due to thermal decomposition, the shape and dimensions of the entire system do not change, so it is thought that cracks and irregular deformation of the GP foamed hardened body do not occur. From the viewpoint of forming a refractory particle framework structure having a continuous particle size, it is preferable that the lightweight refractory aggregate used in the present invention has a continuous grain size rather than a single grain size.

On the other hand, when ordinary sand or silica sand is added as aggregate, the volume ratio of the aggregate is low, for example, as in Comparative Example 9, because ordinary sand and silica sand have a high specific gravity. In that case, the sand particles separate, and the framework structure due to the intertwining of particles described above is not sufficiently obtained. In addition, if the amount of sand added is increased, the sand hinders the foaming and expansion of the GP paste, and since the density of the sand itself is high, a lightweight GP foamed hardened body cannot be obtained. In addition, when powdered aggregate is added, for example, in Comparative Example 8, the volume ratio of powdered P is 55.2 volume%, but the dimensions of the aggregate are small, so the framework effect described above is not sufficiently obtained. For this reason, it is thought that in Comparative Examples 8 and 9, cracking and irregular deformation of the GP foamed hardened body after heating could not be suppressed.

When no inactive filler that does not decompose, melt or deteriorate when heated to 1000°C, such as stone powder, is added (Comparative Example 5), a continuous particle framework structure from fine particles to large particles is not formed, regardless of the addition of lightweight aggregate. Similarly, when the mass ratio of stone powder is low, as in Comparative Example 6, a continuous particle framework structure is not formed due to a lack of fine particles. Therefore, it is believed that the GP paste between the granular aggregate shrinks significantly when heated at high temperatures, causing cracks and irregular deformation in the GP foamed hardened body.

When BFS is used together with FA as an active filler, the strength of the GP foamed hardened body using only FA as the active filler is improved because BFS produces C-A-S-H gel in a condensation polymerization reaction. Therefore, the use of BFS is effective in increasing the strength of the GP foamed hardened body. However, compared to the N-A-S-H gel, which is the product of the condensation polymerization reaction of FA, the fire resistance of the C-A-S-H gel, which is the product of the condensation polymerization reaction of BFS, is low. Therefore, it is preferable to set the mass ratio of BFS to 10 to 20 mass% or less. The specimen of Comparative Example 10, which did not use BFS, had low strength before heating, warped after heating, and many cracks occurred. This is thought to be due to the low strength of the GP foamed hardened body and its low resistance to shrinkage and cracking. It was also confirmed that the specimen of Comparative Example 10 sunk after foaming and expansion due to a slow development of strength.

5.2 Single-sided Heating Test Table 6 shows the changes in dimensions, density, and thermal conductivity before and after the single-sided heating test, as well as the warpage after single-sided heating.

The dimensions after one-sided heating decreased in the same way as when the entire surface was heated, but the rate of decrease was smaller than when the entire surface was heated. In the case of the examples, the rate of decrease in both the length and width dimensions was mostly less than 1.0%, and the rate of decrease in volume was less than 5.0%. Regardless of whether the specimens were examples or comparative examples, the bulk density was decreased from before heating, which is the opposite of when the entire surface was heated. This was because the rate of decrease in volume was smaller compared to the degree of mass decrease after one-sided heating. As shown in Figure 14, there is a tendency for the rate of decrease in density to be smaller as the mass proportion of stone powder increases. This is because when a large amount of stone powder is added, the rate of decrease in volume after one-sided heating is smaller, or the mass decrease in the GP paste is smaller.

The thermal conductivity of some of the test specimens was measured after heating. Comparing the thermal conductivity measured before and after heating, it was found that the thermal conductivity after heating increased when the density before heating was low, but decreased when the density before heating was relatively high. This is because, as shown in Figure 13, when the GP foamed hardened body is heated, it melts, sinters, and becomes porous. As the body becomes porous, the thermal conductivity of the GP foamed hardened body decreases. However, when the density before heating is very small, the internal voids become connected and expand after heating, making it easier for thermal convection to occur, and it is thought that the thermal conductivity increases instead.

15A and 15B show the crack occurrence state before and after heating on the heated surface and the back surface, and the measured value of the warpage after heating. In Examples 1 to 3 of the present invention, in which the mass ratio of CSP is 20 to 40 mass% and the volume ratio of granular P is 48 to 50 volume%, almost no cracks occurred on the heated surface and the back surface of the test specimen, and the maximum warpage was about 2.5 mm.
In contrast, in Comparative Examples 4 to 11, cracks occurred on the heated surface and the back surface, and large warping occurred on the side (mostly 2.5 mm or more). In particular, many cracks occurred on the heated surface, making it almost impossible to continue using the specimen after heating. In Comparative Example 9, when the specimen was heated on the entire surface, cracks and irregular deformation did not occur much, as shown in FIG. 12C, but when the specimen was heated on one side, cracks occurred and warping was large. This is probably because the surface area-volume ratio of the plate-shaped specimen when heated on one side is larger than that of the rectangular column specimen when heated on the entire surface, and the silica sand particles, which have a small volume ratio, are too dispersed, reducing the skeletal effect. In addition, as shown in FIG. 16, although there is variation in the occurrence and measurement of warping, the higher the mass ratio of stone powder, the smaller the warping after heating on one side was observed. However, as mentioned above, considering the specific strength before heating, it is not preferable to increase the mass ratio of stone powder significantly, and it is preferable to keep it at 50 mass% or less.
Furthermore, as described above, by adding fibers or reinforcing materials to the GP foamed cured product of the embodiments, the dimensional change of the GP foamed cured product after one-sided heating can be further reduced, and the occurrence of cracks and irregular deformation after heating can be completely suppressed.

