KR20220094065A - Carbon fiber reinforced fast-curing geopolymer, and Preparation method thereof - Google Patents

Abstract

The high-speed curing type geopolymer according to the present invention is metakaolin; calcium compounds; carbon fiber; Fumed silica having a specific surface area of 150-250 m ² /g; And alkali activator, it has high brittleness, fast curing, free molding, and excellent non-combustible performance, so it can be used as a structurally stable non-combustible finishing composite material for fire-resistance performance, and can be quickly cured and molded into irregular shapes It can be applied as a reinforcing material for repairing and repairing damaged or damaged concrete structures.

Description

Carbon fiber reinforced fast-curing geopolymer and its manufacturing method {Carbon fiber reinforced fast-curing geopolymer, and Preparation method thereof}

The present invention relates to a geopolymer capable of high-speed curing and a method for preparing the same.

Geopolymer is one of the cement alternative materials, and it is starting to attract attention as a substitute or additive for the existing Portland cement. Geopolymer is a cement-based material of amorphous aluminosilicate and is an aluminosilicate eco-friendly binder synthesized through a polycondensation reaction between a geopolymer precursor and an alkali activator. As the precursor, natural minerals or industrial by-products such as fly ash are used as raw materials, so it is an inorganic material that can be widely used economically.

The structure of the geopolymer is created by the chemical reaction of alkali polysilicate and oxide aluminosilicate constituting the Si-O-Al bond. It is a material named geopolymer because it forms a network similar to that of a polymer during the curing process. . Geopolymers can be synthesized at room temperature or at low temperatures below 100°C, and carbon dioxide emissions during the manufacturing process are extremely low, which is expected to reduce carbon dioxide emissions by up to 70% compared to cement. In addition, geopolymers can be manufactured from industrial by-products such as fly ash, and are characterized by a large range of changes in physical properties depending on manufacturing conditions.

Although research on geopolymers has been continuously conducted due to the advantages of the geopolymers, most of them have been proposed as cement additives or substitutes, and recent studies have been conducted on ceramic fiber-ceramic matrix composite materials. There are few studies on geopolymer-only materials with high temperature stability.

In addition, since optimization of the raw material of the geopolymer and the alkali activator greatly depends on the geopolymer precursor (e.g. fly ash, metakaolin, etc.), it is necessary to optimize the synthesis conditions according to the starting material and target physical properties.

Since geopolymer is a high-purity ceramic material, it has high heat resistance and fire resistance, can be cured at a low temperature of 100°C or less, and its manufacturing method is simple. If it is a material that can be cured at high speed with these characteristics, it can be used as an industrial heat-resistant member that requires heat resistance, or as a repair and finishing material for buildings.

Therefore, the present inventors conducted research on a high-speed curing type geopolymer with an increased curing rate. Here, high-speed refers to a geopolymer manufactured by curing for 0.5 to 1 hour and subsequent drying for 1-2 days, whereas conventional geopolymer cement goes through a drying period of 7-28 days. Using metakaolin as the main raw material, geopolymers according to various manufacturing process parameters were studied and it was confirmed that there was a remarkable effect.

On the other hand, when looking only at the research on the composition ratio of geopolymer active agents that have been studied for a long time, it is almost impossible to grasp the role of active agents only by simple linear comparison between references. For example, in Paper A, high strength was expressed when the ratio of KOH:K ₂ SiO ₃ was 1:2, and in Paper B, high strength was expressed when it was 2:1. Surprisingly, it is thought that the difference in the optimized activator ratio even with the same activator is due to the different amount of raw material used in the two papers [Paper A: B. Singh, Ishwarya G., M. Gupta, SK Bhattacharyya, Geopolymer concrete; Paper B: A review of some recent developments. Construction and Building Materials, 2015. 85: p.78-90]. In multivariate studies such as this, the target properties can be reached only when several variables are simultaneously optimized. In fact, the design of experiments (DOE) technique is widely used in pharmaceuticals with many variables [Cao, B., et al. ., How To Optimize Materials and Devices via Design of Experiments and Machine Learning: Demonstration Using Organic Photovoltaics. ACS Nano, 2018. 12(8): p. 7434-7444]. However, among geopolymer studies, there have been no cases of optimization through DOE yet.

