Characterization of physical and mechanical properties of ferronickel slag based-geopolymer with POFA activator

Geopolymer is an environmentally friendly binder material resulting from the synthesis of aluminosilicate materials in an alkaline environment. Indonesia is the world's leading producer of palm oil and ferronickel, but comparable to the industrial waste it produces, such as ferronickel slag and palm oil fuel ash (POFA). Geopolymer with ferronickel slag precursor showed better mechanical properties than POFA. Although it has a low compressive strength, the high content of Si and low Al in POFA is expected to be suitable as an activator for geopolymers made from nickel slag. This study aims to explore ferronickel slag geopolymer with a POFA activator, which will be compared with a standard activator. This geopolymer product will be characterized by its phase, microstructure, compressive strength, flowability, and setting time. The results of this study indicate that geopolymer with POFA activator exhibited a compressive strength of 7.57 MPa at 28 days, flowability of 56.99%, initial setting time of 95 minutes, and final setting time of 135 minutes. The XRD analysis showed the presence of a high-intensity calcium silicate hydrate (C-S-H) phase. The resulting microstructure had a rough and porous surface, and the ettringite phase was also present, which affected the low compressive strength obtained. Therefore, using POFA as an activator in geopolymer showed unsatisfactory properties.