KR20210079913A - Cement concrete admixture composition loaded coal combustion high carbon fly-ash - Google Patents

Abstract

The present invention relates to a cement concrete admixture composition comprising 300-1,500 parts by weight of low-calcium fly ash generated by a pulverized coal boiler in a coal-fired power plant which has a separate desulfurization facility and combusts coal, for 100 parts by weight of high-calcium fly ash generated by a circulating fluidized bed boiler in the coal-fired power plant which performs in-furnace desulfurization by mixing coal and limestone in a combustion furnace without the separate desulfurization facility. According to the present invention, the cement concrete admixture composition uses the high-calcium fly ash of the coal-fired power plant of an in-furnace desulfurization type in the circulating fluidized bed boiler, which has not been used so far, as a concrete admixture while satisfying relevant Korean industrial standard (KS L5405) quality standards.

Description

Cement concrete admixture composition comprising coal-fired high calcium fly ash {CEMENT CONCRETE ADMIXTURE COMPOSITION LOADED COAL COMBUSTION HIGH CARBON FLY-ASH}

The present invention relates to a cement-concrete admixture composition, and more particularly, in-furnace desulfurization coal-fired high-calcium fly ash is used as an auxiliary raw material to reduce shrinkage at the initial stage of hardening, and low-calcium fly ash is used as pozzolan in the medium and long-term curing period It relates to a cement-concrete admixture composition used as a main material to express activity.

In Korea, after undergoing various technical reviews and verifications, referring to cases in developed countries, the quality standard of industrial products is set as a national standard (KS: Korean Industrial Standard), and there is a system to certify products that conform to the standard. Therefore, if the developed product is a national standardized product, it is very important to have a quality suitable for the standard of the verified KS standard in order to be widely used in the market as an industrial product. Fly ash (KS L 5405) and fine blast furnace slag powder (KS F 2563) are representative products stipulated by the Korean national standard to be used as an admixture material for cement, and these products are used by almost all ready-mixed concrete companies.

Cement concrete and cement mortar are synthetic materials used in almost all construction projects. Cement mortar or cement concrete is composed of cement, water, aggregate, chemical admixture, etc., and has the shape of a plastic fluid before it is completely hardened.

Cement mortar or cement concrete loses plasticity during a chemical hydration reaction between cement and water and completely hardens. In this process, moisture on the surface of the cement mortar or cement concrete evaporates, and water is consumed between the cement hydrates, which undergo a hydration reaction. Tensile stress is generated in the area, resulting in cracks due to drying shrinkage. Since cracks occurring in these structures have various adverse effects, various technologies have been developed and constructed to prevent cracks due to such shrinkage.

Conventionally, in order to physically resist the tensile stress of cement mortar or cement concrete, concrete or mortar has been manufactured by including long and thin fibers or steel materials in the concrete material. is not being utilized.

Recent technologies to prevent drying shrinkage include the technology of using an expanding agent that compensates for the drying shrinkage that occurs during the hydration process of cement, and the addition of chemicals to cement mortar or cement concrete to prevent water evaporation to reduce drying shrinkage. technology has been developed and is being applied in some fields.

As an example of a technology for preventing water evaporation, Korean Patent Registration No. 10-1568765 proposes a technology that functions to suppress evaporation of moisture on the surface during the initial curing process by adding trehalose to cement mortar and concrete. Trehalose is a non-reducing disaccharide fermented with starch as a raw material. However, it is judged that there are few construction examples of such a technology, and in Korea's building construction specifications and concrete standard specifications, it is stipulated to cover the concrete after pouring and to take care to prevent rapid evaporation of moisture.

For example, in Korean Patent Registration No. 10-0130401, for the technology of using a swelling agent that compensates for drying shrinkage, calcium sulfoaluminate 20wt%, aluminum sulfate 19wt%, anhydrite 40wt%, quicklime 17.5wt%, lower fatty acid alcohol alkyl ether 1wt% , a non-shrinkable admixture technology for preventing cracks in cement mortar and concrete, characterized in that it is composed of 0.5wt% of stearate, 1wt% of high-grade dispersant and 1wt% of potassium dichromate was proposed.

