JPH10236860A - Cement composition having resistance to sulfuric acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compsn. suitable to be used for such a place where problems about corrosion by sulfate radicals are caused, and to improve resistance against acid rain by incorporating a cement and a water-soluble org. compd. having an alkali metal sulfonate as a substituent. SOLUTION: A cement such as portland cement normal cement, medium heat cement, sulfate-resistant cement, slag cement and fly ash cement by 100 pts.wt. is compounded with a water-soluble org. compd. having an alkali metal sulfonate as a substituent selected from naphthalenesulfonate, ligninsulfonate, nitrogen-contg. sulfonate, etc., by 0.5 to 4 pts.wt., preferably 1.0 to 3.5 pts.wt., more preferably 1.7 to 3.2 pts.wt. If necessary, 30 to 100 pts.wt. of calcium carbonate having 1μm to 1mm particle size with industrial purity, limestone powder, limestone aggregate or precipitated calcium carbonate prepared by the reaction of calcined limestone and carbonic acid gas is also compounded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a sulfuric acid-resistant cement composition suitable for use in places where corrosion by sulfate groups is a problem, such as sewers and hot springs, and having improved acid rain resistance. About.

[0002]

2. Description of the Related Art Corrosion of hardened cement by sulfuric acid or sulfate has been a problem in places exposed to an environment containing sulfuric acid such as sewers and hot springs. The problem is not limited to problems in limited places such as sewers and hot springs, but is a problem for the entire structure using cement. When the cement composition comes into contact with sulfuric acid, it forms sparingly soluble gypsum, and at the same time, silicic acid, alumina and the like dissolve to form silica and alumina gel. This effect of sulfuric acid on cement naturally depends on the acid concentration. pH greater than 2 (sulfuric acid concentration 0.1%
Below) In the case of mild, as in the case of corrosion by carbon dioxide, sulfate or low-concentration acid, densification of the cement composition is effective in terms of suppressing penetration of corrosive substances into the interior. Although the corrosion resistance can be improved by lowering the water-cement ratio while ensuring workability by using a high-performance AE water reducing agent, it is difficult to cope with severe cases. , It is said that it is difficult to expect the cement composition to have acid resistance. As a method for preventing deterioration by acid at a pH of 2 or less (sulfuric acid concentration of 0.1% or more),
Anti-corrosion that prevents the cement composition from coming into contact with chemically corrosive substances by coating the cement composition with a polymer in the cement composition or the surface of the cement composition with a corrosion-resistant material (for example, epoxy resin or unsaturated polyester resin). A coating (lining) material is used. However, polymer cements and anticorrosive coatings are not only expensive, but are not versatile because special steps are involved during manufacturing or construction. In some cases, it is not necessary to improve the sulfuric acid resistance.

[0003]

It is an object of the present invention to overcome these problems of the prior art. That is, the present invention provides a cement composition that gives a cured product with improved sulfuric acid resistance without requiring a special step or a large cost burden during the production of the cement composition or the construction using the cement composition. Aim.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a cement composition containing 0.5 to 4 parts by weight of a water-soluble organic compound having an alkali metal salt of sulfonic acid as a substituent per 100 parts by weight of cement. Hereinafter, the present invention will be described in detail.

[0005] In producing a cement product from a cement composition, as a means for reducing the water-cement ratio while ensuring high workability, it is a well-known method to add a water reducing agent. There are various water reducing agents depending on the difference in the main organic components constituting the water reducing agent. Among them, a water-soluble organic compound having a sulfonate as a substituent such as naphthalene sulfonate or melamine sulfonate is one of them. It is. However, in this case, the purpose of adding the water-soluble organic compound is to ensure the fluidity of the slurry containing cement when the water-cement ratio is reduced, so that the amount of addition naturally achieves the purpose. The addition is generally performed in an amount of 1 part by weight or less based on a solid component per 100 parts by weight of cement. For example, a water reducing agent commercially available from Kao Corporation under the trade name of Mighty 150 contains naphthalene sulfonate as a main organic component, and the amount added per 100 parts by weight of cement component is 0.6 to It is stated in the manual to be 2.4 parts by weight. Mighty 150
Is an aqueous solution containing about 40% by weight of a solid component containing naphthalenesulfonic acid as a main component. Therefore, the amount added on a solid component basis is 0.2% per 100 parts by weight of the cement component.
4 to 0.96 parts by weight.

