JP2603599B2 - Artificial lightweight aggregate and manufacturing method thereof - Google Patents

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 applied to an aggregate of structural lightweight concrete and a method for producing the same.

[0002]

2. Description of the Related Art At present, raw materials for artificially produced lightweight aggregates are limited to expanded shale or coal ash discharged from coal-fired power plants. All of them are manufactured by baking to make the surface one step before melting and foaming the inside.

On the other hand, when a mixer truck and a ready-mixed concrete plant are washed from a ready-mixed concrete factory, ready-mixed concrete residues equivalent to about 5% of the production amount are discharged. After removal, the cement component is concentrated with a thickener and then dehydrated. There are approximately 5,000 ready-mixed concrete factories nationwide,
0.5 to 1.8 million tons are discharged as industrial waste. At present, part of the dewatered sludge of the ready-mixed concrete is recycled as a raw material for cement or the like.

[0004] Waste sand of green sand discharged from a foundry is designated as a management type industrial waste, and the amount of waste sand generated per ton of cast iron and cast steel is about 300 kg.
Estimated to reach 2 million tons annually in Japan.
At present, many business establishments outsource wastewater to landfills by outsourcing waste treatment companies.

[0005]

In a conventional artificial lightweight aggregate made of expanded shale or coal ash, the appropriate range of the sintering temperature is as narrow as 20 to 40 ° C., so that the aggregates are fused to each other. It was easy to do so, causing a decrease in yield. On the other hand, the technical problem in the case of using coal ash as a raw material has a drawback that a molded and dried sample has a small breaking load due to compression and is easily powdered.

[0006] In a coal-fired power plant, since powdered coal is burned at a high temperature, particles are spherical and vitrification has already progressed. Light aggregate of expanded shale also forms a glass layer (amorphous). In such cases, generally,
Has the property of being easily attacked by alkali. For this reason, there has been a problem that an alkali-aggregate reaction is caused to cause cracks due to hydration expansion and strength is deteriorated. There is no problem as long as it is used for high-rise buildings as long as it is covered with other exterior materials and is not exposed to the wind and rain, but when used for civil engineering such as piers, alkali-aggregate reaction is required. It cannot be ignored.

On the other hand, the dewatered sludge of ready-mixed concrete is partially recycled as described above, but most of the sludge is self-hardening, so that it is solidified, landfilled, and backfilled. Recycling the calcium source was a challenge.

In addition, the cost of landfill disposal of waste sand is around 12,000 yen per ton, and it is difficult to reduce the burden of disposal costs and secure landfill sites in the future. Recycling sand was an issue.

The present invention has been made in view of such a conventional situation, and uses dewatered sludge from a ready-mixed concrete plant and waste sand from a foundry as raw materials to simultaneously solve the problem of recycling both industrial wastes. It is an object of the present invention to provide a low-cost artificial lightweight aggregate which can be applied to structural lightweight concrete aggregate (JIS A 5002) which is high in strength and does not cause an alkali aggregate reaction, and which can be applied to structural lightweight concrete aggregate (JIS A 5002). I have.

[0010]

In order to achieve the above object, the artificial lightweight aggregate of the present invention is characterized by using raw concrete dewatered sludge and cast waste sand as main raw materials. And
The mixing ratio of the ready-mixed dewatered sludge and the casting waste sand is most preferably 1.0: 1.0 to 2.5 in terms of dry matter weight.

The basis for setting the range of the mixing ratio as described above depends on the moldability, green strength and physical properties of the aggregate after firing. That is, if mixed in this range, molding is easy and self-hardening, so that the breaking load after molding is stable. Furthermore, as an aggregate after firing, it can pass all JIS standards.