However, as can be seen by examining the characteristics of the constituent materials, these technologies are expensive materials several times that of cement, so there is a limit to their use in actual industry.

In addition, in the case of commercially available aluminum sulfate, it is common that the moisture content is 15% or more. Therefore, if mixed in advance, it is clear that it will react with calcium sulfoaluminate, a special cement with rapid hardening/expandability, so it is a pre-mixed product. It is difficult to manufacture, and it is difficult to construct a concrete and mortar manufacturing facility equipped with each storage and metering device as there are 8 types of raw materials to use as raw materials for manufacturing concrete or mortar before pouring on site. In general, the admixture material should be used within 10 to 20% of the weight of cement, but even assuming that 20% of the weight of cement is used, 0.5% wt to 1 wt% of the non-shrink admixture composition is too small. It can be evaluated as a difficult technology to be commercialized due to the fact that it cannot be mixed and dispersed evenly in the field.

In addition, Korean Patent Registration No. 10-0403831 proposes a shrinkage reducing agent for preventing cracks in concrete and a technology related to a concrete composition using the same. Here, a shrinkage reducing agent prepared by mixing 30 to 80 wt% of fly ash, 2 to 5 wt% of anhydrite, 8 to 20 wt% of limestone powder, and 10 to 60 parts by weight of blast furnace slag powder, and this shrinkage reducing agent 1 to 40 A technology related to a concrete composition prepared by adding aggregates commonly used to raw materials in which weight % and 10 to 99 weight % of cement are mixed is presented. Raw materials contributing to shrinkage reduction or expansion in this proposed technology will be the free CaO component contained in fly ash, the active CaO component contained in anhydrite, and the free CaO component contained in the fine powder of blast furnace slag. Among the constituent materials, limestone powder does not contribute to expansion, and how chemical components other than the free CaO component contained in fly ash, the active CaO component contained in anhydrite, and the free CaO component contained in the fine blast furnace slag powder contribute to the expansion It is generally not known whether Therefore, in the technology presented above, it is determined that the sufficiency of the function is unclear because the chemical components contributing to the expansion of each component are not analyzed and presented.

Korean Patent Registration No. 10-1568765 Korean Patent Registration No. 10-0130401 Korean Patent Registration No. 10-0403831

Accordingly, in the present invention, as a solution to various problems caused by drying shrinkage during the drying of cement mortar or cement concrete composition, fly ash (KS L) stipulated in Korean national standards to be used as an admixture material for cement. 5405) to reduce the initial heat of hydration and reduce shrinkage within the range that satisfies the quality standard, thereby reducing the initial drying shrinkage during curing of concrete and mortar to provide an admixture material composition for concrete that exhibits the effect of preventing cracks. There is a purpose.

In order to solve the above technical problems, the cement-concrete admixture composition according to the present invention performs desulfurization in a furnace by mixing coal and limestone in a combustion furnace without a separate desulfurization facility. High calcium fly generated by a circulating fluidized bed boiler in a coal-fired power plant With respect to 100 parts by weight of ash, it is characterized by comprising 300 to 1500 parts by weight of low-calcium fly ash generated by a pulverized coal boiler of a coal-fired power plant that is equipped with a separate desulfurization facility and burns coal to generate electricity.

In addition, according to an embodiment of the present invention, the cement concrete admixture composition is silicon dioxide (SiO ₂ ) 45.0% or more, free calcium oxide (Free CaO) 2.5% or less, reactive calcium oxide (CaO) 10% or less, sulfur trioxide (SO ₃₎ 3.5% or less, magnesium (MgO) 4.0% or less, total phosphate (P ₂ O ₅₎ 5.0% or less, a water-soluble phosphate _{(P 2 O 5) 100㎎ /} ㎏ hereinafter chloride oxide (cl ^-) 0.05% Hereinafter, it is characterized in that the chemical composition of 5.0% or less of total alkali is satisfied.

