JPS6353004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reducing air bubbles on the surface of secondary concrete products. In addition to properties such as strength, durability, and dimensions, concrete products place great importance on the fineness of the surface texture from the viewpoint of aesthetics and commercial value. Conventionally, many methods have been proposed for making the surface of concrete products finer. For example, when fresh concrete is charged into a formwork for concrete products and compacted, a spatula-like object is inserted along the inner circumferential surface of the formwork and moved up and down to remove air bubbles. One method is to mix a small amount of antifoaming agent with a release agent. However, the former method requires a lot of labor and requires further improvement in effectiveness, while the latter method is not very effective. In addition, when implementing these methods, the slump of concrete for vibration compaction, which is suitable for workability at about 5 to 8 cm, should be increased to about 10 to 18 cm to reduce air bubbles on the surface of the concrete product. Mixed concrete must be used. This results in separation of the material during compaction by the vibrator.
A drawback arises in that durability such as freeze-thaw resistance of the resulting concrete product is reduced. The present inventors conducted research to find a method for reducing air bubbles on the surface of secondary concrete products that eliminates these drawbacks, and as a result, we discovered that air-entraining agents, which were conventionally thought to only increase air bubbles on the concrete surface, If an anionic air-entraining agent with little dispersion effect is selected from among them and the mixed composition obtained by adding this to the concrete material is subjected to vibration compaction, the number of air bubbles on the surface of the resulting concrete product will be reduced. This surprising finding led us to complete the present invention. The gist of the present invention is to add an anionic air-entraining agent with almost no dispersion effect to a concrete material, and to obtain a mixed composition with a slump of 5 to 15 cm, which is then subjected to vibration compaction. This is a method of reducing air bubbles on the surface of products. Secondary concrete products to which the present invention is applied include road products (flat plates, U-shaped, L-shaped, boundary blocks, etc.), irrigation and drainage products (furiums, blocks, etc.), and earth retaining and bank protection products (top plates, etc.). ), products for slabs, girders, construction products, etc. Anionic air-entraining agents that have little dispersion effect can entrain fine, stable air bubbles into concrete, and suitable examples include resinates, alkylbenzene sulfonates, and alkylbenzene sulfonate triphosphates. Those containing ethanolamine salt as an active ingredient are shown, and the amount added is 0.03 to 0.06% based on the weight of cement. Commercial products that fall under these categories include Vinsol,
Examples include Darex AEA, Newrex, and Rigpol AE. Although the slump of concrete varies depending on the type and size of the secondary concrete product, it is necessary to adjust the slump to 5 to 15 cm in order to reduce air bubbles on the surface. If the slump is less than 5 cm, workability will be poor, and if it is more than 15 cm, material separation during vibration compaction will be significant and the freeze-thaw resistance of the resulting concrete product will be reduced, which is not preferred. In addition, in the method of the present invention, vibration compaction is
It is preferable to carry out the process at 8000 vpm or higher; below this, it is difficult to effectively reduce the surface bubbles of concrete products. According to the present invention, the number of air bubbles on the surface of the secondary concrete product is reduced, resulting in finer texture, increased freeze-thaw resistance due to entrained air, and improved workability.
Further, as breathing is reduced, material separation is also reduced. Next, embodiments of the present invention will be described by way of examples. Examples 1 and 2 and Comparative Examples 1 to 3 A mold shown in FIG.
A rod vibrator was inserted into locations B, C, D, and E for 5 seconds, held for 5 seconds, and then pulled out for 5 seconds to perform vibration compaction. The vibrating part of the rod vibrator had a diameter of 27 mm and a frequency of 14000 vpm. The cement used in the concrete mix shown in Table 1 is ordinary Portland cement, the fine aggregate is river sand from Fujikawa with a specific gravity of 2.62 and a coarse grain ratio of 2.76, and the coarse aggregate is crushed stone from Mizuho with a maximum dimension of 20 mm and a specific gravity of 2.56. ,
The coarse particle ratio is 6.83, and the air entraining agent with almost no dispersion effect contains a resinate as an active ingredient (trade names: Vinsol and W, manufactured by Yamaso Chemical Co., Ltd.).
Product name Dalex manufactured by R.Grace Co., Ltd.
AEA) was used. In this case, Example 1 used Vinsol, and Example 2 used Dalex AEA. The release agent is a commercially available product (product name: Panel Release Oil 2 manufactured by Kotobuki Chemical Industry Co., Ltd.).
No.) was used. After the concrete has hardened, it is removed from the mold, and the entire surface of the resulting concrete product is covered with cellophane paper, and the air bubbles present on each surface are copied. , 3>D≧2
mm, 2>D≧1, and the number of each was counted. The results are shown in Table 2. However, air bubbles on the poured surface of concrete products were not measured. Comparative Example 1 was plain concrete with a cement usage amount of 300 kg/ ^m3 , and Comparative Example 2 was Example 1 with lignin sulfonate as an active ingredient instead of the air entraining agent Vinsol, which is also known as a dispersant. Comparative Example 3 uses an air entraining agent (trade name Pozolith No. 5L manufactured by Nisso Master Builders Co., Ltd.) containing a polyalkylaryl sulfonate as an active ingredient, which is known as a high-performance water reducing agent. Things (product name Mighty)
150 (manufactured by Kao Soap Co., Ltd.), and the other concrete materials that are the same as those in Example 1 are mixed in the proportions shown in Table 1, and the resulting mixed composition is molded according to Example 1. The number of bubbles on the surface of the product was measured, and the results are shown in Table 2, and the results are shown in a bar graph in FIG. As is clear from this table and figure, concrete products using anionic air-entraining agents with almost no dispersion effect have a total number of surface bubbles of 38% and 49% compared to plain concrete products, which is approximately
A reduction of 50-60% was observed. In contrast, the concrete product obtained using the air-entraining agent of Comparative Example 1 had only 10% fewer air bubbles compared to plain concrete, and the high performance of Comparative Example 2 was achieved using the water-reducing agent. The concrete product obtained by this method had 2.8 times more air bubbles than plain concrete.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a perspective view of the formwork used in the examples, Figure 2 shows the position where the bar vibrator is inserted, and Figure 3 is a bar graph showing the number of surface bubbles in the concrete products of Examples 1 and 2 and Comparative Examples 1 to 3. This is what is shown. A, B, C, D, E: Insertion position of the rod vibrator.

Claims (1)

[Claims] 1. Reducing surface bubbles in secondary concrete products, which are characterized by adding an anionic air-entraining agent with almost no dispersion effect to concrete materials to obtain a mixed composition with a slump of 5 to 15 cm, and then vibrating compaction. how to.