The reason why the amount of the water reducing agent measured based on the solid components is set to 1 part by weight or less per 100 parts by weight of cement is because excessive addition may cause a delay in curing, Even if it is added, the improvement of the fluidity will reach a plateau, and there is no merit in terms of securing the fluidity, but it is a major factor that is economically a negative factor. That is, the advantage brought about by adding an excess of the required minimum amount required in terms of ensuring fluidity has not been recognized. The present inventors, by increasing the addition amount of a water reducing agent containing a water-soluble organic compound having a sulfonate as a substituent than the amount generally performed for the purpose of ensuring fluidity, after curing. The present inventors have found that a cement composition having significantly improved sulfuric acid resistance can be obtained, and have reached the present invention.

[0007] The mechanism of the improvement in sulfuric acid resistance brought about by the addition of a water-soluble organic substance having a sulfonate as a substituent serves as a water reducing agent for this substance, that is, densification of the hardened body structure by reducing the water cement ratio. It cannot be explained only by itself, and it is presumed that the added organic substance, which originally has sulfuric acid resistance, forms a coating layer on the surface of cement particles to improve the sulfuric acid resistance of the cured product.

As the compound used in the present invention as a water-soluble organic substance having a sulfonate as a substituent, an alkali metal salt of each sulfonic acid such as naphthalenesulfonic acid, ligninsulfonic acid, melaminesulfonic acid and nitrogen-containing sulfonic acid is used. Among them, alkali metal salts of naphthalenesulfonic acid are preferable because they hardly inhibit the setting and hardening of the cement, and thus do not require the use of a setting accelerator. These sulfonates are generally commercially available in the form of an aqueous solution or powder as a sodium salt, but they can be used as they are.

The amount of the water-soluble organic compound having an alkali metal salt of sulfonic acid as a substituent is 0.5 to 4 parts by weight, preferably 1.0 to 4 parts by weight, per 100 parts by weight of cement.
3.5 parts by weight, more preferably 1.7 to 3.2 parts by weight. It should be noted that the addition amount referred to here does not refer to the total amount of the additive that is commercially available in the form of an aqueous solution, but replaces the alkali metal salt of sulfonic acid contained therein and remaining after removing water. It refers to the weight of a solid component mainly composed of an organic substance having a base. When the addition amount is less than 0.5 part by weight, it has a function as a water reducing agent, but the effect of improving sulfuric acid resistance is small, and when it is more than 4 parts by weight, not only is it disadvantageous in terms of cost, but also Is undesirably caused by a delay in the curing of the resin.

The cement used in the present invention includes Portland cement, ordinary cement, moderate heat cement,
Examples thereof include sulfate-resistant cement, blast furnace cement, and fly ash cement.

By adding calcium carbonate to cement obtained by adding a water-soluble organic substance having an alkali metal salt of sulfonic acid as a substituent to cement, a cement composition having further improved sulfuric acid resistance can be obtained. . It is presumed that calcium carbonate not only suppresses the generation of ettringite when the hardened body comes into contact with the sulfate group, but also improves the sulfuric acid resistance by densifying the hardened body structure. Calcium carbonate used in the present invention is based on calcium carbonate even if it is not pure,
For example, those of industrial purity can be used. Also, limestone powder, limestone aggregate, or so-called light calcium carbonate produced by pulverizing a natural mineral and then reacting it with carbon dioxide gas once can be used. Calcium carbonate is preferably used as a powder having a particle size of 1 μm to 1 mm.

The amount of calcium carbonate added is
It is preferable that the amount is 30 to 100 parts by weight with respect to 0 parts by weight. If the amount is less than 30 parts by weight, the effect of improving the sulfuric acid resistance is small, and if the amount is more than 100 parts by weight, the improvement effect of the sulfuric acid resistance is hardly recognized in proportion to the amount added. This is because there is a case where the strength of the sheet decreases and it becomes a negative factor.

In the preparation of the cement composition of the present invention, the respective components can be mixed in advance prior to kneading.
The method of adding each component when kneading by adding the aggregate and other admixtures is the most preferable method.