According to the present invention, a circulating fluidized bed that mixes coal and limestone, which has not been used well until now, because it is recognized that there is a risk of deterioration of the performance of concrete by causing abnormal coagulation or excessive expansion during hydration of concrete due to the high composition ratio of CaO and MgO In-furnace desulfurization method coal-fired power plant fly ash is mixed with low-calcium fly ash generated from pulverized coal boilers in coal-fired power plants equipped with separate desulfurization facilities to generate power by burning coal in a certain ratio, and in-furnace desulfurization method coal-fired high calcium fly ash It is effective to provide a cement-concrete admixture composition in which low-calcium fly ash is used as an auxiliary raw material to reduce shrinkage in the early stage of hardening, and low-calcium fly ash is used as a main material to express pozzolan activity in the medium and long-term curing period.

In addition, by replacing some cement generally used in building construction, it is possible to prevent indiscriminate mining of limestone in Baekdudaegan for cement production, and by recycling high-calcium coal-burning materials and low-calcium coal-burning materials generated as industrial by-products. It also has the effect of preserving the environment.

1 is a schematic diagram schematically illustrating a process in which coal ash having different chemical components is generated according to a desulfurization process operation method.

Hereinafter, the present invention will be described in more detail as follows.

The terminology used herein is used to describe specific embodiments, not to limit the present invention. As used herein, the singular forms may include the plural forms unless the context clearly dictates otherwise. Also, as used herein, “comprise” and/or “comprising” refers to the presence of the recited shapes, numbers, steps, actions, members, elements, and/or groups of those specified. and does not exclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups.

The cement-concrete admixture composition, which solves the problem of defects caused by drying shrinkage according to the present invention, generates a circulating fluidized bed boiler in a coal-fired power plant that performs desulfurization in a furnace by mixing coal and limestone in a combustion furnace without a separate desulfurization facility. With respect to 100 parts by weight of high-calcium fly ash, it is characterized in that it contains 300 to 1500 parts by weight of low-calcium fly ash generated by a pulverized coal boiler of a coal-fired power plant that is equipped with a separate desulfurization facility and burns coal to generate electricity.

As is well known, fly ash generated in pulverized coal boilers is a vitrified material whose main component is silicon dioxide. However, in order to improve the efficiency of power generation facilities, high calcium fly ash generated in an in-furnace desulfurization furnace using a circulating fluidized bed boiler for mixing and burning coal and limestone without a separate desulfurization facility is produced in a pulverized coal boiler equipped with a separate flue gas desulfurization facility. Compared to the generated fly ash, the ratio of calcium oxide (CaO) and magnesium oxide (MgO) is high.

Therefore, when used as a concrete admixture material, it is not widely used due to the risk of abnormal coagulation and excessive expansion, and high-calcium fly ash generated in an in-furnace desulfurization furnace using a circulating fluidized bed boiler that mixes and burns coal and limestone. It is mistaken for fly ash from pulverized coal boilers equipped with desulfurization facilities and is used without technical review, but there are also side effects such as problems with the concrete structure.

Therefore, by identifying the quality characteristics of high-calcium fly ash and low-calcium fly ash and setting the mixing ratio well, the intended functions of fly ash, such as reducing heat of hydration, improving workability, reducing unit quantity, and reducing drying shrinkage, are achieved. There is a need for a cement concrete admixture composition comprising high calcium fly ash.

In-furnace desulfurization type circulating fluidized bed boiler generated from S thermal power plant of Korea Southern Power Coal-fired high-calcium fly ash and low-calcium fly ash generated from S-fired power plant of Korea South-East Power We investigated and averaged the chemical composition over a long period of time. When only CaO and MgO were managed to compose the mixing ratio, the remaining chemical components and physical performance were found to satisfy the KS L 5405 (fly ash) standard.

Therefore, in the present invention, it is an object of the present invention to provide a cement concrete admixture composition without cracking problems due to drying shrinkage by appropriately mixing such high calcium fly ash and low calcium fly ash.

