JP3072423B2 - Manufacturing method of high-strength artificial aggregate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to backfill materials for quay walls, seawalls, retaining walls, etc., pile materials for soil improvement (sand compaction pile, sand for sand drain method), roadbed materials for road works, The present invention relates to a method for manufacturing high-strength artificial aggregates using coal ash, which is used as general civil engineering and building aggregates (sand and gravel substitutes) such as lightweight aggregates for concrete. Specifically, limestone is used as a fluid medium. Coal fired fluidized bed furnace combustion ash (hereinafter, referred to as
Fluidized bed ash. ) To increase the long-term strength
The present invention relates to a method for producing a high-strength artificial aggregate . Fluid bed furnaces include pressurized fluidized bed furnaces and atmospheric pressure fluidized bed furnaces. Those ashes which contain a large amount of lime and are self-hardening are referred to as so-called "fluidized bed ash" in the present invention. included.

[0002]

2. Description of the Related Art The annual demand for aggregates such as sand and gravel for civil engineering and construction in Japan is 850 million tons, which is related to recent environmental conservation issues. However, the impact on the promotion of public works projects is also a concern and a major problem. Emergency imports are being made from China and elsewhere, but there is an urgent need to develop alternative sand that can be supplied in large quantities permanently using industrial waste (by-product) such as slag and coal ash.

[0003] Electric power companies, general contractors, cement companies and the like have been early in the effective use of coal ash as road base materials, sand pile materials for soft ground, seawalls, backfill materials for retaining walls, lightweight aggregates for concrete. Although many development tests and test constructions have been carried out, they have not yet become widespread.

A method of granulating and solidifying coal ash by adding cement and water to coal ash using “JP-B 4-24304”, “JP-B 7-34855”, “JP-B 7-74484”, etc. Regarding, using a high-speed mixing granulator equipped with high-speed rotating blades in a mixing vessel that rotates at a low speed, it cannot be made with a general pan-type rolling granulator, and the particle size is small (0.15 to 5 mm diameter) and relatively Proposed a method of manufacturing fine aggregate with high strength, and conducted a wide range of application research on raw materials for building materials, lightweight aggregate for concrete secondary products, roadbed materials, flow-resistant asphalt pavement materials, etc. We have been conducting tests and trial constructions and accumulating results.

Further, Subami et al., “JP-A-8-113777”
In the industry, while adding water to coal ash and a small amount of cement, which is the most common method, granulate and cure using a dish-type or drum-type granulator, and the particle size is 50 mm or less. Manufactures coarse aggregate and uses it as backing material for retaining walls, roadbed material, or pile material for ground improvement (for sandstones, construction wheels, sandstones and trains)
It has been proposed to use it for various purposes, and many trial constructions have been conducted.

With regard to fluidized bed ash, Kanra et al. Contain a large amount of limestone reaction products (quick lime and gypsum) in the ash, so landfill disposal is more difficult than general combustion ash, but it is strong when kneaded with water. Focusing on becoming a solid, with the assistance of the government, form molding with a vibration press molding machine and 60
After developing a high temperature curing of ℃ × 12hrs., Re-crushing and classifying it and developing it for use in roadbed materials, etc., installed practical-scale equipment and provided a wide range of product aggregates. I have. [For example, Kagura Kazuo et al. “Aggregate Resources” Vol.28, No.112,
p.181-191 (1997))

In addition, Ishii et al. Have developed a sintering method for adding a small amount of binder, pulverized coal, and water to coal ash, granulating the mixture, and firing at a high temperature in a sintering machine to obtain a durable artificial lightweight aggregate. To manufacture lightweight aggregates for high-rise buildings with actual-scale equipment,
Has achieved many achievements. [For example, Kuniyoshi Ishii “Clean Japan” Vol.85, p.27-30 (1990)]

In this sintering method, the production cost is high, but a high quality product with high strength can be obtained. Therefore, Narishima et al. By adding granulated limestone powder to coal ash and granulating and sintering, the water content is low (<3%),
We have proposed a method for producing high-quality artificial lightweight aggregate for concrete with high absolute dry specific gravity (> 2.0) and high compressive strength (> 400 kgf / cm ² ), and we are promoting its practical use.

