JPH0244781B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a hardened material using coal ash discharged during coal combustion as a main raw material. / and molded anhydrous gypsum added at a kneading temperature of 25 to 60℃.
The present invention relates to a method for producing a hydrated hardened product with high mechanical strength by adjusting the amount of quicklime added in advance so that the temperature of the quicklime is at ℃, kneading it with seawater or water, and curing at room temperature. [Prior Art] In recent years, the development of alternative energy to petroleum in order to reduce dependence on petroleum has become a national issue in Japan, and coal energy is attracting attention as one of the pillars of energy. One of the challenges in the practical application of coal utilization technology to cope with the large consumption of coal as a primary energy source is the disposal of large amounts of coal ash generated during coal combustion. When burning coal, usually almost 10 to 20 of the coal usage
% coal ash is generated. The so-called pulverized coal combustion ash generated from a typical pulverized coal combustion boiler is classified into bottom ash, cinder ash, and fly ash, depending on where it is generated, of which fly ash accounts for the majority of the amount generated. Conventionally, in Japan, a portion of fly ash has been reused as cement admixtures, cement raw materials, etc., and the rest has been disposed of in landfills. However, it is not possible to expect enough demand to meet the huge amount of coal ash that will be generated in the future through current recycling methods alone. With the tightening of environmental regulations, it is becoming difficult to secure land for coal ash disposal. It is expected that it will be difficult to process all the coal ash that will be produced. In addition, when considering large-scale processing technology for coal ash, it is important that there is no environmental pollution.
It is also necessary to aim for reuse as much as possible. This is because in a country with limited domestic resources and limited land, it is important to reuse coal ash as a resource rather than simply dumping it. In view of these points, the present inventors have proposed
As shown in Publication No. 155064, 50-85% by weight of coal ash discharged during coal combustion, 10-40% by weight of slaked lime or/and quicklime, 5-40% by weight of dihydrate gypsum, hemihydrate gypsum or/and type anhydrous gypsum. We have developed a method for producing a cured product by adding water to a mixed powder consisting of 10% and kneading it. In subsequent research, the present inventors found that the kneading temperature was
It has been found that if the amount of quicklime added to the mixed powder is adjusted in advance so that the temperature is 60°C, a hardened product with higher strength can be obtained without requiring external heating during kneading. The above-mentioned Japanese Patent Application Laid-Open No. 56-155064 describes coal ash/
Molding the lime/gypsum mixture and keeping the relative humidity at 70~
It describes a method of curing in 100% humid air and then treating with steam at 80 to 100°C. Furthermore, Japanese Patent Application Laid-Open No. 48-93620 discloses a cementitious mixture containing flyash, lime and a sulfate compound. Furthermore, JP-A-56-164055 describes the first step of kneading at around 30°C with the addition of 2 to 10% of an admixture that promotes the hardening of cement through the formation of ettringite, and the process of kneading the kneaded material. A method for producing lightweight concrete is disclosed, which includes a second step of curing at around 25°C. [Problems to be solved by the invention] In the method described in JP-A-56-155064, the combination of raw materials is almost the same, but the temperature of the kneaded material varies depending on the temperature of the raw materials and the combination of raw materials. The temperature range is 0 to 100°C, and the treatment is performed at a temperature higher than room temperature. Furthermore, there is no suggestion of any technical idea of adjusting the kneading temperature with quicklime. Furthermore, in the method described in JP-A-48-93620, the blending range of coal ash/lime/gypsum-based