Void system-targeted design of concrete using superabsorbent polymers: Enhancing frost resistance and mechanical performance

To overcome the poor stability and uncontrollability of the void system created by traditional air-entraining agents (AEA), a void system-targeted design method based on the water absorption capacity of superabsorbent polymers (SAPs) was proposed. Hardened cement pastes void system analysis was used to verify the accuracy of this method in designing air content, void size distribution, and spacing factor. Subsequently, seven types of SAP concretes with targeted void systems were prepared to evaluate frost resistance and compressive strength systematically. Finally, scanning electron microscopy (SEM) was employed to examine the microstructural evolution during freeze-thaw cycles, mercury intrusion porosimetry (MIP) was used to assess the influence of SAP on pore structure, and nanoindentation was conducted to characterize the properties of the interfacial transition zone (ITZ) between SAP void and matrix. Results showed that SAPs effectively balance frost resistance and compressive strength. At a fixed water-to-cement ratio of 0.408, the incorporation of 200–400 µm SAP at 0.4 % dosage improved frost resistance by 450 cycles. Using the same dosage of 10–30 µm SAP enhanced frost resistance by 375 cycles without compromising compressive strength. The mechanism of SAP voids in enhancing frost resistance was similar to that of AEA voids. In addition, the internal curing zones surrounding SAP voids suppressed crack propagation during freeze-thaw cycling and altered microcrack development paths. The water absorption and internal curing effects of SAP contributed to pore structure refinement and improved micromechanical properties, thereby enhancing both frost resistance and compressive strength.