JP2005075699A - Manufacturing method for high performance lightweight aggregate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high performance lightweight aggregate by using coal ash and industrial waste glass, or the like. <P>SOLUTION: In the manufacturing method for the high performance lightweight aggregate, the industrial waste glass or further volcanic glass powder are added to coal ash fine powder having ≤ 10 μm diameter, then SiC powder is added to the mixture in the range of 0.05-1.0%, the mixture is retained at 600-800°C for 0.5-5 h when it is heated, and the mixture is burned at 1,150-1,250°C. The coal ash after previously removing carbon by using a fluidized bed kiln can also be used as a raw material. Alternatively, the carbon also can be removed from the coal ash by a centrifugal separator, or the like. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lightweight aggregate for concrete. In particular, the present invention relates to a low-water-absorbing, ultra-light, high-strength, high-performance lightweight aggregate composed of closed cells.

Due to the decrease in petroleum resources, dependence on coal-fired power generation tends to increase globally. On the other hand, nuclear power generation has a social anxiety due to a series of management mistakes in safety measures, making it difficult to construct a new nuclear power plant. And the processing and reuse of the coal ash discharged | emitted with coal combustion in the midst of the demand for coal energy has become a big problem. As its utilization method, the method of mixing in cement and concrete is the most effective, but the consumption is limited and a new application is being studied. However, the amount used by new applications is still not sufficient. Among them, various uses as a raw material for lightweight aggregates have been studied.
In other words, high-performance lightweight concrete is effective for construction and civil engineering structures, but from the lessons learned from the Great Hanshin Earthquake, we were able to experience the need for lighter superstructure. No matter how strong the whole structure is, it is inevitable to reduce the weight of the superstructure. In particular, in Japanese society and many developing countries, which are extremely concentrated in urban areas, there is a fear that disasters will become larger due to population concentration in cities. Buildings are layered up and up, and the viaduct is only complex with two or three layers. What is necessary for the safety of these structures is high strength and light weight of the superstructure. Then, aiming at such a thing, in patent documents 1-10 etc., various proposals which use coal ash effectively as artificial lightweight aggregate are made.

In addition, some industrial waste glass is restricted in reuse due to the high cost of sorting due to the variety of coloring, and its recycling is incomplete. And there is no example which was successful enough as an artificial lightweight aggregate by combining industrial waste glass with coal ash.
JP 2000-313679 A JP 2000-26142 A JP 11-314977 A Japanese Patent Laid-Open No. 11-180753 Japanese Patent Laid-Open No. 11-180752 JP-A-10-87357 Japanese Patent Laid-Open No. 9-309752 JP-A-9-278502 Japanese Patent Laid-Open No. 9-25146 Japanese Patent Laid-Open No. 7-41343

1) A conventional lightweight aggregate using coal ash has a problem in that carbon contained in the raw material is used as a foaming source. There is also a problem in trying to foam with SiC that requires an oxidizing atmosphere without considering the reducing atmosphere with carbon.
Specifically, in the conventional method, carbon remains until the coal ash melts, and in the structure closed after melting, oxygen from the air remaining in the voids, or dissolved oxygen contained in the glass layer reacts with the carbon. Although CO ₂ gas is used for foaming, the amount of carbon contained in coal ash is much larger than that used for foaming. Therefore, excessive carbon works as a reducing agent in the structure closed by melting, and Fe ₂ O ₃ in the glass phase is reduced to FeO. FeO drastically lowers its viscosity in the glass phase, and before it can be temperature controlled, it becomes softer than necessary and the bubble film breaks, concentrating on the core of the grain where the oxygen supply is farthest away. , And further develops coarse bubbles in the center.

  Furthermore, the cracked gas such as clay minerals of foaming sources contained in these carbon and shale is generated as foaming gas before the glass phase is formed during heating, and all gas passages are closed. As long as the molten glass does not block the passage, it remains as continuous pores. And the mineral part with high fire resistance is not vitrified, but remains only in the stage of unglazed or sintered. Therefore, it is difficult to find a balanced raw material in which the generation of such a glass phase and the end of gas generation due to thermal decomposition occur simultaneously.