First, in the cement-concrete admixture composition of the present invention, without a separate desulfurization facility used as an auxiliary raw material for reducing shrinkage at the initial stage of curing, coal and limestone are mixed in a combustion furnace to perform in-furnace desulfurization. High-calcium fly ash generated by fluidized bed boilers will be reviewed.

'In-furnace desulfurization method coal-fired high calcium fly ash' used throughout the specification of the present invention is usually used in a desulfurization method coal-fired boiler in a furnace by mixing coal and limestone in a combustion furnace without a separate desulfurization facility. It means fly ash excluding bottom ash (bottom ash) among high-calcium incineration ash, which is generated in the process of mixing and burning coal and limestone to prevent the emission of sulfur (S) components contained in coal to the atmosphere. .

High calcium of 'high calcium fly ash' used throughout the specification of the present invention means that the total CaO component in the fly ash is 10% by weight or more.

Power plants that burn coal by the desulfurization method in the furnace include KEPCO subsidiaries such as Samcheok Thermal Power Plant, Yeosu Thermal Power Plant, and Donghae Thermal Power Plant, as well as small and medium-sized cogeneration plants scattered across the country, which generate a large amount of high calcium fly ash. It is a reality that technology development for recycling is urgently required.

In a coal-fired power plant, coal is burned, water is heated with the heat, and the generated steam rotates a turbine to produce electricity. In this process, the power plant operates a desulfurization process in order to prevent the sulfur oxides contained in coal from being released into the atmosphere and polluting the environment. The process by which these different coal ash is generated is schematically shown.

Referring to this, in the combustion process of a pulverized coal boiler operating an off-site desulfurization system equipped with a separate desulfurization facility, since CaO and SO ₃ components are collected in separate treatment facilities, silicon dioxide (SiO ₂ ) is the main component, and CaO and SO ₃ This low, that is, low calcium fly ash (coal ash) coal ash is generated.

The low calcium of 'low calcium fly ash' used throughout the specification of the present invention means that the total CaO component in the fly ash is 5% by weight or less.

Conversely, in a coal-fired power plant that operates an in-furnace desulfurization process that mixes coal and limestone without a separate desulfurization facility, high calcium fly ash (coal ash) containing relatively high content of _{CaO and SO 3 components is generated.} .

In the desulfurization process in a furnace in which coal and limestone are mixed as shown in FIG. 1 , _{in the gypsum-type particles in which decarboxylated CaO of limestone (CaCO 3} ) and a sulfated material are combined, the chemical component is detected as CaO, and this component is mainly composed of concrete Since it contributes to the heat generation and expansion of the air, an appropriate mixing ratio thereof becomes an important element technology.

On the other hand, in the case of high calcium fly ash generated by a circulating fluidized bed boiler in a coal-fired power plant that performs in-furnace desulfurization by mixing coal and limestone in a combustion furnace without a separate desulfurization facility, the CaO component is relatively high, but it causes side reactions in the composition. There is a problem that _{materials are included or the content of SiO 2} , which is an active ingredient of pozzolan activity, is relatively low. For this reason, the physical properties of the final manufactured product also have to show results that fall short of the KS standard.

As a result, high-calcium fly ash generated by circulating fluidized bed boilers in coal-fired power plants that perform in-furnace desulfurization by mixing coal and limestone in a combustion furnace without a separate desulfurization facility is not guaranteed in quality when used alone in a concrete admixture composition. there is a problem.

Therefore, in the present invention, with respect to 100 parts by weight of high calcium fly ash generated by a circulating fluidized bed boiler of a coal-fired power plant that performs in-furnace desulfurization by mixing coal and limestone in a combustion furnace without having the separate desulfurization facility, a separate desulfurization facility is provided. It was intended to solve the problem by mixing and using 300 to 1500 parts by weight of low-calcium fly ash generated from pulverized coal boilers in coal-fired power plants that are equipped with coal to generate electricity.

