KR20220152855A - Curing method of cementitious materials using alkaline activator aqueous solution - Google Patents

Abstract

A curing method of a cement composition according to an embodiment of the present invention includes: a step of compressing and molding a cement composition containing blast furnace slag fine powder, silica sand, and liquid sodium silicate; a preliminary curing step of curing the cement composition in an air-dry condition; a first curing step of curing a preliminarily cured cement composition in an alkaline activator aqueous solution; and a secondary curing step of curing the primarily cured cement composition in a relative humidity atmosphere of 95 % or more.

Description

Curing method of cement composition using aqueous alkali activator {CURING METHOD OF CEMENTITIOUS MATERIALS USING ALKALINE ACTIVATOR AQUEOUS SOLUTION}

One embodiment of the present invention relates to a method for curing a cement composition using an aqueous alkali activator solution. More specifically, one embodiment of the present invention relates to a method for curing a cement composition using an aqueous alkali activator solution in which strength is developed even when cured for a relatively short time.

Greenhouse gas emissions, including carbon dioxide, are one of the causes of global warming, which increases the frequency and extent of natural disasters around the world. Portland Cement's cement clinker production accounts for about ₄ % of global CO2 emissions (2017 statistics) and is considered a serious problem in the construction industry.

The use of CO ₂ to accelerate the curing of cement-based materials is known as one of the ways to lower the CO ₂ concentration in the atmosphere. Calcium silicates, such as alite and belite of Portland cement, are spontaneously carbonated to form calcium carbonate (CaCO ₃ ). During the CO ₂ curing process, CaCO ₃ is precipitated in the pores of cast mortar and concrete, so the early CO ₂ cured cement-based material rapidly increases in strength. The pore densification refines the microstructure, including the cement paste matrix and interfacial transition zone, resulting in higher strength in a shorter time.

It is also known how to reduce CO ₂ emissions by using an alternative cement that replaces Portland cement. Calcium sulfoaluminate cement has the advantage of being able to perform the firing process at a low temperature. Compared to the firing of Portland cement, the firing temperature is reduced by about 100 to 200 °C, which contributes to a reduction in CO ₂ emissions. Alkali-activated binders, which also include geopolymers synthesized from industrial by-products such as blast furnace slag and fly ash, are one promising alternative. Blast furnace slag also contains large amounts of calcium silicate. Hydration is vulnerable to carbonization, which potentially requires an alkali activator. Alkaline activators allow calcium to dissolve from slag particles, and calcium participates in the formation of CSH gels, contributing to the development of strength.

In one embodiment of the present invention, it is intended to provide a method for curing a cement composition using an aqueous alkali activator solution. More specifically, in one embodiment of the present invention, it is intended to provide a method for curing a cement composition using an aqueous alkali activator solution in which strength is developed even when cured for a relatively short time.

A cement composition curing method according to an embodiment of the present invention includes the steps of compressing and molding a cement composition containing blast furnace slag fine powder, silica sand, and liquid sodium silicate; A preliminary curing step of curing the cement composition in an air-conditioned state; A first curing step of curing the pre-cured cement composition in aqueous alkali activator solution; and a secondary curing step of curing the primary cured cement composition in a relative humidity atmosphere of 95% or more.

The cement composition includes 100 parts by weight of blast furnace slag fine powder, 100 to 500 parts by weight of silica sand, and 10 to 50 parts by weight of liquid sodium silicate.

The blast furnace slag fine powder includes SiO ₂ : 30 to 33 wt%, Al ₂ O ₃ : 12 to 14 wt%, and CaO: 43 to 48 wt%.

The weight ratio of SiO ₂ to Na ₂ O in the liquid sodium silicate may be 2.0 to 3.5.

In the molding step, the cement composition may be compressed to 0.5 MPa or more.

In the preliminary curing step, the cement composition may be cured for 3 to 12 hours in a relative humidity atmosphere of 60% or less.

In the first curing step, the aqueous alkaline activator solution may include one or more of KOH, NaOH, and Na ₂ SiO ₃ .