  2) Patent literature and our experiments confirm that there is a method in which SiC powder is added to coal ash as a blowing agent, and the remaining carbon is oxidized and burned up to the melting temperature so that it does not remain in the molten phase. Yes. However, this is a gentle temperature rise curve, and the actual rotary kiln cannot actually eliminate the black core phenomenon. In the vicinity of the burner, the temperature of the material to be heated has risen suddenly due to the direct fire of the burner or sudden radiant heat, and there is a large temperature difference between the surface and the inside. This makes the foaming more difficult.

3) Also, coal ash has a high melting point, and high melting point may reach 1400 ° C. For this reason, a very high temperature is required for the production of the glass phase necessary for SiC foaming, and it is disadvantageous in terms of thermal efficiency to apply the conventional method as it is with coal ash.
In the present invention, industrial waste glass or the like is effectively utilized to promote the vitrification of coal ash, and the finely pulverized raw material forms a uniform glass phase, which is foamed using SiC. It is intended to provide high-performance lightweight aggregate.

The present invention has the following configuration in order to solve the above-described problems.
(1) The manufacturing method of the high-performance lightweight aggregate which concerns on this invention makes the coal ash which removes the carbon content which is contained beforehand into a fine powder of 10 micrometers or less, and this is both industrial waste glass powder and volcanic glass powder. A thickener is added, SiC powder is added in the range of 0.05 to 1.0% by weight, granulated, and then fired at 1150 to 1320 ° C.
(2) In the method for producing a high-performance lightweight aggregate according to the present invention, when removing carbon contained in coal ash, coal ash is retained at 600 to 800 ° C. for 0.5 to 5 hours and then fired. (1), characterized by the above.
(3) The method for producing a high-performance lightweight aggregate according to the present invention uses a material obtained by removing unburned carbon from coal ash using a fluidized bed kiln as a raw material. It is.
(4) The method for producing a high-performance lightweight aggregate according to the present invention uses a raw material obtained by removing unburned carbon in coal ash with a centrifuge. It is.
(5) The method for producing a high-performance lightweight aggregate according to the present invention comprises adding industrial waste glass powder and SiC to coal ash, granulating them into fine particles having a diameter of 50 μm to 1000 μm, and firing them using a fluidized bed kiln. It is what is described in the above item (1).
Since the high-performance lightweight aggregate produced by this production method is fine, oxygen in the air is sufficiently supplied to the inside of the object to be heated, and a fine foam can be obtained without causing a black core phenomenon. When industrial waste glass powder and SiC are added to coal ash and the diameter is less than 50 μm, overfire may occur, and when it exceeds 1000 μm, the black core phenomenon cannot be sufficiently suppressed. From the viewpoint of granulation of fine particles, 500 μm to 1000 μm is particularly preferable.

That is, in the present invention, the coal ash as a raw material is pulverized into a fine powder of 10 μm or less, and after removing the carbon content, a thickener is added to the industrial waste glass powder and / or volcanic glass powder. It is basically granulated and fired. Since industrial waste glass powder has uneven collection and has a problem in stable supply, volcanic glass powder such as shirasu, anti-fluorite, obsidian, nacre, rhyolite, etc. is appropriately added and adjusted. Moreover, the shape retention property at the time of baking is maintained by adding suitably thickeners, such as bentonite. The amount of SiC used is preferably in the range of 0.05 to 1.0%. If it is less than 0.05%, foaming is not sufficient, and if it exceeds 1.0%, open bubbles are likely to occur, which is not preferable.
SiC is well known as a high-temperature refractory and does not decompose up to 1400 ° C. alone. However, in the present invention, when a glass phase is generated during firing, it reacts with wetting to generate a decomposition gas and cause a foaming phenomenon. . If it sees from a SiC refractory, it will be eroded by molten glass.

