Effect of atmospheric pressure on air content and air void parameters of concrete

The effects of atmospheric pressure changes on the air-entraining capability of air-entraining admixtures and the air void parameters of hardened concrete are 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 when at normal atmospheric pressure (101 kPa). The air content of fresh concrete decreases linearly as atmospheric pressure drops. The air void parameters of concrete mixed when atmospheric pressure is low are worse than when it is mixed under normal atmospheric pressure. However, when the air content of hardened concrete reaches a certain value (4%) as the dosage of air-entraining admixtures is increased, the spacing factor could achieve freezing-thawing resistance (300 mu m). The enhanced surface tension of liquids at low atmospheric pressure may contribute to the decreased air-entraining capability of air-entraining admixtures.