JP2000226242A - Production of lightweight aggregate for highly strong concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lightweight aggregate having a high strength and a low water absorption by adding a foaming agent and SiC to an expandable clay as a raw material, and then calcining the mixture. SOLUTION: The expandable clay includes Tienchin clay, loess and Hwang Ho deposits. The expandable clay and SiC are homogeneously and finely ground and mixed and then compactly molded. When the molded product is liquidized at a calcination temperature of 1,100-1,200 deg.C, the SiC is wetted and reacted with the melted liquid to generate a gas. When the SiC is covered with uniform glass or the like, the generated gas is closed in the sealed spaces to produce independent spherical pores. When fine clay is used, a finely grinding process can be omitted. For example, the employment of the loess permits the omit of the finely grinding process. The lightweight aggregate is, for example, obtained by adding 0.2% of SiC to loess, milling the mixture with a pot mill for 6 hr to prepare the milled product having an average particle diameter of 3 μm, dehydrating and drying the milled product, forming the dried product into about 10 mm pellets, calcining the pellets at 900 deg.C in an electric oven and then foaming the pellets at 1,160 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high-strength lightweight aggregate for concrete.

[0002]

2. Description of the Related Art Shale, which is a raw material of artificial lightweight aggregate, is obtained by hardening clay under the influence of soil pressure or denaturation, and its mineral composition and properties against overheating are similar to those of expanded clay. Various raw materials are similar to each other in chemical composition
O ₃ is the main component and is often in the range shown in Table 1 below.

[0003]

[Table 1]

The mineral composition is mainly quartz, feldspar, volcanic ash, diatom, limestone, and clay minerals such as illite, kaolin, montmorillonite, and a small amount of a combination of iron ore, calcite, dolomite, pyrite and the like. There are many. In addition, the raw material having expandability generally contains an organic substance.

[0005] Among them, there are many minerals which self-decompose when heated. CaCo ₃ undergoes thermal dissociation at around 800 ° C. to generate CO ₂ gas. However, if the heating rate is high, it may not be completely decomposed and may cause foaming at a temperature at which a liquid phase is generated. In addition, it includes clay minerals such as illite (mica clay mineral), vermiculite, montmorillonite (bentonite), and kaolinite as gas-generating minerals, and generates gas by thermal decomposition. When sulfide is present, SO ₂ gas is generated. Most of these occur at 900 ° C. or lower, but if the rate of temperature rise is high, it occurs up to the point when the solution is generated and may be involved in foaming. Examples of the decomposition reaction and its peak temperature are described below.

Calcite CaCO ₃ CaO + CO ₂ 910 ° C. peak (70
0 ° C.) Dolomite CaCO ₃ CaCO ₃ + MgO + CO ₂ decomposition temperature 6
70 ° C. (500 to 700 ° C.) CaCO ₃ ... CaO + CO ₂ decomposition temperature 670 ° C. to 9
Degradation 10 ° C. kaolin minerals _{A1 2 O 3 · 2SiO 2 ·} 2H 2 O ...... Al 2 O 3 · SiO 2
+ 2H ₂ O 930 ° C. Table 2 shows examples of chemical components of the lightweight aggregate raw material.

[0007]

[Table 2]

[0008] However, at the same time, iron compounds such as hematite and pyrite and carbon and organic substances corresponding thereto greatly affect foaming. Shale and foamed clay are not oxidized if the temperature rise rate is high.
e ₂ O ₃ is reduced to FeO or Fe ₃ O ₅ to generate CO ₂ gas, and FeO is a substance having a low melting point, which promotes liquid phase inside and facilitates foaming.

6Fe ₂ O ₃ + C... 4Fe ₃ O ₅ + CO ₂ 2Fe ₃ O ₅ + C... 6FeO + CO ₂ Basically, when the inside of the grain becomes a reducing atmosphere, Fe ₂ O ₃
Is reduced to generate CO ₂ gas and foam.
Although FeO promotes foaming, it can go too far to cause black core phenomenon and create large cavities inside the grains.

Shale and foamed clay are produced using the above-mentioned foaming mechanism. The raw material contains more iron and is more suitable for corrosive substances of microorganisms and plants as a carbon source. In order to make the material lighter, waste oil and waste containing carbon are added. Then, the temperature curve is made steep, and the carbon source is kept up to the high-temperature foaming region, and a reducing atmosphere is generated inside the raw material to cause foaming.

