Effect of activator dosage on the post-fire autogenous self-healing of alkali-activated slag

Alkali-activated slag (AAS) is a potential alternative binder for ordinary Portland cement (OPC) with a lower carbon footprint. Despite its higher mechanical and durability performances than OPC, AAS are susceptible to severe microstructural decompositions when it exposed to elevated temperatures. Nevertheless, post-fire self-healing of AAS was revealed as an inherent property densifying the matrix microstructures, restoring its mechanical strengths, and extending its durability. This paper examines the influence of activator dosages on the post-fire self-healing of AAS matrix. This study adopted a mixed solution of sodium hydroxide and sodium silicate as the activator. Different dosages reflecting various levels of activations (i.e. low, medium, and high) were selected according to the silicate modulus (M s ) and sodium oxide percentage (Na 2 O%). Results showed that mixtures with low activation dosage exhibited the lowest post-fire damage percentages and highest self-healing ability. Calcite precipitations were able to close surface cracks up to 250 µm. This precipitation improves the matrix durability by preventing aggressive substances from ingress. Moreover, mixtures with high activation dosage acquired the highest mechanical recovery, approximately 20 % of the compressive strength with respect to fire-damaged specimens. The higher ion concentrations of the high activation dosage were effectively diffused to initiate the hydration reaction of existing un-hydrated slag particles, increasing the microstructure intensity. These findings emphasize that different dosages of alkali-activated slag could be effectively utilized to produce fire-resistant construction materials with enhanced resilience. The specific dosage can be tailored for different applications depending on the desired outcome, whether focused on durability or mechanical recovery. • Dissolute slag and fast initiating the geopolymerization reaction are dominating post-fire self-healing. • Calcite precipitations improve the matrix durability. • Water post-fire curing was revealed as an effective mechanism to enhance the AAS self-healing. • Intensive ion concentrations support the formation of hydration products and calcite precipitations.