JP2003201157A - Method of producing high strength, lightweight aggregate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To advantageously produce a high strength, lightweight aggregate free from a black core phenomenon with the handling time reduced as possible. <P>SOLUTION: A mixture of loess and SiC is pulverized, and is molded, and is fired. At this time, the mixture is halved. Either is subjected to wet grinding, and the other is subjected to dry grinding, and both ground matters are kneaded, and are molded by extrusion molding. It is also possible that the mixture is subjected to dry grinding, and, after that, water is added thereto, and molding is performed by a briquet machine. Further, a foaming assistant can be added thereto. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a high-strength lightweight aggregate suitable for use in structural lightweight concrete.

[0002]

2. Description of the Related Art Lightweight concrete has the advantages that it can be made lighter than ordinary concrete and has excellent heat insulating properties. In addition, high-strength and lightweight concrete is used for high-rise buildings,
When used for expressways and bridges with large spans, the superstructure can be made lighter, which is advantageous for external forces such as earthquakes. Therefore, the aggregate used for such lightweight concrete is required to be lightweight and have high strength.

The artificial lightweight aggregate is a light and strong aggregate having voids inside and having a surface covered with dense glass.
It is made from expanded clay, expanded shale, etc., as raw materials, through the steps of crushing, granulating, and firing. During the firing, gas such as CO ₂ generated by the dissociation of CaCO ₃ contained in the raw material, the reaction of iron oxide and carbon, etc. is confined inside to foam to form voids.

That is, the expanded clay, which is one of the raw materials for the artificial lightweight aggregate, is a loess that has been soiled with organic substances and microorganisms for many years, and contains minerals and clay that generate gas due to thermal decomposition. In addition to having carbon sources such as organic substances and carbides. Therefore, at the time of firing, the iron content Fe ₂ O ₃ in the mineral is reduced by this carbon to become FeO, and the melting point of the mineral is lowered, so that vitrification easily occurs. In such a state, the gas generated by the thermal decomposition of minerals and the reduction reaction of iron is trapped in the solid phase and foams. Expanded clay is produced from all over the world. In Northern Europe, heat insulating blocks and the like have been manufactured as raw materials for lightweight aggregates since ancient times, and in China, heat insulating blocks and the like are manufactured from yellow river deposits and the like as raw materials. When such expanded clay is used as a lightweight structural aggregate, good properties can be obtained by using an extrusion molding machine capable of high-density molding and controlling foaming.

Further, shale is used as a raw material for a lighter aggregate having higher strength. A shale is a layer of expanded clay that is hardened and petrified over the course of geological time under the influence of geopressure or degeneration as a result of being deposited in multiple layers. The mineral composition of shale and the property against heating are similar to those of expanded clay, and foam according to the same principle as that of expanded clay. Shale is mainly used as a lightweight structural aggregate that requires strength because of its high density of raw materials, and structural lightweight artificial aggregates made from such shale are produced in large numbers in the United States and Japan.

As described above, in the conventional lightweight aggregate using expanded clay or shale as a raw material, glass formed by melting Fe ₂ O ₃ into FeO by carbon reduction during heating and melting in the firing step. The viscosity of the clay is reduced, and foaming is performed by the gas generated by the decomposition and reaction of the clay mineral. However, according to such a foaming mechanism, gas is already generated at the stage before the glass is generated from the raw material mineral at the time of heating in the firing step. Therefore, the gas tends to escape without being confined inside the molten glass, and the pores are likely to be formed in communication with the outside. Further, when the firing atmosphere becomes a reducing atmosphere, the viscosity of the glass portion locally decreases due to the generation of FeO by the reaction between the carbon source inside the grains and the iron oxide, and the walls between the generated bubbles are easily destroyed. Tend to form open cells. from these things,
With conventional lightweight aggregates, it is difficult to obtain a structure of closed cells unless well-balanced conditions are met, and there are cases where the aggregates have poor performance with high water absorption and small specific strength.

A method of manufacturing a lightweight aggregate using a novel foaming mechanism, which is completely different from the foaming mechanism as described above, is disclosed in Japanese Patent Laid-Open No.
No. 00-226242. In the method for producing a lightweight aggregate disclosed in this publication, expanded clay, loess or yellow river sediment is used as a raw material, and SiC is used as a foaming agent.
Then, finely pulverized and densified, then fired to obtain a foamed lightweight aggregate. According to this manufacturing method,
It is said that since SiC hardly reacts at a temperature lower than the vitrification temperature, it is unlikely to form open cells, and it is easy to generate closed cells, so that a high-strength and lightweight aggregate can be obtained.