raw materials is almost the same, but hydrated lime is used as the lime, and no heat treatment is performed. Therefore, the kneading temperature is less than 25°C. Furthermore, there is no suggestion of any technical idea of adjusting the kneading temperature with quicklime. Furthermore, in the method described in JP-A No. 56-164055, the kneading temperature is set at around 30°C because materials such as quicklime that rapidly generate a large amount of reaction heat during hydration are not used as raw materials. In order to achieve this, the kneading temperature must be set to around 30°C by heating the kneaded material with an external heat source or by preheating the raw materials and water. Further, the reason why the kneading temperature is set at around 30°C is to promote the ettringite production reaction, which is different from the purpose of the present invention, which is to accelerate the rate of elution of alumina from coal ash. Note that this publication does not suggest any technical idea of adjusting the kneading temperature with quicklime. In view of the above points, the present invention utilizes coal ash in large quantities in the civil engineering sector, such as as a soil material for sea surface reclamation and land reclamation, as a soil improvement material for soft ground, and as a road base material for road construction. Therefore, it is an object of the present invention to provide a method for producing a hardened soil body having high compressive strength using coal ash as a main raw material. [Means and effects for solving the problems] In order to achieve the above object, the method for producing a hardened material using coal ash as a main raw material of the present invention is to reduce the amount of coal ash emitted from coal ash by weight of 50 to 94 kg. %, slaked lime or/and quicklime 5-40% by weight, dihydrate gypsum, hemihydrate gypsum or/and type anhydrous gypsum 1-40% by weight, adding water to a mixed powder and kneading to produce a hardened product. , the kneading temperature is 25-60℃
After adjusting the amount of quicklime added in the mixed powder in advance so that It is characterized by being cured at room temperature. In addition, the method of the present invention involves adjusting the amount of quicklime added in the mixed powder in advance so that the kneading temperature is 25 to 60°C, and then kneading the mixed powder with seawater or water. It is characterized by being cured at room temperature without being molded into a specific shape. In the method of the present invention, the amount of mixed water (wt% of water added to 100 wt% of powder) is 10 to 60%,
Desirably it is 30-50%. Hereinafter, the configuration of the present invention will be explained in detail. In general, the typical properties of coal ash, such as components, composition, and particle size distribution, greatly depend on the coal's production area and combustion history. First of all, it depends on where the coal comes from.
The proportions of ingredients such as SiO ₂ , Al ₂ O ₃ , CaO, Fe ₂ O ₃ , Na ₂ O, K ₂ O are different, and secondly, the coal ash currently generated in Japan is mainly pulverized coal combustion ash. The particle size distribution differs depending on the location of occurrence and collection method. Therefore, when producing a hydrated material with high compressive strength using coal ash as the main raw material and curing at room temperature, the appropriate manufacturing conditions for the hydrated material may vary depending on the composition and particle size distribution of the coal ash. different. Factors that have a large contribution rate as manufacturing conditions are the mixing ratio of raw material powder, kneading time and kneading temperature, and room temperature curing time. The main component of the hydrated hardened product produced by curing at room temperature is ettringite (3CaO・Al ₂ O ₃・3CaSO ₄・
32H ₂ O) and various forms of calcium silicate hydrate (xCaO・ySiO ₂・zH ₂ O), but the one that contributes most to early strength development is ettringite.
For this reason, the appropriate mixing ratio of the raw material powder is the one most favorable for the production of ettringite, and the amount of slaked lime etc. to be added is 5 to 40% by weight, preferably 15 to 40% by weight.