In the first curing step, the concentration of the alkali activator in the aqueous alkali activator solution may be 1 to 5M.

In the first curing step, the alkaline activator aqueous solution may be obtained by dissolving carbon dioxide for 5 minutes to 1 hour.

In the first curing step, the aqueous alkaline activator solution may be pH 8 to pH 14.

The preliminary curing step, the first curing step and the second curing step may be carried out at a temperature of 15 to 50 ° C, respectively.

1 is a result of measuring the compressive strength of a cement composition cured using slag 1 in Example.
2 is a result of measuring the compressive strength of a cement composition cured using slag 2 in Example.

Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is only for referring to specific embodiments and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising" as used herein specifies particular characteristics, regions, integers, steps, operations, elements and/or components, and the presence or absence of other characteristics, regions, integers, steps, operations, elements and/or components. Additions are not excluded.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

A cement composition curing method according to an embodiment of the present invention includes the steps of compressing and molding a cement composition containing blast furnace slag fine powder, silica sand, and liquid sodium silicate; A preliminary curing step of curing the cement composition in an air-conditioned state; A first curing step of curing the pre-cured cement composition in aqueous alkali activator solution; and a secondary curing step of curing the primary cured cement composition in a relative humidity atmosphere of 95% or more.

Hereinafter, the curing method of the cement composition will be described in detail for each step.

First, a cement composition containing fine blast furnace slag powder, silica sand, and liquid sodium silicate is compacted and molded.

The cement composition includes blast furnace slag fine powder, silica sand and liquid sodium silicate. As cement compositions, blast furnace slag finely powdered silica sand and liquid sodium silicate are widely known, and appropriate ones can be selected and used. In addition, cement is included, and the type of cement is not particularly limited.

The blast furnace slag fine powder plays a role of generating CSH hydrate contributing to the development of strength in the cement composition. The blast furnace slag fine powder may include SiO ₂ : 30.0 to 33.0 wt%, Al ₂ O ₃ : 12.0 to 14.0 wt%, and CaO: 43.0 to 48.0 wt%. The blast furnace slag fine powder may further include various oxides in addition to the aforementioned SiO ₂ , Al ₂ O ₃ , and CaO. For example, at least one of Na ₂ O, K ₂ O, MgO, MnO, TiO ₂ , SO ₃ , P ₂ O ₅ , Fe ₂ O ₃ , BaO, ZrO ₂ , V ₂ O ₅ , SrO and Y ₂ O ₃ may further include. These may further contain up to 5% by weight each. More specifically, the blast furnace slag fine powder may include SiO ₂ : 30.0 to 31.0 wt%, Al ₂ O ₃ : 13.0 to 13.5 wt%, and CaO: 45.0 to 48.0 wt%.

Since silica sand is composed of SiO ₂ as a main component and is widely known in the field of cement compositions, a detailed description thereof will be omitted. More specifically, No. 4 silica sand may be used, which has an average particle size of 1.2 to 1.5 mm.

100 to 500 parts by weight of silica sand may be included with respect to 100 parts by weight of the blast furnace slag fine powder. If the silica sand is too small, a problem may occur in securing the amount of air in the composition. If there is too much silica sand, there may be a problem in mixing the composition due to insufficient binder. More specifically, silica sand may be included in an amount of 250 to 350 parts by weight based on 100 parts by weight of the blast furnace slag fine powder. In one embodiment of the present invention, the weight part means a relative weight ratio with respect to the blast furnace slag fine powder.

Sodium silicate (Na ₂ SiO ₃ ) can be added in liquid form. A weight ratio of SiO ₂ to Na ₂ O (SiO ₂ /Na ₂ O) in the liquid sodium silicate may be 2.0 to 3.5. Sodium silicate added in an appropriate ratio should be used to properly alkali-activate the blast furnace slag powder. More specifically, it may be 2.5 to 3.3.

10 to 50 parts by weight of sodium silicate may be included with respect to 100 parts by weight of the blast furnace slag fine powder. Too little sodium silicate can cause problems with insufficient alkali activation. Too much silica sand can cause material separation problems in creating the composition. More specifically, 35 to 50 parts by weight of sodium silicate may be included based on 100 parts by weight of the blast furnace slag fine powder. Since sodium silicate is a liquid, the weight of sodium silicate is defined as the weight including the solvent.

