Facile synthesis and optimization of reactive bunsenite for the production of thermally stable geopolymeric composite

Abstract

In this investigation, the impact of texture characteristics and the degree of crystallinity of the bunsenite phase (NiO) on the mechanical performance and fire resistivity of the geopolymeric composites is addressed for the first time. NiO with different characteristics is prepared by applying two calcination-temperatures (400 and 600 °C) to obtain NiO-400 and NiO-600, respectively. Seven mixes were prepared; the control specimen was fabricated by mixing 50% slag+50%fly-ash + NaOH-solution and the other six mixes contained the same component modified with 0.5, 1, 2% NiO-400 or NiO-600. The compressive-strength at 3 and 28-days and fire resistivity up to 1000 °C were studied. Also, the phase composition and micro-structure were examined using XRD and TGA/DTG as well as SEM, respectively. The results showed that increasing calcination-temperature leads to decreasing surface area and increasing the degree of crystallinity of NiO. The composites modified with NiO-400 significantly enhanced the strength and fire resistivity of the control specimen, while NiO-600 demonstrated a lower effect. This refers to increasing the calcination-temperature is accompanied by decreasing the degree of reactivity, which reflects on the properties of geopolymeric composites. Regardless of the NiO-type, 1 w.% exhibited the highest strength. Adding NiO induced the formation of NiAl2O4, CaNi(SiO3)2 and NaAlSi2O6.H2O, which is compatible with enhancing mechanical and fire resistivity results.