Performance evaluation of cement paste incorporating ferro-nickel slag powder under elevated temperatures

This study investigated the fire resistance performance in terms of physical and chemical properties of the cement paste incorporating an iron by-product (i.e., ferronickel slag; FNS) at elevated temperatures (200 °C, 400 °C, 600 °C, and 800 °C). The cement pastes partially replaced with FNS, ground granulated blast-furnace slag (GGBS), and pulverized fly ash (PFA) at 30%, 60%, and 30%, respectively, were fabricated to compare the performance with other pozzolanic binders. All the pastes were kept at the water to binder ratio (W/B) of 0.467. The specimen was cured for 28 days and exposed to set temperatures. After/before heating, compressive strength and mercury intrusion porosimetry (MIP) were measured to evaluate the fundamental properties. Simultaneously, a variation in phase composition was examined using X-ray diffraction (XRD) and thermogravimetry (TG). As a result, despite lower strength at room temperature for the blended paste, those specimens were always higher than ordinary Portland cement (OPC) one after heating. Among them, FNS modified paste ranked the highest value in the residual strength after 400 °C, indicating 30.7% at 800 °C, which is consistent with a change in porosity and average pore size. This may be attributed to the presence of hydrotalcite and ferric/ferrous hydroxide, which is observed in the XRD results of FNS incorporated paste even after exposure to high temperatures. However, the optimum replacement level of FNS powder should be verified to secure a better performance in the given and a more severe temperature environment.