Enhancing the properties of UPOFA-based geopolymer mortar via the incorporation of eggshell ash and silica fume

Abstract

The aim of this study is to utilize the largest amount of ultrafine palm oil fuel ash (UPOFA) with the incorporation of additives namely eggshell ash (ESA) and silica fume (SF) in the manufacture of geopolymer mortar through the use of a statistical design program (Taguchi). The efficiency of UPOFA source material in the production of geopolymer products has been investigated via four factors, namely the NaOH concentration (moles), Na-silicate: NaOH ratio, eggshell ash (ESA) content, and silica fume (SF) content, where each factor contains three different levels. Each of these factors was examined on three levels in order to obtain an optimal mixture. Nine (9) geopolymer mortar mixtures were prepared according to the proposed [L09 (3 × 4)] matrix by the Taguchi method. The performance of the samples was evaluated by compressive strength, ultrasonic-pulse velocity (UPV), porosity (P%), water absorption (Abs%) and density. The results showed that the optimum mixture consisting of 77 wt% UPOFA, 11.5 wt% of ESA and 11.5 wt% SF, achieved a very high compressive strength of 125.4 MPa after 28 days of curing. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses of the optimized UPOFA-based geopolymer mortar mixture indicated that the properties of the mixture were greatly improved with calcium silicate hydrate (C–S–H) gel as the main binding phases within the synthesized UPOFA-based geopolymer mortar. Therefore, through the production of this geopolymer mortar, a large amount of UPOFA in combination with ESA and SF could be one of the solutions for the environmental and landfill disposal problems in Malaysia, besides promoting greener Portland cement free binder with potentially superior properties and performance.