The present inventors conducted further research to further improve the strength of the high-speed curing type geopolymer, and used carbon fiber to overcome the disadvantage of weak brittleness of the ceramic material. The present invention has been completed by discovering that remarkable physical effects can be achieved by controlling the optimum ratio of active agents.

It is an object of the present invention to provide a high-speed curing type geopolymer having an increased curing speed and flexural strength and a method for manufacturing the same.

The high-speed curing type geopolymer according to the present invention is metakaolin; calcium compounds; carbon fiber; Fumed silica having a specific surface area of 150-250 m ² /g; and an alkali activator.

As another embodiment of the present invention, the method for producing a high-speed curing type geopolymer according to the present invention,

mixing a first alkali active agent and fumed silica to provide a first composition;

a first dispersing step of dispersing the first composition;

mixing the dispersed first composition with a second alkali activator and carbon fibers to provide a second composition;

a second dispersing step of dispersing the second composition;

providing a third composition by mixing metakaolin and a calcium compound in the dispersed second composition; and

It is preferable to include; mixing, casting and curing the third composition.

In addition, it is preferable that the first and second dispersion steps are sonicated for 5 to 15 minutes.

In addition, it is preferable to perform the curing step at 20 ~ 40 ℃.

Moreover, it is preferable that metakaolin and kaolin are calcined at 700-900 degreeC for 3-5 hours.

In addition, the calcium compound is preferably calcium hydroxide (Ca(OH) ₂ ), calcium oxide (CaO) or calcium carbonate (CaCO ₃ ).

In addition, the carbon fiber is preferably heat-treated at 200 to 300 ℃ for 1 to 4 hours.

In addition, the fumed silica is preferably included in a molar ratio of 2.5 ≤ SiO ₂ /Al ₂ O ₃ ≤ 3.0.

In addition, it is preferable that the alkali activator is at least one of KOH and K ₂ SiO ₃ .

In addition, by adding water to the alkali activator, it is preferably included in a molar ratio of 5.0 ≤ H ₂ O/K ₂ O ≤ 7.0.

In addition, it is preferable that the alkali activator includes KOH and K ₂ SiO ₃ in a weight ratio of 2 to 6:1 to 3.

In addition, it is preferable that the KOH is included in a ratio of 0.57 to 0.7 based on the weight of metakaolin.

In addition, the K ₂ SiO ₃ is preferably included in a ratio of 0.4 to 0.45 based on the weight of metakaolin.

The high-speed curing type geopolymer prepared according to the present invention has high brittleness, fast curing, free molding, and excellent non-combustible performance, so it can be used as a structurally stable non-combustible finishing material composite for fire resistance performance. In addition, it can be applied as a reinforcing material for repairing and repairing damaged and damaged concrete structures that require rapid hardening and forming into irregular shapes.

1 schematically shows the XRD analysis results of metakaolin in the presence or absence of carbon fibers and before and after calcination.
Figure 2 schematically shows a method for producing a fast-setting geopolymer according to the present invention.
3 schematically shows a three-point bending test method according to the present invention.
Figure 4 schematically shows the effect on the flexural strength of the three elements (K ₂ SiO ₃ , KOH, Fumed SiO ₂ ) in the first DOE method.
FIG. 5 schematically shows, in colormap, the flexural strength as a function of alkali activator (K ₂ SiO ₃ and KOH) content in the first DOE method.
6 schematically shows the effect on the flexural strength of two elements (K ₂ SiO ₃ , KOH) in the second DOE method.
7 is a colormap schematically showing the flexural strength as a function of alkali activator (K ₂ SiO ₃ and KOH) content in the second DOE method.
8 schematically shows the effect on the flexural strength of two elements (K ₂ SiO ₃ , KOH) in the third DOE method.
9 is a colormap schematic representation of flexural strength as a function of alkali activator (K ₂ SiO ₃ and KOH) content in the third DOE method.
FIG. 10 schematically shows the flexural strength as a function of alkali activator (K ₂ SiO ₃ and KOH) content in the first, second and third DOE methods as an overall colormap.
11 schematically shows the weight loss measurement results using the TGA method at a temperature change from room temperature to 900°C.
12 schematically shows the fire resistance and heat resistance test results for the samples of the third to seventh DOE methods.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiment of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

In describing the present embodiments, the same names and reference numerals are used for the same components, and thus overlapping additional descriptions are omitted below. In the drawings referenced below, no scale ratio applies.

