Durability Enhancement of Coal-Fired Biomass Ash Concrete Using Bio-Inspired Self-Healing Coatings

Premature deterioration of reinforced concrete is driven largely by moisture and chloride ingress, which accelerate steel corrosion and shorten service life. This study investigates a dual strategy to enhance durability while supporting circular-economy goals: (i) incorporating coal-fired biomass ash (CBA) as a fine-aggregate replacement (0%, 20%, and 50%) and (ii) applying bio-inspired surface treatments to reduce transport pathways. To capture variability in CBA performance across different environmental and material contexts, two concrete systems—produced in India and the UK—were evaluated, each subjected to a distinct coating approach: a bacterial self-healing treatment or a cinnamaldehyde (CNM) organic barrier. Mechanical, transport, and multi-scale characterization was performed, including compressive strength, capillary absorption, chloride migration (NT Build 492), SEM/EDS, XRF, and XRD. The 20% CBA mixes maintained or slightly improved strength, while higher CBA contents increased porosity but reduced chloride transport in the UK mix. The bacterial coating reduced long-term water absorption by over 80% through CaCO3 mineralization, offering strong moisture resistance. The CNM coating decreased chloride migration by up to 68% via hydrophobic and ionic-blocking effects. Overall, moderate CBA with self-healing treatment enhances moisture control, whereas higher CBA with CNM provides effective chloride protection, extending the service life of CBA-based concrete.