Influence of Superabsorbent Polymers and Biobased Hydrogels on Freeze–Thaw Resistance of Cement Mortar

Abstract Air-entraining agents are commonly used in concrete to enhance freeze-thaw (F-T) resistance by introducing additional voids; however, this often results in reduced strength. Superabsorbent polymers (SAPs), primarily used for internal curing, also generate voids upon desorption and may offer F-T resistance benefits. This study investigates two commercial SAPs and a cornstarch-based hydrogel (in gel and powder forms), each incorporated at 0.2% of cement mass with additional water for workability. Mortar specimens were subjected to 200 F-T cycles in a brine solution and evaluated for compressive strength, mass change, surface scaling, and material characterization. Micro-CT scanning was conducted to assess void structure in both surface and core regions. Results showed that the air-entraining agent reduced surface scaling but did not prevent strength loss. After 200 F–T cycles, SAP mixtures exhibited a slight increase in compressive strength, while cornstarch hydrogel mixtures maintained strength with no mass loss or notable chloride penetration and scaling. Microstructural analysis revealed lower pore connectivity and enhanced matrix integrity in mortars containing SAPs and cornstarch hydrogels. Overall, these results demonstrate the potential of bio-based and synthetic absorbent polymers as sustainable alternatives to conventional air-entraining agents for enhancing long-term durability under severe saline F-T conditions.