Geopolymer composition and production method of geopolymer composition

Abstract

To provide a geopolymer composition improved in flowability and compression strength, and to provide a simple production method of the same with a low environmental load.SOLUTION: A geopolymer composition contains modified fly ash as undersize obtained by classifying fly ash with a sieve, and an alkali source. A production method of the geopolymer composition includes classifying fly ash with a sieve so as to obtain undersize as modified fly ash, and mixing the modified fly ash thus obtained with an alkali source. The modified fly ash is preferably undersize of a sieve of an opening 120 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to improving the freshness of geopolymers. [Background technology]

[0002] Geopolymers are defined as "materials that are hardened without using cement clinker, using a raw material (active filler) whose main component is amorphous aluminum silicate, and at least one aqueous solution (alkali source) of an alkali metal silicate, carbonate, or hydroxide" (Non-Patent Document 1). In addition to emitting less CO2 during production compared to hardened cement, geopolymers are attracting attention as construction materials with excellent acid resistance, heat resistance, etc.

[0003] In recent years, fly ash-based geopolymers, in which fly ash is used as an active filler and slag powder is partially substituted, have become mainstream in order to increase strength. However, when fly ash with a high content of unburned carbon or coarse particles is used, it adversely affects the fluidity immediately after mixing.

[0004] Therefore, Patent Document 1 discloses a geopolymer that uses fly ash in which unburned carbon has been reduced by a flotation method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-186143 [Non-patent literature]

[0006] [Non-Patent Document 1] Kazuo Ichinomiya and two others, "Current Status and Future Prospects of Geopolymers," Concrete Engineering, 2018, Vol. 56, No. 5, p. 410 Summary of the Invention [Problem to be solved by the invention]

[0007] The geopolymer manufacturing method described in Patent Document 1 uses modified fly ash, obtained by flotation of a solution containing fly ash dispersed in water, to produce a geopolymer composition. It is described that the fluidity of the geopolymer composition is increased, but its strength remains the same. Furthermore, the resulting fly ash contains moisture, which complicates the formulation management of the geopolymer. Furthermore, the large amount of water required for the modification process is likely to result in high energy consumption and processing costs. Furthermore, flotation involves the addition of foaming agents and collectors to the solution, but the use of surfactants such as foaming agents and collectors is considered to be a method that places a significant burden on the environment. Therefore, a simple, environmentally friendly technology for improving both the compressive strength and fluidity of geopolymer compositions has yet to be disclosed.

[0008] The present invention has been made based on the above circumstances, and its object is to provide a geopolymer composition having improved fluidity and compressive strength and a simple and environmentally friendly production method thereof. [Means for solving the problem]

[0009] As a result of extensive research conducted by the inventors to easily obtain a geopolymer composition with improved fresh properties and compressive strength, they discovered that by using fly ash (hereinafter also referred to as modified fly ash) in a geopolymer composition that has reduced unburned carbon, which is the under-sieve fraction of fly ash obtained by sieving, the effect of improving the fluidity and compressive strength of the geopolymer can be easily achieved without placing a significant burden on the environment.

[0010] That is, the first invention is a geopolymer composition containing modified fly ash, which is an undersized fraction obtained by classifying fly ash through a sieve, and an alkaline source.

[0011] The modified fly ash is preferably the undersize fraction of a sieve with an opening of 120 μm or less. The geopolymer composition preferably further contains ground granulated blast furnace slag.

[0012] The second invention is a method for producing the geopolymer composition, in which fly ash is classified with a sieve to obtain the undersized fraction as modified fly ash, and then the obtained modified fly ash is mixed with an alkali source.

[0013] The third invention is a geopolymer hardened body that is a hardened product of a geopolymer composition containing modified fly ash, which is an undersized fraction obtained by classifying fly ash through a sieve, an alkali source, and water.

[0014] The fourth invention is a method for producing a hardened geopolymer, characterized by curing the geopolymer composition at a temperature range of 5°C to 90°C. [Effects of the Invention]

[0015] The geopolymer composition of the present invention uses modified fly ash, which is the undersized fraction classified by a sieve, so it has sufficient fluidity for construction work and has high strength development.

