Enhancing Freeze-Thaw Resistance of Alkali-Activated Slag by Metakaolin

Incorporating metakaolin (MK) into slag to prepare alkali-activated materials can reduce shrinkage and improve the durability of alkali-activated slag (AAS). But its durability under freeze-thaw conditions is unknown. In this paper, the effects of MK content on the freeze-thaw properties of AAS were investigated from the perspective of gel composition and pore solution. The experimental results showed that the addition of MK generates a gel mixture of C-A-S-H and N-A-S-H with a cross-linked structure and decreases the content of bound water and pore water absorption. With the increase of alkali dosage, water absorption decreased to 0.28% and then increased to 0.97%, and the leaching rate of ions was Ca²⁺ > Al³⁺ > Na⁺ > OH^-. When the alkali dosage was 8 wt % and the MK content was 30 wt %, the compressive strength loss rate of AAS was 0.58% and the mass loss rate was 0.25% after 50 freeze-thaw cycles.