Sodium rosinate is a hydrophobic surfactant with high surface activity at the solution-air interface, significantly reducing surface tension. When stirring a liquid containing sodium rosinate, it easily incorporates air, resulting in a higher concentration of bubbles. Moreover, due to sodium rosinate's good elastic effect, the surface rheology of the solution becomes better once it reaches a certain concentration, and the film thickness remains stable as well. These factors contribute to the high stability of the produced bubbles.

An air-entraining agent is an admixture that introduces a large number of uniformly distributed tiny bubbles into the concrete mixing process, reducing the bleeding and segregation of the concrete mixture, improving its workability, and significantly enhancing the frost resistance and durability of the hardened concrete. What are the main functions of air-entraining agents?

Enhance the workability of concrete mixtures.

2. Significantly improved the concrete's impermeability and frost resistance.

3. Decrease the concrete strength. Generally, for every 1% increase in the air content of concrete, its compressive strength decreases by 4% to 6%, and its flexural strength by 2% to 3%.

Sodium rosinate is commonly used in mortar to enhance its workability and reduce its bulk density. As an air-entraining agent, sodium rosinate introduces a large number of discontinuous, minute, and closed bubbles at appropriate dosages, which can improve the workability of mortar to some extent and alter the pore distribution in early freezing conditions. This helps resist frost heave stress caused by the freezing of unhydrated water. Its mechanism of action is primarily manifested in the following aspects:

Sodium rosinate, at appropriate concentrations, can improve the pore size distribution of cement-based materials, reducing the porosity to below 20% while decreasing the proportion of harmful large pores and increasing the proportion of beneficial small pores that enhance early frost resistance. This lowers the probable pore size, benefiting both the impermeability and durability of cement-based materials.

2. During early freezing stages, sodium rosinate, used as an air-entraining agent in high quantities, can lead to a decrease in strength, which is significantly related to the porosity of the specimen. Moreover, the detrimental effects of increased harmful pores outweigh the frost-resistant properties of harmless pores.

3. Sodium rosinate primarily improves early frost resistance by acting on the pore structure. When fly ash is present along with an accelerator, it can promote the hydration process, but it does not significantly enhance the hydration of cement and other binding materials.