This study examined crack repair methods using alginate gel films (1.5 wt.%) mixed with healing agents under wet and dry actions. The healing agents consist of Bacillus subtilis (natto) as an aerobic microorganism and glucose as an organic carbon source, thereby producing insoluble calcium carbonate in the gel films in the presence of calcium ions. In this study, repaired surface in cracked mortar specimens (50×100mm) was observed by microscope. In addition, water absorption test was carried out in assessing the effectiveness of crack repair for the cases of alginate gel films with or without calcium carbonate precipitation induced by the microbial activities. Based on the observations made by microscope, precipitates in white color were clearly observed after 8 weeks on the cracked surface of specimens especially under wet conditions. In the case of the specimens with higher sealing rate of crack repair, the alginate gel films were remained intact under dry and wet actions, which is advantageous to keep moisture by swelling. Water absorption test was carried out using repaired mortar specimens with average crack size of 0.5 mm. Based on the results obtained, water absorption rate is substantially decreased in the specimens with increasing sealing rate of crack repair. The results suggest that higher crack sealing rate associated with calcium carbonate precipitation leads to higher resistance against water absorption tested in accordance with ASTM C 1585.
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