KR101018007B1 - Method for manufacturing concrete using coal ash as binder - Google Patents

Abstract

The present invention relates to a method of producing cement concrete using coal ash, and its purpose is to apply coal ash, a by-product of a coal-fired power plant adjusted to an appropriate powder, as a binder instead of cement which emits a large amount of carbon dioxide during production. By applying a suitable ratio of NaOH and sodium silicate as an activator, it is to provide a method of manufacturing cementless concrete exhibiting a quality equivalent to or higher than that of ordinary concrete. The method for producing cement cement concrete using coal ash of the present invention for achieving the above object includes a binder, an activator, a fine aggregate, a coarse aggregate, water and a high performance water reducing agent as a blending raw material, and a process of blending and mixing these blending raw materials. In the method of producing concrete through curing process, the binder is composed of a coal circuit of 5,000 ~ 10,000cm ² / g powder to break the glass film at room temperature of 5 ~ 40 ℃, the activator 6 ~ 15Mole NaOH and sodium silicate in a ratio of 0.75: 1.25 ~ 1.25: 0.75 by weight, mix the blending material with the binder and the activator added, undergo agitation, and air dry at room temperature of 5-40 ° C. Make it raw.

Fly Ash, Cemented Concrete, Cement ZERO Concrete, NaOH, Sodium Silicate

Description

Manufacturing method of cementless concrete using coal ash {METHOD FOR MANUFACTURING CONCRETE USING COAL ASH AS BINDER}

The present invention relates to a method for producing cement cement (cement ZERO concrete) using coal ash, more specifically, a method that can produce concrete without using cement by using a coal ash made of high-molecular powder by milling in an appropriate manner. It is about.

With various efforts to prevent global warming (adopted in 1997, ending the Kyoto Protocol in effect in 2005), in December 2007, the Bali Roadmap was adopted in Bali, Indonesia, until 2009. Negotiations are in progress for a climate change agreement. Accordingly, there is a need to significantly reduce the amount of greenhouse gas emissions such as carbon dioxide worldwide.

Meanwhile, since the cement industry is a major carbon dioxide emission industry in addition to the steel industry, about 0.9 tons of carbon dioxide is produced to produce 1 ton of cement, which is the basis for the production of concrete. Therefore, methods and alternative materials are urgently required.

Domestic cement production is about 60 million tons per year, releasing about 54 million tons of carbon dioxide. As part of the remedy, research to replace cement using industrial by-products is constantly underway.

Coal ash, an industrial by-product of coal-fired power plants, emits 6 million tonnes a year and is increasing every year. Currently, about 50% of the coal ash generated is recycled as raw materials for cement production (clay substitutes) and mineral admixtures, but the remainder is being treated by shore and land reclamation. Many environmental problems are caused by the leaching of coal ash composed of leachate and fine powder generated during the process.

In general, when coal ash is used in concrete, it is replaced by a part of cement (about 10 to 30%), but it is necessary to increase the usage more than the present time in order to make up about 50% of the coal ash emitted from thermal power plants. have. Such coal ash is also used in the production of concrete, a conventional technique for producing concrete using only coal ash without using any cement, and reacts by breaking the glassy film of coal ash through a high temperature curing process of 60 ° C or higher. There is a way to secure more than 30MPa by inducing. However, this method has a problem of energy consumption and carbon dioxide emission due to high temperature curing.

Other methods include curing at room temperature of about 20 ℃, but this method has little reaction to destroy the glass coating of coal ash, so the strength of concrete is mostly 10MPa or less, so it is safe when applied to structures such as bridges and buildings. It is pointed out that there is a problem in usability.

Accordingly, the present inventors have proposed the present invention as a result of repeated studies and experiments to solve the above problems, the present invention is a by-product of the thermal power plant adjusted to the appropriate powder as a binder instead of cement to discharge a large amount of carbon dioxide during manufacturing The purpose of the present invention is to provide a method of manufacturing cementless concrete having an equivalent quality or higher than that of ordinary concrete by applying phosphorous ash and applying an appropriate ratio of NaOH and sodium silicate as activators.

The method for producing cement cement concrete using coal ash of the present invention for achieving the above object includes a binder, an activator, a fine aggregate, a coarse aggregate, water and a high performance water reducing agent as a blending raw material, and a process of blending and mixing these blending raw materials. In the method of producing concrete through curing process, the binder is composed of a coal circuit of 5,000 ~ 10,000cm ² / g powder to break the glass film at room temperature of 5 ~ 40 ℃, the activator 6 ~ 15Mole NaOH and sodium silicate are characterized in that the ratio of 0.75 ~ 1.25: 1.25 ~ 0.75 by weight ratio.

