Synergistic Enhancement of Physicomechanical Performance and Microstructural Integrity in Hydrothermally Synthesized Autoclaved Lightweight Aggregates Through Quicklime–Fly Ash Blends

Herein, fly ash aggregates (FAAs) were synthesized through a hydrothermal process, utilizing fly ash (FA) and quicklime at a temperature of 180 °C under saturated steam conditions. The study focused on analyzing the ramifications of varying quicklime content on the physicomechanical attributes of the resultant FAAs. A comprehensive examination of mineralogical composition, microstructure, insoluble matter content, and loss on ignition was conducted to elucidate the mechanisms through which quicklime influences the cylinder compressive strength of the FAAs. An observed trend indicated that as the quicklime content increased, the water requirement during the granulation process also increased. Consequently, there was a gradual augmentation in the water absorption capacity of the FAAs, accompanied by a progressive decrement in their apparent density. The augmentation in the filling effect, attributed to the hydration products, led to a steady rise in cylinder compressive strength as the quicklime content escalated from 5 wt.% to 25 wt.%. However, beyond this threshold, between 25 wt.% and 45 wt.%, a decrement in cylinder compressive strength was noted due to the deterioration of the micro-aggregate effect. The interplay between the filling effect and the micro-aggregate effect resulted in the cylinder compressive strength of the FAAs peaking at 13 MPa at a quicklime content of 25 wt.%. The overarching objective of this research is to propose an efficacious approach for mitigating solid waste, with a particular emphasis on reducing the burden of FA. This study provides insights into optimizing FAAs through the modulation of quicklime content, thereby fostering advancements in waste management and resource recovery.