Concrete is the most widely used construction material worldwide due to its good mechanical properties, durability, and affordability. However, Portland cement production contributes approximately 5–8% of global anthropogenic CO₂ emissions. Supplementary cementitious materials (SCM), which can partially replace Portland cement, present the greatest potential for reducing the environmental impact of the construction industry. Recently, there has been increasing interest in research on the potential use of wood ash (WA) as an SCM. Utilization of WA in concrete promotes waste reuse and offers a sustainable option for SCM. However, since the characteristics of WA can vary significantly depending on its source and production conditions, further research is needed to optimize its effective use.

This study aims to investigate the potential use of WA as an SCM and compare it with coal fly ash (FA), focusing on enhancing its reactivity and performance in both cement-based and alkali-activated materials through mechanochemical activation (MCA; high-energy grinding). The properties of WAs and the effect of MCA were examined, including Strength Activity Index (SAI), Frattini, R3 test, TGA/DTG, XRD and SEM-EDS analysis. WA was used to replace 10 wt.% and 20 wt.% of Portland cement in concrete and of ground granulated blast furnace slag (GGBFS) in alkali-activated mortars. Workability, strength, hydration behaviour, and microstructural properties were evaluated. The leaching behavior of WA was evaluated through batch tests, and the environmental performance of selected concrete mixes containing WA was further investigated using dynamic surface leaching tests (DSLT) on monolithic concretes. The frost durability of these concrete mixes was examined using the de-icing salt frost scaling test.

MCA significantly increased the fineness and specific surface area of WA significantly, resulting in enhanced reactivity. Depending on their chemical composition, some WAs exhibited predominantly pozzolanic behavior, while others showed latent hydraulic properties. The use of WA after MCA in concrete and alkali-activated mortars led to improvements in strength, cumulative heat release and microstructure compared to unground WA. At lower replacement levels, the compressive strength improved compared with the control sample in certain mixes. In air-entrained concrete, it improves frost durability by reducing surface scaling. MCA improved the environmental compatibility by reducing the leaching of most heavy metals, despite stainless-steel grinding media increasing Cr and Ni concentrations. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) showed that, after MCA, WAs with higher pozzolanic oxide contents clustered more closely with FA.