The effect of acid attack on CFBC fly ash-based geopolymer paste with different alkaline activator

This research aims to identify the effect of acid attack caused by acid mine water with a pH of 2.65 on geopolymer paste based on CFBC fly ash class F with variations of alkaline activator solutions of 2M, 4M, and 8M. Cylindrical specimens of geopolymer paste were steam cured for 2 hours at 65 degrees Celsius to obtain initial strength at one day. The specimens were then cured under three conditions: acid mine water immersion, tap water immersion, and room temperature. The result shows that CFBC fly ash required more OH-for the geopolymerization reactions, resulting in 8M NaOH increased workability compared to 4M and 2M. However, excessive NaOH results in Na leaking out into the liquid, forming efflorescence on the surface and causing a decrease in compressive strength. The 50% fly ash composition required 8M NaOH to obtain a stable geopolymer paste at three different curing conditions. The interaction of acid mine water for 42 days failed to damage the polysialate bonds in the geopolymeration reaction. Therefore, the CFBC fly ash-based geopolymer paste was proven to resist acid attacks and has potential as a heavy metal adsorbent and pH adjuster in acid mine water.