JP2000109351A - Production of artificial lightweight aggregate and artificial lightweight aggregate obtained by same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce an uncalcined artificial lightweight aggregate having high strength, high quality and low water absorption at a low cost by adding easily available low-cost additives. SOLUTION: A mixture obtained by mixing coal ash, cement and calcium sulfate is pulverized and the pulverized mixture is slurried by adding water in a water to solid ratio equivalent to 50-100 wt.%. The resultant slurry is cast in a mold and semi-hardened, the semi-hardened body is shaped and cured with high-pressure steam and the surface of the resultant aggregate is coated with paraffin. At least one of calcium oxide and calcium hydroxide may further be added to the mixture and a blowing agent may further be added to the pulverized mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial lightweight aggregate, and more particularly, to recycling coal ash generated from a coal-fired power plant or a coal-fired boiler as an artificial lightweight aggregate for civil engineering and construction. TECHNICAL FIELD The present invention relates to a method for producing an artificial lightweight aggregate for effective use by making it into an artificial lightweight aggregate, and an artificial lightweight aggregate obtained by the method.

[0002]

2. Description of the Related Art Coal has abundant resources and lower price per unit calorific value than petroleum. Therefore, domestic energy policy has planned or implemented a significant increase in the use of coal, especially as fuel for power generation. It is getting. As a result, coal ash generated from coal-fired power plants and coal-fired boilers
It increases almost in proportion to the amount of coal used. Therefore, the effective use of coal ash, which is rapidly increasing, is a major issue.

In order to effectively utilize a large amount of coal ash, utilization as an artificial lightweight aggregate is suitable because of its large demand.

[0004] However, although coal ash is partially aggregated by the sinter great method, its utilization as an artificial lightweight aggregate is extremely small in Japan at present. The cause is that coal-fired power plants and coal-fired boilers use coal that generates high melting point ash in order to reduce the adhesion of ash to boiler water pipes and boiler walls. is there.

That is, coal ash generated from a coal-fired power plant or a coal-fired boiler generally has a high melting point. Therefore, in order to produce a lightweight aggregate, a large amount of low-melting clay or shale is mixed and fired. There must be. However, it is difficult to secure a large amount of these clays and shale, and it takes a lot of money to mine, transport, pre-process and mix these clays and shale. And the low utilization rate of coal ash per unit product is not preferable for effective utilization of coal ash.Furthermore, the conventional artificial lightweight aggregate thus obtained has a low water absorption rate. However, coal ash has not been effectively reused as an artificial lightweight aggregate because of its high cost and various difficulties in using it as an aggregate.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can be easily and inexpensively manufactured. An object of the present invention is to provide a method for producing a non-fired artificial lightweight aggregate having high strength, high quality and low water absorption, and an artificial lightweight aggregate obtained by this method.

[0007]

Means for Solving the Problems The present inventors have increased the utilization rate of coal ash per unit product to increase its effective utilization rate, and produced inexpensive high-strength, low water absorption artificial lightweight aggregates. As a result of intensive studies on the method, a slurry was prepared by adding a predetermined amount of water to a mixed and crushed product of coal ash, cement, calcium sulfate, and, if necessary, calcium oxide and / or calcium hydroxide. After casting in a mold and semi-curing, molding the resulting semi-cured product to a desired size, applying high-pressure steam curing to an aggregate, and coating the surface of the aggregate with paraffin, The inventors have found that the problems can be solved, and have completed the present invention.

[0008] That is, in order to achieve the above object, in a first embodiment of the present invention, a mixture obtained by mixing coal ash, cement, and calcium sulfate is pulverized, and water / solid After adding a water having a ratio of 50 to 100% by weight to obtain a slurry, the mixture is cast into a mold and semi-cured.
The obtained semi-cured product is molded and then subjected to high-pressure steam curing, and then the surface of the obtained aggregate is coated with paraffin, and the mixture is further treated with calcium oxide and / or calcium hydroxide. At least one selected material is added, and a foaming agent is further added to the pulverized product. The amounts of the cement and calcium sulfate added are 10 to 50% by weight, 0.5 to 50% by weight, respectively. 10% by weight (in terms of CaSO ₄ ), the amount of the calcium oxide and / or calcium hydroxide added is 1 to 50% by weight in terms of CaO, and the mixture has an average particle size of 15 μm or less, preferably 10 μm. The present invention is characterized by a method for producing an artificial lightweight aggregate that is ground as follows.

