The study of geopolymers has become an interesting concern for many scientists, especially in the infrastructure sector, due to having inherently environmentally friendly properties and fewer energy requirements in production processes. Geopolymer attracts many scientists to develop practical synthesis methods, useful in industrial-scale applications as supplementary material for concrete. This study investigates the geopolymerization of fly ash and geothermal silica-based dry activator. The dry activator was synthesized between NaOH and silica geothermal sludge through the calcination process. Then, the geopolymer mortar was produced by mixing the fly ash and dry activator with a 4:1 (wt./wt.) ratio. After mixing homogeneously and forming a paste, the casted paste moved on to the drying process, with temperature variations of 30, 60, and 90 °C and curing times of 1, 3, 5, 7, 14, 21, 28 days. The compressive strength test was carried out at each curing time to determine the geopolymer’s strength evolution and simulate the reaction’s kinetics. In addition, ATR-FTIR spectroscopy was also used to observe aluminosilicate bonds’ formation. The higher the temperature, the higher the compressive strength value, reaching 22.7 MPa at 90 °C. A Third-order model was found to have the highest R² value of 0.92, with the collision frequency and activation energy values of 1.1171 day⁻¹ and 3.8336 kJ/mol, respectively. The utilization of coal fly ash and silica geothermal sludge as a dry activator is, indeed, an approach to realize the circular economy in electrical power generations.

The geopolymer structures are formed through polymerization of silicate and aluminate species. The resulted structure is predicted to be similar with zeolite. In this study, geopolymer samples were made from mix powder of geothermal silica and bentonite, then activated with sodium hydroxide and sodium silicate. The effect of silica content, NaOH molarity and curing temperature effect were investigated on geopolymer IR spectra and compared with 3A zeolite IR spectra. Pearson correlation value (r) and spectral similarity correlation (Corr) were used to assess spectra similarity between geopolymer samples and zeolite. The development of geopolymer bond and microstructure of samples were then investigated by FTIR technique. IR spectra of geopolymer samples show that Si-O-Al absorption bands are formed around 900-1300 cm^-1 and 400-800 cm^-1. The optimum of silica contents, NaOH molarity and curing temperature obtained from the experiment were 140 grams, 10 M and 80°C with Corr value of 922 and compressive strength of 7,59 MPa. Corr value is proven to have relation with material strength. Higher Corr value is identified to have higher aluminosilicate species which contributes to higher compressive strength.