[0009]

As described above, the development of artificial aggregates using coal ash (hereinafter referred to as "coal ash aggregates") has been promoted from an early stage, but is still widespread. Has not been reached. The reasons for this are the lack of cost competitiveness, including transportation, and the quality of coal ash aggregates for cheap natural sand and crushed stone, etc. It is determined that the strength is large and weak.

[0010] At present, aggregates such as natural sea sand and crushed stone are traded at 2500 to 3000 yen / ton including transportation costs, and it is very difficult to compete with them. In order for coal ash aggregate to spread widely in the market, it is essential to be able to compete with the market price, and it is necessary to review the conventional manufacturing method and drastically simplify the process to reduce equipment and operating costs, Measuring down is the most important task. It is said that the coal ash aggregate produced by the sintering method has a production cost several times higher than the transaction price of natural sea sand and crushed stone, etc. due to energy costs and equipment costs, and is used for high-value buildings with high added value. It is thought that it is limited to use for light-weight building materials.

Since coal ash is fine and has a large specific surface area, a small amount of a binder (cement, slaked lime, bentonite, etc.) is added to the coal ash, and water is added thereto while adding a general pan-type rolling granulator or rotary mixing granulator. About 30% of the weight of the powder
Need water. The amount of water required for the hydration reaction of cement is about 30% of the cement amount (approximately 3% when the amount of cement added is 10%). However, since 90% or less and 10% or more air bubbles remain, there is a problem that the quality of the product aggregate becomes porous and low in strength with a water content of 25 to 40%.

In addition, these granules have a low strength immediately after granulation, and there is a large amount of surface water (cement paste) on the particle surfaces.
As a countermeasure, re-crushing / classification and on-line high-temperature curing equipment were required, and there was a problem that the process became complicated and cost increased.

[0013] Under these circumstances, the inventors at the stage of studying various granulation methods have found that general pulverized coal combustion ash contains relatively hard components such as silica, alumina, and iron. The high temperature, the melting of the ash, and the formation of glassy spherical beads are the causes of difficulty in granulation in high-pressure compression granulation. Fluid bed ash, on the other hand, uses limestone as the fluidizing medium, and is mainly composed of lime, silica, and gypsum, and its particle shape is irregular and easily entangled. Because it ’s big
It has been found that a granulated product having a high density and a high initial strength can be obtained by compression granulating a fluidized bed ash at a high pressure.

Since fluidized bed ash contains a large amount of lime, it produces a hydration-reactive substance similar to cement clinker (lime silicate) in a furnace and has self-hardening properties when water is added. This produces an ettringite by performing an efficient hydration reaction with a small amount of water in the compacted and compacted microstructure, compared to simply adding a small amount of cement to general pulverized coal combustion ash and compressing and granulating. It was found that a very high strength was developed. Here, to solve the problem that the strength development of fluidized bed ash appears only in the initial strength, the strength development characteristics are further improved by adding a small amount of ordinary Portland cement to this, and the medium to long-term strength development is remarkable. It has been confirmed that it has a great effect. Furthermore, it has been confirmed that a part of the fluidized bed ash can be replaced with pulverized coal combustion ash within the effective range of the expression intensity.

The present invention has been made in view of such circumstances, and solves the above-mentioned problems. The present invention uses a fluidized bed ash , adds cement and water thereto, and performs compression granulation at a high pressure to produce the ash. An object of the present invention is to provide a method for producing a high-strength artificial aggregate which is excellent in process, physical properties, workability, economy, and the like, and can be suitably used as aggregate for general civil engineering and construction (sand, gravel substitute).

[0016]

SUMMARY OF THE INVENTION In order to solve the problem, the present invention is to increase the long-term strength by using fluidized bed ash.
A method for producing a high-strength artificial aggregate, characterized in that cement and water are added to the fluidized bed ash and compression granulation is performed under high pressure. It is also possible to mix the ash replacing part of the fluidized bed ash pulverized coal combustion ash.

