JPH07172951A - Production of alc - Google Patents

Abstract

PURPOSE:To produce an ALC panel excellent in a foamed state, remarkably reduced in the number of large air bubbles and having a remarkably uniform distribution of air bubbles by admixing a reducing agent with a slurry, kneading the resultant mixture, subsequently adding an aluminum powder coated with water glass, kneading the obtained mixture and then casting in a mold. CONSTITUTION:This method for production of ALV (high-temperature and high-pressure steam curing light-weight foamed concrete) is carried out by adding powdery aluminium as a foaming agent to a slurry containing a calcareous material composed of cement and lime, a siliceous raw material such as silica stone or silica sand and water as the main raw materials, kneading the resultant mixture and subsequently casting it into a mold. In the production method, a reducing agent is added to the slurry and the resultant mixture is kneaded. After adding an aluminium powder coated with water glass and kneading the obtained mixture, the kneaded material is cast into the mold. Ferrous sulfate or sodium sulfite is recommendably used as the reducing agent and the concentration or the amount is suitably controlled according to the reactivity of the powdery aluminium, the temperature of the raw material slurry, etc. Water glass forms a remarkably thin oxide coating film on the surface of aluminium and thereby aluminium can be prevented from reacting with an alkali.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing lightweight aerated concrete (ALC) at high temperature and high pressure steam curing using a foaming agent.

[0002]

2. Description of the Related Art ALC is a calcareous raw material made of cement and lime, a siliceous raw material such as silica stone and silica sand, and a slurry containing water as a main raw material. Then, it is transferred to an autoclave and subjected to high temperature and high pressure steam curing to be manufactured. The ALC thus obtained needs to have an extremely uniform appearance as a building material, and in particular, the coarse air bubbles present on the surface not only spoil the aesthetics of the product and reduce the commercial value, but also paint and the like. When applying, it is necessary to fill in holes. Furthermore, in recent years, the demand for high-grade and high-quality feelings for building materials has increased, and the designability of ALC surfaces and surface treatment methods have diversified. It is also required that the conventional foaming state of aluminum makes it difficult to obtain a uniform cell distribution.

It is considered that the coarse air bubbles are caused by air bubbles trapped inside the injection pipe from the mixer to the mold and near the injection port during stirring in the mixer. In particular, when the aluminum powder started foaming inside the slurry injection pipe and near the injection port, the slurry viscosity increased, and when the slurry viscosity increased, coarse air entrapped in the raw material slurry was difficult to escape and coarse bubbles were generated. . In addition, when the raw material slurry foams, volume expansion occurs, the specific gravity of the slurry decreases, and the difference in specific gravity from the coarse bubbles decreases, so that the buoyancy acting on the coarse bubbles decreases and the coarse bubbles are formed. Also,
When foaming started during mixing of raw materials and during slurry injection, the bubbles formed were destroyed or associated with each other, resulting in increase of coarse bubbles and nonuniformity of bubble diameter. On the other hand, if the foaming speed is delayed after foaming starts, the slurry loses fluidity and condenses due to the progress of the hydration reaction of quick lime, cement, etc., making it impossible to obtain a homogeneous product such as cavities around the reinforcing bars. .

Furthermore, when an oxidizing substance such as hexavalent chromium is present in the raw material, for example, in cement, the surface of the aluminum powder is oxidized, the reaction with the alkali in the slurry is inhibited, and the foaming is significantly delayed. As a result, the start timing of foaming changes due to fluctuations in the hexavalent chromium content, and therefore a constant foaming state cannot be maintained at all times.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to remove coarse bubbles appearing on the surface and to have a uniform inner bubble diameter distribution. It is to provide a method of manufacturing.

[0006]

According to the present invention, aluminum powder is added as a foaming agent to a slurry containing a calcareous raw material composed of cement and lime, a siliceous raw material such as silica stone and silica sand, and water as main raw materials. AL to be injected into the mold after kneading
In the manufacturing method of C, a reducing agent is added to the slurry and kneaded, and then aluminum powder having a coating formed of water glass is added, and the mixture is kneaded and then poured into a mold.

