Mechanical, microstructural, durability, and energy analysis of fly ash geopolymer modified with autoclaved aerated concrete block waste

The global construction industry is witnessing a steady rise in cement demand, contributing significantly to CO₂ emissions, while concurrently generating substantial quantities of waste materials, notably construction and demolition waste (CDW). This study explores the utilization of these waste streams in developing sustainable construction materials, focusing on fly ash-based geopolymers and incorporating Autoclaved Aerated Concrete (AAC) block waste. Geopolymers, characterized by inorganic polymers with aluminosilicate materials, offer a promising alternative to traditional cement-based materials. Initially, 10% AAC waste and 90% fly ash (FA) were used to evaluate alkaline activator solutions with 1:2 and 1:1 ratios including sodium hydroxide and sodium metasilicate with 10 molarity and 12 molarity. Then, AAC block waste (10%, 20%, and 30% by weight) was added to fly ash-based geopolymer mortar, taking into account the results of the earlier analysis utilizing the ideal alkali activator solution 1:2 ratio and 12 molarity. Mechanical properties, including compressive strength, were evaluated at 3, 7, and 28 days. Durability properties such as carbonation resistance and water absorption were also assessed. Energy performance was evaluated using the eQuest simulation tool. Results demonstrated that geopolymer mortar incorporating AAC waste achieved a maximum compressive strength of 14.89 MPa while meeting other performance criteria as revealed from microstructural analysis. The incorporation of AAC waste into geopolymer mortars resulted in a 0.72% reduction in space cooling energy consumption and a 0.35% decrease in total electricity consumption compared to conventional burnt clay bricks. Given the increasing use of AAC blocks and the associated waste generation, this study highlights the potential of geopolymer technology to valorize AAC waste and contribute to sustainable building materials development.