JPS5855096B2 - Cement composition for plastering - Google Patents

Description

[Detailed description of the invention] The present invention relates to cement compositions for plastering.

For details, see Portland cement with fly ash and 2
To provide a cement composition for plastering that does not cause cracks and contains a specific amount of water gypsum.

Portland cement has a large shrinkage when it hardens and dries, and its biggest drawback is that it causes cracks in concrete and mortar.

In order to compensate for this deficiency, various research studies have been proposed.

For example, there are methods of mixing additives such as water-soluble polymers, resin emulsions, latex, and fibers, or methods of mixing swelling agents such as calcium sulfoaluminate.

However, these admixtures are not only expensive but also ineffective unless used in large quantities, and cannot necessarily be said to be the best method.

On the other hand, there has been an attempt to add gypsum to Portland cement to form an Ettlin guide at the beginning of water use, and use its expandability to compensate for shrinkage and prevent cracks, but it is not possible to expect a sufficient effect from using gypsum instead of Portland cement. do not have.

Furthermore, a method has been proposed in which borlan activated by calcining kaolin, white earth, etc. and insoluble anhydrite are added to Portland cement. ~4 weeks) is not very effective in preventing cracks as the compensation is insufficient.

Moreover, it had the disadvantage of being economically disadvantageous because it required calcination of anhydrite and bollan.

The present inventors have been diligently conducting research to obtain a cement composition for plastering that does not cause cracks at a low cost. However, by blending specific amounts of specific characteristics with Portland cement, we unexpectedly found that fly ash and dihydrate gypsum were They discovered that when a specific amount is used, it becomes a plastering cement that hardly cracks, leading to the completion of the present invention.

The present invention is a plastering cement composition comprising 100 parts by weight of Portland cement, 5 to 45 parts by weight of fly ash, and 12 to 44 parts by weight of gypsum dihydrate.

The Portland cement used in the present invention is not particularly limited, and any commercially available cement can be used.

Generally commercially available Portland cement contains a large amount of dihydrate gypsum, so when mixing dihydrate gypsum, which will be described later, it is necessary to take into account the amount of gypsum contained in the mixture.

Further, the fly ash used in the present invention is typified by combustion ash generated when coal powder is combusted, but the one normally used in fly ash cement is most suitable.

The fly ash is usually used in powder form, and is generally 2000 to 3000 cI? Blaine of about L/g is preferable.

Furthermore, the dihydrate gypsum used in the present invention is Ca SO4.2H
Natural gypsum, chemical gypsum, flue gas desulfurization gypsum, etc. can be used without particular limitation as long as they are represented by 20.

In the present invention, as will be described later, the composition ratio of gypsum is larger than that of conventional gypsum, so it must be used in the form of dihydrate gypsum.

Generally, as gypsum, gypsum hemihydrate, insoluble anhydrite, etc. may be blended into Portland cement, but in the present invention, when these gypsum hemihydrate, insoluble anhydrite, etc. are used, the cement contains 3~4 or more modulus. It cannot be used because it exhibits rapid setting and cannot prevent initial contraction.

In the present invention, fly ash and dihydrate gypsum are blended with Portland cement, but the composition ratio of fly ash and dihydrate gypsum in the cement composition for plastering is important.

That is, the amount of fly ash is in the range of 5 to 45 parts by weight, preferably 15 to 2 parts by weight, per 100 parts by weight of Portland cement.
It is necessary to mix within the range of 5 parts by weight.

If the fly ash content is smaller than the above lower limit, the effects of the present invention will not be sufficiently exhibited.

Furthermore, if the content of the fly ash is larger than the above-mentioned upper limit, the effect not only tends to decrease in terms of preventing crack formation, but also the mortar strength sharply decreases, which is not preferable.

When fly ash is blended within the specified range, particularly from 15 to 25 parts by weight per 100 parts by weight of Portland cement, the effects of reducing mortar shrinkage and preventing cracking are synergistic, and almost no cracking occurs.

The dihydrate gypsum in the present invention is Portland cement 100.
12 to 44 parts by weight, preferably 20 to 3 parts by weight
It is necessary to mix it so that it is 5 parts by weight.

The blending ratio of dihydrate gypsum in the present invention is an important factor.

