Geopolymer composition and geopolymer hardened body

Abstract

To provide a geopolymer composition that exhibits excellent compressive and adhesion strength after curing.SOLUTION: The geopolymer composition contains an active filler, water, an alkaline activator and fine aggregate, and the fine aggregate comprises crushed limestone sand.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to geopolymer compositions and hardened geopolymers. [Background technology]

[0002] Patent Document 1 discloses a strength-enhancing aid for geopolymer compositions, which contains at least one compound selected from the group consisting of alkaline earth metal oxides, inorganic calcium salts, inorganic aluminum salts, nitrates, and organic strength-enhancing components.

[0003] Patent Document 2 discloses a method for producing a geopolymer using coal bottom ash, in which the compressive strength of the geopolymer is increased by removing it from the mold, curing it in an oven, and irradiating it with microwaves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-095192 [Patent Document 2] Special Publication No. 2021-512037 Summary of the Invention [Problem to be solved by the invention]

[0005] Geopolymer compositions harden through condensation polymerization caused by the reaction of an active filler with an alkaline activator. Strength-enhancing additives and curing methods have been studied to increase the mechanical strength of geopolymer compositions after hardening. However, the use of strength-enhancing additives increases material costs, and special curing methods increase construction costs. It is desirable to increase the mechanical strength of geopolymer compositions after hardening without relying on strength-enhancing additives or special curing methods.

[0006] It is against this background that the present disclosure has been made. The present disclosure aims to provide a geopolymer composition that has excellent compressive strength and adhesive strength after hardening. An object of the present disclosure is to provide a hardened geopolymer body having excellent compressive strength and adhesive strength. [Means for solving the problem]

[0007] Specific means for solving the above problems include the following aspects. <1> Contains an activated filler, water, an alkaline activator, and fine aggregate, The fine aggregate includes crushed limestone sand. Geopolymer composition. <2> The proportion of the crushed limestone sand in the fine aggregate is 50% by mass to 100% by mass. <1> The geopolymer composition according to claim 1. <3> The alkaline activator comprises sodium carbonate. <1> or <2> The geopolymer composition according to claim 1. <4> The active filler contains at least one of ground granulated blast furnace slag and fly ash. <1> ~ <3> 2. The geopolymer composition according to claim 1 . <5> <1> ~ <4> A hardened geopolymer, which is a hardened product of the geopolymer composition described in any one of the above. [Effects of the Invention]

[0008] According to the present disclosure, a geopolymer composition is provided that has excellent compressive strength and adhesive strength after curing. According to the present disclosure, a hardened geopolymer body having excellent compressive strength and adhesive strength is provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing flow values ​​of geopolymer compositions. [Figure 2] 1 is a graph showing the compressive strength of a hardened geopolymer body. [Figure 3]1 is a graph showing the adhesive strength of a hardened geopolymer body. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes embodiments of the present invention. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the present invention.

[0011] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit value of the numerical range may be replaced with the value shown in the examples.

[0012] In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0013] In the present disclosure, when referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified.

[0014] <Geopolymer composition> The geopolymer composition of the present disclosure is a composition in a state called a slurry, fresh, etc., and the geopolymer composition of the present disclosure hardens to obtain the hardened geopolymer of the present disclosure.

[0015] The geopolymer composition of the present disclosure contains an active filler, water, an alkali activator, and a fine aggregate, wherein the fine aggregate comprises crushed limestone sand.

[0016] The inventors of the present disclosure have discovered that by replacing the fine aggregate of geopolymer mortar or geopolymer concrete from natural sand with crushed limestone sand, the compressive strength and bond strength after hardening are improved. The main component of crushed limestone sand is calcium carbonate (CaCO3). Because calcium carbonate exhibits the same reactivity as alkaline activators, the surface of the crushed limestone sand becomes part of the geopolymer structure, which results in a stronger bond between the crushed limestone sand and the paste, and it is thought that the resulting mixture will have superior compressive strength and adhesive strength after hardening compared to when natural sand is used as fine aggregate.

[0017] The materials that make up the geopolymer composition of the present disclosure are described in detail below.

[0018] [Active filler] The active filler is generally a powder based on aluminum silicate. Examples of active fillers include ground granulated blast furnace slag, fly ash, metakaolin, silica fume, ground zeolite, ground granulated refuse incineration ash molten slag, ground granulated sewage sludge molten slag, volcanic ash, rice husk ash, fluidized bed coal ash, paper sludge incineration ash, and mixtures of at least two of these.

