Enhancement of compressive strength in geopolymers: a study on fly ash characteristics and solid activation using dry method

Geopolymers are manufactured using the dry method with fly ash sourced from the Pacitan power plant in East Java (class C) and the Muara Enim Power Plant in South Sumatra (class F). The process begins with preparing the fly ash, followed by solid activators from NaOH and fly ash calcined at 400, 500, and 650 °C to create a geopolymer paste. Compressive strength analysis evaluates the mechanical properties of the geopolymers, with functional group analysis conducted using FTIR. The optimum conditions for the solid activator were found at a calcination temperature of 500 °C, yielding sodium silica (Na2SiO3) compositions of 39% for Pacitan and 39.5% for Muara Enim fly ash. The geopolymer from Pacitan power plant achieved a maximum compressive strength of 16.0 MPa with an alkaline concentration of 8.33 M. In comparison, Muara Enim’s geopolymer reached 0.2 MPa at 2.94 M. This study is novel in exploring the use of calcination to produce solid activators as an alternative to liquid activators, reducing cost and complexity in the production of geopolymers. Pacitan fly ash exhibited a higher amorphous phase (66.43%) and CaO content (15.288%), enhancing mechanical strength due to its self-cementing properties and increased reactivity.