[0008]

However, in the technique described in the above-mentioned Japanese Patent Laid-Open No. 2000-226242, expanded clay, loess, and yellow river deposits that can be easily obtained from mainland China as a raw material for lightweight aggregates. Is used. Of these raw materials, expanded clay and yellow river deposits both contain a large amount of carbides and organic substances serving as carbon sources.
Therefore, when expanded clay or yellow river sediment is used as a raw material, foaming occurs due to the reaction between carbon and iron-containing minerals, and there is a possibility that a black foamed part with an extremely large bubble diameter is generated in the core of the aggregate. there were.

Such a phenomenon is called a black core phenomenon, and in the technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 2000-226242, in order to avoid this black core phenomenon, a large amount of organic matter such as expanded clay and yellow river deposits is used. By calcining the contained raw material in advance or decreasing the temperature rising rate in the firing step, the carbon content is preferentially oxidized and removed before reaching the temperature at which foaming occurs. Therefore, there has been a problem that productivity is lowered due to a decrease in temperature rising rate during calcination and firing, and labor and cost are increased.

Further, when the loess mainly composed of silty parts and sand that are water-classified in the Yellow River is used as a raw material, the black core phenomenon is suppressed because the amount of the clay component that causes the black core phenomenon is small. . However, since the loess, which is mainly composed of silty parts and sand, has a coarser particle size than clay, it must be finely pulverized to obtain the desired foaming property, and the labor and cost of the fine pulverization are required. That was a problem.

Therefore, the present invention advantageously solves the above problems, and provides a high-strength, lightweight aggregate free from the black core phenomenon.
It is an object of the invention to propose a method that can be advantageously manufactured with as little labor as possible.

[0012]

SUMMARY OF THE INVENTION The present invention is a method of using a Si and Si.
A method for producing a high-strength lightweight aggregate by crushing a mixture of C, followed by molding and firing, wherein the above mixture is divided into two, one is wet crushed and the other is dry crushed to obtain both crushed products. It is characterized by kneading and forming by vacuum extrusion molding.

The present invention also relates to a method for producing a high-strength lightweight aggregate by crushing a mixture of loess and SiC, molding and firing the mixture, and dry crushing the above mixture, adding water, and briquette. The feature is that it is formed by a machine.

Further, in the present invention, a foaming aid can be added to the above-mentioned mixture of loess and SiC.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, unsoiled loess, which has not been effectively used as a resource, is positively used as one of the raw materials. Loess is
It is also called weathered sediment, and the fine particles of weathered dust around the desert area where climate is severe are transported while being sifted by the wind and accumulated for many years. The material that is transported from the deserts of West Asia and deposited in China is called loess. Even in the US, fine silt and dust transported from the desert are accumulated in the Midwest to form grasslands and grasslands. In that region, Adobe
It is called. In addition, rock powder in the past glaciers and melting ice runoff deposits is the source of loess, which is deposited in the surrounding area by being blown up by the wind during the ice sheet receding period. They are widely distributed in Northern Europe, Eastern Europe, and the Russian plains, and locally distributed in France and Germany. These loess is a mixture of many rock minerals and its chemical composition is an average of ground minerals.

[0016] In an area where the climate is harsh and the habitat of microorganisms is small and plants are not inhabited, such as an arid area or a high temperature area where the temperature is severe, the loess soil does not progress and remains as fine sand. is there. The Loess Plateau of China is 5000
Due to the Chinese history of 1 year, the vegetation was artificially destroyed and it became a barren area, but the once destroyed green space has not revived, and its desertification is approaching Beijing year by year. The deposit is l
It is a kind of oess and its layer height is several tens to several hundreds of meters, and its cross section has many layers with a fairly white iron content.

[0017] Such a loess which is not soiled has a small amount of organic matter. Therefore, the use of the loess as a raw material of the lightweight aggregate according to the present invention suppresses the occurrence of the black core phenomenon due to the organic matter. Moreover, since such a loess is finer than silt and sand, it requires less grinding energy. Further, among the loess, those showing white color have less iron content, and even if the iron removal treatment is not performed, the black core phenomenon may not occur, which is more advantageous.