Also, during firing, the carbon content in the coal ash is completely removed by allowing it to stay in the furnace at 600 to 800 ° C. for 0.5 to 5.0 hours at the time of heating and heating, and the vitreous material melts and foams. When starting, there is no residual carbon and no coarse bubbles are generated. If the calcination is less than 0.5 hour, carbon may remain in the coal ash, and if it exceeds 5 hours, a black core phenomenon may occur, which is not preferable.
At the time of firing, the foaming effect is mainly due to the amount of SiC used, and the foaming can be easily adjusted. The amount of SiC used is preferably in the range of 0.05 to 1.0%. If it is less than 0.05%, foaming is not sufficient, and if it exceeds 1.0%, open bubbles are likely to occur, which is not preferable.
Since coal ash is already exposed to high temperatures and has no self-foaming minerals other than unburned carbon, if residual carbon is removed by oxidation, foaming occurs only with the added SiC, so it is easy to Control becomes possible. Therefore, before the raw material is finely pulverized, the carbon is removed by firing at 600 ° C. to 800 ° C. in a fluidized bed kiln. In the fluidized bed kiln, the fine coal ash powder has many contact opportunities with the combustion gas, and the carbon can be reliably removed by adjusting the residence time. Thereafter, it is cooled and pulverized to 10 μm or less, industrial waste glass or further volcanic glass powder and a thickener are added, and SiC powder is added in the range of 0.05 to 1.0%, and granulated. The granulated product is fired in a normal rotary kiln.

In the resulting coarse aggregate, the performance of the product depends on the fine pulverization of raw materials and the uniform dispersion of SiC. For this reason, a wet ball mill or tube mill having excellent fine grindability and uniform mixing may be used. In that case, the coal ash becomes a slurry having a water content of about 50%. By applying the slurry to a centrifugal separator, carbon and ash are separated and the carbon is burned to obtain coal ash suitable for SiC foaming. The coal ash from which carbon has been removed is finely pulverized and fired and foamed with the same composition as above.
Another method is to remove unburned carbon from coal ash using a fluidized bed kiln.

Table 1 shows typical examples of chemical components of each raw material used in the present invention.

  The blending ratio of the aggregate particle raw materials is as follows. The amount of volcanic glass is within the total amount of industrial waste glass. That is, a part of 5 to 30 parts of the industrial waste glass is replaced with volcanic glass, or in some cases, is replaced entirely or no volcanic glass is added. That is, industrial waste glass and volcanic glass can each be used alone as vitreous, but the amount of coal ash is relatively large because the purpose of the present invention is its effective utilization. For example, 60 to 90 parts are preferable. Moreover, it is good to add 5-10 parts of thickeners.

  According to the present invention, it is possible to effectively provide a high-performance aggregate that is high in strength and lightweight by using waste materials such as coal ash and industrial waste glass. The resulting product has closed cells and low water absorption. Therefore, it is useful for effective use of resources and weight reduction of a structure constructed using the resources. The present invention is suitable for both the production of coarse aggregates and the production of fine aggregates.

Coal ash having an average particle diameter of 10 μm or less and industrial waste glass shown in Table 1 are mixed at a blending ratio of 9: 1 to 3: 7, and 5 wt% bentonite and 0.2 wt% SiC powder are mixed therein. In addition, 110% of the total amount of water was added, placed in a pot mill, filled with alumina balls, and wet-ground and mixed for 6 hours. In addition, the industrial waste glass powder used the brown bottle for drinks, and the thing which carried out the ball mill dry grinding | pulverization with the steel ball was used.
The pulverized and mixed raw material slurry was poured into a gypsum mold to absorb water appropriately, and half was taken out in a clay state, granulated, made into a sphere having a particle size of about 15 mm, and then naturally dried. The other half was removed from the plaster mold and completely dried at 120 ° C. This was crushed and formed into a particle size of about 15 mm.

  Firing was performed using the firing apparatus illustrated in FIG. Reference numeral 1 denotes a calcining rotary furnace, and the raw materials are charged from 2 and calcined with an upper burner 3. The temperature was in the range of 600 to 800 ° C., and the rotation was adjusted to maintain a residence time of 3 to 5 hours. Thereafter, it is fired and foamed at 1150 to 1320 ° C. by the lower burner 5 in the lower main firing rotary furnace 4. After firing, the product is transferred to a cooling furnace 6 and cooled to obtain a product.

