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. © 2021, Springer Nature Switzerland AG.