[0019] Preferred forms of the active filler include at least one of ground granulated blast furnace slag (BFS) and fly ash (FA). Geopolymer compositions containing BFS tend to have high compressive strength in hardened form. Geopolymer compositions containing FA tend to have excellent fluidity and workability.

[0020] A preferred form of active filler is a mixture of ground granulated blast furnace slag (BFS) and fly ash (FA). By mixing BFS and FA, geopolymer compositions and hardened geopolymers with a good balance of fluidity, workability, and mechanical strength can be obtained. The mixing ratio of BFS to FA is not limited and may be selected depending on the target fluidity, workability, pot life, setting time, pore structure, mechanical strength, etc. The mass ratio of BFS to FA (BFS:FA) is, for example, 20:80 to 80:20, 30:70 to 70:30, or 40:60 to 60:40.

[0021] An example of an embodiment of the active filler contains only BFS and FA, and the mass ratio of BFS to FA (BFS:FA) in this embodiment is, for example, 20:80 to 80:20, 30:70 to 70:30, or 40:60 to 60:40.

[0022] The qualities of the BFS (e.g., density, specific surface area) and the FA (e.g., density, specific surface area) are not limited and may be selected depending on the target fluidity, workability, pot life, setting time, pore structure, mechanical strength, etc. Examples of BFS include ground granulated blast furnace slag 3000, 4000, 6000, and 8000 as specified in JIS A6206:2013 "Ground granulated blast furnace slag for concrete." Examples of FA include types I, II, III, and IV as specified in JIS A6201:2015 "Fly ash for concrete."

[0023] [Water and alkaline activator] Water is the site where the components contained in the active filler and the alkaline activator are dissolved or ionized, and where the reaction takes place to form the geopolymer structure through a condensation polymerization reaction.

[0024] Alkaline activators are also referred to in the art as alkaline stimulants, alkalis, bases, etc. The alkaline activator is generally at least one selected from the group consisting of alkali metal silicates, alkali metal hydroxides, and alkali metal carbonates. The alkaline activator may be, for example, at least one selected from the group consisting of sodium silicate, potassium silicate, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0025] The water and alkaline activator included in the geopolymer composition are generally derived from an aqueous solution of the alkaline activator (referred to in this disclosure as an "alkaline solution"), i.e., by mixing the active filler with the alkaline solution, the water and alkaline activator are included in the geopolymer composition. In other words, a geopolymer composition comprising an active filler, water, and an alkaline activator is a geopolymer composition obtained by mixing an active filler with an alkaline solution.

[0026] Examples of alkaline solutions used to form the geopolymer composition include sodium water glass (i.e., sodium silicate solution), potassium water glass (i.e., potassium silicate solution), sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, potassium carbonate aqueous solution, and a mixture of at least two of these. From the viewpoint of ensuring workability, water may be further mixed.

[0027] The type and concentration of the alkaline solution may be selected depending on the level of reactivity to ensure a usable time, the mechanical strength after curing, and the like.

[0028] Examples of embodiments of the alkaline solution include a mixture of sodium water glass, water and sodium hydroxide; a mixture of sodium water glass and aqueous sodium hydroxide; and a mixture of sodium water glass, water and aqueous sodium hydroxide.

[0029] Examples of embodiments of the alkaline solution include a mixture of sodium water glass, water and sodium carbonate; a mixture of sodium water glass and aqueous sodium carbonate solution; and a mixture of sodium water glass, water and aqueous sodium carbonate solution.

[0030] Generally, the more alkaline an alkaline activator is, the more reactive it is with the active filler. Therefore, the more alkaline an alkaline activator is, the higher the mechanical strength of the cured geopolymer composition tends to be, and the more alkaline an alkaline activator is, the shorter the pot life tends to be. Based on the above technical common sense, when comparing sodium hydroxide and sodium carbonate as alkaline activators, sodium hydroxide is preferred from the viewpoint of the high mechanical strength of the geopolymer hardened body, and sodium carbonate is preferred from the viewpoint of the long usable life of the geopolymer composition.