There is also a method shown in FIG. 2 as a method for removing carbon in coal ash. 7 is a fluidized bed, the fluidized bed portion is previously maintained at 600 to 800 ° C., coal ash is charged from above, the bed height is kept at about 300 mm, bubbling is carried out for about 500 seconds, and carbon in the coal ash is burned and removed. Then, it cooled to 300 degreeC, the excess gas was sent, and it collected with the cyclone separator 8. FIG. This cycle was repeated to ensure a predetermined amount.
And the raw material which mix | blended according to said mixing | blending with this as a raw material was finely pulverized to 7 micrometers in the dry-type pot mill, and it granulated to the coarse aggregate size to about 1.5-3 mm with the bread-type pelletizer. . It was held until the moisture content reached 3% with a drier, and baked with a temperature curve of a normal rotary kiln for 45 minutes from the temperature rise to firing. Since the coal ash was previously removed, the coal ash could be fired without causing a black core phenomenon.
The raw material pulverized by the above method was granulated from 1000 μm to 50 μm with a high-speed agitation granulator, fired in a fluidized bed kiln and foamed to obtain a high-performance lightweight fine-grained foam. According to this method, it is possible to effectively use coal ash without removing residual carbon in advance.

  There is also a carbon removal method using a centrifuge. FIG. 3 is a diagram illustrating a separation state of the coal ash slurry after the centrifugal separation when the centrifugal separator is used. The coal ash was easily pulverized to about 30 μm with a wet mill, and the carbon adhering to the coal ash was separated. The slurry was centrifuged in a 450 mm diameter centrifuge. It was rotated for 30 minutes at a rotational speed of 3000 rpm in a plastic cylinder having a diameter of 30 mm and a length of 100 mm. Inside the cylinder, a light gray portion 10 of coal ash accumulates at the bottom, a dark gray layer 11 is several millimeters above it, clear water 12 is above it, and black carbon 13 is slightly above it. It was floating. The light gray portion 10 accumulated in the lower part was used for firing.

<Examples 1-8>
Coal ash, industrial waste glass, volcanic glass, and SiC were blended as shown in Table 2 below, and a thickener (bentonite) was added as a binder, followed by firing at each temperature. The specific gravity, vacuum water absorption rate, and crushing strength of the product are also shown. Furthermore, the same test was conducted on other commercially available products (Comparative Example 1 and Comparative Example 2). In addition, an ultralight shale aggregate was used as Comparative Example 1, and a Chinese expanded clay aggregate was used as Comparative Example 2.

The physical properties were measured as follows.
◎ 24-hour water absorption test After measuring the absolute dry weight of the fired particles, they were placed in a cloth bag with a weight, submerged in water stretched to a depth of 4 to 5 cm, and allowed to absorb water for 24 hours. The surface of the particles taken out was wiped with a cloth, the weight was measured as a dry surface, and the water absorption was determined. The measurement was carried out in three states: the state as it was after firing, the state where the particles were broken at the center to expose the foamed surface, and the state where the surface layer was peeled off using a ball mill.

◎ Measurement of vacuum water absorption rate After measuring the absolute dry weight of the fired particles, they were placed in a cloth bag with a weight and placed on the bottom of the vacuum vessel. The interior was evacuated using a vacuum pump (maximum 50 Torr), held for 30 minutes, water was added from the top to a depth of about 20 cm, and water was absorbed for 2 hours while maintaining the internal pressure in a vacuum. After returning the inside of the apparatus to atmospheric pressure, the particles were taken out, and the surface of the particles was wiped with a wet cloth to make the surface dry, and then the weight was measured to determine the water absorption rate.

Specific gravity After measuring the absolute dry weight of the fired particles, the specific gravity was measured using a specific gravity bottle. The measurement was performed for the entire particles under each firing condition, and for the spherical particles (non-destructive), the specific gravity of one particle was measured.
◎ Measurement of crushing load Pressure was applied from the top to one calcined particle that had been completely dried to destroy the particle. Crushing was stopped when the particles broke and the peak value of the pressure applied to the particles was taken as the crushing load (kg). The particle size of the particles was measured before breaking. Moreover, the cross-section was observed after the fracture to confirm the presence of embraced bubbles and the like.

  4 and 5 are graphs showing the relationship between vacuum water absorption and specific gravity. It can be seen that the aggregates of the examples of the present invention do not become large even with the vacuum water absorption rate and are closed cells. 6 and 7 are graphs showing the relationship between compressive strength and specific gravity. Although the compressive strength increases when increasing to 20% or 30% rather than adding 10% industrial waste glass, volcanic glass has the same effect. Therefore, even if it is difficult to procure industrial waste glass, it can be supplemented with volcanic glass such as shirasu, so the procurement of raw materials is stable.

