JPH0926421A - Evaluation method of efflorescence generated in cement-based products - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to simply measure the generation of efflorescence in a short time by using alcohol containing water solution of pH indicator exhibiting alkalinity. SOLUTION: The lower 1/2 part of a cement product in thickness direction is dipped, for example, in water to absorb water. The absorbed water is gradually moved to a surface layer which is not dipped in water. At this time, the alkali component in the product is moved to the surface layer with the absorbed water. When it is coated with a pH indicator having a color change area to the alkaline side to the alkali component such as pH indicator of thymol blue or phenol red, the color is exhibited in the color change area in response to the pH. The generation of efflorescence is predicted according to the degree of the coloring. Accordingly, the time up to a predetermined coloring area is measured to predict the easiness of generating the efflorescence in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating efflorescence generated in cement-based products, and is preferably used as a method for evaluating efflorescence of a sizing board used for the outer wall of a house.

[0002]

2. Description of the Related Art Cement-based products are used as outer walls,
When exposed outdoors, more or less efflorescence may be formed on the surface with the passage of time, impairing the appearance. This phenomenon is mainly caused by calcium hydroxide, sodium hydroxide, potassium hydroxide and other alkaline components contained in cement-based products being carried along with water such as rainwater and moving to the surface of cement-based products. This phenomenon occurs because carbon dioxide in the air precipitates as water-insoluble carbonate. Conventionally, in order to prevent the generation of such efflorescence, measures have been taken such as applying a paint that suppresses the movement of alkali content, or curing the base material by autoclaving to fix the alkali content. Specifically, after applying a color coating containing a pigment that changes color due to alkaline to the coated surface of the cement-based product, it is made to absorb water from the back surface, and the pigment is a color pigment due to the alkaline component that has been entrained in water and moved to the surface. A method for evaluating efflorescence resistance based on the degree of discoloration is known.

[0003]

However, in the above-mentioned conventional efflorescence evaluation method, the pretreatment of the sample is complicated, and it takes several days to several tens of days until the judgment, and the quality control of the production process is performed. There was a problem that it could not be used for.

Therefore, an object of the present invention is to provide a method for evaluating a cement-based product, which can easily evaluate the generation of efflorescence and in a short time, and can promptly utilize the result for production process control.

[0005]

The present invention has the following constitution in order to achieve the above object.

"Evaluation method of efflorescence produced in cement-based products characterized by using an alcohol-containing aqueous solution of an alkaline pH indicator." That is, an alcohol-containing aqueous solution of an alkaline pH indicator is Apply to the coated surface of cement-based products,
The occurrence of efflorescence can be determined from the color area of the indicator. Hereinafter, the present invention will be described in detail.

Approximately 1/2 lower part in the thickness direction of cement-based products
Is immersed in water to allow the cement-based product to absorb water. The absorbed water gradually moves to the surface layer (painted surface) that is not immersed. At this time, the alkaline component in the cement-based product is carried along with the absorbed water and moves to the surface layer part. When a pH indicator having a color changing region on the alkaline side, such as thymol blue, phenol red, cresol red, or m-cresol purple, is applied to this alkaline component, a color is developed in each color changing region depending on the pH. The generation of efflorescence is predicted by the degree of this coloration. It can be predicted that the generation of efflorescence is suppressed when the degree of coloration is small. On the contrary, when the degree of coloration is large, it is expected that efflorescence is generated in a short time. Therefore, it is possible to predict the easiness of the occurrence of efflorescence in a short time by measuring the time required to reach a certain coloring area, and it can be effectively used for the quality control of the process. This coloration gradually disappears in the process in which the alkaline component is neutralized by carbon dioxide gas in the air.

For the preparation of this indicator solution, a mixed solvent of alcohol and water is used as a solvent. If the proportion of alcohol in the mixed solvent exceeds 75% by volume, the coloration disappears in a short time after the indicator is applied, and it tends to be judged. While 25
If it is less than the volume%, the coated surface repels the indicator even if it is applied, and it tends to be difficult to judge.