[0011] These foaming methods have a low cost and are immediately linked to a reduction in weight. However, the cell structure has a large number of continuous ventilation holes, a high water absorption and a low specific strength. Therefore, in order to maintain strength and water absorption as a structural aggregate, it is necessary to raise the specific gravity. At present, the specific gravity of the structural aggregate is about 1.3, and the light weight effect is insufficient. It is.
Ultra-light (1.0 or less) has high water absorption,
Because of its low strength, products with low added value such as heat-insulating blocks and lightweight blocks for partitions cannot be used.

The plains extending around Beijing and Tianjin in China are covered with old sediments by the Yellow River. Originally loess caused by the flooding of the Yellow River, it has been soild for tens of thousands or thousands of years, has many clays, is fine, and has a large concentration of iron in some places. It is a fertile land in agriculture. Light-weight aggregates (porcelain granules) are produced on a small scale using this soil by many local enterprises. They are fired by simple equipment using the above-mentioned reduced foaming of Fe ₂ O ₃ and carbon generated from organic matter. Although the cost is low, the strength is low, the water absorption is high, and it is used solely for blocks for thermal insulation. Table 3 shows an example of a conventional lightweight structural aggregate, and Table 4 shows an example of a conventional ultra-light aggregate.

[0013]

[Table 3]

[0014]

[Table 4]

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive lightweight aggregate having a high strength and a small water absorption. Further, the use of a clay-based raw material greatly reduces the need for the fine grinding step.

[0016]

The high-strength ultralight aggregate developed by the present inventors is characterized by using SiC as a foaming agent and pulverizing raw materials. The foaming mechanism by SiC is set in an environment completely different from the conventional foaming method of shale and expanded clay.

I hate organic matter and carbon residue.
Also, less iron is easier to control. SiC ceramics are used as high-temperature refractories, and the operating temperature can be up to 1600 ° C. And, at the firing temperature of 1200 ° C. of the present invention, it is slightly oxidized. However, when raw materials such as rhyolite are fired at about 1200 ° C., they are wetted by the molten liquid phase, react, oxidize and emit gas such as CO ₂ to foam. Reacting in the liquid phase requires, for example, a low melting bottle glass (softened at 800 ° C.) of about 800
It is also evident from the experimental results that foaming occurs when the temperature reaches ℃ and a liquid phase is generated. Moreover, even when the temperature reaches a predetermined melting point even in an N ₂ gas atmosphere, the liquid phase reacts with the liquid phase and foams. This is presumed to be due to the supply of oxygen not only from the outside air but also from the liquid phase for the SiC oxidation reaction. Such a foaming mechanism is optimal for generating closed cells. High-temperature ceramic materials such as Si ₃ O ₄ silicon nitride and BN boron nitride can also be used as foaming agents. Table 5 below shows a composition example of the natural glass.

[0018]

[Table 5]

It is an amorphous natural glass and is made of Ig. Most of the Loss is structured water and is released up to 800 ° C. Cogaite is a type of rhyolite lava that emerges on the surface and is gradually cooled. Lost water has already been released and does not have. Other volcanic rocks and volcanic ash have been blown up from volcanoes and are found in Ig. Has loss.

This method has been used for foams and lightweight aggregates mainly made of natural glass (rhyolites), anti-firestone and volcanic ash shirasu. (Japanese Patent No. 1405185)
Many of these raw materials are generated from volcanoes and have received heat history, and many of them have not yet been mixed with organic matter or soiled. It indicates that no reduction action is caused by the residual carbon during firing.

In addition, the content of iron is relatively small, such as 0.8 to 2.5%, and the reduction foaming of Fe ₂ O ₃ does not occur unless the inside of the furnace becomes a reducing atmosphere. Therefore SiC
And it is easy to control specific gravity and bubble size. Further, by finely pulverizing the raw material, the cell shape becomes fine, closed cells can be formed, and a high-strength foam having a small water absorption can be obtained. Table 6 shows examples of these.

[0022]

[Table 6]

However, when trying to use an existing rotary kiln or planning a new factory near the market, there is a case where there is no natural glass near the installation location. Especially in China, there are few active volcanoes and relatively new volcanic products, and even though they are undergoing denaturation, few are in the form of natural glass and many are becoming soiled.

Therefore, the present invention intends to apply foaming with SiC to a crystalline raw material even in a place where expanded clay or loess is easily and easily handled, such as in mainland China. When shale and expanded clay are uniformly pulverized and mixed and densely formed, if they are liquefied at a firing temperature of 1100 ° C to 1200 ° C, SiC wets the melt and reacts to generate gas. Is the same. At this time, since the gas is confined in a sealed space by being covered with the surrounding uniform glass and the gas is formed at a high density, there is no escape area for the gas and an independent true spherical bubble grows.

