Influence of pre-treatments on strength and hydrocalumite content in a self-hardened binder exclusively derived from biomass fly ash

Woody biomass combustion for heat and power production generates substantial amounts of biomass fly ash (BFA), typically disposed of in landfills. Valorizing this residue can be achieved by exploiting its self-hardening properties. This study investigates the effects of pre-treatments on BFA characteristics and self-hardened specimens' mechanical response and mineralogical phase development. Pre-treatments involved sieving BFA at 63 μm and grinding BFA to pass the 63 μm sieve. Self-hardened specimens were prepared merely by adding distilled water to the BFA powders and curing for 7, 30, 90, and 120 days. Reducing particle size increased compressive strength and hydrocalumite content in samples cured for 120 days. After 120 days, the sieved BFA sample had the highest hydrocalumite content (29.1 wt.%). The ground and sieved samples showed the greatest compressive strength (8.1 MPa). This suggests that hydrocalumite alone does not account for the strength; better compactness and higher concentrations of reactive species (Ca, Si, S, Al, and Cl) in the ground powder likely contributed to forming more amorphous or low-crystallinity hydration products that enhance specimen strength. Using BFA as a precursor for producing hydrocalumite-containing self-hardened binders offers a promising method for valorizing this residue, leveraging its adsorption capabilities for affordable environmental remediation solutions.