Sustainable Geopolymer Tuff Composites Utilizing Iron Powder Waste: Rheological and Mechanical Performance Evaluation

Geopolymers are a sustainable alternative to Portland cement, with the potential to significantly reduce the carbon footprint of conventional cement production. This study investigates the valorization of industrial waste iron powder (IP) as a fine filler in geopolymers synthesized from volcanic tuff (VTF). Composites were prepared with IP substitutions of 5%, 10%, and 20% by weight, using sodium hydroxide and sodium silicate as alkaline activators. Microstructural and phase analyses were conducted using scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence (XRF), X-ray diffraction (XRD), and differential scanning calorimetry (DSC), while rheological properties, compressive strength, and flexural strength were assessed. The impact of curing temperatures (25 °C and 80 °C) on mechanical performance was evaluated. Results revealed that air content increased to 3.5% with 20% IP substitution, accompanied by a slight rise in flow time (0.8–2 s). Compressive and flexural strengths at 25 °C decreased by up to 22.48% and 28.39%, respectively. Elevated curing at 80 °C further reduced compressive and flexural strengths by an average of 45.30% and 64.68%, highlighting the adverse effects of higher temperatures. Although these formulations are not suitable for load-bearing applications, the findings suggest potential for non-structural uses, such as pavement base layers, aligning with sustainable construction principles by repurposing industrial waste and reducing reliance on energy-intensive cement production.