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

Concrete blending raw materials in the cement concrete manufacturing method of the present invention is composed of a binder, an activator, a fine aggregate, coarse aggregate, water, a high performance water reducing agent and the like. That is, the cement concrete manufacturing method of the present invention is characterized in that the use of coal ash as a binder, instead of adding cement, and using NaOH and sodium silicate as an activator in the conventional method for producing concrete.

The coal ash uses a powder of 5,000 cm 2 / g to 12,000 cm 2 / g, when the coal ash powder of less than 5,000 cm 2 / g is used, the reaction does not occur and do not solidify and harden, 12,000 cm 2 / In the case of using more than g, the compressive strength does not increase so much as the powder is no longer increased, and there is a problem such as energy consumption due to high powdering.

The coal ash may be discharged from a coal-fired power plant, and the like, and the low powder at the time of discharge may be milled by an appropriate method using conventional methods, for example, ball milling, jet mill, vibration mill, etc. To use it.

Coal ash generated in thermal power plants or the like usually has a powder degree of 2000 to 4000 cm 2 / g, which is adjusted to an appropriate range of powder degree.

The NaOH and sodium silicate are added as an activator, and is added in a ratio of 0.75: 1.25 to 1.25: 0.75 by weight. When the ratio of sodium silicate is less than 0.75 times NaOH, the amount of Si necessary for the polymerization reaction decreases. When the intensity is small, and exceeds 1.25 times compared to NaOH, there is a problem that the Na ions become smaller and the initial strength becomes smaller.

The NaOH is used in the 6 ~ 15Mole, less than 6M NaOH workability is good, but the strength is insufficient to apply to the general concrete structure, the compressive strength is high when using NaOH exceeding 15M, There is a problem that it is difficult to secure workability.

Concrete prepared in the present invention using the compounding material to which the binder and the activator as described above is added, wherein the remaining compounding material can be blended by the usual blending ratio, and also not listed separately, but usually added It can also be made of the desired concrete by the addition of a variety of additives.

After blending the blended raw materials in an appropriate ratio, the mixture is stirred and cured, and the curing in the present invention can be performed at a wide temperature range by a conventional method. However, in consideration of energy consumption, carbon dioxide emissions, and the like, it is more preferable to carry out air curing at room temperature of 5 to 40 ° C. That is, the effect of curing temperature on the strength is because the strength increases as the temperature is higher, because curing at 5 ℃ or more is excellent in terms of strength, because 40 ℃ is the maximum temperature in the summer.

As mentioned above, when concrete is prepared with a binder composed of 5,000 to 12,000 cm2 / g coal and an activator composed of sodium silicate and NaOH in an appropriate ratio without using cement, curing at room temperature of 5 to 40 ° C is achieved. Even if implemented, the quality of the concrete can be secured.

Specifically, the workability exhibiting the workability of concrete can be maintained for about 1 hour, it is possible to secure a compressive strength of 15MPa or more at 7 days of age, and 30MPa or more at 28 days of age. The dry shrinkage was 450x10 ^-6 (exposure 91 days) and was very low and showed excellent durability such as sulphate, freeze-thawing, carbonation and salting. In addition, assuming that 6 million tons of coal ash are currently emitted in Korea, and about 50% of them are recycled, assuming that the remaining 3 million tons is used for concrete, 2.7 million tons of carbon dioxide can be reduced.

Embodiments according to the present invention can be modified in many different forms, the scope of the present invention is not limited to the embodiments described below.

Example 1 Effect of Coal Ash Powder

This embodiment is to analyze how the powder of coal ash affects the cement concrete manufacturing method of the present invention.

It has the composition as shown in Table 1, and the powder discharged to the thermal power plant also prepared a coal ash of 3,550 cm 2 / g.

SiO ₂
(%) Al ₂ O ₃
(%) Fe ₂ O ₃
(%) CaO
(%) MgO
(%) SO ₃
(%) lg. loss
(%) density
(g / cm ³⁾ Powder
(cm ² / g) 58.20 26.28 7.43 6.51 1.10 0.30 3.20 2.18 3,550

The prepared coal ash was ball milled to prepare powder levels of 5,000 cm 2 / g, 7,500 cm 2 / g, 10,000 cm 2 / g and 12,000 cm 2 / g, respectively. And an activator composed of sodium silicate (Na ₂ O = 10%, SiO ₂ = 30%, solids 38.5%, specific gravity 1.39) and 9M NaOH (purity 98%) in a 1: 1 ratio by weight.