Fast curing geopolymers are multi-variable in their manufacturing conditions (chemical component molar ratio (SiO ₂ , Al ₂ O ₃ , K ₂ O, Ca(OH) ₂ , H ₂ O), and each raw material (MK, fumed silica, Ca (OH) ₂ , KOH, K ₂ SiO ₃ ))) on the final physical properties, the variables with the least change were fixed, and flexural strength, which is important as a structural material, was selected as an index.

The high-speed curing type geopolymer according to the present invention is metakaolin; calcium compounds; carbon fiber; Fumed silica having a specific surface area of 150-250 m ² /g; and an alkali activator.

The kaolin (DJ 5041-1400 Daejung Chemicals & Metals Co., Ltd, S.Korea) is used as the main raw material, and it is preferably calcined at 700-900°C for 3-5 hours. Specifically, in the experiment of the present invention, metakaolin powder (MK) obtained by calcining at 800° C. for 4 hours in an electric furnace was used. As shown in FIG. 1 , peaks of kaolinite and quartzite can be clearly identified in the XRD pattern of kaolin before calcination. In the XRD pattern after calcination, the main peaks of kaolinite and quartzite are slightly observed, but it can be confirmed that metakaolin of aluminosilicate in amorphous phase is generated.

In addition, considering the flexural strength, it is preferable that the average particle size of the metakaolin is 3 to 10 μm.

The calcium compound is preferably calcium hydroxide (Ca(OH) ₂ ), calcium oxide (CaO) or calcium carbonate (CaCO ₃ ). As a calcium compound necessary for controlling the curing rate, in the present invention, calcium hydroxide (Ca(OH) ₂ ) (DJ 2511-4400 Daejung Chemicals & Metals Co., Ltd, S.Korea) was used.

In addition, Ca forms a calcium silicate crystal phase in a Si source and a base atmosphere, and the crystal phase acts as a nucleation site of the geopolymer and serves as a curing accelerator to speed up the curing rate. Such calcium silicate is also formed during the curing process of cement and plays a role in expressing the strength of cement. However, when the content of Ca is high, the interfacial area between the crystals made of Ca and the geopolymer increases, and this interface causes a decrease in strength, and molding becomes impossible due to local hardening. As a result, it is preferable that the molar ratio be 4.0 ≤ calcium compound/Al ₂ O ₃ ≤ 4.7.

It is preferable that the carbon fiber is heat-treated at 200 to 300° C. for 3 to 5 hours. Specifically, in the present invention, carbon fibers (HD Fiber, S. Korea) were used in the experiment after removing the sizing agent from the surface through heat treatment at 250° C. for 4 hours.

Carbon fiber is preferably used in a ratio of 0.03 or less based on the weight of metakaolin. When more carbon fibers than the above range are used, the fiber surface area is increased, and the relatively weak interfacial area is widened rather than the effect of improving strength due to the fibers, so that the flexural strength is rather reduced.

The fumed silica (Fumed-SiO ₂ ) preferably has a specific surface area of 150 to 250 m ² /g. Specifically, in Examples of the present invention, 200±25 m ² /g of fumed silica (Konasil K-200, OCI, S.Korea) was used.

Since there is a difference in flexural strength depending on the use and state (liquid, solid) of silica (SiO ₂ ) with a small particle shape and a large surface area, the geopolymer raw material with fluidity in contact with the active agent penetrates to increase the filling rate. The fumed silica with a parental structure is most preferred.

On the other hand, in the case of dry silica, as the SiO ₂ content increases, the flexural strength decreases. It is presumed that this is because excessive particle content contributes to the formation of pores rather than an increase in the filling rate with the geopolymer.

SiO ₂ and Al ₂ O ₃ form the basic structure of the geopolymer, and the alkali activator is a chemical component that causes the geopolymer reaction. Even in a geopolymer to which the same Si/Al/K molar ratio is applied, the physical properties of the geopolymer may vary depending on the fraction supplied for each raw material. Therefore, in the mixing ratio, when the fumed silica is included in a molar ratio of 2.5 ≤ SiO ₂ /Al ₂ O ₃ ≤ 3.0, the flexural strength of the geopolymer can be maintained high.