[0031] In the geopolymer composition of the present disclosure, the alkali activator preferably contains sodium carbonate from the viewpoint of having a long usable time and excellent compressive strength and adhesive strength after hardening. As shown in the examples below, the geopolymer composition of the present disclosure, in which the alkaline activator contains sodium carbonate, has a longer pot life and superior compressive strength and adhesive strength after hardening compared to the alkaline activator containing sodium hydroxide. The superior compressive strength and adhesive strength after hardening of the alkaline activator containing sodium carbonate compared to the alkaline activator containing sodium hydroxide is unexpected given the above-mentioned common technical knowledge. While the detailed mechanism of this unexpected effect is unknown, it is presumed to be due to the combination of crushed limestone sand (mainly composed of CaCO3) and sodium carbonate (Na2CO3). The geopolymer composition of the present disclosure has a long usable time and excellent compressive strength and adhesive strength after hardening. Therefore, it is more preferable that the alkaline activator contains sodium silicate and sodium carbonate.

[0032] When sodium carbonate is used as the alkaline activator, the amount used may be selected depending on the target fluidity, workability, pot life, setting time, pore structure, mechanical strength, etc. For example, the amount of sodium carbonate used is in the range of 1 to 5 parts by mass per 100 parts by mass of crushed limestone sand.

[0033] [Crushed limestone sand] The geopolymer composition of the present disclosure contains crushed limestone sand as fine aggregate. The quality of the crushed limestone sand (e.g., density, specific surface area) can be selected according to the target fluidity, workability, usable life, setting time, pore structure, mechanical strength, etc., within the range of the crushed sand standards specified in JIS A5005:2020 "Crushed stone and crushed sand for concrete."

[0034] In the geopolymer composition of the present disclosure, the mass ratio of crushed limestone sand to the entire fine aggregate is, for example, 10% by mass to 100% by mass, 20% by mass to 100% by mass, 30% by mass to 100% by mass, 40% by mass to 100% by mass, 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, 100% by mass.

[0035] In the geopolymer composition of the present disclosure, from the viewpoint of excellent compressive strength and adhesive strength after hardening, it is preferable that more than half of the fine aggregate is crushed limestone sand. That is, in the geopolymer composition of the present disclosure, from the viewpoint of excellent compressive strength and adhesive strength after hardening, it is preferable that the mass ratio of crushed limestone sand to the entire fine aggregate is 50% by mass to 100% by mass, and the higher the mass ratio of crushed limestone sand, the more preferable. The mass ratio of crushed limestone sand to the entire fine aggregate is preferably 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, or 100% by mass.

[0036] [Other aggregates] The geopolymer composition of the present disclosure may contain other aggregates besides crushed limestone sand, including various fine and coarse aggregates conventionally used in geopolymer mortar, geopolymer concrete, cement mortar, or cement concrete.

[0037] Examples of fine aggregates other than crushed limestone sand include river sand, mountain sand, land sand, sea sand, silica sand, crushed sand, blast furnace slag fine aggregate, and recycled fine aggregate derived from concrete waste. Examples of coarse aggregate include crushed stone such as andesite, rhyolite, hard sandstone, and limestone, river gravel, mountain gravel, land gravel, blast furnace slag coarse aggregate, and recycled coarse aggregate derived from concrete waste. The type and content of these aggregates may be selected depending on the target mechanical strength of the hardened geopolymer body.

[0038] [Other ingredients] The geopolymer composition of the present disclosure may contain a chemical admixture, including any chemical admixture conventionally used in geopolymer mortar, geopolymer concrete, cement mortar, or cement concrete.

[0039] The geopolymer compositions of the present disclosure may contain reinforcing materials, such as metal fibers, carbon fibers, glass fibers, basalt fibers, and organic fibers.

[0040] <Method of manufacturing geopolymer composition> The geopolymer composition of the present disclosure can be obtained by mixing the above-described materials. The mixing of the materials can be carried out, for example, by kneading using a mixer.

[0041] The order of mixing materials when preparing a geopolymer composition is not limited. For example, first, the active filler and aggregate are mixed in a mixer, and then an alkaline solution is added to the mixer and mixed. Furthermore, if necessary, a chemical admixture may be added to the mixer and mixed. When mixing the active filler and aggregate in the mixer, a reinforcing material may be added and mixed as needed.

[0042] The mixing ratio of the active filler to the alkaline solution may be appropriately set depending on the type of active filler and the type and concentration of the alkaline solution. For example, 100 parts by mass of the active filler is mixed with 10 to 100 parts by mass of the alkaline solution.

[0043] <Hardened geopolymer> The hardened geopolymer of the present disclosure can be obtained by hardening the geopolymer composition of the present disclosure. The geopolymer composition generally hardens to form a hardened body by a condensation polymerization reaction accompanied by dehydration.