If less than 300 parts by weight of low-calcium fly ash generated in pulverized coal boilers of coal-fired power plants equipped with the above separate desulfurization facility and generating power by burning coal is included, the ratio of CaO and MgO in the mixture is relatively high to reduce shrinkage in the early stage of curing The function is too large to cause excessive expansion, and when it is included in excess of 1500 parts by weight, the ratio of CaO and MgO in the mixture is relatively low, so that the function of reducing shrinkage in the initial stage of curing is insufficient.

The composition of the chemical composition of the cement-concrete admixture composition according to the present invention comprising the above composition is silicon dioxide (SiO ₂ ) 45.0% or more, free calcium oxide (Free CaO) 2.5% or less, based on 100% by weight of the total, Reactive calcium oxide (CaO) 10% or less, sulfur trioxide (SO ₃ ) 3.5% or less, magnesium oxide (MgO) 4.0% or less, total phosphate (P ₂ O ₅ ) 5.0% or less, chloride (cl ^- ) 0.05% or less, total Alkali 5.0% or less, water-soluble phosphate (P ₂ O ₅ ) It is characterized in that it satisfies 100 mg/kg or less.

The Korean industrial standard, KS L 5405 (fly ash), stipulates the chemical composition in consideration of the characteristics of the material, and the content is silicon dioxide (SiO ₂ ) 45.0% or more, free calcium oxide (Free CaO) 2.5% or less, reactivity Calcium oxide (CaO) 10% or less (but not measured when the total CaO is less than 10%), sulfur trioxide (SO ₃ ) 3.5% or less.

In addition, as of July 11, 2018, the use of alternative fuels other than coal (wood pellets, biosolid fuels, livestock manure solid fuels, sewage sludge solid fuels, and unburned carbon residues generated after fly ash refining in thermal power plants) The KS L 5405 standard was revised according to the added quality items: Magnesium oxide (MgO) 4.0% or less, total phosphate (P ₂ O ₅ ) 5.0% or less, water-soluble phosphate (P ₂ O ₅ ) 100 mg/kg or less, chloride (cl ^- ) 0.05% or less, 5.0% or less of total alkali, etc. are prescribed|regulated.

As described above, the reason that the chemical composition of fly ash is stipulated in the Korean Industrial Standard is to prevent deterioration of concrete performance due to abnormal coagulation or excessive expansion during hydration of concrete.

The upper and lower limits of the above chemical components are stipulated in the Korean Industrial Standard KS L 5405 (fly ash). it won't be possible

Hereinafter, preferred embodiments of the present invention will be described in detail. The following examples are only for illustrating the present invention, and the scope of the present invention should not be construed as being limited by these examples. In addition, although specific compounds are used for illustration in the following examples, it is obvious to those skilled in the art that similar effects can be exerted even when equivalents thereof are used.

Control group: Confirmation of ingredients and quality of high-calcium fly ash through a request test

High-calcium fly ash obtained by mixing and burning desulfurization limestone and coal in the furnace to be used in the present invention was requested by an authorized agency for all items of KS L 5405 and its components were analyzed, and the results are shown in Table 1 below.

Referring to Table 1 below, in the case of high calcium fly ash according to Control 1, CaO 24.9% and reactive CaO 9.4% were relatively high, and the SO ₃ component was 9.3% each, which greatly exceeded the KS standard of 3.5%. MgO was also measured at 8.45%, which greatly deviated from the standard value of 4.0%, and the free CaO item was also measured as 8.7%, which greatly deviated from the standard value of 2.5 or less.

In addition, since there are many such undesirable components, SiO ₂ , an active ingredient of pozzolan activity, was measured to be 28.3%, which was significantly lower than the acceptance criterion of 45.0 or more, which is also the standard value. Looking at the physical performance, the flow ratio was measured to be 92%, which was dissatisfied with the KS standard of 95% or more.

When looking at the above inspection and measurement results, it was confirmed that the high calcium fly ash did not meet the Korean industrial standard inspection items and standards by five. Therefore, it was confirmed that additional components with a composition that can satisfy these standards are required.

