KR940011451B1 - Process for the preparation of heat cement - Google Patents

Abstract

The high strength, ultra low exothermic cement compsn. is produced by (a) adding 6-15 wt.pts. of an anhydrous gypsum, 2-5 wt.pts. of an anhydrous sodium sulphate and 200-300 wt.pts. of a blast furnace slag to 100 wt.pts. of a clinker for a portland cement to make a base cement of 3000-4000 cm2/g powder degree, and (b) adding 10-30 wt.pts. of a paper ash powder of 8000-12000 cm2/g powder degree to 100 wt.pts. of the base cement, and then mixing them. The paper ash powder is composed of 25-60 wt.% SiO2, 35-70 wt.% Al2O3 infinitesimal Fe2O3, CaO, MgO, Na2O and K2O.

Description

Composition of high strength ultra low heat cement

Recently, as the size of concrete structures has increased, there have been cases where mass concrete has been constructed in concrete structures of large and long bridges other than dams, substructures such as bridges, foundations of high-rise buildings, nuclear power plants, and port structures. It is increasing.

Since the construction of such structures involves a large amount of cement, the heat of hydration generated during the reaction of the cement with water is greatly increased. The heat of hydration generated in the mass concrete generally shows a temperature difference of about 50 ° C. or more between the inside and the outside of the concrete structure, and the temperature risk difference between the inside and the outside of the structure causes the risk of cracking.

Therefore, in order to prevent the occurrence of cracks, the construction side uses a method such as cooling the raw material with water or liquid nitrogen in advance, or by embedding a water-cooled pipe in the mass concrete to reduce the heat of hydration of the cement. Low calorific cement, that is, medium-heat cement with low content of 3CaO Al ₂ O ₃ (C ₃ A) in clinker mineral, mixed cement with blast furnace slag and fly ash. However, this type of cement has a limitation in lowering the heat of hydration, and there is a problem that the risk of temperature cracking at an early age may be greater because the initial strength expression rate is lowered in proportion to the lowering of the heat of hydration.

Therefore, it is necessary to develop a new cement having lower heat of hydration and good strength than the low heat generating cement. Known methods for producing low calorific cement can be roughly divided into a method of controlling the particle size of the cement itself, a method of varying the type and content of clinker-generated minerals and a method by adding a mixture.

First, there is a method of controlling the particle size of the cement itself is Japanese Patent Application Laid-open No. Hei 1-28254, this method is to remove the fine portion, that is, particles of 1 to 15 micrometers or less in the cement particle size distribution.

Cement produced by this method has a large particle size, so that the specific surface area reacting with water is reduced, thereby delaying the hydration reaction and thus reducing the heat of hydration. However, in order to manufacture such cement, a separation method of fine powder must be taken separately, and in the process of mass production, the separation method of fine powder is practically impossible, and in terms of quality, problems such as a decrease in initial strength expression rate due to delayed hydration reaction are also not possible. exist.

Secondly, Japanese Patent Application Laid-open Nos. Hei 2-302347 and Hei 2-12026 are used to vary the type and content of clinker-generated minerals. The former is mixed with the slag to the raw material for cement production, and then calcined at 1100 ° to 1200 ° C to produce 2CaO.SiO ₂ (C ₂ S), 11 CaO.7Al ₂ O ₃ . It is a cement mainly composed of CaF ₂ (C ₁₁ A ₇ CaF ₂ ) and CaF (PO ₄ ) ₃ minerals. The latter is a low-temperature calcined mineral having 48 to 70% of C ₂ S and less than 4% of C ₃ A. It is a cement production method in which blast furnace slag or limestone is mixed with a clinker, so that the powder is 3000 to 5000 cm 2 / g.

However, most of the cement engineers recognize that C ₂ S minerals, which are the basis of these patents, are difficult to manufacture C ₂ S principal clinkers in the actual site-klon, and the initial strength expression rate is low in terms of quality. Has a problem.

Third, the method of adding a mixture is based on a mixed cement in which a large amount of blast furnace slag and fly ash is added to Portland cement (usually heavy heat cement or crude cement), and a small amount of limestone powder and gypsum are added thereto. Japanese Patent Application Laid-Open No. 61-97154 is added, and the fineness is controlled by adjusting the weight ratio of gypsum and slag to 0.04 to 0.15 and ultra-particulating to Blaine specific surface area of 5500 to 7500 cm2 / g. There is Japanese Patent Application Laid-Open No. 55-162457 to which a crude steel cement of ˜4500 cm 2 / g is added at a weight ratio of 15 to 35%.

