Microcapsule-embedded Microbial Self-repairing Concrete Crack Process Performance Study

As the extensively used construction material all over the world, concrete is liable to cracking on the surface and inside, which reduces the life of the concrete. Using certain microorganisms capable of mineralization in nature to repair cracks in concrete has been receiving more and more attentions in recent years. However, due to the hostile environment in concrete, the mineralized microbes used to heal the concrete cracks must be embedded in the form of spore. Microcapsulation is a rising technology in recent years, which can protect the spore from harming. Therefore, it is necessary to investigate how to improve the spore germination efficiency under the appropriate condition and the properties of microcapsule.Due to the alkaline environment inside the concrete, the bacterium used in the study was basophilic Bacillus alkalisediminis H4. Firstly we investigated the factors that affected the spore germination, and then the characteristics of microcapsules made of ethyl cellulose and epoxy resin respectively was evaluated.Our experimental results confirmed that H4 possesses the ability of precipitating calcium carbonate. It grows and propagates quickly, with preferable growth conditions being 30?, p H 9.5-11. Based on the physiological properties of H4, light absorption was used to evaluate the spore germination condition. The results showed that CAPS is the optimum germination buffer; inosine is the optimum germinant, and the optimal concentration is 10 mmol/L; Na Cl is the optimum inorganic salt with the optimal concentration being 200 mmol/L; the spore germination ratio reaches 83.64% as p H is 10.0. Spore germination needs O2 and nutritional substrates, but O2 has different functions in different stages.Ethyl cellulose biomicrocapsule(EC) was prepared and then introduced into concrete. Wedge-mould could result in the formation of cracks inside the concrete specimens and breakage of microcapsules. The average crack width was 42?m. After the formation of crack,the specimen was incubated in the media to allow H4 to heal the cracks. The result showed that H4 is able to seal the crack in 30 d. Scanning electron microscopy(SEM) and X-ray energy analysis(EDS) revealed that the precipitation occurring in the medium is calcite. The result of capillary water absorption showed that the addition of microcapsule had a positive effect on decreasing capillary water absorption of the specimens.Furthermore, epoxy resin biomicrocapsule(EP) was prepared and the mineralization performance of the encapsulated bacterium was characterized. The results showed that: the mean size of biomicrocapsule was about 510 ~ 540?m. The size distributions of biomicrocapsule were: MCC(cellulose microciystalline)321.7~472.2?m, MCC + coating 362.7~474.2?m, MCC + spores 121.8~716.9?m, MCC + spores + coating459.7~716.9?m. X-ray diffraction(XRD) analysis revealed that mass ratio of core and wall material was about 5:1. The microcapsules showed good waterproof property. After the specimen embedded with biomicrocapsules was incubated for 30 d, the crack disappeared. Scanning electron microscopy(SEM) and X-ray energy analysis(EDS) revealed that the precipitation in the medium was calcite. X-ray diffractometry analysis(XRD) confirmed calcium carbonate was produced on the surface of the cracks.