Reducing CO 2 Emissions in Urban Infrastructure: The Role of Siliceous Fly Ash in Sustainable Mortar Design

The incorporation of industrial by-products such as fly ash (FA) into cementitious materials plays a vital role in promoting environmental sustainability during cement production. This study evaluates the feasibility of using siliceous fuel fly ash, sourced from thermal power stations in the Rhenish region of Germany, as a partial cement replacement in mortar formulations. Mortar specimens with FA replacement levels ranging from 5 wt% to 30 wt% were prepared and tested. Data were collected through standardized laboratory testing of mechanical properties (compressive and flexural strength), physical characteristics (porosity, sorptivity) and microstructural analysis via SEM and XRD. The results showed that increasing FA content generally led to reductions in strength and increases in porosity and sorptivity, due to the mineralogical composition and higher water demand linked to the porous FA structure. However, when FA was used at levels not exceeding 10 wt%, the physical and mechanical properties remained within acceptable limits for construction applications. Additionally, the use of plasticizing admixtures proved effective in mitigating workability and strength issues by reducing the water-to-binder ratio. These findings highlight that, despite certain limitations, siliceous FA can be safely and effectively used in low percentages, contributing to sustainable mortar production and reducing reliance on Portland cement. In addition, the use of fly ash contributes to reduced CO 2 emissions and lower production costs, promoting sustainable and cost-efficient construction solutions.