Microencapsulated Bacillus-Based Self-Healing Concrete: Crack Closure Kinetics, Durability Recovery, and Lifecycle Cost-Benefit Analysis

Author(s): Vikram N. Subramanian Department of Civil and Structural Engineering.

Affiliation: Independent Researcher

Page No: 8-13

Volume, Issue & Publishing Year: Volume 3 Issue 3,Aug-2026

Journal: International Journal of Advanced Engineering Application (IJAEA)

ISSN NO: 3048-6807

Abstract:
Microcracking in reinforced concrete structures provides ingress pathways for moisture, chloride, and carbon dioxide that accelerate reinforcement corrosion and reduce service life, with conventional repair approaches requiring reactive maintenance interventions that are costly and disruptive over a structure's operational lifetime. Microbially induced calcium carbonate precipitation (MICP), using ureolytic bacteria of the Bacillus genus, offers an autonomous crack-healing mechanism in which encapsulated bacterial spores activate upon crack-induced water ingress and precipitate calcite that fills and seals the crack, but the comparative performance of available encapsulation strategies and the resulting durability and economic benefits under realistic crack-width distributions remain incompletely characterised.This study evaluates Bacillus pseudofirmus spores encapsulated via five methods - direct mixing, lightweight aggregate impregnation, hydrogel encapsulation, and microcapsules with melamine-formaldehyde or sodium alginate shells - across bacterial concentrations of 10⁵-10⁹ cells/mL in M30 grade concrete. Crack closure was monitored over 28-day wet-dry healing cycles for cracks ranging 0.1-0.8 mm using digital image correlation, with compressive strength recovery, water permeability, rapid chloride migration coefficient, and SEM/EDX precipitate characterisation assessed at 28 and 56 days. A lifecycle cost model compared cumulative costs of conventional concrete with periodic repair against bacterial self-healing concrete over a 30-year service horizon.
The optimum bacterial concentration of 10⁷ cells/mL achieved 93% crack closure by 28 days for cracks up to 0.3 mm, with healing efficiency falling below the practically significant 80% closure threshold for initial crack widths exceeding approximately 0.45 mm. Alginate microcapsule encapsulation achieved the highest bacterial survival (83% at 28 days) and healing efficiency (93%) among the five methods tested, substantially outperforming direct mixing (18% survival, 22% efficiency). Compressive strength recovery reached 96.7% of uncracked control strength after 56 days of healing, and water permeability was reduced by 83% relative to control at optimum bacterial concentration. Lifecycle cost analysis indicated a break-even point at approximately 6.5 years, beyond which bacterial self-healing concrete's avoided repair costs outweighed its higher initial material cost, with cumulative 30-year costs 62.7% lower than conventional concrete requiring periodic repair.

Keywords: self-healing concrete, microbially induced calcium carbonate precipitation, MICP, Bacillus, microencapsulation, crack healing, durability, chloride migration, lifecycle cost, sustainable construction

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