The finer the dust, the smaller the grain boundaries and the smaller the bubbles. It is important to supply oxygen from inside the glass phase as the voids are sealed. At this time, if there is unoxidized carbon, oxygen is deprived and the atmosphere becomes a reducing atmosphere, and the foaming of SiC occurs, thereby causing the foaming of non-uniform and many open cells by Fe ₂ O ₃ or the like. It is natural in terms of dynamics that the closer to the true sphere, the higher the strength. As a result,
The lower the iron content, the better the inside of the aggregate becomes white and gray if the iron content is low.

Shale and expanded clay contain a large amount of carbon and organic substances serving as carbon sources. In the case of anti-firestone, when a reducing atmosphere is reached (iron content of 0.8%), foaming of iron occurs, and an extremely large black foaming portion of bubbles may be observed in the core of the aggregate. In the ceramics industry, this phenomenon is commonly called black brick or roof tile, and is called black core. The cause of the black core phenomenon is that unburned carbon is left during sintering, the inside becomes an extremely reducing atmosphere, and Fe ₂ O _{3 and the} like are reduced to FeO or Fe ₃ O ₅ and become black. As the melting point of FeO further decreases, liquefaction is promoted because FeO has a low melting point, and the walls of the bubbles become less viscous. If the heating rate is high, the gas-generating mineral is carried over without being reacted until foaming, becomes a foaming source, foams in the cell wall, and destroys the wall.

Accordingly, the present invention provides a method of calcining and oxidizing an organic substance such as expanded clay first, and terminating the gas generation reaction of the foamed mineral so as not to remain at the melting temperature.
This is a method of firing and foaming in an oxidizing atmosphere at a temperature of 00 ° C.

Alternatively, by reducing the firing temperature curve, organic substances such as corrosive substances of microorganisms and plants can be removed from 600 ° C. to 9 ° C.
By burning and oxidizing at 00 ° C. so as not to leave carbon C in the object to be heated, sufficient air is supplied to the vicinity of the foaming temperature and the inside of the furnace is always kept in an oxidizing atmosphere to suppress foaming of Fe ₂ O ₃ . In order to perform decarburization and thermal decomposition by calcination, the residence time around 900 ° C. is set to be long.

The plains around Beijing and Tianjin, China, are covered with old sediments by the Yellow River. Originally loess caused by the flooding of the Yellow River, it has been soild during tens of thousands or thousands of years, is rich in clay, is fine, and has a high concentration of iron in some places. It is a fertile land in agriculture. Light-weight aggregates (porcelain granules) are produced on a small scale using this soil by many local enterprises. They are fired by simple equipment using the above-mentioned reduced foaming of Fe ₂ O ₃ and carbon generated from organic matter. Although the cost is low, the strength is low, the water absorption is high, and it is used solely for blocks for thermal insulation.

In the present method, the fine pulverizing step is intended to be omitted by utilizing the fine points of clay. Soiled loess is advantageous because it can reduce the cost of pulverization because it has a lot of clay.
0.2% of SiC as a foaming agent was added to the above sediment, pulverized by a pot mill for 6 hours to make an average particle diameter of 3 μm, dehydrated and dried to form a pellet of about 10 mm, and heated to 1160 ° C. in an electric furnace in 20 minutes. Table 7 shows a comparison between the foamed product and the product calcined at 900 ° C. and the product calcined and foamed at 1160 ° C.

[0031]

[Table 7]

The product having a black core therein was void and was not a product. However, calcining improved the black core phenomenon. Next, the carbon is completely burned by baking slowly without baking twice, and the reaction of the heated gas generating mineral is terminated to bring it to the foaming temperature. (Baking time: 4 hours, temperature: 1170 ° C to 1190 ° C) The results are shown in Table 8.

[0033]

[Table 8]

The loess of China is the fine dust that has been weathered from the Taklamakan Desert and the northern desert, and is carried by the wind. The large-scale area of the loess is the Ordos Plateau. Xi'an is at the foot of the Ordos Plateau and close to the Loess Plateau. The loess has a thickness of several tens of meters to several hundreds of meters and a depth of one meter from the surface of the ground, and is exposed to severe nature. In some places, there are many white outcrops, which are considered to be low in iron. They become the raw materials of the present invention by being subjected to a deironing treatment. On the other hand, the Yellow River transports loess as a large amount of sediment to the downstream China Plain, as if it were collecting the loess eroded from the Loess Plateau.