In addition, from the viewpoint of flexural strength, the particle size of the silica is preferably 0.01 to 0.1 μm.

The alkali activator includes 6M potassium hydroxide (KOH) (DJ 6597-4405 Daejung Chemicals & Metals Co., Ltd, S.Korea) and potassium metasilicate (K ₂ SiO ₃ ) (DJ 6617-4405 Daejung Chemicals & Metals Co., Ltd.). , Ltd, S. Korea) was used.

The most important factors for high-speed curing are the reaction rate and homogeneity of the geopolymer. The factor that has the greatest influence on this is the H ₂ O/K ₂ O ratio. When the H ₂ O content is low, the fluidity of the activator is low, making molding difficult, and curing occurs non-uniformly. Therefore, an appropriate amount of H ₂ O can be separately added to induce a homogeneous reaction with the particle phase and to improve the filling rate with carbon fibers. K ₂ O promotes geopolymerization through charge balance. Therefore, it is preferable that the molar ratio is 5.0 ≤ H ₂ O/K ₂ O ≤ 7.0.

More specifically, when both potassium hydroxide and potassium metasilicate are used as alkali activators as in the manufacturing method below, the potassium hydroxide is preferably used in a ratio of 0.3 to 07 relative to the weight of metakaolin, and the potassium metasilicate is It is preferably used in a ratio of 0.6 to 1.2 based on the weight of metakaolin. In addition, it is more preferable to include potassium hydroxide: potassium metasilicate in a weight ratio of 2-6:1-3.

As another embodiment of the present invention, the method for producing a high-speed curing type geopolymer according to the present invention,

mixing a first alkali active agent and fumed silica to provide a first composition;

a first dispersing step of dispersing the first composition;

mixing the dispersed first composition with a second alkali activator and carbon fibers to provide a second composition;

a second dispersing step of dispersing the second composition;

providing a third composition by mixing metakaolin and a calcium compound in the dispersed second composition; and

It is preferable to include; mixing, casting and curing the third composition.

In addition, it is preferable that the first and second dispersion steps are sonicated for 4 to 12 minutes.

In addition, it is preferable to perform the curing step at 20 ~ 40 ℃.

When the first alkali active agent is KOH and the second alkali active agent is K ₂ SiO ₃ , it is preferably included in a weight ratio of 2-6:1∼3.

On the other hand, to measure the bending strength of the geopolymer prepared according to the present invention, a three-point bending test was performed with a UTM tester (5982B13133, Instron Co., Ltd, USA). As shown in FIG. 3 , the formula used to calculate the flexural strength at a rate of 0.5 mm/min after fixing the specimen to a span length of 40 mm is as follows.

Modulus of rupture = MOR = 3FL /(2bd ² )

In the above equation, F is the measured force, L is the distance between supports, and b and d are the width and thickness of the specimen.

In addition, the curing time was measured by taking a small amount of geopolymer in a slurry state of manual mixing on an iron mold and measuring the degree of surface hardening over time. During the measurement, a cotton swab was used to roll it on the surface at intervals of 20 seconds and check from time to time. The time at which the geopolymer did not come off when rolled on the surface was recorded as complete cure.

Additionally, check the temperature measurement and time to decompose by high heat (TGA (Thermal Gravimetric Analysis, TGA/DSC 1/LF/1100, Mettier Toledo), 45(±2mm) * 50(±2mm) cylindrical sample and make it non-combustible A non-flammability test (The FESTEC Non-Comb 2005, FESTEC International Co., Ltd., S.Korea) was conducted to confirm the possibility of using a finishing material as a material (KS F ISO 1182). SEM analysis (FESEM, JSM 7610F, JEOL) was also performed to observe the difference in structure.

Hereinafter, the present invention will be described in more detail through a specific manufacturing method.

<Production of geopolymer>

Basic information of reagents used in Examples of the present invention is summarized in Table 1 below.