The cement composition thus prepared may be molded by injecting into a mold and compressing it.

The molding pressure may be 0.5 MPa or more. If the molding pressure is too low, it is difficult to obtain an appropriate shape. If the molding pressure is too high, the amount of voids in the molded body is small, and the alkali activator may not be evenly supplied during the underwater curing process described later. More specifically, the molding pressure may be 0.7 to 1.5 MPa.

Next, in the preliminary curing step, the cement composition is cured in an air-dried state.

Air condition means a condition with low humidity in the atmosphere. By curing in an air-dry state, some of the moisture remaining in the molded body can be removed, so that the alkali activator can be evenly supplied during the underwater curing process to be described later. More specifically, the air-conditioned condition may be a relative humidity atmosphere of 60% or less. More specifically, it may be a relative humidity atmosphere of 50% or less.

In the preliminary curing step, the temperature may be 15 to 50 °C. More specifically, it may be 20 to 30 °C. More specifically, it may be 23 to 25 °C.

The pre-curing step may be performed for 3 to 12 hours. By curing for the above-mentioned time, it is possible to ensure that the alkali activator is evenly supplied in the underwater curing process to be described later. More specifically, it may be performed for 5 to 6.5 hours.

Next, in the first curing step, the pre-cured cement composition is cured in water in an alkaline activator aqueous solution. In the primary curing step, an alkali activator is supplied to the cement composition to develop strength.

At this time, the alkali activator aqueous solution may include at least one of KOH, NaOH, and Na ₂ SiO ₃ as an alkali activator. Alkaline activators promote the reaction of calcium ions in slag to improve strength. More specifically, KOH may be included.

The concentration of the alkali activator in the aqueous alkali activator solution may be 1 to 5M. If the concentration of the alkali activator is too low, the function of the alkali activator described above cannot be properly performed, and the strength improvement is not adequately achieved. If the concentration of the alkali activator is too high, safety problems may arise in operation. More specifically, the concentration of the alkali activator in the aqueous alkali activator solution may be 1 to 1.5M.

The aqueous alkaline activator solution may include carbon dioxide. Carbon dioxide may exist dissolved in an aqueous solution. The aqueous alkaline activator solution may be obtained by dissolving carbon dioxide for 5 minutes to 1 hour. By dissolving carbon dioxide, strength can be further improved through a carbonation reaction, and it can also contribute to reducing greenhouse gases. However, if too much carbon dioxide is included, the pH of the alkaline activator aqueous solution decreases, reducing the reaction of calcium ions in the slag, and thus reducing the strength.

By treating as described above, 0.1 to 1 mole of carbon dioxide can be dissolved in the alkaline activator aqueous solution with respect to 1 mole of the alkali activator. More specifically, the alkaline activator aqueous solution may be obtained by dissolving carbon dioxide for 5 to 25 minutes. More specifically, it may be dissolved for 15 to 25 minutes.

An aqueous alkali activator solution containing an appropriate alkali activator and carbon dioxide may have a pH of 8 to 14. If the pH is too low, an alkali activator is not properly included, or carbon dioxide is too much, so proper strength cannot be obtained. When the pH is too high, too much alkaline activator or too little carbon dioxide is included, an appropriate strength cannot be obtained. More specifically, the pH may be 10 to 14.0. More specifically, it may be 12 to 13.5.

In the first curing step, the temperature may be 15 to 50°C. More specifically, it may be 20 to 30 °C. More specifically, it may be 23 to 25 °C.

The first curing step may be performed for 1 to 5 days. By curing for the above-mentioned period of time, the alkali activator can be evenly supplied. More specifically, it may be performed for 2 to 3 days.

Next, in the secondary curing step, the primary cured cement composition is cured in a relative humidity atmosphere of 95% or more. By performing primary curing in a high-humidity atmosphere before secondary curing in a carbon dioxide atmosphere, the specimen can be demolded in a short time from the mold. If the humidity in the primary curing step is too low, demolding may be difficult in a short time, and drying shrinkage may occur. More specifically, the relative humidity of the secondary curing step may be 80 to 85%.