The method also seeks to utilize fresh sediments that have been washed in the Yellow River stream, are not currently inhabited by microorganisms, and have not yet undergone soil conversion. The Yellow River deposits a large amount of silt and clay in a wide river downstream. Such loess, on the whole, raises the riverbed by sedimentation. It causes the Yellow River to become a ceiling river, and dredging is constantly being done in preparation for floods. The present method seeks to effectively use so-called troubled loess as a resource. The foaming agent Si
C is added, finely pulverized, deironed, and dehydrated by a filter press to obtain a raw material. By performing the iron removal treatment, the iron content can be reduced by nearly half, and the inside of the fired product becomes grayish cream and the bubbles are fine.

The chemical components of the various loess are shown in Table 9 below. The silt part of the Yellow River sediment is Ig. The loss is small, indicating that it does not contain organic matter. Table 9 shows the chemical composition of Yellow River sediment and Tianjin expanded clay.

[0037]

[Table 9]

Mineral composition: X-ray analysis and thermal analysis. Loess: High in calcite and quartz, including feldspar. Illite is particularly common among minerals. Calcite average 1
1.6% (3.6 to 20.9) Quartz is about 20% and the composition of clay mineral is illite 50%, kaolin 15 to 20
%, Less than 15% smectite and less than 10% chlorite and vermiculite.

Yellow River sedimentary sand: Fewer calcites and mainly feldspar and quartz. Kakusen stone is seen. Ig. Loss is extremely small. At 830 ° C, there is some weight loss due to the decomposition of calcite. Yellow River sedimentary clay: Kaolin mineral, mica, and vermiculite are found as quartz, calcite, and clay minerals. Therefore I
g. Loss is as high as 8.4%. Although calcite has a large amount of CO ₂ dissociation, thermal analysis shows a total weight loss of 11% and thermal dissociation from clay is also observed.

Yellow River sediment silt: High in quartz and feldspar.
Ig. Loss is 3.6%. According to thermal analysis, CO ₂ is dissociated from calcite, and a small amount of dissociation is observed, including some clay minerals. These raw materials are subjected to a deironing process, and there are differences depending on each raw material.

The Yellow River sedimentary sand contains 3.55% of iron, but contains a large amount of iron sand in the ore and can be easily removed with a magnet. The sintering color is fairly close to white, but the formability is poor and the gray becomes slightly more intense when about 20% of Yellow River sedimentary clay is added as a clay component.

Since the Yellow River sedimentary clay has a large amount of clay, its particles are small and it is difficult to remove iron. Still, it will be removed while repeating.
It can be used by removing iron. However, the ocher coloration does not disappear. Yellow river sediment silt has iron sand similar to the Yellow River sedimentary sand, and it is easy to remove iron before crushing.

However, compared to the Yellow River sedimentary sand, there are clay minerals and it is difficult to remove iron, but it is better than clay. When pulverized, clay content comes out and moldability is good.

The raw material containing no organic matter is subjected to a deironing treatment and fired in a small electric furnace at a temperature gradient close to that of the actual machine. 0.2 kg of foaming agent SiC and water 2
Kg is added and pulverized and mixed in a pot mill for 6 hours to make the average particle size from 3 microns to 7 microns.

A 10000 Gauss bar magnet is put into the slurry, and iron is removed while stirring. Dehydrate with a plaster mold to obtain clay-like clay. And from there, it is made while looking at grains of about 10 mm in diameter. After drying it at 110 ° C., it is fired in an electric furnace. Table 10 shows an example of firing in an electric furnace for 45 minutes.

[0046]

[Table 10]

Thus, when these raw materials were subjected to the iron removal treatment, the above-mentioned good results were obtained. 500kg of various raw materials
300 kg of raw material, 400 kg of water, and 800 kg of cobblestone for grinding were placed in a ball mill and ground for 24 hours to make the average particle size 7 to 10 microns. The pulverized slurry was deironed by wet iron removal (10,000 gauss).

Dewatered with a filter press (filter),
The mixture was kneaded and kneaded with a vacuum kneading machine, and the mixture was dried in a rotary furnace. When the strength reached a certain level after drying, it was crushed, classified to a diameter of 15 mm to 3 mm, and fired in a rotary furnace of an actual machine.

Using a rotary kiln with a diameter of the front-end baking section of 1.6 m and a length of 15 m behind and a residual heat drying section of 1.2 m in diameter and 20 m in length, the fuel was finely pulverized and injected into coal for combustion. An oxidizing atmosphere with an oxygen concentration of 15.2% was maintained in the kiln. The kiln residence time of the feedstock is about 30 to 45 minutes.
Table 11 shows the combustion status of the rotary kiln.

[0050]

[Table 11]

Table 12 shows the firing results.

