Experimental Study On Recovery Characterization Of Mechanical Properties For Crack Self-Healing Concrete

The characteristic of low tensile strength of concrete makes it easy to produce micro-cracks on the surface of the structure,which greatly affects the performance of structure.Therefore,the autonomous repair of cracks has become a current research hotspot.Microbial self-healing technology is based on the microbial induced carbonate precipitation,without human control and operation.It can diagnose and healing cracks in time,and is considered to be the most potential crack-healing technology.However,the survival ratio of microorganisms is severely reduced due to the high alkaline environment inside the concrete and the squeeze during continuous hydration.So a good porous medium is needed to support the microorganisms to promote precipitation.The recycled aggregate has the characteristics of looseness and porosity,and its alkaline degree has been reduced after long-term carbonization,which provides a space for the survival of microorganisms.Therefore,in this study,recycled aggregate was used as a carrier,and Bacillus pasteurii was used as a self-healing agent to prepare a self-healing concrete.The feasibility of crack healing was verified,and an apparent healing prediction model was established.Then mechanical recovery efficiency and healing mechanism of self-repairing concrete were analyzed.By comparing the healing capacity of self-healing concrete specimens prepared with recycled aggregate and the specimens with other carriers,combining strength and economic analysis,it is found that the recycled aggregate as a carrier has outstanding advantages.Finally,the morphology and composition of the material produced were characterized by scanning electron microscope(SEM)and electronic data switching(EDS).The orthogonal test was used to explore the optimal solution of the healing capacity under multiple factors,such as carrier particle size,bacterial solution concentration,crack width,etc.The best mix ratio for healing capacity of self-healing concrete was obtained.According to the relationship between the apparent healing capacity and time for the specimens with carriers,direct-inoculated bacteria and without bacteria,a prediction model of healing capacity based on this mix was established.The four-point bending loading was used to test cracking load,ultimate load,and flexural rigidity after crack healing for different test beams.The results showed that the self-healing concrete test beams with recycled aggregate had the highest recovery of cracking load,ultimate load and flexural rigidity.Based on the comparison between the predicted stiffness value and the measured stiffness value at different healing ratio,the restoration of the stiffness was verified.The predicted stiffness values were compared with the measured value,which reveals the nature of the stiffness restoration.Combining the principles of chemical compatibility and interfacial bonding strength,the relationship between crack healing capacity and mechanical property recovery of concrete was analyzed in depth.Based on Fictitious Crack Model,the cohesion of crack tip was calculated,which reveals the essence of the improvement of the macro-mechanical properties for the concrete members after healing.Finally,the correlation mechanism between the healing capacity and the mechanical properties was established to provide theoretical support for the promotion of self-healing concrete.