Physicochemical and Microstructural Characterization of Sunflower Husk Ash and Thermal Power Plant Electrofilter Ash: A Preliminary Assessment for Construction Applications

The construction sector is under increasing pressure to reduce natural-resource consumption and the environmental impact associated with Portland cement production. In this context, ashes generated by biomass combustion and thermal power plants may represent secondary resources for mineral binder-based construction materials, provided that their characteristics and performance are adequately established. This study comparatively characterized sunflower husk ash (SHA) and thermal power plant electrofilter ash (EFA) from Romanian sources. The experimental program comprised scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, pH and electrical-conductivity measurements, and preliminary sieve-based dimensional screening. The two ashes exhibited substantially different profiles. SHA was heterogeneous, strongly alkaline, highly conductive, and rich in K-, Ca-, Mg-, sulphate-, chloride-, and phosphate-bearing constituents, whereas EFA showed a predominantly silico-aluminous and iron-bearing profile, lower conductivity, and crystalline phases including quartz, hematite, and anhydrite. These results demonstrate that SHA and EFA cannot be treated as interchangeable ash-based materials and provide a basis for selecting subsequent investigations. They do not, however, establish pozzolanic activity, supplementary cementitious performance, or compatibility with specific construction applications. Validation in cementitious or lime-based systems must therefore include reactivity, workability, mechanical performance, dimensional stability, durability, and soluble-salt-related testing.