Figure 17 shows the temperature rise on the backside of the specimens of the Example and Comparative Example in a one-sided heating test. Compared to the Comparative Examples, the maximum temperature in the Example was slightly lower, and the temperature rise rate (gradient or inclination of the curve in the rising stage) was smaller. The temperature rise was particularly fast in Comparative Examples 9 and 11, which did not use silica sand or granular P. Furthermore, the temperature rise in Comparative Example 10, in which no BFS was added, was faster and the maximum temperature was higher than in Example 2, which had a similar formulation except for the addition of BFS.
As described above, it was found that the addition of BFS and the use of stone powder and lightweight refractory aggregate improve the thermal insulation properties of the GP foamed hardened body or at least have no adverse effects.

6. Summary The test results above can be summarized as follows:
When the GP foamed hardened material is heated to 1000°C, it becomes porous and its dimensions and volume decrease. When the entire surface is heated, the volume decreases more and the density increases, but when one side is heated, the volume decreases less and the density after heating decreases. In addition, due to melting and sintering, the compressive strength increases after heating. When the density before heating is small, the thermal conductivity after heating increases, but when the density before heating is relatively large, it decreases.
The GP foamed hardened body without adding an appropriate amount of lightweight fire-resistant aggregate and non-active filler will shrink significantly after heating, causing irregular deformation, resulting in cracks. On the other hand, if an appropriate amount of lightweight fire-resistant aggregate and heat-stable non-active filler is added, the lightweight GP foamed hardened body can be produced without any problems, and the non-active filler and lightweight fire-resistant aggregate form a particle framework structure with continuous particle size, suppressing the shrinkage of the GP foamed hardened body due to heating, and preventing cracks and irregular deformation. It is generally known that if heat-resistant fibers or reinforcing materials are further added, the bending strength can be increased and cracks and irregular deformation due to heating can be completely prevented.
In order to obtain both strength and fire resistance of the GP foamed cured material, the mass ratio of BFS is preferably 10 to 20 mass%. Since the condensation polymerization reaction product of MK is the same as FA, that is, N-A-S-H gel, the fire resistance of the GP foamed cured material is not affected even if the mass ratio of MK is high, but from the viewpoint of mass utilization of waste, it is also recommended that the mass ratio of MK be 10 to 20 mass%.

Claims (3)

A geopolymer-based lightweight fireproof material having a density of 1.0 g/cm3 or ^less , which is obtained by adding an alkaline solution to a mixture containing an active filler, a non-active filler, a lightweight fireproof aggregate, and a foaming agent, kneading the mixture, and curing the mixture.
The active filler is a mixture of at least one first active filler selected from fly ash, finely ground molten slag from municipal waste incineration ash, and finely ground molten slag from sewage sludge incineration ash, and at least one second active filler selected from finely ground blast furnace slag and metakaolin, the mass ratio of the second active filler being 10 to 20 mass% based on 100 mass% of the total amount of the active filler and the inactive filler;
The inactive filler is a stone powder that does not harden in the alkaline solution or that, even if hardened, has a compressive strength of 5 N/mm2 ^or less and maintains its physical and chemical properties even when heated to 1000°C, and the mass ratio of the inactive filler is 20 to 50 mass% in a ratio of 100 mass% of the total amount of the inactive filler and the active filler,
The lightweight refractory aggregate maintains its physical and chemical properties even when heated to 1000°C, has a density of 1.65 g/cm3 ^or less, has a particle size distribution in which the proportion of particle sizes of 5 mm or more is 0 mass% and the proportion of particle sizes of less than 0.15 mm is 5 mass% or less, and when the total volume of the lightweight refractory aggregate, the active filler, and the inactive filler is 100 volume%, the volume proportion of the lightweight refractory aggregate is 40 to 60 volume%. This is a geopolymer-based lightweight refractory material. The geopolymer-based lightweight fireproof material according to claim 1, wherein the alkaline solution is at least one selected from the group consisting of silicates, hydroxides, and carbonates of alkali metals. The geopolymer-based lightweight fireproof material according to claim 1 or 2, wherein the foaming agent is at least one selected from metallic silicon, metallic aluminum, and hydrogen peroxide.