High-Temperature Behavior of CaO-FeOx-Al2 O3-SiO2-Rich Alkali Activated Materials

Alkali-activated materials (AAMs) provide an opportunity to up-cycle several residues into added-value materials. Although generally praised for their performance under thermal loads, the thermal behavior of AAMs is dictated by a multitude of factors and the performance of CaO-FeOx-rich systems may differ from geopolymers. Therefore, this work ascertains the high-temperature resistance of CaO-FeOx-Al2 O3-SiO2-rich AAMs. Mortars were exposed to different heating rates (≤10◦ C/min) and temperatures (≤1100◦ C), and volume and mass loss, apparent density, compressive strength (CS), mineralogical composition, and morphology were evaluated. At low heating rates, the main effects noted were densification and a gradual lightening of color as the temperature rose. CS underwent an abrupt decline at 750◦ C and recovered at higher temperatures, reaching a maximum value of 184 ± 13 MPa at 1100◦ C. With an increased heating rate to 10◦ C/min, the strength loss at 750◦ C persisted, but maximum CS was halved when firing at 900◦ C. At 1100◦ C, a significant reduction of CS was observed, but all samples maintained their integrity. Except for 1100◦ C at 10◦ C/min, all sintered-AAMs presented residual CS above 40 MPa. These results demonstrate that CaO-FeOx-Al2 O3-SiO2-rich AAMs present interesting thermal behavior and can be potentially used to produce glass-ceramics or refractory materials from secondary resources.