Experimental Evaluation of the Necessity of Low-Temperature Thermal Treatment for Mechanically Activated Waste Rock Wool as a Supplementary Cementitious Material

Waste rock wool (WRW) has attracted increasing attention as a supplementary cementitious material (SCM) because of its mineral composition and its potential for reducing industrial waste. Although thermal treatment is commonly applied during WRW recycling, the practical necessity of additional low-temperature thermal treatment after mechanical activation remains unclear. This study evaluated the feasibility of mechanically activated WRW as an SCM by comparing materials with and without subsequent thermal treatment at 250 °C. Cement paste containing 15 wt.% WRW was prepared, and the effects of thermal treatment were evaluated through X-ray fluorescence (XRF), scanning electron microscopy (SEM), compressive strength testing, and thermogravimetric analysis (TGA). The XRF and SEM results revealed only negligible differences in chemical composition and particle morphology between the thermally treated and non-thermally treated WRW. Although both WRW mixtures exhibited lower early-age compressive strengths than the Plain mixture, comparable or higher long-term strengths were achieved. The TGA results also showed only minor differences in calcium hydroxide content and degree of hydration between the two WRW mixtures. Overall, additional low-temperature thermal treatment provided limited practical benefits beyond mechanical activation alone. These findings demonstrate that mechanically activated WRW without subsequent thermal treatment is a feasible supplementary cementitious material, offering a simplified and more energy-efficient recycling strategy for cementitious applications.