Deciphering the crack and pore self-healing effects of sustainable eco-friendly bio-mortar under coastal zone multi-interfaces

Coastal concrete structures support coastal element cycling and ecosystem services, but cracks from corrosion, loading, and wet-dry cycles threaten safety and disrupt nearshore biogeochemical cycles. Microbially Induced Calcium Carbonate Precipitation (MICP) represents a promising low-carbon strategy for autonomous crack healing; yet, its efficacy and mechanisms within these complex coastal environments remain elusive. Herein, the zonal self-healing performance of MICP across atmospheric, tidal, and submerged zones was evaluated using marine-origin Bacillus subtilis (BS)-based mortar (BSM) and Sporosarcina pasteurii (BP)-based mortar (BPM), with ordinary mortar (OM) serving as a control. Results indicate that the marine environment exerts a distinct zonal regulation on healing efficiency. The tidal zone, characterized by wet-dry cycles and ion enrichment, provided optimal conditions for microbial mineralization. Notably, BSM achieved a healing efficiency of nearly 80% within 11 days, with healing products observed filling both internal and external pores. This superior performance is attributed to the enhanced metabolic activity the BS strain. Conversely, negligible healing was observed in the atmospheric zone due to insufficient moisture for bacterial activation. Micro-analyses confirmed that the healing precipitates consisted primarily of calcium carbonate crystals with minor magnesium-containing compounds. BSM shows strong adaptability in complex marine environments, offering a sustainable, sustainable solution to enhance the durability of coastal infrastructure, bolster coastal resilience, and safeguard biogenic element cycles.