However, when blast furnace slag and fly ash are added in a large amount, the heat of hydration is lowered, but there are various other problems. That is, in case of blast furnace slag, in order to increase the potential hydraulic properties, it is usually added with a high density of 4000 cm2 / g or more, so that the drying shrinkage increases, and the potential hydraulic properties of the slag often have a large temperature dependence. It is known that the rise of adiabatic temperature is relatively high.

Long-term strength expression is poor when using a large amount of fly ash, and some of the unburned carbon content in the fly ash loses its unique function by adsorbing the admixture added to improve the concrete properties, for example, the air entrainer. There is a problem.

In addition, the medium heat cement or crude steel cement used here usually has a disadvantage in that the production cost of the cement is high when producing a small amount of raw materials because the combination of raw materials having a different composition from the portland cement.

Specifically, the ultra low heat cement is generally used by mixing 200 parts by weight or more of slag, fly ash, etc. with 100 parts by weight of medium heat cement. In this case, the heat of hydration for 28 days is generally lower than 60 cal / g. It has a disadvantage that it is difficult to apply to the site of the structure that requires high strength, low strength, low absolute strength. In order to solve these disadvantages, the fineness of the slag is used as a fine powder (6000 to 8000 cm 2 / g), but it is difficult to grind into a fine powder in the actual manufacturing process, and even if it is produced, the price is high and economical is low.

In order to solve the shortcomings of the prior art, the present invention is usually pulverized by adding anhydrous gypsum (CaSO ₄ ), anhydrous manganese (Na ₂ SO ₄ ) and blast furnace slag to a clinker (hereinafter referred to as "clinker") for producing portland cement. After that, it is a high-strength, ultra-low calorific cement composition made by appropriately mixing the alumina siliceous paper ash produced in the papermaking industry. That is, while the heat of hydration is lower than that of the medium heat cement or the mixed cement, the strength is good and the manufacturing method is easy.

In other words, slag has high temperature dependence when it is highly fine powder due to the hydration characteristics of the slag, and cement produced only by the two-component system of cement and high fine powder slag has a limitation in reducing the heat of hydration. In addition to anhydrous forage and blast furnace slag, a five-component system with added waste ash is used.

Hereinafter, the present invention will be described in detail.

In the present invention, it is appropriate to delay the initial hydration of the calcium aluminate mineral (3CaO · Al ₂ O ₃ ), which has the highest heat of hydration among the cement components, and to reduce the strength of hydration. Based on the research that can be solved through the following results, the base cement for the ultra-low heat generation will be described.

6 to 15 parts by weight of anhydrous gypsum, 2 to 5 parts by weight of anhydrous manganese and 200 to 300 parts by weight of blast furnace slag were added to the clinker and mixed and divided to obtain a base cement at a level of 3000 to 4000 cm 2 / g. First prepare.

Using a anhydrite instead mainly used for high yisuseok (CaSO ₄ .2H ₂ O) to an existing cement manufacturing in the present invention, and the addition amount is also not as high 6-15 parts by weight of the clinker during the hydration reaction with the solubility of anhydrite This is because the hydration reaction rate of C ₃ A (see Table 1), which has the highest initial hydration rate and the highest heat of hydration, can be appropriately controlled.

TABLE 1

Heat of hydration of clinker mineral (cal / g)

In general, during the hydration of cement using high solubility dihydrate gypsum or hemihydrate gypsum, sulfate ions (SO ₄ ^2- ) are eluted in an aqueous solution within a short period of time, and reacted with C ₃ A to ethrinzite, a high sulfate hydrate. to produce an _{Ettringite) (C 3 A.3CaSO 4 .32H} 2 O). When the sulfate ion is depleted and depleted in the aqueous solution by this reaction, C ₃ A reacts with ethrinzite to transfer to low sulfate monohydrate, monosulfate (C ₃ A.CaSO ₄ .12H ₂ O), which generates high heat. . These are represented by the following scheme.

2C ₃ A + C ₃ A.3 CaSO ₄ .32H ₂ O (ettringite) + 4H ₂ O → 3 (C ₃ A.CaSO ₄ .12H ₂ O) (monosulfate)

(Hydration enthalpy △ H = -96.0Kcal / mol, free energy change △ G = -77.0Kcal / mol)

In the present invention, however, by using anhydrous gypsum having low solubility, sulfate ions are slowly eluted in an aqueous solution to react with C ₃ A to continuously generate ethrinzite. In addition, in the present invention, unlike ordinary cement, anhydrous gypsum added in a large amount continuously releases sulfate ions and continues to produce ethrinite, resulting in a higher amount of ethrinzite, which contributes to higher strength than ordinary cement, resulting in high strength. In addition, low sulfate hydrate monosulfate is not produced, it is an excellent invention that can significantly reduce the heat of cement hydration by inhibiting the generation of a large amount of heat due to the transition of the estrinite to monosulfate.

