Effect of Adding Sago and Sintering to the Properties of Geopolymer Mortar

Abstract

Geopolymer is an alternative cementitious material produced by rich Alumino Silicate mineral materials (Si-Al) combine with alkaline activator. The objectives in this study are to introduce pores by using sago as pore former and to determine the effect of curing time and sintering process to geopolymer mortar properties. There are three compositions of mortar used in this study with different sago content (10%, 20%, and 30%) and each composition of mortar have different curing time (1, 3 and 7 days). Fly ash, silica powder, alkaline activator (sodium silicate solution (Na2SiO3) and sodium hydroxide (NaOH) and sago were mixed together based on their composition and the mixture were put into steel cubic mould (50 mm x 50 mm x 50 mm) and left at room temperature for curing process. After the mortar reaches their curing time, it will be sintered at 1000 °C. The physical changes of the mortar were analysed before and after the sintering process. The microstructure of mortar was observed using Scanning Electron Microscope (SEM). Compression test was done to geopolymer mortars by using ADR-Auto 3000 from ELE instrument (ASTM C109 standard) to determine the mechanical properties. Fourier-transform infrared (FTIR) analysis used to determine the functional group exist in geopolymer mortar and X-ray Diffraction (XRD) was used to determine the phase. Besides that, Energy dispersive X-ray spectroscopy (EDX) use to measure percentage elements exist in a mortar. Geopolymer mortar with 10% sago content, 7 days of curing and undergo sintering process have the highest compressive strength (13.46 N) compare to the other geopolymer mortar composition. The 30% sago mortar contain many pores after sintering contributes its brittleness and cannot be tested for compressive strength. Longer curing days give enough time for the geopolymerisation process to create strong Si-O-Al bond or Jadeite (N-A-S-H gels) while sintering process helps to speed up the geopolymerisation process take place in a mortar. Formation of jadeite (N-A-S-H gels) influenced the strength of the mortar. The increasing phase of jadeite increases the strength of the mortar. As sago content increase, the pores in geopolymer also increase but the ratio Al2O3:SiO2 decrease resulting low formation of Jadeite. Hence the compressive strength of geopolymer mortar decrease.