Effect of NaOH Concentration on the Mechanical and Microstructural Properties of Fly Ash-Based Geopolymer

This study offers a comprehensive investigation into the influence of varying NaOH concentrations on the mechanical and microstructural properties of Class F fly ash-based geopolymers. The activator solution used for this study was sodium hydroxide (NaOH) solution. The concentrations of NaOH solutions were kept at 6 Molars, 8 Molars, 10 Molars, 12 Molars, 14 Molars, and 16 Molars, respectively. The ratio of activator solution to fly ash powder was kept at 0.3, and the geopolymer specimens were cured at 60℃ for 50 hours. After curing, mechanical properties such as compressive strength, flexural strength, and hardness values were determined. The fractured surface of geopolymer specimens was analyzed using FESEM, TEM, XRD, FTIR, etc. The water absorption test under tape water was conducted for 7, 14, and 28 days. The lowest water absorption of 7.46% was achieved within 28 days of curing. Further, the durability study of geopolymer specimens was conducted under high temperatures of 200℃, 400℃, 600℃, 800℃, and 1000℃, respectively. After exposure, the compression test of the exposed specimens was conducted to reveal the residual compressive strength. To study the microstructural properties, the fractured specimens after the mechanical test (compression test) were analyzed by using FESEM-EDS. Fly ash-based geopolymers have a wide range of potential applications across various fields such as construction and civil engineering, refractory and high-temperature applications, heritage and monument restoration, transportation infrastructure, marine and coastal applications, 3D printing, and advanced manufacturing fields, etc., due to their eco-friendliness, durability, and strong mechanical properties.