On the other hand, if the ratio of the casting waste sand is set to 2.5 or more, the plasticity becomes poor and the molding becomes difficult. Conversely, 1.0
If it is made below, although it has plasticity, the water content becomes 35% or more, the specific gravity of the baked aggregate becomes small, and it tends to self-destruct due to absorption of carbon dioxide gas and the like, and the property of becoming fine sand appears. In addition, if the mixture is mixed outside the above range and molded, the raw breaking load is reduced, the powder is powdered at the time of firing, the dust concentration is increased, and a dust collector is required. Further, as for the quality of the aggregate (JIS A 5002), sulfur trioxide and clay lumps are specified, and as shown in Table 7, when the ratio of cement residue is higher than 1.0: 0.8, Sulfur oxide becomes 0.5% or more, and it is out of the standard as a lightweight aggregate. In addition, a self-destructive effect is exerted, and the clay mass becomes 1% or more, which is also out of the standard.

[0013] Among the cast waste sands, dust-collecting dust, sand-treated dust, open-frame dust, shot dust and shot sand, and waste sand thinned out to prevent deterioration of the green sand flowing on the production line, as strength-adding materials. At least one of them is used.

The composition of waste sand is roughly classified into thinned waste sand, shot type (shot dust and shot sand) and non-shot type (dust collection dust, sand processing dust, and open dust). The discharge ratio of non-shot type and shot type waste sand is about 2: 1. Basically, each company emits a different amount of dust, but they can be mixed and used as raw materials. Regarding the thinned waste sand and shot type waste sand, the ratio of quartz is high, and the ratio of montmorillonite clay and feldspar is low. There is no significant difference in mineral composition between dust collection, sand treatment and open dust (non-shot type) (see Table 3). In the production of lightweight aggregate, raw materials are prepared so that the ratio of silica to calcium is constant.

As a molding material and a self-hardening material, ordinary Portland cement, early-strength Portland cement,
Use dewatered sludge of ready-mixed concrete such as moderate heat Portland cement, white Portland cement, blast furnace cement, silica cement and fly ash cement.

Further, the strength-adding material may include at least one or more of a sludge of a silica stone mine, a sludge of a quarry, a dewatered sludge of fine particles coming out of a rapid sedimentation filtration step of a water purification plant, and diatomaceous earth.

The above-mentioned dewatered sludge and the like are used for the purpose of finely adjusting the final composition ratio in the preparation of raw materials for the casting waste sand and the raw concrete residue. What is required of these fine-tuning raw materials is that their chemical compositions have little fluctuation.

On the other hand, in the method for producing an artificial lightweight aggregate of the present invention, the ready-mixed dewatered sludge is mixed with waste sand from a foundry and then molded, and then dried, and the dried product is subjected to 1,000 to 1,1.
It is characterized in that a fired product is obtained by firing at 200 ° C. It is most preferable to set the mixing ratio of the ready-mixed dewatered sludge and the casting waste sand to 1.0: 1.0 to 2.5 in terms of dry matter weight, and to fire after molding.

In the above method, the firing temperature is set at 1.0
The reason for setting the temperature to 00 to 1,200 ° C. is that if the temperature is raised to 1,200 ° C. or more, the sample is completely melted. On the other hand, when the temperature is less than 1,000 ° C., sintering does not progress, the breaking load is reduced to 30 kgf or less, the water absorption becomes 40% or more, and it cannot be used as a lightweight aggregate. In the quality of lightweight aggregate (JIS A 5002), the ignition loss is specified to be 1% or less. The loss on ignition is the rate of weight loss when heated at 1,000 ° C.
The reason is that firing at 000 ° C. or lower may result in rejection of JIS standards. The sintering state differs between the oxidizing atmosphere state of the electric furnace and the oxygen limitation (about 10% O ₂ concentration) by the rotary kiln. Sintering at the same firing temperature tends to progress more easily in a rotary kiln, which is clearly recognized in terms of water absorption and the like.

[0020]

[Operation] Although the ready-mixed dewatered sludge alone can be molded, even if it is fired, the strength as an aggregate cannot be expected at all. On the other hand, casting waste sand alone is extremely difficult to mold, and at a firing temperature of 1000 ° C to 1200 ° C,
It cannot be sintered and has no function as an aggregate. However, the chemical reaction (precipitation of anorthite) and sintering of the mixed waste made possible an artificial lightweight aggregate with higher strength.