[0007]

In the present invention, the reducing agent is added in an amount necessary to reduce an oxidizing substance in the raw material, for example, hexavalent chromium to trivalent chromium, so that the oxidizing property is extinguished so that the reducing agent is always constant. The foamed state can be maintained. Water glass forms an extremely thin oxide film on the surface of aluminum and suppresses the reaction between aluminum and alkali, but the film is broken for a certain period of time and the reaction of aluminum starts. However, the reaction rate after the start of the reaction, that is, the foaming rate is not affected.
That is, a reducing agent in an amount necessary to reduce an oxidizing substance is added, and after its oxidizing property is killed, an aluminum powder having a very thin film formed with water glass is added to react the aluminum with an alkali. By performing the process of temporarily suppressing, it became possible to control the time from the start of foaming to the end of foaming. For this reason, entrainment of air during mixing of the raw materials or discharge of the raw materials is suppressed, so that coarse bubbles can be removed, and the foaming state becomes constant. Examples of the reducing agent used include ferrous sulfate, sodium sulfite, potassium hydrogen sulfite, sodium hydrogen sulfite, and the like, among which ferrous sulfate or sodium sulfite is inexpensive,
Most preferred because it does not impair the physical properties of ALC. The concentration and amount may be appropriately adjusted depending on the reactivity of the aluminum powder and the temperature of the raw material slurry.

[0008]

EXAMPLES Examples will be described below. (Example) The raw material composition is as shown in Table 1. Aluminum powder was added to an aqueous solution containing 0.5% by weight of water glass (J sodium silicate No. 3) with respect to aluminum to form a film on the aluminum surface. The mixture of the solid raw material and water was stirred for 2 minutes while adjusting the temperature to 45 ° C., and then an aqueous solution containing 0.2 wt% of ferrous sulfate as a water-soluble reducing agent relative to cement was added to the raw material slurry. After stirring for 1 minute, the film-treated aluminum powder was added, and after 20 seconds, the raw material slurry was taken for 70 seconds.
It was discharged into a mold of 0 mL × 1.5 mW × 0.6 mH. The foaming started 30 seconds after the completion of the raw material injection, and the subsequent reaction was also quick. In the foaming measurement, a change in foaming height on the surface of the slurry was measured with time. The result of foaming measurement is shown in FIG.

[0009]

[Table 1]

A molded product obtained by semi-curing the product with a piano wire is used.
After cutting into cm thickness, autoclave curing was performed, 10 m ² was randomly selected from either side of the obtained product, and the number of coarse bubbles of 3 mm or more was measured to determine the number per 1 m ² . Further, the bubble size distribution was measured by an image processing device. Table 2 shows the results of measuring the number of coarse bubbles and the bubble size distribution. Coarse cell count was very good as 25 / m ^2. Moreover, it is 7 cm x 7 c from the surface where the coarse bubbles are measured.
When five points were randomly selected from the visual field of m and the bubble size distribution was measured by an image processing device, bubbles of 0.5 to 1.5 mm occupied 83% of the whole and were in a very uniform bubble state.

(Comparative Example 1) Untreated aluminum powder,
A ferrous sulfate was not added, and the other components were the same as those of the examples, and the production was performed by the same method. Foaming had started before the injection of the mold. The result of the foaming measurement is shown in FIG. 1, and the result of the measurement of the number of coarse bubbles and the bubble diameter distribution is shown in Table 2. The number of coarse bubbles is 110 /
It is as many as m ^2, and looking at the distribution state of the bubble diameter, relatively large bubbles of 2.0 to 3.0 mm occupy 12%, while 0.5
Micro bubbles of less than mm occupy 47%. It is considered that the reason for the large number of fine bubbles is that aluminum foaming started during stirring in the mixer and the formed bubbles were destroyed.

(Comparative Example 2) A coating was produced by using aluminum powder as a coating, adding no ferrous sulfate, and otherwise using the same composition and method as in Example. The result was that foaming was significantly delayed compared to the examples. The result of the foaming measurement is shown in FIG. 1, and the result of the measurement of the number of coarse bubbles and the bubble diameter distribution is shown in Table 2. The number of coarse bubbles was 24 / m ² , which was almost the same as that of the example. When the bubble size distribution was measured with an image processing device, it was 0.5-
The amount of bubbles of 1.5 mm was 75% of the whole, which was slightly lower than that of the example, and cavities were formed around the reinforcing bars, which was unfavorable for the product. The cavities around the rebar were
It is considered that the foaming rate was significantly delayed.

[0013]

[Table 2]

[0014]

According to the present invention, it is possible to obtain an ALC panel in which the foaming state is good, the number of coarse bubbles is remarkably small at 25 / m ² , and the bubble diameter distribution is very uniform.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of time-dependent measurement of changes in foaming height on the surface of a slurry.

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Claims (2)

[Claims] 1. An aluminum powder as a foaming agent is added to a slurry containing a calcareous raw material consisting of cement and lime, a siliceous raw material such as silica stone and silica sand, and water as a main raw material, and after kneading, a mold is formed. In the manufacturing method of ALC to be poured, a reducing agent is added to the slurry and kneaded, and then aluminum powder having a film formed of water glass is added, and the mixture is kneaded and then poured into a mold to produce ALC. Method. 2. The manufacturing method according to claim 1, wherein the aluminum powder having the coating film is produced by suspending the aluminum powder in an aqueous solution of the water glass.