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Air-entraining agent is mostly anionic surfactant. in water vapor interface, hate water-based directionally adsorpt to the air side. On the hydrosphere cement, cement or its hydrated ion adsorp with hydrophilic group, and hate water based depart from cement and its hydration ions to form hydrophobic adsorption layer which try to close to the surface of the air. Because the ions close to the air surface and air-entraining agent adsorpt to the surface of the molecules in the air hydrosphere, which significantly reduce the surface tension of water, and make the concrete in the mixing process produce a large number of fine bubbles,.The bubbles with the directional adsorption layer of the same charge, hence, they mutually exclude and can be evenly distributed; In addition, many anion entraining agents have calcium salt precipitation in cement aqueous solution with high calcium content which adsorbed on bubble film and can effectively prevent bubbles from bursting. and the introduction of small uniform bubbles can be stable in a certain period of time.
It can be seen from the above mechanism that the interfacial activity of the air entrainer is similar to that of the water reducer. The difference is that the interfacial activity of the air entrainer mainly occurs on the liquid-solid interface, while the interfacial activity of the air entrainer mainly occurs on the gas-liquid solid interface. It is not difficult to see that the main role of the air entrainer is to introduce bubbles, then to disperse and moisten.
Because the air entrainer can significantly reduce the surface tension and interface energy of water, it is easy to produce many small closed bubbles in the mixing process of water solution, most of the bubbles are below 200 m in diameter, when the dry mortar containing air entrainer is mixed with water.
The air entrainer introduces stable microbubbles into the mortar by physical action.This reduces the density of wet mortar, improves the construction performance, and increases the yield of wet mortar.The air trapped in the mortar gives the concrete better insulation but also reduces strength.The amount of air-entraining agent varies with the type of dry mortar and air-entraining agent, but the amount of air-entraining agent is usually very low, generally only 0.002%~0.01% of cement quality, not more than 0.05% of cement quality.
There are many factors about the mortar of air content. It ncludes the characteristic and the dosage of cement and admixture water-cement ratio (water/cement ratio) of air-entraining agent varieties and dosage of aggregate mortar mixer type and capacity, quality and size distribution mixing temperature consistency mixture temperature and air-entraining agent dosage, although minimal, but air-entraining agent on the performance of the dry powder mortar effect is the main part. The main part is following:
1:Improve the workability of dry mortar
2Reduce the strength of dry mortar
3Improve the impermeability and frost resistance of mortar
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