Effect of different ratio of geopolymer paste based fly ash-metakaolin on compressive strength and water absorption

This paper presents the effect of different solid to solid (S/S) ratio by mixing the fly ash and metakaolin as geopolymer paste on the compressive strength and water absorption. Fly ash is a waste materials produced by combustion of coal at power plant while metakaolin was obtained by calcining the kaolin at 750 °C for 4 hours. Different weight percentage of S/S ratio of fly ash/metakaolin used were 50%:50% (Mix 1), 70%:30% (Mix 2) and 90%:10% (Mix 3). Alkaline activators that act as binder were sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) solutions. The ratio of Na₂SiO₃/NaOH is 2.5 to 1. The mixture then placed into cylinder mould and left for 7, 14 and 28 days before it be tested. The product obtained were observed and it shows that Mix 2 has highest compressive strength for 28 days that was 41.22 MPa and has lower water absorption. The pore size decreases and permeability also decreases hence the strength potentially improve. (paper)