Semester of Graduation
Master of Construction Science and Management (MCSM)
Bert S. Turner Department of Construction Management
Calcium carbonate precipitation through microbial means is a promising pathway for concrete self-healing technologies, mainly for its microcrack sealing attributes. The main goal of this project was to study and optimize the crack healing efficiency of hydrogel encapsulated bacteria in concrete. To achieve this purpose, Bacillus pseudiformus was implemented as the bacteria strain at a concentration of 108 cells/ml. This bacterium strain along with yeast extract was combined along with three different mineral precursors corresponding to magnesium acetate, calcium lactate, and sodium lactate. All these three precursors were evaluated at two concentrations (67.76 mM/l and 75 mM/l). For each combination, three sets of mortar cubes along with three sets of mortar beams were prepared. Furthermore, the mechanical properties of these specimens were characterized by compressive and flexural strength tests. Moreover, once the beams were cracked after the flexural strength test, they were subjected to 28 days of wet/dry cycles in which the corresponding crack width was monitored. Once the wet/dry cycles finished, the specimens were retested to determine the strength recovery of the samples.
As for the compressive strength tests, the samples that displayed the most promising results were the ones in which calcium lactate at a concentration of 75 mM/l along with bacteria and yeast extract were implemented. This specimen also displayed the best results in terms of self-healing efficiency. As for the flexural strength recovery, no significant difference was found among the specimens. Moreover, the healing products of this specimen were characterized under scanning electron microscopy (SEM) and energy X-ray dispersive spectroscopy (EDS). These analyses revealed a high presence of calcium rich crystals (i.e., calcium carbonate or calcium hydroxide crystals) proper of the bacterial activities.
After, the results from the mortar specimens were analyzed, a scale-up concrete study was performed based on the best performing mortar samples ( the ones in which calcium lactate at a concentration of 75 mM/l along with bacteria and yeast extract were implemented) and compared to a control sample of plain concrete. The results from the concrete analysis indicated that the addition of calcium lactate favors both concrete’s compressive and flexural strength. Nevertheless, the plain concrete control specimen displayed better healing efficiency after being subjected to wet/dry cycles. The reason for this behavior is that these samples experimented significantly narrower cracks after the flexural testing. Nevertheless, the results from the samples containing calcium lactate and bacteria were very promising since they substantially outperformed the results from previous studies. SEM/EDS analysis was finally conducted in both specimens, revealing the presence of calcium rich crystals as the healing product of the specimens. Finally, a cost analysis on the direct costs of bioconcrete was performed revealing that the bioconcrete costs 28.5% more than conventional concrete.
Hungria, Ricardo, "Optimizing the Self-Healing Efficiency of Hydrogel Encapsulated Bacteria in Concrete" (2022). LSU Master's Theses. 5531.
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