Influence of micro Fe2O3 and MgO on the physical and mechanical properties of the zeolite and kaolin based geopolymer mortar

Abstract

Geopolymer binders can be used as a sustainable alternative to Portland cement. Despite the extensive research regarding the influence of different parameters on the properties of geopolymers, the studies investigating the effect of Fe2O3 and MgO on the performance of geopolymer concrete are minimal. This study investigates the impact of micro Fe2O3 and MgO additives on the physical and mechanical properties of the geopolymer binder. For this reason, the binder was developed by replacing 10%, 20%, and 30% kaolin with zeolite. In addition, Fe2O3 and MgO amounts in the binder were increased by substituting 4%, 6%, and 8% Fe2O3 and MgO with zeolite. The binder was activated with NaOH containing 15% Na (Na/binder) by weight. Geopolymer mortar specimens were prepared by mixing binder, sand, and NaOH-water solution, and the physical and mechanical properties of geopolymer specimens were investigated. Results show that replacing zeolite with kaolin and adding micro Fe2O3 and MgO increase the geopolymer specimens' unit weight, compressive strength, flexural strength, and ultrasonic pulse velocity (UPV). Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) spectra show no significant difference between the zeolite and zeolite + kaolin based geopolymer specimens. However, hematite mineral phases and periclase and forsterite mineral phases are prominent in geopolymer specimens incorporating micro Fe2O3 and MgO, respectively. Scanning electron microscopy (SEM) analysis shows a dense structure in the zeolite + kaolin based geopolymer specimens than zeolite based geopolymer specimens. Energy dispersive spectroscopy (EDS) analysis shows sodium aluminosilicate and calcium silicate hydrates as the main hydration products of all the geopolymer specimens. Based on the results, adding Kaolin, Fe2O3, and MgO in a zeolite-based geopolymer improves the physical and mechanical properties of the specimens.