Abstract

Geopolymer is an inorganic polymer formed from aluminosilicate material in fly ash from coal combustion waste, which is activated using sodium silicate and potassium hydroxide. This study utilized fly ash type F waste and coconut fiber sourced from local plantations. A series of tests were conducted to optimize the mechanical performance of compressive strength, flexural strength, and tensile strength of geopolymer mortar with different fiber content (0%, 0.25%, 0.5%, 0.75%, 1%, 1.5%, 1.75%, 2.00%) and aspect ratio of coconut fiber waste (L/D = 100, 200, 300). The mixture composition used an aggregate to fly ash ratio of 65%:35%, a fly ash to alkali ratio of 62%:38%, and a Na<inf>2</inf>SiO<inf>3</inf> to KOH ratio of 2:1. The results showed that the addition of coconut fiber increased the compressive, flexural, and tensile strength and optimal performance was observed at a certain fiber content. However, excessive fibers reduce the mechanical performance of geopolymer mortar. This study offers an alternative to develop environmentally friendly mortars based on waste materials and promotes the use of natural fibers. Fiber-reinforced geopolymers show good resistance to acidic, sulfate, high-temperature, and chemical environments, exhibiting low shrinkage, improved ductility, better microcrack resistance, and better mechanical performance that contribute to sustainable construction practices.