[0009] A second embodiment of the present invention is the above-mentioned first embodiment.
And an artificial lightweight aggregate having a bulk specific gravity of less than 1.5 and a water absorption of 10% or less obtained by the production method according to the embodiment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be more specifically described below. In the present invention, coal ash, cement, calcium sulfate, and, if necessary, calcium oxide and / or calcium hydroxide are mixed and pulverized, and a desired amount of water is added to the pulverized material to form a slurry. After that, the semi-cured material is cast into a mold and semi-cured. The semi-cured product is molded and subjected to a predetermined high-pressure steam curing to form an aggregate, and the surface of the aggregate is coated with paraffin to reduce the cost and artificial weight. Aggregate can be manufactured.

The coal ash used in the present invention is not particularly limited, and includes, for example, raw powder which is a mixture of fly ash and synda ash, fly ash conforming to JIS A6201, coarse powder, and clinker ash. Coal ash can be used. The particle size of the coal ash is not particularly limited.

The cement used in the present invention is not particularly limited. For example, ordinary Portland cement, fast-strength Portland cement, very fast-strength Portland cement, medium-strength Portland cement, sulfate-resistant Portland cement, white Examples include cement, super-hard cement, alumina cement, silica cement, blast furnace cement, fly ash cement and the like.

The calcium sulfate is not particularly limited, and examples thereof include gypsum dihydrate, gypsum hemihydrate, and flue gas desulfurization gypsum. Next, a calcium source added as necessary is used to develop a higher strength by a pozzolanic reaction with silica or alumina, which is a main component in coal ash, so that calcium oxide,
Calcium hydroxide is preferred.

The mixture of coal ash, cement, calcium sulfate, and further, calcium oxide and / or calcium hydroxide is used so that the mixed raw material of the aggregate has an average particle size of 15 μm or less, preferably 10 μm or less. Needs to be finely ground. The pulverization method used at this time may be any method as long as it can be pulverized to a predetermined average particle diameter, and examples thereof include a pot mill, a vibration mill, a ball mill such as a planetary mill, a collision type jet pulverizer, a turbo pulverizer, and the like. . In addition, the above mixture was mixed with an average particle size of 15
The reason for pulverizing to less than μm is that when the average particle size exceeds 15 μm, the crushing strength of the finally obtained aggregate decreases and the water absorption increases, and the crushing strength increases as the average particle size decreases. However, the average particle size is 1
It is difficult to reduce the average particle diameter to 1 μm or less.
Is the lower limit.

The amounts of cement and calcium sulfate, and furthermore, calcium oxide and / or calcium hydroxide in the aggregate formation are 10 to 10 respectively from the viewpoint of improving the strength and water absorption of the artificial lightweight aggregate and improving the utilization of coal ash. It is preferably 50% by weight, 1 to 50% by weight in terms of CaSO ₄ , and 0.5% to 10% by weight in terms of CaO. If the ratio is outside these ranges, the resulting artificial lightweight aggregate will have poor strength and an increased water absorption. In addition, the utilization rate of coal ash cannot be improved.

The mixture of coal ash, cement, calcium sulfate, and further, calcium oxide and / or calcium hydroxide is wet-kneaded with a predetermined amount of water. A kneading device can be used.

The amount of water used for the wet kneading must be 50 to 100% by weight based on the solid content. The reason is that if it is less than 50% by weight, the desired bulk specific gravity cannot be obtained, while if it exceeds 100% by weight, it takes a long time to reach a semi-cured state, and thus the productivity is deteriorated.

During the wet kneading as described above, a foaming agent is further added as required. The foaming agent is preferably aluminum powder, and the addition amount is not particularly limited, but is preferably 0.1% by weight or less based on the solid content. At this time, it is preferable to simultaneously use a foam stabilizer.

