Self-healing concrete represents a paradigm shift in infrastructure durability, substantially reducing lifecycle costs and maintenance burdens. This study presents a comprehensive investigation into the autonomous crack-sealing behavior of alkali-activated geopolymer concrete (AAGC) prepared from fly ash (FA) and ground granulated blast-furnace slag (GGBS) binders activated with NaOH/Na₂SiO₃ solutions. Specimens were subjected to controlled mechanical cracking (width: 100–500 μm) and subsequently exposed to three distinct healing environments: wet-dry cycling, water immersion, and ambient atmospheric conditions. The self-healing performance was evaluated through crack width measurement, water permeability, compressive strength recovery, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and thermogravimetric analysis (TGA). Results demonstrate that AAGC specimens achieved up to 94.3% crack sealing efficiency within 56 days under wet-dry cycling conditions for cracks ≤200 μm. The primary healing mechanisms were identified as: (i) continued geopolymerization via unreacted aluminosilicate precursors, (ii) calcium silicate hydrate (C-S-H) gel precipitation, (iii) calcium aluminate silicate hydrate (C-A-S-H) formation, (iv) ettringite crystallization, and (v) zeolitic phase nucleation. Compressive strength recovery reached 87.6% at 90 days for optimally healed specimens. Kinetic modeling revealed that the healing process follows a first-order exponential decay, with rate constants strongly dependent on the NaOH molarity (8–12 M), GGBS-to-FA ratio (0.5–2.0), and ambient temperature. These findings establish AAGC as a highly promising low-carbon, self-healing structural material for critical civil infrastructure applications.
Thepe et al. (2026) studied this question.