JP2001261391A - Method of producing artificial light-weight aggregate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing an artificial light-weight aggregate having a low specific gravity controlled over a wide range at a low production cost by granulating with a simple facility and curing by high-pressure steam curing. SOLUTION: The objective method comprises the 1st step to form a slurry by kneading a siliceous raw material, a calcareous raw material and water, adding a foaming agent and mixing the mixture, the 2nd step to store the produced slurry, the 3rd step to granulate the cake by extruding the cake in the course of curing to a viscosity of 30-1,500 Pa.s using a screw extruder while keeping the bubbles and the 4th step to perform the high-pressure steam curing of the granulated product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an artificial lightweight aggregate, and more particularly to a method for granulating an artificial lightweight aggregate composition cake.

[0002]

2. Description of the Related Art Artificial lightweight aggregates have many problems in cost as compared with crushed aggregates. That is, artificial lightweight aggregate (hereinafter, referred to as
In general, as a method of manufacturing aggregates), granulation is performed by rolling, extruding, or the like, and then firing is performed. A foaming agent is added to foam during the firing process, or the firing method is changed. Thus, a material having a controlled specific gravity is obtained.
However, it is necessary to pursue even lower costs.

Therefore, the present inventors have proposed a method for producing an aggregate using high-pressure steam curing, which has extremely low energy cost, instead of the above-described firing. That is, in order to lower the specific gravity of the aggregate using high-pressure steam curing, generally, the slurry is cast into a mold, then the mold is released, and the semi-cured state is such that only the cake can be handled (ball test value:
(About 24 to 20 mm). However,
In the aggregate manufacturing method using high-pressure steam curing, it is difficult to control the aggregate specific gravity to be wide and particularly low. In addition, this method requires a large number of molds and cutting devices in practical production, so equipment costs and operating costs increase,
As a result, manufacturing costs increase.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to produce granules with a simple facility and use a high-pressure steam curing to produce an aggregate having a wide specific gravity and a particularly low controlled aggregate at a low cost. It is to provide a method of manufacturing with.

[0005]

According to a first aspect of the present invention, there is provided a method for producing an aggregate, which comprises mixing a siliceous raw material, a calcareous raw material and water to form a slurry. First step, second step for storing the prepared slurry, 3
The cake that is hardening at 0 to 1500 Pascal second (Pa · s) is extruded with a piston type or screw type,
It has a third step of granulating and a fourth step of high-pressure steam curing of the granulated material.

According to a second aspect of the present invention, there is provided a method for producing an aggregate, comprising kneading a siliceous raw material, a calcareous raw material, and water, and then adding a foaming agent such as metallic aluminum powder or air or the like. Water in which bubbles are dispersed is added and mixed further to form a first step of preparing a slurry, a second step of storing the prepared slurry, and 30 to 1500 while holding bubbles.
There is a third step of extruding the cake hardening to Pa · s by a piston type or a screw type to granulate, and a fourth step of curing the granulated material with high pressure steam.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A slurry is prepared by kneading siliceous raw materials such as silica stone and calcareous raw materials such as quicklime, slaked lime and cement, and, if necessary, gypsum. At this time, the use of siliceous industrial waste such as coal ash, sewage sludge, construction sludge, or a processed material obtained by appropriately treating them, or calcareous industrial waste as the siliceous raw material or calcareous raw material reduces the production cost of aggregate. This is advantageous not only for further reduction, but also for industrial waste disposal because a large demand for aggregate can be expected.

[0008] Coal ash is generated from a coal-fired power plant or a coal-fired boiler, and is not particularly limited. Examples of coal ash include fly ash, coarse powder, and clinker ash that conform to JISA6201.

The calcareous material is used to develop strength by a pozzolanic reaction with silica or alumina, which is a main component of the siliceous material, and examples thereof include quick lime, slaked lime, and cement. Although the cement is not particularly limited, for example, normal Portland cement, fast-strength Portland cement, ultra-high-strength Portland cement, moderately heated Portland cement, sulfate-resistant Portland cement, white cement, ultra-fast cement, alumina cement specified in JIS standards , Silica cement, blast furnace cement, fly ash cement and the like.