<Examples 9 to 13>
Next, coal ash, industrial waste glass, volcanic glass (anti-fluorite), and SiC were blended as shown in Table 3 below (SiC is an outer shell), a thickener (bentonite) was added as a binder, and fired at each temperature. The specific gravity, vacuum water absorption rate, and crushing strength of the product are also shown.

In addition, the measurement of the physical property was performed similarly to the said Examples 1-8.
As a result, the relationship between the vacuum water absorption rate and the specific gravity of the lightweight aggregates in Examples 9 to 14 is graphed in FIGS. It can be seen that the aggregates of Examples 9 to 14 of the present invention are closed cells without increasing the vacuum water absorption rate. Further, FIG. 10 is a graph showing the relationship between the compressive strength and the specific gravity of the aggregates of Examples 9-11. Although the compression strength increases when 20% and 30% are increased compared to 10% of industrial waste glass, volcanic glass has the same effect. Therefore, even when it is difficult to procure industrial waste glass, it can be supplemented with volcanic glass such as shirasu, so the procurement of raw materials is stable.

Observation of Foamed Cross Section FIG. 11 shows a photograph of the fracture surface of the aggregate according to the present invention taken with a scanning electron microscope. A photograph of a commercial product is also shown. FIG. 11 (a) is a fracture surface of Example 5, (b) is Example 10, (c) is an expanded clay aggregate made in China, and (d) is a shale lightweight aggregate.
As is clear from FIG. 11A, a true bubble shape independent of the uniform matrix portion can be visually recognized on the fracture surface of Example 5, and from FIG. Is visible. On the other hand, the fracture surfaces of (c) and (d) are made of gas generated by thermal decomposition of clay minerals and the like, and the shape and quantity of bubbles cannot be artificially controlled, so there are no open bubbles or irregular pores. I understand that.

It is explanatory drawing of an example of the apparatus suitable for implementing this invention. It is explanatory drawing which removes the carbon in coal ash using a cyclone separator. It is a figure which shows the isolation | separation state of the coal ash slurry after the centrifugation in the case of utilizing a centrifuge. It is a graph which shows the specific gravity of the lightweight aggregate in Examples 1-5, and the change of a vacuum water absorption. It is a graph which shows the change of the specific gravity and vacuum water absorption of the lightweight aggregate in Examples 6-8. It is a graph which shows the specific gravity of the lightweight aggregate in Examples 1-5, and the change of a crushing load. It is a graph which shows the specific gravity of the lightweight aggregate in Examples 6-8, and the change of a crushing load. It is a graph which shows the change of the specific gravity and vacuum water absorption of the lightweight aggregate in Examples 9-11. It is a graph which shows the change of the specific gravity and vacuum water absorption of the lightweight aggregate in Examples 12-14. It is a graph which shows the specific gravity of the lightweight aggregate in Examples 9-11, and the change of a crushing load. It is the photograph which image | photographed the fracture surface of the aggregate with the scanning electron microscope. (A) is a photograph of Example 5, (b) is Example 10, (c) is a photograph of a fracture surface of an expanded clay aggregate made in China, and (d) is a fracture surface of a shale lightweight aggregate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Calcining rotary furnace 2 Material inlet 3 Burner 4 Main baking furnace 5 Burner 6 Cooling zone 7 Fluidized bed 8 Cyclone separator

Claims (5)

Coal ash that removes carbon in advance is made into a fine powder of 10 μm or less, and industrial waste glass powder and / or volcanic glass powder are added thereto, and SiC powder is added to 0.05 to 1.0% by weight to this. A method for producing a high-performance lightweight aggregate, characterized by adding and granulating in the range of 1 to 1320 ° C. 2. The method for producing a high-performance lightweight aggregate according to claim 1, wherein when removing carbon contained in the coal ash, the coal ash is retained at 600 to 800 ° C. for 0.5 to 5 hours and then fired. . 2. The method for producing a high-performance lightweight aggregate according to claim 1, wherein a material obtained by removing unburned carbon from coal ash using a fluidized bed kiln is used as a raw material. 2. The method for producing a high-performance lightweight aggregate according to claim 1, wherein unburned carbon in coal ash is removed by a centrifugal separator as a raw material. The high-performance lightweight aggregate according to claim 1, characterized in that industrial waste glass powder and SiC are added to coal ash, granulated into fine particles having a diameter of 50 µm to 1000 µm, and fired and foamed using a fluidized bed kiln. Production method.

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