Improving the freeze-thaw resistance of geopolymers is of great significance to ensure their durability in cold regions. This study presents an experimental investigation of optimal slag content for geopolymer composites under freeze-thaw cycles with different freezing temperatures. Firstly, five kinds of geopolymer composites with 10.0%, 20.0%, 30.0%, 40.0%, and 50.0% slag contents and 1.0% fiber content were prepared. Freeze-thaw cycle tests at −1.0 ℃, −20.0 ℃, and −40.0 ℃ were carried out for these geopolymer composites and their physical and mechanical properties after the freeze-thaw cycle were tested. The results show that the porosity of the geopolymer composites decreases as the slag content increases. Their mass loss ratio and strength loss ratio increase gradually as the freezing temperature decreases. The mass loss ratio and strength loss ratio of geopolymer composites after freeze-thaw cycles all decrease as the slag content increases. Considering the physical and mechanical properties of geopolymers after freeze-thaw cycles, the optimal slag contents are 40.0% and 50.0%.