That is, if the amount of dihydrate gypsum is less than the lower limit, the effect of preventing mortar from cracking is insufficient, and if it is more than the upper limit, cracks tend to occur more easily.

Although there are some differences depending on the blending ratio of fly ash, in general, the blend of dihydrate gypsum is most effective between 23 and 30 parts by weight per 100 parts by weight of Portland cement, and the optimal point for preventing cracks is found, and the blend is too small. Even if there is too much, the effect tends to decrease in a pyramidal manner.

Such an effect is only exhibited in combination with a specific amount of fly ash, and is not exhibited at all even when, for example, gypsum hemihydrate or insoluble anhydrite is used.

As mentioned above, commercially available Portland cement generally contains about 2 to 4% dihydrate gypsum, so when determining the blend of dihydrate gypsum in the present invention, portland cement 2 mixed in the product.
It is necessary to consider the amount of water gypsum.

In other words, if you are using portland cement with 3rd grade dihydrate gypsum mixed in, and if you are going to mix 255 parts by weight of dihydrate gypsum to 100 parts by weight of portland cement, then mix it into portland cement. It is preferable to subtract 3 parts by weight of dihydrate gypsum and add 211 parts by weight of dihydrate gypsum.

As is clear from the above description, the present invention exhibits the effect of providing an excellent cement composition for plastering by blending specific amounts of inexpensive specific substances into Portland cement.

However, in the present invention, the specification of specific substances and their blending amounts are important, and even if these limits are exceeded or other similar substances are substituted, the effects of the present invention cannot be achieved.

EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be described below, but the present invention is not limited to these Examples.

Example 1 Portland cement with the chemical composition shown in the table (containing about 4 tons of dihydrate gypsum), fly ash (2600 branes)
and dihydrate gypsum (3620 Blaine) were used as raw materials, respectively.

Each of the above raw materials, sand, and water were mixed in a Hobart mixer in accordance with JISR5201-1977 to produce mortar as shown in Table 2.

However, the formulation in Table 2 shows the formulation of each raw material in parts by weight, and for Portland cement it is 100 parts by weight excluding the content of dihydrate gypsum, and for gypsum, it is the amount contained in Portland cement and the added dihydrate. The amount of plaster was added and displayed.

The mortar was subjected to a crack test, a strength test and a shrinkage test using the following measurement methods.

(1) 2 week strength Measured based on JISR5201-1977.

(2) Crack test The size of the specimen is 100W x 100H
A crack was caused as a free shrinkage part at a length of 100%.

The curing conditions were as follows: 24 hours after molding the specimen, it was demolded and left at room temperature (20±2°C) for 24 hours.

Thereafter, it was placed in a shrinkage curing box at 30° C. and a relative humidity of 55%, and the number of days from the day it was removed from the mold until cracks (0.1% in cracks) appeared was defined as the number of days in which cracks occurred.

(3) Shrinkage rate: Shape the bottom according to how to make the strength measurement specimen specified in JISR5201, mold after 24 hours, and then JISA1
It was measured based on the 129 Mortar and Concrete Length Change Test Method.

These results are shown in Table 3 for the number of days of crack occurrence and shrinkage rate, and Table 4 for the strength after 2 weeks.

In Tables 2 to 4, /16.1 to 5, 8 to 9, 12 to
Nos. 13 and 16 are comparative examples.

Comparative Example l Ferrosilicon dust (particle size 0.05 to 1.0μ) was used instead of the fly ash in Table 2 of Example.

SiO2 content 94.0 and reexamination S i 0293
．． It was carried out in the same manner as in the example except that Section 3) was used.

The results were as shown in Table 5.

Comparative Example 2 β-type hemihydrate gypsum (
The same procedure as Comparative Example 1 was carried out except that Blane 3650) was used.

The results were as shown in Table 5.

Comparative Example 3 The same procedure as Comparative Example 2 was carried out except that insoluble anhydrite (Blaine 3600) was used instead of β-type hemihydrate gypsum in Comparative Example 2.

The results are shown in Table 5.

Claims (1)

[Claims] 1. A cement composition for plastering consisting of 100 parts by weight of Portland cement, 5 to 45 parts by weight of fly ash, and 12 to 44 parts by weight of dihydrate gypsum.