Gelatin-based air-entraining agents for ordinary portland cement: Chelate Ca²⁺ and reduce surface tension

Introducing uniform, stable, and small pores by adding air-entraining agents (AEAs) is an effective strategy for improving the freeze-thaw resistance and workability of cement concrete materials. In this study, the gelatin with hydrophobic and hydrophilic functional groups was used as an AEA for cement concrete materials and systematically studied its effect on the performance of cement mortar specimens. The results showed that gelatin has a surfactant-like function and can effectively reduce the surface tension of the gas-liquid interface. In an alkaline environment, Ca2+ ions in cement pore solution chelate with carboxylate ions formed by carboxyl ionization, further enhancing the performance of gelatin-based AEAs. Thanks to the reduction in surface activity and carboxyl ionization, introducing gelatin increased the porosity of cement mortar specimens from 0.53% to 2.69%. Furthermore, introducing an appropriate amount (>0.1 wt%) of gelatin does not significantly impact the workability or mechanical properties of cement mortar. Based on these characteristics, gelatin has potential as an AEA for cement concrete materials.