The amount of the calcareous raw material is from 1 to 50% by weight in terms of calcium oxide (hereinafter, the weight% indicating the composition is simply referred to as "%") from the viewpoint of improving the strength of the aggregate and the utilization rate of the siliceous raw material. ), Preferably from 1 to 40%.

The amount of water used for kneading is 4 to the total solid weight.
It is preferably set to 0 to 80%. If it is less than 40%, the viscosity of the slurry is so high that it cannot be discharged from the mixer in a short time.
On the other hand, if it exceeds 80%, it takes a long time to cure the raw cake, and the aggregate strength is reduced.

The kneading method is not particularly limited, and a known kneading apparatus can be used. It is preferable to stir with warm water of about 40 to 90 ° C. in order to promote kneading.
At this time, a foaming agent such as a metal aluminum powder to be foamed and expanded, or a surfactant and water containing air bubbles and the like mixed therein are added to the slurry so that bubbles are retained in the slurry so that the aggregate has a desired specific gravity. Add. When the desired specific gravity is 1.0, the amount of the metal aluminum powder to be added to the slurry is about 0.02% with respect to the solid content of the raw material. In the case of No. 5, it is also about 0.06%. In addition, desired specific gravity 1.5 to
1.3 is controlled by the ratio of water to raw material solids. Examples of the surfactant include a fatty acid salt, a glycerin fatty acid ester, an alkylbenzene sulfonate, a polyoxyethylene, an alkyl ether, and a sulfate.
By preparing a slurry in this manner, a desired specific gravity, particularly a low aggregate, can be used over a wide range, for example, 0.5 to 1.5.
Can be manufactured over a range of

The slurry is cured until it has a viscosity necessary for extrusion in the next step (the required time is, for example, 1 to 3).
(About an hour) to store the slurry.

When the calcareous raw material hydrates or reacts with the siliceous raw material to form calcium silicate hydrate, the slurry is hardened (the slurry after the hardening starts is referred to as “cake”). Therefore, it is preferable to keep or warm the stored cake so that no temperature difference occurs between the inside and the outside of the stored cake.

[0015] As the extrusion proceeds, the stored cake moves downward while being hardened while being hardened by compaction or kneading as much as possible.

The viscosity of the cake to be extruded is 30 ~ 1500P
a · s. If the viscosity of the cake is less than 30 Pa · s,
During extrusion, air bubbles cannot be retained inside (exfoliation) and the specific gravity cannot be reduced, or the extruded cake cannot maintain its shape (can not be granulated). On the other hand, 150
If it exceeds 0 Pa · s, the extrusion resistance becomes excessive and it becomes difficult to extrude, or the cake itself is compacted and the air bubbles held in the cake are crushed, so that the specific gravity cannot be reduced.

In order to minimize the shearing force applied to the whole cake, a piston type or screw type 1 MPa / cm ²
Extrude with the following extrusion stress. This is because a cake that retains air bubbles and has fluidity has a strong thixotropic property, and its viscosity is extremely reduced when subjected to shearing force. At the time of extrusion, in order to reduce the extrusion resistance, a vibration having a frequency of 50 to 300 Hz and an amplitude of 0.2 to 2 mm is applied to the cake from the dice by using a vibration device (for example, manufactured by Daito Vibration Engineering Co., Ltd.). It is preferred to partially reduce the viscosity. A metal wire mesh may be used for the dice.

FIG. 1 is a partially cutaway front view showing the outline of a screw type casting / extruding tank used for carrying out the method of the present invention. The casting / extrusion tank 10 includes a storage unit 11.
And the extruding part 12, and the tank side wall 13 can be heated in order to keep or warm the stored cake and the extruded cake. The storage unit 11 stores the slurry cast at regular time intervals. The extruding part 12 has one screw drive shaft 12a, a screw blade 12b, and a die 12c. The screw blade 12b is rotated by the rotation of the screw drive shaft 12a, and an extruding force is applied to the cake. Then, a plastic cake cured to a desired viscosity while holding a desired amount of bubbles is extruded from the die 12c.

