Potential Use of Silica Fume Coupled with Slag in HVFA Concrete Exposed to Elevated Temperatures

In this study, cement was partially replaced with a Class-F fly ash (FA) at a level of 70% to produce high-volume fly ash (HVFA) concrete (F70). The F70 was modified by partially replacing the FA with an equal combination of silica fume (SF) and slag at levels of 10 and 20% by weight. All HVFA concrete types were compared to plain portland cement (PC) concrete. After curing, the specimens were exposed to elevated temperatures ranging from 400 to 1,000 degrees C with an interval of 200 degrees C. Weight and compressive strength before and after firing were thoroughly explored. The various decomposition phases were identified using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated a higher relative strength of all HVFA concrete types. The F70 exhibiting the highest relative strength. The 10% SF + 10% slag blend exhibited good fire performance followed by the 5% SF + 5% slag blend up to 600 degrees C; then severe degradation in residual strength was observed at 800 and 1,000 degrees C. (C) 2015 American Society of Civil Engineers.