Effect of Sodium Hydroxide Concentration on the Mechanical Property of Non Sodium Silicate Fly Ash Based Geopolymer

Alkali activator and materials rich in Si and Al are the requirements for the geopolymer synthesis. The common activator use is sodium hydroxide with silicate solution. There is limited literature on the mechanical property of geopolymer in the absence of silicate solution. In this study, fly ash was used as the raw material to provide Si and Al and sodium hydroxide (NaOH) as the only activator for the synthesis of geopolymer. This study describes the effect of varying the sodium hydroxide concentration with respect to curing time and temperature on mechanical properties of non-sodium silicate fly ash based geopolymer. The samples were prepared by mixing fly ash with 8, 10 and 12 M of NaOH concentration and cured in room temperature and 60°C for 1, 7 and 28 days. The highest alkali concentration of 12 M showed the fastest setting time and the highest compressive strength regardless of days of curing. The highest compressive strength obtained for curing at 60°C was 59.81 MPa and 45 min was recorded for the setting time. Meanwhile, at room temperature, the highest strength obtained was 17.71 MPa and 248 min for setting time.