Crystallization properties of molten blast furnace slag at different cooling rates

Blast furnace slag, as a potentially active gelling material, is an important functional material for cement concrete making. However, the effective utilization of blast furnace slag depends on its amorphous formation ability in the cooling process with phase change. In the present study, single hot thermocouple technique is employed to investigate the crystallization properties of molten blast furnace slag under various cooling rates based on isothermal cooling and continuous cooling experiments. The slag with basicity of 0.934 is adopted and its characteristic temperatures are obtained. The crystal growth rate increases and then turns to drop with an increase in the isothermal temperature. The critical cooling rate of the testing blast furnace slag is about 9 °C/s. The results of continuous cooling experiments indicate that the critical cooling rate is about 6 °C/s. Meanwhile, shortened crystal incubation time and lower crystal onset temperature are reached with increasing cooling rate. The generated crystal in the testing blast furnace slag is Gehlenite showing columnar or plate-like structures.