Using the coal ash and the activator thus prepared to prepare concrete in the formulation as shown in Table 2 and then measured the slump and compressive strength, the results for the slump is shown in Figure 1, the results for the compressive strength, respectively, Figure 2 .

Here, the slump test was performed for 1 hour and 30 minutes from the time when the concrete was stirred and discharged from the mixer according to KS F 2402, and the compressive strength was manufactured at Φ100x200mm circumferential test body at 20 ° C (humidity 65 ± 5%) was cured and measured according to KS F 2405 at 7, 28 and 91 days of age.

combination Unit weight (kg / m ³ ) water cement Coal ash Sodium silicate NaOH Fine aggregate Coarse aggregate General Concrete 175 350 - - - 643 1118 Cement Concrete 15 - 405 78 78 567 1052

As can be seen in Figure 1, when analyzing the slump change results according to the powder of coal ash, the slump change is large with the passage of time, general concrete using cement, the slump is less than 75mm after about 1 hour The castle is falling dramatically.

In addition, when the powder used for the cementless concrete is 3,550cm 2 / g coal ash, there is little change in slump even if time passes, because the reaction does not occur, so it does not condense and harden.

Although the slump lowered as the powder level increased from 5,000 cm 2 / g to the powder level, the slump was found to have sufficient workability of 100 mm or more even after 1 hour after pouring.

In addition, as can be seen in Figure 2, when analyzing the results of the compressive strength different from the powder of coal ash, the compressive strength is 3MPa or less when using the 3,550 cm2 / g coal ash powder used in conventional cement cement concrete Significantly lowered strength and can not be used in the structure, and the powder degree satisfying the conditions of the present invention from 5,000 cm 2 / g to 12,000 cm 2 / g powder density tends to increase the compressive strength, which is This is because the specific surface area of the coal ash that can be reacted is increased, thereby easily destroying the glass film of the coal ash, thereby increasing the reactivity.

Coal ash with a powder level of 5,000 cm2 / g is 17 ~ 25MPa at 7 days of aging, 32 ~ 42MPa at 28 days, and 36 ~ 47MPa at 91 days of age, showing higher strength than ordinary concrete and replacing the existing concrete structures. It is expected to use enough.

Example 2: Influence of NaOH molarity

This embodiment is to analyze how the concentration of NaOH in the cement concrete manufacturing method of the present invention affects.

Sodium silicate (Na ₂ O = 10%, SiO ₂ = 30%, solids 38.5%, specific gravity 1.39) and 3M, 6M, 9M, 12M, 15M, 18M NaOH (purity 98%) in a 1: 1 ratio by weight An activator and a powder were also prepared using concrete of 7,500 cm 2 / g coal ash as shown in Table 2, and then measured the slump and the compressive strength, respectively, and the results are shown in Table 3 below.

Here, the slump was measured 10 minutes after the concrete was discharged from the mixer, the compressive strength was measured at 28 days.

Item Normal
concrete Powder level 3550 (conventional technology) Powder level 7500 (invention) 3M 6M 9M 12M 15M 18M 3M 6M 9M 12M 15M 18M slump
(mm) 125 134 135 132 131 130 128 167 165 163 162 161 123 Compressive strength
(MPa) 29 0.9 1.3 2.5 2.7 3.1 4.7 19 32 36 39 42 43

As can be seen in Table 3, when the powder used in the conventional cement concrete, 3,550 cm 2 / g coal ash is used, the slump has little effect on the molar concentration of NaOH, and even if the molar concentration is increased, the compressive strength of 3MPa The strength was so low that it could not be used in the structure.

On the contrary, in the case of using a powder degree 7,500 cm 2 / g, which satisfies the conditions of the present invention, the slump change was not large up to NaOH 15M, and the compressive strength was increased as the NaOH molar concentration was increased. Quality could be secured.

However, when the NaOH molar concentration is 3M outside the scope of the present invention, the compressive strength is somewhat lower to 19 MPa, and the compressive strength is hardly increased at 18M, and the slump is greatly reduced.

Example 3: Influence of Curing Temperature

This embodiment is to analyze how the curing temperature affects the cement concrete manufacturing method of the present invention.

Activated powder containing 7,500 cm2 / g coal ash and sodium silicate (Na ₂ O = 10%, SiO ₂ = 30%, solids 38.5%, specific gravity 1.39) and 9M NaOH (purity 98%) in a 1: 1 ratio by weight Prepare the concrete in the formulation as shown in Table 2 using the agent and then measure the compressive strength at 7, 28, 91 days for curing curing at 5 ℃, 10 ℃, 20 ℃, 30 ℃, 40 ℃, 50 ℃ The results are shown in FIG. 3.