30% by weight, and the amount of dihydrate gypsum added is limited to 1 to 40% by weight, preferably 5 to 20% by weight. Furthermore, the room temperature curing conditions are mainly due to the processing time. When cured at room temperature, it usually takes a few days to a week for ettringite to form and exhibit a compressive strength of several kg/cm ² or more, which is sufficient to withstand normal civil engineering work. The particle size distribution of coal ash also has a large effect on the properties of the hydrated hardened material. Generally, as the particle size of coal ash becomes smaller, that is, as the specific surface area becomes larger, the hydrated hardened material tends to exhibit a predetermined strength with a short curing time. This is because the formation reaction of ettringite is a through solution reaction, and the dissolution rate of alumina (Al ₂ O ₃ ) contained in coal ash is significantly lower than that of slaked lime and dihydrate gypsum. This is because it can be estimated that the production rate of ettringite depends on the dissolution rate of alumina. In this way, the properties of the hydrated material are greatly influenced by manufacturing conditions such as the components and composition of the coal ash, the amount of other raw material powders added, the amount of water mixed, the kneading method and kneading time, and the room temperature curing period. Therefore, it is necessary to appropriately select each manufacturing condition according to the required characteristics of the hydrated and cured product. The present invention is capable of producing a hydrated product with high initial strength through a simple and short kneading process by simultaneously kneading raw material powder containing slaked lime and quicklime in an appropriate ratio with seawater or water. It is intended to be manufactured by curing at room temperature under the kneading time. In the present invention, when the raw material powder is kneaded with seawater or water due to the addition of quicklime, a digestive reaction of quicklime (CaOH ₂ O -→ Ca(OH) ₂₎ occurs, and a part of the kneaded water is converted into main digestion. The amount of seawater or water used in the reaction and kneading of the raw material powder is reduced, producing the same effect as reducing the amount of mixed water, and improving the compressive strength of the cured product. On the other hand, the heat generated during the digestion reaction of quicklime usually increases the kneading temperature. An increase in the kneading temperature increases the amount of Al ₂ O ₃ eluted from the coal ash, and the pozzolanic reaction is promoted. However, a significant increase in the kneading temperature promotes pseudo-coagulation of the kneaded material, thereby reducing the operability during kneading and casting. For this reason, the appropriate kneading temperature when adding quicklime is 25-60℃, preferably 35-60℃.
It is 45℃. The temperature of the kneaded material using the kneader is determined from the heat balance by determining the weight, temperature, specific heat of the raw material powder, the weight, temperature, and temperature of the water.
It is well known that it is determined by the specific heat, the amount of heat dissipated or input from the kneader (in the case of heating with a heater, etc.), and the amount of heat generated or absorbed by the kneading of the raw material powder. However, as mentioned above, the technical concept of adjusting the kneading temperature to 25 to 60° C. by utilizing the calorific value of quicklime during kneading is not disclosed in any conventional literature. The amount of quicklime to achieve a predetermined kneading temperature can be determined as follows. (1) First, determine the kneading temperature. (2) Determine the amount of coal ash, gypsum, slaked lime, and water. (3) Measure the ambient temperature and water temperature. (4) Assuming the amount of quicklime added, the specific heat of the raw material powder,
Total calorific value of quicklime, heat dissipation amount of kneading machine, and (1)
Based on the data in ~(3), calculate the amount of quicklime added at which the heat balance becomes zero. (5) Add the specified amount of raw material powder and water and mix. (6) Dispense the kneaded material at a predetermined temperature. In the present invention, the amount of mixed water is 10 to 60% by weight, but if the amount of mixed water is reduced, the strength will increase, but the moldability will deteriorate, and if the amount of mixed water is less than 10% by weight, molding will not be possible. Furthermore, when the amount of mixed water is increased, the fluidity increases and it becomes difficult to solidify, so the amount of mixed water is limited to about 60% by weight. Therefore, in the present invention, the desirable amount of water to be mixed is 30 to 50% by weight. Furthermore, when seawater is used as the kneading water, there is an advantage that the initial strength of the hydrated and hardened product is enhanced and the room temperature curing period is shortened. The strength of this hydrated hardened material is due to the formation of ettringite.
The presence of salts such as NaCl and MgCl ₂ increases the rate of ettringite formation and increases the strength of the hydrated hardened product. [Example] Next, Examples and Comparative Examples will be described.
The raw material coal ash in Examples and Comparative Examples is commercially available fly ash, and the composition and properties are shown in Table 1.