That is, the method of the present invention includes the following characteristic items. By employing a high-pressure compression granulation method capable of granulating with a small amount of water, the arrangement of coal ash particles is made dense, and a dense granulated product having a large apparent specific gravity is obtained. As the coal ash, fluidized bed ash suitable for a compression granulation method that is easy to press in terms of particle shape and chemical composition is used. Fluidized bed ash is used because it has a reaction characteristic that allows the hydration reaction to efficiently proceed with a small amount of water in a dense tissue and develop strength. However, the hydration reaction of fluidized bed ash has a large initial strength, but is inferior in elongation at medium and long-term strengths. The case where only water is allowed to be added will be described later. By the synergistic effect of these, finally, a dense and high-strength granulated material comparable to the final strength of the standard blended concrete using general natural sand is obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the present invention is characterized in that, in the above configuration, the cement amount is 5 to 12 parts by weight , and the water addition amount is 100 parts by weight of the powder obtained by adding cement to fluidized bed ash.
13 to 20 parts by weight , the pressing force of compression granulation is 800 to 1500 kg
f / cm ² .

Here, when the amount of cement added is less than the lower limit, the effect of developing medium- and long-term strength is small. In addition, even if it is added above the upper limit, the effect of increasing the strength is small and the cost is high.
Therefore, from a practical point of view, it is appropriate to use the above 5 to 12 parts by weight.

When the pressing force of the compression granulation is lower than the lower limit , the compaction is insufficient [apparent specific gravity <1.8 (see FIG. 1), compaction ratio <83.
% (See FIG. 2)] , the strength expression is also reduced and is insufficient.
Further, even if the upper limit is exceeded , the consolidation does not proceed any further because of the internal frictional resistance of the ash particles, and the effect is small. Accordingly
From the practical point of view, the above-mentioned range of 800 to 1500 kgf / cm is appropriate.

The amount of water added, a compression granulation ash, must be selected in consideration of granulated after hydration reactivity (strength development), the following lower limit, cracking of the granulated particles The number of defects increases, and the strength development due to the hydration reaction after granulation decreases. In addition, even if water is added at the upper limit or more , it is squeezed out during the compression granulation and has no effect. Therefore, considering the practical aspects, upper
13 to 20 parts by weight are suitable. In addition, if only a small amount of cement and water are added to general pulverized coal combustion ash, it is easily broken even by compression granulation, and it is difficult for the hydration reaction with a small amount of water in the compacted particles to proceed, and strength is exhibited. The present inventors have confirmed that is small.

Here, in the utilization range of the artificial aggregate, there is a case where only water is added without addition of cement, and the method of the present invention includes this. That is, in the range of use of artificial aggregates, for example, as a roadbed material, use as backfill material, etc., without necessarily adding cement, the strength developed by high-pressure compression granulation with relatively little water is sufficient This is because there are also various uses, and it can be similarly considered as a production process according to the method of the present invention.

In the method of the present invention, an internal lubricant for compression granulation and / or a water reducing agent for solidifying cement may be added.

Here, the internal lubricant is talc, magnesium stearate, or graphite. However, since the above-mentioned water also functions as the internal lubricant, it may be considered to include this. The water reducing agent is mainly composed of a sulfonate such as an alkyl allyl sulfonate and a melamine sulfonate, and these are added alone or in combination.

In this case, the addition of a small amount of the internal lubricant reduces the internal friction coefficient of the powder, improves the propagation of pressure, and promotes the compaction during compression granulation. In addition, the addition of a small amount of a cement admixture (a water reducing agent such as an alkyl allyl sulfonate) for reducing the amount of water added at the time of cement solidification enhances strength development. Therefore, the compaction of the granules in the method of the present invention,
And contribute to the development of strength, and can be used in combination.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings.

(Example 1) 1800 parts by weight of fluidized bed ash, 75 parts by weight of ordinary Portland cement (corresponding to 4% of the mixed powder), and 281 parts by weight of water (corresponding to 15% of the mixed powder) are sufficiently mixed and kneaded. Then, a pressure-molded product of about 20 mmφ × 30 mmH was prepared by applying a pressure of 200 to 2000 kgf / cm ^{2 with} a pressure-molding mold, and its physical properties were measured and evaluated. Table 1 shows the chemical composition of the fluidized bed ash used in this example.