The slurry thus prepared is cast into a mold and semi-cured. The temperature condition at this time is preferably 30 to 90 ° C. in consideration of productivity. The mold is not particularly limited.For example, a batch-type box or a mold having a piano wire mesh for subdividing a semi-cured body, and a mold that can be continuously cast and subdivided in a size suitable for the press-off device. Is mentioned. The wire diameter and aperture of the piano wire mesh are not particularly limited either, and may be appropriately selected so as to obtain an aggregate having a desired particle size.

The semi-cured body is cut with a tensioned piano wire or broken with a steel round bar or the like to make the granules fine. The holes are crushed and densified, or further compacted.

Next, curing performed on the semi-cured body obtained as described above will be described. As the curing method, wet curing, steam curing at normal pressure, and steam curing at high pressure are known. In the present invention, a high-pressure steam curing method is used. This is because the use of normal-pressure steam curing alone requires long-term curing until the strength is developed, resulting in poor productivity, and also has a disadvantage in that the strength is inferior to that of aggregates subjected to high-pressure steam curing. This high-pressure steam curing is performed in an autoclave, but the conditions vary depending on the mixing ratio of cement, calcium oxide and / or calcium hydroxide or calcium sulfate. Therefore, it is necessary to determine the conditions in advance according to these ratios. preferable. However, from the viewpoint of productivity and aggregate strength, curing is generally performed at 120 ° C. to 250 ° C. for 1 hour or more, preferably 3 hours or more.

Next, after high-pressure steam curing is performed to form an aggregate, the surface of the obtained aggregate is coated with paraffin. At this time, the amount of paraffin to be added is 2 to 10% by weight, preferably 4 to 10% by weight, based on the aggregate weight.
8% by weight.

[0023]

EXAMPLES Examples of the present invention will be described below along with comparative examples. However, the present invention is not limited to the following examples. The main components of the coal ash used in the following Examples and Comparative Examples of the present invention were SiO ₂ : 56.20% by weight, Al ₂ O
₃ : 32.10% by weight, Fe ₂ O ₃ : 3.57% by weight,
CaO: 0.59% by weight, MgO: 1.40% by weight, N
a ₂ O: 0.22% by weight, K ₂ O: 0.48% by weight.

Example 1 An aggregate-mixed raw material composed of 79% by weight of coal ash, 20% by weight of cement, and 1% by weight of gypsum hemihydrate was mixed and pulverized by a ball mill so that the average particle diameter became 5 μm. . Next, 86.7 g of water was added to 130 g of the pulverized material so that the ratio of water / solid content became 67% by weight, and the mixture was kneaded with a universal mixing stirrer to form a slurry. It was cast and semi-cured at 40 ° C. in a 95% relative humidity atmosphere for 3 hours. After releasing the semi-cured molded product, the aperture is 10 mm and the wire diameter is 0.25 mm.
Cut it into a cube with a diameter of 10 mm while cutting it off with a piano wire mesh of φ, and roll it with a pan pelletizer to about 1
It was processed into a spherical shape of 0 mmφ. This was filled in an autoclave and subjected to high-pressure steam curing at 185 ° C. (steam pressure of 10.5 kg / cm ² ) for 8 hours to form an aggregate. The obtained aggregate was immersed in paraffin wax (Wako Pure Chemical Industries, Ltd., mp51-53 ° C: trade name) dissolved at 70 ° C to coat the surface so that the coating amount was 7% by weight. An artificial lightweight aggregate a (Example 1) was obtained.

In order to evaluate the aggregate a thus obtained, the bulk specific gravity and the water absorption were measured based on JIS A 1110, and the crushing strength was measured by a uniaxial compressive breaking load.
The results are shown in Table 1 below. The crushing strength was measured for each aggregate having a diameter of 10 mm by a crushing tester,
The average was determined.

As can be seen from Table 1, the aggregate a of Example 1 has a bulk specific gravity of 1.48, a water absorption of 7.8% and a crushing strength of 14
It was 1 kgf.

Example 2 and Comparative Example 1 Aggregate b (Example 2) and aggregate c were prepared in the same manner as in Example 1 except that the coating amount of paraffin wax was changed to 6% by weight and 0% by weight, respectively. (Comparative Example 1) was obtained. The obtained aggregates b and c were measured in the same manner as in Example 1, and the results are shown in Table 1.