However, adding too much anhydrous gypsum greatly reduces the heat of hydration, but delays condensation and worses the long-term strength development rate, while adding too little anhydrous gypsum results in flash setting and poor workability. In the present invention, it was confirmed through the experiment that the addition amount of anhydrous gypsum is 6 to 15 parts by weight of the clinker is suitable.

The reason for adding 2-5 parts by weight of anhydrous forget-me-not is to promote the hydration reaction of calcium silicate phases (C ₃ S and C ₂ S), which have a high heat release rate of clinker minerals, and the potential hydraulic properties of added slag. It is because it promotes and the strength expression characteristic becomes favorable.

However, when the added amount of anhydrous forget-me-not is 6 parts by weight or more, a rapid freezing phenomenon is lowered workability and long-term properties are also reduced.

The present invention is 10 to 30% by pulverizing paper ash, which is a waste by-product of the papermaking industry, to about 8,000 to 12,000 cm 2 / g with respect to 100 parts by weight of the base cement in order to have a higher strength than the base cement prepared as described above. By mixing to produce an ultra-low calorific cement which is the final product of the present invention. Paper ash, which is a waste of the paper industry, is an alumina silicate material (see Table 2) in chemical composition, and its crystal state is mostly in the glass phase, and it is easy to be pulverized with high powder due to its good crushability.

TABLE 2

Chemical Composition of Paper Ash (Wt.%)

The action of paper ash added to the base cement is as follows.

The fine particles of paper ash fill up the block structure of cement hydrate, which becomes a mass after mixing with water, and play a role of ball bearing, which greatly improves the fluidity and can deposit hydrate at the early stage of hydration due to the fine mineral powder effect. By increasing the space therein, the cement hydration reaction is promoted, thereby densifying the tissue development of the hydrate. In addition, this paper ash is pozzolan reactive in the presence of stimulants such as alkalis and sulfates, contributing to the improvement of strength.

As a result of measuring the pozzolan strength according to KSF5401, the papermaking ash showed 84 kg / cm 2 of pozzolanic activity much higher than slag powder 30 Kg / cm 2 and fly ash 43 Kg / cm 2.

In other words, a portion of the silicate alumina mineral present in the paper ash is dissolved as silicate ions (Si ⁴⁺ ) and aluminum ions (Al ³⁺ ) in an aqueous solution, which is dissolved in base cement (Ca). ²⁺ ), and reacts with sulfate ions (SO ₄ ^-2 ) and hydroxide ions (OH ⁻ ) to contribute to the initial strength enhancement by producing calcium silicate hydrates or ethrinzide hydrates.

On the other hand, when the amount of paper ash is added to 10 parts by weight or less, the effect of fine mineral powder is reduced, and when it is added to 30 parts by weight or more, the amount of paper ash is added since the strength compensation due to the latent hydraulic properties of the blast furnace slag is not sufficiently expressed. Experimental results confirm that 10 to 30 parts by weight is suitable, which is considered to be possible to ultra-low heat generation due to the relatively reduced cement content due to the addition of paper ash.

In particular, paper ash has the advantage of being easily pulverized because of its high crushing properties.The specific surface area of the crushed ash is added to 8000-12000cm2 / g, resulting in high strength of the reaction surface area due to the ultra fine powder effect. In addition, the fluidity of the fine particles and the role of ball bearings between the particles can be improved.

Hereinafter, the present invention will be described based on Examples.

EXAMPLE

Table 4 shows the results of measuring the flowability, compressive strength and heat of hydration of the cement of the present invention by adding the paper ash which is the waste of Ssangyong Paper Co., Ltd. to the base cement in the ratio shown in Table 3.

At this time, the test method was performed according to Japanese Industrial Standard (JIS) to compare with Japanese products.

On the other hand, Table 5 shows the physical performance of the product catalog of Japanese Patent Application Publication Nos. 55-162457 and 61-97154 and Tsumidomo Cement Co., Ltd. for comparison with the present invention.

