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

[Image: see text] 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 Ca(2+) > Al(3+) > 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.