JPS5941940B2 - Method for producing heat-resistant gypsum composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a gypsum composition with improved heat resistance.

More specifically, 2 to 10% by weight of alkaline earth metal phosphate is added to gypsum or gypsum-cement slurry based on the unit weight of gypsum to prevent a decrease in the hydration rate of the gypsum composition. The present invention also relates to a method for producing a gypsum composition, which is characterized in that it also prevents a decrease in bending strength.

Conventionally, it is clear that the solidified form of a gypsum composition forms dihydrate gypsum and maintains its strength.

However, as is already known, when this dihydrate gypsum undergoes a chemical change at high temperatures, particularly at temperatures above 50°C, it is dehydrated from dihydrate gypsum to hemihydrate gypsum.

Furthermore, the hemihydrate gypsum that is produced is not β-type hemihydrate gypsum, but β-type hemihydrate gypsum.
The strength of type hemihydrate gypsum is significantly lower than that of dihydrate gypsum,
It may become unbearable for use as building materials, etc.

Gypsum or gypsum in a place exposed to sunlight in the summer
Cement-based compositions are heated to 50°C or higher, sometimes up to 60-80°C, and the heated gypsum composition undergoes the above-mentioned dehydration reaction internally, resulting in
Even water gypsum becomes β-type hemihydrate gypsum with weak bending strength, and β
Products made from molded hemihydrate gypsum also have low bending strength, which poses a risk of collapse.

Later, in order to suppress the dehydration reaction of the gypsum composition at high temperatures and prevent a decrease in bending strength, a gypsum-cement composition, in which cement was added to gypsum, was used, but this was also insufficient and at high temperatures. The bending strength decreased due to the dehydration reaction.

The present inventors have conducted extensive research with the aim of minimizing the dehydration reaction of gypsum or a gypsum-cement composition, that is, dihydrate gypsum, at high temperatures, and furthermore, have found that gypsum or By adding 2-10% by weight of alkaline earth metal phosphate to the gypsum-cement slurry based on the unit weight of gypsum, the dehydration reaction at high temperatures, especially at 60 to 80°C, is suppressed as much as possible.
Furthermore, they discovered a scale that reduces the decrease in bending strength compared to conventional products and maintains durability such as no cracking as a product, and completed this invention.

The gypsum used in the present invention is α
Type or β-type hemihydrate gypsum may be used, but β-type hemihydrate gypsum or a composition of it and cement is preferred for building materials that require high bending strength.

Further, any alkaline earth metal phosphate added to suppress the dehydration reaction is effective, but magnesium phosphate is particularly preferred.

The amount added is preferably 2 to 10% by weight based on the unit weight of gypsum or gypsum-cement type gypsum.

If it is less than 2% by weight, it is difficult to suppress the dehydration reaction, and if it is more than 10% by weight, there will be no improvement in heat resistance, or it will have a negative effect on bending strength and other properties.

The cement used as a raw material is usually Portland cement, but other types of cement may also be used.

Further, fine aggregate having a particle size commonly used in gypsum-cement compositions may be added, and the amount added may be the amount normally added to gypsum-cement compositions.

In addition, depending on the purpose, water reducing agents, anti-floating agents, hardening regulators, antifoaming agents, waterproofing agents, etc. may be added in required amounts to improve the resulting gypsum composition.

The amount of water added to obtain a slurry may be within the commonly used range.

The heat-resistant gypsum composition of the present invention can be produced by adding and mixing an alkaline earth metal phosphate during the production of a conventional gypsum composition.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

The specimens used in the Examples and Comparative Examples are slurries made by adding the required amount of alkaline earth metal phosphate, water, additives such as water reducers, and sand as necessary to gypsum or gypsum-cement system. C, vertical 1-5 (Z771, horizontal 3c
It was poured into a mold with a length of 20 cIrL and molded after hardening.

The bending strength retention rate (%) was determined by curing the above specimens indoors for 2 weeks, then holding them in a constant bath at 45°C for 48 hours, and measuring the bending strength using a Tensilon tensile tester. Another 5 samples were prepared and kept in a constant mixing tank at 45°C for 48 hours.
The book specimens were further kept in a 70°C constant abyss tank for 30 days, and the bending strength was measured, and the bending strength was calculated from the average value of each.

The hydration rate retention rate (%) was calculated from the average value of the hydration rates of five specimens whose bending strength was measured.

Example 1 A gypsum-cement type raw material containing 1,600 g (80% by weight) of α-type soil and water gypsum and 400 g (20% by weight) of Portland cement was prepared, and 80 g (based on the unit weight of gypsum) of magnesium phosphate octahydrate was added to this. 5% by weight (calculated as magnesium phosphate), Melment (manufactured by Showa Denko) 20I as a water reducing agent (1.0% by weight based on gypsum-cement)
, 0.4g of X-50-418K (manufactured by Shin-Etsu Chemical Co., Ltd.) as a silicone antifoaming agent (0.02g for gypsum-cement)
% by weight) and further added 500 g of water and sufficiently kneaded to form a slurry.

A specimen was prepared using this slurry, and the hydration rate retention and bending strength retention were measured.

The hydration rate retention rate was 45% and the bending strength retention rate was 74%.

Example 2 An experiment was carried out in the same manner as in Example 1, except that the α-type earth and water gypsum-cement raw material in Example 1 was replaced with α-type earth and water gypsum.

The hydration rate retention rate was 28% and the bending strength retention rate was 59%.

Example 3 An experiment was conducted in the same manner as in Example 1, except that barium phosphate was used instead of magnesium phosphate octahydrate.

The hydration rate retention was 40% and the bending strength retention rate was 65%.

Example 4 An experiment was conducted in the same manner as in Example 1, except that 2000 g of No. 6 silica sand (100% by weight based on the unit weight of cement) was added to the gypsum-cement slurry.

The hydration rate retention rate was 43% and the bending strength retention rate was 69%.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1, except that magnesium phosphate octahydrate was replaced with magnesium sulfate heptahydrate.

The hydration rate retention was 29% and the bending strength retention rate was 47%.

Comparative Examples 2, 3 and 4 In Examples 1, 2 and 4, magnesium phosphate 8
The experiment was carried out in the same manner as in Examples 1, 2 and 4, except that no aqueous salt was added.

The hydration rate retention rates were 25%, 13%, and 32%, and the bending strength retention rates were 45%, 29%, and 66%.

Claims (1)

[Claims] 1 Add alkaline earth metal phosphate to gypsum or gypsum-cement slurry at a rate of 2 to 20% based on the unit weight of gypsum.
A method for producing a heat-resistant gypsum composition, characterized by adding 10% by weight.