Production of lightweight aggregate (LWA) by sintering blend of waste coal combustion ash (WCCA) and waste glass (WG): understanding the effect of WCCA chemical and mineralogical composition

This study investigated lightweight aggregates (LWAs) production using blends of waste coal combustion ash (WCCA) and soda-lime waste glass (WG), with a focus on understanding how the chemical and mineralogical composition of WCCA influences sintering behavior and LWA performance. LWAs were fabricated at a sintering temperature of 1100 °C using six types of WCCA with varying mass contents of Fe 2 O 3 , loss on ignition (LOI), amorphous phase, and mineral phases. The WG was used with contents ranging from 0 to 50 wt%. X-ray computed tomography (X-CT) and physical/mechanical testing showed that LWAs produced with 50% WG exhibited improved strength-to-specific gravity due to fewer large voids and higher solid integrity. However, at lower WG contents (25–40%), successful LWA formation was only achieved when the WCCA had favorable compositional traits, specifically, higher Fe 2 O 3 , LOI, amorphous content, and lower high-melting-point minerals such as mullite. These conditions promoted partial melting, enhanced gas generation, and facilitated iron oxide reduction during sintering, all of which were essential for producing structurally stable and well-bloated LWAs. On the other hand, dissolution and pH measurements revealed that WG contributed minimally to chemical activation of WCCA prior to sintering but acts as a binder during sintering. The findings demonstrated that the suitability of WCCA for WCCA/WG-based LWAs production is strongly governed by WCCA melt-forming and iron oxide reduction potential, which is controlled by its chemical and mineralogical composition. Understanding the effect of WCCA composition on sintering was found essential for optimizing WCCA/WG blend ratios and provide guidance for the future scale-up WCCA/WG-based LWAs production using WCCA and WG industrial byproducts.