Source Manufacturer (Prod. No.) Solid content (%) BET surface area (m ² /g) Kaolin Daejeonghwageum (DJ 5041-1400) - - Ca(OH) ₂ Daejeonghwageum (DJ 2511-4400) - - 6M KOH Daejeonghwageum (DJ 6597-4405) 40.1 - K ₂ SiO ₃ Daejeonghwageum (DJ 6617-4405) 42.1 - Fumed-SiO ₂ OCI (Konasil K-200) - 200 ± 25 carbon fiber chop HD Fiber - -

As shown in FIG. 2, a 6M KOH solution was prepared by dissolving KOH pellets in 1 L of distilled water for 2 hours. The alkali solution (pH13~) was treated with a sonicator for 5 minutes so that the solid fumed silica was dispersed, and then potassium metasilicate solution was added.

Then, after the carbon fiber was added, it was treated with an ultra sonicator for 10 minutes for even dispersion. If the carbon fiber is hardened in a state in which the carbon fiber is not dispersed, it becomes difficult to penetrate the geopolymer into the agglomeration zone of the carbon fiber, and the mechanical strength is naturally lowered. Therefore, the sonication process is added as above, and the processing time can be added as needed.

Next, metacaulin and calcium hydroxide are added, and hardening proceeds at the same time as calcium is added in the process of manual mixing (the surface is hardened within 30 minutes), so a quick operation is required.

Thereafter, it was cast in a silicone mold (12 × 120 × 5 mm), dried at room temperature for one day, and further cured at room temperature in a desiccator for 7 days.

(1) Primary DOE

As shown in Table 2 below, samples were prepared by fixing the amounts of carbon fiber (0.1 g), calcium (2.5 g) and metakaolin (20 g), and by changing the content of other components, and the flexural strength was measured.

As shown in FIG. 4 for samples 1 to 27 prepared as described above, as the amount of KOH increased, the flexural strength increased, and it was confirmed that an inflection point was formed based on 9 g (0.45 W_MK), fumed silica 0.6 g ( When 0.03 W_MK) was added, the strength was slightly improved compared to the strength without the addition of fumed silica. Similarly, potassium metasilicate (K ₂ SiO ₃ ) also showed an inflection point where the flexural strength value increased (+) at 18 g (0.90 W_MK) and then decreased.

As shown in FIG. 5 , it was confirmed that high mechanical properties could be exhibited only when the amount of KOH increased and the amount of K ₂ SiO ₃ decreased.

(2) 2nd DOE

In the case of including carbon fibers in the first DOE, it was confirmed that the change in alkali activator was an important factor. Therefore, as shown in Table 3 below, samples were prepared by fixing the amounts of carbon fiber, calcium, metakaolin and fumed silica, and by changing the contents of other components, and flexural strength and curing time were measured.

As described in Table 3 and FIG. 6, when the amount of KOH increases, the flexural strength increases, but when the amount of K ₂ SiO ₃ increases, the flexural strength decreases.

Further, referring to FIG. 7 , this trend is more pronounced. Higher flexural strength can be obtained as it falls within the range of the lower right corner.

(3) 3rd DOE

As shown in Table 4 below, samples were prepared by fixing the amounts of carbon fiber, calcium, metakaolin and fumed silica, and by changing the contents of other components, and flexural strength and curing time were measured.

As described in Table 4 and FIG. 7, the amount of KOH showed an inflection point at 12 g, and when the amount of K ₂ SiO ₃ increased, the flexural strength increased.

Further, referring to FIG. 8 , as it falls within the range of the upper left corner, higher flexural strength can be obtained.

From the above experimental results, it was confirmed that the amount of KOH and K ₂ SiO ₃ activator containing K had a greater effect on flexural strength than the dry silica ratio when carbon fiber was added. The sample showing the highest flexural strength was composed of a molar ratio of 2.7 ≤ SiO ₂ / Al ₂ O ₃ ≤ 2.8 and 5.5 ≤ H ₂ O / K ₂ O ≤ 6.4.

On the other hand, thermal stability and mass change were checked through the curve of temperature-weight change through thermogravimetric analysis (TGA: Thermal Gravimetric Analysis, TGA/DSC 1/LF/1100, Mettler Toledo) with 3-7 samples of DOE ( 11).

