Analysis of the Encapsulation of Bacillus Subtilis in Iron Oxide Nanoparticles for the Repair of Cracks and Improvement of Mechanical Properties of Self-Repairing Concrete Subjected to Saline Environments

Concrete faces durability challenges caused by moisture, temperature changes, and chemical attack, which generate cracking, reduce structural integrity, and increase maintenance needs. Cement production also produces considerable environmental impacts, reinforcing the need for sustainable repair strategies. This study evaluated the encapsulation of Bacillus subtilis in iron oxide nanoparticles to improve crack healing and mechanical performance of concrete under saline exposure. Nanoparticles were synthesized by chemical coprecipitation, and viable Bacillus subtilis colonies were isolated and encapsulated to ensure protection in the alkaline matrix. Encapsulated bacteria were incorporated into concrete at concentrations of 0, 2.8 × 10⁹, 2.8 × 10¹², 2.8 × 10¹⁶, 2.8 × 10¹⁸, and 2.8 × 10²⁰ cells/mL. Slump, compressive, tensile, and flexural strengths, as well as sulfate resistance, were evaluated using three replicates per dosage. The 2.8 × 10¹⁶ cells/mL dosage achieved the best performance, improving mechanical strength and sulfate resistance compared with the control mix. Crack-healing capacity increased by 18% in induced fissures and was effective in real cracks, confirming activation of the biological repair mechanism. A cost increase of S/70 demonstrated economic feasibility. The findings show that encapsulating Bacillus subtilis in iron oxide nanoparticles enhances durability and offers a sustainable solution for concrete in aggressive environments.