As can be seen from Table 1, aggregate b of Example 2 has a bulk specific gravity of 1.46, a water absorption of 9.8%, and a crushing strength of 13
5 kgf, and the aggregate c of Comparative Example 1 had a bulk specific gravity of 1.
44, although the crushing strength is 103 kgf,
It was as high as 1%.

Example 3 An aggregate d (Example 3) was obtained in the same manner as in Example 1 except that 89% by weight of coal ash, 10% by weight of cement, and 1% by weight of gypsum hemihydrate were used. The obtained aggregate d
Was measured in the same manner as in Example 1, and the results are shown in Table 1.
Are shown together.

As can be seen from Table 1, the aggregate d of Example 3 has a bulk specific gravity of 1.38, a water absorption of 7.1%, and a crush strength of 48.
kgf.

Example 4 Aggregate e (Example 4) in the same manner as in Example 1 except that 85% by weight of coal ash, 10% by weight of cement, 4% by weight of calcium oxide, and 1% by weight of gypsum hemihydrate were used. I got The same measurement as in Example 1 was performed for the obtained aggregate e, and the results are shown in Table 1.

As can be seen from Table 1, the aggregate e of Example 4 has a bulk specific gravity of 1.48, a water absorption of 9.5%, and a crushing strength of 93.
kgf.

Comparative Example 2 The procedure of Example 1 was repeated, except that water was added so that the ratio of water / solid content became 23%, and then processed into a spherical shape of about 10 mmφ while rolling with a pan pelletizer. An aggregate f (Comparative Example 2) was obtained. The same measurement as in Example 1 was performed for the obtained aggregate f, and the results are shown in Table 1.

As can be seen from Table 1, the aggregate f of Comparative Example 2 had a water absorption of 8.5% and a crushing strength of 42 kgf, but had a high bulk specific gravity of 1.69.

Example 5 At the time of kneading, 0.026 g of aluminum powder and 0.09 g of oleic acid were added.
An aggregate g (Example 5) was obtained in the same manner as in Example 1, except that water was added so that the water / solid content ratio became 67% by weight, and the mixture was semi-cured for 4 hours. The same measurement as in Example 1 was performed on the obtained aggregate g, and the results are shown in Table 1.

As can be seen from Table 1, the aggregate f of Example 5 has a bulk specific gravity of 1.30, a water absorption of 8.3%, and a crush strength of 82.
kgf.

Example 6 Aluminum powder 0.078
g and aggregate h (Example 6) in the same manner as in Example 5 except that water was added so that the ratio of water / solid content was 67% by weight.
I got The same measurement as in Example 1 was performed for the obtained aggregate h, and the results are shown in Table 1.

As can be seen from Table 1, the aggregate g of Example 6 has a bulk specific gravity of 1.07, a water absorption of 9.0%, and a crushing strength of 40.
kgf.

Example 7 An aggregate i (Example 7) was obtained in the same manner as in Example 5, except that 84% by weight of coal ash, 15% by weight of cement, and 1% by weight of gypsum hemihydrate were used. Aggregate i obtained
Were measured in the same manner as in Example 1, and the results were shown in Table 1.
Are shown together.

As can be seen from Table 1, the aggregate i of Example 7 has a bulk specific gravity of 1.28, a water absorption of 7.4%, and a crush strength of 54.
kgf.

Example 8 An aggregate-mixed raw material was prepared with an average particle size of 10
An aggregate j (Example 8) was obtained in the same manner as in Example 5, except that the mixture was pulverized to μm and semi-cured for 4.5 hours. The same measurement as in Example 1 was performed for the obtained aggregate j, and the results are shown in Table 1.

As can be seen from Table 1, aggregate j of Example 8 has a bulk specific gravity of 1.26, a water absorption of 8.1%, and a crush strength of 80.
kgf.

Example 9 After the semi-cured molded product was released from the mold,
An aggregate k (Example 9) was obtained in the same manner as in Example 5, except that the jig was filled and subjected to compaction granulation and processed into a spherical shape of about 10 mmφ. The same measurement as in Example 1 was performed for the obtained aggregate k, and the results are shown in Table 1.

