JPH11106245A - Artificial aggregate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To readily obtain artificial aggregate that has practical properties despite of the kinds of coal ash by crushing coal ash so that its average particle size may becomes less than a specific value, forming the ash and firing the formed product. SOLUTION: Coal ash is crushed into particles less than 5 μm that can be readily attained by using a generally used crushing means and the resultant particles are molded and fired. When necessary, the crushed particles are combined with a melting point-lowering agent with a Blaine's specific surface area of 2,000-7,000 cm<2> /g preferably in an amount of 20-60, more preferably 30-50 pts.wt. based on 100 pts.wt. of the coal ash, molded and fired. The melting point-lowering agent is, for example, an iron sauce for cement as iron ore, blast furnace slag, blast furnace dust, copper slag, igneous rock, cement clay as weathering shale, amorphous glass substance as quartz trachyte, obsidian, volcanic ash or glass waste. As a result, artificial aggregate with an absolutely dried specific gravity of >=2.0 and water absorption of <=3% for 24 hours.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-strength, high-specific-gravity, low-water-absorbing artificial aggregate produced from coal ash. The artificial aggregate produced by the method of the present invention is used as a substitute for natural aggregate in producing ordinary concrete products.

[0002]

2. Description of the Related Art The use of aggregates is essential for the production of concrete products. Conventionally, natural materials have been used as aggregates.However, in addition to depletion of resources due to long-term use, mining is often restricted for environmental protection reasons, and shortages and quality deterioration are problems. Development of alternative products is required. On the other hand, coal is being used as fuel in thermal power plants and various factories, but coal ash, which is discharged in large quantities from it, does not proceed as intended, and its accumulation becomes a problem. There is a strong demand for the development of an effective utilization method that uses a large amount of. As a means of solving these two problems at once, research and development of artificial aggregates using coal ash have been advanced, and many techniques have already been disclosed. However, most of them are artificial lightweight aggregates for lightweight concrete utilizing the generation of low-density bodies by heating and foaming. Few. In order for artificial aggregate for ordinary concrete to have practicality, the absolute dry specific gravity is 2.0 or more and the water absorption rate for 24 hours is 3
% Or less, but the reason is that it is difficult to produce aggregates having this property using coal ash of various histories as a main raw material.

As an example which has made this possible, see Japanese Patent Application Laid-Open No. 7-2
Japanese Patent Publication No. 064491 discloses a method for producing an artificial aggregate using coal ash whose particle diameter has been adjusted. With this method, it is possible to produce aggregate that satisfies the above characteristics irrespective of the type of coal ash, but the technical idea is to mix the powders having different particle size distributions to make the granulated material before firing compact. In addition to the pulverization, complicated classification operations are required, and the particle size distribution conditions required for the powder are complicated, and as a result, the applicable range is narrow and adjustment is difficult. Have. Further, depending on the size of the coal ash, even if the particle size is adjusted, the density of the granulated product before firing does not increase, and an aggregate having characteristics required in practical use may not be obtained.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an artificial aggregate using coal ash as a main raw material and having practical characteristics and a method for producing the same. Specifically, regardless of the type of coal ash, the absolute dry specific gravity is 2.0 or more and the 24-hour water absorption is 3%.
It is an object of the present invention to provide an artificial aggregate having the following characteristics and a manufacturing method capable of easily and stably manufacturing the artificial aggregate.

[0005]

Means for Solving the Problems Coal ash has different particle diameters and other characteristics depending on the type of coal used for combustion, and the characteristics of aggregates manufactured using the same vary. If pulverized so that the average particle size of the coal ash is 10 μm or less, the aggregate satisfying the target characteristics can be stably obtained regardless of the type of the coal ash and without any special particle size distribution adjustment. It was found that the present invention was obtained, and the present invention was completed. That is, the present invention relates to a method for producing an artificial aggregate, characterized in that coal ash pulverized so as to have an average particle diameter of 10 μm or less is formed and then fired, and an artificial aggregate produced by the method. . The present invention has an average particle diameter of 10 μm.
The present invention relates to a method for producing an artificial aggregate, characterized in that a melting point lowering agent is further added to coal ash adjusted as described below, followed by molding and firing, and an artificial aggregate produced by the method. Hereinafter, the present invention will be described in detail.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Coal ash is mainly composed of alumina and silica, and contains oxides of metals such as iron, calcium, magnesium, sodium and potassium as flux components. Consists of a crystalline phase of When the coal ash is heated to a temperature higher than the softening point of the glass phase after forming the coal ash, the glass phase softens or forms a melt, acts as a glue material that bonds the particles to each other and fills the gap between the particles, has a high density, and It is considered that aggregate having a low water absorption is generated. Therefore, it is expected that the size of the gap between the particles formed in the coal ash after the molding greatly affects the density and the water absorption of the produced artificial aggregate. On the other hand, it is considered that the size of the gap formed between the particles depends primarily on the particle diameter. For example, for three types of coal ash A, B, and C having an average particle size of greater than 10 μm,
FIG. 1 shows the absolute dry specific gravity and the 24-hour water absorption of the aggregate obtained when the aggregate is formed and fired without reducing the average particle size by performing a pulverizing treatment. It can be seen that none of them gives an artificial aggregate having the desired properties.

