JP3362956B2 - Manufacturing method of artificial lightweight aggregate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an artificial lightweight aggregate mainly used for a structure or a non-structured building or structure.

[0002]

2. Description of the Related Art Conventionally, the main raw material used in the production of foam-type artificial lightweight aggregates has a large number of closed cells in the fired body as the particle size is made smaller, resulting in artificial lightweight aggregates with high strength and low water absorption. It is known that it can be manufactured. However, the smaller the particle size, the more grinding energy, that is, the grinding cost, is required.

Further, the smaller the specific gravity of the aggregate is, the thinner the thickness of the bubbles is, so that the surface of the aggregate is frequently scraped or crushed during concrete mixing, which causes an increase in the water absorption rate of the aggregate. There is a problem that the strength is reduced. This means that the original performance of the aggregate, which is to reduce the weight of concrete, is reduced.

Further, in the case of concrete using the foamed artificial lightweight aggregate, the elastic modulus of the concrete decreases as the specific gravity of the aggregate decreases. This occurs because the density of concrete decreases, which is a demerit for evaluating concrete strength.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a foam type artificial lightweight aggregate having a low water absorption rate, a high strength and a high elastic modulus. A further object of the present invention is to provide a foamed artificial lightweight aggregate in which the strength is slightly reduced even when the particle size of the raw material is increased.

[0006]

Under these circumstances, the inventors of the present invention have conducted intensive studies and as a result, have fired pellets for producing artificial lightweight aggregates to foam only the inner core of the pellets and densify the outer shell. As a result, they have found that low specific gravity and high strength can be realized, and have completed the present invention.

That is, in the present invention, the main raw material is a crushed product of acidic volcanic rocks, acidic volcanic ejecta or tuff, and a granulated product of the main raw material, a foaming agent and a binder is used as the main raw material and a binder. The present invention relates to a method for producing an artificial lightweight aggregate comprising a foamed inner core and a dense outer shell, which is characterized in that the mixture is coated with the mixture to prepare pellets and the pellets are fired.

The pellet surface is coated with a high melting point to prevent fusion (Japanese Patent Laid-Open Nos. 4-238845 and 3-88748). To increase combustion efficiency (JP-A-57-11868, JP-A-59-18701, JP-A-59-21569), after firing fly ash granulated pellets, It is known that the surface layer is prevented from peeling off the aggregate surface by impregnating it with an aqueous solution of a solidifying agent (Japanese Patent Laid-Open No. 1-272246). No technology has been known for densifying the shell to achieve low water absorption, high strength and high elastic modulus.

Among the main raw materials used in the present invention, acid volcanic rocks include rhyolite, pearlite, andesite and the like, and acidic volcanic ejecta include rhyolite-quartz andesite volcanic ash, volcanic pumice. Examples of tuff include rhyolite-quartz andesitic tuff. Since all of these are rich in glass, the decrease in viscosity with the increase in temperature is gentle and the baking is easy. Further, these are materials which are foamed when a foaming agent is added and which are well densified near the foaming temperature when not added, and are suitable for the purpose of the present invention.

These main raw materials are preferably crushed to have an average particle size of 30 μm or less, and more preferably 20 μm.
It is better to use it after crushing. Further, the main raw materials used for the inner core and the outer shell do not need to have the same average particle size,
It is also possible to have different average particle sizes.

Examples of the foaming agent used in the present invention include silicon carbide and silicon nitride. The blending amount of the foaming agent may vary depending on the type of main raw material, the degree of fineness, the firing temperature, etc.
The content in the inner core of the pellet is preferably 1 to 7% by weight, more preferably 2 to 5% by weight, based on the main raw material.

The binder used in the present invention includes clay minerals such as bentonite, chlorite and sericite, and bentonite is particularly preferable. The amount of binder is
Although it may vary depending on the average particle size of the main raw material and the like, it is preferably 1 to 7% by weight, particularly 3 to 5% by weight based on the main raw material.

Pellets are prepared, for example, by first mixing the main raw material, a foaming agent and a binder, adding an appropriate amount of water, kneading, granulating to produce an inner core, and then spraying water on the inner core surface. It is produced by forming a shell by rolling the powder on the mixed powder of the main raw material and the binder, with water on the surface. Here, the weight ratio of the inner core to the outer shell is 1: 0.5-
It is preferably 1: 5, and particularly preferably 1: 1 to 1: 3. When the weight ratio of the inner core to the outer shell is less than 1: 0.5, the outer shell becomes thin,
The outer shell strength is reduced, which is not preferable. On the other hand, 1: 5
If it exceeds, the specific gravity becomes large, which is not preferable.

By firing the pellets thus obtained, the artificial lightweight aggregate of the present invention can be manufactured. The firing is performed at a temperature equal to or higher than the softening point of the main raw material and the foaming temperature of the foaming agent. The specific temperature varies depending on the type of main raw material used, components, etc., but is preferably 1100 to 1350 ° C.