The chemical composition of dewatered sludge using ordinary Portland cement most frequently used in ready-mixed concrete plants is shown in Table 1 in comparison with cement. Dewatering the sludge has about 20% water of hydration, since it is also contained fine sand, SiO ₂ as compared to ordinary portland cement is relatively increased. This valuable calcium source reacts with silica as a strength-adding material, and can produce a high-strength aggregate. The dewatered sludge of the ready-mixed concrete has a self-hardening property for 4 days even if discharged in a wet state, and is excellent in moldability.

As the cement, Portland cement is predominantly used, but there are many types. However, the variation range of the chemical composition excluding alumina cement is only 50 to 65% as CaO. Accordingly, dewatered sludges such as ordinary Portland cement, early-strength Portland cement, moderately heated Portland cement, white Portland cement, blast furnace cement, silica cement, fly ash cement and the like are also suitable as raw materials for aggregate.

[Table 1]

Since casting waste sand is designated as a management type industrial waste, a test for dissolution of heavy metals from waste sand (Notification No. 13 of the Environment Agency) was conducted. Table 2 shows the dissolution test results. None of the items exceeded the standards, and they were harmless and confirmed that they did not hinder recycling.

[Table 2]

The green sand in the foundry is a synthetic sand composed of silica sand, bentonite, coal powder, starch and the like. This green sand circulates through the process of kneading → molding → pouring → framing → sand processing. From the production process, dust collection, sand processing dust, framing dust, shot dust and shot sand Waste or waste sand comes out. Therefore, five representative samples of waste sand were collected from a pig iron foundry and subjected to chemical analysis, and the chemical composition was estimated from the norm calculation to estimate the mineral composition. Table 3 shows the results. The mineral composition of each foundry waste sand is
28-70% for quartz, 19-41% for clay, 5-20 for feldspar
%, Carbon 0 to 23%.

[Table 3]

From Table 3, it can be seen that the waste sand is based on quartz, and is a component of the high strength of the aggregate. Further, since montmorillonite is contained in an amount of 20 to 40%, it functions as a plastic material when molding the aggregate and as a sintering aid when burning. Furthermore, carbon is reduced to about 1
When the aggregate is ignited for the first time, it contains carbon necessary for self-combustion and can be burned with low fuel consumption.

From the above, it is possible to provide an unprecedented structural lightweight concrete aggregate (JIS A 5002) by effectively utilizing the characteristics of the industrial wastes such as the dewatered sludge and the mold waste sand. Is now available. Thus, Table 4 shows a comparison between the aggregate of the present invention and the aggregate of the conventional example from the viewpoint of the raw material and the product as the aggregate.

[Table 4]

It can be seen that the raw materials (industrial waste) of both the dewatered sludge and the casting waste sand according to the present invention satisfy all the essential conditions required for the production of aggregate so as to complement each other. The specific gravity of the coarse aggregate as a product is about 10% larger than that of other foamed products (the product of the present invention is composed of coarse aggregate and fine aggregate. The specific gravity of fine aggregate is 1.6.
Compared with coarse aggregate). On the other hand, the conventional aggregate-based products are vitrified, and the alkali-aggregate reaction is likely to proceed, and there is a risk of cracking due to expansion.

[0028]

Embodiments of the present invention will be described below.

A. Example 1 A fixed ratio of dewatered sludge of ready-mixed concrete and casting waste sand (in terms of dry matter, cement dewatered sludge 1.0: 2.8-
The mixture was repeatedly mixed by a screw-type mixer at 0.8), and then formed into pellets (φ13.2 mm) having a length of 20 mm. Next, after drying this molded body, put it in an electric furnace,
It was fired in an oxidizing atmosphere under a heating condition of 1,100 ° C. × 1 h. The chemical compositions of the dewatered sludge and the casting waste sand used in the experiment are as shown in Table 5 (the dewatered sludge used was the sample 1 in Table 1).

