Synthesis of Acid-Based Fly Ash Geopolymer with Pure Phosphoric Acid Compare with P-Leachate Activator

Acid-based geopolymers (ABG) have gained attention as eco-friendly alternatives to Ordinary Portland cement. This study synthesized ABG by activating fly ash with commercial H3PO4 and an alternative P leachate from sewage sludge. The ABG was synthesized at different molar concentrations of 4M, 6M, 8M, 10M, and 12M, while P-leachate geopolymer (PFA) was synthesized with liquid/solid ratios of 0.2-0.5. The unconfined compressive strength (UCS) was used to measure the geopolymer performance, which was also studied using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The P concentration was higher than the alternative P source; however, the Al concentration was low, resulting in a lower UCS compared to ABG FA. ABG FA activated with 8M reported a UCS of 11.53 MPa. The strength of ABG FA was attributed to the Si-O-P-O-Si, (PO4)5-, (AlO4)5, and Al-O-Si networks and the participation of H2PO4- in geopolymerization. The PFA exhibited the formation of a Si-O-Al-O-P unit and a P-O vibration band, and the microstructure was composed of cenospheres covered with some minor gelatinous particles.