The Influencing Factors for Volume Stability of Ladle Slag

The purpose of this study was to investigate the mechanism causing the unsoundness of ladle slag. Calcination temperature may have an impact on the level of reactivity of f-CaO. When CaO was produced at a higher temperature, the reactivity of CaO was lower. For example, dead burnt CaO (DCaO) was produced at higher temperatures than light burnt CaO (LCaO); therefore, DCaO had less reactivity than LCaO. In a hydration test, DCaO (1500 °C) showed 62 times lower reactivity than LCaO (900 °C), which meant that DCaO would result in the delay of hydration of CaO easily. Additionally, DCaO would cause unsoundness more easily than LCaO when adding the same number of cementitious materials. For this reason, using ASTM C114-18 (Standard Test Methods for Chemical Analysis of Hydraulic Cement) to quantify DCaO content may underestimate DCaO content by up to 20%. Conversely, this method was more suitable for f-CaO since it had high reactivity. Moreover, this study demonstrated that ladle slag would cause unsoundness when added into the cementitious material because it was produced from a higher temperature process (over 1500 °C), which generates the DCaO. Therefore, when reusing ladle slag, the problem of low reactivity of DCaO should be considered.