Influence of SiO2, Al2O3, CaO, and Na2O on the elevated temperature performance of alkali‐activated treated palm oil fuel ash‐based mortar

Abstract

AbstractThe mechanical, physical, and chemical changes due to oxides molar ratios (SiO2/Al2O3 and SiO2/CaO), and various Na2O concentrations of treated palm oil fuel ash (TPOFA)‐based alkali‐activated mortar (AAM) after being exposed to different elevated temperatures up to 1,000°C were investigated. The source materials (SMs) and alkaline activator (AA) were used as the main base material to produce the AAM. The SMs consist of TPOFA with and without mineral additives (Ca(OH)2, Al(OH)3, and silica fume (SF)). The AA was characterized by various Na2O concentrations of 7.1, 6.0, and 5.5% relative to the AAB weight. The results indicated that the relative compressive strength (CS) improved significantly from 9.20 to 34.62% after being exposed to 800°C. This was mainly due to the decrease in the total oxide's ratio of SiO2/Al2O3 and SiO2/CaO from 14.84 and 6.98% to 4.27 and 2.03%, respectively. The relative CS has increased from 0.0 to 101.38% after exposed to 1,000°C when Na2O concentration reduced from 7.1 to 5.5%. This was due to the formation of more N–A–S–H and C–A–S–H gel binders as indicated at 28 days, which were transformed to nepheline (NaAl(SiO4)) and wollastonite (CaSiO3) phases after exposure to 800°C and 1,000°C, respectively.