The Influence of Carbonate Binder Content on the Mechanical and Physical Properties of Artificial Lightweight Aggregates Produced by Carbonization Using Wood Waste Fly Ash

Large amounts of wood waste fly ash (WWFA) are generated in bioenergy plants, yet their potential for reuse in construction materials remains underexplored. In this study, artificial lightweight aggregates (ALWAs) were produced by cold-bonded granulation of WWFA with hydrated lime, followed by carbonation curing (20 °C, 64% RH, 19% CO2). The aggregates were evaluated according to EN 13055:2016 classification criteria, with testing performed following the relevant European standards, including EN 1097-3 and EN 1097-6 for density and water absorption, EN 1097-11 for crushing resistance, and EN 1367-7 for freeze–thaw resistance. All ALWAs met the lightweight aggregate classification, with bulk densities of 1010.9–1060.0 kg/m3 and crushing resistances up to 2.74 N/mm2, exceeding that of lightweight expanded clay aggregate (LECA) (1.26 N/mm2). XRD confirmed CaCO3 formation, SEM revealed binder- and w/m-dependent porosity and crystal morphology, and freeze–thaw resistance indicated suitability for non-structural applications. These results demonstrate that WWFA-based ALWAs are a sustainable alternative to natural aggregates, combining waste valorization with competitive performance.