[0016] The method for producing a geopolymer composition of the present invention involves obtaining modified fly ash, which is the undersized fraction obtained by classifying fly ash through a sieve, and then using this modified fly ash to produce a geopolymer composition.This method results in a geopolymer composition with sufficient fluidity for construction work and high strength.Furthermore, since the production method of the present invention is a dry process, it has the advantage of being simple and low environmental impact compared to the flotation method, as it does not discharge water containing surfactants such as foaming agents and collectors or heavy metals eluted from the fly ash. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments. In this specification, "parts" and "%" are based on mass unless otherwise specified.

[0018] <Geopolymer composition> The geopolymer composition of the present invention contains at least modified fly ash, which is the undersized fraction obtained by classifying fly ash through a sieve, and an alkali source, and optionally contains ground blast furnace slag.

[0019] (Modified fly ash) In the present invention, modified fly ash, which is the undersize fraction obtained by classifying fly ash through a sieve, is used. Fly ash is fine ash recovered from the exhaust gas in a dust collector among the ash by-products of combustion in boilers of thermal power plants and the like, using either or both of coal and biomass fuel as fuel. Fly ash is particularly preferably fly ash for concrete, which is primarily composed of SiO2 and Al2O3 and is classified as Classes I to IV according to JIS A 6201 based on particle size and flow value. While the fly ash is not particularly limited, Classes I and II, which have fine particle size and are highly reactive, are more preferred.

[0020] Sieving fly ash is simpler and less environmentally hazardous than flotation, resulting in fly ash with reduced unburned carbon. Large fly ash particles containing a large amount of unburned carbon are removed as the oversize fraction, resulting in the modified fly ash, which is the undersize fraction, having reduced unburned carbon. The reduced unburned carbon improves the fluidity of the resulting geopolymer composition. Furthermore, when organic admixtures are used to harden the geopolymer composition, the adsorption of the organic admixture to the unburned carbon prevents the admixture from being fully effective. Therefore, the modified fly ash is preferably the undersize fraction of a sieve with a mesh size of 120 μm or less, more preferably the undersize fraction of a sieve with a mesh size of 100 μm or less, and particularly preferably the undersize fraction of a sieve with a mesh size of 45 μm or less.

[0021] (ground granulated blast furnace slag) The geopolymer composition of the present invention may contain ground granulated blast furnace slag. By including ground granulated blast furnace slag, the strength of the hardened geopolymer composition can be improved. It also makes it possible to eliminate the need for heat curing during curing. These factors improve the productivity of the hardened geopolymer composition.

[0022] Ground granulated blast furnace slag is produced during the production of pig iron and contains CaO, SiO2, Al2O3, and MgO as its main components. Examples of ground granulated slag include those containing 20% ​​to 60% by mass of calcium, calculated as calcium oxide (CaO). The type of slag is not particularly limited, and either blast furnace slag or steelmaking slag may be used, with blast furnace slag being preferred from the perspective of reactivity. In particular, the use of ground granulated blast furnace slag 4000 for concrete, as specified in JIS A 6206, is more preferred from the perspective of the strength development and shrinkage properties of the hardened geopolymer body produced using the resulting geopolymer composition at room temperature.

[0023] The fly ash content of the total mass of fly ash and ground slag powder is preferably 50 to 90% by mass, more preferably 60 to 85% by mass. A content of 50% by mass or more is preferable from the viewpoint of maintaining good fluidity when mixed with water, making it easy to achieve sufficient workability, and also from the viewpoint of expanding the effective use of fly ash. Furthermore, a content of 90% by mass or less ensures good strength development of the hardened geopolymer composition at an early age.

[0024] (Alkaline source) The alkali source is a salt containing alkali metal ions (Li+, Na+, K+, etc.) as constituent ions, and representative alkali metal salts include alkali metal silicates, alkali metal carbonates, alkali metal hydroxides, etc.

[0025] Examples of alkali metal silicates include sodium silicate, potassium silicate, and lithium silicate. Examples of alkali metal carbonates include sodium carbonate, potassium carbonate, and lithium carbonate. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Sodium silicate solution No. 1 and sodium hydroxide solution are preferred because they have excellent strength and durability, and are relatively inexpensive and readily available. The alkali metal salts may be in the form of liquid or powder, or anhydrous, hydrated, or aqueous solution.

[0026] The molar ratio (Si / AL) of silicon contained in the alkali metal silicate to the alkali metal element contained in the alkali metal salt is preferably 0.05 to 0.85. By setting the Si / AL to 0.05 or more, the compressive strength of the hardened geopolymer can be ensured even at room temperature, and by setting the Si / AL to 0.85 or less, the fluidity of the geopolymer composition can be ensured, making it easy to use in field work. From the above points, it is more preferable that the Si / AL be 0.2 to 0.75.

