Effect of Low Atmospheric Pressure on Air Content of Fresh Concrete

The effects of atmospheric pressure changes on the air entraining capability of air-entraining admixtures was studied using a low-pressure test chamber to simulate plateau environments with thin air and low atmospheric pressure. Results indicate that the atmospheric pressure of the environment significantly affects the performance of air-entraining admixtures. The air content of fresh concrete decreases by approximately 20%–49% when the atmospheric pressure is 50 KPa with respect to the normal atmospheric pressure (101 KPa). The air content of fresh concrete decrease linearly as atmospheric pressure dropped. The higher the air content of fresh concrete mixed in ordinary pressure, the faster the air content of fresh concrete decreases with the drop of air pressure. The concrete with high slump shows more resistance to drop of air-content due to low air pressure than the concrete with low slump. Therefore, in order to meet the design requirements of air content of air-entrained concrete for different constructions in the plateau regions, it is necessary to increase the dosages of air entraining agents to according to different pressure conditions and types of air-entraining agent.