Utilization of flue gas desulfurization gypsum and pond ash as supplementary cementitious materials

Abstract The escalating environmental burden of conventional cement production and the accumulation of coal combustion by-products necessitate the development of innovative, low-carbon construction materials. This study investigates the valorization of two prevalent industrial wastes, flue gas desulfurization gypsum (FGDG) and pond ash (PA), as sustainable supplementary cementitious materials (SCMs) for mortar. Pretreated FGDG (thermally activated to β-hemihydrate) and ground PA were incorporated as partial cement replacements in mortar mixes, exploring various percentages up to 20%. Our findings demonstrate that optimized blends of FGDG and PA can effectively replace up to 20% of ordinary Portland cement without compromising mortar compressive strength. These SCMs actively participate in hydration reactions, forming critical binding phases such as calcium silicate hydrate (C-S-H) from PA’s silica and ettringite from FGDG’s calcium sulfate with PA’s alumina. Microstructural analysis, through SEM, confirmed the development of dense, crystalline structures and an increased C-S-H gel content, which contributes to mortar solidification and a reduction in drying shrinkage within specific limits. However, a crucial threshold was identified: FGDG content exceeding 5% led to problematic expansion, decreased mechanical strength, and elevated water absorption due to excessive ettringite formation. This research underscores the significant potential of pretreated FGDG and PA to reduce the environmental footprint of cement-based materials. By identifying optimal replacement levels and critical limitations, this study provides a vital pathway for the effective and sustainable utilization of industrial wastes in the construction sector.