The extruded cake is cut by its own weight or, when vibration is applied to the dice, by its own weight and vibration.
Granulated.

In the screw type, the length of the screw blade is preferably about 1 to 3 turns of the screw drive shaft. If it is less than one revolution, the extrusion ability is insufficient, while if it exceeds three revolutions, kneading of the cake proceeds, and the viscosity of the cake increases (in some cases, the cake is clogged in the screw blade). In addition, in a general screw type in which the length of the screw blade is not suppressed to 1 to 3 turns, the frictional resistance between the container side wall and the cake is extremely reduced, so that the cake remains clogged in the screw blade. It is no longer conveyed and cannot be extruded. The clogging in the screw blade can be easily eliminated by using two screw drive shafts. When extruding with two screw drive shafts, these drive shafts may be rotated in the same direction or in different directions, but the rotation in different directions is preferred because the degree of kneading is small.

The extrusion direction is preferably vertically downward because the weight of the cake used for cutting and granulating the extruded cake works most effectively.

The extruded cake is preferably kept warm or heated so that there is no temperature difference between the inside and the outside of the extruded cake.

The equipment used in the method of the present invention may be simple as described above, and is greatly simplified as compared with the conventional low-specific-gravity aggregate manufacturing equipment that performs mold casting, demolding and cutting. For example, the casting / extruding tank having a diameter of about 3 m and a height of about 5 m, and a vibration device and a particle spraying device (described later) provided as necessary may be used. No formwork or cake cutting equipment is required. On the other hand, the conventional equipment described above is, for example, 10
6 mx 1.5 mx to produce aggregate at m ³ / h
About 8 to 10 0.6 m molds are required, and a cake cutting device and a moving device for moving the demolded cake to the cake cutting device are also required.

The extruded granules, which have a large amount of moisture on the surface and tend to adhere to each other, are sprayed on the granules, sprayed with high-temperature drying air, or used in combination. Thus, it is preferable to prevent the granules from adhering to each other. The raw material and composition of the dry powder may be the same as that of the slurry, but a material having a higher strength as extruded by high-pressure steam curing (for example, coal ash or cement powder) may be used. A material capable of further increasing the strength or imparting other desired functions may be coated on the granules coated with the dry powder.

A specific method of dusting the dried powder is, for example, by moving a conveyor belt on which the dried powder is spread to a layer thickness of about 1 to 3 times the grain size under a die, and extruding the extruded granules. Drop and immerse in the powder layer. If the dry powder layer is too thin, the dry powder cannot be sufficiently dusted on the granules, while if too thick, the dusting effect does not increase. Also,
The granulated material may be dropped on the thinly laid dry powder, and the dried powder may be sprinkled thereon, or the dried powder dispersed in an air stream may be sprayed on the granulated material.

Since the surface of the as-extruded granules is concentrated in water, the dried powder that has been dusted is less likely to be separated from the granules, and the dusting effect can be reliably obtained.

[0027] Since the dried powder that has been dusted is accompanied by the dry powder that has not been dusted, the accompanying dry powder is separated from the dusted granulated material. The separated accompanying dry powder is used as a raw material for preparing a slurry or reused as a dry powder for spraying.

If the size of the granulated product is larger than the desired size, the granulated product is crushed by a crusher or the like to adjust the size to a desired size. Make a square. This rolling is also useful for improving the strength of the granulated material by performing densification of the dry powder that is bulkyly covered with low-density particles including bubbles.