[0027] (water) The water is not particularly limited and may be tap water, ion-exchanged water, pure water, or the like.

[0028] The molar ratio AL / W of the alkali metal element contained in the alkali metal salt to water is preferably 0.05 to 0.3. By setting the AL / W ratio to 0.05 or more, the compressive strength of the hardened geopolymer can be ensured even at room temperature, and by setting the AL / W ratio to 0.3 or less, the fluidity of the geopolymer composition can be ensured, making it easy to use in field work. From the above perspective, the AL / W ratio is more preferably 0.05 to 0.18, and even more preferably 0.08 to 0.12.

[0029] The volume ratio (AL+W) / P of the total of the alkali metal salt and water to the total of the fly ash and ground granulated blast furnace slag is preferably 0.5 to 2.0, and more preferably 0.08 to 1.3 in order to ensure fluidity and strength.

[0030] (aggregate) In addition to the above, various aggregates can be added to the geopolymer composition of the present invention depending on the application of the geopolymer composition. For example, known aggregates used in concrete such as lightweight aggregate, ordinary aggregate, heavy aggregate, limestone aggregate, slag aggregate, and silica sand can be added.

[0031] (admixtures, additives) In addition to the above, various admixtures and additives can be added to the geopolymer composition of the present invention depending on the intended use of the geopolymer composition. For example, known materials used in concrete such as fluidizers, shrinkage reducing agents, rust inhibitors, waterproofing agents, setting retarders, antifoaming agents, dust reducing agents, pigments, calcium carbonate powder, etc.

[0032] <Method of manufacturing geopolymer composition> The method for producing a geopolymer composition of the present invention includes classifying fly ash through a sieve to obtain the undersized fraction as modified fly ash, and then mixing the resulting modified fly ash with an alkali source. By classifying fly ash through a sieve to obtain modified fly ash with less unburned carbon, a geopolymer composition with sufficient fluidity for construction work and high strength can be obtained, resulting in a simple and environmentally friendly production method.

[0033] (Fly ash modification) The fly ash is classified using a sieve, and the undersize fraction is obtained as modified fly ash.

[0034] The sieve can be a known classifier, such as a gyratory airflow sieve, a centrifugal airflow sieve, a centrifugal dispersion sieve, a circular vibrating sieve, or a rocking sieve. Among these, a centrifugal dispersion sieve has the advantage of high processing capacity per unit screen area and can effectively classify fly ash (coarse powder) even when it contains moisture and has high cohesive properties. While a rocking sieve is inferior to a centrifugal dispersion sieve in processing capacity per unit screen area, it places less strain on the device due to vibration and is therefore particularly effective when classifying large amounts of fly ash.

[0035] If unsieved fly ash is used, it contains large fly ash particles containing a large amount of unburned carbon, which adversely affects the fluidity immediately after mixing. Furthermore, if organic admixtures are used to harden the geopolymer composition, the organic admixtures are adsorbed by the unburned carbon, preventing their full effectiveness. To improve the fluidity of the geopolymer composition immediately after mixing and to prevent the organic admixtures from interfering with their effectiveness, the sieve openings are preferably 120 μm or less, more preferably 100 μm or less, and particularly preferably 45 μm or less.

[0036] (Mixing modified fly ash with alkaline source) The method for producing the geopolymer composition of the present invention includes mixing the modified fly ash obtained by the above-mentioned fly ash modification with an alkaline source. The geopolymer composition of the present invention is obtained by mixing and kneading modified fly ash, an alkali source, water, aggregate, etc. If necessary, blast furnace slag powder, various admixtures, etc. may be blended and mixed.

[0037] The geopolymer composition of the present invention can also be prepared as a premixed geopolymer composition by mixing modified fly ash with alkali metal powder as an alkali source. The premixed geopolymer composition may further contain ground blast furnace slag and aggregate, or powder additives (admixtures, additives). The premixed geopolymer composition can be easily produced by mixing and kneading the composition with water.

[0038] In the method for producing a geopolymer composition of the present invention, admixtures, additives, aggregates, etc. may be mixed simultaneously or sequentially in predetermined amounts and kneaded using a kneading device. Examples of admixtures and additives include known materials used in concrete, such as superplasticizers, shrinkage-reducing agents, rust inhibitors, waterproofing agents, setting retarders, antifoaming agents, dust-reducing agents, pigments, and calcium carbonate powder. Examples of aggregates include known aggregates used in concrete, such as lightweight aggregate, ordinary aggregate, heavy aggregate, limestone aggregate, slag aggregate, and silica sand. The kneading device is not particularly limited, and examples include forced twin-shaft mixers used for mixing concrete.