[Table 5]

From the fired aggregate, the breaking load, the shrinkage in the diameter direction, the absolute dry gravity, the water absorption and the optimum mixing ratio were determined from X-ray diffraction (Table 6).

[Table 6]

As shown in Table 6, among the aggregates fired at each ratio, as shown in Table 6, the sample No. 5 has the largest breaking load. Moreover, since the water absorption is relatively small, it is considered that this is the optimum ratio of the aggregate. Also, it can be seen from a comprehensive viewpoint that the mixing ratio is preferably 1.0: 2.0 to 1.2.

Usually, the water content of the dewatered sludge and the waste sand of the ready-mixed concrete is about 50% and 20%. Therefore, the mixing ratio of the raw materials in the wet state of Sample No. 5 is about 1.0: 1.0. Becomes The shrinkage rate of the fired aggregate is 7.6 to 12.9% based on the length at the time of molding, and the shrinkage rate decreases as the ratio of waste sand increases. On the other hand, as a result of X-ray diffraction of this aggregate and examination of the mineral composition, all were composed of quartz and anorthite.

B. Example 2 Using fresh concrete dewatered sludge and casting waste sand having the same composition as in Example 1, the addition ratio was 1: 1 in a wet state.
And after mixing using a vacuum kneader, JIS A
According to 5002, a total of 100 kg was granulated to have diameters of 20 mm, 15 mm, 10 mm, and 5 mm. Further, a plate-like molded body (20 cm square thickness 2 cm) was also prepared. Next, after drying these aggregates, about 20 kg of a plate-shaped sample was crushed by a crusher. The spheroidized sample and the crushed sample were separately fired at 1,100 ° C. using a rotary kiln (length: 3.00 m, inner diameter: 0.30 m).

Regarding the aggregate obtained by the above-mentioned trial production,
Lightweight concrete aggregate for structure (JIS A 5002)
As a quality test. Table 7 shows the results. The physical properties of the prototype artificial lightweight aggregate satisfied the JIS standard, and it was confirmed that it could be used practically.

[Table 7]

Next, using the artificial lightweight aggregate thus produced, a water cement ratio of 40, which is a designated condition based on JIS, was used.
%, A slump of 8 cm, and a plain concrete were prepared under the condition that no admixture material was used, and it was confirmed whether or not physical property values determined by JIS (for example, a compressive strength material age of 28 days) were obtained.
Table 8 shows the materials used and the blending design, and Table 9 shows the blending values (thousand liters). Table 10 shows the particle size distribution of the artificial lightweight aggregate used for the concrete. The experimentally produced aggregate has a size of 5 to 15 mm.

[Table 8]

[Table 9]

[Table 10]

Samples fired in a rotary kiln (Table 8:
Example 2) and the sample fired in an electric furnace (Table 6: Example 1) have significantly different water absorption rates. As described above, this is because in a rotary kiln, the frame is directly connected to the aggregate. The water absorption is low due to the contact and the sintering promoted by the restriction of oxygen.

About the produced plain concrete,
Table 11 shows the classification of the lightweight aggregate and the physical properties of the concrete. As can be seen from Table 11, similarly to the quality test of the aggregate (Table 7), all the specifications of the artificial lightweight aggregate for a structure were satisfied, and it was confirmed that it was sufficiently practical.

[Table 11]

[0038] JIS A for artificial lightweight aggregates
Alkali silica reactivity test by 5308 (chemical method)
Was performed. As shown in Table 12, the alkali silica reactivity causing the cracks caused by the aggregate passed the standard, and it was confirmed that the silica was sufficiently practical for public works.

[Table 12]

C. Example 3 Next, an example of an aggregate in which a raw material for fine adjustment is added in addition to the raw material preparation of the ready-mixed dewatered sludge and the casting waste sand to adjust the final composition ratio will be described. Raw materials for fine adjustment include sludge from a quarry, a silica stone mining plant sludge, a water purification plant sludge, diatomaceous earth, and the like. The chemical compositions (components) of each are as shown in Table 13.