[0052]

[Table 12]

The cylinder pressure strength is specified in GB-2839 to be equal to or higher than the specified cylinder pressure strength of 3.0 Mpa. This time it is twice that. 1. Tianjin clay requires decarburization firing in advance. 2. In the Yellow River silt, the magnetic separator worked well to remove iron. It was washed by the Yellow River and had little organic matter.

3. Yellow River clay did not work because black core was first formed. This is as if elutriation was naturally performed from the silt part, but the clay minerals were concentrated and deironing did not work well. However, compared to Tianjin clay, there is less organic matter,
When iron is carefully removed with a magnet, the firing color becomes gray. Even if the temperature was raised at a high speed in an electric furnace for 30 minutes, a normal product was obtained. It was found that this can be achieved by reducing the concentration of clay mud and repeating magnetic separation several times. Then, for the purpose of separating the magnetism, the powder was finely pulverized to an average particle size of 5 microns, the concentration of the slurry was reduced, and the product was fired several times through a de-ironing machine and fired in the same process. . Since the Yellow River clay is already very fine, the grinding cost was low.

[0055] Volcanic ash sometimes undergoes denaturing action and becomes zeolite. In China, zeolite is widely distributed in China, and some have low iron content. In addition, zeolite is not exposed to soil formation because it is produced in the form of rock. The chemical composition is similar to rhyolite and is a suitable raw material for SiC foaming.

[0056]

[Table 13]

The procedure was carried out as shown in Table 14 below using the above zeolite.

[0058]

[Table 14]

Zeolite is more expensive than loess, and requires fine pulverization because it is produced in the form of a rock. However, bubbling with zeolite can be treated like natural glass with good results. If the raw material production area is shifted to the factory location, those costs can be absorbed.

[0060]

According to the present invention, a lightweight aggregate useful as an aggregate for concrete can be manufactured by effectively utilizing a large amount of unused resources. Since this lightweight aggregate has a low water absorption rate, it does not adversely affect the water-cement ratio when used as a concrete aggregate, so that concrete with stable strength can be formed. Moreover, since it is lightweight and has high strength, it can be applied to high-rise buildings.

In recent years, skyscrapers have been built around the world, and lighter and stronger aggregates are desirable. In addition, as the building becomes higher, the pumping method using a concrete pump becomes more advantageous. However, if the aggregate absorbs water during the pumping, not only the workability of the concrete fluctuates but also the hose may become blocked. Also, if it is performed in cold climates, concrete may be damaged by freeze-thawing of the water absorbed by the aggregate. In order to eliminate such a problem, an aggregate having a small water absorption is required. Moreover, if the strength of the aggregate is high, it can be used for structural concrete.

However, conventionally known expanded clay-based lightweight aggregates are widely produced in China, Europe, etc., but not for the purpose of strength and water absorption which can be applied to structures, but exclusively for heat insulation. It is only partially used for low-rise building walls and roofing materials as a non-structural partition concrete block or precast product.

In Japan, about 800,000 m ³ of structural lightweight aggregate is produced annually, but natural volcanic gravel is used for non-structural use and low specific gravity (400 kg to 500 kg /
Lightweight aggregate of M ³⁾ is never produced, recently, even in the low specific gravity is as aggregate ultra lightweight high strength comparable for the conventional structure is produced, in concrete using it A curtain wall having a specific gravity of 1.0 and a compressive strength of 200 kg / cm ² is being adopted. In Japan, the light weight aggregate for structural use by the Japan Society of Construction and Civil Engineers has a floating rate of 10
There is a guideline within%. Those with low specific gravity have low strength. In addition, the separation problem of the mortar and the aggregate was the reason. However, the aggregate according to the present invention has high strength even if the specific gravity is 1.0 or less, and has substantially developed a concrete separation reducing agent. Now those problems are being resolved. Everyone wants ultra-light, high-strength concrete as long as it's actually safe. By using these raw materials, it is possible to produce ultra-light and high-strength concrete aggregates, even if they are not natural vitreous raw materials. Fulfill. Advantageous Effects of Invention According to the present invention, it is possible to not only effectively utilize loess and the like which are a large amount of unused resources in China, but also to treat sediment that has been treated as a troublesome cause of a ceiling river for flood control of the Yellow River. , Its social contribution is great.

Claims (3)

[Claims] An expansive clay is used as a raw material and a blowing agent, SiC, is used as a starting material.
A method for producing lightweight aggregate for high-strength concrete, characterized by adding and firing. 2. The method for producing lightweight aggregate for high-strength concrete according to claim 1, wherein sediment of loess and Yellow River in China is used. 3. The method for producing a high-strength concrete lightweight aggregate according to claim 1, wherein zeolite is used as a raw material.