[0044] An example of an embodiment of the method for producing a hardened geopolymer of the present disclosure includes pouring a geopolymer composition into a mold to obtain a molded body and hardening the molded body. The geopolymer composition poured into the mold may be subjected to treatment such as degassing according to a conventional method. The molded body may be removed from the mold before or during hardening.

[0045] In the method for producing a hardened geopolymer body of the present disclosure, the curing temperature and curing time for hardening the geopolymer composition are not limited. Depending on the target mechanical strength of the hardened geopolymer body, room temperature curing, heat curing, steam curing, autoclave curing, water curing, air curing, sealed curing, or a combination thereof may be used. [Example]

[0046] The geopolymer composition and hardened geopolymer of the present disclosure will be specifically described below using examples. The geopolymer composition and hardened geopolymer of the present disclosure are not limited to the following examples.

[0047] <Material> The following materials were prepared for the geopolymer composition: BFS (ground granulated blast furnace slag): density 2.91 g / cm 3 , specific surface area 4240cm 2 / g FA (fly ash): density 2.32 g / cm 3 , specific surface area 3680cm 2 / g Sodium water glass: sodium silicate No. 2, density 1.50 g / cm 3 Water: Tap water NaOH: 10 mol / L sodium hydroxide solution ·Na2CO3: Sodium carbonate anhydrous ·Standard sand: absolute dry density 2.64g / cm 3 , water absorption rate 0.42%, surface dry density 2.65g / cm 3 Mountain sand: Kimitsu, bone dry density 2.57g / cm 3 , water absorption rate 1.57%, surface dry density 2.61g / cm 3 ·Crushed limestone sand: bone dry density 2.55g / cm 3 , water absorption rate 2.17%, surface dry density 2.60g / cm 3

[0048] <Preparation of Geopolymer Composition (1)> Geopolymer mortars were prepared for the purpose of measuring the flow value. The formulation is shown in Table 1. The amounts of sodium water glass, water, aqueous sodium hydroxide solution, and anhydrous sodium carbonate were set so that the molar amounts and molar ratios of SiO2 and Na2O contained in the alkaline solution were the same when using aqueous sodium hydroxide solution and when using anhydrous sodium carbonate.

[0049] [Table 1]

[0050] <Flow value measurement> An alkaline solution was prepared by mixing sodium water glass, water, and an aqueous solution of sodium hydroxide or anhydrous sodium carbonate, and was allowed to stand until it reached room temperature. Geopolymer mortar was mixed by machine in accordance with JIS R5201:2015 "Physical Testing Methods for Cement." The active filler and fine aggregate were placed in a mixing bowl and mixed at low speed for 30 seconds. The alkaline solution was then added and mixed at low speed for 90 seconds, followed by a pause. After scraping off the mortar adhering to the mixing bowl and paddle, the mixture was mixed at high speed for 90 seconds. Flow measurements were taken 30 and 60 minutes after mixing, and every 30 minutes thereafter, until flow measurements could no longer be performed. The flow measurements at 15 strokes are shown in Table 2 and Figure 1.

[0051] [Table 2]

[0052] The flow value immediately after mixing was higher for the mortars using NaOH (Reference Example 1, Comparative Example 1, and Example 1) than for the mortars using Na2CO3 (Reference Example 2, Comparative Example 2, and Example 2). For the mortars using NaOH (Reference Example 1, Comparative Example 1, and Example 1), the flow value could not be measured after 30 minutes, regardless of the type of fine aggregate. For the mortars using Na2CO3 (Reference Example 2, Comparative Example 2, and Example 2), the flow value could be measured for 6 hours or more, regardless of the type of fine aggregate. It has been confirmed that geopolymer compositions using standard sand as fine aggregate have a longer pot life when the alkali activator is sodium carbonate than when the alkali activator is sodium hydroxide. This time, it was found that geopolymer compositions using natural fine aggregate also have a longer pot life when the alkali activator is sodium carbonate than when the alkali activator is sodium hydroxide.

[0053] For both NaOH and Na2CO3, the mortars using crushed limestone sand as fine aggregate (Examples 1 and 2) had higher flow values ​​immediately after mixing than the mortars using pit sand as fine aggregate (Comparative Examples 1 and 2). Furthermore, the combination of crushed limestone sand and Na2CO3 (Example 2) always had a higher flow value than the combination of pit sand and Na2CO3 (Comparative Example 2) until the end of its usable time. It was found that the geopolymer composition with crushed limestone sand as fine aggregate had a longer pot life than the geopolymer composition with mountain sand as fine aggregate.

