An investigation on Portland cement replaced by high-volume GGBS pastes modified with micro-sized metakaolin subjected to elevated temperatures

Ground granulated blast-furnace slag (designated as GGBS) has been utilized as building material due to the environmental, economic and technical benefits. In this study, the possibility of improving compressive strength of high-volume GGBS (HVS) paste before and after being exposed to elevated temperatures using metakaolin (MK) in micro-size (mMK) has been investigated. Portland cement (PC) has been partially substituted with GGBS at level of 70%, by weight, to produce HVS paste. Afterword, GGBS was partially substituted with mMK at levels ranging from 2% to 10% with an increment of 2%, by weight. After curing, the specimens were subjected to elevated temperatures ranging from 400 °C to 1000 °C with an interval of 200 °C for 2 h. Weight and compressive strength before and after being exposed to elevated temperatures have been thoroughly explored. The various decomposition phases formed were identified using X-ray diffraction (XRD) and thermogravimetric (TGA) analyses. The morphology of the formed hydrates was studied using scanning electron microscopy (SEM). The results showed that the compressive strength before and after being exposed to elevated temperatures increased with increasing mMK content. For all mixtures, the residual compressive strength at 400 °C reached its maximum peak value.