[0039] <Method of manufacturing hardened geopolymer> In the method for producing a hardened geopolymer body of the present invention, the geopolymer composition obtained by the method for producing a geopolymer composition described above is poured and cured.

[0040] The method for producing a hardened geopolymer of the present invention is a method for producing a hardened geopolymer by obtaining a geopolymer composition using the above-mentioned manufacturing method of the present invention and then curing the obtained geopolymer composition at a temperature range of 5°C to 90°C.

[0041] The geopolymer composition obtained by the above manufacturing method may be poured and then cured to obtain a hardened geopolymer.

[0042] (Pouring process) In the casting process, the geopolymer composition obtained by the method for producing a geopolymer composition of the present invention is poured into a formwork. After pouring, it is preferable to compact it using a known compaction method. This results in a dense hardened geopolymer body.

[0043] (Curing process) In the curing process, after the casting process, the geopolymer composition is cured at a temperature range of 5°C to 90°C to obtain a hardened geopolymer composition. In particular, when an alkali silicate and an alkali carbonate are used in combination with the geopolymer composition, a hardened geopolymer composition with excellent compressive strength can be obtained by curing at room temperature of 5 to 35°C. Other curing conditions are not particularly limited, and commonly used curing conditions may be used. For example, steam curing, sealed curing, air curing, underwater curing, etc. may be used.

[0044] The method for producing a geopolymer composition of the present invention produces a geopolymer composition with sufficient fluidity for construction work and high strength development. Furthermore, since the production method of the present invention involves dry processing of fly ash, compared to flotation methods, it has the advantage of being simple and environmentally friendly, eliminating the discharge of surfactants such as foaming agents and collectors, and water containing heavy metals eluted from the fly ash. Furthermore, during fly ash modification, unburned carbon in the fly ash is removed. This prevents the unburned carbon from adsorbing and neutralizing the admixture, thereby enhancing the effectiveness of the admixture. Therefore, the hardened geopolymer obtained using the geopolymer composition of the present invention has a lower environmental impact than hardened geopolymer compositions of conventional geopolymer compositions and can be used in a variety of applications, such as as a concrete binder, in place of cement compositions.

[0045] <Other embodiments> The geopolymer composition, manufacturing method of the geopolymer composition, hardened geopolymer body, and manufacturing method of the hardened geopolymer body according to the present invention are not limited to the above-described embodiments, and various modifications may be made within the scope of the present invention. Furthermore, some of the configurations of certain embodiments may be omitted. Also, well-known technologies may be added to the configurations of certain embodiments. [Example]

[0046] The present invention will be described in more detail below with reference to specific examples. However, the present invention is not limited to the following examples. Various modifications and applications are also included in the present invention as long as the features of the present invention are not significantly impaired.

[0047] (raw materials) (1) Fly ash (FA) Biomass co-combustion ash: Biomass co-combustion ash obtained from thermal power generation using coal and biomass as fuel. Coal ash: Fly ash type II (compliant with JIS A 6201) (2) Ground granulated slag (BFS): Ground granulated blast furnace slag 4000 (compliant with JIS A 6206) alkali metal salts (3) 1.5WG1: Sodium silicate solution (No. 1) (SiO2 / Na2O molar ratio = 2.01, manufactured by Kishida Chemical Co., Ltd.) diluted 1.5 times with water. (4) NaOH32%: 32% sodium hydroxide aqueous solution (in-house production) Other Ingredients (5) Aggregate: Fine aggregate (JIS standard sand) (6) Water: Ion-exchanged water

[0048] (Comparative Examples 1 to 6) Comparative Examples 1 to 6 are geopolymer compositions prepared using coal ash or biomass-mixed combustion ash as is, without using modified fly ash.

[0049] In Comparative Examples 1 to 3, coal ash was used as the fly ash, and in Comparative Examples 4 to 6, biomass-mixed combustion ash was used as the fly ash. Fly ash, slag powder, 32% sodium hydroxide aqueous solution, 1.5 times diluted water glass No. 1 solution, and water were weighed according to the recipe in Table 1, poured into a Hobart mixer, and stirred for 1 minute. The aggregate was then poured in and mixed for 30 seconds, scraped off for 15 seconds, and then mixed for another 2 minutes to obtain a uniformly mixed geopolymer composition as mortar.

