The impact of fly ash on self-healing of slag-based engineered geopolymer composites

This study explores the influence of varying fly ash dosages on the self-healing behaviour of slag-based engineered geopolymer composites (EGCs). The findings reveal that altering the fly ash content significantly impacts the self-healing performance of EGCs. Under dry-wet cycle conditions, EGCs with lower fly ash dosages exhibit enhanced self-healing, while in a sustained 10 % NaCl solution environment, higher fly ash dosages result in superior self-healing. This divergence in performance is attributed to the different healing products formed in each environment. Specifically, a mix design (Mix4 in this research) showed apparent 150 % recovery without completely visible crack healing, which is considered as extended strain capacity rather than healing of properties at the same strain range. This phenomenon is explained by the different mechanisms governing mechanical property recovery and crack healing. Mechanical recovery is primarily driven by the formation of healing products in the interface between the fibre and matrix, whereas crack healing relies on the extensive generation and accumulation of products within the cracks. These two mechanisms have varying demands for the quantity of healing products, with mechanical property recovery requiring significantly less than crack healing.