Preparation of Green Autoclaved Bricks from Quarry Sludge Using Hydrothermal Synthesis and Calcium Hydroxide

The feasibility of reusing waste quarry sludge (QS) as a siliceous material was evaluated in this study. By activating the reactivity of wet QS using calcium-based materials, a new environmentally friendly brick was prepared through pressing and autoclaving processes. The compressive strength and microstructural characteristics of the QS combined with calcium-based materials were evaluated using mechanical performance tests, X-ray diffraction, thermogravimetric /differential scanning calorimetry, and scanning electron microscopy. Results demonstrate that Ca(OH)2 effectively activates the reactivity of QS, with an optimized Ca/Si molar ratio of 1.22 yielding the highest compressive strength of 75 MPa. The morphology of the solidified phase was determined by the dosage of QS. A curing temperature of 220 °C and an exposure time of 10 h contributed to the enhanced reactivity of QS, resulting in the formation of plate-like tobermorite and C–S–H gel, which induced a denser structure in the QS-based autoclaved brick and further promoted strength development. This work provides a fundamental framework for the effective utilization of QS through hydrothermal activation.