Strength Properties of Coffee Waste Based Geopolymers

A considerable amount of coffee waste is disposed in the landfills annually. This study aims to investigate the possible use of coffee waste based geopolymers as a green construction material for landfills. Coffee is an organic and a biodegradable material. In order to use coffee waste as a construction material, the strength development of a coffee-based geopolymer was observed. Fly ash or rice husk ash were used as a precursor. These precursors were preferred because they are silica and alumina rich materials. Alkaline activator formed of sodium silicate and sodium hydroxide (Na₂SiO₃–NaOH) was used to trigger the geopolymerization process. Three variables were tested, the ratio of Na₂SiO₃–NaOH; effect of ash type, and curing time on the strength development of coffee-based geopolymers. By adding 30% of ash into coffee waste, a geopolymer was synthesized with an activator/ash ratio of 1.7 and Na₂SiO₃–NaOH ratio of 90–10%, which provided the highest (up to 1000 kPa) unconfined compressive strengths. This paper denotes that the coffee based-geopolymerization products will further develop the organic material into a nondegradable material, therefore suggesting geopolymers as an option to stabilize highly organic soils.