TABLE 3

Cement Manufacturing Conditions of the Invention

Note) Base cement is 250 parts by weight of blast furnace slag of Pohang Steel Co., Ltd., 10 parts by weight of Namhae Chemical Co., Ltd., anhydrous gypsum, and 100 parts by weight of clinker for manufacturing ordinary Portland cement. Consists of parts by weight.

TABLE 4

Mortar Flow, Compressive Strength and Heat of Hydration of Cement of the Invention

As shown in Table 4, the cement composition of the present invention has a large flow rate compared to general portland cement, so that the required amount of work can be reduced, and the heat of hydration is low at about two-quarter level of general portland cement, but the strength is low. It is high.

TABLE 5

Physical performance of Japanese products (comparative example)

According to the measurement results of Table 4, the base cement powder is adjusted to 3,000 to 4,000 cm 2 / g, the paper ash powder is adjusted to 8,000 to 12,000 cm 2 / g, and the paper ash is 10 parts by weight based on 100 parts by weight of the base cement (Example 1 to 3), 20 parts by weight (Examples 4 to 6), and 30 parts by weight (Examples 7 to 9) under all the conditions of addition, the heat of hydration was mostly 50 Cal / g or less, which showed good strength and good fluidity. The flow value (Flow) is also shown to be good due to the filling of the voids and the role of ball bearing according to the addition of paper ash.

Table 6 compares the heat of hydration of Portland cement according to the US ASTM classification and the cement of the present invention. When the low heat cement of the US ASTM classification is compared with the cement of the present invention, the heat of hydration is reduced by an average of 25 to 30%. Engineering Handbook 1050, edited by Japan Ceramics Association, 1989 edition)

TABLE 6

Comparison of Heat of Hydration with Portland Cement by US ASTM Classification

These results are generally compared with the Japanese products of Table 5, where the initial strength is low when the heat of hydration is low and the hydration heat is high when the initial strength is high, and the present invention has excellent strength expression characteristics at all ages from initial strength to late strength. It can be seen that it is a breakthrough cement product with extremely low properties, and as shown in Table 6, it is an ultra low calorific cement having a significantly lower hydration calorific value than the low heat cement according to the ASTM classification.

The ultra low heat cement of the present invention has a low heat of hydration but a low heat of hydration, whereas the low heat of hydration is low at 50 cal / g on the 28th day, and the strength at the early age and later than 28 days is higher than that of general portland cement. It is a very innovative invention that can express stability against structure cracking by increasing the strength of buildings and reducing the shrinkage of drying.

As a side effect of this study, there is an advantage that the utilization of waste resources and environmental pollution can be reduced by using paper ash which is currently produced as land waste in the paper industry.

As described above, the contents of the present invention have not been seen in the past. In the past, the research mainly lowered only the heat of hydration, and thus, blast furnace slag and fly ash were added to prepare ultra-low heat cement, but the expression rate of initial compressive strength was poor as the heat of hydration decreased. There is a problem as a structural material.

In this study, anhydrous gypsum is added as an alternative to conventional hydrated gypsum used in cement manufacturing, and the amount of addition is also increased to control the initial hydration reaction rate, and an appropriate amount of anhydrous forage is added to calcium silicate mineral and latent hydraulic blast furnace slag. It accelerated the hydration reaction of to induce high strength.

In addition, fly ash produced in Korea is 10 ~ 15% of unburned carbon compared to fly ash produced in Japan, and it is not suitable for use in ultra-low heat cement that requires high functional quality due to its large particle size. By properly processing and using paper ash, which is a large amount of waste produced in the process, the reduction of heat of cement hydration and the development of the structure of the hydrate are densified, which makes it possible to manufacture high strength ultra low heat cement having excellent strength expression characteristics.

Claims (2)

Based on 100 parts by weight of clinker for making Portland cement, 6-15 parts of anhydrous gypsum, 2-5 parts of anhydrous manganese and 200-300 parts of blast furnace slag were used, and the base cement ground to a powder level of 3,000-4,000 cm 2 / g was used. In the low heat cement composition, 10-30 parts by weight of the paper ash powder pulverized to a level of 8,000-12,000 cm 2 / g with respect to 100 parts by weight of the base cement is added, homogeneous and mixed to produce a low heat Cement composition. The composition of claim 1, wherein the ash ash powder is composed of 25-60 wt% SiO ₂ , 35-70 wt% Al ₂ O ₃ and trace amounts of Fe ₂ O ₃ , CaO, MgO, Na ₂ O and K ₂ O. Ultra low heat cement composition, characterized in that.