Experimental Study On Self-repairing Performance Of Cement-based Materials Based On Microbial-induced Mineralization

Early cracking of concrete depends mainly on two factors: on the one hand,the intrinsic properties of materials such as shrinkage,elastic modulus,tensile strength and creep relaxation,these properties are closely related to the hardening process of concrete,It changes with the development of the age;on the other hand,the external factors,such as the shape of the structural member,the constraint,and ambient temperature and humidity conditions.The laws of stress,strain and temperature development under the early constraints of concrete in the actual operation stage are analyzed.The main findings are as follows:(1)Microorganism samples were collected from the natural resources and environmental conditions in the hinterland of the reservoir area,and the target microorganisms were screened and induced in the laboratory,the microbial environment is highly adaptable and non-toxic,and is identified as a Bacillus alcalophilus by Gram staining and microscopic examination.Through the compatibility test,the microbial experiment and the civil engineering material test are organically combined,and the three major block tests are carried out in parallel to promote and control each other.Finally,a certain concentration of the bacterial liquid is added to the concrete test block prefabricated with micro cracks.It has been found that the crack self-healing effect is significant,which lays a foundation for the engineering practice of microbial triggering crack self-healing of cement-based materials.(2)The basic mechanical indexes of different batches of concrete blocks of different ages were determined,and in the laboratory,prefabricated microcracks simulate the occurrence and development of cracks in cement-based materials,the dynamic damage detection of the crack is carried out with the fiber grating sensor.Then find the optimum concentration of bacteria(bubble concentration,buffer concentration)under different concentration gradients,and the type of medium and the culture period depend on the specific requirements for microbial survival.In the case of shortening the test period,the rate of mutation is accelerated by ultraviolet irradiation or the like.After obtaining the target microorganism,the culture is carried out according to the concentration required by the experiment,and then separated and purified,Prepare a reasonable concentration of microorganisms and buffers in a sterile environment and find that the activity of the enzyme affects the yield of the bacteria,therefore,the amount of yeast dipping powder and cottonseed cake powder will affect the yield.According to the analysis,the yeast extract concentration showed a slow upward trend before 2,and gradually decreased after 2,indicating that the mass concentration of 2 was optimum;the same analysis found that cottonseed cake powder is optimal at a mass concentration of 3;analytical data shows that the pH value of 11 is optimal.It has been found that the higher the enzyme activity,the higher the efficiency of inducing calcium carbonate deposition and the faster the microbes self-healing cracks.(3)In the test of sealing the concrete crack,using Universal testing machine preloading crack.In the project test,another test point of the crack of the concrete specimen can be obtained by data indicating that the optical fiber is embedded inside the specimen and the change of internal and external stress is received.During the test,the overall strain range of the test piece is gradually increased,at this time,the test piece has plasticity inside,and the fit between the fiber-optic pipeline and the cement-based material is not high,and the displacement is easy to occur,so that the sensing signal is disordered.Slowly return to normal after 60 minutes to 90 minutes,the phenomenon indicates that the hydration property of the test cement-based test block increases with time,the internal object fit degree increases,and the strain response tends to be stable.However,in the four to eight hour phase,cracks will gradually appear and there will be significant changes in the test chart.It is observed that the strain reaches the maximum at about 200 minutes,and then drops rapidly after a few minutes,it can be seen from the study that the cement-based material near the fiber has cracked,but it does not damage the buried structure of the fiber,thus obtaining the time of concrete cracking and the time of healing.