Characteristics of palm oil fuel ash geopolymer mortar activated with wood ash lye cured at ambient temperature

Abstract

The development of geopolymer cement has gained recognition in recent years as an innovative cementitious material that can be used as an alternative for ordinary Portland cement. However, using aggressive chemicals such as sodium hydroxide (NaOH) as an alkaline activator and oven curing has limited geopolymer technology to laboratory research only. This study investigates the properties of a user-friendly geopolymer mortar produced using untreated palm oil fuel ash (POFA) and ground granulated blast furnace slag (GGBS) activated with wood ash (WA) lye and sodium silicate (Na₂SiO₃) under ambient curing conditions. The effectiveness of WA lye as an alkaline activator in geopolymer production was examined using three sets of liquid binder ratios (L/B) and five sets of alkaline activator ratios (AARs) to optimise the L/B and AAR. Using the optimised L/B and AARs, five combined groups containing 0, 10%, 20%, 30% and 40% GGBS were produced and tested for their rheological, mechanical and durability properties. Results show that the setting time and flowability of the mortar decreased with the addition of GGBS. The compressive and flexural strength of the investigated specimens were found to be in the range of 20.23–28.17 MPa and 4.04–4.48 MPa for 30% and 40% GGBS content, respectively. Moreover, the investigated durability properties improved with the increase of the GGBS content. In addition, the dense microstructure and geopolymerisation reaction products improved with the increase of GGBS content, as indicated in the scanning electron microscopy and Fourier transform infrared analyses. The study revealed that an economised user-friendly WA lye activated geopolymer mortar can be produced at ambient curing conditions by partially replacing untreated POFA with 30% GGBS, thereby eliminating the necessity of NaOH alkaline activator and oven curing.