The sulfur-resistant cement composition of the present invention comprises, in addition to a base cement as a basic component, a water-soluble organic compound having an alkali metal salt of sulfonic acid as a substituent, calcium carbonate and water, Aggregates such as sand and gravel, hardening accelerators, hardening retarders, reinforcing steel rust inhibitors, etc., do not cause any problems even if known additives are added, paste,
As a material for mortar and concrete, it can be used by a conventionally known working method. Specific examples of the application include concrete products such as concrete pipes, concrete U-shaped grooves, concrete piles, and the like, as well as buildings, structures, and anticorrosive coating layers applied to the surfaces thereof.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference to the following examples. (1) Raw materials In carrying out each example, the following raw materials were used. Cement: ordinary Portland cement, sulfate resistant cement, fly ash cement, blast furnace cement B [all manufactured by Ube Industries, Ltd.] Limestone powder: Blaine specific surface area 6400 cm ² / g Light calcium carbonate: Average particle size 1 to 3 μm [Yonesho Lime Industry Co., Ltd.] Water-soluble organic substance: naphthalene sulfonate [trade name: Mighty 150, manufactured by Kao Corporation], nitrogen-containing sulfonate [trade name: Pallfine MF, manufactured by Takemoto Yushi Co., Ltd.], carboxyl group-containing polyether [ Product name: Mighty 3000H,
Both manufactured by Kao Corporation and polycarboxylates (trade name: Leobuild SP8S, manufactured by NMB) were commercially available as a water reducing agent for cement in the form of an aqueous solution. Aggregate: Toyoura standard sand JIS R5201 compliant product

(2) Preparation of Cement Mortar Cement mortar was prepared by mixing Toyoura standard sand, water, and a predetermined amount of a water-soluble organic substance with cement. The weight ratio of cement to Toyoura standard sand was 1: 2. Since the water-cement ratio is different for each example, it is indicated as necessary. (3) Preparation of cement paste Cement was mixed with water and a predetermined amount of a water-soluble organic substance to prepare a cement paste. Water cement ratio is W / C
= 0.3.

(4) Curing The above-mentioned (2) is placed in a form frame of 4 cm long × 4 cm wide × 16 cm long.
Alternatively, the cement mortar or the cement paste prepared by the method of (3) was poured, and firstly cured in the air in a constant temperature room at 20 ° C. for 24 hours. The samples after air curing for one day and night were subjected to additional curing under various curing conditions. Additional curing conditions vary from case to case and are described as necessary. (5) Evaluation of sulfuric acid resistance Evaluation of sulfuric acid resistance of samples after curing
The test was carried out in accordance with the S draft "Chemical resistance test method by dipping in concrete solution". That is, 2% of the cement mortar or the cement paste after completion of the curing (pH about 0.
7) or dipped in 5% (pH about 0.3) sulfuric acid aqueous solution,
After 13 weeks, it was removed from the aqueous sulfuric acid solution. The removed mortar or cement paste is cut, and the length of the portion that is not clearly discolored is measured.
The corrosion depth was calculated by dividing the value obtained by subtracting the length of the undiscolored portion from m by 2. The sulfuric acid resistance index was calculated as the reciprocal of the value of the ratio of the corrosion depth when adding a water-soluble organic substance to the corrosion depth when no water-soluble organic substance was added, as shown in the following equation. ───────────────

Examples 1 to 9 and Comparative Examples 1 to 4 First, sulfate-resistant Portland cement was used as cement.
The effect of the amount of the organic substance added was examined on mortar prepared by selecting a naphthalene sulfonate having a sulfonate as a water-soluble organic substance [Mighty 150 manufactured by Kao Corporation].
The water cement ratio was W / C = 0.5 (weight ratio), and additional curing was performed in water at 20 ° C. until the age of 28 days. Table 1 shows the results of sulfuric acid resistance evaluation when immersed in a 2% sulfuric acid solution. From the results shown in Table 1, the addition amount of the naphthalene sulfonate to 100 parts by weight of the cement was 0.4% in terms of the solid component.
It can be seen that, when the amount exceeds the weight part, the sulfuric acid resistance index indicating the sulfuric acid resistance is improved twice or more.

[0019]

[Table 1]

Examples 10 and 11 and Comparative Example 5 Here, a mortar prepared by adding and mixing a predetermined amount of naphthalene sulfonate [Mighty 150 manufactured by Kao Corporation] as a water-soluble organic substance to sulfate-resistant Portland cement was used. An example when the test sulfuric acid solution concentration is increased to 5% is shown. The water cement ratio is W / C = 0.5 (weight ratio),
The additional curing was performed under the conditions of steam curing (65 ° C., 5 hours) and subsequent curing in water (20 ° C., 7 days). Table 2 shows the results of the sulfuric acid resistance evaluation. It can be seen that the addition of the naphthalene sulfonate doubles the sulfuric acid resistance index even when the sulfuric acid concentration is as high as 5%.

