Experimental Study on Characteristics of Fly Ash–GGBS-Based Geopolymer Concrete with Demolition Waste as Fine Aggregate

In an effort to tackle the issues of carbon dioxide (CO2) emissions from the cement industry and land pollution caused by the disposal of construction waste, this study aimed to investigate the potential of fly ash-ground granulated blast-furnace slag (GGBS)–based geopolymer concrete (FG-GPC) and demolition waste fine aggregate (DWF) as environmentally sustainable alternatives to conventional cement concrete and natural fine aggregate, respectively. The experimental procedure included optimizing the FG-GPC variables (Na2SiO3/NaOH and NaOH molarity) and investigating the properties of FG-GPC with the addition of DWF in various proportions (0%, 25%, 50%, 75%, and 100% by volume). To investigate the mechanical and physical parameters of FG-GPC with DWF, compressive strength, split tensile strength, flexural strength, elastic modulus, water absorption, density, effective porosity and ultrasonic pulse velocity were determined. The microstructural properties of FG-GPC were studied using scanning electron microscope (SEM) tests on selected samples. The experimental findings indicated that the strength and physical properties of FG-GPC were progressively diminished when adding DWF to the mix. Nonetheless, FG-GPC with 25%–50% DWF replacement showed a lower drop in concrete properties, indicating that employing construction and demolition (C&D) waste as a fine aggregate might have environmental and economic advantages.