In Situ Thermomechanical Evolution of Geopolymer‐Bonded Castables Containing Alternative Aluminosilicate Precursors

Abstract

Geopolymer binders have emerged as promising alternatives to calcium aluminate cement (CAC) for refractory castables, although their thermomechanical behavior during heating remains poorly understood. This work investigates high‐alumina refractory castables bonded with geopolymers produced from metakaolin (MK), calcined kaolin (CC), and an aluminum sulfate extraction residue (RESA). Physical and mechanical properties were correlated with in situ elastic modulus measurements, optical dilatometry, x‐ray diffraction, ATR‐FTIR, scanning electron microscopy, and thermal shock resistance. All geopolymer‐bonded castables developed adequate green mechanical strength after curing, with apparent porosity below 6%, demonstrating their suitability as alternative binders. Unlike the CAC reference, which exhibited a pronounced stiffness loss due to cement dehydration, the geopolymer‐bonded systems showed a continuous increase in elastic modulus during heating, associated with condensation of the aluminosilicate network, viscous‐flow sintering, and nepheline formation. The MK‐based castable exhibited the highest flexural strength (24.6 MPa), lowest apparent porosity after firing (11.9%), and highest elastic modulus after thermal treatment. RESA‐based formulations also developed stable ceramic bonding and thermal shock resistance comparable to the CAC reference. These findings demonstrate that the high‐temperature performance of geopolymer‐bonded refractory castables is primarily governed by the evolution and stability of the intergranular bonding phase, providing guidelines for the design of sustainable refractory binders.