JP2592496B2 - Admixture for concrete - Google Patents

Description

The present invention relates to an admixture for cement, mortar, and concrete, and more particularly to an air entraining agent (hereinafter referred to as an AE agent). The present invention relates to an AE agent capable of preventing a decrease in the amount of air in cement, mortar and concrete over time.

[Conventional technology]

By using an AE agent that gives air entrainment to cement slurries, mortars and concrete, (1) improvement in freeze-thaw resistance, (2) improvement in workability, (3) improvement in pumpability, (4) air bubbles And (5) a reduction in unit water volume due to an increase in the water retention capacity of the above. Commonly used AE agents include anionic surfactants such as resin acid Na salt, alkylbenzene sulfonate, triethanolamine salt of alkyl sulfonic acid, polyoxyethylene alkyl sulfate, and polyoxyethylene alkyl phenol. Nonionic activators and the like. Examples of the air entraining type water reducing agent include lignin sulfonate and alkylnaphthalene sulfonate formalin high-condensate. On the other hand, examples of the low-foaming water reducing agent, that is, a water reducing agent in which the amount of air in concrete is 3% or less in a usual amount, include β-naphthalenesulfonic acid formalin polycondensate, melamine formalin condensate sulfonate, and the like. . Usually, the amount of air entrained in concrete by the combined use of an AE agent and a water reducing agent is constant (4 ± 1% according to the standards of the Architectural Institute of Japan, and it is preferable that there is no decrease over time.

[Problems to be solved by the invention]

However, the amount of air entrained by the conventional AE agent depends on factors such as the water-cement ratio of the concrete, the mix of the concrete, the softness of the concrete, the replacement ratio of fly ash of the cement, and the water reducing agent used in combination, especially the low foaming water reducing water In the case of β-naphthalenesulfonic acid formalin high-condensate salt, which is an agent, the amount of air was greatly reduced with time, and the conventional AE agent was not satisfactory in use.

[Means for solving the problem]

The present invention has been made to improve the above-mentioned disadvantages of the conventional AE agent. Normally, concrete contains air bubbles of 1 to 2% without using an AE agent, but air bubbles are actively entrained by using an AE agent. When an anionic surfactant is used as the AE agent, since the surface tension of the water in the concrete is lowered, bubbles are easily introduced by a little stirring as compared with water containing no surfactant. In the surrounding water, the lipophilic group of the anionic activator is oriented toward the gas side, and the hydrophilic group is oriented toward the water side. As the addition amount of the activator increases, the distance between the molecules becomes closer, the intermolecular attraction increases, and the bubbles are stabilized. However,
It is said that when a low-foaming water reducing agent is added to the active agent, it enters between the molecules of the activator, weakens the intermolecular attractive force, and easily breaks bubbles. Of course, defoaming may be performed by cement, aggregate, or blades of a mixer. In addition, the diameter of the entrained bubble is 20
When the thickness is less than μm, the internal pressure of the bubbles rapidly increases, and the bubbles dissolve in water and disappear.

The present inventors have conducted intensive studies on a method capable of entraining air bubbles one after another even if air bubbles in concrete entrained by the activator have disappeared, and as a result, a fatty acid having 8 to 18 carbon atoms and a carbon number of 1 It has been found that by adding a water emulsion having an average particle size of 0.05 to 10 μm of a fatty acid ester composed of alcohols of 10 to 10 to concrete, a target air volume can be maintained for a long time, and the present invention has been completed. When the product of the present invention is added to concrete, hydrolysis gradually occurs due to alkali ions eluted from the concrete, and is decomposed into fatty acids and alcohols. This fatty acid reacts with the alkali ions of the cement, gradually dissolves in the concrete, lowers the surface tension of the concrete, embraces the air with the stirring power of the concrete mixer, and foams the air. The aim is to stabilize the amount over time. In the present invention, the fatty acid is generally a straight-chain saturated or unsaturated acid having one COOH group at a terminal and a carbon chain, and has 8 to 18 carbon atoms. good. On the other hand, alcohols have 1 to 10 carbon atoms, and lower alcohols are desirable in view of the fatty acid content after hydrolysis, that is, the AE agent content. The emulsion of the fatty acid ester is emulsified with an anionic or nonionic surfactant, and the particle size can be adjusted by selecting the stirring power and the emulsifier. If the particle size is too small, a large amount of air will be generated initially, and it will not be possible to hold air for a long time. On the other hand, if the particle size is too large, the surface area of the fatty acid ester will be small, and the undissolved particles will remain in the concrete as the amount of addition to the cement for obtaining the target air amount increases, and the strength of the concrete will decrease, which is not preferable. . For these reasons, the preferred average particle size of the product of the present invention is 0.05 to 20 μm, more preferably
0.05 to 10 μm.

