Abstract :

The study examined the physical, mechanical, and crack-healing properties of concrete produced using Metakaolin-Bacillus subtilis and Metakaolin-Quicklime as self-healing agents. Two concrete specimens of grade M30 were produced; the first specimens were prepared incorporating metakaolin and quicklime of replacement percentages of 5, 10, and 15 by weight of cement, respectively, and the second, incorporating metakaolin of the same replacement percentages and 10 ml Bacillus subtilis. The mechanical properties were conducted at 28 days on concrete cubes of size 150 × 150 × 150 (mm3) and concrete beams of size 400 × 100 × 100 (mm3). The self-healing efficiency was evaluated through crack induction, and subsequent analyses included a comparative examination of the crack closure mechanisms for each agent. The compressive strength at 28 days’ curing age showed that 10% replacement of metakaolin-bacillus subtilis yields the best strength of 41.2 MPa, a 17.8% increase over the control specimen. Also, the combined blend of metakaolin and quicklime showed the highest strength at 10% replacement, which gained a 53% increase over the control specimen. The comparative analysis between metakaolin-quicklime and metakaolin-Bacillus subtilis reveals that both combinations exhibit self-healing properties through different mechanisms. In conclusion, the study establishes the efficacy of metakaolin, quicklime, and Bacillus subtilis as promising selfhealing agents in concrete, showcasing their unique mechanisms and paving the way for enhanced durability and structural integrity in construction applications.

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