Investigation of the evolutionary behavior and stabilization mechanism of foams with different properties in cement paste

To investigate foam stability in fresh pastes, four different types of foaming agents (i.e., anionic surfactant, SDS; cationic surfactant, CTAB; nonionic surfactant, OP; amphoteric surfactant, HP) were selected to explore their evolution in this study, the mechanism of this evolutionary behavior was studied via the Zeta potential test, XRD test, surface tension test. The results showed that the relationship between volumetric collapse and variation of foam diameter was significant for different types of foaming agents. Whenever the volume of the foam concrete paste collapsed, the large bubbles decreased substantially, which was a result of Ostwald ripening making it difficult to maintain the stability of the foam in the fresh paste. This evolutionary behavior has been proven to be related to the interaction between the foams and the cement particles, where the surface charges of foams played a crucial role in this interaction relationship. The negatively charged bubbles, i.e., SDS, can produce a strong adsorption on positively charged cement particles (e.g., C3A) or hydration products (e.g., i.e., ettringite), forming a thick adsorption layer in the bubble film, which could reduce the air permeability of the bubble film, thus reducing the rate of bubbles Ostwald ripening and improving the stability of foam in the paste.