In addition, in order to check whether the material is suitable as a building finishing material to prevent the generation of flames and toxic gases and the spread of fire in the event of a fire of a structure, it must pass the performance standards through the non-combustible performance test method of the Korean Industrial Standards. The maximum temperature in the furnace for 20 minutes after the start of the heating test should not rise more than 20K, and the mass reduction rate of the specimen after the end of the test should be 30% or less. So, as a 3-7 sample of the 3rd DOE, a Non-Combustibility Test was additionally analyzed for the purpose of compliance with the Ministry of Land, Infrastructure and Transport standards (KS F ISO 1182) (see Fig. 12), and the mass reduction rate was 30% or less. It was confirmed that it is suitable as a non-combustible material.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible within the scope without departing from the technical spirit of the present invention described in the claims. It will be apparent to those of ordinary skill in the art.

Claims (22)

metakaolin; calcium compounds; carbon fiber; Fumed silica having a specific surface area of 150-250 m ² /g; And a high-speed curing type geopolymer prepared including an alkali activator. The high-speed curing type geopolymer according to claim 1, wherein the meta-kaolin is calcined at 700-900° C. for 3-5 hours. The fast-setting geopolymer according to claim 1, wherein the calcium compound is calcium hydroxide (Ca(OH) ₂ ), calcium oxide (CaO), or calcium carbonate (CaCO ₃ ). The high-speed curing type geopolymer according to claim 1, wherein the carbon fiber is heat-treated at 200 to 300° C. for 3 to 5 hours. The high-speed curing type geopolymer according to claim 1, wherein the fumed silica is contained in a molar ratio of 2.5 ≤ SiO ₂ /Al ₂ O ₃ ≤ 3.0. The fast-setting geopolymer according to claim 1, wherein the alkali active agent is at least one of KOH and K ₂ SiO ₃ . The high-speed curing type geopolymer according to claim 1, wherein water is added to the alkali activator in a molar ratio of 5.0 ≤ H ₂ O/K ₂ O ≤ 7.0. The high-speed curing type geopolymer according to claim 1, wherein the alkali active agent contains KOH and K ₂ SiO ₃ in a weight ratio of 2-6:1-3. The high-speed curing type geopolymer according to claim 6, wherein the KOH is contained in a ratio of 0.57 to 0.7 based on the weight of metakaolin. The high-speed curing type geopolymer according to claim 6, wherein the K ₂ SiO ₃ is contained in a ratio of 0.4 to 0.45 based on the weight of metakaolin. mixing a first alkali active agent and fumed silica to provide a first composition;
a first dispersing step of dispersing the first composition;
mixing the dispersed first composition with a second alkali activator and carbon fibers to provide a second composition;
a second dispersing step of dispersing the second composition;
providing a third composition by mixing metakaolin and a calcium compound in the dispersed second composition; and
Mixing, casting, and curing the third composition; A method of producing a fast-curing geopolymer comprising a. [Claim 12] The method of claim 11, wherein the first and second dispersing steps are performed by sonication for 4 to 12 minutes. The method of claim 11, wherein the curing is performed at 20 to 40°C. The method of claim 11, wherein the meta-kaolin is calcined at 700-900° C. for 3-5 hours. The method of claim 11, wherein the calcium compound is calcium hydroxide (Ca(OH) ₂ ), calcium oxide (CaO), or calcium carbonate (CaCO ₃ ). The method of claim 11, wherein the carbon fiber is heat-treated at 200 to 300° C. for 3 to 5 hours. The method of claim 11, wherein the fumed silica is contained in a molar ratio of 2.5 ≤ SiO ₂ /Al ₂ O ₃ ≤ 3.0. The method of claim 11, wherein the alkali activator is at least one of KOH and K ₂ SiO ₃ . 12. The method of claim 11, wherein the alkali active agent is added with water in a molar ratio of 5.0 ≤ H ₂ O/K ₂ O ≤ 7.0. The method of claim 11, wherein the alkali activator comprises KOH and K ₂ SiO ₃ in a weight ratio of 2 to 6:1 to 3 by weight. The method of claim 18, wherein the KOH is contained in a ratio of 0.57 to 0.7 based on the weight of metakaolin. The method of claim 18, wherein the K ₂ SiO ₃ is contained in a ratio of 0.4 to 0.45 based on the weight of metakaolin.

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