Effect of Microwave Irradiation on Hydrothermal Treatment of Blast Furnace Slag

The effect of microwave irradiation on the hydrothermal treatment of blast furnace (BF) slag was investigated using a 2.45 GHz microwave irradiation system. The comparison of the features of a microwave-hydrothermal (M-H) reaction with those of a conventional hydrothermal (C-H) reaction showed that in both these reactions, tobermorite (Ca5Si6O16(OH)2·4H2O) was formed as the major phase in the treated samples. When the BF slag was hydrothermally treated by the C-H reaction, tobermorite was formed in the vapor state as the major phase at 200°C after a holding time of 48 h; in the M-H reaction, tobermorite was rapidly formed within 3 h at the same temperature. It was elucidated that microwave irradiation promoted the hydrothermal reaction to a significant extent. Furthermore, effects of microwave irradiation on BF slag subjected to hydrothermal hot-pressing were investigated. After microwave irradiation, the compressive strength of the slag compact and rate of porosity in the compact after treatment increased and decreased, respectively, in comparison with those before treatment. Moreover, microwave irradiation was advantageous over conventional heating at the same temperature in that it enhanced the compressive strength of the BF slag.