New Techniques to Measure Physical and Mechanical Properties of Air Bubbles Extracted from Cement Paste

AbstractUsing new techniques based on atomic force microscopy (AFM) and scanning electron microscopy (SEM), the stiffness, thickness, and microstructures of the shell of air bubbles extracted from air-entrained cement paste were examined, and coalescence resistances of pairs of bubbles were measured. The surface tension of air-entraining admixture (AEA) solutions in water and lime water also was determined. The results showed that air bubbles associated with synthetic AEAs had thinner and more-flexible shells than those with neutralized vinsol resin (NVR). The stiffness and thickness of the bubble shells were shown to be correlated with the differences in the stability of air bubbles in concrete among the same AEAs reported in a previous study. A mechanism leading to the differences in bubble shell properties between the AEAs is proposed based on the results of the surface tension testing and the particle-stabilized bubble theory, but further work remains to verify and refine this potential mechanism.