However, the coal ash A shown in FIG. 1 is subjected to a pulverizing treatment to prepare six kinds of powders having mutually different average particle diameters.
FIG. 2 is a plot of the apparent specific gravity of the fired body obtained by heating and firing at 0 ° C. with respect to the average particle diameter of the powder after preparation. In addition, the apparent specific gravity of the fired body obtained by firing it linearly increases, and at least with respect to the apparent specific gravity, a fired body having two or more values that a practical aggregate should have can be obtained. That is, although there are various factors that determine the properties of coal ash and, in turn, the properties of artificial aggregates produced therefrom, the inventors,
The size of coal ash was found to be a major factor in determining the characteristics of the artificial aggregate to be produced, and the size of the coal ash was adjusted by adjusting the size of the coal ash particles so that the average particle size became a certain value or less. Regardless, it was actually confirmed that stable production of artificial aggregate having practical characteristics was possible, and the present invention was completed.

The most important feature of the present invention based on the above knowledge is that the coal ash is pulverized and adjusted so that the average particle diameter becomes 10 μm or less. After dividing the particle size into a plurality of stages, a cumbersome processing method of preparing a final powder by remixing a prescribed amount of the powder at each particle size stage is not required.

Generally, the average particle size of coal ash is larger than 10 μm, and pulverization of the coal ash is required for carrying out the present invention. Any method using a mold roller mill or the like can be used without any problem. However, in the pulverization, it is necessary to check in advance the relationship between the pulverization conditions, such as pulverization equipment, pulverization time, and the average particle diameter of the obtained powder. It can be easily carried out by measuring the average particle size by a known means.

The most characteristic feature of the present invention is to use coal ash having an average particle size of 10 μm or less. However, reducing the average particle size by using a special pulverizing means can reduce the obtained aggregate properties. Although there is no problem from the point of view of crushing, it is not preferable from the point of crushing cost, and it is preferable to use coal ash having an average particle diameter of 5 μm or more easily achievable by general crushing means.

Coal ash, which has been pulverized in accordance with a condition that gives a powder having an average particle diameter of 10 μm, which has been obtained in advance, can be generally used as it is. Depending on the pulverization conditions or coal ash, a treatment for once removing coarse particles through a sieve may be added. The coal ash obtained by this method is a mixture of powders of various particle sizes, and its particle size distribution may fluctuate depending on pulverization conditions, but the average particle size is 10 μm.
If it is below, there will be no obstacle to obtaining the aggregate having the target characteristics.

Coal ash adjusted to have an average particle size of 10 μm or less gives an artificial aggregate having target properties irrespective of the type of coal ash. The specific gravity, the water absorption and the strength are further improved, and preferable results can be obtained.

The melting point depressants usable in the present invention include iron concentrates, blast furnace slag, blast furnace dust, iron sources for cement such as copper calami, clay for cement such as igneous rocks and weathered shale, and quartz coarse. Natural or artificial substances mainly composed of amorphous glass, such as face rock, obsidian, perlite, volcanic ash, and waste glass, can be mentioned. These can be added as one kind or a mixture of two or more kinds. When the melting point lowering material is added, the amount added is such that the average particle diameter is 1
The content is preferably 20 to 60 parts by weight, and more preferably 30 to 50 parts by weight, based on 100 parts by weight of coal ash adjusted to be 0 μm or less. If the addition amount of the melting point lowering material is too small, the effect of addition is not sufficiently exhibited, and if it is too large, it not only leads to high cost, but also becomes easy to foam depending on coal ash,
In some cases, an aggregate having desired properties cannot be obtained.
As the melting point lowering material, it is desirable to use a material having a Blaine specific surface area of 2000 to 7000 cm ² / g in order to increase the mixing property with coal ash and avoid segregation thereof.

The powder after particle size adjustment is molded before firing, and any known molding method such as bread granulation, pressure molding and extrusion molding can be used without any problem. Among them, a method using a bread granulator is the most preferable molding method from the viewpoint of easiness of controlling the particle size and cost. In addition, the pressure molding method increases the density of the molded body after molding, and further leads to an increase in the density and crushing strength of the aggregate after firing. This is a particularly preferred method for the purpose of production. In forming, an inorganic binder such as water glass, clay and bentonite or an organic binder such as cellulose, polyvinyl alcohol, dextrin and pulp waste liquid may be added without any problem. The shape and particle size of the molded product are adjusted according to the purpose of use of the aggregate, but a spherical aggregate having a particle size of 5 to 20 mm is most commonly used.

