JP2557065B2 - Method for producing steam curing light weight air bubble concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to steam-cured lightweight cellular concrete (hereinafter referred to as ALC).
Abbreviated)).

[Conventional technology]

ALC is a siliceous raw material such as crushed silica stone or silica sand,
Lime and raw materials such as cement are the main raw materials, and aluminum powder as a foaming agent and water are added to this to make a slurry, which is then semi-cured by foaming, then transferred to an autoclave and steam is introduced, and the temperature is raised. Manufactured by a steam curing method that uses pressure.

The ALC raw material is poured into the mold as a slurry and first undergoes a foaming process. This foaming process is normally completed within 20 to 40 minutes after the slurry is poured into the mold.

When the foaming is completed, the slurry loses its fluidity and is condensed due to the progress of hydration reaction of quicklime, cement and the like. If the slurry condenses before this foaming is completed, the slurry without fluidity expands, causing cracks or fine cracks, which not only increases the defective rate of the product but also compresses the ALC. It may cause a decrease in strength and bending strength. Therefore, in the past, it was necessary to manufacture it with great care in adjusting the timing of foaming and setting.

This timing was adjusted by adjusting the alkalinity of the mixed raw material, adjusting the temperature when pouring the raw material slurry into the mold, and adding aluminum powder to the raw material slurry. However, it was not possible to deal with the fact that the timing of foaming changed due to changes in the components contained in the raw materials such as cement, silica stone, and lime.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for producing ALC which does not have the above-mentioned drawbacks and which can always obtain substantially constant foaming and exhibits desirable physical properties.

The inventors of the present application, as a result of diligent examination of what component in the raw material causes the delay of foaming, paying attention to the fact that foaming is delayed when an oxidizing substance such as hexavalent chromium is present in the raw material, As a result of further research, it was found that this oxidizes the surface of metallic aluminum powder as a foaming agent and inhibits the reaction between aluminum and alkali in the slurry, which significantly delays foaming. The present invention has been accomplished by finding that when a raw material having a limited content of hexavalent chromium in the cement is used, it does not affect foaming of the slurry.

[Means for solving problems]

The method of the present invention is a powdery siliceous raw material, a cement or cement and lime powder as a calcareous raw material as a main raw material, in the method for producing a steam-curing lightweight cellular concrete using aluminum powder as a foaming agent, hexavalent chromium as the cement. It is configured to use cement with a content of 5 ppm or less.

[Action]

When the content of oxidizing substances in the ALC raw material was investigated, hexavalent chromium was generally present in the Portland cement used as a calcareous raw material in an amount of 0.4 to 20 ppm, and sometimes exceeded 20 ppm. This chromium is considered to be contained in the raw material for manufacturing Portland cement.

Hexavalent chromium in cement is water-soluble chromium trioxide (Cr
It seems that it is contained in the form of O ₃ ), and it elutes quickly when the main raw material and water are mixed to form a slurry, and when aluminum as a foaming agent is added to this, hexavalent chromium becomes an oxidizing agent. And forms an oxide film on the aluminum surface. For this reason, it is considered that the reaction between aluminum and alkali is delayed and the foaming is delayed.

The content of hexavalent chromium in the cement used is set to 5 ppm or less because the delay of foaming increases almost in proportion to the content of hexavalent chromium, whereas the content of 5 ppm or less is somewhat This is because, even if the foaming delay is caused, free water is not generated, bubbles are not disturbed due to the condensation of the slurry before the completion of foaming, cracks are not generated, and ALC having desirable physical properties can be obtained.

〔Example〕

 Examples will be described below.

The raw material is silica stone crushed in the mixing ratio shown in Table 1, powdered quick lime, and cement with different Cr ⁶⁺ content, and this is mixed with water to form a slurry, and then aluminum powder is added. Foaming was measured.

The foaming was measured by pouring the slurry into a mold having a length of 12 cm, a width of 12 cm, and a depth of 70 cm, and measuring the change with time of the distance from the upper end of the mold to the surface of the slurry. The results are shown in Fig. 1.

In Fig. 1, curve A is the foaming curve of test No. 1, and since the content of Cr ⁶⁺ in the cement was as low as 2.0 ppm, foaming started immediately after pouring into the mold and completed in about 20 minutes. Cage,
It can be said that the foaming curve is almost ideal. The curve B is the foaming curve of Test No. 2 and the content of Cr ⁶⁺ in the cement is 4.5 ppm. Although the completion of foaming is slightly delayed as compared with the curve A, there was no particular inconvenience.

On the other hand, curves C and D are the foaming curves of Test Nos. 3 and 4, respectively, and the contents of Cr ⁶⁺ in the cement are 7.0 ppm and 15 ppm, respectively, and about 3 to 5 from immediately after the injection into the mold until the foaming starts. It takes about 40 to 60 minutes to complete the foaming. As a result, defects such as generation of free water, turbulence of air bubbles due to condensation of slurry before the completion of foaming, and generation of cracks occurred.

〔effect〕

As described in detail above, according to the method of the present invention, ALC
Since the amount of Cr ⁶⁺ contained in the cement, which is the main raw material of the, is small, it does not hinder the foaming of aluminum so much that the foaming is performed in a timely manner, so that cracks and fine cracks of the semi-plastic material may occur. It is possible to produce an ALC that is prevented and has good physical properties.

[Brief description of drawings]

FIG. 1 shows the relationship between the elapsed time and the foaming state in each test example. In the figure, the vertical axis represents foaming height and the horizontal axis represents elapsed time.

Claims (1)

(57) [Claims] 1. A method for producing a steam-cured lightweight cellular concrete using a powdery siliceous raw material, cement or cement and lime powder as main raw materials and aluminum powder as a foaming agent, and hexavalent chromium as the cement. A method for producing a steam-cured lightweight cellular concrete, which comprises using a cement having a content of 5 ppm or less.