[0050] (Examples 1 to 24) Examples 1-12 are geopolymer compositions made using modified fly ash.

[0051] The coal ash or biomass-mixed combustion ash was passed through sieves with openings of 120 μm, 90 μm, and 38 μm using an ultrasonic sieve (manufactured by Artec Ultrasonics), and the fraction that passed through each sieve was obtained as modified fly ash.

[0052] Examples 1, 5, 9, 13, 17, and 21 used modified fly ash obtained by passing fly ash through a sieve with a mesh size of 120 μm. Examples 2, 6, 10, 14, 18, and 22 used modified fly ash obtained by passing fly ash through a sieve with a mesh size of 90 μm. Examples 3, 7, 11, 15, 19, and 23 used modified fly ash obtained by passing fly ash through a sieve with a mesh size of 38 μm. Examples 4, 8, 12, 16, 20, and 24 used modified fly ash obtained by passing fly ash through a sieve with a mesh size of 38 μm, and reduced (AL+W) / P to have a flow roughly the same as that of raw ash. The fly ash and slag powder, 32% sodium hydroxide aqueous solution, 1.5 times diluted water glass No. 1 solution, and water were weighed according to the recipe in Table 1, poured into a Hobart mixer, and stirred for 1 minute. The aggregate was then poured in and mixed for 30 seconds, scraped off for 15 seconds, and then mixed for another 2 minutes to obtain a uniformly mixed geopolymer composition as mortar.

[0053] The contents of various slag powders, which are believed to contribute to compressive strength and 15-pile mortar flow value (fluidity), as well as AL / W (molar ratio), Si / AL (molar ratio), and (AL+W) / P (volume ratio) were all set to the same values. The standard sand volume relative to the total mortar volume was also set to the same value.

[0054] [Table 1]

[0055] *AL / W: Sodium hydroxide, the molar ratio of sodium to water contained in No. 1 water glass. *Si / AL: The molar ratio of silicon (contained in sodium hydroxide and No. 1 water glass) to sodium. *(AL+W) / P: The volume ratio of a solution of sodium hydroxide, No. 1 water glass, and water to fly ash and slag powder.

[0056] [15 shot mortar flow test] Immediately after mixing, the mortars of Comparative Examples 1 to 6 and Examples 1 to 24 were subjected to 15 dropping motions and then measured for 15 strokes in accordance with the mortar flow test described in JIS A 5201. The results are shown in Table 2.

[0057] [Compression strength test] The mortars of Comparative Examples 1 to 6 and Examples 1 to 24 were sealed in φ (diameter) x 100 mm containers, heated at a temperature increase rate of 20°C / h, and held at 60°C and 95% RH for 24 hours. After curing, the mortars were subjected to a compressive strength test in accordance with the compressive strength test method specified in JIS A 1108 to measure their compressive strength. The results are shown in Table 2.

[0058] [Table 2]

[0059] As shown in Table 2, Examples 1 to 3, 5 to 7, 9 to 11, 13 to 15, 17 to 19, and 21 to 23 had increased flow and compressive strength compared to Comparative Examples 1 to 6. Furthermore, Examples 4, 8, 12, 16, 20, and 24, in which (AL+W) / P was reduced and the formulation was adjusted to the same flow as Comparative Examples 1 to 6, had significantly increased compressive strength.

Claims

1. A geopolymer composition comprising modified fly ash, which is the undersized fraction obtained by classifying fly ash through a sieve, and an alkali source.

2. The geopolymer composition according to claim 1, wherein the modified fly ash is an undersized fraction of a sieve having an opening of 120 μm or less.

3. The geopolymer composition according to claim 1, further comprising ground granulated blast furnace slag.

4. The method for producing a geopolymer composition according to claim 1, comprising classifying fly ash with a sieve to obtain the undersized fly ash as modified fly ash, and then mixing the obtained modified fly ash with an alkali source.

5. A geopolymer hardened body is a hardened product of a geopolymer composition containing modified fly ash, which is the undersized fraction obtained by classifying fly ash through a sieve, an alkali source, and water.

6. A method for producing a geopolymer hardened body, comprising curing a geopolymer composition containing modified fly ash, which is the undersized fraction obtained by classifying fly ash through a sieve, an alkali source, and water, at a temperature range of 5 ° C to 90 ° C.

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