The admixture for concrete of the present invention can be used in combination with other admixtures such as a commercially available water reducing agent, an anti-slump loss agent, and an early strength agent. As the form of the product of the present invention, there are a granular material and a water suspension, and it is also possible to mix it in cement in advance. As for the time of addition to the concrete, it can be added at any time up to the time of placing the concrete, and the effect is sufficiently exhibited. When transporting concrete by a ready-mixed concrete mixer truck, it is desirable to provide appropriate stirring. Also, in the case of mixed concrete, remixing is necessary.

The amount added to the cement varies depending on the composition of the concrete, the softness, and the type of the admixture, but is usually 0.01 to 0.3% based on the cement.

〔Example〕

 Hereinafter, the effects of the present invention will be described with reference to examples.

Example 1 To 100 parts by weight of various fatty acid esters shown in Table 1, 3 parts by weight of a polyoxyethylene alkyl sulfate Na salt (trade name: Emal D3D (manufactured by Kao Corporation)) as an emulsifier,
1 part by weight of modified silicone emulsion (trade name: Antifoam E2O (manufactured by Kao Corporation)) and 500 parts of water as an antifoaming agent
Parts by weight were stirred and emulsified by stirring at 300 rpm for 1 hour. Also,
Emulsions without the addition of defoamers were also prepared. The average particle size of this emulsion was measured (manufactured by Shimadzu Corporation: sedimentation type particle size distribution analyzer / SA-CP3 type). The obtained suspension is added to concrete, and the amount of air changes over time,
Slump and compressive strength were measured. The water reducing agent used in combination is β-
A highly condensed naphthalenesulfonic acid formalin Ca salt, a lower olefin (carbon number 4) and a micronized product of a maleic anhydride copolymer (average particle size 0.10 μm) are blended at a solid content ratio of 95: 5. 0.5% of cement was added per minute. The mixer used was a tilting cylinder type, which was stirred for up to 60 minutes by rotating 4 times per minute after concrete kneading.

<Concrete composition> W / C = 55.5% S / A = 50.0% C = 320 kg / m ³ (Central Portland cement) Fine aggregate = Kinokawa coarse aggregate = Takarazuka crushed stone The results are shown in Table 1. Each of the anionic AE agents of Comparative Products 2 and 3 is an aqueous solution of a Na salt and cannot maintain the amount of concrete air for a long time. On the other hand, the emulsion of the fatty acid ester of the present invention can maintain the target air amount (4 ± 1%) for a long time. In addition, the fatty acid ester added without emulsification (Comparative product 1) has poor mixing property with concrete, requires a large amount of addition to obtain a target air amount, and has a long target air amount. (4 ± 1
%) Cannot be maintained, which is not preferred.

Claims (2)

(57) [Claims] An average particle size of a fatty acid ester comprising a fatty acid having 8 to 18 carbon atoms and an alcohol having 1 to 10 carbon atoms is from 0.05 to 10 μm.
An admixture for concrete containing a water emulsion. 2. The concrete admixture according to claim 1, further comprising a water reducing agent.