Microscopic Repair Process And Characterization Of Microbial Self-repair In Concrete

Building materials such as concrete,stone,etc.are often subjected to various physical,chemical and biological factors during service,so micro-cracks usually exist inside the building materials.This phenomenon is common in the field of civil engineering.Due to the presence of micro-cracks,corrosive gases and water can enter the concrete's internal structure,which affects the durability and water-tightness of the concrete.Therefore,the cracks must be repaired.Self healing of cracks in concrete by mineralization microorganisms has been widely recognized in recent years.In this study,Bacillus sp.B6 was screened from the sediments in Mangrove district,Futian,Shenzhen,Guangdong Province to study its optimal germination conditions.Bacillus sp.B6 is an alkali-tolerant bacterium that can survive in a strong alkali environment.The optimum conditions for germination of B6 spores were studied by light absorption method.The results showed that the optimal germination agent is inosine.The optimal germination concentration of inosine is 10 mmol/L.The best inorganic salt species is sodium chloride with the suitable concentration being 200 mmol/L;the optimum pH for germination was 11;CAPS is the optimal buffer.Moreover,microcapsules with ethyl cellulose(EC)as the shell material was constructed to encapsulate DSM 8715 spores and then introduced into cementitious specimens.After the specimens were cleaved with a wedge-shaped mold,the cracks penetrated the microcapsules,and broke microcapsules.After that,the self-healing of crack by DSM8715 was observed with a stereomicroscope and XCT,respectively.Furthermore,the efficiency of self-healing process was further confirmed by ESEM observation and EDS analysis.The results showed that the self-healing behavior of microorganisms in concrete starts from outside the cracks,and the induced material is calcium carbonate precipitate.Finally,iodine ion permeation experiments were carried out in concrete specimens after self-healing process accomplished.Five surfaces of the specimens were wrapped with epoxy resin,leaving only one surface with cracks for infiltration experiments.The results showed that,due to the presence of microcapsules(no bacteria),the permeability of the aseptic specimens was the fastest in 6h,followed by the specimen with no microcapsule embedded.However,the specimens with bacterial encapsulated did not show any iodide ion infiltration in 6h,12 h,18 hours.This result further confirmed internal microbial self-healing of concrete cracks.