Investigation on the impact of low atmospheric pressure on bubble stability in cement-based Materials

With more infrastructures being built in high-altitude regions, the impact of low atmospheric pressure on the stability of air bubbles in cementitious materials has aroused extensive attention. However, its influence is still inconclusive since it is difficult to isolate the factor of air pressure and study it. To solve this problem, the study investigated the bubble dynamic evolution in cement paste at standard atmospheric pressure (P = 0.1 MPa) and low atmospheric pressure (LAP = 0.8P, 0.6P, 0.4P, 0.2P) and revealed the mechanism of bubble instability under low atmospheric pressure. We established the bubble dynamic evolution equation in cement paste, computed the real-time bubble radius, resultant force, and critical time at dif- ferent air pressure by MATLAB software. Results show that the maximum resultant force decreases by 50.0–57.7% when air pressure drops from P to 0.2P; both critical time (t) and radius increment (ΔR) increase with the reduction of air pressure and the increase of initial radius. It indicates that when at 0.2P, the resultant force which inhibits bubble expansion is reduced, the time required to prevent bubble expansion increases by 94–137%, and ΔR grows 122–140% larger than that at P, and the bubble is more prone to instability and rupture than that at P. The key to improving bubble stability in low atmospheric pressure is to reduce the initial radius of bubbles and increase the strength of the bubble film. This work firstly discovered the impact of low atmospheric pressure on bubble dynamic evolution in cement paste and proposed a new perspective to explore bubble stability at low atmospheric pressure. © Wroclaw University of Science and Technology 2023.