Effects of initial damage on self-healing of fly ash-based engineered geopolymer composites (FA-EGC)

Abstract

The effect of initial damage levels on self-healing properties and the mechanism of fly ash-based engineered geopolymer composites (FA-EGC) was investigated. FA-EGC paste with an ultimate tensile strain exceeding 5.4% was prepared using fly ash, composite alkali activator, and PVA fibers. The FA-EGC specimens were pre-damaged by 1.5%, 2.0%, and 2.5% tensile strains, then self-healed for 7, 14, and 28 days. The self-healing properties of FA-EGC were studied by uniaxial tension, apparent crack characteristic, water absorption, and ultrasonic pulse velocity methods. The self-healing products were characterized by XRD, FTIR, BET, and SEM-EDS. The model of the relationship between initial damage levels and initial internal crack characteristics was built. The results showed that FA-EGC had significant multiple cracking characteristics, strain-hardening behavior, and ultra-high tensile ductility after 28 days of self-healing. After self-healing, the ultimate tensile strength of pre-damage FA-EGC recovered to 97.86% compared with the control specimen, and the ultimate tensile strain recovered to 94.50%. Moreover, the strain of ultra-high tensile ductility FA-EGC was up to 5%. Self-healing products were mainly amorphous aluminosilicate and calcium carbonate phases. The self-healing rate was determined by initial internal crack width according to the model, and FA-EGC had an initial damage threshold (about 2.0% tensile strain) with the lowest mean crack width and the highest self-healing rate.