Examples 1-5 and Comparative Examples 1-2: Preparation of admixture composition

With respect to 100 parts by weight of the high-calcium fly ash of the control group, each admixture composition was prepared by mixing low-calcium fly ash having the composition shown in Table 1 below.

Examples 1 to 5 are samples in which 300, 500, 900, 1300, and 1500 parts by weight of low calcium fly ash are added to 100 parts by weight of high calcium fly ash as the control, respectively, and mixed evenly.

In addition, Comparative Examples 1 and 2 are samples in which 290 parts by weight and 1600 parts by weight of low calcium fly ash were added to 100 parts by weight of high calcium fly ash as the control, respectively, and mixed evenly.

chemical composition
(weight%) KS standard control Example comparative example One 2 3 4 5 One 2 Soluble Phosphate ^*
(P ₂ O _5, mg/kg) 100 or less 11.1 11.4 12.4 3.2 3.0 3.1 8.4 12.6 Total Phosphate (P ₂ O ₅ ) 5.0 or less 0.20 0.87 0.80 0.77 0.70 0.68 0.64 0.47 Chloride (Cl ^- ) 0.05 or less 0.01 0.02 0.02 0.01 0.01 0.01 0.01 0.02 total alkali 5.0 or less 0.33 0.78 0.80 0.53 0.47 0.46 0.09 1.21 MgO 4.0 and below 8.45 2.77 3.07 3.43 3.50 3.71 4.83 4.17 SiO ₂ 45.0 or higher 28.3 56.5 53.5 54.8 50.4 53.9 46.6 50.0 free CaO 2.5 or less 8.7 1.9 1.8 1.7 1.8 1.6 3.6 2.6 Total CaO 24.9 7.4 7.1 6.7 6.7 6.1 13.1 11.2 Reactive CaO 10.0 or less 9.4 and below 5.5 5.3 5.0 4.9 4.5 9.6 8.5 SO ₃ 3.5 or less 9.3 1.5 1.9 2.2 2.5 2.4 4.2 3.4 Density (20℃,g/cm2) 1.95 or higher 2.3 2.3 2.3 2.3 2.4 2.3 2.3 2.3 Fineness (specific surface area, brain method, cm2/g) over 3000 6400 3710 4110 4250 4320 4390 4850 4550 moisture(%) 1.0 or less 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Stability (autoclave expansion, %) 0.8 or less 0.3 0.3 0.3 0.3 0.4 0.4 0.3 0.3 Flow value ratio (%) 95 or more 92 100 100 100 100 100 97 96 Fineness (45㎛ sieve powder, mesh method) 40 or less 29 17 16 16 15 15 25 21 activity index
(28 days,%) 80 or more 105 91 90 91 92 93 95 92 Loss on ignition (%) 5.0 or less 2.5 3.5 3.5 3.9 3.8 4.0 3.1 3.8 (Note) * The content of water-soluble phosphate (P ₂ O ₅ ) is mg per kg of fly ash as defined in KS L 5405, the Korean industrial standard.

Experimental Example 1: Measurement of chemical components and physical properties

Each of the admixture compositions prepared according to Table 1 was commissioned by two authorized organizations to examine the chemical composition and physical performance, and the results are shown in Table 1 above.

Referring to the results of Table 1, in the case of Comparative Example 1 containing less than 300 parts by weight of low-calcium fly ash, the MgO component in the mixture was 4.83%, which is higher than the standard value of 4.0%, and the free CaO component was also 3.6%, which is 2.5, which is the standard value. It can be seen that the content is higher than % or less. In this case, the function of reducing the shrinkage at the initial stage of curing is too large, which may cause excessive expansion, which is not preferable.

In addition, in the case of Comparative Example 2 in which the low-calcium fly ash exceeds 1500 parts by weight, the ratio of CaO and MgO in the mixture is relatively low, so it can be predicted that it will bring undesirable results in promoting shrinkage reduction at the initial stage of curing. have.

