XV International Conference on Durability of Building Materials and Components DBMC 2020, Barcelona C. Serrat, J.R. Casas and V. Gibert (Eds) Effect of Crack Repair by Bio-Based Materials Using Alginate and Bacillus Subtilis under Wet and Dry Environment Part-I Keiyu Kawaai 1 , Takahiro Nishida 2 and Atsushi Saito 3 1 Civil and Environmental Engineering, Ehime University, 3, Bunkyocho, Matsuyama, Ehime, Japan, kkawaai@cee.ehime-u.ac.jp 2 National Research and Development Agency, National Institute of Maritime, Port and Aviation Technology, Port and Airport Research Institute, Japan, nishida-ta@p.mpat.go.jp 3 Reseach Center, Hazama Ando Corporation, Japan, atsushi.saito@ad-hzm.co.jp Abstract. 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. Keywords: Self-Healing, Aerobic Microorganisms, Bio-Composite, Water Absorption. 1 Introduction Recently, repair materials associated with microbial induced calcium carbonate precipitation (MICCP) have been intensively studied in the field of self-healing concrete e.g. (Jonkers et al., 2010). We proposed a liquid based repair system comprising dry yeast, organic carbon sources, calcium sources mixed with Tris alkali buffering solution (Kawaai et al., 2016; Putri at el., 2016). The grout used for repairing cracks in concrete is supposed to seep into deeper zones in cracks, joints and gaps spatially distributed in larger areas. Then, calcium carbonate precipitation mainly contributing to the sealing effect can be formed in the cracks well before 24 hours (Kawaai et al., 2016). It has been reported that the precipitation rate was largely dependent on the concentration of constituents, pH levels, and ambient environment such as temperature. The effect of temperature is significant in facilitating the precipitation process (Putri et al., 2016), thus leading to a larger amount of precipitates formed compared to those tested in normal room conditions. Apart from the grout system, the activity of Bacteria added to mixing water was observed to be limited owing to the pore solution with highly alkaline environment (Jonkers, 2011). In order