The granules are subjected to high-pressure steam curing. Curing methods include wet curing, normal-pressure steam curing and high-pressure steam curing.In the method of the present invention, high-pressure steam curing is used alone, or normal-pressure steam curing and high-pressure steam curing are combined. It is preferably used. Atmospheric steam curing alone requires long-term curing until strength is developed, and is poor in productivity. The conditions of the high-pressure steam curing performed in the autoclave are 110 ° C. to 250 ° C. for 1 hour or more, preferably 3 hours or more from the viewpoint of productivity and aggregate strength. By this curing, the specific gravity of the produced aggregate can be arbitrarily controlled over a wide range, for example, in the range of 0.5 to 1.5.

[0030]

The present invention will be further described below with reference to examples and comparative examples.

Example 1 80% of coal ash, 5% of calcium oxide, 15% of ordinary Portland cement and 50% of water based on the total solid content were mixed with a mixer to prepare a slurry. The main components of the coal ash are as follows. That is, SiO ₂ : 59.
3%, Al ₂ O ₃ : 31.6%, Fe ₂ O ₃ : 2.9%, C
aO: 0.9%, MgO: 0.5 %, Na 2 O: 0.2
%, K ₂ O: 0.3%. The water temperature is 60 ° C
And

Approximately 10 liters of the prepared slurry was cast into the casting and extrusion tank shown in FIG. At this time, a lid was placed on the lower part of the die so that the slurry was not discharged. In addition,
The dimensions relating to the casting extruder are as follows. That is, the inner diameter of the tank: 205 mm, the height of the tank: 500 mm, the opening of the die (manufactured by Ebara Kiko Co., Ltd.): 10 mm □, the thickness of the die (extrusion direction): 25 mm, the diameter of the screw blade (manufactured by Ebara Kiko Co., Ltd.): 200 mm, screw blade pitch: 40 mm, screw blade length: two rotations of the screw drive shaft.

About 1 hour after casting, the cake viscosity becomes 30
When Pa · s was reached, the lid at the bottom of the die was removed, and the screw blade was rotated to extrude the cake. The cake viscosity was measured with a cylindrical rotary viscometer.

A stainless steel pad was prepared in advance under a die by mixing a dry powder having the same composition as the solid content at the time of preparing the slurry and laying the mixture with a layer thickness of about 20 mm. Then, while moving the stainless steel pad, the granulated material extruded from the die and cut was received on the dry powder layer on the stainless steel pad. The granulated material coated with the dry powder was sieved with a sieve having a mesh size of 5 mm and collected on the sieve.

The granules on the sieve were compacted with a dry powder on the surface while being rolled by a pan pelletizer to smooth the surface.

The granulated material having a smooth surface was treated at a temperature of 5
After pre-curing for 3 hours in a constant temperature and humidity of 0 ° C. and a relative humidity of 95%, the mixture was put into an autoclave and subjected to high-pressure steam curing at 185 ° C. for 8 hours.

In order to evaluate the produced aggregate, the bulk specific gravity and the crushing strength were measured. The bulk specific gravity is JIS A1
135 was measured. The crushing strength is about 10m
The particle size and the uniaxial compression fracture load of 15 sample aggregates having a diameter of m were measured, and a regression equation of the strength with respect to the particle size was obtained.
The strength of the aggregate having a diameter of 10 mm was calculated using the regression equation. Table 1 shows the evaluation results.

[Example 2] When the cake viscosity became 550 Pa · s about 2 hours after casting, the lid at the bottom of the die was removed and the screw blade was rotated to extrude the cake. Tested similarly. Table 1 shows the evaluation results.

Example 3 When the cake viscosity reached 1500 Pa · s about 3 hours after casting, the lid at the bottom of the die was removed and the screw blade was rotated to extrude the cake. Tested similarly. Table 1 shows the evaluation results.

Example 4 In the same manner as in Example 1, a slurry was prepared using a mixer. Next, 0.02% of metallic aluminum powder based on the blended raw material solids was added to the slurry and mixed and stirred. The slurry to which the metal aluminum powder was added was cast into the casting and extrusion tank of Example 1. The test was performed in the same manner as in Example 2 after extruding the cake by rotating the screw blade. Table 1 shows the evaluation results.