In the secondary curing step, the temperature may be 15 to 50 °C. More specifically, it may be 20 to 30 °C. More specifically, it may be 23 to 25 °C.

The second curing step may be performed for 3 to 28 days.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for exemplifying the present invention, and the present invention is not limited thereto.

Production Example: Preparation of blast furnace slag fine powder

Two types of blast-furnace slag (ground-granulated blast-furnace slag, GGBFS, Hyundai Steel) were prepared. Therefore, the components of the fine powder of slag were analyzed using an X-ray fluorescence analyzer and summarized in Table 1. The unit of Table 1 is % by weight. Others included BaO, ZrO ₂ , V ₂ O ₅ , SrO and Y ₂ O ₃ .

CaO SiO ₂ Al ₂ O ₃ Na ₂ O _K2O MgO MnO TiO ₂ SO ₃ P ₂ O ₅ Fe ₂ O ₃ Others* slag 1 44.5 32.7 13.9 0.3 0.6 3.6 0.5 0.8 2.3 0.0 0.5 0.3 slag 2 48.0 30.8 13.3 0.2 0.5 3.1 0.5 0.9 1.8 0.0 0.6 0.3

As summarized in Table 1, it can be confirmed that lime and silica are the main components of the blast furnace slag fine powder.

Example

It was prepared by mixing fine blast furnace slag powder and No. 4 silica sand (average particle size of 1.2 to 1.5 mm) with liquid sodium silicate. The liquid sodium silicate used herein was a product having a weight ratio of SiO ₂ /Na ₂ O of 3.1. Each was used after being mixed with water in a one-to-one volume ratio. When using the blast furnace slag fine powder of slag 1, 35 parts by weight of sodium silicate aqueous solution was mixed with 100 parts by weight of slag, and when using blast furnace slag fine powder of slag 2, 50 parts by weight of sodium silicate aqueous solution was mixed with 100 parts by weight of slag. Silica sand was mixed at 300 parts by weight based on 100 parts by weight of the blast furnace slag fine powder. After mixing for about 5 minutes with a planetary mixer, a molded body was produced by compression molding at a force of 1 MPa in a 40 mm square mold. At this time, the sample weight was constantly weighed and compression molded so that the amount of voids relative to the total volume of the manufactured specimen was 17% by volume. The fabricated samples were dried in an air-dry condition of about 45% relative humidity for 6 hours. Thereafter, the dried samples were cured in water in a 1M molarity aqueous solution of potassium hydroxide. At this time, the 1M molarity aqueous solution of potassium hydroxide was classified into five types according to the dissolved amount of carbon dioxide, and each sample was cured. A solution in which carbon dioxide was not dissolved at all had a pH value of about 14 in a 1 M molarity aqueous solution of potassium hydroxide, and was named Example 1. In addition, the 1M molarity aqueous solution of potassium hydroxide dissolved in carbon dioxide for 10 minutes had a pH value between 13 and 14 and was named Example 2. In addition, the potassium hydroxide aqueous solution dissolved in carbon dioxide for 20 minutes had a pH value between 12 and 13, and was named Example 3. The aqueous solution dissolved for 30 minutes had a pH value between 11 and 12 and was named Example 4. In this way, the sample was cured in water for 66 hours (3 days after sample production) in an aqueous solution of 1M molarity of potassium hydroxide. After curing in water, additional curing was carried out in the air at 95% relative humidity and 25 ° C for up to 28 days.

In addition, for comparison, a comparative example (Control) was prepared in which the sample was dried in an air-conditioned state and then cured in air at 95% relative humidity and 25 ° C.

Each sample was measured for compressive strength at 3, 7 and 28 days after mixing. For the compressive strength, an average value was calculated by measuring each of the four samples. The measured compressive strength is summarized in FIG. 1 for the sample using slag 1 and FIG. 2 for the sample using slag 2.

