Effect of particle properties on the resulting bubble quality and stability: From solution foam to air-entrained cement mortars

The development of air bubbles determines the quality of air-void structure and the durability of concrete. Recently, air bubbles stabilized by nanoparticles has received considerable attention for the improvement of air-void structure in cement mortar . However, the relationship between particle properties and the resulting bubbles quality and stability remains unclear. In this study, the SiO 2 particles with different wettability , sizes and charge types were obtained by chemical modification. These modified SiO 2 particles were added to the solutions and cement mortars and the prepared mixtures were characterized for the evolution and structure of the entrained bubbles. The influence mechanism of particle properties on the bubbles in solutions and cement mortars was also investigated. The experimental results show that the particles with intermediate wettability (60° ≤ θ ≤ 110°) and smaller sizes (around 50 nm) decreased the time-dependent changes of air contents, meanwhile induced smaller bubble size in both solution and mortars. Since most of the air-entraining agents were charged surfactants , which have electrostatic attraction interactions with oppositely charged SiO 2 particles, thus the addition of oppositely charged SiO 2 particles further inhibit the loss of air contents within 2 h. The analysis of granule structure around bubbles reveals that the particles with suitable structures tend to strongly absorb on both the surface and interlayer of bubbles as aggregates, forming a rigid and incompressible grid structure to prevent the Ostwald ripening of bubbles.