[0028]

[Table 1]

FIG. 1 shows the apparent specific gravity of a press-formed product, and FIG. Here, the compaction ratio is given by [compacting ratio = apparent specific gravity of compression molded body / average true specific gravity of mixed powder (including water)]. Therefore, the difference between the compaction ratio of 1.00 and the actual compaction ratio is the porosity. In addition,
The average true specific gravity of the mixed powder (including water) is the reciprocal of a value (average specific volume) obtained by dividing (dividing) the weight blending ratio of each component by the true specific gravity of each component and adding.

As can be seen from the figure, by applying a pressure of 200 kgf / cm ² to 2000 kgf / cm ² and compressing and molding, the apparent specific gravity increases from 1.58 to 1.90, and the porosity is about
Has decreased densified from 25% to 10%, the compressive strength, as shown in FIG. 3, at 7 days strength of about 200 kgf / cm ^2, the strength of the standard formulation concrete equivalent using standard natural sand This shows that a molded product having the same can be obtained.

It should be noted that the compaction by pressurization is performed for both apparent specific gravity (FIG. 1) and compaction rate (FIG. 2) from 1400 kgf / cm ² to 2000 kgf / cm ^2.
It shows a state where the pressure almost rises even when the pressure is increased to cm ² . This is considered to be due to the internal frictional resistance between the particles of the compounded powder, and by adding a small amount of an internal lubricant (talc, magnesium stearate, or water) for reducing the friction coefficient, the apparent specific gravity can be reduced. 1.95, compaction rate is 0.
We have confirmed that it can be increased to 95.

FIG. 4 shows a pressure of 1400 kgf / cm ² , cement /
It shows a change in compressive strength when the amount of water is changed at a powder ratio of 4%.

The amount of water added is such that the effect of reducing the internal frictional resistance coefficient between the particles during compression and accelerating the compaction, the effect on the strength development by the subsequent hydration reaction, and the granulation during compression granulation It is necessary to select in consideration of the properties (that is, the strength, cracks, chipping, peelability, etc.) of the granules. Cement / powder ratio 4 of FIG.
In%, the higher the amount of water added, the better the results. In the case of pressure molding of 1000 kgf / cm ² or more, 20
The addition of water of 23% or more is meaningless because it is squeezed out by pressurization.

FIG. 5 shows a pressure of 1400 kgf / cm ² and a water / powder ratio.
20% shows the change in compressive strength when the amount of cement in the powder is changed.

As can be seen from the figure, the pressurization (consolidation) of the fluidized bed ash provided a relatively high initial strength of 100 kgf / cm ² per day, and a small amount of ordinary Portland cement. In the medium and long term, for example, with a 28% strength of 15% cement, it is equivalent to the ultimate strength of standard compound concrete using natural sand.
This shows that an excellent high strength of 540 kgf / cm ² can be obtained in a relatively short period of one month.

As shown in FIG. 5, the present inventors have found that, even with the addition of 15% cement, ordinary pulverized coal combustion ash has a daily strength of 33 kgf / cm ² and a 28-day strength of 120 kgf / cm 2. It is about ² and it has been confirmed that cement hardening of fine coal ash (pulverized coal combustion ash) is extremely difficult.

(Example 2) Regarding compression granulation, a roll-type compression granulation tester (roll diameter 228 mm, roll width 38 mm, roll pressure 10
Ton) was used to form an almond-type granulated product (28 × 18 × 10 mm), and a trial production test was performed. The raw materials were 92 parts by weight of fluidized bed ash, 8 parts by weight of ordinary Portland cement, and 1 part each of water.
0, 13, and 15 parts by weight were sufficiently mixed and kneaded, and granulated while being press-fitted with a screw-type pressurized feeder provided in a granulator.

As the granulated product, a relatively hard granulated product having an apparent specific gravity of 1.75 to 1.83, a crushing strength immediately after granulation of 4 to 7 kg, and almost no cracks or chips was obtained. Since there was almost no surface water (cement paste) and no risk of re-condensation, it could be stored and cured in bulk in the warehouse.

The granules were stored and cured in a thermo-hygrostat at a temperature of 20 ± 0.5 ° C. and a saturation humidity, and the development of strength due to cement solidification was measured over time. FIG. 6 shows the result.

The amount of water added during the mixing of the raw materials 10, 13, 15% /
In the (powder amount), the smaller the moisture content, the smaller the elongation of strength after 7 days of material age, and the higher the moisture content, the higher the strength of the granulated product.