Examples of alcohols include methanol, ethanol, n-propanol and tert-butanol.

By this efflorescence evaluation method, the effect of preventing efflorescence on cement-based products can be confirmed in a short time and easily.

Cement-based products are preferably used as building materials, specifically, ceramic sizing boards,
Used for lightweight cellular concrete, gypsum board, calcium silicate building materials, fiber reinforced concrete, etc.

[0012]

【Example】

Example 1 An example in which the present invention is applied to an efflorescence measurement method for a ceramic sizing board will be described. First, a ceramic sizing board prepared in advance was coated with a coating material to which an additive for lowering water absorption and water permeability was added (this sample is referred to as Sample 1). On the other hand, as a comparative sample, a coating material to which no additive was added was applied to a ceramic sizing board (this sample is referred to as sample 2).

Next, in order to confirm the effect of the efflorescence evaluation, an acceleration test was conducted on both samples as described below, and the degree of efflorescence of both samples was determined by the method according to the present invention.

Samples 1 and 2 were cut into 100 × 100 mm squares (thickness: 12 mm, and the back surface side half (6
mm) and placed in water at room temperature. Then, every one hour, 0.2 was preliminarily adjusted to the surface opposite to the water-immersed surface of both samples.
5W / V% thymol blue solution (ethanol / water = 50
(/ 50 volume ratio) was applied to the entire surface with a writing brush, and the time until the surface was colored was measured. Table 1 shows the measurement results.

This coloration is a result of the coloration of thymol blue due to the exudation of the alkaline component. From Table 1, Sample 1 is coated with a water-absorbing and water-permeation-preventing coating, and the leaching of the alkaline component is suppressed and the time required for color development increases. That is, it was determined that the occurrence of efflorescence could be suppressed. It can be seen that Sample 2 is coated with a paint that has not been subjected to water absorption and water permeation preventive treatment, so that coloration occurs in a short time and leaching of the alkaline component occurs quickly. Therefore, in this case, it was determined that the efflorescence was poor as a result.

Examples 2 to 4 In the same manner as in Example 1, the pH indicator shown in Table 1 was used for evaluation. Table 2 shows the obtained results.

For all indicators, the same results as in Example 1 were obtained, and the quality of the efflorescence of the sizing board could be judged in a short time.

Comparative Example 1 Samples 1 and 2 of Example 1 were used to apply a paint containing an alkaline pigment as a main component on the coated surface. After drying at room temperature for 1 day, the plate was placed in room temperature water up to the back half (6 mm degree) in the thickness direction in the same manner as in Example 1 and the time until coloration was measured. Table 2 shows the obtained results. It was found that it took 4 days to develop the color of Sample 2 having poor efflorescence, which is not applicable to production process control.

Comparative Examples 2 to 3 Evaluation was carried out in the same manner as in Example 1 except that the volume ratio of ethanol / aqueous solution was changed to 20/80, and the wettability with the coating film was poor and it could not be judged. The evaluation was performed by changing the volume ratio to 80/20, but the drying speed was fast, and the coloration was unclear, and it could not be determined.

[Table 1]

[0020]

By using the efflorescence evaluation method of the present invention, it becomes possible to easily measure the occurrence of efflorescence of cement-based products in a short time.

Claims (3)

[Claims] 1. A method for evaluating efflorescence produced in a cement-based product, which comprises using an alcohol-containing aqueous solution of a pH indicator which is alkaline and exhibits coloration. 2. The volume ratio of water to alcohol in the alcohol-containing aqueous solution is 25/75 or more, 75/2.
The method for evaluating efflorescence produced in the cement-based product according to claim 1, which is 5 or less. 3. The method for evaluating efflorescence produced in a cementitious product according to claim 1, wherein the pH indicator is selected from thymol blue, phenol red, cresol red and m-cresol purple.