A mixture of coffee grounds and fly ash in cementless geopolymer concrete

This research discusses the compressive strength of geopolymers made from coffee grounds as an additional material in geo-polymer fly-ash based concrete. The research aims to design a geopolymer concrete mix based on coffee grounds and fly ash, determine the compressive strength of geopolymer concrete based on coffee grounds and fly ash, and identify the optimal percentage of coffee grounds in geopolymer concrete production. The study has limitations, such as a concrete strength of 35 MPa, testing at 7, 14, and 28 days, and the use of an alkali activator with a molarity of 8. The research method employed involved experiments conducted in the material and concrete laboratory with the variable percentage of coffee grounds ranging from 0% to 20%. The use of coffee powder in the geopolymer concrete mixture as a replacement for fly ash has an impact on reducing the slump value by up to 18.52 % and reducing the specific gravity of the concrete by up to 6.55%. However, the use of up to 10% coffee powder still produces compressive strength values above the minimum requirement for structural concrete compressive strength, namely 20 MPa. Thus, a mixture with 10% coffee grounds can still be used as an alternative construction material that is more economical and sustainable.