Freezing–Thawing Resistance of MKG

Understanding the composition-dependent features of geopolymer materials as well as their freezing–thawing (F-T) resistance is essential for their effective application in cold climates. In this work, the Si/Al ratio and the Na/Al ratio were controlled to create geopolymer mortars based on metakaolin (MKG). The pore structure was evaluated through mercury intrusion porosimetry, while compression tests were conducted to determine strength; both parameters showed obvious correlations with material composition. Mass loss, strength loss, visual rate, and microscopic observation were utilized to evaluate changes in material characteristics and microstructure brought on by F-T stresses. The strength-porosity connection appeared to essentially follow a linear pattern, according to the results. Capillary pore volume rose with increases in the Si/Al ratio, whereas gel pore volume and F-T resistance dropped. Increases in the Na/Al ratio reduced gel pore volume, but generally improved F-T resistance. MKG mortar with a Na/Al ratio of 1.26 exhibited the lowest total pore volume and the best F-T resistance. Our experimental results suggest that air voids connected by capillary pores facilitate relaxation of hydraulic pressures induced by pore liquid freezing. This study help clarify the compositional dependence of pore structure, strength, and F-T resistance of MKG materials, providing fundamental information for their use in engineering applications in cold regions.