Potassium-rich calcinated waste coffee husk ash as an alkali activator in one-part geopolymer concrete

Abstract The study explores the possibilities of using calcinated waste coffee husk ash (WCA) as a natural alkaline activator in one-part geopolymer concrete. WCA was calcinated at 1000 °C for 2–14 hours at 2-hour intervals, and physicochemical characteristics were determined, including pH, water solubility, and Loss on Ignition (LOI). The effect of calcination period on the reactivity of WCA and its impact on the mechanical performance of geopolymer concrete was evaluated by replacing part of GGBS with WCA. These findings suggest that the 12-hour calcination of WCA shows better performance with a maximum pH (13.98), water solubility (54.5%), and calcination efficiency (LOI = 23.15%). Concrete mixes that used 15 percent replacement with 12-hour calcinated WCA (C12H15) noted the highest mechanical performance, which has 16 percent increased compressive strength at 28 days, relative to 10-hour calcinated WCA mixes. The optimized mixes were further proved to be superior in terms of fresh and mechanical performance, as confirmed by workability, compressive strength, and split tensile strength tests. The research confirms that properly calcinated WCA has the potential to replace traditional chemical activators, which would be a green, cost-effective, and environmentally friendly option in a massive building. This also solves the environmental issue of waste disposal of coffee husks, which would ensure sustainable construction without affecting the structural performance. Based on reported literature, one-part geopolymer systems can reduce carbon emissions by about 30–40% compared to conventional OPC concrete.