Can Microbial Concrete Materials Replace Conventional Repair Technologies?
Current microbial concrete repair technology has not yet reached a stage where it can replace conventional concrete repair methods. The primary limitation is that microbial-induced calcium carbonate precipitation (MICP) requires an adequate supply of nutrients within the concrete matrix or microbial capsules. Once these nutrients are depleted, newly formed microcracks can no longer be repaired. Because the nutrient dosage must be carefully controlled to avoid adversely affecting the mechanical properties of the concrete, the amount of nutrients that can be incorporated into the concrete or microbial capsules is typically sufficient for only two bacterial activation cycles. Consequently, bacteria are generally capable of autonomously repairing microcracks at the same crack location only twice. After the available nutrients are exhausted, the self-healing capability is permanently lost, and subsequent microcracks at that location can no longer be repaired autonomously.
Another, less obvious limitation of MICP-based concrete repair is the time required for the healing process. Initially, repairing a concrete microcrack of approximately 1,000 μm in width using MICP required up to one year. In practical engineering applications, if a cracked concrete structure were exposed to real mechanical loading conditions rather than being kept under controlled laboratory conditions, the crack would likely propagate significantly during that year, rendering the repair ineffective. Recent advances have substantially reduced the healing time. Sporosarcina pasteurii (Sp) has been selected by researchers to shorten the healing time to approximately four days and to heal cracks up to 4,130 μm wide [Sohail M.G. et. al. 2022]. However, this represents the performance limit achieved under highly optimized experimental conditions designed to maximize the crack-healing capability of bacteria within concrete. The possibility of a second repair cycle after nutrient depletion was beyond the scope of this study, and therefore the feasibility of a second healing cycle remains unaddressed.
Based solely on these two important factors, the enhancement of MICP technology has approached a significant bottleneck. Therefore, enabling microbial concrete materials to replace conventional repair technologies in the near future remains a highly challenging task. Nevertheless, the ability to “automatically repair” microcracks without causing damage to the concrete matrix is an exceptional mechanism that gives microbial concrete significant research value.
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