Abstract
At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks.
Highlights
Micro-cracks are an almost inevitable feature of general concrete
Bacillus pasteurii can be made to sporulate by heating
Bacillus pasteurii pasteurii spores spores in in the the lightweight lightweight aggregate re-administering nutrients to restore activity, andand the aggregatecan canbe bereactivated reactivatedinto intobacteria bacteriabyby re-administering nutrients to restore activity, urease test confirmed that bacteria in the lightweight aggregate could induce to Microbiologically Induced Calcium Carbonate Precipitation (MICP)
Summary
Micro-cracks are an almost inevitable feature of general concrete. That some small cracks can be repaired on their own based on the continuous hydration of cement or other physical and mechanical behaviors. This phenomenon is generally called “autogenous healing” or “concrete self-healing” in the concrete world. In the interior of concrete, calcium carbonate precipitation has been considered by most scholars to be the most important factor affecting the autogenous healing of concrete. The main behavior of the microbiologically induced calcium carbonate crystallization effect is calcium carbonate precipitation.
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