It is to be noted that expanded clay is soil that has been soiled with organic substances and microorganisms for many years, and expanded clay contains a large amount of organic substances and foams during sintering, so it can be used as a raw material for lightweight aggregates. As mentioned above, there are problems. The composition of loess used in the present invention is compared with that of the conventional lightweight aggregate raw materials expanded clay and shale.
Shown in.

[0019]

[Table 1]

In the present invention, in addition to the above-mentioned
Add iC and mix. This SiC is used as a foaming agent because it undergoes an oxidation reaction with surrounding molten glass at a high temperature during firing to generate a gas such as CO ₂ . SiC
Depending on the composition of the loess, the addition amount of
It is about 2.0%. If it is less than 0.1%, the effect of addition is not sufficient, and if it is added in excess of 2.0%, abnormal foaming occurs.

The mixture of loess and SiC is milled.
The finer the raw material before sintering, the smaller the grain boundaries during sintering, the smaller the bubbles generated, and the greater the proportion of closed cells. Is preferred, which is preferable. Therefore, conventionally, in order to obtain the finest possible pulverization, a wet type ball mill was mainly used for pulverization. However, the dehydration treatment after such wet pulverization is a heavy burden.

Therefore, in the present invention, dry pulverization is also used, that is, the mixture is divided into two parts, one is wet pulverized by a wet ball mill or the like, and the other is dry pulverized by a dry tube mill or the like. Knead. Thus, by adding and mixing the pulverized product obtained by the dry pulverization to the pulverized product obtained by the wet pulverization, the water content of the entire pulverized product is relatively lowered. Then, the pulverized product after kneading is subjected to vacuum extrusion molding. By using the vacuum extrusion molding, the pulverized product is dehydrated and is densely molded. Thus, it becomes possible to omit the dehydration treatment after the wet pulverization. After vacuum extrusion molding, it is dried according to a conventional method, then crushed, classified into coarse aggregate size, and then fired.

In the present invention, it is also possible to carry out molding by a briquette machine without wet crushing, that is, after dry crushing the mixture, adding water thereto. By performing only dry pulverization with a tube mill or the like, the dehydration treatment can be omitted, and the labor and cost of pulverization can be greatly reduced. After the dry pulverization, a minimum amount of water of 3 to 7% for handling is added, the mixture is molded with a briquette machine, and then firing is performed according to a conventional method.

Further, in the present invention, a foaming aid can be added to the mixture of loess and SiC. By adding a foaming aid, it is possible to promote foaming of the raw material,
Therefore, it is possible to avoid a decrease in the proportion of closed cells, which is a concern as a result of using dry pulverization and the pulverized particle size becomes coarse. Even if the proportion of closed cells does not decrease, the proportion of closed cells can be further improved by adding a foaming aid, so that a lightweight aggregate with less water absorption and high strength can be obtained. be able to.

Examples of the foaming aid include alkali-containing amorphous materials such as volcanic glass and volcanic ash, alkali-containing minerals such as feldspar, zeolite and waste bottle glass, and one or more selected from them may be added. it can. The use of waste bottle glass also has an advantage in terms of effective utilization of resources by recycling. A suitable blending ratio of these foaming aids is 5 to 30 mass%. Table 2
In, specific examples of the foaming aid that can be used in the present invention,
It is shown together with its component composition.

[0026]

[Table 2]

Experiments were conducted in the laboratory in which various foaming aids shown in Table 3 were added to the loess, mixed and pulverized by a dry tube mill, molded, and then fired in an electric furnace.
Table 4 shows the results of examining the firing temperature at that time and the characteristics of the obtained aggregate. From Table 4, it can be seen that the addition of the foaming aid has a low water absorption rate and a high-strength aggregate can be obtained.

[0028]

[Table 3]

[0029]

[Table 4]

Next, the volcanic glass as a foaming aid was mixed with shirasu, anti-firestone, pearlite, etc. at various ratios, mixed and pulverized, and then molded and fired to obtain an aggregate, and the water absorption rate was increased. The examined results are shown in Tables 5 and 6. In addition,
Table 5 shows a baking temperature of 1140 ° C., and Table 6 shows a baking temperature of 115.
This is the case at 0 ° C., and in either case SiC was 0.2 ma.
ss% is added. The change in water absorption from these tables shows that the water absorption increases as the amount of volcanic glass added decreases. Therefore, it can be seen that the addition of volcanic glass is effective in improving the water absorption rate.