[Table 13]

A 10 mm spherical molded body was prepared by mixing the dewatered sludge sludge, the casting waste sand, and the fine powders for fine adjustment described above at an addition ratio (in terms of dry matter) of 0.45: 0.50: 0.05. Was created respectively. Next, these aggregates were dried and fired in an electric furnace at 1,100 ° C. × 1 h, and the breaking load and specific gravity thereof were measured. Table 14 shows the results.
Shown in From Table 14, it was confirmed that there was no significant difference including the breaking load even when 10% of the raw material for fine adjustment was added.

[Table 14]

[0041]

The present invention has established a technique for producing an artificial lightweight aggregate for a structure which is high in strength and does not cause an alkali aggregate reaction by combining a ready-mixed dewatered sludge and a casting waste sand. . Currently, the amount of the generated waste is about 3.5 million tons on both sides, and most of the waste is landfilled at waste disposal sites and the like. However, in the near future, it is difficult to secure landfill sites, and this has become a major issue from the viewpoint of environmental protection. In Japan, ready-mixed concrete plants and foundries are averagely distributed,
Since the collection of these wastes is easy, if the aggregate of the present invention is produced near a large consumption area, it is possible to further reduce the transportation cost as compared with the conventional aggregate, and It has a very high target value.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shizuo Nakabayashi No. 1 Tomicho-cho, Kanazawa-shi, Ishikawa Prefecture Inside the Ishikawa Industrial Testing Laboratory (72) Inventor Yoshiharu Kitamura 4-1 Wakamatsucho, Nonoichi-cho, Ishikawa-gun, Ishikawa Kanazawa Fresh Concrete Co., Ltd. Nonoichi Factory (72) Inventor Shoji Sakamoto 4-1 Wakamatsucho, Nonoichi-cho, Ishikawa-gun, Ishikawa Prefecture Kanazawa Ready-mix Concrete Co., Ltd. Nonoichi Factory (72) Inventor Nobuhiro Motoya Wakamatsucho, Nonoichi-cho, Ishikawa Prefecture No. 4 Kanazawa Ready Concrete Co., Ltd. Nonoichi Factory (56) References JP-A-6-106156 (JP, A) JP-A-2-293358 (JP, A)

Claims (7)

(57) [Claims] An artificial lightweight aggregate characterized by using ready-mixed dewatered sludge and casting waste sand as main raw materials. 2. The artificial lightweight aggregate according to claim 1, wherein the mixing ratio of the ready-mixed dewatered sludge and the casting waste sand is 1.0: 1.0 to 2.5 in terms of dry matter weight. . 3. The casting waste sand, as a strength-adding material,
Claims: At least one of dust collected dust, sand treated dust, unsealed dust, shot dust and shot sand, and at least one of waste sand thinned out to prevent deterioration of green sand flowing on a production line. The artificial lightweight aggregate according to claim 1 or 2. 4. The use of dewatered sludge of ready-mixed concrete such as ordinary Portland cement, early-strength Portland cement, moderately heated Portland cement, white Portland cement, blast furnace cement, silica cement and fly ash cement as a molding material and a self-hardening material. The artificial lightweight aggregate according to claim 1, 2 or 3, wherein: 5. The strength-adding material includes at least one of sludge from a silica stone mine, sludge from a quarry, dewatered sludge of fine particles from a rapid sedimentation filtration step in a water purification plant, and diatomaceous earth. Terms 1, 2, 3
Or the artificial lightweight aggregate according to 4. 6. Mixing of the ready-mixed dewatered sludge and waste sand from a foundry, molding, drying, and drying the dried product.
A method for producing an artificial lightweight aggregate, characterized in that a fired product is obtained by firing at 000 to 1,200 ° C. 7. The method according to claim 6, wherein the mixing ratio of the ready-mixed dewatered sludge and the casting waste sand is 1.0: 1.0 to 2.5 in terms of dry matter weight, and the mixture is fired after molding. Production method of artificial lightweight aggregate.