[0054] <Preparation of Geopolymer Composition (2)> Geopolymer mortar was prepared to form specimens for measuring mechanical strength. The mix ratio is shown in Table 3. The amounts of sodium water glass, water, sodium hydroxide solution, and anhydrous sodium carbonate were adjusted so that the molar amounts and molar ratios of SiO2 and Na2O contained in the alkaline solution were the same when using sodium hydroxide solution and when using anhydrous sodium carbonate.

[0055] [Table 3]

[0056] An alkaline solution was prepared by mixing sodium water glass, water, and an aqueous solution of sodium hydroxide or anhydrous sodium carbonate, and was allowed to stand until it reached room temperature. The geopolymer mortar was mixed by machine in accordance with JIS R5201:2015 "Physical testing methods for cement."

[0057] <Evaluation of compressive strength> The specimens were formed immediately after mixing the mortar. A cylindrical specimen frame measuring 50 mm in diameter and 100 mm in length was used in the mold. Mortar was packed into the mold to approximately half its height, and immediately thereafter, the mold was vibrated for 30 seconds using a table vibrator to level the specimen surface. The remaining sample was then packed into the mold to approximately half its height using a spoon, and the mold was again vibrated for 30 seconds using a table vibrator to level the specimen. After leveling, the mortar mound was scraped off and the top surface was smoothed. The specimens were then sealed with an impermeable cap or wrapping film and placed in a humidity chamber at 20°C for sealed curing until they reached the specified age. After reaching the specified age, the specimens were demolded, and both bottom surfaces of the cylindrical specimens (the surfaces compressed during the compression test) were polished to a height of 95–100 mm. Compressive strength (N / mm2) according to JIS A1108:2018 "Concrete compressive strength test method" 2 ) was measured. The average value of the three test specimens is shown in Table 4 and Figure 2. The compressive strength was 40 N / mm 2 It is desirable that there be more than this.

[0058] <Evaluation of adhesive strength> A cement mortar base was prepared as a test substrate for the bond strength test in accordance with the provisions of JIS A6916:2014 "Architectural surface preparation coating materials." A water absorption adjuster was applied to the cement mortar base, and geopolymer mortar was molded into a 40mm x 40mm x 5mm plate on top of it. The specimen was sealed and cured for two days, and then left to stand at a temperature of 20±2°C and a relative humidity of 60±5%. After 28 days of age, the bond strength (N / mm) was measured in accordance with the provisions of JIS A6916:2014 "Architectural surface preparation coating materials." 2 ) was measured. The average value of three test specimens is shown in Table 4 and Figure 3. The adhesive strength was 1.0 N / mm 2 It is desirable that there be more than this.

[0059] [Table 4]

[0060] For both NaOH and Na2CO3, the hardened bodies in which the fine aggregate was crushed limestone sand (Examples 11 and 12) had higher compressive strength and bond strength values ​​than the hardened bodies in which the fine aggregate was pit sand (Comparative Examples 11 and 12). It was found that the geopolymer composition with crushed limestone sand as fine aggregate had higher compressive strength and bond strength after hardening than the geopolymer composition with mountain sand as fine aggregate.

[0061] The combination of mountain sand and Na2CO3 (Comparative Example 12) had lower compressive strength and adhesive strength than the combination of mountain sand and NaOH (Comparative Example 11). This was presumably due to the difference in alkalinity of the alkaline activator. On the other hand, the combination of crushed limestone sand and Na2CO3 (Example 12) had higher compressive strength and bond strength at 28 days than the combination of crushed limestone sand and NaOH (Example 11). This was unexpected considering the alkalinity of the alkali activator.

[0062] A geopolymer composition in which the fine aggregate contains crushed limestone sand and the alkali activator contains sodium carbonate is a preferred embodiment from the viewpoint of having a long usable time and excellent compressive strength and adhesive strength after hardening.

Claims

1. Contains an activated filler, water, an alkaline activator, and fine aggregate, The fine aggregate includes crushed limestone sand. Geopolymer composition.

2. The geopolymer composition according to claim 1, wherein the proportion of the crushed limestone sand in the fine aggregate is 50% by mass to 100% by mass.

3. 2. The geopolymer composition of claim 1, wherein the alkaline activator comprises sodium carbonate.

4. 2. The geopolymer composition of claim 1, wherein the active filler comprises at least one of ground granulated blast furnace slag and fly ash.

5. A hardened geopolymer body, which is a hardened product of the geopolymer composition according to any one of claims 1 to 4.

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