[Table] The test methods for coal ash and hydrated hardened bodies are shown below. The Blaine specific surface area was measured using a powder specific surface area measuring instrument SS-100 manufactured by Shimadzu Corporation, using the air permeation method. Bending strength test uses 20×20 as a test piece
For the compressive strength test, a 20 x 20 x 20 (mm) test piece was used as the test piece, and a universal testing machine manufactured by Instron was used as the testing device. The test method was based on the constant deflection method. In Examples and Comparative Examples, room temperature curing was carried out indoors without direct sunlight. Details of Examples and Comparative Examples are shown in Table 2. Example 1 85 parts of coal ash, 10 parts of quicklime, 5 parts of dihydrate gypsum, and 40 parts of seawater were simultaneously kneaded to form a slurry. The kneading temperature was 40°C. This slurry was cured indoors at room temperature for 7 days to obtain a hydrated and hardened product. The properties of the hydrated and cured product were as shown in Table 2. Example 2 85 parts of coal ash, 5 parts of slaked lime, 5 parts of quicklime, 5 parts of dihydrate gypsum, and 40 parts of seawater were simultaneously kneaded to form a slurry. The kneading temperature was 32°C. This slurry was cured indoors at room temperature for 7 days to obtain a hydrated and hardened product. The properties of the hydrated and cured product were as shown in Table 2. Comparative Example 1 85 parts of coal ash, 10 parts of slaked lime, 5 parts of dihydrate gypsum, and 40 parts of seawater were simultaneously kneaded to form a slurry. The kneading temperature was 22°C. This slurry was cured indoors at room temperature for 7 days to obtain a hydrated and hardened product. The properties of the hydrated and cured product were as shown in Table 2. Comparative Example 2 85 parts of coal ash, 10 parts of slaked lime, 5 parts of dihydrate gypsum, and 40 parts of seawater were simultaneously kneaded to form a slurry. Kneading was performed by external heating, and the kneading temperature was 40°C.
This slurry was cured indoors at room temperature for 7 days to obtain a hydrated and hardened product. The properties of the hydrated and cured product were as shown in Table 2.

〔Effect of the invention〕

As explained above, in the method of the present invention, the rapid and large amount of heat generated by the hydration of quicklime in coal ash/lime/gypsum-based materials is utilized, and the amount of quicklime added can be determined by controlling the raw material temperature, raw material amount, and kneading machine. By appropriately adjusting the amount of heat dissipated, etc., it is possible to knead at 25 to 60°C, elute a large amount of alumina from the coal ash, and then cure at room temperature to form a hardened product with high strength. Further, in order to raise the kneading temperature, there is no need to heat the kneaded material with an external heat source such as a heater or to preheat the raw material powder and water. As described above, the method of the present invention does not use coal ash, which is an emission from coal combustion, quicklime, which is an inexpensive raw material, or quicklime and slaked lime, dihydrate gypsum, hemihydrate gypsum, and/or type anhydrous gypsum. By kneading in water and then curing at room temperature, it is possible to easily and inexpensively produce a hydrated hardened material with high compressive strength, and the method of the present invention makes effective use of coal ash. It is useful as a technology that contributes to the production of soil materials for reclamation, land reclamation, road construction, etc. in the fields of civil engineering and architecture. Furthermore, since the method of the present invention kneads the raw material powder and water at the same time, the process is extremely simplified, the kneading time is shortened, and the hydrated hardened product can be produced at a lower cost. have.

Claims (1)

[Claims] 1. 50-94% by weight of coal ash discharged during coal combustion, 5-40% by weight of slaked lime or/and quicklime,
In a method of producing a hardened product by adding water to a mixed powder consisting of 1 to 40% by weight of dihydrate gypsum, hemihydrate gypsum or/and type anhydrous gypsum and kneading, the kneading temperature is set at 25 to 60°C. After adjusting the amount of quicklime added in the mixed powder in advance, the mixed powder is kneaded with seawater or water, the kneaded product is molded using a mold or a molding container, and then cured at room temperature. A method for producing a hardened material using coal ash as a main raw material, characterized in that: 2 50-94% by weight of coal ash discharged during coal combustion, 5-40% by weight of slaked lime or/and quicklime,
In a method of producing a hardened product by adding water to a mixed powder consisting of 1 to 40% by weight of dihydrate gypsum, hemihydrate gypsum or/and type anhydrous gypsum and kneading, the kneading temperature is set at 25 to 60°C. After adjusting the amount of quicklime added in the mixed powder in advance, the mixed powder is kneaded with seawater or water, and the kneaded product is cured at room temperature without being molded into a specific shape. A method for producing a hardened product using coal ash as the main raw material.