Implementation of Bacteria for Microcrack Closer of Concrete

Hot-weather casting of concrete pavement is usually accompanied with initiation of microcracking. Such cracking can exhibit a durability problem since it allows the ingress of water and harmful chemicals such as sulphates and chlorides into the concrete which may cause premature corrosion of the steel reinforcement, and concrete matrix degradation. Implementation of bacteria as a healing agent to precipitate CaCo3 on the formed micro-cracks can support the durability. The continuous precipitation of calcite by hydration of cement helps in production of calcium carbonate precipitation with the help of bacteria. In this work, Bacillus subtilis bacteria of soil origin was cultured in the laboratory, the concentration of bacteria cell in normal saline (NaCl, 9 g/l) suspension was 106 cell/ml. Concrete beam specimens of (100 x 100 x 500 mm) size have been prepared in the laboratory, then separated to three sets. The first set was the control specimens cured in water bath for 7 and 28 days at 20°C. the second set of specimens was subjected to controlled flexure pre-cracking, then subjected to healing and curing in a water bath which contains the prementioned bacteria at 20°C for 7 days for healing and curing. The third set was subjected to healing and curing in a water bath which contains the prementioned bacteria at 20°C for 7 and 28 days and then tested for flexure properties. It was noted that the healing process by bacteria have improved the flexural properties of concrete by (16) % as compared to those of control mixture after 28 days of curing. On the other hand, specimens practiced the controlled pre-cracking exhibit (33) % improvement in flexural strength properties after the healing process provided by the bacteria. as compared to those of control mixture after 7 days of curing. It was concluded that implementation of bacteria in the curing water of concrete can furnish the required healing concept of microcracking in concrete. Such technique can be considered as an ecofriendly and sustainable solution for maintenance.

Keywords: Bacteria, Maintenance, Concrete, Pavement, healing, pavement.