Efflorescence behaviour of ternary blended geopolymers containing waste clay brick powder: Performance assessment and microstructural evolution

Waste clay brick powder (WCBP) is increasingly gaining attention as a sustainable and widely available low carbon precursor for geopolymer production, owing to its high aluminosilicate content. Despite its utilisation potential, the effect of WCBP on efflorescence formation in alkali-activated systems remains limited, particularly in relation to efflorescence behaviour. This study examines the efflorescence behaviour of WCBP-based geopolymer binders under different curing conditions and environmental exposures through a performance-based risk assessment approach. Visual inspection was used to assess efflorescence severity, while microstructural and mineralogical characteristics were analysed using XRD, FTIR, TGA, SEM, and EDS. The results indicate that incorporating 20–40% WCBP reduces efflorescence, which is due to the formation of low-calcium N-A-S-H gels, lower alkali and calcium availability, and the development of a denser matrix. However, higher WCBP content (i.e., 60%) beyond this range increased efflorescence. This increase in efflorescence is attributed to higher porosity and excess unreacted alkalis, which promote ionic transport and salt crystallization. This study demonstrates the importance of optimizing both WCBP content and curing conditions to improve the durability performance and efflorescence resistance of geopolymer systems for construction applications. • Moderate WCBP incorporation (20–40%) improved matrix densification and reduced capillary absorption. • High WCBP content (60%) increased porosity, alkali migration, and efflorescence in submerged conditions. • Efflorescence triggered crystalline phase growth (quartz, calcite) and reduced amorphous gel content. • WCBP at 40% showed optimal performance with minimal efflorescence and the least strength degradation.