[0021]

[Table 2]

Examples 12 to 14 and Comparative Examples 6 to 8 Here, examples are shown in which the product form is changed from mortar to cement paste and the cement type is changed. The examined cements were sulfate-resistant Portland cement, fly ash cement B, and blast furnace cement B, and used a naphthalene sulfonate [Mighty 150 manufactured by Kao Corporation] as a water-soluble organic substance. The water-cement ratio is W / C = 0.3 (weight ratio), and steam curing (65
(5 ° C., 5 hours) and subsequent curing in water (20 ° C., 7 days), and the sulfuric acid resistance test was performed with a 5% sulfuric acid solution. Table 3 shows the results. It can be seen that, even when the product form is a cement paste, the addition of naphthalene sulfonate improves the sulfuric acid resistance index to about twice that in the case of no addition, regardless of the cement type.

[0023]

[Table 3]

Examples 15 to 24 and Comparative Examples 9 and 10 Here, examples in which calcium carbonate is added in addition to the naphthalene sulfonate will be described. The cement types studied are sulfate-resistant Portland cement and ordinary Portland cement. Naphthalene sulfonate [Mighty 150 manufactured by Kao Corporation] based on 100 parts by weight of cement
A mortar was prepared by adding 0.96 parts by weight (as solid matter) and a predetermined amount of calcium carbonate. The water / cement ratio was W / C = 0.45 (weight ratio), and steam curing (65
(5 ° C., 5 hours) and subsequent curing in water (20 ° C., 7 days), and the sulfuric acid resistance test was performed with a 5% sulfuric acid solution. Table 4 shows the results. By adding 30 parts by weight or more of calcium carbonate to 100 parts by weight of the cement component in addition to the naphthalene sulfonate, the sulfuric acid resistance index is 2 in comparison with the case without calcium carbonate regardless of the type of calcium carbonate. It can be seen that the improvement is at least 4 times, and at least 4 times as much as when neither naphthalene sulfonate nor calcium carbonate is contained.

[0025]

[Table 4]

Examples 19 and 25 and Comparative Examples 9 and 11 Here, examples in which the type of the added organic substance is changed will be described. A mortar was prepared by adding 2.4 parts by weight (as an aqueous solution) of an aqueous solution of a water-soluble organic substance shown in Table 5 to 100 parts by weight of sulfate-resistant Portland cement. Water cement ratio is W / C
= 0.45 (weight ratio), additional curing by steam curing (65 ° C., 5 hours) and subsequent curing in water (20 ° C., 7 days), and the sulfuric acid resistance test was performed with a 5% sulfuric acid solution. . Table 5 shows the results. While having a sulfonate as a substituent in the molecule, a naphthalene sulfonate and a nitrogen-containing sulfonate have an effect of improving sulfuric acid resistance, whereas a water reducing agent having no sulfonate has a resistance to sulfuric acid. It can be seen that a negative effect is exhibited on the improvement of the sulfuric acid property.

[0027]

[Table 5]

[0028]

Industrial Applicability The cement composition according to the present invention not only enables the production of a cement product having excellent sulfuric acid resistance, but also allows a simple addition of a water-soluble organic compound having a sulfonate as a substituent to cement. It can be prepared by a method and can be easily and inexpensively prepared in a facility for manufacturing ordinary cement products. Therefore, the cement composition according to the present invention can be applied not only to cement products used in places where there is a high possibility of being exposed to sulfates, such as hot springs and sewage facilities, but also to acid rain, which has recently become a problem. Since it shows high durability, it is of great utility value for general cement products.

Claims (4)

[Claims] 1. A sulfur-resistant cement composition comprising a water-soluble organic compound having an alkali metal salt of sulfonic acid as a substituent in an amount of 0.5 to 4 parts by weight per 100 parts by weight of cement. 2. The resistant composition according to claim 1, wherein the content of the water-soluble organic compound containing an alkali metal salt of sulfonic acid as a substituent is 1.0 to 3.5 parts by weight based on 100 parts by weight of cement. Sulfate cement composition. 3. The sulfuric acid-resistant cement composition according to claim 1, wherein the water-soluble organic compound containing an alkali metal salt of sulfonic acid as a substituent is an alkali metal salt of naphthalenesulfonic acid. 4. A sulfuric acid resistant cement composition comprising the cement composition according to claim 1, further comprising 30 to 100 parts by weight of calcium carbonate powder based on 100 parts by weight of cement.