The specific gravity of the artificial lightweight aggregate of the present invention is controlled by changing the weight ratio of the inner core of the pellet to the outer shell, the amount of the foaming agent added to the inner core of the pellet, the firing time or the firing temperature. You can

[0016]

FIG. 1 is an explanatory view of the mechanism until the end of foaming in the pellet firing process of the method of the present invention. Pellets (a) are
As the temperature rises, it first sinters and becomes slightly densified (b). When the temperature is further raised, both the outer shell and the inner core start to soften, the foaming agent and the raw material react with each other in the inner core to start foaming and expand, and the outer shell becomes densified (c). The outer shell is softened, and the voids are reduced accordingly, and the outer shell becomes more compact than that in (c). Since the outer shell is softened, it deforms so that the whole expands according to the expansion of the inner core
(d).

As described above, according to the method of the present invention, in the temperature range in which the aggregate foams, the outer shell containing no foaming agent has a high density because it is in a softened state, while the inner core contains the foaming agent and thus foams. The overall aggregate will also be lighter. Since the outer shell has already softened, it will not crack or crack even if the inner core expands.

The thus-obtained artificial lightweight aggregate of the present invention has a low strength because the foamed inner core is low in specific gravity and rich in pores, but the strength of the aggregate as a whole is high in the high density outer shell. It is a highly strong aggregate because it is highly dependent.

[0019]

The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

<Main raw materials and additives> Rhyolite (an anti-firestone from Niijima, Tokyo), which is a type of acidic volcanic rocks in a ball mill, and volcanic pumice (a quartz andesite pumice tuff from Fukushima Prefecture), which is a type of acidic volcanic ejecta. ), And tuff (quartz andesite fine-grained tuff from Shirasawa, Aoba-ku, Sendai-shi) were crushed to the average particle size shown in Table 1 and used as the main raw material.

[0021]

[Table 1]

As the foaming agent, silicon carbide (average particle size 3.4
.mu.m) or silicon nitride (average particle size 3.1 .mu.m) was added to the pellet core of the present invention in an amount of 0.3 to 0.5% by weight, and a conventional type pellet in an amount of 0.2 to 0.3% by weight. Bentonite (manufactured by Wyoming, USA) was used as a binder, and 5% by weight was added when the average particle size of the main raw material exceeded 11.5 μm, and 3% by weight was added when it was 11.5 μm or less.

<Granulation method> Inner core: The mixed powder of the main raw material, the foaming agent, and the binder is well stirred, and an appropriate amount of water is added to the mixture, which is well kneaded. And When this was dried and the weight and diameter were measured, the average dry weight was 0.79 ± 0.05 g and the average diameter was 8 ± 0.3 mm. Outer shell: After water was sprayed on the surface of the inner core with a sprayer, it was rotated on a pan filled with a mixed powder of a main raw material and a binder to coat the mixed powder to form an outer shell. The pellets thus produced were dried to measure the dry weight, and the inner core weight was subtracted to obtain the outer shell weight. The average diameter of this pellet was 10 to 12 mm.

<Baking conditions> The above pellets were heated from room temperature to a baking temperature at 20 ° C / minute in an electric furnace, held at the baking temperature for 5 minutes, and then cooled to 1000 ° C at 20 ° C / minute. After that, the electric furnace was turned off and naturally cooled in the furnace. The firing temperature is 1240 to 1300 ° C for pellets mainly made of rhyolite,
Pellets containing volcanic pumice or tuff as the main raw material have a softening temperature lower than that of rhyolite.
The range was 40 ° C.

The above aggregate production conditions are shown in Tables 2 to 7 for each main raw material, each granulation type, and each foaming agent. Tables 2 to 6 are aggregates produced by the method of the present invention (hereinafter referred to as “inventive aggregates”), and as raw materials, Table 2, Table 5, Table 6 and Table 7 are rhyolite, Table 3 is volcanic pumice, Table No. 4 used tuff, Table 6 used silicon nitride as a foaming agent, and others used silicon carbide. Table 5
Indicates that the average particle size of the main raw material is changed between the outer shell and the inner core. Table 7 shows conventional aggregates made from rhyolite.

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

[Table 5]

[0030]

[Table 6]

[0031]

[Table 7]

<Physical Properties of Fired Product> Specific gravity, water absorption and point load fracture strength of the fired product were measured. The fracture at point load is tensile fracture, and the tensile strength σ _t was calculated from the stress at fracture as σ _t = 0.9F ₀ / d ² . Here, F ₀ is the breaking load, and d is the length between the load points of the aggregate. Average particle size 6.
Table 8 shows the measurement results of the water absorption rate of aggregates made of 8 μm rhyolite, and Tables 9 to 10 show the measurement results of tensile strength of various aggregates. When the cut surface of the fired product was observed, it was found that in the aggregate of the present invention, the outer shell and the inner core were strongly adhered to each other, and the foaming state of the inner core was good.

[0033]

[Table 8]

As is clear from Table 8, in the conventional type aggregate, the water absorption rate increases as the specific gravity decreases. On the other hand, it is recognized that the aggregate of the present invention has a very small water absorption rate regardless of the specific gravity because the surface is dense.

