Improving the mechanical properties of rapid air cooled ladle furnace slag powder by gypsum

The aim of this research is supporting the recycling of ladle furnace slag from steel making industry. Ladle furnace slag is generally treated as a waste because of its volume instability with free-CaO and free-MgO crystalized during the slow cooling process. Regarding this by-product, from the previous research, rapid cooling technique with high pressured air was introduced, and rapid hardening properties of rapidly cooled ladle furnace slag (RCLFS) was introduced. In spite of outstanding rapid hardening performance, because of hydrogarnet, the main hydration product of main component for rapid reaction, RCLFS has low compressive strength and severe shrinkage as the drawbacks. In this research, to resolve these drawbacks, gypsum was incorporated and induced formation of ettringite. By using modified Bogue equation, the required appropriate amount of gypsum was determined as 37% of RCLFS weight, and a series of experiments were conducted to prove it. From the results of the experiment, when the RCLFS contained gypsum, ettringite was generated and due to the ettringite, compressive strength was continuously increased with decreased porosity. This result is expected to contribute to recycle the RCLFS as a rapid hardening material with more stable performances.