As shown in FIGS. 1 and 2, at the age of 3 days, the comparative example did not develop strength, but developed strength in a 1M aqueous solution of potassium hydroxide and a 1M aqueous solution of potassium hydroxide in which carbon dioxide was dissolved. However, in the case of Example 4 in which a relatively large amount of carbon dioxide was dissolved, the sample composed of slag 1 did not develop strength. It is believed that the development of strength due to sufficient alkali activator replenishment in the sample occurred by initially curing the sample in water with an alkali activator. In addition, in FIG. 1, the strength expression of the sample cured in water in the potassium hydroxide aqueous solution of Example 2 in which carbon dioxide was appropriately dissolved was the best. It can be seen that this further accelerated the strength expression of the sample due to the carbonation reaction. At 7 days of age, the comparative example still did not develop strength. On the contrary, the strength development of the samples additionally cured in air at 25°C and 95% relative humidity after water curing in aqueous potassium hydroxide solution was excellent. In particular, strength development was excellent in the sample of Example 2 in which carbon dioxide was appropriately dissolved regardless of the type of slag in FIGS. 1 and 2. On the other hand, Fig. 1, Example 4 using slag 1 still showed no strength development. In the final 28-day strength, there was strength development of the sample of Comparative Example. In the samples using slag 1 (FIG. 1), the strength of the comparative sample was higher than that of the sample cured in water in a 1M molarity aqueous solution of potassium hydroxide, and the samples using slag 2 (FIG. 2) were also similar in strength. However, among the samples using slag 1 and slag 2, the strength expression of Example 3 was the best.

At the initial age of 3 days, the initial strength expression of the samples cured in water in an alkaline activator aqueous solution was superior to that of the comparative example. After 28 days of age, the comparative sample exhibited a similar level of strength to the samples cured in water in an alkaline activator aqueous solution, but better strength development occurred in the samples of Example 3b. It was found that curing in water with a solution of adjusting the pH of the aqueous solution to 12 by dissolving carbon dioxide in an aqueous alkali activator solution is more excellent in final strength development.

The present invention is not limited to the examples and can be manufactured in various different forms, and those skilled in the art to which the present invention pertains may change other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this can be implemented. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims (11)

compressing and molding a cement composition containing blast furnace slag fine powder, silica sand, and liquid sodium silicate;
A preliminary curing step of curing the cement composition in a dry state;
A first curing step of curing the pre-cured cement composition in aqueous alkali activator solution; and
A cement composition curing method comprising a secondary curing step of curing the primary cured cement composition in a relative humidity atmosphere of 95% or more. According to claim 1,
The cement composition includes 100 parts by weight of the blast furnace slag fine powder, 100 to 500 parts by weight of the silica sand, and 10 to 50 parts by weight of the liquid sodium silicate. According to claim 1,
The blast furnace slag fine powder is SiO ₂ : 30 to 33% by weight, Al ₂ O ₃ : 12 to 14% by weight, CaO: 43 to 48% by weight Curing method of a cement composition. According to claim 1,
The method of curing a cement composition wherein the weight ratio of SiO ₂ to Na ₂ O in the liquid sodium silicate is 2.0 to 3.5. According to claim 1,
A cement composition curing method of compressing the cement composition to 0.5 MPa or more in the molding step. According to claim 1,
In the preliminary curing step, the cement composition is cured in a relative humidity atmosphere of 60% or less for 3 to 12 hours. According to claim 1,
In the first curing step, the aqueous alkali activator solution contains at least one of KOH, NaOH and Na ₂ SiO ₃ Curing method of a cement composition. According to claim 1,
In the first curing step, the concentration of the alkali activator in the aqueous alkali activator solution is 1 to 5M. According to claim 1,
In the first curing step, the potassium activator aqueous solution is a method of curing a cement composition in which carbon dioxide is dissolved for 5 minutes to 1 hour. According to claim 1,
In the first curing step, the aqueous alkaline activator solution is pH 8 to pH 14 curing method of the cement composition. According to claim 1,
The preliminary curing step, the first curing step, and the second curing step are each performed at a temperature of 15 to 50 ° C.

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