Improving the air bubble stability of air-entrained mortar in low air pressure environments via adopted rheology and surface tension methods

Abstract

Air bubble stability in cementitious materials in low air pressure (AP) environments is influenced by the Ostwald ripening process, which causes coarsening behavior of air bubbles. This research reports the enhancement of air bubble stability in low AP via the adoption of rheology and surface tension methods. Besides, the evolution of air bubbles during the cement early hydration process is proposed. It was found that incorporating viscosity-modifying agents (VMAs) and shrinkage-reducing admixtures (SRAs) resulted in improving air bubble stability by 37.7 % and 23.4 %, upon undergoing AP change from 100 to 60 kPa. Calculation of air bubbles via ripening equations under low AP revealed that VMA induced a notable decrease in the effective diffusion flux within fresh cement mortar, leading to a reduction of 9.8 % in air bubble ripening within 120 min. Conversely, SRAs were primarily aimed at reducing the initial dimensions of air bubbles.