As can be seen from Table 1, the aggregate k of Example 9 has a bulk specific gravity of 1.38, a water absorption of 7.7%, and a crush strength of 69.
kgf.

Example 10 Example 9 was carried out except that 77% by weight of coal ash, 20% by weight of cement and 3% by weight of gypsum hemihydrate were used.
In the same manner as in Example 1, an aggregate 1 (Example 10) was obtained. The same measurement as in Example 1 was performed for the obtained aggregate 1 and the results are shown in Table 1.

As can be seen from Table 1, the aggregate 1 of Example 10
Has a bulk specific gravity of 1.35, a water absorption of 7.8%, and a crush strength of 6
It was 1 kgf.

Comparative Example 3 The procedure of Example 5 was repeated, except that the high-pressure steam curing was not performed, and only the normal-pressure steam curing was performed for 7 days.
An aggregate m (Comparative Example 3) was obtained. The same measurement as in Example 1 was performed on the obtained aggregate m, and the results are shown in Table 1.

As can be seen from Table 1, the aggregate m of Comparative Example 3 had a bulk specific gravity of 1.38 and a water absorption of 8.7%, but had a low crushing strength of 15 kgf.

[Comparative Examples 4 and 5] Aggregate n (comparative example 4) made of mesalite, which is a commercially available artificial lightweight aggregate, and aggregate o (comparative example 5) made of F-lite are described in Example 1.
The same measurement was performed, and the results are shown in Table 1.

As can be seen from Table 1, aggregates n and o of Comparative Examples 4 and 5 have bulk specific gravities of 1.38 and 1.40 and crush strengths of 87 kgf and 55 kgf, respectively, but have a water absorption of 12.
It was as high as 9% and 14.0%.

[0051]

[Table 1]

[0052]

As described above, according to the present invention, non-fired artificial lightweight aggregates can be efficiently produced at low cost using coal ash generated from a coal-fired power plant or a coal-fired boiler as a raw material. it can. Therefore, it is possible to recycle industrial waste, especially to civil engineering and building materials, without reclaiming and processing it, which greatly contributes to environmental conservation and stable supply of energy.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shingo Sudo 3-18-5, China, Ichikawa, Chiba Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Koji Kawamoto 3-18-, China, Ichikawa, Chiba 5 Sumitomo Metal Mining Co., Ltd. Central Research Laboratory F term (reference) 4D004 AA36 BA02 CA04 CA45 CC11 CC12 CC13 CC20 DA03 DA09 DA10 DA11 DA20

Claims (8)

[Claims] 1. A mixture obtained by mixing coal ash, cement, and calcium sulfate is pulverized, and water / water is added to the pulverized material.
After adding water having a solid content ratio of 50 to 100% by weight to form a slurry, the mixture is cast into a mold and semi-cured. The resulting semi-cured product is molded and then subjected to high-pressure steam curing. A method for producing an artificial lightweight aggregate, comprising coating the surface of the obtained aggregate with paraffin. 2. The method for producing an artificial lightweight aggregate according to claim 1, wherein at least one selected from calcium oxide and / or calcium hydroxide is further added to said mixture. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein a foaming agent is further added to the pulverized material. 4. The method according to claim 1, wherein the amounts of the cement and the calcium sulfate are 10 to 50% by weight and 0.5 to 10% by weight (in terms of CaSO ₄ ), respectively.
The method for producing an artificial lightweight aggregate according to any one of claims 1 to 3. 5. The amount of the calcium oxide and / or calcium hydroxide added is 1 to 50% by weight in terms of CaO.
The method for producing an artificial lightweight aggregate according to any one of claims 2 to 4, wherein 6. The method for producing an artificial lightweight aggregate according to claim 1, wherein the mixture is pulverized so as to have an average particle size of 15 μm or less. 7. The method for producing an artificial lightweight aggregate according to claim 6, wherein the mixture is pulverized so as to have an average particle size of 10 μm or less. 8. The method according to claim 1, which has a bulk specific gravity of less than 1.5 and a water absorption of 1
An artificial lightweight aggregate characterized by being 0% or less.