A preliminary study of alkali-activated slag blended with silica fume under the effect of thermal loads and thermal shock cycles

The elevated temperature performance of alkali-activated ground granulated blast-furnace slag/silica fume (SF) at ratios of 100/0, 95/5, 90/10 and 85/15 wt.%, activated with sodium silicate is presented. The specimens were exposed to elevated temperatures ranging from 400 °C to 1000 °C with an increment of 200 °C. Compressive strengths before and after firing were measured. Water quenching test was applied to determine thermal shock resistance of various mixtures. The various decomposition phases formed were identified using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectra (EDS). The results indicated that the compressive strengths before and after firing increased with the presence of SF up to 800 °C, then decreased at 1000 °C in comparison with neat activated slag specimens. The relative strength of the neat alkali-activated slag paste was superior and the inclusion of SF had adversely impact on the thermal shock resistance.