Microstructure and residual properties of raw and ground ferronickel slag incorporated self-compacting concrete exposed to elevated temperatures.

• Mechanical & microstructural properties of GFNS incorporated HSSCC are examined as a function of temperature. • SEM, XRD, UPV, and TGA tests were performed to examine the residual behaviour. • Specimens undergo continuous mass reduction with temperature rise. • HSSCC incorporating GFNS shows higher residual compressive strength up to 400 °C in comparison to control specimen. • Cracks and changes in microstructures occurred as a result of high temperatures. Fire safety is a vital parameter for any structure as fire can accidentally occur at any time. This study presents the experimental results on residual strength and deterioration behaviour after high-temperature exposure of high-strength self-compacting concrete (HSSCC) produced using ferronickel slag (FNS). Four HSSCC mixtures were studied using up to 50 % ground FNS (GFNS) as cement replacement and 40 % raw FNS as sand replacement. Cylinder specimens were exposed to 200, 400, and 600 °C for two hours in a furnace. Cracking, change of colour, mass loss, residual compressive strength, thermogravimetric analysis, and ultrasonic behaviour of the specimens were studied. Morphological changes were examined by scanning electron microscopy (SEM), and phase detection was carried out by X-ray diffraction (XRD). The highest mass loss of 8 % was observed in the specimens containing 50 % GFNS, at 600 °C. At 400 °C, compressive strength decreased by about 45 % for the control mixture. In contrast, strength loss for the mixtures containing 20–50 % GFNS was in the range of 17–27 %. However, at 600 °C, compressive strength for all the mixes reduced drastically, by more than 50 %. This is considered to be mainly due to the occurrence of cracks, which was evidenced by the increased travel time of the ultrasonic waves through the specimens. Network of fine cracks were also observed on the surface of all the specimens. The SEM images and XRD results showed the distinct morphological changes at different temperatures for different mixes that correlated with the compressive strength results. Thus, the use of raw and ground FNS offers a wide and viable window of opportunity in production of HSSCC with resistance against high temperature exposure. [ABSTRACT FROM AUTHOR]