A Novel Approach for Geopolymer Setting Control: Heat Pre-treatment of Ground Granulated Blast Furnace Slag

This study aimed to develop a technology for delaying the setting of geopolymer (GP) or alkali-activated material (AAM) that utilizes ground granulated blast-furnace slag (BFS) as a precursor. The approach involved pre-treating the BFS through heating. A detailed investigation was conducted to understand how the heating temperature and duration influenced the chemical characteristics of the BFS, as well as the setting behavior and compressive strength of the resulting GP. The experimental results indicated that when BFS was heat-treated at temperatures below 750°C, it maintained its amorphous state regardless of the heating time. Consequently, its reactivity remained almost equivalent to that of unheated BFS. A stable and effective delay in setting time was specifically observed after a 12-hour heat treatment at 700°C. In contrast, BFS heat-treated at 800°C led to its crystallization, which significantly increased the setting time but also reduced its reactivity. The results demonstrate that by blending the heat-treated crystalline BFS with the untreated amorphous BFS in an appropriate ratio, it is possible to achieve a desired GP setting time, providing a viable method for precise control.