Innovative Approaches to Enhancing Concrete Compressive Strength: An Extensive Investigation of Biochar-Embedded and Self-Repairing Techniques

Concrete, prized for its longevity, durability, strength, and resilience under heavy loads, is a cornerstone material in the construction industry worldwide. Despite its advantages, the persistent issue of cracking under rather low tensile loads undermines its performance, affecting strength, resilience, and overall durability. Various techniques have been used to address this challenge, but it remains a challenge. This paper presents an experimental investigation of the compressive response of 132 concrete samples treated with two innovative techniques: (1) incorporating biochar into the concrete mix; and (2) stimulating self-healing by spraying the surface of cracked concrete specimens with four types of high-alkalinity-tolerant, calcite-precipitation microorganisms, namely Bacillus subtilis, Bacillus megaterium, Sporosarcina pasteurii, and Pseudomonas stutzeri. Two methodologies were employed for crack generation: applying a target compressive load (Method 1), and using a standardized 0.5-mm-thick (0.02 in.) Teflon shim inserted into fresh concrete mix (Method 2). This study demonstrates that superficial application of bacterial cultures can stimulate self-healing in cracked concrete, either restoring its original conditions or enhancing its strength. A comprehensive comparative investigation with different experimental programs showed that both methodologies examined yield consistent results and are effective for stimulating the self-healing potential of concrete. These findings highlight the potential of this affordable and ecofriendly approach to significantly improve the mechanical robustness and endurance of concrete structures.