Adding air-entraining agents will definitely lead to a decrease in the strength of concrete. This is because after adding air-entraining agents, many closed bubbles will be formed in the concrete. The bubbles occupy a certain amount of concrete space and reduce the concrete cross-section. Therefore, air-entraining agents cannot be added casually and must be determined by the laboratory through tests while ensuring that various design indicators are met.
Air-entraining agent is an admixture mainly used to improve the impermeability, frost resistance, and salt freeze erosion resistance of concrete. The main principle is that the small bubbles introduced by the air-entraining agent cut off the passage of capillary tubes and reduce capillary action, thereby improving the impermeability of concrete. These tiny closed bubbles can release the expansion pressure of ice crystals in the capillary during the freezing process, thereby avoiding the generation of damaging pressure, reducing and preventing the destructive effects of freezing and thawing, and improving the frost resistance of concrete. Air-entraining agents can also effectively improve the workability of concrete and reduce collapse damage.
Why does air-entraining agent improve the workability of concrete?
Through the analysis of the mechanism of air-entraining agent, we will discuss the effect of air-entraining agent on the performance of fresh concrete and the frost resistance and pressure resistance of concrete. The effects of strength and flexural strength are reviewed. Tests show that under the same cement dosage and slump conditions, the greater the air-entraining agent content, the greater the air content of the concrete, and the greater the compressive strength loss rate; when the air content is less than 6%, as the As the air content increases, the toughness of concrete increases; when the amount of air-entraining agent is constant, as the slump of the concrete mixture increases, the air content of concrete changes in a parabolic shape. When the water consumption of concrete is constant, the greater the amount of air-entraining agent, the greater the slump of concrete; when used in combination with naphthalene-based water-reducing agents, the air content of concrete will decrease to a certain extent
Air-entraining The function of the agent is to introduce small and uniform bubbles into the concrete. On the one hand, it can change the working performance of the concrete and improve its workability. The strength of concrete is slightly reduced. Due to the existence of tiny bubbles, the generation and development of cracks in the concrete are blocked, which is helpful to improve the impermeability and durability of concrete. Of course, this is based on the proper use of air-entraining agents.
Air entraining will reduce the strength of concrete, especially when the content is very large (>4%). This is the biggest shortcoming of air entraining agents, and it also restricts the large-scale use of air entraining agents in our country. The main reason for its popularization and application is that strength is used as an indicator in many concrete design specifications in our country.
It is rare to add air-entraining agents alone to concrete mixtures. Usually, air-entraining agents and high-efficiency water-reducing admixtures are used at the same time, or an appropriate amount of air-entraining agent is combined with the high-efficiency water-reducing agent. In this way, the increased concrete strength due to the high water-reducing rate of the water-reducing agent can completely compensate for the use of air-entraining agents. Loss of strength due to increased porosity of concrete. </p
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