[0035]

[Table 9]

[0036]

[Table 10]

The relationship between the specific gravity and the tensile strength of the aggregate of the present invention and the conventional type aggregate prepared by using the main raw material having the average particle diameter of 6.8 μm shown in Table 9 is shown in FIG. FIG. 3 shows the relationship between the specific gravity and the tensile strength of the aggregate of the present invention and the conventional aggregate produced by using the main raw material of μm. From FIG. 2 and FIG.
It is recognized that the aggregate of the present invention has a higher tensile strength than the conventional aggregate when compared with the same specific gravity.

FIG. 4 shows the relationship between the average particle size of the main raw material and the tensile strength of the aggregate at a specific gravity of 0.9. As is clear from FIG. 4, the aggregate of the present invention shows a more gradual decrease in strength with an increase in the average particle size of the main raw material than the conventional aggregate. Furthermore, an example of a stress-strain diagram at the time of point load fracture test is shown in FIG. As can be seen from this figure, the displacement amount (strain amount) due to the same stress is smaller in the present invention than in the conventional aggregate. This means that the aggregate of the present invention has a higher elastic modulus. Therefore, the elastic modulus of concrete produced under the same conditions is higher when the aggregate of the present invention is used.

The characteristics of the aggregate of the present invention are summarized as follows by summing up the above results. (1) The tensile strength is higher than that of the conventional type aggregate having the same specific gravity. (2) The decrease in strength with the increase in average particle size is slower than that of the main raw material used for conventional aggregates. (3) Unlike conventional type aggregates, water absorption is low even with low specific gravity. (4) The elastic modulus of concrete can be increased as compared with the case of using the conventional type aggregate having the same specific gravity.

[0040]

EFFECTS OF THE INVENTION Since the aggregate of the present invention has a high strength in the outer shell portion, the surface thereof is not scraped or crushed during concrete kneading. Therefore, the original purpose of the lightweight aggregate can be achieved. Further, since this aggregate has a higher elastic modulus than the conventional type aggregate, it is possible to manufacture concrete having a higher elastic modulus.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a mechanism until the end of foaming in a pellet firing process of the method of the present invention.

FIG. 2 is a graph showing the relationship between the specific gravity and the tensile strength of the aggregate of the present invention and the conventional type aggregate mainly composed of rhyolite having an average particle diameter of 6.8 μm.

FIG. 3 is a diagram showing the relationship between the specific gravity and the tensile strength of the aggregate of the present invention and the conventional aggregate that mainly use volcanic pumice having an average particle size of 21.6 μm.

FIG. 4 is a diagram showing the relationship between the average particle size of the main raw material and the tensile strength of aggregate at a specific gravity of 0.9.

FIG. 5 is a diagram showing a stress-strain diagram during a point load fracture test.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Imai 2-4-2 Daisaku, Sakura City, Chiba Prefecture Central Research Laboratory, Ono Cement Co., Ltd. (72) Ikuo Saito 2-4-2 Daisaku, Sakura City, Chiba Prefecture No. Ono Cement Co., Ltd. Central Research Institute (72) Inventor Takeaki Ogami 2-4 Daisaku, Sakura City, Chiba Prefecture Ono Cement Co., Ltd. Central Research Laboratory (72) Inventor Masaaki Noguchi 2-chome, Sakura City, Chiba Prefecture No. 4-2 Central Research Laboratory, Onoda Cement Co., Ltd. (72) Inventor Akio Shinozaki 1-32, Shibaura, Minato-ku, Tokyo Inside Shimizu Construction Co., Ltd. (72) Kenichi Naito, 1-chome, Shibaura, Minato-ku, Tokyo In 2-3 Shimizu Construction Co., Ltd. (72) Inventor Masatoshi Nakanishi 1-3-2 Shibaura, Minato-ku, Tokyo Inside Shimizu Construction Co., Ltd. (56) References JP-A-47-34607 (JP, A) JP-A-49-59120 (JP, A) JP-A-4-200740 (JP, A) JP-A 61-251530 (JP, A) JP-A-53 -46304 (JP, A) JP 58-140365 (JP, A) JP 63-45154 (JP, A) JP 49-88918 (JP, A) (58) Fields investigated (Int.Cl) . ⁷ , DB name) C04B 14/02 C04B 20/10 C04B 20/04 C04B 14/16

Claims (3)

(57) [Claims] 1. A main raw material is a crushed product of acidic volcanic rocks, acidic volcanic ejecta or tuff, and a granulated product of a mixture of the main raw material, a foaming agent and a binder is a mixture of the main raw material and a binder. A method for producing an artificial lightweight aggregate comprising a foamed inner core and a dense outer shell, which is characterized by coating the pellets and firing the pellets. 2. The production method according to claim 1, wherein the main raw material used for the inner core and the main raw material used for the outer shell have different average particle sizes. 3. The specific gravity of the artificial lightweight aggregate is controlled by changing the weight ratio of the inner core and the outer shell of the pellet, the amount of the foaming agent added to the inner core of the pellet, the firing time or the firing temperature. 2. The manufacturing method according to 2.