Example 5 A test was conducted in the same manner as in Example 4 except that the amount of the metal aluminum powder was changed to 0.04% based on the solid content of the raw material. Table 1 shows the evaluation results.

Example 6 A test was conducted in the same manner as in Example 4 except that the amount of the metal aluminum powder was changed to 0.06% based on the solid content of the raw material. Table 1 shows the evaluation results.

Comparative Example 1 A slurry was prepared and cast in the same manner as in Example 1. About 30 minutes after the casting, when the viscosity of the cake became 20 Pa · s, the lid at the lower part of the die was removed, and the screw blade was rotated to extrude the cake. However, the extruded cake was deformed when dropped into the dry powder, and could not be granulated.

Comparative Example 2 In the same manner as in Example 1, a slurry was prepared using a mixer. Next, 0.02% of metallic aluminum powder based on the blended raw material solids was added to the slurry and mixed and stirred. The slurry to which the metal aluminum powder was added was cast into the casting and extrusion tank of Example 1. About 3.5 hours after casting, the cake viscosity is 20
At the time of 00Pa · s, remove the lid at the bottom of the die,
The cake was extruded by rotating the screw blades. However, the cake was not able to be extruded due to advanced curing.

[0045]

[Table 1]

As can be seen from Table 1, in Examples 1 to 6, the bulk specific gravity was 0.52 to 1.50 and the crushing strength was 5 to 68 kgf.
Aggregates are manufactured.

[0047]

According to the method of the present invention, the specific gravity is controlled to be wide, particularly extremely low (the bulk specific gravity is, for example, 0.5 to 1.0).
5) Aggregates having a crushing strength of, for example, 5 to 70 kgf can be efficiently manufactured with greatly simplified facilities and operations, that is, at low cost. Further cost reduction can be realized by using siliceous industrial waste and calcareous industrial waste such as coal ash, sewage sludge and construction sludge generated in large quantities as siliceous raw materials and calcareous raw materials. Therefore, the method of the present invention greatly contributes to the civil engineering / construction industry and the industrial waste treatment industry.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing an outline of a screw type casting / extruding tank used for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Casting extrusion tank 11 Storage part 12 Extrusion part 12a Screw drive shaft 12b Screw blade 12c Dice 13 Tank side wall

Claims (9)

[Claims] 1. A first step of preparing a slurry by kneading a siliceous raw material, a calcareous raw material, and water, a second step of storing the prepared slurry, and a step of setting a cake hardening to 30 to 1500 Pa · s by a piston. A method for producing an artificial lightweight aggregate having a third step of extruding and granulating by extrusion or a screw method and a fourth step of subjecting the granulated material to high-pressure steam curing. 2. A first step of preparing a slurry by kneading a siliceous raw material, a calcareous raw material, and water, then adding a foaming agent or adding water in which bubbles are dispersed, and further mixing. 2nd step of storing the slurry obtained, extruding the cake which is hardening to 30 to 1500 Pa · s by a piston type or screw type while holding air bubbles, and granulating it, and high pressure steam curing of the granulated material A method for producing an artificial lightweight aggregate having a fourth step. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein the siliceous raw material is siliceous industrial waste. 4. The method for producing an artificial lightweight aggregate according to claim 1, wherein the calcareous raw material is calcareous industrial waste. 5. The method for producing an artificial lightweight aggregate according to claim 2, wherein the foaming agent is metal aluminum powder. 6. The method according to claim 1, wherein the extrusion is performed in a vertically downward direction.
2. The method for producing an artificial lightweight aggregate according to item 1. 7. The screw type according to claim 1, wherein the length of the screw blade is one to three turns of the screw drive shaft.
2. The method for producing an artificial lightweight aggregate according to item 1. 8. The method for producing an artificial lightweight aggregate according to claim 1, wherein the die is extruded while being vibrated. 9. The method for producing an artificial lightweight aggregate according to claim 1, wherein the granulated material is dried by spraying with a dry powder or blowing high-temperature drying air before curing the granulated material with high-pressure steam.