Development of High Strength Concrete with Self-Healing Properties

Abstract - High-strength concrete (HSC) is commonly used in modern infrastructure due to its exceptional load-bearing capacity and durability. However, like conventional concrete, it remains susceptible to microcracking, which affects structural performance and service life. To address this limitation, this study investigates the development of HSC with self-healing properties by incorporating bacteria. Four spore-forming, alkaliphilic bacterial strains—Bacillus subtilis, Bacillus cohnii, Bacillus pseudofirmus, and Bacillus megaterium—were chosen for their ability to thrive in the alkaline concrete matrix and precipitate calcium carbonate (CaCO₃) via urease activity. Concrete specimens were prepared using a mix design targeting a compressive strength of over 40 MPa, with bacterial spores (10 ⁵ cells/ml) added to the mixing water. Mechanical performance was assessed through compressive, split tensile, and flexural strength tests at 7, 14, and 28 days, in accordance with IS standards. Crack-healing behaviour was examined by inducing artificial cracks (0.3–0.5 mm). Linear regression analysis was used to model the relationship between curing age, bacterial strain, and strength development. The results showed significant improvements in strength and healing performance with bacterial incorporation compared to control mixes. Among the strains tested, Bacillus megaterium displayed the highest efficiency, increasing compressive strength by 57%, flexural strength by 37.5%, and tensile strength by 33.3% at 28 days. Regression models achieved strong predictive accuracy (R² values: 0.86–0.97). The study concludes that bacterial incorporation, particularly with B. megaterium, offers a sustainable pathway to improve both the mechanical performance and durability of HSC. This approach not only extends the service life of concrete structures but also reduces maintenance costs, providing a promising solution for resilient and eco-friendly construction. Key Words: High-strength concrete, self-healing, Bacillus, calcium carbonate precipitation, regression modelling, durability