Study On Properties Of Self-healing Concrete Based On Aerobic-anaerobic Binary Microbial Mineralization System

In recent years,with the background of development of the Belt and the Road,national defense,green ecology and other major national strategic projects,civil engineering has ushered in unprecedented innovative development and challenges,and it is urgent need for civil engineering materials with disaster resistance and high durability.Concrete plays an extremely important role in engineering construction.The deterioration of concrete in the environment and the rapid repair of long-term stability of concrete structure are the key to realize the functional integration of high-performance concrete materials and structures.Self-healing concrete,as a material-structure integrated smart concrete that can realize self-diagnosis and self-healing of concrete cracks,is a research hotspot in the field of building materials,and it has great application potential in ensuring the safety and durability of buildings.In view of the long-term survival activity of microbial in concrete,the immobilization coordination of bacteria and nutrient,and the poor effect of depth crack-healing in self-healing concrete,a composite self-healing concrete based on expanded perlite immobilized bacteria technology and fiber reinforcement is proposed in this paper.The optimal design of expanded perlite immobilized bacteria technology in concrete,the effects of different external conditions,self-healing systems and fiber types on the crack-healing capacity of concrete are studied,and the mechanical properties,frost resistance and shrinkage properties of self-healing concrete are studied.The main research contents and conclusions include the following aspects:(1)Research on optimization design of immobilized bacteria technology in expanded perlite.The influence factors of sporulation and spore germination conditions of aerobic bacteria were studied in this paper.The effects of p H value,heat-activation temperature,germinants concentration,nutrients and cation type on spore germination were analyzed.According to the optimum conditions of microbial spore germination,the technology of immobilized bacteria in expanded perlite and the proportion design of"sugar coating"layer(nutrient layer)and protective layer of microbial self-healing agent were studied.The optimum mixture was obtained to increase the number of immobilized microbial spore in expanded perlite and spore germination rate.At the same time,the problem of mismatch between microbial concentration and nutrient concentration in crack area was solved.(2)Research on the effects of external conditions on the crack-healing capacity of concrete.In this paper,the effects of curing conditions,temperature,cracking time and freeze-thaw cycles on the crack-healing capacity of concrete were studied by using a variety of evaluation methods.The results show that crack-healing capacity is better under the condition of dry-wet cycle and water curing.Among them,crack-healing capacity is the best under the condition of dry-wet cycle,while almost all cracks under standard curing can not be completely repaired.When the external temperature is in the range of 25?40?,the self-healing concrete has good crack-healing capacity,and only the cracks with low width can be repaired in low temperature environment.After cracking time of 180d,the concrete specimens still have high crack-healing capacity,which shows that the method of preparing the microbial self-healing agent with"sugar coating"can ensure the later crack-healing percentage.With the increase of freeze-thaw cycles,the crack-healing capacity first increases and then decreases,and the crack-healing capacity is the best under the action of 50-75 freeze-thaw cycles.At the same time,the research results show that the self-healing concrete has greater potential in the marine environment and underground structures.(3)Research on the effects of different self-healing systems on the crack-healing capacity of concrete.In this paper,the effects of the monobasic microbial self-healing system,binary microbial self-healing system and fiber reinforcement on the crack-healing capacity of concrete were studied by combining micro and macro experimental methods.Firstly,a highly-efficient anaerobic denitrifying bacteria KJ-3 was screened by the method directional enrichment and separation.The main mineralized product of this bacterial was vaterite type calcium carbonate.An aerobic-anaerobic binary microbial self-healing system was designed.Secondly,the effects of different fiber types on microbial mineralization deposition shows that basalt fiber is more likely to become the nucleation site of microbial induced calcium carbonate mineralization,and its nucleation mechanism is revealed.Finally,the effects of different self-healing systems on the crack-healing capacity and secondary cracking repair effect of cracks were studied,and it was concluded that the fiber-reinforced binary microbial mineralization self-healing system(S-4)could achieve the optimal repair effect.At the same time,the“bolt”effect of fiber can anchor calcium carbonate and concrete matrix,greatly improve the bond strength between sediment and concrete matrix and the depth crack-healing capacity,solve the problem of poor repair of concrete crack depth,and greatly improve the crack anti permeability ability after repair.(4)Research on the mechanical properties,frost resistance and shrinkage properties of self-healing concrete.Firstly,the appropriate particle size range of self-healing agent and the optimal mixing mode of self-healing concrete were obtained by taking the crushing rate of microbial self-healing agent,apparent density of mixture and concrete strength as indexes.Secondly,the effect of the content of microbial self-healing agent on the physical and mechanical properties,frost resistance and shrinkage performance of concrete was studied.The results show that the compressive strength of concrete decreases with the increase of the content of microbial self-healing agent,and the frost resistance first increases and then decreases.When the content of self-healing agent is 0.6 m~3,it can not only meet the requirements of concrete strength,but also show excellent frost resistance.The strength loss rate after freeze-thaw is much lower than that of normal concrete.At the same time,through the research on the shrinkage performance of microbial self-healing concrete,it is found that the microbial self-healing agent can be used as the internal curing material of concrete,which can inhibit the early free shrinkage of concrete and reduce the drying shrinkage at early-age.