As can be seen in Figure 3, there was almost no change in strength between the curing temperatures of 5 ℃ ~ 20 ℃, the strength tended to increase the higher the temperature from 30 ℃ or more. In the present invention, 40 ℃ or more is in the range of room temperature because it is the maximum temperature in summer, and 5 ℃ is included in the range of room temperature because the average temperature for the construction of general concrete in winter.

Cementum concrete of the present invention using the coal ash adjusted powder degree as described above is believed to be applicable to all four seasons spring, summer, autumn, winter.

Example 4 Dry Shrinkage and Durability

The powder is composed of 7,500 cm2 / g coal ash, sodium silicate (Na ₂ O = 10%, SiO ₂ = 30%, solids 38.5%, specific gravity 1.39) and 9M NaOH (purity 98%) in a 1: 1 ratio by weight. The concrete was prepared in the formulation as shown in Table 2 using the activator and then evaluated for dry shrinkage, sulfate, freeze-thawing, carbonation, and salt resistance, and the results are shown in Table 4 below.

At this time, the dry shrinkage was produced by 100x100x400m footnote test specimens exposed to the air condition (temperature 20 ± 2 ℃, humidity 65 ± 5%) and measured until 91 days of age according to KS F 2424.

In the sulfate test, φ100x200mm columnar specimens and 100x100x400m footnote specimens were prepared and cured at 28 ° C in air condition (humidity 65 ± 5%) for 28 days, and then immersed in 10% sodium sulfate solution for 91 days, followed by changes in compressive strength and length change rate. Was measured.

The freeze-thawing test was made of 100x100x400m footnote specimens and cured in a dry condition (humidity 65 ± 5%) at 20 ℃ for 28 days, and then the temperature range was + 4 ℃ to -18 ℃ and one cycle time was 2 hours 40 minutes. The test was carried out up to 300 cycles to determine the relative dynamic modulus.

Carbonation test was made in φ100 × 200mm circumferential specimen and cured in air condition (humidity 65 ± 5%) at 20 ℃ for 28 days, then in chamber controlled under carbon dioxide concentration 5%, temperature 30 ℃, humidity 50%. After the test body was exposed for 91 days, the test body was divided into two parts, and the surface was sprayed with a 1% solution of phenolphthalene to measure the carbonation depth.

Salt resistance was prepared by φ100x50mm specimen and cured in air condition (humidity 65 ± 5%) at 20 ℃ for 28 days, and then evaluated by electrical acceleration test according to ASTM C 1202.

combination Dry shrinkage
(× 10 ^-6 )  sulfate Carbonation
Depth (mm) Freeze thawing
Relative dynamic modulus
(%) Salt
Total charge
(Chrome) Intensity change rate
(%) Length change rate (%) General Concrete 680 5.4 3.5 13 85 2450 Powder level 3550
(Conventional example) 1350 Destruction Destruction 98 Destruction (Unmeasurable) 8670 7,500 powder
(Invention example) 438 0.2 0.5 3 98 630

As can be seen in Table 4, when the powder used for the conventional cement concrete also uses 3,550 cm 2 / g coal ash (conventional example), there is almost no reaction, so the strength is very low, the shrinkage occurs very large and durability Some of the evaluations showed that the durability was greatly degraded to the point where concrete would be destroyed.

On the contrary, the cementless concrete (invention example) that satisfies the conditions of the present invention has reduced dry shrinkage and durability, as well as conventional concrete, as well as conventional concrete. Therefore, the concrete obtained by the present invention is expected to be sufficiently applicable to the structure.

Considering that about 6 million tons of coal ash is currently emitted in Korea, and about 50% of it is recycled, the remaining 3 million tons of concrete can be used to reduce 2.7 million tons of carbon dioxide.

1 is a graph showing the workability of concrete according to the coal ash powder.

2 is a graph showing the test results of the compressive strength of concrete according to the coal ash powder.

3 is a graph showing the effect of curing temperature on the compressive strength of concrete using only coal ash as a binder.

Claims (2)

In the method for producing concrete through the process of mixing, stirring and curing the compounding raw materials, including binders, activators, fine aggregates, coarse aggregates, water and a high performance water-reducing agent as a compounding raw material, The binder is to be composed of coal powder of 5,000 ~ 10,000cm ² / g powder to break the glass film at room temperature of 5 ~ 40 ℃, The activator is composed of 6 ~ 15 Mole NaOH and sodium silicate in a ratio of 0.75: 1.25 ~ 1.25: 0.75 by weight, The method of manufacturing cement cement concrete using coal ash, characterized in that the blending material is added to the binder and the activator is added, the stirring process, and is air dried at room temperature of 5 ~ 40 ℃. delete

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