[0031]

[Table 5]

[0032]

[Table 6]

[0033]

[Example] (Example 1) Loess: 80 parts, feldspar: 20 parts,
SiO: 0.2 part was used as a raw material, this raw material was put into a 2 ton wet ball mill, 150 parts of water was further added, and alumina balls were pulverized for 12 hours as a medium to obtain a slurry having an average particle diameter of 7 μm. On the other hand, raw materials having the same composition were dry-pulverized and continuously pulverized by a tube mill (continuous type) using an iron medium to obtain a dry powder having an average particle diameter of 12 μm. A wet mill is suitable for ultrafine powder, but a dry mill using iron balls is suitable for mass production. Therefore, the slurry weight of 100
After mixing 200 parts by weight of dry powder with a pug mill, kneading with a muller (a kind of edge runner) to obtain a water content of 3
A dough of about 2% was obtained, and it was subjected to a vacuum extrusion molding machine. In this vacuum extrusion molding, a band-shaped molded body was obtained by using a mold of about 60 mm square. Then, it was dried with a band dryer. When the water content became 3% or less, the molded product was crushed to a particle size of 20 mm or less with a roll breaker. A material with a particle size of 20 mm to 5 mm is used as a raw material of coarse aggregate and is 5 mm.
The following was used as a fine aggregate raw material by removing dry fine powder of about 0.5 mm or less by air classification. The dry fine powder obtained by air classification was sent again to the pug mill. The aggregate raw material was fired in a rotary kiln having a length of 10 m and a diameter of 1.2 m to obtain a high-strength lightweight aggregate. The properties of the aggregate thus obtained are shown in Table 7.

[0034]

[Table 7]

(Example 2) Dry and unmodified loess:
90 parts, waste bottle glass: 20 parts and SiC: 0.2 part were continuously pulverized by a tube mill to obtain a dry fine powder having a particle diameter of 12 μm. Then, 3% of water was added, and the mixture was kneaded and kneaded with an edge runner to make the water content constant, and then aged for 24 hours. Then, put it on a briquette machine and make a thickness of 40
It was molded into a width of 50 mm and a length of 50 mm, crushed with a roll breaker, and classified into 20 mm to 5 mm and 5 mm or less. It was fired in the same rotary kiln as above. The properties of the aggregate thus obtained are as shown in Table 8.

[0036]

[Table 8]

(Example 3) Desert soil in the north of California, USA: 80 parts, volcanic ash in the Rocky Mountains (mainly sand containing glassy pumice): 20 parts, Si
C: 0.2 parts were mixed and pulverized and mixed in a dry ball mill. Steel balls were used as the grinding media. The particle size was 15 μm. Then, 5 parts of water was added to and mixed with a ribbon mixer, and the mixture was aged overnight. Then, it was granulated with a briquette machine, dried with a band dryer, and then fired with a rotary kiln. The properties of the aggregate thus obtained are shown in Table 9.

[0038]

[Table 9]

[0039]

EFFECTS OF THE INVENTION According to the present invention, a high-strength, lightweight aggregate free from the black core phenomenon can be manufactured with the labor and cost required for fine pulverization and dehydration treatment reduced as much as possible. Further, in the present invention, it is possible to make effective use of the unused resource of loess by utilizing the fine powder property of the weathered deposit, and thus it is possible to contribute to society.

Claims (3)

[Claims] 1. After grinding a mixture of loess and SiC,
A method of manufacturing a high-strength lightweight aggregate that is molded and fired,
A method for producing a high-strength lightweight aggregate, which is characterized by dividing the mixture into two, wet pulverizing one of them, and dry pulverizing the other, kneading both pulverized products, and molding by vacuum extrusion molding. 2. After grinding the mixture of loess and SiC,
A method of manufacturing a high-strength lightweight aggregate that is molded and fired,
A method for producing a high-strength lightweight aggregate, which comprises dry-milling the above mixture, adding water thereto, and molding the mixture with a briquette machine. 3. The method for producing a high-strength lightweight aggregate according to claim 1, wherein a foaming aid is added to the mixture of loess and SiC.