Effects of Fe2O3, Carbon, and Sintering Temperature on the Pore Structure of Lightweight Aggregate Fabricated via Sintering a Blend of Waste Coal Combustion Ash and NaOH

Abstract Achieving a balance between density and strength in synthetic sintered lightweight aggregates (LWA) is crucial for their effective performance in various applications such as lightweight concrete. LWA density and strength are governed by the properties and morphology of their solid and pore components. This study explores engineering solid and pore components during LWA sintering by balancing the viscosity of the melt and gas release. Two types of waste coal combustion ash (WCCA), with different iron oxide ( Fe 2 O 3 ) and carbon (C) contents, were utilized, with aqueous NaOH added as a fluxing agent. Fe 2 O 3 powder was added to WCCA to modulate gas generation during sintering. The development of pore structures in LWA was evaluated after rapid sintering at temperatures of 1,000°C–1,100°C. Pore structures were analyzed using X-ray computed tomography, while mineralogical composition was assessed through quantitative X-ray diffractometry. Key properties such as specific gravity and crushing strength were evaluated. The findings reveal that the porosity, strength, and density of LWA can be controlled by modifying the Fe 2 O 3 and C content in WCCA/NaOH blends. WCCA with lower Fe 2 O 3 and C contents yielded LWA with reduced porosity and higher strength, whereas those with higher Fe 2 O 3 and C contents resulted in higher porosity, suitable for applications where strength is less critical.