[0015] The molded body as it is or after drying,
Baking to obtain artificial aggregate. The firing temperature varies between 1150 and 1450 ° C. depending on the type of coal ash. However, in the case of coal ash whose average particle diameter after adjustment is 10 μm or less, all of the target practical characteristics An artificial aggregate satisfying the following conditions can be obtained. Hereinafter, the present invention will be described in more detail with reference to specific examples.

[0016]

【Example】

Examples 1 to 7 and Comparative Examples 1 to 3 (1) Raw material coal ash: A, B, and C3 types of coal ash having the composition, average particle diameter, and Blaine specific surface area shown in Table 1 were used. Melting point lowering material: Clay or blast furnace slag from Himejima, whose composition is shown in Table 1, was added to adjust the amount of flux. (2) Adjustment of average particle size of coal ash 600 g of coal ash is 15 to 120 using a standard ball mill.
A crushing treatment was performed for a minute to obtain a crushed product. About the obtained pulverized material, the average particle diameter was measured using a laser diffraction type particle size analyzer. (3) Molding If necessary, a melting point depressant is added to the coal ash whose average particle diameter has been adjusted, and 100 parts by weight of water is added to water.
Add 2.5 parts by weight with a bread granulator while adding 5 parts by weight.
mm was molded into a spherical molded body. (3) Firing The molded body is dried in an electric furnace in an electric furnace without drying.
Firing was performed in a temperature range of 50 ° C. to obtain an artificial aggregate.

(4) Characteristic evaluation The obtained aggregate was analyzed by the following method to determine the absolute dry gravity, 24
The water absorption over time and the crushing strength were measured, and the characteristics were evaluated. The measured values are shown in Table 2 and FIGS. Absolute dry specific gravity: measured according to JIS A 1135. 24 hour water absorption: Measured according to JIS A 1135. Crushing strength: A load was applied to the aggregate placed on the sample table from above, and the excess weight when the aggregate collapsed was measured. The measurement is performed on ten samples, and the average value is shown.

[0018]

[Table 1]

[0019]

[Table 2]

In Comparative Examples 1 to 3, three types of coal ash having an average particle diameter larger than 10 μm were used without treatment, but both the absolute dry gravity and the 24-hour water absorption were provided as artificial aggregates. The required value has not been reached. Also, the crush strength is low. On the other hand, Examples 1 to 5 using coal ash pulverized so that the average particle diameter becomes 10 μm or less.
In any case, regardless of the type of coal ash, the characteristics that a practical aggregate should have are:
One that satisfies the 4-hour water absorption is obtained. In addition, the crushing strength also shows a value of 170 (kgf) or more, and a satisfactory strength is obtained. . Example 6,
No. 7 is obtained by further adding a melting point lowering material to coal ash which has been pulverized so that the average particle diameter is 10 μm or less.
Compared to Example 1 using the same kind and coal ash having almost the same average particle diameter, the absolute dry weight, the 24-hour water absorption, and the crushing strength are improved in all aspects. It turns out that it is remarkable. Also, although not shown here, the firing temperature range for providing the aggregate having the target properties is as follows:
It becomes wider than the case without addition.

[0021]

According to the present invention, the average particle diameter is 10 μm.
An artificial aggregate having practical properties for ordinary concrete can be manufactured by a simple method of merely pulverizing coal ash as described below. Further, by adding the melting point lowering material, the artificial aggregate of the present invention has a wider firing temperature range for providing an aggregate having target characteristics, and can be manufactured stably. Therefore, the method of the present invention not only solves the problem of natural aggregate deficiency, but also leads to the effective use of coal ash, whose accumulation is a problem, and its utility value in the industrial aspect is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of heating characteristics of a coal ash molded body having an average particle diameter larger than 10 μm.

FIG. 2 is a diagram illustrating an example of a relationship between an average particle diameter of coal ash and an apparent specific gravity of a molded body.

FIG. 3 is a view showing an example of heating characteristics of a coal ash molded body having an average particle diameter of 10 μm or less.

Claims (6)

[Claims] 1. A method for producing an artificial aggregate, comprising forming coal ash pulverized so as to have an average particle diameter of 10 μm or less, followed by firing. 2. A coal ash adjusted to have an average particle diameter of 10 μm or less, and a melting point lowering material is further added thereto, followed by molding.
A method for producing an artificial aggregate, characterized by firing. 3. The method for producing an artificial aggregate according to claim 2, wherein the amount of the melting point depressant added is 20 to 60 parts by weight based on 100 parts by weight of the coal ash. 4. An artificial aggregate produced by forming coal ash ground to a mean particle size of 10 μm or less and then firing. 5. An artificial aggregate produced by adding a melting point lowering material to coal ash adjusted to have an average particle diameter of 10 μm or less, followed by molding. 6. The artificial aggregate according to claim 5, wherein the amount of the melting point depressant added is 20 to 60 parts by weight based on 100 parts by weight of coal ash.