(Reference Example 1) Although deviating from the embodiment of the present invention, in the method of the present invention, a part of fluidized bed ash (abbreviated as PFBC in the figure) is partially replaced with general pulverized coal combustion ash (abbreviated as EP in the figure). 7) shows the expression intensity in the case where the mixed ash is used as a substitute. The expression intensity of the mixed ash decreases in accordance with the replacement ratio of the general pulverized coal combustion ash. But,
Depending on the use of the aggregate such as backfill material and roadbed material and the strength required for the aggregate, the expression strength of the mixed ash may be sufficient. Therefore, the method of the present invention can be improved by changing the mixing ratio (replacement ratio). It is possible to design an aggregate material such that the strength is maintained within a practical range while taking advantage of the characteristic of strength development. At the same time, the use of general pulverized coal combustion ash will be expanded.

As can be seen from the figure, even at 70% replacement (fluidized bed ash 30%, pulverized coal combustion ash 70%), 130 kgf in 28 days of material age.
/ cm ² strength can be obtained. The same strength of ordinary pulverized coal combustion ash alone is about 45 kgf / cm ² . In addition, 70%
Since the above substitution rapidly loses the feature of high strength development of the method of the present invention and deviates from the practical strength range required for aggregate, the replacement rate of fluidized bed ash by general pulverized coal combustion ash is
An upper limit of 70% is appropriate.

(Reference Example 2) FIG. 8 is a flow sheet showing a configuration example of an apparatus system for implementing the method of the present invention. Here, each component of the device system is individually known.

In the production of coal ash aggregate, reduction of the production cost is the most important issue. For that purpose, it is important to simplify the production process as much as possible and to simplify the equipment and operation.

According to the method of the present invention, since the granulated material is durable and easy to handle without fear of cracking, chipping or re-condensation during curing, the manufacturing process can be configured very simply. The main equipment is a mixing / kneading machine and a compression granulator, and the auxiliary equipment (equipment) is a raw material hopper for fluidized bed ash and cement, and a product warehouse that combines natural curing and storage of bulk piles.

[0046]

According to the present invention, there is provided the above-mentioned constitution (particularly by employing a fluidized bed ash and a high-pressure compression granulation method) to produce fine coal ash (pulverized coal combustion ash). The amount of water required during granulation, which became a problem in the cement solidification method, can be kept very low, and the granulated material has high strength and does not have to worry about re-coagulation. The process, such as bulk curing, is very simple, and the manufacturing cost can be reduced.

Further, in the method of the present invention, the consolidation of the granulated material and the development of strength can be enhanced by additionally using an internal lubricant and a water reducing agent for the compression granulation.

[Brief description of the drawings]

FIG. 1 is a data plot of apparent specific gravity versus applied pressure in a first embodiment of the present invention.

FIG. 2 is also a data plot of compaction ratio versus applied pressure.

FIG. 3 is also a data plot of compressive strength versus applied pressure.

FIG. 4 is also a data plot of compressive strength vs. water / powder ratio.

FIG. 5 is also a data plot of compressive strength vs. material age.

FIG. 6 is a data plot of compressive strength vs. age in the second embodiment of the present invention.

FIG. 7 is a data plot of compressive strength versus material age in Reference Example 1 of the present invention.

FIG. 8 is a configuration example of an apparatus system for performing the method of the present invention.
6 is a flow sheet showing (Reference Example 2) .

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 18/10

Claims (1)

(57) [Claims] 1. A method for producing an artificial aggregate using coal ash, wherein a coal-fired fluidized bed furnace combustion ash using limestone as a fluid medium (hereinafter, fluidized bed ash) is used for a long time by compression granulation and reaction solidification. A method for producing a high-strength artificial aggregate that reinforces the expression of strength, wherein the amount of cement is 5 to 12 parts by weight, based on 100 parts by weight of powder obtained by adding cement to the fluidized bed ash, and The amount of water to be added is 13 to 20 parts by weight, and the pressure is 800 to 1500.
A method for producing a high-strength artificial aggregate, comprising compression granulation as kgf / cm ^{2 and} reaction-solidification.