However, as in the embodiment of the present invention, when satisfying the range of 300 to 1500 parts by weight of low calcium fly ash with respect to 100 parts by weight of high calcium fly ash, it was confirmed that all inspection items of fly ash defined in KS L 5405, the Korean industrial standard, were satisfied. became

As a result, when combining the above test results, the cement-concrete admixture composition containing coal-fired high calcium fly ash according to the present invention is desulfurized in a furnace by mixing coal and limestone in a combustion furnace without a separate desulfurization facility. With respect to 100 parts by weight of high-calcium fly ash generated by a circulating fluidized bed boiler in a coal-fired power plant that contains 300 to 1500 parts by weight of low-calcium fly ash, It was confirmed that the admixture material for concrete that satisfies the conditions of KS L 5405, the industry standard, can be provided.

Experimental Example 2: Visual confirmation of dry shrinkage cracks of high-calcium fly ash mixed mortar through plate-shaped specimen production

A test for visually confirming cracks due to expansion was conducted using Examples 2 to 3, Comparative Examples 1 and 2, and the control, which are mixed samples of the prepared high-calcium fly ash and low-calcium fly ash. In this experiment, as shown in Table 2 below, the formulation table described in the fly ash KS standard (KS F 5405) was used.

Content: parts by weight Normal Portland Cement mixed sample fine aggregate water ratio 300 100 1200 200

In the present invention, in order to visually check the cracks of the specimen due to expansion more clearly, the size of the specimen was produced in a plate shape of 20cm x 20cm x 3cm, and air-dried at a temperature of 20±1℃. Crack confirmation according to each sample was visually observed at 3, 7, and 28 days of age, and the results are shown in Table 3 below.

age Example 2 Example 3 Comparative Example 1 Comparative Example 2 control 3 days none none none none none 7 days none none none microcracks microcracks 28 days none none microcracks microcracks crack

When the results of Table 3 are comprehensively summarized, no cracks occurred in all the specimens at the age of 3 days, and microcracks with a crack size of 0.1 mm or less were confirmed in the specimens of Comparative Example 2 and the control group at the age of 7 days. , No cracks were observed in the specimens of Examples 2-3 and Comparative Example 1. At 28 days of age, no cracks occurred in the specimens of Examples 2 and 3 of the present invention, and only microcracks of 0.1 mm or less were observed in the specimens of Comparative Examples 1 and 2. And the control group in which the high calcium fly ash was mixed the most showed relatively large cracks of 0.1 mm or more.

When the above contents are summarized, it was found that the higher the ratio of high calcium fly ash in the mixed sample, the greater the crack initiation time and crack size. is considered to be the cause.

Therefore, it was confirmed that, as in the present invention, by appropriately mixing the low-calcium fly ash with the high-calcium fly ash, it was possible to effectively prevent a defect problem due to the initial shrinkage of curing.

Claims (2)

With respect to 100 parts by weight of high calcium fly ash generated by a circulating fluidized bed boiler of a coal-fired power plant that performs in-furnace desulfurization by mixing coal and limestone in a combustion furnace without a separate desulfurization facility,
A cement-concrete admixture composition comprising 300 to 1500 parts by weight of low-calcium fly ash generated by a pulverized coal boiler of a coal-fired power plant that is equipped with a separate desulfurization facility and generates electricity by burning coal. The method of claim 1,
The cement concrete admixture composition is silicon dioxide (SiO ₂ ) 45.0% or more, free calcium oxide (Free CaO) 2.5% or less, reactive calcium oxide (CaO) 10% or less, sulfur trioxide (SO ₃ ) 3.5% or less, magnesium oxide ( MgO) 4.0% or less, total phosphate (P ₂ O ₅ ) 5.0% or less, water-soluble phosphate (P ₂ O ₅ ) 100 mg/kg or less, chloride (cl ^- ) 0.05% or less, total alkali 5.0% or less Cement concrete admixture composition, characterized in that it is satisfied.

Images